Sensorless vector control of rotary and linear permanent magnet synchronous machines operating at extreme conditions
Permanent magnet motors are known to provide higher torque and better efficiency than induction motors. They have found applications such as propulsion, motion control, traction, etc in industry. To reduce production costs by eliminating the use of position sensor, many sensorless drive schemes have emerged to fulfil this aim. Most of these sensorless algorithms utilise the back-EMF and magnetic saliency of PM motors to predict the rotor position, which is necessary for any closed loop vector controlled drive implementation. At zero or low speed operation, most sensorless schemes failed to perform well because of the inaccuracy in determining the small induced back-EMF. Contrary, at high-speed, the sampling rate of the rotor position must be sufficiently high. Moreover, the stator resistance varies after prolonged operation due to dissipated heat from the motor, which is significant when the motor is loaded and stalled. The author has proposed several sensorless algorithms to tackle these problems. Compensations are made to take account of the non-linearity of the switching devices in the inverter and the effect of dead time phenomenon. Small signal analyses of PM machine models and systems that include the speed and current regulators are carried out to ensure that they are stable for all operating conditions. Simulations and experimental results are presented to demonstrate that the sensorless drives work in practical implementations. Stability analyses are conducted to verify that the proposed sensorless algorithms are stable in both motoring and regenerating regions.