A Reactive Power Controller for a Two-Stage Transformerless PV Grid System by Employing Virtual Inertia Control

The rising integration of photovoltaic (PV) energy with the grid has several impacts on electrical power systems which demands a properly designed control scheme to maintain the power balance along with the voltage stability at the grid integration point commonly known as the Point of Common Coupling (PCC). As the PV systems are non-inertial and produce only active power, hence without regulating the reactive power the
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microgrids often cause reactive power disturbances as well as transmission line impedance errors to the grids. Thus, while penetrating with grids, maintaining active and reactive powers simultaneously with the proper controlling of voltage and frequency of the PV systems is a challenging task. In this work, a virtual inertia control scheme is proposed for a two-stage transformerless PV grid system to maintain both active and reactive power of the system while changing system voltage under variable irradiance conditions. The control scheme is virtual and based on the dynamic equations involved with the synchronous generator. The overall system is simulated under MATLAB/SIMULINK and results are presented showing the control parameter performances including the DC bus voltage, grid voltage, frequency, active power, and reactive power. The results show that with the variation of system voltage, the control scheme is capable of maintaining the active and reactive power by varying the frequency along with the grid and inverter voltage and current.