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  • 1.
    Ahmed, Noman
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Haider, Arif
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Van Hertem, Dirk
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Zhang, Lidong
    ABB Power Systems, Ludvika.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Prospects and challenges of future HVDC SuperGrids with modular multilevel converters2011In: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) / [ed] EPE Association, 2011Conference paper (Refereed)
    Abstract [en]

    In order to transmit massive amounts of power generated by remotely located power plants, especially offshore wind farms, and to balance the intermittent nature of renewable energy sources, the need for a stronger high voltage transmission grid is anticipated. Due to limitations in AC power transmission the most likable choice for such a grid is a high voltage DC (HVDC) grid. However, the concept of the HVDC grid is still under active development as different technical challenges exist, and it is not yet possible to construct such a DC grid. This paper deals with prospects and technical challenges for the future HVDC SuperGrids. Different topologies for a SuperGrid and the possibility to use modular multilevel converters (M2Cs) are presented. A comprehensive overview of different sub-module implementations of M2C is given. An overview of short circuit behaviour of the M2C is also given, as well as a discussion on the choice between cables or overhead lines and DC-side resonance issues.

  • 2.
    Ahmed, Noman
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Haider, Arif
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    M2C-BASED MTDC SYSTEM FOR HANDLING OF POWERFLUCTUATIONS FROM OFFSHORE WIND FARMS2011In: Proceedings of IET RPG-2011 / [ed] IET, 2011Conference paper (Refereed)
    Abstract [en]

    In this paper a modular multilevel converter (M2C) basedmulti-terminal direct current (MTDC) system is proposed forthe connection of offshore wind farms. Each M2C ismodelled with 36 sub-modules per arm with a total of 216sub-modules consisting of half bridges. An open-loopconverter control method is employed for the M2Cs. Powersynchronizationcontrol is used instead of a phase-locked loop(PLL) for synchronization. A voltage controller isimplemented with power-synchronization control as an innerloop. By means of numerical simulations in PSCAD, it isshown that the system is self stabilizing both at steady stateand following power fluctuations of the wind farm.

  • 3.
    Ahmed, Noman
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Haider, Arif
    Van Hertem, Dirk
    ESAT/ELECTA, K.U.Leuven, Belgium.
    Zhang, Lidong
    ABB Power Systems HVDC, Ludvika.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    HVDC SuperGrids with modular multilevel converters - The power transmission backbone of the future2012In: International Multi-Conference on Systems, Signals and Devices, SSD 2012, IEEE , 2012, p. 6198119-Conference paper (Refereed)
    Abstract [en]

    In order to transmit massive amounts of power generated by remotely located power plants, especially offshore wind farms, and to balance the intermittent nature of renewable energy sources, the need for a stronger high voltage transmission grid is anticipated. Due to limitations in ac power transmission the most likable choice for such a grid is a high-voltage dc (HVDC) grid. However, the concept of the HVDC grid is still under active development as different technical challenges exist, and it is not yet possible to construct such a dc grid. This paper deals with prospects and technical challenges for future HVDC SuperGrids. Different topologies for a SuperGrid and the possibility to use modular multilevel converters (M2Cs) are presented. A comprehensive overview of different submodule implementations of M2C is given as well as a discussion on the choice between cables or overhead lines, the protection system for the dc grid and dc-side resonance issues.

  • 4.
    Ahmed, Noman
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Antonopoulos, Antonios
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion. ABB Corporate Research.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Performance of the modular multilevel converter with redundant submodules2015In: IECON 2015 - 41st Annual Conference of the IEEE Industrial Electronics Society, Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 3922-3927, article id 7392712Conference paper (Refereed)
    Abstract [en]

    The modular multilevel converter (MMC) is the state-of-the-art voltage-source converter (VSC) topology used for various power-conversion applications. In the MMC, submodule failures can occur due to various reasons. Therefore, additional submodules called the redundant submodules are included in the arms of the MMC to fulfill the fault-safe operation requirement. The performance of the MMC with redundant submodules has not been widely covered in the published literature. This paper investigates the performance of the MMC with redundant submodules in the arms. Two different control strategies are used and compared for integrating redundant submodules. The response of the MMC to a submodule failure for the two strategies is also studied. Moreover, the operation of the MMC with redundant submodules is validated experimentally using the converter prototype in the laboratory.

  • 5.
    Ahmed, Noman
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Mahmood, Shahid
    Antonopoulos, Antonios
    Harnefors, Lennart
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Efficient Modeling of an MMC-Based Multiterminal DC System Employing Hybrid HVDC Breakers2015In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 30, no 4, p. 1792-1801Article in journal (Refereed)
    Abstract [en]

    The feasibility of future multiterminal dc (MTDC) systems depends largely on the capability to withstand dc-side faults. Simulation models of MTDC systems play a very important role in investigating these faults. For such studies, the test system needs to be accurate and computationally efficient. This paper proposes a detailed equivalent model of the modular multilevel converter (MMC), which is used to develop the MTDC test system. The proposed model is capable of representing the blocked-mode operation of the MMC, and can be used to study the balancing control of the capacitor voltages. In addition, the operation of the MMC when redundant submodules are included in the arms can also be studied. A simplified model of a hybrid high-voltage dc breaker is also developed. Hence, the developed test system is capable of accurately describing the behavior of the MMC-based MTDC system employing hybrid HVDC breakers, during fault conditions. Using time-domain simulations, permanent dc-side faults are studied in the MTDC system. In addition, a scheme to control the fault current through the MMC using thyristors on the ac side of the converter is proposed.

