EPE Association: EPE 2020 - DS2d-2: Modular Multilevel Converters-2

EPE 2020 - DS2d-2: Modular Multilevel Converters-2
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2020 ECCE Europe - Conference > EPE 2020 - Topic 02: Power Converter Topologies and Design > EPE 2020 - DS2d-2: Modular Multilevel Converters-2

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   A Submodule Implementation for Parallel Conduction of Diodes in Modular Multilevel Converters
By Martin GESKE [View]
[Download]

Abstract: This paper presents a new double submodule for Modular Multilevel Converters that supports parallel conduction of freewheeling diodes. The new submodule circuit can reduce semiconductor conduction losses through parallel diode conduction and uses a small number of switches.

   Evaluation of MMCs for High-Power Low-Voltage DC-Applications in Combination with the Module LLC-Design
By Roland UNRUH [View]
[Download]

Abstract: In this paper, a full-bridge modular multilevel converter (MMC) and two half-bridge-based MMCs areevaluated for high-current low-voltage DC-applications such as electrolysis, arc welding or datacenterswith DC-power distribution. Usually, modular multilevel converters are used in high-voltage DC-applications (HVDC) in the multiple kV-range, but to meet the needs of a high-current demand atlow output voltage levels, the modular converter concept requires adaptations. In the proposed concept, the MMC is used to step-down the three-phase medium-voltage of 10kV , and provide up to 1MW to the load. Therefore, each module is extended by an LLC resonant converter to adapt to the specific electrolyzers DC-voltage range of 142-220V and to provide galvanic isolation.The six-arm MMC converter with half-bridge modules can be optimized by removing three arms, and thus halving the number of modules. In addition, the module voltage ripple and capacitor losses are decreased by 22\% and 30\% respectively. By rearranging the components of the half-bridge MMC to build a MMC consisting of full-bridge modules, the voltage ripple is further reduced by 78\% and capacitor losses by 64\%, while ensuring identical costs and volume for all MMCs.Finally, the LLC resonant converter is designed for the most efficient full-bridge MMC. The LLC cannot operate at resonance with a fixed nominal module voltage of 770V because the output voltage is142-220V . By decreasing the module voltage down to 600V , additional points of operation can beoperated in resonance, and the remaining are closer to resonance. The option to decrease the modulevoltage down to 600V , increases the number of required modules per arm from 12 to 15 , which requires to balance the losses of the LLCs and the first stage.

   Figures-of-Merit and current metric for the comparison of IGCTs and IGBTs in Modular Multilevel Converters
By Arthur BOUTRY [View]
[Download]

Abstract: IGCTs and IGBTs are compared in the case of a HVDC MMC. Specific figures of merit, and a currentmetric providing simple means to compare them, are introduced and discussed. Simulation results ofa MMC model and figures of merit are shown to provide consistent results, proving that the proposedfigures of merit are a very simple and fast way to select the best semiconductor switch. Furthermore, ouranalysis supports the growing interest in IGCTs for MMCs, as they are found to produce the lowest levelof losses.

   High Performance LQR Control of Modular Multilevel Converters with Simple Control Structure and Implementation
By Min JEONG [View]
[Download]

Abstract: In this paper, a novel feedback controller concept for grid-connected Modular Multilevel Converters (MMC) is proposed. The controller is based on the Linear Quadratic Regulator (LQR) method and shows outstanding control performance since it is a multi-input multi-output (MIMO) controller. The proposed controller achieves efficient energy balancing control with high bandwidth, such that the required margin for the module capacitance value for dynamic control is reduced and an excellent transient behavior can be accomplished. Alternatively, compact MMC designs can be realized with a reduced capacitance value by sacrificing some transient performance. The implementation requires a relatively low computational effort, and the simple control structure enables a straightforward tuning and time-delay compensation.

   Using Both the Circulating Currents and the Common-Mode Voltage for the Branch Energy Control of Modular Multilevel Converters
By Rebecca DIERKS [View]
[Download]

Abstract: Many degrees of freedom are available for the branch energy control of modular multilevel converters. These degrees of freedom comprise different components of the common-mode voltage and the internalcirculating currents. If all degrees of freedom are used simultaneously, undesired cross-couplings occur in the branch energy control. In the conventional branch energy control, either the internal circulating currents or the common-mode voltage are used to avoid the coupling terms. The paper presents a novel solution that uses both the circulating currents and the common-mode voltage while omitting the couplings. Thereby, the branch currents and thus the losses in the branches can be reduced without affecting the control dynamics. The proposed control approach is validated through simulations and experimentally on a downscaled converter prototype. Furthermore, the improved performance is demonstrated by means of a comparison to the conventional control. In general, the proposed control approach is expected to be especially beneficial for drive systems operated below rated speed and for a low-voltage ride-through of grid-tied converters.

