Method of timing demand and time-of-use functionality with external clock source

A method of associating chronological time with energy consumption includes a step of storing in a utility meter a plurality of energy consumption values, each energy consumption value corresponding to a time interval of a first type. The method also includes obtaining from a source external to the utility meter chronological time information regarding at least one of the plurality of energy consumption values. The method further includes associating each of the energy consumption values with a time interval of the second type, each time interval of the second type associated with at least one chronological time value.

FIELD OF THE INVENTION

The present invention relates generally to utility meter systems, and in particular, to meter systems that communicate usage information using communication networks.

BACKGROUND

Electricity meters are used to measure electricity consumption for many purposes, including billing for the usage of energy. In many cases, an electricity meter merely keeps track of accumulated energy usage. The accumulated usage over a month is then applied to one or more billing rates (e.g. dollars per kilowatt hour) to arrive at the amount to be billed to the customer for the month.

Other billing methods are employed in other cases. Two common alternative billing methods include so-called Time of Use (TOU) and Demand metering. Time of Use metering involves application of different rates to energy usage at different times of day. To this end, a TOU meter may maintain several accumulators, one for each billing rate. During billing accumulated energy usage is added to the appropriate one of the many accumulators, depending on the time of day. Different billing rates are then applied to the accumulated energy usage values in each of the accumulators. Demand metering involves billing based on time periods in which the demand is at or near a maximum level. Such billing/metering methods are known.

Historically TOU and Demand functions have been performed by the end device (i.e. the meter). Industry standards, and in some cases governmental regulations, require relatively accurate determination of the start and finish of time periods used for TOU and Demand operations. Such accuracy can be achieved by referencing the timing off of the 60 Hz power line signal, which is generally fairly accurate. In such cases, however, power line timing information is lost in a power outage, and there must be some ability to recover chronological time information (time of day) after the power returns.

The problem of recover after a power outage can be addressed by including a clock chip and a battery for power to maintain the time during a power outage. In some cases, the clock chip may be used during normal operation as well. There are disadvantages to reliance on the clock chip for timing information, however, which are outlined below:1. The accuracy of clock chips drifts over time, causing devices to become out of synch with the real or actual time;2. Updating the time information in the meter often requires a visit to the physical location with a programming device;3. Even when the time information is updated in the meter, the programming devices also have clock drift, and as a result, meters across the population on a system are never truly set to the same time base;4. The cost of a clock chip and a battery is borne by all metering devices in the system.

To address these problems, some meters now implement two-way communication systems that offer the ability to provide accurate timing information to the meters from a single accurate time base. Keeping the metering devices time synced to the system time greatly improves the accuracy of billing demand and TOU data from the metering devices. However, this solution also has disadvantages. In order to ensure accuracy, all devices must get the correct time within seconds to maintain the integrity of the time-of-use, demand or load profiling data, which is not practical in a system with many metering devices.

There is a need, therefore, for a metering system that addresses one or more of the shortcomings identified above in connection with prior art solutions.

SUMMARY

The invention addresses the above-described need, as well as others, by providing an arrangement that enable storage of energy consumption values in association with a first type of time interval within a meter, and then associating the stored energy consumption values with a second type of time interval, the second type of time interval aligned with or at least anchored or referenced to a chronological clock (e.g. time of day clock). Such a device thus stores energy consumption values in the absence of a standardized clock, and then later associating the energy consumption values with the standardized clock, which may be used to obtain data for standard TOU, Demand or other meter billing or data gathering time periods.

A first embodiment of the invention is a method of associating chronological time with energy consumption. The method includes a step of storing in a utility meter a plurality of energy consumption values, each energy consumption value corresponding to a time interval of a first type. The method also includes obtaining from a source external to the utility meter chronological time information regarding at least one of the plurality of energy consumption values. The method further includes associating each of the energy consumption values with a time interval of the second type, each time interval of the second type associated with at least one chronological time value.

The energy consumption values may be associated with the chronological time value-based time intervals either internal to the meter, or at a remote location from the meter. In the former case, the chronological time information is communicated to the meter. In the latter case, the stored energy consumption values are communicated to a remote facility that has access to chronological time information. Other variations may of course be implemented.

The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference the following detailed description and accompanying drawings.

