Constant Boost Control with Third Harmonic Injection for Quasi-Z Source Inverter used in PV Grid-connected System

Compared to the dual-stage inverter, quasi-Z-source inverter (qZSI) offers higher reliability and lower switch count but suffers from higher voltage stress on components. The qZSI is normally controlled by the simple boost control (SBC) method that adds reference signals to the sinusoidal PWM to generate the shoot-through state. This paper develops a constant boost control method with third harmonic injection. Compared to the SBC, the proposed control method increases the voltage boost and reduces the voltage stress on switches and passive components of the qZSI, making it suitable for PV grid-connected applications. The third harmonic signal is produced and injected in a way that keeps it in phase with the reference sinusoidal signals, regardless of the solar irradiance level. This reduces the total harmonic distortions (THD) and improves the output power quality. Simulation results are presented for validation of the theoretical analysis and controller design.