Three-phase PWM inverters with three-phase output transformer and three-phase filter inductor

In this paper, the different influences of three-limb and multi-limb transformer with Star-Star or Delta-Star connection, three-limb filter inductor, multi-limb filter inductor and position of the LC filter in a three-phase PWM inverter have been analyzed in detail in stationary dq0 frame. The analysis show that three-phase transformer with different limb numbers and connection types have different influences on the ability of suppressing unbalanced load and provide different strategies for output voltage control. Meanwhile, the position of a three-phase filter inductor and filter capacitor will impact the performance and control options of a three-phase inverter at unbalanced load differently. Tests on a 90-kVA 400 Hz three-phase power supply with a three-phase five-limb transformer give good proof of the correctness and effectiveness of the theoretical analysis.