Design and Construction of a Sensorless Circuit for Brushless DC Motor using Third Harmonic back Electromotive Force


1 Department of Electrical Engineering, West Tehran Branch Islamic Azad University, Tehran, Iran

2 Department of Electrical Engineering, Shahid Beheshti University G.C., Tehran, Iran

3 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 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.


1.     Afjei, E., Hashemipour, O., Saati, M. and Nezamabadi, M., "A new hybrid brushless DC motor/generator without permanent magnet", International Journal of Engineering Transactions B Applications,  Vol. 20, No. 1, (2007), 77-86.

2.     Hemalatha, N. and Baskaran, J., "Position sensorless control of permanent magnet brushless DC motor".

3.     Yoon, Y.-H., Lee, T.-W., Park, S.-H., Lee, B.-K. and Won, C.-Y., "New approach to rotor position detection and precision speed control of the BLDC motor", Industrial Electronics, IECON 2006-32nd Annual Conference, IEEE., (2006), 1305-1310.

4.     Mohammed, M.F. and Ishak, D., "Improved BLDC motor performance with digitally filtering back-EMF using dsPIC30F microcontroller", in Research and Development (SCOReD), IEEE Student Conference on, IEEE., (2009), 491-494.

5.     Kim, T.-S., Park, B.-G., Lee, D.-M., Ryu, J.-S. and Hyun, D.-S., "A new approach to sensorless control method for brushless DC motors", International Journal of Control, Automation, and Systems,  Vol. 6, No. 4, (2008), 477-487.

6.     Shen, J. and Iwasaki, S., "Sensorless control of ultrahigh-speed PM brushless motor using pll and third harmonic back EMF", IEEE Transactions on Industrial Electronics,  Vol. 53, No. 2, (2006), 421-428.

7.     Vanisri, A. and Devarajan, N., "Indirect position detection and speed control of PMBLDC motor using labview".

8.     Tamilselvi, B. and Mumtaj, S., "Efficient sensorless speed control approach using comparator with zero cross detection for brushless DC motor", Bonfring International Journal of Power Systems and Integrated Circuits,  Vol. 3, No. 4, (2013), 31-40.

9.     Shen, J. and Iwasaki, S., "Improvement of asic-based sensorless control for ultrahigh-speed brushless DC motor drive", in Electric Machines and Drives Conference, IEMDC'03. International, IEEE. Vol. 2, (2003), 1049-1054.

10.   Shen, J., Zhu, Z. and Howe, D., "Sensorless flux-weakening control of permanent-magnet brushless machines using third harmonic back EMF", IEEE Transactions on Industry Applications,  Vol. 40, No. 6, (2004), 1629-1636.

11.   Shao, J., "Direct back emf detection method for sensorless brushless DC (BLDC) motor drives", Virginia Polytechnic Institute,  (2003),

12.   Shao, J., "An improved microcontroller-based sensorless brushless DC (BLDC) motor drive for automotive applications", IEEE Transactions on Industry Applications,  Vol. 42, No. 5, (2006), 1216-1221.

13.   Gurunathan, C., Murugan, M. And Jeyabharath, R., "A back emf detection method is implemented for sensorless BLDC motor", (2015), KS Rangasamy College of Technology, India. IJAICT.