JP2019022376A - Dc power feeding system - Google Patents

Abstract

To provide a DC power feeding system capable of suppressing a cost increase and simplifying a system by eliminating installation of an inverter required for connecting a DC power generation system typified by photovoltaic power generation with a power system.SOLUTION: A DC power feeding system 10 which is a DC power supply system includes: a DC power supply (a power feeding station 1); a load apparatus 3; a secondary cell 2 sealed with hydrogen; and a power feeding path 7. The secondary cell and the load apparatus are connected in parallel to the DC power supply through the power feeding path. The secondary cell is sealed with hydrogen, thereby preventing degradation in performance by floating charge.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a DC power system using a secondary battery, and more particularly, to a DC power supply system that uses DC power as a power source and supplies DC power to consumers.

  In recent years, interest in distributed power sources, microgrids, renewable energy, and emergency power sources has increased as a supplement to power supply in the power system. Among them, the spread of power generation systems using natural energy such as solar power generation and wind power generation is expanding due to the increase in environmental conservation awareness such as CO2 reduction for the prevention of global warming.

  In a power generation system using natural energy, generated power is easily influenced by natural phenomena, and becomes a disturbance factor in supply and demand adjustment of the power system. As a supplement to this, it has been proposed to adjust the supply and demand by connecting a storage battery to a power generation system such as wind power generation.

  As the storage battery used for such a purpose, a battery capable of floating charging is used. Patent Document 1 discloses 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 performing charge control based on the measured internal pressure of the battery. It is disclosed.

  Photovoltaic power generation is a direct current power source that outputs direct current, and this direct current is converted into alternating current by an inverter and connected to a power system for grid interconnection. In addition, wind power generation is once converted into DC power because of the necessity of power supply and demand adjustment, and this DC current is converted into AC current by an inverter and connected to the power system for grid interconnection.

  As such an example, for example, Patent Document 2 discloses a conversion circuit that converts DC power, an inverter circuit, a transformer circuit that transforms the output of the inverter circuit, and a switch that opens and closes the transformer circuit and the power system. And a configuration for switching the setting of the transformer circuit according to the system voltage of the power system is described.

JP 2010-40297 A JP 2002-112461 A JP 2011-151961 A

  In the case of a nickel-metal hydride secondary battery, the charging reaction itself is an exothermic reaction, so it is not suitable for so-called floating charging, which always maintains a full charge state by continuously charging with a small current under constant voltage control. It is said that. In other words, if floating charging is performed with a nickel-metal hydride secondary battery, a vicious cycle of an increase in battery temperature due to overcharging → a decrease in battery internal resistance → an increase in charging current → a further increase in battery temperature is caused, resulting in an increase in battery internal pressure. Or battery performance. Therefore, when applying the nickel metal hydride secondary battery to an application that is required to be always fully charged, sufficient consideration is required so as not to overcharge.

  With the spread of electronic devices represented by personal computers, the installation of UPS has become indispensable for the stable operation of facilities. The UPS is a facility that receives AC power from the grid at all times and performs floating charging, and supplies power from the UPS when the voltage drops in the system to reduce the influence of the voltage drop.

  Moreover, when storing surplus electric power in a storage battery, a storage battery is floating-charged and the charge state is maintained. That is, when power shortage occurs, the battery is discharged, and when the power becomes excessive, the battery is charged and always kept in a fully charged state.

  The problem to be solved by the present invention is to enable power feeding using a storage battery that does not deteriorate the performance of the battery even if floating charging is performed.

  Since the power generation system using solar energy is a direct current power source that outputs direct current, in order to be connected to the power system, it is necessary to provide an inverter at the output and convert it to alternating current power. Inverters convert DC power into AC power by switching using a semiconductor element. However, high-voltage and large-current semiconductor elements are expensive, and the switching control circuit becomes complicated. In order to connect the DC power source to the power system, it is necessary to install an expensive inverter.

  One of the problems to be solved by the present invention is to suppress an increase in cost by omitting installation of an inverter necessary for connecting a DC power generation system represented by photovoltaic power generation to an electric power system. It is to simplify the system.

