Abstract:
A method and system for shedding loads based upon a power system characteristic, such as voltage or frequency, is provided. In one embodiment, a remote party, such as a power generator or utility, transmits a signal to a control device proximately located with a load device. Upon receipt of the signal, the control device measures the power system characteristic for a predetermined time to establish a baseline threshold. The control device then monitors the power system characteristic. When the power system characteristic falls outside the baseline threshold, the control device sheds load. In one embodiment, the loads are prioritized such that the load of least importance may be shed first.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS  
       [0001]     This application claims priority and benefit under 35 U.S.C. §119(e) from U.S. Provisional Application No. 60/741,801, filed Sep. 7, 2005, which is incorporated by reference for all purposes. 
     
    
     BACKGROUND  
       [0002]     1. Technical Field  
         [0003]     This invention relates generally to load control systems, and more specifically to a method and apparatus for reducing an operating time of a load, such as an air compressor or furnace, when a source voltage falls below a base line established during a predetermined time.  
         [0004]     2. Background Art  
         [0005]     As utilities have become deregulated, the infrastructure for generating and delivering energy has become more complex. A generator produces energy and delivers it to s transmission grid. The owner of the transmission grid then “wheels” the energy to a distribution network. The owner of the distribution network then delivers it to an end user. The generator then bills the end user. The generator then pays the transmission grid owner and distribution network owner from the funds collected.  
         [0006]     A problem with this multi-party network is that the various components may not be perfectly in sync at all times. During extremely hot or extremely cold weather, for example, consumers may demand unusually large amounts of energy for heating or cooling. It is possible that either the generator will not be able to produce sufficient energy, or that the transmission or distribution network will not be able to accommodate sufficient energy.  
         [0007]     What is needed is a way for a remote party, such as a generator or distributor, to monitor characteristics of energy delivered to end consumers, and where problems arise, to be able to shed loads. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.  
         [0009]      FIG. 1  illustrates one embodiment of a method in accordance with the invention.  
         [0010]      FIG. 2  illustrates one embodiment of a system in accordance with the invention.  
         [0011]      FIG. 3  illustrates an alternate embodiment of a system in accordance with the invention. 
     
    
       [0012]     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to control a load device when a source voltage falls below a baseline established at a predetermined time. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.  
         [0014]     It will be appreciated that embodiments of the invention described herein may be comprised of one or more conventional processors and unique stored program instructions that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of load control as described herein. The non-processor circuits may include, but are not limited to, a radio receiver, a radio transmitter, signal drivers, clock circuits, power source circuits, and user input devices. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.  
         [0015]     Embodiments of the invention are now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of “a,” “an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.” Relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.  
         [0016]     Turning to  FIG. 1 , illustrated herein is one embodiment of a method  100  of controlling an electrical load. Initially, as shown in step  101 , an electrical service provider supplies the electrical load with power. At step  102 , the electrical load receives a communication signal from the electrical service provider when system operating conditions exceed at least one predetermined criterion. The communication signal may comprise a one-way communication signal that is delivered from the electrical service provider to a control unit. In one embodiment, the predetermined criterion comprises line losses of an electrical distribution network coupled to the electrical load. In a further embodiment of method  100 , the predetermined criterion comprises ambient temperature. In another embodiment, the predetermined criterion is where operating conditions are most vulnerable as determined by the electrical service provider.  
         [0017]     By way of an example, on a hot day the power consumption may increase by to excessive use of air conditioners to cool homes. This power consumption may put a strain on the electrical service provider and/or the transmission and distribution networks. In such a scenario, a regulation of power consumption may need to be administered. The electrical service provider may analyze ambient temperature, line losses, line capacities, and other associated power demand to may create a predetermined criterion based on the data. The predetermined criterion in this embodiment may be a specific temperature where once the temperature is exceeded power demand may increase above desired levels, forcing power regulation.  
         [0018]     At step  103 , the electrical load, or a control device coupled thereto, receives the communication signal having measurement indicia. The measurement indicia may comprise an indication to begin a base-line measurement of a power system characteristic. The power system characteristic may comprise, but is not limited to, line voltage or frequency. These power system characteristics may be used to characterize the power usage of the electrical load.  
