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  • 1.
    Armendariz, Mikel
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Gonzalez, Rodrigo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Korman, Matus
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. KTH, Superseded Departments (pre-2005), Electrical Systems.
    Method for Reliability Analysis of Distribution Grid Communications Using PRMs-Monte Carlo Methods2017In: 2017 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    This paper presents a method to perform reliability analysis of communication systems for distribution grids. The method uses probabilistic relational models to indicate the probabilistic dependencies between the components that form the communication system and it is implemented by Monte Carlo methods. This method can be used for performing reliability predictions of simulated communication systems and for evaluating the reliability of real systems. The paper contains a case study in which the proposed method is applied to evaluate the reliability of the communication systems that are required for monitoring the network components at low voltage levels using the smart metering infrastructure. This case study is taken from the EU FP7 DISCERN project. Finally, the results are presented in a quantitative way, showing the individual reliability of each component and the combined reliability of the entire system.

  • 2.
    Babazadeh, Davood
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Hohn, Fabian
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Wu, Yimin
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Nordström, Lars
    KTH, Superseded Departments (pre-2005), Electrical Systems. KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Distributed Two-stage Network Topology Processor for HVDC Grid Operation2017In: 2017 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    This paper presents the results of an analysis of distributed two-stage coordination of network topology processor for HVDC grids. In the first stage of the two-stage processor, the substation topology is analyzed locally using an automated graph based algorithm. Thereafter, a distributed algorithm is proposed to used the neighboring information to realize the grid connectivity. For distributed islanding detection, the connectivity problem is formulated as a set of linear equations and solved iteratively using successive-over-relaxation method. The performance of the proposed methods versus conventional one-stage method has been tested in an islandinv, scenario for a 5-terminal HVDC grid.

  • 3.
    Brauer, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    High-Frequency Voltage Distribution Modelling of a Slotless PMSM from a Machine Design Perspective2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The introduction of inverters utilizing wide band-gap semiconductors allow for higher switching frequency and improved machine drive energy efficiency. However, inverter switching results in fast voltage surges which cause overvoltage at the stator terminals and uneven voltage distribution in the stator winding. Therefore, it is important to understand how next generation machine drives, with higher switching frequency, affect the voltage distribution. For this purpose, a lumped-parameter model capable of simulating winding interturn voltages for the wide frequency range of 0-10 MHz is developed for a slotless PMSM. The model includes both capacitive and inductive couplings, extracted from 2D finite element simulations, as well as analytically estimated resistive winding losses. The developed model of a single phase-winding is used to investigate how machine design aspects such as insulation materials and winding conductor distribution affects both voltage distribution and winding impedance spectrum. Validation measurements demonstrate that the model is accurate for the wide frequency range. The sensitivity analysis suggests that the winding conductor distribution affect both impedance spectrum and voltage distribution. For the slotless machine, capacitance between the winding and the stator is several times smaller than capacitance between turns. Therefore, the high-frequency effects are dominated by the capacitance between turns. Insulation materials that affect this coupling does therefore have an impact on the impedance spectrum but does not have any significant impact on the voltage distribution.

  • 4.
    Eiriksson, Eysteinn
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Distribution grid capacity for reactive power support2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The modern power system is changing at a rate faster than would have been expected20 years ago. More and more conventional power plants will be shut down in favour ofdistribution generation (DG). This is happening now with the trend of introducing renewableenergy sources (RES) to the power system.The grids were designed to transfer power from generating units connected to the highvoltage grids towards the end consumers connected to the low voltage grids. With changedpower mix, power flows in the system will change resulting in possible grid problems. Oneof the main problems is keeping the voltage within operational limits of the system. Whenthe generation exceeds the consumption in a distribution network, the power will flow fromthe low voltage network towards the high voltage network (reverse power flow) which willcause the voltage to rise in the low voltage network. Reactive power support from DG canbe a valuable resource to mitigate the problem. Reactive power is necessary to operatethe power system. The main source of reactive power is synchronous generators. If thissource is shut down, the reactive power must come from another source.This thesis investigates if DG could be used to support reactive power to the highvoltage transmission network to control the voltage. For this purpose, a distributionsystem located close toWorms, Germany will be studied. This distribution system consistsof two MV feeders with high penetration of DG, mostly photovoltaic (PV) but also windturbines (WT). Consumption and generation measurement data was provided by the localdistribution system operator (DSO). A few reactive power control methods are introducedand tested on this system. From the results, it is concluded that it is possible to providereactive power support from distribution networks and a voltage dependent reactive powercontrol can be used to this purpose.

  • 5.
    GROULT, Mathieu
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Optimization of Electromechanical Studies for the Connection of Hydro Generation2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The current model for electricity generation is based on power plants connected to the transmission network. This provides electricity to the distribution network and after that to the consumers. To ensure the security of the electrical network and prevent a blackout, the performance of every electricity generation unit connected to the network is quantified in grid codes. In the case of the French transmission system, the requirements regarding the performance are written in a document produced by the French Transmission System Operator (TSO). Various events with various configurations of connection to the network have to be simulated and the corresponding performance has to be evaluated. The aim of these simulations is to determine the stability of the generators and key elements, including the response time on the active power after events such as a short circuit.Taking into account the amount of generators connected to the transmission network, the need for optimization appears and is the purpose of this Master Thesis. To perform those simulations in an efficient way on all the generators owned by the main French electricity producer, EDF, this Master Thesis contributes with a tool called AuDySim coded with the softwares MATLAB and EUROSTAG. The implemented tool allows the user to configure an electricity generation unit before realizing all the simulations specified by the TSO and produces a report containing the results by means of curves and data. The simulations and the production of the report are achieved automatically to create a gain of time and resources.In order to validate the performance of the tool, two case studies are performed on different types of power plants. The two case studies analyzed present a hydraulic and a nuclear power plant. In the results the performance of each type of power plant is assessed focusing on the rotor angle stability of the machine and key elements, such as the voltage and the active power. These results lead to the conclusion that AuDySim fulfills its mission, by achieving automatically an analysis of the performance of an electrical generation unit and producing it in a report.

  • 6.
    Hagnestal, Anders
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    On the Optimal Pole Width for Direct Drive Linear Wave Power Generators Using Ferrite Magnets2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 6, article id 1356Article in journal (Refereed)
    Abstract [en]

    In this work, ferrite magnet linear generators for wave power applications are considered. These machines operate at unusually low speeds, around and even below 1 m/s, at which the optimal geometry differs from standard machines, since the copper loss and the force density become considerably more important. The focus is on translator design, and analytical two-dimensional (2D) expressions for the optimal 2D geometry are derived. Finite Element Analysis (FEA) is also applied to verify the analytical expressions and to determine effects from leakage fluxes and iron saturation. Demagnetization of ferrite magnets is also discussed and calculations are made to show the demagnetization situation for the magnets in different geometries. Finally, an example generator design is made to illustrate the findings. This generator is compared to three other generator concepts. It is concluded that ferrite magnet generators can have at least nearly the same shear stress as surface mounted neodymium magnet generators at low speed if the airgap is 3 mm or less, provided that a proper pole length is chosen, and that they can be economically competitive to neodymium magnet generators for wave power. It is also concluded that the demagnetization situation for the magnets can be severe, and that the choice of magnet grade and pole length is crucial in this respect.

  • 7.
    Hasananpor Divshali, Poria
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Improving Hosting Capacity of Rooftop PVs by Quadratic Control of an LV-Central BSS2017In: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061, Vol. PP, no 99, p. 1-1Article in journal (Refereed)
    Abstract [en]

    High integration of rooftop photovoltaic (PV) plants in distribution systems leads to new technical challenges: reverse-active power and voltage rise in low-voltage (LV) and medium-voltage (MV) grids. These challenges limit the maximum amount of power can be produced by PVs in LV and MV grids, called the hosting capacity (HC). Battery storage systems (BSSs) have been used in many studies to decrease the reverse power and improve the HC by controlling the active power. However, the influence of a central BSS on the HC can be greatly improved by using a quadratic power control, simultaneous active and reactive power control, and by selecting of the optimal battery size, the converter size, and the place of the central BSS. The effectiveness of the quadratic power control was not seen in previous works due to the fact that grids with one level of voltage without modeling of MV/LV transformers were simulated. This paper develops a method to select the optimal size of the battery and converter unit as well as the optimal place of an LV-central BSS having an optimal quadratic power control. The simulation results show considerable effects of the optimal selection of an LV-central BSS on the HC improvement.

