microgrid

Abstract

This microgrid comprises: a renewable energy power generation device that generates DC power by using renewable energy; a power conversion device that converts the DC power received from the renewable energy power generation device into AC power; and a cold heat generation device that executes a heat absorption operation for removing heat from a heat absorption target by means of the DC power received from the renewable energy power generation device.

Description

Microgrid

[0001] The present disclosure relates to a microgrid.

[0002] There is a system in which different types of energy such as electric energy and thermal energy coexist. In such a system, energy transfer occurs between an energy generation device and an energy consumption device. Examples of energy generation devices are power generation devices using renewable energy such as solar power generation devices. Furthermore, during energy transfer, energy conversion such as conversion from DC power to AC power may be involved. Examples of devices for performing energy conversion are power conversion devices such as inverters.

[0003] Patent Document 1 discloses a system including a renewable energy power generation device and an energy storage device. Energy is transported between the renewable energy power generation device and the energy storage device. Patent Document 2 discloses an energy management system including a battery for storing electric energy, a heat accumulator, and a cold accumulator.

[0004] Japanese Unexamined Patent Application Publication No. 2012-200065, Japanese Unexamined Patent Application Publication No. 2019-118178

[0005] Generally, the natural energy received by a renewable energy power generation device increases and decreases. Since this increase and decrease is due to natural phenomena, it is difficult to control by humans. As a result, the power output by the renewable energy power generation device also increases and decreases. Furthermore, a power conversion device may have a lower limit value and an upper limit value of input power in the operation of converting power. Then, when input power that cannot be tolerated by the power conversion device is supplied from the renewable energy power generation device, such power is not effectively utilized. As a result, the improvement of the energy utilization efficiency in the microgrid has been hindered.

[0006] The present disclosure describes a microgrid capable of improving energy utilization efficiency.

[0007] One embodiment of the microgrid described herein comprises a power generation unit that generates DC power using renewable energy, a power conversion unit that converts the DC power received from the power generation unit into AC power, and a thermal function unit that performs a heat absorption operation to remove heat from a heat absorption target using the DC power received from the power generation unit. According to this microgrid, a portion of the DC power generated by the power generation unit that was not converted into AC power is used to perform a heat absorption operation to remove heat from a heat absorption target. As a result, a heat absorption target, which is a heat transfer medium whose temperature has been lowered by the heat absorption operation, can be obtained. Therefore, the energy utilization efficiency of the microgrid can be improved in order to make effective use of the DC power that would otherwise be wasted.

[0008] The above microgrid may further include a DC power utilization unit that performs utilization operations to consume or store DC power received from the power generation unit. If the DC voltage defining the DC power is above a threshold, DC power may not be supplied to the thermal function unit and the thermal function unit may not perform heat absorption operations, while DC power may be supplied to the DC power utilization unit and the DC power utilization unit may perform utilization operations. This operation allows for heat absorption operations based on DC power to be performed under efficient conditions.

[0009] The above microgrid may further include a DC power utilization unit that performs utilization operations to consume or store DC power received from the power generation unit. The thermal function unit may include a heat absorption unit that performs a heat absorption operation to remove heat from a heat absorption target using DC power received from the power generation unit, and a heat dissipation unit that performs a heat dissipation operation to supply heat to a heating target using DC power received from the power generation unit. If the temperature difference between the heat absorption unit and the heat dissipation unit is greater than or equal to a threshold, DC power may not be supplied to the thermal function unit and the thermal function unit may not perform a heat absorption operation, while DC power may be supplied to the DC power utilization unit and the DC power utilization unit may perform a utilization operation. This operation also allows for the performance of a DC power-based heat absorption operation under efficient conditions.

[0010] The above microgrid may further include an information acquisition unit that receives weather information for the location where the power generation unit is installed. Based on the weather information, it may decide whether or not to supply DC power to the thermal function unit to perform its heat absorption operation. This operation also allows for the performance of a heat absorption operation based on DC power under efficient conditions.

[0011] The above microgrid may further include a first power line connected to the power generation unit and the power conversion unit, which transmits DC power from the power generation unit to the power conversion unit, and a second power line connected to the power generation unit and the thermal function unit, which transmits DC power from the power generation unit to the thermal function unit. With this configuration, the DC power generated in the power generation unit can be supplied to both the power conversion unit and the thermal function unit.

[0012] The above microgrid may further include an AC power utilization unit that performs a heat absorption operation using AC power provided by a power conversion unit. The thermal function unit may provide the heat-absorbing object from which heat has been removed in the thermal function unit to the AC power utilization unit. With this configuration, a portion of the energy required for the operation of the AC power utilization unit can be supplemented by the heat-absorbing object from which heat has been removed provided by the thermal function unit. As a result, the energy utilization efficiency of the microgrid can be further improved.

[0013] The power generation section of the microgrid described above may include a photovoltaic power generation system. This configuration allows for power generation using solar energy, which is a renewable energy source.

[0014] The thermal functional part of the above microgrid may include a Peltier element. With this configuration, it is possible to obtain both an object that is a heat transfer medium whose temperature has been raised by DC power and an object that is a heat transfer medium whose temperature has been lowered.

[0015] The microgrids described herein are capable of improving energy utilization efficiency.

[0016] Figure 1 is a block diagram of a microgrid according to the first embodiment. Figure 2 is a block diagram of a cooling / heating device included in the microgrid according to the first embodiment. Figure 3 is a functional block diagram showing the controller of the first embodiment. Figure 4 is a flowchart illustrating the operation of the microgrid according to the first embodiment. Figure 5 is a diagram illustrating the effects of the microgrid. Figure 6 is a block diagram of a microgrid according to the second embodiment. Figure 7 is a block diagram of a cooling / heating device included in the microgrid according to the second embodiment. Figure 8(a) is an example of a circuit when receiving AC power. Figure 8(b) is an example of a circuit when receiving DC power. Figure 9 is an example of an equivalent circuit in the cooling / heating device when receiving DC power. Figure 10 is an example of an equivalent circuit in the cooling / heating device when receiving AC power. Figure 11 is a flowchart illustrating the operation of a microgrid according to the second embodiment. Figure 12 is a block diagram of a microgrid according to the first modification. Figure 13 is a block diagram of a microgrid according to the second modification. Figure 14 is a block diagram of a microgrid according to the third modification.

