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  • 1.
    Aguilera, Miguel
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Semantic and Physical Modeling and Simulation of Multi-Domain Energy Systems: Gas Turbines and Electrical Power Networks2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The ITEA3 OpenCPS (Open Cyber-Physical System Model-Driven CertifiedDevelopment) project focuses on interoperability between the Modelica/UnifiedModeling Language (UML)/Functional Mock-up Interface (FMI) standards, improved(co-)simulation execution speed, and verified code generation. The project aims to developa modeling and simulation framework for cyber-physical and multi-domain systems. Oneof the main use cases for the framework, is the multi-domain equation-based modelingand simulation of detailed gas turbine power plants (including the explicit equation-basedmodeling of turbomachinery dynamics) and the electrical power grid.In this work, UML class diagrams based on the Common Information Model (CIM)standard are used to describe the semantics of the electrical power grid. An extension basedon the standard ISO 15926 has been proposed to derive the multi-domain semanticsrequired by the models that integrate the electrical power grid with the detailed gas turbinedynamics.Furthermore, the multi-domain physical modeling and simulation Modelica language hasbeen employed to create the equation-based models of the use case of this project. Acomparative analysis between the Single-Domain and Multi-Domain model responses hasbeen performed both in time and frequency. The results show some interesting differencesbetween the turbine dynamics representation of the commonly used GGOV1 standardmodel and the less simplified model of a gas turbine.Finally, the models from each domain can be exchanged between two differentstakeholders by means of Functional Mock-Up Units (FMUs), defined by the FMIstandard. Promising test results were obtained with different simulation tools that supportthe standard, which demonstrates the feasibility of exchanging unambiguous multi-domainmodels with a detailed gas turbine representation. This shows the potential of the FMIstandard for manufacturers to exchange equation-based multi-domain models, while at thesame time protecting their intellectual property.

  • 2.
    Ahlfors, Charlotta
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    On the impact of wind power on CO2 emissions in a power system2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis is carried out at KTH Royal Institute of Technology in Stockholmthe spring 2017. The project analyses the impact of wind power in a power system.A fictitious power system, created from the Nordic32 test system, is used for theanalysis. The power sources in the test system are hydro power, nuclear power, CHPand wind power, resembling Swedish conditions. The power production planning inthe system is solved as a mixed integer linear programming problem in GAMS withhourly resolution. From the result of the planning problem calculations of CO2emissions are carried out with Monte Carlo simulations. Different cases with differentamounts of wind power installed in the test system are studied via a stochasticMarkov model. The load model in the test system consists of hourly time seriesdata for a specific day. Furthermore, challenges with wind power as a continuouslyvarying power source are studied. These challenges are balance between productionand consumption in the power system, excess of power etc.The results show that increasing the wind power production results in a decreasein CO2 emissions. This can be seen from the different simulations in the project.However, the results show that increasing the wind power production means that thesystem becomes more sensitive to keep the power balance. Moreover, the dischargecapacity and the efficiency of the hydro power plants are important factors in thetest system.

  • 3.
    Ahmed, Noman
    et al.
    KTH.
    Ängquist, Lennart
    KTH.
    Mehmood, Shahid
    Antonopoulos, Antonios
    Harnefors, Lennart
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Efficient Modeling of an MMC-Based Multiterminal DC System Employing Hybrid HVDC Breakers2016In: 2016 IEEE POWER AND ENERGY SOCIETY GENERAL MEETING (PESGM), IEEE , 2016Conference paper (Refereed)
  • 4.
    Alahakoon, Sanath
    et al.
    Central Queensland University, Australia.
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Emerging energy storage solutions for transportation - A review: An insight into road, rail, sea and air transportation applications2015In: Electrical Systems for Aircraft, Railway and Ship Propulsion, ESARS, IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    Increasing usage of hybrid electric vehicles, plug-in electric vehicles and emerging new concepts in transportation such as electric highways have raised the significant role of energy storage solutions for transportation to its highest level. It is impossible to specify a single energy storage solution that can satisfactorily fulfill the varying performance demands of various applications in transportation. This paper will identify some of the most demanded performance requirements from some of the key applications in transportation and assess the suitability of emerging energy storage solutions against those.

  • 5.
    Ali, Muhammad Taha
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ghandari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Mitigation of Sub-Synchronous Control Interaction in DFIGs using a Power Oscillation Damper2017In: 2017 IEEE Manchester PowerTech, Powertech 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 7980941Conference paper (Refereed)
    Abstract [en]

    The aim of this research work is to analyse subsynchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs) and to design a supplementary control technique for the mitigation of SSCI. A mathematical model of the DFIG is derived and linearized in order to perform an eigenvalue analysis. This analysis pinpoints the parameters of the system which are sensitive in making sub-synchronous modes unstable and hence are responsible for causing SSCI. A power oscillation damper (POD) is designed using a residue method to make the DFIG system immune to the SSCI. The POD control signal acts as a supplementary control, which is fed to the controller of the grid-side converter (GSC). The POD signal is applied to different summation junctions of the GSC controller in order to determine the best placement of the POD for effective mitigation of SSCI and for the increased damping of the system.

  • 6.
    Ali, Muhammad Taha
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH Royal Institute of Technology.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Effect of control parameters on infliction of sub-synchronous control interaction in DFIGs2016In: 2016 IEEE International Conference on Power and Renewable Energy (ICPRE), IEEE conference proceedings, 2016, p. 72-78, article id 7871175Conference paper (Refereed)
    Abstract [en]

    This research work deals with the analysis of sub-synchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs). The time-invariant model of the DFIG is linearized to perform eigenvalue analysis and to obtain the participation factor of each state variable for unstable modes. The sensitivity of system eigenvalues related to sub-synchronous modes is analyzed with respect to all the proportional and integral parameters of the controllers in the rotor-side-converters and grid-side-converters. The major contribution of this research work is the outcomes based on eigenvalue analysis that clearly point out the control parameters to which sub-synchronous modes are highly sensitive. The effect of series compensation level on DFIG system and on the sensitivity of converter control parameters is also studied.

  • 7.
    Almas, M. Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Statnett SF, Res & Dev, Oslo, Norway.
    RT-HIL Implementation of Hybrid Synchrophasor and GOOSE-based Passive Islanding Schemes2016In: 2016 IEEE POWER AND ENERGY SOCIETY GENERAL MEETING (PESGM), IEEE , 2016Conference paper (Refereed)
  • 8.
    Almas, Muhammad Shoaib
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Synchrophasor Applications and their Vulnerability to Time Synchronization Impairment2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Recent years have seen the significance of utilizing time-synchronized, high resolution measurements from phasor measurement units (PMUs) to develop and implement wide-area monitoring, protection and control (WAMPAC) systems. WAMPAC systems aim to provide holistic view of the power system and enable detection and control of certain power system phenomena to enhance reliability and integrity of the grid.

