Energy controller and method for dynamic allocation of priorities of controlled load curtailment to ensure adequate load sharing

• US 4,551,812 A
• Filed: 09/20/1982
• Issued: 11/05/1985
• Est. Priority Date: 06/17/1981
• Status: Expired due to Fees

• Current Assignee: Cyborex Laboratories Incorporated
• Original Assignee: Cyborex Laboratories Incorporated
• Inventors: Matheson, Frederick A., Gurr, George P.
• Primary Examiner(s): Wise, Edward J.
• Application Number:
  US06/420,563
• Time in Patent Office: 1,142 Days
• Field of Search: 364/492, 364/484, 364/493, 307/35, 307/39, 307/44, 307/52, 307/62, 307/40, 307/41
• US Class Current: 700/295
• CPC Class Codes: H02J 2310/60 Limiting power consumption in the network or in one section of the network, e.g. load shedding or peak shaving
• CPC Class Codes: H02J 3/003 Load forecast, e.g. methods or systems for forecasting future load demand
• CPC Class Codes: H02J 3/144 Demand-response operation of the power transmission or distribution network
• CPC Class Codes: Y02B 70/3225 Demand response systems, e.g. load shedding, peak shaving
• CPC Class Codes: Y04S 20/222 Demand response systems, e.g. load shedding, peak shaving

Abstract

An energy controller maintains the total power delivered to an establishment close to a power limit so as to ensure shared operation of all curtailed loads by computing a cumulative priority value (CPV) for each load. The CPV of a particular load is the positive product of a "user-set priority" for that load and the amount of time that load has been shed, or is the negative product of the user-set priority and the amount of time that load has been restored. A processor makes decisions whether to shed or restore a certain load on the basis of the relation of the CPV of that load to the CPV'"'"'s of the other loads. Loads with the highest CPV'"'"'s are restored first and loads with the lowest CPV'"'"'s are shed first. The power limit is adjusted between upper and lower bounds to reflect recent power usage patterns. A minor average and a major average, each of which is most "weighted" by recent power readings, are computed. Generally, low priority loads are shed when both the minor average and the major average exceed the power limit, and are restored when both the minor and major averages are less than the power limit. If the minor and major average, respectively, exceed and are less than the power limit, the processor performs a "look-ahead" operation to predict the likely effect of a shedding operation before determining whether to perform that shedding operation.

Claims

1. A method for controlling delivery of elecrical energy from a power line to an establishment having a plurality of electrical loads in order to maintain the total power delivered to the electrical loads close to a power limit, the electrical loads including a plurality of controlled loads which can be electrically connected to and disconnected from the power line, partially in accordance with user-selected priorities attributed to respect ones of the controlled loads, by means of a control system, the control system including a plurality of load switching means for controllably connecting the controlled loads to and disconnecting the controlled loads from the power line, the control system also including power measuring means for measuring power delivered from the power line to the electrical loads, said method comprising operating a processor to effect the steps of:

(a) for each of said controlled loads, including a first one of said controlled loads,

1. measuring the value of a variable associated with a cumulative effect of operation or non-operation of that controlled load.

2. computing a cumulative priority value for that controlled load, said cumulative priority value being a function of both

(i) said user-selected priority associated with that controlled load, and

(ii) said value of said variable; and

(b) making a decision whether to shed or restore said first controlled load on the basis of whether said first controlled load is less than or exceeds the the value of said cumulative priority value of certain other cumulative priority values of other ones of said controlled loads.

2. The method of claim 1 wherein said variable is an amount of time that said first controlled load has been shed.

3. The method of claim 2 wherein said cumulative priority value is proportional to the product of said user-selected priority and said value of said variable.

4. The method of claim 1 wherein said variable is an amount of time that said first controlled load has been restored.

5. The method of claim 4 wherein said cumulative priority value is negative and is proportional to the product of said user-selected priority and said value of said variable.

6. The method of claim 1 wherein said variable is an amount of time that a control element associated with said first controlled load has been in a predetermined condition.

7. The method of claim 6 wherein said control element includes a thermostat.

8. The method of claim 6 wherein said variable is an amount of time that said control element has been on while said first load has been off.

