Closed loop control of a brushless DC motor at nominal speed

摘要

A brushless DC motor control apparatus and method for regulating the speed of a motor at a nominal speed. The apparatus maintains a nominal motor speed without the use of conventional rotor position location devices such as Hall sensors. The current speed of the motor is determined using the back EMF zero-crossing measured only on complete rotor revolutions to mitigate motor dissymmetry errors. A control system compares the current speed to a desired speed and adjusts the total motor current to attain the desired speed. As a result, highly accurate speed control is maintained.