Abstract:
A method of setting a demand threshold is provided. The method comprises: (a) a control unit arranging a plurality of demand data in a descending or an ascending order as a curve; (b) the control unit connecting a maximum demand datum and a minimum demand datum with a line; and (c) the control unit setting a demand datum with a longest perpendicular distance to the line as a demand threshold.

Description:
[0001]    This application claims the benefit of Taiwan application Serial No. 97151104, filed Dec. 26, 2008, the subject matter of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates in general to a control method and a system thereof, and more particularly to a method of calculating a demand threshold, and a method and a system of demand control. 
         [0004]    2. Description of the Related Art 
         [0005]    Although a convenient store only occupies small area, its energy consumption index is higher than that of a department store or a supermarket. As energy saving consciousness is getting higher, it is very important to design an effective and adequate energy saving system to control the electricity consumption of the convenient store. 
         [0006]    The convenient store is the place to provide service for customers. While putting energy saving solutions into practice, it should be considered if the store operation is affected. In the store management system revealed in Japanese Patent No. JP2006178886, an integrated system combining a POS and a store management platform is provided. The system integrates remote access with energy saving countermeasures which controls electric equipment such as air conditioning and illuminating apparatus. However, the cost to set up these systems is too expensive, which results in a long period of time to recover the cost. Furthermore, the system is too complicated. As a result, the related hardware cost and the software design expense cannot be lowered, which significantly reduces the practicability. 
         [0007]    Moreover, in the in-store equipment remote monitoring system revealed in US Patent No. 2002163431, a monitoring system is provided to collect the parameters such as indoor and outdoor illumination, the refrigerator temperature, outdoor temperature, the frequency of the automatic door, etc. The system predicts the next day&#39;s weather and brightness according to the historical information of the parameters, and calculates the suggested indoor illumination levels and temperature of air-conditioning with reference to the weather forecast. The user can manually adjust the operation of the equipment according to the suggested parameters. However, the cost to build up the system is too expensive. The system is complicated, which results in high related hardware cost and software design expense. The system cannot adjust the operation of the equipment automatically. When the environmental conditions change frequently and affect the decisions, the clerk has to take care of the customers and adjusts the equipment manually, which lowers the practicality greatly. Therefore, it is necessary to develop an automatic and effective energy saving strategy. 
         [0008]    The electric fees of Taiwan Power Company include demand charge, energy charge and penalty charge. The store usually signs a contract with the power company to obtain electricity with lower rates. However, it s stipulated in the contract that the power consumption amount cannot exceed the contracted amount in each period of time in a month. For example, the power consumption amount cannot exceed 75 kWh for each 15 minutes. When the power consumption amount in any period of time segment exceeds the contracted amount, the store has to pay high penalty charge. 
         [0009]    The average available power consumption is 5 kWh. However, when the power consumption within one minute is much higher than 5 kWh, it may result in the total power consumption of the time period exceeding 75 kWh even when the power consumption per minute of the following 14 minutes is lower than 5 kWh. The industrial customer found out that it is safer to set a threshold much lower than 5 kWh, such as 4 kWh. Therefore, the initial concept of demand control is derived accordingly. When the power consumption per minute is higher than 4 kWh, the power consumption has to be lowered. 
         [0010]    However, the conventional method of demand control is manually setting a fixed amount to be the threshold. It is difficult to decide the amount, and the threshold cannot be adjusted according to practical conditions. When the threshold is too high, the power consumption may exceed the contracted amount, which results in high penalty charge. When the threshold is too low, the system sheds loads continuously, and the store cannot operate normally. Furthermore, even the business places of the same type may have different power consumption when the parameters, such as the location, the season, the number of customers and the floor area, are different. A fixed threshold cannot be applied to each store. When the threshold can not reflect the real timing to reduce power consumption, the following control process does not have much meaning. 
       SUMMARY OF THE INVENTION 
       [0011]    The invention is directed to a method of determining a demand threshold, and a method and a system of demand control. The demand threshold is set according to statistic data by a standard method. An adequate demand threshold is provided according to the place and/or controlled object with different properties. Therefore, the method can be applied more widely. 
