Electric power system

Abstract

To improve the power conversion efficiency between a power storage battery and a hydrogen system in an electric power system.SOLUTION: A first power converter DC / DC1 is connected to a DC bus 5. A power storage unit (power storage battery) 3 is connected to the first power converter DC / DC1. Furthermore, a hydrogen system is provided to perform charging and discharging with respect to the power storage unit (power storage battery) 3. The hydrogen system includes a water electrolysis device EC that decomposes electric power into hydrogen, a hydrogen tank 4 that stores the hydrogen, and a fuel cell FC that converts hydrogen into electric power. The hydrogen system is connected, via a second power converter DC / DC2, to a junction point between the first power converter DC / DC1 and the power storage unit (power storage battery) 3.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electric power system including a DC bus, a power storage unit, and a hydrogen system. [Background technology]

[0002] As part of efforts to address environmental concerns about electric energy, it is expected that renewable energy sources such as solar and wind power will increase. However, in order to balance long-term energy supply and demand (power stabilization) in response to seasonal and other unstable natural energy sources, a large-capacity energy storage element is required.

[0003] Storage batteries, currently considered the main energy storage element, have high response, but the amount of energy stored (capacity) is determined at the time of installation. Also, if the capacity is set to be stable throughout the year, the utilization rate of the storage battery will not increase.

[0004] Therefore, we are focusing on hydrogen, which allows for the replacement and refilling of tanks. By adding an energy storage element that uses hydrogen, we can reduce investment in storage batteries and build a system that can withstand long-term fluctuations such as seasonal changes.

[0005] A hydrogen system that can generate hydrogen through water electrolysis (hereafter referred to as the water electrolysis device EC) and generate electricity using fuel cells (hereafter referred to as the fuel cell FC) will enable the long-term balance of energy supply and demand.

[0006] However, hydrogen systems also have their advantages and disadvantages, and the battery and hydrogen systems can be summarized as follows:

[0007] (storage battery) Advantages: It is possible to input and output power with high response, and it can also respond to sudden fluctuations in demand and power generation. Disadvantages: The amount of energy stored (storage capacity) is determined at the time of installation.

[0008] (Hydrogen System) Advantages: Theoretically, the amount of energy stored (storage capacity) is infinite by refilling the hydrogen tank, etc. Disadvantages: Because it handles liquids and gases, it is not suitable for sudden power fluctuations. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 6923231 Summary of the Invention [Problem to be solved by the invention]

[0010] FIG. 1 shows a power grid system that mutually compensates for the advantages and disadvantages of the storage battery and hydrogen systems. FIG. 1(a) shows an example of a supply configuration to a DC load, and FIG. 1(b) shows an example of a supply configuration to an AC load. Current power grid systems generally have the configuration shown in FIG. 1 via a DC bus 5, although there are some differences in the connections to the system power source 1 and the loads. This configuration is disclosed in Patent Document 1.

[0011] The AC-DC converter AC / DC and the first to fifth power converters (DC-DC converters) DC / DC1 to DC / DC5 are configured with semiconductor switches and the like that generate power loss when energized or when switching.

[0012] These power grid systems treat energy storage by batteries 3 and energy storage by hydrogen as equals to the DC bus 5, and the roles of the high-response batteries 3 and the low-response, large-capacity hydrogen system are unclear.

[0013] Furthermore, when the storage battery 3 becomes empty (over-discharged), it is no longer able to adjust power responsively, so it becomes necessary to replenish it with power from the hydrogen system, but because two power converters, the first power converter DC / DC1 and the second power converter DC / DC2 (or the third power converter DC / DC3), must be used between the storage battery and the hydrogen system, the number of semiconductor switches that need to be energized increases, and power conversion efficiency drops.The same is true when the storage battery 3 is overcharged (when power is released from the storage battery 3 to the hydrogen system).