    This thesis focuses on the design, development and experimental validation of WAMPAC applications, and investigates their vulnerability to time synchronization impairment. To this purpose, a state-of-the-art real-time hardware-in-the-loop (RT-HIL) test-bench was established for prototyping of synchrophasor-based applications. This platform was extensively used throughout the thesis for end-to-end testing of the proposed WAMPAC applications. To facilitate the development of WAMPAC applications, an open-source real-time data mediator is presented that parses the incoming synchrophasor stream and provides access to raw data in LabVIEW environment.

    Within the domain of wide-area protection applications, the thesis proposes hybrid synchrophasor and IEC 61850-8-1 GOOSE-based islanding detection and automatic synchronization schemes. These applications utilize synchrophasor measurements to assess the state of the power system and initiate protection / corrective action using GOOSE messages. The associated communication latencies incurred due to the utilization of synchrophasors and GOOSE messages are also determined. It is shown that such applications can have a seamless and cost-effective deployment in the field.

      Within the context of wide-area control applications, this thesis explores the possibility of utilizing synchrophasor-based damping signals in a commercial excitation control system (ECS). For this purpose, a hardware prototype of wide-area damping controller (WADC) is presented together with its interface with ECS. The WADC allows real-time monitoring and remote parameter tuning that could potentially facilitate system operators’ to exploit existing damping assets (e.g. conventional generators) when changes in operating conditions or network topology emerges.

    Finally the thesis experimentally investigates the impact of time synchronization impairment on WAMPAC applications by designing RT-HIL experiments for time synchronization signal loss and time synchronization spoofing. It is experimentally demonstrated that GPS-based time synchronization impairment results in corrupt phase angle computations by PMUs, and the impact this has on associated WAMPAC application. 

  • 9.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Baudette, Maxime
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Statnett.
    Utilizing synchrophasor-based supplementary damping control signals in conventional generator excitation systems2018In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 157, p. 157-167Article in journal (Refereed)
    Abstract [en]

    A supplementary function of Excitation Control Systems (ECSs) for synchronous generators is that of a Power System Stabilizer (PSS). The PSS implementation in these ECSs only allows the use of a limited type of pre-defined local input measurements and built-in PSS algorithms. To adapt existing ECSs to take advantage of synchrophasors technology, this paper proposes and implements a prototype wide-area damping controller (WADC) that provides synchrophasor-based damping input signals to existing ECSs. The developed WADC comprise (i) a real-time mode estimation module, (ii) synchrophasor’s communication latency computation module, and (iii) phasor-based oscillation damping algorithm executing in a real-time hardware prototype controller.

    Through Real-Time Hardware-in-the-Loop (RT-HIL) simulations, it is demonstrated that synchrophasor-based damping signals from the WADC can be utilized together with a commercial ECS, thus providing new options for selection of the best feedback signal for oscillation damping.

  • 10.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Statnett.
    A Hybrid Synchrophasor and GOOSE-Based Power System Synchronization Scheme2016In: IEEE Access, E-ISSN 2169-3536, Vol. 4, p. 4659-4668Article in journal (Refereed)
    Abstract [en]

    The design and real-time hardware-in-the-loop implementation of a hybrid synchrophasors and GOOSE-based automatic synchronization algorithm are presented in this paper. Automatic synchronization is performed by utilizing the synchrophasor measurements from two commercial phasor measurement units (PMUs), while the coordinated control commands to automatic voltage regulator and/or turbine governor control and trip command to the circuit breaker are issued using IEC 61850-8-1 GOOSE messages. The algorithm is deployed inside the PMU using the protection logic equations, and direct communication between the PMUs is established to minimize the communication latencies. In addition, the algorithm is tested using a standard protection relay test-set, and automatic test sequences are executed to validate its performance. It is concluded that the hybrid synchrophasor and GOOSE-based automatic synchronization scheme ensures minimum communication latencies, reduces equipment cost, facilitates interoperability, and performs automatic reconnection adequately.

  • 11.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Statnett.
    A method exploiting direct communication between phasor measurement units for power system wide-area protection and control algorithms2017In: MethodsX, ISSN 1258-780X, E-ISSN 2215-0161, Vol. 4, p. 346-359Article in journal (Refereed)
    Abstract [en]

    Synchrophasor measurements from Phasor Measurement Units (PMUs) are the primary sensors used to deploy Wide-Area Monitoring, Protection and Control (WAMPAC) systems. PMUs stream out synchrophasor measurements through the IEEE C37.118.2 protocol using TCP/IP or UDP/IP. The proposed method establishes a direct communication between two PMUs, thus eliminating the requirement of an intermediate phasor data concentrator, data mediator and/or protocol parser and thereby ensuring minimum communication latency without considering communication link delays. This method allows utilizing synchrophasor measurements internally in a PMU to deploy custom protection and control algorithms. These algorithms are deployed using protection logic equations which are supported by all the PMU vendors. Moreover, this method reduces overall equipment cost as the algorithms execute internally in a PMU and therefore does not require any additional controller for their deployment. The proposed method can be utilized for fast prototyping of wide-area measurements based protection and control applications. The proposed method is tested by coupling commercial PMUs as Hardware-in-the-Loop (HIL) with Opal-RT’s eMEGAsim Real-Time Simulator (RTS). As illustrative example, anti-islanding protection application is deployed using proposed method and its performance is assessed. The essential points in the method are:

    •  Bypassing intermediate phasor data concentrator or protocol parsers as the synchrophasors are communicated directly between the PMUs (minimizes communication delays).

    •  Wide Area Protection and Control Algorithm is deployed using logic equations in the client PMU, therefore eliminating the requirement for an external hardware controller (cost curtailment)

    •  Effortless means to exploit PMU measurements in an environment familiar to protection engineers

  • 12.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Statnett.
    Impact of Time-Synchronization Signal Loss on PMU-based WAMPAC Applications2016In: IEEE PES General Meeting 2016, IEEE , 2016Conference paper (Refereed)
    Abstract [en]

    This paper experimentally assesses the impact of loss of time-synchronization signal on synchrophasor-based Wide-Area Monitoring, Protection and Control applications. Phase Angle Monitoring (PAM), anti-islanding protection and power oscillation damping applications are investigated. Power system models are executed using a real-time simulator with commercial PMUs coupled to them as hardware-in-the-loop. The experiments conclude that a phase angle monitoring application shows erroneous power system state whereas the operating time of an anti-islanding protection application increases due to the loss of time-synchronization signal input to PMUs. In addition, the performance of an oscillation damping controller degrades in the absence of time-synchronization input to the PMUs.

