Claims
- 1. A method of determining the run-time during which power can be supplied from a battery through an inverter of an uninterruptible power supply to a load while such power is being supplied to the load, comprising the steps of:
- (a) determining the current supplied to the load;
- (b) measuring the battery voltage while the battery supplies power to the load;
- (c) determining the remaining run-time t.sub.R (INV) available during which the battery can supply power to the load in accordance with the expression ##EQU7## where: K.sub.1 and K.sub.2 are predetermined constants,
- V.sub.LL is the lower limit of battery voltage below which the battery should not supply power,
- V.sub.FC is the full charge voltage of the battery,
- V.sub.B the measured battery voltage while the battery supplies power to the load, and
- I.sub.o (INV) is the RMS current supplied to the load.
- 2. The method of claim 1 wherein the value of I.sub.o (INV) is determined as either the measured RMS current supplied to the load through the inverter, an estimate of load current based on power consumed in the load and inverter, or an estimate of load current based on battery current.
- 3. The method of claim 1 wherein the remaining run-time is redetermined periodically at regular intervals.
- 4. The method of claim 1 including the step of providing a display to an operator of the remaining run-time.
- 5. The method of claim 3 wherein before power is supplied by the uninterruptible power supply from the battery to the load, power is supplied from an AC power system to the load, and including the steps of:
- (1) recharging the battery with power from the AC power system;
- (2) determining an available run-time t.sub.R (LINE) while power is provided from the AC power system to the load and the battery is being recharged;
- (3) then, when power from the AC power system is no longer supplied to the load and power from the battery is being supplied to the load, displaying the run-time t.sub.R (INV) in accordance with the expression ##EQU8## if t.sub.R (INV) as so determined is less than t.sub.R (LINE) or if the length of time that power has been supplied from the battery through the inverter to the load is greater than a selected period of time, and, if not, then displaying the run-time t.sub.R (INV) as equal to t.sub.R (LINE).
- 6. The method of claim 5 wherein the selected period of time is 30 seconds.
- 7. The method of claim 1 including the additional steps of
- (1) determining when power is available from the AC power system, and then measuring and storing the then existing values of the load current I.sub.o o(INV) and battery voltage V.sub.B (INV),
- (2) discontinuing the supply of power from the battery to the load and supplying power from the AC power system to the load;
- (3) measuring the open circuit battery voltage V.sub.B(OC)M after power is no longer supplied from the battery to the load;
- (4) then recharging the battery at a known rate from the AC power system;
- (5) determining the RMS current I.sub.o (LINE) supplied to the load;
- (6) determining a constant K.sub.3 after power is no longer supplied from the battery to the load in accordance with the following expression: ##EQU9## (7) determining an estimate V.sub.B(OC)C of the open circuit battery voltage which is initially equal to V.sub.B(OC)M and is updated at selected periodic intervals .DELTA.t such that at a time t+.DELTA.t, V.sub.B(OC)C is determined as
- V.sub.B(OC)C (t+.DELTA.t)=V.sub.B(OC)C (t)+K.sub.4 .DELTA.t
- where K.sub.4 is a predetermined constant indicative of the rate of recharge of the battery;
- (8) then determining an estimated battery voltage under load V.sub.BC in accordance with the expression
- V.sub.BC =V.sub.B(OC)C -K.sub.3 I.sub.o (LINE)
- (9) then determining the estimated run-time t.sub.R (LINE) during supply of power to the load from the AC power system in accordance with the expression: ##EQU10##
- 8. The method of claim 7 including the step of displaying to an operator the estimated remaining run-time t.sub.R (LINE) during supply of power to the load from the AC power system.
- 9. The method of claim 7 wherein there is a previous value of K.sub.3 which is used as the value of K.sub.3 if any of the following conditions are not met:
- the percentage of load power drawn is greater than 25% of full load power,
- the time during which the inverter was run and power was supplied by the battery was greater than or equal to a selected period of time,
- the last run-time t.sub.R (INV) estimated during inverter operation is greater than a selected low run-time alarm value,
- the new calculated K.sub.3 changes from the previous value of K.sub.3 by more than a selected minimum, or the new K.sub.3 is less than or equal to ##EQU11## where I.sub.o (RATED) is the maximum rated load current that can be drawn from the inverter.
- 10. The method of claim 7 wherein the remaining run-time t.sub.R (LINE) during supply of power to the load from the AC power system is determined periodically at regular intervals.
