Power System

Abstract

A DC grid GR1 has a bus BUS having connected thereto a power element EL1 which is a power generator and power elements EL2, EL3 which are a plurality of power devices. A plurality of power storage devices BAT that can be charged and can supply electric power are connected to the bus BUS from one end to the other end at a prescribed interval, and conduct transfer of electric power with respect to the bus BUS. By connecting the power storage devices BAT to the bus BUS at the prescribed interval in a dispersed manner, a large electrical inertial force is applied in the bus BUS and any voltage difference therein can be eliminated within a short period of time.

Description

[Technical Field]

[0001] The present invention relates to power systems. [Background technology]

[0002] Smart cities and compact cities, which realize Society 5.0 by highly integrating the cyberspace and physical space of CPS (Cyber ​​Physical System), are expected to realize the efficiency and sophistication of urban and regional functions and services, as well as to achieve both the resolution of social issues such as decarbonization and economic development through changes in industrial structure brought about by digital transformation.

[0003] With the rise in investments that take into account the three elements of environment, society, and governance (ESG investments) and the adoption of the 2030 Agenda for Sustainable Development (Sustainable Development Goals (SDGs)) at the United Nations Summit in September 2015, the number of members of RE100 (Renewable Energy 100%), which is open to companies that have declared that they will operate their businesses using only renewable energy, is also increasing.

[0004] The global smart city market is estimated to reach a cumulative scale of 3,100 trillion yen over the 20 years from 2010 to 2030, with the core energy-related market expected to reach approximately 720 trillion yen for smart grids, approximately 310 trillion yen for next-generation automobiles such as electric vehicles, and approximately 380 trillion yen for renewable energy.As a result, many countries and regions are promoting smart city plans, and some of these plans are already underway.

[0005] Patent Document 1 proposes a system in which distributed power sources including solar power generation, wind power generation, storage batteries, and power storage systems, social infrastructure including EVs and charging stations, a Home Energy Management System (HEMS), a Building Energy Management System (BEMS), and a power plant are interconnected by a communication grid and a power grid.

[0006] Some power grids use a DC bus for power supply, and one example of an invention for stabilizing the voltage of a DC bus in a DC power supply system is the DC power supply system disclosed in Patent Document 2. In this DC power supply system, a solar power generation system and a power storage unit are connected to the DC bus. The power storage unit is configured with two sets of storage batteries, each made up of secondary batteries, connected in series. The two sets of storage batteries are connected in series between the positive and negative bus lines of the DC bus via a battery control unit, with the midpoint grounded. Repeated charging and discharging of each storage battery levels the line voltage between the positive bus line and the midpoint and the line voltage between the negative bus line and the midpoint. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2013 / 172088 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-228023 Summary of the Invention [Problem to be solved by the invention]

[0008] A DC bus is connected to multiple loads, such as power generation systems and electrical equipment. For example, when an EV is connected and a quick charge requiring a temporary large current (power) is performed, the voltage at that point drops, causing temporary voltage unevenness on the DC bus. This voltage unevenness is equalized by current flowing through the electrical resistance of the DC bus if sufficient time passes after the large current (power) load is disconnected. However, if the power cable used in the DC bus is thin and has a high electrical resistance per unit length, it may take a long time for the voltage unevenness to be resolved using this passive equalization alone.

[0009] In the DC power supply system of Patent Document 2, the storage unit is used to level the voltage of the DC bus. However, if the storage units are concentrated at any position on the DC bus, there is a risk of a voltage difference occurring between the storage units and positions far from the storage units.

[0010] The present invention has been made in view of the above, and has an object to eliminate the voltage difference in the DC bus in a shorter time. [Means for solving the problem]

[0011] A power system according to one aspect of the present invention includes a DC bus to which a power generation device and a plurality of power devices are connected, and a plurality of power storage devices connected at predetermined intervals from one end of the DC bus to the other end of the DC bus and supplying and receiving power to and from the DC bus.

[0012] The DC bus may be configured to include a reference line, a first power supply line having a predetermined voltage difference from the reference line, and a second power supply line having a predetermined voltage difference from the reference line.

[0013] The power storage device may include a first power storage device and a second power storage device, a first pole of the first power storage device and a first pole of the second power storage device connected via a first switch, the first pole of the first power storage device connected to the first power supply line, the first pole of the second power storage device connected to the second power supply line via a second switch, the second pole of the first power storage device and the second pole of the second power storage device connected to the reference line, and a balance control unit that controls the first switch and the second switch to equalize the charging rates of the first power storage device and the second power storage device.

[0014] The power storage device may include a first power storage device and a second power storage device, a first pole of the first power storage device connected to the first power supply line via a fourth switch, a second pole of the first power storage device connected to the first pole of the second power storage device or the reference line via a third switch, a first pole of the second power storage device connected to the second power supply line via a second switch, a connection between the first pole of the first power storage device and the first pole of the second power storage device via a first switch, and a second pole of the second power storage device connected to the reference line, and a balance control unit that controls the fourth switch from the first switch to equalize the charging rates of the first power storage device and the second power storage device.

[0015] The second power supply line may be connected to an AC power system via a converter that converts AC to DC.

