Small-signal stability of grids with distributed low-inertia generators taking into account line phasor dynamics

Current design of droop controllers for voltage source inverters is often accompanied by a small-signal stability analysis using the quasistatic model. Whereas the quasistatic approximation is, in general, acceptable for the stability analysis of grids being fed by relatively slow-acting rotating generators, this approach leads to questionable results in presence of distributed generators being equipped with fast-acting, low-inertia inverters. In this paper, the dynamic phasor based modeling of the dynamics of network components is used to adequately assess the small-signal stability of grids in the presence of voltage source inverters. A systematic design procedure for a stable voltage and frequency droop controller is presented. Optimal values for the different parameters of the frequency droop controller are selected according to arbitrary design constraints, while ensuring stability and avoiding endless tuning of the different parameters. Simulations are included to validate the results and to demonstrate the robustness of the droop controller.