Zero Voltage Vector Selection in a Saturation Controller-Based Direct Torque Control for Permanent-Magnet Synchronous Motors

This paper analyzes the effect of zero voltage vectors on the torque and stator flux of a direct torque controlled salient-pole permanent-magnet synchronous motor (PMSM). Four different schemes of using the zero voltage vectors are studied for an adaptive saturation controller-based direct torque control (DTC) system for salient-pole PMSMs. The four schemes generate four different pulse-width modulation (PWM) waveforms in each control cycle of the DTC system, which are three-voltage-vectors-based minimum discontinuous PWM (DPWMMIN), maximum discontinuous PWM (DPWMAX), and discontinuous PWM (DPWM), and four-voltage-vectors-based continuous PWM (CPWM). Compared to the DPWMMIN, DPWM, and DPWMMAX, the CPWM can achieve a lower torque ripple, less steady-state torque error, and more sinusoidal stator current with a higher switching frequency and, therefore, has a higher switching loss of the power converter. The effect of different zero voltage vector selection schemes is verified by both simulation and experimental results for a 200-W salient-pole PMSM drive system.