Microgrid system

Abstract

To provide a microgrid system with excellent responsiveness and robustness at a low cost. [Solution] This microgrid system 10 comprises a DC power generator 12 utilizing renewable energy, an AC power generator 13, a battery storage device 14, a power regulator 18, and a control device 19. The three input / output ports provided in the power regulator 18 are connected to the DC power generator 12 and the AC power generator 13 via the DC grid 15, to the battery storage device 14, and to the power load 11, respectively. While the power regulator 18 is operating at least with current control by the control device 19, the first voltage value V1, which is the voltage supplied from the DC power generator 12 to the DC grid 15, is set higher than the second voltage value V2, which is the voltage supplied from the AC power generator 13 to the DC grid 15.

Description

Technical Field

[0001] The present invention relates to a microgrid system.

Background Art

[0002] In recent years, a microgrid system in which power generation facilities using renewable energy such as solar cells and wind power generation, storage batteries for storing power, and power loads are interconnected via a DC distribution network (DC grid) has attracted attention as a distributed power system with a small environmental load from the perspective of self-sufficiency.

[0003] In this type of power supply system, a plurality of power generation facilities with different power generation characteristics and a storage battery are connected to a DC grid and used to supply power to a power load, and since the above plurality of power facilities can be used for charging the storage battery, in order to efficiently use power in the system, it is important how to adjust the power from each power generation facility and storage battery and supply it to the power load.

[0004] For example, in Patent Document 1, overall monitoring is performed on power converters (converter circuits, inverter circuits) provided in each power source (power generation facility) and storage battery by dedicated communication of a control device, and by transmitting individual commands to each power converter, a microgrid system has been proposed that enables control of the power generation amount of each power source and the supply amount to the power load.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In this type of power supply and demand system, it is necessary to stably and efficiently meet the power supply and demand with limited resources (power generation equipment and storage batteries). Therefore, it is desirable to simplify the structure for controlling the output of power generation equipment and storage batteries in the aforementioned system as much as possible. In this regard, if a centralized control system is used, for example, as in Patent Document 1, the amount of computation required by the control device will inevitably increase, making control delays likely. Furthermore, centralized control also presents problems in terms of robustness. In addition, for this type of system to become widespread, it is essential that the system can be built at low cost and that running costs can be kept low.

[0007] In light of the above circumstances, this specification aims to provide a microgrid system with excellent responsiveness and robustness at a low cost. [Means for solving the problem]

[0008] The aforementioned problems are solved by the microgrid system according to the present invention. Specifically, this system comprises a DC power generator utilizing renewable energy, an AC power generator, a battery storage device, a power adjustment device for adjusting the power input from any of the devices and outputting it to a power load, and a control device for controlling the operation of the power adjustment device. The first input / output port of the power adjustment device is connected to the DC power generator and the AC power generator via the DC grid, the second input / output port is connected to the battery storage device, and the third input / output port is connected to the power load. The control device controls the operation of the power adjustment device based on the voltage state of the DC grid and the charge state of the battery storage device. Furthermore, when the charge rate of the battery storage device is below an upper limit threshold for the charge rate, the power adjustment device is set to current control, and while the power adjustment device is operating at least in current control mode, the first voltage value V1, which is the voltage supplied from the DC power generator to the DC grid, is set higher than the second voltage value V2, which is the voltage supplied from the AC power generator to the DC grid.

[0009] Thus, in the microgrid system according to the present invention, a power adjustment device for making final adjustments to the power supplied to the power load is directly controlled, and this power adjustment device is provided with three input / output ports, to which a DC power generator and an AC power generator are connected via a DC grid, a power storage device is connected, and a power load is connected. In this configuration, the operation of the power adjustment device can be controlled based on the voltage state of the DC grid and the charge state of the power storage device. By creating a structure in which the power within the microgrid system can be controlled in this way, the structure for power control can be simplified. Therefore, it becomes possible to construct a microgrid system with excellent responsiveness and robustness.

[0010] Furthermore, in the microgrid system according to the present invention, while the power regulator is operating at least in current control mode, the first voltage value V1, which is the voltage supplied from the DC power generator to the DC grid, is set higher than the second voltage value V2, which is the voltage supplied from the AC power generator to the DC grid. In order to popularize this type of grid system, it is essential to keep not only the initial cost of constructing the system but also the running costs low. In this regard, the microgrid system according to the present invention allows for the preferential use of power generation equipment (DC power generators) that are more energy-efficient and emit less carbon dioxide, in other words, have a lower environmental impact, compared to existing commercial power generation equipment (AC power generators) such as thermal power plants. Therefore, when considering the capital investment required for measures to reduce the environmental impact, it is possible to provide a microgrid system that is superior in terms of both initial cost and running cost.