[0017] The microgrid of this disclosure will be described in detail below with reference to the attached drawings. In the description of the drawings, the same elements will be denoted by the same reference numeral, and redundant explanations will be omitted.

[0018] Figure 1 is a block diagram of a microgrid 1A according to this embodiment. The microgrid 1A includes a renewable energy power generation device 2 (power generation unit) that generates electricity using renewable energy. The renewable energy power generation device 2 generates DC power Pdc. The DC power Pdc is converted to AC power Pac by a power converter 3 (power conversion unit). The AC power Pac is supplied to a refrigeration device 4, which is an example of an AC power consumer. The DC power Pdc is supplied as DC power Pdc to a cooling and heat generation device 5 (thermal function unit), which is an example of a DC power consumer, without being converted to AC power Pac. The cooling and heat generation device 5 can output a low-temperature heat transfer medium ML using the DC power Pdc. An example of the low-temperature heat transfer medium ML may be chilled water. The low-temperature heat transfer medium ML is supplied to the refrigeration device 4. With this configuration, the low-temperature heat transfer medium ML generated using DC power Pdc is supplied to the refrigeration device 4, which basically operates on AC power Pac. As a result, it becomes possible to utilize DC power Pdc, which was previously unused, so that the energy generated by the renewable energy power generation device 2 can be used without waste. Therefore, the energy efficiency of the microgrid 1A can be increased.

[0019] The microgrid 1A comprises a renewable energy power generation device 2, a power conversion device 3, a refrigeration device 4, a cooling / heating device 5, and a controller 6. Furthermore, the microgrid 1A may include an AC power storage device 71 (AC power utilization unit) and a DC power storage device 72 (DC power utilization unit) as ancillary devices. The microgrid 1A also includes power lines L3, L4, L71, L5, and L72 for transferring power between the respective devices. Power lines L4 and L5 may be provided with switch devices H71 and H72 for permitting or prohibiting the transfer of power to or from the respective devices.

[0020] The renewable energy power generation device 2 includes a photovoltaic power generation panel 21 that generates electricity by receiving sunlight. An example of the renewable energy power generation device 2 may also be a wind power generation facility. The photovoltaic power generation facility generates direct current power Pdc by receiving sunlight. The amount of direct current power Pdc generated by the photovoltaic power generation facility depends on the amount of sunlight received. On sunny days, the amount of direct current power Pdc output by the photovoltaic power generation facility is high. On cloudy or rainy days, the amount of direct current power Pdc output by the photovoltaic power generation facility decreases relatively. During the daytime, the photovoltaic power generation facility outputs a predetermined amount of direct current power Pdc, but at night, the amount of direct current power Pdc output by the photovoltaic power generation facility is zero. Thus, the amount of direct current power Pdc output by the renewable energy power generation device 2, which is a photovoltaic power generation facility, is greatly influenced by the surrounding environment.

[0021] The renewable energy power generation device 2 is connected to the power converter 3 by a power line L3 (first power line). The renewable energy power generation device 2 sends DC power Pdc to the power converter 3 via the power line L3. Furthermore, the renewable energy power generation device 2 is connected to the cooling / heating generator 5 by a power line L5. The renewable energy power generation device 2 sends DC power Pdc to the cooling / heating generator 5 via the power line L5. The renewable energy power generation device 2 includes an output selection unit 22 that switches between sending DC power Pdc to the power converter 3 and sending DC power Pdc to the DC power storage device 72. In this embodiment, the output selection unit 22 is described as a component of the renewable energy power generation device 2, but the output selection unit 22 may be treated as a separate device from the renewable energy power generation device 2.

[0022] The output selection unit 22 may select either sending DC power Pdc to the power converter 3 or sending DC power Pdc to the cooling / heating generator 5, depending on the DC voltage of the DC power Pdc measured by the voltage sensor 23. Alternatively, the output selection unit 22 may select either sending DC power Pdc to the power converter 3 or sending DC power Pdc to the cooling / heating generator 5, depending on the control signal C22 sent from the controller 6. The lower and upper voltage limits of the power converter 3 may be used as conditions for selecting between sending DC power Pdc to the power converter 3 and sending DC power Pdc to the cooling / heating generator 5. For example, if the voltage of DC power Pdc is greater than or equal to the lower voltage limit and less than or equal to the upper voltage limit, sending DC power Pdc to the power converter 3 is selected. If the voltage of DC power Pdc is less than the lower voltage limit, sending DC power Pdc to the cooling / heating generator 5 is selected. Even when the voltage of the DC power Pdc is higher than the upper limit voltage, the operation of sending DC power Pdc to the cooling / heating generator 5 is selected.

[0023] The microgrid 1A includes an AC power system 11 for AC power Pac. The AC power system 11 includes a power converter 3, an AC power storage device 71, and a refrigeration device 4.

[0024] The power converter 3 receives DC power Pdc from the renewable energy power generation device 2 via power line L3. The power converter 3 converts the received DC power Pdc into AC power Pac. In other words, the power converter 3 is a so-called power conditioner. The power converter 3 is connected to the refrigeration device 4 via power line L4 (second power line). The power converter 3 sends AC power Pac to the refrigeration device 4 via power line L4. The power converter 3 is connected to the AC power storage device 71 via power lines L4 and L71. The power converter 3 sends AC power Pac to the AC power storage device 71 via power lines L4 and L71. As an example, the capacity of the power converter 3 is 250 kW. In contrast, the capacity of the renewable energy power generation device 2 is 300 kW. In other words, the capacity of the power converter 3 is smaller than the capacity of the renewable energy power generation device 2.

[0025] The power converter 3 may or may not be able to perform power conversion depending on the form of the DC power Pdc it receives. The power converter 3 does not perform power conversion if the voltage of the received DC power Pdc is lower than the lower limit voltage. In other words, when DC power Pdc with a voltage lower than the lower limit voltage is input, that DC power Pdc is discarded. This is known as undercutting. Similarly, the power converter 3 also does not perform power conversion if the voltage of the received DC power Pdc is higher than the upper limit voltage. In other words, when DC power Pdc with a voltage higher than the upper limit voltage is input, that DC power Pdc is discarded. This is known as peak cutting.

