Abstract:
A non-transitory computer readable storage medium for causing a computer monitoring a power distribution system in which a first customer and a second customer are mixed to execute a process, the process including: acquiring first data measured with a first measurement device which is installed in the first customer and measures the first data at a first time interval; acquiring second data measured with a second measurement device which is installed in the second customer and measures the second data at a second time interval longer than the first time interval; estimating data of the first time interval about an electric power of the second customer by using the acquired first data and the acquired second data; and estimating a value about a voltage or a current for each customer by using the estimated data of the first time interval and the acquired first data.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese 
         [0002]    Patent Application No. 2013-220446, filed on Oct. 23, 2013, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0003]    A certain aspect of the embodiments is related to a non-transitory computer readable storage medium, an estimation apparatus and an estimation method. 
       BACKGROUND 
       [0004]    In recent years, a distributed power source which represents a solar power generation system spreads in a home. Although the solar power generation system has a merit of being environment-friendly, it also has a demerit of having an adverse influence on the quality of an electric power which an electric power company supplies. Especially, there is a problem that a voltage in a power grid may deviate from a stipulated voltage, by the solar power generation system being introduced to homes (customers) in the power grid. The stipulated voltage means a voltage (i.e., a voltage of the range of 95V to 107V in the case of 100V supply) which the electric power company needs to maintain, and which is defined by Electric Utility Law. 
         [0005]    Various methods, such as change of a delivery voltage of a power distribution substation, thickening of an electric wire and revision of a transformer tap, can be considered as a way of controlling a voltage, for example. However, in order to control the voltage, it is necessary to judge which voltage is changed in what manner. On the contrary, there is a method of using sensors installed in the electric wire as a method to know the voltage of the power grid. However, at present, there are very few sensors to the scale of the power grid. 
         [0006]    On the other hand, there is known a method called a power flow calculation as a way of calculating a voltage in the power grid and a current value in the power grid. Here, when a voltage distribution needs to be calculated for each predetermined time (for example, 30 minutes), obtaining an absolute value and a phase of the current in each customer or an active power and a reactive power in each customer is required for each predetermined time. However, now, most electric power meters introduced into the customers measure an integral power consumption only once a month and introduction of a smart meter which can measure an electric power value for each predetermined time (for example, 30 minutes) is limited to some customers. 
         [0007]    Here, Japanese Laid-open Patent Publication No. 2005-57821 discloses a technique that calculates a load current of each customer from an actual measurement value or standard data generally indicated. 
         [0008]    As described above, the actual measurement value of the electric power in the customer is known by only the customer into which the smart meter is introduced. Moreover, even if an electric power value is calculated using the standard data generally indicated, as described in the above-mentioned Japanese Laid-open Patent Publication, the characteristics (for example, the rising of an introductory rate of the solar power generation, etc.) of the customers which change every moment cannot be reflected to the electric power value by such standard data. Therefore, even if the power flow calculation is performed using the electric power value calculated with the use of the above-mentioned standard data, values about the voltage and the current in the power grid cannot be estimated with sufficient accuracy. 
       SUMMARY 
       [0009]    According to an aspect of the present invention, there is provided a non-transitory computer readable storage medium for causing a computer monitoring a power distribution system in which a first customer and a second customer are mixed to execute a process, the process including: acquiring first data measured with a first measurement device installed in the first customer, the first measurement device measuring the first data about an electric power at a first time interval; acquiring second data measured with a second measurement device installed in the second customer, the second measurement device measuring the second data about an electric power at a second time interval longer than the first time interval; estimating data of the first time interval about an electric power of the second customer by using the acquired first data and the acquired second data; and estimating a value about a voltage or a current for each of the first customer and the second customer by using the estimated data of the first time interval and the acquired first data. 
