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  • 1.
    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.

  • 2.
    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).

  • 3.
    Bessegato, Luca
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Harnefors, Lennart
    Ilves, Kalle
    Norrga, Staffan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    A Method for the Calculation of the AC-Side Admittance of a Modular Multilevel Converter2018In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Article in journal (Refereed)
    Abstract [en]

    Connecting a modular multilevel converter to anac grid may cause stability issues, which can be assessed byanalyzing the converter ac-side admittance in relation to the gridimpedance. This paper presents a method for calculating theac-side admittance of modular multilevel converters, analyzingthe main frequency components of the converter variables individually.Starting from a time-averaged model of the converter,the proposed method performs a linearization in the frequencydomain, which overcomes the inherent nonlinearities of theconverter internal dynamics and the phase-locked loop usedin the control. The ac-side admittance obtained analytically isfirstly validated by simulations against a nonlinear time-averagedmodel of the modular multilevel converter. The tradeoff posedby complexity of the method and the accuracy of the result isdiscussed and the magnitude of the individual frequency componentsis shown. Finally, experiments on a down-scaled prototypeare performed to validate this study and the simplification onwhich it is based.

  • 4.
    Bessegato, Luca
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Ilves, Kalle
    Harnefors, Lennart
    Norrga, Staffan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Effects of Control on the AC-Side Admittance of a Modular Multilevel Converter2019In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 34, no 8, p. 7206-7220, article id 8514034Article in journal (Refereed)
    Abstract [en]

    The stability of a modular multilevel converter connected to an ac grid can be assessed by analyzing the converter ac-side admittance in relation to the grid impedance. The converter control parameters have a strong impact on the admittance and they can be adjusted for achieving system stability. This paper focuses on the admittance-shaping effect produced by different current-control schemes, either designed on a per-phase basis or in the $dq$ frame using space vectors. A linear analytical model of the converter ac-side admittance is developed, including the different current-control schemes and the phase-locked loop. Different solutions for computing the insertion indices are also analyzed, showing that for a closed-loop scheme a compact expression of the admittance is obtained. The impact of the control parameters on the admittance is discussed and verified experimentally, giving guidelines for designing the system in terms of stability. Moreover, recommendations on whether a simplified admittance expression could be used instead of the detailed model are given. The findings from the admittance-shaping analysis are used to recreate a grid-converter system whose stability is determined by the control parameters. The developed admittance model is then used in this experimental case study, showing that the stability of the interconnected system can be assessed using the Nyquist stability criterion.

  • 5.
    Bessegato, Luca
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Ilves, Kalle
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Harnefors, Lennart
    Norrga, Staffan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Östlund, Stefan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Control and Admittance Modeling of an AC/AC Modular Multilevel Converter for Railway Supplies2019In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Article in journal (Refereed)
    Abstract [en]

    Modular multilevel converters (MMCs) can be configured to perform ac/ac conversion, which makes them suitable as railway power supplies. In this paper, a hierarchical control scheme for ac/ac MMCs for railway power supplies is devised and evaluated, considering the requirements and the operating conditions specific to this application. Furthermore, admittance models of the ac/ac MMC are developed, showing how the suggested hierarchical control scheme affects the three-phase and the single-phase side admittances of the converter. These models allow for analyzing the stability of the interconnected system using the impedance-based stability criterion and the passivity-based stability assessment. Finally, the findings presented in this paper are validated experimentally, using a down-scaled MMC. 

  • 6.
    Bolognani, S.
    et al.
    University of Padova.
    Peretti, L.
    University of Padova.
    Zigliotto, M.
    University of Padova.
    Online MTPA Control Strategy for DTC Synchronous-Reluctance-Motor Drives2011In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 26, no 1, p. 20-28Article in journal (Refereed)
  • 7.
    Bolognani, S.
    et al.
    University of Padova.
    Peretti, L.
    University of Padova.
    Zigliotto, M.
    University of Padova.
    Parameter sensitivity analysis of an improved open-loop speed estimate for induction motor drives2008In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 23, no 4, p. 2127-2135Article in journal (Refereed)
  • 8. Bongiorno, Massimo
    et al.
    Svensson, Jan
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    On control of static synchronous series compensator for SSR mitigation2008In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 23, no 2, p. 735-743Article in journal (Refereed)
    Abstract [en]

    This paper deals with the analysis and simulation of the static series compensator (SSSC) for subsynchronous resonance (SSR) mitigation. The purpose of the paper is to derive and analyze a novel control strategy for SSSC dedicated for SSR mitigation. Objective of the proposed controller is to increase the network damping only at those frequencies that are critical for the turbine-generator shaft. By using frequency scanning analysis, the effectiveness of the proposed method for mitigation of SSR due to torsional interaction effect is presented and compared with the existing control strategy. Finally, simulation results show the performance of the proposed method in mitigating SSR due to torque amplification effect.

  • 9.
    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.

  • 10. Gregoire, Luc-Andre
    et al.
    Blanchette, Handy Fortin
    Li, Wei
    Antonopoulos, Antonios
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Al-Haddad, Kamal
    Modular Multilevel Converters Overvoltage Diagnosis and Remedial Strategy During Blocking Sequences2015In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, no 5, p. 2777-2785Article in journal (Refereed)
    Abstract [en]

    In this paper, the authors first highlight an existing overvoltage phenomenon that is inherent to the modular multilevel converter (MMC) topology. The latter occurs during the blocking sequences of semiconductor devices if the converter needs to be stopped due to circulating current, loss of control, or unexpected faults. An analysis based on time-domain expressions describing each operating sequence during normal and faulty blocking conditions is used to demonstrate the origin of this overvoltage. Thereafter, system behaviour is obtained when devices gating signals are withheld as well as the exact overvoltage cause. Real-time simulation, with submicrosecond time steps, and experimental results validate the overvoltage phenomena and the proposed remedial strategy to avoid uncontrolled faulty conditions.