[0011] Furthermore, in the microgrid system according to the present invention, when the charge level of the energy storage device is above a lower limit threshold and below an upper limit threshold, and the voltage of the DC grid is equal to the first voltage value V1, the control device may switch between discharging and charging the energy storage device according to the difference between the power generated by the DC power generator and the power load.

[0012] When the voltage of the DC grid is equal to the first voltage value V1, which is the output adjustment value of the DC generator, it means that the DC generator is generating more than the required amount of power. Therefore, by switching between discharging and charging the energy storage device according to the difference between the power generated by the DC generator and the power load, a sufficient amount of power can be supplied to the power load by the DC generator alone, or by both the DC generator and the energy storage device if necessary. Furthermore, if the DC generator alone is generating a sufficient amount of power for the power load, the surplus power can be supplied for charging the energy storage device. Of course, this power supply and demand control can be executed in a very short time by combining a highly responsive 3-port power regulator and its control device, making it possible to stably implement efficient supply and demand control.

[0013] Furthermore, in the microgrid system according to the present invention, if the voltage of the DC grid is lower than the first voltage value V1, the control device may control the operation of the power regulator so that only the power discharged from the energy storage device is supplied to the power load.

[0014] When the DC grid voltage is lower than the first voltage value V1, it means that the amount of power generated by the DC generator is not reaching the required amount. In this case, by controlling the operation of the power regulator to supply only the power discharged from the energy storage device, or the sum of the power discharged from the energy storage device and the power generated by the DC generator, it is possible to supply the required amount of power to the power load without receiving power from the AC generator via the DC grid. Therefore, it is possible to stably supply inexpensive electricity to the power load while minimizing the effects of weather and other factors.

[0015] Furthermore, in the microgrid system according to the present invention, if the charge level of the energy storage device is below a lower threshold and the voltage of the DC grid is equal to the first voltage value V1, the control device may control the operation of the power adjustment device so as to supply the power generated by the DC power generator to the power load, and if there is a surplus of power generated by the DC power generator relative to the required power load, charge the energy storage device with all of the surplus.

[0016] A state where the charge level of the energy storage device falls below the lower threshold means that the discharge from the energy storage device should be stopped or suppressed as much as possible in preparation for unforeseen circumstances. Therefore, if there is a surplus of power generated by the DC power generator relative to the required power load, controlling the system to charge the energy storage device with all of that surplus makes it possible to maximize the charge of the energy storage device while maintaining a minimum power supply to the power load. This makes it possible to avoid situations where the energy storage device experiences a power shortage as much as possible, and further enhances the stability of the system.

[0017] Furthermore, in the microgrid system according to the present invention, when the voltage of the DC grid is equal to the second voltage value V2, the control device may control the operation of the power adjustment device so as to charge the energy storage device while supplying the power generated by the AC power generator to the power load.

[0018] Thus, when the charge level of the energy storage device is below the lower threshold and the DC grid voltage is equal to the second voltage value V2, it means that both the amount of charge in the energy storage device and the amount of power generated by the DC generator are insufficient. Therefore, in such a state, by controlling the power regulator to charge the energy storage device while supplying power generated by the AC generator to the power load, it is possible to avoid a situation where the power supply to the power load is insufficient and to stably supply the required amount of power. In addition, by charging the energy storage device at the same time as supplying power to the power load, the energy storage device can be quickly restored to a state where it has stored a certain amount of power or more, so that the entire grid system can be quickly restored to a stable state.

[0019] Furthermore, in the microgrid system according to the present invention, the control device may, when the charge level of the energy storage device is higher than the upper limit threshold, set the power adjustment device as voltage control to set the third voltage value V3, which is the DC grid voltage, higher than the first voltage value V1.

[0020] By controlling the voltage of the DC grid to a predetermined value in this way, it becomes possible to prevent the output of power from not only the AC power generation device but also the DC power generation device, and to supply the power load only with the power stored in the power storage device. A state where the charging rate of the power storage device is higher than the upper threshold value is presumed to be an overcharged state or a state close thereto for the power storage device. Therefore, by preferentially consuming the power stored in the power storage device (supplying it to the power load), it is possible to return the power storage device to a stable state with less burden while satisfying the required power supply and demand. This can contribute to the extension of the life of this grid system.

Advantages of the Invention

[0021] As described above, according to the present invention, it becomes possible to provide a microgrid system excellent in responsiveness and robustness. Further, by suppressing the initial cost and running cost of this microgrid system to a low level, it becomes possible to promote the spread of this grid system.

