Stability Boundary Acquisition of Weak Grid-Tied Single-Stage Inverter

In several large-scale PV stations, it is reported that as solar radiation increases, whenever the output power reaches to a critical value, the grid-tied inverters will lose the stability. To explain this phenomenon, this paper builds the small-signal impedance model of the single-stage inverter, which considers the effect of DC-link voltage loop and phase-locked loop. Meanwhile, the impedance model is verified through frequency sweep. Based on the model, the output impedance of the inverter and the stability of the weak grid-tied system are analyzed. For the first time, the steady state operating point of the inverter is discussed in the model. It is found that high proportional gain of the DC-link voltage loop, large active current and capacitive reactive current would reduce system stability margin. The stability boundary for a specific prototype is further acquired through numerical method. Finally, experimental tests verify the theoretical analyses.