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Method and apparatus for controlling AC motors

  • US 4,456,868 A
  • Filed: 11/26/1982
  • Issued: 06/26/1984
  • Est. Priority Date: 03/31/1981
  • Status: Expired due to Term
First Claim
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1. An AC motor control method comprising the steps of:

  • (a) a step of obtaining slip frequency, phase difference and primary current amplitude using a speed command and an actual speed;

    (b) a step of determining angular frequency in accordance with the actual speed of the AC motor;

    (c) a step of producing a three-phase current command having a frequency by using the slip frequency, phase difference and primary current amplitude obtained in step (a), as well as said angular frequency; and

    (d) a step of driving the AC motor by said three-phase current command, wherein step (a) includesi computing a torque command from a deviation between said speed command signal and actual speed, where a torque-slip frequency relation and a slip frequency-primary current vector relation which take the secondary leakage reactance of said AC motor into account are predetermined;

    ii finding said slip frequency using the torque command obtained in step (i) and the torque-slip frequency relation; and

    theniii finding said primary current amplitude and phase difference using said slip frequency and slip frequency-primary current vector relation.

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