Nonlinear Disturbance Observer Based Control of Three Phase Grid Forming Inverter for Distributed Generation System

The operation of three phase grid forming inverter for standalone distributed generation (DG) system under unbalanced and nonlinear loading condition is considered. Under unbalanced and nonlinear loading conditions, the output voltage of grid forming inverter gets distorted and its power quality is diminished. Hence, to reject the undesirable effects of load on the output voltage waveform of grid forming inverter, a novel multivariable nonlinear disturbance observer (NDOB) is proposed. The controller and observer are designed in synchronous reference frame (SRF). The observed disturbances are rejected using feed-forward control in the outer voltage control loop. The proposed nonlinear disturbance observer based control (NDOBC) with conventional multi-loop proportional-integral (PI) voltage and current control enhances the power quality of output voltage waveform under load disturbances. The experimental results verifies the effectiveness of proposed observer based disturbance rejection control for three phase grid forming inverter.