Backup protection switch to prevent reverse power flow in a UPS

• US 4,763,014 A
• Filed: 09/21/1987
• Issued: 08/09/1988
• Est. Priority Date: 09/21/1987
• Status: Expired due to Term

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.), Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: American Telephone & Telegraph Company (AT&T, Inc.)
• Inventors: Wright, Daniel A., Model, Michael J.
• Primary Examiner(s): Beha, Jr., William H.
• Application Number:
  US07/099,041
• Time in Patent Office: 323 Days
• Field of Search: 307/46, 307/64, 307/65, 307/66, 307/86, 361/84, 361/102, 361/3
• US Class Current: 307/66
• CPC Class Codes: H02J 9/062 for AC powered loads

Abstract

A UPS system includes a mechanical backup input line isolation switch to provide mechanical isolation between the primary energy source connected to the input line and the secondary energy source upon detection of a failure of an electronic isolation switch normally providing isolation between the input line and the secondary energy source. Detection of such a failure is accomplished by means of a dummy load which is connected in across the input line. Its impedance is sized to permit a small low level of current flow, above normal leakage current levels permitted by a functioning semiconductor electronic line switch, if energy is reverse coupled from the reserve energy source via a failed electronic line switch without draining significant power from the primary energy source when the UPS is normally operative and deriving power from the primary energy source. A power flow direction sensing circuit detects the direction of power flow at the input to which the primary energy source is connected to the UPS and a control circuit responsive to the power flow direction sensing circuit disconnects the input from the primary energy source if reverse power flow is detected by activating a mechanical switch to disconnect the input from the primary energy source.

Claims

1. An uninterruptible power supply, comprising:

a first input for accepting a primary source of energy,

a second input for accepting a reserve source of energy,

an output for accepting a load to be energized,

an energy coupling apparatus for coupling energy from the first and second inputs to the output and capable of coupling energy from the second input to the first input, and including first coupling means for directly coupling the first input to the output and second coupling means for coupling the first input to the output with amplification.

first and second primary disconnect switches for decoupling the first input from the first and second coupling means of the energy coupling apparatus when energy is being supplied to the output from the second input,

a backup disconnect switch for disabling energy flow from a reserve energy source connected to the second input into the first input,

means for faciltating a flow of energy from the second input to the first input should at least one of the first and second primary disconnect switches fail in a mode enabling energy flow through at least one of the first and second primary disconnect switches,

means for sensing energy flow from the energy coupling apparatus to the first input and operative to enable the backup disconect switch to open.

2. An uninterruptible power supply, comprising;

a first input for accepting a primary source of energy,

a second input for accepting a reserve source of energy,

an output for accepting a load to be energized,

an energy coupling apparatus for coupling energy from the first and second inputs to the output and capable of coupling energy from the second input to the first input,

a primary disconnect switch for decoupling the first input from the energy coupling apparatus when energy is being supplied to the output from the second input,

a backup disconnect switch for disabling energy flow from a reserve energy source connected to the second input into the first input,

means for facilitating a flow of energy from the second input to the firs input should the primary disconnect switch fail in a mode enabling energy flow through the primary disconnect switch,

means for sensing a direction of energy flow between the energy coupling apparatus and the first input,

means responsive to the means for sensing a direction of energy flow from the energy coupling apparatus to the first input for activating the backup disconnect switch.

3. An uninterruptible power supply, comprising:

a first input for accepting a primary source of energy,

a second input for accepting a reserve source of energy,

an output for accepting a load to be energized,

a power transformer including first and second windings for receiving energy from the first and second inputs and capable of coupling energy from the second input to the first input,

a primary disconnect switch for decoupling the first input from the first winding of the power transformer when energy is being supplied to the output from the second input,

a backup disconnect switch for disabling energy flow from a reserve energy source connected to the second input into the first input,

means for facilitating a flow of energy from the second input to the first input should the primary disconnect switch fail in a mode enabling energy flow through the primary disconnect switch,

means for sensing a direction of energy flow between the first winding of the power transformer and the first input,

means responsive to the means for sensing a direction of energy flow from the first winding of the power transformer to the first input for activating the backup disconnect switch.

4. An uninterruptible power supply as claimed in claim 3 wherein an end terminal of the first winding is directly connected to the ouput and further including a second disconnect switch for coupling the input to a tap of the first winding, the second disconnect switch being activated to conduct if a signal at the input is to be amplified and the means for facilitating enabling flow of energy from the second input to the first input should the second disconnect switch fail.

5. An uninterruptible power supply, comprising:

a first input for accepting a primary source of energy,

a second input for accepting a reserve source of energy,

an output for accepting a load to be energized,

an energy coupling apparatus for coupling energy from the first and second input to the output and electrically connected to enable the coupling of energy from the second input to the first input, and further including at least a direct electrical connection connecting the first input to the output,

a primary disconnect switch for decoupling the first input from the energy coupling apparatus when energy is being supplied to the output from the second input,

a backup disconnect switch for disabling energy flow from a reserve energy source connected to the second input into the first input,

means for facilitating a flow of energy from the second input to the first input should the primary disconnect switch fail in a mode enabling energy flow through the primary disconnect switch,

means for sensing a current flow to the means for facilitating,

means for ascertaining a direction of current flow connected to the means for sensing a current flow,

means responsive to the means for ascertaining a direction of current flow from the energy coupling apparatus to the first input for activating the backup disconnect switch.

6. An uninterruptible power supply as defined in claim 5 and further including a second disconnect switch for decoupling the first input from the energy coupling apparatus and the means for facilitating energy flow being operative should the second disconnect switch fail.

7. An uninterruptible power supply comprising;

a first input for accepting a primary source of energy,

a second input for accepting a reserve source of energy,

an output for accepting a load to be energized,

a transformer for coupling energy from the first and second input to the output and including;

a primary winding, a secondary winding, and the output being connected to an end terminal of the primary winding;

a first semiconductor disconnect switch connecting the first input to the end terminal of the primary winding,

a second semiconductor disconnect switch connecting the first input to an intermediate tap of the primary winding,

the second input being connected to the secondary winding,

a dummy load connected to the first and second semiconductor disconnect switch and operative for facilitating a current flow supplied from the second input greater than a leakage current of the first and second semiconductor disconnect switch should at least one of the first and second semiconductor disconnect switches fail so as to conduct current,

current direction sensing means including;

current sensing means connected between the dummy load and the first and second semiconductor disconnect switches,

voltage sensing means connected between the dummy load and the first and second semiconductor disconnect switches;

signal phase comparison means for ascertaining a phase relation between signals detected by the current sensing means and the voltage sensing means in order to determine a direction of current flow;

a mechanical switch operative for disabling energy flow from the reserve energy source to the primary energy source and responsive to the signal phase comparison means.

8. An uninterruptible power supply comprising:

a first input for accepting a primary energy source,

a second input for accepting a reserve energy source,

an output for accepting a load to be energized,

coupling means for connecting the first and second inputs to the output,

semiconductor switches operative for disconnecting the first input from the coupling means when power is supplied to the load from the second input,

current enabling means for permitting current flow from the second input to the first input upon failure of the semiconductor switches,

current direction sensing means connected between the first input and the coupling means for detecting reverse current flow from the second input to the first input, and

mechanical isolation means for isolating the first input from the second input in response to the current direction sensing means.