         [0019]     Using least one power system characteristic as may be obtained in step  103 , a base line measurement is performed at step  104 . In one embodiment, the step of performing the base line measurement includes measuring the power system characteristic for at least a predetermined time. The base line measurement occurs proximately with the electrical load. By way of an example, a base line measurement where the power system characteristic is voltage occurring proximately with the electrical load, may be a measurement of the output voltage received from a transmission or distribution network by a local electrical load.  
         [0020]     The base line measurement may be taken over a predetermined time period. In one embodiment, the time period may be a single time interval. In another embodiment, the step of performing the base line measurement may occur by measuring the power system characteristic for at least the predetermined time by taking at least a plurality of measurements of the power system characteristic. This plurality of measurements may be integrated or averaged. For example, the base line measurement of a voltage characteristic may be the average of a series of single voltage measurements taken over a long period of time. In contract, in one embodiment, the base line measurement of a voltage characteristic may be the average of continuous voltage measurements over a short period of time.  
         [0021]     At step  105 , the power system characteristic is processed across the predetermined time to obtain a processed base-line measurement. A differential factor is then retrieved or received at step  106 . The differential factor may be retrieved from a memory within a control unit coupled to the local electrical load. In one embodiment, the differential factor is received along with the based line measurement initiation signal in the communication signal sent from the electrical service provider.  
         [0022]     The differential factor is then used to reduce the processed base line measurement to obtain a threshold value at step  107 . In one embodiment, the step of reducing the processed base line measurement by the differential factor comprises multiplying the processed base-line measurement by the differential factor. Another embodiment of reducing the processed base-line measurement by the differential factor may comprise subtracting the differential factor from the processed base-line measurement.  
         [0023]     At step  108  the power system characteristic is monitored. The power system characteristic may then be compared to the threshold value. At decision  109 , a power characteristic is compared with the threshold value. Where the power system characteristic falls below below the threshold value, at least one local electrical load is shed at step  110 . If the power system characteristic does not fall below the threshold value the power system characteristic may continue to be monitored.  
         [0024]     In one embodiment, the step of shedding the at least one local electrical load may further comprise determining a prioritization of a plurality of loads, and removing the load having a highest priority. For example, the plurality of loads may include high to low power consumption devices, wherein the high power consumption devices have the highest priority. By shedding a local electrical load with a highest priority, the most power will be saved.  
         [0025]     In another embodiment of the step of shedding the at least one local electrical load may comprise determining a prioritization of a plurality of loads, and removing the load having the lowest priority. By way of an example, priority is determined by need of the load. In a hospital environment, a high priority load may include life a support systems while a low priority load may include a vending machine. In the case a local electrical node is shed, the loads that will cause the least disturbances to the local environment will be shed.  
         [0026]     In one embodiment, following the shedding of a local electrical load, the power system characteristic is monitored again at step  111 . At decision  112 , the power system characteristic compared to the threshold value. If the power system characteristic is greater than the threshold value, the at least on local electrical load is actuated at step  113 . Allowing the actuating of shed local electrical loads may allow a dynamic system for shedding and actuating local electrical loads based on power demands.  
         [0027]     In one embodiment, when the power system characteristic exceeds the threshold value by at least a predetermined restart value, the at least one local electrical load is actuated. In another embodiment of actuating additional loads following the shedding of a local electrical load, the at least one local electrical load is actuated when the power system characteristic exceeds the threshold value for at least a predetermined restart time. The hysteresis of these embodiments may eliminate variant fluctuations of the power system characteristic and may only allow actuation of a local electrical load when the power system characteristic consistently remains above the threshold value.  
         [0028]     Turning now to  FIG. 2 , illustrated therein is one embodiment of a load controlling device  200  disposed proximately with an electrical load  201 . The load controlling device  200  comprises a receiver  203 . In one embodiment the receiver  203  is in communication with an electrical services provider  204 . The electrical services provider  204  may provide electrical power to the electrical load  201 . To those familiar in the arts of electrical power, the electrical service provider  204  may be in the form of a voltage source  202  as seen by the electrical load. The receiver  203  is coupled to a controller  205 . The controller  205  may further comprise a memory  206 .  