  • 8.
    Hasananpor Divshali, Poria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. State University of New York, USA.
    Choi, Bong Jun
    Liang, Hao
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Transactive Demand Side Management Programs in Smart Grids with High Penetration of EVs2017In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 10, article id 1640Article in journal (Refereed)
    Abstract [en]

    Due to environmental concerns, economic issues, and emerging new loads, such as electrical vehicles (EVs), the importance of demand side management (DSM) programs has increased in recent years. DSM programs using a dynamic real-time pricing (RTP) method can help to adaptively control the electricity consumption. However, the existing RTP methods, particularly when they consider the EVs and the power system constraints, have many limitations, such as computational complexity and the need for centralized control. Therefore, a new transactive DSM program is proposed in this paper using an imperfect competition model with high EV penetration levels. In particular, a heuristic two-stage iterative method, considering the influence of decisions made independently by customers to minimize their own costs, is developed to find the market equilibrium quickly in a distributed manner. Simulations in the IEEE 37-bus system with 1141 customers and 670 EVs are performed to demonstrate the effectiveness of the proposed method. The results show that the proposed method can better manage the EVs and elastic appliances than the existing methods in terms of power constraints and cost. Also, the proposed method can solve the optimization problem quick enough to run in real-time.

  • 9.
    Hasananpor Divshali, Poria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Improvement of RES hosting capacity using a central energy storage system2017In: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe (ISGT-Europe), Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 1-6Conference paper (Refereed)
    Abstract [en]

    High penetration of renewable energy sources (RESs) in distribution systems leads to reverse active power and voltage rise in low voltage (LV) grids, which limits the hosting capacity. Energy storage systems (ESSs) have been used to improve the hosting capacity by decreasing the reverse active power in some literature. ESSs can still improve the hosting capacity more by providing reactive power. The reactive power shows a little effect in existing researches, because they have mostly simulate LV grids without modeling transformers. However, the high reactance of the transformer magnifies the effectiveness of the reactive power control even more than the active power in some buses. This paper develops an optimal method for placement, sizing, and active and reactive power control of a central ESS to improve the hosting capacity. The simulation results in highly RES penetrated grids at Germany show the effectiveness of the proposed method.

  • 10.
    Herre, Lars
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Söder, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Mathieu, Johanna L.
    University of Michigan Ann Arbor, MI 48109 USA.
    The Flexibility of Thermostatically ControlledLoads as a Function of Price Notice Time2018Conference paper (Refereed)
    Abstract [en]

    Due to increased use of variable renewable energy sources, more capacity for balancing and ancillary services (AS) is required. Non-generating resources such as thermostatically controlled loads (TCLs) can arbitrage energy prices and provide AS due to their thermal energy storage capacity. This paper explores the impact of energy/AS price notice time, i.e. the time between when the price is announced and when it takes effect, on the TCL energy consumption and AS capacity bids, and quantifies trade-offs between notice time and flexibility. We first optimize the energy consumption and AS capacity offers at a given notice time, varied from 24 hours ahead to real-time. We then introduce uncertainty in TCL availability, formulate the stochastic optimization problem, and evaluate how the trade-offs change. We find that price notice time impacts TCL profits, but does not significantly affect the total AS capacity offered over the day. However, AS capacity offers are impacted by uncertainty, which is likely to increase with notice time.

    The full text will be freely available from 2018-11-30 15:11
  • 11.
    Heuvelmans, Matthijs
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    A High-Frequency Semi Co-Axial Transformer With High Insulation Voltage2017In: 2017 19th European Conference on Power Electronics and Applications (EPE'17 ECCE EUROPE), Institute of Electrical and Electronics Engineers (IEEE), 2017Conference paper (Refereed)
    Abstract [en]

    The author is grateful to the Swegrids program and its participants for making this work possible and also wants to thank Staffan Norrga and Hans-Peter Nee for their reviewing efforts and constructive feedback. Last but no least the author wants to thank Patrick Janus for his help with the high voltage insulation testing.

  • 12.
    Iychettira, Kaveri
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    NATIONAL RENEWABLE POLICIES IN AN INTERNATIONAL ELECTRICITY MARKET: A SOCIO-TECHNICAL STUDY2018Doctoral thesis, monograph (Other academic)
  • 13.
    Jahn, Ilka
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Hohn, Fabian
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Norrga, Staffan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Impact of Measurement and Communication on Protection of MTDC Grids2018Conference paper (Refereed)
    Abstract [en]

    The increased demand for renewable energy generation requires higher flexibility of transmission systems. This requirement together with technical progress in high-voltage direct-current (HVDC) technology have resulted in the ambition to build large-scale multi-terminal DC (MTDC) grids. To achieve this goal, vendor interoperability is considered a key element. Standards exist for AC systems,but not for DC systems. This work discusses and evaluates the suitability of AC standards for DC systems. As a result, a different view on substation architecture is developed and two communication protocols are suggested for further investigation in this context.

  • 14.
    Jiang, Xiaolin
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering. KTH.
    Shokri-Ghadikolaei, Hossein
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Fischione, Carlo
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.
    Pang, Zhibo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    A Simplified Interference Model for Outdoor Millimeter-waveNetworks2018In: Mobile Networks and Applications, ISSN 1383-469XArticle in journal (Refereed)
    Abstract [en]

    Industry 4.0 is the emerging trend of the industrial automation. Millimeter-wave (mmWave) communication is a prominent technology for wireless networks to support the Industry 4.0 requirements. The availability of tractable accurate interference models would greatly facilitate performance analysis and protocol development for these networks. In this paper, we investigate the accuracy of an interference model that assumes impenetrable obstacles and neglects the sidelobes. We quantify the error of such a model in terms of statistical distribution of the signal to noise plus interference ratio and of the user rate for outdoor mmWave networks under different carrier frequencies and antenna array settings. The results show that assuming impenetrable obstacle comes at almost no accuracy penalty, and the accuracy of neglecting antenna sidelobes can be guaranteed with sufficiently large number of antenna elements. The comprehensive discussions of this paper provide useful insights for the performance analysis and protocol design of outdoor mmWave networks.

  • 15.
    Johannesson, Daniel
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. ABB Corp Res Ctr, S-72178 Vasteras, Sweden..
    Nawaz, Muhammad
    ABB Corp Res Ctr, S-72178 Vasteras, Sweden..
    Ilves, Kalle
    ABB Corp Res Ctr, S-72178 Vasteras, Sweden..
    Assessment of 10 kV, 100 A Silicon Carbide MOSFET Power Modules2018In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 33, no 6, p. 5215-5225Article in journal (Refereed)
    Abstract [en]

    This paper presents a thorough characterization of 10 kV SiC MOSFET power modules, equipped with third-generation MOSFET chips and without external free-wheeling diodes, using the inherent SiC MOSFET body-diode instead. The static performance (e.g., IDS-VDS, IDS-VGS, C-V characteristics, leakage current, body-diode characteristics) is addressed by measurements at various temperatures. Moreover, the power module is tested in a simple chopper circuit with inductive load to assess the dynamic characteristics up to 7 kV and 120 A. The SiC MOSFET power module exhibits an on-state resistance of 40 m Omega at room-temperature and leakage current in the range of 100 nA, approximately one order of magnitude lower than that of a 6.5 kV Si-IGBT. The power module shows fast switching characteristics with the turn-on (turn-on loss) and turn-off (turn-off loss) times of 130 ns (89 mJ) and 145 ns (33 mJ), respectively, at 6.0 kV supply voltage and 100 A current. Furthermore, a peak short-circuit current of 900 A and a short-circuit survivability time of 3.5 mu s were observed. The extracted characterization results could serve as input for power electronic converter design and may support topology evaluation with realistic system performance predictability, using SiC MOSFET power modules in the energy transmission and distribution networks.