9. A method for controlling delivery of electrical energy from a power line to an establishment having a plurality of electrical loads in order to maintain the total power delivered to the electrical loads close to a power limit, the electrical loads including a plurality of controlled loads which can be electrically connected to and disconnected from the power line, partially in accordance with user-selected priorities attributed to respective ones of the controlled loads, by means of a control system, the control system including a plurality of load switching means for controllably connecting the controlled loads to and disconnecting the controlled loads from the power line, the control system also including power measuring means for measuring power delievered from the power line to the electrical loads, said method comprising operating a processor to effect the steps of:

(a) computing and storing a power consumption number for any one of the controlled loads when that controlled load is electrically disconnected from the power line or is electrically connected to the power line;

(b) obtaining a minor average that represents the average power consumption of the establishment during a first period of time prior to the present time;

(c) obtaining a major average that represents the average power consumption of the establishment during a second period of time prior to the present time, said second period of time being substantially greater than said first period of time;

(d) comparing said major average to said power limit, and comparing said minor average to said power limit;

(e) measuring the values of a variable associated with a cumulative effect of operation or non-operation of respective ones of said controlled loads;

(f) computing a cumulative priority value for each of said controlled loads, respectively, each cumulative priority value being a function of both said user selected priority associated with the controlled load for which that cumulative priority value is computed and said measured value of the variable associated with the controlled load for which that cumulative priority value is computed;

(g) electrically disconnecting the one of said controlled loads presently connected to the power line and having the lowest cumulative priority value from the power line if both said major average and said minor average are greater than said selected power limit;

(h) repeating steps (b), (c), (d), and (e) until either said major average or said minor average is less than said selected power limit;

(i) computing a first power availability number representative of the difference between the selected power limit and said major average; and

(j) comparing a stored power consumption number of the one of said controlled loads not presently electrically connected to the power line and having the highest cumulative priority value with said first power availability number and electrically connecting that controlled load to the power line if the power consumption of that controlled load is less than said first power availability number and both said major average and said minor average are less than said power limit.

10. The method of claim 9 including, if said minor average is above said power limit and said major average is below said power limit, computing a first running sum of the amounts by which said minor average exceeds said power limit and also computing a second running sum of the amounts by which said minor average is less than said power limit over a predetermined time interval, determining whether electrically disconnecting the one of said controlled loads presently connected to the power line and having the lowest cumulative priority value from the power line would increase said second running sum enough to ensure that said second running sum would exceed said first running sum for at least a predetermined amount of time, and if the determination is affirmative, electrically disconnecting said controlled load having the lowest cumulative priority value from the power line.

11. The method of claim 9 wherein said power limit is a floating power limit and including the steps of determining if the present value of said power limit is a fixed lower power limit, and if it is not, then decreasing said power limit by a first predetermined amount before computing said shed running sum or said restore running sum.

12. The method of claim 9 including the steps of determining if the present value of said power limit is a fixed upper power limit, and if it is not, then increasing said power limit by a second predetermined amount before computing said shed running sum or said restore running sum.

13. The method of claim 11 wherein said first predetermined amount is selected to cause said power limit to decrease at a rate that accurately adjusts said power limit in accordance with seasonal changes in average power usage by the user so that substantial money-saving energy curtailment occurs during seasonal periods of relatively low power-usage.

14. The method of claim 12 wherein said second predetermined amount is selected to cause said power limit to increase at a rate that is great enough to avoid undue inconvenience to the user during unexpected short term increases in the daily energy usage by the user.

15. The method of claim 9 wherein said obtaining of said minor average includes attributing substantially more weight to the more recent power readings in said first period of time than to power readings nearer to the beginning of said first period of time.

16. The method of claim 9 wherein said obtaining of said major average includes attributing substantially more weight to the more recent values of said minor average in said second period of time than to said earlier values of said minor average.

17. A system for controlling delivery of electrical energy from a power line to an establishment having a plurality of electrical loads in order to maintain the total power delivered to the electrical loads close to a power limit, the electrical loads including a plurality of controlled loads which can be electrically connected to and disconnected from the power line, partially in accordance with user-selected priorities attributed to respective ones of the controlled loads, by means of a control system, the control system comprising in combination:

(a) a plurality of load switching means for controllably connecting the controlled loads to and disconnecting the controlled loads from the power line;

(b) power measuring means for measuring power delivered from the powerl ine to the electrical loads;

(c) means for measuring the value of a variable associated with a cumulative effect of operation or non-operation of each of said controlled loads, respectively;

(d) means for computing a cumulative priority value for each of said controlled loads, respectively, said cumulative priority value being a function of both

(i) said user-selected priority associated with that controlled load and

(ii) said value of said variable for that controlled load; and

(e) means for making a decision whether to shed or restore a first one of said controlled loads on the basis of whether the value of the cumulativepriority value of said first controlled load exceeds or is less than the cumulative priority values of certain other ones of said controlled loads.

18. The system of claim 17 wherein said variable is an amount of time that said first controlled load has been shed.

19. The system of claim 18 wherein said cumulative priority value is proportional to the product of said user-selected priority and said value of said variable.

20. The system of claim 17 wherein said variable is an amount of time that said first controlled load has been restored.

21. The system of claim 20 wherein said cumulative priority value is negative and is proportional to the product said user-selected priority and said value of said variable.

22. The system of claim 17 wherein said variable is an amount of time that a control element associated with said first controlled load has been in a predetermined condition.

23. The system of claim 22 wherein said control element includes a thermostat.

24. The method of claim 22 wherein said variable is an amount of time that said control element has been on while said first load has been off.

25. A system for controlling delivery of electrical energy from a power line to an establishment having a plurality of electrical loads in order to maintain the total power delivered to the electrical loads close to a power limit, the electrical loads including a plurality of controlled loads which can be electrically connected to and disconnected from the power line, partially in accordance with user-selected priorities attributed to respective ones of the controlled loads, by means of a control system, the control system comprising in combination:

(a) a plurality of load switching means for controllably connecting the controlled loads to and disconnecting the controlled loads from the power line;

(b) power measuring means for measuring power delievered from the power line to the electrical loads;

(c) means for computing and storing a power consumption number for any one of the controlled loads when that controlled load is electrically disconnected from the power line or is electrically connected to the power line;

(d) means for obtaining a minor average that represents the average power consumption of the establishment during the first period of time prior to the present time;

(e) means for obtaining a major average that represents the average power consumption of the establishment during a second period of time prior to the present time, said second period of time being substantially greater than said first period of time;

(f) means for comparing said major average to said power limit, and comparing said minor average to said power limit;

(g) means for measuring the values of a variable associated with a cumulative effect of operation or non-operation of respective ones of said controlled loads;

(h) means for computing a cumulative priority value for each of said controlled loads, respectively, each cumulative priority value being a function of both said user selected priority associated with the controlled load for which that cumulative priority value is computed and the measured value of the variable associated with the controlled load for which that cumulative priority value is computed;

(i) means for electrically disconnecting the one of said controlled loads presently connected to the power line and having the lowest cumulative priority value from the power line if both said major average and said minor average are greater than said selected power limit;

(j) means for computing a first power availability number representative of the difference between the selected power limit and said major average; and

(k) means for comparing a stored power consumption number of the one of said controlled loads not presently electrically connected to the power line and having the highest cumulative priority value with said first power availability number and electrically connecting that controlled load to the power line if the power consumption of that controlled load is less than said first power availability number and both said major average and said minor average are less than said power limit.

26. The system of claim 25 including, if said minor average is above said power limit and said major average is below said power limit, means for computing a first running sum of the amounts by which said monor average exceeds said power limit and also means for computing a second running sum of the amounts by which said minor average is less than said power limit over a predetermined time interval, means for determining whether electrically disconnecting the one of said controlled loads presently connected to the power line and having the lowest cumulative priority value from the power line would increase said second running sum enough to ensure that said second running sum would exceed said first running sum, for at least a predetermined amount of time, and means for electrically disconnecting said controlled load having the lowest cumulative priority value from the power line if the determination is affirmative.

27. The system of claim 25 wherein said power limit is a floating power limit and including means for determining if the present value of said power limit is a fixed lower power limit, and if it is not, then decreasing said power limit by a first predetermined amount before said computing of said shed running sum or said restore running sum.

28. The system of claim 27 wherein said first predetermined amount is selected to cause said power limit to decrease at a rate than accurately adjusts said power limit in accordance with seasonal changes in average power usage by the user so that substantial money-saving energy curtailment occurs during seasonal periods of relatively low power usage.

29. The system of claim 28 wherein said second predetermined amount is selected to cause said power limit to increase at a rate that is great enough to avoid undue inconvenience to the user during unexpected short term increases in the daily energy usage by the user.

30. The system of claim 25 including means for determining if the present value of said power limit is a fixed upper power limit, and if it is not, then increasing said power limit by a second predetermined amount before computing said shed running sum or said restore running sum.

31. The system of claim 25 wherein said means for computing of said minor average attributes substantially more weight to the more recent power readings in said first period of time than to power readings nearer to the beginning of said first period of time.

32. The system of claim 25 wherein said means for computing of said major average attributes substantially more weight to the more recent values of said minor average in said second period of time than to said earlier values of said minor average.