         [0010]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0011]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  is a perspective view of the configuration of a power grid system according to a first embodiment; 
           [0013]      FIG. 2  is a diagram of hardware configuration of an information processing apparatus; 
           [0014]      FIG. 3  is a functional block diagram of the information processing apparatus; 
           [0015]      FIG. 4  is a flowchart illustrating processing of the information processing apparatus; 
           [0016]      FIG. 5  is a diagram illustrating data acquired by respective customers; 
           [0017]      FIGS. 6A to 6C  are diagrams explaining processing of step S 12  of  FIG. 4 ; 
           [0018]      FIG. 7  is a diagram explaining processing of steps S 14  and S 16  of  FIG. 4 ; 
           [0019]      FIG. 8  is a diagram illustrating an example of a result in which a normalized demand curve is selected at random; 
           [0020]      FIG. 9  is a diagram explaining processing of step S 18  of  FIG. 4 ; 
           [0021]      FIG. 10  is a diagram illustrating an example of a voltage distribution acquired as a result of processing of step S 20  of  FIG. 4 ; 
           [0022]      FIG. 11  is a diagram illustrating data acquired by the respective customers and contract plans of the respective customers with respect to a second embodiment; and 
           [0023]      FIG. 12  is a diagram illustrating an example of a result in which a normalized demand curve is selected at random, with respect to the second embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment  
       [0024]    Hereinafter, a detailed description will be given of a first embodiment of a power grid system, based on  FIGS. 1 to 10 . 
         [0025]    A power grid system  100  of the first embodiment includes a power grid (a power distribution system)  80  and an information processing apparatus  20 , as illustrated in  FIG. 1 . The pole transformer  10  and five customers D 1  to D 5  exist in the power grid  80 , as one example. In addition, smart meters  12  are installed in the customers D 1 , D 2 , and D 4  among the customers D 1  to D 5 , and wattmeters (electric power meters)  14  are installed in the customers D 3  and D 5  among the customers D 1  to D 5 . 
         [0026]    The smart meter  12  can acquire a power consumption value (hereinafter simply referred to as “a power value”) as first data at a first time interval (e.g. every 30 minutes), and transmits the acquired power value to the information processing apparatus  20 . When the smart meter  12  acquires the power value every 30 minutes for one month (for 30 days), for example, it can acquire data of 1440 points (=48 points/1 day×30 days). Here, an integral power consumption for each second time interval (e.g. 1 month) can be calculated from the power values acquired by the smart meter  12 . 
         [0027]    The wattmeter  14  is a device that can acquire an integral power consumption as second data at the second time interval (e.g. 1 month) longer than the first time interval. The integral power consumption for one month acquired by the wattmeter  14  is inputted to the information processing apparatus  20 . Here, in the present embodiment, a measurement result of the wattmeter  14  is automatically inputted to the information processing apparatus  20  by communication. However, an input method of the measurement result is not limited to this, and the measurement result of the wattmeter  14  may be inputted to the information processing apparatus  20  by hand. 
         [0028]    The information processing apparatus  20  has hardware configuration as illustrated in  FIG. 2 . As illustrates in  FIG. 2 , the information processing apparatus  20  includes a CPU (Central Processing Unit)  90 , a ROM (Read Only Memory)  92 , a RAM (Random Access Memory)  94 , a storage unit (here, HDD (Hard Disk Drive))  96 , a communication unit  97 , a display unit  93 , an input unit  95  and a portable storage medium drive  99 . Each element of the information processing apparatus  20  is connected to a bus  98 . The display unit  93  includes a liquid crystal display and the like, and the input unit  95  includes a keyboard and a mouse. Moreover, the communication unit  97  communicates with the smart meter  12  and the wattmeter  14 . In the information processing apparatus  20 , the CPU  90  executes a program (including an estimation program) stored in the ROM  92  or the HDD  96 , or a program (including an estimation program) which the portable storage medium drive  99  reads from a portable storage medium  91 , so that functions as an acquisition unit  50 , an estimation unit  52  and an output unit  34  are achieved, as illustrated in  FIG. 3 . In  FIG. 3 , a smart meter DB  42 , a wattmeter DB  44 , a power grid configuration DB  46  and a voltage distribution DB  48  which are stored in the HDD  96  or the like are also illustrated. 
         [0029]    The acquisition unit  50  includes a smart meter data acquisition unit  22  and a wattmeter data acquisition unit  24 . 
