Steady-state analysis of modular multilevel converter (MMC) under unbalanced grid conditions

Shi, Xiuzhi; Li, Yalong; Wang, Zhiqiang; Liu, Bo; Tolbert, Leon M.; Wang, Fred

doi:10.1109/apec.2016.7468236

Cited by 3 publications

(3 citation statements)

References 13 publications

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“…Another consequence of MMC operation under unbalanced grid conditions is the appearance of extra circulating-current components that will increase the converter conduction losses if they are not properly suppressed. In [14][15][16], detailed analytical models were proposed to describe an MMC's circulating currents under unbalanced grid conditions. Moreover, control techniques were proposed to mitigate these extra undesired circulating-current components.…”

Section: Introductionmentioning

confidence: 99%

Modeling and Mitigation Control of the Submodule-Capacitor Voltage Ripple of a Modular Multilevel Converter under Unbalanced Grid Conditions

et al. 2021

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A modular multilevel converter’s (MMC’s) submodule (SM)-capacitor voltage will increase under unbalanced grid conditions. Depending on the imbalance level, the voltage ripple can be considerably high, and it can exceed the pre-defined safe limits. If this occurs, the converter will trip, which can lead to serious stability problems for the grid. This paper first proposes an analytical solution for deriving the three-phase imbalanced SM ripple of an MMC under an unbalanced grid. With this analytical tool, the imbalance mechanism of the SM voltage ripple can be easily understood. What is more, the symmetrical component method is first applied to analyze the three-phase SM capacitor ripple, and the positive-/negative-/zero-sequence components of the three-phase SM voltage ripple are easily identified by the proposed analytical method. Then, based on this powerful analytical tool, the proper circulating-current profile to be injected can be obtained, allowing for the right compensation of the voltage ripple. Based on this approach, two new voltage ripple compensation methods are proposed in this paper. Simulations were carried out to validate the analytical description of the submodule-capacitor voltage ripple proposed in this paper. Moreover, simulation and experimental results are provided to validate the new compensation techniques introduced in this paper.

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Section: Introductionmentioning

confidence: 99%

Modeling and Mitigation Control of the Submodule-Capacitor Voltage Ripple of a Modular Multilevel Converter under Unbalanced Grid Conditions

et al. 2021

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“…The MMC achieves a large number of voltage levels and provides a common DC side, making it well suited for high-voltage direct current (HVDC) transmission systems. The previous studies [10][11][12] point out that when the grid voltage is unbalanced, the external current is no longer symmetrical, and the power also produces the secondary fluctuation component. For the interior of the MMC, there will be a large number of harmonic components of the circulating current, the submodule (SM) capacitor voltage will be fluctuated, increasing the loss of the inverter also affecting the output characteristics.…”

mentioning

confidence: 99%

“…These methods achieve good results when the grid voltage is balance, but when the grid voltage is unbalanced, both the external control method and the internal circulating current control methods will lose their effect and are no longer suitable. The previous studies [10][11][12] point out that when the grid voltage is unbalanced, the external current is no longer symmetrical, and the power also produces the secondary fluctuation component. The internal circulating current component also changes from the double-line-frequency negative sequence component at steady state to the double-line-frequency positive, negative, and zero sequence component.…”

mentioning

confidence: 99%

A new control strategy forMMCunder grid voltage unbalance condition

Sun

Cheng

et al. 2019

Int Trans Electr Energ Syst

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Summary Modular multilevel converter (MMC) is easy to realize more voltage levels, and its structure is easy to connect back to back. It is suitable for high‐voltage direct current (HVDC) transmission system. However, the unbalance of grid voltage will seriously affect performance of HVDC transmission. The Lyapunov‐function‐based control strategy proposed in this paper can well solve the existing problems of MMC under unbalanced power grid. First of all, according to the topological structure of MMC, this paper establishes the mathematic model under the condition of grid unbalance and balance. Secondly, aiming at three different control objectives: (1) eliminate negative sequence current components and keep AC currents balance, (2) eliminate the active power double base frequency ripples, and (3) eliminate the reactive power double base frequency ripples. Then the Lyapunov‐function‐based control strategy is designed, and the circulating current control and capacitors voltage balance control are added to make the overall control strategy. Finally, the simulation of Lyapunov‐function‐based control strategy and traditional PI control strategy based on Matlab/Simulink platform is given. The validity and superiority of the Lyapunov‐function‐based control strategy are proved. And experiments on the hardware platform further verify the feasibility and correctness of the control strategy.

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Online Trajectory Planning During Low-Voltage FRT of a Modular Multilevel Converter

Fehr

Gensior

2020

2020 22nd European Conference on Power Electronics and Applications (EPE'20 ECCE Europe)

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Steady-state analysis of modular multilevel converter (MMC) under unbalanced grid conditions

Cited by 3 publications

References 13 publications

Modeling and Mitigation Control of the Submodule-Capacitor Voltage Ripple of a Modular Multilevel Converter under Unbalanced Grid Conditions

Modeling and Mitigation Control of the Submodule-Capacitor Voltage Ripple of a Modular Multilevel Converter under Unbalanced Grid Conditions

A new control strategy forMMCunder grid voltage unbalance condition

Online Trajectory Planning During Low-Voltage FRT of a Modular Multilevel Converter

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