         [0012]    According to the present invention, a method of calculating a demand threshold is provided. The method includes (a) a control unit arranging demand data in a descending or an ascending order as a curve; (b) the control unit connecting a maximum demand datum and a minimum demand datum with a line; and (c) the control unit setting a demand datum with a longest perpendicular distance to the line as a demand threshold. 
         [0013]    According to the present invention, a method of demand control is provided. The method includes (a) a control unit setting a demand threshold, including arranging demand data in a descending or an ascending order as a curve; connecting a maximum demand datum and a minimum demand datum with a line; and setting a demand datum with a longest perpendicular distance to the line as a demand threshold; (b) a measure unit measuring the power consumption at the end of a time unit and calculating the demand of the time segment accordingly; and (c) shutting down an electric apparatus when the calculated demand is greater than the demand threshold. 
         [0014]    According to the present invention, a demand control system is provided. The system includes a measure unit and a control unit. The measure unit measures the power consumption at the end of a time unit and calculates a demand of the time segment accordingly. A time segment includes several time units. The control unit calculates a demand threshold according to several demand data. When the calculated demand is greater than the demand threshold, an electric apparatus is shut down. 
         [0015]    The invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a flow chart of a method of determining the demand threshold according to the first embodiment of the present invention; 
           [0017]      FIG. 2  shows the geometric relation of the determining process of the demand threshold in  FIG. 1 ; 
           [0018]      FIG. 3  illustrates a block diagram of a demand control system according to the second embodiment of the present invention; and 
           [0019]      FIG. 4  is a flow chart of the demand control method according to the second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The present invention provides a method of determining the demand threshold. The demand threshold is determined according to statistical data objectively. The threshold can be determined properly corresponding to the place or the controlled object of different properties and therefore be applied more widely. The power consumption of a convenient store is illustrated as an example in the following paragraphs. However, one having ordinary skill in the field of the present invention can understand that the method of determining the demand threshold of the present invention is not limited to this application field. 
       First Embodiment 
       [0021]    The present embodiment provides a method of determining a demand threshold. Compared to the conventional demand control method in which an amount is selected to be the demand threshold subjectively, the present embodiment uses a precise algorithm to objectively determine the demand threshold E threshold  based on the historical demand data. Please refer to  FIG. 1  and  FIG. 2 .  FIG. 1  is a flow chart of a method of determining the demand threshold according to the first embodiment of the present invention.  FIG. 2  shows the geometric relation of the determining process of the demand threshold in  FIG. 1 . First, as shown in the step S 202 , several demand data E 1 , E 2 , E 3  . . . E N  are arranged in a descending or a ascending order as a curve C by a control unit ( 120  as shown in  FIG. 3 ). The horizontal axis X is a sequence coordinate with equal intervals. Demand data arranged in a descending order as a curve are taken for example in the present embodiment, but it is not limited thereto. The demand data E 1 , E 2 , E 3  . . . E N  are original power consumption data without demand control and calculated by an measure unit ( 130  as shown in  FIG. 3 ). Such data can reflect the required power consumption of the store when the store operates practically. There are many different ways to obtain the demand data. For example, the power consumption of the store is recorded when the store does not apply any control method. Or, a neglecting time in which no control process is performed can be set in each time segment. The power consumption in the neglecting time is used for representing the demand of the whole time segment. In the present preferred embodiment, the demand data of a time period are arranged in a descending order as the curve C. In each time segment (including N time units), the demand data of some time units (n time units; i.e., the neglecting time) are captured to represent the power consumption of the time period. n is not greater than N. For example, a time period is a week, and a time segment is 15 minutes. There are 4×24×7=672 time segments in a time period. A time unit is one minute. Only the power consumption of the neglecting time (e.g., 3 time units) in a time segment (total 15 time units) is recorded, and the average power consumption per minute in the neglecting time is used as a representing demand datum. Therefore, in the present preferred embodiment, the curve C is composed of 672 demand data of time unit. Also, the first three minutes in each time segment are set as the neglecting time. No equipment will be shut down and no control process will be performed even when the power consumption in the neglecting time is high. Therefore, the power consumption in the neglecting time is recorded and just like the actual demand when the store is not under demand control. As a result, the time to collect the demand data is saved, and approximate real-time data can be obtained. 
