A Generalized-Impedance Based Stability Criterion for Three-Phase Grid-Connected Voltage Source Converters

1  Abstract—The output impedance matrices of three-phase grid-connected voltage source converters (VSCs) are widely used in power system stability analysis. Regardless of how the impedance is modeled, there always exist coupling terms in the impedance matrix, which makes the system a multi-input-multi-output (MIMO) system. As a practical approximation, the coupling terms are generally omitted and the impedance-based stability criterion for the resultant single-input-single-output (SISO) system can be applicable. However, such handling may result in analytical errors. This letter proposes a new stability criterion based on an equivalent SISO system by introducing the concept of generalized-impedances, which can completely keep the coupling terms. Further, the effects of the phase-locked-loop (PLL) parameters on system stability are studied based on the proposed criterion. The effectiveness of the proposed criterion is verified by a hardware-in-the-loop (HIL) simulation based on a RT-LAB platform.