Brushless dc motor control

Abstract

A method and control system to control a brushless DC motor to a preferred position is provided. The advantages that accrue to a system employing the method and apparatus to control the brushless DC motor to a preferred position include optimizing response time, energy usage, coil heating, and ability to hold to a fix position. The method to control the brushless DC motor to a position comprises monitoring actual position of the brushless DC motor, monitoring energy used by the brushless DC motor, and determining a commanded position of the brushless DC motor. A zero torque commutation method is employed to control the brushless DC motor to the commanded position only when a time-rate change in the commanded position is less than a first threshold, a difference between the commanded position and actual position is less than a second threshold, and, the monitored energy used is less than a third threshold. A peak torque commutation method is employed to control the brushless DC motor to achieve the commanded position when the time-rate change in the commanded position is greater than the first threshold, the difference between the commanded position and actual position is greater than the second threshold, or the monitored energy used is greater than the third threshold.