New Permanent Magnet Switching Flux Motor Without Position Sensor Control

Permanent Magnet Flux-Switching Motors (PMFSM ) is a new type of doubly salient motor excited by permanent magnets, developed based on the research of novel doubly salient motors which is evolved from switched reluctance motor. The motor has both coils and permanent magnets in the stator, but not in the rotor, so the structure is very simple and the cost of manufacture is very low. The motor combines the merits of both switched reluctance motor and PM motor, such as high torque density, high efficiency, simple structure, robustness, fault tolerance, etc, and its control method is similar to the conventional Brushless DC Motors.However, in a PMFSM, it is not possible to install inexpensive hall sensors on the stator to detect the rotor position; on the other hand, it is not feasible to install hall sensors on the rotor since a slip ring would be needed which results in low reliability and complex structure. Optical encoder is doable but too expensive. So sensorless control becomes a cheap feasible option.In order to validate the feasibility of sensorless control and the control similarity of PMFSM and BLDCM, a general sensorless controller using the ASIC ML4425 is designed, and is successfully applied to a conventional BLDCM and two novel PMFSMs.In the process of ML4425 controller research, it is found that some motors are difficult to start due to the significant cogging torque. In order to solve this problem, methods of skewing rotor and optimizing slot opening are applied to reduce the cogging torque of PMFSM and BLDCM. The cogging torque is reduced and motors can start successfully.MATLAB Simulink model of PMFSM is designed for further study, which considers the floating phase when the PMFSM is operated in the BLDC mode.A novel sensorless control strategy with initial position estimation is developed, using the unique winding inductance variation with the rotor position. The method is verified with the Simulink model mentioned above.