Power management system, power management method, and program

Abstract

A power management system (1) manages the power of a first electrical apparatus and a second electrical apparatus installed in a facility, and is configured such that different unit fees are set for a first purchased power supplied to the first electrical apparatus and a second purchased power supplied to the second electrical apparatus. The power management system (1) comprises: a first acquisition unit (71) that acquires, from a first measuring instrument electrically connected to the power grid, a first power value obtained by measuring power flowing in reverse to the power grid from a distributed power supply installed in the facility; a second acquisition unit (72) that acquires, from a second measuring instrument electrically connected to the second electrical apparatus, a second power value obtained by measuring the power flowing forward from the power grid; and a calculation unit (74) that calculates the electricity fee using a metering stop mode in which fee calculations based on the second power value are not carried out if the first power value is 0 or greater.

Description

Power management system, power management method and program

[0001] The present invention relates to a power management system, a power management method, and a program.

[0002] Conventionally, a method has been known in which multiple power meters are connected in a parent-child configuration to perform differential metering, thereby measuring power consumption by separating normal power loads from power loads to which dynamic pricing is applied (see Non-Patent Document 1).

[0003] Ministry of Economy, Trade and Industry, Agency for Natural Resources and Energy website [searched August 21, 2023], Internet <URL: https: / / www.enecho.meti.go.jp / category / electricity_and_gas / electric / measure / faq / 017.html>

[0004] However, the technology of Non-Patent Document 1 has the problem that if a facility such as a house has a distributed power source (private power generation equipment) such as a solar cell, the amount of generated electricity consumed by the facility is also measured as purchased electricity.

[0005] Therefore, the present invention provides a power management system, a power management method, and a program that can prevent self-consumption from being measured as purchased power when a distributed power source is present within a facility.

[0006] One aspect of the present invention is a power management system that manages the power of a first electrical device and a second electrical device installed in a facility, and different unit prices are set for the first purchased power supplied to the first electrical device and the second purchased power supplied to the second electrical device.The power management system includes a first acquisition unit that acquires, from a first meter electrically connected to a power grid, a first power value measured by measuring the power flowing backward from a distributed power source installed in the facility to the power grid, a second acquisition unit that acquires, from a second meter electrically connected to the second electrical device, a second power value measured by measuring the power flowing forward from the power grid, and a calculation unit that calculates the electricity fee using a metering stop mode that does not perform fee calculations based on the second power value when the first power value is greater than or equal to 0.

[0007] A power management method according to one aspect of the present invention is a power management method for managing the power of a first electrical device and a second electrical device installed in a facility, wherein different unit rates are set for a first purchased power supplied to the first electrical device and a second purchased power supplied to the second electrical device, and the power management method acquires a first power value measuring the power flowing backward from a distributed power source installed in the facility to the power system from a first meter electrically connected to the power system, acquires a second power value measuring the power flowing forward from the power system from a second meter electrically connected to the second electrical device, and when the first power value is equal to or greater than 0, calculates the electricity charge using a metering stop mode in which charge calculations based on the second power value are not performed.

[0008] A program according to one aspect of the present invention is a program for causing a computer to execute the above-described power management method.

[0009] According to one aspect of the present invention, it is possible to realize a power management system or the like that can prevent self-consumption power from being measured as purchased power when a distributed power source is present within a facility.

[0010] FIG. 1 is a diagram showing the configuration of a power management system according to an embodiment. FIG. 2 is a block diagram showing the functional configuration of a management device according to an embodiment. FIG. 3 is a diagram for explaining a mode for calculating an electricity fee according to an embodiment. FIG. 4 is a flowchart showing the operation of a power management system according to an embodiment. FIG. 5A is a flowchart showing a first example of the operation of a control unit according to an embodiment. FIG. 5B is a flowchart showing a second example of the operation of a control unit according to an embodiment. FIG. 5C is a flowchart showing a third example of the operation of a control unit according to an embodiment. FIG. 6 is a diagram showing the relationship between each power value and the power supplied to a second electrical device according to an embodiment. FIG. 7 is a diagram showing the relationship between the supplied power and whether or not the second meter is metering according to an embodiment.

[0011] (How the present invention was arrived at) Before describing the present invention, how the present invention was arrived at will be described.

[0012] One pricing system for electricity usage in homes and other facilities is called dynamic pricing (DP), in which the unit price (power unit price) changes depending on the time of day. DP is a system that flexibly changes prices according to supply and demand. In particular, DP pricing plans that link the DP power unit price (DP unit price) to the spot price in the retail electricity market have been attracting attention in recent years.

[0013] However, increasing or decreasing the electricity demand associated with daily life in response to changes in the DP unit price (for example, by saving electricity when prices rise) imposes a burden on users. Therefore, it may be desirable to set DP only for power loads that are not directly linked to the electricity demand associated with daily life, such as the power consumption of electric water heaters and the power consumption of charging electric vehicles, and to use the conventional electricity rate system for other electricity consumption. Taking an electric water heater as an example, it is sufficient to heat the water before it is used, but since the timing of heating does not affect the user, it is possible to reduce electricity bills by automatically heating the water when the DP price is low. Furthermore, a power load that is directly linked to electricity demand refers to a power load that consumes electricity due to the user's operation of an electrical appliance (for example, turning on the air conditioner).

[0014] In this case, it is necessary to measure the power consumption separately for the normal power load and the power load to which DP is applied, and a method is proposed as disclosed in Non-Patent Document 1.

[0015] As explained in the "Problem to be Solved by the Invention" section, the method of Non-Patent Document 1 has the problem that if a facility has a distributed power source, the self-consumption portion of the generated power is also measured as purchased power. For example, when a photovoltaic power generation system (e.g., a solar cell 10 and a power conversion system 20 shown in FIG. 1, which will be described later) supplies power to a power load to which a DP is applied (i.e., self-consumption), the technology of Non-Patent Document 1 measures the DP purchased power and the self-consumption power together. Therefore, even if a facility has a distributed power source, it may be desirable to measure the purchased power and the self-consumption separately.

[0016] Therefore, the inventors of the present application conducted extensive research into power management systems and the like that can prevent in-house consumption from being measured as purchased electricity when there is a distributed power source within the facility, and have devised the power management system and the like described below.

[0017] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0018] The embodiments described below are all comprehensive or specific examples, and the numerical values, shapes, components, arrangement and connection of the components, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present invention.

[0019] Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Therefore, for example, the scales of the figures do not necessarily match. Furthermore, in each figure, substantially the same components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0020] Furthermore, in this specification, terms indicating relationships between elements such as "same," as well as numerical values ​​and numerical ranges, are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about several percent (or about 10%).