[0016] The DC bus may be connected to a power gate that controls power interchange with other DC buses. [Effects of the Invention]

[0017] The power system of the present invention includes a DC bus to which a power generation device and a plurality of power devices are connected, and a plurality of power storage devices connected at predetermined intervals from one end of the DC bus to the other end of the DC bus for supplying and receiving electric power to the DC bus. By connecting the plurality of power storage devices to the DC bus at predetermined intervals, a large electrical inertia force can be applied to the DC bus, and voltage differences can be eliminated in a short time. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing the configuration of a network system according to an embodiment. [Figure 2] FIG. 2 is a diagram showing the configuration of a base station and a DC grid. [Figure 3A] FIG. 3A is a diagram illustrating an example of connection of a power storage device and a load to a bus. [Figure 3B] FIG. 3B shows the results of the simulation. [Figure 4A] FIG. 4A is a diagram illustrating an example of connection of a power storage device and a load to a bus. [Figure 4B] FIG. 4B shows the results of the simulation. [Figure 5] FIG. 5 is a diagram showing the configuration of a DC grid. [Figure 6A] FIG. 6A is a diagram showing a method for controlling the first switch and the second switch. [Figure 6B] FIG. 6B is a diagram showing a method for controlling the first switch and the second switch. [Figure 7A] FIG. 7A is a diagram showing a method of controlling a switch in a modified example. [Figure 7B] FIG. 7B is a diagram showing a method of controlling the switches in the modified example. [Figure 7C] FIG. 7C is a diagram showing a method of controlling the switches in the modified example. [Figure 8] FIG. 8 shows a modified example of a DC grid. [Figure 9A] FIG. 9A is a diagram showing the configuration of a three-wire bus. [Figure 9B] FIG. 9B is a diagram showing the configuration of a three-wire bus. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below. In addition, in the description of the drawings, the same or corresponding elements are appropriately designated by the same reference numerals.

[0020] [First embodiment] 1 is a diagram showing the configuration of a network system according to one embodiment of the present invention. Network system 1 is a power and communication converged network that combines a wireless communication network conforming to the 5G (fifth generation mobile communication system) standard, including base station 10A, base station 10B, and multiple antennas (not shown), with a power network formed of multiple DC grids GR1 to G4, which are power transmission networks.

[0021] Base station 10A and base station 10B are wireless base stations forming a 5G wireless communication network. 5G is characterized by "ultra-high speed," "ultra-low latency," and "multiple simultaneous connections." "Ultra-low latency" guarantees a communication latency of, for example, approximately 1 millisecond or less. The wireless communication standard is not limited to 5G, but may be a communication standard for a post-5G generation mobile communication system called B (Beyond) 5G. A communication standard with guaranteed communication latency is preferable. Base station 10A forms a communication area CELL1, which enables communication with wireless terminals performing 5G wireless communication, using multiple antennas (not shown). Base station 10B forms a communication area CELL2, which enables communication with wireless terminals performing 5G wireless communication, using multiple antennas (not shown). The range of communication area CELL1 is, for example, a 1-kilometer radius from base station 10A, but is not limited to this. While FIG. 1 illustrates two base stations 10A and 10B, the number of base stations included in network system 1 is not limited to two and may be three or more.

[0022] Within the communication area CELL1 and the communication area CELL2, a plurality of predetermined buses BUS are installed. The bus BUS, which is a DC bus, is a DC power line to which a plurality of power devices including power generation devices and power storage devices are connected. Within the communication area CELL1 and the communication area CELL2, the plurality of buses BUS form DC grids GR1 to GR4, which are DC power transmission networks.

[0023] A power gate GA is provided for the DC grids, which exchanges power between DC grids GR1 to GR4. A power gate GA is also provided between the DC grid provided in communication area CELL1 and the DC grid provided in communication area CELL2, and controls the amount and direction of power exchanged between the DC grids, thereby exchanging power across communication areas CELL1 and CELL2. The power gate GA has 5G wireless communication capabilities and also functions as a wireless terminal, communicating information with an MEC server 101 (described later) via an antenna (not shown).

[0024] The cloud system 2 is a system that provides various services via a network such as the Internet, and includes a centralized control device 1000. The centralized control device 1000 is connected to a base station 10A and a base station 10B. The centralized control device 1000 is a server device that has the function of controlling power interchange between DC grids GR1 to GR4 included in a communication area CELL1 and DC grids GR1 to GR4 included in a communication area CELL2.

[0025] Fig. 2 is a diagram showing an example of the configuration of the base station 10A and the DC grid GR1. Note that, since the configuration of the base station 10B is the same as that of the base station 10A, Fig. 2 shows the configuration of the base station 10A as a representative, and does not show the configuration of the base station 10B. Also, to prevent the drawing from becoming too complicated, Fig. 2 shows the configuration of the DC grid GR1 as a representative of the DC grids GR1 to GR4 included in the communication area CELL1 formed by the base station 10A.

[0026] Multiple antennas ANT are arranged within the communication area CELL1. The antennas ANT are distributed antennas that form a 5G wireless communication network. The antennas ANT function as RUs (Radio Units) in 5G wireless communication. Each of the multiple antennas ANT connected to base station 10A by optical fiber cables forms a small cell that enables communication with wireless terminals, and these multiple small cells form the communication area CELL1. The small cells formed by the antennas ANT have a radius of, for example, 125 m centered on the antenna ANT. Note that multiple antennas ANT are also connected to base station 10B by optical fiber cables, and each of the multiple antennas ANT connected to base station 10B forms a small cell that enables communication with wireless terminals, and these multiple small cells form the communication area CELL2.

[0027] The base station 10A has an MEC server 101, an AC / DC converter 102, a power storage unit 103, and a CU / DU 104. The DC grid GR1 has a bus BUS, converters CON1 to CON3, power elements EL1 to EL3, and a plurality of power storage devices BAT. The DC grid GR1 is provided within a communication area formed by, for example, four antennas ANT. Note that the number of antennas ANT forming the communication area including the DC grid GR1 is not limited to four, and may be three or less or five or more.

[0028] First, the configuration of the base station 10A will be described. The AC / DC converter 102 is connected to a commercial power system 3. The AC / DC converter 102 converts AC power supplied from the power system 3 into DC power and supplies it to the MEC server 101 and the power storage unit 103.

