Linear quadratic regulator based current control of grid connected inverter for Renewable Energy Applications

Harnessing electrical power from Renewable Energy Sources (RES) to the grid in a more efficient way requires a power electronic converter. But the power electronic devices introduce harmonics thus affecting the quality of power. A high performance controller is essential to control the real and reactive power flow between the RES and grid without affecting the quality of power. In this paper, grid connected Renewable Energy System is modeled as single phase equivalent circuit and an optimal control law is derived using Linear Quadratic Regulator (LQR). The reference currents are generated using instantaneous real - reactive (p - q) theory to have low grid current Total Harmonic Distortion (THD) and power factor closer to unity in the grid side. To show the supremacy of the LQR method, simulation results are compared with the conventional Hysteresis Controller (HC) for three phase three wire system with balanced grid voltage conditions. It is inferred from the results that LQR is superior in its tracking ability and has better stability.