[0021] Furthermore, in this specification, ordinal numbers such as "first" and "second" do not refer to the number or order of components unless otherwise specified, but are used for the purpose of avoiding confusion and distinguishing between components of the same type.

[0022] Furthermore, the "connection" of each component means an electrical connection, and includes not only a case where two components are directly connected, but also a case where two components are indirectly connected with another component inserted between them.

[0023] (Embodiment) Hereinafter, a power management system according to the present embodiment will be described with reference to Figs.

[0024] [1. Configuration of Power Management System] First, the configuration of a power management system 1 according to this embodiment will be described with reference to Figures 1 to 3. Figure 1 is a diagram showing the configuration of a power management system 1 according to this embodiment.

[0025] As shown in FIG. 1, the power management system 1 is a system for managing the power of a first electric device (for example, a home appliance 51) and a second electric device (for example, a charger 52).

[0026] The power management system 1 includes a solar cell 10 ("PV" in FIG. 1 ), a power conversion system 20 ("PCS" in FIG. 1 ), a storage battery 30 ("SB" in FIG. 1 ), power meters 41 and 42 ("M1" and "M2" in FIG. 1 ), home appliances 51 and chargers 52 that are power consumers in the home, a power meter 61 ("M0" in FIG. 1 ), a current sensor 62 ("CT" in FIG. 1 ), and a management device 70, all of which are arranged in a home. FIG. 1 also illustrates a power system 100. The home appliances 51 and chargers 52 are examples of electrical appliances that generate power demand. It should be noted that the power management system 1 is only required to include at least the management device 70.

[0027] A home is an example of a facility. A facility may be a residential facility or a non-residential facility. Examples of residential facilities are detached houses and apartment buildings. Each of the multiple dwelling units in an apartment building may be considered a "facility," or the entire apartment building may be considered a "facility." Examples of non-residential facilities include stores, office buildings, schools, welfare facilities, commercial complexes, hospitals, factories, etc.

[0028] It is assumed that a residential consumer has a contract with an electricity retailer to pay an electricity fee based on the electricity consumed by home appliances 51 under a conventional electricity fee system (fixed electricity unit price), and to pay an electricity fee based on the electricity measured by power meter 42 under a dynamic pricing electricity fee system (DP unit price). It is also assumed that the retailer has a contract to purchase the sold electricity measured by power meter 41 from the consumer. The fixed electricity unit price and the DP unit price are examples of different rate unit prices, and the fixed electricity unit price is an example of a first rate unit price, and the DP unit price is an example of a second rate unit price.

[0029] In addition, when the measurement value of power meter 41 is 0, the amount of power consumed by home appliance 51 can be calculated based on the power value obtained by subtracting the measurement value (power value) of power meter 42 from the measurement value (power value) of power meter 61 (differential metering).

[0030] The solar cell 10 is an electric power device that converts light energy into electrical energy (power) by utilizing the photovoltaic effect. The solar cell 10 is an example of a distributed power source.

[0031] The power conversion system 20 is also called a power conditioner, and converts DC power generated by the solar cell 10 into AC power. The power conversion system 20 is an example of a second control unit.

[0032] The storage battery 30 is a device capable of charging and discharging, and is, for example, a home storage battery. In this embodiment, when the calculation of the electricity rate is in a metering stop mode (described later) and the storage battery 30 is selling power, the storage battery 30 performs charging and discharging so that the measured current of the power meter 61 is maintained in a positive (reverse current) state (power selling state), for example, so that the power value measured by the power meter 61 is maintained at a predetermined value greater than 0 (reverse power state). It can also be said that the storage battery 30 performs charging and discharging so as not to transition from a power selling state to a power purchasing state. The predetermined value is set as appropriate, for example, depending on the amount of fluctuation in the power generated by the solar cell 10. The predetermined value may also be stored in the power conversion system 20, for example.

[0033] The measured current of the power meter 61 can be obtained, for example, based on the measurement result of the current sensor 62. Furthermore, the charge and discharge of the storage battery 30 is controlled by the power conversion system 20, but may also be controlled by, for example, the management device 70. Furthermore, the storage battery 30 may be included in the first electrical device.

[0034] The power meter 41 is electrically connected to the distributed power source (here, the solar cell 10) and is a power sensor that measures the output power (here, the generated power) of the distributed power source as a negative value. For example, the power meter 41 measures forward flow power (purchased power) supplied from the power grid 100 to the storage battery 30 (i.e., purchased under a conventional electricity rate system) as a positive value, and measures reverse flow power (sold power) supplied from the solar cell 10 to the power grid 100 as a negative value.

[0035] Note that the positive and negative polarities of the power are not limited to this. The power meter 41 is connected between the solar cell 10 and the power meter 61. The power meter 41 may be a conventional (analog) power meter or a so-called smart meter. A smart meter is a power meter that measures the amount of power used at shorter intervals (for example, every 30 minutes) than conventional meters and has a communication function. The power meter 41 is an example of a third measuring instrument.

[0036] The power meter 42 is electrically connected to the second electric device (here, the charger 52) and is a power sensor that measures the power supplied to the charger 52. The power meter 42 measures, for example, forward power (purchased power) supplied from the power grid 100 to the charger 52 (i.e., purchased under a dynamic pricing electricity rate system) as a positive value. When power generated by the solar cell 10 is not supplied to the charger 52, the measurement value of the power meter 42 is the power value of the forward power supplied from the power grid 100 to the charger 52.

[0037] The power meter 42 is electrically connected between the power meter 61 and the charger 52. For example, the power meter 42 is connected so as to be able to measure only the power supplied to the charger 52, and is connected to the charger 52 without passing through another power meter, for example. The power meter 42 may be a conventional power meter or a so-called smart meter. The power meter 42 is an example of a second measuring instrument.

[0038] The branch circuit 43 is provided in the distribution board 40 and branches into a wiring connected to the home appliance 51 and a wiring connected to the charger 52. The branch circuit 43 is connected to the wiring connected to the power meter 42.

[0039] The home appliance 51 is an electrical appliance that consumes power and is installed in a home. The home appliance 51 is an appliance that generates power demand and is an example of a first electrical appliance. The first electrical appliance may be any power load that is directly linked to the power demand associated with real life, and examples of the first electrical appliance include home appliances 51 such as air conditioners, refrigerators, and televisions, but may also include electrical appliances other than the home appliance 51.

[0040] When calculating the electricity charges for the first electrical device, a conventional electricity rate system, i.e., a fixed electricity price without dynamic pricing, is applied. The fixed electricity price does not change depending on the electricity supply and demand situation, and is set in advance, for example, at the time of signing the contract.

[0041] The home appliance 51 may be connected to the power meter 41. That is, the home appliance 51 may be supplied with power from the power system 100 via the power meters 61 and 41.

