WO2021100112A1

WO2021100112A1 - Dc power supply system

Info

Publication number: WO2021100112A1
Application number: PCT/JP2019/045229
Authority: WO
Inventors: 堤　香津雄
Original assignee: 株式会社堤水素研究所
Priority date: 2019-11-19
Filing date: 2019-11-19
Publication date: 2021-05-27
Also published as: JP7168243B2; JPWO2021100112A1

Abstract

The present invention addresses the problem of constructing a DC power system by using a secondary battery that can be charged to full battery capacity by using an inexpensive and versatile means without using a dedicated charge control device. Further, provided is a method for using a secondary battery without sacrificing battery life due to floating charging. The DC power system according to the present invention comprises: a floating rechargeable parent battery that is directly connected to the DC power system; and a child battery that is connected to the parent battery without going through a device that regulates charging.

Description

[Replenishment based on Rule 26 09.12.2019] DC power supply system

The present invention relates to a DC power system, and more particularly to a DC power system that enhances power flexibility by using a power storage facility capable of floating charging.

In recent years, there has been increasing interest in distributed generation, microgrids, and renewable energies as a complement to power supply in power grids. Among these, the spread of power generation systems that use natural energy such as solar power generation and wind power generation is expanding against the background of increasing awareness of environmental conservation such as _{CO 2 reduction to prevent global warming.}

In a power generation system that uses natural energy, the generated power is easily affected by natural phenomena, which is a disturbing factor in the supply and demand adjustment of the power system. As a complement to this, it has been proposed to connect a storage battery to a power generation system such as wind power generation to adjust supply and demand.

In addition to power plants that use natural energy, DC power systems that use electric railway power stations and NAS batteries as power sources have been proposed (for example, Patent Document 1). Here, the electric railway has a feature that it consumes DC power during acceleration but can be recovered as regenerative power during deceleration. NAS batteries are characterized in that they use nighttime electricity, which is in low demand, to store electricity and adjust supply and demand.

Secondary batteries are suitable for applications that require quick response of power supply to ensure the stability of the power supply system. It is desirable that the secondary battery used for such an application can be charged in a floating manner. This means that when a power shortage occurs, the secondary battery can be discharged and power can be supplied immediately, and when the power shortage is resolved, the secondary battery needs to be charged to maintain a fully charged state. Because there is sex.

Patent Document 2 describes a charging method that enables floating charging by measuring the internal pressure of an assembled battery in which a plurality of alkaline secondary batteries are connected to each other and controlling the charging of the assembled battery based on the measured internal pressure. Is disclosed.

Japanese Unexamined Patent Publication No. 2010-11711 Japanese Unexamined Patent Publication No. 2010-40297 Japanese Unexamined Patent Publication No. 2013-118768

Generally, the secondary battery is not used after being fully charged. This is because the cycle life is shortened when fully charged, and the life is significantly shortened when overcharged. If the secondary battery is charged to the full capacity, the load on the secondary battery will be heavy and the life of the secondary battery will be shortened. Therefore, the upper limit of charge and the lower limit of discharge of the secondary battery are set within this range. If charge control is performed, the life of the secondary battery can be extended while charging without imposing a burden on the secondary battery, as compared with the configuration of charging to the full capacity (for example, Patent Document 3).

After all, when charging a secondary battery, it is generally widely practiced to stop charging before the battery is fully charged in consideration of battery life. Therefore, even in a secondary battery used for floating charging, by performing charge control as described in Patent Document 3, the battery life characteristics are not sacrificed and the state close to full charge is maintained. It enables the use of the next battery. However, such a charging method has a problem that the charging capacity of the secondary battery is not fully utilized.

Furthermore, in order to stop charging before the secondary battery is fully charged, a control device according to the battery specifications and applications is required, and such a device is not versatile and expensive.

A system has been proposed in which power from a power plant that uses natural energy is stored in a secondary battery to adjust the power, but power that exceeds the capacity of the secondary battery cannot be accepted and natural energy is used effectively. Can not do it. Furthermore, a control device such as a dedicated program or protocol is required to prevent demand response and instantaneous decrease and perform power regeneration by using a charged battery.

The problem to be solved by the present invention is to construct a DC power system using a secondary battery that does not require charge control. It also provides a method of using a secondary battery without sacrificing battery life due to floating charging. Further, a method for utilizing surplus electric power without waste is provided.

