Power Control Based on State Space Strategies for Grid-Oriented Inverters with LCL Filters

Through a third-order mathematical model of grid-oriented LCL-type converters, this paper analyzes the complicated dynamic characteristics and resonance problems which may influence the system stability. To realize active damping for LCL filters and improve dynamic performance of current regulators, a state space current PI controller is proposed whose parameters can be tuned based on the polynomial equations approach. An extended state observer is integrated with the regulation scheme, where additional sensors are not necessary in contrast with conventional active damping strategies. Synchronous reference frame PLL (SRF-PLL) equipped with filter technology is proposed for grid voltage disturbance suppression. This method is then applied to establish a double-closed-loop power regulator that demonstrates improved performance compared with other controllers. The simulation results are displayed to illustrate the efficiency of the regulation methods.