Model Predictive Saturation Controller-Based Direct Torque Control of Permanent-Magnet Synchronous Machines

The conventional direct torque control (DTC) for permanent-magnet synchronous machines (PMSMs) uses hysteresis comparators to determine a single voltage vector per control period based on the torque and stator flux tracking errors. The saturation controller-based DTC (SDTC) is a duty cycle DTC strategy that uses nonlinear adaptive midpoint saturation controllers to determine the duration of two active voltage vectors and a zero voltage vector for each control period. A new voltage vector table and the outputs of the saturation controllers determine the duty cycle for each phase. This paper proposes a novel model predictive SDTC (MPSDTC) strategy for PMSMs with low sampling frequency, fast transient response, and low steady-state torque and flux ripples. The MPSDTC uses a computational model of the SDTC to predict the torque, stator flux linkage, current, etc. of the PMSM in the immediate next control period and possibly future control periods. The predicted values are then used to form a cost function that is minimized to find the optimized saturation controller outputs. The MPSDTC has better transient and steady state torque characteristic than the traditional field-orientated control (FOC) or the SDTC.