Variable Switching Frequency PWM Strategy Based on Circulating Current Suppression in Interleaved Parallel Five-Level Inverter

The interleaved parallel inverter topology possesses the capability of generating multi-level outputs. Through the interleaved pulses in the legs, it can increase the equivalent switching frequency and reduce the harmonic content of output current. However, the high-frequency circulating current is introduced because of the inconsistent paralleled-legs output voltages and control delays, which results in increased losses and higher switching stress. Therefore, a series of problems caused by circulating current need to be solved urgently. In this paper, a coupled inductance circulating current model is established, to suppress the high-frequency circulating current peak value, a circulating current prediction model is derived based on this model. Then a five-level space vector unified modulation method using asymmetric regular sampling is proposed. With the proposed method, switching losses in the interleaved parallel system are decreased significantly. Finally, detailed experimental results are provided to validate the proposed method.