[0026] An example of an AC power demanding device, the refrigeration unit 4, operates using AC power Pac. The refrigeration unit 4 may be a vapor compression type (see Figure 2) equipped with a compressor 41, a condenser 42, an expander 43, and an evaporator 44. The refrigeration unit 4 absorbs heat inside the refrigeration unit 45 by supplying the refrigerant generated in the evaporator 44 to the refrigeration unit 45. AC power Pac is used to drive the compressor 41.

[0027] Furthermore, in addition to the main cooling system 40a including the compressor 41, the refrigeration unit 4 includes an auxiliary cooling system 40b that utilizes a low-temperature heat transfer medium ML provided by the cooling energy generator 5. By utilizing the low-temperature heat transfer medium ML, the AC power Pac required to obtain a predetermined low-temperature state can be reduced. In other words, the DC power Pdc that would have been wasted is used to generate the low-temperature heat transfer medium ML, which is then supplied to the refrigeration unit 4. The refrigeration unit 4, upon receiving the low-temperature heat transfer medium ML, can reduce the AC power Pac it was originally consuming. As a result, the energy efficiency of the microgrid 1A including the refrigeration unit 4 can be improved.

[0028] The AC power storage device 71 receives AC power Pac from the power converter 3 via power lines L4 and L71. The permission and cessation of power transmission to the AC power storage device 71 may be controlled by a switch device H71. The AC power storage device 71 can supply the power stored in the AC power storage device 71 as AC power Pac to the refrigeration device 4. The AC power storage device 71 is a so-called battery. For example, the capacity of the battery may be 50 kWh.

[0029] The microgrid 1A includes a DC system 12 for DC power Pdc. The DC system 12 includes a cooling / heating generator 5 and a DC power storage device 72.

[0030] The cooling device 5 can receive DC power Pdc from the renewable energy power generation device 2 via the power line L5. Furthermore, the cooling device 5 can receive a heat transfer medium MW from the inlet 5a. An example of the heat transfer medium MW may be water. The cooling device 5 operates using DC power Pdc. Specifically, the cooling device 5 has a Peltier element 51, to which DC power Pdc is supplied. The Peltier element 51, upon receiving DC power Pdc, heats the received heat transfer medium MW and absorbs heat from the heat transfer medium MW. As a result, a high-temperature heat transfer medium MH and a low-temperature heat transfer medium ML can be generated. An example of the high-temperature heat transfer medium MH may be hot water. The cooling device 5 provides the high-temperature heat transfer medium MH to the heat transfer medium utilization device 83. The cooling device 5 provides the low-temperature heat transfer medium ML to the refrigeration device 4.

[0031] Figure 2 shows the detailed configuration of the cooling / heating device 5. The cooling / heating device 5 includes a Peltier element 51, a heat-dissipating temperature sensor 52, and a heat-absorbing temperature sensor 53. The Peltier element 51 includes a heat-dissipating surface 51a (heat-dissipating part) and a heat-absorbing surface 51b (heat-absorbing part). The Peltier element 51 releases a predetermined amount of heat from the heat-dissipating surface 51a according to the voltage value of the DC power Pdc. A temperature sensor 52 is provided on the heat-dissipating surface 51a, and the acquired temperature data D52 is provided to the controller 6. A heat-dissipating heat exchange section 54 is located on the heat-dissipating surface 51a. A heat transfer medium MW (water) flows through the heat-dissipating heat exchange section 54. The heat transfer medium MW receives heat from the heat-dissipating surface 51a, and its temperature rises.

[0032] Furthermore, the Peltier element 51 absorbs a predetermined amount of heat from the heat-absorbing surface 51b according to the voltage value of the DC power Pdc. A temperature sensor 53 is also provided on the heat-absorbing surface 51b, and the acquired temperature data D53 is provided to the controller 6. A heat-absorbing side heat exchange section 55 is located on the heat-absorbing surface 51b. A heat transfer medium MW flows through the heat-absorbing side heat exchange section 55 as well. The heat transfer medium MW loses heat from the heat-absorbing surface 51b, so its temperature decreases.

[0033] The cooling and heating device 5 includes a heat transfer medium outlet 5b from which high-temperature heat transfer medium MH flows out, and a refrigerant outlet 5c from which low-temperature heat transfer medium ML flows out. The heat transfer medium outlet 5b is connected to the heat transfer medium utilization device 83. The refrigerant outlet 5c is connected to the refrigeration device 4.

[0034] The DC power storage device 72 receives DC power Pdc from the renewable energy power generation device 2 via power lines L5 and L72. An example of the DC power storage device 72 is a capacitor. The DC power storage device 72 can supply DC power Pdc to the cooling / heating generator 5 as needed.

[0035] The microgrid 1A includes a heat transfer system 13 for a heat transfer medium. The heat transfer system 13 comprises a heat transfer medium supply device 81, a heat storage device 82, and a heat transfer medium utilization device 83.

[0036] The heat transfer medium supply device 81 provides the heat transfer medium MW to the cooling and heat generating device 5 via the piping E5. Furthermore, the heat transfer medium supply device 81 can receive the low-temperature heat transfer medium ML that flows out from the refrigeration device 4 via the piping E81a. Similarly, the heat transfer medium supply device 81 can receive the high-temperature heat transfer medium MH that flows out from the heat transfer medium utilization device 83 via the piping E81b. The heat transfer medium supply device 81 may be equipped with a tank for storing water, a pump for dispensing water, and the like.

[0037] The heat storage device 82 is connected to the refrigeration generator 5 via pipes E4 and E82. The heat storage device 82 can receive high-temperature heat transfer medium MH and low-temperature heat transfer medium ML from the refrigeration generator 5. The heat storage device 82 temporarily holds the received high-temperature heat transfer medium MH and low-temperature heat transfer medium ML. The heat storage device 82 can then provide the held high-temperature heat transfer medium MH to the heat transfer medium utilization device 83 as needed. Similarly, the heat storage device 82 can provide the held low-temperature heat transfer medium ML to the refrigeration device 4 as needed.

[0038] The heat transfer medium utilization device 83 is connected to the cooling and heat generation device 5 and the heat storage device 82 via piping E83. The heat transfer medium utilization device 83 can receive high-temperature heat transfer medium MH from the cooling and heat generation device 5 and the heat storage device 82. The heat transfer medium utilization device 83 may perform a desired function using the high-temperature heat transfer medium MH.