[0029] The power storage unit 103 is composed of one or more storage batteries. A power generation device such as a renewable energy source may be connected to the power storage unit 103. The power stored in the power storage unit 103 is supplied to the MEC server 101 and the CU / DU 104 as driving power. The power storage unit 103 may also supply power to the antenna ANT via a metal cable.

[0030] The CU / DU 104 has the functions of a CU (Central Unit) and a DU (Distributed Unit) in 5G communication. The CU / DU 104 is connected to a plurality of antennas ANT that form a communication area via optical fiber cables. The CU / DU 104 is also connected to the MEC server 101.

[0031] The MEC server 101, which is an example of a control device, is a MEC (Mobile Edge Computing) server device installed in a position close to a wireless terminal. The MEC server 101 includes a control unit 111, a storage unit 112, and a communication unit 113.

[0032] The control unit 111 performs various arithmetic processing to realize the functions of the MEC server 101, and is configured to include processors such as a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), a DSP (Digital Signal Processor), and a GPU (Graphics Processing Unit). The functions of the control unit 111 are realized by the control unit 111 reading out and executing various programs from the storage unit 112.

[0033] For example, by the control unit 111 reading and executing various programs from the memory unit 112, it communicates information with the storage device BAT, the converters CON1 to CON3, and the power elements EL1 to EL3, thereby realizing functions such as comprehensively managing the state of the DC grids GR1 to GR4 installed within the communication area CELL1, centrally controlling the converters CON1 to CON3, controlling the power interchange between the DC grids GR1 to GR4, and controlling the power interchange between the DC grids installed in adjacent communication areas in response to instructions from the centralized control device 1000.

[0034] The storage unit 112 includes, for example, a ROM (Read Only Memory) that stores various programs and data used by the control unit 111 to perform arithmetic processing. The storage unit 112 also includes, for example, a RAM (Random Access Memory) that is used as a workspace when the control unit 111 performs arithmetic processing and for storing the results of the arithmetic processing of the control unit 111. The storage unit 112 may also include an auxiliary storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive).

[0035] The communication unit 113 includes a communication module that performs information communication via wire or wirelessly. The communication unit 113 is connected to the central control device 1000. The communication unit 113 performs information communication with the central control device 1000 via the Internet.

[0036] Next, the configuration of a DC grid GR1, which is an example of a power system, will be described. The bus BUS is composed of a ground line GL, which is an example of a reference line, and a power line PL, which is an example of a first power line, and is, for example, 1 km long. The voltage of the power line PL has a potential difference of, for example, +400 V with respect to the ground line GL. The ground line GL, which is an example of a reference line, may be grounded.

[0037] The power storage device BAT is, for example, a stationary power storage device that can supply and charge power, and is connected to the bus BUS. The stationary power storage device is an example of a permanently installed in-facility power storage device, such as a lithium-ion battery or an electric double layer capacitor. The multiple power storage devices BAT are distributed at predetermined intervals and connected directly to the bus BUS without going through a DC / DC converter. The intervals between the multiple power storage devices BAT are, for example, 100 m to 200 m. Note that, in FIG. 2, three power storage devices BAT are shown to avoid cluttering the drawing, but four or more power storage devices BAT may be connected to the bus BUS. Even when there is only one power storage device BAT or when multiple power storage devices BAT are installed in one location, the voltage of the bus BUS drops with increasing distance from the power storage device BAT. However, by connecting as many power storage devices BAT as possible, even if they have small capacities, to the bus BUS at predetermined intervals without going through a DC / DC converter, a large electrical inertia force can be applied to the bus BUS, and the occurrence of voltage differences in the bus BUS can be suppressed.

[0038] 3B is a graph showing the results of a simulation of voltage changes at the center of the bus BUS when a power storage device BAT is connected to both ends of the bus BUS and a load LO is connected to the center as shown in FIG. 3A. In this simulation, the length of the bus BUS is set to 1 km, and a current of 100 A flows to the load LO. The internal resistance of the power storage device BAT is set to 0.2 Ω, the capacity is set to 25 Ah, and the SOC at the time when power supply to the load starts is set to 80%. The solid line in FIG. 3B indicates the voltage at the position where the power storage device BAT is connected, and the dashed line in FIG. 3B indicates the voltage at the position where the load LO is connected.

[0039] FIG. 4B is a graph showing the results of a simulation of voltage changes at the center of a bus BUS when five power storage devices BAT are distributed along the bus BUS as shown in FIG. 4A and a load LO is connected to the center. In this simulation, the bus BUS is 1 km long and a current of 100 A flows to the load LO. The interval between the power storage devices BAT is 250 m, the internal resistance of the power storage device BAT is 0.5 Ω, the capacity is 10 Ah, and the SOC at the time when power supply to the load starts is 80%. The solid line in FIG. 4B indicates the voltage at the position where the leftmost power storage device BAT is connected, the dashed-dotted line in FIG. 4B indicates the voltage at the position where the second power storage device BAT from the left is connected, and the dashed line in FIG. 4B indicates the voltage at the position where the load LO is connected.

[0040] Comparing the voltage at the position where the load LO is connected in FIG. 3B with FIG. 4B, it can be seen that the case where five power storage devices BAT are distributed has a smaller voltage drop and a higher electrical inertia after the same amount of time has elapsed.

[0041] It is preferable that the number of cells of the plurality of power storage devices BAT be adjusted so as to match the reference voltage set for the bus BUS. A DC circuit breaker that cuts off the current between the bus BUS and the power storage device BAT may be provided between the bus BUS and the power storage device BAT.

