WO2020161766A1

WO2020161766A1 - Direct-current power supply system

Info

Publication number: WO2020161766A1
Application number: PCT/JP2019/003849
Authority: WO
Inventors: 琢真光永
Original assignee: Tdk株式会社
Priority date: 2019-02-04
Filing date: 2019-02-04
Publication date: 2020-08-13

Abstract

[Problem] To suppress variation in the charging rates of a plurality of storage batteries connected to a direct-current bus so as to prevent a reduction in the charge/discharge capability of the storage batteries as an entirety. [Solution] A direct-current power supply system 1 comprises: a direct-current bus 10 serving as the bus of a direct-current power supply; a natural energy power generation device 30 for supplying generated power to the direct-current bus 10; a load device 40 for receiving the supply of power from the direct-current bus 10; a plurality of bidirectional DC/DC converters 23A-23C connected to the direct-current bus 10; a plurality of storage batteries 50A-50C individually connected to the direct-current bus 10 via one of the plurality of bidirectional DC/DC converters 23A-23C; and a power management device 60 for managing the operation of the plurality of bidirectional DC/DC converters 23A-23C on the basis of the generated power, the load power, and the charging rates of the plurality of storage batteries. The power management device 60 controls the output voltages of the bidirectional DC/DC converters 23A-23C corresponding to each storage battery in accordance with the charging rate of each storage battery.

Description

DC power supply system

The present invention relates to a DC power supply system, and particularly to a DC power supply system configured by combining a natural energy power generation device such as a solar power generation device and a plurality of storage batteries.

As a measure to address global environmental problems such as global warming and acid rain, depletion of fossil resources, and security of energy security, the introduction of power generation equipment using natural energy such as wind and solar is advancing. There is.

Especially in isolated areas and undeveloped areas in depopulated areas in the tropical region, power is often supplied mainly by diesel engine generators at present, but the sunlight conditions are good and it is suitable for solar power generation. Therefore, there is a great need for a power supply system that can contribute to the realization of a low-carbon society while improving the economic efficiency by effectively utilizing renewable energy. Even in areas where the power system infrastructure has already been developed, if the power system is shut down due to a natural disaster, etc., the solar power generation system installed in the customer's equipment will be separated from the system to operate autonomously. Expectations are increasing for a DC power supply system that supplies stable and continuous power to a load even when it is stopped.

Regarding a DC power supply system, for example, in Patent Document 1, the demand forecast data of load devices and the power generation output forecast data of a natural energy power generation device are calculated using weather forecast data, and the maximum of the storage battery is calculated based on the demand forecast data and the power generation output data. When it is predicted that the storage battery will be charged in excess of the charging power, the power output from the renewable energy power generation device is suppressed, and when it is predicted that the storage battery will be discharged in excess of the maximum discharge power of the storage battery. Describes a method of suppressing the power consumption of the adjustment load.

Further, in Patent Document 2, a plurality of storage batteries are charged after the power generated by the solar power generation device is temporarily stored in an electric double layer capacitor, and at least one of the plurality of storage batteries to be charged reaches a full charge. In this case, a method is described in which all storage batteries are charged by removing them from the charging target and sequentially selecting and charging other storage batteries that are not the charging target.

International publication 2013/128731 pamphlet JP 2001-69688 A

As described above, when a plurality of storage batteries that can be charged and discharged independently are connected to the DC bus, it is difficult to control the storage batteries so that they are charged and discharged evenly, and there are variations in the charging rate among the storage batteries. Occurs. When any one of the storage batteries precedes to be fully charged, the capacity of the entire storage battery decreases, and it may not be possible to charge the storage battery with the electric power generated by the natural energy power generation device. When a spare storage battery is used, it is possible to prevent waste of generated power, but there is a problem in that the system cost increases due to the provision of the spare storage battery.

When the generated power is suppressed when the storage battery is predicted to be fully charged as in the conventional system described in Patent Document 1, the waste power of the generated power due to the loss cut is large and the storage battery can be charged. Maximum power consumption is reduced.

Further, when the rechargeable battery to be charged is fully charged, as in the conventional system described in Patent Document 2, when another rechargeable battery is selected and sequentially charged, a plurality of rechargeable batteries are charged. Requires the total capacity of a plurality of storage batteries to be sufficiently larger than the maximum power generation amount of the natural energy power generation device, and it is necessary to prepare more storage batteries, which leads to an increase in system cost.