  If the power system is direct current instead of alternating current, no inverter is required. However, since the output of natural energy or renewable energy depends on natural conditions or the like, the power supply is stabilized by using a storage battery (for example, Patent Document 3).

  At present, many electric products have been operated with a direct current inside, and an alternating current received from a power system is converted into a direct current and used. There is a power loss when converting AC to DC. If power can be supplied with direct current, waste of power consumption can be eliminated.

  In order to achieve the above-described object, a DC power supply system according to the present invention is a DC power supply system including a DC power supply, a load facility, a secondary battery, and a power supply path. The secondary battery and the load facility are connected in parallel by the power feeding path, and hydrogen is enclosed in the secondary battery.

  According to this configuration, the charging current decreases when it is close to full charging, and the battery potential finally becomes equal to the charging voltage, so that the fully charged state can be maintained without damaging the secondary battery. Furthermore, even in a nickel metal hydride secondary battery that is not suitable for floating charging, floating charging is possible. It can be applied to uses such as a UPS that always require a fully charged state.

  In the direct current power supply method according to the present invention, the negative electrode active material of the secondary battery is hydrogen. In the direct current power supply method according to the present invention, the secondary battery has a sealed structure. Since the secondary battery employs a sealed structure, hydrogen gas generated from the negative electrode by charging is accumulated inside the secondary battery, and the hydrogen gas pressure increases. As the hydrogen gas concentration increases, the electrode potential of the negative electrode decreases, and as a result, the terminal voltage of the secondary battery increases.

  In the direct current power supply system according to the present invention, the positive electrode of the secondary battery has a metal oxide. In the direct current power supply system according to the present invention, the negative electrode of the secondary battery includes one or more of a hydrogen storage alloy, platinum, and palladium.

  In the direct current power supply method according to the present invention, a separator interposed between the positive electrode and the negative electrode is obtained by hydrophilic treatment of a polyolefin-based nonwoven fabric. Even if the separator provided with hydrophilicity is used in hydrogen gas, the hydrophilicity is hardly lost by hydrogen, and a long life can be expected.

  In the DC power supply system according to the present invention, the DC power supply is a constant voltage power supply. In the DC power supply system according to the present invention, a DC converter connected to an AC power system is connected in parallel to the DC power supply.

  In the DC power feeding method according to the present invention, the state of charge of the secondary battery is determined from the terminal voltage of the secondary battery based on the relationship between the terminal voltage of the secondary battery and the SOC determined in advance. In the DC power feeding method according to the present invention, the discharge start voltage of the secondary battery is equal to the charge end voltage immediately before the secondary battery.

  As described above, according to the DC power feeding method of the present invention, it is possible to perform floating charging that maintains a fully charged state without deterioration of battery performance. And it can apply to the use like which UPS always maintains a full charge state. In addition, the installation of the inverter can be omitted, so that an increase in cost can be suppressed, and the system can be simplified. Furthermore, power loss associated with AC / DC power conversion can be reduced.

It is an axial sectional view of a laminated battery. It is a charging / discharging characteristic view of a secondary battery. Voltage and temperature characteristics after floating charging. It is a charging / discharging characteristic curve which shows the example of a floating charging / discharging characteristic. It is a SOC characteristic figure of a secondary battery. It is a connection electric system figure of a direct-current power feeding system. It is an electrical diagram of a gantry crane.

  Hereinafter, although one embodiment concerning the present invention is described, the present invention is not limited to the following embodiment.

  Prior to describing each embodiment of the present invention, a nickel 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 metal hydride battery as long as the active material is hydrogen. For convenience of explanation, the first electrode will be described as a positive electrode and the second electrode will be described as a negative electrode.

  The current collector is not particularly limited as long as it has a high electrical conductivity and can conduct electricity to the held electrode material. The positive electrode current collector is preferably Ni as the current collector from the viewpoint of good stability in the electrolytic solution and good oxidation resistance. Note that iron coated with nickel may be used. The negative electrode current collector is preferably Ni or the like from the viewpoint of good stability in the electrolyte and reduction resistance. Note that iron coated with nickel or carbon may be used.

