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Downhole pumping system with variable speed pulse width modulated inverter coupled to electrical motor via non-gap transformer

  • US 5,844,397 A
  • Filed: 05/02/1996
  • Issued: 12/01/1998
  • Est. Priority Date: 04/29/1994
  • Status: Expired due to Term
First Claim
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1. A method of operating an electrical motor, comprising the steps of:

  • (a) receiving a driving frequency (f.sub.ω

    ) and a desired chopping frequency (fPWM);

    (b) determining the ratio of fPWM to f.sub.ω

    ;

    (c) identifying an odd multiple of three nearest to the ratio;

    (d) generating a triangular signal having a frequency equal to fω

    times the odd multiple of three;

    (e) generating three sinusoidal signals of the frequency fω

    , wherein the sinusoidal signals are separated by a phase difference of 120 degrees, and wherein all zero-crossing points of the three sinusoidal signals occur simultaneously with zero-crossing points of the triangular signal;

    (f) performing a sine-triangle comparison of the triangular signal and the three sinusoidal signals to generate first, second, and third rectangular signals; and

    (g) driving an induction motor electrically connected to a non-gap transformer that includes first, second, and third phases, by selectively applying voltage to the first, second, and third phases in response to the first, second, and third rectangular signals, respectively.

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