EPE 2020 - DS2d-2: Modular Multilevel Converters-2
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2020 ECCE Europe - Conference > EPE 2020 - Topic 02: Power Converter Topologies and Design > EPE 2020 - DS2d-2: Modular Multilevel Converters-2
	[return to parent folder]

	A Submodule Implementation for Parallel Conduction of Diodes in Modular Multilevel Converters By Martin GESKE	[View] [Download]
Abstract: This paper presents a new double submodule for Modular Multilevel Converters that supports parallel conduction of freewheeling diodes. The new submodule circuit can reduce semiconductor conduction losses through parallel diode conduction and uses a small number of switches.

	Evaluation of MMCs for High-Power Low-Voltage DC-Applications in Combination with the Module LLC-Design By Roland UNRUH	[View] [Download]
Abstract: In this paper, a full-bridge modular multilevel converter (MMC) and two half-bridge-based MMCs areevaluated for high-current low-voltage DC-applications such as electrolysis, arc welding or datacenterswith DC-power distribution. Usually, modular multilevel converters are used in high-voltage DC-applications (HVDC) in the multiple kV-range, but to meet the needs of a high-current demand atlow output voltage levels, the modular converter concept requires adaptations. In the proposed concept, the MMC is used to step-down the three-phase medium-voltage of 10kV , and provide up to 1MW to the load. Therefore, each module is extended by an LLC resonant converter to adapt to the specific electrolyzers DC-voltage range of 142-220V and to provide galvanic isolation.The six-arm MMC converter with half-bridge modules can be optimized by removing three arms, and thus halving the number of modules. In addition, the module voltage ripple and capacitor losses are decreased by 22\% and 30\% respectively. By rearranging the components of the half-bridge MMC to build a MMC consisting of full-bridge modules, the voltage ripple is further reduced by 78\% and capacitor losses by 64\%, while ensuring identical costs and volume for all MMCs.Finally, the LLC resonant converter is designed for the most efficient full-bridge MMC. The LLC cannot operate at resonance with a fixed nominal module voltage of 770V because the output voltage is142-220V . By decreasing the module voltage down to 600V , additional points of operation can beoperated in resonance, and the remaining are closer to resonance. The option to decrease the modulevoltage down to 600V , increases the number of required modules per arm from 12 to 15 , which requires to balance the losses of the LLCs and the first stage.

	Figures-of-Merit and current metric for the comparison of IGCTs and IGBTs in Modular Multilevel Converters By Arthur BOUTRY	[View] [Download]
Abstract: IGCTs and IGBTs are compared in the case of a HVDC MMC. Specific figures of merit, and a currentmetric providing simple means to compare them, are introduced and discussed. Simulation results ofa MMC model and figures of merit are shown to provide consistent results, proving that the proposedfigures of merit are a very simple and fast way to select the best semiconductor switch. Furthermore, ouranalysis supports the growing interest in IGCTs for MMCs, as they are found to produce the lowest levelof losses.

	High Performance LQR Control of Modular Multilevel Converters with Simple Control Structure and Implementation By Min JEONG	[View] [Download]
Abstract: In this paper, a novel feedback controller concept for grid-connected Modular Multilevel Converters (MMC) is proposed. The controller is based on the Linear Quadratic Regulator (LQR) method and shows outstanding control performance since it is a multi-input multi-output (MIMO) controller. The proposed controller achieves efficient energy balancing control with high bandwidth, such that the required margin for the module capacitance value for dynamic control is reduced and an excellent transient behavior can be accomplished. Alternatively, compact MMC designs can be realized with a reduced capacitance value by sacrificing some transient performance. The implementation requires a relatively low computational effort, and the simple control structure enables a straightforward tuning and time-delay compensation.

	Using Both the Circulating Currents and the Common-Mode Voltage for the Branch Energy Control of Modular Multilevel Converters By Rebecca DIERKS	[View] [Download]
Abstract: Many degrees of freedom are available for the branch energy control of modular multilevel converters. These degrees of freedom comprise different components of the common-mode voltage and the internalcirculating currents. If all degrees of freedom are used simultaneously, undesired cross-couplings occur in the branch energy control. In the conventional branch energy control, either the internal circulating currents or the common-mode voltage are used to avoid the coupling terms. The paper presents a novel solution that uses both the circulating currents and the common-mode voltage while omitting the couplings. Thereby, the branch currents and thus the losses in the branches can be reduced without affecting the control dynamics. The proposed control approach is validated through simulations and experimentally on a downscaled converter prototype. Furthermore, the improved performance is demonstrated by means of a comparison to the conventional control. In general, the proposed control approach is expected to be especially beneficial for drive systems operated below rated speed and for a low-voltage ride-through of grid-tied converters.