A comparative study of vector-control strategies for maximum wind-power extraction of a grid-connected wind-driven brushless doubly-fed reluctance generator

Abstract

This paper proposes a vector-control technique of a grid-connected wind-driven Brushless Doubly Fed Reluctance Generator (BDFRG) for maximum wind-power extraction under three strategies, summarised as unity power-factor operation, minimum converter current and minimum copper losses. The adopted generator has two stator windings namely; power winding, directly connected to the grid, and control winding, connected to the grid through a bi-directional converter. In addition, a soft starting method is suggested to avoid the employed converter over-current. The first control strategy can be achieved by adjusting the command power-winding reactive power at zero for a unity power-factor operation. However, the second strategy depends on setting the command d-axis control-winding current at zero to maximise the ratio of the generator electromagnetic-torque per the converter current. This enables the system to get a certain command torque under minimum converter current. On the other hand, the third strategy can be realised by determining the control-winding current angle at which the BDFRG can operate with minimum copper losses. A sample of the obtained simulation results is presented to check the effectiveness of the proposed control strategies.