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Elevator control system

  • US 5,698,823 A
  • Filed: 12/21/1995
  • Issued: 12/16/1997
  • Est. Priority Date: 06/22/1995
  • Status: Expired due to Fees
First Claim
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1. An elevator control system comprising:

  • a synchronous electric motor for driving a sheave and employing a permanent magnet for creating a magnetic flux;

    an inverter including a pulse-width modulation controlled output current feeding the synchronous motor;

    a current transformer for sensing, and generating an output indicating, the output current that the inverter feeds to the synchronous motor;

    speed sensor means directly connected to the synchronous motor for sensing, and generating an output indicating, rotational speed of the synchronous motor;

    angle sensor means directly connected to the synchronous motor for sensing, and generating an output indicting, the angle of rotation of the synchronous motor;

    a controller for issuing a speed command to the synchronous motor; and

    an inverter control circuit comprising a current control section including;

    determining means for determining whether the synchronous motor is rotating at a constant speed based on the output of the speed sensor means;

    input voltage means for computing an input voltage to the synchronous motor based on the output of the speed sensor means and generating an output indicating the input voltage;

    q-axis voltage difference means for computing a difference between a q-axis voltage command and the output of the input voltage means and generating an output indicating the difference;

    memory means for outputting a value corresponding to the output of the q-axis voltage difference means, storing the value when the output of the determining means indicates that the synchronous motor is rotating at a constant speed, and outputting a stored value when the output of the determining means indicates that the synchronous motor is not rotating at a constant speed;

    output means for outputting a d-axis current command corresponding to the output of the memory means, based on a determination that the flux of the permanent magnet is greater than a threshold flux when the difference is negative; and

    subtracter means for outputting a d-axis component current command value comprising a difference obtained by subtracting the d-axis current command from a fixed d-axis component current command value, the current control section using the output of the current transformer, the output of the speed sensor means, and the output of the angle sensor means, as feedback signals, and controlling the input current to be in phase with the flux of the permanent magnet of the synchronous motor so that the input voltage to the synchronous motor has a predetermined value, in phase with the flux of the permanent magnet of the synchronous motor, according to a current command and the speed command issued by the controller, the inverter control circuit generating a pulse width modulated signal fed to a gate drive circuit that controls the inverter.

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