In order to achieve the above object, the DC power system according to the present invention includes a floating rechargeable parent battery connected to the DC power system without a device for adjusting the charge, and a device for adjusting the charge. Is equipped with a child battery connected to the parent battery.

In this configuration, the DC power system and the parent battery are directly connected without a device for adjusting charging. Further, the child battery is also connected to the parent battery without going through a device for adjusting charging.

Floating charging means that the charged battery supplements the electricity consumed by discharging by charging each time. That is, the secondary battery is connected to a device or equipment that becomes a load and a power source for charging, and the amount of electricity reduced by the use of the secondary battery is replenished by charging from the power source. As a result, the secondary battery can be maintained in a substantially fully charged state, and can immediately respond to the demand from the load. Therefore, the floating rechargeable parent battery directly connected to the DC power system maintains a fully charged state without requiring a special control device even when connected to the charger.

In the DC power system according to the present invention, the child battery is connected to an intermediate tap provided on the parent battery. Further, the child battery is a secondary battery mounted on an electric vehicle. Here, it is possible to take out the connection point of the cells constituting the parent battery as an intermediate tap. Further, in the DC power system according to the present invention, the child battery can be floatingly charged.

The DC power system according to the present invention is a secondary battery in which the child battery is attached to any one of a mobile body, a consumer device, and an industrial device. Further, in the DC power system according to the present invention, the moving body is any one of an electric vehicle, a railroad vehicle, a forklift or a crane.

In the DC power system according to the present invention, one or both of the water electrolyzer and the fuel cell and the parent battery are connected in parallel to the DC power system. Further, in the DC power system according to the present invention, a feeder system of an electric railway is connected to the DC power system.

In the DC power system according to the present invention, the child battery is connected to the DC power system via a DCDC converter. Further, in the DC power system according to the present invention, the AC power system and the DC power system are connected by a bidirectional inverter.

In the DC power system according to the present invention, the master battery is a secondary battery in which hydrogen is sealed and the negative electrode active material is hydrogen, and can be charged until the terminal voltage becomes equal to the charging voltage and the charging current stops flowing. Is.

In this configuration, the charging current of the secondary battery filled with hydrogen decreases as it approaches full charge, and finally the battery potential becomes equal to the charging voltage, so that the secondary battery is maintained in a fully charged state without being damaged. Can be done. It can be suitably used for applications that require maintaining a fully charged state.

According to the above-mentioned DC power system, by configuring a DC power system using a power storage facility capable of floating charging, the flexibility of electric power is improved and the secondary battery mounted on the electric vehicle is effectively used. Provides a power system. In addition, it is possible to construct an inexpensive and versatile secondary battery charging system that does not require charge control. Further, the present invention provides a method of using a secondary battery without sacrificing the battery life due to floating charging. As a result, an inexpensive and versatile secondary battery utilization technology is provided.

It is a system diagram for demonstrating the structure of a DC power system. It is a system diagram for demonstrating the modification of the DC power system of FIG. It is a system diagram for demonstrating the connection between a parent battery and a child battery in FIG. It is a system diagram for demonstrating another modification of the DC power system of FIG. It is a figure which shows the example of the control characteristic of a bidirectional inverter. It is a graph which shows the relationship between the voltage of a secondary battery filled with hydrogen gas, and the amount of electricity stored. It is a graph which shows the relationship between the voltage and electric power of a water electrolyzer. It is a graph which shows the relationship between the voltage and electric power of a fuel cell. It is a graph which shows the relationship between voltage and electric power when a secondary battery, a water electrolyzer and a fuel cell are integrated.

Hereinafter, an embodiment according to the present invention will be described, but the present invention is not limited to the following embodiments.

Prior to explaining one embodiment of the present invention, a nickel-metal hydride battery will be described as an example of a secondary battery to which the present invention is applied. The type of the secondary battery is not limited to the nickel hydrogen battery as long as the negative electrode active material is hydrogen.

The current collector is not particularly limited as long as it has high electrical conductivity and can energize the held electrode material. The negative electrode current collector is preferably Ni from the viewpoint of stability in the electrolytic solution and reduction resistance. In addition, iron coated with nickel or carbon may be used. The positive electrode current collector is preferably Ni from the viewpoint of stability in the electrolytic solution and oxidation resistance.

