Study Direct Torque Control Of Brushless DC Motor With Sensorless

With the development of power electronics technology and ceaseless advance of permanent magnet material, the high performance MCU and digital signal processors (DSP) have made great development at full speed and their cost-performance ratio have been rising constantly. Brushless DC Motor (BLDCM) is appealing candidates for many high performance motion control applications. Their popularity is justified by several advantages over commonly used motors in these applications, such as highly efficient, high power density and rapid dynamic response. Beside these, the absence of the external rotor excitation slip rings on the rotor and brushes obsolete, eliminates the commutation spark, makes the BLDCM more suitable for these applications with very strict conditions, but BLDCM have biggish torque ripple, so in these strict occasions, the smoothness of torque is requested. So in BLDCM control system, the minimization of torque ripple must be considered. The use of sensorless control reduces the size of BLDCM, lowers its costs and reinforces its interference immunity, thereby widening its application areas. As a consequence, the research on position-sensorless control for BLDCM has been a hot spot all along in recent years.The state-of-art and some general control methods of BLDCM are firstly discussed. The operating principle and composition of BLDCM are illustrated, nd its mathematical model is analyzed. This paper successfully realized sensorless control system of BLDCM by adapting the back-EMF (back eletromagnetic force) zero-crossing detection menthod. Based on the mathematical model of BLDCM, this paper systemiclly proposed BLDCM DTC strategy and discusses DTC considering the features of BLDCM. The control scheme is designed in detail both in aspect of hardware and software. And Variable Structure Sliding Mode (VSSM) applies to BLDCM successfully. The VSSM made up the shortage of DTC and enhance the performance of BLDCM better. Simulation studies show that the direct torque control scheme can effectively inhibit the brushless DC motor torque ripple. Last a DSP based control system is designed for experimental use.