Discrete Diagonal State Estimator based Current Control for Grid Connected PWM Converter with an LCL filter

In this paper, the control and state observer for grid connected PWM converter with LCL filter has been discussed. The discrete state-space observer is designed in the d-q synchronous reference frame. Using the coordinate change of the matrix, the alternative state equation, which has diagonal system matrix, is obtained. Discretization of alternative state equation using Zero-Order Hold method is suggested, and the discrete form is simpler than that derived by original system matrix. By considering control stability with respect to the relation between filter resonant frequency and sampling frequency, current control scheme with feedback signal from state observer is also proposed. The digital delay to the PWM and sampling is considered for digital implementations.