Control of Three-Phase Grid-Connected Inverter Using dq Axis Theory

In this paper, the controller design and MATLAB Simulation of a 3-ɸ grid-connected inverter (3-ɸ GCI) are implemented. Sinusoidal pulse width modulation (SPWM) scheme with unipolar switching in dq axis theory or synchronous reference frame is used to control 3-ɸ inverter. The objective of the paper is to design a model in MATLAB/Simulink employing dq theory to control active and reactive grid current separately and maintain total harmonic distortion (THD) less than 5% as per IEEE standard. The control mechanism includes a PI controller and phase-locked loop (PLL). The parameters of the controller have been selected in such way that the injected grid current should be sinusoidal and Unity Power Factor (UPF) along with better dynamic response. The system has been implemented a DC-link high-voltage, 3-ɸ inverter, an LCL filter, and a PLL algorithm. The dq axis theory is preferred as it is easy to implement, active and reactive current can be separately controlled. The simulation results have been verified with the theoretical approach successfully.