Research and Algorithm Improvement of Permanent Magnet Synchronous Motor Direct Torque Control

Permanent Magnet Synchronous Motor (PMSM) has been widely used in many fields for its advantages of small size, high efficiency, simple structure and low noise. In order to further improve performance of PMSM, it is necessary to do further research of its control strategy. Therefore, this paper mainly studied the direct torque control (DTC) strategy and its improved algorithm of PMSM. In this paper, we first introduce the mathematical model of PMSM and the zero vectors DTC, and then compares the traditional PID controller and the new adaptive PID controller. In order to better explain the problem, this paper makes a comparative simulation of the traditional DTC and the zero vectors DTC and the simulation results are shown in figure 1-8. By analyzing the results, we can find that the simulation that the flux waveform, three phase current waveform, the electromagnetic torque waveform, the speed waveform and the pulse of the DTC control with zero vectors have been improved obviously. In response time, the two can respond more quickly. So, this fully proves the superiority of the zero vector DTC control. And at the same time, we make a comparative simulation of the traditional PID control and the new PID control, and the simulation results are shown in figure 8Figure 11. By analyzing and comparing the simulation results, we can find that the torque and speed pulse of the new adaptive PID controller is smaller, and its response time is shorter, and its anti-interference ability is stronger, and the steady state performance of the motor is improved remarkably. 1.INTRODUCTION Magnetic synchronous motor (PMSM) has the advantages of small size, simple structure, light weight, high efficiency, large torque inertia ratio and so on [1]. Compared with DC motor, it has no brush DC (direct current) motor and the commentator, which avoids a series of problems brought by this. Compared with the induction motor, the PMSM does not need exciting current, so its power factor is high, and the active power loss of the stator resistance is small, and the rotor parameters can be measured, and the control performance is better [2]. Compared with the common synchronous motor, the permanent magnet synchronous motor saves the excitation device, simplifies the system structure and improves the efficiency. Permanent magnet synchronous motor system with advanced control algorithms, such as vector control or direct torque control, can achieve high precision and wide range of speed regulation or positioning control, and its dynamic performance is good. Therefore, permanent magnet synchronous motor has been more and more widely used in various fields [3]. In 1980s, Japanese scholar Takahashi I and German scholar Depenhrok M proposed the direct torque control (DTC) for asynchronous motor for the first time. The control of the motor in the speed control system is essentially the control of the motor torque, and DTC is a direct torque control target, through the use of torque and flux linkage double closed loop structure to obtain fast torque response. It is another important AC speed regulation control strategy after the vector control. The main idea is to select the appropriate stator voltage space vector directly according to the torque and flux linkage of the motor. Compared with vector control, DTC has the advantages of simple structure, fast response, and strong robustness to parameter variation and so on. It is mainly used in the induction motor, and the application of PMSM in the induction motor has to be further studied [4, 5]. Because the method does not need the complex rotational coordinate transformation, the 6th International Conference on Machinery, Materials, Environment, Biotechnology and Computer (MMEBC 2016) © 2016. The authors Published by Atlantis Press 888 parameter dependence of the motor is low, and its robustness is good. Therefore, it has aroused wide attention since it was put forward. Later on the basis of the traditional DTC, a number of improvements have been made, such as adding a zero vector function in the traditional direct torque to reduce the torque ripple in the control process. In this paper, the neural network control is applied to the PID control system, so as to enhance the robustness of the system, further reducing the torque ripple, and improve the steady state performance of the motor. 2.RESEARCH CONTENTS 2.1 PMSM mathematical model The expression of the voltage, torque and stator flux linkage in the and β coordinates of the PMSM is as follows [6]: