Brushlesss dc (BLDC) motors and their drives are penetrating the market of home
appliances, HVAC industry, and automotive applications in recent years because of theirhigh efficiency, silent operation, compact form, reliability, and low maintenance.Traditionally, BLDC motors are commutated in six-step pattern with commutationcontrolled by position sensors. To reduce cost and complexity of the drive system,ensorless drive is preferred. The existing sensorless control scheme with theconventional back EMF sensing based on motor neutral voltage for BLDC has certaindrawbacks, which limit its applications.In this thesis, a novel back EMF sensing

scheme, direct back EMF detection, forsensorless BLDC drives is presented. For this scheme, the motor neutral voltage is notneeded to measure the back EMFs. The true back EMF of the floating motor winding canbe detected during off time of PWM because the terminal voltage of the motor is directlyproportional to the phase back EMF during this interval. Also, the back EMF voltage isreferenced to ground without any common mode noise. Therefore, this back EMF sensingmethod is immune to switching noise and common mode voltage. As a result, there areno attenuation and filtering necessary for the back EMFs sensing.This unique back EMF sensing method has superior performance to existing methodswhich rely on neutral voltage information, providing much wider motor speed range atlow cost.Based on the fundamental concept of the direct Back EMF detection, improvedcircuitry for low speed /low voltage and high voltage applications are also proposed inthe thesis, which will further expand the applications of the sensorless BLDC motordrives.Starting the motor is critical and sometime difficult for a BLDC sensorless system. A practical start-up tuning procedure for the sensorless system with the help of a dctachometer is described in the thesis. This procedure has the maximum accelerationperformance during the start-up and can be used for all different type applicationsAn advanced mixed-signal microcontroller is developed so that the EMF sensingscheme is embedded in this low cost 8-bit microcontroller. This device is truly SOC(system-on-chip) product, with high-throughput Micro core, precision-analog circuit, insystem
programmable memory and motor control peripherals integrated on a single die.
A microcontroller-based sensorless BLDC drive system has been developed as well,
which is suitable for various applications, including hard disk drive, fans, pumps,blowers, and home appliances