Proportional Multi Resonant Controller based Cascaded Voltage Control Scheme of Three Phase Four Leg Inverter for Nonlinear loads in OFF Grid Solar Photovoltaic Applications

OFF grid solar inverter can act as main source of power in the localities with frequent outages or absence of grid, and has to cater to wide variety of linear or nonlinear loads. Non linear loads with power electronic converters can create problems in power quality at the point of common coupling (PCC) through harmonic injection. In case of ON grid operation, power quality is normally maintained by utility, and the task of solar inverter is only to inject current at unity power factor (UPF) with less Total Harmonic Distortion (THD). However for OFF grid operation, it also has to maintain voltage of PCC with good power quality. This requires compensation of harmonics generated by nonlinear loads. In this paper cascaded voltage control with a proportional multi resonant (PMR) controller is proposed for a three phase four leg inverter, to achieve this objective. Controllers are designed with bode plot tools and are tuned for resonance at fundamental and dominant harmonic frequencies to achieve necessary harmonic compensation. Simulations in PSIM software are used to verify the efficacy of control algorithms.