Studies On Several Problems Of Permanent Magnet Motor Control System

As the development of permanent magnetic materials and advanced control technology, permanent magnet motor draws people's great attention by the advantage of its simple structure, smaller size, light weight, low loss, high efficiency and so on, and is also used more and more widely in industry, agriculture, national defense and daily life. According to the difference between induced electromotive force and drive current of permanent magnet motor, permanent magnet motor can be divided into permanent magnet brushless DC motor (Brushless DC Motor, BLDCM) and permanent magnet synchronous motor (Permanent Magnet Synchronous Motor, PMSM). BLDCM is applied great extensively into electric cars, home appliances and other control fields as the merit of its high power density, simple control and low cost, but also with the disadvantage of bigger torque ripple and large core excess loss. So, its application have much restrict in servo drive system with the requirements of high-precision and high performance (especially in low-speed direct drive occasions). Because of the excellence of its high power factor, fast dynamic response, wide speed range as well as stable operation, greater overload performance and so on, PMSM gradually becomes the main part of the drive motor in modern industrial control systems, but also with relatively complex control system. So, the various problems on PMSM control systems have benn highly concerned. Based on the analysis to the present control models of permanent magnet motor, profound research is carried on the several questions to permanent magnet motor control system in this paper, and the main research results are as follows:1. On the basis of having a explicit description about the structure, working principle, mathematical model, three-phase six-state PWM control mode of BLDCM, the characteristic of five kinds of chopped waves are analyzed and compared. Have given BLDCM out working four quadrants. Based on control method of adopting low-speed energy feedback in braking, a voltage pump-raised circuit is proposed to release excess feedback energy, and the simulation and experiment results both show correctness and feasibility of the circuit.2. Have given PMSM out various of vector control strategies based on rotary coordinates d-q axis. As conventional speed regulator and position regulator cannot meet the characteristic of fast dynamic response to high-performance PMSM, the method of variable structure combined with differential negative feedback as well as variable structure method are introduced respectively into speed regulator and position regulator. The simulation and experiment results both show that the dual variable structure control system can effectively optimize the fast dynamic response of the whole system.3. Taken the mathematical model of PMSM as the starting point, the control method of sensorless permanent magnet synchronous motor is analyzed profoundly. Sliding mode state observer is designed to achieve the estimation of permanent magnet synchronous motor rotor position and speed sensor, conbined with control method of sliding mode variable structure, and the strategy about inductance parameter(Ld,Lq) in dq coordinate system, phase resistance rs and the flux factor (?)f are calculated according to measuring the static three-phase motor inductance and resistance parameters of PMSM. The experimental results show that the method is feasible.4. For the starting difficulties about sensorless PMSM, steady-state model of PMSM is established to realize the estimation of low speed rotor position and velocity so as to complete permanent magnet synchronous motor starting process. This method can effectively achieve steady start of sensorless permanent magnet synchronous motor with a simple algorithm, starting current, switching smooth, high reliability, and experimental results show that the method is correct and effective5. For the probem of sliding mode shaking about using sliding variable structure to realize permanent magnet synchronous motor sensorless vector control, Kalman filter is applied at the output of EMF. Then, sign switching function sign(s) is replaced by saturation function sat(s), so as to make sliding observer-EMF waveform become more smooth and accurate, and also more suitable for high performance applications. Smulation results show the method is correct and feasible.