240°-Clamped PWM in Three Phase Grid-Connected PV Converter Application

This paper presents the control scheme for a two-stage, grid connected Photovoltaic (PV) inverter that uses a low-loss PWM method called 240°-Clamped PWM (240CPWM) in the DC-AC stage. The main advantage of using 240CPWM is that it results in at least 86% less switching loss with similar THD as compared to conventional space vector PWM (CSVPWM). In a typical grid connected PV converter with conventional PWM methods, the DC-DC stage is responsible for Maximum Power Point Tracking (MPPT) and DC-AC stage controls the DC link voltage and injects sinusoidal currents into the grid. With 240CPWM in the inverter, DC-DC stage can no longer track the MPP because it needs to control the DC link voltage dynamically in a six-pulse pattern. So, the DC-AC stage is designed to track the MPP with an outer slower loop and control the grid currents accordingly with an inner faster loop. Simulation and experimental results with a 10-kW prototype are shown with THD close to 5% and efficiency of the DC-AC stage with 240CPWM greater than 99%.