         [0030]    The smart meter data acquisition unit  22  acquires data of the power values measured at the first time interval (30 minutes) as demand data from the smart meter  12 , and stores the data in the smart meter DB  42 . Here, the data (time-series data) of the power values every 30 minutes for each customer (D 1 , D 2 , D 4 ) is stored in smart meter DB 42 . In addition, the integral power consumption for each customer for one month calculated from the data of the power value every 30 minutes is also stored in the smart meter DB  42 . 
         [0031]    The wattmeter data acquisition unit  24  acquires the integral power consumption at the second time interval (e.g. 1 month) from the wattmeter  14 , and stores the integral power consumption in the wattmeter DB  44 . Here, the integral power consumptions of every month about the customers (D 3 , D 5 ) are stored in the wattmeter DB 44 . 
         [0032]    The estimation unit  52  includes a demand data correction unit  26  as a first acquisition unit, a multiple set demand data creation unit  28  as a second acquisition unit, a power flow calculation unit  30 , and a voltage distribution derivation unit  32 . The demand data correction unit  26  normalizes data (it is also called “demand data”) of the power values acquired in the smart meters  12  installed in the customers D 1 , D 2 , and D 4 . The demand data correction unit  26  derives a relational expression between the demand data before the normalization, and normalized demand data and the integral power consumption for each customer (D 1 , D 2 , D 4 ). 
         [0033]    The multiple set demand data creation unit  28  assigns B sets of demand data to all the customers. Note that detailed processing of the multiple set demand data creation unit  28  is described later. 
         [0034]    The power flow calculation unit  30  performs the power flow calculation using the B sets of demand data assigned to each customer, and calculates B kinds of voltage values in each time of each customer. In the above-mentioned calculation, the power flow calculation unit  30  refers to the power grid configuration DB  46  storing circuit information in the power grid. 
         [0035]    The voltage distribution derivation unit  32  calculates (estimates) a voltage distribution (i.e., a probability distribution of voltage values) in each time of each customer, based on the calculation result of the power flow calculation unit  30 , and stores the voltage distribution in the voltage distribution DB  48 . Here, the voltage distribution in each time of each customer, acquired as a result of B kinds of the power flow calculation, is stored in the voltage distribution DB  48 . 
         [0036]    The output unit  34  outputs data stored in the voltage distribution DB  48  by displaying the data on the display unit  93 , for example, in response to a request of the user of the information processing apparatus  20 . In addition, the output unit  34  outputs the data stored in the voltage distribution DB  48  to a voltage control device, not shown. Thereby, the voltage control device can control a voltage in the power grid. As a result, it is possible to maintain the voltage in the power grid in a stipulated voltage or less. 
         [0037]    (Processing of Information Processing Apparatus  20 ) Next, a detailed description will be given of processing of the information processing apparatus  20  along with a flowchart of  FIG. 4 , by reference to other drawings if desired. Here, as a premise of the processing of  FIG. 4 , the smart meter data acquisition unit  22  and the wattmeter data acquisition unit  24  store the data acquired for one month in the smart meter DB 42  and the wattmeter DB 44 , respectively. 
         [0038]    More specifically, the data on the power value of 1440 points (=48 points/1 day x  30 ) measured every 30 minutes by the smart meter  12  for one month (30 days) and the integral power consumption for one month acquired from the smart meter  12  are stored in the smart meter DB  42  as the demand data about each of the customers D 1 , D 2  and D 4 , as illustrated in  FIG. 5 . Note that a part of the 1440 points is illustrated in  FIG. 5 . In addition, the integral power consumption for one month acquired from the wattmeter  14  is stored in the wattmeter DB 44  as the demand data about each of the customers D 3  and D 5 . 
         [0039]    In the processing of  FIG. 4 , first, the demand data correction unit  26  acquires the data for one month from the smart meter DB  42  and the multiple set demand data creation unit  28  acquires the data of the integral power consumption for one month from the wattmeter DB  44 , in step S 10 . Next, in step S 12 , the demand data correction unit  26  performs processing which normalizes the demand data acquired from the smart meter DB 42 . 
         [0040]    Specifically, in step S 12 , the demand data correction unit  26  normalizes the demand data by unifying to 0 an average of the power values of 1440 points about each customer (D 1 , D 2 , D 4 ) in which the smart meter  12  is installed, and unifying variance of the power values of 1440 points to 1. 