  • 6.
    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)
  • 7.
    Ahmed, Noman
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Continuous modeling of open-loop control based negative sequence current control of modular multilevel converters for HVDC transmission2013In: Eur. Conf. Power Electron. Appl., EPE, 2013Conference paper (Refereed)
    Abstract [en]

    Negative sequence currents are obtained during ac-side asymmetrical faults of converters in highvoltage direct current (HVDC) transmission systems. Consequently, second order harmonics in the dc-side voltage and current, unbalanced ac-side currents, and power oscillations can be observed. This paper presents a negative sequence current control (NSCC) scheme that eliminates second order harmonic ripples in the voltage and current of the dc-side during unbalanced grid conditions. Controllers for this purpose are investigated using a continuous model of the modular multilevel converter (M2C). The proposed scheme utilizes an open-loop controller for lower level control of the M2C. The continuous model used also has the capability to model blocking and deblocking events which may be used during protective actions. Simulation results reveal that the proposed NSCC scheme is effective in suppressing dc-side voltage and current ripples. Moreover, it keeps the ac-side phase currents balanced during asymmetrical fault conditions.

  • 8.
    Ahmed, Noman
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Antonopoulos, Antonios
    ABB Corporate Research Center, Sweden.
    Harnefors, Lennart
    ABB Corporate Research Center, Sweden.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    A computationally efficient continuous model for the modular multilevel converter2014In: IEEE Journal of Emerging and Selected Topics in Power Electronics, ISSN 2168-6777, Vol. 2, no 4, p. 1139-1148, article id 6840290Article in journal (Refereed)
    Abstract [en]

    Simulation models of the modular multilevel converter (MMC) play a very important role for studying the dynamic performance. Detailed modeling of the MMC in electromagnetic transient simulation programs is cumbersome, as it requires high computational effort and simulation time. Several averaged or continuous models proposed in the literature lack the capability to describe the blocked state. This paper presents a continuous model, which is capable of accurately simulating the blocked state. This feature is very important for accurate simulation of faults. The model is generally applicable, although it is particularly useful in high-voltage dc applications.

  • 9.
    Ahmed, Noman
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Efficient Modeling of Modular Multilevel Converters in HVDC-Grids Under Fault Conditions2014In: 2014 IEEE PES General Meeting | Conference & Exposition, IEEE Computer Society, 2014, p. 6939166-, article id 6939166Conference paper (Refereed)
    Abstract [en]

    High-voltage direct current (HVDC) grids using modular multilevel converters (M2Cs) have strongly been considered for the integration of distant renewable energy sources and also as a backbone to the existing ac-grids. The dynamic performance of the M2C is of particular interest in these grids. For electromagnetic transient (EMT) programs, modeling of HVDC-grids using detailed M2C models is unrealistic, as it requires extremely high computational effort and simulation time. In this paper an HVDC-grid test system is developed using a continuous simulation model of the M2C. The model is also capable of describing the blocking events of the M2C. Using time-domain simulations in PSCAD/EMTDC, the dynamic performance of the M2C in HVDC-grids under fault conditions is investigated. Simulation results reveal that the continuous M2C model can efficiently be used to study the dynamic performance of the M2C in HVDC-grids with high computational speed, under different fault conditions.

  • 10.
    Ahmed, Noman
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Validation of the continuous model of the modular multilevel converter with blocking/deblocking capability2012In: AC and DC Power Transmission (ACDC 2012), 10th IET International Conference on, 2012Conference paper (Refereed)
    Abstract [en]

    This paper presents the continuous model for the Modular Multilevel Converter (M2C). The model operates in two modes, either operating as a voltage source in deblocked mode or as a rectifying diode bridge in blocked mode. The model is validated by comparison with a detailed M2C model having 36 submodules per arm, using different control strategies. The comparison is based on time-domain simulations in PSCAD/EMTDC. The continuous model shows a very good agreement with the detailed model.

  • 11.
    Anpalahan, Peethamparam
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Design Steps towards a High Power Factor Transverse Flux Machine2001In: Proc. of the European Conference on Power Electronics and Applications (EPE), Graz, Austria, August 2001 / [ed] EPE, 2001Conference paper (Refereed)
    Abstract [en]

    This article describes a topology of three-phase transverse flux machine and the derivation of ananalytical model which does not exist in the literature. Three dimensional finite element analysis isalso used to get more accurate results. Steps carried out to obtain a better power factor are presented.

  • 12.
    Antonopoulos, Antonios
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Ilves, Kalle
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    On Interaction between Internal Converter Dynamics and Current Control of High-Performance High-Power AC Motor Drives with Modular Multilevel Converters2010In: Proc. IEEE Energy Conversion Congress and Exposition (ECCE), 2010, p. 4293-4298Conference paper (Refereed)
    Abstract [en]

    The modular multilevel converter (M2C) is a promising converter technology for various high-voltage highpower applications. The reason to this is that low-distortion output quantities can be achieved with low average switching frequencies per switch and without output filters. With the M2C the output voltage has such a low harmonic content that highpower motors can be operated without any derating. However, the apparent large number of devices, requires more complex converter control techniques than a two-level counterpart. Even though there have been several ways suggested to control the converter itself, it is still a challenge to investigate the interaction of these controllers with an external motor current controller. It is shown in the paper that the anticipated interaction will not result in any problems neither for the converter nor for the motor control itself.