The shape of the current collector includes a linear shape, a rod shape, a plate shape, a foil shape, a net shape, a woven fabric, a non-woven fabric, an expand, a porous body, an embossed body, or a foam, and among them, the filling density can be increased, and the output An embossed body or a foam is preferable because of its good properties.

Examples of the negative electrode material include hydrogen storage alloys, platinum, and palladium. Of these, from the viewpoint of hydrogen storage capacity, charge / discharge characteristics, self-discharge characteristics, and cycle life characteristics, it is preferable to use a quintuple alloy containing MmNiComnAl misch metal, which is an AB5 type rare earth-nickel alloy. Alternatively, it is preferably a LaMgNi-based alloy called a superlattice hydrogen storage alloy. In addition, you may use 1 type or 2 or more types of these alloys. The positive electrode material is preferably a metal oxide. For example, silver oxide, manganese dioxide, nickel oxyhydroxide can be mentioned.

The conductive auxiliary agent is for imparting conductivity to the active material and increasing its utilization rate. The conductive auxiliary agent is preferably a carbon material that does not elute into the electrolytic solution during discharge and is not easily reduced by hydrogen. The conductive auxiliary agent used for the positive electrode is more preferably graphitized soft carbon.

The negative electrode material, binder, and conductive auxiliary agent are mixed and kneaded into a paste. This paste is applied or filled in the current collector and dried. Then, the current collector is rolled with a roller press to produce a negative electrode. Similarly, the positive electrode material, the binder, and the conductive auxiliary agent are mixed and kneaded into a paste. This paste is applied or filled in the current collector and dried. Then, a positive electrode is produced by rolling the current collector with a roller press.

Examples of the binder include sodium polyacrylate, methyl cellulose, carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), ethylene-vinyl alcohol, ethylene vinyl acetate copolymer (EVA), polyethylene (). PE), polypropylene (PP), fluororesin, styrene-ethylene-butylene-styrene copolymer (SEBS) can be mentioned.

Alternatively, polytetrafluoroethylene (PTFE) may be used as a binder. PTFE is less likely to be reduced by hydrogen, is less likely to deteriorate even when used for a long period of time in a hydrogen atmosphere, and can be expected to have a long life.

When the total of the negative electrode material, the binder, and the conductive auxiliary agent is 100% by mass, the mass ratio of the binder to be blended in the negative electrode is preferably set to 20% by mass or less, preferably 10% by mass or less. It is more preferable to set it to 5% by mass or less. The binder has poor electron conductivity and ionic conductivity, and if the proportion of the binder exceeds 20% by mass, it becomes difficult to increase the capacity. When the total of the positive electrode material, the binder, and the conductive auxiliary agent is 100% by mass, the mass ratio of the binder to be blended in the positive electrode is preferably set to 20% by mass or less, and 10% by mass or less. It is more preferable to set it to 5% by mass or less.

The electrolytic solution is not particularly limited as long as it is used in a battery using hydrogen as an active material, but for example, salts such as potassium hydroxide (KOH), lithium hydroxide (LiOH), and sodium hydroxide (NaOH) are added to water. The one dissolved in is preferable. From the viewpoint of the output characteristics of the battery, the electrolytic solution is preferably an aqueous sodium hydroxide solution.

As the separator, a known one used for batteries using hydrogen as an active material can be used. Examples of the shape of the separator include a microporous film, a woven fabric, a non-woven fabric, and a green compact, and among these, a non-woven fabric is preferable from the viewpoint of output characteristics and production cost. The material of the separator is not particularly limited, but it is preferably having alkali resistance, oxidation resistance, and reduction resistance. Specifically, polyolefin fibers are preferable, and for example, polypropylene or polyethylene is preferable. Other materials include polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, and aramid. Further, these separators may be coated with ceramics to improve heat resistance, liquid friendliness, and gas permeability.

Since polyolefin fibers are hydrophobic, they need to be treated with hydrophilicity. When used in a hydrogen gas atmosphere, a separator treated with fluorine gas is preferable. Further, a separator coated or coated with a metal oxide on the surface is preferable.