DETAILED DESCRIPTION

FIG. 1shows a metering system that includes a data concentration system10and a plurality of customer premise metering units12. The customer premise metering units12include a metering device14, a data store16and communication circuit18. Each metering device14is a device that is configured to generate energy consumption information regarding a load. Each data store16is a memory device or set of memory devices that store energy consumption information, among other things, as discussed herein. The communication circuit18is a device configured to communicate information to and from the data concentration system10. In an exemplary embodiment, the communication circuit18includes a radio.

FIG. 2shows in further detail the metering unit12according to at least some embodiments of the present invention. The metering unit12is an apparatus for measuring energy consumption that includes a measurement circuit110, a processing circuit120, a communication circuit18, an optional display140and a data store16. All of the above listed elements are preferably supported by a meter housing13, which may a plurality of known forms. The metering unit12shown inFIG. 2includes an optional chronological clock circuit130, which is useful in an embodiment described below in connection withFIG. 5.

In the embodiment described herein, the measurement circuit110is a circuit operable to generate a first digital signal representative of a line voltage waveform and a second digital signal representative of a line current waveform. To this end, the measurement circuit110may suitably comprise current and voltage sensors, not shown, and one or more analog-to-digital converters, not shown. Many circuits capable of generating digital voltage and circuit waveform signals are well known in the art. Suitable examples of input circuits having such capabilities are described in U.S. Pat. Nos. 6,374,188; 6,564,159; 6,121,158 and U.S. Pat. No. 5,933,004, all of which are incorporated herein by reference.

The processing circuit120is a device that employs one or more processing devices such as microprocessors, microcontrollers, digital signal processors, discrete digital circuits and/or combinations thereof. The processing circuit120is operable to generate energy consumption data based on the first digital signal and the second digital signal. For example, the processing circuit120may generate watt-hours, VAR-hrs, power factor, root-mean-square voltage and/or current, or combinations of any of the foregoing. Various processing circuits operable to generate energy consumption data from digital voltage and digital current measurement signals are well known in the art. Suitable examples of such circuits are described in U.S. Pat. Nos. 6,374,188; 6,564,159; 6,121,158 and U.S. Pat. No. 5,933,004.

The processing circuit120is further operable to generate energy consumption values corresponding to a time interval of a first type. The energy consumption data preferably represent a quantity of energy (real, VA or VAR) accumulated over the time interval of the first type. The time interval of the first type is preferably a relatively small interval in comparison to a demand, TOU or load profiling time interval. For example, the time interval of the first type should be less than one minute, and preferably less than ten seconds. If the TOU, demand or load profiling time interval is relatively small, for example, 5 to 15 minutes, then the time interval of the first type should be one the order of one second or less. If the TOU, demand or load profiling time interval is more than an hour, then the time interval of the first type may be somewhat larger. Additional detail regarding the relationship between the time interval of the first type and the corresponding standard billing time interval is provided further below.

It will be appreciated that the energy consumption data generated for metering purposes often represents an accumulation of energy for even a smaller time interval. Some measurement circuits such as the circuit110, either alone, or in combination with the processing circuit120, generate pulse signals representative of a particular quantum of accumulated consumed energy. Other meters generate accumulated energy usage signal for consecutive sub-second intervals. In such cases, the processing circuit120accumulates such energy consumption information, in whatever form, for each successive time interval of the first type.

The processing circuit120is further operable to store the plurality of energy consumption values in the data store16. In other words, for each time interval of the first type, the processing circuit120stores the accumulated energy consumption value. Preferably, the energy consumption values are stored in a manner such information regarding the order in which the energy consumption values were generated is retained. For example, the energy consumption values may be stored with a counter that identifies a sequence number for each energy consumption value. In another embodiment, the energy consumption values may be stored in a table in the data store16, which may be a random access memory, EEPROM, or other memory. In still other embodiments, the data store16may be circular buffer, FIFO device, or other memory that stores data in the order in which it is received. In such cases, no additional data need be stored. Other known methods may be used.

The communication circuit18is a device operable to communicate data between the metering unit12and one or more remote devices. In a system such as that shown inFIG. 1, the communication circuit18would be operable to communicate directly or indirectly with the data concentration system10. To this end, the communication circuit18may suitably include a radio, a telephone modem, a power line carrier modem, or other known communication device configured for use with utility meters.

