A discrete-time direct-torque and flux control for direct-drive PMSG wind turbines

This paper proposes a novel discrete-time direct-torque and flux control (DTFC) scheme for a permanent-magnet synchronous generator (PMSG) used in a variable-speed direct-drive wind power generation system. The proposed DTFC does not rely on machine parameters, such as the inductances and permanent-magnet flux linkage, while the main advantages of the DTC, e.g., fast dynamic response and no need of coordinate transform, are preserved. The stator flux linkage is estimated by an adaptive low-pass filter (LPF), in which a variable cutoff frequency is used. The adaptive LPF stator flux observer can achieve high estimation precision over a wide operating range of the PMSG. A space-vector modulation (SVM) module is integrated into the control scheme of the PMSG to achieve a fixed switching frequency as well as lower flux and torque ripples when comparing with the conventional DTC. The overall control scheme is simple to apply and is robust to parameter uncertainties and variations. The effectiveness of the proposed discrete-time DTFC scheme is verified by simulation and experimental results on a 2.4-kW PMSG used in a variable-speed direct-drive wind turbine system.