Circulating current suppression of power conversion systems under unbalanced conditions: Large-signal model-based analysis

This paper proposes a large-signal model-based circulating current control approach to achieve the circulating current suppression and power quality improvement for power conversion systems (PCSs) under unbalanced conditions. Specifically, first of all, the adaptive capacitive virtual impedance (VI) is developed based on the change of the current difference to minimize the positive-sequence circulating current (PSCC). The robust droop control is introduced to tune the positive-sequence voltage output and implement the load sharing. Secondly, the negative-sequence reference signal is generated to enable negative-sequence current sharing. The secondary control signal is integrated with the positive-sequence voltage output to modify the voltage reference of the PCS and realize the unbalanced voltage compensation. Finally, the zero-sequence circulating current (ZSCC) controller is proposed by introducing the Q-PR controller and the feedforward term to suppress the ZSCC and attenuate the effect of filtering parameters on zero-axis current. The Lyapunov theory-based stability analysis is provided to prove the stabilization of the system modeled by a large signal. Experiments are presented to demonstrate the effectiveness of the proposed approach.