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Generalized discontinuous pulse width modulator

  • US 6,023,417 A
  • Filed: 02/20/1998
  • Issued: 02/08/2000
  • Est. Priority Date: 02/20/1998
  • Status: Expired due to Term
First Claim
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1. An apparatus for use with a PWM controller and inverter, the controller comparing modulating signals to a carrier signal to generate firing signals for turning PWM inverter switches on and off thereby connecting each of first, second and third inverter output lines alternately between positive and negative DC buses and generating high frequency voltage pulses on each output line, the high frequency pulses on each line together generating low frequency alternating voltages, the positive DC bus having a DC bus voltage value, the apparatus for providing modulating signals which cause minimum harmonic distortion in the generated voltages, the controller providing three initial sinusoidal modulating signals, the apparatus comprising:

  • an identifier which receives at least one of the initial modulating signals and determines a modulating index;

    a comparator which compares the modulating index to a threshold index, anda selector which;

    when the modulating index is less than the threshold index, provides a first signal set including first, second and third PWM signals corresponding to the first, second and third output lines, the first set having identical 120 degree phase shifted waveforms; and

    when the modulating index is greater than the threshold index, provides a second signal set including first, second and third PWM signals corresponding to the first, second and third output lines, the second set having identical 120 degree phase shifted waveforms;

    wherein, below the threshold index, the first set causes relatively less generated voltage harmonic distortion than the second set and, above the index, the second set causes relatively less generated voltage distortion than the first set.

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