         [0041]    When the demand data about the customer D 1  is expressed by “P 1     —     1 , . . . , P 1     —     1440 ”, and normalized demand data about the customer D 1  is expressed by “P 1     —     1,n , . . . , P 1     —     1440,n ”, the demand data correction unit  26  normalizes the demand data by using a following formula (1). 
         [0000]        P   1     —     i,n =( P   1-1   −P   1     —     mean ) /P   1     —     sd    (1)
 
         [0042]    Where the P 1     —     mean  is a sample mean of P 1     —     1 , . . . , P 1     —     1440 , and the P 1     —     sd  is a sample standard deviation of P 1     —     1 , . . . , P 1     —     1440 . 
         [0043]    Here, the sample mean P 1     —     mean  is expressed by a following formula (2), and the sample standard deviation P 1     —     sd  is expressed by a following formula (3). 
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         [0044]    Note that an image of normalization of step S 12  is illustrated in the  FIGS. 6A to 6C . By subtracting the sample average from the demand data illustrated in  FIG. 6A , an average can be set to 0 as illustrated in  FIG. 6B . Moreover, by dividing the subtractive result by the sample standard deviation, variance can be set to 0 as illustrated in  FIG. 6C . 
         [0045]    Returning to  FIG. 4 , in next step S 14 , the demand data correction unit  26  performs processing that calculates a relation formula between the demand data, the normalized demand data and the integral power consumption. 
         [0046]    In step S 14 , the demand data correction unit  26  calculates k 0  and k 1  of a following formula (4) by using the demand data (it is also called a demand curve), the normalized demand data (it is also called a normalized demand curve), the integral power consumption, and a least-squares method. 
         [0000]      argmin Σ∥DemandCurve−IntegralPower Consumption( k   0   +k   1 ×NormalizedDemandCurve)∥  (4)
 
         [0047]    Specifically, when the demand data about the customer Dj (j=1, 2, 4) in which the smart meter  12  is installed is expressed by P j     —     1 , . . . , P j     —     1440 , the normalized demand data is expressed by P j     —     1,n , . . . , P j     —     1440 , and the integral power consumption per one month is expressed by W j , the demand data correction unit  26  calculates k 0  and k 1  of a following formula (5). 
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         [0048]    Then, the demand data correction unit 26 creates a following formula (6). 
         [0000]      Demand Curve≈Integral Power Consumption( k   0   +k   1 ×Normalized Demand Curve)   (6)
 
         [0049]    Note that the processing of step S 14  described above is processing indicated by marks (A), (B) and (C) in  FIG. 7 . 
         [0050]    Next, in step S 16  of  FIG. 4 , the multiple set demand data creation unit  28  performs processing which assigns a plurality of sets of demand data for each time slot and each customer. In this case, the multiple set demand data creation unit  28  assigns B sets of demand data (i.e., demand curves) each having 1440 points to all the customers. Then, the multiple set demand data creation unit  28  performs the following processing according to whether the smart meter  12  is installed in each customer. 
         [0051]    (In the case of the customers D 1 , D 2  and D 4  in which the smart meters  12  are installed) 
         [0052]    In this case, the multiple set demand data creation unit  28  directly assigns (or copies) the demand data (i.e., the demand curve) of 1440 points measured by the smart meter  12  installed in each corresponding customer as demand data from first set to B-th set about each of the customers D 1 , D 2  and D 4 . Here, this processing is processing indicated by marks (D), (E) and (F) in  FIG. 7 . 
         [0053]    (In the Case of the Customers D 3  and D 5  in Which the Smart Meters  12  Are Not Installed) 
         [0054]    In this case, the multiple set demand data creation unit  28  randomly selects B sets of normalized demand data (i.e., normalized demand curve) about the customers D 1 , D 2  and D 4  in which the smart meters  12  are installed, for each of the customers D 3  and D 5 . The multiple set demand data creation unit  28  assigns demand data (i.e., demand curve) acquired by correcting the selected normalized demand data (i.e., normalized demand curve) using the relation formula (i.e., the formula (6)) calculated in step S 14 , as demand data (i.e., demand curve) from first set to B-th set of each of the customers D 3  and D 5 . Note that the present processing is processing that estimates data of the first time interval about the electric power of each of the customers D 3  and D 5 . The present proceeding is not limited to a case where the B sets of the normalized demand data (i.e., normalized demand curve) about each of the customers D 1 , D 2  and D 4  are selected at random. The multiple set demand data creation unit  28  may select the B sets of the normalized demand data (i.e., normalized demand curve) about each of the customers D 1 , D 2  and D 4  in accordance with a prescribed rule. 
