The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Seung-ki Sul - One of the best experts on this subject based on the ideXlab platform.
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A New Topology of Multilevel VSC Converter for a Hybrid HVDC Transmission System
IEEE Transactions on Power Electronics, 2017Co-Authors: Jae-jung Jung, Joonhee Lee, Shenghui Cui, Seung-ki SulAbstract:This paper introduces a new multilevel converter topology for a hybrid HVDC system comprising line-commutated converter (LCC) and voltage source converter (VSC). Among the existing modular multilevel converter (MMC) topologies for the hybrid HVDC, a mixed MMC structure with half-bridge Submodules (HBSMs) and full-bridge Submodules (FBSMs) has characteristics of reduced system cost, low operation loss, but still keeping capability to cope with dc short-circuit fault. However, it is very difficult for the conventional hybrid MMC structure to balance the submodule capacitor voltages under dc-bus voltage sliding since each MMC arm is a mixture of HBSMs and FBSMs. To solve the defect of the conventional hybrid MMC structure, an asymmetric mixed MMC, in which one arm is made of series-connected HBSMs and other arm is made of FBSMs, is devised. The proposed asymmetric MMC can regulate the dc-bus voltage freely without uncontrollable submodule capacitor voltages. The problems of the conventional MMC structure and the validity of asymmetric MMC are verified by both computer simulation and experimental results.
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a comprehensive dc short circuit fault ride through strategy of hybrid modular multilevel converters mmcs for overhead line transmission
IEEE Transactions on Power Electronics, 2016Co-Authors: Shenghui Cui, Seung-ki SulAbstract:The modular multilevel converter (MMC) is a promising candidate for voltage-sourced-converter-based high-voltage direct current (VSC-HVDC) transmission. The dc short-circuit fault management is a crucial issue especially for overhead line transmission, where the nonpermanent dc short-circuit faults occasionally occur. In this paper, a comprehensive dc short-circuit fault ride through (FRT) strategy is proposed for a hybrid MMC which combines half-bridge Submodules and full-bridge Submodules. By the proposed method, the hybrid MMC-based VSC-HVDC system is able to ride through a pole-to-pole short-circuit fault supporting the ac grid as a static synchronous compensator. Moreover, the transmission system can still transmit one-half of the rated active power in case of a pole-to-ground short-circuit fault without increasing power semiconductor stresses or requiring higher insulation levels of the electric equipment. The proposed method ensures successful regulation of arm currents and submodule capacitor voltages during the FRT process. Validity of the proposed strategy is verified by both computer simulation and experiment results.
Staffan Norrga - One of the best experts on this subject based on the ideXlab platform.
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implications of capacitor voltage imbalance on the operation of the semi full bridge submodule
IEEE Transactions on Power Electronics, 2019Co-Authors: Stefanie Heinig, Kalle Ilves, Staffan Norrga, Keijo Jacobs, Luca Bessegato, Panagiotis Bakas, Hanspeter NeeAbstract: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 500 A if the voltage difference is 10 V before paralleling and increases to 2500 A if the difference is 40 V. However, neglecting very unlikely cases, the maximum voltage difference predicted by simulations is not higher than 20–30 V 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.
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performance of the modular multilevel converter with redundant Submodules
Conference of the Industrial Electronics Society, 2015Co-Authors: Noman Ahmed, Staffan Norrga, Antonios Antonopoulos, Lennart Harnefors, Lennart Angquist, Hanspeter NeeAbstract: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.
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semi full bridge submodule for modular multilevel converters
International Conference on Performance Engineering, 2015Co-Authors: Kalle Ilves, Staffan Norrga, Lennart Harnefors, Luca Bessegato, Hanspeter NeeAbstract:The energy variations in each arm of the modular multilevel converter comprises two components. The first component relates to the difference between the instantaneous input and output power of each phase-leg, and the second component relates to the energy which is moved back and forth between the two arms of the phase-leg. The latter component can be reduced or even eliminated if the peak-to-peak amplitude of the alternating voltage is greater than the pole-to-pole voltage of the dc link. This will, however, require Submodules which can insert negative voltages. Therefore, a semi-full-bridge submodule which uses less semiconductors than the conventional full-bridge is proposed. Simulation results shows that by using the negative voltage-levels the capacitor voltage ripple can be reduced by up to 59%. Experimental results also shows that a 7-level voltage waveform can be generated using only one semi-full-bridge submodule with two capacitors per arm.
