Comprehensive Parameter Design of Parallel PLL-based VSGs Considering Feedforward Signals

Under very weak grid conditions, phase-locked loop (PLL) performance can be declined and may cause instability or fluctuations in the power system. Besides, the interaction between parallel PLL-based Virtual synchronous generators (VSGs) during contingencies, and their contribution to stability enhancement, is a complicated problem that can be affected by their virtual inertia coefficients and the PLL controller parameters. Thus, an appropriate parameters design at different grid impedances is necessary for paralleled PLL-based VSGs. Furthermore, feedforward signals are a part of the controller and can be beneficial in initial short-term effect elimination. None the less, their effect on the stability of PLL-based VSGs and their parameters design has not been studied so far. In this paper, first, all equations of paralleled PLL-based VSGs are presented, and the system model is explained. Then, the small-signal stability analysis of the power system is obtained, and eigen values migration considering different values of grid impedance and virtual inertia coefficients is analyzed. Moreover, a strategy is introduced to attain maximum power system stability at various short-circuit capacity ratios (SCCRs). Next, the adaptive neuro-fuzzy inference system (ANFIS) method is applied, and all VSG and PLL parameters in a system with and without feedforward signals are obtained. It is demonstrated that the power system stability is improved by using feedforward signals. Finally, the eigen values analysis, and the accuracy of the ANFIS technique in finding the optimized values, is validated through comprehensive simulations in various scenarios.