[0039] Controller 6 controls the destination of AC power Pac. This control is performed by providing a control signal C71 to a switch device H71 located on the power line L4. Controller 6 controls the destination of DC power Pdc. This control is performed by providing a control signal C72 to a switch device H72 located on the power line L5. Furthermore, Controller 6 controls the destination of high-temperature heat transfer medium MH and low-temperature heat transfer medium ML. These controls are performed by providing control signals C82 and C83 to valve devices H82 and H83. Controller 6 receives voltage data D23 from the voltage sensor 23. Furthermore, Controller 6 receives temperature data D52 and D53 from the temperature sensor 52. Using this data, Controller 6 generates the aforementioned control signals C71, C72, C82, and C83.

[0040] As shown in Figure 3, the controller 6 is a computer having at least a processor 6a and a memory 6b. The processor 6a implements several functional components shown in Figure 3 by executing a predetermined program P. The memory 6b holds information necessary for controlling the microgrid 1A, in addition to the predetermined program P. For example, the memory 6b holds a voltage threshold D23T and a temperature difference threshold D50T.

[0041] The controller 6 has the following functional components: a voltage data acquisition unit 61, a temperature data acquisition unit 62, a voltage determination unit 63, a temperature difference determination unit 64, and a control signal output unit 65. The voltage data acquisition unit 61 receives voltage data D23 from the voltage sensor 23. The voltage data acquisition unit 61 stores the received voltage data D23 in the memory 6b. The voltage data D23 stored in the memory 6b may be the data received by the voltage data acquisition unit 61 itself, or it may be data that has undergone predetermined calculation processing.

[0042] The temperature data acquisition unit 62 receives temperature data D52 and D53 from temperature sensors 52 and 53. The temperature data acquisition unit 62 stores the received temperature data D52 and D53 in memory 6b. The temperature data D52 and D53 stored in memory 6b may be the data received by the temperature data acquisition unit 62 itself, or they may have undergone predetermined calculation processing.

[0043] The voltage determination unit 63 determines whether the voltage data D23 stored in the memory 6b is a value that allows DC power Pdc to be sent to the cooling device 5. The voltage determination unit 63 reads the voltage data D23 and the voltage threshold D23T from the memory 6b. The voltage determination unit 63 determines whether the voltage data D23 is higher than the voltage threshold D23T. If the voltage data D23 is higher than the voltage threshold D23T, the voltage determination unit 63 stores a determination result in the memory 6b indicating that DC power Pdc will not be sent to the cooling device 5. If the voltage data D23 is lower than the voltage threshold D23T, the voltage determination unit 63 stores a result in the memory 6b indicating that DC power Pdc will be sent to the cooling device 5.

[0044] The temperature difference determination unit 64 determines whether the temperature difference indicated by the temperature data D52 and D53 stored in the memory 6b is a value that allows the DC power Pdc to be sent to the cooling and heating generator 5. The temperature difference determination unit 64 reads the temperature data D52 and D53 and the temperature difference threshold value D50T from the memory 6b. The temperature difference determination unit 64 obtains temperature difference data using the temperature data D52 and D53. Next, the temperature difference determination unit 64 determines whether the temperature difference data is higher than the temperature difference threshold value D50T. When the temperature difference data D50 is higher than the temperature difference threshold value D50T, the temperature difference determination unit 64 stores in the memory 6b a determination result indicating that the DC power Pdc is not sent to the cooling and heating generator 5. When the temperature difference data D50 is lower than the temperature difference threshold value D50T, the temperature difference determination unit 64 stores in the memory 6b a result indicating that the DC power Pdc is sent to the cooling and heating generator 5.

[0045] The control signal output unit 65 generates a control signal C72 using the determination result of the voltage determination unit 63 and the determination result of the temperature difference determination unit 64. When both the determination result of the voltage determination unit 63 and the determination result of the temperature difference determination unit 64 indicate that the DC power Pdc is to be sent to the cooling and heating generator 5, the control signal output unit 65 gives the switch device H72 a control signal C72 for causing the renewable energy power generation device 2 to supply the DC power Pdc to the cooling and heating generator 5. When at least one of the determination result of the voltage determination unit 63 and the determination result of the temperature difference determination unit 64 is a determination result indicating that the DC power Pdc is not sent to the cooling and heating generator 5, the control signal output unit 65 gives the switch device H72 a control signal C72 for causing the renewable energy power generation device 2 to supply the DC power Pdc to the DC power storage device 72.

[0046] Next, the operation of the microgrid executed by the controller 6 will be described while referring to the flowchart shown in FIG. 4.

[0047] First, the controller 6 obtains voltage data D23 from the voltage sensor 23 and obtains temperature data D52 and D53 from the temperature sensors 52 and 53 (S11). This operation is executed by the voltage data acquisition unit 61 and the temperature data acquisition unit 62. This operation may include obtaining data by the voltage data acquisition unit 61 and the temperature data acquisition unit 62 and storing the data in the memory 6b.

[0048] Next, the controller 6 determines whether the voltage data D23 is higher than the voltage threshold D23T (S12). This operation is executed by the voltage determination unit 63. When the voltage determination unit 63 determines that the voltage data D23 is higher than the voltage threshold D23T (S12: YES), the voltage determination unit 63 stores in the memory 6b a determination result indicating that the DC power Pdc is not sent to the thermoelectric generator 5. Then, based on the result, the control signal output unit 65 provides a control signal C72 for causing the DC power storage device 72 to be supplied with the DC power Pdc from the renewable energy power generation device 2 to the switch device H72 (S13).

[0049] When the voltage determination unit 63 determines that the voltage data D23 is lower than the voltage threshold D23T (S12: NO), the voltage determination unit 63 stores in the memory 6b a determination result indicating that the DC power Pdc is sent to the thermoelectric generator 5. Next, the controller 6 determines whether the temperature difference data is higher than the temperature difference threshold D50T (S14). This operation is executed by the temperature difference determination unit 64.

[0050] If the temperature difference determination unit 64 determines that the temperature difference data D50 is higher than the temperature difference threshold D50T (S14: NO), it stores a determination result in memory 6b indicating that DC power Pdc will not be sent to the cooling / heating generator 5. Then, the control signal output unit 65 provides a control signal C72 to the switch device H72 to supply DC power Pdc from the renewable energy power generation device 2 to the DC power storage device 72 based on this result (S15). If the temperature difference determination unit 64 determines that the temperature difference data D50 is lower than the temperature difference threshold D50T (S14: YES), it stores a determination result in memory 6b indicating that DC power Pdc will be sent to the cooling / heating generator 5. Then, the control signal output unit 65 provides a control signal C72 to the switch device H72 to supply DC power Pdc from the renewable energy power generation device 2 to the cooling / heating generator 5 based on this result (S16).