[0042] The charger 52 is a charging facility (or a charging / discharging facility) that charges a storage battery mounted on a vehicle that can run on electricity, such as an EV (Electric Vehicle) or a PHEV (Plug-in Hybrid Electric Vehicle), and is an example of a second electric device. The second electric device is an electric load that is not directly linked to the electric power demand associated with real life, and may be, for example, an electric water heater.

[0043] The DP unit price is applied to the second electric appliance when calculating the electricity charge.

[0044] In this way, different electricity unit prices (fee unit prices) are set for the purchased power supplied to the first electrical appliance (first purchased power) and the purchased power supplied to the second electrical appliance (second purchased power) in the power management system 1. The number of first electrical appliances and the number of second electrical appliances included in the power management system 1 are not particularly limited, as long as they are one or more.

[0045] Note that a power unit price other than the DP unit price may be applied as the power unit price for the second electric device. The power unit price for the second electric device may be any power unit price different from the power unit price for the first electric device, for example, a fixed power unit price different from the fixed power unit price for the first electric device.

[0046] The power meter 61 is a power sensor connected between the distribution board 40 (e.g., the power meters 41 and 42) and the power grid 100, and measures at least one of forward-flow power from the power grid 100 (forward-flow power) and reverse-flow power from the solar cell 10 to the power grid 100 (reverse-flow power). The power meter 61 measures, for example, power supplied from one of a retail electricity supplier and a power receiving point to the other (that is, power supplied (purchased) from the power grid 100 to the home, and power sold from the home to the power grid 100). In this way, the power meter 61 functions as at least one of a power receiving power meter that measures power supplied from the power grid 100, and a power selling power sold reversely from the home to a retail electricity supplier at a predetermined unit price using the FIT system (Feed-In Tariff).

[0047] In this embodiment, the power meter 61 can measure both forward power and reverse power. Furthermore, the power meter 61 measures the power flowing backward from the solar cell 10 to the power grid 100 as a positive value, but the positive and negative values ​​of the power are not limited to this. The power meter 61 is an example of a first measuring instrument.

[0048] The power receiving point where the power meter 61 is installed may be a responsibility separation point between the area belonging to the house and the area belonging to the power grid 100, or it may be a location where an inlet switchboard (low voltage) or a power receiving equipment (high voltage) is located.

[0049] The electricity retailer is a business that buys and sells electricity based on the measurement values ​​of the power meter 61. The electricity retailer sells electricity to ordinary households, buildings, factories, etc. The measurement values ​​of the power meter 61 are transmitted to the electricity retailer.

[0050] The current sensor 62 is provided on dedicated wiring in the house between the power meter 61 and the distribution board 40, and measures the current flowing through the wiring. The current sensor 62 can also be said to be provided at a power receiving point. The current sensor 62 measures the current flowing from the power system 100 to the distribution board 40 (for example, forward current) and the current flowing from the distribution board 40 (for example, from the solar cell 10) to the power system 100 (reverse current). By providing such a current sensor in the power management system 1, the house can meet the conditions for using the FIT system.

[0051] The management device 70 manages the power of the first electric appliance and the second electric appliance. When a distributed power source is present in the home, the management device 70 performs various processes to prevent the amount of self-consumption of electricity from being measured as the amount of purchased electricity. The management device 70 may be installed in the home or may be installed remotely from the home. The management device 70 may be realized, for example, by a control terminal for controlling the home appliances 51 installed in the home, or may be realized by a server device connected to each meter and each sensor so as to be able to communicate with them.

[0052] FIG. 2 is a block diagram showing the functional configuration of the management device 70 according to this embodiment.

[0053] 2, the management device 70 includes a first acquisition unit 71, a second acquisition unit 72, a third acquisition unit 73, a calculation unit 74, a control unit 75, and a notification unit 76. Each component of the management device 70 is realized, for example, by a microcomputer, a processor, or the like (hardware) constituting the management device 70 executing a computer program (software) stored in a storage unit (not shown).

[0054] The first acquisition unit 71 acquires a first power value, which is obtained by measuring the power flowing backward from the solar cell 10 to the power grid 100 as a positive value, from the power meter 61. The first acquisition unit 71 includes a communication interface that is communicably connected to the power meter 61 via a wired or wireless connection.

[0055] The second acquisition unit 72 acquires a second power value, which is obtained by measuring the forward power flow from the power grid 100 as a positive value, from the power meter 42. The second acquisition unit 72 includes a communication interface that is communicably connected to the power meter 42 via a wired or wireless connection.

[0056] The third acquisition unit 73 acquires a third power value, which is obtained by measuring the output power of the solar cell 10 as a negative value, from the power meter 41. The third acquisition unit 73 includes a communication interface that is communicably connected to the power meter 41 via a wired or wireless connection.

[0057] The calculation unit 74 calculates the electricity rate for the home. When the third power value is 0, the calculation unit 74 calculates the electricity rate for the second circuit including the charger 52 in a metering execution mode that performs rate calculation based on the second power value and the DP unit price. In other words, when the power generated by the solar cell 10 is 0 and self-consumption is not possible, and therefore the current is in-flow (power is purchased), the calculation unit 74 uses the second power value measured by the power meter 42 to calculate the electricity rate for the second circuit (here, the charger 52). The metering execution mode means that the calculation unit 74 (or the power management system 1) operates to calculate the electricity rate under a dynamic pricing fee structure using the second power value.

[0058] 3A and 3B are diagrams for explaining modes for calculating electricity charges according to this embodiment, in which (a) of Fig. 3 is a diagram for explaining a metering execution mode, and (b) of Fig. 3 is a diagram for explaining a metering stop mode.

[0059] As shown in (a) of Figure 3, when the reverse flow power measured by the power meter 41 is 0, the calculation unit 74 determines that all of the power measured by the power meter 42 is power supplied from the power grid 100 (X in (a) of Figure 3), and calculates the electricity rate for the second circuit under the dynamic pricing fee system. In other words, the calculation unit 74 calculates the electricity rate for the charger 52 using the dynamic pricing fee system.

[0060] 2 , when the first power value is equal to or greater than 0, the calculation unit 74 operates in a metering stop mode in which the calculation unit 74 does not measure the electricity fee for the second circuit including the charger 52. In other words, when reverse power flow (electricity is being sold) and the purchased power is 0, the calculation unit 74 does not calculate the electricity fee for the second circuit. The metering stop mode means that the calculation unit 74 prohibits the calculation of the electricity fee for the second circuit.