[0042] The power element EL1 is, for example, a solar power generation device capable of generating and supplying power, and is connected to the converter CON1. ​​A solar power generation device is an example of a power generation device that generates power using renewable energy. The converter CON1 has a function of converting the voltage of the DC power supplied by the power element EL1 and outputting the converted voltage to the bus BUS. Note that the power element EL1 is not limited to a solar power generation device, but may be a renewable energy source such as a wind power generation device or a geothermal power generation device. Note that if the power element EL1 is an element that does not control the amount of power generated from the viewpoint of efficiency, such as a solar power generation device, the converter CON1 may execute MPPT (Maximum Power Point Tracking) control, which operates when power corresponding to the amount of power generated by the power element EL1 is input, so that the output power to the bus BUS is maximized at that amount of power generated.

[0043] The power element EL2 is, for example, an on-board power storage device capable of supplying, consuming, and charging power, and is connected to the converter CON2. The on-board power storage device is mounted on an electric vehicle EV and is an example of a mobile, non-stationary power storage device. The converter CON2 has the function of converting the voltage of DC power supplied by the power element EL2 and outputting it to the bus BUS, and also converting the voltage of DC power supplied from the bus BUS and outputting it to the power element EL2 for charging. The converter CON2 is provided, for example, in a charging station or residential charging equipment, but may also be mounted on the electric vehicle EV.

[0044] As an example, the power element EL3 is a ZEH (Net Zero Energy House) that can supply, consume, and charge power, and is connected to the converter CON3. The ZEH has, for example, a solar power generation device, a storage battery, and electrical appliances such as an air conditioner and a refrigerator as power loads. The converter CON3 converts the voltage of the DC power supplied by the power element EL3 and outputs it to the bus BUS, and also converts the voltage of the DC power supplied from the bus BUS and outputs it to the power element EL3, thereby charging the storage battery of the power element EL3.

[0045] In addition, in the bus BUS, the diameter can be made thicker to provide a large capacity in areas where a large load is connected and a large current flows, such as for rapid charging of power element EL2, and the diameter can be made narrower to provide a small capacity in areas where a large load is not connected, such as power element EL3.

[0046] The converters CON1 to CON3 have sensors that measure electrical characteristic values ​​of the power of the bus BUS, and measure, as electrical characteristic values, for example, the current value, voltage value, and power value of the bus BUS. In addition, the power storage device BAT, the converters CON1 to CON3, and the power elements EL1 to EL3 also function as wireless terminals equipped with 5G wireless communication capabilities, and communicate information with the MEC server 101 via the antenna ANT. For example, the power storage device BAT transmits information such as power storage capacity and power storage state to the MEC server 101. In addition, the power elements EL1 to EL3 transmit information such as power generation capacity, power generation state, power storage capacity, power storage state, and power load to the MEC server 101, and the converters CON1 to CON3 transmit the measured electrical characteristic values ​​to the MEC server 101.

[0047] The converters CON1 to CON3 also store control information defining rules for autonomous control and determine their own operation according to these rules. For example, the rules indicated by the control information stored by each converter CON1 to CON3 are defined so that power in the bus BUS is smoothed according to the power supply and reception states of the power elements EL1 to EL3. In each of the DC grids GR1 to GR4, the converters CON1 to CON3 perform autonomous decentralized control according to these rules. In the DC grids GR1 to GR4, the power generation capacity, power generation state, power storage capacity, power storage state, power load, and electrical characteristic values ​​of the bus BUS fluctuate from moment to moment. However, by performing the autonomous decentralized control in each of the DC grids GR1 to GR4, these fluctuations can be counteracted, power in the bus BUS is smoothed, and power supply and demand within the DC grids GR1 to GR4 can be stabilized. Note that various control methods, such as feedback control, can also be applied to the DC grids GR1 to GR4.

[0048] The rules held by the converters CON1 to CON3 can be updated by the MEC server 101. The MEC server 101 acquires information such as power generation capacity, power generation state, power storage capacity, power storage state, and power load transmitted from the power storage device BAT and the power elements EL1 to EL3, and information on electrical characteristic values ​​such as current value, voltage value, and power value of the bus BUS transmitted from the converters CON1 to CON3, generates rules suitable for power smoothing of the bus BUS based on the acquired information, and updates the rules held by the converters CON1 to CON3 with the generated rules.

[0049] Furthermore, in this embodiment, if a power shortage occurs in a DC grid installed within the communication area CELL1, and if a DC grid installed within the same communication area CELL1 has excess power, the MEC server 101 controls the power gate GA to allow power to be lent from that DC grid to the DC grid with the power shortage. In this embodiment, the MEC server 101 identifies, for example, the DC grid with the power shortage based on the electrical characteristic values ​​of the buses BUS of the acquired DC grids GR1 to GR4, and controls the power gate GA so that power is lent to the identified DC grid.

[0050] For example, when power is exchanged between DC grid GR1 and DC grid GR2, the MEC server 101 communicates with a power gate GA located between DC grid GR1 and DC grid GR2, and controls this power gate GA to exchange power from DC grid GR1 to DC grid GR2 or from DC grid GR2 to DC grid GR1.

[0051] Furthermore, for example, when power is exchanged between DC grid GR3 and DC grid GR2 via DC grid GR1, the MEC server 101 communicates with the power gate GA between DC grid GR1 and DC grid GR2 and the power gate GA between DC grid GR1 and DC grid GR3, and controls these power gates GA to exchange power from DC grid GR2 to DC grid GR3 or from DC grid GR3 to DC grid GR2.

[0052] If a failure occurs in the antenna ANT due to a disaster, for example, it will become impossible to acquire information from the power storage device BAT, the power elements EL1-EL3, and the converters CON1-CON3 via the antenna ANT. In this case, for example, by dispatching a mobile base station in the form of a vehicle, the power storage device BAT, the power elements EL1-EL3, and the converters CON1-CON3 can be quickly restored to the wireless communication network, and the MEC server 101 can acquire information from the power storage device BAT, the power elements EL1-EL3, and the converters CON1-CON3 to exchange power between DC grids.