Brief Description of the Drawings

[0022] [Figure 1] It is a diagram showing the overall configuration of a microgrid system according to an embodiment of the present invention. [Figure 2] It is a diagram showing an example of the circuit configuration of the power conditioner shown in FIG. 1. [Figure 3] It is a diagram showing an example of the circuit configuration of the control device shown in FIG. 1. [Figure 4] It is a flowchart showing the flow of power control in the microgrid system shown in FIG. 1. [Figure 5] It is a continuation of the flowchart shown in FIG. 4. [Figure 6] It is a graph showing the relationship between the voltage of the DC grid shown in FIG. 1 and the switching between voltage control and current control. [Figure 7] It is a diagram showing a modified example of the circuit configuration of the power conditioner shown in FIG. 1. [Figure 8] It is a diagram showing a modified example of the circuit configuration of the power conditioner shown in FIG. 7. [Figure 9]This figure shows a modified example of the circuit configuration of the power regulator shown in Figure 7. [Modes for carrying out the invention]

[0023] The contents of a microgrid system according to one embodiment of the present invention will be described below with reference to the drawings.

[0024] Figure 1 shows the main components of a microgrid system 10 according to one embodiment of the present invention. As shown in Figure 1, this microgrid system 10 is a system capable of satisfying the power supply and demand between multiple power sources (power generators, energy storage devices) and a power load 11, and comprises a DC power generator 12 as a power source, an AC power generator 13 as a power source, an energy storage device 14, a DC grid 15, a first power regulator 16, a second power regulator 17, a third power regulator 18, and a control device 19. Of these, the third power regulator 18 corresponds to the power regulator according to the present invention. The details of each element and the relationships between each element will be described below.

[0025] The DC power generator 12 is a power generation device that utilizes renewable energy, and is equivalent to, for example, a solar power generation device. This DC power generator 12 is connected to the DC grid 15 via the first power adjustment device 16, thereby enabling the DC power generated by the DC power generator 12 to be supplied to the DC grid 15 after a predetermined adjustment has been made.

[0026] The first power regulator 16 is configured to adjust the voltage of the DC power input from the DC generator 12 to a predetermined magnitude (in this case, the first voltage value V1) while at least the third power regulator 18, which will be described later, is in current control mode, so that the adjusted power can continue to be output as DC power to the DC grid 15.

[0027] In Figure 1, an example is shown where one DC power generator 12 is connected to the DC grid 15, but of course, this is not the only example. Two or more DC power generators 12 may be connected to the DC grid 15 via the same number or fewer (at least one) first power regulators 16 as the two or more DC power generators 12. Furthermore, the type of DC power generator 12 is not particularly limited, and equipment for DC power generation using renewable energy other than solar power, such as hydroelectric power generators, wind power generators, and geothermal power generators, may be considered as DC power generators 12. Of course, equipment for DC power generation using two or more different types of renewable energy may also be considered as DC power generators 12.

[0028] The AC power generator 13 is a power generation device that utilizes finite resources such as oil, coal, natural gas, and nuclear fuel as energy, and corresponds to a power generation facility capable of supplying AC power, for example, commercial power. This AC power generator 13 is connected to the DC grid 15 via the second power adjustment device 17, thereby enabling the AC power generated by the AC power generator 13 to be supplied to the DC grid 15 after a predetermined adjustment has been made.

[0029] The second power regulator 17 is configured to adjust the voltage of the AC power input from the AC power generator 13 to a predetermined magnitude (in this case, the second voltage value V2) while at least the third power regulator 18, which will be described later, is in current control mode, and to convert the adjusted AC power into a DC current that can be output to the DC grid 15.

[0030] In Figure 1, an example is shown where one AC power generator 13 is connected to the DC grid 15, but of course, this is not the only example. Two or more AC power generators 13 may be connected to the DC grid 15 via the same number or fewer (at least one) second power regulators 17 as the two or more AC power generators 13.

[0031] The energy storage device 14 is a secondary battery capable of repeated discharge and charging, and is directly connected to the third power regulator 18 without going through the DC grid 15. The type of battery that can be used in the energy storage device 14 is not particularly limited; known batteries such as lead-acid batteries, nickel-metal hydride batteries, lithium-ion batteries, and NAS batteries are applicable.

[0032] The third power regulator 18, as a power adjustment device according to the present invention, has three input / output ports. The first input / output port is connected to a DC power generator 12 and an AC power generator 13 via a DC grid 15, the second input / output port is connected to a power storage device 14, and the third input / output port is connected to a power load 11. By connecting in this manner, the third power regulator 18 can supply power to the power load 11 by applying a predetermined adjustment to either the power generated by either the DC power generator 12 or the AC power generator 13 connected via the DC grid 15, and the power stored in the power storage device 14, or to both.

[0033] Figure 2 shows an example of the circuit configuration of the third power regulator 18. In this illustrated example, the third power regulator 18 comprises a power conversion circuit 20 and a capacitor-split type power conversion circuit 30.

[0034] The power conversion circuit 20 includes an X-phase switching arm 22X, a Y-phase switching arm 22Y, a capacitor C0, a primary winding 28, a positive terminal 24p, and a negative terminal 24n.

