Research On Key Problem Of Permanent Magnet Synchronous Motor Sensorless Vector Control

With small size, high power density, high efficiency, low noise, fast dynamic response, permanent magnet synchronous motor(PMSM) is widely used in marine electrical propulsion, wind power generation and other fields. To improve the security, reliability and economy of the motor control system, the control technique of PMSM without sensor has become a hot area in this field. However there is no control strategy which can be used to estimate the rotor position among the whole speed including low and zero speed without sensors, and now different kind of sensorless control strategy is chosen in different speed range. The essay takes the permanent magnet synchronous motor used in the marine electric propulsion system as the research object, three key issues of full range sensorless control including startup, position identification of high speed and the influence factors for the performance are discussed in detail. The main works and achievements are outlined as follows:1. Based on sliding mode variable structure,the rotor position identification strategy of PMSM is established, in which the information of back electromotive force is used.To weaken the chattering phenomenon caused by the working mechanism of the sliding mode variable structure, a new sliding mode observer and position extraction unit is founded:(1) The concept of quasi-sliding mode observer is introduce by replacing the sign function with the saturation function;(2) Through a combination of low pass filter(LPF)and phase lock loop(PLL),the rotor position is accurately identified without considering the phase delay of the back electromotive force.2. In view of the motor back electromotive force is too small to be extracted effectively under low or zero speed, the startup strategy of I/F is adopted, which realizes the reliable starting of the motor and the controllable adjustable of the starting current. To avoid the mutation of rotor position used in the coordinate transformation when switching from the start-up to the closed loop of identification values, a transition period with speed closed loop, position closed loop with time delay is introduced, avoiding the large fluctuation of the motor speed.3. The factors for the performance of the sensorless control system are studied. The influence of motor parameter deviation on sliding mode variable structure position identification strategy is analyzed emphatically, and then a unified formula for calculating the influence of position identification according to the parameter deviation and stator current when error occurs is obtained. Secondly, the influence of harmonic components in the nonideal sampling current and the delay time of digital control on the position identification error is analyzed.4.Under the circumstance of MATLAB / Simulink platform, Some control algorithms including the position identification of sliding mode variable structure, I/F setup and the influence of parameter error on position identification are carried out. Moreover, they are also run on the hardware platform and the experiment results show the validity of the theoretical analysis and the feasibility of the estimation strategy。...