Brushless DC motor control under varying load conditions

Abstract

Brushless direct current motors (BLDCMs) are popular in various applications due to their high-power density, wide speed range and control flexibility. They work without brushes and require electronic commutation, where stator's currunt state is synchronized with rotor position. Various methods are used to determine the rotor position. Sensorless method of position detection is preferable instead of external sensors, because external sensors are not cost effective and they create wiring complexity. This thesis presents control methods and driver algorithms for BLDCM under variable load conditions from start-up to continuous run with speed regulation. The inductive sense method, which is one of the sensorless position measurement methods, is used when the motor is stationary and at low speed. The rotor position was accurately calculated by using this method based on inductance differences. Afterwards, back electromotive force (BEMF) sense method was used at high speed.The drive parameters, mainly the step time and excitation step, are adjusted according to the rotor position to drive the motor efficiently. The dynamic control of the drive parameters is done by estimating the load with the rotor position.