  As the shape of the current collector, there are a linear shape, a rod shape, a plate shape, a foil shape, a net shape, a woven fabric, a non-woven fabric, an expanded, a porous body, an embossed body, or a foamed body. An embossed body or a foamed body is preferable because of good characteristics.

  The positive electrode material is preferably a metal oxide. Examples thereof include silver oxide, manganese dioxide, and nickel oxyhydroxide. Examples of the negative electrode material include a hydrogen storage alloy, platinum, and palladium. Among these, from the viewpoints of hydrogen storage capacity, charge / discharge characteristics, self-discharge characteristics, and cycle life characteristics, it is preferable to be an AB5 type rare earth-nickel alloy containing a MmNiCoMnAl misch metal. Alternatively, a LaMgNi system called a superlattice hydrogen storage alloy is preferable. These alloys may be used alone or in combination of two or more.

  The conductive auxiliary agent is for imparting conductivity to the active material and increasing its utilization rate. The conductive additive used in this example is preferably a carbon material that does not elute into the electrolyte during discharge and is difficult to be reduced by hydrogen.

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

  Examples of the binder include polyacrylic acid soda, methyl cellulose, carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), ethylene-vinyl alcohol, ethylene vinyl acetate copolymer (EVA), polyethylene ( PE), polypropylene (PP), fluororesin, and styrene-ethylene-butylene-styrene copolymer (SEBS).

  Further, polytetrafluoroethylene (PTFE) may be used as a binder. PTFE is difficult to be reduced by hydrogen, and it is difficult to deteriorate even when used for a long time in a hydrogen atmosphere, and a long life can be expected.

  When the total of the positive and negative electrode materials, the binder, and the conductive auxiliary agent is 100% by weight, the weight ratio of the binder mixed in the positive and negative electrodes is preferably set to 20% by weight or less. % Is more preferable, and it is more preferable to set it to 5% by weight or less. The binder is poor in electron conductivity and ion conductivity, and when the proportion of the binder exceeds 20% by weight, it is difficult to increase the capacity.

  The positive electrode for an alkaline secondary battery of this embodiment may contain other components than the above-mentioned essential components as long as the purpose of the present invention is not impaired. The positive electrode for an alkaline secondary battery according to this embodiment is obtained, for example, by sufficiently and uniformly mixing a positive electrode material and a conductive additive, adding a binder thereto, and kneading it into a paste.

  The electrolyte is not particularly limited as long as it is used in a battery using hydrogen as an active material. For example, a salt such as potassium hydroxide (KOH), lithium hydroxide (LiOH), or sodium hydroxide (NaOH) in water. What was melt | dissolved is suitable. From the viewpoint of battery output characteristics, the electrolytic solution is preferably an aqueous sodium hydroxide solution.

  As a separator, a well-known thing used for the battery which uses hydrogen as an active material can be used. Examples of the shape of the separator include a microporous film, a woven fabric, a nonwoven fabric, and a green compact. Among these, a nonwoven fabric is preferable from the viewpoint of output characteristics and production cost. The material of the separator is not particularly limited, but preferably has alkali resistance, oxidation resistance, and reduction resistance. Specifically, polyolefin fibers are preferable, and for example, polypropylene or polyethylene is preferable. In addition to these, materials such as polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, and aramid can be used. Moreover, the separator which coat | covered ceramics to these separators and improved heat resistance, lyophilicity, gas permeability, etc. may be sufficient.

  Since polyolefin fibers are hydrophobic, they need to be subjected to a hydrophilic treatment. When used in a hydrogen gas atmosphere, a separator subjected to fluorine gas treatment is preferred. Moreover, the separator which apply | coated or coat | covered the metal oxide on the surface of the separator is preferable.

