Modified PWM Technique For Torque Ripples Reduction In Three Phase PM BLDC Motors
Loading...
Date
2012-04
Authors
Salah, Wael Abdel Muhdi Yacoup
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Permanent magnet (PM) brushless DC motors are used in many applications due to
their high efficiency, high torque density, and compact sizes, which make this type of
motors more popular over the other types. This research work focused on torque
improvement of PM brushless DC motors by minimizing the generated torque ripples
during the commutation period. The approaches and methods adopted in this project
are presented thoroughly, along with the mathematical analysis and Matlab-Simulink
modeling. Torque ripples in PM brushless DC motor drives usually originate from
the motor design structure and from the control side in the form of current ripples.
The torque ripples coming from the control side appear in the form of spikes and dips
on the output torque. They occur because of phase current rate mismatch during the
phase current commutation period. Practically, the current rise and decay rates
between the phases are not equal, where the current in the energized phase reaches its
maximum value before or after the de-energized phase current reaches zero. Hence,
the main objective of this research is to estimate and control the rate of the energized
phase current to match approximately the de-energized phase current rate during the
current commutation period. As a result, the torque ripples are minimized. To
accomplish this objective, a modified pulse-width modulation (PWM) strategy is
applied to the energized phase to slow down the phase current at low speed and to
speed up the phase current at high speed. A comparison between the modified PWM
and the conventional control techniques showed a 45% average reduction in torque
ripples when the proposed technique was applied under different loading conditions
and at different speeds. Experimental results of the proposed technique, in general,
indicated a torque ripple factor reduction compared with conventional PWM control.
To summarize, results indicated that torque ripples are effectively reduced when the
PM brushless DC motor drive operates within the constant-torque operating region.
Therefore, the experimental and simulation results of the modified PWM technique
validated and verified the functionality of the proposed strategy.
Description
Keywords
Modified PWM technique for torque ripples , in three phase PM BLDC motors