Microgrid and method for operating a microgrid

Abstract

To improve utilization efficiency of energy.SOLUTION: The microgrid 1 includes a power generation unit 2 that generates DC power Pdc, a power conversion unit 4 that converts the DC power Pdc received from the power generation unit 2 into AC power Pac, and a power demand unit 3 that is capable of performing an AC operation based on the AC power Pac received from the power conversion unit 4 and a DC operation based on the DC power Pdc received from the power generation unit 2. The power demanding unit 3 includes a power consuming unit 3C that operates by receiving the alternating-current power Pac or the direct-current power Pdc and a power providing unit 3C that supplies the alternating-current power Pac or the direct-current power Pdc to the power consuming unit 3S.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a microgrid and a method of operating a microgrid. [Background technology]

[0002] A so-called microgrid may include, as basic components, a renewable energy power generation device and a power conversion device. An example of a renewable energy power generation device is a solar power generation device. The power output from a solar power generation device is direct current (DC) power, but the form of this power may not match the form of power required by power consumers. Therefore, a power conversion device converts the form of power output by the power generation device into the form of power required by the power consumers.

[0003] For example, Patent Document 1 describes a microgrid system including a photovoltaic power generation device equipped with a power conditioner that converts direct current to alternating current. Patent Document 2 discloses a system including a power generation unit, a PCS, a non-specific load, and a specific load. Patent Document 3 discloses a system equipped with a DC power combiner that combines power output from a solar cell with power supplied from an AC power source. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-114905 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-172619 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-19415 Summary of the Invention [Problem to be solved by the invention]

[0005] In general, the amount of natural energy received by a renewable energy power generation system fluctuates. Because this fluctuation is due to natural phenomena, it is difficult for humans to control. As a result, the power output from the renewable energy power generation system also fluctuates. Furthermore, a power conversion system may have upper and lower limits for the input power during power conversion. As a result, if the input power received from the renewable energy power generation system is greater than the input power that the power conversion system can tolerate, the power cannot be effectively utilized. As a result, improving the energy utilization efficiency in a microgrid has been hindered.

[0006] Therefore, the present invention provides a microgrid and a method for operating the microgrid that can improve energy utilization efficiency. [Means for solving the problem]

[0007] A microgrid according to one embodiment of the present invention includes a power generation unit that generates DC power, a power conversion unit that converts the DC power received from the power generation unit into AC power, and a power demand unit that is capable of AC operation based on the AC power received from the power conversion unit and DC operation based on the DC power received from the power generation unit, and the power demand unit includes a power consumption unit that operates by receiving AC power or DC power, and a power supply unit that provides AC power or DC power to the power consumption unit.

[0008] With this configuration, the DC power generated by the power generation unit can be converted to AC power for use, or can be used as DC power as is. As a result, it is possible to select whether to convert the DC power to AC power for use or to use it as DC power as is, depending on the form of the DC power. This reduces the amount of power that is wasted due to device limitations, thereby improving the energy utilization efficiency in the microgrid.

[0009] In the microgrid, the power consumption unit may include a plurality of heater elements that generate heat by Joule heat. With this configuration, the electrical energy generated by the power generation unit can be converted into thermal energy for use.

[0010] In the microgrid, the power generation unit may include a solar power generation device. With this configuration, power can be generated using sunlight, which is a renewable energy source.

[0011] The microgrid may further include a DC power storage unit that directly receives DC power output from the power generation unit, stores the DC power, and provides the stored DC power to the power demand unit. With this configuration, the DC power can be stored as is without being converted into AC power.

[0012] The microgrid may further include an external connection unit that receives external AC power from the power grid, and the power demand unit may receive the external AC power from the power grid via the external connection unit. With this configuration, the AC power shortage can be made up for by receiving it from outside.

[0013] In the above microgrid, the power consumption unit may constitute a common consumption circuit unit including three heater elements that generate heat by Joule heating in both AC and DC operation, and the power supply unit may include an AC power supply unit for AC operation, a DC power supply unit for DC operation, and an additional switching circuit unit provided between the DC power supply unit and the common consumption circuit unit for switching between a circuit configuration for AC operation and a circuit configuration for DC operation. This configuration makes it possible to realize a power consumption unit that can accept both AC power and DC power.

[0014] In the above microgrid, the common consumption circuit may include three heater elements that generate heat by Joule heating, and the additional switching circuit unit may operate the common consumption circuit unit as a circuit in which the three heater elements are delta-connected in AC operation, and operate the common consumption circuit unit as a circuit in which the three heater elements are series-connected in DC operation. With this configuration, a power consumption unit that can accept both AC power and DC power can be realized without changing the circuit configuration of the power consumption unit.

[0015] The above microgrid may further include a control unit that controls operation of the power demand unit, wherein the power conversion unit converts the DC power received from the power generation unit into AC power and provides the converted AC power to the power demand unit when the voltage of the DC power received from the power generation unit is equal to or greater than a lower limit voltage and equal to or less than an upper limit voltage. The control unit may alternatively perform AC operation control, which guides the AC power to the power demand unit via the power conversion unit and operates the power consumption unit as a circuit with three heater elements connected in delta when the voltage of the DC power output by the power generation unit is equal to or greater than the lower limit voltage and equal to or less than the upper limit voltage, and DC operation control, which guides the DC power to the power demand unit without passing through the power conversion unit and operates the power consumption unit as a circuit with three heater elements connected in series when the voltage of the DC power output by the power generation unit is lower than the lower limit voltage or higher than the upper limit voltage. This configuration makes it possible to perform an operation of providing AC power to the power demand unit and an operation of providing DC power to the power demand unit.

