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Wednesday, 20 December 2017

A Low Cost Speed Estimation Technique for Closed Loop Control of BLDC Motor Drive

This paper proposes a sensorless speed control technique for Brushless DC Motor (BLDC) drives by estimating speed from the hall sensor signals. Conventionally, the speed is measured using precision speed encoders. Since these encoders cost almost half of the entire drive system, there arises the need for a low cost speed estimation technique. This is proposed by measuring the frequency of the in-built-hall sensor signals. Here, a closed loop speed control of BLDC motor is proposed using a current controlled pulse width modulation (PWM) technique. Since BLDC motor is an electronically commutated machine, the commutation period is determined by a switching table that shows the hall signals’ status. The entire system was simulated in MATLAB/Simulink and the performance of the system was analyzed for different speed and torque references.

1.      Brushless DC Motor (BLDC)
2.      Speed estimation
3.      Hall sensors
4.      Current controlled PWM
5.       Inverter



Fig.1. Proposed Block Diagram


Fig. 2. Speed and Torque response of the BLDC drive for reference speed of 3000rpm; (a) Speed; (b) Electromagnetic torque developed

 Fig. 3. Speed and Torque response of the BLDC drive for reference speed of
2000rpm; (a) Speed; (b) Electromagnetic torque developed

Fig. 4. Stator current measured for speed (reference) of 3000rpm and applied
torque 0.5Nm

Fig. 5. Back EMF measured for speed (reference) of 3000rpm and applied
torque 0.5Nm

 Fig. 6. Speed and Torque response in sensored and sensorless mode for a reference speed of 2500rpm; (a) Speed response in sensored mode; (b) Speed response in sensorless mode; (c) Change in applied torques


This paper proposes a low cost speed estimation technique for BLDC motor drive. This method was found to be working for the entire range of speeds below the rated speed. The performance of the system was comparable with that of the conventional speed encoder based control technique. Actual speed was found to maintain the reference speed for different values of load torques. This was verified successfully by using MATLAB/Simulink. Since the proposed speed estimation technique does not require the motor parameters like resistance, inductance etc., the system is suitable for robust applications, especially in industries.
The future scope of the work can be extended as explained below:
• Although the work emphasizes on speed encoder-less control technique, the cost of the system can be further reduced by replacing the hall sensors with a suitable low cost counterpart.
• Since the torque-ripples are found to be appreciably high, novel techniques for its reduction can be studied.
[1] Hsiu-Ping Wang and Yen-Tsan Liu, “Integrated Design of Speed- Sensorless and Adaptive Speed Controller for a Brushless DC Motor,” IEEE Transactions on Power Electronics, Vol. 21, No. 2, March 2006.
[2] K.S.Rama Rao, Nagadeven and Soib Taib, “Sensorless Control of a BLDC Motor with Back EMF Detection Method using DSPIC,” 2nd IEEE International Conference on Power and Energy, pp. 243-248, December 1-3, 2008.
[3] W. Hong, W. Lee and B. K. Lee, “Dynamic Simulation of Brushless DC Motor Drives Considering Phase Commutation for Automotive Applications,” Electric Machines & Drives Conference,2007 lEMDC’07 IEEE International, , pp. 1377-1383, May 2007.
[4] B. Tibor, V. Fedak and F. Durovsky, “Modeling and Simulation of the BLDC motor in MATLAB GUI,” Industrial Electronics (lSIE), 2011 IEEE International Symposium on Industrial Electronics, Gdansk, pp. 1403-1407, June 2011.

[5] V. P. Sidharthan, P. Suyampulingam and K. Vijith, “Brushless DC motor driven plug in electric vehicle,” International Journal of Applied Engineering Research, vol. 10, pp. 3420-3424, 2015.