Sequence-Impedance-Based Harmonic Stability Analysis and Controller Parameter Design of Three-Phase Inverter-Based Multibus AC Power Systems

Three-phase inverter-based multibus ac power systems could suffer from the harmonic instability issue. The existing impedance-based stability analysis method using the Nyquist stability criterion once requires the calculation of right-half-plane (RHP) poles of impedance ratios, which would result in a heavy computation burden for complicated systems. In order to analyze the harmonic stability of multibus ac systems consisting of both voltage-controlled and current-controlled inverters without the need for RHP pole calculation, this paper proposes two sequence-impedance-based harmonic stability analysis methods. Based on the summary of all major connection types including mesh, the proposed Method 1 can analyze the harmonic stability of multibus ac systems by adding the components one by one from nodes in the lowest level to areas in the highest system level, and accordingly, applying the stability criteria multiple times in succession. The proposed Method 2 is a generalized extension of the impedance-sum-type criterion to be used for the harmonic stability analysis of any multibus ac systems based on Cauchy's theorem. The inverter controller parameters can be designed in the forms of stability regions in the parameter space, by repetitively applying the proposed harmonic stability analysis methods. Experimental results of inverter-based multibus ac systems validate the effectiveness of the proposed harmonic stability analysis methods and parameter design approach.