Therefore, an object of the present invention is to provide a DC power supply system capable of suppressing variations in charging rates of a plurality of storage batteries connected to a DC bus and preventing a decrease in charge/discharge capacity of the entire storage battery.

In order to solve the above problems, a DC power supply system according to the present invention includes a DC bus that is a bus for DC power supply, a natural energy power generation device that supplies generated power to the DC bus, and a load power supply from the DC bus. A load device, a plurality of bidirectional DC/DC converters connected to the DC bus, and a plurality of storage batteries respectively connected to the DC bus via any one of the plurality of bidirectional DC/DC converters A power management device that manages the operations of the plurality of bidirectional DC/DC converters based on the generated power, the load power, and the charging rates of the plurality of storage batteries. It is characterized in that the output voltage of the bidirectional DC/DC converter corresponding to each storage battery is controlled according to the charging rate.

According to the present invention, it is possible to prevent variations in the charging rates of a plurality of storage batteries that are supplied with generated power from a natural energy power generation device via a DC bus, and prevent a decrease in the charge/discharge capacity of the entire storage battery.

In the present invention, the plurality of bidirectional DC/DC converters include first and second DC/DC converters, and the plurality of storage batteries are respectively connected to the first and second DC/DC converters. The power management apparatus includes first and second storage batteries, and when the charging rates of all the storage batteries including the first and second storage batteries are equal to or less than a first threshold value, the power management device includes the first and second storage batteries. Output voltages of all the bidirectional DC/DC converters including the bidirectional DC/DC converter are set to a first voltage, and a charging rate of at least the first storage battery is larger than the first threshold value, and at least the first threshold value is set. When the charging rate of the second storage battery is less than or equal to the first threshold value, it is preferable to set the output voltage of the first bidirectional DC/DC converter to a second voltage higher than the first voltage. .. In this case, it is preferable that the first threshold value is 80% or more and 95% or less of the maximum capacity of the first and second storage batteries. In this way, when at least one of the plurality of storage batteries approaches the full charge in advance, the storage battery is not fully charged, and the other storage batteries that are not close to the full charge are given priority. Therefore, the generated power can be efficiently charged. Therefore, the charging rates of a plurality of storage batteries can be equalized, and a decrease in the charging ability of the entire storage batteries can be prevented.

The power management device may be configured such that when the charging rates of all storage batteries including the first and second storage batteries are equal to or higher than a second threshold value that is smaller than the first threshold value, the first and second bidirectional operations are performed. Output voltages of all bidirectional DC/DC converters including DC/DC converters are set to the first voltage, and a charging rate of at least the first storage battery is smaller than the second threshold value, and at least the second threshold value. It is preferable that the output voltage of the first bidirectional DC/DC converter is set to a third voltage lower than the first voltage when the charging rate of the storage battery is equal to or higher than the second threshold value. In this case, the second threshold value is preferably 5% or more and 20% or less of the maximum capacities of the first and second storage batteries. In this way, when at least one of the plurality of storage batteries approaches the empty (0%) in advance, the other storage batteries that are not close to the empty are given priority without completely emptying the storage battery. Therefore, the load power can be efficiently supplied. Therefore, the charging rates of a plurality of storage batteries can be equalized, and a decrease in the charging ability of the entire storage batteries can be prevented.

In the present invention, it is preferable that the first voltage is a reference voltage of the DC bus. For example, when the reference voltage of the DC bus is 350V, the first voltage is set to 350V, the second voltage is set to 370V, and the third voltage is set to 330V, so that the charging rates of the plurality of storage batteries are equalized. Therefore, it is possible to prevent a decrease in the charging capacity of the entire storage battery.

According to the present invention, it is an object of the present invention to provide a DC power supply system capable of preventing variations in charging rates of a plurality of storage batteries connected to a DC bus and preventing a decrease in charge/discharge capacity of the entire storage battery.

