Dynamic analysis of DC-DC converter internal to an offshore wind farm

Abstract

This study investigates the feasibility of integrating a single-switch active rectifier layout in an offshore wind farm. The proposed active rectifier topology consists of cascade connection of a diode-rectifier and a DC-DC boost converter. A DC collection grid is considered inside the wind farm, which supplies power to a land grid. Each wind conversion units within the DC collection grid includes a turbine, a generator, and an active rectifier. The DC-DC stage of the active rectifier allows regulating the frequency of generator, controlling the DC voltage to follow the reference signal, mitigating the distortion or ripple in the current signal, and maintaining the fault-ride through capability of the wind farm. The AC output signal from the wind-turbine-generators is converted to DC signal through a non-controlled full-bridge diode rectifier and a controlled DC-DC converter. The dynamic model of the DC-DC boost converter cascaded with the diode-rectifier is derived; and the contribution of pulse width modulation (PWM)-controller to the mitigation of signal variations is evaluated. The results prove consistency of the closed loop PWM-controller, which reduces significantly the gain of disturbances. The results are presented in the form of small-signal transfer functions and simulated using MATLAB software.