Flux profile control for startup of an induction motor

• US 4,845,418 A
• Filed: 04/18/1988
• Issued: 07/04/1989
• Est. Priority Date: 08/27/1986
• Status: Expired due to Term

• Current Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Original Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Inventors: Conner, Craig R.
• Primary Examiner(s): Smith, Jr., David
• Application Number:
  US07/185,239
• Time in Patent Office: 442 Days
• Field of Search: 318/778, 318/436, 318/430, 318/431, 318/803, 318/807-811, 318/779
• US Class Current: 318/778
• CPC Class Codes: B66B 1/30 effective on driving gear , e.g. acting on power electronics, on inverter or rectifier controlled motor
• CPC Class Codes: H02P 21/34 Arrangements for starting

Abstract

A method of controlling current in an AC motor to inhibit small torques on an unloaded motor output shaft and to improve buildup of steady-state operating flux in a rotor includes supplying current to the stator windings through a plurality of semiconductor switches, operating the semiconductor switches to supply a plurality of gradually increasing currents to the stator windings over a time interval corresponding to approximately one rotor time constant to bring flux in the rotor up to approximately 10% of a steady-state operating flux in the rotor, operating the semiconductor switches to supply a current that is the maximum current rated for pulsed operation of the semiconductor switches for a time interval over which a product of current and time is sufficient to produce steady-state operating flux in the rotor, and then reducing the stator current to a level for maintaining steady-state operating flux in the rotor. A microelectronic apparatus for carrying out the method is also disclosed.

Claims

1. In a vector control apparatus for controlling flux-producing current and torque-producing current, a method of supplying flux-producing current to windings of a stator in an AC motor to improve buildup of steady-state operating flux in a rotor of the motor, where initially flux is not established in the rotor, the method comprising:

supplying current to the windings of the stator through an inverter which includes a plurality of semiconductor switches;

commanding flux-producing current to a high level than a level required to maintain steady-state operating flux in the rotor;

operating the semiconductor switches in the inverter in response to the commanding of the flux-producing current to supply an initial flux-producing current to the windings of the stator up to the maximum current rated for pulsed operation of the semiconductor switches, wherein the initial current is greater than the steady-state flux-producing current for maintaining normal saturated flux in the rotor;

maintaining the initial current for a time interval over which the product of initial current and time is sufficient to produce a steady-state operating flux in the rotor; and

after such interval, operating the semiconductor switches in the inverter to reduce current supplied to the windings of the stator to a current for maintaining steady-state operating flux in the rotor.

2. The method of claim 1, further comprising:

resolving the current supplied to the plurality of semiconductor switches into a flux-producing component and a torque-producing component; and

commanding the torque-producing component to zero during the time interval in which flux in the rotor is brought up to the steady-state operating flux.

3. The method of claim 2, further comprising:

calculating a phase angle of the current to be supplied to the plurality of semiconductor switches based on a slip angle for operation of the AC motor; and

commanding the slip angle to zero during the time interval in which flux in the rotor is brought up to the steady-state operating flux in the rotor.

4. The method of claim 1, further comprising:

calculating a phase angle of the current to be supplied to the plurality of semiconductor switches based on a slip angle for operation of the AC motor; and

commanding the slip angle to zero during the time interval in which flux in the rotor is brought up to the steady-state operating flux in the rotor.

5. The method of claim 4, further comprising:

resolving the current supplied to the plurality of semiconductor switches into a flux-producing component and a torque-producing component; and

commanding the torque-producing component to zero during the time interval in which flux in the rotor is brought up to the steady-state operating flux.

6. In a vector control apparatus for controlling flux-producing current and torque-producing current, a method of controlling flux-producing current supplied to windings of a stator in an AC motor, where initially flux is not established in a rotor in the AC motor, to inhibit production of transient torques on a motor output shaft driven through the rotor, the method comprising:

supplying current to the windings of the stator through an inverter which includes a plurality of semiconductor switches;

commanding the flux-producing current to establish operating flux in the rotor up to approximately 10% of a steady-state operating flux in the rotor;

operating the semiconductor switches in the inverter in response to the commanding of the flux-producing current to supply a plurality of gradually increasing currents to the windings of the stator over a time interval corresponding to approximately one rotor time constant to bring flux in the rotor up to approximately 10% of a steady-state operating flux in the rotor; and

after the interval corresponding to approximately one rotor time constant, commanding increased flux-producing current and operating the semiconductor switches in the inverter to increase the current supplied to the windings of the stator for establishing and maintaining the steady-state operating flux in the rotor.

7. In a vector control apparatus for controlling flux-producing current and torque-producing current, a method of controlling current supplied to windings of a stator in an AC motor to improve buildup of steady-state operating flux in a rotor of the AC motor, where initially flux is not established in the rotor, and while inhibiting production of transient torques on a motor output shaft driven through the rotor, the method comprising:

supplying current to the windings of the stator through an inverter which includes a plurality of semiconductor switches;

commanding the flux-producing current to establish operating flux in the rotor up to approximately 10% of a steady-state operating flux in the rotor;

operating the semiconductor switches in the inverter in response to the commanding of the flux-producing current to supply a plurality of gradually increasing currents to the windings of the stator over a time interval corresponding to approximately one rotor time constant to bring flux in the rotor up to approximately 10% of a steady-state operating flux in the rotor;

after the time interval corresponding to approximately one rotor time constant,

commanding the flux-producing current to a higher level than a level required to maintain steady-state operating flux in the rotor;

operating the semiconductor switches in the inverter in response to the commanding of the flux-producing current to the higher level to supply a flux-producing current to the windings of the stator up to the maximum current rated for pulsed operation of the semiconductor switches, wherein the current to the windings of the stator includes flux-producing current that is greater than the steady-state flux-producing current for maintaining normal saturated flux in the rotor;

maintaining the maximum current for a time interval over which the product of current and time is sufficient to produce a steady-state operating flux in the rotor; and

after such interval, operating the semiconductor switches in the inverter to reduce current supplied to the windings of the stator to a current for maintaining steady-state operating flux in the rotor.

