| Brushless dc (BLDC) motors and their drives are penetrating the market of home appliances, HVAC industry, and automotive applications in recent years because of their high efficiency, silent operation, compact form, reliability and low maintenance. Traditionally, BLDC motors are commutated in six-step pattern with commutation controlled by position sensors. To reduce cost and complexity of the drive system, sensorless drive is preferred. The existing sensorless control scheme with the conventional back EMF sensing based on motor neutral voltage for BLDC has certain drawbacks, which limit its applications.In this thesis, a back EMF sensing scheme, direct back EMF detection, for sensorless BLDC drives is presented. For this scheme, the motor neutral voltage is not needed to measure the back EMFs. The true back EMF of the floating motor winding can be detected during off time of PWM because the terminal voltage of the motor is directly proportional to the phase back EMF during this interval. Also, the back EMF voltage is referenced to ground without any common mode noise. Therefore, this back EMF sensing method is immune to switching noise and common mode voltage. As a result, there are no attenuation and filtering necessary for the back EMFs sensing.This unique back EMF sensing method has superior performance to existing methods which rely on neutral voltage information, providing much wider motor speed range at low cost.It will further expand the applications of the sensorless BLDC motor drives.Controller hardware circuit design, which include power supply module, power drive circuit, voltage current detection, control, signal detection, over-current protection circuit, etc. Finally, we test the system, and modify the problems existing in the design. |
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