Analysis and Suppression of Zero Sequence Circulating Current in a Direct Parallel System of Three-phase PWM Inverters
Circulating current suppression is one of the important key technologies for achieving a direct parallel system of three-phase PWM inverters.Firsty,establish a zero-sequence circulating current mathematical model of a three-phase PWM inverter directly parallel system in synchronous rotating coordinates,and then analyze the circulating current suppression principle in detail combined with the inverter space vector modulation algorithm.On this basis,a circulating current suppression strategy based on proportional resonance and non-zero vector duty cycle feedforward control was proposed.The strategy can further suppress power frequency fluctuations in the parallel zero-sequence circulating current by adjusting the zero vector in the inverter space vector,while reducing the amplitude/effective value of the circulating current.Finally,comparative experimental waveforms under different suppression strategies were provided through prototype experiments,which can fully demonstrate the effectiveness of the proposed strategy.The research achievement can provide technical support for the reliable and stable operation of three-phase PWM inverter direct parallel systems.
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