  • 16.
    Jürgensen, Jan Henning
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Brodersson, Anna Lilly
    Vattenfall Eldistribution AB.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Nordström, Lars
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    The Proportional Hazard Model and the Modelling of Recurrent Failure Data: Analysis of a Disconnector Population in Sweden2017In: 2017 Cigré SC B3 (Substations) Colloquium, 18 - 20 September 2017, Recife, Brazil, 2017, p. 1-8Conference paper (Refereed)
    Abstract [en]

    Failure rate estimation is an important tool for planning and operating decision making in asset management of the power system. Moreover, the knowledge of how different explanatory variables impact the failure rate of the power system equipment is crucial for substation design. This study investigates 2191 work orders of 1626 non-current breaking disconnectors with 344 major failures. In particular, this paper analyses the disconnector failure data regarding recurrent failure data. Since the original PHM cannot handle recurrent event data, different extensions were developed such as the Andersen-Gill (AG), Prentice, Williams and Peterson (PWP), and the Wei, Lin, and Weissfeld (WLW) model. These models are applied to the disconnector dataset with 140 recurrent time-to-failure processes. The explanatory variables age at admission, remote control, preventive maintenance, and voltage level are assessed. The results show that preventive maintenance has a significant and positive impact on the recurrences with all tested methods. Also remote control, voltage level, and age are significant covariates. Compared to the single failure study previously conducted, where age had no significance, age is significant when assessing the recurrent failure which is the most critical difference to the analysis without recurrences.

  • 17.
    Khastieva, Dina
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Dimoulkas, Ilias
    KTH.
    Amelin, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Optimal Investment Planning of Bulk Energy Storage Systems2018In: Sustainability, ISSN 2071-1050, E-ISSN 2071-1050, Vol. 10, no 3, article id 610Article in journal (Refereed)
    Abstract [en]

    Many countries have the ambition to increase the share of renewable sources in electricity generation. However, continuously varying renewable sources, such as wind power or solar energy, require that the power system can manage the variability and uncertainty of the power generation. One solution to increase flexibility of the system is to use various forms of energy storage, which can provide flexibility to the system at different time ranges and smooth the effect of variability of the renewable generation. In this paper, we investigate three questions connected to investment planning of energy storage systems. First, how the existing flexibility in the system will affect the need for energy storage investments. Second, how presence of energy storage will affect renewable generation expansion and affect electricity prices. Third, who should be responsible for energy storage investments planning. This paper proposes to assess these questions through two different mathematical models. The first model is designed for centralized investment planning and the second model deals with a decentralized investment approach where a single independent profit maximizing utility is responsible for energy storage investments. The models have been applied in various case studies with different generation mixes and flexibility levels. The results show that energy storage system is beneficial for power system operation. However, additional regulation should be considered to achieve optimal investment and allocation of energy storage.

  • 18. Khodadadi, A.
    et al.
    Hasanpor Divshali, Poria
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. VTT Technical Research Center of Finland, Finland.
    Nazari, M. H.
    Hosseinian, S. H.
    Small-signal stability improvement of an islanded microgrid with electronically-interfaced distributed energy resources in the presence of parametric uncertainties2018In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 160, p. 151-162Article in journal (Refereed)
    Abstract [en]

    This paper deals with the concept of small signal stability (SSS) issue in an electronically-interfaced microgrid with large penetration of distributed energy resources (DERs) subjected to the parametric uncertainties. Utilizing a method to enhance SSS of the system stemmed from industrial experiences is the first achievement of this study, which is realized by employing two extra feed-forward loops in the power controller section of DER unit. This control structure damps the active and reactive power oscillations by shifting the dominant eigenvalues to the left half-plane (LHP) in case of any changes in the operating point or droop coefficients. For investigating the impacts of parametric uncertainties on the overall stability, the basic theorem of the proposed robust control strategy, frequency-domain modeling of the microgrid, robustness and close-loop stability analyses are outlined. This method shows that improving the power control section topology results in higher stability margins in case of uncertain load perturbations. Furthermore, it demonstrates how much load variations are allowed to preserve SSS of the system in the frequency-domain which is a more convenient approach and takes less time than time-domain simulations. Finally, time-domain simulations conducted in MATLAB/Simulink on the sample test system will show proper results of the frequency-domain findings.

  • 19.
    Kotb, Omar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    On Stability Enhancement in AC/DC Power Systems through Multi-terminal HVDC Controllers2018Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Due to the increasing share of renewable energy sources in modern power systems and electricity market deregulation, heavy inter-regional and cross-border power flows are becoming a commonplace in system operation. Moreover, large-scale integration of renewable energy sources is expected to pace up, therefore new solutions have to be developed to integrate these intermittent sources, which are also characterized by being distributed over large geographical areas, such as offshore wind farms. Multi-Terminal High Voltage Direct Current (MTDC) networks are expected to form a solution for the integration of renewable energy sources to the existing interconnected AC grid. The type of converters used in the MTDC networks is however a subject of debate, as both Line Commutated Converters (LCCs) and Voltage Source Converters (VSCs) can be used. Moreover, the coordinated control of the MTDC networks with the AC system poses a challenge to the system operators, as it requires the consideration of both AC and DC system dynamics.

     

    In response to these challenges, this thesis aims to discuss the following aspects of the MTDC networks: control of a hybrid MTDC with both LCCs and VSCs, as well as the utilization of an embedded VSC-MTDC for stability enhancement. The thesis also investigates the supply of passive AC systems using a hybrid MTDC network.

     

    In the investigation of an AC/DC power system with a hybrid MTDC network, first, the combined AC/DC system is modeled. Next, a Small Signal Stability Analysis (SSSA) of the system is conducted, based on which the Power Oscillation Damping (POD) controllers were designed to enhance stability in the connected AC systems.

     

    In the utilization of an embedded VSC-MTDC network for stability enhancement in the AC/DC system, the operating point adjustment strategy is investigated, which is implemented through the adjustment of setpoints for the active and reactive power controllers in the network converters. Finally, the design and placement of a Multi-Input Single Output (MISO) controller is investigated, where the control strategy is based on Modal Linear Quadratic Gaussian (MLQG) control using Wide Area Measurement Systems (WAMS) signals.

  • 20.
    Li, Wei
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    PMU-based State Estimation for Hybrid AC and DC Grids2018Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Power system state estimation plays key role in the energy management systems(EMS) of providing the best estimates of the electrical variables in the grid that arefurther used in functions such as contingency analysis, automatic generation control,dispatch, and others. The invention of phasor measurement units (PMUs) takes thepower system operation and control into a new era, where PMUs’ high reportingrate and synchronization characteristics allow the development of new wide-areamonitoring, protection, and control (WAMPAC) application to enhance the grid’sresiliency. In addition, the large number of PMU installation allows the PMU-onlystate estimation, which is ready to leap forward today’s approach which is based onconventional measurements.At the same time, high voltage direct current (HVDC) techniques enable totransmit electric power over long distance and between different power systems,which have become a popular choice for connecting variable renewable energy sourcesin distant locations. HVDCs together with another type of power electronic-baseddevices, flexible AC transmission system (FACTS), have proven to successfullyenhance controllability and increase power transfer capability on a long-term costeffectivebasis. With the extensive integration of FACTS and HVDC transmissiontechniques, the present AC networks will merge, resulting in large-scale hybrid ACand DC networks. Consequently, power system state estimators need to considerDC grids/components into their network models and upgrade their estimationalgorithms.This thesis aims to develop a paradigm of using PMU data to solve stateestimations for hybrid AC/DC grids. It contains two aspects: (i) formulating thestate estimation problem and selecting a suitable state estimation algorithm; (ii)developing corresponding models, particularly for HVDCs and FACTS.This work starts by developing a linear power system model and applying thelinear weighted least squares (WLS) algorithm for estimation solution. Linear networkmodels for the AC transmission network and classic HVDC links are developed. Thislinear scheme simplifies the nonlinearities of the typical power flow network modelused in the conventional state estimations and has an explicit closed-form solution.However, as the states are voltage and current phasors in rectangular coordinates,phasor angle is not an explicit state in the modeling and estimation process. Thisalso limits the linear estimators’ ability to deal with the corrupt angle measurementsresulting from timing errors or GPS spoofing. Additionally, it is cumbersome toselect state variables for an inherently nonlinear network model, e.g., classic HVDClink, when trying to fulfill its linear formulation requirement.In contrast, it is more natural to use PMU measurements in polar coordinatesbecause they can provide an explicit state measurement set to be directly used inthe modeling and estimation process without form changes, and more importantly,it allows detection and correction for angle bias which emerges due to imperfectsynchronization or incorrect time-tagging by PMUs. To this end, the state estimationproblem needs to be formulated as a nonlinear one and the nonlinear WLS is applied for solution. We propose a novel measurement model for PMU-based state estimationwhich separates the errors due to modeling uncertainty and measurement noise sothat different weights can be assigned to them separately. In addition, nonlinearnetwork models for AC transmission network, classic HVDC link, voltage sourceconverter (VSC)-HVDC, and FACTS are developed and validated via simulation.The aforementioned linear/nonlinear modeling and estimation schemes belongto static state estimator category. They perform adequately when the system isunder steady-state or quasi-steady state, but less satisfactorily when the system isunder large dynamic changes and the power electronic devices react to these changes.Testing results indicate that additional modeling details need to be included toobtain higher accuracy during system dynamics involving fast responses from powerelectronics. Therefore, we propose a pseudo-dynamic modeling approach that canimprove estimation accuracy during transients without significantly increasing theestimation’s computational burden. To illustrate this approach, the pseudo-dynamicnetwork models for the static synchronous compensator (STATCOM), as an exampleof a FACTS device, and the VSC-HVDC link are developed and tested.Throughout this thesis, WLS is the main state estimation algorithm. It requiresa proper weight quantification which has not been subject to a sufficient attentionin literature. In the last part of thesis, we propose two approaches to quantify PMUmeasurement weights: off-line simulation and hardware-in-the-loop (HIL) simulation.The findings we conclude from these two approaches will provide better guidancefor selecting proper weights for power system state estimation.