FIG. 1 is a block diagram schematically showing a configuration of a DC power supply system according to an embodiment of the present invention. 2A and 2B are diagrams for explaining the operation of the DC power supply system, in which FIG. 2A shows the charging operation of the storage battery and FIG. 2B shows the discharging operation of the storage battery. FIG. 3 is a schematic diagram for explaining control of the bidirectional DC/DC converter by the power management device, showing a case where the charging rates of the storage batteries 50A to 50C are not more than the second threshold and not less than the first threshold. There is. FIG. 4 is a schematic diagram illustrating a control method of the bidirectional DC/DC converter by the power management device, and illustrates a case where the charging rate of the storage battery 50A is larger than the first threshold value. FIG. 5 is a schematic diagram illustrating a control method of the bidirectional DC/DC converter by the power management device, and illustrates a case where the charging rates of the

storage batteries

50A and 50B are larger than the first threshold value. FIG. 6 is a schematic diagram for explaining the control method of the bidirectional DC/DC converter by the power management device, and shows the case where the charging rates of the

storage batteries

50A, 50B, 50C are larger than the first threshold value. FIG. 7 is a schematic diagram illustrating a control method of the bidirectional DC/DC converter by the power management device, and illustrates a case where the charging rate of the storage battery 50A is smaller than the second threshold value.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram schematically showing the configuration of a DC power supply system according to an embodiment of the present invention.

As shown in FIG. 1, the DC power supply system 1 includes a DC bus 10 serving as a bus for DC power supply, DC/DC converters 21 to 23 connected to the DC bus 10, and a DC bus via the DC/DC converter 21. A natural energy power generation device 30 connected to the DC power supply device 10, a load device 40 connected to the DC bus 10 via the DC/DC converter 22, and a storage battery 50 connected to the DC bus 10 via the DC/DC converter 23. , Comparing the amount of power generated by the natural energy power generator 30 with the amount of load power generated by the load device 40, charging the storage battery 50 when the amount of power generation exceeds the amount of load power, and the amount of load power exceeds the amount of power generation The power management apparatus 60 that manages the entire system including the operations of the DC/DC converters 21 to 23 and the power management apparatus 60 that can communicate with the power management apparatus 60 via a communication network 70 such as the Internet so that the storage battery 50 is discharged. Further, the administrator terminal 71 is further provided.

The voltage of the DC bus 10 is, for example, a high voltage DC transmission line of 350±100V. Therefore, when connecting a device operating at a voltage lower than that to the DC bus 10, it is necessary to connect via a DC/DC converter. The DC/DC converter 21 is a one-way DC/DC converter (step-up converter) that boosts the generated power of, for example, 240 V from the natural energy power generation device 30 to 350 V and supplies the boosted power to the DC bus 10, and the DC/DC converter 22 is Is a one-way DC/DC converter (step-down converter) that steps down the electric power of 350 V on the DC bus 10 to 24 V and supplies it to the load device 40. The DC/DC converter 23 is a bidirectional DC/DC converter that steps down or boosts the power on the DC bus 10 and supplies it to the storage battery 50, and boosts or steps down the power from the storage battery 50 and supplies it to the DC bus 10. is there. The DC/DC converters 21 to 23 have an ON/OFF command receiving function and a power amount adjustment command receiving function, and are configured to be communicable with the power management device 60.

The natural energy power generation device 30 is, for example, a solar power generation device 30A or a wind power generation device 30B. In the present embodiment, the photovoltaic power generation device 30A includes a photovoltaic power generation panel and a power conditioner, and is connected to the DC bus 10 via the DC/DC converter 21A. The wind turbine generator 30B includes a wind turbine generator body and a power conditioner, and is connected to the DC bus 10 via a DC/DC converter 21B. The DC/

DC converters

21A and 21B may be built in each power conditioner. The power conditioner has an MPPT (Maximum Power Point Tracking) function, an ON/OFF command receiving function, a power amount adjustment command receiving function, a power generation information transmitting function, and the like, and is configured to communicate with the power management device 60. .. The type and number of the natural energy power generation devices 30 connected to the DC bus 10 are not particularly limited, but it is preferable to include the solar power generation device 30A. The electric power generated by the solar power generation device 30A and the wind power generation device 30B is supplied to the load device 40 and the storage battery 50 via the DC bus 10.

The load device 40 is, for example, a PC, an air conditioner, a TV, an LED lighting, or the like. These load devices 40A to 40D are connected to the DC bus 10 via the DC/DC converters 22A to 22D, respectively, and receive power from the DC bus 10.