  • 11. Haghbin, Saeid
    et al.
    Khan, Kashif
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Zhao, Shuang
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Alakula, Mats
    Lundmark, Sonja
    Carlson, Ola
    An Integrated 20-kW Motor Drive and Isolated Battery Charger for Plug-In Vehicles2013In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 28, no 8, p. 4013-4029Article in journal (Refereed)
    Abstract [en]

    For vehicles using grid power to charge the battery, traction circuit components are not normally engaged during the charging time, so there is a possibility to use them in the charger circuit to have an on-board integrated motor drive and battery charger. An isolated high-power three-phase integrated motor drive and charger based on a split-phase permanent magnet motor is presented in this paper. The motor winding connections are reversible by a relay-based switching device for traction and battery charging. In traction mode, the motor is a classical three-phase motor, but in charging mode it is a rotating isolating transformer providing a three-phase voltage source for the inverter to charge the battery. A mathematical model of the motor with six stator windings is presented for an arbitrary phase shift in windings. For the charging mode, the split-phase motor grid synchronization process and charge control are explained including the developed controller. A 20-kW system is designed and implemented to verify the proper operation of the proposed system. Simulation and practical results are provided to show the system performance in terms of functionality, dynamic response, and efficiency. Moreover, some discussions, recommendations, and limitations are provided to give more practical insights.

  • 12.
    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.

  • 13.
    Hassanpoor, Arman
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Häfner, J.
    Jacobson, B.
    Technical Assessment of Load Commutation Switch in Hybrid HVDC Breaker2015In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, no 10, p. 5393-5400Article in journal (Refereed)
    Abstract [en]

    The development of a large-scale high-voltage direct current (HVDC) power grid requires a reliable, fast, and low-loss circuit breaker. The load commutation switch (LCS) is an essential part of ABB's 1200-MW hybrid HVDC breaker concept, which builds up a low-loss conducting path for the load current. The technical requirements for the LCS are expressed in this paper by studying the operation principle of the hybrid HVDC breaker. The voltage stress over the LCS is determined based on a dc grid with 320 and 2 kA rated voltage and current. A system model of the hybrid HVDC breaker is developed in PSCAD/EMTDC to study the design criteria for snubber circuit and arrester blocks. It is observed that conventional snubber circuits are not suitable for a bidirectional LCS as the current of snubber capacitors prevent the fast interruption action. A modified snubber circuit is proposed in this paper along with two more alternatives for the LCS to overcome this problem. Moreover, the power loss model for a semiconductor device is discussed in this paper based on the 4.5-kV StakPak IGBT. The model is used to calculate the conduction power losses for different LCS topologies. Ultimately, a matrix of 3 × 3 IGBT modules is selected to provide a reliable LCS design which can handle several internal fault cases with no interruption of operation. A full-scale prototype has been constructed and tested in ABB HVDC Center, Ludvika, Sweden. The experimental test results are also included in the paper in order to verify the calculation and simulation study.

  • 14.
    Hassanpoor, Arman
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems. ABB Corporate Research Vasteras, Sweden.
    Nami, Alireza
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Tolerance Band Adaptation Method for Dynamic Operation of Grid-Connected Modular Multilevel Converters2016In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, no 99, p. 1-1Article in journal (Refereed)
    Abstract [en]

    The use of modular multilevel converters (MMC) in high-voltage direct current (HVDC) transmission systems has grown significantly in the past decade. The efficiency, cell capacitor voltage ripple and dynamic performance are three contradictory aspects of the MMC which are related to the converter switching scheme. Previously introduced tolerance band-based schemes enable efficient and simple control for grid-connected MMCs. This paper addresses the dynamic operation of tolerance band switching schemes by proposing a dynamic boundary setting technique for steady-state operation and a switching scheme scheduling controller for transient fault handling. The performance of proposed methods are validated in a realistic point-to-point HVDC link, modeled in real-time digital simulator (RTDS) where two converters with 512 cells per arm are implemented. Utilizing the proposed methods will enable efficient implementation of tolerance band-based schemes for different operating points, and also a robust transient fault handling.

  • 15.
    Hassanpoor, Arman
    et al.
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Roostaei, Amin
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electric power and energy systems.
    Lindgren, Markus
    Optimization-Based Cell Selection Method for Grid-Connected Modular Multilevel Converters2016In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 31, no 4, p. 2780-2790Article in journal (Refereed)
    Abstract [en]

    Modular multilevel converters (MMCs) are widely used in different applications. Due to low-loss operation, compactness, and high modularity, MMC is extremely attractive for high-voltage direct-current (HVDC) transmission systems. The HVDC station loss is highly related to the converter switching pulse pattern, which is generated by modulation algorithm and cell selection methods. This paper formulates the switching pulse pattern generation, as a versatile optimization problem. The problem constraints and objectives are formulated for HVDC applications and compared with similar problems in the field of computer science. To overcome the computational complexity in solving the introduced optimization problem, a heuristic method is proposed for cell selection algorithm. The method utilizes the current level in order to obtain lossless switching at zero-current crossings. The study of the proposed method, in a time-domain simulation platform, shows that the method can reduce the switching converter losses by 60% compared to carrier-based modulation, maintaining the same capacitor voltage ripple. Eventually, the practical functionality of the proposed method is verified in a real-time digital simulator, RTDS, for a 512-level converter in a point to point HVDC link. Although this paper focuses on HVDC, the mathematical model is applicable for any MMC application.

  • 16.
    Hassanpoor, Arman
    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.
    Tolerance band modulation methods for modular multilevel converters2015In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, no 1, p. 311-326, article id 6739183Article in journal (Refereed)
    Abstract [en]

    Modular multilevel converters (M2Cs) are increasingly used in high-voltage direct current (HVDC) systems. The efficiency of M2Cs is influenced by the modulation and cell selecting methods, which determines the switching frequency and capacitor voltage ripple in the converter station. A new approach to modulation of the M2C is presented in this paper. Tolerance band methods are employed to obtain the switching instants, and also cell selection. The proposed methods overcome the modulation problem for converters with few cells on one hand and also reduce the sorting efforts for cell balancing purposes of many cells converter on the other hand. Three different algorithms are also proposed to balance the cell capacitor voltages. The evaluation is done in time-domain simulation by which the performance of each method is studied in both the steady-state and transient cases. It is observed that using tolerance band methods not only reduces the switching frequency but also allows for handling severe fault cases in a grid-connected system. Eventually, the most promising tolerance band method has been implemented and verified in a real-time digital simulator, RTDS®. The average switching frequency of 70 Hz has been achieved for the system under study, while the capacitor voltage ripple is limited to 10% of the nominal cell voltage.