- 11. A method of determining the run-time during which power can be supplied from a battery through an inverter of an uninterruptible power supply to a load while power is being supplied to the load from an AC power system, comprising the steps of:
- (a) measuring the open circuit voltage V.sub.B(OC)M of the battery when the battery is not being charged and is not supplying power to a load;
- (b) then charging the battery at a known rate from the AC power system;
- (c) estimating a new open circuit battery V.sub.B(OC)C voltage while the battery is recharging based on the measured open circuit battery voltage V.sub.B(OC)M and the length of time t the battery has been recharged;
- (d) determining the RMS current I.sub.o (LINE) being supplied to the load;
- (e) estimating the battery voltage V.sub.BC under load conditions as the estimated open circuit voltage V.sub.B(OC)C minus a value equal to the load current I.sub.o (LINE) times a selected constant;
- (f) determining the estimated run-time t.sub.R (LINE) based on the load current I.sub.o (LINE), the estimated battery voltage V.sub.BC under load, the lower limit of battery voltage V.sub.LL, and the full charge battery voltage V.sub.FC.
- 12. The method of claim 11 wherein the estimated run-time t.sub.R (LINE) is determined in accordance with the following expression: ##EQU12## where K.sub.1 and K.sub.2 are predetermined constants, and I.sub.o (LINE) is a measured value of RMS current supplied to the load or an estimate of load current based on power consumed in the load.
- 13. The method of claim 11 including the step of providing a display to an operator of the remaining run-time.
- 14. The method of claim 11 wherein the remaining run-time is redetermined periodically at regular intervals.
- 15. The method of claim 11 wherein the estimate V.sub.B(OC)C of the open circuit battery voltage is initially equal to V.sub.B(OC)M and is updated at selected periodic intervals .DELTA.t such that at a time t+.DELTA.t, V.sub.B(OC)C is determined as
- V.sub.B(OC)C (t+.DELTA.t)=V.sub.B(OC)C (t)+K.sub.4 .DELTA.t
- where K.sub.4 is a predetermined constant indicative of the rate of recharge of the battery.
- 16. The method of claim 11 wherein the estimated battery voltage under load V.sub.BC is determined as
- V.sub.BC =V.sub.B(OC)C -K.sub.3 I.sub.o (LINE)
- where ##EQU13## and V.sub.B (INV)=a measured battery voltage before switching from inverter to AC power system power,
- I.sub.B (INV)=a measured RMS load current before switching from inverter to AC power system power,
- V.sub.B(OC)M =measured open circuit battery voltage.
- 17. A method of operating an uninterruptible power supply and determining the run-time during which power can be supplied from a battery through an inverter of the uninterruptible power supply to a load while power is being supplied to the load from an AC power system, comprising the steps of:
- (a) supplying power to the load from the battery through the inverter when power is not available from the AC power system;
- (b) determining when power is available from the AC power system, and then determining and storing the then existing values of the load current I.sub.o (INV) and battery voltage V.sub.B (INV),
- (c) discontinuing the supply of power from the battery to the load and supplying power from the AC power system to the load;
- (d) measuring the open circuit battery voltage V.sub.B(OC)M after power is no longer supplied from the battery to the load;
- (e) then recharging the battery at a known rate from the AC power system;
- (f) determining the RMS current I.sub.o (LINE) supplied to the load;
- (g) determining a constant K.sub.3 after power is no longer supplied from the battery to the load in accordance with the following expression: ##EQU14## where V.sub.(B(OC)M is measured open circuit battery voltage; (h) determining an estimate V.sub.B(OC)C of the open circuit battery voltage which is initially equal to V.sub.B(OC)M and is updated at selected periodic intervals .DELTA.t to such that at a time t+.DELTA.t, V.sub.B(OC)C is determined as
- V.sub.B(OC)C (t+.DELTA.t)=V.sub.B(OC)C (t)+K.sub.4 .DELTA.t
- where K.sub.4 is a predetermined constant indicative of the rate of recharge of the battery;
- (i) then determining an estimated battery voltage under load V.sub.BC in accordance with the expression
- V.sub.BC V.sub.B(OC)C -K.sub.3 I.sub.o (LINE)
- (j) then determining the estimated run-time t.sub.R (LINE) during supply of power to the load from the AC power system in accordance with the expression: ##EQU15## where V.sub.LL is the lower limit of battery voltage below which the battery should not supply power, and K.sub.1 and K.sub.2 are predetermined constants.
