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

• Current Assignee: Fumito Komatsu
• Original Assignee: Fumito Komatsu
• Inventors: Komatsu, Fumito
• Primary Examiner(s): Mullins, Burton S.
• Application Number:
  US09/787,754
• Time in Patent Office: 489 Days
• Field of Search: 318/105, 318/107, 318/700, 318/720, 318/721, 318/724, 310/68.B, 310/68.R
• US Class Current: 318/721
• CPC Class Codes: H02P 1/50 by changing over from asynchronous to synchronous operation H02P1/48 takes precedence

Abstract

A small synchronous motor with high reliability so devised that transition from start operation to synchronous operation is ensured. A microcomputer 22 switching-controls the current application range to a range where the rectified current flowing through a rectifying bridge circuit 20 and an A-coil alternately is inverted during one turn of a permanent magnet rotor 5 to suppress the input on the inverted side with respect to the non-inverted side and thereby to start a synchronous motor, turns off first to fourth transistors 16-19 when the rotational speed of the permanent magnet rotor regulated by the power source frequency and measured by a power source frequency measuring section 24, and turns on triacs SW1 and SW2, thereby making a switch to the synchronous operation circuit 21.

Claims

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.

2. The synchronous motor according to claim 1, wherein said control means controls said switching means for a predetermined time, during the start operation, so as to control the current application range of the inverted minus side of the rectified current, which is supplied from the AC power source and full-wave-rectified, flowing through the A-coil.

3. The synchronous motor according to claim 1,

further comprising third measuring means including: a sensor plate having slits, which are formed in a circumferential direction so as to introduce the current toward the coils; and

an optical sensor detecting the slits, wherein said control means controls said switching means and switching-controls the current direction toward the A-coil of the coils, during the start operation, on the basis of output signals of the optical sensor.

4. The synchronous motor according to claim 3,

wherein said third measuring means including:

a sensor plate having slits, which are formed in the circumferential direction so as to make the current application range of the inverted minus side of the rectified current, which is supplied from the AC power source and full-wave-rectified, flowing through the A-coil shorter; and

an optical sensor for detecting the slits, and wherein said control means controls said switching means so as not to apply the current to the inverted minus side of the rectified current, within a prescribed angular range, on the basis of the output signals of the optical sensor.

5. The synchronous motor according to claim 1,

wherein said first measuring means includes:

a sensor plate having slits and shading sections, which are alternately formed and divide a portion between magnetic poles into odd number of parts; and

an optical sensor detecting the slits and the shading sections, wherein said control means controls said switching means, detects the stop pole of said permanent magnet rotor on the basis of the output signals of said optical sensor, supplies the current to the A-coil to securely rotate said permanent magnet rotor in the normal direction during the start operation, switches the current direction toward the A-coil with measuring the rotational angle and the positions of the magnetic poles of said permanent magnet rotor, and apply no current to the inverted minus side of the rectified current within a prescribed angular range.

6. The synchronous motor according to claim 1,

wherein said control means repeatedly controls said switches SW1 and SW2 so as to transfer from the synchronous operation to the start operation and transfer to the synchronous operation again when power swing occurs.

7. The synchronous motor according to claim 1, wherein the stator core includes main core sections, from each of which a subcore section extends in the opposite direction of the rotational direction of said permanent magnet rotor, and magnetic permeability of the main core section is greater than that of the subcore section.

8. The synchronous motor according to claim 1, wherein said stator has a bobbin, which is attached to the stator core and includes a core shaft, whose axial line is perpendicular to an axial line of said permanent magnet rotor, and flanges, which are respectively provided on the both ends of the core shaft, and said coils are serially wound around the bobbin.

9. A synchronous motor, comprising:

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

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 stator including coils, which are an A-coil and a B-coil wound round a stator core and serially connected via an intermediate tap;

a start operation circuit being connected to the AC power source and the intermediate tap of the coils and further connected to the A-and B-coils in parallel with respect to the AC power source, wherein a first and a second diode for flowing the rectified current through the A-coil and a first and a second transistor, which can be switching-controlled so as to alternately changing the direction of the rectified current, are respectively connected in parallel, a third and a fourth diode for flowing the rectified current through the B-coil and a third and a fourth transistor, which can be switching-controlled so as to alternately changing the direction of the rectified current, are respectively connected in parallel, the AC current of the AC power source is rectified by a first to a fourth diode, and the first to the fourth transistors are switching-controlled so as to alternately flow the rectified current through the A-coil and the B- coil according to the rotational angle of the permanent magnet rotor and start said permanent magnet rotor as a DC brushless motor;

a synchronous operation circuit being connected to the AC power source and the B-coil so as to synchronously rotate said permanent magnet rotor as an AC synchronous motor;

a switch SW1 switching the connection between said start operation circuit, to which the AC power source and the intermediate tap are connected, and said synchronous operation circuit, to which the AC power source and the B-coil are connected; and

control means alternately changing the current direction of the rectified current flowing through the coils, turning on/off the third and the fourth transistors of said start operation circuit so as to make a current application angular range, in which the current flows to the coils during one turn of said permanent magnet rotor, of the A-coil greater than that of the B-coil and converge the rectified current to the A-coil during the start operation, turning off the third and fourth transistors, which are connected to the B-coil, and turning on the first and second transistors, which are connected to the A-coil 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, and controlling said switch SW1 to change the connection from the intermediate tap to the B-coil so as to transfer the synchronous operation by said synchronous operation circuit.

10. The synchronous motor according to claim 9,

wherein one combination of the third and fourth diodes and the third and fourth transistors, which are respectively connected in parallel, of said start operation circuit is omitted so as to make current intensity of the A-coil greater than that of the B-coil during the start operation.

11. The synchronous motor according to claim 9,

wherein said first measuring means includes a sensor plate having slits, which define directions and application range of the current flowing through the A-coil and the B-coil, wherein said first measuring means detects the slits, said control means switching-controls the first to the fourth transistors of said start operation circuit so as to make current intensity of the A-coil greater than that of the B-coil, during the start operation, on the basis of output signals of said first measuring means.

12. The synchronous motor according to claim 9,

wherein said control means repeatedly controls said switch SW1 so as to transfer from the synchronous operation to the start operation and transfer to the synchronous operation again when power swing occurs.

13. The synchronous motor according to claim 9, wherein the stator core includes main core sections, from each of which a subcore section extends in the opposite direction of the rotational direction of said permanent magnet rotor, and magnetic permeability of the main core section is greater than that of the subcore section.

14. The synchronous motor according to claim 9, wherein said stator has a bobbin, which is attached to the stator core and includes a core shaft, whose axial line is perpendicular to an axial line of said permanent magnet rotor, and flanges, which are respectively provided on the both ends of the core shaft, and the A-coil and the B-coil are serially wound around the bobbin.