Position sensorless direct torque control for six-phase permanent magnet synchronous motor under two-phase open circuit

A position sensor is usually required in the existing fault-tolerant direct torque control (FT-DTC) system for the multiphase permanent magnet synchronous motor (PMSM). Thus, the volume, weight, and cost of the system is increased, and the reliability is decreased. The conventional high-performance position sensorless strategies for the multiphase motor under fault-free condition cannot be directly applied to FT-DTC system. To improve this situation, a high-speed position sensorless FT-DTC strategy for a six-phase symmetrical winding PMSM with two opened phases is proposed in this study. Firstly, modified variables and a new rotating coordinate system are defined to achieve the symmetrical and decoupled mathematical model. Secondly, a stator flux observer based on the modified variables and a new coordinate system is proposed. According to the current model of modified stator flux, the estimated modified stator current can be achieved. Then, the estimated error of the modified stator current is sent to the integrator of the modified stator flux observer to correct the voltage model. Finally, the proposed stator flux observer is applied in FT-DTC for six-phase PMSM with two opened phases to realize the position sensorless operation at high speed. The experimental results verify the feasibility and effectiveness of the proposed strategy.