The storage battery 50 includes a plurality of storage batteries 50A to 50C, and each storage battery 50A to 50C includes a storage battery main body (battery cell) and a BMU (Battery Management Unit) for monitoring and controlling the charging state. The storage batteries 50A to 50C are connected to the DC bus 10 via the bidirectional DC/DC converters 23A to 23C, respectively, and the power generated by the natural energy power generation device 30 is less than the power consumed by the load device 40 (load power). When the load power is larger than the generated power, the excess power of the generated power is charged, and when the load power is larger than the generated power, the excess power is discharged to supplement the shortage of the load power. The storage batteries 50A to 50C have substantially the same maximum capacity and charge/discharge performance. The BMU of the storage battery 50 has an ON/OFF command receiving function, a DC bus voltage adjustment command receiving function, a charging/discharging current amount adjustment command receiving function, a storage battery information transmitting function, etc., and is configured to communicate with the power management device 60. Has been done. The SOC (State Of Charge: remaining capacity (Ah)/full charge capacity (Ah)×100) indicating the charging rates of the storage batteries 50A to 50C is appropriately notified to the power management apparatus 60.

The DC power supply system 1 may further include a diesel generator 35. The amount of generated power can be forcibly increased by operating the diesel generator 35 when the amount of power generated by the natural energy power generation device 30 is small or when the remaining amount of the storage battery 50 is small. Therefore, it is possible to suppress load power and avoid power failure, and it is possible to stably supply power to the load device 40. Further, the diesel generator 35 can be used as a power source when starting up the entire system including the DC bus 10. Since the diesel generator 35 generally has an AC output, the diesel generator 35 is connected to the DC bus 10 via the AC/DC converter 24.

The power management device 60 is a computer system equipped with an EMS (Energy Management System). The power management device 60 can remotely control the input/output operations of the DC/DC converters 21 to 23, and can control the power generation amount of the natural energy power generation device 30 and the power demand of the load device 40. In order to maintain the voltage of the DC bus 10, the power management device 60 commands the natural energy power generation device 30, the load device 40, and the storage battery 50, and collects information from these devices. The collection of commands and information to these devices is performed using a communication method such as RS-232C, RS-485, CAN (Controller Area Network), Ethernet, Wi-Fi.

2A and 2B are diagrams for explaining the operation of the DC power supply system 1, where FIG. 2A shows the charging operation of the storage battery 50 and FIG. 2B shows the discharging operation of the storage battery 50. There is.

As shown in FIG. 2A, when the amount of power generated by the natural energy power generation device 30 is larger than the load power amount of the load device 40, the storage battery 50 charges the surplus of the generated power amount. The generated power from the natural energy power generation device 30 is supplied to the storage battery 50 via the DC/DC converter 21, the DC bus 10, and the DC/DC converter 22.

As shown in FIG. 2B, when the load power amount of the load device 40 is larger than the power generation amount of the natural energy power generation device 30, the storage battery 50 is discharged to supply the necessary power to the load device 40. Electric power from the storage battery 50 is supplied to the load device 40 via the DC/DC converter 23, the DC bus 10 and the DC/DC converter 22.

3 to 7 are schematic diagrams illustrating a method of controlling the bidirectional DC/DC converters 23A to 23C by the power management device 60.

As shown in FIG. 3, the SOC of each of the storage batteries 50A to 50C is less than or equal to the upper threshold (first threshold) SOC _TH set near the maximum capacity (100%), and set near 0%. When the lower threshold (second threshold) SOC _TL or more, the power management apparatus 60 sets the output voltage (grid target voltage) of the DC/DC converters 23A to 23C to the DC bus 10 to 350V which is the reference voltage of the DC bus 10. It is maintained at (first voltage). The first threshold SOC _TH is preferably set to 80% or more and 95% or less of the maximum capacity of the storage batteries 50A to 50C, and the second threshold SOC _TL is 5% or more of the maximum capacity of the storage batteries 50A to 50C. It is preferable to set it to be not more than %.

