Research On Digital Control Method Of PMSM Based On Time Optimal Control Strategy

With the development of modern power electronics and the developments of materials,a high-speed and high-power machine is appearing in some special applications such as electric actuator. Electric actuators are more cost-effective than their hydraulic and pneumatic counterparts. Electric actuators benefit from cleaner, simpler, and more energy-efficient power transmission. Electric actuator integration is easier with programmable controls, and maintenance is minimized with no parts replacement or lubrication needed except in extreme conditions. Recently, domestic research on electric actuation mainly facused on low power DC motor, the permanent magnetic synchronous motor(PMSM) with high power and torque density, high speed and efficiency, will become a trend of electric actuator development inevitably. Therefore the study of high-power electric actuator drive control system has both theoretical and practical significance.This paper mainly researches the key techniques of high-power PMSM in the aspects of the stability of the current regulator at high speed and the high dynamic performance of the current in a wide range of speed. The effectiveness of the proposed method is comfirmed by compuer simulations and experiments on the platform cnstructed with DSP.Firstly, this paper established the mathematical model of PMSM by using complex vector algebia and also by using a matrix algebra. The principles of instanceous torque control, referred to as vector control are described based on dq reference frame theory. And to extend the operating region of electric machine, the capability curve of the machine is further investigated using the flux weakening control concept.Secondly, The instability probelms of the current regulators have been studied analytically by using complex root locus analysis method. In order to enhance the overall performance of the current control loop, the error caused by inherent delay of full-digital implementation of a current regulator is analyzed by using complex vector algebia. A comparative study with conventional methods has been carried out and the proposed method for the error compensation has been verified by using a computer simulation.Thirdly, To improve the current dynamic performance at high speed without degrade the dynamic performance of the current regulator, the time optimal current controller that guarantees the fastest transient response is proposed. The basic concept is to find the optimal control voltage for tracking the reference current with minimum time under the voltage limit constraint. Considering the feasibility of practical application, the improved time optimal conrol method is proposed. Using this method, the reference values of dq currents are modified so that the currents follow the so-called "shortcut" trajectory in the dq coordinate plane. The speed loop is designed based on the proposed current regulator and the effectiveness of the method in the dynamic performance of both current and speed is comfirmed by computer simulations.Finally, The physical experimental setup is constructed based on DSP2808, and the principle of some important circuits are introduced. By using this platform, experiments are given to verify the accuracy and reliability of the proposed methods.