  • 21.
    Li, Wei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Vanfretti, Luigi
    Chow, Joe H.
    Pseudo-Dynamic Network Modeling for PMU-Based State Estimation of Hybrid AC/DC Grids2018In: IEEE Access, E-ISSN 2169-3536, Vol. 6, p. 4006-4016Article in journal (Refereed)
    Abstract [en]

    This paper presents a PMU-based state estimation (SE) algorithm that uses a pseudo-dynamic network modeling approach. The pseudo-dynamic network model combines different equations with static network equations. Then it applies the weighted least squares algorithm to solve an over-determined least squares estimation problem. The proposed method can improve SE accuracy during both steady state and transient conditions without increasing the computational burden. In addition, the proposed modeling approach is applied to networks containing both a STATCOM and a voltage source converter-HVdc to demonstrate how to develop and apply a pseudo-dynamic SE model. Case studies aim to illustrate and verify the performance of the proposed method under steady state and transient conditions.

  • 22.
    Mahmood, Farhan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Synchrophasor based Steady State Model Synthesis of Active Distribution Networks2018Doctoral thesis, monograph (Other academic)
    Abstract [en]

    With the increased penetration of distributed energy resources (DERs) at lower voltage levels, distribution networks (DNs) are being transformed into active grids. This has led to a paradigm shift in the operation, planning and control of DNs. Traditional monitoring infrastructure is unlikely to satisfy the requirements that active distribution networks (ADNs) pose in terms of higher speed networking, time synchronization and signal resolution, precision and accuracy, scope, etc. As a result, high performance monitoring infrastructures are needed to fully utilize the potential of sensing devices at DNs, capable of monitoring ADNs in real-time. In this context, phasor measurement units (PMUs) have emerged as one of the most promising alternatives for ADNs monitoring in real-time.

    The focus of this thesis is to exploit PMU measurements to perform real-time steady state model synthesis (SSMS) of ADNs. To this end, methods for pre-processing PMU data are developed in this thesis. As the focus of this thesis is the development of a steady state PMU application, the methods presented herein extract the quasi-steady state component in PMU measurements and feeds them to the SSMS application. In addition, the methods are capable of filtering noise, compensating for missing data, and removing the outliers in PMU signals in real-time.

    The synthesis method can be applied to multiple sections of unbalanced ADNs requiring measurements from multiple PMUs. The proposed approach is generic and can be applied to any portion of a DN with any feeder configuration. The performance and the effectiveness of the proposed methodology have been illustrated in details by using real-time hardware-in-the-loop (HIL) experiments.

    A detailed sensitivity analysis of the SSMS application is performed in order to show how sensitive the output of the SSMS method is to changes in its inputs. An extended version of the total vector error (TVE) was developed as an evaluation metric. The location of PMUs, system operating point and the occurrence of different disturbances are considered when evaluating the SSMS method. The sensitivity analysis is performed through several case studies as discussed above.

    Finally, the thesis provides extensive experimental validation experiments on the SSMS application. Syncrophasor measurements acquired from real PMUs installed at an actual active distribution feeder in a university campus were used for this purpose. A detailed performance assessment of the SSMS method is conducted for different conditions. Additionally, a comprehensive analysis is performed to help power system operators to determine how to configure the SSMS application.

  • 23.
    Mahmood, Farhan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Vanfretti, Luigi
    Rensselaer Polytech Inst, Dept Elect Comp & Syst Engn, Troy, NY 12180 USA..
    Pignati, Marco
    Ecole Polytech Fed Lausanne, Distributed Elect Syst Lab, CH-1015 Lausanne, Switzerland..
    Hooshyar, Hossein
    Rensselaer Polytech Inst, Dept Elect Comp & Syst Engn, Troy, NY 12180 USA..
    Sossan, Fabrizio
    Ecole Polytech Fed Lausanne, Distributed Elect Syst Lab, CH-1015 Lausanne, Switzerland..
    Paolone, Mario
    Ecole Polytech Fed Lausanne, Distributed Elect Syst Lab, CH-1015 Lausanne, Switzerland..
    Experimental Validation of a Steady State Model Synthesis Method for a Three-Phase Unbalanced Active Distribution Network Feeder2018In: IEEE Access, E-ISSN 2169-3536, Vol. 6, p. 4042-4053Article in journal (Refereed)
    Abstract [en]

    This paper presents the field validation of a method that performs steady-state model synthesis (SSMS) of active distribution networks using syncrophasor measurements. The validation is performed by applying the SSMS method on a real active distribution feeder network by utilizing the measurements from real phasor measurement units (PMUs) installed at the EPFL campus. An extended version of total vector error and a power flow comparison at the PMU buses are used as performance assessment metrics. A real-time hardware-in-the-loop simulations set up at the Distributed Energy System Laboratory is used for further performance assessment of the SSMS application. The effectiveness of the SSMS application is demonstrated by testing it extensively for several different case studies.

  • 24.
    Mazidi, Peyman
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. Comillas Pontifical University.
    From Condition Monitoring to Maintenance Management in Electric Power System Generation with focus on Wind Turbines2018Doctoral thesis, monograph (Other academic)
    Abstract [en]

    With increase in the number of sensors installed on sub-assemblies of industrial components, the amount of data collected is rapidly increasing. These data hold information in the areas of operation of the system and evolution of health condition of the components. Therefore, extracting the knowledge from the data can bring about significant improvements in the aforementioned areas.

    This dissertation provides a path for achieving such an objective. It starts by analyzing the data at the sub-assembly level of the components and creates four frameworks for analysis of operation and maintenance (O&M) for past, present and future horizons at the component level. These frameworks allow improvement in operation, maintenance planning, cost reduction, efficiency and performance of the industrial components. Next, the dissertation evaluates whether such models can be linked with system level analysis and how providing such a link could provide additional improvements for system operators. Finally, preventive maintenance (PM) in generation maintenance scheduling (GMS) in electric power systems is reviewed and updated with recent advancements such as connection to the electricity market and detailed implementation of health condition indicators into the maintenance models. In particular, maintenance scheduling through game theory in deregulated power system, for offshore wind farm (OWF) and an islanded microgrid (MG) are investigated.

    The results demonstrate improvements in reducing cost and increasing profit for the market agents and system operators as well as asset owners. Moreover, the models also deliver an insight on how direct integration of the collected operation data through the developed component level models can assist in improving the operation and management of maintenance for the system.

  • 25.
    Millinger, Jonas
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. KTH.
    Wallmark, Oskar
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Soulard, Juliette
    KTH.
    High Frequency Characterization of Losses in FullyAssembled Stators of Slotless PM Motors2018In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367Article in journal (Refereed)
    Abstract [en]

    Abstract—The recent emerge of wide band-gap (WBG) powertransistors enables higher switching frequencies in electricalmotor drives. Their full utilization from a system point ofview requires quantification of the corresponding time-harmonicmotor losses. As an initial step, this paper presents a uniquestudy of stator losses for three different commercially availablenon-oriented silicon-iron (SiFe) steel grades (with laminationthicknesses 0.1, 0.2 and 0.3 mm). The investigations cover awide frequency range (10-100 kHz) at different levels of DC-bias(up to 1.6 T). Iron losses are identified from measurements onfully assembled stators, deploying a novel technique. By utilizingfully assembled stators, no additional samples are required.Manufacturing influence is inherently incorporated. Results showthat measured iron losses are twice as high at 10 kHz comparedto Epstein test results, which emphasizes the need to incorporatemanufacturing influence on iron losses at high frequencies. Thelevel of DC-bias is also observed to have a significant impacton iron losses (up to 30 %). Even though thinner laminationsare known for reducing iron losses, the reduction is much lowerthan anticipated in the studied frequency range due to skin effect.Using 0.1 mm lamination gauge instead of 0.3 mm reduces lossesby 50 % at 10 kHz, while the same substitution at 100 kHz onlyreduces losses by 30 %. Future work includes loss separation incomplete converter-fed machines.

