Sensorless Start-Up Strategy for a 315 kW High-Speed Brushless DC Motor with Small Inductance and Non-ideal Back-EMF


This paper presented a novel sensorless start-up strategy for a 315kW high-speed magnetic suspension brushless DC (BLDC) motor with small inductance and non-ideal back electromotive force (back-EMF). Two key strategies on the sensorless start-up strategy of BLDC motor were presented: (1) small current start-up strategy for the high-speed BLDC motor with small inductance, and (2) self-adaption control strategy to compensate the commutation error for the BLDC motor with non-ideal back-EMF in the start-up stage. A hybrid pulse width modulation (PWM) strategy based on the load torque was proposed to limit the start-up current. An optimal motor start-up curve based on the system parameters was presented, and a self-adaption control strategy was proposed to solve the synchronous switching problem. The effectiveness and feasibility of the proposed method were verified by a series of experiments on the 315 kW-20000 rpm magnetic suspension blower platform.


  1. BLDC motor
  2. Small inductance
  3. Non-ideal back-EMF
  4. Sensorless
  5. Start-up strategy
  6. Self-adaption control strategy



This paper analyzed the main factors that influence the sensorless start-up performance of the high-power high-speed BLDC motor with small inductance and non-ideal back-EMF. A reliable start-up strategy was proposed by improving the detection of the initial rotor position, the closed-loop acceleration, and the synchronous switching process. The important conclusions were listed as follows.

(1) The rotor initial position can be positioned by the “two step” detection strategy. The start-up current can be adjusted according to the load torque in real time. Therefore, the method proposed in this paper ensured that the motor can start-up successfully under the load condition.

(2) The speed-up curve in the external-synchronization stage was optimized by analyzing the relationship between the motor speed and the terminal voltage. The rotor rotating time from the stationary position to a specify position was obtained by analyzing the average torque in 1/6 cycle and the rotor inherent characteristic.

(3) The synchronous switching process was improved by estimating the commutation error angle and the free decelerating. The influence of the back-EMF shape was analyzed by Eq. (28) and (29). The problems of high frequency noise and the rotor position error were solved by the free decelerating.


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[2] W. Li, J. Fang, H. Li, J. Tang, “Position sensorless control without phase shifter for high–speed BLDC motors with low inductance and non-ideal back EMF,” IEEE Trans. Power Electron., vol. 31, no. 2, pp. 1354–1366, Feb. 2016.

[3] S. Chen, G. Liu, S. Zheng, “Sensorless control of BLDCM drive for a High-Speed maglev blower using a low pass filter,” IEEE Trans. Power Electron., vol. 32, no. 11, pp. 8845–8856, Nov. 2017.

[4] S. Shinnaka, “New “D-state-observer”-based vector control for sensorless drive of permanent-magnet synchronous motors,” IEEE Trans. Ind. Appl., vol. 41, no. 3, pp. 825–833, Jun. 2005.

[5] G. Liu, C. Cui, K. Wang, B. Han, S. Zheng, “Sensorless control for high–speed brushless DC motor based on the line–to–line back EMF,” IEEE Trans. Power Electron., vol. 31, no. 7, pp. 4669–4683, Jul. 2016.

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