Method and apparatus for line power monitoring for uninterruptible power supplies

Claim 2

AC line waveform monitoring apparatus for detecting AC line power faults and providing a fault signal for control of an uninterruptible power supply comprising: (a) means for sampling an AC line power signal at times synchronized with the cycle of the AC line waveform; (b) means for producing a reference waveform at selected sample times during the period of the AC line signal given previous reference waveform values and a prior cycle wherein a reference waveform value at each sample time comprises a selectively weighted average of value at that sample time in the prior cycle of the AC line signal and the previous reference waveform value at that sample time; (c) an uninterruptible power supply including an auxiliary power supply battery, the uninterruptible power supply receiving the AC line power and normally providing the AC line power to a load and responsive to a fault signal to switch to provide power to the load from the battery; (d) means for comparing the AC line signal waveform with the reference waveform at corresponding times in the reference waveform and the signal waveform and providing the fault signal to the uninterruptible power supply so that it provides power to the load from the battery when a selected difference condition is exceeded.

Claim 3

The apparatus of claim 1 wherein the means for producing a reference waveform does so in accordance with the expression: REF.sub.i,k =(1-a)REF.sub.i,k-1 +(a)SAMP.sub.i,k-1 where a is choosen such that 0<a<1, REF i ,k is the present value of the reference at the i th sample point in the k th cycle, REF i ,k-1 is the value of the reference at the i th sample point in the (k-1)th cycle and SAMP i ,k-1 is the value of the sample of the AC line input waveform at the i th sample point in the (k-1)th cycle.

Claim 4

The apparatus of claim 2 wherein a=0.5.

Claim 5

The apparatus of claim 2 wherein the means for comparing compares to determine if the difference condition is exceeded in accordance with the expression: |SAMP.sub.i,k -REF.sub.i,k |≧D.sub.i where D i is a chosen tolerance value for the sample point i.

Claim 6

The apparatus of claim 4 wherein the value of D i is choosen to be a constant for all of the sample points i.

Claim 7

The apparatus of claim 1 wherein the apparatus is adapted for monitoring 60 Hz line power and wherein the means for sampling samples at a selected number of points in each cycle which are equally spaced in time.

Claim 8

The apparatus of claim 6 wherein the means for sampling samples at a rate of 64 times a cycle.

Claim 9

The apparatus of claim 1 wherein the means for sampling includes an analog to digital converter for converting the sampled analog value to digital data.

Claim 10

The apparatus of claim 1 wherein the means for sampling includes means for phase-locking the sample times to the period of the AC line signal so that sampling is carried out at equally spaced points in time over each cycle of the AC line waveform.

Claim 11

The apparatus of claim 1 further including means for providing an estimate of the RMS value of the AC line waveform and providing the fault signal if the RMS estimate value falls below a selected minimum value.

Claim 12

The apparatus of claim 10 wherein the means for estimating the RMS value carries out a root-mean square calculation on the reference waveform created by the means for producing a reference waveform.

Claim 13

The apparatus of claim 2 further including means for providing an estimate of the RMS value of the AC line waveform and providing the fault signal if the RMS estimate values falls below a selected minimum value, and wherein the RMS estimate V rms (est) is calculated in accordance with the expression: ##EQU3## where n is the number of samples per cycle, and wherein the fault signal is provided if V mrs (est) is less than the selected minimum RMS value.

Claim 14

The apparatus of claim 1 wherein the means for comparing compares the absolute value of the difference between the reference waveform and the AC line signal waveform at each sample point with a selected difference level and provides a signal to increment a counter if the difference exceeds or is equal to the level and a signal to decrement the counter if the difference is less than the selected level, and wherein the fault signal is provided if the count in the counter exceeds a selected value indicative of the fault.

Claim 15

The apparatus of claim 12 wherein the number of samples n per cycle is 64.