[0053] Incidentally, the smoothing control of power supply and demand in DC grids GR1 to GR4 installed in the communication areas CELL1 and CELL2 may not function effectively if the balance of power supply and demand exceeds a certain limit. For example, even if the MEC server 101 and the individual converters CON1 to CON3 in DC grids GR1 to GR4 operate to smooth power supply and demand, if the amount of power generation, power consumption, power load fluctuation, etc. that can be adjusted by DC grids GR1 to GR4 is exceeded, power interchange beyond the range that DC grids GR1 to GR4 can supply is required.

[0054] In such a case, in the network system 1, the centralized control device 1000 controls the interchange of power from one of the communication areas CELL1 and CELL2 to the other. Specifically, when a power shortage occurs in a DC grid installed in the communication area CELL1 or CELL2, if the DC grid installed in one of the communication areas has excess power, the centralized control device 1000 controls the MEC server 101 of the base station 10A and the MEC server 101 of the base station 10B, so that power is interchanged from that DC grid to the DC grid that is experiencing a power shortage.

[0055] For example, the centralized control device 1000 acquires information such as power generation capacity, power generation state, power storage capacity, power storage state, and power load acquired by the MEC server 101 from the power storage device BAT and the power elements EL1 to EL3, as well as information on electrical characteristic values ​​of the buses BUS acquired from the converters CON1 to CON3. The centralized control device 1000 identifies a DC grid that is short of power based on the acquired information and instructs the MEC server 101 of the base station 10A and the MEC server 101 of the base station 10B to transfer power to the identified DC grid. In response to instructions from the centralized control device 1000, the MEC server 101 of the base station 10A and the MEC server 101 of the base station 10B control, among the power gates GA within their respective communication areas, the power gates GA located on the path from the bus BUS of the DC grid that supplies power to the bus BUS of the DC grid that receives power. This makes it possible to smooth the supply and demand of power even between DC grids installed in different communication areas.

[0056] As described above, according to this embodiment, by distributing a plurality of power storage devices BAT at predetermined intervals and connecting them to the bus BUS without using a DC / DC converter, it is possible to apply a large electrical inertia force to the bus BUS and to eliminate voltage differences in a short period of time. Furthermore, according to this embodiment, since a large electrical inertia force is applied to the bus BUS by distributing a plurality of power storage devices BAT, it is possible to increase the diameter of the bus BUS in areas where a large current flows and decrease the diameter of the bus BUS in areas where a large current does not flow, which allows for more diversity in the bus configuration than when the entire bus BUS has the same capacity and diameter.

[0057] Furthermore, if there is only one power storage device BAT connected to the bus BUS, if a failure occurs in that power storage device BAT, power supply from that power storage device BAT will be disabled. However, if multiple power storage devices BAT are distributed, power supply can be continued from the power storage devices BAT that are not experiencing a failure. Furthermore, if multiple power storage devices BAT are distributed, power can be supplied to the bus BUS from power storage devices BAT other than the power storage device BAT that is undergoing maintenance or live-line work, making maintenance and live-line work easier than when there is only one power storage device BAT connected to the bus BUS. Furthermore, if multiple power storage devices BAT are distributed, it becomes easier to network the DC grid.

[0058] Furthermore, according to this embodiment, even if a disaster causes a failure in the antenna ANT covering the areas of the DC grids GR1 to GR4, for example, by quickly installing a mobile base station that complements the wireless communication network, it is possible to restore the power elements EL1 to EL3, converters CON1 to CON3, and power storage device BAT included in the DC grids GR1 to GR4 to the wireless communication network, thereby enhancing resilience compared to the power network system disclosed in Patent Document 1. Furthermore, according to this embodiment, even if a disaster occurs, autonomous decentralized control is performed in each of the DC grids GR1 to GR4, so that the DC grids GR1 to GR4 can be operated. Furthermore, according to this embodiment, even if a disaster occurs, the base stations 10A and 10B and the DC grids GR1 to GR4 operate using storage batteries and power generation facilities, so that power interchange is possible within the communication areas, enhancing resilience.

[0059] [Second embodiment] Next, a second embodiment of the present invention will be described. The second embodiment differs from the first embodiment in the configuration of the DC grid, but the other configurations are the same as those of the second embodiment. Therefore, in the following description, the same components as those of the first embodiment will be assigned the same reference numerals and their description will be omitted, and only the differences from the first embodiment will be described.

[0060] 5 is a diagram showing the configuration of a DC grid GR11 according to the second embodiment. The DC grid GR11 includes a plurality of first power storage devices BAT1, a plurality of second power storage devices BAT2, a plurality of first switches SW1, a plurality of second switches SW2, and a plurality of cell balancing units BAL. The cell balancing unit BAL is an example of a balancing control unit.

[0061] In the second embodiment, the bus BUS is a three-wire system and includes a first power supply line PL, which is an example of a first power supply line, a second power supply line ML, which is an example of a second power supply line, and a ground line GL, which is an example of a reference line. The first power supply line PL has a potential difference of +400V with the ground line GL, and the second power supply line ML also has a potential difference of +400V with respect to the ground line GL. The ground line GL, which is an example of a reference line, may be grounded. The second power supply line ML is connected to the power system 3 via an AC / DC converter ACON, which converts AC power to DC power. Converters CON1 to CON3 are connected to the first power supply line PL.