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a submodule implementation for parallel connection of capacitors in modular multilevel converters
European Conference on Power Electronics and Applications, 2013Co-Authors: Kalle Ilves, Franz Taffner, Staffan Norrga, Antonios Antonopoulos, Lennart Harnefors, Hanspeter NeeAbstract:The modular multilevel converter is a suitable converter topology for high-voltage high-power applications and consists of series-connected Submodules. Typically, these Submodules are half-bridges with dc capacitors. A voltage ripple in the submodule capacitors is inevitable due to the current flowing in the arms. The converter should therefore be controlled in such a way that the capacitor voltages are kept balanced and close to their nominal values over time. This paper presents a new submodule circuit which alleviates the balancing of the capacitor voltages. The proposed submodule circuit consists of two capacitors and eight switches, forming a three-level submodule. Ideally, the voltage and current rating of the switches can be chosen such that the combined power rating of the semiconductors is the same as for equivalent 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 simulation results and experiments on a laboratory prototype. It is found that the parallel connection of the submodule capacitors will, in fact, significantly improve the balancing of the capacitor voltages.
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a new modulation method for the modular multilevel converter allowing fundamental switching frequency
IEEE Transactions on Power Electronics, 2012Co-Authors: Kalle Ilves, Antonios Antonopoulos, Staffan NorrgaAbstract: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.
Kalle Ilves - One of the best experts on this subject based on the ideXlab platform.
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implications of capacitor voltage imbalance on the operation of the semi full bridge submodule
IEEE Transactions on Power Electronics, 2019Co-Authors: Stefanie Heinig, Kalle Ilves, Staffan Norrga, Keijo Jacobs, Luca Bessegato, Panagiotis Bakas, Hanspeter NeeAbstract: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 500 A if the voltage difference is 10 V before paralleling and increases to 2500 A if the difference is 40 V. However, neglecting very unlikely cases, the maximum voltage difference predicted by simulations is not higher than 20–30 V 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.
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semi full bridge submodule for modular multilevel converters
International Conference on Performance Engineering, 2015Co-Authors: Kalle Ilves, Staffan Norrga, Lennart Harnefors, Luca Bessegato, Hanspeter NeeAbstract:The energy variations in each arm of the modular multilevel converter comprises two components. The first component relates to the difference between the instantaneous input and output power of each phase-leg, and the second component relates to the energy which is moved back and forth between the two arms of the phase-leg. The latter component can be reduced or even eliminated if the peak-to-peak amplitude of the alternating voltage is greater than the pole-to-pole voltage of the dc link. This will, however, require Submodules which can insert negative voltages. Therefore, a semi-full-bridge submodule which uses less semiconductors than the conventional full-bridge is proposed. Simulation results shows that by using the negative voltage-levels the capacitor voltage ripple can be reduced by up to 59%. Experimental results also shows that a 7-level voltage waveform can be generated using only one semi-full-bridge submodule with two capacitors per arm.
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a submodule implementation for parallel connection of capacitors in modular multilevel converters
European Conference on Power Electronics and Applications, 2013Co-Authors: Kalle Ilves, Franz Taffner, Staffan Norrga, Antonios Antonopoulos, Lennart Harnefors, Hanspeter NeeAbstract:The modular multilevel converter is a suitable converter topology for high-voltage high-power applications and consists of series-connected Submodules. Typically, these Submodules are half-bridges with dc capacitors. A voltage ripple in the submodule capacitors is inevitable due to the current flowing in the arms. The converter should therefore be controlled in such a way that the capacitor voltages are kept balanced and close to their nominal values over time. This paper presents a new submodule circuit which alleviates the balancing of the capacitor voltages. The proposed submodule circuit consists of two capacitors and eight switches, forming a three-level submodule. Ideally, the voltage and current rating of the switches can be chosen such that the combined power rating of the semiconductors is the same as for equivalent 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 simulation results and experiments on a laboratory prototype. It is found that the parallel connection of the submodule capacitors will, in fact, significantly improve the balancing of the capacitor voltages.
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a new modulation method for the modular multilevel converter allowing fundamental switching frequency
IEEE Transactions on Power Electronics, 2012Co-Authors: Kalle Ilves, Antonios Antonopoulos, Staffan NorrgaAbstract: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.
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steady state analysis of interaction between harmonic components of arm and line quantities of modular multilevel converters
IEEE Transactions on Power Electronics, 2012Co-Authors: Kalle Ilves, Staffan Norrga, Antonios Antonopoulos, Hp NeeAbstract: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.