- 18. The method of claim 17 including the step of displaying to an operator the estimated remaining run-time t.sub.R (LINE) during supply of power to the load from the AC power system.
- 19. The method of claim 17 wherein there is a previous value of K.sub.3 which is used as the value of K.sub.3 if any of the following conditions are not met:
- the percentage of load power drawn is greater than 25% of full load power,
- the time during which the inverter was run and power was supplied by the battery was greater than or equal to a selected period of time,
- the last run-time t.sub.R (INV) estimated during inverter operation is greater than a low run-time alarm value, the new calculated K.sub.3 changes from the previous value of K.sub.3 by more than a selected minimum, or the new K.sub.3 is less than or equal to ##EQU16## where I.sub.o (RATED) is the maximum rated load current that can be drawn from the inverter.
- 20. The method of claim 17 wherein the remaining run-time t.sub.R (LINE) during supply of power to the load from the AC power system is determined periodically at regular intervals.
- 21. An uninterruptible power system connectible to AC power system lines at its input terminals and to a load at its output terminals, comprising:
- (a) an auxiliary power supply battery;
- (b) a power supply path from the input terminals to the output terminals to normally supply power from an AC power system connected to the input terminals to a load connected to the output terminals;
- (c) means, including an inverter, responsive to control signals for interrupting the supply of power through the power supply path from the AC power system lines to the load and for selectively providing AC power from the battery to the power supply path through the inverter and thence to the load;
- (d) control means for providing control signals, upon occurrence of a line fault on the AC power system lines, to the means responsive to control signals to cause the supply of power to the load to be transferred from the AC power system to the battery and from the battery back to the AC power system when power is available therefrom, the control means further including means for determining the current supplied to the load during supply of power to the load from the battery,
- (e) means for measuring the battery voltage while the battery supplies power to the load, and
- (f) means for determining the remaining run-time t.sub.R (INV) available during which the battery can supply power to the load in accordance with the expression ##EQU17## where: K.sub.1 and K.sub.2 are predetermined constants,
- V.sub.LL is the lower limit of battery voltage below which the battery should not supply power,
- V.sub.FC is the full charge voltage of the battery,
- V.sub.B is the measured battery voltage while the battery supplies power to the load, and
- I.sub.o (INV) is the RMS current supplied to the load.
- 22. The system of claim 21 wherein the value of I.sub.o (INV) is determined by the control means as either measured RMS current supplied to the load through the inverter, an estimate of load current based on power consumed in the load and inverter, or an estimate of load current based on battery current.
- 23. The system of claim 21 including means for providing a display to an operator of the remaining run-time.
- 24. The system of claim 21 wherein the control means redetermines the remaining run-time periodically at regular intervals.
- 25. The system of claim 21 wherein the control means further includes means for, determining when power is available from the AC power system, and then measuring and storing the then existing values of the load current I.sub.o (INV) and battery voltage V.sub.B (INV), for discontinuing the supply of power from the battery to the load and supplying power from the AC power system to the load; for measuring the open circuit battery voltage V.sub.B(OC)M after power is no longer supplied from the battery to the load, for recharging the battery at a known rate from the AC power system, for determining the RMS current I.sub.o (LINE) supplied to the load, for determining a constant K.sub.3 after power is no longer supplied from the battery to the load in accordance with the following expression: ##EQU18## determining an estimate V.sub.B(OC)C of the open circuit battery voltage which is initially equal to V.sub.B(OC)M and is updated at selected periodic intervals .DELTA.t such that at a time t+.DELTA.t, V.sub.B(OC)C is determined as
- V.sub.B(OC)C (t+.DELTA.t)=V.sub.B(OC)C (t)+K.sub.4 .DELTA.t
- where K.sub.4 is a predetermined constant indicative of the rate of recharge of the battery, for
- then determining an estimated battery voltage under load V.sub.BC in accordance with the expression
- V.sub.BC =V.sub.B(OC)C -K.sub.3 I.sub.o (LINE)
- and for then determining the estimated run-time t.sub.R (LINE) during supply of power to the load from the AC power system in accordance with the expression: ##EQU19##
- 26. The system of claim 25 including means for displaying to an operator the estimated remaining run-time t.sub.R (LINE) during supply of power to the load from the AC power system.