[0062] The plurality of first power storage devices BAT1, which are an example of first storage batteries, and the plurality of second power storage devices BAT2, which are an example of second storage batteries, are stationary power storage devices that can be supplied with and charged with power, similar to the power storage device BAT. The plurality of first power storage devices BAT1 and second power storage devices BAT2 are distributed around the bus BUS at predetermined intervals, similar to the power storage device BAT of the first embodiment. The negative poles (second poles) of the first power storage devices BAT1 and second power storage devices BAT2 are connected to the ground line GL.

[0063] The first power storage device BAT1 has a positive electrode (first electrode) connected to the first power line PL and the first switch SW1. The first switch SW1 is connected to the positive electrode (first electrode) of the second power storage device BAT2 in addition to the first power storage device BAT1, and performs disconnection and connection between the positive electrode of the first power storage device BAT1 and the positive electrode of the second power storage device BAT2.

[0064] The positive electrode of the second power storage device BAT2 is connected to the second switch SW2 in addition to the first switch SW1. The second switch SW2 is connected to the second power supply line ML in addition to the second power storage device BAT2, and performs disconnection and connection between the second power supply line ML and the positive electrode of the second power storage device BAT2.

[0065] The cell balance unit BAL is connected to the first switch SW1 and the second switch SW2, and has the function of equalizing the SOC (State Of Charge) of the first storage battery BAT1 and the second storage battery BAT2, and suppressing variations in the SOC of the paired first storage battery BAT1 and second storage battery BAT2.

[0066] 6A and 6B are diagrams illustrating a method for controlling the first switch SW1 and the second switch SW2. When power is supplied from the first power storage device BAT1 and the second power storage device BAT2 to the first power line PL, the cell balance unit BAL turns on the first switch SW1 and turns off the second switch SW2, as shown in Fig. 6A. By controlling the first switch SW1 and the second switch SW2 in this manner, during times of high power consumption, such as daytime, the first power storage device BAT1 and the second power storage device BAT2 can supply more power than in the first embodiment.

[0067] Furthermore, during times of low power consumption, such as at night, power is supplied from the first power storage device BAT1 to the first power supply line PL. In this case, as shown in FIG. 6B , the cell balance unit BAL turns off the first switch SW1 and turns on the second switch SW2 (step 11). As a result, the plurality of first power storage devices BAT1 supply power to the first power supply line PL. Furthermore, by performing step 11, the SOCs of the plurality of second power storage devices BAT2 are equalized via the second power line ML. Note that a DC / DC converter may be provided between the second power storage device BAT2 and the second power line ML to generate a potential difference in the second power supply line ML, thereby actively achieving equalization of the SOCs in a short period of time.

[0068] If the SOC of the second power storage device BAT2 is below a predetermined value after the SOCs of the plurality of second power storage devices BAT2 have been equalized, power may be supplied to the second power storage device BAT2 from the power grid 3 via the AC / DC converter ACON, thereby charging the plurality of second power storage devices BAT2 so that the SOC becomes equal to or above the predetermined value. After the SOCs of the plurality of second power storage devices BAT2 have been equalized, the cell balance unit BAL turns on the first switch SW1 and turns off the second switch SW2, thereby equalizing the SOCs of the first power storage device BAT1 and the second power storage device BAT2 (step 12). By performing step 12, the SOCs of the first power storage device BAT1 and the second power storage device BAT2 are equalized. If the SOCs of the first power storage device BAT1 and the second power storage device BAT2 are not uniform, the cell balance unit BAL equalizes the SOCs of the first power storage device BAT1 and the second power storage device BAT2 by repeating the operations of steps 11 and 12. According to this configuration, the SOC of the first power storage device BAT1 is controlled by the second power storage device BAT2 and the cell balance unit BAL, and therefore, compared to a configuration in which the SOC is controlled by charging from the first power supply line PL, it is possible to control the SOC without disturbing the voltage of the first power supply line PL.

[0069] In the second embodiment, when power interchange is performed between DC grids, the first switch SW1 is turned off, the second switch SW2 is turned on, and the switch SW11 included in the power gate GA is turned on (step 21). As a result, the SOCs of the multiple second power storage devices BAT2 are equalized with respect to the multiple second power storage devices BAT2 connected to the adjacent DC grid via the second power line ML. After the SOCs of the multiple second power storage devices BAT2 have been equalized, the cell balance unit BAL turns on the first switch SW1 and turns off the second switch SW2, thereby equalizing the SOCs of the first power storage device BAT1 and the second power storage device BAT2 (step 22). In this way, the SOCs are equalized by performing steps 21 and 22. If the SOCs of the first power storage device BAT1 and the second power storage device BAT2 are not uniform, the cell balance unit BAL equalizes the SOCs of the first power storage device BAT1 and the second power storage device BAT2 by repeating the operations of steps 21 and 22. This allows power interchange of the second power storage device BAT2 between adjacent DC grids.

[0070] Alternatively, voltage sensors may be installed at predetermined intervals in the first power line PL, and the MEC server 101 may acquire the measurement results of the voltage sensors to detect a voltage drop in the first power line PL. In this case, when a large current is required, such as for rapid charging of the power element EL2, while the first switch SW1 is turned off during the nighttime hours, a voltage drop near the converter CON2 may be detected based on the measurement results of the voltage sensor, and the first switch SW1 near the converter CON2 may be turned on to suppress the voltage drop in the first power line PL. In addition, when performing such control, a DC / DC converter may be disposed between the positive electrode of the first power storage device BAT1 and the positive electrode of the second power storage device BAT2 to boost the voltage of the second power storage device BAT2, thereby enabling the voltage of the first power line PL to be equalized in a short time. In such a case, if the second switch SW2 is also turned on, power can be obtained from the power grid 3, and the voltage of the first power line PL can be equalized in a short time.

