Inaccurate commutation in brushless dc motor (BLDCM) will induce current harmonic and increase motor loss, which reduce motor efficiency. Meanwhile, for the sensorless BLDCM, the motor commutation is seriously affected by detection errors and calculation errors, which are caused by the nonideal conditions and the parameters variation. In this paper, a novel commutation error correction method is proposed to determine optimal commutation instant for the sensorless high-speed BLDCM. First, the relationship between commutation error and motor phase current is analyzed. According to this relationship, an initial commutation error can be calculated and compensated in one conduction interval. Then, online commutation corrections are performed to compensate for the residual error in following conduction intervals. The correction accuracy of commutation instant is determined by the phase current integral difference. This method is insensitive to motor parameters and back electromotive force waveform. Therefore, the commutation error is effectively eliminated in the whole speed range. Finally, the feasibility and effectiveness of the proposed method are evaluated by experimental results.

Winding currents contain lots of harmonics if motors rotate at a high speed. This paper addresses two key challenges on the harmonic suppression: 1) using the multiple synchronous rotating frame transformations (MSRFTs) to get the primary signals, and 2) proposing the closed-loop detection system (CDS) to extract the harmonics accurately. First, the mathematical model containing the harmonics was built. Second, the MSRFTs were introduced and the high-precision detection method called the CDS was analyzed. The CDS has a higher harmonic detection accuracy than the open-loop method and can enhance the disturbance rejection capability of the system. Third, the parameter-independent compensation algorithm was proposed to enhance the robustness against the motor parameter variations, which was combined with the compensation calculated by the mathematical model to suppress the harmonics. The effectiveness of the proposed harmonic suppression strategy was verified by the experiments on the turbo molecular pump.

This paper focuses on the start-up strategy of a high-speed 100-kW brushless dc motor with small inductance using a voltage comparator. This paper includes three key technique contributions: 1) determining zero-speed positioning, 2) removing high-frequency disturbances, and 3) optimizing the controller parameters. The sensorless low-current start-up strategy is based on an amplification circuit: a low-pass filter circuit and a signal modulate circuit. The amplification circuit is used to amplify the amplitude of back electromotive force for detecting the rotor position at low speed, the low-pass filter circuit is used to remove high-frequency disturbances, and the signal modulate circuit is used to obtain the rotor position signal. A hysteresis control strategy is proposed against the load disturbance in the start-up stage. Experimental results show that the proposed sensorless start-up strategy can realize a low-current start-up.