[0016] Another aspect of the present invention is a method for operating a microgrid, the microgrid including: a power generation unit that generates DC power; a power conversion unit that converts the DC power received from the power generation unit into AC power; and a power demand unit that is capable of AC operation based on the AC power received from the power conversion unit and DC operation based on the DC power received from the power generation unit and includes a plurality of heater elements that generate heat by Joule heating, the power demand unit including a power consumption unit that receives AC power or DC power and a power supply unit that provides AC power or DC power to the power consumption unit, and the power conversion unit converts the DC power into AC power when the DC power received from the power generation unit is equal to or higher than a lower limit voltage and equal to or lower than an upper limit voltage. The power generation unit has an AC operation step in which the power is converted into electric power and supplied to the electric power demand unit, and when the voltage of the DC power output by the power generation unit is equal to or higher than the lower limit voltage and equal to or lower than the upper limit voltage, the AC power is led to the electric power demand unit via the power conversion unit, and the electric power consumption unit has a circuit configuration in which three heater elements are delta-connected; and when the voltage of the DC power output by the power generation unit is lower than the lower limit voltage or higher than the upper limit voltage, the DC power is led to the electric power demand unit without passing through the power conversion unit, and the electric power consumption unit has a circuit configuration in which three heater elements are connected in series.

[0017] According to this method, it is possible to select between supplying AC power to the power demand unit and supplying DC power to the power demand unit depending on the voltage of the DC power generated by the power generation unit. This reduces the amount of power that is wasted due to device limitations, thereby improving the energy utilization efficiency in the microgrid. [Effects of the Invention]

[0018] According to the present invention, a microgrid and a method for operating a microgrid that can improve energy utilization efficiency are provided. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a block diagram of a microgrid according to an embodiment. [Figure 2]FIG. 2 is a block diagram of the power demand unit. [Figure 3] Figure 3(a) shows an example of the circuit when receiving AC power, and Figure 3(b) shows an example of the circuit when receiving DC power. [Figure 4] FIG. 4 shows an example of an equivalent circuit in the power demand section when AC power is received. [Figure 5] FIG. 5 shows an example of an equivalent circuit in the power demand section when receiving DC power. [Figure 6] FIG. 6 is a flow chart illustrating a method of operating a microgrid. [Figure 7] FIG. 7 is a diagram for explaining the effect of the microgrid. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0021] FIG. 1 is a block diagram of a microgrid 1 according to this embodiment. The microgrid 1 includes a power generation unit 2 that generates power using renewable energy. The power output by the power generation unit 2 is provided to a power demand unit 3. The power demand unit 3 generates steam V using the provided power. The power demand unit 3 can generate steam V based on AC power Pac, or can generate steam V based on DC power Pdc. This makes it possible to use the power output by the power generation unit 2 without waste. Below, individual elements of the microgrid 1 will be described. In particular, the power demand unit 3 that constitutes the microgrid 1 will be described in detail.

[0022] The microgrid 1 receives renewable energy and outputs steam V. A water supply unit 90 is connected to the microgrid 1, and receives water W, which is the source of the steam V. A steam utilization unit 91 is connected to the microgrid 1, and the generated steam V is provided to the steam utilization unit 91. An example of the steam utilization unit 91 is a sewage treatment system. The steam utilization unit 91, which is a sewage treatment system, includes sewage treatment equipment 911 and sewage sludge drying equipment 912. The sewage treatment equipment 911 discharges sludge G in the process of treating sewage. The sludge G is sent to the sewage sludge drying equipment 912. The sewage sludge drying equipment 912 dries the sludge G using the steam V. Note that the steam utilization unit 91 is not limited to the sewage treatment system described above.

[0023] The microgrid 1 includes a power generation unit 2, a power conversion unit 4, a DC power storage unit 5, an AC power storage unit 6, a power demand unit 3, and a control unit .

[0024] An example of the power generation unit 2 is a solar power generation facility. Another example of the power generation unit 2 may be a wind power generation facility. A solar power generation facility generates DC power by receiving sunlight. The DC power generated by a solar power generation facility depends on the level of sunlight received. When the weather is clear, the DC power output by the solar power generation facility is high. When it is cloudy or rainy, the DC power output by the solar power generation facility decreases relatively. Also, at night, the DC power output by the solar power generation facility is zero. In this way, the DC power output by the power generation unit 2, which is a solar power generation facility, is greatly affected by the surrounding environment.

[0025] The power generation unit 2 is connected to the power conversion unit 4 by a power line L24. The power generation unit 2 sends DC power Pdc to the power conversion unit 4 via the power line L24. Furthermore, the power generation unit 2 is connected to the DC power storage unit 5 by a power line L25. The power generation unit 2 sends DC power Pdc to the DC power storage unit 5 via the power line L25. The power generation unit 2 may include an output selection unit that switches between an operation of sending DC power Pdc to the power conversion unit 4 and an operation of sending DC power Pdc to the DC power storage unit 5.

