Novel, Highly Efficient Algorithm for the Control of Three-Phase Brushless DC Motors

Three-Phase brushless DC motors (BLDC) have become increasingly popular in many fields including industrial controls and remote-control hobby toys. They offer many advantages over their brushed counterparts such as smaller size, longer service life, and increased efficiency; however, one drawback is that commutation must be handled electrically using a controller rather than by a mechanical commutator. Rotor position must be estimated in order to accurately commutate the motor, this is calculated either by sensors (sensored) or by measuring the generated Back-Electromotive Force (sensorless). There are two primary methods of brushless DC motor commutation, trapezoidal and sinusoidal. Both methods have advantages and disadvantages, as well as unique sets of rotor position estimation strategies. This paper will discuss in detail the development of a novel motor control algorithm that employs one method of sensorless trapezoidal control of BLDC motors where the BEMF is integrated after a zero-crossing event, the various challenges associated with direct BEMF measurement, and demonstrate a practical implementation of the new algorithm. Using a robust, high frequency sampling scheme and on-the-fly detection strategies, this new algorithm overcomes many of the shortcomings of similar control algorithms currently available on the market. As a result, this new algorithm provides even more robust control over BLDC motors, increased efficiency, and improved dynamic performance compared to its counterparts while simultaneously requiring little to no additional hardware in practical implementations. Topics investigated include BLDC motors, sensored and sensorless rotor estimation, PWM strategies, terminal voltage sensing, third harmonic voltage sensing and integration, sample timing, switching noise, and current recirculation.