[0035] The X-phase switching arm 22X (hereinafter simply referred to as switching arm 22X) includes switching elements E5 and E6 connected in series. The Y-phase switching arm 22Y (hereinafter simply referred to as switching arm 22Y) includes switching elements E7 and E8 connected in series. IGBTs or MOSFETs can be used for each of the switching elements E5 to E8. When IGBTs are used as switching elements E5 to E8, two IGBTs are connected in series, meaning that the collector terminal of one IGBT is connected to the emitter terminal of the other IGBT. When MOSFETs are used as switching elements E5 to E8, two MOSFETs are connected in series, meaning that the drain terminal of the other MOSFET is connected to the source terminal of the other MOSFET. In addition, each of the switching elements E5 to E8 includes a diode. When IGBTs are used for switching elements E5 to E8, the anode terminal is connected to the emitter terminal and the cathode terminal is connected to the collector terminal. When MOSFETs are used for switching elements E5 to E8, the anode terminal is connected to the source terminal and the cathode terminal is connected to the drain terminal.

[0036] Switching arms 22X and 22Y are connected in parallel. Specifically, the terminal of switching element E5 opposite to switching element E6 (the upper terminal) is connected to the terminal of switching element E7 opposite to switching element E8 (the upper terminal). Also, the terminal of switching element E6 opposite to switching element E5 (the lower terminal) is connected to the terminal of switching element E8 opposite to switching element E7 (the lower terminal).

[0037] A capacitor C0 is connected in parallel to the switching arms 22X and 22Y. That is, capacitor C0 is connected between the two parallel connection points of switching arms 22X and 22Y. The upper parallel connection point of switching arms 22X, 22Y and capacitor C0 is connected to the positive terminal 24p, and the lower parallel connection point of switching arms 22X, 22Y and capacitor C0 is connected to the negative terminal 24n. A primary winding 28 is connected between the connection points of switching elements E5 and E6 and the connection points of switching elements E7 and E8.

[0038] The same applies to the following switching elements E1 to E4 as well, regarding the use of IGBTs, MOSFETs, etc., for each switching element E5 to E8, the inclusion of diodes in each switching element E5 to E8, the definition of series connection of switching elements E5 to E8, and the definition of parallel connection of switching arms.

[0039] The capacitor-split power conversion circuit 30 comprises a U-phase switching arm 36U, a V-phase switching arm 36V, a capacitor arm C, a secondary winding 32, a reactor L, a positive terminal 34p, and a negative terminal 34n.

[0040] The U-phase switching arm 36U comprises switching elements E1 and E2 (first switching element and second switching element) connected in series. The V-phase switching arm 36V comprises switching elements E3 and E4 (third switching element and fourth switching element) connected in series. The capacitor arm C comprises an upper capacitor Cu and a lower capacitor Cd (first capacitor and second capacitor) connected in series. The U-phase switching arm 36U, the V-phase switching arm 36V, and the capacitor arm C are connected in parallel. The upper and lower parallel connection points of the U-phase switching arm 36U, the V-phase switching arm 36V, and the capacitor arm C are connected to the positive terminal 34p and the negative terminal 34n, respectively.

[0041] A secondary winding 32 is connected between the connection points of switching elements E1 and E2 and the connection points of switching elements E3 and E4. The secondary winding 32 is magnetically coupled to the primary winding 28 and together with the primary winding 28 constitutes a transformer. A reactor L is connected between a tap located at an intermediate point in the conductors constituting the secondary winding 32 and the connection points of the upper capacitor Cu and the lower capacitor Cd. The tap may be a center tap located at the midpoint of the conductors constituting the secondary winding 32.

[0042] The third power regulator 18 further includes a reactor L1, a second port capacitor C2, a second port positive terminal 26p, and a second port negative terminal 26n.

[0043] The lower parallel connection points of switching arm 22X, switching arm 22Y, and capacitor C0 are connected to the negative terminal 24n as well as the second port negative terminal 26n. One end of reactor L1 is connected to the tap of primary winding 28, and the other end of reactor L1 is connected to the second port positive terminal 26p. The second port capacitor C2 is connected between the second port positive terminal 26p and the second port negative terminal 26n.

[0044] In the microgrid system 10 shown in Figure 1, a DC power generator 12 and an AC power generator 13 are connected between the positive terminal 24p and the negative terminal 24n of the third power regulator 18 via a DC grid 15. A power storage device 14 is connected between the positive terminal 26p and the negative terminal 26n of the second port. A power load 11 is connected between the positive terminal 34p and the negative terminal 34n. In this case, the positive terminal 24p and the negative terminal 24n correspond to the first input / output ports. The positive terminal 26p and the negative terminal 26n of the second port correspond to the second input / output ports, and the positive terminal 34p and the negative terminal 34n correspond to the third input / output ports.

