ABSTRACT
In order to
improve the stability of brushless DC (BLDC) motors at low speed, a
high-stability position-sensorless control method is proposed in this paper.
Because the back electromotive force (EMF) is very small at low speed, a novel
algorithm is proposed to detect the zero crossing point (ZCP) of back EMF
accurately. First, the line-to-line back EMF is computed based on the
mathematical model of BLDC motors. Then, a low pass filter (LPF) with alterable
cut-off frequency is used to reduce the disturbance of the line-to-line back
EMF. Last, the commutation signal is obtained through. However, the commutation
signal is delayed by the LPF. For this reason, based on the three-phase back
EMF, a novel compensation algorithm including an open-loop and a close-loop is proposed
to compensate commutation error. Moreover, the speed feedback has a big delay
at low speed. According to this, a novel speed calculation algorithm is
presented to decrease the delay. Both the simulation and experimental results
validate the high stability and reliability of the proposed method.
KEYWORDS
1. Brushless
DC (BLDC) Motor
2. Sensorless
control
3. Back
electromotive force (EMF)
4. Zero
crossing point (ZCP)
5. Commutation
error
6. High
stability
7. Low speed
SOFTWARE: MATLAB/SIMULINK
CONCLUSION
This paper
proposed a novel position-sensorless control method for BLDC motors at low speed.
This method includes three new algorithms. (1) A novel ZCP detection algorithm which
combined G function and a digital LPF with alterable cut-off frequency. (2) A
new speed calculation algorithm. (3) A novel compensation algorithm. The
simulation and experimental results show that the commutation error is less
than 1.5% at around 1.7 ~ 17% of the rated speed. Therefore, the stability and
reliability are verified.
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