[0061] Note that the first power value being 0 or greater means that surplus power generated by the solar cell 10 is being sold. In other words, when the first power value is 0 or greater, the power generated by the solar cell 10 is supplied to the home appliances 51 and charger 52 in the home, and no power is supplied from the power grid 100. In other words, when the first power value is 0 or greater, the power of the home appliances 51 and charger 52 in the home is supplied by the self-consumption of power generated by the solar cell 10. Note also that the first power value being 0 or greater is synonymous with the power purchased from the power grid 100 being 0.

[0062] As shown in Fig. 3(b), when the forward current power (purchased power) measured by the power meter 61 is zero, the calculation unit 74 determines that all of the power measured by the power meter 42 is generated power supplied from the solar cell 10 (Y in Fig. 3(b)), and since the power measured by the power meter 42 is self-consumed power, the calculation unit 74 does not calculate the electricity charge for the second circuit using the power measured by the power meter 42. In this case, all of the power consumed by the second circuit is covered by self-consumption, so no electricity charge is incurred for the second circuit.

[0063] In this way, the calculation unit 74 calculates the electricity charges for the house while switching between the metering stop mode and the metering execution mode. Note that it is sufficient for the calculation unit 74 to calculate the electricity charges using at least the metering stop mode.

[0064] Referring again to FIG. 2 , the control unit 75 controls the operation of the second electric device (here, the charger 52) based on each acquired power value. The operation includes at least one of operation and stop. The control unit 75 controls the operation of the charger 52, for example, by notifying the charger 52 of a control signal via the notification unit 76. The control unit 75 may also operate the second electric device so that the first power value is in a reverse power state. For example, when the first power value is in a reverse power state, the control unit 75 may control the operation amount of the second electric device, i.e., the power consumption amount of the second electric device, so as to maintain the reverse power state. For example, when the second electric device is the charger 52, the control unit 75 may control the charging power to the electric vehicle, the charging time, the charging time zone, etc. as the operation amount of the second electric device.

[0065] The functions of the control unit 75 may be provided in each of the home appliance 51 and the charger 52. The control unit 75 is an example of a first control unit.

[0066] The notification unit 76 notifies various types of information to external devices. The notification unit 76 includes a communication interface that is connected to the external devices via a wired or wireless connection.

[0067] The notification unit 76 may notify the external device of, for example, the metering mode of the power meter 61 and the metering mode of the second circuit including the charger 52. Here, the external device may be, for example, the second electric device, such as an electric water heater such as EcoCute (registered trademark) or a charger such as ELSEEV (registered trademark). The external device may also be a control device that controls the second electric device. This makes it possible to cause the external device to perform an operation according to the metering mode.

[0068] Referring again to FIG. 1, the power system 100 is a system operated by an electricity retailer and includes a system power source.

[0069] 2. Operation of the Power Management System Next, the operation of the power management system 1 configured as described above will be described with reference to Figs. 4 to 7. Fig. 4 is a flowchart showing the operation (power management method) of the power management system 1 according to this embodiment. In Fig. 4, it is assumed that the second electric device is in operation at step S11.

[0070] 4, the management device 70 acquires each power value (S11). Specifically, the first acquisition unit 71 acquires the first power value from the power meter 61, the second acquisition unit 72 acquires the second power value from the power meter 42, and the third acquisition unit 73 acquires the third power value from the power meter 41. The timing of acquiring each power value is not particularly limited, and they may be acquired at the same time or at different times. It is sufficient that at least the first power value and the second power value are acquired in step S11.

[0071] Next, the calculation unit 74 determines whether the purchased power is zero based on the first power value (S12). If the first power value is zero (or greater than or equal to zero), the calculation unit 74 determines that the purchased power is zero. If the calculation unit 74 determines that the purchased power is zero (Yes in S12), the calculation unit 74 calculates the electricity rate in metering stop mode so that the electricity rate for the self-consumed power value is not charged because the second power value measured by the power meter 42 is the self-consumed power value (S13). In calculating the electricity rate for the home, the calculation unit 74 does not calculate the electricity rate for the second circuit for the period in which the purchased power is determined to be zero.

[0072] Furthermore, when the calculation unit 74 determines that the purchased power is not zero (No in S12), it further determines whether or not the state is a mixed state (S14). The mixed state is a state in which both the power generated by the solar cell 10 and the power purchased from the power grid 100 are supplied to the second electrical device. In this case, the second power value is the power value that is the sum of the power generated by the solar cell 10 and the power purchased from the power grid 100. In other words, the power generated by the solar cell 10 and the power purchased from the power grid 100 cannot be separated. The mixed state is an example of the second state.

[0073] If the first power value is negative and the third power value is positive, the calculation unit 74 determines that the state is a mixed state. If the calculation unit 74 determines that the state is a mixed state (Yes in S14), the calculation unit 74 proceeds to step S13, and if the calculation unit 74 determines that the state is not a mixed state (No in S14), the calculation unit 74 proceeds to step S15.

[0074] Next, if the answer to step S14 is No, the calculation unit 74 determines whether the first power value is negative and the third power value is equal to or less than 0 (S15). If the calculation unit 74 determines that the first power value is negative and the third power value is equal to or less than 0 (Yes in S15), the calculation unit 74 proceeds to step S16, and if the calculation unit 74 determines that the first power value is negative and the third power value is not equal to or less than 0 (No in S15), the calculation unit 74 proceeds to step S13.

[0075] Next, if the answer to step S15 is Yes, the calculation unit 74 calculates the electricity fee in the metering execution mode because only purchased power from the power grid 100 is supplied to the charger 52 (S16).

[0076] Next, the notification unit 76 notifies the external device of the current weighing mode (S17). For example, when the external device acquires the current weighing mode, it can perform an operation according to the weighing mode.

[0077] Next, the operation of the control unit 75 will be described with reference to Figures 5A to 5C. Figures 5A to 5C are flowcharts showing examples of the operation (power management method) of the control unit 75 according to this embodiment.

[0078] 5A , the control unit 75 determines whether the third power value is equal to or greater than a fifth power value, which is the sum of a fourth power value, which is a measured value of the total power consumption of the house excluding the power consumption of the second electrical appliance, and the rated power consumption of the second electrical appliance (S21). If it is determined that the third power value is equal to or greater than the fifth power value (Yes in S21), the control unit 75 operates the second electrical appliance (S22). For example, if the third power value transitions from a state in which it is less than the fifth power value to a state in which it is equal to or greater than the fifth power value, the control unit 75 starts operation of the second electrical appliance that was stopped.

[0079] The total power consumption of the home excluding the power consumption of the second electrical appliance refers to, for example, the total power consumption of all electrical appliances installed in the home, excluding electrical appliances under a DP unit price contract. In other words, the total power consumption of the home excluding the power consumption of the second electrical appliance refers to the total power consumption of the home, including the rated power consumption of the second electrical appliance. The fifth power value may include, for example, the amount of power consumed by the home appliance 51 and the amount of power stored in the storage battery 30 by power supply from the power grid 100. The fourth power value may be calculated by summing the measurement values ​​in the branch circuits, or may be calculated by measurement values ​​obtained by other measurement methods.

