Uninterruptable power supply

• US 5,880,537 A
• Filed: 01/10/1997
• Issued: 03/09/1999
• Est. Priority Date: 01/10/1997
• Status: Expired due to Term

• Current Assignee: Emerson Electric Company
• Original Assignee: Caterpillar Incorporated
• Inventors: Windhorn, Allen E.
• Primary Examiner(s): Gaffin, Jeffrey A.
• Assistant Examiner(s): PALADINI, ALBERT WILLIAM
• Application Number:
  US08/781,757
• Time in Patent Office: 788 Days
• Field of Search: 307/64, 307/66, 307/68, 307/67, 307/45, 307/46, 307/47, 320/2, 322/10, 322/11, 322/29, 318/107
• US Class Current: 307/64
• CPC Class Codes: H02J 9/066 characterised by the use of dynamo-electric machines H02J9/08 takes precedence

Abstract

An uninterruptable power supply, operating normally under power supplied by a utility, has a main motor, a smaller induction motor, and a mechanical load such as a generator coaxially coupled together. A battery is connected to the smaller induction motor through an inverter. The induction motor is normally idled at a frequency lower than that of the utility, and therefore operates as an induction generator which is used to charge the battery through the inverter. Upon utility failure, the utility line is disconnected and the induction motor is powered by the battery through the inverter. The frequency of the inverter may be increased to maintain the rotational speed of the system at a nearly constant level.

Claims

1. An uninterruptable power supply for normal operation under power supplied by a utility, and without interruption upon failure of the utility, comprising:

a main motor connectable to the utility;

an AC induction motor capable of generating an output current as an induction generator;

a mechanical load;

said main motor, said AC induction motor, and said mechanical load mechanically coupled together for rotation;

battery means to supply DC current;

current conversion means operatively electrically connected between said AC induction motor and said battery means to receive said output current from said AC induction motor and convert said output current to direct current so as to charge said battery means during normal operation, and to receive said DC current from said battery means and convert said battery current to AC motor driving current of a predetermined frequency to power said induction motor during a failure of the utility.

2. The uninterruptable power supply of claim 1, wherein said main motor is a synchronous motor.

3. The uninterruptable power supply of claim 1, wherein said main motor, said AC induction motor, and said mechanical load are coaxially coupled.

4. The uninterruptable power supply of claim 1, wherein said induction motor is smaller than said main motor.

5. The uninterruptable power supply of claim 1, wherein said induction motor is approximately half the size of said main motor.

6. The uninterruptable power supply of claim 1, where said current conversion means is an inverter capable of converting DC current to AC motor driving current and converting said output current to direct current.

7. The uninterruptable power supply of claim 1, and further comprising control means operatively connectable to the utility power supply to detect utility failure and to increase said frequency of said motor driving current from said current conversion means upon such a utility failure to cause said battery means to power said induction motor.

8. The uninterruptable power supply of claim 7, and further comprising:

control means operatively electrically connected to said current conversion means to increase said frequency of said current conversion means, to detect utility power failure and to control operation of said AC induction motor, said main motor, and said mechanical load.

9. The uninterruptable power supply of claim 1, and further comprising:

control means operatively electrically connected to said current conversion means to increase said frequency of said current conversion means upon utility failure to cause said battery means to power said induction motor, to detect a utility power failure, and to control operation of said AC induction motor, said main motor, and said mechanical load.

10. The uninterruptable power supply of claim 9, wherein said induction motor is approximately half the size of said main motor.

11. The uninterruptable power supply of claim 1, wherein said mechanical load is a generator.

12. A method of providing uninterruptable electric power to a load driven by a main motor using power from a utility at normal utility line frequency in normal operation, an induction motor and a mechanical load mechanically coupled together with said main motor, and current conversion means electrically connected between the induction motor and a battery to deliver current therebetween, comprising:

operating the main motor under utility power when utility power is available;

energizing the induction motor through the current conversion means at a frequency slightly below line frequency when utility power is available;

charging the battery through the current conversion means by using the induction motor as an induction generator when utility power is available; and

operating the induction motor under battery power through the current conversion means during failure of the utility power to operatively engage the mechanical load.

13. The method of providing uninterruptable power to a load as described in claim 12, and further comprising:

detecting when utility power has failed and in response thereto switching off utility power to the main motor once operation of the utility power has switched to battery power.

14. The method of providing uninterruptable power to a load as described in claim 12, and further comprising:

detecting that power from the utility has become available after utility failure;

synchronizing the frequency of the induction motor to the main motor;

connecting the main motor to utility power when frequency synchronization is present between main motor and induction motor; and

using the induction motor to charge the battery through the current conversion means.

15. The method of providing uninterruptable power to a load as described in claim 12, and further comprising:

increasing the frequency of the current from the conversion means to the induction motor to operate the mechanical load at normal utility line frequency upon failure of the utility.

16. The method of providing uninterruptable power to a load as described in claim 14, and further comprising:

reducing the frequency of current from the current conversion means to the induction motor so that the induction motor functions as an induction generator.

17. An uninterruptable power supply for normal operation under power supplied by a utility, and without interruption upon failure of the utility, comprising:

a main motor connectable to the utility;

an AC induction motor capable of generating an output current as an induction generator;

a mechanical load;

said main motor, said AC induction motor, and said mechanical load being mechanically coupled together for rotation, the AC induction motor being operatively positioned therebetween said main motor and said mechanical load;

battery means to supply DC current;

current conversion means operatively electrically connected between said AC induction motor and said battery means to receive said output current from said AC induction motor and convert said output current to direct current so as to charge said battery means during normal operation when said AC induction motor is rotated by said main motor, and to receive said DC current from said battery means and convert said battery current to AC motor driving current of a predetermined frequency to power said induction motor during a failure of the utility, the AC induction motor being continuously energized by the current conversion means.