         [0022]    Although the time period, time segment, time unit and the neglecting time are disclosed as above, anyone who has ordinary skill in the field of the present invention understands that the above time parameters are regulatable. Also, the demand data arranged in a descending order as a curve are disclosed as above, but anyone having ordinary skill in the understands that the way to arrange demand data is not limited thereto. The present invention is not limited thereto and changeable corresponding to the applied field and the purpose. 
         [0023]    Then, as shown in the step S 204 , the control unit  120  connect the maximum demand datum E max  and the minimum datum E min  of the demand data E 1 , E 2 , E 3  . . . E N  with a line L. Later, a line segment W perpendicular to the line L is constructed. The intersection point between the line segment W and the curve C is set as C (x′) . The intersection point between the line segment W and the line L is set as L (x) . Therefore, when x is determined, L (x)  and C (x′)  can be obtained. Subsequently, x 0  to x n  are substituted for x to obtain the maximum value of L (x) -C (x′) , and C (x′)  in the equation is the demand threshold. In other words, the perpendicular distance between the demand data E 1 , E 2 , E 3  . . . E N  on the curve C and the line L is calculated respectively to find out the demand datum with the maximum perpendicular distance to the line L, and the demand datum is set to be the demand threshold E threshold , as shown in the step S 206 . For example, the demand data E 1 , E 2 , E 3  . . . E N  which are in a descending order according to the value representing by the vertical axis are orderly arranged at equal interval along the horizontal axis to form the curve C in  FIG. 2 . The line L (the line connecting the maximum demand datum E max  and the minimum demand datum E min ) and the curve C only intersect at the maximum demand datum E max  and the minimum demand datum E min . The line W is constructed perpendicular to the line L. The line W is moved along the entire line L, and the perpendicular distance between each point on the curve C and the line L is calculated to find out the demand datum C (x′)  with longest perpendicular distance between the curve C and the line L. The demand datum C (x′)  is set to be the demand threshold E threshold . 
         [0024]    The method of determining the demand threshold of the present embodiment further includes the step S 208  of the control unit  120  checking whether there is updated demand datum or not. If there is, the demand threshold E threshold  will be updated accordingly. In the present preferred embodiment, the demand data generated in the 96 time segments during the day and the demand data of the previous 6 days are calculated again at the end of the day by following the steps S 202 -S 206  to obtain a new demand threshold. In other words, the control system updates the demand threshold according to the latest demand data. The present embodiment not only provides a standard method to set the demand threshold but also adjusts the demand threshold according to the present conditions. Therefore, the demand threshold is set more flexibly and can be applied more widely. However, anyone who has ordinary skill in the field of the present invention can understand that the time interval to update the demand threshold is a changeable parameter depending on the application field and the purpose. The present invention is not limited thereto. 
         [0025]    The method of determining the demand threshold of the present invention is disclosed as above. The following paragraphs are about how to apply the above method of determining the demand threshold to the method of demand control. 
       Second Embodiment 
       [0026]    The present embodiment relates to an application of the method of determining the demand threshold, and more particularly to a method and a system of demand control applying the above method of determining the demand threshold. What is worth mentioning is that the control steps can be modified differently, especially about the step of determining whether the power consumption of this time segment will exceed the demand threshold or not and the step of the control strategy if the calculated demand is exceeded demand threshold. The description and drawings disclosed by the present embodiment are only an example under the spirit of the present invention. The present invention is not limited thereto. 