[0080] Here, the third power value being equal to or greater than the fifth power value means that the second electrical device can be operated using only the power generated by the solar cell 10, that is, it is assumed that the power purchased from the power grid 100 is zero. Furthermore, the third power value being less than the fifth power value means that it is assumed that the second electrical device cannot operate without the power purchased from the power grid 100 in addition to the power generated by the solar cell 10 (for example, the rated power consumption of the second electrical device cannot be covered).

[0081] Furthermore, if the control unit 75 determines that the third power value is less than a fifth power value obtained by adding the fourth power value and the rated power consumption of the second electric device (No in S21), the control unit 75 does not operate the second electric device. In other words, if the determination in step S21 is No, the control unit 75 keeps the second electric device in a stopped state.

[0082] In this way, the control unit 75 operates the second electrical appliance when the power generated by the solar cell 10 alone is sufficient to supply power to each electrical appliance in the house, and keeps the second electrical appliance in a stopped state (or stops the second electrical appliance) when the power generated by the solar cell 10 alone is not sufficient to supply power to the second electrical appliance.

[0083] If the answer to step S21 is Yes, the calculation unit 74 operates in the measurement stop mode.

[0084] If the control unit 75 is set to give priority to the second electrical device in using the power generated by the solar cell 10, the control unit 75 may determine whether the third power value is equal to or greater than the rated power consumption of the second electrical device, and may operate the second electrical device if it determines that the third power value is equal to or greater than the rated power consumption of the second electrical device. For example, the control unit 75 may operate the second electrical device that was stopped when the third power value transitions from a state in which it is less than the rated power consumption of the second electrical device to a state in which it is equal to or greater than the rated power consumption of the second electrical device.

[0085] 5B , the control unit 75 determines whether the second electric device has transitioned to the mixed state while the second electric device is operating (S31). The control unit 75 determines whether the current state is the mixed state based on the first power value and the third power value.

[0086] Next, when the control unit 75 determines that the second electric appliance has transitioned to the mixed state while it is operating (Yes in S31), it stops the second electric appliance (S32). For example, when the state transitions to the mixed state from a state in which only the power generated by the solar cell 10 or only the power purchased from the power grid 100 is supplied to the second electric appliance and the second electric appliance is operating, the control unit 75 stops the operation of the second electric appliance that was operating.

[0087] Furthermore, if the control unit 75 does not determine that the second electric appliance has transitioned to the mixed state while it is operating (No in S31), the control unit 75 does not stop the second electric appliance. In other words, if the determination in step S31 is No, the control unit 75 maintains the operating state of the second electric appliance.

[0088] In this way, the control unit 75 stops the second electrical device when the state transitions from one in which the power supply to the second electrical device can be covered by either the power generated by the solar cell 10 alone or the power purchased from the power grid 100 alone to a state in which the power supply to the second electrical device is covered by both the power generated by the solar cell 10 and the power purchased from the power grid 100.

[0089] In addition, the calculation unit 74 operates in a metering stop mode when the power supply to the second electrical device is covered solely by the power generated by the solar cell 10, and operates in a metering execution mode when the power supply to the second electrical device is covered solely by the power purchased from the power grid 100.

[0090] 5C, the control unit 75 determines whether or not the power purchase is currently in progress based on the first power value (S41). If the first power value is a negative value, the control unit 75 determines that the power purchase is in progress. Note that, at the time of step S41, the power purchase state is assumed to be mixed and the second electric device is stopped.

[0091] Next, the control unit 75 determines whether the third power value has changed from a state greater than zero to a state equal to or less than zero (S42). The control unit 75 determines whether the state has transitioned from the mixed state to a state in which the power supply to the second electric device is covered only by the power purchased from the power grid 100.

[0092] Next, when the control unit 75 determines that the third power value has become equal to or less than 0 (Yes in S42), it operates the second electric device that has been stopped (S43).

[0093] Furthermore, if the determination in either step S41 or S42 is No, the control unit 75 does not operate the second electric appliance, i.e., the control unit 75 keeps the second electric appliance in the stopped state.

[0094] Here, the determination of the metering mode by the calculation unit 74 and the control of the second electric device by the control unit 75 will be further described with reference to Fig. 6 and Fig. 7. Fig. 6 is a diagram showing the relationship between each power value and the power supplied to the second electric device according to this embodiment. Fig. 7 is a diagram showing the relationship between the supplied power and whether or not the second meter is measuring according to this embodiment.

[0095] In the following description, positive will also be referred to as "plus" and negative will also be referred to as "minus." In addition, in Figures 6 and 7, positive will also be referred to as "+," negative will also be referred to as "-," and zero will also be referred to as "0."

[0096] In addition, in the first power values ​​shown in Figures 6 and 7, "+" indicates a state in which power is being sold, "-" indicates a state in which power is being purchased, and "0" indicates a state in which the purchased power and sold power are zero. A "+" second power value indicates a state in which the second electrical appliance is operating (a state in which power is being consumed), and "0" indicates a state in which the second electrical appliance is stopped (a state in which power is not being consumed). When the second power value changes from "0" to "+" (e.g., arrow A or F in Figure 6), it means that the stopped second electrical appliance has started operating, and when the second power value changes from "+" to "0" (e.g., arrow H in Figure 6), it means that the operating second electrical appliance has stopped. A "+" third power value indicates a state in which power generated by the solar cell 10 is supplied to the second electrical appliance (or the second electrical appliance and the power grid 100). Furthermore, when the first power value is greater than or equal to 0 and the third power value is positive, this means that the third power value is greater than or equal to the fifth power value (i.e., the power generated by the solar cell 10 is greater than or equal to the fifth power value).

[0097] The specific circuit shown in FIG. 7 is a circuit including the second measuring instrument and the measurement target of the second measuring instrument, for example, the second circuit.

[0098] 6 and 7 , if the first power value and the third power value are positive when the second electric appliance is not operating, this indicates 100% self-supply, so the control unit 75 operates the second electric appliance (arrow A in FIG. 6 , S22 in FIG. 5A ), and the calculation unit 74 calculates the electricity bill for the home in a metering stop mode in which the second meter (here, power meter 42) is measuring "no metering" (e.g., no metering) ( FIG. 7 ). 100% self-supply means that all of the power required for the second electric appliance is supplied by the power generated by solar cell 10 (i.e., zero purchased power).

