Adaptive Saturation Controller-Based Direct Torque Control for Permanent-Magnet Synchronous Machines

This paper proposes a novel direct torque control (DTC) scheme for permanent-magnet synchronous motor (PMSM) drives using a relatively low sampling frequency. Unlike the conventional DTC in which a single voltage vector is selected according to the outputs of the hysteresis controllers, the proposed DTC uses nonlinear adaptive-midpoint saturation controllers to regulate the torque and flux tracking errors and determine the durations of multiple voltage vectors which are selected from a new switching table. The proposed DTC naturally inherits most intrinsic merits of the conventional DTC, e.g., fast dynamics, robust to disturbances, no coordinate transformation, etc. Meanwhile, the steady-state torque and flux ripples which afflict the conventional DTC are significantly reduced. Moreover, by adjusting the midpoints of the saturation controllers adaptively, the steady-state torque tracking error, which is a common issue in the DTC schemes particularly when the sampling frequency is relatively low, is fully eliminated. The effectiveness of the proposed adaptive saturation controller-based DTC is verified by experimental results on a 180-W PMSM drive system.