  • 17.
    Heinig, Stefanie
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Jacobs, Keijo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Ilves, Kalle
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Bessegato, Luca
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Bakas, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Norrga, Staffan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Implications of Capacitor Voltage Imbalance on the Operation of the Semi-Full-Bridge Submodule2019In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 34, no 10, p. 9520-9535, article id 8598807Article in journal (Refereed)
    Abstract [en]

    Future meshed high-voltage direct current grids require modular multilevel converters with extended functionality. One of the most interesting new submodule topologies is the semi-full-bridge because it enables efficient handling of DC-side short circuits while having reduced power losses compared to an implementation with full-bridge submodules. However, the semi-full-bridge submodule requires the parallel connection of capacitors during normal operation which can cause a high redistribution current in case the voltages of the two submodule capacitors are not equal. The maximum voltage difference and resulting redistribution current have been studied analytically, by means of simulations and in a full-scale standalone submodule laboratory setup. The most critical parameter is the capacitance mismatch between the two capacitors. The experimental results from the full-scale prototype show that the redistribution current peaks at 500A if the voltage difference is 10V before paralleling and increases to 2500A if the difference is 40V. However, neglecting very unlikely cases, the maximum voltage difference predicted by simulations is not higher than 20-30V for the considered case. Among other measures, a balancing controller is proposed which reduces the voltage difference safely if a certain maximum value is surpassed. The operating principle of the controller is described in detail and verified experimentally on a down-scaled submodule within a modular multilevel converter prototype. It can be concluded that excessively high redistribution currents can be prevented. Consequently, they are no obstacle for using the semi-full-bridge submodule in future HVDC converters.

  • 18.
    Ilves, Kalle
    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.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    A New Modulation Method for the Modular Multilevel Converter Allowing Fundamental Switching Frequency2012In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 27, no 8, p. 3482-3494Article in journal (Refereed)
    Abstract [en]

    This paper presents a new modulation method for the modular multilevel converter. The proposed method is based on a fixed pulse pattern where harmonic elimination methods can be applied. In the proposed modulation method, the pulse pattern is chosen in such a way that the stored energy in each submodule remains stable. It is shown that this can be done at the fundamental switching frequency without measuring the capacitor voltages or using any other form of feedback control. Such a modulation scheme has not been presented before. The theoretical results are verified by both simulations and experimental results. The simulation results show successful operation at the fundamental switching frequency with a larger number of submodules. When a smaller number of submodules are used, harmonic elimination methods may be applied. This is verified experimentally on a converter with eight submodules per phase leg. The experimental results verify that stable operation can be maintained at the fundamental switching frequency while successfully eliminating the fifth harmonic in the ac-side voltage.

  • 19.
    Ilves, Kalle
    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.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Steady-State Analysis of Interaction Between Harmonic Components of Arm and Line Quantities of Modular Multilevel Converters2012In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 27, no 1, p. 57-68Article in journal (Refereed)
    Abstract [en]

    The fundamental frequency component in the arm currents of a modular multilevel converter is a necessity for the operation of the converter, as is the connection and bypassing of the submodules. Inevitably, this will cause alternating components in the capacitor voltages. This paper investigates how the arm currents and capacitor voltages interact when the submodules are connected and bypassed in a sinusoidal manner. Equations that describe the circulating current that is caused by the variations in the total inserted voltage are derived. Resonant frequencies are identified and the resonant behaviour is verified by experimental results. It is also found that the effective values of the arm resistance and submodule capacitances can be extracted from the measurements by least square fitting of the analytical expressions to the measured values. Finally, the analytical expression for the arm currents is verified by experimental results.

  • 20.
    Ilves, Kalle
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    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.
    Analysis and Operation of Modular Multilevel Converters With Phase-Shifted Carrier PWM2015In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, no 1, p. 268-283Article in journal (Refereed)
    Abstract [en]

    Many publications have been presented on the modulation and control of the modular multilevel converter, some of which are based on phase-shifted carrier modulation. This paper presents an analysis of how the switching frequency affects the capacitor voltages, circulating currents, and alternating voltages using phase-shifted carrier modulation. It is found that switching frequencies that are integer multiples of the fundamental frequency should be avoided as they can cause the capacitor voltages to diverge. Suitable switching frequencies are derived for which the arm and line quantities will be periodic with symmetric operating conditions in the upper and lower arms. Thus, the practical outcome of this paper is a detailed description of how the switching frequency should be chosen in order to achieve advantageous operating conditions. The theoretical results from the analysis are validated by both simulations and experimental results.

  • 21.
    Ilves, Kalle
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Harnefors, Lennart
    ABB Corporate Research, Västerås, Sweden .
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Predictive Sorting Algorithm for Modular Multilevel Converters Minimizing the Spread in the Submodule Capacitor Voltages2015In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, no 1, p. 440-449Article in journal (Refereed)
    Abstract [en]

    The balancing of the capacitor voltages in modular multilevel converters becomes increasingly difficult when the switching frequency is reduced. Typically, a reduced switching frequency will increase the spread in the capacitor voltages and, thus, the voltage ripple in the individual submodules. This paper presents a capacitor voltage balancing strategy which aims to combine a low switching frequency with a low capacitor-voltage ripple. This is done by a predictive algorithm that controls the converter in such a way that the stored charge in the submodule capacitors is evenly distributed among all the submodules when the capacitor voltages reach their maximum values. In this way, it is possible to limit the peak voltages in the submodule capacitors at switching frequencies as low as 2-3 times the fundamental switching frequency. The proposed capacitor voltage balancing strategy is validated by both simulations and experimental results with 130-Hz and 140-Hz switching frequency. In the simulations, the capacitor voltage ripple was reduced by 24% compared to the case when a conventional sorting algorithm is used, and the experimental results show that it is possible to combine the proposed voltage balancing strategy with a circulating-current controller.

