Torque control of a wind power permanent magnet generator in a flux weakening region

In this paper a flux weakening method for a wind power permanent magnet generator is proposed. In a wind energy conversion system, the rotor speed increases with the wind speed, hence a flux weakening (FW) algorithm should be implemented as a part of the control structure in order to prevent generator voltage from exceeding the maximum permissive value. On the other hand, it is essential to provide an accurate torque control in order to maintain an optimum operating point. The proposed FW method is based on the voltage and torque PI controllers which generate the additional current references. While the voltage PI controller ensures operation on the voltage limit, the torque PI controller provides accurate tracking of the torque reference. With the proposed method, the current accurately tracks optimum trajectory which lies on the intersection of the voltage limit and the constant torque curve for the torque reference. Experimental verification was carried out on a 375 kW interior PMG.