Optimum feed-forward control for UPFC converters in large-scale non-grid-connected wind power applications

The three-phase PWM rectifier is one of the core techniques applied in large scale wind power system. DC-bus voltage usually fluctuates as the variation of load and ac voltage, which may hurt the safety and reliability of the system. In order to restrain dc-bus voltage fluctuation and improve system dynamic response, a direct current control and dual close loop control structure in d-q synchronous reference frame are employed. By analyzing the factors which influence the fast transient response, an optimum feed-forward control strategy is proposed based on the power balance relationship between the input and output of rectifier. With this control, the dc-bus voltage is immunized from not only variation of load but also variation of grid voltage, and the capacitance of the dc link capacitors can be reduced at same transient response demand of system. Simulation results show that the proposed control scheme has satisfactory steady-state characteristics and fast transient response.