[0014] For the reasons stated above, the challenge in power grid systems is to increase the efficiency of power conversion between storage batteries and hydrogen systems. [Means for solving the problem]

[0015] The present invention was devised in view of the above-mentioned problems in the related art, and one aspect of the present invention is a hydrogen system comprising: a DC bus; a first power converter connected to the DC bus; a power storage unit connected to the first power converter; a second power converter connected to a connection point between the first power converter and the power storage unit; a water electrolysis device that decomposes electricity into hydrogen; a hydrogen tank that stores the hydrogen; and a fuel cell that converts the hydrogen into electricity, wherein the second power converter is connected to the hydrogen system, and the hydrogen system charges and discharges the power storage unit.

[0016] In one aspect, the present invention is characterized in that it includes a third power converter connected between the fuel cell and a connection point between the first power converter and the power storage unit, and the second power converter is connected to the water electrolysis device.

[0017] In one aspect, the power converter is characterized by comprising a first switch connected between the second power converter and the water electrolysis device, and a second switch connected between the second power converter and the fuel cell.

[0018] In one aspect, the power supply system further comprises a first switch connected between the second power converter and the water electrolysis device, and a first diode connected between the second power converter and the fuel cell.

[0019] In one aspect, the power supply circuit further comprises a second switch connected in parallel to the first diode.

[0020] In one aspect, the water electrolysis device further includes a second diode connected between the first switch and the water electrolysis device, and a third switch connected in parallel to the second diode.

[0021] In one aspect, the fuel cell power supply includes a first switch connected between the second power converter and the water electrolysis device, a second diode connected between the first switch and the water electrolysis device, a third switch connected in parallel to the second diode, and a second switch connected between the second power converter and the fuel cell. [Effects of the Invention]

[0022] According to the present invention, it is possible to increase the efficiency of power conversion between a storage battery and a hydrogen system in a power grid system. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic diagram showing a conventional power grid system. [Figure 2] 1 is a schematic diagram showing a power grid system according to a first embodiment. [Figure 3] 1A and 1B are schematic diagrams illustrating power paths according to a conventional example and the first embodiment. [Figure 4] FIG. 10 is a schematic diagram showing a power grid system according to a second embodiment. [Figure 5] FIG. 10 is a schematic diagram showing a power grid system according to a third embodiment. [Figure 6] FIG. 10 is a schematic diagram showing a power grid system according to a fourth embodiment. [Figure 7]FIG. 10 is a schematic diagram showing a power grid system according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, first to fifth embodiments of the power system according to the present invention will be described in detail with reference to FIGS.

[0025] [Embodiment 1] Fig. 2 is a schematic diagram showing the power system in the present embodiment 1. The power system in the present embodiment 1 may be connected to an AC load or a DC load, as shown in Fig. 1(a) and Fig. 1(b).

[0026] The system power supply 1 is connected to the DC bus 5 via an AC / DC converter. The AC / DC converter converts the system voltage into a DC bus voltage. The DC bus 5 is a DC bus common to power generation and storage. For example, if the system power supply is 200Vac, the DC bus voltage becomes approximately 300Vdc.

[0027] The natural energy power generation device 2 is a power generation device that uses natural energy. Although shown as a solar panel in Fig. 2, it may be replaced with other power generation devices such as wind power generation. The natural energy power generation device 2 is connected to the DC bus 5 via a fourth power converter DC / DC4.

[0028] The power storage unit 3 is, for example, a storage battery. Hereinafter, it will be referred to as the storage battery 3. The storage battery 3 is a device that temporarily stores power with high response. Lithium-ion batteries are currently the mainstream, but other types of batteries may be used, or they may be replaced with a high-response capacitor or the like. The storage battery voltage is, for example, 48 Vdc. The storage battery 3 is connected to the DC bus 5 via the first power converter DC / DC1.

[0029] The water electrolysis device EC generates hydrogen and oxygen through electrolysis and converts electricity into hydrogen. The hydrogen tank 4 is a device that temporarily stores hydrogen gas. It can be stored as a gas, or it can be replaced with an adsorption alloy or a device that compresses it into a liquid. The fuel cell FC generates electricity from hydrogen and oxygen and converts the hydrogen into electricity.

[0030] The second power converter DC / DC2 is connected between the water electrolysis device EC and the connection point between the first power converter DC / DC1 and the storage battery 3. The third power converter DC / DC3 is connected between the connection point between the first power converter DC / DC1 and the storage battery 3 and the fuel cell FC.