  • 13.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric power and energy systems. Statnett.
    RT-HIL Implementation of Hybrid Synchrophasor and GOOSE-based Passive Islanding Schemes2015In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 31, no 3, p. 1299-1309Article in journal (Refereed)
    Abstract [en]

    Real-time hardware-in-the-loop performance assessmentof three different passive islanding detection methodsfor local and wide-area synchrophasor measurements is carriedout in this paper. Islanding detection algorithms are deployedwithin the phasor measurement unit (PMU) using logic equations.Tripping decisions are based on local and wide-area synchrophasorsas computed by the PMU, and trips are generated usingIEC 61850-8-1 generic object-oriented substation event messages.The performance assessment compares these islanding detectionschemes for the nondetection zone and operation speed underdifferent operating conditions. The testbench that is demonstratedis useful for a myriad of applications where simulation exercises inpower system computer-aided design software provide no realisticinsight into the practical design and implementation challenges.Finally, different communication latencies introduced due tothe utilization of synchrophasors and IEC 61850-8-1 GOOSEmessages are determined.

  • 14.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Statnett.
    Baudette, Maxime
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    BabelFish—Tools for IEEE C37.118.2-compliant real-time synchrophasor data mediation2017In: SoftwareX, ISSN 2352-7110, Vol. 6, p. 209-216Article in journal (Refereed)
    Abstract [en]

    BabelFish (BF) is a real-time data mediator for development and fast prototyping of synchrophasor applications. BF is compliant with the synchrophasor data transmission IEEE Std C37.118.2-2011. BF establishes a TCP/IP connection with any Phasor Measurement Unit (PMU) or Phasor Data Concentrator (PDC) stream and parses the IEEE Std C37.118.2-2011 frames in real-time to provide access to raw numerical data in the LabVIEW environment. Furthermore, BF allows the user to select ‘‘data-of-interest’’and transmit it to either a local or remote application using the User Datagram Protocol (UDP) in order to support both unicast and multicast communication. In the power systems Wide Area Monitoring Protection and Control (WAMPAC) domain, BF provides the first Free/Libre and Open Source Software (FLOSS) for the purpose of giving the users tools for fast prototyping of new applications processing PMU measurements in their chosen environment, thus liberating them of time consuming synchrophasor data handling and allowing them to develop applications in a modular fashion, without a need of a large and monolithic synchrophasor software environment.

  • 15.
    Almas, Muhammad Shoaib
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Statnett.
    Singh, Ravi Shankar
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH Royal Institute of Technology.
    Jonsdottir, Gudrun Margret
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH Royal Institute of Technology.
    Vulnerability of Synchrophasor-based WAMPAC Applications’ to Time Synchronization Spoofing2018In: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061, Vol. 9, no 5, p. 4601-4612Article in journal (Refereed)
    Abstract [en]

    This paper experimentally assesses the impact of time synchronization spoofing attacks (TSSA) on synchrophasor-based Wide-Area Monitoring, Protection and Control applications. Phase Angle Monitoring (PAM), anti-islanding protection and power oscillation damping applications are investigated. TSSA are created using a real-time IRIG-B signal generator and power system models are executed using a real-time simulator with commercial phasor measurement units (PMUs) coupled to them as hardware-in-the-loop. Because PMUs utilize time synchronization signals to compute synchrophasors, an error in the PMUs’ time input introduces a proportional phase error in the voltage or current phase measurements provided by the PMU. The experiments conclude that a phase angle monitoring application will show erroneous power transfers, whereas the anti-islanding protection mal-operates and the damping controller introduces negative damping in the system as a result of the time synchronization error incurred in the PMUs due to TSSA.The proposed test-bench and TSSA approach can be used to investigate the impact of TSSA on any WAMPAC application and to determine the time synchronization error threshold that can be tolerated by these WAMPAC applications.

  • 16. Alobaidli, Hanan
    et al.
    Nasir, Qassim
    Iqbal, Asif
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Guimaraes, Mario
    Challenges of Cloud Log Forensics2017In: Proceedings of the SouthEast Conference, ACM , 2017, p. 227-230Conference paper (Refereed)
    Abstract [en]

    The forensics 1 investigation of cloud computing is faced by many obstacles originating from the complex integration of technologies used to build the cloud and its sheer size. In this research we aim to provide an insight into cloud computing log forensics, as logs are an important source of forensic evidence in the cloud. This is followed with conclusions regarding the issues faced by researchers in log forensics in cloud computing that will aid the research process.

  • 17.
    Amelin, Mikael
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Hersoug, Ellef
    Options for Rural Electrification in Developing Countries. A Case Study in Kasulu, Tanzania.1997Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 18.
    Andersson, Dorothea
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Simulation of industrial control system field devices for cyber security2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Industrial Control Systems (ICS) are an integral part of modernsociety, not least when it comes to controlling and protecting criticalinfrastructure such as power grids and water supply. There is a need to testthese systems for vulnerabilities, but it is often difficult if not impossible to doso in operational real time systems since they have been shown to be sensitiveeven to disturbances caused by benign diagnostic tools. This thesis exploreshow ICS field devices can be simulated in order to fool potential antagonists,and how they can be used in virtualized ICS for cyber security research. 8different field devices were simulated using the honeypot daemon Honeyd,and a generally applicable simulation methodology was developed. It was alsoexplored how these simulations can be further developed in order to functionlike real field devices in virtualized environments.

  • 19. Angioni, A.
    et al.
    Hooshyar, Hossein
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Garcia, C.C.
    et al.,
    A distributed automation architecture for distribution networks, from design to implementation2018In: Sustainable Energy, Grids and Networks, ISSN 0284-4354, E-ISSN 2352-4677, Vol. 15, p. 3-13Article in journal (Refereed)
    Abstract [en]

    With the current increase of distributed generation in distribution networks, line congestions and PQ issues are expected to increase. The smart grid may effectively coordinate DER, only when supported by a comprehensive architecture for automation. In IDE4L project such architecture is designed based on monitoring, control and business use cases. The IDE4L instance of SGAM architecture is derived and explained in details. The automation actor are specified in terms of interfaces, database and functions. The division in these three layers boosted the implementation phase as dedicated interfaces, databases or application has been developed in a modular way and can be installed in different HW/SW. Some implementation instances are presented and the main output of the architecture is discussed with regards to some indexes as communication traffic and level of distribution of automation functions.