[0099] Furthermore, if the first power value changes from positive to zero while the third power value remains positive while the second electrical appliance is operating, the second electrical appliance can maintain 100% self-supply, although it cannot sell electricity, so the control unit 75 maintains operation of the second electrical appliance (arrow B in Figure 6, S22 in Figure 5A), and the calculation unit 74 maintains the metering stop mode (Figure 7) and calculates the electricity bill.

[0100] Furthermore, if the first power value changes from zero to negative while the third power value remains positive while the second electrical appliance is operating, the power supplied to the second electrical appliance is in a mixed state (Yes in S31 shown in Figure 5B), so the control unit 75 stops the second electrical appliance (arrow C in Figure 6, S32 shown in Figure 5B), and the calculation unit 74 calculates the electricity charge in the metering stop mode (Figure 7).

[0101] Furthermore, while the second electrical device is stopped, the control unit 75 maintains the stopped state of the second electrical device while the first power value is transitioning from negative to positive while the third power value remains positive (transitioning in the direction of arrow D in Figure 6), or while the third power value is transitioning from positive to zero while the first power value remains negative (transitioning in the direction of arrow E in Figure 6).

[0102] Furthermore, if the third power value changes from positive to zero while the first power value remains negative while the second electric device is not operating, this means that 100% power is being supplied to the system, so the control unit 75 operates the second electric device (arrow F in FIG. 6 , S43 in FIG. 5C ), and the calculation unit 74 calculates the electricity charge for the second circuit in a metering execution mode in which the measurement of the second meter (here, the power meter 42) is “metered at the second rate” (for example, metering at the DP unit price) ( FIG. 7 ). Note that metering at the second rate means calculating the electricity charge for the second circuit using the second power value of the second meter and the DP unit price.

[0103] Furthermore, if the third power value changes from zero to negative while the first power value remains negative while the second electrical appliance is operating, the system maintains a 100% supply state, so for example, the control unit 75 maintains the operation of the second electrical appliance (arrow G in Figure 6, S43 in Figure 5C), and the calculation unit 74 maintains the metering implementation mode (Figure 7) to calculate the electricity bill.

[0104] Furthermore, the control unit 75 stops the second electric device as needed (arrow H in FIG. 6 ). If the second electric device is the charger 52, the control unit 75 stops the second electric device when charging of the electric vehicle is completed.

[0105] Furthermore, if, while the second electrical appliance is operating, a transition occurs from a state in which the first power value and the third power value are positive, or a state in which the first power value is zero and the third power value is positive, to a state in which the first power value is negative and the third power value is positive, i.e., a mixed state, the control unit 75 stops the second electrical appliance.

[0106] Furthermore, when the state transitions from one in which the first power value is a negative value and the third power value is a positive value to one in which the first power value is a negative value and the third power value is 0 or less, the control unit 75 operates the second electrical device.

[0107] In this way, the control unit 75 operates the second electric device only during the period when 100% self-supply is possible and the period when 100% grid supply is possible. Also, the calculation unit 74 calculates the electricity charge using the second power value measured by the second meter and the DP unit price only during the period when 100% grid supply is possible.

[0108] 7 , when the power management system 1 is in the mixed state, it does not perform metering using the second meter or differential metering ("No differential metering" in FIG. 7 ). When the first power value is negative and the third power value is positive, the control unit 75 (or the calculation unit 74) may, for example, stop measurement using the second meter, or may prohibit the calculation unit 74 from using the second power value measured by the second meter to calculate the electricity bill, and from calculating the amount of power obtained by subtracting the second amount of purchased power based on the second power value measured by the second meter from the first amount of purchased power based on the first power value measured by the first meter.

[0109] When the system is in the mixed state and the second electric device is operating, the calculation unit 74 may calculate the electricity rate for the second circuit in the same way as the electricity rate for the first circuit including the first electric device. In this case, the calculation unit 74 uses a fixed electricity unit price instead of a DP unit price to calculate the electricity rate for the second circuit.

[0110] Furthermore, the calculation unit 74 uses either the fixed electricity unit price or the DP unit price as the unit price used to calculate the electricity rate for the first circuit. For example, the calculation unit 74 may use the higher of the fixed electricity unit price or the DP unit price as the unit price. In other words, when the fixed electricity unit price is lower than the DP unit price, the calculation unit 74 uses the DP unit price as the unit price.

[0111] (Effects, etc.) The invention derived from the disclosure of this specification and the effects, etc. obtained by the invention will be described below.

[0112] (Invention 1) An energy management system 1 manages the power of a first electric device and a second electric device installed in a facility, wherein different unit prices are set for first purchased power supplied to the first electric device and second purchased power supplied to the second electric device, and the energy management system includes: a first acquisition unit that acquires, from a first meter electrically connected to an electric power grid, a first power value that measures power flowing backward from a distributed power source installed in the facility to the electric power grid; a second acquisition unit that acquires, from a second meter electrically connected to the second electric device, a second power value that measures power flowing forward from the electric power grid; and a calculation unit that calculates an electricity charge in a metering stop mode when the first power value is equal to or greater than 0, and does not perform charge calculations based on the second power value.

[0113] As a result, when the first power value is equal to or greater than 0, that is, when the amount of power purchased from the power grid 100 is 0, the fee calculation based on the second power value is not performed. In this case, the second power value is the power generated by the solar cell 10 (that is, the amount of power consumed by the facility). Therefore, since the second power value, which measures only the power generated, is not used in the fee calculation, it is possible to prevent the amount of power consumed by the facility from being measured as the amount of power purchased when there is a distributed power source within the facility.

[0114] (Invention 2) The power management system 1 of Invention 1 further includes a third acquisition unit that acquires a third power value measured from a third meter electrically connected to the distributed power source, the third power value being the output power of the distributed power source, and the calculation unit calculates the electricity charge in a metering implementation mode that calculates the charge based on the second power value when the third power value is 0.

[0115] As a result, when the self-consumption is zero, that is, when the power to the second electrical appliance is 100% supplied from the grid, the electricity charge can be calculated using the DP unit price. In this case, the self-consumption amount is not included in the second power value, so it is possible to prevent the self-consumption amount from being measured as the amount of purchased power.

[0116] (Invention 3) The power management system 1 of Invention 2 further includes a first control unit that operates the second electrical device when the third power value is equal to or greater than the power value obtained by adding the fourth power value and the rated power consumption of the second electrical device, where the measured value of the total power consumption of the facility excluding the power consumption of the second electrical device is a fourth power value.

[0117] This allows the second electric appliance to operate when only the amount of electricity consumed by the electric appliance is being supplied to the second electric appliance. In this case, by measuring in the metering stop mode, it is possible to prevent the amount of electricity consumed by the electric appliance from being measured as the amount of purchased electricity.