A separator that has been imparted with hydrophilicity by treatment with fluorine gas or coated with a metal oxide can be expected to have a long life because the hydrophilicity is not easily lost by hydrogen even when used in hydrogen gas.
In the fluorine gas treatment, for example, the fiber surface of the non-woven fabric can be made hydrophilic by exposing the non-woven fabric to fluorine gas diluted with an inert gas in an airtight space. Examples of the metal oxide include titanium oxide, zirconia, yttrium oxide, hafnium oxide, calcium oxide, magnesium oxide, and scandium oxide. Of these, zirconia (ZrO ₂ ) or yttrium oxide (Y ₂ O ₃ ) is preferable. Since the metal oxide has hydrophilicity and is not easily deteriorated by hydrogen, it can maintain hydrophilicity for a long period of time and suppress the dryout of the electrolytic solution.

The negative electrode and the positive electrode are overlapped with each other via a separator impregnated with an electrolytic solution in advance and stored in the outer body of the battery, and then sealed to assemble the battery. After the battery assembly is completed, the air inside the battery is removed by evacuating from the electrolyte and hydrogen gas supply ports. Next, a 4 MPa hydrogen gas tank is connected to the hydrogen gas supply port, and hydrogen gas is sealed inside the battery. At this point, the negative electrode is chemically charged by hydrogen gas and is in a fully charged state. Preferably, the battery is regulated to have a positive electrode.

The hydrogen gas supplied to the battery is held in the gap inside the battery, so it does not require a special space like a hydrogen storage chamber. The size of the battery does not increase to hold the hydrogen gas. Then, the oxygen gas generated at the positive electrode immediately combines with the hydrogen gas held in the voids of the positive electrode to become water, so that the conductive auxiliary agent contained in the positive electrode is not oxidized. Further, since the oxygen gas leaked to the outside of the positive electrode is combined with the hydrogen gas sealed in the battery and the hydrogen gas held in the hydrogen storage alloy, the hydrogen storage alloy is not oxidized.

In a secondary battery, the charging reaction itself is an exothermic reaction, so if you try to keep the battery fully charged by continuously charging it under constant voltage control, the battery temperature will rise due to overcharging → the internal resistance of the battery will decrease → charging. It causes a vicious cycle of increasing current → further increasing battery temperature, leading to an increase in battery internal pressure and deterioration of battery performance. Therefore, when applying the secondary battery to applications that require it to be maintained in a fully charged state at all times, sufficient consideration should be given to prevent overcharging, or charge control should be performed to prevent overcharging. It is necessary to do.

According to the hydrogen-filled battery of the present invention, when floating charging is performed, hydrogen gas is generated from the negative electrode, and as the charging progresses, the amount of hydrogen gas generated increases and the hydrogen gas concentration inside the battery rises. According to the Nernst equation, the potential of the negative electrode decreases as the hydrogen gas concentration inside the battery increases. As a result, the terminal voltage of the battery gradually rises and finally becomes equal to the charging voltage. That is, as charging progresses, the battery potential rises and when it becomes equal to the charging voltage, the charging current stops flowing, and charging is virtually stopped. Here, the hydrogen gas generated from the negative electrode is stored in the battery as chemical energy.

From the above, the secondary battery of the present invention can be charged in a floating manner without taking measures to limit the amount of charge. As a result, the secondary battery can always be maintained in a fully charged state without sacrificing battery life. This can be said to be the first feature of the battery filled with hydrogen.

The second feature of the hydrogen-filled battery is that the discharge starts from the voltage at which charging is completed. That is, the discharge starts from the voltage at the end of charging. However, when switching from charging to discharging, a voltage drop due to the switching of the redox reaction may be observed, but the degree of the voltage drop is slight.

It should be noted here that the end of charging is not exactly the time when charging is simply stopped. The end of charging is the time when as much charging as possible is completed without sacrificing the life, and in the secondary battery according to the present invention, the charging current does not flow and charging ends. Actually, it takes time for the charging current to become zero because a minute current continues to flow as it approaches full charge. The discharge start voltage is the voltage at the start of discharge of the battery that has been charged as it is. Therefore, the battery is in a state before it is discharged due to use or spontaneously discharged.

The DC power system according to the present invention will be described with reference to FIG. FIG. 1 is a system diagram showing a schematic configuration of a DC power system. The AC power system 11 is connected to the DC power system 21 via a bidirectional inverter 12. A large number of consumers 13 are connected to the AC power system 11, and AC power can be supplied to each customer 13. A power storage facility 22, a water electrolysis device 25, a fuel cell 26, and a BPS (Battery Power System) 27 are connected to the DC power system 21, and a large number of child batteries 23 are connected to the power storage facility 22 which is a master battery. ..

