Circulation suppression of synchronous/interleaving paralleled 400-Hz three-phase four-leg inverter based on third harmonics injection

In this study, the third harmonic injection method based on analogue circuit is applied in the interleaving parallel three-phase four-leg (3P4L) inverter, the adverse effects of injected signals on the circulating current are found, and the corresponding control strategy solution is proposed. At the beginning of this study, by using the large-signal model of leg, it is proved that four legs can be decoupled, on the basis of this conclusion, the current sharing control strategy based on dual-loop scheme and third harmonic injection can be applied in paralleled 3P4L inverter, however, peak value of circulating current is increased by zero-sequence component which is caused by injected signals. Therefore, output impedance analysis method is applied, and the control strategy including zero-sequence component feedforward loop is proposed, which can be implemented with analogue circuit, and is suitable for the 400 Hz synchronous/interleaving paralleled inverter systems. Finally, the effectiveness of the control strategy is verified by simulation and experiment.