ABSTRACT:
Brushless DC motor drives (BLDC) are finding expanded use in
high performance applications where torque smoothness is essential. The nature
of the square-wave current excitation waveforms in BLDC motor drives permits
some important system simplifications compared to sinusoidal permanent magnet
AC (PMAC) machines. However, it is the simplicity of the BLDC motor drive that
is responsible for causing an additional source of ripple torque commonly known
as commutation torque to develop. In this paper, a compensation technique for
reducing the commutation torque ripple is proposed. With the experimental
results, the proposed method demonstrates the effectiveness for a control
system using the BLDC motors that requires high speed and accuracy.
KEYWORDS:
1.
Brushless DC motor drives
2.
Commutation
3.
Torque ripple
4.
Trapezoidal back EMF
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. The block diagram of the speed controller.
EXPECTED SIMULATION RESULTS:
Fig.
2. Experimental result in low-speed range (without compensation).
Fig.
3. Experimental result in low-speed range (with compensation).
Fig.
4. Experimental result in the high-speed range (without compensation).
Fig.
5. Experimental result in the high-speed range (with compensation).
Fig.
6. Experimental result in the high-speed range (with compensation).
Fig.
7. Sine wave response for the proposed speed controller.
CONCLUSION:
This paper has proposed a compensation
technique for reducing the commutation torque ripple in high-performance BLDC
motor drives. The idea is to equalize the mismatched times of two commutated
phase currents during the commutation intervals. In low-speed operation, a
method to slow down the rising time of the on-going phase current can be a
desirable technique. In high-speed operation, a method to slow down the falling
time of the off-going phase current becomes a desirable strategy. However, it
is not easy to implement the proposed strategies by using cost-effective
one-chip microprocessors because it is needed to calculate the commutation time
intervals within the sampling period in low and high speed operation. Instead
of calculating the commutation time intervals, two dimensional lookup tables
that describe the relation of the commutation time interval and the motor
parameters such as the back EMF and the initial motor current, are used. For
the experiments, a 16-bit microprocessor was used for the controller.
Additionally a CPLD (1600 gates) was used to generate gate signals of the
inverter and the commutation time signals. To verify the feasibility of the
propose method, it is applied to the spindle motor drive control for the
industrial sewing machines. The effects of torque ripple are particularly
undesirable in the industrial sewing machines. They lead to speed oscillations
which cause deterioration in the performance. In addition, the torque ripple
may excite resonances in the mechanical portion of the drive system, produce
acoustic noise. With the experimental results, the proposed method demonstrates
the effectiveness for a high-performance control system using the BLDC motors
that requires high speed and accuracy.
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