[0071] When the first power storage device BAT1 and the second power storage device BAT2 are connected in parallel, the positive electrodes of the first power storage device BAT1 and the second power storage device BAT2 may be connected to the ground line GL. In this case, the negative electrode of the first power storage device BAT1 is connected to the first power supply line PL and the first switch SW1. The first switch SW1 is connected to the negative electrode of the second power storage device BAT2 in addition to the first power storage device BAT1, and performs disconnection and connection between the negative electrode of the first power storage device BAT1 and the negative electrode of the second power storage device BAT2. The negative electrode of the second power storage device BAT2 is connected to the second switch SW2 in addition to the first switch SW1. The second switch SW2 is connected to the second power supply line ML in addition to the second power storage device BAT2, and performs disconnection and connection between the second power supply line ML and the negative electrode of the second power storage device BAT2. In this configuration, the negative electrode is the first pole and the positive pole is the second pole.

[0072] In the second embodiment, the voltage of the first power supply line PL may be set to +800 V relative to the ground line GL, and the voltage of the second power supply line ML may be set to +400 V relative to the ground line GL. Figures 7A, 7B, and 7C are diagrams showing the connection configuration of the first power storage device BAT1, the second power storage device BAT2, and the switches in this case. In Figures 7A, 7B, and 7C, the cell balance unit BAL is omitted to avoid cluttering the drawings.

[0073] The switch SW21 (first switch) is connected to the cell balancing unit BAL, the positive electrode (first electrode) of the first power storage device BAT1, and the positive electrode (first electrode) of the second power storage device BAT2. The switch SW22 (second switch) is connected to the cell balancing unit BAL, the second power supply line ML, and the positive electrode of the second power storage device BAT2. The switch SW23 (third switch) is connected to the cell balancing unit BAL, the negative electrode (second electrode) of the first power storage device BAT1, the positive electrode of the second power storage device BAT2, and the ground line GL. The switch SW24 (fourth switch) is connected to the cell balancing unit BAL, the first power supply line PL, and the positive electrode of the first power storage device BAT1. The negative electrode (second electrode) of the second power storage device BAT2 is connected to the ground line GL. The cell balancing unit BAL is an example of a balancing control unit.

[0074] 7A , when power is supplied from the first power storage device BAT1 and the second power storage device BAT2 to the first power line PL, the cell balance unit BAL turns off the switch SW21, turns off the switch SW22, and turns on the switch SW24, and connects the negative electrode of the first power storage device BAT1 to the positive electrode of the second power storage device BAT2 via the switch SW23. This connects the first power storage device BAT1 and the second power storage device BAT2 in series between the first power line PL and the ground line GL.

[0075] When equalizing the SOCs of the first power storage device BAT1 and the second power storage device BAT2, first, as shown in Fig. 7B, the cell balancer BAL turns switch SW21 off, turns switch SW22 on, and turns switch SW24 on, and connects the negative electrode of the first power storage device BAT1 to the positive electrode of the second power storage device BAT2 by switch SW23 (step 21). Next, as shown in Fig. 7C, the cell balancer BAL turns switch SW21 on, turns switch SW22 on, and turns switch SW24 off, and connects the negative electrode of the first power storage device BAT1 to the ground line GL by switch SW23 (step 22). Note that steps 21 and 22 are alternately performed for the pair of adjacent first power storage device BAT1 and second power storage device BAT2 so that the voltage of the first power supply line PL is maintained at 800 V. If the SOCs of the first power storage device BAT1 and the second power storage device BAT2 are not equalized after performing steps 21 and 22, steps 21 and 22 are repeated until equalization is achieved. In this way, by alternately performing steps 21 and 22 for the pair of adjacent first power storage device BAT1 and second power storage device BAT2, the SOCs of the pair of first power storage device BAT1 and second power storage device BAT2 are equalized.

[0076] Furthermore, when power interchange is performed between DC grids, switch SW11 is turned on and steps 21 and 22 are performed. Here too, steps 21 and 22 are performed alternately for the pair of adjacent first and second power storage devices BAT1 and BAT2 so that the voltage of the first power supply line PL is maintained at 800 V. Also, in this configuration, when switch SW22 is turned on, power may be supplied from power system 3 to second power storage device BAT2 via AC / DC converter ACON.

[0077] When the first power storage device BAT1 and the second power storage device BAT2 are connected in series, the potential of the first power supply line PL may be set to -800 V with respect to the ground line GL, and the potential of the second power supply line ML may be set to -400 V with respect to the ground line GL. In this case, the negative electrode of the first power storage device BAT1 is connected to switches SW21 and SW24, and the positive electrode of the first power storage device BAT1 is connected to switch SW23. Furthermore, the negative electrode of the second power storage device BAT2 is connected to switches SW21, SW22, and SW23, and the positive electrode of the second power storage device BAT2 is connected to the ground line GL. In this configuration, the negative electrode is the first pole and the positive electrode is the second pole.

[0078] [Variations] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be implemented in various other forms. For example, the above-described embodiments may be modified as follows to implement the present invention. The above-described embodiments and the following modifications may be combined with each other. The present invention also includes configurations in which the components of the above-described embodiments and modifications are appropriately combined. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments and modifications, and various modifications are possible.

[0079] Fig. 8 is a diagram showing a modified example of the DC grid GR1. In the first embodiment described above, the power storage device BAT is connected to the bus BUS without a DC / DC converter. However, in the DC grid GR21 shown in Fig. 8, a plurality of power storage devices BAT are connected to the bus BUS at predetermined intervals via DC / DC converters DCON. The DC / DC converter DCON has a function of converting the voltage of DC power supplied by the power storage devices BAT and outputting it to the bus BUS, and also converting the voltage of DC power supplied from the bus BUS and outputting it to the power storage devices BAT, thereby charging the power storage devices BAT. In this modified example, by connecting a plurality of power storage devices BAT to the bus BUS at predetermined intervals in a distributed manner, it is possible to suppress voltage differences in the bus BUS and to impart a large electrical inertial force.

