The Design of Brushless DC Motor Systems

In critical applications requiring use of a brushless dc motor, the electronics designer is faced with a complex problem. The motor typically has at least five independent parameters that must be specified properly to obtain the best performance. The gear ratio must be selected, and in addition, several parameters in the electronic commutation and control circuitry must be optimized. In this paper the basic control problem is described, the appropriate equations are derived, and a systematic method is outlined for arriving at an optimum configuration. It immediately becomes apparent that all applications and possible motor types cannot be covered by the same analysis. However, the results of this paper should be useful in most small motor applications in which the motor speeds are sufficiently low that motor winding inductance can either be neglected or compensated simply by advancing the drive pulse phase as described.