  • 22.
    Ilves, Kalle
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Harnefors, Lennart
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    On Energy Storage Requirements in Modular Multilevel Converters2014In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 29, no 1, p. 77-88Article in journal (Refereed)
    Abstract [en]

    The modular multilevel converter is a promising topology for high-voltage and high-power applications. By using submodules equipped with dc-capacitors excellent output voltage waveforms can be obtained at low switching frequencies. The rated energy storage of the submodule capacitors is a driving factor of the size, cost, and weight of the submodules. Although the modular multilevel converter has been thoroughly investigated in the literature, a more detailed analysis of the energy-storage requirements will provide an important contribution for dimensioning and analysis of modular multilevel converters. Such an analysis is presented in this paper. The analysis relates the power transfer capability to the stored energy in the converter and the findings are validated by both simulations and experimental results. The required size of the submodule capacitors in a 4.5 MW grid-connected converter is first calculated and the calculated operating range is then compared with simulation results. The experimental results show that if the average capacitor voltage is allowed to increase 10% above the nominal value an energy storage to power transfer ratio of 21 J/kW can be achieved. It is concluded that the presented theory can relate the power transfer capability to the energy storage in the converter and is thus a valuable tool in the design and analysis of modular multilevel converters.

  • 23.
    Ilves, Kalle
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Taffner, Franz
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Antonopoulos, Antonios
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Harnefors, Lennart
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    A Submodule Implementation for Parallel Connection of Capacitors in Modular Multilevel Converters2015In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, no 7, p. 3518-3527Article in journal (Refereed)
    Abstract [en]

    In modular multilevel converters there is a trade-off between the switching frequency and the voltage ripple in the submodule capacitors. The reason for this is that it becomes increasingly difficult to balance the capacitor voltages when the switching frequency is reduced. This paper presents a new submodule circuit which improves the balancing of the capacitor voltages at low switching frequencies. The proposed submodule circuit consists of two capacitors and eight switches, forming a three-level submodule. Ideally, the voltage and current ratings of the switches can be chosen such that the combined power rating of the semiconductors is the same as for the equivalent solution with conventional half-bridge submodules. The proposed submodule circuit provides the possibility of connecting the two capacitors in parallel when the intermediate voltage level is used. This will reduce the capacitor voltage ripple, especially at low switching frequencies and thus allow for a reduction of the size, weight, and cost of the submodule capacitors. The proposed submodule circuit is validated by both simulations and experimental results. It is found that the parallel connection of the submodule capacitors will, in fact, significantly improve the balancing of the capacitor voltages.

  • 24.
    Johannesson, Daniel
    et al.
    ABB Corporate Research.
    Nawaz, Muhammad
    ABB Corporate Research.
    Development of a Simple Analytical PSpice Model for SiC-Based BJT Power Modules2016In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 31, no 6, p. 4517-4525Article in journal (Refereed)
    Abstract [en]

    A simple analytical Spice-type model has been developed and verified for the first time for 4H-SiC-based bipolar junction transistor (BJT) power module with voltage and current rating of 1200 V and 800 A. The simulation model is based on a temperature-dependent silicon carbide (SiC) Gummel-Poon model for high-power applications. PSpice simulations are performed to extract technology-dependent modeling parameters coupled with static and dynamic characteristics of BJTs at different temperatures and validated against the measured data. Influence of various circuit elements, for instance, stray inductance and base resistance and internal device modeling parameters, carrier life time, and emitter doping, on switching losses has been studied. The performance of the SiC BJT model is fairly accurate and correlates well with the measured results over a wide temperature range.

  • 25.
    Johannesson, Daniel
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. ABB Corp Res Ctr, S-72178 Vasteras, Sweden..
    Nawaz, Muhammad
    ABB Corp Res Ctr, S-72178 Vasteras, Sweden..
    Ilves, Kalle
    ABB Corp Res Ctr, S-72178 Vasteras, Sweden..
    Assessment of 10 kV, 100 A Silicon Carbide MOSFET Power Modules2018In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 33, no 6, p. 5215-5225Article in journal (Refereed)
    Abstract [en]

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

  • 26.
    Kargarrazi, Saleh
    et al.
    Stanford Univ, Dept Aeronaut & Astronaut, Stanford, CA 94305 USA..
    Elahipanah, Hossein
    KTH, School of Electrical Engineering and Computer Science (EECS), Electronics, Integrated devices and circuits.
    Saggini, Stefano
    DIEGM Univ Udine, I-33100 Udine, Italy..
    Senesky, Debbie
    Stanford Univ, Dept Aeronaut & Astronaut, Stanford, CA 94305 USA..
    Zetterling, Carl-Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Electronics, Integrated devices and circuits.
    500 degrees C SiC PWM Integrated Circuit2019In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 34, no 3, p. 1997-2001Article in journal (Refereed)
    Abstract [en]

    This letter reports on a high-temperature pulsewidth modulation (PWM) integrated circuit microfabricated in 4H-SiC bipolar process technology that features an on-chip integrated ramp generator. The circuit has been characterized and shown to be operational in a wide temperature range from 25 to 500 degrees C. The operating frequency of the PWM varies in the range of 160 to 210 kHz and the duty cycle varies less than 17% over the entire temperature range. The proposed PWM is suggested to efficiently and reliably control power converters in extreme environments.

  • 27.
    Katic, Janko
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rodriguez, Saul
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Rusu, Ana
    KTH, School of Information and Communication Technology (ICT).
    A High-Efficiency Energy Harvesting Interface for Implanted Biofuel Cell and Thermal Harvesters2017In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 33, no 5, p. 4125-4134, article id 7940053Article in journal (Refereed)
    Abstract [en]

    A dual-source energy harvesting interface that combines energy from implanted glucose biofuel cell and thermoelectric generator is presented. A single-inductor dual-input dual-output boost converter topology is employed to efficiently transfer the extracted power to the output. A dual-input feature enables the simultaneous maximum power extraction from two harvesters, while a dual-output allows a control circuit to perform complex digital functions at nW power levels. The control circuit reconfigures the converter to improve the efficiency and achieve zero-current and zero-voltage switching. The measurement results of the proposed boost converter, implemented in a 0.18 μm CMOS process, show a peak efficiency of 89.5% when both sources provide a combined input power of 66 μW. In the single-source mode, the converter achieves a peak efficiency of 85.2% at 23 μW for the thermoelectric source and 90.4% at 29 μW for the glucose biofuel cell. The converter can operate from minimum input voltages of 10 mV for the thermoelectric source and 30 mV for the glucose biofuel cell. 

