EP0416569A2
Expired / Lapsed
EP
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Method and apparatus for line power monitoring for uninterruptible power supplies
Assignee: Best Power Technology Inc
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Filing: 1990-09-05
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Granted: —
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Expires: 2010-09-05
Abstract
Abstract AC line monitoring is provided for uninterruptible power supplies to detect AC power system line faults by comparing the presently received cycle of the AC power line signal with a reference waveform. The reference waveform is formed of a composite of waveforms from prior cycles which adapts over time to the shape of the AC power line waveform, so that waveforms other than pure sinusoids can be accepted without triggering false fault conditions. The composite reference waveform may be formed of essentially all samples from prior cycles with exponentially decaying weighting. An excessive deviation of the current waveform from the reference waveform results in a fault being detected which causes switching of the uninterrupible power supply to provide backup power. The RMS value of the power line voltage is also estimated on a substantially real time basis, preferably by calculating the RMS value of the reference waveform, to provide a fault condition signal when the estimated RMS value falls below a selected level, which also can be utilized to cause switching of the uninterruptible power supply.
Inventors
- 👤 Richard V. Baxter
- 👤 Frederick A. Stich
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-28 14:39
CPC Classifications
H; H02; H02H; H02H3/00; H02H3/24; H02H3/50
Claims Analysis
Total Claims: 46
Claim 1
Independent Claim
114 words
AC line waveform monitoring apparatus comprising: (a) means for sampling an AC line 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 wherein each reference value at each sample time comprises a selectivly weighted average of sample values over a plurality of prior cycles of the AC line signal; (c) means for comparing the values of samples at sample times in a new cycle of the AC line signal waveform with the reference values at the corresponding cycle sample times and providing a fault signal when a selected difference condition is exceeded.
Claim 2
Dependent Claim
114 words
AC line waveform monitoring apparatus comprising: (a) means for sampling an AC line 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 wherein each reference value at each sample time comprises a selectivly weighted average of sample values over a plurality of prior cycles of the AC line signal; (c) means for comparing the values of samples at sample times in a new cycle of the AC line signal waveform with the reference values at the corresponding cycle sample times and providing a fault signal when a selected difference condition is exceeded.
Claim 3
Dependent Claim
98 words
The apparatus of Claim 1 wherein the means for producing a reference waveform does so in accordance with the expression: REF i,k = (1-a)REF i,k-1 + (a)SAMP 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 samp!e of the AC line input waveform at the i th sample point in the (k-1)th cycle.
Claim 4
Dependent Claim
7 words
The apparatus of Claim 2 wherein a=0.5.
Claim 5
Dependent Claim
46 words
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 i,k - REF i,k | ≧ D i where D i is a chosen tolerance value for the sample point i.
Claim 6
Dependent Claim
24 words
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
Dependent Claim
37 words
The apparatus of Claim 1 wherein the apparatus is adapted for monitoring 60Hz 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
Dependent Claim
19 words
The apparatus of Claim 6 wherein the means for sampling samples at a rate of 64 times a cycle.
Claim 9
Dependent Claim
25 words
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
Dependent Claim
45 words
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
Dependent Claim
37 words
The apparatus of Claim 1 further including means for providing an estimate of the RMS value of the AC line waveform and providing a fault signal if the RMS estimate value falls below a selected minimum value.
Claim 12
Dependent Claim
32 words
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
Dependent Claim
80 words
The apparatus of Claim 2 further including means for providing an estimate of the RMS value of the AC line waveform and providing a 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: 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 14
Dependent Claim
92 words
The apparatus of Claim 1 wherein the means for comparing compares the absolute value of the difference between the reference waveform and the new cycle of the AC line signal at each sample point with a selected difference level and provides the fault signal to increment a counter if the difference exceeds or is equal to the level and decrements the counter if the difference is less than the selected level, and wherein a fault signal is provided if the count in the counter exceeds a selected value indicative of a fault.
Claim 15
Dependent Claim
15 words
The apparatus of Claim 12 wherein the number of samples n per cycle is 64.
Claim 16
Dependent Claim
193 words
AC line waveform monitoring apparatus comprising: (a) means for sampling an AC line 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 wherein each reference value at each sample time comprises a selectivly weighted average of sample values over a plurality of prior cycles of the AC line signal in accordance with the expression: REF i,k = (1-a)REF i,k-1 + (a)SAMP 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. (c) 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 a fault signal if the RMS estimate value falls below a selected minimum value.
Claim 17
Dependent Claim
193 words
AC line waveform monitoring apparatus comprising: (a) means for sampling an AC line 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 wherein each reference value at each sample time comprises a selectivly weighted average of sample values over a plurality of prior cycles of the AC line signal in accordance with the expression: REF i,k = (1-a)REF i,k-1 + (a)SAMP 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. (c) 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 a fault signal if the RMS estimate value falls below a selected minimum value.
Claim 18
Dependent Claim
7 words
The apparatus of Claim 15 wherein a=0.5.