[0045] The control device 19 can control the operation of the third power regulator 18. Specifically, the control device 19 has a first voltmeter 40a and a first ammeter 41a that can measure the voltage Vdc and current of the DC grid 15, respectively; a second voltmeter 40b and a second ammeter 41b that can measure the voltage and current of the energy storage device 14, respectively; and a third voltmeter 40c and a third ammeter 41c that can measure the voltage and current of the power supplied from the third power regulator 18 to the power load 11, respectively. The control device 19 can switch the third power regulator 18 between voltage control and current control based on the voltage state of the DC grid 15 and the charge state of the energy storage device 14.

[0046] Figure 3 shows an example of the circuit configuration of the control device 19. This control device 19 has a first PI controller 42 and a second PI controller 44. In this case, when the voltage of the third power regulator 18 is controlled, the control device 19 functions as a voltage control circuit 19a related to the combination of the first PI controller 42 and the second PI controller 44. When the difference between the voltage command value Vdc2_ref for the DC grid 15 and the measured voltage value Vdc2 of the DC grid 15 is input to the first PI controller 42, the first PI controller 42 outputs a first control signal according to the input value. The difference between the first control signal and the current Idc1 flowing through the reactor L1, and the sum of this difference and the current command value Idc1_ref for the current flowing through the reactor L1, is input to the second PI controller 44. The second PI controller 44 outputs a second control signal according to the input value. The second control signal becomes the duty cycle that controls the on / off state of the switching elements included in the power conversion circuit 20 and the capacitor-split type power conversion circuit 30. The second control signal controls the power conversion circuit 20 and the capacitor-split type power conversion circuit 30 to operate under voltage control.

[0047] In contrast, when the third power regulator 18 controls the current, the control device 19 functions as a current control circuit 19b by the second PI controller 42. The first control signal is set to 0, and the difference between the current command value Idc1_ref for the current flowing through the reactor L1 and the current Idc1 flowing through the reactor L1 is input to the second PI controller 42. The second PI controller 42 outputs a second control signal according to this input value. The second control signal becomes the duty cycle that controls the on / off state of the switching elements included in the power conversion circuit 20 and the capacitor-split type power conversion circuit 30. The second control signal controls the power conversion circuit 20 and the capacitor-split type power conversion circuit 30 to be current-controlled.

[0048] The control device 19 controls the operation of the third power regulator 18 by switching between the voltage control and current control described above, and thereby enables the power supply from each power source (DC generator 12, AC generator 13, and energy storage device 14) to the power load 11 or to the energy storage device 14 to be controlled in a desired manner. Figure 4 shows a flowchart illustrating the flow of a control method according to one example. As shown in Figure 4, the control device 19 is configured to monitor the charge state (more precisely, the charge rate) of the energy storage device 14 using the second voltmeter 40b and the second ammeter 41b, and to change the control mode of the third power regulator 18 according to the charge rate.

[0049] First, the control device 19 determines whether the charge level (SOC) of the energy storage device 14 is equal to or greater than a preset upper threshold SOCH, based on the magnitudes of the voltage and current of the energy storage device 14 measured by the second voltmeter 40b and the second ammeter 41b (step S1). If it determines that the charge level is equal to or greater than the upper threshold SOCH, the control device 19 sets the third power regulator 18 to voltage control (see Figure 5) and controls the voltage Vdc of the DC grid 15 to the third voltage value V3 (step S2).

[0050] Here, as shown in Figure 6, the third voltage value V3 is set to a value higher than either the voltage of the power supplied from the DC generator 12 to the DC grid 15 after being adjusted by the first power regulator 16 (first voltage value V1) or the voltage of the power supplied from the AC generator 13 to the DC grid 15 after being adjusted by the second power regulator 17 (second voltage value V2). As a result, the inflow of power from the DC generator 12 and the AC generator 13 to the DC grid 15 is cut off, the charging of the energy storage device 14 is suppressed, and the discharge from the energy storage device 14 causes the voltage Vdc of the DC grid 15 to become the third voltage value V3, and the required power is supplied to the power load 11 (step S3).

[0051] Furthermore, if the charge level (SOC) of the energy storage device 14 is not equal to or greater than a preset upper threshold SOCH, the control device 19 determines the subsequent control mode based on whether the charge level (SOC) is less than or equal to a lower threshold SOCL. Specifically, the control device 19 determines whether the charge level (SOC) is greater than or equal to the lower threshold SOCL and less than the upper threshold SOCH (step S4), and if it determines that the charge level (SOC) is greater than or equal to the lower threshold SOCL and less than the upper threshold SOCH, it switches the third power regulator 18 to current control (step S5).

