Sensorless BLDC Motor Commutation Point Detection and Phase Deviation Correction Method

ABSTRACT:

 Phase-to-neutral voltage or neutral-to-virtual neutral voltage zero-crossing points (ZCPs) detection method is usually used for sensorless BLDC motor commutation control. Unfortunately, neither of them can be realized in lower speed range. In this paper, a simple commutation point detection method is proposed based on detecting inactive phase terminal to dc-link midpoint voltage. It eliminates the requirement of neutral wire or virtual neutral voltage and provides an amplified version of back electromotive force (EMF) at the ZCPs which makes the lower speed range detection possible. As the speed increasing, commutation point error is enlarged due to the low pass filter (LPF) et al. Utilizing the symmetry of the terminal to midpoint voltage the phase error can be corrected. However, due to the nonlinear relationship between the detected voltage difference and phase error, it is difficult to regulate the error fast and robustly. Therefore, a novel phase regulator based on fuzzy neural network (FNN) is proposed in this paper with simple structure and learning ability. The validity of the proposed ZCPs detection method and commutation instant shift correction method are verified through experimental results.

KEYWORDS:

 

1.      Brushless motor

2.      Efficiency

3.      Electric drive

4.      Energy saving

5.      Evaporative cooler

6.      Power control

SOFTWARE:MATLAB/SIMULINK

CONCLUSION:

In this paper, application of a brushless motor drive for a 5000 m3/h commercial evaporative cooler to replace a conventional SPIM has been investigated. Efficiency test results indicate an improved efficiency of at least 75% compared to SPIM. This would improve the energy ranking grade of the evaporative cooler system from IE1 to IE5. Challenges involved in airflow reduction due to various pressure differences caused by restrictions in ducting systems (length, bends, etc.) were discussed. A newly constant power control method was proposed to replace the conventional constant speed control method to overcome such challenges. Various approaches were expressed for determination of feedback power, required in the proposed power control method. For simplicity and cost efficiency, the input current of the drive, proportional to the feedback power was employed for this purpose. Air flow rate test results confirmed that the proposed method could maintain a desired flow at longer ducting systems or operating conditions yielding higher pressure differences. Further improvements may be achieved in increasing the system reliability and cost efficiency, using sensorless control methods or employing directly coupled brushless motor assembly.

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