Claim 19
Dependent Claim
47 words
The apparatus of Claim 15 wherein the RMS estimate V rms (est) is calculated in accordance with the expression: 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
Dependent Claim
37 words
The apparatus of Claim 15 wherein the apparatus is adapted for monitoring 60Hz 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
Dependent Claim
19 words
The apparatus of Claim 18 wherein the means for sampling samples at a rate of 64 times a cycle.
Claim 22
Dependent Claim
25 words
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
Dependent Claim
45 words
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
Dependent Claim
85 words
The apparatus of Claim 15 including means for comparing the absolute value of the difference between the reference waveform and the new cycle of the AC line signal 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 a fault signal is provided if the count in the counter exceeds a selected value indicative of a fault.
Claim 25
Dependent Claim
15 words
The apparatus of Claim 17 wherein the number of samples n per cycle is 64.
Claim 26
Dependent Claim
206 words
An uninterruptible power supply comprising: (a) an auxilliary power supply battery; (b) power transfer means, connected to the auxillary 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 wherein each reference value at each sample time comprises a selectivly weighted average of sample values over a plurality of prior cycles of the AC line signal; (3) means for comparing the values of samples at sample times in a new cycle of the AC line signal waveform with the reference values at the corresponding cycle sample times and providing a fault signal when a selected difference condition is exceeded, and for determining from the fault signals 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
Dependent Claim
206 words
An uninterruptible power supply comprising: (a) an auxilliary power supply battery; (b) power transfer means, connected to the auxillary 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 wherein each reference value at each sample time comprises a selectivly weighted average of sample values over a plurality of prior cycles of the AC line signal; (3) means for comparing the values of samples at sample times in a new cycle of the AC line signal waveform with the reference values at the corresponding cycle sample times and providing a fault signal when a selected difference condition is exceeded, and for determining from the fault signals 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
Dependent Claim
99 words
The power supply of Claim 24 wherein the means for producing a reference waveform does so in accordance with the expression: REF i,k = (1-a)REF i,k-1 + (a)SAMP 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
Dependent Claim
8 words
The power supply of Claim 25 wherein a=0.5.
Claim 30
Dependent Claim
38 words
The power supply of Claim 25 wherein the means for comparing compares in accordance with the expression: |SAMP i,k - REF i,k |≧ D i where D i is a chosen tolerance value for the sample point i.
Claim 31
Dependent Claim
25 words
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
Dependent Claim
36 words
The power supply of Claim 24 wherein the power supply receives 60Hz 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
Dependent Claim
20 words
The power supply of Claim 29 wherein the means for sampling samples at a rate of 64 times a cycle.
Claim 34
Dependent Claim
26 words
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
Dependent Claim
46 words
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
Dependent Claim
50 words
The power supply of Claim 24 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 value falls below a selected minimum value.
Claim 37
Dependent Claim
33 words
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
Dependent Claim
92 words
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: 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
Dependent Claim
92 words
The power supply of Claim 24 wherein the means for comparing compares the absolute value of the difference between the reference waveform and the new cycle of the AC line signal at each sample point with a selected difference level and a fault signal to increment a counter if the difference exceeds or is equal to the level and decrements the counter if the difference is less than the selected level, and wherein a fault condition is determined if the count in the counter exceeds a selected value indicative of a fault.
Claim 40
Dependent Claim
16 words
The power supply of Claim 24 wherein the number of samples n per cycle is 64.
Claim 41
Independent Claim
115 words
A method of AC line waveform monitoring comprising the steps of: (a) sampling an AC line signal at times synchronized with the cycle of the AC line waveform; (b) averaging together the sample values over a plurality of cycles of the AC line signal to create a reference waveform wherein each reference value at each sample time comprises a selectively weighted average of the sample values from the plurality of cycles; (c) comparing the values of samples at sample times in a new cycle of the AC line signal waveform with the reference values at the corresponding cycle times to determine when a selected difference condition between the reference and the new cycle is exceeded.
Claim 42
Independent Claim
115 words
A method of AC line waveform monitoring comprising the steps of: (a) sampling an AC line signal at times synchronized with the cycle of the AC line waveform; (b) averaging together the sample values over a plurality of cycles of the AC line signal to create a reference waveform wherein each reference value at each sample time comprises a selectively weighted average of the sample values from the plurality of cycles; (c) comparing the values of samples at sample times in a new cycle of the AC line signal waveform with the reference values at the corresponding cycle times to determine when a selected difference condition between the reference and the new cycle is exceeded.
Claim 43
Dependent Claim
32 words
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 backward in time.
Claim 44
Dependent Claim
50 words
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
Dependent Claim
28 words
The method of Claim 38 further including the step of estimating the RMS value of the AC line waveform and comparing that value with a selected minimum value.
Claim 46
Dependent Claim
26 words
The method of Claim 41 wherein the step of estimating the RMS values is preformed by carrying out a root-mean square calculation on the reference waveform
References Cited (Backward Citations)
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