Linear Quadratic Estimation Control for Single Stage PV System Integrated to Single Phase Utility

A linear quadratic estimation (LQE) based control for single stage single-phase grid integrated solar photovoltaic (PV) system is proposed in this paper. The mathematical approach minimizes the mean-squared estimation error and replaces the phase locked loop (PLL) and its associated problems to synchronize the PV converter system to the single-phase grid. The PV converter system uses a voltage source converter (VSC), which harvests the peak power generated from the PV array and injects it into the single-phase grid. The harmonics analysis of grid current is meeting an IEEE-519 power quality standard. In addition, VSC mitigates nonlinear load current harmonics, improves power factor of the system even when PV generation is not available. It also improves dynamic response on sudden connection and disconnection of nonlinear load and under varying irradiance. The reference VSC input voltage is determined by incremental conductance (INC) based maximum power point tracking. The proportional integral (PI) controller sustains VSC input voltage at the set point voltage, and the loading on the PI controller is reduced by using feed-forward loop, thus transient response of the solar system is enhanced. This control algorithm for the solar PV system, is authenticated by experimental results.