  • 26.
    Moiseeva, Ekaterina
    et al.
    KTH.
    Hesamzadeh, Mohammad Reza
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Bayesian and Robust Nash Equilibria in Hydrodominated Systems Under Uncertainty2018In: IEEE Transactions on Sustainable Energy, ISSN 1949-3029, E-ISSN 1949-3037, Vol. 9, no 2, p. 818-830Article in journal (Refereed)
    Abstract [en]

    In this paper, we model strategic interaction of multiple producers in hydrodominated power systems under uncertainty as an equilibrium problem with equilibrium constraints (EPEC), reformulated as a stochastic mixed-integer linear program with disjunctive constraints. We model strategic hydropower producers who can affect the market price by submitting strategic bids in quantity, price, and ramp rate. The bids are submitted to the system operator who minimizes the dispatch cost. We take into account the hydrospecific constraints and uncertainty in the system. Solving the problem results in finding Nash equilibria. We discuss two types of Nash equilibria under uncertainty: Bayesian and robust Nash equilibria. Large EPEC instances can be solved using a decomposition method-Modified Benders Decomposition Approach. This method eliminates the problem of tuning the disjunctive parameter and reduces the memory requirements, resulting in improved computation time.

  • 27. Nategh, Shafigh
    et al.
    Zhang, Hui
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Wallmark, Oskar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Aldo, Boglietti
    Transient thermal modeling and analysis of railway traction motors2018In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948Article in journal (Refereed)
    Abstract [en]

    This paper presents a practical approach to modeland analyze transient thermal effects in open air-cooled electrictraction motors. The developed thermal modeling method enablesaccurate estimation of temperature in critical parts of the motorincluding winding and bearing. Advantages of both numericaland analytical modelling methods are exploited with the aim ofrealizing accurate estimation of hot spot temperatures in tractionmotors while keeping the computation time within a reasonablerange. Computational fluid dynamics (CFD) simulations arecarried out to model the cooling fan’s performance and airflow distribution in the motor in order to provide heat transferboundary inputs to the developed combined finite element (FE)and lumped parameter (LP) thermal model. The combinationof the FE and LP models keeps the size of the model relativelysmall and enables running transient calculations reasonably fast.Also, the developed model provides the possibility to studythe influence of stator and rotor duct blockages on the motorthermal performance which is a common root of failure intraction applications during operation in dirty environments. Theproposed thermal model is verified using experimental results ona traction motor equipped with temperature sensors in motorcritical parts and a good agreement between estimated andmeasured temperatures is achieved. Finally, a calibrated fullyanalytical model using the abovementioned developed model isimplemented to further reduce simulation running time andcalculate motor temperature under normal running condition.

  • 28.
    Nilsson, Martin
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    On Efficient Transmission Balancing Operation: Capturing the Normal State Frequency and Active Power Dynamics2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In an electric power system, there will always be an electric balance. Nevertheless, System Operators (SOs) often uses the term imbalance. Here, the term imbalance refers to the difference between trades and real-time measurements. This thesis defines the term imbalance and develops a framework helping SOs in finding better decisions controlling these imbalances. 

    Imbalances are controlled by many decisions made at various stages before real-time. A decision can be to increase the flexibility in production and consumption. However, this is not the only decision affecting real-time balancing operation. Other decisions are grid code requirements, such as ramp rates of HVDC and generation; balancing market structure, such as imbalance fees and trading period lengths; and the strategies used in the system-operational dispatch.

    The purpose of this thesis is to create a new possibility for SO to find decisions improving the balancing operation. 

    In order to find and compare decisions, the thesis develops a framework that evaluates many different decisions made at various stages before real-time. The framework consists of the following. First, it develops an intra-hour model using multi-bidding zone data from a historical time-period; able to capture the normal state frequency and active power dynamics. The model creates high-resolution data from low-resolution measurements using several data-processing methods. The uncertainty from the historical time-period is re-created using many sub-models with different input data, time-scales and activation times of reserves. Secondly, the framework validates the model and identifies system parameters based on simulated frequencies and frequency measurements in the normal state operation. Finally; new decisions' are modelled, tested, and evaluated on their impact on selected targets supporting corporate missions of the SOs.

    The goal of the framework is that it should be able to find better decisions for balancing operation but also that it should be applicable for real and large power systems. To verify this, the framework is tested on a synchronous area containing 11 bidding zones in northern Europe. Results show that the framework can be validated and trusted.

    Three new decisions, made at various stages before real time, have been modelled, tested and evaluated. The modelled decisions were (i) lower ramp rates for generation, (ii) increased capacities for automatic reserves, and (iii) a new strategy for the system-operational dispatch. One implication of applying the balancing evaluation framework on data from July 2015 is that all tested decisions improve several selected targets supporting the corporate missions of the SOs. 

    The conclusion is that the balancing framework is useful as a simulation tool in helping SOs in finding more efficient decisions for transmission system balancing operation.

  • 29.
    Olauson, Jon
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    ERA5: The new champion of wind power modelling?2018In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 126, p. 322-331Article in journal (Refereed)
    Abstract [en]

    Output from meteorological reanalyses are used extensively in both academia and industry for modelling wind power. Recently, the first batch of the new ERA5 reanalysis was released. The main purpose of this paper is to compare the performance of ERA5 and MERRA-2 (a commonly used reanalysis today) in terms of modelling i) the aggregated wind generation in five different countries and ii) the generation for 1051 individual wind turbines in Sweden. The modelled wind power generation was compared to measurements. In conclusion, ERA5 performs better than MERRA-2 in all analysed aspects; correlations are higher, mean absolute and root mean square errors are in average around 20% lower and distributions of both hourly data and changes in hourly data are more similar to those for measurements. It is also shown that the uncertainty related to long-term correction (using one year of measurements and reanalysis data to predict the energy production during the remaining 1e5 years) is 20% lower for ERA5. In fact, using one year sample data and ERA5 gives slightly more accurate estimates than using two years of sample data and MERRA-2. Additionally, a new metric for quantifying the system size and dispersion of wind farms is proposed.

  • 30.
    Oluic, Marina
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Berggren, Bertil
    ABB Corp Res, S-72178 Vasteras, Sweden..
    Echavarren, Francisco M.
    Comillas Pontificia Univ, Inst Res Technol, ICAI Sch Engn, Madrid 28015, Spain..
    Ghandari, Mehrdad
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Rouco, Luis
    Univ Pontificia Comillas, Inst Invest Tecnol, Madrid 28015, Spain..
    On the Nature of Voltage Impasse Regions in Power System Dynamics Studies2018In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 33, no 3, p. 2660-2670Article in journal (Refereed)
    Abstract [en]

    This paper presents a fundamental study of voltage collapses that occur on a post-fault trajectory of a stressed power system in seconds after large disturbances. The focus of the study are voltage collapses that are induced by certain load models. Using an n-machine-N-bus power system model, the paper explicitly shows that the voltage collapse is caused by the non-existence of a real, positive solution for a load voltage magnitude in different areas of a relative rotor angle space when the load is of non-linear type. These "areas without voltage solution" are denoted as Voltage Impasse Regions (VIR) and are mathematically characterized as trigonometric functions of (n-1) relative rotor angles. Once the post-fault trajectory enters a VIR, voltage magnitude solutions become complex or negative, the algebraic Jacobian becomes singular, and the behaviour of a system becomes undefined. The case study has been carried out using a simple 3-machine-1-load system with static load models. In the study, VIR appeared and enlarged as the non-linear (constant power and constant current) load increased. Furthermore, the non-convergence of time-domain solution occurred exactly at VIR, thereby confirming that the problem is of structural nature.

