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| Control Strategy Based on the Energy Balance for Reducing Sub-Module Capacitor Voltage Fluctuation of Modular Multilevel Converter |
| Li Kai1, Zhao Zhengming1, Yuan Liqiang1, Lu Sizhao2 |
1. State Key Lab of Control and Simulation of Power System and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing 100084 China;
2. Kunming University of Science and Technology Kunming 650504 China |
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Abstract Capacitors are the key elements in the sub-modules of the modular multilevel converter (MMC). Reducing sub-module capacitor voltage fluctuation is a dual requirement to improve capacitor reliability and reduce converter costs. Firstly, the influence of different circulating currents to the capacitor voltage fluctuation is analyzed in this paper. It is shown that injecting the typical 2nd order circulating current can reduce the capacitor voltage fluctuation greatly without increasing too much loss. Secondly, after introducing the existing energy-balance based control strategy with the line-cycle time scale, the control strategy with the control-cycle time scale is proposed. It can reduce the capacitor voltage fluctuation by injecting the 2nd order circulating current and improve the transient performance at the same time. Compared with the traditional proportional-integral controller, the proposed energy-balance based control strategy avoids the complicated adjusting process of parameters, which can be used in various conditions. Finally, both simulation and experimental results verify the proposed control strategy.
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Received: 09 March 2017
Published: 01 August 2017
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2017, Vol. 32 
