INDUCTION MOTOR CONTROL SYSTEM

• US 3,781,616 A
• Filed: 10/13/1971
• Issued: 12/25/1973
• Est. Priority Date: 10/13/1971
• Status: Expired due to Term

• Current Assignee: Westinghouse Air Brake Technologies Corporation
• Original Assignee: Boris Mokrytzki, Peter W. Hammond
• Inventors: Mokrytzki, Boris, Hammond, Peter W.
• Primary Examiner(s): Rubinson, Gene Z.
• Application Number:
  US05/188,949
• Time in Patent Office: 804 Days
• Field of Search: 318/230,231,308,318,336,340,388,392,393,404,415,416
• US Class Current: 318/801
• CPC Class Codes: B60L 2200/26 Rail vehicles
• CPC Class Codes: B60L 2220/12 Induction machines
• CPC Class Codes: B60L 9/22 polyphase motors
• CPC Class Codes: H02M 7/49 Combination of the output voltage waveforms of a plurality of converters
• CPC Class Codes: H02P 2207/01 Asynchronous machines
• CPC Class Codes: H02P 27/047 V/F converter, wherein the voltage is controlled proportionally with the frequency
• CPC Class Codes: H02P 27/048 using AC supply for only the rotor circuit or only the stator circuit

Abstract

This disclosure relates to a control system for dynamically reenergizing a rotating induction motor. A pair of inverters supply power to the windings of the induction motor through an inductive reactor. A tachometer senses the rotational speed of the rotor of the induction motor and applies a signal to a programmed logic circuit for pulse width modulating the power of the inverters over a constant torque range and for step wave shaping the power of the inverters over a constant horsepower range. In the event of an interruption of power, the reapplied power to the induction motor is reduced and the frequency of the reapplied power is readjusted at or near the actual synchronous speed of the induction motor so that little, if any, current surges occur upon reenergizing of the induction motor.

Claims

1. A control system for reenergizing a rotating induction motor comprising, a system of converters for supplying polyphase voltage to said induction motor, a speed sensing means for measuring the speed of said induction motor, and a programmed logic circuit means coupled to said converter system and responsive to said speed sensing means for causing the frequency of said polyphase voltage to substantially agree with the frequency which is representative of the synchronous speed of said induction motor at the time that said polyphase voltage is reapplied to said induction motor and reducing the amplitude of said polyphase voltage which is reapplied to said induction motor.

2. The control system as defined in claim 1, wherein said system of converters includes a pair of inverters one of which is phase shifted in one direction with respect to a reference point and the other of which is phase shifted in the other direction with respect to the reference point.

3. A control system for dynamically reenergizing a rotating induction motor comprising, a pair of three-phase inverters for supplying polyphase voltage to said induction motor through a reactor, a speed sensing means for measuring the speed of said induction motor, and a programmed logic circuit coupled to said pair of inverters and responsive to said speed sensing means for decreasing the amplitude of said polyphase voltage when an interruption occurs in the system and for readjusting the frequency of said polyphase voltage to the frequency which is representative of the synchronous speed of said induction motor at the time that said polyphase voltage is reapplied to said induction motor.

4. The control system as defined in claim 3, wherein said induction motor includes a pair of three-phase wye connected windings and a squirrel-cage rotor.

5. The control system as defined in claim 3, wherein said pair of three-phase inverters are phase shifted relative to each other in order to eliminate the fifth and seventh harmonics of the fundamental of said polyphase voltage.

6. The control system as defined in claim 3, wherein said reactor parallels said induction motor and said pair of three-phase inverters.

7. The control system as defined in claim 3, wherein said programmed logic circuit includes a pulse width modulation network for varying the amplitude of said polyphase voltage produced by said pair of three-phase inverters.

8. The control system as defined in claim 3, wherein said logic circuit includes a phase angle control network for varying the amplitude of said polyphase voltage produced by said pair of three-phase inverters.

9. The control system as defined in claim 3, wherein said induction motor includes a pair of three-phase wye connected windings which are mechanically displaced with respect to each other.

10. The control system as defined in claim 9, wherein said pair of three-phase inverters have outpuTs which are electrically shifted relative to each other.

11. The control system as defined in claim 10, wherein said mechanical displacement of said pair of wye connected windings is substantially equal to the electrical shift of said outputs of said pair of three-phase inverters.

12. The control system as defined in claim 3, wherein said induction motor includes a pair of three-phase windings which are parallel coupled to said pair of three-phase inverters by said reactor.

13. The control system as defined in claim 12, wherein said reactor includes a plurality of main windings and a plurality of auxiliary windings.

14. The control system as defined in claim 13, wherein said main winding of one phase is associated with an auxiliary winding of another phase.

15. The control system as defined in claim 3, wherein said programmed logic circuit includes a six-step wave form control network for varying the frequency of said polyphase voltage.

16. The control system as defined in claim 8, wherein said phase angle control network shifts the phase angle of the output of one of siad pair of three-phase inverters forward a given amount and shifts the phase angle of the output of the other one of said pair of three-phase inverters backward the same amount.

17. The control system as defined in claim 3, wherein said induction motor includes a first and a second wye connected winding arrangement which are parallel coupled to respective ones of said pair of polyphase inverters by said reactor which includes a multitude of windings.

18. A system for starting and running an induction motor and for reenergizing an induction motor in motion comprising, a d.c. voltage source, a pair of phase shifted inverters supplied by said d.c. voltage source, an inductive reactor coupling an output of said pair of phase shifted inverters to the stator windings of said induction motor, a tachometer driven by the rotor of said induction motor, a programmed logic circuit responsive to said tachometer for controlling the output of said pair of inverters so that said induction motor is operated as a constant torque device over a portion of its operating range and so that the induction motor is operated as a constant horespower device over the remaining portion of its operating range.

19. The system as defined in claim 18, wherein said induction motor includes a squirrel cage rotor.

20. The system as defined in claim 19, wherein said pair of inverters are connected in parallel with the dual three-phase wye connected windings by said inductive reactor.

21. The system as defined in claim 18, wherein said inductive reactor includes a plurality of main windings and a plurality of auxiliary windings one of which is intercoupled with one of said main windings.

22. A system comprising, a. a polyphase induction motor, b. a reactor, c. a polyphase inverter, d. a d.c. supply source, e. a logic circuit, f. a speed sensing means, said polyphase induction motor including a pair of mechanically displaced three-phase wye connected stator windings and a squirrel cage rotor, said reactor including a plurality of main windings and a plurality of auxiliary windings connected to said stator windings, said polyphase inverter including a pair of electrically displaced three-phase switching sections connected to said main windings, said d.c. supply source providing power for said polyphase inverter, said logic circuit including a pulse width modulation section and a phase angle control section which are connected to said polyphase inverter, said speed sensing means measuring the speed of said squirrel cage rotor and causing said logic circuit to pulse width modulate the output of said inverter so that said polyphase induction motor initially runs as a constant torque device on startup and upon reaching a base speed said logic circuit causes the output of said inverter to produce a stepped wave voltage which thereafter allows said polyphase induction motor to run as a constAnt horsepower device, said speed sensing means controlling said logic circuit in a manner such that the amplitude of the output of said polyphase inverter is decreased and that the frequency of the output of said polyphase inverter is made to substantially correspond with the frequency of the synchronous speed of the rotating rotor of said polyphase induction motor.