Frequency Characteristic and Impedance Analysis on Three-Phase Grid-Connected Inverters Based on DDSRF-PLL

Decoupled double synchronous reference frame phase locked loop (DDSRF-PLL) can effectively eliminate negative-sequence fundamental frequency component, which means the PLL control loop will have an effect on the frequency characteristics and stability of grid-connected inverters. Based on the three-phase LCL-type grid-connected inverter, the positive- and negative-sequence output impedance model of the grid-connected inverter and the frequency characteristics of DDSRF-PLL were firstly derived. Meanwhile, the regulator parameters of DDSRF-PLL were designed and its effect on impedance stability of inverter was analyzed. Then, the frequency characteristics of DDSRF-PLL and the output impedance model of the grid-connected inverter were verified by the simulation and experimental results. Finally, the stability of the grid-connected with different PLL bandwidths was analyzed and verified by experimental results.