Claim 16

AC line waveform monitoring apparatus for detecting AC line power faults and providing a fault signal for control of an uninterruptible power supply comprising: (a) means for sampling an AC line power signal at times synchronized with the cycle of the AC line waveform; (b) means for producing a reference waveform at selected sample times during the period of the AC line signal given previous reference waveform values and a prior cycle wherein a reference waveform value at each sample time comprises a selectively weighted average of sample values over a plurality of prior cycles of the AC line signal in accordance with the expression: REF.sub.i,k =(1-a)REF.sub.i,k-1 +(a)SAMP.sub.i,k-1 wherein a is chosen such that 0<a<1, REF i ,k is the present value of the reference of the i th sample point in the k th cycle, REF i ,k-1 is the value of the reference at th ei th sample point in the (k-1)th cycle and SAMP i ,k-1 is the value of the sample oft he AC line input waveform at the i th sample point in the (k-1)th cycle; (c) an uninterruptible power supply including an auxiliary power supply battery, the uninterruptible power supply receiving the AC line power and normally providing the AC line power to a load and responsive to a fault signal switch to provide power to the load from the battery; (d) means for estimating the RMS value of the AC line signal by carrying out a root-mean square calculation on the reference waveform and providing the fault signal to the uninterruptible power supply so that it provides power to the load from the battery if the RMS estimate value falls below a selected minimum value.

Claim 17

AC line waveform monitoring apparatus for detecting AC line power faults and providing a fault signal for control of an uninterruptible power supply comprising: (a) means for sampling an AC line power signal at times synchronized with the cycle of the AC line waveform; (b) means for producing a reference waveform at selected sample times during the period of the AC line signal given previous reference waveform values and a prior cycle wherein a reference waveform value at each sample time comprises a selectively weighted average of sample values over a plurality of prior cycles of the AC line signal in accordance with the expression: REF.sub.i,k =(1-a)REF.sub.i,k-1 +(a)SAMP.sub.i,k-1 wherein a is chosen such that 0<a<1, REF i ,k is the present value of the reference of the i th sample point in the k th cycle, REF i ,k-1 is the value of the reference at th ei th sample point in the (k-1)th cycle and SAMP i ,k-1 is the value of the sample oft he AC line input waveform at the i th sample point in the (k-1)th cycle; (c) an uninterruptible power supply including an auxiliary power supply battery, the uninterruptible power supply receiving the AC line power and normally providing the AC line power to a load and responsive to a fault signal switch to provide power to the load from the battery; (d) means for estimating the RMS value of the AC line signal by carrying out a root-mean square calculation on the reference waveform and providing the fault signal to the uninterruptible power supply so that it provides power to the load from the battery if the RMS estimate value falls below a selected minimum value.

Claim 18

The apparatus of claim 15 wherein a=0.5.

Claim 19

The apparatus of claim 15 wherein the RMS estimate V rms (est) is calculated in accordance with the expression: ##EQU4## where n is the number of samples per cycle, and wherein a fault signal is provided if V rms (est) is less than the selected minimum RMS value.

Claim 20

The apparatus of claim 15 wherein the apparatus is adapted for monitoring 60 Hz line power and wherein the means for sampling samples at a selected number of points in each cycle which are equally spaced in time.

Claim 21

The apparatus of claim 18 wherein the means for sampling samples at a rate of 64 times a cycle.

Claim 22

The apparatus of claim 15 wherein the means for sampling includes an analog to digital converter for converting the sampled analog value to digital data.

Claim 23

The apparatus of claim 15 wherein the means for sampling includes means for phase-locking the sample times to the period of the AC line signal so that sampling is carried out at equally spaced points in time over each cycle of the AC line waveform.

Claim 24

The apparatus of claim 15 including means for comparing the absolute value of the difference between the reference waveform and the AC line signal waveform at each sample point with a selected difference level and incrementing a counter if the difference exceeds or is equal to the level and decrementing the counter if the difference is less than the selected level, and wherein the fault signal is provided if the count in the counter exceeds a selected value indicative of a fault.

Claim 25

The apparatus of claim 17 wherein the number of samples n per cycle is 64.

Claim 26

An uninterruptible power supply comprising: (a) an auxiliary power supply battery; (b) power transfer means, connected to the auxiliary power supply battery and to AC line power, for responding to control signals to provide power to an AC output from either the AC line power or the battery; (c) control means for providing control signals to the power transfer means, the control means comprising: (1) means for sampling the AC power line signal at times synchronized with the cycle of the AC line waveform; (2) means for producing a reference waveform at selected sample times during the period of the AC line signal given previous reference waveform values and a prior cycle wherein a reference waveform value at each sample time comprises a selectively weighted average of the value at that sample time in the prior cycle of the AC line signal and the previous reference waveform value at that sample time; (3) means for comparing the AC line signal waveform with the reference waveform at corresponding times in the reference waveform and the signal waveform and providing a fault signal when a selected difference condition is exceeded, and for determining from the fault signal when a selected fault condition has occurred and then controlling the power transfer means to switch to supply power from the battery during the fault condition.

