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Introduction 1.1 Background research In recent years, with the development of electronics technology, microelectronic technology, micro-computer technology, sensor technology, rare earth permanent magnetic materials  and motor control theory, AC servo control technology has made great strides. AC servo system has been gradually replacing the DC servo system a foregone conclusion [1]. With the development of modern control theory and the aid of computer technology, it is possible to constitute a high-precision, fast response AC servo drive system. Thus, in recent years, countries around the world in high-precision speed and position control applications, have been replaced by hydraulic drive via AC and DC power transmission. Since the 1980s, along with inexpensive permanent magnet materials appear, the permanent magnet synchronous motor has been greatly developed in countries all around the world, led by Germany and Japan set off a wave of development and production of permanent boom magnet synchronous motors and servo controllers, CNC[2] machine tools, industrial robots and other low-power applications. The permanent magnet synchronous motor servo system is the main trend. Permanent magnet synchronous motor control technology has also matured and is still maturing. Conventional synchronous motor concept and application range today have been greatly expanded permanent magnet synchronous motors.
There is no exaggeration to say that the permanent magnet synchronous motor is either small or large, from the general to the drive control precision servo drive, from daily life to a variety of sophisticated science and technology as the main drive motor occurs. And the prospects will become increasingly apparent.  Since the permanent  magnet synchronous motor has a simple structure, small size, high efficiency, torque current ratio, the amount of low moment of inertia, easy to heat and maintain the advantages. Especially with the decline in the price of permanent magnet materials. The permanent magnet machine causes the favor of many research and development staff and the emergence of a new type of permanent magnet materials, in a small and medium-power, high-precision, high reliability, wide speed range servo control system[3], Especially in the case of aerospace, CNC machine tools, machining centers, robots have been widely applied.  Although the permanent magnet synchronous motor control technology has been greatly developed. And a variety of Japanese control technology has gradually matured, such as SVPWM, DTC, SVM-DTC[4], and so adaptive methods applied in practice. However, in practice, various control strategies have some shortcomings, such as low-speed characteristics, too dependent on motor parameters, etc. Therefore, the control  strategy research on the problems has great significance. This study is based on this project.
1.2 Research status Motor control technology is the core of the servo drive control. From the history of the development point of view, the development of motor  control is closely related to the motor technology, power devices, microelectronic devices, sensors, micro-computers and control theory. The initial servo system in the United States was born artillery aiming at servo system. Since then, with the development and progress of science and technology production, servo system has made great progress. In 1971, German scholars have proposed new ideas, new theories and new technologies transform AC motor vector control. It appears on the epoch-making significance for AC motor control technology. Because of this vector by converting alternating magnetic field orientation constitutes a closed loop control system, control performance can be comparable with the current system. Vector control in electromechanical energy  conversion, and space vector motor unified theory developed based on the theory. It first applied three-phase induction motor, and soon expanded to a three-phase permanent magnet synchronous motors. Since the three-phase induction motor is running, the heat will cause the rotor parameters change. And the observed dependence of the rotor field in the rotor parameter is difficult to accurate observation, so that the actual control is difficult to achieve the effect of the results of theoretical analysis, which is the vector control practice deficiencies. Therefore the vector control of permanent magnet synchronous motors are widely used in low-power and high-precision applications. Vector Control Simulation of Surface- mounted Permanent Magnet Machine(2):http://www.youerw.com/yingyu/lunwen_41335.html