Design Of Control System For Permanent Magnet Brushless DC Motor

The brushless DC motor (BLDCM) is a new style motor that has stator (armature) windings and a permanent-magnet (PM) or salient-pole soft-iron rotor. Permanent-magnet BLDCM has lots of merits, such as high torque, high efficiency, simple control, low maintenance. As the development of power electronics, permanent-magnet materials and new control theories, permanent-magnet brushless DC motors have extensive application foreground in high performance servo and drive areas.This dissertation analyzes in detail on structure and operation principle of permanent-magnet BLDCM. Accurate mathematic model was built simply by using phase variables, and motor characteristics were analyzed. As the same as traditional DC motor, the torque produced by the motor is directly proportional to the current fed by the armature windings and generated voltage at the armature terminals is directly proportional to the motor velocity. Armature reaction and breaking modes are discussed, especially emphasizing flux-weakening control and regenerative braking.Double closed loop PI control strategy was adopted in this control system. Based on the compare of various control modes that are applied on permanent-magnet BLDCM, a DSP-based-control strategy has been put forward. Then the control software and system debug were completed. The design of control hardware included control circuit, current sampling circuit, position detection circuit, drive and inversion circuit. In software design, functional modules and digital PI algorithm have been discussed in detail.The results of experiment show that the control strategy of permanent-magnet BLDCM proposed by this dissertation is correct and feasible. Control system has high reliability as well as excellent control effects. This dissertation offers some theory reference and practical methods for the applications of permanent-magnet BLDCM.