[0080] In the first embodiment described above, the bus BUS is a two-wire system, but it may be a three-wire system. FIGS. 9A and 9B are diagrams illustrating an example of a three-wire bus BUS. The bus BUS illustrated in FIG. 9A has a first power line PL, a second power line ML, and a neutral line NL. The first power line PL has a potential difference of +400 V with respect to the neutral line NL, and the second power line ML has a potential difference of −400 V with respect to the neutral line NL. In the case of the bus BUS illustrated in FIG. 9A , the converter CON2 that performs fast charging for the power element EL2 and supplies power to the power element EL2 requiring high power may supply power at 800 V via the first power line PL and the second power line ML, and the converter CON3 that supplies power to home appliances that do not require high power may supply power at 400 V via the first power line PL and the neutral line NL or the second power line ML and the neutral line NL. For example, in the case of an air conditioner that requires a large amount of power among home appliances, power may be supplied at 800 V via the first power supply line PL and the second power supply line ML. Also, a power storage device BAT may be connected to the first power supply line PL to suppress a voltage drop in the first power supply line PL when power is supplied to the power element EL2.

[0081] In the bus BUS shown in FIG. 9B, the first power line PL has a potential difference of +400V with the neutral line NL, and the second power line ML has a potential difference of +400V with the neutral line NL. In the case of the bus BUS shown in FIG. 9B, for example, power is supplied to a power element EL2 requiring high power. Converter CON2 may supply power via the neutral line NL and the second power line ML, and converter CON3, which supplies power to a home appliance requiring stable power, may supply power at 400V via the neutral line NL and the first power line PL. In this way, by separating the power line to which a load requiring high power is connected from the power line to which a load requiring stable power is connected, voltage fluctuations in the power line to which the load requiring stable power is connected can be suppressed. Note that a power storage device BAT may be connected to the second power line ML to suppress voltage drop in the second power line ML when power is supplied to the power element EL2.

[0082] In the above-described embodiment, the size of the communication area CELL1 and the communication area CELL2 is 1 km in radius, but the size of the communication area CELL1 and the communication area CELL2 is not limited to a 1 km radius and may be less than 1 km in radius or more than 1 km in radius. Also, in the above-described embodiment, the size of the small cell is 125 m in radius, but the size of the small cell is also not limited to a 125 m radius and may be less than 125 m in radius or more than 125 m in radius. Also, the length of the bus BUS is not limited to 1 km and may be less than 1 km or more than 1 km.

[0083] In the above-described embodiment, when power interchange is performed between DC grids, the power interchange may be performed by bidirectional wireless power transmission. In the case of wireless power interchange, the grids are not physically connected to each other, so the construction of a power transmission configuration is easy. Furthermore, compared to a configuration in which the grids are physically connected to each other, it is easier to cut off power between DC grids. [Industrial Applicability]

[0084] The present invention can be used in an integrated power and communication network system. [Explanation of symbols]

[0085] 1 Network System 2. Cloud System 3 Power system 10A, 10B base station 101 MEC Server 102 AC / DC converter 103 Power storage unit 104 CU / DU 111 Control Unit 112 Storage section 113 Communications Department 1000 Centralized control device ANT antenna BAT power storage device BAT1 First power storage device BAT2 Second power storage device BAL Cell balancing section BUS CELL1, CELL2 communication area CON1~CON3 converter EL1~EL3 power elements GA Power Gate GL ground wire GR1~GR4, GR11, GR21 DC grid LO load ML 2nd power line NL Neutral wire PL 1st power line SW1 First switch SW2 Second switch SW21 to SW24 switches

Claims

1. A DC bus comprising a reference line, a first power supply line having a predetermined voltage difference with respect to the reference line, and a second power supply line having a predetermined voltage difference with respect to the reference line, and to which a power generation device and a plurality of power devices are connected; a plurality of power storage devices connected at predetermined intervals from one end to the other end of the DC bus to supply and receive electric power to and from the DC bus; Equipped with the power storage device includes a first power storage device and a second power storage device, a first electrode of the first power storage device and a first electrode of the second power storage device are connected via a first switch; a first pole of the first power storage device is connected to the first power supply line; a first electrode of the second power storage device is connected to the second power supply line via a second switch; a second pole of the first power storage device and a second pole of the second power storage device are connected to the reference line; a balance control unit that controls the first switch and the second switch to equalize the charging rates of the first power storage device and the second power storage device;

2. A DC bus comprising a reference line, a first power supply line having a predetermined voltage difference with respect to the reference line, and a second power supply line having a predetermined voltage difference with respect to the reference line, and to which a power generation device and a plurality of power devices are connected; a plurality of power storage devices connected at predetermined intervals from one end to the other end of the DC bus to supply and receive electric power to and from the DC bus; Equipped with the power storage device includes a first power storage device and a second power storage device, a first pole of the first power storage device is connected to the first power supply line via a fourth switch; a second pole of the first power storage device is connected to a first pole of the second power storage device or the reference line via a third switch; a first electrode of the second power storage device is connected to the second power supply line via a second switch; a first electrode of the first power storage device and a first electrode of the second power storage device are connected via a first switch; a second electrode of the second storage device is connected to the reference line; a balance control unit that controls the first switch to the fourth switch to equalize the charging rates of the first power storage device and the second power storage device;

3. The second power line is connected to an AC power system via a converter that converts AC to DC. The power system according to claim 1 or 2.

4. The DC bus is connected to a power gate that controls power interchange with other DC buses. The power system according to any one of claims 1 to 3.

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