[0052] When the third power regulator 18 is set to current control, the voltage Vdc of the DC grid 15 fluctuates between the first voltage value V1 and the second voltage value V2 (see Figure 6). Therefore, the control device 19 continues to monitor the voltage state of the DC grid 15 and determines the subsequent control mode based on the voltage Vdc (=Vdc2) of the DC grid 15 measured by the first voltmeter 40a. That is, when the third power regulator 18 is set to current control, it determines whether the voltage Vdc of the DC grid 15 is equal to the first voltage value V1 (step S6). If it is determined that the voltage Vdc of the DC grid 15 is equal to the first voltage value V1, it is determined that the DC power generator 12 is generating a certain amount or more of power, and power is supplied from the DC power generator 12 to the power load 11 (step S7), and the energy storage device 14 is charged or discharged as necessary (step S8).

[0053] In this case, the DC power generator 12 functions as a power source and supplies power from the DC power generator 12 to the power load 11. If the amount of power generated by the DC power generator 12 alone is insufficient to supply the power load 11, the energy storage device 14 is discharged, and the DC power generator 12 and the energy storage device 14 supply power to the power load 11 together. On the other hand, if the power generated by the DC power generator 12 exceeds the amount required by the power load 11 (i.e., there is an excess of power), the excess power is charged into the energy storage device 14. In either case, since the voltage Vdc of the DC grid 15 is equal to the first voltage value V1, the power from the AC power generator 13, which is adjusted to a second voltage value V2 lower than the first voltage value V1, is cut off and not supplied to the DC grid 15.

[0054] On the other hand, in step S6, if it is determined that the voltage Vdc of the DC grid 15 is different from the first voltage value V1 (in this case, if it is determined to be lower than the first voltage value V1), it is assumed that the amount of power generated by the DC power generator 12 is less than a certain amount due to weather, time, etc., and power is supplied to the power load 11 from both the DC power generator 12 and the energy storage device 14 by discharging the energy storage device 14 (step S9). At this time, by adjusting the magnitude of the voltage supplied (discharged) from the energy storage device 14 so that the voltage Vdc of the DC grid 15 is slightly higher than the second voltage value V2, the power from the AC power generator 13 is cut off and not supplied to the DC grid 15.

[0055] Next, the control method when the charge level (SOC) of the energy storage device 14 is less than the lower threshold SOCL will be explained with reference to Figure 5. That is, as shown in Figure 5, in step S4, the control device 19 determines whether the charge level (SOC) is greater than or equal to the lower threshold SOCL and less than the upper threshold SOCH. If it determines that the charge level (SOC) is less than the lower threshold SOCL, the third power regulator 18 switches to current control (step S10).

[0056] In this case as well, the voltage Vdc of the DC grid 15 fluctuates between the first voltage value V1 and the second voltage value V2 (see Figure 6). Therefore, the control device 19 continues to monitor the voltage state of the DC grid 15 and determines the subsequent control mode based on the voltage Vdc of the DC grid 15 measured by the first voltmeter 40a. That is, when the third power regulator 18 is set to current control, it determines whether the voltage Vdc of the DC grid 15 is equal to the first voltage value V1 (step S11). If it is determined that the voltage Vdc of the DC grid 15 is equal to the first voltage value V1, it is determined that the DC power generator 12 is generating a certain amount or more of power and supplies power from the DC power generator 12 to the power load 11. In addition, the energy storage device 14 is charged as needed (step S12).

[0057] In this case, only the DC power generator 12 functions as a power source, supplying power from the DC power generator 12 to the power load 11. On the other hand, if the power generated by the DC power generator 12 exceeds the amount required for the power load 11, and there is a surplus in the generated power, the surplus power is charged to the energy storage device 14, as shown in Figure 5 (step S13). In either case, since the voltage Vdc of the DC grid 15 is equal to the first voltage value V1, the power from the AC power generator 13, which is adjusted to a second voltage value V2 lower than the first voltage value V1, is cut off and not supplied to the DC grid 15.

[0058] On the other hand, in step S11, if it is determined that the voltage Vdc of the DC grid 15 is different from the first voltage value V1 (i.e., lower than the first voltage value V1), it is further determined whether the voltage Vdc of the DC grid 15 has dropped to a value equal to the second voltage value V2 (step S14). If it is still above the second voltage value V2, power is supplied from the DC generator 12 to the power load 11. Alternatively, if the DC generator 12 alone is insufficient, power is supplied to the power load 11 from both the DC generator 12 and the AC generator 13 (step S15). Also, in this state, considering that the charge level SOC of the energy storage device 14 is less than the lower threshold SOCL, the energy storage device 14 is charged with the amount of power supplied to the DC grid 15 that exceeds the required supply amount to the power load 11 (surplus) (step S16). In particular, in step S14, if it is determined that the voltage Vdc of the DC grid 15 has dropped to a value equal to the second voltage value V2, power is supplied to the power load 11 only from the AC power generator 13, and the energy storage device 14 is charged with the power supplied from the AC power generator 13 (step S17). In this case, only the AC power generator 13 functions as a power supply source.