L Zajac - One of the best experts on this subject based on the ideXlab platform.
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modular multilevel converter with different submodule concepts part i capacitor voltage balancing method
IEEE Transactions on Industrial Electronics, 2013Co-Authors: E Solas, Gonzalo Abad, J A Barrena, S Aurtenetxea, A Carcar, L ZajacAbstract:This paper presents a modulation strategy for the modular multilevel converter (MMC) which provides the voltage balancing of the capacitors of different Submodules comprising the converter. Not only is this modulation applicable to MMCs constructed with classic two level (2L) Submodules, but it is also effective for arrangements with different submodule concepts, for instance, topologies like neutral point clamped (NPC), flying capacitors (FCs), neutral point piloted (NPP), etc. Therefore, firstly, the general modulation philosophy is explained applied to the two level (2L) submodule concept, and secondly, the extension to 3L-NPC and 3L-FC submodule topologies is analyzed. After that, the validation of the studied modulation strategy is carried out by means of successful simulation results, at different switching frequencies and number of Submodules. The corresponding experimental results are shown in Part II of this paper after having implemented the aforementioned modulation strategy in a real test bench. In addition to this, a comparison based on thermal analysis and sizing of elements among the four studied submodule topologies is also included.
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modular multilevel converter with different submodule concepts part ii experimental validation and comparison for hvdc application
IEEE Transactions on Industrial Electronics, 2013Co-Authors: E Solas, Gonzalo Abad, J A Barrena, S Aurtenetxea, A Carcar, L ZajacAbstract:This paper is the continuation of part I in which a modulation strategy for the modular multilevel converter, which provides voltage balancing of the capacitors of different Submodules comprising the converter, is presented. Here, the validation of the studied modulation strategy is carried out by means of successful experimental results in a downscaled real test bench. First, the converter Submodules are 2L topologies, and then the connections are changed to configure 3L-FC Submodules showing the effectiveness and implementability of the proposed modulation in different submodule concepts. Finally, a comparison based on thermal analysis and sizing of elements among 2L, 2L serializing several insulated gate bipolar transistors per valve, 3L-FC, and 3L-NPC submodule concepts is made.
Antonios Antonopoulos - One of the best experts on this subject based on the ideXlab platform.
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performance of the modular multilevel converter with redundant Submodules
Conference of the Industrial Electronics Society, 2015Co-Authors: Noman Ahmed, Staffan Norrga, Antonios Antonopoulos, Lennart Harnefors, Lennart Angquist, Hanspeter NeeAbstract: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.
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a submodule implementation for parallel connection of capacitors in modular multilevel converters
European Conference on Power Electronics and Applications, 2013Co-Authors: Kalle Ilves, Franz Taffner, Staffan Norrga, Antonios Antonopoulos, Lennart Harnefors, Hanspeter NeeAbstract:The modular multilevel converter is a suitable converter topology for high-voltage high-power applications and consists of series-connected Submodules. Typically, these Submodules are half-bridges with dc capacitors. A voltage ripple in the submodule capacitors is inevitable due to the current flowing in the arms. The converter should therefore be controlled in such a way that the capacitor voltages are kept balanced and close to their nominal values over time. This paper presents a new submodule circuit which alleviates the balancing of the capacitor voltages. The proposed submodule circuit consists of two capacitors and eight switches, forming a three-level submodule. Ideally, the voltage and current rating of the switches can be chosen such that the combined power rating of the semiconductors is the same as for equivalent 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 simulation results and experiments on a laboratory prototype. It is found that the parallel connection of the submodule capacitors will, in fact, significantly improve the balancing of the capacitor voltages.
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a new modulation method for the modular multilevel converter allowing fundamental switching frequency
IEEE Transactions on Power Electronics, 2012Co-Authors: Kalle Ilves, Antonios Antonopoulos, Staffan NorrgaAbstract: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.
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steady state analysis of interaction between harmonic components of arm and line quantities of modular multilevel converters
IEEE Transactions on Power Electronics, 2012Co-Authors: Kalle Ilves, Staffan Norrga, Antonios Antonopoulos, Hp NeeAbstract: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.
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a new modulation method for the modular multilevel converter allowing fundamental switching frequency
International Conference on Performance Engineering, 2011Co-Authors: Kalle Ilves, Antonios Antonopoulos, Staffan NorrgaAbstract: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. Modulation methods with harmonic elimination based on calculated pulse patterns have been presented for other multilevel topologies. However, similar modulation schemes have not yet been presented for the modular multilevel topology. 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.