[0031] The hydrogen system comprises the water electrolysis device EC, fuel cell FC, and hydrogen tank 4. As described above, the hydrogen system is connected to the connection point between the first power converter DC / DC1 and the storage battery 3 via the second and third power converters DC / DC2 and DC / DC3.

[0032] The power capacity (power that can be supplied per unit time) of each of the above converters is shown below as an example. AC / DC converter: Depends on the power capacity to compensate for the load, assuming a 10kW AC load. Fourth power converter DC / DC4: 10kW Depends on the power capacity of the solar panels. First power converter DC / DC1: 10kW Depends on the amount of solar power generation and load consumption. Second and third power converters DC / DC2, DC / DC3: 1kW Capacity that can compensate for the difference in the amount of charge and discharge of battery 3 in one day.

[0033] Here, the roles of the storage battery 3 and the hydrogen system will be clarified. (Storage battery 3) Because it can operate with high response, it serves to absorb fluctuations in natural energy generation and load fluctuations. (Hydrogen system) If the storage battery 3 is over-discharged or over-charged, power adjustment becomes impossible, so power adjustment is performed on the storage battery 3 to prevent the storage battery 3 from being over-discharged or over-charged.

[0034] As these roles indicate, the purpose of the hydrogen system is to charge and discharge the storage battery 3 in order to maintain a constant SOC (State Of Charge) of the storage battery 3. Therefore, rather than treating the storage battery 3 and the hydrogen system as equals as in the past, the hydrogen system is treated as a device to complement the storage battery 3.

[0035] Therefore, a configuration is required that minimizes power conversion loss between the storage battery 3 and the hydrogen system. To achieve this, the hydrogen system must be connected to the storage battery 3 itself. Fig. 3(a) shows the power path of a conventional power grid system, and Fig. 3(b) shows the power path of the power grid system of this embodiment 1. In the configuration of Fig. 3(a), there are two DC / DC power converters between the storage battery 3 and the hydrogen system, but in the configuration of Fig. 3(b), there is only one DC / DC power converter between the storage battery 3 and the hydrogen system.

[0036] As described above, according to the first embodiment, the hydrogen system charges and discharges the storage battery 3, thereby maintaining a constant SOC of the storage battery 3 and preventing the storage battery 3 from being overcharged or overdischarged. Furthermore, as in the configuration of Figure 2, there is only one DC / DC power converter between the storage battery 3 and the hydrogen system, which increases the power conversion efficiency between the storage battery 3 and the hydrogen system.

[0037] [Embodiment 2] Figure 4 shows a power grid system according to the second embodiment. Components similar to those in Figure 2 are assigned the same reference numerals, and their description will be omitted. In the second embodiment, as shown in Figure 4, the third power converter DC / DC3 is omitted, and the second power converter DC / DC2 is used both as the water electrolysis device EC and the fuel cell FC. Furthermore, a first switch SW1 is provided between the second power converter DC / DC2 and the water electrolysis device EC, and a second switch SW2 is provided between the second power converter DC / DC2 and the fuel cell FC.

[0038] In the configuration shown in Figure 2, the water electrolysis system EC and fuel cell FC require second and third power converters DC / DC2 and DC / DC3, respectively, but the second and third power converters DC / DC2 and DC / DC3 do not operate simultaneously, as their purpose is to adjust the power supplied to the storage battery 3. Therefore, as shown in Figure 4, by using first and second switches SW1 and SW2, such as electromagnetic contactors, to switch the connection between the second power converter DC / DC2 and the water electrolysis system EC or fuel cell FC, it is possible to combine the power converters of the hydrogen system into one.

[0039] When the water electrolysis device EC is operating (when the hydrogen system is charging), the first switch SW1 is turned ON and the second switch SW2 is turned OFF, and when the fuel cell FC is operating (when the hydrogen system is discharging), the first switch SW1 is turned OFF and the second switch SW2 is turned ON.