    The full text will be freely available from 2019-04-27 13:00
  • 20.
    Armendariz, Mikel
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Babazadeh, Davood
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Brodén, Daniel
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Strategies to improve the voltage quality in active low-voltage distribution networks using DSO's assets2017In: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695, Vol. 11, no 1, p. 73-81Article in journal (Refereed)
    Abstract [en]

    This study addresses the problem of voltage variations in active low-voltage distribution networks caused by distributed photovoltaic (PV) generation. Three strategies based on model predictive control (MPC) are introduced to flatten the voltage profile in a cost-optimal way. The compared strategies are the business as usual approach that manipulates a controllable on-load tap changer at the primary substation, the problematic feeder control strategy (CS) that adds an additional degree of freedom by controlling the critical secondary substations (SSs), and finally the compensation strategy, which controls the primary substation and compensates the non-critical SSs. A sensitivity analysis on the CSs has been conducted comparing the voltage variation reduction and the asset utilization with regard to the accuracy of the prediction models and the forecasted disturbance data. The results show that better (and more costly) characterisation of these parameters only provide a marginal improvement in the reduction of the voltage variations due to the restriction caused by the heavy tap change penalisation. Moreover, the tested case-study shows that the problematic feeder CS outperforms the compensation strategy in terms of larger voltage variation reduction for similar asset utilisation.

  • 21.
    Armendariz, Mikel
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Babazadeh, Davood
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Barchiesi, Michele
    Department of Electrical, Electronic and Inf. Engineering University of Bologna.
    A Method to Place Meters in Active Low Voltage Distribution Networks using BPSO Algorithm2016Conference paper (Refereed)
    Abstract [en]

    This paper proposes a method to be used by a DSOto optimally place sensors at MV/LV substation and some lowvoltage cable distribution cabinets. This method aims to improvethe estimation of the grid states at low voltage distributionnetworks. This method formulates a multi-objective optimizationproblem to determine the optimal meter placementconfiguration. This formulation minimizes the low voltage stateestimation error and the cost associated to a particular meterdeployment configuration. The method uses Binary ParticleSwarm Optimization (BPSO) to solve the optimization problemand it has been tested on a network based on the Cigré LVbenchmark grid. The simulation results show that the methodcan be applied to both situations where smart metermeasurements are available and situations where they are not. Inthe latter situation the measurements are replaced by pseudomeasurements,which represent meter readings by using smartmeter historical data and prediction models.

  • 22.
    Armendariz, Mikel
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Heleno, Miguel
    Lawrence Berkeley National Laboratory.
    Cardoso, Gonçalo
    Lawrence Berkeley National Laboratory.
    Mashayekh, Salman
    Lawrence Berkeley National Laboratory.
    Stadler, Michael
    Lawrence Berkeley National Laboratory.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Coordinated Microgrid Investment and Planning Process Considering the System Operator2017In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 200, p. 132-140Article in journal (Refereed)
    Abstract [en]

    Nowadays, a significant number of distribution systems are facing problems to accommodate more photovoltaic (PV) capacity, namely due to the overvoltages during the daylight periods. This has an impact on the private investments in distributed energy resources (DER), since it occurs exactly when the PV prices are becoming attractive, and the opportunity to an energy transition based on solar technologies is being wasted. In particular, this limitation of the networks is a barrier for larger consumers, such as commercial and public buildings, aiming at investing in PV capacity and start operating as microgrids connected to the MV network. To address this challenge, this paper presents a coordinated approach to the microgrid investment and planning problem, where the system operator and the microgrid owner collaborate to improve the voltage control capabilities of the distribution network, increasing the PV potential. The results prove that this collaboration has the benefit of increasing the value of the microgrid investments while improving the quality of service of the system and it should be considered in the future regulatory framework.

  • 23.
    Armendariz, Mikel
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Johansson, Christian
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Yunta Huete, Angel
    Unión Fenosa Distribución.
    García Lobo, Miguel
    Gas Natural Fenosa Engineering.
    A Method to Design Optimal Communication Architectures in Advanced Metering Infrastructures2017In: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695, Vol. 11, no 2, p. 339-346Article in journal (Refereed)
    Abstract [en]

    This paper proposes a method to determine the optimal communication architecture in advance metering infrastructures (AMI). The method starts by indicating suitable groups of meters that share similar characteristics such as distance to the secondary substation and mutual proximity. Then it connects each group of meters to the AMI-Head End through a communication architecture formed by wireless and Power Line Communication (PLC) technologies. The optimality criterion takes into account the Capital Expenditures (CAPEX), Operational Expenditures (OPEX) and the Quality of Service (QoS) in the communication architecture. The method is tested on a LV network based on real utility data provided by EU FP7 DISCERN project partners. These tests show that the method is consistent with planning foresight and can be useful to assist in the AMI communication architecture designing process.

  • 24.
    Armendariz, Mikel
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Paridari, Kaveh
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Wallin, Edel
    Vattenfall R&D.
    Comparative Study of Optimal Controller Placement Considering Uncertainty in PV Growth and Distribution Grid Expansion2018In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 155C, p. 48-57Article in journal (Refereed)
    Abstract [en]

    Distributed generation (DG) and especially grid-connected residential photovoltaic (PV) systems areemerging and high penetration levels of these can have an adverse impact on several low voltage (LV)distribution grids in terms of power quality and reliability. In order to reduce that effect in a cost-effectivemanner, the traditional distribution grid planning process is being reengineered by incorporating the gridcontrol operations and considering the uncertainties e.g., DG power, demand and urban/rural expansionplans. One of the challenges is to determine if the required technology deployment to operate the gridscan provide a better solution in terms of quality and cost than the traditional approach, which is prin-cipally based on cable reinforcement and change of transformers. In addition, if controllers were to bedeployed, it would be important to determine where they should be placed and at what stage of theexpansion planning, especially when the planning is assumed to be non-deterministic.Therefore, following this situation, in this paper we propose an optimal way to deploy and to operateutility’s controllable resources at the distribution grid and additionally we consider the uncertaintiesrelated to PV growth and distribution grid expansion. Thus, we include the non-deterministic multistageperspective to the controller placement problem. Furthermore, we perform a techno-economic analysis ofthe results and we show that an optimal controller placement allows removing the overvoltage problemsarising in the LV grid in a more cost-effective way compared to a typical traditional grid reinforcementapproach.

  • 25.
    Armendariz, Mikel
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH - Royal Institute of Technology.
    Rodrigo, Gonzalez
    KTH, School of Electrical Engineering (EES). KTH - Royal Institute of Technology.
    Korman, Matus
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH - Royal Institute of Technology.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. KTH - Royal Institute of Technology.
    Method for Reliability Analysis of Distribution Grid Communications Using PRMs-Monte Carlo Methods2017Conference 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 fromthe 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.