A separator imparted with hydrophilicity by treatment with fluorine gas or application of a metal oxide is less likely to lose hydrophilicity by hydrogen even when used in hydrogen gas, and a long life can be expected.
In the fluorine gas treatment, for example, the fiber surface of the nonwoven fabric can be hydrophilized by exposing the nonwoven fabric to a fluorine gas diluted with an inert gas in an airtight space. Examples of the metal oxide include titanium oxide, zirconium oxide, yttrium oxide, hafnium oxide, calcium oxide, magnesium oxide, and scandium oxide. Zirconia (ZrO ₂ ) or yttrium oxide (Y ₂ O ₃ ) is preferred. Since the metal oxide has hydrophilicity and is not easily deteriorated by hydrogen, it can maintain the hydrophilicity for a long period of time and suppress the dry-out of the electrolytic solution.

  The laminated battery 11 shown in FIG. 1 includes an exterior body 15, a current collector rod 17, and an electrode body 13 housed inside the exterior body as main components. The exterior body 15 includes a bottomed cylindrical can 12 and a disk-shaped lid member 16 attached to the opening 12c of the cylindrical can. The lid member 16 is closely fitted in the opening 12c of the cylindrical can after the electrode body 13 is accommodated.

  An electrode body 13 composed of a positive electrode 13a, a negative electrode 13b, and a separator 13c interposed between the positive electrode 13a and the negative electrode 13b is laminated in the axial direction of the cylindrical can 12 (X direction in FIG. 1), and the outer package 15 Is housed inside. The outer edge portion 13ab of the positive electrode is in contact with the inner surface 12a of the cylindrical can, and the positive electrode 13a and the cylindrical can 12 are electrically connected. A current collecting rod 17 passes through the center of the electrode body 13. The peripheral edge portion 13ba of the hole of the negative electrode is in contact with the shaft portion 17a, and the negative electrode 13b and the current collecting rod 17 are electrically connected.

  Since the laminated battery 11 does not have a hydrogen storage chamber in the battery, the size of the battery does not increase. The hydrogen gas supplied to the battery is not held in a special space such as a hydrogen storage chamber, but is held in a gap inside the battery. Examples of such a gap include a gap between the positive electrode and the outer package serving as the current collector, a gap between the negative electrode and the current collector rod serving as the current collector, a gap between the electrodes, and a gap between the electrode and the separator. . Furthermore, hydrogen gas is also retained in the voids existing inside the electrode. In particular, oxygen generated at the positive electrode is immediately combined with hydrogen gas held in the gap of the positive electrode to become water, so that the conductive additive contained in the positive electrode is not oxidized. In addition, hydrogen gas is replenished to the space | gap of a positive electrode from an electrode surface. Further, oxygen leaking out of the positive electrode is combined with the hydrogen gas sealed in the battery and the hydrogen gas held in the hydrogen storage alloy, so that the hydrogen storage alloy is not oxidized.

  Since the outer diameter of the negative electrode 13b is larger than the inner diameter of the cylindrical can 12, the negative electrode 13b is strongly pressed against the cylindrical can 12 and is in close contact with it. The heat generated in the negative electrode 13 b is directly transmitted to the cylindrical can 12. The heat generated in the positive electrode 13a is transferred to the negative electrode 13b through the separator 13c. Although the separator 13c is difficult to transmit heat, it is thin and only one sheet does not hinder heat conduction. As described above, the heat generated in the electrodes 13a and 13b is transmitted to the cylindrical can 12 with a small thermal gradient, and it is possible to suppress the temperature rise inside the laminated battery.

  If floating charging is performed with a conventional nickel metal hydride secondary battery, the battery temperature rises due to overcharging, resulting in a decrease in battery internal resistance and an increase in charging current. An increase in charging current causes a vicious circle that causes a further increase in battery temperature. When the temperature inside the battery is deteriorated due to the temperature rise inside the battery, if the temperature rise inside the battery is suppressed, the increase in current due to overcharging is suppressed.

  When floating charging is performed, hydrogen gas is generated from the negative electrode. Since the battery employs a sealed structure, the amount of generated hydrogen gas increases and the concentration of hydrogen gas inside the battery increases as charging progresses. 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 rises slowly and finally becomes equal to the charging voltage of the DC power supply. That is, as the charging progresses, the battery potential rises, and if it becomes equal to the voltage of the DC power supply, the charging current stops flowing and the charging is effectively stopped.