[0059] As described above, in the microgrid system 10 according to this embodiment, a power adjustment device (here, a third power adjustment device 18) for making the final adjustment of the power supplied to the power load 11 is controlled by the control device 19, and this third power adjustment device 18 is provided with three input / output ports, to which a DC power generator 12 and an AC power generator 13 are connected via the DC grid 15, a power storage device 14 is connected, and the power load 11 is connected (see Figure 1). Furthermore, in this case, the operation of the third power adjustment device 18 can be controlled based on the voltage state of the DC grid 15 and the charge state of the power storage device 14. By making the power within the microgrid system 10 controllable in this way, the structure for power control can be simplified. Therefore, it is possible to construct a microgrid system 10 with excellent responsiveness and robustness.

[0060] Furthermore, in the microgrid system 10 according to this embodiment, while the third power regulator 18 is operating at least in current control mode, the first voltage value V1, which is the voltage supplied from the DC power generator 12 to the DC grid 15, is set higher than the second voltage value V2, which is the voltage supplied from the AC power generator 13 to the DC grid 15. By setting the first voltage value V1 and the second voltage value V2 in this way, if sufficient power is being generated by the DC power generator 12, the power generation equipment (DC power generator 12), which is energy-inexpensive and has a low environmental impact, can be used preferentially (steps S6, S7). Therefore, considering the capital investment required for measures to reduce the environmental impact, it is possible to provide a microgrid system 10 that is advantageous in terms of both initial cost and running cost.

[0061] Furthermore, in this embodiment, when discharge from the energy storage device 14 is permitted (the state of charge SOC is above the lower threshold SOCL and below the upper threshold SOCH), and the voltage Vdc of the DC grid 15 is lower than the first voltage value V1, the operation of the third power regulator 18 is controlled to supply only the power discharged from the energy storage device 14 to the power load 11 (step S8). In this way, when the amount of power generated by the DC power generator 12 is insufficient, the operation of the third power regulator 18 is controlled to supply only the power discharged from the energy storage device 14 to the power load 11, thereby supplying the necessary amount of power to the power load 11 without receiving power from the AC power generator 13 via the DC grid 15. Therefore, it is possible to stably supply energy-inexpensive power to the power load while minimizing the effects of weather and other factors.

[0062] Although one embodiment of the present invention has been described above, it goes without saying that the microgrid system according to the present invention may have configurations other than those described above, without departing from the spirit of the invention.

[0063] Figure 7 shows a modified example of the third power regulator 18. This example shows a 3-port / 2-port type third power regulator 18. The third power regulator 18 comprises power converters 30a to 30c and a 3-phase power converter 50. Each of the power converters 30a to 30c has the same configuration as the capacitor-split type power converter circuit 30 shown in Figure 2 and performs the same switching operation.

[0064] The three-phase power converter 50 comprises switching arms 52A to 52C, primary windings 28a to 28c, reactors La to Lc, capacitors C3 and C4, positive terminals 56p and 58p, and negative terminals 56n and 58n. Switching arm 52A comprises switching elements Sap and San connected in series. Switching arm 52B comprises switching elements Sbp and Sbn connected in series. Switching arm 52C comprises switching elements SCP and Scn connected in series.

[0065] Switching arms 52A-52C and capacitor C3 are connected in parallel. The upper parallel connection point of switching arms 52A-52C and capacitor C3 is connected to the positive terminal 56p, and the lower parallel connection point of switching arms 52A-52C and capacitor C3 is connected to the negative terminal 56n. Primary winding 28a is connected between the connection point of switching elements Sap and San and the connection point of switching elements Sbp and Sbn. Primary winding 28b is connected between the connection point of switching elements Sbp and Sbn and the connection point of switching elements Scp and Scn. Primary winding 28c is connected between the connection point of switching elements Scp and Scn and the connection point of switching elements Sap and San.

[0066] One end of reactor La is connected to the tap of primary winding 28a. One end of reactor Lb and one end of reactor Lc are connected to the taps of primary winding 28b and primary winding 28c, respectively. The other ends of reactors La to Lc are connected to the positive terminal 58p. The lower parallel connection point of switching arms 52A to 52C and capacitor C3 is connected to the negative terminal 56n as well as the negative terminal 58n. Capacitor C4 is connected between the positive terminal 58p and the negative terminal 58n.

[0067] In a configuration such as the microgrid system 10 shown in Figure 1, a DC power generator 12 and an AC power generator 13 are connected between the positive terminal 56p and the negative terminal 56n of the third power regulator 18 via a DC grid 15. A power storage device 14 is connected between the positive terminal 58p and the negative terminal 58n. A three-phase power load 11 is connected between the positive terminal 34p and the negative terminal 34n.