[0051] The controller 6 repeats the above steps S11 to S16 at predetermined intervals.

[0052] <Effects> The microgrid 1A comprises a renewable energy power generation device 2 that generates DC power Pdc using renewable energy, a power conversion device 3 that converts the DC power Pdc received from the renewable energy power generation device 2 into AC power Pac, and a cooling device 5 that performs an endothermic operation to remove heat from a heat-absorbing object using the DC power Pdc received from the renewable energy power generation device 2. According to this microgrid 1A, an endothermic operation is performed to remove heat from a heat-absorbing object using a portion of the DC power Pdc generated by the renewable energy power generation device 2 that was not converted into AC power Pac. As a result, a low-temperature heat transfer medium ML, which is a heat transfer medium whose temperature has been lowered by the endothermic operation, can be obtained. Therefore, the energy utilization efficiency of the microgrid 1A can be improved in order to effectively utilize the DC power Pdc that would otherwise be wasted.

[0053] Figure 5 shows the daily variation in the electricity generated by the renewable energy power generation device 2. The horizontal axis represents time, and the vertical axis represents the electricity generated by the renewable energy power generation device 2. The renewable energy power generation device 2 generates electricity by receiving sunlight from sunrise t1 to sunset t2. On the other hand, the renewable energy power generation device 2 generates almost no electricity before sunrise t1 or after sunset t2. As a result, the electricity generated before sunrise t1 and after sunset t2 (regions A1 and A2) has a voltage lower than the lower limit voltage. Therefore, during this period, the cooling device 5 is supplied with DC power Pdc. The electricity generated from sunrise t1 to sunset t2 (region A3) has a voltage above the lower limit, so during this period, the cooling device 5 is supplied with AC power Pac. Note that the electricity generated from sunrise t1 to sunset t2 may have a voltage that exceeds the upper limit voltage. In this case, any excess power (region A4) exceeding the capacity of the power converter 3 is stored in the DC power storage device 72. As a result, the electricity generated by the renewable energy power generator 2 is not wasted, thus improving the energy utilization efficiency in the microgrid 1A.

[0054] The microgrid 1A includes a DC power storage device 72 that stores DC power Pdc received from the renewable energy power generation device 2. When the DC voltage defining the DC power Pdc is above a threshold, the cooling device 5 is not supplied with DC power Pdc and does not perform heat absorption operation. Instead, the DC power Pdc is supplied to the DC power storage device 72 and the DC power storage device 72 stores DC power. This operation allows for heat absorption operation based on DC power Pdc to be performed under efficient conditions.

[0055] The microgrid 1A further includes a DC power storage device 72 that stores DC power Pdc received from the renewable energy power generation device 2. The cooling / heating generator 5 includes a heat-absorbing surface 51b that performs a heat absorption operation by removing heat from a heat absorption target using DC power Pdc received from the renewable energy power generation device 2, and a heat-dissipating surface 51a that performs a heating operation by supplying heat to a heating target using DC power Pdc received from the renewable energy power generation device 2. When the temperature difference between the heat-absorbing surface 51b and the heat-dissipating surface 51a is greater than or equal to a threshold, DC power Pdc is not supplied to the cooling / heating generator 5 and the cooling / heating generator 5 does not perform a heat absorption operation, and DC power Pdc is supplied to the DC power storage device 72 and the DC power storage device 72 stores DC power Pdc. This operation also allows for the performance of a heat absorption operation based on DC power Pdc under efficient conditions.

[0056] The microgrid 1A includes power lines L3 and L5. The first power line L3 is connected to the renewable energy power generation device 2 and also to the power converter 3, and sends DC power Pdc from the renewable energy power generation device 2 to the power converter 3. The second power line L5 is connected to the renewable energy power generation device 2 and also to the cooling device 5, and sends DC power Pdc from the renewable energy power generation device 2 to the cooling device 5. With this configuration, the DC power Pdc generated by the renewable energy power generation device 2 can be supplied to the power converter 3 and the cooling device 5, respectively.

[0057] The microgrid 1A includes a refrigeration unit 4 that performs an endothermic operation using AC power Pac provided by the power converter 3. The refrigeration generator 5 provides the refrigeration unit 4 with the heat absorbed by the refrigeration generator 5. With this configuration, a portion of the energy required for the operation of the refrigeration unit 4 can be supplemented by the low-temperature heat transfer medium ML from which heat has been removed by the refrigeration generator 5. As a result, the energy utilization efficiency of the microgrid 1A can be further improved.

[0058] <Second Embodiment> The cooling and heat generation device 5, which is the thermal function unit of the first embodiment, operated using only DC power Pdc. The cooling and heat generation device 5 may be operable with both DC power Pdc and AC power Pac. The microgrid 1B of the second embodiment shown in Figure 6 is equipped with a cooling and heat generation device 9 that can operate with either DC power Pdc or AC power Pac. The microgrid 1B of the second embodiment differs from the microgrid 1A of the first embodiment in that a branched power line L9 leading to the cooling and heat generation device 9 is provided on the power line L4 connected to the output of the power converter 3. The cooling and heat generation device 9 that can operate with either DC power Pdc or AC power Pac will be described in detail below.

[0059] As shown in Figure 7, the cooling device 9 receives AC power Pac from the power converter 3 via the power line L9. Furthermore, the cooling device 9 may also receive AC power Pac from the power grid. The cooling device 9 can receive DC power Pdc via the power line L5. The cooling device 9 operates using either AC power Pac or DC power Pdc. Specifically, the cooling device 9 has a Peltier element module, to which either AC power Pac or DC power Pdc is supplied.

[0060] The cooling and heating device 5 includes a power consumption unit 9C and a power supply unit 9S. Furthermore, the power supply unit 9S includes an AC power supply unit 91, a DC power supply unit 92, and an additional switching circuit unit 93. These are electrical circuits composed of electrical components such as resistive elements and switching elements.

[0061] The power consumption unit 9C, which is supplied with power, performs the desired function by consuming the supplied power.

[0062] The power consumption unit 9C has multiple Peltier element modules 9M1, 9M2, and 9M3. The multiple Peltier element modules 9M1, 9M2, and 9M3 are connected in parallel to each other. Each Peltier element module 9M1, 9M2, and 9M3 contains three Peltier elements 9R1, 9R2, and 9R3. The connection configuration of the three Peltier elements 9R1, 9R2, and 9R3 that make up the Peltier element modules 9M1, 9M2, and 9M3 does not change when AC power Pac is applied and when DC power Pdc is applied.

[0063] The AC power supply unit 91 switches between a configuration in which the power converter 3 and the AC power storage device 71 are connected to the power consumption unit 9C, and a configuration in which the power consumption unit 9C is disconnected from the power converter 3 and the AC power storage device 71. The AC power supply unit 91 includes a switch element T91. The switch element T91 switches between conducting and disconnecting in response to a control signal C91 provided by the controller 6. When the switch element T91 is conducting, the power converter 3 and the AC power storage device 71 are connected to the power consumption unit 9C. When the switch element T91 is disconnected, the power converter 3 and the AC power storage device 71 are disconnected from the power consumption unit 9C.

[0064] The DC power supply unit 92, via the additional switching circuit unit 93, switches between a configuration that connects the renewable energy power generation device 2 to the power consumption unit 9C and a configuration that disconnects the power consumption unit 9C from the renewable energy power generation device 2. The DC power supply unit 92 includes a switch element T92. The switch element T92 switches between conducting and disconnecting in response to a control signal C92 provided by the controller 6. When the switch element T92 is conducting, the renewable energy power generation device 2 is connected to the power consumption unit 9C. When the switch element T92 is disconnected, the renewable energy power generation device 2 is disconnected from the power consumption unit 9C.

[0065] The additional switching circuit section 93 switches between the circuit configuration of the cooling and heat generating device 9 when it receives AC power Pac (see Figure 8(a)) and the circuit configuration of the cooling and heat generating device 9 when it receives DC power Pdc (see Figure 8(b)). As mentioned above, the connection configuration of the first Peltier element 9R1, the second Peltier element 9R2, and the third Peltier element 9R3, which will be described later, remains the same for the power consumption section 9C when it receives AC power Pac and when it receives DC power Pdc. By switching the additional switching circuit section 93 to the AC circuit configuration 93ac for the power consumption section 9C, a circuit configuration of the cooling and heat generating device 9 that realizes the desired operation with AC power Pac is formed. Similarly, by switching the additional switching circuit section 93 to the DC circuit configuration 93dc for the power consumption section 9C, a circuit configuration of the cooling and heat generating device 9 that realizes the desired operation with DC power Pdc is formed.

[0066] Referring to Figure 8(a), the circuit configuration of the cooling / heating device 9 when receiving AC power Pac will be explained. First, the power consumption unit 9C includes three first Peltier elements 9R1, a second Peltier element 9R2, and a third Peltier element 9R3. The first Peltier element 9R1 is connected to the U-phase terminal 9P1 and the V-phase terminal 9P2. The second Peltier element 9R2 is connected to the V-phase terminal 9P2 and the W-phase terminal 9P3. The third Peltier element 9R3 is connected to the W-phase terminal 9P3 and the U-phase terminal 9P1. At first glance, the three first Peltier elements 9R1, the second Peltier element 9R2, and the third Peltier element 9R3 appear to be in a so-called delta connection. The circuit configuration of the power consumption unit 9C shown in Figure 8(a) is referred to as the common consumption circuit unit 9CR.

[0067] Now let's focus on the W-phase terminal 9P3. The W-phase terminal 9P3 includes a second W-phase terminal section 9P32 connected to the second Peltier element 9R2, and a third W-phase terminal section 9P33 connected to the third Peltier element 9R3. When viewed as a standalone power consumption unit 9C, the second W-phase terminal section 9P32 and the third W-phase terminal section 9P33 are not electrically connected.

[0068] The second W-phase terminal 9P32 is connected to power line L922, and the third W-phase terminal 9P33 is connected to power line L923. An additional switching circuit 93 is provided on these power lines L922 and L923. The additional switching circuit 93 has a switch element T931 provided between power lines L922 and L923. When receiving AC power Pac, the circuit configuration of the cooling / heating generator 9 is a so-called delta connection. Therefore, the additional switching circuit 93 makes the switch element T931 conductive. As a result, the second W-phase terminal 9P32 and the third W-phase terminal 9P33 become conductive. Consequently, the three Peltier elements 9R1, 9R2, and 9R3 form a delta connection. Looking at the power consumption unit 9C as a whole, as shown in Figure 9, the respective Peltier element modules 9M1, 9M2, and 9M3, which are in a delta connection, are connected in parallel to each other.

[0069] The AC power supply unit 91 includes a U-phase switch element T911 connected to the U-phase terminal 9P1, a V-phase switch element T912 connected to the V-phase terminal 9P2, and a W-phase switch element T913 connected to the second W-phase terminal 9P32 of the W-phase terminal 9P3. When receiving AC power Pac, the U-phase switch element T911, the V-phase switch element T912, and the W-phase switch element T913 are all made conductive.

[0070] The DC power supply unit 92 includes a second W-phase switch element T922 connected to the second W-phase terminal 9P32 and a third W-phase switch element T923 connected to the third W-phase terminal 9P33. When AC power Pac is received, both the second W-phase switch element T922 and the third W-phase switch element T923 are disconnected.

[0071] Next, with reference to Figure 8(b), the circuit configuration of the cooling / heating device 9 when receiving DC power Pdc will be explained. When receiving AC power Pac, the three Peltier elements 9R1, 9R2, and 9R3 of the power consumption unit 9C were in a delta connection. On the other hand, when receiving DC power Pdc, the three Peltier elements 9R1, 9R2, and 9R3 of the power consumption unit 9C are in a series connection.

[0072] When the AC power supply unit 91 receives DC power Pdc, the U-phase switch element T911, the V-phase switch element T912, and the W-phase switch element T913 are all disconnected. When the DC power supply unit 92 receives DC power Pdc, the second W-phase switch element T922 and the third W-phase switch element T923 are made conductive. The additional switching circuit unit 93 disconnects switch element T931.