  • 31.
    Paridari, Kaveh
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Sandels, Claes
    Aggregator strategy for planning demand response resources under uncertainty based on load flexibility modeling2018In: 2017 IEEE International Conference on Smart Grid Communications, SmartGridComm 2017, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 338-343, article id 8340694Conference paper (Refereed)
    Abstract [en]

    Nowadays, end-users can participate in demand response (DR) programs, and even slight load reductions from many houses can add up to major load shifts in the power system. Aggregators, which act as mediators between end-users and distribution system operator (DSO), play an important role here. The aggregator contracts the end-users for DR programs, plans ahead for times when customers should shift their load, and controls the load shifts in the running time. In this paper, our main focus is on planning the end-users for load shifting. Here, we first define and formulate the flexibilities (e.g., Stamina, repetition, and capacity) related to the dynamic loads such as space heating systems (SHSs) in detached houses. Assuming some end-users being contracted for DR program, based on estimation of their house characteristics and load flexibilities, an algorithm is then proposed to plan the SHSs for load shifting. In this algorithm the states in which a flexible load can be planned, kept in backup, or unavailable are considered by the aggregator. Another algorithm has been proposed here to deal with the different sources of uncertainties (which cause some of the planned SHSs to become unavailable). Numerical results are presented at the end, which discuss performance of the proposed strategy in terms of load flexibilities, load shifts in response to DR signals, and sensitivity analysis. Here, how to estimate the houses characteristics is a difficult issue, and we approximate them based on available models in the literature.

  • 32.
    Raj Kumar Bharathi, Nieraj
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Electrical Networks of CorPower Wave Farms: Economic Assessment and Grid Integration Analysis of Voltage2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    On the path towards the commercialisation of wave energy, there are still certaindevelopmental challenges to be tackled by industry and academia. One of these challengesis the grid integration of wave farms along with the development of the offshore electricalnetworks for the farms. These networks are distinct from those of offshore wind farms oncertain features – connection layouts, electrical interface equipment (subsea connectors),power ratings and cable lengths amongst many others. These differences apart from somechallenges unique to wave farms make the corresponding research attractive.CorPower Ocean AB has been developing a 250 𝑘𝑊 point-absorber type Wave EnergyConverter (WEC) and the thesis investigates the afore-mentioned challenges with a stagewiseanalysis of wave farms comprising the CorPower WECs. Prior research on electricalnetworks for CorPower WECs is limited and in this regard the objective is to gain apreliminary insight into the electrical architecture of a pre-commercial wave farm.Furthermore, the entire study is based at the wave test site of the European Marine EnergyCentre (EMEC).Analysis of network architecture and operational constraints resulted in 4 networkvariants for the farm ratings of 2 𝑀𝑊 and 10 𝑀𝑊. Three of the variants are applied to a2 𝑀𝑊 farm and are subjected to a varied analysis after which the standout variant is chosenfor subsequent modelling and analysis in the form of a 10 𝑀𝑊 farm. The comparativeanalysis includes an investigation into the capital expenditure (CAPEX), the associatedcost uncertainty, technology readiness level (TRL) of the electrical components andnetwork efficiency.Dynamic modelling and simulation of the networks is then performed on DIgSILENTPowerFactory to provide the network efficiency and voltage quality parameters includingstep voltage change, operational voltage limits and voltage flicker. The voltage quality ofthe modelled networks at the connection point are largely found to be compliant to theUK Distribution Code, applicable at the EMEC site. But, the same could not be said for theresults at some of the internal points of the electrical networks of the wave farms as thevoltage levels at certain terminals were found to be on the higher side.From the results of the thesis, a greater understanding of the compatibility of variants fora 2 𝑀𝑊 farm and 10 𝑀𝑊 farm of 250 𝑘𝑊 point-absorber WECs, has been obtained.Overall, it is believed that the thesis has contributed to the growing reservoir ofinformation on offshore electrical networks of wave farms and the corresponding gridintegration issues.

  • 33.
    Ren, Guorui
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. Harbin Institute of Technology, Harbin, China.
    Liu, J.
    Wan, J.
    Li, F.
    Guo, Y.
    Yu, D.
    The analysis of turbulence intensity based on wind speed data in onshore wind farms2018In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 123, p. 756-766Article in journal (Refereed)
    Abstract [en]

    Wind speed turbulence intensity is crucial for wind turbine structure design and aerodynamic loads calculation. In the study, the actual turbulence intensity observations are compared with the Normal Turbulence Model defined by IEC standard. The results show that the Normal Turbulence Model overestimates the turbulence intensity. A new turbulence intensity model is proposed based on the actual observations, which shows better performance than the Normal Turbulence Model. Then the variation pattern of turbulence intensity during a day is analyzed. The turbulence intensity exhibits obvious daily periodicity in two wind farms. Furthermore, the causes of daily periodicity are discussed and verified by the wind speed dataset 3. Finally, an improved time-varying turbulence intensity model is developed according to the daily periodicity.

  • 34.
    Ren, Guorui
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. Harbin Institute of Technology, Harbin, Heilongjiang, China.
    Wan, J.
    Liu, J.
    Yu, D.
    Söder, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Analysis of wind power intermittency based on historical wind power data2018In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 150, p. 482-492Article in journal (Refereed)
    Abstract [en]

    As wind power provides an increasingly larger share of electricity supply, the challenges caused by wind power intermittency have become more and more prominent. A better understanding of wind power intermittency would contribute to mitigate it effectively. In the present study, the definition of wind power intermittency is given firstly. Based on the definition, wind power intermittency is quantified by duty ratio of wind power ramp (DRWPR). This index provides system operators quantitative insights into wind power intermittency. Furthermore, some characteristics of wind power intermittency can be extracted by the index, such as the differences between wind speed intermittency and wind power intermittency, the differences of wind power intermittency between different scales and so on. The wind power intermittency of a Chinese wind farm is studied in detail based on the proposed index and historical data.

  • 35.
    Renbi, Abdelghani
    et al.
    Luleå Tekniska Universitet .
    Risseh, Arash
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Qvarnström, Rikard
    Luleå Tekniska Universitet .
    Delsing, Jerker
    Luleå Tekniska Universitet .
    Impact of etch factor on characteristic impedance, crosstalk and board density2012In: International Symposium on Microelectronics, no 1, p. 312-317Article in journal (Refereed)
    Abstract [en]

    Signal integrity becomes more important when the length of the Printed Wiring Board (PWB) traces surpasses λ/10 where λ denotes the wavelength. For fast digital communication purpose and low energy consumption in CMOS technology, faster rise time of the clock which means higher harmonic frequency, has always been preferable. In this case, the importance of considering signal integrity gets a higher priority as issues such reections and crosstalk between adjacent traces cannot be omitted, especially in dense High Density Interconnect (HDI) boards. Several factors control the effect of reections and the crosstalk such as the shape and dimension of the traces, the isolator characteristics which is inserted between the trace and the ground plane, the nearness and the geometry of the nearby conductors. In other words, these factors control the characteristic impedance of the traces and the mutual inductances and capacitances between the adjacent traces. Although these factors have been taken into account during the design phase for good signal integrity, the manufacturing process, which differs from vendor to vendor, has a great impact on the above factors. PWB manufacturing process may result in many different variations, which involve the dielectric constant, the thickness of the insulator, the trace width and the copper foil thickness. In addition to these variations, the etching quality that falls mainly in three different categories of trapezoidal trace form. In this paper we present the effect of three different etching shapes on the characteristic impedance. Moreover, it is concluded that one could gain space which can be used for shrinking the electronics and/or saving the raw material when trading the characteristic impedance error for space. Similar method is followed to investigate the crosstalk reduction between two adjacent microstriplines when tolerating the error in the characteristic impedance. This procedure can only be applied when a 90° etch angle process is feasible.

  • 36.
    Risseh, Arash
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Goupil, Christophe
    Condensed Matter and Electronics at Universite Paris Diderot.
    Electrical Power Conditioning System for Thermoelectric Waste Heat Recovery in Commercial Vehicles2018In: IEEE TRANSACTIONS ON TRANSPORTATION ELECTRIFICATION, ISSN 2332-7782, no 99Article in journal (Refereed)
    Abstract [en]

    A considerable part of the fuel energy in vehicles never reaches the wheels and entirely converts to waste heat. In a heavy duty vehicle (HDV) the heat power that escapes from the exhaust system may reach 170 kW. The waste heat can be converted into useful electrical power using thermoelectric generator (TEG). During the last decades, many studies on the electrical power conditioning system of TEGs have been conducted. However, there is a lack of studies evaluating the electrical instrumentation, the impact of the converter-efficiency, and the TEG arrangement on a real large-scale TEG on-boarda drivable vehicle. In this study, the most important parameters for designing electrical power conditioning systems for two TEGs, developed for a real-scale HDV as well as experimental results demonstrating the recovered electrical power, are presented. Eight synchronous inter-leaved step-down converters with 98 % efficiency with perturb and observe maximum power point tracker was developed and tested for this purpose. The power conditioning system was communicating with the on-board computers through the controller area network and reported the status of the TEGs and the recovered electrical power. The maximum recovered electrical power from the TEGs reached 1 kW which was transmitted to the electrical system of the vehicle, relieving the internal combustion engine.