         [0029]     In one embodiment, a power system characteristic measurement module  207  may be operable with the controller  205 . The power system characteristic measurement module  207  may be configured to establish a processed base-line measurement  208  of a power system characteristic  209  in response to the receiver  203  receiving a communication signal  210 . Those familiar in the arts will recognize that the communication signal  210  may be sent over one other following technologies, but is not limited to satellite communication, WANs, WiFi Networks, and other similar networks.  
         [0030]     The electrical services provider  204  may generate the communication signal  210  upon a predetermined threshold being exceeded. In one embodiment, the predetermined threshold being exceeded comprises load losses of a power distribution grid  211  exceeding one of a predetermined load loss threshold. A further embodiment of the predetermined threshold being exceeded may include an ambient temperature exceeding a predetermined threshold.  
         [0031]     The communication signal  210  may comprise measurement indicia  211  therein. The measurement indicia  211  may comprise, but is not limited to the power system characteristic. The power system characteristic  209  may comprise, but is not limited to, line voltage or frequency. The power system characteristic  209  may be used to characterize the power usage of the electrical load  201 .  
         [0032]     In one embodiment, a threshold module  213  is operable with the controller  205 . The threshold module  213  may be configured to determine a threshold value  214  by retrieving from memory or receiving from a receiver a differential factor  215 . The differential factor  205  may be retrieved from within the load controlling device  200 , perhaps from a non-volatile memory device. In one embodiment, the differential factor  215  is received along with the measurement indicia  211  in the communication signal sent from the electrical service provider  204 .  
         [0033]     The differential factor  215  may be used to reduce the processed base-line measurement  208 . In one embodiment, the differential factor  215  reduces the processed base-line measurement  208  by multiplying the processed base-line measurement  208  by the differential factor  215 . Another embodiment of reducing the processed base-line measurement  208  by the differential factor  215  may comprise subtracting the differential factor  215  from the processed base-line measurement  208 .  
         [0034]     In one embodiment, the controller  205  is coupled to a comparison module  216 . The comparison module  216  may be configured to monitor the power system characteristic  207 . The comparison module  216  may further be used to determine when the power system characteristic  207  falls below the threshold value  214 . A load shedding module  217  is operable with the comparison module  216 . In one embodiment the load shedding module  217  is configured to decouple power to at least the electrical load  201 . Power is decoupled from the electrical load  201  when the comparator module  216  indicates that the power system characteristic  209  has fallen below the threshold value  214 .  
         [0035]     By way of example, the power system characteristic  209  is the output voltage dropped over the electrical load. The power system characteristic  209  is sent to the characteristic measurement module where a processed base-line measurement of the output voltage is established. The processed base-line measurement of the output voltage is next subtracted by the differential factor  215  to create an output voltage threshold value. The comparison module  216  monitors the output voltage to determine if it drops over the output voltage threshold.  
         [0036]     In one embodiment, the load controlling device  200  comprises a restart module  218 . The restart module  218  is connected to the comparison module  216 . The restart module  218  may be configured to recouple power to the at least one electrical load  210 . Power may be recoupled to at least one electrical load  201  when the comparator module  216  indicates that the power system characteristic  209  exceeds the threshold value  214 .  
         [0037]     In one embodiment, when the power system characteristic  209  exceeds the threshold value  214  by at least a predetermined amount, the at least one electrical load  201  is actuated. In another embodiment of actuating additional loads following the shedding of a local electrical load, the at least one electrical load is actuated when the power system characteristic  209  exceeds the threshold value  214  for at least a predetermined restart time.  
         [0038]     Turing to  FIG. 3 , illustrated therein is one embodiment of a system for controlling power delivery  300  to an electrical load  201 . The system for controlling power delivery  300  may comprise a power distribution grid  301  having multiple nodes. The power distribution grid  301  can include any power distribution system and variations to those familiar with the art. In one embodiment, an electrical services provider  204  is coupled to a first node  302  of the power distribution grid  301 . The electrical services provider  204  may be capable of generating a communication signal  210  having measurement indicia therein. In one embodiment, the at least one electrical load  201  is coupled to a second node  303  of the power distribution grid  301 . A load controlling devices may further be coupled to the second node of the power distribution grid  301 .  
         [0039]     In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Thus, while preferred embodiments of the invention have been illustrated and described, it is clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions, and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the following claims. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention.