Demand control apparatus and power distribution control system

Abstract: Object of the present invention is to provide a power distribution control system which can distribute the electric energy to houses, factories and other customers while considering the demand variable from one minute to the next and various customer situations. The demand control apparatus is adapted to compute the quantity of working current in each of the loads from a difference between the total quantities of working current before and after shut-off in that load and to re-start the load within a range defined by a difference between a set quantity of current and the total quantity of working current after shut-off in the load in accordance with its priority level. The power distribution control system includes a center communication terminal and a plurality of customer's communication terminals operatively connected to the center communication terminal through communication lines. Each of the customer's communication terminals is responsive to a presentation signal from the center communication terminal for outputting a response signal to the center communication terminal.

Description: Field of the Invention: The present invention relates to a demand control apparatus for reducing the total power used by a group of loads. Description of the Related Art: Recently, many consumers have been widely attempting to save the energy by setting the maximum working power level or power demand value to suppress the total quantity of electric power consumed within the range defined by the set demand value. The conventional demand control systems are known to be of such a type that a warning or control command is produced for a load or loads in which the input power exceeds the set power level or that any load having a larger working power is preferentially shut off, as described in Japanese Patent Laid-Open No. Sho 57-71233. There is also known a demand control apparatus which comprises a plurality of loads classified into on-off controllable loads and producing loads so that when the working power level consumed exceeds the set demand level, the number of producing loads are first reduced to control the working power level into a target level and the on-off controllable loads will be finally shut off, as described in Japanese Patent Laid-Open No. Sho 57-101526. Japanese Patent Laid-Open No. Sho 55-103043 further describes a demand control apparatus which can produce a failure signal when the total quantity of electric power consumed exceeds the target level even if all the loads to be controlled are controllably shut off. However, the demand control apparatus described in Japanese Patent Laid-Open No. Sho 57-71233 requires the registration of an electric working power. Although the system can effectively suppress the working power level below the set demand level since any load having a larger working power is preferentially shut off, the sequence of preference cannot be changed depending on the magnitude of working power so that the electric power will be effectively used within the range defined by the set demand value. The demand control apparatus of the Japanese Patent Laid-Open No. Sho 57-101526 also cannot change the sequence of preference for loads and select the type of instruments to be controlled. Thus, the demand control apparatus cannot be used in houses, factories and others, depending on various situations. Finally, the control system of Japanese Patent Laid-Open No. Sho 55-103043 can only generate a failure signal without carrying out any actual procedure. The conventional demand control systems raises a further problem when any one of the loads or instruments is shut off. For example, when a plurality of instruments such as a rice cooker, a water heater, an air conditioner and so on are used in a typical house in the morning, if any one instrument is shut off, it will be very inconvenient. Document EP-A-0 464 423 discloses a demand control apparatus being connected to a group of loads and adapted to shut off totally or partially or to reduce to a possible quantity of working current the power supply to loads in accordance with their set priorities so that the total quantity of working current in the group of loads will be equal to or lower than a set quantity of working current, said apparatus comprising power detecting means for detecting and calculating the total quantity of working current or the quantity of working current in each of the loads, and restart means to restart one or more loads in accordance with their priority within a range defined by permissible working current quantity. Document EP-A-0 372 961 discloses an add/shed system for adding/shedding loads to maintain the power consumption of a building below a predetermined level. According to this document a demand control apparatus is connected to a group of loads and adapted to shut off the power supply to loads in accordance with their set priority levels. Further total power consumption is detected. Further, restart means for adding loads are provided, which restart a load according to its priority level if the sum of the present total power consumption and the known power consumption of the respective load is lower than a permissible set working current quantity. It is therefore an object of the present invention to provide a demand control apparatus which can properly set the total quantity of working energy for a group of loads below a given level depending on circumstances of houses, factories and so on. SUMMARY OF THE INVENTION To this end, the present invention provides a demand control apparatus as defined in claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic block diagram of a demand control apparatus. Fig. 2 is a view illustrating the sequence of control in the demand control apparatus shown in Fig. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to Fig. 1, there is shown a demand control apparatus constructed in accordance with the first embodiment of the present invention. The demand control apparatus is connected to loads 1, 2 and 3 and adapted to shut off the power supply to the respective loads in accordance with the set priority level so that the total quantity of working power in the group of loads will be maintained at or below a power setting level. The control of the demand control apparatus is carried out in such a manner as shown in Fig. 2. For simplification, it is now assumed that two instruments, that is, one instrument a having its working current equal to 10 A and another instrument b having its working current equal to 5 A are used. It is also assumed that the set demand level is equal to 8 A and that the priority level of the instrument a is higher than that of the instrument b . When both the instruments are turned on, the total quantity of working current becomes equal to 15 A which will exceed the demand level. Thus, the demand control apparatus will shut off the power supply to the instrument b having its lower priority level. The total quantity of working current becomes equal to 10 A. However, this also exceeds the set demand level. Consequently, the instrument a will be also shut off. The demand control apparatus comprises a power detecting section or means 5 for computing the amount of working current in an instrument when it is shut off from the power supply, the computation being based on a difference between the total quantities of working current in that instrument before and after shut-off, as shown in Fig. 2. It is now judged by the power detecting section 5 that the quantity of working current in the instrument a is 10 A while that of the instrument b is 5 A. The demand control apparatus also comprises a re-start control section or means 6 for comparing a now permissible quantity of current with the quantity of current in a load and for re-starting that load according to its priority level within the range defined by the permissible quantity of current. The re-start control section 6 first compares the permissible quantity of current with the quantity of working current in the instrument a having the highest priority level. Since the quantity of working current in the instrument a exceeds the permissible level, it will not be re-started by the re-start control section 6. Subsequently, the quantity of working current in the instrument b is compared with the permissible quantity of current. Since the quantity of working current in the instrument b is within the permissible range, it will be re-started. If an instrument c having its quantity of working current equal to 2 A is connected to the demand control apparatus in addition to the instruments a and b , the instrument c will be re-started since its quantity of working current is within the permissible range.

Claims: A demand control apparatus connected to a group of loads and adapted to shut off the power supply to loads in accordance with their set priority levels so that the total quantity of working current in the group of loads will be equal to or lower than a set quantity of current, said apparatus comprising power detecting means (5) for computing the quantity of working current in each of the shutoff loads from a difference between the total quantities of working current before and after shut-off of said load; and re-start control means (6) for further comparing the quantity of working current in each of said previously shut-off loads in accordance with information of the quantity of working current in the load detected by said power detecting means with a difference between the set quantity of current and the total quantity of working current at the present time and for controlling the restart of one or more of said previously shut-off loads in accordance with their priority levels and according to the result of said comparing if the quantity of working current of said one or more loads is within a range defined by said difference between the set quantity of current and the total quantity of working current at the present time.

Inventors: INOUE MASAHIRO, IWATSUBO RIEKO, KUSHIRO NORIYUKI, MARUYAMA KAZUHIRO, INOUE, MASAHIRO, IWATSUBO, RIEKO, KUSHIRO, NORIYUKI, MARUYAMA, KAZUHIRO, Inoue, Masahiro, c/o Mitsubishi Denki K.K., Iwatsubo, Rieko, c/o Mitsubishi Denki K.K., Kushiro, Noriyuki, c/o Mitsubishi Denki K.K., Maruyama, Kazuhiro, c/o Mitsubishi Denki K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1993
Main classification: H02J3
IPC codes: H02J13, H02J3