  • 13.
    Antonopoulos, Antonios
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Mörée, Gustav
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Experimental evaluation of the impact of harmonics on induction motors fed by modular multilevel converters2014In: Proceedings - 2014 International Conference on Electrical Machines, ICEM 2014, 2014, p. 768-775Conference paper (Refereed)
    Abstract [en]

    Inverter-based electrical-machine drives suffer from significantly higher losses compared to sinusoidal-supply-based alternatives, fed directly from the grid. Using multilevel inverters it becomes possible to partially mitigate the effects of the switched supply waveform, while keeping the advantages of variable-speed operation. This paper aims to evaluate the increase of the losses occurring in an induction motor (IM) fed by a modular multilevel converter (M2C), when compared to grid-connected operation, in order to evaluate the impact of the inverter-generated harmonics in the machine. It is confirmed that the losses created in the motor due to the harmonic content of the inverter-generated waveforms are very low, and almost equivalent to a purely sinusoidal supply. The investigation includes an analysis of the harmonic content from experimental waveforms obtained by an 11-kW IM laboratory setup, and it is further supported by measurements of the temperature rise in the IM-stator windings. It is concluded that the M2C could create the conditions even for high-power motors to be operated without any derating.

  • 14.
    Antonopoulos, Antonios
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Siemaszko, Daniel
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Ilves, Kalle
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Vasiladiotis, Michail
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Evaluation of Control and Modulation Methods forModular Multilevel Converters2010In: Proc. Int. Power Electronics Conf. (IPEC), 2010, p. 746-753Conference paper (Refereed)
    Abstract [en]

    The modular multilevel converter is a promising converter technology for various high-voltage high-power applications. Despite the apparent simplicity of the circuit, the inherent dynamics of the converter and the balancing of the sub-module capacitor voltages impose high requirements on the control system, which can be implemented in quite different ways. To illustrate this, and to provide a guidance for future research on the subject, this paper presents an evaluation of four different control and modulation methods. The investigation is based on experiments on a down-scaled 10 kVA converter having 10 submodules per phase leg. The main items to be investigated are dynamics within the sub-modules, arm voltages and circulating currents. It is found that the suggested open-loop control method provides the fastest arm-voltage response and that the balancing approach based on a sorting algorithm is substantially faster and less complicated to implement than the method using a dedicated voltage controller for each sub-module.

     

     

  • 15.
    Antonopoulos, Antonios
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion. ABB, Sweden.
    Ilves, Kalle
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Global Asymptotic Stability of Modular Multilevel Converters2014In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 61, no 2, p. 603-612Article in journal (Refereed)
    Abstract [en]

    Modular multilevel converters require that the controller is designed so that the submodule capacitor voltages are equalized and stable, independent of the loading conditions. Assuming that the individual capacitor-voltage sharing is managed effectively, an open-loop strategy has been designed to ensure that the total amount of energy stored inside the converter always will be controlled. This strategy, using the steady-state solutions of the dynamic equations for controlling the total stored energy in each converter arm, has proven to be effective. The intention of this paper is to explain in a rigorous way the mechanism behind the suggested strategy and to prove that, when this open-loop strategy is used, the system becomes globally asymptotically stable. Experimental verification on a three-phase 10-kVA prototype is presented.

  • 16.
    Antonopoulos, Antonios
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ilves, Kalle
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Stability Analysis of Modular Multilevel Converters With Open-Loop Control2013In: 39th Annual Conference of the IEEE Industrial Electronics Society, IECON 2013, IEEE , 2013, p. 6316-6321Conference paper (Refereed)
    Abstract [en]

    Modular multilevel converters (M2Cs) require that the controller is designed so that the submodule capacitor voltages are equalized and stable, independent of the loading conditions. Provided that the individual capacitor voltage sharing is managed effectively, an open-loop strategy can been designed to ensure that the total amount of energy stored inside the converter always will be controlled. This strategy, using the steady-state solutions of the dynamic equations for controlling the total stored energy in each converter arm, has proven to be effective. The intention of this paper is to explain in a rigorous way the mechanism behind the suggested strategy, and to prove that, when this open-loop strategy is used, the system becomes globally asymptotically stable.

  • 17.
    Antonopoulos, Antonios
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Optimal selection of the average capacitor voltage for modular multilevel converters2013In: 2013 IEEE Energy Conversion Congress and Exposition, ECCE 2013, IEEE , 2013, p. 3368-3374Conference paper (Refereed)
    Abstract [en]

    Variable-speed drives have reduced voltage requirements when operating below the base speed. In a modular-multilevel-converter-based (M2C-based) motor drive it is then possible to operate with reduced voltage in the submodule capacitors, than at the base speed. In this sense, a greater capacitor-voltage ripple can be accommodated, without exceeding the maximum peak-capacitor voltage. This paper presents an analytical investigation for the optimal selection of the average capacitor voltage for M2Cs, when the motor is operating with rated torque, below the base speed. This method does not require any power exchange between the converter arms, so it keeps the conduction losses at the minimum level. Additionally, the method decreases the switching losses, due to the decreased capacitor-voltage level. The overall ratings of the converter remain the same as in the base-speed operation. It is shown that this method can be applied at a speed range between the base speed and down to approximately one third of it, i.e, an operating range that covers the requirements for typical pump- and fan-type applications. The results obtained from the analytical investigation are experimentally verified on a down-scaled laboratory prototype M2C.