[0073] As a result, as shown in Figure 8(b), a series circuit is formed that passes through the power line L922, the second W-phase terminal 9P32, the second Peltier element 9R2, the first Peltier element 9R1, the third Peltier element 9R3, the third W-phase terminal 9P33, and the power line L923 in this order.

[0074] Looking at the power consumption unit 9C as a whole, as shown in Figure 10, the Peltier element modules 9M1, 9M2, and 9M3, which are connected in series, are connected in parallel to each other.

[0075] According to the connection configuration shown in Figures 9 and 10, the voltage and current acting on a single Peltier element can be made equivalent, regardless of whether the input power is AC or DC.

[0076] The controller 6 controls the operation of the renewable energy power generation device 2, the power converter 3, the AC power storage device 71, and the cooling / heating device 9. As already mentioned, the controller 6 may provide a control signal C9 to the renewable energy power generation device 2 to determine whether to provide the DC power Pdc generated to the power converter 3 or to the DC power storage device 72. The controller 6 may also provide control signals C91 and C92 to the cooling / heating device 9 to switch between a circuit configuration for receiving AC power Pac and a circuit configuration for receiving DC power Pdc. Furthermore, the controller 6 may obtain voltage data D23 related to the DC power Pdc generated by the renewable energy power generation device 2 from the renewable energy power generation device 2 in order to generate these control signals C9, C91, and C92.

[0077] <How the microgrid operates> The operation method of the microgrid 1B of the second embodiment will be explained with reference to the flowchart shown in Figure 11. The operation method of the microgrid 1B may be performed by the controller 6, for example. First, the controller 6 obtains voltage data D23 related to the DC power Pdc generated by the renewable energy power generation device 2 (S21). Next, the controller 6 obtains the generated voltage from the voltage data D23 related to the DC power Pdc and determines whether or not it is above the lower limit voltage (S22). If the generated voltage is not above the lower limit voltage (S22: NO), the controller 6 performs DC operation (S23). When performing DC operation (S23), the controller 6 outputs a control signal C9 that causes the renewable energy power generation device 2 to output DC power Pdc to the DC power storage device 72. Furthermore, the controller 6 outputs a control signal C9 to configure the circuit to operate the cooling / heating device 9 with DC power Pdc (see Figure 8(b)).

[0078] On the other hand, if the generated voltage is above the lower limit voltage (S22: YES), the controller 6 then determines whether the generated voltage is below the upper limit voltage (S24). If the generated voltage is below the upper limit voltage (S24: YES), the controller 6 performs AC operation (S25). Specifically, when performing AC operation (S25), the controller 6 outputs a control signal C9 that causes the renewable energy power generation device 2 to output DC power Pdc to the power conversion device 3. Furthermore, the controller 6 outputs a control signal C9 to configure the circuit to operate the cooling / heating device 9 with AC power Pac (see Figure 8(a)).

[0079] If the generated voltage is not below the upper limit voltage (S24: NO), the controller 6 performs DC operation (S26). When in DC operation (S26), the controller 6 outputs a control signal C9 that causes the renewable energy power generation device 2 to output DC power Pdc to the DC power storage device 72. Furthermore, the controller 6 outputs a control signal C9 to configure the circuit to operate the cooling / heating device 9 with DC power Pdc (see Figure 8(b)).

[0080] The controller 6 repeats the above steps S21 to S26 at predetermined intervals.

[0081] <Modifications> The microgrids illustrated in this disclosure are not limited to the embodiments described above, and can be modified in various ways without departing from the spirit of the invention.

[0082] In this embodiment, a Peltier element is used as an example of a thermal function unit. However, the specific example of a thermal function unit is not limited to a Peltier element, as long as it is capable of performing a heat absorption operation using DC power. For example, it could be an air cooling device such as an air cooling fan or blower equipped with a motor driven by DC power. Alternatively, the specific example of a thermal function unit could be an absorption chiller or an air conditioner.

[0083] Figure 13 shows an example of a microgrid 1D employing an absorption chiller 5D as the thermal function unit. The absorption chiller 5D has a thermal cycle consisting of an evaporator 59a, an absorber 59b, a regenerator 59c, and a condenser 59d. As the heat transfer medium moves through this thermal cycle and undergoes a phase change, heat absorption from the heat transfer medium can be produced. An example of the heat transfer medium may be a mixture of water and an absorbent. In the regenerator 59c of this cycle, the heat transfer medium is heated by a heater 59h. The microgrid 1D uses DC power Pdc output from the renewable energy power generation device 2 as the energy source for this heater 59h. This microgrid 1D can also generate cooling by utilizing DC power Pdc, which was not previously utilized. As a result, the energy efficiency of the microgrid 1D can be increased.

[0084] The microgrid of the embodiment included a device for storing electricity and a device for storing a heat transfer medium. The microgrid only needs to include at least a renewable energy power generation device 2 which is a power generation unit, a power conversion device 3, and a cooling / heat generation device 5 which is a thermal function unit. In other words, the device for storing electricity and the device for storing a heat transfer medium may be included as needed, and as shown in Figure 12, the microgrid 1C can also have a simplified configuration in which the device for storing electricity and the device for storing a heat transfer medium are omitted.

[0085] In this embodiment, DC voltage and the temperature difference of the Peltier element 51 are exemplified as parameters for determining whether or not to supply DC power to the cooling / heating generator 5 to operate it. Other conditions may be used to determine whether or not to operate it. As shown in Figure 14, weather information at the location where the solar power generation panels 21 are arranged may be used to determine whether or not to operate the cooling / heating generator 5. The controller 6D of the microgrid 1E includes a weather information acquisition unit 66 and a weather information determination unit 67. The weather information acquisition unit 66 acquires weather information from outside the microgrid 1E via wired or wireless communication means. The controller 6D then uses the weather information determination unit 67 to determine whether or not to operate the cooling / heating generator 5.

[0086] For example, the weather information determination unit 67 stores in memory 6b a determination result indicating that DC power Pdc will not be sent to the cooling device 5 if the weather information D66 is "cloud cover above a certain level or solar radiation below a certain level". The weather information determination unit 67 also stores in memory 6b a result indicating that DC power Pdc will be sent to the cooling device 5 if the weather information D66 is "cloud cover above a certain level or solar radiation below a certain level".

