Performance Improvement Of Brushless Dc Motor

Recently, the permanent magnet Brushless DC motors is becoming popular in various applications. This is mainly due to the availability of low cost power electronic control devices and the improved permanent magnet characteristics, moreover to its high output power to frame size ratio, low rotor inertia, high dynamic response, less maintenance and compact size favour the application of these machines in electric vehicles also. However, the motor has a disadvantage of high cost compared with the direct current motor because it is necessary to use solid-state power semiconductors and rotor position sensors to remove brushes of the DC motor.This thesis illustrates the construction of the brushless DC motor. The motor is composed of stator, which is divided into six cylindrical poles. Each two opposite poles give one phase of the three-phase motor. Also it discusses its theory of operation, and it includes a number of proposed drive circuits which can be used to drive the motor.In this thesis, the effect of rotation speed variation on the instantaneous motor characteristics are introduced, the effect of the supply voltage variation and back EMF constant variation on the average motor characteristics are also introduced.