The meter display140, which is optional, may be a digital display such as a liquid crystal display. It will be appreciated that the exact nature of the display is not particularly important to the implementation of the invention. Nevertheless, there is an advantage of including at least some display capabilities. LCD displays, moreover, have been found to have a particularly advantageous set of qualities for use in electronic meters.

The chronological clock circuit130, which is not necessary for the embodiment described below in connection withFIG. 3, is a circuit maintains ongoing chronological clock information (e.g. time of day). Preferably, the chronological clock circuit130is operable to receive, from time to time, system standard chronological time information from an external source through the communication circuit18or otherwise. Such information synchronizes the clock circuit130with other clock circuits of other metering units and/or the data concentration system10. The chronological clock circuit130ordinary updates its calendar/clock value by referencing timing information from the power line signal. Such circuits are known in the art, and may be in part or in whole carried out by the processing circuit120hardware.

Referring again toFIG. 1, the data concentration system10is a device that is operable to receive energy consumption information from a plurality of metering units12and store the information. The data concentration system10provides the stored information to a billing system, not shown, that may or may not be co-located with the data concentrator10. The data concentration system10at a minimum includes a processing circuit22(such as one or more microprocessors) and associated circuitry and one or more memory or storage devices24. The data concentration system10may be configured as a data server that provides energy consumption information to other computers or systems via wired or wireless networks. Suitable data concentrator systems are known in the art.

The configuration ofFIG. 1may be used to carry out a variety of methods according to the present invention. Two of such methods are described below in relative detail. Alterations and modifications of those methods are within the scope of the invention. A first method relates to a configuration in which the metering unit12does not perform any TOU, demand or load profiling operations locally, but rather transmits the energy consumption values to the data concentration system10. The data concentration system10then associates the energy consumption values to the billing system time periods to obtain TOU, demand and/or load profiling information.

FIG. 3shows a flow diagram of an exemplary set of operations of the processing circuit120of the metering unit12and the processing circuit22of the data concentration system10in accordance with the first method described above. In steps302-308, the processing circuit120generates energy consumption values corresponding to time intervals of the first type, and stores the energy consumption values in the data store16.

In particular, the processing circuit120in step302obtains energy consumption data representative of energy being consumed by a load. To this end, brief reference is made toFIG. 2. In particular, the meter12is connected to measure power flowing through power lines96. The measurement circuit110generates a digital voltage signal, which preferably is a series of digital samples that represent a scaled version of the voltage waveform(s) on the one or more of the power lines96. The measurement circuit110also generates a digital current signal, which preferably is a series of digital samples that represent a scaled version of the current waveform(s) on the one or more of the power lines96.

The processing circuit120receives the digital voltage and current signals and generates energy consumption data, for example, data representative of kilowatt-hours or the like. The processing circuit120optionally provides information representative of at least some of the energy consumption data to the display140. Thus, in the embodiment ofFIG. 2, the processing circuit120in part generates the energy consumption data. In other embodiments, a separate processing circuit may be used to generate the energy consumption data.

In step304, new energy consumption data is added to a running total for a current time interval. The time interval is a time interval of the first type, described further above, which is preferably much smaller than a billing time interval. In step306, the processing circuit120determines whether the current time interval has expired or passed. If so, then in step308, the processing circuit120stores the accumulated running total to the data store16. The accumulated running total represents the energy consumption value for the time interval. Once the energy consumption value is stored, the processing circuit120starts a new running total for the next time interval energy consumption value and proceeds to step310, discussed further below. It will be appreciated that the data store16preferably stores the energy consumption value so as to retain the order in which it was generated with respect to the other energy consumption values of other time intervals.

If, however, in step306it is determined that the current time interval has not expired, then the processing circuit120returns to step302directly to obtain further data for the current time interval.

It will be appreciated that the timing for the current time interval may be obtained using a timing circuit or algorithm within the processing circuit that is referenced to the power line signal. For example, the processing circuit120may be configured to count zero crossings of the power line signal based on the digital voltage measurement signal generated by the measurement circuit110. One-hundred and twenty zero crossings occur for each second of in a power line signal. Thus, the beginning and end of each successive time interval may be determined by counting the appropriate amount of zero crossings. Because the power line signal is relatively precise, the duration of the timing intervals of the first type will be relatively accurate and consistent. However, the chronological time (e.g. the actual time of day) associated with the timing intervals need not be known, and even if known, need not be accurate, within the metering unit12.

