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Synchronous motor

  • US 6,424,114 B1
  • Filed: 03/21/2001
  • Issued: 07/23/2002
  • Est. Priority Date: 09/25/1998
  • Status: Expired due to Fees
First Claim
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1. A synchronous motor comprising:

  • a housing;

    a permanent magnet rotor rotatably attached in the housing and rotating about an output shaft;

    a stator including coils wound round a stator core;

    an A-coil segment and a B-coil segment, which are connected in series, included in said coils;

    first measuring means for measuring rotational speed of said permanent magnet rotor and positions of magnetic poles thereof;

    second measuring means for measuring frequency of an AC power source;

    a start operation circuit rectifying alternate current, which is supplied from the AC power source, with a rectifying bridge circuit and changing the direction of the rectified current, which flows through the A-coil of said coils, according to rotational angle of said permanent magnet rotor by controlling switching means so as to start said permanent magnet rotor as a DC brushless motor;

    a synchronous operation circuit shorting the AC power source and the A- and the B-coils so as to synchronously rotate said permanent magnet rotor as an AC synchronous motor;

    switches SW1 and SW2 being provided between the AC power source and the coils and switching the connection to said synchronous operation circuit; and

    control means turning off said switches SW1 and SW2 to disconnect said synchronous operation circuit and controlling said switching means during the start operation, starting with suppressing input of the inverted minus side of the AC power source, which is full-wave-rectified and flows through the A-coil of the coils via the rectifying bridge circuit, so as to make the current application range of the minus side shorter than that of the plus side, turning off said switching means and turning on said switches SW1 and SW2 when the rotational speed of said permanent magnet rotor, which is measured by said first measuring means, reaches near synchronous speed with respect to the frequency of the power source, which is measured by said second measuring means, thereby said start operation circuit using the A-coil is disconnected and said synchronous operation circuit using the A- and B-coils is connected to transfer to the synchronous operation.

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