P plus Resonant Control of a Z-Source Inverter for Mains Voltage Drop Compensation

Z-Source inverters, consisting of both inductors and capacitors as DC-link components, provide unique boost capability in contrast to conventional inverters. The simple structure needs no additional switching elements and only small step-up chokes. Due to the oscillatory arrangement of both inductors and capacitors in the DC-link, voltages and currents exhibit a characteristical six-pulse ripple when using the Z-source inverter with an AC supply. The consequences are distortion of the output voltage and self-boosting due to unwanted shoot-through states and oscillating DC-link voltage due to mains voltage rectifying. An active rectifier topology in combination with a damped mains filter is proposed to prevent any unwanted shoot-through states. Besides, regenerating operation of the Z-source inverter with AC supply is enabled. Resting on this new structure with minimized passive components, a state space description is given. Subsequently, a simple and robust P+resonant closed loop control is designed to avoid load current harmonics caused by mains voltage rectifying. For each frequency component of the six-pulse ripple, a separate controller is employed. The phase-shift of the Z-source network is compensated by additional all-pass filters. Experimental results verify the suitability.