Stability Analysis and Grid Disturbance Rejection for a 60-kW SiC-Based Filterless Grid-Connected PV Inverter

With increased switching frequency and multilevel topology, it is possible for a wide-bandgap-device-based grid-connected converter to achieve filterless function and utilize the grid impedance for its switching harmonic attenuation. In this paper, a filterless grid-connected SiC inverter is designed and demonstrated. Stability has been analyzed with a focus on grid disturbance rejection. The analysis shows that the conventional control method with instantaneous grid voltage feedforward (IGVF) will significantly limit the bandwidth or stability margin of a filterless grid-connected inverter, thus make the inverter sensitive to grid disturbance. Two grid voltage feedforward control methods, which require little additional computation resources, are proposed to suppress the grid voltage disturbance. The closed form equations for control parameters are derived. The effects of the proposed feedforward methods are also compared with that of conventional IGVF. Finally, the grid-connected experimental results of a 60-kW SiC-based 5-level photovoltaic inverter are provided to verify and compare the proposed control methods.