Variable Switching Frequency PWM for Three-Level Grid-Connected Inverters with LCL Filters

With the rapid development of photovoltaic (PV) power generation, three-level grid-connected inverter play an important role in photovoltaic systems for its excellent performance. This paper gives the theoretical analysis of current ripple prediction for three-level inverters based on equivalent converter-load model and briefly introduces the variable switching frequency PWM (VSFPWM) based on this prediction method to control three-level inverters with LCL filters. The VSFPWM could make a wide range of frequency changes and obtain better efficiency by reducing the switching losses. The variable switching frequency control could also attenuate EMI noises without increasing current ripple peak value and meet the power quality requirements. Simulation and experimental results in a prototype inverter are provided to verify the proposed methods.