[0026] The output selection unit may itself evaluate the voltage level of the DC power Pdc, and select either an operation of sending the DC power Pdc to the power conversion unit 4 or an operation of sending the DC power Pdc to the DC power storage unit 5. Furthermore, the output selection unit may select either an operation of sending the DC power Pdc to the power conversion unit 4 or an operation of sending the DC power Pdc to the DC power storage unit 5 in accordance with a control signal C2 sent from the control unit 7. A lower limit voltage and an upper limit voltage of the power conversion unit 4, which will be described later, may be used as conditions for selecting between the operation of sending the DC power Pdc to the power conversion unit 4 and the operation of sending the DC power Pdc to the DC power storage unit 5. For example, when the voltage of the DC power Pdc is equal to or higher than the lower limit voltage and equal to or lower than the upper limit voltage, the operation of sending the DC power Pdc to the power conversion unit 4 is selected. When the voltage of the DC power Pdc is lower than the lower limit voltage, the operation of sending the DC power Pdc to the DC power storage unit 5 is selected. When the voltage of DC power Pdc is higher than the upper limit voltage, the operation of supplying DC power Pdc to DC power storage unit 5 is also selected.

[0027] The power conversion unit 4 receives DC power Pdc from the power generation unit 2 via the power line L24. The power conversion unit 4 converts the received DC power Pdc into AC power Pac. In other words, the power conversion unit 4 is a so-called power conditioner. The power conversion unit 4 is connected to the power demand unit 3 via the power line L43. The power conversion unit 4 sends AC power Pac to the power demand unit 3 via the power line L43. The power conversion unit 4 is connected to the AC power storage unit 6 via the power line L63. The power conversion unit 4 sends AC power Pac to the AC power storage unit 6 via the power line L63. The AC power storage unit 6 is a so-called storage battery.

[0028] As an example, the capacity of the power conversion unit 4 is 250 kW. In contrast, the capacity of the power generation unit 2 is 300 kW. In other words, the capacity of the power conversion unit 4 is smaller than the capacity of the power generation unit 2.

[0029] The power conversion unit 4 may or may not be able to perform power conversion operations depending on the form of the DC power Pdc it receives. The power conversion unit 4 does not perform power conversion operations when the voltage of the received DC power Pdc is lower than a lower limit voltage. In other words, when DC power Pdc with a voltage lower than the lower limit voltage is input, the DC power Pdc is discarded. This is known as undercutting. Similarly, the power conversion unit 4 does not perform power conversion operations when the voltage of the received DC power Pdc is higher than an upper limit voltage. In other words, when DC power Pdc with a voltage higher than the upper limit voltage is input, the DC power Pdc is discarded. This is known as peak shaving.

[0030] The AC power storage unit 6 receives AC power Pac from the power conversion unit 4 via the power line L63. The AC power storage unit 6 can output the power stored in the power demand unit 3 as AC power Pac via the power line L63. The AC power storage unit 6 is a so-called storage battery. As an example, the capacity of the storage battery is 50 kWh.

[0031] The DC power storage unit 5 receives DC power Pdc from the power generation unit 2 via the power line L25. The DC power storage unit 5 sends the stored DC power Pdc via the power line L25 to the power demand unit 3. An example of the DC power storage unit 5 is a capacitor.

[0032] The power demand unit 3 can receive AC power Pac from the power conversion unit 4 via the power line L43. The power demand unit 3 can receive AC power Pac from the AC power storage unit 6 via the power line L63. Furthermore, the power demand unit 3 can also receive AC power Pac from the power grid 95 via the external connection unit 8. The power demand unit 3 can receive DC power Pdc from the DC power storage unit 5 via the power line L53. And the power demand unit 3 can receive water W from the water supply unit 90.

[0033] The power demand unit 3 operates using one of AC power Pac and DC power Pdc. Specifically, the power demand unit 3 has a heater module, to which one of AC power Pac and DC power Pdc is sent. Upon receiving the power, the heater module generates heat and boils the water W received from the water supply unit 90. As a result, steam V can be generated.

[0034] The power demand unit 3 will be described in more detail. As shown in Fig. 2, the power demand unit 3 includes a power consumption unit 3C and a power supply unit 3S. Furthermore, the power supply unit 3S includes an AC power supply unit 31, a DC power supply unit 32, and an additional switching circuit unit 33. These are electric circuits configured with electric components such as resistance elements and switch elements.

[0035] The power consumption unit 3C, to which power is given, consumes the given power to perform a desired function. In this embodiment, the power consumption unit 3C converts electrical energy into thermal energy and gives the thermal energy to water W to generate steam V.

[0036] The power consumption unit 3C has a plurality of heater modules 3M1, 3M2, and 3M3. The heater modules 3M1, 3M2, and 3M3 are connected in parallel to one another. Each of the heater modules 3M1, 3M2, and 3M3 includes three heater elements 3R1, 3R2, and 3R3. The connection configuration of the three heater elements 3R1, 3R2, and 3R3 that make up the heater modules 3M1, 3M2, and 3M3 does not change depending on whether AC power Pac is applied or DC power Pdc is applied.

[0037] The AC power supply unit 31 alternately switches between a configuration in which the power conversion unit 4 and the AC power storage unit 6 are connected to the power consumption unit 3C and a configuration in which the power consumption unit 3C is disconnected from the power conversion unit 4 and the AC power storage unit 6. The AC power supply unit 31 includes a switch element T31. The switch element T31 alternately switches between a conductive state and a disconnected state in response to a control signal C31 provided from the control unit 7. When the switch element T31 is conductive, the power conversion unit 4 and the AC power storage unit 6 are connected to the power consumption unit 3C. When the switch element T31 is disconnected, the power conversion unit 4 and the AC power storage unit 6 are disconnected from the power consumption unit 3C.

