Induction motor torque/flux control system

• US 4,885,518 A
• Filed: 08/21/1987
• Issued: 12/05/1989
• Est. Priority Date: 08/21/1987
• Status: Expired due to Term

• Current Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Original Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Inventors: Schauder, Colin D.
• Primary Examiner(s): Smith, Jr., David
• Application Number:
  US07/087,939
• Time in Patent Office: 837 Days
• Field of Search: 318/798, 318/806, 318/803, 318/805, 318/807-811
• US Class Current: 318/798
• CPC Class Codes: H02P 21/06 Rotor flux based control involving the use of rotor position or rotor speed sensors

Abstract

An inductio motor torque/flux control system the motor flux is forced down while accelerating and force up while decelerating to maintain a required flux level at all speeds. This is achieved through vectory control by generating a direct current component in relation to the flux demand while imposing limits thereto corresponding to the maximum desirable resultant current vector, and by generating a quadrature current component which is held between limits defined by the sum of the squres of the two current components. The three-phase currents of the motor generated by vector control transformation are used to control a voltage-source inverter in a bang-bang fashion. The conventional bang-bang technique is improved by tying up one pole while controlling in the bang-bang mode the two other poles. To this effect the motor back emf is detected when the poles are simultaneously tied to one of the DC link terminals, and the tied-up pole is selected by the emf so detected.

Claims

1. In an AC induction motor drive including:

first means responsive to a flux demand for generating a first signal representative of a direct component reference current;

second means responsive to a torque demand for generating a second signal representative of a quadrature component reference current;

third means responsive to a speed signal for generating a third signal representative of a position angle characterizing the current resultant vector of said direct and quadrature components; and

fourth means responsive to said first, second and third signals for generating three coordinate phase currents for the motor drive;

the combination of

means within said first means for dynamically responding to said flux demand and first limiting means respopnsive to said dynamically responding means for limiting said first signal in magnitude within a predetermined maximum value LIM;

second limiting means responsive to said first limiting means for establishing with said first signal a limit ALIM defined by the square of said first signal being made equal to (LIM² -ALIM²);

said second limiting means being operative upon said second means for limiting said second signal so that said resultant vector remain within the limit ALIM.

2. The motor drive of claim 1 with said first limiting means establishing a limit ±

LIM to said first signal when the motor drive experienced a speed change outside normal speed range of operation of the motor drive; and

with said second limiting means establishing a limit ALIM for said second signal, the limit ALIM being defined by the square of said first signal being equal to (LIM² -ALIM²).

3. The motor drive of claim 2 with the provision of computer means for computing ALIM=√

(LIM² -i_d²);

where i_d is the amplitude of the first signal as derived from said first means.

4. The motor drive of claim 3 with said microprocessor means being responsive to a speed representative signal and providing in relation thereto said flux demand signal, said flux demand being constant in said speed range, and said flux demand having a gradient in relation to the speed outside said range;

whereby said first signal is varied in relation with said flux demand gradient and within said limit ±

LIM when the speed is outside said speed range.