  • 37.
    Risseh, Arash
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Kostov, Konstantin
    The Mads Clausen Institute, SDU Electrical Engineering, Sonderborg, Denmark.
    Fast Switching Planar Power Module With SiC MOSFETs and Ultra-low Parasitic InductanceManuscript (preprint) (Other academic)
    Abstract [en]

    Parasitic inductances, caused by the package of semiconductor devices in power converters, are limiting theswitching speed and giving rise to higher switching losses than necessary. In this study a half-bridge planar power module with Silicon Carbide (SiC) MOSFET bare dies was designed and manufactured for ultra-low parasitic inductance. The circuit structure was simulated and the parasitic inductances were extracted from ANSYS-Q3D. The values were then fed into LT-Spice to simulate the electrical behavior of the half-bridge.The experimental and simulation results were compared to each other and were used to adjust and easily extend the simulation model with additional MOSFETs for higher current capability. It was shown that the proposed planar module, with four parallel SiC MOSFETs at each position, is able to switch 600V and 400A during 40 and 17ns with EON and EOFF equal to 3.1 and 1.3 mJ, respectively. Moreover, unlike the commercial modules, this design allows double-sided cooling to extract the generated heat from the device, resulting in lower operating temperature.

  • 38.
    Risseh, Arash
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Nee, Hans-Peter
    KTH, Superseded Departments (pre-2005), Electrical Systems.
    Kostov, Konstantin
    The Mads Clausen Institute, SDU Electrical Engineering, Sonderborg, Denmark.
    Realization of a Planar Power Circuit With Silicon Carbide MOSFETs on Printed Circuit BoardManuscript (preprint) (Other academic)
    Abstract [en]

    Silicon Carbide (SiC) MOSFETs offer excellent properties as switches in power converters. However, the package of the device is an issue that prevents utilizing the advantages of SiC, as for instance fast switching speed. The packages of currently available SiC devices are the same as those previously used for silicon devices with moderate electrical and thermal characteristics resulting in accelerated aging and reliability issues. Furthermore, the parasitic inductance caused by the package, limits the switching time and operating frequency. By excluding the package, the parasitic inductances will be eliminated to a large extent. In this study, the procedure of manufacturing a half-bridge planar power module, using four SiC MOSFET bare dies and PCB, is described. According to simulations in ANSYS-Q3D, the parasitic inductance Lstray of the structureis approximately 96% lower than most commercial half-bridge modules. It is also shown that double-side cooling can bee mployed for the proposed module if substrates with low thermal resistance are used.

  • 39.
    Singh, Ravi Shankar
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Hooshyar, Hossein
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH.
    Experimental Real-Time Testing of a Decentralized PMU Data-Based Power Systems Mode Estimator2017In: 2017 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    This paper presents the results and testing of a Phasor Measurement Unit (PMU) data-based mode estimation application deployed within a decentralized architecture using a real-time test platform. This work is a continuation of that in [1], which described a decentralized mode estimation architecture that enables the application to better detect local modes whose observability is affected by other more observable modes. The tests in this paper were carried out using an active distribution network (ADN) comprised of a high voltage network connected to a distribution grid including renewable energy resources (RES). The developed application was run in a decentralized architecture where each PMU was associated with its own processing unit which was running the application to estimate modes from the time-series data. The results of the decentralized mode estimation architecture are analyzed and compared with its centralized counterpart.

  • 40.
    Soares, Rudi
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. KTH.
    Bessman, Alexander
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Wallmark, Oskar
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Lindbergh, Göran
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Svens, Pontus
    Scania.
    An Experimental Setup with Alternating Current Capability for Evaluating Large Lithium-Ion Battery Cells2018In: BatteriesArticle in journal (Refereed)
    Abstract [en]

    In the majority of applications using lithium-ion batteries, batteries are exposed to some harmonic content apart from the main charging/discharging current. The understanding of the effects that alternating currents have on batteries requires specific characterization methods and accurate measurement equipment. The lack of commercial battery testers with high alternating current capability simultaneously to the ability of operating at frequencies above 200 Hz, led to the design of the presented experimental setup. Additionally, the experimental setup expands the state-of-the-art of lithium-ion batteries testers by incorporating relevant lithium-ion battery cell characterization routines, namely hybrid pulse power current, incremental capacity analysis and galvanic intermittent titration technique. In this paper the hardware and the measurement capabilities of the experimental setup are presented. Moreover, the measurements errors due to the setup’s instruments were analysed to ensure lithium-ion batteries cell characterization quality. Finally, this paper presents preliminary results of capacity fade tests where 28 Ah cells were cycled with and without the injection of 21 A alternating at 1 kHz. Up to 300 cycles, no significant fade in cell capacity may be measured, meaning that alternating currents may not be as harmful for lithium-ion batteries as considered so far.

  • 41.
    Song, Meng
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Amelin, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Price-Maker Bidding in Day-Ahead Electricity Market for a Retailer With Flexible Demands2018In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 33, no 2, p. 1948-1958Article in journal (Refereed)
    Abstract [en]

    This study develops a short-term planning model to determine the bidding curves on a day-ahead market for a price-maker retailer with flexible power demand. It concerns the interactions between the spot price and the flexible demand. Both conditional value-at-risk and volume deviation risk are taken into account. A numerical study using the data from the Nordic electricity market is performed to investigate the influence of risk factors on the retailer's profit, risk levels, average spot price, and total consumption. Three types of price elasticity are compared to show that the retailer can benefit from the flexibility in demand side in some cases. The flexibility also leads to lower spot prices so that the customers in real-time price-based demand response can face a lower electricity price for per-unit power consumption.

  • 42. Stamatiou, Georgios
    et al.
    Beza, Mebtu
    Bongiorno, Massimo
    Harnefors, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Analytical derivation of the DC-side input admittance of the direct-voltage controlled modular multilevel converter2017In: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695, Vol. 11, no 16, p. 4018-4030Article in journal (Refereed)
    Abstract [en]

    The input admittance of a converter, connected to other dynamic subsystems, is a useful tool to investigate whether poorly damped oscillations or even unstable conditions might occur at certain frequencies. This is of interest in applications employing the modular multilevel converter (MMC), where the internal dynamics of the converter and the increased number of control loops greatly affect the MMC's dynamic behaviour, compared to other types of converters. In this study, the dc-side input admittance of the direct-voltage controlled MMC is derived analytically and verified via small-signal perturbation in a detailed non-linear time-domain simulation model. The MMC's input admittance is parametrically studied and compared to the dc-side input admittance of an equivalent two-level converter.

  • 43.
    Stankovic, Stefan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Söder, Lennart
    KTH, Superseded Departments (pre-2005), Electric Power Systems.
    Analytical Estimation of Reactive Power Capability of a Radial Distribution System2018In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679Article in journal (Refereed)
    Abstract [en]

    The control of reactive power exchange between grids of different voltage levels has always been a concern for system operators. With production moving from the transmission to the distribution level, its importance increases. This paper proposes a novel approach to estimate reactive power capability of the grid as a whole. A linearized analytical model for an estimation of available reactive power exchange at the interface between two grids has been developed. The maximum estimation error for the scenarios we tested was only 2%. The model gives the relation between important grid parameters and the supported reactive power. The conclusions drawn from the model are confirmed on typical Swedish distribution network with scattered wind power and small industry consumers. Common scenarios in development of distribution grids are applied to show relevant parameters influence. One studied scenario is replacement of overhead lines with cables. It is shown that this particular change enhances the reactive power capability of the grid which is directly seen from the analytical analysis without running any optimal power flow. The analytical model proposed in this paper gives fundamental understanding of the reactive power capability of radial distribution grids.