[0068] Figures 8 and 9 show third power regulators 60 and 62, which apply the third power regulator 18 according to this embodiment as a circuit capable of generating three-phase alternating current.

[0069] The third power regulator 60 shown in Figure 8 is configured in the same way as shown in Figure 7, with inverters 64a, 64b, and 64c further connected to each of the power converters 30a, 30b, and 30c. The third power regulator 62 shown in Figure 9 is configured by providing switching elements between the phases of the secondary winding 32 of the three-phase power converter 50 shown in Figure 7 to form a converter 66, and further connecting an inverter 68 to the converter 66 by providing switching elements.

[0070] In the configurations of these third power regulators 60 and 62, the same control method for switching between voltage control and current control as shown in the third power regulator 18 in Figures 2 and 7 can be applied. [Explanation of Symbols]

[0071] 10 Microgrid Systems 11 Power load 12 DC power generator 13 AC power generator 14. Energy storage device 15 DC grids 16. First Power Regulator (DC Generator) 17. Second Power Regulator (AC Power Generator) 18, 60, 62 Third Power Regulator (DC Grid) 19 Control device 19a Voltage control circuit 19b Current control circuit 20 Power Conversion Circuit 22X Switching Arm 22Y Switching Arm 24n,34n,56n,58n negative terminal 24p,34p,56p,58p positive terminal 26n Second port negative terminal 26p Second port positive terminal 28, 28a, 28b, 28c Primary winding 30 Capacitor-Splitting Power Conversion Circuit 30a, 30b, 30c, 32 Secondary winding 36U U-phase switching arm 36V V-phase switching arm 40A, 40B, 40C voltmeter 41a,41b,41c Ammeter 42 First PI Controller 44 Second PI Controller 50 Three-phase power converter 52A, 52B, 52C Switching Arm 64a, 64b, 64c, 68 Inverter 66 Converter C Capacitor Arm C0, C3, C4 Capacitors C2 Second port capacitor Cd lower capacitor Cu upper capacitor Switching elements E1, E2, E3, E4, E5, E6, E7, E8 Switching elements: Sap, Sbp, Scp, San, Sbn, Scin Idc1 Measured Current Value (DC Grid) Idc1_ref Current command value (DC grid) L, L1, La, Lb, Lc reactor SOC charging rate SOCH upper threshold SOCL Lower Threshold V1 First voltage value (DC power generator) V2 Second voltage value (AC power generator) V3 Third voltage value (DC grid) Vdc2 Measured voltage value (DC grid) Vdc2_ref Voltage command value (DC grid)

Claims

1. The system comprises a DC power generation device utilizing renewable energy, an AC power generation device, a power storage device, a power adjustment device for adjusting the power input from any of the aforementioned devices and outputting it to a power load, and a control device for controlling the operation of the power adjustment device. A microgrid system in which, of the three input / output ports provided in the power adjustment device, the DC power generator and the AC power generator are connected to the first input / output port via a DC grid, the energy storage device is connected to the second input / output port, and the power load is connected to the third input / output port, The control device controls the operation of the power regulator based on the voltage state of the DC grid and the charge state of the energy storage device, and when the charge rate of the energy storage device is below the upper limit threshold of the charge rate, it sets the power regulator to current control, and A microgrid system in which, while the power regulator is operating at least in the current control, a first voltage value V1, which is the voltage supplied from the DC power generator to the DC grid, is set higher than a second voltage value V2, which is the voltage supplied from the AC power generator to the DC grid.

2. The microgrid system according to claim 1, wherein when the charge level of the energy storage device is above the lower limit threshold and below the upper limit threshold, and the voltage of the DC grid is equal to the first voltage value V1, the control device switches between discharging and charging the energy storage device according to the difference between the power generated by the DC power generator and the power load.

3. The microgrid system according to claim 2, wherein when the voltage of the DC grid is lower than the first voltage value V1, the control device controls the operation of the power adjustment device to supply to the power load only the power discharged from the energy storage device or the sum of the power discharged from the energy storage device and the power generated by the DC power generator.

4. The microgrid system according to claim 1, wherein when the charge level of the energy storage device is below the lower threshold and the voltage of the DC grid is equal to the first voltage value V1, the control device supplies the power generated by the DC power generator to the power load, and if there is a surplus of power generated by the DC power generator for the required power load, the control device controls the operation of the power adjustment device to charge the energy storage device with all of the surplus.

5. The microgrid system according to claim 4, wherein when the voltage of the DC grid is equal to the second voltage value V2, the control device controls the operation of the power adjustment device to charge the energy storage device while supplying the power generated by the AC power generator to the power load.

6. The microgrid system according to claim 1, wherein the control device, when the charge level of the energy storage device is higher than the upper limit threshold, sets the power adjustment device as the voltage control to set the third voltage value V3, which is the voltage of the DC grid, higher than the first voltage value V1.

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