Frequency Scanning-Based Contributions Identification of Current Control Loop and PLL on DQ Impedance Characteristics of Three-Phase Grid-Connected Inverter

Complex space vector and complex transfer function theory is used to theoretically establish the dq impedance model of current-controlled grid-connected inverter (GCI) with considering phase-locked loop (PLL) dynamics, where contributions of current control loop and PLL on dq impedance characteristics are clearly identified. On its basis, this paper presents a frequency scanning-based black box identification method of the contributions of current control loop and PLL on dq-domain impedance characteristics of the GCI. Three-phase small-signal voltage vector perturbation which is aligned with point of common coupling (PCC) voltage vector is injected into PCC in series way, so that grid current responses which are only determined by the dynamics of current control loop are excited. In addition, parallel current injection to excite PCC voltage responses is theoretically proved to be not applicable for extracting the dynamics of current control loop and PLL. The effectiveness of the presented dq-domain impedance characteristics division method is verified by both frequency scanning results and time-domain simulation results obtained in Matlab/Simulink environment.