- 27. The system of claim 26 wherein there is a previous value of K.sub.3 which is used as the value of K.sub.3 if any of the following conditions are not met:
- the percentage of load power drawn is greater than 25% of full load power,
- the time during which the inverter was run and power was supplied by the battery was greater than or equal to a selected period of time,
- the last run-time t.sub.R (INV) estimated during inverter operation is less than a selected low run-time alarm value,
- the new calculated K.sub.3 changes from the previous value of K.sub.3 by more than a selected minimum, or the new K.sub.3 is greater than or equal to ##EQU20## where I.sub.o (RATED) is the maximum rated load current that can be drawn from the inverter.
- 28. The system of claim 26 wherein the control means determines the remaining run-time t.sub.R (LINE) during supply of power to the load from the AC power system periodically at regular intervals.
- 29. An uninterruptible power system connectible to AC power system lines at its input terminals and to a load at its output terminals, comprising:
- (a) an auxiliary power supply battery;
- (b) a power supply path from the input terminals to the output terminals to normally supply power from an AC power system connected to the input terminals to a load connected to the output terminals;
- (c) means, including an inverter, responsive to control signals for interrupting the supply of power through the power supply path from the AC power system lines to the load and for selectively providing AC power from the battery to the power supply path through the inverter and thence to the load;
- (d) charger means for recharging the battery;
- (e) control means for providing control signals, upon occurrence of a line fault on the AC power system lines, to the means responsive to control signals to cause the supply of power to the load to be transferred from the AC power system to the battery and from the battery back to the AC power system when power is available therefrom, the control means further including means for measuring the open circuit voltage V.sub.V(OC)M of the battery when the battery is not being charged and is not supplying power to a load, then controlling the charger means to charge the battery at a known rate from the AC power system; and further for estimating a new open circuit battery voltage V.sub.B(OC)C while the battery is recharging based on the measured open circuit battery voltage V.sub.B(OC)M and the length of time t the battery has been recharged, determining the RMS current I.sub.o (LINE) being supplied to the load, estimating the battery voltage V.sub.BC under load conditions as the estimated open circuit voltage V.sub.B(OC)C minus a value equal to the load current I.sub.o (LINE) times a constant, and determining the estimated run-time t.sub.R (LINE) based on the load current I.sub.o (LINE), the estimated battery voltage V.sub.BC under load, the lower limit of battery voltage V.sub.LL, and the full charge battery voltage V.sub.FC.
- 30. The system of claim 29 wherein the estimated run-time t.sub.R (LINE) is determined by the control means in accordance with the following expression: ##EQU21## where K.sub.1 and K.sub.2 are predetermined constants and I.sub.o (LINE) is measured by the control means or estimated based on power supplied to the load.
- 31. The system of claim 29 including means for providing a display to an operator of the remaining run-time.
- 32. The system of claim 29 wherein the remaining run-time is redetermined by the control means periodically at regular intervals.
- 33. The system of claim 29 wherein the control means initially estimates V.sub.B(OC)C, the open circuit battery voltage, as equal to V.sub.B(OC)M and then updates the estimate at selected periodic intervals .DELTA.t such that at a time t+.DELTA.t, V.sub.B(OC)C is determined as
- V.sub.B(OC)C (t+.DELTA.t)=V.sub.B(OC)C (t)+K.sub.4 .DELTA.t
- where K.sub.4 is a predetermined constant indicative of the rate of recharge of the battery.
- 34. The system of claim 29 wherein the estimated battery voltage under load V.sub.BC is determined by the control means as
- V.sub.BC =V.sub.B(OC)C -K.sub.3 I.sub.o (LINE)
- where ##EQU22## and V.sub.B (INV)=a measured battery voltage before switching from inverter to AC power system power,
- I.sub.B (INV)=a measured RMS load current before switching from inverter to AC power system power,
- V.sub.B(OC)M =measured open circuit battery voltage.
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of prior application Ser. No. 07/702,733, filed May 17, 1991, by Frederick A. Stich, et al., entitled Back-Up Uninterruptible Power System, the disclosure of which is incorporated herein by reference.
US Referenced Citations (12)
Foreign Referenced Citations (1)
Number |
Date |
Country |
903081396 |
Jan 1991 |
EPX |
Non-Patent Literature Citations (1)
Entry |
Paper entitled "Explanation of Run Time to Go Calculation Phase 3 MicroFerrups (Models MD350-MD2KVA)", no date. |
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
702733 |
May 1991 |
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