Double edge PWM vs Single edge

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rezaxyz

Joined: 10 Aug 2006
Posts: 19

15 Mar 2008 22:42 single edge pwm

Hi,

Can anyone explain why double edge PWM is better for motor control than single edge?

Thank you

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mister_rf

Joined: 27 Feb 2008
Posts: 243
Helped: 59
Location: Romania

16 Mar 2008 11:46 double edge pwm

The idea it's to obtain PWM techniques to guarantee high quality output voltage with reduced harmonics and sinusoidal input current irrespective of the load. A double-edged modulation techniques combine both the leading edge
and the trailing edge of each pulse move with respect to the unmodulated carrier.
The double sampling provides reduced phase delay in the control loop over single-edge modulation and solves the large signal issues related to the set-reset. The added benefit of double-edge modulation is that it doubles the sampling rate of the error signal.
The line-to-line voltage across the load will have most of its ripple at a frequency of twice the switching frequency, and will have a spectrum with minimum even harmonics and no significant component below twice the switching frequency. Motor ripple current is therefore low and motor losses are reduced.

http://www.nxp.com/acrobat_download/applicationnotes/APPCHP3.pdf
http://www.ro.feri.uni-mb.si/projekti/pdf/AC_motor_book.pdf
http://www.icgst.com/acse/Volume6/Issue3/P1110615003.pdf
http://powerelectronics.com/mag/power_new_control_method/
http://www.swinburne.edu.au/iris/pdf/profiles/ManojPendharkar.pdf