The bidirectional inverter 12 has, for example, the control characteristics shown in FIG. 5, and the direction and characteristics of the electric power can be changed. When the operating voltage is larger than the reference voltage V0, it is forward-converted and converted from AC power to DC power, and when it is smaller than the reference voltage V0, it is reverse-converted and converted from DC power to AC power. The reference voltage V0 may be a changeable set value, or may be adjusted by using a control variable specified separately. The control characteristics of the bidirectional inverter 12 can be changed by adjusting the parameters.

For example, when the voltage of the AC power system 11 is larger than the predetermined value and the voltage of the DC power system 21 is smaller than the predetermined value, the AC power system 11 to the DC power system 21 are automatically adjusted according to the control characteristics of the bidirectional inverter 12. It is possible to transmit power to the power grid and adjust the power, and vice versa.

The DC power system 21 and the power storage equipment 22 capable of floating charging are directly connected. Directly connected here means that it is connected without going through a device that regulates charging. In general, when a secondary battery is overcharged, its life characteristic deteriorates remarkably, so control is performed to stop charging before it is fully charged. Since the power storage equipment 22 can be charged in a floating manner, such a control device is not required.

The power storage equipment 22 may be a secondary battery using a hydrogen storage alloy as a negative electrode material and hydrogen as a negative electrode active material. An example of such a secondary battery is a nickel-metal hydride battery filled with hydrogen gas. Such a secondary battery can be charged until the terminal voltage becomes equal to the charging voltage and the charging current stops flowing. At this time, the voltage at the end of charging and the voltage at the start of discharging are equal. It is possible to maintain a fully charged state at all times without sacrificing battery life.

The power storage equipment 22 is a so-called "parent battery", and a "child battery" is connected to the parent battery 22. The slave battery 23 may be directly connected to the DC power system 21. Here, the child battery 23 is a secondary battery capable of floating charging. The child battery 23 may be directly connected to the DC power system 21 and the parent battery 22 without going through a device for adjusting charging. Further, if the child battery 23 is a nickel-metal hydride battery filled with hydrogen gas as described above, it is possible to always maintain a fully charged state without sacrificing the battery life.

Since the charging from the power storage equipment 22 to the child battery 23 is a connection between secondary batteries having a small internal resistance, it is possible to charge in a shorter time than charging by AC power in a conventional charging stand. Further, since the power storage equipment 22 is maintained in a fully charged state, the child battery 23 is also fully charged.

As shown in FIG. 2, a part of the power storage equipment 22 and the child battery 23 may be connected in parallel. FIG. 3 shows an example of connection between the plurality of intermediate taps t1, t2, t3, tc provided in the power storage equipment 22 and the child batteries 23a, 23b, 23c. That is, DC power of various specifications can be taken out by the intermediate taps t1, t2, t3, and tc provided in the power storage equipment 22. Higher voltage power can be extracted from an intermediate tap in which a large number of cells are connected in series. A large amount of power can be extracted from an intermediate tap in which a large number of cells are connected in parallel. If these intermediate taps and the child battery 23 are connected in parallel, the child battery 23 can be charged.

In the power storage equipment 22 composed of a large number of cells, a DC power supply having a desired voltage specification can be configured by taking out the cells connected in series as an intermediate tap. A DC power supply having a desired capacity can be configured by taking out the cells connected in series and connected in parallel as an intermediate tap. By appropriately selecting the intermediate tap, the child battery 23 can be charged according to the specifications and applications of the child battery 23.

As an example of the child battery 23, a battery mounted on an electric vehicle can be specifically considered, but a battery mounted on a moving body such as a railroad vehicle, a forklift or a gantry crane may be used. Further, the child battery 23 may be a secondary battery attached to any one of consumer equipment and industrial equipment. Examples of consumer equipment include personal computers, telephone equipment, vacuum cleaners, and the like. Examples of industrial equipment include industrial robots and cargo handling machines.

If the load of the DC power system 21 increases and the voltage of the DC power system 21 drops below the voltage of the power storage facility 22, power is supplied from the power storage facility 22 to the DC power system 21. This power flow is determined by the magnitude of the voltage and does not require a special control device. That is, the DC power system 21 and the power storage equipment 22 are directly connected to each other. Since the power storage equipment 22 is a floating rechargeable secondary battery, it maintains a fully charged state without sacrificing battery life.