  • 28.
    Kjellqvist, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930). KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Östlund, Stefan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics (closed 20110930).
    Active Snubber Circuit for Source Commutated Converters Utilizing the IGBT in the Linear Region2008In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 23, no 5, p. 2595-2601Article in journal (Refereed)
    Abstract [en]

    This paper describes a gate control method where an IGBT is controlled in its linear region by means of closed loop control in order to regulate the voltage slope during turn-on and to clamp the voltage of an anti-parallel diode in a source commutated converter. Controlling the voltage slope may be necessary in a high voltage converter to avoid emission of EMI or to avoid triggering oscillations which may cause insulation failure. Controlling the switching trajectory without influence from the device characteristics is important where series-connection is necessary to increase the overall blocking voltage. The control method has been verified by means of a prototype.

  • 29. Krismer, Florian
    et al.
    Schroth, Sebastian
    Ertl, Hans
    Kostov, Konstantin Stoychev
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Kolar, Johann Walter
    Analysis and Practical Relevance of CM/DM EMI Noise Separator Characteristics2017In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 32, no 4, p. 3112-3127Article in journal (Refereed)
    Abstract [en]

    This work investigates sources of measurement errors that result for common mode/differential mode (CM/DM) separators in a practical measurement environment, with a particular focus on the recently presented input impedance criterion for CM/DM separators, derives the respective analytical expressions, and employs a detailed analytical model to verify the obtained findings. Furthermore, a method is derived, which determines the worst-case measurement error by reason of cross coupling for given measured DM and CM output voltage components. Based on an example, this work illustrates how the obtained expressions can be advantageously used in a computer program to automatically decide whether a particular spectral measurement component represents a useful measurement result or if it is strongly affected by cross coupling (CM to DM and DM to CM). Finally, the paper presents the realization and accompanying experimental results of an active CM/DM separator, which allows for low realization effort and features competitive separation capabilities (DMTR/CMRR > 50 dB and CMTR/DMRR > 42 dB for frequencies up to 10 MHz).

  • 30. Li, Shichao
    et al.
    Sun, Fei
    An, Di
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Increasing Efficiency of a Wireless Energy Transfer System by Spatial Translational Transformation2018In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 33, no 4, p. 3325-3332Article in journal (Refereed)
    Abstract [en]

    A magnetic translational projector (MTP) designed by transformation optics is applied to improve energy transfer efficiency in a wireless power transfer (WPT) system. Our numerical simulation results showtheMTP can greatly enhance energy transfer efficiency (e.g., nearly two orders, compared to the case without our MTP) in the WPT system, which is much larger than that of a previous method (i.e., using magnetic super-lens). A 3-D reduced MTPcomposed of layered isotropicmagnetic materials is designed, whose performance is verified by our 3-D numerical simulation in 10 MHz. The influence of loss in metamaterial on the performance of the proposed MTP is also studied, which shows that the MTP can still enhance energy transfer efficiency when loss exists. Further simulation is also carried out to show that the function of the MTP is not sensitive to large perturbation. Finally, detailed experimental suggestion for implementing the simplified MTP, which is composed of layered medium is given and then verified by our numerical simulation.

  • 31.
    Lim, Jang-Kwon
    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.
    Bakowski, Mietek
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Analysis and Experimental Verification of the Influence of Fabrication Process Tolerances and Circuit Parasitics on Transient Current Sharing of Parallel-Connected SiC JFETs2014In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 29, no 5, p. 2180-2191Article in journal (Refereed)
    Abstract [en]

    Operation of parallel-connected 4H-SiC vertical junction field effect transistors (VJFETs) from SemiSouth is modeled using numerical simulations and experimentally verified. The unbalanced current waveforms of parallel-connected VJFETs are investigated with respect to the spread in the critical parameters of the device structure and to the influence of the parasitic inductances in the measurement circuit. The device structures are reconstructed based on scanning electron microscopy (SEM) analysis, electrical characterization, and device simulations. The doping concentration and profile depth of a p-grid formed by angular implantation are studied as main contributors that influence the variation of the on-state characteristics, and the threshold voltage of the experimental devices. It has been shown elsewhere that similar differences in p-grid also lead to differences in gate-source breakdown voltage. The switching performance of the parallel-connected JFETs is measured using single and double gate drivers in a double-pulse test and compared with simulations. The switched current and voltage waveforms from measurements are reproduced in simulation by introducing the parasitics. From the analysis, it is found that reasonable differences in doping levels and profiles of the p-grid give rise to significant differences in device parameters. However, even with these parameter differences and circuit asymmetries, it is possible to successfully operate parallel-connected VJFETs of this type.

  • 32.
    Magnusson, Jesper
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Saers, R.
    Liljestrand, L.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Separation of the energy absorption and overvoltage protection in solid-state breakers by the use of parallel varistors2014In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 29, no 6, p. 2715-2722Article in journal (Refereed)
    Abstract [en]

    Hybrid and solid-state breakers offer new possibilities in the power grid by enabling faster switching, and by simplifying dc breaking. However, they consists of expensive power electronic components that are sensitive to overvoltage transients and require energy absorbing elements mounted in parallel. At turn-off, the rapidly decreasing current in the power electronic switch and the presence of an inherent stray inductance leads to hazardous overvoltage transients across the breaker. This paper investigates the possibility to split the overvoltage protection and energy absorption into two separate components. By optimizing the voltage ratio between two varistors, one can dimension a small electronics varistor for overvoltage protection and a large power electronics varistor for energy absorption. With this setup the power electronics varistor is allowed to be in a circuit with a large stray inductance and can thus be placed further away without causing an uncontrolled overvoltage. It is shown both in circuit simulations as well as in a small-scale experiment that if the voltage ratio between the two varistors is large enough, the inner varistor only has to absorb 1-2% of the system energy.

  • 33.
    Nee, Hans-Peter
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Kolar, Johann W.
    Friedrichs, Peter
    Rabkowski, Jacek
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Special Issue on Wide Bandgap Power Devices and Their Applications, 20142014In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 29, no 5, p. 2153-2154Article in journal (Refereed)
  • 34.
    Nikouie Harnefors, Mojgan
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Jin, Lebing
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Harnefors, Lennart
    ABB, Corporate Research, Sweden.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    DC-link stability analysis and controller design for the stacked polyphase bridges converter2017In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 32, no 2, p. 1666-1674, article id 7451258Article in journal (Refereed)
    Abstract [en]

    The stacked polyphase bridges (SPB) converter consists of several submodules that all are connected in series to a voltage source. The total dc-link voltage should split in a balanced way among the submodules. This does not always occur inherently. This paper presents an analysis of the capacitor voltage stability for the SPB converter. From the analysis, criteria for stability are derived and three alternatives of a suitable balancing controller are designed. The proposed controller alternatives and their associated stability properties are verified on an experimental setup and by simulation.

