Centralized Reactive Power Control for a Wind Farm under Impact of Communication Delay

Abstract

Generally, a wind turbine may have inferior reactive power dynamic performance where constant power control is adopted by a wind farm equipped with doubly fed induction generators (DFIGs). As a result, power system disturbance may incur grid faults where the wind farm cannot provide enough reactive power to the grid. This paper proposes a novel reactive power control strategy with centralized management for a wind farm. The real-time signal representing the voltage at a specified remote location -- a point of common coupling (PCC), is taken into account as an increment of the given value of the reactive power before being transmitted into each wind turbine by the distributed communication networks. In order to implement real-time regulation with reactive power output to the entire wind farm, this signal is meanwhile fed into the control loop in the rotor-side converter. Considering the issue of widely geographical distribution for each individual wind turbine, this paper studies the impact of communication delay on the system performance. As simulation results showing, in both of the cases of grid faults and wind speed fluctuation, the system with this control strategy can provide reactive power complement and keep the bus voltage stable. By using frequency domain analysis, this research also explores that different delay time may result in control failure due to multi-frequency harmonic incurred in the cases of long-term delay.