A Control Method of Suppressing Resonance for Inverter Using LCL Filter with Consideration of Grid Equivalent Inductance Effect

The LCL filter has been widely applied in the system with larger-capacity and lower switching-frequency grid-connected inverter. But resonance easily occurs in the LCL filter, especially in the new energy power systems with multiple inverters. In this paper, the LCL filter resonance formula is deduced. According to the characteristics of equivalent series inductance for grid-side inductor and power grid when the grid current resonates, and a novel control strategy with such double closed loop as the first differential of grid-side inductance voltage and network current is proposed by combining with the structure of the LCL filter. In addition, without increasing the number of sensors, the system damping is added in inner loop of the first differential grid-side inductance voltage, which effectively restrains the resonance of LCL. In the outer current loop, the network current can be controlled directly to ensure higher power factor and improve the utilization efficiency of inverter. By comparing with the simulation of feedback control for capacitor current, the simulation results show that the control strategy has better effect on restraining current resonance in environment of grid-connected inverter, and improving network current quality.