Stationary-frame-based generalized control diagram for PWM AC-DC front-end converters with unbalanced grid voltage in renewable energy systems

In this paper, a stationary-frame-based generalized control diagram for PWM AC-DC front-end converter is presented. During the unbalanced fault of grid voltage, commonly two control objectives should be fulfilled. The first one is the balanced grid-connected current, and the second one is the stable DC bus voltage. In order to reach the generalized control diagram, proportional-resonant (PR) controller is used to control the positive and negative sequence of the grid-connected current simultaneously. Meanwhile, the generation of current references for different operation modes is derived. Hence, the control scheme can be automatically adaptable for different grid conditions. The low voltage ridethrough (LVRT) capability can be enhanced. A detailed simulation model comprised of a programmable grid source and three-phase PWM AC-DC front-end converter is implemented in MATLAB/Simulink. Simulation tests are performed to validate the proposed method.