Direct torque control (DTC) technology in asynchronous motor is one of new frequency transformation drive technology after the vector control technology. In recent years people begin to apply it to the synchronous motors. This paper introduces the application station of direct torque control in permanent magnet synchronous motor drives, discusses several key problems and analyses its development direction in the future.

With the widely use of Permanent Magnet Brushless DC Motor (BLDCM) in many fields, the superiority in the control method of position sensor-less is more and more obvious. In this paper several control methods of position sensor-less for BLDCM are presents, and a novel technique, the method of speed-independent position function, is introduced to detect the rotor position of BLDCM. This method may detect the rotor position from almost zero speed to high speed, and may also give the commutation time.