Research On Field Oriented Control Of Permanent Magnet Synchronous Motor

As an important part of electric drive, the permanent magnet AC servo system plays a more and more significant role in industry, agriculture, aerospace and other fields. The permanent magnet synchronous motor(PMSM) is applied in small-medium power drive occasions in wide range for its excellent performance. In order to improve the performance of the PMSM control system, the magnetic field oriented control methods were analyzed in details. Based on the platform of all-digital PM AC servo control system, the control methods with and without the position sensor under field oriented control have been studied deeply. A hybrid control method was presented, which compensated the shortages of the former methods and improved the control precision of system.The mathematic models of PMSM in three-phase stationary coordinate, two-phase stationary coordinate and two-phase rotating coordinate were analyzed in details. The control theory and realizing methods were analyzed deeply for both vector control and direct torque control, which was the base for the research in the following chapters. Five vector control modes were discussed. The features, applying situations and the characteristic curves of them were compared and analyzed. The influence caused by load angle in DTC and the angle's relationship with torque were analyzed. The dynamic and static performance of the two field oriented control methods were compared by simulation and experiments. The similarities and differences for both were concluded.The application of neural network for vector control was discussed. A compound control that combines CMAC neural network which is applied in robots control in most cases and PID controller was presented to the permanent AC speed-regulation system. The CMAC actualized the feed-forward control and got the inverse dynamic model of controlled target by network training. The conventional PID controller realized the feedback control to guarantee the stability and contain the disturbance. The improved Albus algorithm was applied to accelerate the learning and convergence speed of CMAC. Comparison with simple PID control was given, which proves the design has improved the dynamic and static performance and the robust of the system.A space vector torque control method was presented in this paper, which was essentially a direct torque control based on space vector PWM. The components of stator voltage in two phase rotating coordinate was deduced from the stator voltage calculate model with the detected signals by DTC, which were used to compose the stator voltage. By the continuous modulation of space vector PWM, the discrete modulation method of DTC was avoided and the pulsation of current and torque was remedied. The structure of the space vector torque control was designed. The results of simulation and experiment have proved the validity.The requirement for precision at low speed of servo system is higher and higher today. The performance of low speed is an important indicator for the drive system and should be paid much more attention. The influences from stator current, friction force, slot effect and the control system that affect the performance of low speed were discussed in details. A control method that change the parameters and structure of regulator based on the given speed was designed to reduce the speed ripple caused by the factors above. The influence caused in the course of arithmetic implementation was also compensated. The performance of PMSM at low speed was improved by this means.The methods presented above under field oriented control all depended on the signals from position sensor. Besides this, the field oriented control methods without the sensor were studied also. After the generalization for the sensorless control methods at present time, the rotor initial position detection method was studied by analyzing the detect principle, which is based on the idea of bit by bit changing voltage vector injection. The simulation and experiments were made to prove the validity of the method. The emphasis was put on the research of sensorless control method based on extended Kalman filter (EKF).The recurrence equations of extended Kalman filter were analyzed. And the method was carried out in vector control. Considering the characteristics of direct torque control, different input and output were set and the EKF sensorless control was achieved in DTC. The initial position of rotor was not demanded for extended Kalman filter, which is necessary in direct torque control. The method has realized the estimation of the stator magnetic flux and rotor speed, and improved the correctness of the stator magnetic flux observing as well as the robustness to parameters changing and load disturbing.In this paper, a hybrid control method based on the variation ofβangle was presented to reach higher control precision. Theβangle was defined in vector diagram and theβvalue of max torque was deduced according to the electromagnetic torque equation. Based on this, the relationship of torque, variation of load andβangle was analyzed under the i_d=0 control. The hybrid control structure was designed based on theβangle observation. The control modes of frequency commutation and position commutation were adopted in different situations. The mode of transient control was designed to eliminate the fluctuation caused by the switching. The stable working zone ofβangle was deduced, based on which the switching condition for different modes was studied. The validity was proved by the simulation and experimental results. Based on this, a sensorless control method was presented, which made the system operate at the high-precision frequency commutating mode in most time and change to the position commutating mode when the load was fluctuating. The sensorless control based on EKF in former part was used in the position commutating. The hybrid control presented in this paper was combined well with the sensorless control. This method has improved the control accuracy after removing the position sensor and eliminated the dependence for the detecting and calculating of inaccurate signals at the same time. A new direction for sensorless control was indicated by this method.