Field weakening induction drive

• US 4,677,360 A
• Filed: 03/13/1986
• Issued: 06/30/1987
• Est. Priority Date: 03/13/1986
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Garces, Luis J.
• Primary Examiner(s): Smith, Jr., David
• Application Number:
  US06/839,203
• Time in Patent Office: 474 Days
• Field of Search: 318/800, 318/803, 318/805, 318/807-812
• US Class Current: 318/803
• CPC Class Codes: H02P 21/09 Field phase angle calculation based on rotor voltage equation by adding slip frequency and speed proportional frequency

Abstract

A speed control using decoupled flux and torque commands obtains constant horsepower operation by modifying the slip according to the torque requirements. The slip is modified by a value representative of the torque producing current. Control is kept in the torque command and the slip command with the field producing command free to change according to the motor speed, voltage available and the rotor time constant.

Claims

1. A control capable of operating an induction machine at full inverter voltage in the field weakening mode comprising:

means coupled to said induction machine for generating a signal proportional to induction machine speed;

means responsive to an external speed command signal and machine speed for generating a speed error signal;

means responsive to said speed error signal for generating a torque producing current command signal;

means responsive to said torque producing current command signal for generating a slip command signal;

means responsive to machine voltages and currents for generating a signal proportional to an actual torque producing current signal;

means responsive to said actual torque producing current signal and said torque producing current command for generating an error signal;

means responsive to said error signal for generating a slip correction signal;

means responsive to said slip correction signal for modifying said slip command signal to generate a modified slip command signal, said slip command signal being increased by said slip correction signal when said limited torque producing current signal;

means responsive to said signal proportional to induction machine speed for generating a flux producing current command signal; and

current control converter means responsive to said torque producing current command signal, flux producing current command signal, and said modified slip command for generating multiphase, variable frequency currents to said induction machine.

2. A control capable of operating an induction machine at full inverter voltage in the field weakening mode comprising:

means coupled to said induction machine for generating a signal proportional to induction machine speed;

means responsive to an external speed command signal and machine speed for generating a speed error signal;

means responsibe to said speed error signal for generating a torque producing current command signal;

limiting means responsive to said torque producing current component command signal for limiting the maximum allowed magnitude of said torque producing current command and thereby providing a limited torque producing current command signal;

means responsive to said limited torque producing current command signal for generating a slip command signal;

means responsive to machine voltages and currents for generating a signal proportional to an actual torque producing current signal;

means responsive to said actual torque producing current signal and said limited torque producing current command for generating an error signal;

means responsive to said error signal for generating a slip correction signal;

means responsive to said slip correction signal for modifying said slip command signal to generate a modified slip command signal, said slip command signal being increased by said slip correction signal when said limited torque producing current command signal exceeds said actual torque producing current signal;

means responsive to said signal proportional to induction machine speed for generating a flux producing current command signal; and

current control and converter means responsive to said limited torque producing current command signal, flux producing current command signal, and said modified slip command for generating multiphase, variable frequency currents to said induction machine.

3. The control of claim 2 further comprising:

means for determining power supplied to said motor during motoring and by said motor during regeneration; and

means for reducing the maximum allowed magnitude of said torque producing current signal by said limiting means when the power supplied to said motor during motoring and the power supplied by the motor during regeneration exceed a predetermined amount.

4. A method of controlling an induction machine to obtain operation in the field weakening mode with full inverter voltage comprising the steps of:

generating a speed error signal from a commanded speed signal and a signal representative of actual motor speed;

generating a torque producing current command from the speed error signal;

generating a signal representative of the actual torque producing current from machine voltages and currents;

generating a slip command from the torque producing current command;

generating a slip correction signal from the difference between the signal representative of the actual torgue producing current and torque producing current command;

modifying the slip command by the slip correction signal so that when the commanded torque producing current exceeds the signal representative of the actual torque producing current the slip command will be increased;

generating a field producing current command responsive to motor speed; and

supplying the modified slip command, torque producing current command and field producing current command to the induction motor.

5. The method of claim 4 further comprising the step of:

limiting the maximum allowed magnitude of said torque producing current command.

6. The method of claim 5 further comprising the steps of:

determining the power supplied to said motor during motoring and by said motor during regeneration; and

reducing the maximum allowed magnitude of said torque producing current signal by the limiting step when the power supplied to the motor and when the power supplied by the motor exceeds a predetermined amount.