Research On The Position-Sensorless Control Strategy Of Pmsm At Full Speed Range

Sensorless control of permanent magnet synchronous machines (PMSMs) was a hot issue in the area of electrical machine controls in recent years. Different control strategies and position-or speed-sensorless algorithms had been studied into details. This thesis mainly studies the PMSM control strategies and sensorless algorithms from the viewpoint of system integration. According to the requirements of the specific application, proper integration of control strategies and sensorless algorithms is proposed to realize a sensorless operation at full speed range. Experimental verifications were carried out on both a pump-used testing platform and an air-conditioning compressor system. The main researches and innovations of the thesis are on the following areas:1. Two conventional initial-rotor-position orientation methods are introduced, which are: the pre-orientation method and the position identification method based on voltage pulses injections. The inherent principle of the voltage pulses injection estimation process is studied, and the performance with respect to the estimation accuracy is considered as well. Based on the given accuracy solution, a new modified five-pulses voltage injection method is proposed, which imporves the estimation accuracy significantly.2. The self-starting strategy with speed-open-loop and current-closed-loop processes is studied, which is also called the I/F control. The startup process with respect to the torque-versus-power angle relationship is deduced, which is named as the principle of self-stabilization. The rule for self-stabilization is proposed, as well as the requirements that ensure the startup procedure successfully. It is a guidance to design the system parameters during acceleration.3. The transient process from the speed-open-loop current-closed-loop state to the double-closed-loops state is studied in details. A novel method is proposed to ensure a smooth and stable transition which is based on a decreasing process of the current amplitude. The design rule of the key state-parameters is given. Combined with the I/F starting process and the transition process, this strategy can realize a smooth and robust self-starting, which is suitable for all types of PMSMs under different load conditions, with very few paremeters to design. 4. The dynamic performance and rubostness of the back-EMF based sensorless control of PMSM is tested and verified by experiments. Then the influence on back-EMF based sensorless control of PMSM due to parameter variations and measurement errors is studied. The analysis consists of the influence of resistance and inductance variations due to temperature and flux saturation, current and voltage errors due to measurement uncertainties, and signal delay caused by softwares. It is found that the most significant impact of estimation error is caused by the sofeware delay and dq-inductions error. The corresponding useful compensation methods are provided.5. The performance of the flux observer and speed observer in the vector control strategy is analyzed. Some effective methods to eliminate the zero drift of pure integration in flux observer are discussed, and the method to reduce speed oscillations in speed observer is discussed as well. Furthermore, the rules of designing PI parameters of speed loop and current loop are deduced.Finally, a PMSM sensorless system used in variable-frequency air conditioner compressor is built to verify those theroies proposed above. The experimental platform including hardware and software designs are introduced and the method to test important machine parameters are given. The performance of the air conditioning system using proposed all-speed-range sensorless control strategy is tested, such as the stability and efficiency. The unique phenomenons and causes during the startup, transition and normal running processes are analyzed as well.