When the output voltages of the bidirectional DC/DC converters 23A to 23C are uniformly set to 350 V as described above, the generated power is supplied from the natural energy power generation device 30 to the DC bus 10 and the voltage of the DC bus 10 is When trying to exceed 350 V, current flows from the DC bus 10 toward the storage batteries 50A to 50C, and the storage batteries 50A to 50C are charged. On the other hand, when power is consumed by the load device 40 and the voltage of the DC bus 10 is about to fall below 350V, a current flows from the storage batteries 50A to 50C toward the DC bus 10 and the storage batteries 50A to 50C are discharged. ..

Even if the output voltage of the bidirectional DC/DC converters 23A to 23C is uniformly set to 350V as described above, there is some variation in the magnitude of the current flowing into each storage battery. Even if the variation in the magnitude of the current flowing into each storage battery is very small, the variation in the charging rate of each storage battery becomes very large due to the long-term stacking. FIG. 3 shows a state in which the charging rates of the storage batteries 50A to 50C have some variations.

As shown in FIG. 4, the charging of the storage batteries 50A to 50C progresses, the SOC of one storage battery 50A (first storage battery) becomes larger than the first threshold value SOC _TH , and the other two

storage batteries

50B and 50C (first storage battery). 2) is greater than or equal to the second threshold SOC _TL and less than or equal to the first threshold SOC _TH , the power management device 60 changes the output voltage of the bidirectional DC/DC converter 23A connected to the storage battery 50A to another value. It is set higher than the output voltage of the two bidirectional DC/

DC converters

23B and 23C. For example, the output voltage of the bidirectional DC/DC converter 23A is set to 370V (second voltage), and the output voltages of the other bidirectional DC/

DC converters

23B and 23C are maintained at 350V (first voltage). ..

By doing so, the storage battery 50A is less likely to be charged than the

other storage batteries

50B and 50C, and it is possible to prevent the storage battery 50A from being fully charged, and all the storage batteries 50A to 50C can be charged and discharged. It is possible to maintain a good state. Therefore, it is possible to prevent waste of the generated power of the natural energy power generation device due to loss reduction. Further, it is possible to prevent the system from going down by suppressing the voltage fluctuation of the DC bus 10.

As shown in FIG. 5, the SOCs of the two

storage batteries

50A and 50B (first storage battery) both become larger than the first threshold SOC _TH , and the SOC of the other storage battery 50C (second storage battery) becomes the first When it is equal to or greater than the threshold value SOC _{TL of} 2 and equal to or less than the first threshold value SOC _TH , the power management device 60 sets the output voltage of the bidirectional DC/

DC converters

23A and 23B connected to the

storage batteries

50A and 50B to the other one. It is set higher than the output voltage of the DC/DC converter 23C. For example, the output voltage of the bidirectional DC/

DC converters

23A and 23B is set to 370V, and the output voltage of the bidirectional DC/DC converter 23C is maintained at 350V.

By doing so, the

storage batteries

50A and 50B are less likely to be charged than the other storage batteries 50C, and it is possible to prevent the

storage batteries

50A and 50B from being fully charged, and all the storage batteries 50A to 50C are charged. The dischargeable state can be maintained.

As shown in FIG. 6, when all the SOCs of the three storage batteries 50A to 50C exceed the threshold SOC _TH , the output voltages of all the bidirectional DC/DC converters 23A to 23C are lower than the reference voltage of the DC bus. A high voltage (for example, 370V) is applied. Alternatively, the output voltages of all the bidirectional DC/DC converters 23A to 23C may be returned to the reference voltage (350V) of the DC bus 10. Further, when all the storage batteries 50A to 50C are fully charged, it is preferable that the power management apparatus 60 stop the power generation operation of the natural energy power generation apparatus 30.

As shown in FIG. 7, the discharge of the storage batteries 50A to 50C progresses, the SOC of one storage battery 50A (first storage battery) becomes smaller than the second threshold SOC _TL , and the other two

storage batteries

50B and 50C (first storage battery). 2) is greater than or equal to the second threshold SOC _TL and less than or equal to the first threshold SOC _TH , the power management device 60 changes the output voltage of the bidirectional DC/DC converter 23A connected to the storage battery 50A to another value. It is set lower than the output voltage of the two bidirectional DC/

DC converters

23B and 23C. For example, the output voltage of the bidirectional DC/DC converter 23A is set to 330V (third voltage), and the output voltages of the other two bidirectional DC/

DC converters

23B and 23C are maintained at 350V (first voltage). To be done.