         [0055]    It is assumed that a result in which the normalized demand data (i.e., normalized demand curve) are selected at random is illustrated in  FIG. 8 , for example. As illustrated in  FIG. 8 , the normalized demand data (i.e., normalized demand curve) about the customer D 2  is selected as the first set of the customer D 3 . Therefore, the multiple set demand data creation unit  28  assigns data acquired by correcting the normalized demand data (i.e., normalized demand curve) P 2     —     i,n  about the customer D 2  by a following formula (7), as the first set of the demand data (i.e., demand curve) P 3     —     i  of 1440 points about the customer D 3 . 
         [0000]        P   3     —     i   =W   3 ( k   0   k   1   ·P   2     —     i,n )   (7)
 
         [0056]    Note that the multiple set demand data creation unit  28  assigns the demand data (i.e. demand curve) to the second to the B-th sets about the customer D 3  and the first to the B-th sets about the customer D 5  in the same manner as mentioned above. 
         [0057]    Note that the above-mentioned processing is processing indicated by marks (G1), (G2), (H1) and (H2) in  FIG. 7 . Here, the multiple set demand data creation unit  28  transmits a result of the above-mentioned processing to the power flow calculation unit  30 . 
         [0058]    Next, in step S 18  of  FIG. 4 , the power flow calculation unit  30  performs a plurality of sets (B sets) of power flow calculation for each time slot using the result of the processing received from the multiple set demand data creation unit  28 . 
         [0059]    In this case, since the power flow calculation unit  30  acquires the B sets of electric power data (i.e., power values) about all the customers every 30 minutes (every 1 point), the power flow calculation unit  30  can calculate voltage values of 30 minute intervals about the respective customers by performing the power flow calculation 1440 points x B times. An example of a result of the power flow calculation is indicated by  FIG. 9 . Here, the power flow calculation unit  30  transmits the result of the power flow calculation to the voltage distribution derivation unit  32 . 
         [0060]    Next, in step S 20  of  FIG. 4 , the voltage distribution derivation unit  32  calculates a distribution (i.e., a probability distribution) of the voltage for each time slot using the calculation result of the power flow calculation unit  30 . 
         [0061]    Here, as the calculation result of the power flow calculation unit  30 , the B sets of voltage data for each 30 minutes (for each 1 point) about all customers are acquired by the above processing. Therefore, when the voltages (1 to B sets) of first point (i.e., initial time) as a voltage at a certain point are given by v 1 , . . . , v B , the distribution (i.e., the probability distribution) of the voltage is estimated by a normal distribution of v mean  which is a sample mean of v 1 , . . . , v B , and v sd  which is a sample standard deviation of v 1 , . . . , v B . Here, the v mean  and the v sd  are expressed by following formulas (8) and (9). 
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         [0062]    For example, in case of the distribution of the voltage at a certain time (e.g. time T on o-month/x-day) about the customer D 1 , the voltage values of the first to B-th sets at the certain time (e.g. time T on o-month/x-day) about the customer D 1  illustrated by a broken line frame of  FIG. 9  are extracted, and the extracted result can be expressed as illustrated in  FIG. 10  by setting a voltage to a horizontal axis and setting a frequency to a vertical axis. 
         [0063]    Thus, after the processing of  FIG. 4  is completed, the output unit  34  outputs the data stored in the voltage distribution DB  48  to a voltage control device, not shown, for example. In this case, the voltage control device control a voltage in the power grid using the inputted data, so that the voltage in the power grid can be maintained in a stipulated voltage or less. Alternatively, the output unit  34  displays the data stored in the voltage distribution DB  48  on the display unit  93  according to a request from a user. 