[0038] The DC power supply unit 32 switches, via the additional switching circuit unit 33, between a configuration in which the DC power storage unit 5 is connected to the power consumption unit 3C and a configuration in which the power consumption unit 3C is disconnected from the DC power storage unit 5. The DC power supply unit 32 includes a switch element T32. The switch element T32 switches between a conductive state and a disconnected state in response to a control signal C32 provided from the control unit 7. When the switch element T32 is conductive, the DC power storage unit 5 is connected to the power consumption unit 3C. When the switch element T32 is disconnected, the DC power storage unit 5 is disconnected from the power consumption unit 3C.

[0039] The additional switching circuit unit 33 switches the circuit configuration of the power demand unit 3 between when receiving AC power Pac (see FIG. 3(a)) and when receiving DC power Pdc (see FIG. 3(b)). As described above, the connection configuration of the first heater element 3R1, the second heater element 3R2, and the third heater element 3R3 (described later) remains the same when receiving AC power Pac and when receiving DC power Pdc. By switching the additional switching circuit unit 33 to an AC circuit configuration 33ac for this power consumption unit 3C, a circuit configuration of the power demand unit 3 that realizes a desired operation using AC power Pac is formed. Similarly, by switching the additional switching circuit unit 33 to a DC circuit configuration 33dc for the power consumption unit 3C, a circuit configuration of the power demand unit 3 that realizes a desired operation using DC power Pdc is formed.

[0040] Referring to FIG. 3(a), the circuit configuration of the power demand unit 3 when receiving AC power Pac will be described. First, the power consumption unit 3C includes three heater elements: a first heater element 3R1, a second heater element 3R2, and a third heater element 3R3. The first heater element 3R1 is connected to a U-phase terminal 3P1 and a V-phase terminal 3P2. The second heater element 3R2 is connected to a V-phase terminal 3P2 and a W-phase terminal 3P3. The third heater element 3R3 is connected to a W-phase terminal 3P3 and a U-phase terminal 3P1. At first glance, the three heater elements, the first heater element 3R1, the second heater element 3R2, and the third heater element 3R3, appear to be connected in a so-called delta configuration. The circuit configuration of the power consumption unit 3C shown in FIG. 3(a) is referred to as a common consumption circuit unit 3CR.

[0041] Now, let us focus on the W-phase terminal 3P3. The W-phase terminal 3P3 includes a second W-phase terminal 3P32 connected to the second heater element 3R2 and a third W-phase terminal 3P33 connected to the third heater element 3R3. When viewed as a single power consumption unit 3C, there is no electrical continuity between the second W-phase terminal 3P32 and the third W-phase terminal 3P33.

[0042] The second W-phase terminal 3P32 is connected to the power line L322, and the third W-phase terminal 3P33 is connected to the power line L323. An additional switching circuit 33 is provided between these power lines L322 and L323. The additional switching circuit 33 has a switch element T331 provided between the power lines L322 and L323. When AC power Pac is received, the circuit configuration of the power demand unit 3 is a so-called delta connection. Therefore, the additional switching circuit 33 turns on the switch element T331. This brings the second W-phase terminal 3P32 and the third W-phase terminal 3P33 into conduction. As a result, the three heater elements 3R1, 3R2, and 3R3 form a delta connection. Looking at the entire power consumption unit 3C, as shown in FIG. 4, the heater modules 3M1, 3M2, and 3M3 in the delta connection are connected in parallel with each other.

[0043] AC power providing unit 31 includes a U-phase switch element T311 connected to U-phase terminal 3P1, a V-phase switch element T312 connected to V-phase terminal 3P2, and a W-phase switch element T313 connected to second W-phase terminal portion 3P32 of W-phase terminal 3P3. When AC power Pac is received, U-phase switch element T311, V-phase switch element T312, and W-phase switch element T313 are all conductive.

[0044] The DC power supply unit 32 includes a second W-phase switch element T322 connected to the second W-phase terminal 3P32 and a third W-phase switch element T323 connected to the third W-phase terminal 3P33. When receiving the AC power Pac, the second W-phase switch element T322 and the third W-phase switch element T323 are both disconnected.

[0045] Next, with reference to Figure 3(b), the circuit configuration of the power demand unit 3 when receiving DC power Pdc will be described. When receiving AC power Pac, the three heater elements 3R1, 3R2, and 3R3 of the power consumption unit 3C are delta-connected. On the other hand, when receiving DC power Pdc, the three heater elements 3R1, 3R2, and 3R3 of the power consumption unit 3C are series-connected.

[0046] When receiving DC power Pdc, AC power supply unit 31 disconnects U-phase switch element T311, V-phase switch element T312, and W-phase switch element T313. When receiving DC power Pdc, DC power supply unit 32 connects second W-phase switch element T322 and third W-phase switch element T323. Additional switching circuit unit 33 disconnects switch element T331.

[0047] As a result, as shown in Figure 3(b), a series circuit is formed that passes through the power line L322, the second W-phase terminal portion 3P32, the second heater element 3R2, the first heater element 3R1, the third heater element 3R3, the third W-phase terminal portion 3P33, and the power line L323 in this order.

