A Flux Vector-Based Discrete-Time Direct Torque Control for Salient-Pole Permanent-Magnet Synchronous Generators

This paper proposes a flux vector-based discrete-time direct torque control (DTC) scheme for salient-pole permanent-magnet synchronous generators (PMSGs) used in the variable-speed, direct-drive wind energy conversion systems (WECSs). The discrete-time control law is derived from the perspective of flux space vectors and load angle with the torque and stator flux information only. The saliency of the PMSG is eliminated by the active flux concept. Compared with the existing space vector modulation (SVM)-based DTCs, the proposed scheme removes the use of PI regulators and is less dependent on the machine parameters, e.g., stator inductances and permanent-magnet flux linkage, while maintaining the fast dynamic response of the system. By integrating the SVM into the control scheme, the torque and flux ripples are greatly reduced and the switching frequency becomes fixed. The effectiveness of the proposed DTC scheme is verified by real-time simulations implemented on an OPAL-RT real-time simulator and experimental results for a 180-W salient-pole PMSG used in a direct-drive WECS.