Study on the use of zero voltage vectors in the PMSM DTC system

Effects of zero voltage vectors on the amplitude of stator flux, torque angle and torque of permanent magnet synchronous motor (PMSM) direct torque control (DTC) system are studied. Due to voltage drop on stator resistance, the application of zero voltage vectors decreases the amplitude of stator flux. Due to the move of rotor flux, it decreases torque angle, furthermore, decreases torque. Thus it is wrong to for the switching table for the induction motor (IM) DTC system to use zero voltage vectors to increase the amplitude of stator flux and torque. As the application of zero voltage vectors can´t produce negative torque, when the PMSM operates as a brake, zero voltage vectors may make the DTC system out of order. Simulation and experimental results of the surface PMSM and interior PMSM DTC system are proposed to testify theoretical analysis.