Method and apparatus for adaptive and corrective determination of battery run-time in uninterruptible power systems
First Claim
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 a calculated remaining run-time tR (n) available during which the battery can supply power to the load for a current iteration n of the run-time determination;
(b) determining a corrected remaining run-time tR '"'"'(n) in accordance with the expression;
##EQU17## where;
tS is a time period between iterations of the run-time determination, andtR (n-1) is the calcuate remaining run-time determined during a next previous iteration of the run-time determination; and
(c) setting an estimated determined run-time tRD (n) to the corrected run-time tR '"'"'(n) if the corrected run-time does not vary by more than a selected correction factor from a corrected run-time tR '"'"'(n-1) determined during a next previous iteration of the run-time determination, otherwise setting tRD (n) to an estimated determined run-time tRD (n-1) from a previous iteration of the run-time determination less an amount of time tS elapsed since the previous iteration.
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Accused Products
Abstract
The run-time available from an uninterruptible power system is accurately determined both during supply of power from the battery to the load and during the time where power is supplied directly from an AC power system to the load. During power outages, where power is supplied from the battery through the inverter to the load, the remaining run-time is first estimated by calculation and then corrected by modification of the calculated value according to the reciprocal of the run-time slope. Alternatively, a scaling factor is used as part of the first run-time calculations and a correction factor which applies more corrective weight as the time on inverter progresses may be used. During power outages and when power is supplied from the AC power system to the load the maximum available run-time is extrapolated from a table of values representing maximum available run-times at various levels of power being supplied to the load from a fully charged battery. These values are updated after inverter runs to reflect actual system run-times. The maximum run-times are thereby adapted to reflect battery aging and other unique characteristics of the system.
55 Citations
36 Claims
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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:
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(a) determining a calculated remaining run-time tR (n) available during which the battery can supply power to the load for a current iteration n of the run-time determination; (b) determining a corrected remaining run-time tR '"'"'(n) in accordance with the expression;
##EQU17## where;
tS is a time period between iterations of the run-time determination, andtR (n-1) is the calcuate remaining run-time determined during a next previous iteration of the run-time determination; and (c) setting an estimated determined run-time tRD (n) to the corrected run-time tR '"'"'(n) if the corrected run-time does not vary by more than a selected correction factor from a corrected run-time tR '"'"'(n-1) determined during a next previous iteration of the run-time determination, otherwise setting tRD (n) to an estimated determined run-time tRD (n-1) from a previous iteration of the run-time determination less an amount of time tS elapsed since the previous iteration. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. An uninterruptible power system connectable to AC power system lines at its input terminals and to a load at its output terminals, comprising:
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(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; (e) means for determining a calculated remaining run-time tR (n) available during which the battery can supply power to the load for a current iteration n of a run-time determination; (f) means for determining a corrected remaining run-time tR '"'"'(n) in accordance with the expression;
##EQU21## where;
tS is a time period between iterations of the run time determination, andtR (n-1) is the calculated remaining run-time determined during a next previous iteration of the run-time determination; and (g) means for setting an estimated determined run-time tRD (n) to the corrected run-time tR '"'"'(n) if the corrected run-time does not vary by more than a selected correction factor from a corrected run-time tR '"'"'(n-1) determined during a next previous iteration of the run-time determination, otherwise setting tRD (n) to an estimated determined run-time tRD (n-1) from a previous iteration of the run-time determination less an amount of time tS elapsed since the previous iteration. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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28. 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:
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(a) measuring the battery voltage VB while the battery supplies power to the load; (b) calculating a base equation reference at an iteration of the run-time determination N near a start of power being supplied from the battery to the load in accordance with the expression;
##EQU25## where;
Base(N) is the base equation reference at the Nth iteration of the run-time calculation,VB (N) is the measured battery voltage at the Nth iteration, VLL (N) iS the lower limit of battery voltage below which the battery should not supply power at the Nth iteration, and VFC (N) is the full charge voltage of the battery; (c) computing a scaling factor KS at an iteration n of the run-time determination in accordance with the following expression;
##EQU26## where;
tS is a time period between iterations of the run-time determination, andBase(n) is the base equation calculated at the nth iteration of the run-time calculation; (d) setting a converged scaling factor KS '"'"' equal to the scaling factor KS for the nth iteration when the scaling factors for two consecutive iterations of the run-time determination converge to within a selected amount; (e) computing a correction factor KC for an iteration n of the run-time determination in accordance with the following expression;
##EQU27## (f) setting a corrected run-time tR '"'"'(n) for the nth iteration of the run-time determination equal to the product of the converged scaling factor KS '"'"'the correction factor KC and the base equation calculated at the nth iteration of the run-time calculation Base(n). - View Dependent Claims (29, 30, 31, 32)
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33. An uninterruptible power system connectable to AC power system lines at its input terminals and to a load at its output terminals, comprising:
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(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 measuring the battery voltage VB while the battery supplies power to the load, for calculating a base equation reference at an iteration of a run-time determination N near a start of power being supplied from the battery to the load in accordance with the expression;
##EQU28## where;
Base(N) is the base equation reference at the Nth iteration of the run-time calculation,VB (N) is the measured battery voltage at the Nth iteration, VLL (N) iS the lower limit of battery voltage below which the battery should not supply power at the Nth iteration, and VFC (N) is the full charge voltage of the battery; for computing a scaling factor KS at an iteration n of the run-time determination in accordance with the following expression;
##EQU29## where;
tS is a time period between iterations of the run-time determination, andBase(n) is the base equation calculated at the nth iteration of the run-time calculation; for setting a converged scaling factor KS '"'"' equal to the scaling factor KS for the nth iteration when the scaling factors for two consecutive iterations of the run-time determination converge to within a selected amount; for computing a correction factor KC for an iteration n of the run-time determination in accordance with the following expression;
##EQU30## for setting a corrected run-time tR '"'"'(n) for the nth iteration of the run-time determination equal to the product of the converged scaling factor KS '"'"' the correction factor KC and the base equation calculated at the nth iteration of the run-time calculation Base(n). - View Dependent Claims (34, 35)
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36. A method for determining the maximum run-time during which power can be supplied from a battery to a load, comprising the steps of:
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(a) storing one or more starting values, each starting value representing the maximum run-time from a fully charged battery supplying power to a selected percentage of a full load; (b) extrapolating maximum run-times from the starting values; (c) calculating a remaining run-time available while power is being supplied to the load from the battery; (d) updating the starting values by extrapolation from the calculated remaining run-time available, wherein updating the starting values includes extrapolating a calculated run-time from an end of a period in which power was supplied to the load from a battery which was fully charged at a start of the period plus the duration of the period.
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Specification