In step310, which is reached after an energy consumption value is stored for a timing interval, the processing circuit120determines whether it is time to communicate stored energy consumption values to the data concentration system10. If so, then, in step312, the processing circuit120communicates the energy consumption values stored in the data store16to the processing circuit22of the data concentration system10. Typically, the processing circuit120communicates a plurality of energy consumption values corresponding to a plurality of timing intervals of the first type. Under normal circumstance, the processing circuit120communicates the energy consumption values for all of the timing intervals of the first type that have passed since the previous execution of step312.

The communication in step312is effected by the communication circuit18of the meter unit12, which communicates the data to a compatible communication circuit, not shown, of the data concentration system10. The processing circuit120of the metering unit12then returns to step302to start obtaining new energy consumption values for subsequent time intervals of the first type.

If, however, in step310, the processing circuit120determines that it is not yet time to communicate values to the data concentration system10, then the processing circuit120proceeds directly from step310to step302.

It will be appreciated that the conditional steps306and310may suitably be interrupt-driven instead of being performed sequentially as shown inFIG. 3. In other words, instead of step306, the processing circuit120may instead repeat steps302and304until an interrupt is generated indicating that the current timing interval is completed. Similarly, instead of step310, the processing circuit120may instead repeatedly perform the sequence loop of steps302,304,306and308until an interrupt is generated indicating that it is time to communicate values to the data concentrator10. In such a case, the interrupt may be generated by a timer within the processing circuit120or as a result of a polling signal provided by the data concentrator10.

In any event, referring now to the data concentrator10, the processing circuit22of the data concentrator10receives a set of energy consumption values (ECVs) in step314. In step316, the processing circuit22preferably obtains (internally or from another source) chronological clock information (such as the time of day, or some other system-wide time value). The processing circuit22uses the chronological clock information to associate the ECVs with billing time periods. To this end, it will be appreciated that the approximate chronological time for each time period of the received ECVs may be determined by estimating the chronological time of the most recent ECV and knowing the duration of the time periods of the first type. For example, if the time intervals of the first type are each ten seconds, and if thirty ECVs are received when the locally obtained chronological clock information is 10:05:00, then the processing circuit22can determine that the last of the thirty ECVs covers from 10:04:50 to 10:05:00, and that the first of the thirty ECVs covers 10:00:00 to 10:00:10. Because the thirty ECVs are stored and preferably communicated such that the order of their generation may be reproduced, the processing circuit22can associate each of the ECVs with a particular ten second period between 10:00:00 and 10:05:00. The processing circuit22may then associate the ECVs into a particular billing time interval, which will likely be in excess of five minutes.

When the processing circuit associates the ECVs into a particular billing time interval, the energy consumption values for the interval may be accumulated to identify energy consumption totals for the billing (load profiling) time interval. Alternatively, in the case of a TOU meter, the ECVs may be multiplied by a particular use rate based on the associated billing time interval, and then added to a billing total for the metering unit12.

Thus, in this embodiment, the processing circuit22maintains the TOU, demand, and/or load profiling data for the metering unit12, and preferably for a plurality of other metering units. In contrast to a normal TOU, demand or load profiling meter, the metering unit12in this embodiment does not perform measurements and then directly associating energy consumption measurements with a particular billing (or load profiling) time interval. Instead, the metering unit12performs measurements to obtain the ECVs for more refined time intervals, but which are not necessarily tied to an accurate chronological clock. The metering provides these ECVs to the data concentrator10, which uses accurate clock information to backfill the ECVs into the proper billing or load profiling interval or period for that meter.

FIG. 4is a representative drawing that illustrates an exemplary performance of steps314and316by the processing circuit22.FIG. 4shows a plurality of ECVs402received from the metering unit12, and a plurality of load profiling time intervals404into which the ECVs402are mapped. The processing circuit22receives the ECVs402and obtains the accurate chronological time information406, which shows a time of 5:06. Fifteen ECVs402a. . .402oare received, and the processing circuit22has prior knowledge that the ECVs correspond to timing intervals of thirty seconds. The load profiling time intervals404a,404band404care assumed to be five minutes each.