  • 18.
    Antonopoulos, Antonios
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Optimal Selection of the Average Capacitor Voltage for Variable-Speed Drives With Modular Multilevel Converters2015In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, no 1, p. 227-234Article in journal (Refereed)
    Abstract [en]

    Variable-speed drives have reduced voltage requirementswhen operating below the base speed. In a modularmultilevel-converter-based (M2C-based) motor drive it is thenpossible to operate with reduced voltage in the submodulecapacitors, than at the base speed. In this sense, a greatercapacitor-voltage ripple can be accommodated, without exceedingthe maximum peak-capacitor voltage. This paper presents ananalytical investigation for the optimal selection of the averagecapacitor voltage for M2Cs, when the motor is operating withrated torque, below the base speed. This method does not requireany power exchange between the converter arms, so it keepsthe conduction losses at the minimum level. Additionally, themethod decreases the switching losses, due to the decreasedcapacitor-voltage level. The overall ratings of the converterremain the same as in the base-speed operation. It is shownthat this method can be applied at a speed range betweenthe base speed and down to approximately one third of it,i.e, an operating range that covers the requirements for typicalpump- and fan-type applications. The results obtained from theanalytical investigation are experimentally verified on a downscaledlaboratory prototype M2C.

  • 19.
    Antonopoulos, Antonios
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    On Dynamics and Voltage Control of the Modular Multilevel Converter2009In: 2009 13th European Conference on Power Electronics and Applications, EPE '09, IEEE , 2009, p. 3353-3362Conference paper (Refereed)
    Abstract [en]

    This paper discusses the impact of modulation on stability issues of the Modular Multilevel Converter (M2C). The main idea is to describe the operation of this converter system mathematically, and suggest a control method that offers stable operation in the whole operation range. A possible approach is to assume a continuous model, where all the modules in each arm are represented by variable voltage sources. and as a result, all pulse width modulation effects are disregarded. After simulating this model and testing different control methods, useful conclusions on the operation of the M2C have been extracted. The control methods are then implemented on a model with discrete half-bridge modules, in order to compare the results and to validate continuous model approach. When assuring that this model functions as expected, the goal of this paper is to conclude into a self-stabilizing voltage controller. A controller is proposed, which eliminates circulating currents between the phase legs and balances the arm voltages regardless of the imposed alteranting current.

  • 20.
    Antonopoulos, Antonios
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ilves, Kalle
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Harnefors, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Modular multilevel converter AC motor drives with constant torque from zero to nominal speed2014In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 50, no 3, p. 1982-1993Article in journal (Refereed)
    Abstract [en]

    Modular multilevel converters are shown to have a great potential in the area of medium-voltage drives. Low-distortion output quantities combined with low average switching frequencies for the semiconductor devices create an ideal combination for very high-efficiency drives. However, the large number of devices and capacitors that have to conduct the fundamental-frequency current require more complex converter control techniques than its two-level counterpart. Special care needs to be taken for starting and operation at low speeds, where the low-frequency current may cause significant unbalance between the submodule capacitor voltages and disturb the output waveforms. In this paper, principles for converter operation with high torque in the whole speed range are investigated. Experimental results from a down-scaled 12-kVA prototype converter running a loaded motor at various speeds between standstill and the rated speed are also provided.

  • 21.
    Antonopoulos, Antonios
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ilves, Kalle
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Modular multilevel converter ac motor drives with constant torque form zero to nominal speed2012In: 2012 IEEE Energy Conversion Congress and Exposition, ECCE 2012, IEEE , 2012, p. 739-746Conference paper (Refereed)
    Abstract [en]

    Modular multilevel converters (M2Cs) are shown to have a great potential in the area of medium-voltage drives. Low-distortion output quantities, combined with low average switching frequencies for the semiconductor devices create the ideal combination for very high-efficiency drives, both from an electric motor and an inverter point of view. With M2Cs the output voltage has such a low harmonic content that high-power motors can be operated without any derating. However, the large number of devices and the existence of capacitors that have to conduct the fundamental frequency current, requires more complex converter control techniques than its two-level counterpart. Special care needs to be taken under starting and operation with low frequency, where the low-frequency current may cause significant unbalance between the submodule capacitor voltages, disturb the output waveforms, and eventually cause the converter to trip. In this paper, principles for converter operation with high torque in the whole speed range, from standstill to rated speed will be investigated. The converter-control method utilizes estimation of the capacitor voltage variation, based on equations describing steady-state conditions. Experimental results from a down-scaled 12 kVA prototype converter running a loaded motor from zero up to the rated speed are provided in the paper.

  • 22.
    Antonopoulos, Antonios
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Siemaszko, Daniel
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Ilves, Kalle
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Vasiladiotis, Michail
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Inner Control of Modular Multilevel Converters - An Approach using Open-loop Estimation of Stored Energy2010In: Proc. Int. Power Electronics Conf. (IPEC), 2010, p. 1579-1585Conference paper (Refereed)
  • 23.
    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.

