A Control Strategy for a Grid Connected PV and Battery Energy Storage System

Photovoltaic generation will continue to grow with urbanization, electrification, digitalization, and de-carbonization. However, PV generation is variable and intermittent, non-inertia and asynchronous with the demand, posing significant challenges in generation dispatch, strategic spinning reserve and power system stability. Battery Energy Storage Systems (BESS) are key in enabling the integration of higher quanta of solar PV into utility power grids. Grid connected PV, BESS and PV-BESS have been modelled on MATLAB/Simulink. The control strategy of the grid connected PV inverter operates PV at MPP and ensures grid side current control to determine the amount of power delivered. These objectives have been achieved using PWM on two successive control strategies. The VSI control determines the modulation index for generating an output current that is both sinusoidal and in phase with the grid-side voltage. The Perturb & Observe based MPPT is used. Current-controlled H-bridge PWM single-stage three-phase and bi-directional two stage three phase inverters with LCL low pass filters are implemented on MATLAB/Simulink. The critical components in the control circuit are the PLL, P&O MPPT, feed-forward input power control and a Proportional Integral (PI) based grid-side current controller. A sinusoidal grid current is successfully fed to the grid from the grid connected solar PV and grid connected BESS. An FFT analysis performed on the grid side currents shows the total harmonic distortion (THD) is below the limit specified in IEEE-519.