         [0027]      FIG. 3  illustrates a block diagram of a demand control system according to the second embodiment of the present invention. Referring to  FIG. 3 , the demand control system of the present embodiment includes a measure unit  110  and a control unit  120 . When a time unit in a time segment ends, the measure unit  110  measures the power consumption in the time unit and then calculates the demand of the time segment according to the measurement. The measure unit  110  is for example a digital electric meter. The control unit  120  is for example a computer or an embedded system. The control unit  120  calculates the demand threshold E threshold  according to plenty of demand data of several previous time segments. Also, the control unit  120  determines whether the power demand of that time segment, which is calculated at the end of each time unit ends according to the power consumption is greater or less than the demand threshold E threshold . Different control process is performed according to the determined decision. 
         [0028]      FIG. 4  is a flow chart of the demand control method according to the second embodiment of the present invention. Please refer to the step S 200  in  FIG. 4 . First, the demand threshold E threshold  is determined by the control unit  120 . The determining method is disclosed in the above embodiment. After the demand threshold E threshold  is determined, as shown in the step S 210 , the measure unit  110  sums up the power consumption Ez at the end of a time unit. For example, the power consumption is summed up every minute. 
         [0029]    The method of demand control of the present embodiment further includes the step S 212  of determining if it is the beginning of a time segment. If yes, all electric equipment is turned on. 
         [0030]    The method of demand control of the present embodiment further includes the step S 216  of the measure unit  110  determining if it is the neglecting time. If yes, the demand datum of the time segment is determined according to the power consumption of the neglecting time, for updating the demand threshold (the step S 208  in  FIG. 3 ). When the current time unit is not the neglecting time, as shown in the step S 220 , the power consumption is measured by the measure unit  110  at the end of the time unit. The demand datum is calculated according to the measured power consumption, and then whether the calculated demand datum exceeds the demand threshold E threshold  or not is determined by the control unit  120 . 
         [0031]    When the calculated demand datum is greater than the demand threshold E threshold , as shown in the step S 222 , the first electric apparatus  130  is shut down. When the above condition is not satisfied, the method goes to the step S 210  of the measure unit  110  calculating the power consumption in the next time unit. In other words, when the calculated demand exceeds the demand threshold, the electric apparatus is shut down to lower the total power consumption in the whole time segment. When the calculated demand is less than the demand threshold, keep observing the power consumption in the next time unit without performing any process or restarting any electric apparatus. 
         [0032]    In the preferred embodiment, when the calculated demand is greater than the demand threshold again in the same time segment, another electric apparatus is shut down. For example, when the calculated demand E 4  of the fourth minute is greater than the demand threshold E threshold , the first electric apparatus is shut down. Then, when the demand in the same time segment exceeds the demand threshold again, the second electric apparatus  132  can be shut down to lower down the total power consumption in the whole time segment. In other words, several electric apparatuses to be shut down can be ranked in priority order for maintaining the normal operation of the store. When the demand exceeds the demand threshold several times, the electric apparatuses will be shut down according to the priority order. However, anyone who has ordinary skill in the field of the present invention can understand that the control strategy when the demand threshold is exceeded several times is changeable. The present invention is not limited thereto. Modification can be made according to the application field and the purpose. 
         [0033]    The method of determining the demand threshold, and the method and system of demand control disclosed by the above embodiments of the present invention provide a standard method (for example, the steps S 202 -S 206 ) to calculate the demand threshold. An adequate demand threshold is calculated according to the historical approximate demand. It is avoided that the demand threshold is too high, which results in penalty charge when the power consumption exceeds the contracted amount. It is also avoided that the demand threshold is too low, which results in continuously shutting down electric apparatuses and not being able to operate normally. Furthermore, the calculating method of the demand threshold of the present embodiment can provide adequate demand threshold according to the field/controlled object with different properties and can be applied more widely. Moreover, the demand threshold of the present invention can be adjusted dynamically. The demand threshold is updated every time interval (the step S 208 ) for reflecting the power consumption difference due to the factors such as season or number of customers. As a result, the demand threshold which is controlled accordingly has more flexibility and can be applied more widely. 
         [0034]    While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.