  • 24.
    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.

  • 25.
    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.

  • 26.
    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).

  • 27.
    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.

  • 28.
    Colmenares, Juan
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Kargarrazi, Saleh
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Elahipanah, Hossein
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    High Temperature Passive Components for Extreme EnvironmentsManuscript (preprint) (Other academic)
    Abstract [en]

    Silicon carbide is an excellent candidate when high temperature power electronics applications are considered. Integrated circuits as well as several power devices have been tested at high temperature. However, little attention has been paid to high temperature passive components that could enable the full SiC potential. In this work, the high temperature performances of different passive components have been studied. Integrated capacitors in bipolar SiC technology has been tested up to 300 °C and, two different designs of inductors have been tested up to 600 °C.

  • 29.
    Colmenares, Juan
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Kargarrazi, Saleh
    KTH, School of Information and Communication Technology (ICT), Elektronics, Integrated devices and circuits.
    Elahipanah, Hossein
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    High-Temperature Passive Components for Extreme Environments2016In: 2016 IEEE 4TH WORKSHOP ON WIDE BANDGAP POWER DEVICES AND APPLICATIONS (WIPDA), IEEE conference proceedings, 2016, p. 271-274Conference paper (Refereed)
    Abstract [en]

    Silicon carbide is an excellent candidate when high temperature power electronics applications are considered. Integrated circuits as well as several power devices have been tested at high temperature. However, little attention has been paid to high temperature passive components that could enable the full SiC potential. In this work, the high-temperature performances of different passive components have been studied. Integrated capacitors in bipolar SiC technology have been tested up to 300 degrees C and, three different designs of inductors have been tested up to 700 degrees C.

  • 30.
    Colmenares, Juan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Peftitsis, Dimosthenis
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Rabkowski, Jacek
    Switching Performance of Parallel-Connected Power Modules with SiC MOSFETs2014In: 2014 International Power Electronics Conference, IPEC-Hiroshima - ECCE Asia 2014, IEEE conference proceedings, 2014, p. 3712-3717Conference paper (Refereed)
    Abstract [en]

    Parallel connection of silicon carbide power modules is a possible solution in order to reach higher current ratings. Nevertheless, it must be done appropriately to ensure a feasible operation of the parallel-connected power modules. High switching speeds are desired in order to achieve high efficiencies in medium and high-power applications but parasitic elements may give rise to a non-uniform current sharing during turn-on and turn-off, leading to non-uniformly distributed switching losses. This paper presents the switching performance of parallel-connected power modules populated with several silicon carbide metal-oxide-semiconductor field-effect-transistors chips. It is experimentally shown that turn-on and turn-off switching times of approximately 50 ns and 100 ns, respectively, can be reached, while an acceptably uniform transient current sharing is obtained. Moreover, based on the obtained results, an efficiency of approximately 99.35% for a three-phase converter rated at 312 kVA with a switching frequency of 20 kHz can be estimated.

  • 31.
    Colmenares, Juan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Peftitsis, Dimosthenis
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Rabkowski, Jacek
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Dual-function gate driver for a power module with SiC junction field transistors2013In: 2013 IEEE ECCE Asia Downunder - 5th IEEE Annual International Energy Conversion Congress and Exhibition, IEEE ECCE Asia 2013, IEEE , 2013, p. 245-250Conference paper (Refereed)
    Abstract [en]

    Driving a high-power module which is populated with several parallel-connected silicon carbide junction field-effect transistor chips must be done appropriately. Parasitic elements may give rise to oscillations during turn-on and turn-off. Fast and oscillation-free switching performance is desired in order to achieve a high efficiency. The key-issue in order to fulfill these two requirements is the design of a sophisticated gate driver. This paper proposes a dual-function gate-drive unit which is able to switch the module with an acceptable speed without letting the current and voltage suffer from significant oscillations. It is experimentally shown that turn-on and turn-off switching times of approximately 140 ns and 165 ns respectively can be reached, while the magnitude of the current oscillations is kept at an acceptable level. Moreover, using the proposed gate driver an efficiency of approximately 99.6% is expected for a three-phase converter rated at 125 kVA and having a switching frequency of 2 kHz.

  • 32.
    Colmenares, Juan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Peftitsis, Dimosthenis
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Rabkowski, Jacek
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion. Warsaw University of Technology, Poland .
    Sadik, Diane-Perle
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Dual-Function Gate Driver for a Power Module With SiC Junction Field-Effect Transistors2014In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 29, no 5, p. 2367-2379Article in journal (Refereed)
    Abstract [en]

    Silicon Carbide high-power modules populated with several parallel-connected junction field-effect transistors must be driven properly. Parasitic elements could act as drawbacks in order to achieve fast and oscillation-free switching performance, which are the main goals. These two requirements are related closely to the design of the gate-drive unit, and they must be kept under certain limits when high efficiencies are targeted. This paper deeply investigates several versions of gate-drive units and proposes a dual-function gate-drive unit which is able to switch the module with an acceptable speed without letting the current suffer from significant oscillations. It is experimentally shown that turn-on and turn-off switching times of approximately 130 and 185 ns respectively can be reached, while the magnitude of the current oscillations is kept at an adequate level. Moreover, using the proposed gate driver an efficiency of approximately 99.7% is expected for a three-phase converter rated at 125 kVA and having a switching frequency of 2 kHz.

