Method and apparatus for determination of battery run-time in uninterruptible power system
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 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 tR (INV) available during which the battery can supply power to the load in accordance with the expression ##EQU7## where;
K1 and K2 are predetermined constants,VLL is the lower limit of battery voltage below which the battery should not supply power,VFC is the full charge voltage of the battery,VB the measured battery voltage while the battery supplies power to the load, andIo (INV) is the RMS current supplied to the load.
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Accused Products
Abstract
The run-time on battery power available from an uninterruptible power system is accurately determined both during supply of power from the battery through an inverter 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 output voltage of the battery is directly measured as is the output current supplied to the load. The remaining run-time is determined utilizing the measured battery voltage, the measured output current, and system specifications including the full charge open circuit voltage of the battery, the allowable lower limit of battery voltage, and constants which are characteristic of the uninterruptible power supply and the battery. When power is supplied from the AC power system to the load, the open circuit voltage of the battery is measured initially, and then during the time that the battery is being recharged the open circuit battery voltage is calculated based on the initial open circuit voltage adjusted by a factor porportional to the time that the battery has been charged. The calculated open circuit voltage is used to calculate a battery voltage under load conditions by subtracting a term proportional to output current. These estimates are then utilized to calculate run-time in a manner similar to that used to calculate run-time when the battery is loaded. Thus, the inverter need not be turned on to supply power to the load solely for the purpose of testing the battery.
312 Citations
34 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 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 tR (INV) available during which the battery can supply power to the load in accordance with the expression ##EQU7## where;
K1 and K2 are predetermined constants,VLL is the lower limit of battery voltage below which the battery should not supply power, VFC is the full charge voltage of the battery, VB the measured battery voltage while the battery supplies power to the load, and Io (INV) is the RMS current supplied to the load. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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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:
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(a) measuring the open circuit voltage VB(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 VB(OC)C voltage while the battery is recharging based on the measured open circuit battery voltage VB(OC)M and the length of time t the battery has been recharged; (d) determining the RMS current Io (LINE) being supplied to the load; (e) estimating the battery voltage VBC under load conditions as the estimated open circuit voltage VB(OC)C minus a value equal to the load current Io (LINE) times a selected constant; (f) determining the estimated run-time tR (LINE) based on the load current Io (LINE), the estimated battery voltage VBC under load, the lower limit of battery voltage VLL, and the full charge battery voltage VFC. - View Dependent Claims (12, 13, 14, 15, 16)
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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:
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(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 Io (INV) and battery voltage VB (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 VB(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 Io (LINE) supplied to the load; (g) determining a constant K3 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 VB(OC)C of the open circuit battery voltage which is initially equal to VB(OC)M and is updated at selected periodic intervals Δ
t to such that at a time t+Δ
t, VB(OC)C is determined as
space="preserve" listing-type="equation">V.sub.B(OC)C (t+Δ
t)=V.sub.B(OC)C (t)+K.sub.4 Δ
twhere K4 is a predetermined constant indicative of the rate of recharge of the battery; (i) then determining an estimated battery voltage under load VBC in accordance with the expression
space="preserve" listing-type="equation">V.sub.BC V.sub.B(OC)C -K.sub.3 I.sub.o (LINE)(j) then determining the estimated run-time tR (LINE) during supply of power to the load from the AC power system in accordance with the expression;
##EQU15## where VLL is the lower limit of battery voltage below which the battery should not supply power, and K1 and K2 are predetermined constants. - View Dependent Claims (18, 19, 20)
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21. An uninterruptible power system connectible 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 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 tR (INV) available during which the battery can supply power to the load in accordance with the expression ##EQU17## where;
K1 and K2 are predetermined constants,VLL is the lower limit of battery voltage below which the battery should not supply power, VFC is the full charge voltage of the battery, VB is the measured battery voltage while the battery supplies power to the load, and Io (INV) is the RMS current supplied to the load. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28)
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29. An uninterruptible power system connectible 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) 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 VV(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 VB(OC)C while the battery is recharging based on the measured open circuit battery voltage VB(OC)M and the length of time t the battery has been recharged, determining the RMS current Io (LINE) being supplied to the load, estimating the battery voltage VBC under load conditions as the estimated open circuit voltage VB(OC)C minus a value equal to the load current Io (LINE) times a constant, and determining the estimated run-time tR (LINE) based on the load current Io (LINE), the estimated battery voltage VBC under load, the lower limit of battery voltage VLL, and the full charge battery voltage VFC. - View Dependent Claims (30, 31, 32, 33, 34)
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Specification