Claim 27

An uninterruptible power supply comprising: (a) an auxiliary power supply battery; (b) power transfer means, connected to the auxiliary power supply battery and to AC line power, for responding to control signals to provide power to an AC output from either the AC line power or the battery; (c) control means for providing control signals to the power transfer means, the control means comprising: (1) means for sampling the AC power line signal at times synchronized with the cycle of the AC line waveform; (2) means for producing a reference waveform at selected sample times during the period of the AC line signal given previous reference waveform values and a prior cycle wherein a reference waveform value at each sample time comprises a selectively weighted average of the value at that sample time in the prior cycle of the AC line signal and the previous reference waveform value at that sample time; (3) means for comparing the AC line signal waveform with the reference waveform at corresponding times in the reference waveform and the signal waveform and providing a fault signal when a selected difference condition is exceeded, and for determining from the fault signal when a selected fault condition has occurred and then controlling the power transfer means to switch to supply power from the battery during the fault condition.

Claim 28

The power supply of claim 24 wherein the means for producing a reference waveform does so in accordance with the expression: REF.sub.i,k =(1-a)REF.sub.i,k-1 +(a)SAMP.sub.i,k-1 where a is choosen such that 0<a<1, REF i ,k is the present value of the reference at the i th sample point in the k th cycle, REF i ,k-1 is the value of the reference at the i th sample point in the (k-1)th cycle and SAMP i ,k-1 is the value of the sample of the AC line input waveform at the i th sample point in the (k-1)th cycle.

Claim 29

The power supply of claim 25 wherein a=0.5.

Claim 30

The power supply of claim 25 wherein the means for comparing compares in accordance with the expression: |SAMP.sub.i,k -REF.sub.i,k |D.sub.i where D i is a chosen tolerance value for the sample point i.

Claim 31

The power supply of claim 27 wherein the value of D i is choosen to be a constant for all of the sample points i.

Claim 32

The power supply of claim 24 wherein the power supply receives 60 Hz line power and wherein the means for sampling samples at a selected number of points in each cycle which are equally spaced in time.

Claim 33

The power supply of claim 29 wherein the means for sampling samples at a rate of 64 times a cycle.

Claim 34

The power supply of claim 24 wherein the means for sampling includes an analog to digital converter for converting the sampled analog value to digital data.

Claim 35

The power supply of claim 24 wherein the means for sampling includes means for phase-locking the sample times to the period of the AC line signal so that sampling is carried out at equally spaced points in time over each cycle of the AC line waveform.

Claim 36

The power supply of claim 24 further including means for providing an estimate of the RMS value of the AC line waveform and providing the fault signal to the power transfer means to switch to supply power from the battery if the RMS estimate value falls below a selected minimum value.

Claim 37

The power supply of claim 33 wherein the means for estimating the RMS value carries out a root-mean square calculation on the reference waveform created by the means for producing a reference waveform.

Claim 38

The power supply of claim 25 further including means for providing an estimate of the RMS value of the AC line waveform and providing a signal to the power transfer means to switch to supply power from the battery if the RMS estimate values falls below a selected minimum value, and wherein the RMS estimate V rms (est) is calculated in accordance with the expression: ##EQU5## where n is the number of samples per cycle, and wherein the signal is provided if V rms (est) is less than the selected minimum RMS value.

Claim 39

The power supply of claim 24 wherein the means for comparing compares the absolute value of the difference between the reference waveform and the AC line signal waveform at each sample point with a selected difference level and provides a signal to increment a counter if the difference exceeds or is equal to the level and a signal to decrement the counter if the difference is less than the selected level, and wherein the fault condition is determined if the count in the counter exceeds a selected value indicative of the fault.

Claim 40

The power supply of claim 24 wherein the number of samples n per cycle is 64.

Claim 43

The method of claim 38 wherein the step of averaging is carried out to provide exponential averaging of the samples over the prior cycles with weights decreasing exponentially going back in time.

Claim 44

The method of claim 38 further including the step of phase-locking the sample times at which the AC line signal is sampled with the period of the AC line signal so that sampling is carried out at equally spaced points in time over each cycle of the AC line waveform.

Claim 45

The method of claim 38 further including the step of estimating the RMS value of the AC line waveform and comparing the value with a selected minimum value.

Claim 46

The method of claim 41 wherein the step of estimating the RMS values is performed by carrying out a root-mean square calculation on the reference waveform.