  • 26.
    Armendáriz, Mikel
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Cost-effective Communication and Control Architectures for Active Low Voltage Grids2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The monitoring and control of low voltage distribution grids has historically been disregarded due to the unidirectional flow of power. However, nowadays the massive integration of distributed energy resources into distribution grids, such as solar photovoltaics, distributed storage, electric vehicles and demand response programs, presents some challenges. For instance, the unidirectional top-down power flow is being replaced by power flows in any direction: top-down and bottom-up. This paradigm shift adds extra regulatory, economic, and technical complexity for the Distribution System Operators (DSO). Thus to overcome the possible operational constraints, thermal limits, or voltage problems in the grid, an update of the existing electricity infrastructures is required. In response to this new situation, this thesis investigates the cost-effective communication and control architectures that are required for active low voltage grid monitoring and control applications, considering the regulatory constraints and the efficient utilization of the assets from a DSO’s perspective. The solutions include: i) optimal sensor placement configuration to perform low voltage state estimation, ii) optimal metering infrastructure designs for active low voltage monitoring applications, iii) coordinated control strategies to allow the integration of microgrid-like structures into the distribution grids, iv) optimal placement of actuators for operating the control strategies, v) a multiagent-based control solution for self-healing and feeder reconfiguration applications, and vi) a framework model and simulations to assess the reliability of the ICT infrastructure that enables the monitoring and control applications. As concluding remark, since the deployment of technology at low voltage grids is restricted to assets owned by the DSO, the operability of the grid is limited. This condition makes it so that the required communication and control enhancement solutions shall prioritize cost-effectiveness over comprehensiveness and complexity. Thus, the results from the presented studies show that it is essential to perform thorough cost-benefit analyses of the potential improvement solutions for each grid, because this will allow deploying the right technology only at the necessary locations.

  • 27.
    Augustin, Tim
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Jahn, Ilka
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Transient Behaviour of VSC-HVDC Links with DC Breakers Under Faults2017In: 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]

    In future high-voltage direct current (HVDC) systems, a large number of HVDC breakers will be required.In this paper, the influence of HVDC breakers on the transient performance of point-to-point HVDC links in both asymmetrical and symmetrical monopolar configuration with half-bridge modular multilevel converters is studied with simulations in PSCAD. As HVDC breakers, the active resonant breaker and ABB’s hybrid breaker are considered. The analyzed scenarios include DC line faults, DC bus faults, and AC faults between the converter and the transformer. The highest DC breaking capability is required during DC line faults in the asymmetric and symmetric monopole. The converter stress is highest for DC bus faults and unbalanced converter AC faults in the asymmetric monopole and for DC bus pole-to-pole faults in the symmetric monopole. During DC pole-to-ground faults in the symmetric monopole, the HVDC breaker combined with DC side arrestors yields the lowest overvoltage stress on the cable of the healthy pole. The fault current shapes depend strongly on the interaction of the converter and the travelling waves on the lines, and differ from the fault current shapes in typical HVDC breaker test circuits. Furthermore, the active resonant breaker and the ABB hybrid breaker perform similarly in the used benchmarks due to the very fast DC line fault detection.

  • 28.
    Augustin, Tim
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Modelling of HVDC breakers for HVDC grid simulations2017In: IET Conference Publications, Institution of Engineering and Technology, 2017, Vol. 2017, article id CP709Conference paper (Refereed)
    Abstract [en]

    This paper deals with the modelling of high-voltage direct current (HVDC) breakers in PSCAD. The models are aimed at HVDC grid simulation and are kept as simple as possible. An overview is given over recently proposed HVDC breaker concepts. Assumptions and simplifications are explained as well. The main result is that even these simplified models are too detailed for grid simulations. The reason for this is that from a grid perpective the only thing that matters is when the metal-oxide varistor is inserted. The models can be used to estimate interruption times.

  • 29.
    Babazadeh, Davood
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Distributed Control of HVDC Transmission Grids2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Recent issues such as priority access of renewable resources recommended by European energy directives and increase the electricity trading among countries lead to new requirements on the operation and expansion of transmission grids. Since AC grid expansions are limited by legislative issues and long distance transmission capacity, there is a considerable attention drawn to application of HVDC transmission grids on top of, or in complement to, existing AC power systems. The secure operation of HVDC grids requires a hierarchical control system. In HVDC grids, the primary control action to deal with power or DC voltage deviations is communication-free and local. In addition to primary control, the higher supervisory control actions are needed to guarantee the optimal operation of HVDC grids. However, the implementation of supervisory control functions is linked to the arrangement of system operators; i.e. an individual HVDC operator (central structure) or sharing tasks among AC system operators (distributed structure).

    This thesis presents distributed control of an HVDC grid. To this end, three possible supervisory functions are investigated; coordination of power injection set-points, DC slack bus selection and network topology identification. In this thesis, all three functions are first studied for the central structure. For the distributed solution, two algorithms based on Alternating Direction Method of Multipliers (ADMM) and Auxiliary Problem Principle (APP) are adopted to solve the coordination of power injection. For distributed selection of DC slack bus, the choice of parameters for quantitative ranking of converters is important. These parameters should be calculated based on local measurements if distributed decision is desired. To this end, the short circuit capacity of connected AC grid and power margin of converters are considered. To estimate the short circuit capacity as one of the required selection parameters, the result shows that the recursive least square algorithm can be very efficiently used. Besides, it is possible to intelligently use a naturally occurring droop response in HVDC grids as a local measurement for this estimation algorithm. Regarding the network topology, a two-stage distributed algorithm is introduced to use the abstract information about the neighbouring substation topology to determine the grid connectivity.

  • 30.
    Babazadeh, Davood
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Hohn, Fabian
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Wu, Yiming
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Distributed Two-stage Network Topology Processor for HVDC Grid Operation2017In: 2017 IEEE Manchester PowerTech, Powertech 2017, IEEE, 2017, article id 7980841Conference 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 islanding scenario for a 5-terminal HVDC grid.

  • 31.
    Babazadeh, Davood
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Muthukrishnan, Arvind
    KTH, School of Electrical Engineering (EES).
    Mitra, Pinaki
    HVDC, ABB Sweden, Ludvika.
    Larsson, Tomas
    HVDC, ABB Sweden, Ludvika.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Real-Time Estimation of AC-Grid Short Circuit Capacity for HVDC Control Application2016In: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695Article in journal (Refereed)
    Abstract [en]

    Being able to estimate the AC grid strength using Short Circuit Capacity (SCC) fromthe perspective of a connected HVDC station allows adjustment of converter control parameters orto select the converter’s operational control mode. The short circuit capacity can be calculated byestimation of the grid’s impedance and its equivalent voltage. This paper presents the operationaland practical challenges in real-time implementation of the grid estimation algorithms especiallyfor HVDC applications. This paper shows that the Recursive Least Square (RLS) algorithm can bevery efficiently used for the real-time estimation of SCC. This technique forms a regression prob-lem using algebraic complex equations with an objective to minimize the error between estimatedand measured parameters. The algorithm has been reformulated and simplified to make it non-complex without the use of matrices, in order to facilitate further implementation on an industrialreal-time controller. The performance of the real-time implementation has been evaluated usinga HIL platform. A sensitivity analysis has been also carriedout to study the impact of differentparameters and operational conditions on the performance of the estimation algorithm. Finally, theactual application of real-time SCC estimation for the HVDCsystems has been demonstrated.

