Bi-directional AC-AC Z-source inverter with active rectifier and feedforward control

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 characteristical dynamic behavior especially 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 front end topology in combination with a damped 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 feedforward control is designed to avoid load current harmonics caused by mains voltage rectifying. Experimental results verify the suitability.