电动机英文文献.doc

Sensorless Brushless dc Motor Using the MC68HC908MR32 Embedded Motion Control Development System Motorola’s MC68HC908MR32 (MR32) microcontroller (MCU) is specifically designed for motor control applications. The MR32 is suitable for ac induction motors as well as brushless dc (BLDC) motors. The pulse-width modulator motor control (PWMMC) module can be configured to control brushless dc (BLDC) motors using several different PWM strategies. BLDC motors are being designed into many applications that require fractional horsepower, highly efficient, variable speed motors. Brushless dc motors have several advantages over other motor types. For instance: ? Because BLDC motors do not have brushes to wear out, they have a longer life and greater reliability than normal brushed dc motors. ? BLDC motors offer performance similar to dc motors with a high starting torque and a high no-load speed. ? BLDC motors typically have a higher efficiency than ac induction or switched reluctance motors. The permanent magnets used in the rotor means that less energy is wasted in rotor losses. BLDC motors require electronic control. Some BLDC motors use Hall effect sensors to provide absolute position sensing. This results in more wires and higher cost. Sensorless control eliminates the need for Hall effect sensors, using the back-EMF (electromotive force) of the motor to estimate the rotor position. Sensorless control is essential for low-cost variable speed applications such as fans and pumps. Refrigerator and air conditioning compressors also require sensorless control when using BLDC motors. Using Hall effect sensors inside a compressor is not practical because the environment is not suitable and the number of electrical connections would be problematic. Also, compressors are difficult to start and are perhaps the most demanding sensorless BLDC application. The motor must achieve high torque on the first rotation to overcome the piston compression. The MR32 is a new member of the low-cos