The processing circuit22determines that the last ECV402ocorresponds to a time of between 5:05:30 and 5:06:00, which maps to the load profiling interval404c. The processing circuit22further determines that the prior ECV402ncorresponds to a time of between 5:05:00 and 5:05:30, which also maps to the load profiling interval404c. The processing circuit22further determines that the next prior ECV402mcorresponds to a time of between 5:04:30 and 5:05:00, which maps to the load profiling interval404b. In a similar manner, the processing circuit22determines that the ECVs402d-4021all correspond to times of between 5:00:00 and 5:04:30, and thus map the load profiling interval404b, and that the ECVs402a-402calso correspond to times of between 4:58:30 and 5:00:00, and thus map the load profiling interval404a.

Because the example is a load profiling meter, the processing circuit22maintains an accumulated energy consumption sum for each load profiling interval404x. Thus, in the case of ECVs402a-402c, the processing circuit22will add the ECVs to an existing value for the load profiling interval404a, add the ECVs402d-402mto generate a value for the load profiling interval404b, and add the ECVs402nand ECVo to generate a value for the load profiling interval404c. Additional ECVs for subsequent time intervals will eventually be added to the load profiling interval404cwhen they are received from the metering unit12.

Referring again generally toFIG. 3, it will be noted that the processing circuit22may provide some billing or load profiling information back to the metering unit12, if desired, through additional communications. In most cases, the processing circuit22instead makes the energy consumption information available to billing processes and/or systems, or to other systems, not shown.

The above described embodiment reduces the need for a highly accurate calendar clock within the metering unit12. Thus, the metering unit12may maintain a less accurate chronological clock, if any. There is no need for a highly accurate chronological clock because all of the calendar or time of day sensitive energy consumption information is determined and stored at the data concentrator10. Nevertheless, the duration of the ECV timing intervals at the metering unit12can be highly accurate relatively inexpensively by referencing the timing intervals directly or indirectly to the 60 Hz AC power line signal.

It will be appreciated that the example ofFIG. 4is given by way of illustration only, and would not typically be implemented precisely as shown. In particular, in order to ensure that the billing (or load profiling) interval totals are accurate in the data concentrator10, the timing intervals of the first type must have relatively high granularity with respect to the billing or load profiling intervals. Thus, for example, if the defined demand interval for a metering unit12is five minutes, then using one minute ECV intervals can provide significant error, because as much as half or more of every fifth ECV would be associated with the wrong demand interval. However, if the metering unit12has defined TOU periods that are no less than 3 hours, then a one minute or thirty second ECV interval may subject the calculation to a tolerable amount of error.

In general, it may be preferable to limit the ECV intervals to one second, as they do not necessarily require a lot of memory. In particular, if updates to the data concentrator10are only made every hour, then metering unit12would only need to store up to approximately 3600 ECVs between communications to the concentrator10. If the updates to the data concentrator10are only made once per day, then the metering unit12would still only have to store approximately 86000 ECVs. Such storage in the data store16would not be exceedingly expensive.

It will be appreciated, however, that those of ordinary skill in the art may readily determine their own combination of ECV intervals and the time between communications to the data concentrator based on billing time intervals, metering error, accuracy requirements and other factors.

In another embodiment of the invention, the metering unit12is configured to maintain a local chronological clock (130) and generate TOU, demand and/or load profiling information locally within the metering unit12. However, after a power interruption, the metering unit12performs operations similar to those ofFIG. 3to enable the metering unit12to obtain accurate TOU, demand and/or load profiling information immediately after power is restored.

FIG. 5illustrates an exemplary set of steps performed by the processing circuit120of the metering unit12in this other embodiment of the invention. In such an embodiment, the processing circuit120includes the chronological clock circuit130. The clock circuit130from time to time receives a standard time reference from a remote source, such as the data concentrator10, another meter, or the like. Such meter processing circuits and clock calendar circuits are known.

