The Restrain of Harmonic Circulating Currents between Parallel Inverters

In inverters, distortions of output sine voltages caused by factors like dead-times of power switches can be well compensated by instantaneous voltages and/or currents feedback regulators such as PID or repetitive controllers. However, in our experiments, we found that the dead-time differences between inverters would result in significant harmonic circulating currents, and instantaneous regulators had limited effects on restraining them, esp. in large parallel power supply systems where the filter reactors and output impedances in each inverters must be small. In this paper, for analyses of harmonic circulating currents, an inverter model that considered the bias in SPWM voltage as a disturbance was established. The research on restraining of harmonic circulating currents by instantaneous feedback regulators indicated that there had been relationships in inverters between output voltage distortions and harmonic circulating currents. The experiments and simulations based on the duel loop voltage and current feedback controls demonstrated that instantaneous feedback regulators that achieve good waveforms could also lead to good restraining on the harmonic circulating currents