[0087] In short, the microgrid 1E includes a weather information determination unit 67 (information acquisition unit) that receives weather information for the location where the renewable energy power generation device 2 is installed. The controller 6D, which includes the weather information determination unit 67, determines, based on the weather information D66, whether or not to supply DC power Pdc to the cooling device 5 to perform its heat absorption operation. This operation also allows the heat absorption operation based on DC power Pdc to be performed under efficient conditions.

[0088] <Note> This disclosure includes the following components.

[0089] This disclosure [1] is a microgrid comprising: a power generation unit that generates DC power using renewable energy; a power conversion unit that converts the DC power received from the power generation unit into AC power; and a thermal function unit that performs a heat absorption operation that removes heat from a heat absorption target using the DC power received from the power generation unit.

[0090] The present disclosure [2] is "a microgrid according to [1] above, further comprising a DC power utilization unit that performs a utilization operation for consuming or storing the DC power received from the power generation unit, wherein when the DC voltage defining the DC power is equal to or greater than a threshold, the DC power is not supplied to the thermal function unit and the thermal function unit does not perform the heat absorption operation, and the DC power is supplied to the DC power utilization unit and the DC power utilization unit performs the utilization operation."

[0091] The present disclosure [3] is "a microgrid according to [1] or [2] above, further comprising a DC power utilization unit that performs a utilization operation for consuming or storing the DC power received from the power generation unit, wherein the thermal function unit includes a heat absorption unit that performs a heat absorption operation for removing heat from a heat absorption target using the DC power received from the power generation unit, and a heat dissipation unit that performs a heating operation for supplying heat to a heating target using the DC power received from the power generation unit, wherein when the temperature difference between the heat absorption unit and the heat dissipation unit is greater than or equal to a threshold, the DC power is not supplied to the thermal function unit and the thermal function unit does not perform the heat absorption operation, and the DC power is supplied to the DC power utilization unit and the DC power utilization unit performs the utilization operation."

[0092] This disclosure [4] is "a microgrid according to any one of the above [1] to [3], further comprising an information acquisition unit that receives weather information at the location where the power generation unit is installed, and which determines whether or not the DC power is supplied to the thermal function unit to perform the heat absorption operation of the thermal function unit based on the weather information."

[0093] The present disclosure [5] is "a microgrid according to any one of the above [1] to [4], further comprising: a first power line connected to the power generation unit and the power conversion unit, which transmits the DC power from the power generation unit to the power conversion unit; and a second power line connected to the power generation unit and the thermal function unit, which transmits the DC power from the power generation unit to the thermal function unit."

[0094] This disclosure [6] is "a microgrid according to any one of the above [1] to [5], further comprising an AC power utilization unit that performs a heat absorption operation using the AC power provided from the power conversion unit, wherein the thermal function unit provides the heat absorption target from which heat has been removed in the thermal function unit to the AC power utilization unit."

[0095] This disclosure [7] states that "the power generation unit is a microgrid according to any one of the above items [1] to [6], including a photovoltaic power generation device."

[0096] This disclosure [8] states that "the thermal function unit is a microgrid according to any one of [1] to [7] above, including a Peltier element."

[0097] [Other] The microgrid described in this disclosure enables improved efficiency in the use of energy generated by the microgrid. The microgrid described in this disclosure contributes to United Nations Sustainable Development Goal (SDG) 7, "Ensure access to affordable, reliable, sustainable and modern energy."

[0098] 1A, 1C, 1D, 1E Microgrid 2 Renewable energy power generation device (power generation unit) 3 Power conversion device (power conversion unit) 5 Cooling and heating device (thermal function unit) 5D Absorption chiller (thermal function unit) 9R1, 9R2, 51 Peltier element 51a Heat dissipation surface (heat dissipation unit) 51b Heat absorption surface (heat absorption unit) 67 Weather information determination unit (information acquisition unit) 71 AC power storage device (AC power utilization unit) 72 DC power storage device (DC power utilization unit) D66 Weather information L3 Power line (first power line) L4 Power line (second power line) Pac AC power Pdc DC power ML Low temperature heat transfer medium MH High temperature heat transfer medium MW Heat transfer medium

Claims

1. A microgrid comprising: a power generation unit that generates DC power using renewable energy; a power conversion unit that converts the DC power received from the power generation unit into AC power; and a thermal function unit that performs a heat absorption operation that removes heat from a heat absorption target using the DC power received from the power generation unit.

2. The microgrid according to claim 1, further comprising a DC power utilization unit that performs a utilization operation for consuming or storing the DC power received from the power generation unit, wherein when the DC voltage defining the DC power is above a threshold, the DC power is not supplied to the thermal function unit and the thermal function unit does not perform the heat absorption operation, and the DC power is supplied to the DC power utilization unit and the DC power utilization unit performs the utilization operation.

3. The microgrid according to claim 1, further comprising a DC power utilization unit that performs a utilization operation for consuming or storing the DC power received from the power generation unit, wherein the thermal function unit includes a heat absorption unit that performs a heat absorption operation to remove heat from a heat absorption target using the DC power received from the power generation unit, and a heat dissipation unit that performs a heating operation to transfer heat to a heating target using the DC power received from the power generation unit, wherein when the temperature difference between the heat absorption unit and the heat dissipation unit is greater than or equal to a threshold, the thermal function unit is not supplied with DC power and the thermal function unit does not perform the heat absorption operation, and the DC power utilization unit is supplied with DC power and the DC power utilization unit performs the utilization operation.

4. The microgrid according to claim 1, further comprising an information acquisition unit that receives weather information for the location where the power generation unit is installed, and which determines whether or not to supply the DC power to the thermal function unit to perform the heat absorption operation of the thermal function unit based on the weather information.

5. The microgrid according to claim 1, further comprising: a first power line connected to the power generation unit and the power conversion unit, which transmits the DC power from the power generation unit to the power conversion unit; and a second power line connected to the power generation unit and the thermal function unit, which transmits the DC power from the power generation unit to the thermal function unit.

6. The microgrid according to claim 1, further comprising an AC power utilization unit that performs a heat absorption operation using the AC power provided from the power conversion unit, wherein the thermal function unit provides the heat absorption target from which heat has been removed in the thermal function unit to the AC power utilization unit.

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

8. The microgrid according to claim 1, wherein the thermal function section includes a Peltier element.

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