Sensor-less control of a half-wave rectified brushless synchronous motor

The goal of this research is to realize a complete sensorless system which can operate in the whole speed range, from standstill to rated speed, using the “half-wave rectified brushless synchronous motor” we proposed as a novel servo motor. An EMF with bias frequency is induced in the rotor winding of this motor by the MMF which rotates at synchronous speed and pulsates at bias frequency. The field poles are excited by the field current obtained by rectifying this EMF with a diode inserted into the field winding. This motor has a simple and robust brushless structure and is maintenance free. This motor also provides torque control operation over the speed range from zero to the rated speed. If there is any displacement between the axis of rotating MMF and the axis of the rotor, the impedance of the field circuit varies. Therefore, the rotor position can be detected only by measuring bias frequency components of armature voltage. This method provides us with the whole sensorless control (position and speed sensorless) over the speed range from zero to the rated speed