A Semi Discontinuous PWM Method for Mitigating Oscillation in a Three-level Grid-tied PV Inverter

This paper presents a semi-discontinuous PWM (DPWM) method for a three-phase three-level PV inverter. Different from the conventional DPWM in which the zero sequence signal is stepped changed during the clamping period, the semi-DPWM is achieved by injecting a continuously changed signal with optimum slew rate in the modulation, which reduces the grid current oscillation as well as the switching loss. A detailed analysis of the grid current oscillation and the proposed semi-DPWM method is presented. The experiment is carried out on a 48 kW PV inverter and compared with the space vector PWM (SVPWM). The results show that the proposed semi DPWM method achieves the balance between the oscillation mitigation and the efficiency, the performance of grid current with semi-DPWM is maintained as good as that with SVPWM while the efficiency is increased from 97.03% and 97.22%.