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Communications in Control Science and Engineering (CCSE) Volume 3, 2015
Design of Fuzzy Double-hysteresis-loop DTC System for New Type TFPM Xiaoqing Yuan*1, Zongyang Yu2 College of Mechanical Engineering, Northwestern Polytechnical University, P.O.Box:403, Xi’an, China 710072
1,2 *1
yuan@nwpu.edu.cn; 2815989042@qq.com
Abstract Transverse flux permanent-magnet motor has the advantages of high torque density. However, because of its own structural defects, the traditional direct torque control has the problem of torque fluctuations, especially at low speed, so it is not available for the control system of TFPM. Analyzing the motors mathematical model, we can conclude superiority of zero vector. So in this paper we take the place of traditional flux and torque hysteresis controller with new double hysteresis loop controller respectively. And then we use fuzzy logic method to improve the controller’s performance. We build system simulation models to compare three methods’ advantages. The research results show that the new fuzzy double hysteresis loop control system has a high precision and a better speed respond characteristic. And at the same time it reduces system torque fluctuations and improves the low speed performance. Keywords Transverse Flux Permanent-Magnet Motor; Zero Vector; Double Hysteresis Loop; Fuzzy Logic
Introduction Transverse Flux Permanent-Magnet Motor (TFPM) is a kind of motor of which the main flux magnetic circuit is distributed in three-dimensional space. And it is characterized by low speed and high torque density (Shi et al., 2013), which has a strong adaptability in low speed direct drive. The structure and control system design of the TFPM is becoming the hot spots in the present research. Direct Torque Control (DTC) is a kind of motor control theory which can be applied to the weak magnetic speed regulation. Its control idea is novel, with efficient control performance and simple system structure. But there are also some technical defects, for example: the torque pulsation fluctuates seriously, the performance of low speed is poor (Zhang et al., 2011; Xia et al., 2014). The traditional DTC system is no longer suitable for TFPM because of the characteristics of low speed and large torque. A new kind of double six-phase TFPM is proposed with analyzing its mathematical model and working principle. And the improved DTC system which is more suitable for the new type TFPM is designed. In this paper, the theory that zero vector can effectively reduce the torque ripple and improve the performance of the system is put forward after analyzing. A new zero vector combining scheme is proposed, which is based on double hysteresis control of the stator flux and torque, replacing the original single hysteresis loop. On this basis, fuzzy logic is combined with double hysteresis loop. And at last it forms a new fuzzy double hysteresis control system which can be used for TFPM specially. The simulation results show that the fuzzy double hysteresis control system has good response characteristics, high control precision and strong robustness. It can effectively improve performance of the control system of double six-phase TFPM. Motor Model Design and Zero Vector Analysis Structure and Operational Principle for TFPM In this paper, a new type of double six-phase TFPM mechanism is presented. The new motor has multi-phase composite structure. It can be divided into two modules with twelve phases in all. Each module is composed of two stator units and a rotor disk unit. And each stator unit is equipped with three-phase winding which has a phase difference of 120 degree. The two modules should be staggered with a certain mechanical angle for assembly. A 3D model of one module is shown in Fig. 1 (Su, 2014). 40