No-Circulation Current Commutation Modulation Strategy for Parallel Resonant DC Link Inverter

To solve the problem of large circulation current loss in a parallel resonant dc link inverter, the no-circulation current commutation modulation strategy based on SVPWM method is proposed. In this modulation strategy, the main switches still maintain the sequence generated by the original modulation strategy, and the auxiliary commutation circuit still operates once in every pulsewidth modulation cycle. Besides, the switching time of the auxiliary switches can be adjusted dynamically according to the load current. When the commutation process of the auxiliary commutation circuit ends, no constant current is circulating freely through the switches of the inverter. It effectively eliminates the circulation current loss and improves the efficiency. At the same time, the time of the zero-voltage notch is not fixed, and it can also change with the load current changes. In the full load range, the duration of zero-voltage notch is shortened, which improves the utilization rate of the bus voltage. This modulation strategy is suitable for any resonant dc link inverter with circulation current. In this article, the operation principle and circuit characteristics are analyzed based on the equivalent circuits in different operation modes. Finally, the validity of the modulation strategy is verified on a 10 kW/16 kHz prototype.