A Semidiscontinuous PWM Method for Suppression of the Resonant Current in a 48 Kw Grid-Tied PV Inverter

In conventional discontinuous pulsewidth modulation (DPWM) methods, the drastic change of the modulation index during the clamping transient results in grid current oscillation, which deteriorates the power quality. This article presents a semi-DPWM method for a three-level T-type grid-connected PV inverter. The semi DPWM is achieved by injecting a continuous sinusoidal signal during the clamping transient, which reduces the grid current oscillation and reduces the total harmonic distortion of the current. First, a detailed analysis of the grid current oscillation is presented, then a semi-DPWM method is proposed to suppress the oscillation current. The experiment is carried out on a 48-kW grid-tied PV inverter to validate the effectiveness of the method. Compared with the space vector PWM, results show that more than 42.5% switching loss has been reduced with the semi DPWM and the efficiency is increased from 97.03 to 97.22% at the rated load. Besides, the semi DPWM method significantly suppresses the current oscillation and maintains good power quality under various operation conditions.