Photovoltaic Virtual Inertia Using a Modified VSM Model in PowerFactory for Frequency Stability

Photovoltaic plants do not intrinsically have natural inertia. Natural inertia in power systems comes from the stored kinetic energy of the rotating parts of a synchronous machine. The inertia of the synchronous machine keeps the power system from being too sensitive to disturbances in the system. When a disturbance in the power system occurs that affects the frequency stability of the power system, the primary response of the synchronous machines is to expend the stored energy in the rotors. This immediate response of synchronous machines is emulated in PV plants by taking advantage of the fast response of power electronic devices. This study aims to propose a new control strategy using a modified VSM model in DIgSILENT PowerFactory as the base model. The base model is modified to include a fast frequency response component directly embedded into the inputs of the control system. The proposed control strategy utilizes the deviation of the frequency from the nominal value and applies it directly to the reference power and mechanical time constant.