Impedance-based Stability Criterion for the Stable Evaluation of Grid-connected Inverter Systems with Distributed Parameter Lines

For a multi-inverter grid-connected system, the stability of the point of common coupling (PCC) voltage is evaluated considering the distribution parameters of the transmission lines. First, the systems on both sides of the PCC are equalized, a small-signal equivalent circuit similar to the “current source-grid” is established, and a mathematical model for the voltage of the PCC is derived. Then, using Euler's formula and Nyquist stability criterion, the PCC voltage stability of the grid-connected system is evaluated by the impedance analysis method under the premise that the single-side excitation is stable. In addition, the grid-connected conditions causing PCC voltage instability are studied. A phase compensation method based on an impedance phase compensation control strategy is introduced. The stability of the grid-connected system is improved by compensating the phase margin at the equivalent impedance crossover-section frequency on both sides of the grid-connected system PCC. Finally, a simulation circuit is built to simulate and analyze the proposed model and phase compensation method. The simulation results verify the accuracy and effectiveness of the theoretical analysis.