         [0064]    As can be seen from the description mentioned above, the demand data correction unit  26  and the multiple set demand data creation unit  28  realize a function as a first estimation unit that estimates the demand data of the customer in which the smart meter is not installed. In addition, the power flow calculation unit  30  and the voltage distribution derivation unit  32  realize a function as a second estimation unit that estimates the voltage distribution in the power grid  80  for each customer. 
         [0065]    As described above, according to the first embodiment, the demand data correction unit  26  acquires the demand data measured by the smart meter  12 , and the multiple set demand data creation unit  28  acquires the data of the integral power consumption measured by the wattmeter  14 . Then, the demand data correction unit  26  and the multiple set demand data creation unit  28  estimate the demand data of each of the customers (D 3  and D 5 ) in which the smart meter  12  is not installed (i.e., data of the first time interval about the power value of each of the customers (D3 and D5)) by using the demand data measured by the smart meters  12  installed in the customers (D 1 , D 2  and D 4 ) and the data of the integral power consumption measured by the wattmeters  14  installed in the customers (D 3  and D 5 ) (S 12  to S 16 ). And then, the power flow calculation unit  30  and the voltage distribution derivation unit  32  calculate (estimate) the voltage distribution for each customer by using the estimated demand data of the customers (D 3  and D 5 ) and the measured demand data of the customers (D 1 , D 2  and D 4 ). Thus, in the present embodiment, the demand data of the customers (D 3  and D 5 ) in which the smart meters  12  are not installed are estimated from an own integral power consumption and the demand data of other customers (D 1 , D 2  and D 4 ) in the power grid  80 . Therefore, the demand data of each customer, which has reflected the characteristics (for example, the rising of an introductory rate of the solar power generation, etc.) of the customers in the power grid  80 , can be estimated with high accuracy. Moreover, the voltage distribution for each customer can be estimated with high accuracy by using the demand data of each customer estimated with high accuracy. 
         [0066]    In the first embodiment, in step S 16 , the multiple set demand data creation unit  28  selects the B sets of the normalized demand data about each of the customers (D 1 , D 2  and D 4 ) at random, and calculates the B sets of the demand data about each of the customers (D 3  and D 5 ) by using the selected normalized demand data. Then, the power flow calculation unit  30  performs the power flow calculation with the use of the B sets of the demand data, and the voltage distribution derivation unit  32  calculates (estimates) the voltage distribution about each of the customers (D 1  to D 5 ) with the use of a result of the power flow calculation. Therefore, in the present embodiment, the voltage distribution about each of the customers can be estimated with high accuracy by using the B sets of the demand data about the customers (D 3  and D 5 ) estimated with the use of the normalized demand data about the customers (D 1 , D 2  and D 4 ). 
       Second Embodiment 
       [0067]    Next, a detailed description will be given of a power grid system according to a second embodiment, based on  FIGS. 11 and 12 . 
         [0068]    In the second embodiment, 10 customers exists in the power grid as illustrated in  FIG. 11 , as one example. In addition, smart meters  12  are installed in customers D 1 , D 2 , D 6 , D 7  and D 9  among these customers, and wattmeters  14  are installed in remaining four customers D 3 , D 5 , D 8  and D 10 . In addition, contract plans about all the customers are understood. A contract plan 1 is a normal plan of electricity charges, and the customers D 1 , D 3 , D 4 , D 5 , D 7 , D 9  and D 10  contract the contract plan 1. A contract plan 2 is a plan having expensive electricity charges for daytime and inexpensive electricity charges for night, and the customers D 2 , D 6  and D 8  contract the contract plan 2. 
         [0069]    Here, since the device configuration of the second embodiment is the same as that of the first embodiment except for the member of the above-mentioned customers, a detailed description thereof is omitted. 
         [0070]    (As to Processing of Information Processing Apparatus  20 ) 
         [0071]    Also in the second embodiment, the information processing apparatus  20  basically performs the processing of  FIG. 4 , but the processing of steps S 14  and S 16  differs from corresponding processing of the above-mentioned first embodiment. Therefore, hereinafter, a detailed description will be given of the processing of steps S 14  and S 16 . 
