Impedance Readjusting Method of Grid-Connected Inverter Cluster with PR Control Strategy

The connection to the large-scale new energy, which uses power electronic converter as interface, has changed the dynamic characteristics of power grid. The sub/super synchronous oscillations occur frequently and restricts the absorption of new energy. In order to further study, this paper firstly establishes sequence impedance model of single inverter under PI and PR closed-loop control by introducing harmonic linear method. On this basis, the equivalent impedance model for grid-connected inverter cluster is proposed. By comparing the dynamic characteristics of the impedance of clustered inverters under different control strategies and the system stability after joining the weak gird, this paper concludes that under the same stability margin of current loop, the stability margin of system based on quasi-PR control is larger than system based on PI control, and that means quasi-PR control strategy can reduce the risk of sub/super synchronous oscillation. Finally, the Matlab/Simulink models of inverter cluster under different control strategies are built, and the stability and instability phenomena of grid-connected system are simulated, which verifies the theoretical analysis that inverter cluster under quasi-PR control is more stable.