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| Voltage Ripple Principle and Restrain Method of Floating Capacitors in a New Modular Multilevel Converter |
| Wang Kui, Zheng Zedong, Li Yongdong |
| State Key Lab of Control and Simulation of Power System and Generation Equipments Tsinghua University Beijing 100084 China |
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Abstract Modular multilevel converter (MMC) is a highly attractive multilevel converter topology for medium and high voltage applications during recent years. In this paper, a new MMC topology and the associated voltage ripple problem of floating capacitors are studied. Based on the instantaneous output power of a half bridge, power ripple and energy variation in a period can be derived. Then the mathematic expression of voltage ripple amplitude is acquired. This problem becomes more severe when the fundamental frequency is lower. This paper proposes a method to restrain the lower frequency voltage ripple. By adding high frequency zero-sequence voltage and phase circulating current to increase the power ripple frequency, the energy ripple amplitude can be reduced and then voltage ripple is also reduced. A three-phase five-level prototype is built up to verify the validity of the method by simulation and experimental results.
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Received: 25 September 2010
Published: 07 March 2014
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2011, Vol. 26 