  • 33.
    Colmenares, Juan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Peftitsis, Dimosthenis
    Rabkowski, Jacek
    Sadik, Diane-Perle
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Tolstoy, Georg
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    High-Efficiency 312-kVA Three-Phase Inverter Using Parallel Connection of Silicon Carbide MOSFET Power Modules2015In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 51, no 6, p. 4664-4676Article in journal (Refereed)
    Abstract [en]

    This paper presents the design process of a 312-kVA three-phase silicon carbide inverter using ten parallel-connected metal-oxide-semiconductor field-effect-transistor power modules in each phase leg. The design processes of the gate-drive circuits with short-circuit protection and power circuit layout are also presented. Measurements in order to evaluate the performance of the gate-drive circuits have been performed using a double-pulse setup. Moreover, electrical and thermal measurements in order to evaluate the transient performance and steady-state operation of the parallel-connected power modules are shown. Experimental results showing proper steady-state operation of the power converter are also presented. Taking into account measured data, an efficiency of approximately 99.3% at the rated power has been measured for the inverter.

  • 34.
    Colmenares, Juan
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Peftitsis, Dimosthenis
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Tolstoy, Georg
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Sadik, Diane-Perle
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Rabkowski, Jacek
    High-efficiency three-phase inverter with SiC MOSFET power modules for motor-drive applications2014Conference paper (Refereed)
    Abstract [en]

    This paper presents the design process of a 312 kVA three-phase silicon carbide inverter using ten parallel-connected metal-oxide-semiconductor field-effect-transistor power modules in each phase-leg. The design processes of the gate-drive circuits with short-circuit protection and the power circuit layout are also presented. Electrical measurements in order to evaluate the performance of the gate-drive circuits have been performed using a double-pulse setup. Experimental results showing the electrical performance during steady-state operation of the power converter are also shown. Taking into account measured data, an efficiency of approximately 99.3% at the rated power has been estimated for the inverter.

  • 35.
    Colmenares, Juan
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Sadik, Diane-Perle
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Reliability Analysis of a High-Efficiency SiC Three-Phase Inverter2016In: IEEE Journal of Emerging and Selected Topics in Power Electronics, ISSN 2168-6777, E-ISSN 2168-6785, Vol. 4, no 3, p. 996-1006Article in journal (Refereed)
    Abstract [en]

    Silicon carbide as an emerging technology offers potential benefits compared with the currently used silicon. One of these advantages is higher efficiency. If this is targeted, reducing the on-state losses is a possibility to achieve it. Parallel-connecting devices decrease the on-state resistance and therefore reduce the losses. Furthermore, increasing the amount of components such as parallel connection of devices introduces an undesired tradeoff between efficiency and reliability, since an increased component count increases the probability of failure. A reliability analysis has been performed on a three-phase inverter rated at 312 kVA, using parallel-connected power modules. This analysis shows that the gate voltage stress has a high impact on the reliability of the complete system. Decreasing the positive gate-source voltage could, therefore, increase the reliability of the system approximately three times without affecting the efficiency significantly. Moreover, adding redundancy in the system could also increase the mean time to failure by approximately five times.

  • 36.
    Colmenares, Juan
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Sadik, Diane-Perle
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Reliability analysis of a high-efficiency SiC three-phase inverter for motor drive applications2016In: 2016 IEEE Applied Power Electronics Conference and Exposition (APEC), Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 746-753, article id 7467955Conference paper (Refereed)
    Abstract [en]

    Silicon Carbide as an emerging technology offers potential benefits compared to the currently used Silicon. One of these advantages is higher efficiency. If this is targeted, reducing the on-state losses is a possibility to achieve it. Parallel-connecting devices decrease the on-state resistance and therefore reducing the losses. Furthermore, increasing the amount of components introduces an undesired tradeoff between efficiency and reliability. A reliability analysis has been performed on a three-phase inverter for motor drive applications rated at 312 kVA. This analysis has shown that the gate voltage stress determines the reliability of the complete system. Nevertheless, decreasing the positive gate-source voltage could increase the reliability of the system approximately 8 times without affecting the efficiency significantly. Moreover, adding redundancy in the system could also increase the mean time to failure approximately 5 times.

  • 37. de Toledo, Paulo Fischer
    et al.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Frequency domain model of an HVDC link with a line-commutated current-source converter. Part I: fixed overlap2009In: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695, Vol. 3, no 8, p. 757-770Article in journal (Refereed)
    Abstract [en]

    This study presents a frequency-domain model of an high voltage direct current (HVDC) transmission link with a line-commutated current-source converter. Using space-vector transfer functions between superimposed oscillations in the control signal and the AC and DC sides, expressions for voltages and currents have been derived. The dynamic properties of the HVDC link, taking the characteristics of the networks on both the AC and the DC sides into consideration, can be studied by applying classical Bode/Nyquist/Nichols control methods. The resulting model was validated by time-domain studies in PSCAD/EMTDC. The model is described in two papers. In this paper (Part I), it has been assumed that the overlap angle during commutation remains constant. It is shown in the validation that this assumption introduces resonances that cause severe errors at certain network conditions. In the second paper (Part II), the model is extended so as to cope with the varying overlap angle in order to bring the frequency-domain model into agreement with the results obtained from time-domain simulations.