  • 35.
    Norrga, Staffan
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Experimental study of a soft-switched isolated bidirectional AC-DC converter without auxiliary circuit2006In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 21, no 6, p. 1580-1587Article in journal (Refereed)
    Abstract [en]

    An isolated ac-dc converter topology includes a capacitively snubbered. voltage source converter (VSC) and a cycloconverter, coupled by a medium frequency transformer. The topology offers the possibility of bilateral power flow as well as three-level pulse width modulation on the ac side. It is shown that by alternately commutating the VSC and the cycloconverter it is possible to achieve either zero-voltage or zero-current switching conditions for all semiconductor devices in all points of operation. This is the case without any need for auxiliary semiconductor devices. At low load the transformer current may be insufficient for recharging the VSC snubber capacitors. In this case, however, it is possible to utilize the cycloconverter for providing a current path by which a quasi-resonant commutation can be made. The design and operation of a 40-kVA prototype converter system is described. It is shown how the rather complex switching logic required for implementing the chosen algorithm for commutation and modulation can be realized by using modern programmable logic devices [field programmable gate array (FPGA)]. Measurement results from the prototype converter are presented and analyzed. The measurements indicate that the,studied commutation algorithm works well in practice.

  • 36.
    Peftitsis, Dimosthenis
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Baburske, R.
    Rabkowski, Jacek
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Lutz, J.
    Tolstoy, Georg
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Challenges regarding parallel connection of SiC JFETs2013In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 28, no 3, p. 1449-1463Article in journal (Refereed)
    Abstract [en]

    State-of-the-art silicon carbide switches have current ratings that are not sufficiently high to be used in high-power converters. It is, therefore, necessary to connect several switches in parallel in order to reach sufficient current capabilities. An investigation of parallel-connected normally ON silicon carbide JFETs is presented in this paper. The device parameters that play the most important role for the parallel connection are the pinch-off voltage, the gate-source reverse breakdown voltage, the spread in the on-state resistances, and the variations in static transfer characteristics of the devices. Moreover, it is experimentally shown that a fifth factor affecting the parallel connection of the devices is the parasitic inductances of the circuit layout. The temperature dependence of the gate-source reverse breakdown voltages is analyzed for two different designs of silicon carbide JFETs. If the spread in the pinch-off and gate-source reverse breakdown voltages is sufficiently large, there might be no possibility for a stable off-state operation of a pair of transistors without forcing one of the gate voltages to exceed the breakdown voltage. A solution to this problem using individual gate circuits for the JFETs is given. The switching performance of two pairs of parallel-connected devices with different combinations of parameters is compared employing two different gate-driver configurations. Three different circuit layouts are considered and the effect of the parasitic inductances is experimentally investigated. It is found that using a single gate circuit for the two mismatched JFETs may improve the switching performance and therefore the distribution of the switching losses significantly. Based on the measured switching losses, it is also clear that regardless of the design of the gate drivers, the lowest total switching losses for the devices are obtained when they are symmetrically placed.

  • 37.
    Peftitsis, Dimosthenis
    et al.
    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.
    Self-powered gate driver for normally on silicon carbide junction field-effect transistors without external power supply2013In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 28, no 3, p. 1488-1501Article in journal (Refereed)
    Abstract [en]

    The very low on-state resistance, the voltage-controlled gate, and the relative simplicity of fabrication of the normally ON silicon carbide junction field-effect transistor (JFET) make this device the most important player among all state-of-the-art silicon carbide transistors. However, the normally ON nature counts as the main factor which keeps this device far from being considered as an alternative to the silicon insulated-gate bipolar transistor. A self-powered gate driver without external power supply for normally ON silicon carbide JFETs is presented in this paper. The proposed circuit is able to handle the short-circuit currents when the devices are subjected to the dc-link voltage by utilizing the energy associated with this current. On the other hand, it supplies the necessary negative gate-source voltage during the steady-state operation. A detailed description of the operating states in conjunction with a theoretical analysis of the proposed self-powered gate driver is presented. The first part of the experimental investigation has been performed when the proposed circuit is connected to a device which is directly subjected to the dc-link voltage. The second set of measurements were recorded when the self-powered gate-driver was employed as the driver of normally ON components in a half-bridge converter. From the experimental results, it is shown that the short-circuit current is cleared within approximately 20μs after the dc-link voltage is applied, while the power consumption when all devices are kept in the OFF state equals 0.37W. Moreover, it is experimentally shown that the proposed gate driver can properly switch when it is employed in a half-bridge converter. Finally, limitations regarding the range of the applications where the self-powered gate drive can efficiently operate are also discussed.

  • 38.
    Peftitsis, Dimosthenis
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Rabkowski, Jacek
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Self-Powered Gate Driver for Normally-ON SiC JFETs: Design Considerations and System Limitations2014In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 29, no 10, p. 5129-5135Article in journal (Refereed)
    Abstract [en]

    A circuit solution to the normally-ON property of the normally-ON silicon carbide junction field-effect transistor, namely the self-powered gate driver, has been recently proposed. This letter sheds some light on the design process of the self-powered gate driver concept as well as limitations from the system perspective. It is experimentally shown that the parameters of the self-powered gate driver must be chosen taking into account a tradeoff between a fast response and stable operation of the driver. Moreover, the influence of the shoot-through current in the fast activation of the self-powered gate driver is also presented.

