Research on three-phase inverter with unbalanced load

One of important performances of three-phase inverter is output voltage symmetry. Unsymmetrical output voltage is caused mainly by unbalanced load. The mechanism distorting output voltage fundamental waveform of an inverter under unbalanced load is analyzed based on symmetrical component decomposing and superimpose theory. It is present that positive-, negative- and zero-sequence components of output voltage show different effect of compensating. This problem is related to not only controller characteristic but also the inherent nature of the inverter circuit The method to improve the output voltage symmetry of inverter is proposed in this paper. Theoretical analysis is confirmed well through both simulation and experimental results on a 35 kW DSP-controlled three-phase inverter.