[0040] As described above, according to the second embodiment, the same effects as those of the first embodiment can be achieved. In addition, the number of DC / DC power converters connected to the hydrogen system can be reduced by one, which reduces costs and makes the system more compact. [Embodiment 3] Figure 5 shows a power grid system according to the third embodiment. Components similar to those in Figure 4 are given the same reference numerals, and their description will be omitted. As shown in Figure 5, the third embodiment does not include the second switch SW2 of the second embodiment, and instead has a first diode D1 provided between the second power converter DC / DC2 and the fuel cell FC. The first diode D1 has an anode on the fuel cell FC side and a cathode on the second power converter DC / DC2 side.

[0041] The configuration in Figure 4 requires separate circuits to operate the first switch SW1 and the second switch SW2. However, because the current direction required by the water electrolysis system EC differs from the current direction required by the fuel cell FC, the second switch SW2 on the fuel cell FC side can be replaced with a first diode D1, as shown in Figure 5. The fuel cell FC side of the second power converter DC / DC2 typically has a smoothing capacitor. If a charge remains in the capacitor, turning on the second switch SW2, such as an electromagnetic contactor, can apply a voltage to the fuel cell FC, causing a reverse current. Reverse current flowing through the fuel cell FC accelerates its lifespan. Therefore, by replacing the second switch SW2 with the first diode D1, reverse current can be suppressed.

[0042] The first switch SW1 is turned ON when the water electrolysis device EC is operating (when the hydrogen system is charging), and the first switch SW1 is turned OFF when the fuel cell FC is operating (when the hydrogen system is discharging).

[0043] As described above, according to the third embodiment, the same effects as those of the first and second embodiments can be achieved. Furthermore, the configuration of Fig. 5 omits the second switch SW2 for disconnecting the fuel cell FC, thereby simplifying the circuit. Furthermore, by replacing the second switch SW2 with the first diode D1, reverse current and deterioration of the lifespan of the fuel cell FC can be suppressed.

[0044] [Embodiment 4] Fig. 6 shows a power grid system according to the fourth embodiment. The same components as those in Fig. 5 are given the same reference numerals and their description will be omitted. As shown in Fig. 6, in the fourth embodiment, a second switch SW2 is provided in parallel with the first diode D1.

[0045] If a transient current flows when the water electrolysis system EC or fuel cell FC is started or stopped, the lifespan of the water electrolysis system EC or fuel cell FC will be shortened. Meanwhile, if a current flows through the first diode D1 during operation, a conduction loss will occur in the diode D1. To prevent this, as shown in Figure 6, a first diode D1 is provided to prevent the transient current, and a second switch SW2 is provided to prevent loss due to the first diode D1 during operation. This makes it possible to prevent shortening of the lifespan and suppress a decrease in efficiency.

[0046] Before starting up the fuel cell FC, the second switch SW2 is turned OFF. Then, after starting up the fuel cell FC and passing the transient current generated when the fuel cell FC starts up through the first diode D1, the second switch SW2 is turned ON. When the second switch SW2 is ON, current flows through the second switch SW2 instead of the first diode D1, thereby reducing losses. Furthermore, when stopping the fuel cell FC, the second switch SW2 is turned OFF in advance to pass current through the first diode D1, allowing the transient current generated when the fuel cell FC is stopped to flow through the first diode and preventing current from flowing back into the fuel cell FC. In other words, the second switch SW2 is ON during periods when current is flowing except when the fuel cell FC is starting up or stopping, and is OFF at all other times.

[0047] As in the second and third embodiments, the first switch SW1 is turned on when the water electrolysis device EC is operating (when the hydrogen system is charging) and turned off when the fuel cell FC is operating (when the hydrogen system is discharging).

[0048] As described above, according to this embodiment 4, the same effects as those of embodiments 1 to 3 can be achieved. Furthermore, the configuration of Fig. 6 can prevent deterioration in the lifespan of the fuel cell FC and suppress a decrease in efficiency due to the first diode D1.