[0048] Looking at the power consumption unit 3C as a whole, as shown in FIG. 5, the heater modules 3M1, 3M2, and 3M3 connected in series are connected in parallel with each other.

[0049] According to the connection configurations shown in FIGS. 4 and 5, the voltage and current acting on one heater element can be made equal regardless of whether the input power is AC or DC.

[0050] The control unit 7 controls the operations of the power generation unit 2, the power conversion unit 4, the AC power storage unit 6, and the power demand unit 3. As already described, the control unit 7 may provide the power generation unit 2 with a control signal C2 that determines whether the generated DC power Pdc is provided to the power conversion unit 4 or to the DC power storage unit 5. The control unit 7 may provide the power demand unit 3 with control signals C31, C32 for switching between a circuit configuration that receives the AC power Pac and a circuit configuration that receives the DC power Pdc. Furthermore, the control unit 7 may obtain data D2 related to the DC power Pdc generated by the power generation unit 2 from the power generation unit 2 in order to generate these control signals C2, C31, C32.

[0051] <How a microgrid works> A method of operating the microgrid will now be described. The method of operating the microgrid may be executed by, for example, the control unit 7. First, as shown in FIG. 6, the control unit 7 obtains data D2 related to the DC power Pdc generated by the power generation unit 2 (S1). Next, the control unit 7 obtains the generated voltage from the data D2 related to the DC power Pdc and determines whether it is equal to or greater than a lower limit voltage (S2). If the generated voltage is not equal to or greater than the lower limit voltage (S2: NO), the control unit 7 performs DC operation (S3). In DC operation (S3), the control unit 7 outputs a control signal C2 that causes the power generation unit 2 to output DC power Pdc toward the DC power storage unit 5. Furthermore, the control unit 7 outputs a control signal C3 to configure the power demand unit 3 to operate using DC power Pdc (see FIG. 3(b)).

[0052] On the other hand, if the generated voltage is equal to or higher than the lower limit voltage (S2: YES), the control unit 7 next determines whether the generated voltage is equal to or lower than the upper limit voltage (S4). If the generated voltage is equal to or lower than the upper limit voltage (S4: YES), the control unit 7 performs AC operation (S5). Specifically, during AC operation (S5), the control unit 7 outputs a control signal C2 that causes the power generation unit 2 to output DC power Pdc toward the power conversion unit 4. Furthermore, the control unit 7 outputs a control signal C3 that causes the power demand unit 3 to have a circuit configuration (see FIG. 3(a)) that operates using AC power Pac.

[0053] If the generated voltage is not equal to or less than the upper limit voltage (S4: NO), the control unit 7 executes DC operation (S6). During DC operation (S6), the control unit 7 outputs a control signal C2 that causes the power generation unit 2 to output DC power Pdc toward the DC power storage unit 5. Furthermore, the control unit 7 outputs a control signal C3 that causes the power demand unit 3 to have a circuit configuration (see FIG. 3(b)) that operates using DC power Pdc.

[0054] The control unit 7 repeats the above steps S1 to S3 at a predetermined timing.

[0055] <Action and effect> The microgrid 1 includes a power generation unit 2 that generates DC power Pdc, a power conversion unit 4 that converts the DC power Pdc received from the power generation unit 2 into AC power Pac, and a power demand unit 3 that is capable of AC operation based on the AC power Pac received from the power conversion unit 4 and DC operation based on the DC power Pdc received from the power generation unit 2. The power demand unit 3 includes a power consumption unit 3C that operates by receiving the AC power Pac or the DC power Pdc, and a power supply unit 3S that provides the AC power Pac or the DC power Pdc to the power consumption unit 3C.

[0056] According to this configuration, the DC power Pdc generated by the power generation unit 2 can be converted to AC power Pac for use, or can be used as DC power Pdc as is. As a result, depending on the form of the DC power Pdc, it is possible to select between converting it to AC power Pac for use, or using it as DC power Pdc as is. This reduces the amount of power that is wasted due to device limitations, thereby improving the energy utilization efficiency in the microgrid 1.

[0057] Conversion from DC to AC and AC to DC involves power loss. However, with this configuration, the generated DC power can be used either as DC power or after a single conversion from DC to AC. In other words, the number of power conversions can be reduced, thereby suppressing the loss of electrical energy that occurs during power conversion.

[0058] Furthermore, by using DC power as is, there is no conversion loss that occurs when converting DC power to AC power, so energy loss can be reduced and the power factor of the heater element can be improved.

[0059] FIG. 7 shows the daily change in power generated by the power generation unit 2, which is a solar power generation device. The horizontal axis represents time, and the vertical axis represents power generated by the power generation unit 2. The power generation unit 2 receives sunlight and generates power from sunrise t1 to sunset t2. However, the power generation unit 2 generates almost no power before sunrise t1 or after sunset t2. As a result, the voltage of the power generated before sunrise t1 or after sunset t2 (areas A1 and A2) is lower than the lower limit voltage. Therefore, during this period, DC power Pdc is supplied to the power demand unit 3. The voltage of the power generated from sunrise t1 to sunset t2 (area A3) exceeds the lower limit, so AC power Pac is supplied to the power demand unit 3 during this period. Note that the voltage of the power generated from sunrise t1 to sunset t2 may exceed the upper limit voltage. In this case, the amount of power exceeding the capacity of the power conversion unit 4 (area A4) is stored in the DC power storage unit 5. As a result, the power generated by the power generating unit 2 is not wasted, and the energy utilization efficiency in the microgrid 1 can be improved.