  • 32.
    Babazadeh, Davood
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Muthukrishnan, Arvind
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Mitra, Pinaki
    HVDC, ABB Sweden, Ludvika.
    Larsson, Tomas
    HVDC, ABB Sweden, Ludvika.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Selection of DC Voltage Controlling Station in an HVDC Grid2016In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 144, p. 224-232Article in journal (Refereed)
    Abstract [en]

    This paper proposes a real-time quantitative evaluation of HVDC converters’ in an HVDC grid to select the suitable DC slack converter. This real-time evaluation considers the strength of connecting AC grid and the converter's on-line capacity margin as selection metrics. The strength of AC grid is evaluated in real-time by the estimation of grid short circuit capacity using recursive lease square algorithm. Given these selection metrics, the credibility of HVDC stations in controlling the DC voltage can be offered to the system operator in real-time for further operational decisions. This paper also studies the practical aspect of the estimation algorithm regarding selection of the operating points. As major contribution, it suggests to intelligently use a naturally occurring droop response in HVDC grids as a second operating point in the estimation algorithm to calculate the short circuit capacity. The method has been tested through set of scenarios using a real-time co-simulation platform. This platform includes real-time power system simulator to model AC/DC grid, industrial HVDC controllers and corresponding ICT systems. The results show that the proper selection of DC slack station can improve the AC system response and DC voltage drops during disturbances.

  • 33.
    Babazadeh, Davood
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Muthukrishnan, Arvind
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Mitra, Pinaki
    HVDC, ABB Sweden, Ludvika.
    Larsson, Tomas
    HVDC, ABB Sweden, Ludvika.
    Short Circuit Capacity Estimation for HVDC Control Application2016In: Power Systems Computation Conference (PSCC), 2016, IEEE conference proceedings, 2016Conference paper (Refereed)
    Abstract [en]

    This paper studies various operational aspects ofrecursive least square algorithm as a potential solution for theestimation of short circuit capacity in HVDC application. Inthis work, low computational requirement, minor operationalcomplication and acceptable accuracy of the estimated gridparameters have been considered as the performance metricsfor the selection of the suitable estimation algorithm. The chosenalgorithm forms a regression problem using at least two algebraiccomplex equations based on two different operating points. Theappropriate selection of the second operating point which fulfillsthe minimum required accuracy and convergence rate is of greatimportance, particularly in the practical implementation. Thispaper proposes and analyzes several choices of providing thesecond operating point for the estimation algorithm adopted toHVDC application. Furthermore, a sensitivity analysis has beencarried out to assess the impact of different parameters andoperational conditions such as execution time on the performanceof the estimation algorithm for the HVDC control purposes.

  • 34.
    Babazadeh, Davood
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Distributed Security-Constrained Secondary Control of HVDC grids in the Presence of Wind UncertaintyIn: Sustainable Energy, Grids and Networks, ISSN 0284-4354, E-ISSN 2352-4677Article in journal (Refereed)
    Abstract [en]

    This paper proposes a distributed coordination of converters in an HVDC grid in order to provide close-to-real-time optimal DCvoltage and power profiles in the presence of wind uncertainty. This coordination is a part of HVDC grid secondary control actionthat carries out after the automatic primary control response by DC voltage droop controlling converters. It aims to optimize thegrid operation by finding the new DC power and voltage set-points that minimize the operational costs due to wind fluctuations andprediction error. Furthermore, the N-1 secure operation of HVDC grid is considered in this distributed coordination by adding a setof security constraints that tightens the upper and lower bounds of the problem variables. The coordination problem is formulatedas a convex optimization problem and therefore a modified version of alternating direction method of multipliers is adopted to solvethe problem in distributed manner. The performance of distributed coordination has been tested by a set of scenarios. The resultsimply that the distributed coordination is eligible in terms of time and complexity to be considered as either the main option forsecondary coordination or a complementary back-up solution for the central coordination.

  • 35.
    Bakas, Panagiotis
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. ABB Corporate Research, Sweden.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. ABB Corporate Research, Sweden.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Nami, A.
    Ilves, K.
    Dijkhuizen, F.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Hybrid Topologies for Series and Shunt Compensation of the Line-Commutated Converter2016In: 8th International Power Electronics and Motion Control Conference - ECCE Asia, IPEMC 2016-ECCE Asia, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 3030-3035, article id 7512779Conference paper (Refereed)
    Abstract [en]

    This paper presents two concepts for enabling the operation of a line-commutated converter (LCC) at leading power angles. The concepts are based on voltage or current injection at the ac side of an LCC, which can be achieved in different ways. However, this paper focuses on the voltage and current injection by series-connected full-bridge cells that can generate voltages that approximate ideal sinusoids. Thus, hybrid configurations of an LCC connected at the ac side in series or in parallel with fullbridge cells are presented. Finally, these hybrid configurations are compared in terms of voltage and current rating.

  • 36.
    Bakas, Panagiotis
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. ABB Corporate Research, Sweden.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. ABB Corporate Research, Sweden.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Nami, Alireza
    ABB Corporate Research, Sweden.
    Ilves, Kalle
    ABB Corporate Research, Sweden.
    Dijkhuizen, Frans
    ABB Corporate Research, Sweden.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    A Review of Hybrid Topologies Combining Line-Commutated and Cascaded Full-Bridge Converters2017In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 32, no 10, p. 7435-7448, article id 7750589Article, review/survey (Refereed)
    Abstract [sv]

    This paper presents a review of concepts for enabling the operation of a line-commutated converter (LCC) at leading power angles. These concepts rely on voltage or current injection at the ac or dc sides of the LCC, which can be achieved in different ways. We focus on the voltage and current injection by full-bridge (FB) arms, which can be connected either at the ac or dc sides of the LCC and can generate voltages that approximate ideal sinusoids. Hybrid configurations of an LCC connected at the ac side in series or in parallel with FB arms are presented. Moreover, a hybrid configuration of an LCC connected in parallel at the ac side and in series at the dc side with an FB modular multilevel converter (MMC) is outlined. The main contribution of this paper is an analysis and comparison of the mentioned hybrid configurations in terms of the capability to independently control the active (P) and reactive power (Q).

