Impedance Network Impact on the Controller Design of the QZSI for PV Applications

Due to its buck-boost capability with a continuous input current, the quasi-Z-source inverter (qZSI) is increasingly used for renewable energy, e.g., photovoltaic (PV) systems. The quasi-Z-source network (qZSn) enables an additional state, i.e., shoot-through (ST) state, which extends the entire system reliability to some extent. Unlike the conventional two-stage inverter with a large dc-link decoupling capacitor, the qZSn is strongly coupled with the ac part, making the system dynamically interactive. However, the controller for the ac part of the qZSI is generally designed like that for the conventional voltage source inverter (VSI), which may become ineffective. This paper thus presents the small-signal modeling of the three-phase qZSI and the effect of the impedance network on the control of the qZSI is then analyzed. The resonance due to the load and input changes has been analyzed and then used in the ac controller design. Both simulation and experimental tests are presented to verify the theoretical analysis and designed controller.