ABSTRACT:
This paper presents a torque ripple compensation technique
for a Brushless DC (BLDC) motor drive that is operated without a DC link
capacitor. The motor drive, which uses a single switch control strategy,
resembles that of a buck converter during operation at any switching state. A
simple buck converter based model is therefore proposed to predict the behaviour
of the BLDC motor drive at constant speed. Using the model, the impact of
operation without the DC link capacitor on the torque produced by the BLDC
motor drive is investigated in detail. Theoretical behaviour of the BLDC motor
drive is compared with Matlab/Simulink based simulations to demonstrate the
validity of the compensation technique and the analysis. Experimental results
of a 250 W prototype motor drive are also presented to further validate the
theoretical analysis as well as the effectiveness of the proposed technique.
Results convincingly indicate that the BLDC motor drive with torque ripple
compensation offers comparable performance.
KEYWORDS:
1.
Brushless
machines
2.
Torque ripple compensation
SOFTWARE:
MATLAB/SIMULINK
Fig.
1. (a) A typical BLDC motor drive; and (b) a BLDC motor drive without
a
DC link capacitor.
Fig.
2. Case 1 with M1 for E = 95V: (a) vin(t) and E; (b) im(t) by theoretical
analysis;
(c) im(t) by simulation;
and (d) im(t) by experiment.
Fig.
3. Case 2 with M2 for E = 80V: (a) vin(t) and E; (b) im(t) by theoretical
analysis;
(c) im(t) by simulation;
and (d) im(t) by experiment.
Fig.
4. Case 3 with M1 for E = 65 V: (a) vin(t) and E; (b) im(t) by
theoretical
analysis; (c) im(t) by simulation;
and (d) im(t) by experiment.
Fig.
5. A comparison between the comprehensive model and the simple
model:
(a) case 1 with M1; (b) case 2 with M2; and (c) case 3 with
M1.
Fig.
6. Proposed compensation for case 1: (a) simulated im(t) without a capacitor and with a 150 μF capacitor;
(b) simulated im(t) with proposed compensation;
(c) experimental im(t); and (d) DC
link voltage with proposed compensation.
Fig.
7. Proposed compensation for case 3: (a) simulated im(t) without a capacitor and with a 150 μF
capacitor; (b) simulated im(t)
with
proposed compensation; (c) experimental im(t); and (d) DC
link voltage with proposed compensation.
CONCLUSION:
A
simple mathematical model and a compensation technique for inherent torque
ripples of a BLDC motor drive, operated without a DC link capacitor, have been
proposed. The simplicity of the model permits the controller to be implemented
on inexpensive microcontroller platforms with very low resources. With the
proposed technique for compensating torque ripples, comparable performance to a
conventional BLDC motor drive with a large DC link capacitor can be achieved.
However, with the torque ripple compensation technique, the overall complexity
of the motor drive has been increased, which is a major disadvantage. Based on
the application, major augmentations in both hardware and firmware may be
required. The good agreement between the theoretical results, simulated results
and experimental results demonstrate the accuracy of the simple buck model and
the effectiveness of the proposed compensation technique. The proposed
compensation technique is expected to be useful for manufacturing low cost BLDC
motor drives with comparable performance.
REFERENCES:
[1]
R. Krishnan, Electric
Motor Drives, Modeling, Analysis, and Control. Prentice Hall,
2001.
[2]
R. Krishnan, Permanent
Magnet Synchronous and Brushless DC Motor Drives.
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[3]
J. F. Gieras, Permanent
Magnet Motor Technology - Design and Applications:
CRC Press, 2010.
[4]
V. Sankaran, F. Rees, and C. Avant, “Electrolytic capacitor life testing and
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[5]
H. K. Samitha Ransara and U. K. Madawala, "A Low Cost Brushless DC Motor
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