Referring now toFIG. 5, in step502, the processing circuit120obtains energy consumption data. Step502may suitably be the same as step302ofFIG. 3. In step504, the processing circuit120updates running energy consumption totals. Such totals typically include overall energy consumption, plus one of a TOU total (rate*energy consumption, where the rate is dependent on the time of day, week, month or season), a demand period total, or a load profiling period total. Such operations are well known in the art. The timing information for the various TOU, demand and load profiling operations is provided by the clock calendar circuit or operations of the processing circuit120. The processing circuit120repeats steps502and504in the absence of a power interruption.

Assume that an interruption in power occurs. In step506, the processing circuit120in this embodiment goes into a low power mode in which it maintains a counter that counts clock cycles of the interruption. The low power mode may be powered by a battery or a supercapacitor or ultracapacitor. Processors having the ability to operate in such a lower power mode are known in the metering art. Alternatively, the processing circuit120may shut down altogether, as would occur in the event of an extended power outage anyway.

Eventually, the utility power is restored. In step508, the processing circuit120detects the restoration of power. After step508, the processing circuit120in step510begins obtaining energy consumption data in a manner similar to step502. The processing circuit120also starts a timing interval of the first type similar to that described above in connection withFIG. 3.

In step512, new energy consumption data is added to a running total for a current time interval of the first type. As discussed above, the time interval of the first type is preferably much smaller than the TOU, demand or load profiling time interval of the metering unit12. In step514, the processing circuit120determines whether the current time interval has expired or passed. If so, then in step516, the processing circuit120stores the accumulated interval running total to the data store16similar to step308ofFIG. 3. In any event, once the energy consumption value is stored, the processing circuit120starts a new running total for the next time interval energy consumption value and proceeds to step518, discussed further below.

If, however, in step514it is determined that the current time interval has not expired, then the processing circuit120returns to step510directly to obtain further data for the current time interval.

The start and stop times for each time interval may be obtained using a timing circuit or algorithm within the processing circuit that is referenced to the AC power line signal. It is advantageous to use the power lines as the reference in most embodiments in order to reduce the accuracy requirements of the clock circuit130within the metering unit12.

In step518, the processing circuit120determines whether it has received standard or system chronological clock synchronization information from an external source. In particular, after restoration, data concentrator10or another external system will eventually provide current standard clock information to the metering unit12through communication circuit18to allow the metering unit12to synchronize to a standard time reference. If such standard clock information has not been received, then processing circuit120returns to step510to accumulate energy consumption data for a new timing interval.

If synchronizing clock information has been received, however, then the processing circuit120returns to step502to begin normal processes, but also performs step520in parallel (i.e. interleaved or otherwise). In step520, the processing circuit120uses the chronological clock information to associate the ECVs generated and stored in steps512and514with appropriate billing time periods. Step520is thus similar to step316ofFIG. 3, except that it is performed by the processing circuit120of the metering unit12inFIG. 5. As with step316ofFIG. 3, the approximate chronological time for each time period of the received ECVs may be determined by estimating the chronological time of the most recent ECV and knowing the duration of the time periods of the first type.

Thus, in this embodiment, the processing circuit120of the metering unit12maintains its own TOU, demand, and/or load profiling data. However, the processing circuit120uses a method similar to that illustrated inFIG. 3to temporarily store time interval energy consumption data after a power interruption until the clock of the metering unit12can be resynchronized to a time standard. Once the standard clock information is made available to the metering unit12, backfills the ECVs into the proper billing or load profiling intervals or periods.

The embodiment ofFIG. 5thus allows for the use of a chronological clock circuit within a meter that does not require a highly accurate crystal driver. Using the power line signal, the chronological clock circuit130will keep relatively accurate time until a power interruption. After power is restored, the chronological clock circuit130within the metering unit12may have an inaccurate chronological clock reference (i.e. wrong time of day) or may have no chronological clock reference, similar to a VCR or electronic clock that flashes 12:00 am. However, because energy consumption values are stored in accurate increments of time (based on the power line signal), the metering unit12may operate for minutes or hours without a standard synchronizing chronological clock reference. Once the reference is received, the processing circuit120merely backfills the ECVs generated without the chronological clock into the proper billing intervals once the clock circuit is resynchronized.

The above described embodiments are merely exemplary. Those of ordinary skill in the art may readily devise their own implementations that incorporate the principles of the present invention and fall within the spirit and scope thereof.