  • 38.
    de Toledo, Paulo Fischer
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Frequency domain model of an HVDC link with a line-commutated current-source converter. Part II: varying overlap2009Article in journal (Refereed)
    Abstract [en]

    The second part of the description of a frequency-domain model of a high-voltage direct current (HVDC) transmission link with line-commutated current-source converters is presented in this study. The model is based on transfer functions between superimposed oscillations in the control signal and the AC- and DC-side voltages and currents. In 'Part I' of the description the overlap angle was assumed to be constant. At certain resonance frequencies severe deviations were obtained between the calculated transfer functions and the ones extracted from time-domain simulations. In this study (Part II), the model has been extended to deal with varying overlap angle. It is shown that the agreement between transfer functions calculated in frequency- and time-domain has improved substantially.

  • 39. Demetriades, G. D.
    et al.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Small-signal analysis of the half-bridge soft-swithing uni-directional converter employing extended state-space averaging2008In: PESC Record - IEEE Annual Power Electronics Specialists Conference, 2008, p. 385-391Conference paper (Refereed)
    Abstract [en]

    In the present paper the small-signal model of the half-bridge soft-switched Single Active Bridge is derived. In order to derive the small-signal model of the specific topology an extended state-space averaging method based on half-cycle symmetry has been used and is briefly described in the paper. The results obtained have been verified experimentally.

  • 40. Demetriades, Georgios D.
    et al.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Characterisation of the Soft-switched Single-Active Bridge Topology Employing a Novel Control Scheme for High-power DC-DC Applications2005In: 2005 IEEE 36th Power Electronic Specialists Conference (PESC), Vols 1-3, 2005, p. 1947-1951Conference paper (Refereed)
    Abstract [en]

    The half-bridge SAB topology is the simplest soft-switched topology known to the authors and is firstly presented in (G.D. Demetriades). In the present paper the SAB topology is thoroughly studied and the aspects as stability and efficiency are addressed as well. High-frequency oscillations occurring during the discontinuous-time interval are reported.

  • 41. Demetriades, Georgios D.
    et al.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Characterization of the Dual-Active Bridge Topology for High-Power Applications Employing a Duty-Cycle Modulation2008In: 2008 IEEE POWER ELECTRONICS SPECIALISTS CONFERENCE, VOLS 1-10, NEW YORK, NY: IEEE , 2008, p. 2791-2798Conference paper (Refereed)
    Abstract [en]

    In the present paper the Dual-Active Bridgetopology employing a duty-cycle modulation is studied. Thebehavior of the converter at steady-state is examined.Additionally, the small-signal model of the topology ispresented and the dynamic behavior is examined.Simulations and experimental results are presented. It isworth noticing that the converter is operated under softswitchingconditions in a wide load range.

  • 42. Demetriades, Georgios D.
    et al.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Dynamic Modeling of the Dual-Active Bridge Topology for High-Power Applications2008In: 2008 IEEE POWER ELECTRONICS SPECIALISTS CONFERENCE, VOLS 1-10, NEW YORK: IEEE , 2008, p. 457-464Conference paper (Refereed)
    Abstract [en]

    In the present paper the staedy-state and thedynamic behavior of the Dual-Active Bridge topology havebeen studied. The small-signal model of the converter hasbeen derived and theoretical and experimental results arepresented.The Dual-Active Bridge is an attractive solution for highpowerapplications where a bi-directional operation is needed.

  • 43. Demetriades, Georgios D.
    et al.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Small-signal analysis of the half-bridge soft-switching uni-directional converter employing extended state-space averaging2008In: Proc of IEEE PESC 2008, Rhodes, Greece / [ed] IEEE, 2008, p. 385-391Conference paper (Refereed)
    Abstract [en]

    In the present paper the small-signal model ofthe half-bridge soft-switched Single Active Bridge is derived.In order to derive the small-signal model of the specifictopology an extended state-space averaging method basedon half-cycle symmetry has been used and is brieflydescribed in the paper. The results obtained have beenverified experimentally.

  • 44.
    Engström, Jörgen
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Magnussen, Freddy
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Analytical Calculation of Winding Losses of Inverter-Fed PM Synchronous Motors with Air-Gap Windings and Surface Mounted Magnets1997In: Proc. of the 7th European Conference on Power Electronics and Applications EPE'97, 1997Conference paper (Refereed)
  • 45.
    Fischer de Toledo, Paulo
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Frequency-domain modelling of sub-synchronous torsional interaction of synchronous machines and a high voltage direct current transmission link with line-commutated converters2010In: IET GENERATION TRANSMISSION & DISTRIBUTION, ISSN 1751-8687, Vol. 4, no 3, p. 418-431Article in journal (Refereed)
    Abstract [en]

    The authors describe a model of a system that includes a high voltage direct current (HVDC) transmission link with line-commutated current source converters (LCC) closely connected to a synchronous generator used to perform analysis of sub-synchronous torsional interaction (SSTI) in the frequency domain. The model of the HVDC transmission link adequately represents the converters in the frequency domain and includes all essential controls for the operation of the converters, including a new sub-synchronous damping control used to mitigate interaction between the recti. er LCC and the shaft of the synchronous machine. The frequency domain model has been validated against time domain simulations showing good agreement.