By doing so, it is possible to prevent the storage battery 50A that has become nearly empty from being discharged more easily than the

other storage batteries

50B and 50C, and to prevent the storage battery 50A from becoming completely empty, and all the storage batteries 50A to 50C are A chargeable/dischargeable state can be maintained. When the SOC of the two

storage batteries

50B, 50C becomes smaller than the second threshold SOC _TL , the output voltage of the corresponding two bidirectional DC/

DC converters

23A, 23B may be lowered.

As described above, the DC power supply system 1 according to the present embodiment includes the plurality of storage batteries 50A to 50C connected to the DC bus 10 via the bidirectional DC/DC converters 23A to 23C and the bidirectional DC/DC converter 23A. Power management device 60 for controlling the operations of the storage batteries 50A to 23C. Since the output voltage is changed, it is possible not only to suppress the variation in the charging rate between the storage batteries 50A to 50C and prevent the charging/discharging ability of the entire storage battery 50 from decreasing, but also to stabilize the DC bus 10.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. It goes without saying that it is included in the range.

For example, although three storage batteries are used in the above embodiment, the number of storage batteries may be any number as long as it is two or more (a plurality). Further, in the above embodiment, the output voltage of the DC/DC converter is changed in two steps (350 V→370 V) based on one SOC threshold value. However, the DC/DC converter output voltage is changed by using two or more SOC threshold values. It is also possible to change the output voltage in multiple stages (for example, 350V→360V→370V).

1 DC power supply system 10

DC bus

21, 21A, 21B DC/DC converter (step-up converter)
22,21A-21D DC/DC converter (step-down converter)
23, 23A to 23C Bidirectional DC/DC converter 24 AC/DC converter 30 Natural energy power generation device 30A Solar power generation device 30B Wind power generation device 35

Diesel generator

40, 40A to 40D Load device 50

Storage battery system

50A, 50B, 50C Storage battery 60 power management device 70 communication network 71 administrator terminal

Claims

A DC bus that is a bus for DC power supply,
A natural energy power generator that supplies power to the DC bus,
A load device that receives load power from the DC bus,
A plurality of bidirectional DC/DC converters connected to the DC bus;
A plurality of storage batteries each connected to the DC bus via any one of the plurality of bidirectional DC/DC converters;
A power management device that manages the operations of the plurality of bidirectional DC/DC converters based on the generated power, the load power, and the charging rates of the plurality of storage batteries;
The DC power supply system, wherein the power management device controls the output voltage of the bidirectional DC/DC converter corresponding to each storage battery according to the charging rate of each storage battery.
The plurality of bidirectional DC/DC converters include first and second DC/DC converters,
The plurality of storage batteries include first and second storage batteries respectively connected to the first and second DC/DC converters,
The power management device,
All bidirectional DC/DC converters including the first and second bidirectional DC/DC converters when the charging rates of all the storage batteries including the first and second storage batteries are equal to or lower than a first threshold value. Set the output voltage of the first voltage,
At least when the charging rate of the first storage battery is larger than the first threshold value and at least the charging rate of the second storage battery is equal to or less than the first threshold value, the first bidirectional DC/DC converter. 2. The DC power supply system according to claim 1, wherein the output voltage of is set to a second voltage higher than the first voltage.
The DC power supply system according to claim 2, wherein the first threshold value is 80% or more and 95% or less of the maximum capacity of the first and second storage batteries.
The power management device,
Including the first and second bidirectional DC/DC converters when the charging rates of all the storage batteries including the first and second storage batteries are greater than or equal to a second threshold value that is smaller than the first threshold value. Set the output voltage of all bidirectional DC/DC converters to the first voltage,
At least when the charging rate of the first storage battery is smaller than the second threshold value and at least the charging rate of the second storage battery is equal to or higher than the second threshold value, the first bidirectional DC/DC converter. The DC power supply system according to claim 2 or 3, wherein the output voltage is set to a third voltage lower than the first voltage.
The DC power supply system according to claim 4, wherein the second threshold value is 5% or more and 20% or less of a maximum capacity of the first and second storage batteries.
The DC power supply system according to any one of claims 1 to 5, wherein the first voltage is a reference voltage of the DC bus.