[0060] The power consumption unit 3C includes a plurality of heater elements 3R1, 3R2, and 3R3 that generate heat by Joule heat. With this configuration, the electrical energy generated by the power generation unit 2 can be converted into thermal energy and utilized.

[0061] The power generation unit 2 includes a solar power generation device. With this configuration, power can be generated using sunlight, which is a renewable energy source.

[0062] The microgrid 1 further includes a DC power storage unit 5 that directly receives DC power Pdc output by the power generation unit 2, stores the DC power Pdc, and provides the stored DC power Pdc to the power demand unit 3. With this configuration, the DC power Pdc can be stored as is without being converted to AC power Pac.

[0063] The microgrid 1 further includes an external connection unit that receives AC power Pac from the power grid 95. The power demand unit 3 receives the AC power Pac from the power grid 95 via the external connection unit. With this configuration, the AC power Pac that is in short supply can be supplied from outside.

[0064] The power consumption unit 3C constitutes a common consumption circuit unit 3CR including three heater elements 3R1, 3R2, and 3R3 that generate heat by Joule heating during both AC and DC operation. The power supply unit 3S may include an AC power supply unit 31 for AC operation, a DC power supply unit 32 for DC operation, and an additional switching circuit unit 33 provided between the DC power supply unit 32 and the common consumption circuit unit 3CR for switching between a circuit configuration for AC operation and a circuit configuration for DC operation. This configuration enables the realization of a power consumption unit 3C that can accept both AC power Pac and DC power Pdc.

[0065] The common consumption circuit unit 3CR includes three heater elements 3R1, 3R2, and 3R3 that generate heat by Joule heating. During AC operation, the additional switching circuit unit 33 operates the common consumption circuit unit 3CR as a circuit in which the three heater elements 3R1, 3R2, and 3R3 are delta-connected. During DC operation, the additional switching circuit unit 33 operates the common consumption circuit unit 3CR as a circuit in which the three heater elements 3R1, 3R2, and 3R3 are series-connected. This configuration makes it possible to realize a power consumption unit 3C that can accept both AC power Pac and DC power Pdc without changing the circuit configuration of the power consumption unit 3C.

[0066] The microgrid 1 further includes a control unit 7 that controls the operation of the power demand unit 3. When the voltage of the DC power Pdc received from the power generation unit 2 is equal to or higher than a lower limit voltage and equal to or lower than an upper limit voltage, the power conversion unit 4 converts the DC power Pdc into AC power Pac and provides it to the power demand unit 3. The control unit 7 may alternatively perform AC operation control, in which the control unit 7 guides the AC power Pac to the power demand unit 3 via the power conversion unit 4 and operates the power consumption unit 3C as a circuit in which three heater elements 3R1, 3R2, and 3R3 are connected in delta when the voltage of the DC power Pdc output by the power generation unit 2 is equal to or greater than the lower limit voltage and equal to or less than the upper limit voltage, or DC operation control, in which the control unit 7 guides the DC power Pdc to the power demand unit 3 without passing through the power conversion unit 4 and operates the power consumption unit 3C as a circuit in which three heater elements 3R1, 3R2, and 3R3 are connected in series when the voltage of the DC power Pdc output by the power generation unit 2 is lower than the lower limit voltage or higher than the upper limit voltage. This configuration makes it possible to perform an operation of providing the AC power Pac to the power demand unit 3 and an operation of providing the DC power Pdc to the power demand unit 3.

[0067] The operating method of the microgrid 1 includes an AC operation step S12 in which, when the voltage of the DC power Pdc output by the power generation unit 2 is equal to or greater than the lower limit voltage and equal to or less than the upper limit voltage, the AC power Pac is guided to the power demand unit 3 via the power conversion unit 4, and the power consumption unit 3C is configured as a circuit in which three heater elements 3R1, 3R2, and 3R3 are delta-connected; and a DC operation step S13 in which, when the voltage of the DC power Pdc output by the power generation unit 2 is smaller than the lower limit voltage or larger than the upper limit voltage, the DC power Pdc is guided to the power demand unit 3 without passing through the power conversion unit 4, and the power consumption unit 3C is configured as a circuit in which three heater elements 3R1, 3R2, and 3R3 are connected in series.

[0068] According to this method, it is possible to select between an operation of supplying AC power Pac to the power demand unit 3 and an operation of supplying DC power Pdc to the power demand unit 3, depending on the voltage of DC power Pdc generated by the power generation unit 2. This makes it possible to reduce the amount of power that is wasted without being used due to device constraints, thereby improving the energy utilization efficiency in the microgrid 1.

[0069] <Modification> The microgrid and the operating method of the microgrid of the present invention are not limited to the above-described embodiment, and various modifications are possible without departing from the spirit and scope of the present invention.

[0070] For example, when comparing the magnitude of two numbers, either of the two criteria "greater than or equal to" or "greater than" may be used. Either of the two criteria "less than or equal to" or "under" may be used.