  • 46. Fischer, P.
    et al.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    A new control scheme for an HVDC transmission link with capacitor-commutated converters having the inverter operating with constant alternating voltage2012In: 44th International Conference on Large High Voltage Electric Systems 2012, 2012, p. 1-11Conference paper (Refereed)
    Abstract [en]

    Experience and theoretical analysis show that the voltage and power stability becomes an important issue when high-voltage direct current (HVDC) systems using line-commutated converters (LCC) are connected to AC systems with low short-circuit capacity and that these problems become more pronounced the lower the short-circuit capacity of the connected AC system is, as compared with the rating of the HVDC converter station. Normally some additional equipment, like static or synchronous compensators, will be installed in order to improve the performance of the HVDC transmission system, when it is connected to a weak AC system. The cost of the substation thereby will be increased. The Capacitor-Commutated Converter (CCC), which has been developed by ABB, offers an alternative to the LCC in this kind of application. It reduces the reactive power interaction between the converter and the connected AC system. The CCC is, in principle, a classical converter provided with a series capacitor placed between the converter valves and the converter transformer. In this paper a new control strategy that can be used together with such a CCC is presented. In the new control system the inverter emulates the operation of a Voltage Source Converter, in the sense that, beside the control of the active power flow through the converter, the reactive power exchange with the AC network can also be managed in order to adjust the alternating voltage of the converter bus. Studies have shown that the interaction between the inverter and the connected AC system is significantly reduced, when the CCC is used together with this new control strategy. Keeping the alternating voltage constant makes it possible to control the DC-side voltage of the HVDC transmission system, allowing the rectifier converter to control the active power by means of controlling the direct current. This combination allows stable operation of the HVDC transmission system even under severe network conditions associated with low short-circuit power in the connected AC network at the inverter side. In the paper it is shown that, with the new control scheme, it is possible to operate the inverter into an almost passive AC network (a network with very few rotating generators, resulting in almost no short circuit power). Simulation results have indicated satisfactory operation of the HVDC transmission with the inverter operating into a network having a Short-Circuit Ratio as low as 0.2 (SCR ≈ 0.2). To the knowledge of the authors, operation of a line-commutated converter at such low SCR values has never been reported previously. A description of the new control scheme will be presented. The calculated performance in a practically implemented installation, the Rio Madeira Back-to-Back system, will be illustrated.

  • 47.
    Haider, Arif
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Ahmed, Noman
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Open-loop approach for control of multi-terminal DC systems based on modular multilevel converters2011In: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) / [ed] EPE Association, 2011Conference paper (Refereed)
    Abstract [en]

    In this paper a multi-terminal direct current (MTDC) system with modular multilevel converters (M2Cs) is suggested. An open loop control method is used for the control of the converters. Each converter is modeled with 36 sub-modules per arm with a total of 216 sub-modules consisting of half bridges. Power-synchronization control is used instead of a phase-locked loop (PLL) for synchronization. Thus, the short circuit capacities of the ac systems are no longer limiting factors and the instability caused by the PLL in weak ac systems is avoided [10]. A direct voltage controller is implemented with power-synchronization control as an inner loop in one station. Several scenarios are analyzed to demonstrate control flexibility and ride-through capability for grid transients. By means of analytical calculations and time simulations in PSCAD/EMTDC, the validity of the proposed MTDC system is confirmed.

  • 48.
    Harnefors, Lennart
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion. ABB, Sweden.
    Antonopoulos, Antonios
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ilves, Kalle
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Global asymptotic stability of current-controlled modular multilevel converters2015In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, no 1, p. 249-258, article id 6883248Article in journal (Refereed)
    Abstract [en]

    In this paper, previously developed stability results for open-loop sum-capacitor-voltage control of modular multilevel converters are extended. To give improved damping, circulating-current feedback is included in the control law. With the output-current control loop and a first-order measurement lag taken into account, global asymptotic stability is proven. Careful consideration of the on-line sum-capacitor-voltage reference computation is given, since this is the most critical part of the control system.

  • 49. Harnefors, Lennart
    et al.
    Antonopoulos, Antonios
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Global asymptotic stability of modular multilevel converters with measurement lag and circulating-current control2013In: Power Electronics and Applications (EPE), 2013, IEEE , 2013, p. 1-10Conference paper (Refereed)
    Abstract [en]

    In this paper, previously developed stability results for open-loop sum-capacitor-voltage control of modular multilevel converters are extended. To obtain improved damping, circulating-current feedback is included in the control law. A first-order measurement lag is added to this feedback. With these additions, global asymptotic stability is proven. Careful consideration of the online control-law computation is given, since this is the most critical part of the control system. Experimental results verify the theory.

  • 50.
    Harnefors, Lennart
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Antonopoulos, Antonios
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Dynamic Analysis of Modular Multilevel Converters2013In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 60, no 7, p. 2526-2537Article in journal (Refereed)
    Abstract [en]

    Theory for the dynamics of modular multilevel converters is developed in this paper. It is shown that the sum capacitor voltage in each arm often can be considered instead of the individual capacitor voltages, thereby significantly reducing the complexity of the system model. Two selections of the so-called insertion indices, which both compensate for the sum-capacitor-voltage ripples, are considered. The dynamic systems which respectively result from these selections are analyzed. An effective dc-bus model, which takes into account the contribution from the submodule capacitors, is obtained. Finally, explicit formulas for the stationary sum-capacitor-voltage ripples are derived.

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