  • 44.
    Stankovic, Stefan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Söder, Lennart
    KTH, Superseded Departments (pre-2005), Electrical Systems. KTH, Superseded Departments (pre-2005), Electric Power Systems. KTH, Superseded Departments (pre-2005), Energy Technology.
    Optimal Power Flow Based on Genetic Algorithms and Clustering Techniques2018In: Power Systems Computational Conference PSCC 2018, 2018Conference paper (Refereed)
    Abstract [en]

    Optimal power flow problems have been studied extensively for the past decades. Two approaches for solving theproblem have been distinguished: mathematical programming and evolutionary algorithms. The first is fast but is not converging to a global optimum for every case. The second ones are robust but time-consuming. This paper proposes a method that combines both approaches to eliminate their flaws and take advantage of their benefits. The method uses properties of genetic algorithms to group their chromosomes around optima in the search space. The centers of these groups are identified by clustering techniques and furthermore used as initial points for gradient based search methods. At the end, the proposed method finds global optimum and its closest local optima. Continuous Newton-Raphson method is used to overcome ill-conditioned points in a search space when calculating power flows. The proposed method is compared against similar methods showing considerable improvement.

  • 45.
    Söder, Lennart
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Pellinger, Christoph
    Forschungsstelle für Energiewirtschaft e.V., Germany .
    Lopez-Botet Zulueta, Miguel
    EDF, France, .
    Milligan, Michael
    NREL, US, .
    Kiviluoma, Juha
    VTT, Technical Research Centre of Finland – Finland .
    Flynn, Damian
    University College Dublin, Ireland, .
    Orths, Antje
    Energinet.dk, Denmark, .
    Silva, Vera
    EDF, France, .
    O’Neill, Barbara
    NREL, US.
    Comparison of Integration Studies of 30-40 percent Energy Share from Variable Renewable Sources2017In: 16th International Workshop on Large-Scale Integration of Wind Power into Power Systems as well as on Transmission Networks for Offshore Wind Power Plants, Berlin, 2017, article id WIW17-049, 2017Conference paper (Other academic)
    Abstract [en]

    The amount of wind and solar power in the world is quickly increasing. The background for this development is improved technology, decreased costs for the units, and increased concern regarding environmental problems of competing technologies such as fossil fuels. For the future there are large possibilities for increasing shares. However there have been questions raised concerning the challenges of integrating larger shares of variable renewable power such as wind and solar power. Because of this many studies have been performed concerning larger amounts of variable generation for different regions in the world. The aim of this paper is to compare seven of these ones in order to identify general challenges and results as well as the connection between used method and results. 

  • 46. Tohidi, Yaser
    et al.
    Hesamzadeh, Mohammad Reza
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Regairaz, Francois
    Modified Benders Decomposition for Solving Transmission Investment Game With Risk Measure2018In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 33, no 2, p. 1936-1947Article in journal (Refereed)
    Abstract [en]

    This paper proposes a mathematical model for transmission investment game where there are several transmission planners (TPs). The model is developed assuming a simultaneous-move game between TPs. Each TP maximizes the total surplus (producers', consumers', and transmission surplus) minus the investment cost of its region given the investment decisions of rival TPs. The transmission investment risk is also considered using the probability-of-shortfall measure. We assume one market operator who dispatches the generators in all TP's regions. The risk-constrained Nash equilibria model is formulated as amixed-integer linear program (MILP). To solve the proposed MILP, a solution algorithm is proposed that combines the standard branch-and bound algorithm (BB) with a proposed modified benders decomposition algorithm (MBD). The proposed BB-MBD algorithm is also parallelized to improve the computation performance. To improve the coordination between TPs, a supporting budget mechanism is also mathematically modeled in the MILP. The numerical results are carried out using the 9-bus 3-area and the IEEE Three Area RTS-96 networks. The computational performance of proposed BB-MBD is compared with standard BB algorithm.

  • 47. Trashchenkov, S.
    et al.
    Astapov, Victor
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. School of Engineering, Tallinn University of Technology, Tallinn, Estonia.
    The applicability of zero inflated beta distributions for stochastic modeling of PV plants' power output2018In: 2018 19th International Scientific Conference on Electric Power Engineering, EPE 2018 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 1-6Conference paper (Refereed)
    Abstract [en]

    Uncertainty of generation is the inherent property of renewable energy sources such as photovoltaic panels. Issues such as optimal choice of equipment, energy management, and reliability of energy supply in distribution grids and microgrids should take into account this uncertainty. Usually this type of uncertainty is modeled by setting distributions of climate conditions (solar irradiation, temperature, wind speed). The specific values of power output in this case are determined by weather conditions and specifications of equipment. Such approach demands huge amount of systematic meteorological observations. This paper investigates the setting of generation output for photovoltaic plants without distributions of weather conditions. The proposed method assumes the use of hourly average generation data. The data are divided into samples. The samples are fitted by degenerated, beta or zero inflated beta distributions. Degenerated and beta distributions are presented as special cases of the more general zero inflated beta distributions.

  • 48.
    Velander, Erik
    et al.
    Bombardier Transportat Sweden AB, Dept Medium Power Tract Converter Design, S-72173 Vasteras, Sweden..
    Bohlin, Georg
    Bombardier Transportat Sweden AB, Tract Syst Dept, S-72173 Vasteras, Sweden..
    Sandberg, Asa
    Bombardier Transportat Sweden AB, Tract Syst Dept, S-72173 Vasteras, Sweden..
    Wiik, Thomas
    Bombardier Transportat Sweden AB, Dept Medium Power Tract Converter Design, S-72173 Vasteras, Sweden..
    Botling, Fredrik
    Bombardier Transportat Sweden AB, Dept Converter Control, S-72173 Vasteras, Sweden..
    Lindahl, Martin
    Bombardier Transportat Sweden AB, Dept Medium Power Tract Converter Design, S-72173 Vasteras, Sweden..
    Zanuso, Giovanni
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    An Ultralow Loss Inductorless dv/dt Filter Concept for Medium-Power Voltage Source Motor Drive Converters With SiC Devices2018In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 33, no 7, p. 6072-6081Article in journal (Refereed)
    Abstract [en]

    In this paper, a novel dv/dt filter is presented targeted for 100-kW to 1-MW voltage source converters using silicon carbide (SiC) power devices. This concept uses the stray inductance between the power device and the converter output as a filter component in combination with an additional small RC-link. Hence, a lossy, bulky, and costly filter inductor is avoided and the resulting output dv/dt is limited to 5-10 kV/mu s independent of the output current and switching speed of the SiC devices. As a consequence, loads with dv/dt constraints, e.g., motor drives can be fed from SiC devices enabling full utilization of their high switching speed. Moreover, a filter-model is proposed for the selection of filter component values for a certain dv/dt requirement. Finally, results are shown using a 300-A 1700-V SiC metal-oxide-semiconductor field-effect transistor (MOSFET). These results show that the converter output dv/dt can be limited to 7.5 kV/mu s even though values up to 47 kV/mu s weremeasured across the SiC MOSFET module. Hence, the total switching losses, including the filter losses, are verified to be three times lower compared to when the MOSFET dv/dt was slowed down by adjusting the gate driver.

  • 49.
    Yao, Yanmei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Sadarangani, Chandur
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Zhang, Hui
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Efficiency Improvement of a 12-Pole 17.5 kW Induction Motor Using Converter-fed Wound Rotor2017In: 2017 20TH INTERNATIONAL CONFERENCE ON ELECTRICAL MACHINES AND SYSTEMS (ICEMS), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    This paper investigates an induction machine using a novel concept of a converter-fed rotor. The stator is directly connected to the grid while the rotor is fed by a converter with a floating capacitor over the dc-link. In earlier work this topology has shown to be capable of improving the power factor and efficiency of a 4-pole induction machine. This paper explores the possibility to improve the power factor and efficiency of a squirrel-cage 12-pole 17.5 kW induction machine by redesigning the cage rotor to a wound rotor to enable connection of the rotor windings to the converter. A standard 12-pole squirrel-cage induction machine (SCIM) with an inherent low power factor is studied. A wound rotor induction machine (WRIM) is then analytically designed. The performance of the designed WRIM using the analytical model is shown to agree with the results from the finite element (FEM) simulations, thus verifying the correctness of the model. The analytical model is then further used to design different WRIMs with different dimensions and rotor slot numbers. Performances of these designed WRIMs show good potential for power factor and efficiency improvement. Particularly, an optimum efficiency improvement of 6.8%, compared with the original SCIM, has been achieved.

  • 50.
    Yiming, Wu
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Wang, Yujue
    Washington State University.
    Hauser, Carl
    Washington State University.
    Adaptive Cyber-Security Scheme Incorporating QoS Requirements for WAMC Applications2018In: Power Systems Computation Conference (PSCC2018), 2018Conference paper (Refereed)
12 1 - 50 of 59
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