[0118] (Invention 4) The power management system 1 of Invention 2 or 3 further includes a first control unit that operates the second electric device so that the first power value is in a reverse power state.

[0119] This allows the first power value to be maintained in a reverse power state, i.e., a state in which only the self-consumption power is supplied to the second electrical device. In this case, by measuring in the metering stop mode, it is possible to prevent the self-consumption power from being measured as the amount of purchased power.

[0120] (Invention 5) In the power management system 1 of Invention 3 or 4, when the first power value is a power value measured with the power flowing back from the distributed power source to the power grid as a positive value and the third power value is a power value measured with the output power of the distributed power source as a positive value, the first control unit stops the second electric device when, while the second electric device is in operation, a transition occurs from a first state in which the first power value and the third power value are positive values ​​to a second state in which the first power value is a negative value and the third power value is a positive value.

[0121] As a result, when the system transitions to the mixed state, the second electric appliance is stopped, so calculation of the electricity charge is unnecessary. In other words, the second power value is not used in calculating the electricity charge. Therefore, in the mixed state, it is possible to prevent the amount of self-consumption electricity from being measured as the amount of purchased electricity.

[0122] (Invention 6) In the power management system 1 of Invention 3 or 4, when the first power value is a power value measured with the power flowing back from the distributed power source to the power grid as a positive value and the third power value is a power value measured with the output power of the distributed power source as a positive value, the first control unit operates the second electrical device when a transition is made from a third state in which the first power value is a negative value and the third power value is a positive value to a fourth state in which the first power value is a negative value and the third power value is equal to or less than 0.

[0123] As a result, when self-consumption is zero, that is, when the power to the second electric appliance is 100% supplied from the grid, the second electric appliance operates. Here, the second power value indicates the value of power purchased from the power grid 100. Therefore, in a 100% grid supply state, it is possible to prevent the amount of self-consumption from being measured as the amount of purchased power.

[0124] (Invention 7) In the power management system 1 of any of Inventions 2 to 6, in the metering execution mode, the calculation unit calculates the electricity charge for the first electrical device using an amount of power obtained by subtracting a second amount of purchased power based on the second power value measured by the second meter from a first amount of purchased power based on the first power value measured by the first meter.

[0125] This makes it possible to prevent the second purchased amount of electricity from being double-counted in the metering execution mode.

[0126] (Invention 8) In the power management system 1 of any of Inventions 3 to 6, when the first power value is a power value measured with the power flowing back from the distributed power source to the power grid as a positive value and the third power value is a power value measured with the output power of the distributed power source as a positive value, the first control unit stops measurement by the second metering instrument or prohibits the calculation unit from calculating the amount of power obtained by subtracting the second amount of purchased power based on the second power value measured by the second metering instrument from the first amount of purchased power based on the first power value measured by the first metering instrument when the first power value is a negative value and the third power value is a positive value.

[0127] This makes it possible to prevent the second purchased amount of electricity from being double-counted in the mixed state.

[0128] (Invention 9) The power management system 1 of any of Inventions 1 to 8, wherein the rate unit price includes a first rate unit price applied to the first purchased power supplied to the first electric device and a second rate unit price applied to the second purchased power supplied to the second electric device, and when the second rate unit price is higher than the first rate unit price, the calculation unit calculates the electricity rate for the first electric device using the second rate unit price.

[0129] As a result, the higher unit price is used, which can prevent the electricity rate from being calculated as being unfairly low.

[0130] (Invention 10) The power management system 1 according to any one of inventions 1 to 9 further comprises a notification unit that notifies an external device of the measurement mode of the first measuring device.

[0131] This makes it possible to operate the external device in accordance with the mode of the first meter.

[0132] (Invention 11) The power management system 1 according to any one of Inventions 1 to 10 further comprises a notification unit that notifies an external device of a metering mode in the second circuit including the second electric device.

[0133] This allows the external device to operate in accordance with the measurement mode in the second circuit.

[0134] (Invention 12) The power management system 1 of any of Inventions 1 to 11, further comprising a second control unit that, when the first power value is a power value measured with power flowing back from the distributed power source to the power grid as a positive value, controls charging and discharging of a storage battery connected to the distributed power source in the metering stop mode so that the first power value becomes a predetermined value greater than zero.

[0135] This makes it easier to maintain the reverse power state even if the amount of power generated by the solar cell fluctuates, making it possible to prevent a transition to the mixed state.

[0136] (Invention 13) A power management method for managing the power of a first electrical device and a second electrical device installed in a facility, wherein different unit prices are set for first purchased power supplied to the first electrical device and second purchased power supplied to the second electrical device, the power management method acquiring a first power value measuring power flowing backward from a distributed power source installed in the facility to the power grid from a first meter electrically connected to the power grid, acquiring a second power value measuring power flowing forward from the power grid from a second meter electrically connected to the second electrical device, and when the first power value is equal to or greater than 0, calculating an electricity charge in a metering stop mode in which charge calculation based on the second power value is not performed.

[0137] This provides the same effects as the above-mentioned power management system.

[0138] (Invention 14) A program for causing a computer to execute the power management method of invention 13.

[0139] This provides the same effects as the above-mentioned power management system.

[0140] While the power management system according to one or more aspects has been described above based on the embodiments, the present disclosure is not limited to these embodiments. As long as the modifications do not deviate from the spirit of the present invention, modifications that a person skilled in the art can conceive of to the present embodiments and modifications constructed by combining components of different embodiments may also be included in the present invention.

[0141] For example, in the above embodiment, an example has been described in which management device 70 includes control unit 75, but this is not limiting, and management device 70 may not include control unit 75. In other words, management device 70 may not control the operation of the second electric device.

[0142] In the above embodiments, each component may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0143] The order in which the steps in the flowchart are executed is merely an example for specifically explaining the present invention, and other orders may be used. Some of the steps may be executed simultaneously (in parallel) with other steps, or some of the steps may not be executed.

[0144] The division of functional blocks in the block diagram is an example, and multiple functional blocks may be realized as a single functional block, one functional block may be divided into multiple blocks, or some functions may be moved to another functional block.Furthermore, the functions of multiple functional blocks having similar functions may be processed in parallel or in time-sharing by a single piece of hardware or software.

[0145] Furthermore, the management device 70 according to the above embodiment may be realized as a single device or may be realized by multiple devices. When the management device 70 is realized by multiple devices, the components of the management device 70 may be distributed in any manner among the multiple devices. When the management device 70 is realized by multiple devices, the communication method between the multiple devices is not particularly limited, and may be wireless communication or wired communication. Furthermore, wireless communication and wired communication may be combined between the devices.

