Stability analysis of three-phase PV inverter under inductive grid impedance condition

In many cases, the grid is not ideal voltage source but a weak grid which contains inductive grid impedance. The influence of grid impedance is not considered in the conventional design of photovoltaic (PV) inverters. Impedance mismatch is likely to deteriorate the stability of the cascaded system of PV inverter and grid, even making the system unstable. From the perspective of the impedance, this paper analyzed the stability of PV inverter with L-filter and LCL-filter under the condition of inductive grid impedance, and the stability criterion and output admittance model were researched respectively. Through the model order reduction and matrix approximating, the stability analysis of inverter cascaded with grid which was usually complemented based on the generalized Nyquist stability criterion (GNC) is simplified. Drawing on the method in which the admittance models of the DC power are built, the calculation process of the d channel output admittance which was usually derived from the closed-loop state matrices is simplified. According to the proposed simplified criterion and the established d channel output admittance model, the stability of PV inverter cascaded with grid was analyzed, and the influence of filter parameters on stability margin of the cascaded system was studied. Experimental results validate the proposed theoretical stability analysis. © 2014 Chin. Soc. for Elec. Eng.