  The charge / discharge characteristics of the battery were measured using a nickel metal hydride battery having the structure shown in FIG. Prior to the measurement, the battery is filled with hydrogen gas in the following manner. That is, the lid member 16 of the nickel metal hydride battery 11 is provided with a supply port 19 for supplying an electrolyte and hydrogen gas, and a hydrogen gas tank 20 can be connected to the supply port 19.

  The negative electrode and the positive electrode are overlapped with each other through a separator previously impregnated with an electrolytic solution and accommodated in an exterior body, and sealed to assemble a battery. After battery assembly is complete, a vacuum is drawn to remove the air inside the battery. Next, a hydrogen gas tank of 4 MPa is connected and hydrogen gas is sealed inside the battery. Vacuum is again applied, and hydrogen gas is supplied into the battery from a 4 MPa hydrogen gas tank.

  FIG. 2 shows a charge curve and a discharge curve of a battery enclosing hydrogen gas used in the present invention. A part of the charging characteristic of the battery in which hydrogen gas is not sealed is indicated by a broken line. In FIG. 2, a battery without hydrogen gas sealed has a vicious cycle of battery temperature rise → battery internal resistance drop → charge current increase → battery temperature rise when overcharged, as indicated by the broken line. Increases rapidly. On the other hand, it can be seen that the battery in which the hydrogen gas indicated by the solid line in FIG. 2 is sealed has good charging characteristics without repeating the vicious circle described above.

  An assembled battery is configured for the unit cell used in the measurement of FIG. 2, and the discharge characteristics after floating charging and the overall temperature of the battery are measured. The results are shown in FIG. Curve (1) in the figure is the total voltage of the battery pack. It turns out that the favorable discharge characteristic is shown. Curve (2) in the figure is the temperature of each part inside the battery, and curve (3) is the room temperature at the time of measurement. It can be seen that there is no variation in the battery temperature, and the temperature hardly increases. This is because the heat generated inside the battery is quickly released to the outside.

  FIG. 4 shows a charge / discharge characteristic curve when the charge voltage is a parameter and floating charge is performed using the nickel metal hydride battery according to the present invention. The vertical axis represents the battery potential in units of V (volts), and the horizontal axis represents SOC in units of%. The peak potential changes depending on the charging voltage. As charging progresses, hydrogen gas is generated, the hydrogen gas concentration inside the battery rises, the electromotive voltage rises, and the battery potential increases. When the battery potential becomes equal to the charging voltage, the charging current stops flowing.

The characteristic curve shown in FIG. 4 is an example of a nickel metal hydride battery when nickel oxyhydroxide is used as the positive electrode material. When the positive electrode material is silver oxide, the characteristic curve is slightly lower than the electrode potential shown in FIG. In the case of manganese dioxide, the electrode potential is slightly lowered (about 0.2 V).

  Another feature in FIG. 4 is that discharge starts from a voltage at which charging is stopped. As shown in FIG. 4, the discharge is started from a voltage that shows a peak in charge. In the conventional nickel metal hydride battery, the discharge start voltage is not equal to the charge end voltage. However, when switching from charging to discharging, the potential due to the switching of the oxidation-reduction reaction may decrease, but the degree is slight.

  FIG. 5 shows an SOC characteristic diagram of the battery when nickel oxyhydroxide is used as the positive electrode material. In the characteristic diagram, the horizontal axis indicates the floating voltage in V units, and the vertical axis indicates the SOC in% units. The floating voltage and the SOC are theoretically in a linear relationship as shown by a broken line in FIG. Specifically, when the floating voltage is 1.28V, the SOC is 0%, and when the floating voltage is 1.5V, the SOC is 100%. The points indicated by dots are measurement results, and are slightly deviated from the theoretical values due to measurement errors. From this figure, it can be seen that the state of charge (SOC) of the battery can be easily known by measuring the voltage of the battery.

