Normalized LMF and CC-ROGI-FLL Techniques for Seamless Synchronization of Double Stage SPV-BES Based Microgrid to Utility Grid

This paper deals with the performance of the control strategy designed for a double-stage solar photovoltaic (SPV) - battery energy storage (BES) based microgrid (MG). This system uses an improved P&O control to track the MPP point of the SPV array. The system uses a normalized least mean fourth (NLMF) control in grid-integrated (GI) mode and a voltage-based control in standalone (SA) mode to control the voltage source converter (VSC) switches. The VSC control helps in power quality (PQ) improvements, power factor enhancements, frequency variation mitigation, seamless synchronization, and local unbalanced load compensation. Moreover, it uses a complex coefficient-reduced order generalized integrator-based frequency locked loop (CC-ROGI-FLL) for a fast and accurate detection of grid phase angle, load phase angle, and grid frequency to realize seamless synchronization of the MG to the utility grid. The CC-ROGI-FLL also helps in polluted grid compensation and frequency variation mitigation. A bidirectional converter (BDC) is used to administer the charging and discharging of the BES and to maintain the voltage at the DC link. The system is simulated in MATLAB/Simulink and the results are presented here to prove the efficacy of the control strategy.