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.
- BLDC motor
- Small inductance
- Non-ideal back-EMF
- Start-up strategy
- Self-adaption control strategy
Fig. 1. The block diagram of novel sensorless start-up strategy.
EXPECTED SIMULATION RESULTS:
Fig. 2. The comparisons experiment results of sensorless start-up strategy. (a) The start-up stage based on traditional sensorless “three-step” start-up method. (b) The start-up stage based on the sensorless start-up strategy proposed in this paper.
Fig. 3. The phase current and line-to-line voltages in the start-up stage without commutation compensation. (a) The synchronous error angle caused the waveform distortion in the start-up stage. (b) The synchronous error angle caused the motor out of step in the start-up stage.
Fig. 4. The comparisons experiment results of sensorless strategy under heavy load. (a) The start-up stage based on traditional sensorless “three step” start-up strategy. (b) The start-up stage based on the sensorless start-up strategy proposed in this paper
Fig.5. The curves of electromagnetic torque and the motor speed when the load torque changed in the start-up stage. (a) The curves under traditional sensorless start-up strategies. (b) The curves under sensorless start-up strategies proposed in this paper.
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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