  • 39.
    Peftitsis, Dimosthenis
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Tolstoy, Georg
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Antonopoulos, Antonios
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Rabkowski, Jacek
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Lim, Jang-Kwon
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Bakowski, Mietek
    Acreo AB.
    Ängquist, Lennart
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    High-Power Modular Multilevel Converters With SiC JFETs2012In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 27, no 1, p. 28-36Article in journal (Refereed)
    Abstract [en]

    This paper studies the possibility of building a modular multilevel converter (M2C) using silicon carbide (SiC) switches. The main focus is on a theoretical investigation of the conduction losses of such a converter and a comparison to a corresponding converter with silicon-insulated gate bipolar transistors. Both SiC BJTs and JFETs are considered and compared in order to choose the most suitable technology. One of the submodules of a down-scaled 3 kVA prototype M2C is replaced with a submodule with SiC JFETs without antiparallel diodes. It is shown that the diode-less operation is possible with the JFETs conducting in the negative direction, leaving the possibility to use the body diode during the switching transients. Experimental waveforms for the SiC submodule verify the feasibility during normal steady-state operation. The loss estimation shows that a 300 MW M2C for high-voltage direct current transmission would potentially have an efficiency of approximately 99.8% if equipped with future 3.3 kV 1.2 kA SiC JFETs.

  • 40.
    Rabkowski, Jacek
    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.
    Parallel-Operation of Discrete SiC BJTs in a 6-kW/250-kHz DC/DC Boost Converter2014In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 29, no 5, p. 2482-2491Article in journal (Refereed)
    Abstract [en]

    This paper describes issues related to parallel connection of SiC bipolar junction transistors (BJTs) in discrete packages. The devices are applied in a high-frequency dc/dc boost converter where the switching losses significantly exceed the conduction losses. The design and construction of the converter is discussed-with special emphasis on successful parallel-operation of the discrete BJTs. All considerations are experimentally illustrated by a 6-kW, 250-kHz boost converter (300 V/600 V). A special solution for the base-drive unit, based on the dual-source driver concept, is also shown in this paper. The performance of this driver and the current sharing of the BJTs are both presented. The power losses and thermal performance of the parallel-connected transistors have been determined experimentally for different powers and switching frequencies. An efficiency of 98.23% (+/- 0.02%) was measured using a calorimetric setup, while the maximum temperature difference among the four devices is 12 degrees C.

  • 41.
    Rabkowski, Jacek
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Tolstoy, Georg
    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.
    Low-Loss High-Performance Base-Drive Unit for SiC BJTs2012In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 27, no 5, p. 2633-2643Article in journal (Refereed)
    Abstract [en]

    Driving a silicon carbide bipolar junction transistor is not a trivial issue, if low drive power consumption and short-switching times are desired. A dual-source base-drive unit with a speed-up capacitor consisting of a low-and a high-voltage source is, therefore, proposed in this paper. As a significant base current is required during the conduction state, the driver power consumption is higher than for other semiconductor switches. In the presented solution, the steady-state base current is provided by a low-voltage source and is optimized for lowpower losses. On the contrary, a second source with a higher voltage and speed-up capacitor is used in order to improve the switching performance of the device. The proposed driver has experimentally been compared to other standard driver solutions by using a double-pulse circuit and a 2-kW dc/dc boost converter. Switching times of 20 ns at turn-ON and 35 ns at turn-OFF were recorded. Finally, the efficiency of the converter was determined experimentally at various switching frequencies. From power loss measurements at 100-kHz switching frequency using the proposed driver in a 2-kW dc/dc boost converter, it was found that the efficiency was approximately 99.0%. In the same operating point, the driver power consumption was only 0.08% of the rated power.

  • 42.
    Ranstad, Per
    et al.
    Alstom Power.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Linner, Jörgen
    Alstom Power.
    Peftitsis, Dimosthenis
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    An Experimental Evaluation of SiC Switches in Soft-Switching Converters2014In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 29, no 5, p. 2527-2538Article in journal (Refereed)
    Abstract [en]

    Soft-switching converters equipped with insulated gate bipolar transistors (IGBTs) in silicon (Si) have to be dimensioned with respect to additional losses due to the dynamic conduction losses originating from the conductivity modulation lag. Replacing the IGBTs with emerging silicon carbide (SiC) transistors could reduce not only the dynamic conduction losses but also other loss components of the IGBTs. In the present paper, therefore, several types of SiC transistors are compared to a state-of-the-art 1200-V Si IGBT. First, the conduction losses with sinusoidal current at a fixed amplitude (150 A) are investigated at different frequencies up to 200 kHz. It was found that the SiC transistors showed no signs of dynamic conduction losses in the studied frequency range. Second, the SiC transistors were compared to the Si IGBT in a realistic soft-switching converter test system. Using a calorimetric approach, it was found that all SiC transistors showed loss reductions of more than 50%. In some cases loss reductions of 65% were achieved even if the chip area of the SiC transistor was only 11% of that of the Si IGBT. It was concluded that by increasing the chip area to a third of the Si IGBT, the SiC vertical trench junction field-effect transistor could yield a loss reduction of approximately 90%. The reverse conduction capability of the channel of unipolar devices is also identified to be an important property for loss reductions. A majority of the new SiC devices are challenging from a gate/base driver point-of-view. This aspect must also be taken into consideration when making new designs of soft-switching converters using new SiC transistors.

  • 43.
    Tolstoy, Georg
    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.
    Palmer, Patrick R.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    A Discretized Proportional Base Driver for Silicon Carbide Bipolar Junction Transistors2014In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 29, no 5, p. 2408-2417Article in journal (Refereed)
    Abstract [en]

    Silicon carbide (SiC) bipolar junction transistors (BJTs) require a continuous base current in the on-state. This base current is usually made constant and is corresponding to the maximum collector current and maximum junction temperature that is foreseen in a certain application. In this paper, a discretized proportional base driver is proposed which will reduce, for the right application, the steady-state power consumption of the base driver. The operation of the proposed base driver has been verified experimentally, driving a 1200-V/40-A SiC BJT in a dc-dc boost converter. In order to determine the potential reduction of the power consumption of the base driver, a case with a dc-dc converter in an ideal electric vehicle driving the new European drive cycle has been investigated. It is found that the steady-state power consumption of the base driver can be reduced by approximately 60%. The total reduction of the driver consumption is 3459 J during the drive cycle, which is slightly more than the total on-state losses for the SiC BJTs used in the converter.