         [0072]    (As to Step S 14 ) 
         [0073]    In step S 14 , the demand data correction unit  26  performs processing that calculates a relation formula between the demand data, the normalized demand data and the integral power consumption. 
         [0074]    In this case, the demand data correction unit  26  solves k 0     —     plan#m  and k 1     —     plan#m (m=1, 2) of a following formula (10) by using a least squares method for each of the contract plans 1 and 2. 
         [0000]      arg min Σ∥Demand Curve of Contract Plan m−Integral Power Consumption( k   0     —     plan#m   +k   1     —     plan#m ×Normalized Demand Curve of Contract Plan  m )   (10)
 
         [0075]    Then, the demand data correction unit  26  creates a relation formula (m=1, 2) of a following formula (11). 
         [0000]      Demand Curve of Contract Plan  m≈ Integral Power Consumption( k   0     —     plan#m   +k   1     —     plan#m ×Normalized Demand Curve of Contract Plan  m )   (11)
 
         [0076]    Specifically, when the demand data in the contract plan 1 about a customer D j  (j=1, 4, 7, and 9) in which the smart meter  12  is installed is expressed by “P j     —     1 , . . . , P j     —     1440 ”, normalized demand data thereof is expressed by “P j     —     1,n , . . . , P j     —     1440,n ”, and the integral power consumption for one month is expressed by “W j ”, the demand data correction unit  26  solves k 0     —     plan#1  and k 1     —     plan#1  of a following formula (12). 
         [0000]    
       
         
           
             
               
                 
                   
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         [0077]    Similarly, when the demand data in the contract plan 2 about a customer D j  (j=2 and 6) in which the smart meter  12  is installed is expressed by “P j     —     1 , . . . , P j     —     1440 ”, normalized demand data thereof is expressed by “P j     —     1,n , . . . , P j     —     1440,n ”, and the integral power consumption for one month is expressed by “W j ”, the demand data correction unit  26  solves k 0     —     plan#2  and k 1     —     plan#2  of a following formula (13). 
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         [0078]    As a result, with respect to the contract plan 1, a relation formula indicated by a following formula (14) is created. 
         [0000]      Demand Curve≈Integral Power Consumption( k   0     —     plan#1   +k   1     —     plan#1 ×Normalized Demand Curve)   (14)
 
         [0079]    With respect to the contract plan 2, a relation formula indicated by a following formula (15) is created. 
         [0000]      Demand Curve≈Integral Power Consumption( k   0     —     plan#2   +k   1     —     plan#2 ×Normalized Demand Curve)   (15)
 
         [0080]    (As to Step S 16 ) 
         [0081]    In step S 16 , the multiple set demand data creation unit  28  performs processing which assigns a plurality of sets of demand data for each time slot and each customer. 
         [0082]    In this case, the multiple set demand data creation unit  28  assigns the B sets of demand data each having 1440 points to all the customers. Then, the multiple set demand data creation unit  28  performs the following processing according to whether the smart meter  12  is installed in each customer. 
         [0083]    (In the Case of the Customers D 1 , D 2 , D 4 , D 6 , D 7  and D 9  in Which the Smart Meters  12  are Installed) 
         [0084]    In this case, the multiple set demand data creation unit  28  directly assigns (or copies) the demand data (i.e., the demand curve) of 1440 points measured by the smart meter  12  installed in each corresponding customer as demand data from first set to B-th set about each of the customers D 1 , D 2 , D 4 , D 6 , D 7  and D 9 . 
         [0085]    (In the Case of the Customers D 3 , D 5 , D 8  and D 10  in Which the Smart Meters  12  are Not Installed) 
         [0086]    In this case, the multiple set demand data creation unit  28  randomly selects B sets of normalized demand data about the customers in the same contract plan in which the smart meters  12  are installed, for each of the customers D 3  D 5 , D 8  and D 10 . Then, the multiple set demand data creation unit  28  selects the selected normalized demand data (i.e., normalized demand curve), and then corrects the demand data with the use of the relation formula. 