  • 37.
    Ballesteros, Maria
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Reliability of Thermal Relays in Automotive Applications2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Despite the vast increase of relays in automotive applications, little is known of how to perform reliability tests on them. Reliability of relays is defined as the probability of a relay to function without failure, when operated correctly, for a given period of time, under stated conditions.Accordingly, there is a need for improving life-expectancy test methods for relays. The immediate objective of this research project is to develop a guideline of how to check reliability of relays.Identifying the main parameters that affect reliability, perform an endurance test and material analyses of the tested relays were the main areas of interest in this work. In addition, common failure modes during the relays performance were identified.The results show that supplied voltage, breaking current and load type are parameters that affect arc duration and, thus, the contact damage. Most common failure modes were contact welding and increase in contact resistance due to arc erosion and oxide formation. Moreover, contact resistance stability has been proved to be a factor capable to determine the quality of contacts and to predict early failures in relays.

  • 38. Barth, C.
    et al.
    Colmenares, Juan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Foulkes, T.
    Coulson, K.
    Sotelo, J.
    Modeer, T.
    Miljkovic, N.
    Pilawa-Podgurski, R. C. N.
    Experimental evaluation of a 1 kW, single-phase, 3-level gallium nitride inverter in extreme cold environment2017In: Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 717-723, article id 7930773Conference paper (Refereed)
    Abstract [en]

    This work investigates the potential for high power density, high efficiency power conversion at extreme cold temperatures, for hybrid electric aircraft applications. A 1 kW GaN-based 3-level power converter was designed and successfully tested from room temperature down to -140 °C, using a custom milled cold-plate. Along with the first demonstration of a flying capacitor multi-level converter and associated components at such low temperature, this work characterized the effect on power conversion losses of various components as a function of temperature. A key finding is that careful attention must be paid to the passive component losses which can increase as the temperature is reduced.

  • 39.
    Baudette, Maxime
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Singh, Ravi Shankar
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Peric, Vedran S.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Løvlund, Stig
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    ’In silico’ testing of a real-time PMU-based tool for power system mode estimation2016In: 2016 IEEE Power and Energy Society General Meeting, PESGM 2016, IEEE Computer Society, 2016, p. 1-5, article id 7741638Conference paper (Refereed)
    Abstract [en]

    This paper presents an overview of the software implementation of a real-time mode estimator application and its testing. The application was developed to estimate inter-area modes from both ambient and ring-down synchrophasor data from multiple phasor measurement units (PMU). The software application was implemented in LabVIEW using Statnett’s synchrophasor software development kit (S3DK), to receive real-time synchrophasor measurements. The different features of the application were tested using two types of experiments presented herein. The first experiment is performed using emulated signals from a simple linear model. The second experiment was designed to use a linearized representation of the KTH-Nordic32 power system model. These experiments are used to carry out quantitative analyses of the tool’s performance.

  • 40.
    Bessegato, Luca
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Harnefors, Lennart
    Ilves, Kalle
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Control of Direct AC/AC Modular Multilevel Converters Using Capacitor Voltage Estimation2016In: 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16 ECCE EUROPE), IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    This paper applies a control method based on current control and sum-capacitor-voltage estimation to the direct ac/ac modular multilevel converter. As capacitor voltages are estimated, their measurements are not needed in the high-level control, which simplifies the communication between the main controller and the submodules of the converter. The stability of the internal dynamics of the converter, using the aforementioned control method, is studied using Lyapunov stability theory, proving that the system is globally asymptotically stable. The behavior of the converter is simulated focusing on three-phase 50 Hz to single-phase 16 (2)/(3) Hz conversion, which is typical for railway power supply systems of some European countries. Simulation results are in agreement with the expected behavior of the converter, both in steady-state and dynamic situations.

  • 41.
    Bessegato, Luca
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ilves, K.
    Harnefors, Lennart
    Ac-side admittance calculation for modular multilevel converters2017In: 2017 IEEE 3rd International Future Energy Electronics Conference and ECCE Asia, IFEEC - ECCE Asia 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 308-312Conference paper (Refereed)
    Abstract [en]

    Power electronic converters may interact with the grid, thereby influencing dynamic behavior and resonances. Impedance and passivity based stability criteria are two useful methods that allow for studying the grid-converter system as a feedback system, whose behavior is determined by the ratio of grid and converter impedances. In this paper, the ac-side admittance of the modular multilevel converter is calculated using harmonic linearization and considering five specific frequency components of the converter variables. The proposed model features remarkable accuracy, verified through simulations, and insight into the influence of converter and control parameters on the admittance frequency characteristics, which is useful for understanding grid-converter interaction and designing the system.

  • 42.
    Bessegato, Luca
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ilves, Kalle
    Harnefors, Lennart
    Control of Modular Multilevel Matrix Converters Based on Capacitor Voltage Estimation2016In: IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia), 2016, IEEE, 2016, p. 3447-3452, article id 7512848Conference paper (Refereed)
    Abstract [en]

    In this paper, a control method based on capacitor voltage estimation is applied to the modular multilevel matrix converter topology. By using such control method, capacitor voltage measurement is not needed in the high-level control. A state-space model of the converter and the control method is developed. Lyapunov stability theory is used to prove global asymptotic stability of the internal dynamics of the converter. Simulation results showing the behavior of the converter in steady-state and dynamic situations are presented.

  • 43.
    Bessman, Alexander
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Soares, Rúdi Cavalerio
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Behm, Mårten
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Lindbergh, Göran
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Svens, P.
    Investigating the aging effect of current ripple on lithium-ion cells2015In: ECS Transactions, Electrochemical Society, 2015, Vol. 69, no 18, p. 101-106Conference paper (Refereed)
    Abstract [en]

    We have built an experimental setup which exposes twelve cells to a well-defined ripple current. It consists of a system for cycling high capacity cells in parallel with a triangular current waveform superimposed on top of the direct current. The frequency of the waveform is variable up to 50 Hz, and the sum of the DC and AC components can have a magnitude of -40 A to 40 A. Current is measured over a 500 μω shunt resistor. The voltage and current of each cell is read simultaneously at a sample rate up to 4 MS/s, allowing for precise impedance measurements even for high frequency harmonics. The cells are cycled at 40 °C. The experiment has been designed to eliminate indirect effects of the AC harmonics as far as possible. This system is being used to test whether or not AC harmonics affect Li-ion aging.

  • 44.
    Bessman, Alexander
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Soares, Rúdi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Vadivelu, Sunilkumar
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Svens, Pontus
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Ekström, Henrik
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Lindbergh, Göran
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Challenging Sinusoidal Ripple-Current Charging of Lithium-Ion Batteries2018In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 65, no 6, p. 4750-4757Article in journal (Refereed)
    Abstract [en]

    Sinusoidal ripple-current charging has previously been reported to increase both charging efficiency and energy efficiency and decrease charging time when used to charge lithium-ion battery cells. In this paper, we show that no such effect exists in lithium-ion battery cells, based on an experimental study of large-size prismatic cells. Additionally, we use a physics-based model to show that no such effect should exist, based on the underlying electrochemical principles.