  • 44.
    Velander, Erik
    et al.
    Bombardier Transportat Sweden AB, Dept Medium Power Tract Converter Design, S-72173 Vasteras, Sweden..
    Bohlin, Georg
    Bombardier Transportat Sweden AB, Tract Syst Dept, S-72173 Vasteras, Sweden..
    Sandberg, Asa
    Bombardier Transportat Sweden AB, Tract Syst Dept, S-72173 Vasteras, Sweden..
    Wiik, Thomas
    Bombardier Transportat Sweden AB, Dept Medium Power Tract Converter Design, S-72173 Vasteras, Sweden..
    Botling, Fredrik
    Bombardier Transportat Sweden AB, Dept Converter Control, S-72173 Vasteras, Sweden..
    Lindahl, Martin
    Bombardier Transportat Sweden AB, Dept Medium Power Tract Converter Design, S-72173 Vasteras, Sweden..
    Zanuso, Giovanni
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    An Ultralow Loss Inductorless dv/dt Filter Concept for Medium-Power Voltage Source Motor Drive Converters With SiC Devices2018In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 33, no 7, p. 6072-6081Article in journal (Refereed)
    Abstract [en]

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

  • 45.
    Velander, Erik
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Bombardier Transportation Sweden AB.
    Bohlin, Georg
    Sandberg, Åsa
    Wiik, Thomas
    Lindahl, Martin
    Botling, Fredrik
    Zanuso, Giovanni
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    An Ultra-Low Loss Inductorless dv/dt Filter Concept for Medium Power Voltage Source Motor Drive Converters with SiC DevicesIn: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Article in journal (Refereed)
  • 46. Velander, Erik
    et al.
    Kruse, Lennart ( Zdansky)
    Wiik, Thomas (Lundstrom)
    Wiberg, Anders
    Colmenares, Juan
    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.
    An IGBT Turn-ON Concept Offering Low Losses Under Motor Drive dv/dt Constraints Based on Diode Current Adaption2018In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 33, no 2, p. 1143-1153Article in journal (Refereed)
    Abstract [en]

    In this paper, a new low-loss turn-ON concept for the silicon insulated-gate bipolar transistor (Si-IGBT) in combination with silicon p-i-n diode is presented. The concept is tailored for two-level motor converters in the 100 kW to 1 MW range under the constraint that the output voltages slopes are limited in order to protect the motor windings. Moreover, analyses of the IGBT turn-ON and diode reverse recovery voltage slopes are presented concluding that the diode reverse recovery is the worst case. The concept includes a low-cost measurement of the free-wheeling diode current and temperature by the gate driver without necessity of acquiring this information from the converter control board. By using this concept, the output dv/dt at the diode turn-OFF can be kept approximately constant regardless of the commutated current and junction temperature. Hence, the switching losses could be decreased for the currents and temperatures where the voltage slopes are lower when using a conventional gate driver optimized for the worst case. Moreover, results are shown for one such power semiconductor, showing a total switching loss reduction of up to 28% in comparison with a gate driver without current and temperature measurement. Finally, this concept is particularly suitable for high power semiconductor modules in half-bridge configuration which are recently proposed by several suppliers.

  • 47.
    Velander, Erik
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems. Bombardier Transportation Sweden AB.
    Kruse, Lennart
    Wiik, Thomas
    Wiberg, Anders
    Colmenares, Juan
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    An IGBT Turn-ON Concept Offering Low Losses Under Motor Drive dv/dt Constraints Based on Diode Current AdaptionIn: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107Article in journal (Refereed)
  • 48.
    Wallmark, Oskar
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Lundberg, S.
    Bongiorno, M.
    Input Admittance Expressions for Field-Oriented Controlled Salient PMSM Drives2012In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 27, no 3, p. 1514-1520Article in journal (Refereed)
    Abstract [en]

    This paper presents analytical expressions for the converter input admittance in field-oriented controlled permanentmagnet synchronous motor (PMSM) drives. The effect of rotorsaliency is taken into consideration and the derived admittance expressions are valid for maximum-torque-per-ampere as well ashigh-speed (field weakening) operation. Experimental results illustrate the validity of the derived admittance expressions. The presented work can be used to predict dc-link voltage instabilities inPMSM drives in, e.g., railway traction, aerospace and automotive applications.

  • 49. Zdanowski, Mariusz
    et al.
    Kostov, Konstantin
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Rabkowski, Jacek
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Barlik, Roman
    Nee, Hans-Peter
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Design and Evaluation of Reduced Self-Capacitance Inductor in DC/DC Converters with Fast-Switching SiC Transistors2014In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 29, no 5, p. 2492-2499Article in journal (Refereed)
    Abstract [en]

    The paper presents an inductor with reduced self-capacitance, designed and evaluated with fast-switching SiC transistors in dc-dc converters. A conventional inductor with the same core and number of turns was also build for comparison. The two inductors are tested experimentally on two different 2 kW, 100 kHz dc-dc converters with silicon carbide switches-one with a junction field-effect transistor (JFET) and the other with a bipolar junction transistor (BJT). Replacing the conventional inductor with the one that has lower self-capacitance improved the switching performance of the converter and reduced its electromagnetic emissions. Furthermore, the efficiency of the converter is improved-in the case of the JFET boost converter the power losses were reduced by 16% and by 20% in the case of BJT.

  • 50.
    Zhang, Hongyang
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. ABB, Power Grids Div, S-72164 Vasteras, Sweden.
    Harnefors, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. ABB, Corp Res, S-72178 Vasteras, Sweden..
    Wang, Xiongfei
    Aalborg Univ, Dept Energy Technol, DK-9220 Aalborg, Denmark..
    Gong, Hong
    Aalborg Univ, Dept Energy Technol, DK-9220 Aalborg, Denmark..
    Hasler, Jean-Philippe
    ABB, Power Grids Div, S-72164 Vasteras, Sweden..
    Stability Analysis of Grid-Connected Voltage-Source Converters Using SISO Modeling2019In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 34, no 8, p. 8104-8117Article in journal (Refereed)
    Abstract [en]

    The interaction of a grid-connected voltage-source converter with a weak grid is of significant interest. In this paper, the converter together with the grid impedance is modeled as a single-input single-output (SISO) system. Provided that certain assumptions hold, this allows us to apply the standard SISO Nyquist stability criterion for stability analysis and controller design. The derivedmodel is verified against time-domain simulations and experiments. Themethod facilitates the design of the converter control system with adequate stability margins.

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