[0071] In the above-described embodiment, all three heater modules 3M1, 3M2, and 3M3 are configured as circuits compatible with AC power (FIG. 3(a)) or circuits compatible with DC power (FIG. 3(b)). For example, among the three heater modules 3M1, 3M2, and 3M3, heater modules 3M1 and 3M2 may be configured as circuits compatible with AC power, and heater module 3M3 may be configured as a circuit compatible with DC power. In this case, the power demand unit 3 can operate by receiving both AC power Pac and DC power Pdc. For example, both the power shown in area A3 and the power shown in area A4 in FIG. 6 can be supplied to the power demand unit 3.

[0072] In this way, the microgrid 1 of this embodiment can accommodate the following seven operation modes. First mode: Operation using DC power Pdc from the power generation unit 2. Second mode: Operation using AC power Pac from the power generation unit 2. Third mode: Operation using AC power Pac from the power grid 95. Fourth mode: Operation using DC power Pdc and AC power Pac from the power generation unit 2. Fifth mode: Operation using DC power Pdc from the power generation unit 2 and AC power Pac from the power grid 95. Sixth mode: Operation using AC power Pac from the power generation unit 2 and AC power Pac from the power grid 95. Seventh mode: Operation using DC power Pdc from the power generation unit 2, AC power Pac from the power generation unit 2, and AC power Pac from the power grid 95.

[0073] <Additional remarks> The present disclosure includes the following configurations.

[0074] This disclosure provides: [1] "a power generation unit that generates DC power; a power conversion unit that converts the DC power received from the power generation unit into AC power; a power demand unit capable of AC operation based on the AC power received from the power conversion unit and DC operation based on the DC power received from the power generation unit, The power demand unit a power consumption unit that operates by receiving the AC power or the DC power; a power supply unit that supplies the AC power or the DC power to the power consumption unit.

[0075] The present disclosure is [2] "The microgrid described in [1] above, wherein the power consumption unit includes a plurality of heater elements that generate heat by Joule heat."

[0076] The present disclosure provides: [3] "The microgrid according to [1] or [2] above, wherein the power generation unit includes a solar power generation device.

[0077] The present disclosure is [4] "a microgrid according to any one of [1] to [3] above, further comprising a DC power storage unit that directly receives the DC power output by the power generation unit, stores the DC power, and provides the stored DC power to the power demand unit."

[0078] The present disclosure further provides [5] "an external connection unit for receiving external AC power from a power grid, The microgrid according to any one of the above [1] to [4], wherein the power demand unit receives the external AC power from the power grid via the external connection unit.

[0079] The present disclosure states, [6] "The power consumption unit constitutes a common consumption circuit unit including three heater elements that generate heat by Joule heat both in the AC operation and in the DC operation, The microgrid according to any one of the above [1] to [5], wherein the power supply unit includes an AC power supply unit for the AC operation, a DC power supply unit for the DC operation, and an additional switching circuit unit provided between the DC power supply unit and the common consumption circuit unit, and configured to switch between a circuit configuration for the AC operation and a circuit configuration for the DC operation.

[0080] The disclosure states, [7] "The common consumption circuit includes three heater elements that generate heat by Joule heat, In the AC operation, the additional switching circuit unit operates the common consumption circuit unit as a circuit in which three of the heater elements are delta-connected, The microgrid according to the above-mentioned [6], wherein, in the DC operation, the additional switching circuit unit operates the common consumption circuit unit as a circuit in which three of the heater elements are connected in series.

[0081] The present disclosure further includes a control unit for controlling the operation of the power demand unit, the power conversion unit converts the DC power into AC power and provides the AC power to the power demand unit when a voltage of the DC power received from the power generation unit is equal to or higher than a lower limit voltage and equal to or lower than an upper limit voltage; The control unit an AC operation control that, when a voltage of the DC power output by the power generation unit is equal to or higher than the lower limit voltage and equal to or lower than the upper limit voltage, guides the AC power to the power demand unit via the power conversion unit and operates the power consumption unit as a circuit in which the three heater elements are delta-connected; and when the voltage of the DC power output by the power generation unit is lower than the lower limit voltage or when the voltage of the DC power output by the power generation unit is higher than the upper limit voltage, the DC operation control is alternatively performed to guide the DC power to the power demand unit without passing through the power conversion unit, and to operate the power consumption unit as a circuit in which three of the heater elements are connected in series.

[0082] The present disclosure is [9] "A method for operating a microgrid, the microgrid comprising: a power generation unit that generates DC power; a power conversion unit that converts the DC power received from the power generation unit into AC power; and a power demand unit that is capable of AC operation based on the AC power received from the power conversion unit and DC operation based on the DC power received from the power generation unit, and includes a plurality of heater elements that generate heat by Joule heating, the power demand unit including a power consumption unit that receives the AC power or the DC power, and a power supply unit that provides the AC power or the DC power to the power consumption unit, the power conversion unit converting the DC power received from the power generation unit into AC power and providing the AC power to the power demand unit when the DC power received from the power generation unit is equal to or higher than a lower limit voltage and equal to or lower than an upper limit voltage, an AC operation step of directing the AC power to the power demand unit via the power conversion unit when the voltage of the DC power output from the power generation unit is equal to or higher than the lower limit voltage and equal to or lower than the upper limit voltage, and configuring the power consumption unit as a circuit in which three of the heater elements are delta-connected; and a DC operation step of, when the voltage of the DC power output by the power generation unit is lower than the lower limit voltage or higher than the upper limit voltage, directing the DC power to the power demand unit without passing through the power conversion unit, and configuring the power consumption unit as a circuit in which three of the heater elements are connected in series."