         [0087]    It is assumed that a result in which the normalized demand data are selected at random is illustrated in  FIG. 12 , for example. In this case, the normalized demand data about the customer D 7  is assigned as the first set of the customer D 3  having the contract plan 1. Therefore, the first set of the demand data (i.e., demand curve) of 1440 points about the customer D 3  is calculated from the normalized demand data (i.e., normalized demand curve) about the customer D 7  according to a following formula (16). 
         [0000]        P   3     —     i   =W   3 ( k   0     —     plan#1   +k   1     —     plan#1   ×P   7     —     i,n )   (16)
 
         [0088]    According to  FIG. 12 , the normalized demand data about the customer D 2  is assigned as the first set of the customer D 8  having the contract plan 2. Therefore, the first set of the demand data (i.e., demand curve) of 1440 points about the customer D 8  is calculated from the normalized demand data (i.e., normalized demand curve) about the customer D2 according to a following formula (17). 
         [0000]        P   8     —     i   =W   8 ( k   0     —     plan#2   +k   1     —     plan#2   ×P   2     —     i,n )   (17)
 
         [0089]    Here, other processing of  FIG. 4  is the same as the corresponding processing of the first embodiment. 
         [0090]    As described above, according to the second embodiment, in step S 14 , the demand data correction unit  26  calculates the relation formula (formula (14) or (15)) for every contract plan. Then, in step S 16 , when the multiple set demand data creation unit  28  calculates the B sets of demand data about the customers in which the smart meters  12  are not installed, the multiple set demand data creation unit  28  randomly assigns the B sets of demand data about the customers, in which the smart meters  12  are installed, which have the common contract plans with the customers in which the smart meters  12  are not installed, and corrects the assigned demand data by using the relation formula calculated for every contract plan. Thus, when the B sets of demand data about the customers in which the smart meters  12  are not installed are calculated, it is possible to more accurately calculate the B sets of demand data about the customers in which the smart meters  12  are not installed, by using the demand data about the customers having a common characteristic. Moreover, the voltage distribution of each customer is calculated using the demand data calculated in this way, and hence the voltage distribution of each customer can be calculated more accurately. 
         [0091]    Here, the above-mentioned second embodiment explains about the case where the customers are grouped according to the contract plan, but a grouping of the customers is not limited to this. For example, the grouping may be performed based on the integral power consumption for each customer, information indicating whether a solar power generation apparatus is installed in the customer, or information indicating whether the customer is an apartment or a solitary house, or the like. 
         [0092]    Here, the above-mentioned first and second embodiments conclusively explain about the case where the voltage distribution of each customer in each time is calculated, but a calculation object is not limited to this. For example, a value about a current of each customer in each time may be calculated 
         [0093]    Here, the above-mentioned first and second embodiments explain about the case where the smart meter data acquisition unit  22  acquires the value of the power consumption about the customer from the smart meter  12 , but an acquisition object is not limited to this. For example, the smart meter data acquisition unit  22  may acquire values of a current and an electric power amount from the smart meter  12 . Moreover, the above-mentioned first and second embodiments explain about the case where the wattmeter data acquisition unit  24  acquires the value of the electric power amount (the integral power consumption) about the customer from the wattmeter  14 , but an acquisition object is not limited to this. For example, the wattmeter data acquisition unit  24  may acquire values of a current and an electric power from the wattmeter  14 . 
         [0094]    In addition, the above-described processing functions may be achieved by a computer. In this case, a program is provided in which processing contents of functions that the processor needs to have are described. By executing the program on the computer, the above-described processing functions are achieved on the computer. The program in which processing contents are described may be stored in a non-transitory computer-readable recording medium (here, a carrier wave is excepted). 
         [0095]    In the case of distributing the program, portable recording media, such as DVDs (Digital Versatile Disk) and CD-ROMs (Compact Disc Read Only Memory), in which the program is stored are sold. In addition, the program may be stored in a memory device of a server computer and then transferred from the server computer to another computer via a network. 
         [0096]    A computer for executing the program stores the program, which is originally stored in a portable recording medium or transferred from the server computer, in its own memory device. Subsequently, the computer reads the program from its own memory device and performs processing according to the program. Note that the computer is able to read the program directly from the portable recording medium and perform processing according to the program. In addition, the computer is able to perform processing according to sequentially received programs each time the programs are transferred from the server computer. 
         [0097]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.