Control strategy of a HVDC-Diode Rectifier connected type-4 off-shore wind farm

This paper presents a distributed control scheme for voltage and frequency regulation in a point of common connection (PCC) of a wind farm feeding energy to the grid via an HVDC-Diode Rectifier (HVDC-DR) link. Each wind turbine uses a Permanent Magnet Synchronous Generator (PMSG) with a full back-to-back VSI topology connected between the machine terminals and the PCC. The reference voltage and frequency in each wind turbine is obtained from P/V and Q/f droop characteristics respectively, where Q is the reactive power supplied by each wind energy system an P is the active power obtained from the optimum power wind turbine characteristic. PI controllers process the voltage and frequency errors and set d − q axis reference currents. These currents are imposed at the output of the wind energy systems by fast current control loops. The scheme allows for islanded and grid connected operation. Maximum power transfer from each wind turbines to the PCC is achieved, with good dynamic performance. The strategy has been validated by means of detailed simulations of the system.