Flux profile control for startup of an induction motor

Claim 3

The method of claim 1, wherein said time interval corresponds to approximately one rotor time constant.

Claim 4

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.

Claim 5

The method of claim 3, 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.

Claim 6

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.

Claim 7

The method of claim 5, 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.

Claim 12

Apparatus for 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 motor, the apparatus comprising: means for providing power to a DC bus; drive means including a plurality of semiconductor switches coupled to the DC bus 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 that is the maximum current rated for pulsed operation of the semiconductor switches; wherein said control means further controls the semi­conductor switches to maintain the initial current for a time interval over which a product of current and time is sufficient to produce a steady-state level of operating flux in the rotor; and wherein after such time interval, said control means is operable for reducing the current supplied to the windings of the stator to a current for maintaining a steady-state operating flux in the rotor.

Claim 13

Apparatus for 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 motor, the apparatus comprising: means for providing power to a DC bus; drive means including a plurality of semiconductor switches coupled to the DC bus 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 that is the maximum current rated for pulsed operation of the semiconductor switches; wherein said control means further controls the semi­conductor switches to maintain the initial current for a time interval over which a product of current and time is sufficient to produce a steady-state level of operating flux in the rotor; and wherein after such time interval, said control means is operable for reducing the current supplied to the windings of the stator to a current for maintaining a steady-state operating flux in the rotor.

Claim 14

The apparatus of claim 9, wherein said time interval corresponds to approximately one rotor time constant.

Claim 15

The apparatus of claim 9, 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.

Claim 16

The apparatus of claim 11, 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.

Claim 17

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 of 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.

Claim 18

The apparatus of claim 13, 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.

Claim 19

Apparatus for controlling current supplied to wind­ings of a stator in an AC motor to inhibit production of transient torques on a motor output shaft driven through a rotor, the apparatus comprising: means for providing power to a DC bus; drive means including a plurality of semiconductor switches coupled to the DC bus for supplying current to the windings of the stator; control means coupled to the drive means for controlling the semiconductor switches 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 wherein after the time interval corresponding to approx­imately one rotor time constant, said control means controls the semiconductor switches to increase the current supplied to the windings of the stator to a current for establishing and maintaining the steady-state operating flux.

Claim 20

Apparatus for controlling current supplied to wind­ings of a stator in an AC motor to inhibit production of transient torques on a motor output shaft driven through a rotor, the apparatus comprising: means for providing power to a DC bus; drive means including a plurality of semiconductor switches coupled to the DC bus for supplying current to the windings of the stator; control means coupled to the drive means for controlling the semiconductor switches 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 wherein after the time interval corresponding to approx­imately one rotor time constant, said control means controls the semiconductor switches to increase the current supplied to the windings of the stator to a current for establishing and maintaining the steady-state operating flux.

Claim 21

Apparatus for 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 motor, 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 including a plurality of semiconductor switches coupled to the DC bus for supplying current to the windings of the stator; control means coupled to the drive means for controlling the semiconductor switches 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; wherein after a time interval corresponding to approxi­mately one rotor time constant, said control means is operable for controlling said semiconductor switches to conduct a 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 level of operating flux in the rotor; and wherein after the last-mentioned time interval, said control means is operable for controlling the semiconductor switches to reduce the current supplied to the windings of the stator to a current for maintaining a steady-state oper­ating flux in the rotor.

Claim 22

Apparatus for 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 motor, 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 including a plurality of semiconductor switches coupled to the DC bus for supplying current to the windings of the stator; control means coupled to the drive means for controlling the semiconductor switches 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; wherein after a time interval corresponding to approxi­mately one rotor time constant, said control means is operable for controlling said semiconductor switches to conduct a 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 level of operating flux in the rotor; and wherein after the last-mentioned time interval, said control means is operable for controlling the semiconductor switches to reduce the current supplied to the windings of the stator to a current for maintaining a steady-state oper­ating flux in the rotor.