a Siadatan - Islamic Azad University, West Tehran Branch, Tehran, Iran
s Ghasemi - Department of Electrical Engineering, Shahid Beheshti University G.C., Tehran, Iran
s.s Shamsabad Farahani - Department of Electrical Engineering, Islamshahr branch, Islamic Azad University, Islamshahr, Iran

In this paper the method of sensorless startup of direct current brushless motor using third harmonic back Electromotive Force (EMF) and motor startup using microcontroller for pulse width modulation, power switch control and motor output analysis is presented which renders RPM control and high speed achievement for motor. The microcontroller is used for processor and metal-oxide semiconductor field-effect transistor (MOSFETs) are used for power circuit. Besides, the motor does not have any sensors to detect rotor position. Furthermore, the microcontroller modulates pulse width, controls power circuit and analyses motor output. The innovation in this research is that the third harmonic function is used for motor control and is compared with the Back-EMF force to recognize zero crossing. Moreover, N-type MOSFETs are used in power circuit high side and low side which are useful in the current rate of MOSFETs due to their similarities. Also, the IR2101 MOSFET drive is utilized for startup which improves the firing time of MOSFETs. Besides, using tantalum capacitors and putting resistor by the gate route of MOSFETs is efficient. Finally, experimental results are given to verify the validation of the proposed method.

Brushless DC Motor,Pulse Width Modulation,Third Harmonic Back Electromotive Force,Zero Crossing,