Investigation Of High Frequency Signal Injection Based Sensorless Operation For PMSM

Permanent magnet (PM) synchronous motors have been widely used as AC drives over the last two decades due to their high efficiency, high power density and no dc field winding in the rotor. Motion control of PM synchronous motors requires accurate position and velocity signals to realize field orientation. In conventional motion control systems, optical encoders or electromagnetic resolvers are used for this purpose. However, these additional sensors increase the costs of the system and decrease the reliability. With this background, sensorless operation is fast becoming a requirement, the elimination of position and velocity sensors has been an attractive prospect. In last several years, there have been numerous publications on sensorless operation, but most of these techniques only rely on the fundamental machine equations, which limits the low speed and zero speed operation of the machine, and are sensitive to the machine parameters, such as stator inductance and resistance. Thus, the thesis focuses on the sensorless operation in the whole speed region, including zero speed.Firstly, the sensorless methods were divided into two general categories according to the performance at low and zero speeds. All of the methods for sensorless operation in the whole speed region have three basic features: deterministic spatial saliencies, persistent excitation, and noise filtering estimation with high bandwidth.Secondly, based on the saliency tracking idea, two high frequency signal injection methods, i.e. the rotating high frequency voltage or current signal injection and fluctuating high frequency voltage signal injection, were discussed in this thesis. The basic principles of rotor position self-sensing using these high frequency signal injection methods were presented and the simulation models for sensorless vector control systems of a PM synchronous motor were established using two proposed rotor position estimation methods. Comparative study of simulation shows that the saliency-tracking scheme using fluctuating high frequency voltage signal injection possesses simpler configuration and better speed-adjustable performance both in static and dynamic; but it is easier to implement for the saliency-tracking scheme using rotating high frequency voltage signalinjection method.Finally, a experiment system for sensorless vector control operation of a low-power inset-type PM synchronous motor using the rotating high frequency voltage signal injection was developed. Some key techniques in implementation were discussed in detail. The experimental investigation indicates that the rotor position self-estimation scheme, based on the rotor saliency-tracking approach, is capable of precisely estimating the rotor position and speed and the sensorless vector control of PM synchronous motor, using the proposed rotor position estimation method, possesses acceptable static and dynamic performance. Tracking the position of a spatial saliency allows the sensorless method not to be sensitive to parameter variations and to possess good robustness.