Method and apparatus for line power monitoring for uninterruptible power supplies
First Claim
1. 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.
4 Assignments
0 Petitions
Accused Products
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.
88 Citations
42 Claims
-
1. 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
-
-
15. 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;
space="preserve" listing-type="equation">REF.sub.i,k =(1-a)REF.sub.i,k-1 +(a)SAMP.sub.i,k-1wherein a is chosen such that 0<
a<
1, REFi,k is the present value of the reference of the i th sample point in the k th cycle, REFi,k-1 is the value of the reference at th ei th sample point in the (k-1)th cycle and SAMPi,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. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23)
-
-
24. 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. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37)
-
-
38. A method of AC line waveform monitoring for detecting AC line power faults and controlling an uninterruptible power supply 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 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; (c) comparing the AC line signal waveform with the reference waveform at corresponding times in the reference waveform and the signal waveform to determine when a selected difference condition between the reference waveform and the signal waveform is exceeded and providing a fault signal when the difference condition is exceeded; (d) providing the fault signal to an uninterruptible power supply to cause it to switch to provide power to a load from a battery in the uninterruptible power supply. - View Dependent Claims (39, 40, 41, 42)
-
Specification