[0146] Furthermore, each component described in the above embodiments may be implemented as software or, typically, as an LSI, which is an integrated circuit. These components may be individually integrated into a single chip, or some or all of them may be integrated into a single chip. Here, the term "LSI" is used, but depending on the level of integration, it may also be referred to as an IC, system LSI, super LSI, or ultra LSI. Furthermore, the integrated circuit implementation method is not limited to LSI, and may be implemented using a dedicated circuit (a general-purpose circuit that executes a dedicated program) or a general-purpose processor. After LSI fabrication, a field programmable gate array (FPGA) that can be programmed or a reconfigurable processor that can reconfigure the connections or settings of circuit cells within the LSI may also be used. Furthermore, if an integrated circuit technology that replaces LSI emerges due to advances in semiconductor technology or a derivative technology, that technology may naturally be used to integrate the components.

[0147] A system LSI is an ultra-multifunctional LSI manufactured by integrating multiple processing units on a single chip. Specifically, it is a computer system that includes a microprocessor, ROM (Read Only Memory), RAM (Random Access Memory), etc. Computer programs are stored in the ROM. The system LSI achieves its functions when the microprocessor operates in accordance with the computer program.

[0148] Another aspect of the present invention may be a computer program that causes a computer to execute each of the characteristic steps included in the power management method shown in any of FIGS. 4 to 5C.

[0149] Furthermore, for example, the program may be a program to be executed by a computer. Another aspect of the present invention may be a computer-readable non-transitory recording medium on which such a program is recorded. For example, such a program may be recorded on a recording medium and distributed or circulated. For example, the distributed program may be installed in a device having another processor, and the program may be executed by the processor, thereby causing the device to perform each of the above processes.

[0150] REFERENCE SIGNS LIST 1 Power management system 10 Solar cell (distributed power source) 20 Power conversion system (second control unit) 30 Storage battery 40 Distribution board 41 Power meter (third measuring instrument) 42 Power meter (second measuring instrument) 51 Home appliance (first electrical appliance) 52 Charger (second electrical appliance) 61 Power meter (first measuring instrument) 71 First acquisition unit 72 Second acquisition unit 73 Third acquisition unit 74 Calculation unit 75 Control unit (first control unit) 76 Notification unit 100 Power system

Claims

1. An energy management system that manages the power of a first electrical device and a second electrical device installed in a facility, wherein different unit prices are set for first purchased power supplied to the first electrical device and second purchased power supplied to the second electrical device, and the energy management system comprises: a first acquisition unit that acquires, from a first meter electrically connected to an electric power grid, a first power value that measures power flowing backward from a distributed power source installed in the facility to the electric power grid; a second acquisition unit that acquires, from a second meter electrically connected to the second electrical device, a second power value that measures power flowing forward from the electric power grid; and a calculation unit that calculates an electricity charge in a metering stop mode that does not perform charge calculations based on the second power value when the first power value is equal to or greater than 0.

2. The power management system according to claim 1, further comprising a third acquisition unit that acquires a third power value measured from a third meter electrically connected to the distributed power source, the third power value being the output power of the distributed power source, and the calculation unit calculates the electricity charge in a metering execution mode that performs charge calculations based on the second power value when the third power value is 0.

3. The power management system according to claim 2, further comprising a first control unit that operates the second electrical device when the measured value of the total power consumption of the facility excluding the power consumption of the second electrical device is a fourth power value and the third power value is equal to or greater than the power value obtained by adding the fourth power value and the rated power consumption of the second electrical device.

4. The power management system according to claim 2, further comprising a first control unit that operates the second electrical device so that the first power value is in a reverse power state.

5. The power management system according to claim 3 or 4, wherein, when the first power value is a power value measured with the power flowing back from the distributed power source to the power grid as a positive value and the third power value is a power value measured with the output power of the distributed power source as a positive value, the first control unit stops the second electrical device when, while the second electrical device is in operation, a transition occurs from a first state in which the first power value and the third power value are positive values to a second state in which the first power value is negative and the third power value is positive.

6. The power management system according to claim 3 or 4, wherein, when the first power value is a power value measured with the power flowing back from the distributed power source to the power grid as a positive value and the third power value is a power value measured with the output power of the distributed power source as a positive value, the first control unit operates the second electrical device when a transition occurs from a third state in which the first power value is a negative value and the third power value is a positive value to a fourth state in which the first power value is a negative value and the third power value is equal to or less than 0.

7. The power management system according to any one of claims 2 to 4, wherein in the metering execution mode, the calculation unit calculates the electricity charge for the first electrical device using the amount of power obtained by subtracting the second amount of purchased power based on the second power value measured by the second meter from the first amount of purchased power based on the first power value measured by the first meter.

8. The power management system according to claim 3 or 4, wherein, when the first power value is a power value measured with the power flowing back from the distributed power source to the power grid as a positive value and the third power value is a power value measured with the output power of the distributed power source as a positive value, the first control unit stops measurement by the second metering instrument or prohibits the calculation unit from calculating an amount of power obtained by subtracting a second amount of purchased power based on the second power value measured by the second metering instrument from a first amount of purchased power based on the first power value measured by the first metering instrument when the first power value is a negative value and the third power value is a positive value.

9. The power management system described in any one of claims 1 to 4, wherein the rate unit price includes a first rate unit price applied to the first purchased power supplied to the first electrical equipment and a second rate unit price applied to the second purchased power supplied to the second electrical equipment, and when the second rate unit price is higher than the first rate unit price, the calculation unit calculates the electricity rate for the first electrical equipment using the second rate unit price.

10. The power management system according to any one of claims 1 to 4, further comprising a notification unit that notifies an external device of the measurement mode of the first measuring device.

11. The power management system according to any one of claims 1 to 4, further comprising a notification unit that notifies an external device of the metering mode in the second circuit including the second electrical device.

12. The power management system according to any one of claims 1 to 4, further comprising a second control unit that, when the first power value is a power value measured with the power flowing back from the distributed power source to the power grid as a positive value, controls charging and discharging of a storage battery connected to the distributed power source in the metering stop mode so that the first power value becomes a predetermined value greater than 0.

13. A power management method for managing the power of a first electrical device and a second electrical device installed in a facility, wherein different unit prices are set for first purchased power supplied to the first electrical device and second purchased power supplied to the second electrical device, the power management method comprising: acquiring, from a first meter electrically connected to an electrical grid, a first power value measuring power flowing backward from a distributed power source installed in the facility to the electrical grid; acquiring, from a second meter electrically connected to the second electrical device, a second power value measuring power flowing forward from the electrical grid; and calculating an electricity charge in a metering stop mode in which charge calculations based on the second power value are not performed when the first power value is equal to or greater than 0.

14. A program for causing a computer to execute the power management method according to claim 13.

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