[0083] [others] The microgrid and the method of operating the microgrid disclosed herein can improve the efficiency of energy utilization generated by the microgrid. The microgrid and the method of operating the microgrid disclosed herein contribute to Goal 7 of the Sustainable Development Goals (SDGs) led by the United Nations, which is to "ensure access to affordable, reliable, sustainable and modern energy." [Explanation of symbols]

[0084] 1. Microgrid 2 Power Generation Department 3 Electricity demand department 3C power consumption part 3CR common consumption circuit section 3M1, 3M2, 3M3 heater modules 3P1 U phase terminal 3P2 V phase terminal 3P3 W phase terminal 3P32 2nd W phase terminal section 3P33 3rd W phase terminal section 3R1 First heater element 3R2 Second heater element 3R3 Third heater element 3S power supply section 31 AC power supply department 32 DC power supply section 33 Additional switching circuit section 33ac AC circuit configuration 33dc DC circuit configuration T31 Switch Element T32 Switch Element T311 U-phase switch element T312 V-phase switch element T313 W-phase switch element T322 2nd W-phase switch element T323 Third W-phase switch element T331 Switch Element 4 Power conversion section 5 DC power storage unit 6 AC power storage unit 7 Control Unit 8 External connection part 90 Water supply section 91 Steam Utilization Section 95 Power system 911 Sewage treatment facilities 912 Sewage sludge drying equipment Pac AC power Pdc direct current power S12 AC operation step S13 DC operation step

Claims

1. a power generation unit that generates DC power; a power conversion unit that converts the DC power received from the power generation unit into AC power; a power demand unit capable of AC operation based on the AC power received from the power conversion unit and DC operation based on the DC power received from the power generation unit, The power demand unit a power consumption unit that operates by receiving the AC power or the DC power; a power providing unit that provides the AC power or the DC power to the power consuming unit.

2. The microgrid of claim 1 , wherein the power consuming unit includes a plurality of heater elements that generate heat by Joule heating.

3. The microgrid according to claim 1 , wherein the power generation unit includes a solar power generation device.

4. 2. The microgrid according to claim 1, further comprising a DC power storage unit that directly receives the DC power output by the power generation unit, stores the DC power, and provides the stored DC power to the power demand unit.

5. further comprising an external connection unit for receiving external AC power from a power grid; The microgrid according to claim 1 , wherein the power demand unit receives the external AC power from the power grid via the external connection unit.

6. the power consumption unit constitutes a common consumption circuit unit including three heater elements that generate heat by Joule heat both in the AC operation and in the DC operation, 2. The microgrid according to claim 1, wherein the power providing unit includes: an AC power providing unit for the AC operation; a DC power providing unit for the DC operation; and an additional switching circuit unit provided between the DC power providing unit and the common consumption circuit unit, the additional switching circuit unit switching between a circuit configuration for the AC operation and a circuit configuration for the DC operation.

7. the common consumption circuit includes three heater elements that generate heat by Joule heat; In the AC operation, the additional switching circuit unit operates the common consumption circuit unit as a circuit in which three of the heater elements are delta-connected, The microgrid according to claim 6 , wherein, in the DC operation, the additional switching circuitry operates the common consumption circuitry as a circuit in which three of the heater elements are connected in series.

8. a control unit that controls an operation of the power demand unit, the power conversion unit converts the DC power into AC power and provides the AC power to the power demand unit when a voltage of the DC power received from the power generation unit is equal to or higher than a lower limit voltage and equal to or lower than an upper limit voltage; The control unit an AC operation control that, when a voltage of the DC power output by the power generation unit is equal to or higher than the lower limit voltage and equal to or lower than the upper limit voltage, guides the AC power to the power demand unit via the power conversion unit and operates the power consumption unit as a circuit in which the three heater elements are delta-connected; and DC operation control that, when a voltage of the DC power output by the power generation unit is lower than the lower limit voltage or when a voltage of the DC power output by the power generation unit is higher than the upper limit voltage, guides the DC power to the power demand unit without passing through the power conversion unit and causes the power consumption unit to operate as a circuit in which three of the heater elements are connected in series.

9. A method for operating a microgrid, the microgrid comprising: a power generation unit that generates DC power; a power conversion unit that converts the DC power received from the power generation unit into AC power; and a power demand unit that is capable of AC operation based on the AC power received from the power conversion unit and DC operation based on the DC power received from the power generation unit, and includes a plurality of heater elements that generate heat by Joule heating, wherein the power demand unit includes a power consumption unit that receives the AC power or the DC power, and a power supply unit that provides the AC power or the DC power to the power consumption unit, and when the DC power received from the power generation unit is equal to or higher than a lower limit voltage and equal to or lower than an upper limit voltage, the power conversion unit converts the DC power to the AC power and provides it to the power demand unit, an AC operation step of, when a voltage of the DC power output from the power generation unit is equal to or higher than the lower limit voltage and equal to or lower than the upper limit voltage, directing the AC power to the power demand unit via the power conversion unit and configuring the power consumption unit as a circuit in which three of the heater elements are delta-connected; a DC operation step of, when the voltage of the DC power output by the power generation unit is lower than the lower limit voltage or when the voltage of the DC power output by the power generation unit is higher than the upper limit voltage, directing the DC power to the power demand unit without passing through the power conversion unit, and configuring the power consumption unit as a circuit in which three of the heater elements are connected in series.

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