Instantaneous grid voltage estimation based on the Newton-Raphson optimization for grid connected VSC applications

This paper presents a proportional-resonant current control scheme for three-phase grid connected voltage source converters (VSCs) which does not require ac side voltage sensors. In the proposed method, a non-linear model is derived for the grid connected converter which relates the instantaneous grid voltage value to the filter parameters and the generated converter voltage in each switching period. The non-linear model is solved in each period using the Newton-Raphson optimization; then the reference current for the current control loop is generated from the estimated grid voltages. Using an estimator instead of voltage sensors not only reduces the size and cost but also improves the reliability of the converter system and protects it from grid voltage disturbances and noises.