Energy Storage MMC Low-frequency Equalization Hybrid Control Strategy
Aiming at the large fluctuation of capacitor voltage amplitude of conventional MMC submodule,the low-frequency equalization switching control strategy is proposed for energy storage MMC,which comprehensively uses the high-frequency injection control method and the energy storage MMC control method to solve the problem of capacitor voltage fluctuation of submodules.Firstly,the cause of submodule voltage fluctuation in low frequency MMC is analyzed,and then the two methods of suppressing the capacity of the submodules at low frequencies of high frequency injection and energy storage MMC are described,and then the hybrid control strategy of low-frequency voltage equalization of the energy storage MMC is proposed,and the formula of the circulation current is derived.Compared with high frequency injection,it can decrease the current and cycle of bridge arm,reduce the current stress and system loss of the device,and reduce the capacitance requirements of the supercapacitor compared with the energy storage MMC method.Finally,Matlab/Simulink is used to simulate the low-frequency equalization hybrid control strategy of energy storage MMC,and the effectiveness of the proposed control strategy is verified.
modular multilevel converterlow frequency controlsubmodule voltage equalization controlcirculation control
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