  • 45.
    Bidadfar, Ali
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Hooshyar, Hossein
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Monadi, Mehdi
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Decoupled voltage stability assessment of distribution networks using synchrophasors2016In: Power and Energy Society General Meeting (PESGM), 2016, 2016, article id 7741644Conference paper (Refereed)
    Abstract [en]

    This paper presents a real-time voltage stabilityassessment in distribution networks (DNs) capable of separatingthe effects of the transmission and distribution network by usingsynchronized phasor measurements. The method aims to assisttransmission and distribution system operators to quantify theneed of their services in different parts of the DN in order toprovide adequate voltage support to their specific stakeholders.The method uses data from phasor measurement units (PMUs) toestimate models for both DN and transmission network (TN). ATh´evenin equivalent model is estimated for the TN and a T-modelfor the DN. By applying the superposition theorem on these twomodels, the contribution of each network to the overall systemvoltage stability can be distinguished at a specific bus (equippedwith a PMU). The method has been validated by a hardware-inthe-loop setup which consists an OPAL-RT real-time simulatorand three PMUs.

  • 46.
    Bidadfar, Ali
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Zhang, Lidong
    Harnefors, Lennart
    Namayantavana, Sanaz
    KTH.
    Abedi, Mehrdad
    Karrari, Mehdi
    Gharehpetian, Gevork B.
    Power System Stability Analysis Using Feedback Control System Modeling Including HVDC Transmission Links2016In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 31, no 1, p. 116-124Article in journal (Refereed)
    Abstract [en]

    A general platform is introduced to study the dynamics of power systems with high voltage dc (HVDC) transmission links. Small-signal stability, voltage stability, and interaction phenomena of power systems with both line-commutated-converter HVDC (LCC-HVDC) and voltage-source-converter HVDC (VSC-HVDC) are addressed using the proposed platform. In this platform, the entire power system is modeled as a multivariable feedback control system (FCS) which consists of three interconnected blocks. The contents as well as the inputs and outputs of the blocks are selected such that the conventional analysis tools for power system stability are applicable, both in the time and frequency domains. In the FCS model, the relationships between different instabilities are clear, and participant agents of each instability can be determined. The model is developed in a modular and hybrid style, to make it feasible for a large power system. The proposed model is validated against an electromagnetic transient simulation program (PSCAD) using time responses.

  • 47. Biggar, D.
    et al.
    Hesamzadeh, Mohammad Reza
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Modelling the hedging decisions of a generator with market power2011In: 17th Power Systems Computation Conference, PSCC 2011, Power Systems Computation Conference ( PSCC ) , 2011Conference paper (Refereed)
    Abstract [en]

    The incentive on an electricity generating firm to exercise market power depends strongly on the volume the firm has pre-sold in the forward or hedge markets. Therefore, in order to forecast the effect of mergers and other market developments on market power outcomes, it is essential to model the hedging decisions of dominant generating firms. This paper shows that a dominant firm's profit-maximizing choice of hedge level depends on the extent to which the hedge price varies with the firm's hedging decision. In the case in which the hedge price is independent of the firm's hedge level, the optimal choice of hedging is an "all or nothing" decision. In this case, there is no equilibrium level of hedging in pure strategies. This outcome may explain the observed lack of hedge market liquidity in wholesale electricity markets with substantial market power. We also model the equilibrium hedging outcome in a two-stage Cournot oligopoly and show that, even if the hedge price is independent of the hedging decisions of the firms, a rational expectations equilibrium can exist with high levels of hedging if there are enough firms in the market.

  • 48. Bird, Lori
    et al.
    Lew, Debra
    Milligan, Michael
    Carlini, E. Maria
    Estanqueiro, Ana
    Flynn, Damian
    Gomez-Lazaro, Emilio
    Holttinen, Hannele
    Menemenlis, Nickie
    Orths, Antje
    Eriksen, Peter Borre
    Smith, J. Charles
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Sorensen, Poul
    Altiparmakis, Argyrios
    Yasuda, Yoh
    Miller, John
    Wind and solar energy curtailment: A review of international experience2016In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 65, p. 577-586Article, review/survey (Refereed)
    Abstract [en]

    Greater penetrations of variable renewable generation on some electric grids have resulted in increased levels of curtailment in recent years. Studies of renewable energy grid integration have found that curtailment levels may grow as the penetration of wind and solar energy generation increases. This paper reviews international experience with curtailment of wind and solar energy on bulk power systems in recent years, with a focus on eleven countries in Europe, North America, and Asia. It examines levels of curtailment, the causes of curtailment, curtailment methods and use of market based dispatch, as well as operational, institutional, and other changes that are being made to reduce renewable energy curtailment.

  • 49. Bjuhr, O.
    et al.
    Segeljakt, K.
    Addibpour, M.
    Heiser, F.
    Lagerström, Robert
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Software architecture decoupling at ericsson2017In: Proceedings - 2017 IEEE International Conference on Software Architecture Workshops, ICSAW 2017: Side Track Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 259-262, article id 7958500Conference paper (Refereed)
    Abstract [en]

    In order to evaluate and increase modularity this paper combines a method for visualizing and measuring software architectures and two algorithms for decoupling. The combination is tested on a software system at Ericsson. Our analysis show that the system has one large cluster of components (18% of the system, a Core), all interacting with each other. By employing cluster and dominator analysis we suggest 19 dependencies to be removed in order to decouple the Core. Validating the analysis output with experts at Ericsson six of the suggested dependencies where deemed impossible to remove. By removing the remaining 13 dependencies Ericsson would improve the architecture of their system considerably, e.g. core size would go down to 5%.

  • 50.
    Blaauwbroek, Niels
    et al.
    TU/Eindhoven.
    Nguyen, H.P.
    TU/Eindhoven.
    Slootweg, J.G.
    TU/Eindhoven.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems. KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Interfacing solutions for power hardware-inthe- loop simulations of distribution feeders for testing monitoring and control applications2017In: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695Article in journal (Refereed)
    Abstract [en]

    The need for advanced monitoring and control applications (MCAs) in future distribution networks calls for highly accurate and fully integrated simulation solutions for the purpose of performance assessment of these MCAs. Offline simulation using models of the power system, measurement equipment, local controllers and the information and communication infrastructure do not always resemble reality accurate enough. Therefore, power hardware-in-the-loop (PHIL) simulations are considered a cost-effective approach to overcome these challenges. This study presents the design of a PHIL-interface that allows to integrate a physical low-voltage feeder within a larger real-time simulated distribution network. Using the combination of the physical network and the larger simulated network, MCAs can be tested for scalability as well as accuracy. A data acquisition and processing system is presented that acquires all the true system states of both the physical feeder and the real-time simulated network, such that the MCAs can be verified in real-time. The functioning of the PHIL-interface is validated using practical results and illustrated using a test case for the performance assessment of a branch current state estimation algorithm.

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