  Many methods for measuring the SOC of a battery have been proposed, but many of them have complicated measurement or calculation methods, and many of them have errors in measurement results. However, in the battery capable of floating charge proposed in the present invention, the relationship between the battery potential and the SOC is linear and can be obtained theoretically. Therefore, by measuring the battery potential, it is easy and accurate. The state of charge (SOC) of the battery can be easily known. However, since the relationship between the potential and the SOC depends on the positive electrode material, it is necessary to prepare a theoretical value suitable for the positive electrode material.

FIG. 6 is a connection electric system diagram for explaining a DC power feeding method using a battery according to the present invention. The power supply station 1 is a power plant of a DC power source and supplies a DC current to the DC power system 10. The power feeding station 1 may be, for example, a solar power station, or a wind power station or a combination of wind power generation and a battery.

  The battery 2 and the load facility 3 are connected to the power supply station 1 in parallel. The battery 2 is a battery capable of floating charging as described above. The load facility 3 is a facility in a consumer who uses a direct current as a load. Although UPS etc. are mentioned as load equipment, it is not limited to this. A feeding station 1, a battery 2 and a load facility 3 are connected by a feeding line 7 to constitute a DC feeding system.

  A direct current may be connected to the DC power system 10 from the commercial power system 6 via the transformer 5 and the rectifier 4.

  FIG. 7 is an electrical system diagram of the gantry crane. A gantry crane is an example of equipment in which floating charging is performed. The AC power received from the system is stepped down by the transformer 22 and then converted into DC power by the converter 23, and the inverter 26 is inversely converted to AC power having an appropriate frequency and voltage to drive the cargo handling motor 27. In the wharf that is not blessed with electric power circumstances, electric power is obtained from the large diesel generator 21 directed toward the inside of the machine room.

  Since the cargo handling motor 27 requires a large amount of electric power instantaneously, the battery 28 assists the electric power for driving the cargo handling motor 27. For this reason, the battery 28 needs to be fully charged in preparation for unexpected cargo handling, and is floatingly charged by a direct current from the converter 23.

  The direct current power supply method of the present invention can be suitably used for an electric power system using a power generation facility using natural energy as a power source.

DESCRIPTION OF SYMBOLS 1 Feeding station 2 Battery 3 Load equipment 5 Transformer 6 Electric power system 7 Feed line 10 DC power system 11 Cylindrical laminated battery 12 Cylindrical can 13 Electrode body 14 Insulation board 15 Outer body 16 Lid member 17 Current collector 18 Bearing 21 Generator 21 22 Transformer 23 Converter 26 Inverter 27 Motor 28 Battery

Claims (10)

A direct current power supply system comprising a direct current power supply, a load facility, a secondary battery, and a power supply path,
For the DC power source, the secondary battery and the load facility are connected in parallel by the power supply path,
A DC power feeding method in which hydrogen is sealed in the secondary battery.   The DC power feeding method according to claim 1, wherein the negative electrode active material of the secondary battery is hydrogen.   The DC power feeding method according to claim 2, wherein the secondary battery has a sealed structure.   The direct current power supply system according to claim 3, wherein the positive electrode of the secondary battery has a metal oxide.   The DC power feeding method according to claim 3, wherein the negative electrode of the secondary battery includes one or more of a hydrogen storage alloy, platinum, and palladium.   The DC power feeding method according to any one of claims 1 to 5, wherein the separator interposed between the positive electrode and the negative electrode is obtained by hydrophilic treatment of a polyolefin-based nonwoven fabric.   The DC power supply method according to any one of claims 1 to 6, wherein the DC power supply is a constant voltage power supply.   The DC power supply according to any one of claims 1 to 7, wherein a charging state of the secondary battery is determined from a terminal voltage of the secondary battery based on a relationship between a terminal voltage of the secondary battery and SOC obtained in advance. method.   The DC power feeding method according to any one of claims 1 to 3, wherein a DC converter connected to an AC power system is connected in parallel to the DC power supply. The DC power feeding method according to any one of claims 1 to 8, wherein a discharge start voltage of the secondary battery is equal to a charge end voltage immediately before the secondary battery.

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