8. In a vector control apparatus for controlling flux-producing and torque-producing current supplied to windings of a stator in an AC motor to improve buildup of steady-state operating flux in a rotor of the motor, where initially flux is not established in the rotor, the apparatus comprising:

means for providing power to a DC bus;

drive means coupled to the DC bus and including an inverter with a plurality of semiconductor switches for supplying current to the windings of the stator;

control means coupled to the drive means for controlling the semiconductor switches to supply an initial current to the windings of the stator up to the maximum current rated for pulsed operation of the semiconductor switches, wherein the initial current is greater than the steady-state flux-producing current for maintaining normal saturated flux in the rotor;

wherein said control means further controls the semiconductor switches in the inverter to maintain the initial current for a time interval over which the product of current and time is sufficient to produce a steady-state operating flux in the rotor; and

wherein after such time interval, said control means is operable for reducing the initial current supplied to the windings of the stator to a current for maintaining a steady-state operating flux in the rotor.

9. The apparatus of claim 8, wherein

said control means includes means for resolving the current to be supplied through the semiconductor switches into a flux-producing component and a torque-producing component;

and

wherein said control means includes means for commanding the torque-producing component to zero during the time interval in which flux in the rotor is brought up to the steady-state operating flux.

10. The apparatus of claim 9, wherein

said control means includes means for calculating a phase angle of the current to be supplied to the plurality of semiconductor switches based on a slip angle for operation of the AC motor;

and

wherein said control means includes means for commanding the slip angle to zero during the time interval in which flux in the rotor is brought up to the steady-state operating flux.

11. The apparatus of claim 8, wherein

said control means includes means for calculating a phase angle of the current to be supplied to the plurality of semiconductor switches based on a slip angle for operation of the AC motor;

and

wherein said control means includes means for commanding the slip angle to zero during the time interval in which flux in the rotor is brought up to the steady-state operating flux.

12. The apparatus of claim 11, wherein

said control means includes means for resolving the current supplied to the plurality of semiconductor switches into a flux-producing component and a torque-producing component;

and

wherein said control means includes means for commanding the torque-producing component to zero during the time interval in which flux in the rotor is brought up to the steady-state operating flux.

13. In a vector control apparatus for controlling flux-producing current and torque-producing current supplied to windings of a stator in an AC motor, where initially flux is not established in a rotor in the AC motor, to inhibit production of transient torques on a motor output shaft driven through the rotor, the apparatus comprising:

means for providing power to a DC bus;

drive means coupled to the DC bus and including an inverter with a plurality of semiconductor switches for supplying current to the windings of the stator;

means for commanding the flux-producing current to a higher level than a level required to maintain steady-state operating flux in the rotor;

means responsive to the means for commanding and coupled to the drive means for controlling the semiconductor switches in the inverter to supply a plurality of gradually increasing currents to the windings of the stator over a time interval corresponding to approximately one rotor time constant to bring flux in the rotor up to approximately 10% of a steady-state operating flux in the rotor; and

after the time interval corresponding to approximately one rotor time constant, said means for controlling controls the semiconductor switches in the inverter to increase the current supplied to the windings of the stator to a current for establishing and maintaining the steady-state operating flux.

14. In a vector control apparatus for controlling flux-producing current and torque-producing current supplied to windings of a stator in an AC motor to improve buildup of staedy-state operating flux in a rotor of the AC motor, where initially flux is not established in the rotor, and while inhibiting production of transient torques on a motor output shaft driven through the rotor, the apparatus comprising:

means for providing power to a DC bus;

drive means coupled to the DC bus and including an inverter with a plurality of semiconductor switches for supplying current to the windings of the stator;

means for commanding the flux-producing current to establish operating flux in the rotor up to approximately 10% of a steady-state operating flux in the rotor;

means responsive to the means for commanding and coupled to the drive means for controlling the semiconductor switches in the inverter to supply a plurality of gradually increasing currents to the windings of the stator over a time interval corresponding to approximately one rotor time constant to bring flux in the rotor up to approximately 10% of a steady-state operating flux in the rotor;

means for commanding the flux-producing current to a higher level than a level required to maintain steady-state operating flux in the rotor;

means responsive after a time interval corresponding to approximately one rotor time constant for commanding the flux-producing current to a higher level than a lever required to maintain steady-state operating flux in the rotor;

wherein, said control means is responsive to the means for commanding current to a higher level for controlling said semiconductor switches in the inverter to conduct a higher level current up to the maximum current rated for pulsed operation of the semiconductor switches for a time interval over which a product of current and time is sufficient to produce a steady-state operating flux in the rotor, wherein the the higher level current is greater than the steady-state flux-producing current for maintaining normal saturated flux in the rotor; and

wherein after the last-mentioned time interval, said control means is operable for controlling the semiconductor switches in the inverter to reduce the current supplied to the windings of the stator to a current for maintaining the steady-state operating flux in the rotor.