For example, when the child battery 23 is a battery mounted on an electric vehicle, the total power capacity of the child battery 23 becomes enormous because the number of electric vehicles is large. When a power shortage occurs in the DC power system 21, a part of the power of the child battery 23 can be promptly and effectively utilized to contribute to the stability of the DC power system 21. Since the parent battery 22 and the child battery 23 are connected without a device for adjusting the charge, it is possible to achieve power interchange without delay in control.

As shown in FIG. 4, the power storage equipment 22 and the child battery 23 may be connected via a bidirectional DCDC converter 24. If the bidirectional DCDC converter 24 is used, the voltage specifications of the child battery 23 and the voltage of the DC power system 21 can be matched.

Surplus power from a power plant (not shown) using natural energy provided in the DC power system 21 can be stored in the power storage facility 22. Further, if the DC power system 21 has a power shortage and the voltage drops, the power storage facility 22 can supply power.

When there is a surplus in the electric power of the DC power system 21, it can be stored as fuel gas by performing water electrolysis using the water electrolyzer 25, so that the surplus electric power can be effectively utilized. When the power of the DC power system 21 becomes insufficient, the fuel cell 26 makes it possible to make up for the power shortage by generating electricity using fuel gas of oxygen and hydrogen.

FIG. 6A is a graph showing an example of the characteristics of the power storage equipment 22 in which hydrogen gas is sealed when the voltage is taken on the horizontal axis and the amount of electricity is stored on the vertical axis. FIG. 6B is a graph showing the characteristics of the water electrolyzer 25 when voltage is taken on the horizontal axis and electric power is taken on the vertical axis. FIG. 6C is a graph showing the power generation characteristics of the fuel cell 26 when voltage is taken on the horizontal axis and electric power is taken on the vertical axis. FIG. 7 is a graph showing the relationship between voltage and electric power when the power storage equipment 22, the water electrolyzer 25, and the fuel cell 26 are integrated.

When the voltage of the DC power system 21 drops, the power from the power storage facility 22 and the fuel cell 26 is supplied to the DC power system 21. On the contrary, when the voltage is larger than the specified voltage of the DC power system 21, the power storage equipment 22 is charged and the water electrolyzer 25 generates fuel gas and stores surplus power.

As shown in FIG. 7, the DC power system 21 having the power storage equipment 22, the water electrolysis device 25, and the fuel cell 26 operates in response to the voltage of the DC power system 21 to automatically adjust the supply and demand in the DC power system 21. ..

BPS27 is, for example, a feeder system for electric railways. It is possible to supply DC power to the train 28 and recover the regenerative power from the train 28.

A DC power system equipped with a floating chargeable power storage facility can suitably configure a DC power system.

11 AC power system 12 Bidirectional inverter 13 Consumer 21 DC power system 22 Power storage equipment (parent battery)
23 Child battery 24 Bidirectional DCDC converter 25 Water electrolyzer 26 Fuel cell 27 BPS (Battery Power System)
28 train

Claims

A DC power system including a floating rechargeable master battery connected to the DC power system without a device for adjusting charge and a child battery connected to the master battery without a device for adjusting charge. ..
The DC power system according to claim 1, wherein the child battery is connected to an intermediate tap provided on the parent battery.
The DC power system according to claim 2, wherein the child battery can be floatingly charged.
The DC power system according to claim 2 or 3, wherein the child battery is a secondary battery attached to any one of a mobile body, a consumer device, and an industrial device.
The DC power system according to claim 4, wherein the moving body is any one of an electric vehicle, a railroad vehicle, a forklift, and a crane.
The DC power system according to any one of claims 1 to 5, wherein either or both of the water electrolyzer and the fuel cell and the parent battery are connected in parallel to the DC power system.
The DC power system according to any one of claims 1 to 6, wherein the feeder system of an electric railway is connected to the DC power system.
The DC power system according to any one of claims 1 to 7, wherein the child battery is connected to the DC power system via a DCDC converter.
The DC power system according to any one of claims 1 to 8, wherein the AC power system and the DC power system are connected by a bidirectional inverter.
The parent battery is a secondary battery in which hydrogen is sealed and the negative electrode active material is hydrogen, and can be charged until the terminal voltage becomes equal to the charging voltage and the charging current stops flowing. The DC power system described in item 1.