| Permanent Magnet Synchronous Motor (PMSM) is widely applied in different domains such as numerical controlled machine tools and industrial robots because of its high power density, high torque/inertia ratio, high efficiency and free maintenance. Vector control is a popular method to the PMSM servo system whose purpose is to improve the performance of the torque control of the motor. But this method is complex to implement as to its flux weakening and sensor-less technology. Direct torque control (DTC) finds another way to solve those problems, which is firstly proposed for induction motor and applied hi the PMSM in recent years. This method is a novelty to PMSM and its good transient characteristic absorbs many researchers.This paper focuses on the direct torque control in the Synchronous motor especially in the PMSM including improved method and new scheme of DTC, flux weakening operation and sensor-less technology. This paper also sets out to simulation research of the DTC method in Electrical-Magnet Synchronous Motor.A variable-speed DTC PMSM system is set up to verify the DTC theory in PMSM, that is to control the toque by controlling the torque angle of motor if the stator flux linkage keeps constant. This paper points out the function of the space voltage vector by which the torque angle can be changed according to the need of torque of the motor. The zero-voltage vector, whose function is to keep the output torque unchanged, is applied to a switching table to minish the ripple of the torque and improve the performance of the steady characteristic of the system.The initial scheme, in which the stator flux linkage is kept constant, has a low efficiency and a lot of reactive current when the load is light and system is in the steady operation. So a new scheme, which changes the amplitude of stator flux linkage according to the load of the system, is proposed to improve the efficiency of the motor. Compared with constant flux linkage DTC, the proposed scheme has higher efficiency in the steady operation with light load and the change of flux linkage gives less influence on the transient response.The DTC system with constant stator flux linkage has good transient and steady characteristics.The available speed range is l:100.The low speed reaches 20rpm.The speed response time is about 190ms,which speed changs from 0 to 1450rpm without load.The torque step response time is lms,that torque changs from 0 to rating torque 5N.m.The flux weakening operation is applied the PMSM system to extend the speed range of this variable-speed system. A prototype motor is Surface-mounted PMSM. The simulated and experimental results verify the availability of the proposed scheme. In the flux weakening operation the system controls the torque of motor through the torque anglewhich is the same principle of DTC in the constant torque operation. Therefore, the transform of two operations is smooth and easy. On the other hand, the application of the space voltage vector can realize the maximum utilization of the bus DC voltage of the inverter.The sensor-less technology is also discussed in this paper. The rotor position is open -loop controlled in the DTC system. The speed information can be acquired from the stator flux linkage and the inverter drive signal comes from the switching-table through the comprehensive consideration about the torque status, flux linkage status and the position sector of the stator flux linkage. So the estimation of the stator flux linkage is most important to the sensor-less Synchronous Motor system. This paper applied many methods to eliminate the estimation error of the flux linkage. Finally, a sensor-less DTC PMSM system is implement and has a good performance.Few research refers to the DTC in Electrical Magnet Synchronous Motor(EMSM). This paper analyses the characteristic of DTC in this kind of motor and simulates the scheme of this motor without the damper winding. The operation, which expects the power factor of the motor equals to l,can be realized in DTC EMSM system by a...
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