[0049] [Embodiment 5] FIG. 7 shows a power grid system according to the fifth embodiment. The same parts as those in FIG. 6 are given the same reference numerals and their description will be omitted. In the fifth embodiment, as shown in FIG. 7, a second diode D2 is provided between the first switch SW1 and the water electrolysis device EC. The second diode D2 has an anode on the first switch SW1 side and a cathode on the water electrolysis device EC side. A third switch SW3 is provided in parallel with the second diode D2. The insertion position of the first switch SW1 is It may be moved between the connection point of the second diode D2 and the third switch SW3 and the water electrolysis device EC.

[0050] The first switch SW1 is provided to prevent the power generated by the fuel cell FC from circulating to the water electrolysis system EC, and is turned ON when the water electrolysis system EC is operating, and OFF when the fuel cell FC is operating.

[0051] The first diode D1 and second diode D2 are diodes that prevent reverse current from flowing in the water electrolysis system EC and fuel cell FC, respectively, and suppress transient currents when the water electrolysis system EC and fuel cell FC are started up and stopped. Reverse current flow would shorten the lifespan of the water electrolysis system EC and fuel cell FC, so these diodes are used to prevent this. This is particularly effective when there is a potential difference between the second power converter DC / DC2 and the water electrolysis system EC or fuel cell FC at start-up.

[0052] To suppress conduction loss in the first diode D1, the second switch SW2 is ON during periods when current is applied other than when the fuel cell FC is started up or stopped, and is OFF during other periods, as in embodiment 4. To suppress conduction loss in the second diode D2, the third switch SW3 is ON during periods when current is applied other than when the water electrolysis apparatus EC is started up or stopped, and is OFF during other periods.

[0053] The first diode D1 may be omitted. In this case, the second switch SW2 is turned OFF when the water electrolysis apparatus EC is operating (when the hydrogen system is charging), and the second switch SW2 is turned ON when the fuel cell FC is operating (when the hydrogen system is discharging). The operations of the first switch SW1 and the third switch SW3 are the same as when the first diode D1 is included.

[0054] As described above, according to the fifth embodiment, the same effects as those of the first to fourth embodiments can be achieved. In addition, it is possible to prevent the lifespan of the water electrolysis apparatus EC and the fuel cell FC from being shortened, and to suppress a decrease in efficiency due to the first diode D1 and the second diode D2.

[0055] Although the present invention has been described in detail above only with respect to the specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention, and it is natural that such modifications and variations fall within the scope of the claims. [Explanation of symbols]

[0056] 1…System power supply 2. Natural energy power generation equipment 3...Storage unit (battery) EC…Water electrolysis device 4...Hydrogen tank FC…Fuel cell 5...DC bus AC / DC: AC-DC converter DC / DC1 to DC / DC5: 1st to 5th power converters (DC-DC converters) SW1~SW3...1st~3rd switches D1, D2...first and second diodes

Claims

1. DC bus and a first power converter connected to the DC bus; a power storage unit connected to the first power converter; a second power converter connected to a connection point between the first power converter and the power storage unit; a hydrogen system including a water electrolysis device that decomposes electricity into hydrogen, a hydrogen tank that stores the hydrogen, and a fuel cell that converts the hydrogen into electricity; the second power converter is connected to the hydrogen system; The power grid system is characterized in that the hydrogen system charges and discharges the power storage unit.

2. a third power converter connected between the fuel cell and a connection point between the first power converter and the power storage unit, 2. The electric power system according to claim 1, wherein the second power converter is connected to the water electrolysis device.

3. a first switch connected between the second power converter and the water electrolysis device; a second switch connected between the second power converter and the fuel cell; 2. The power system according to claim 1, further comprising:

4. a first switch connected between the second power converter and the water electrolysis device; a first diode connected between the second power converter and the fuel cell; 2. The power system according to claim 1, further comprising:

5. 5. The power system according to claim 4, further comprising a second switch connected in parallel to the first diode.

6. a second diode connected between the first switch and the water electrolysis device; a third switch connected in parallel to the second diode; 6. The power system according to claim 5, further comprising:

7. a first switch connected between the second power converter and the water electrolysis device; a second diode connected between the first switch and the water electrolysis device; a third switch connected in parallel to the second diode; a second switch connected between the second power converter and the fuel cell; 2. The power system according to claim 1, further comprising:

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