Research On Suppressing Phase-to-phase Circulating Current Of Modular Multilevel Converter

With the development of power electronic technology, voltage source converter has beenwidely used in high voltage dc transmission system. But the dielectric strength and currentcapacity etc. of the existing power switch device cannot satisfy the demand of the highpressure and high power electronic applications, and generally, the price of high voltagepower switching device relatively expensive. However, the requirement of the traditional twolevel or three level voltage source converter to the withstand voltage and capacity of thepower switch devices is quite high. In the power switch device without essential breakthroughpremise, the birth of modular multilevel converter (MMC) to HVDC transmission technologyhas brought the gospel.This paper firstly introduces the traditional two-level and multilevel converter, and roughintroduces some commonly used multilevel modulation mode. Then it expounds thetopological structure and working principle of MMC in detail, and establishes the relatedequivalent mathematical model of MMC. Secondly, it puts forward implementation of thecarrier phase shift sinusoidal pulse width modulation and recent level approximationmodulation mode in the MMC. At the same time, it puts forward several balance control waysof the sub-modular capacitance voltage. Finally, according to the already establishedmathematical model, it particularly analyses the generating mechanism of the phase-to-phasecirculating current, and research the circulation main ingredients, thus, it puts forward twonew ways of suppressing the phase-to-phase circulating current.According to the proposed various modulation mode, sub-module capacitance voltagebalance control strategy, and ways of suppressing the phase-to-phase circulating current, itbuilds more main circuits of MMC and the simulation module of corresponding controlcircuits to verify the different control manners by simulation. Known through the analysis ofcomparing the simulation results that choose the traditional sort contributes to suppress thephase-to-phase circulating current, and suppressor of the phase-to-phase circulating currentcan effectively inhibit alternate with circulation composition in the MMC bridge arm.