Research On Control Strategy Of High-performance Permanent Magnet Synchronous Motor

Due to the advantages such as high efficiency, small size, light weight,Permanent Magnetic Synchronous Motors (PMSM) has been widely applied in manyindustrial areas.Recent years, with the rapid development of power electronics, motormanufacturing technology and modern motor control theories, domestic technologiesof permanent magnet motor and corresponding drive controller hardware areprogressively getting mature. However, advanced control technologies whichinvisibly exist in control chips have become bottlenecks restricting the developmentof high-performance permanent magnet motors in our country. Therefore,researches in high-performance motor control technology with independentintellectual property rights, especially in the most promising permanent magnet motorcontrol technology, which is currently the research focus in domestic motor controlfield. Against this background, in order to improve the performance of permanentmagnet synchronous motor control, studies of operation conditions of permanentmagnet synchronous motors under normal load and special load have been conductedin this paper. Directed at the shortcomings exist in traditional control algorithms, anew control strategy has been proposed, the validity and usefulness of these strategieshave been verified by simulation and experiment.The main results of research and innovation of this paper are as follows:(1) A mathematical model of permanent magnet synchronous motor via spacevector method has been established, and on the basis of this model, studies ofmaximum torque current control methods in vector control have been conducted.For the contradiction in accuracy and dynamic response speed of traditional look uptable method, a new control algorithm based on curve analog of maximum torquecurrent has been proposed. First, according to the basic theory of maximum torquecurrent control algorithm, constraint relations between electromagnetic torque andcurrent component have been established, and iterative method has been utilized forobtaining the optimal solution. Then a curvilinear relationship betweenelectromagnetic torque and current component is obtained by numerical analysismethod. According to the characteristics of the curve, considering the controlaccuracy, difficulties of calculation and complexity of the DSP implementation, thecurve is divided into three segments to conduct mathematical analog. The maximum number power of each function is2, and those2-functions have been applied toanalog the relationship curve. Instead of discrete spots of traditional look up tablemethod, the control process has been simplified and the performance of system hasbeen improved.(2) Through the study of direct torque control method of permanent magnetsynchronous motor, the shortcomings existed in traditional control algorithms havebeen discovered. In order to solve these problems, a direct torque control algorithmsbased on adaptive model reference has been proposed. For the shortcomings of highsystem cost and low stability, the adaptive model reference of control theory has beenapplied to identify the speed of permanent magnet synchronous motor. Thus,position encoder could be left out, not only has the system reliability been improvedbut the cost has been reduced.As for the relatively large estimating error of stator flux conducted byconventional voltage stator method, a method to estimate stator flux by rotor positionand stator current has been used in the new control algorithm, velocity impact little tothis method, and the accuracy of estimates could be improved. Due to the frequencyof inverter switching is not constant, dual PI controller has been used algorithminstead of double hysteresis controller in traditional algorithms, and the switchingfrequency has been fixed by the use of voltage space vector modulation method.By optimizing the corresponding link, the performance of permanent magnetsynchronous motor direct torque control could be effectively improved by new controlalgorithm.The frequency converter is mainly applied for AC motor speed regulation, and isalso an ideal solution. However, the high-frequency common-mode voltageproduced by frequency converter has become important factor hindering developmentof permanent magnet synchronous motor control system. Common voltage sourcePWM converter has been taken as example, based on the common-mode voltagegeneration mechanism, according to the feature that common-mode voltage is set by aseries of specific frequency harmonics, a new control strategy using the quasiresonant controller for suppressing the common-mode voltage has been proposed.Because the gain at the resonant frequency is infinite, zero steady-state error controlfor the sine signal with the same frequency can be realized. The resonant controllerhas been connected to the conventional PI controller, the high-amplitude part of thecommon-mode has been compensated, and the common-mode voltage has beensuppressed. With the widely using of the Permanent magnetic synchronous motors (PMSM)on refrigerant system, how to suppressing the low-range of speed ripple of the PMSMis coming to the focus. In order to improve the permanent of magnet synchronousmotor driving compression refrigeration system at low speed operation condition, aproportion based on sliding mode observer resonant control strategy has beenproposed in this paper. When the compressor is running in stable condition, itconnects the traditional PI controller with a variable frequency resonant controller.In this way, an adaptive proportional-resonant controller has been formed up. Thusthe reference torque current is mainly constituted by the reference current generatedby PI controller together with compensation current generated by resonant controller.As for the role of the compensation torque current, it enables the electromagnetictorque a better track of the load torque and speed to achieve the ripple suppression.When the compressor is running in variable conditions, in order to reduce theinfluence of the mutation load torque to permanent magnet synchronous motor controlsystem, and improve the system disturbance rejection performance, sliding modeobserver has been used to observe the load torque and conduct a feed forwardcompensation by the observed torque to overcome the influence of torque transients tothe speed control characteristic.The control methods mentioned in chapter3,4and5have been tested in a2.5kWPMSM experimental platform. Chapter6is researches of PMSM applied incompression system; an experimental platform has been established for test.