Optical storage and charging integrated system configuration method based on area modularization

Abstract

The invention discloses a light storage and charging integrated system configuration method based on area modularization, and the method comprises the steps: building the relation between an energy supply device, an energy storage device and a charging device and the usable area based on equipment type selection; the energy supply output characteristic of the energy supply device, the charging and discharging characteristic of the energy storage device and the charging load characteristic of the charging device under the unit area are obtained; according to the energy supply output characteristic, the charging and discharging characteristic and the charging load characteristic, constructing an optimal configuration model taking the optimal benefit of the light storage and charging integrated system as a target function under the multi-factor constraint condition; solving the model to obtain an area optimal scheme of the energy supply device, the energy storage device and the charging device; by establishing a system income model, solving is carried out by taking the optimal income cost of the system in the whole life cycle of the system as a target function, the area relation of all parts of the optical storage and charging integrated system is obtained, and then the optimal configuration of an energy supply device, a charging device and an energy storage device of the system is obtained, so that the overall income of the optical storage and charging integrated system is improved.

Description

Technical Field

[0001] The present invention relates to the field of new energy, and more specifically, to a configuration method for a photovoltaic energy storage charging integrated system based on area modularization. Background Art

[0002] In recent years, new energy technologies have developed rapidly, and photovoltaic energy storage charging integrated projects have emerged in an endless stream. However, the reasonable planning of photovoltaic energy storage charging integrated systems still needs to be considered. On the premise of considering various factors such as policy factors, environmental factors, and market factors, by using the limited area of the system, reasonably configuring the ratio among photovoltaic, energy storage, and charging, and maximizing the overall benefits of the system, this is extremely important for the photovoltaic energy storage charging integrated market.

[0003] Currently, the focus of photovoltaic energy storage charging integrated systems is mostly on the system operation stage. Patent CN 117394318A proposes an optimized scheduling method for a photovoltaic energy storage charging integrated system considering multiple operation modes, constructs an objective optimization model, and solves the objective function through several constraint conditions to obtain the optimal scheduling strategy as the output strategy; Patent CN 118229014A proposes an energy management algorithm applied to a photovoltaic-energy storage-charging integrated power station, uses the method of BP neural network, and gives the optimal solution of system operation by predicting and optimizing the energy flow and distribution. The planning and design of the system in the initial stage also mostly focus on energy storage configuration. Patent CN 117474252A discloses an energy storage configuration method, device, equipment, and medium for a photovoltaic energy storage charging integrated power station. By constructing a cost and benefit model of the photovoltaic energy storage integrated power station, with the overall annual average net income of the photovoltaic energy storage charging integrated power station being the maximum as the objective function, an accurate and best-benefit energy storage configuration plan for the photovoltaic energy storage charging integrated power station is solved. The above patents do not involve how to allocate the areas of the energy supply device, energy storage device, and charging device in the photovoltaic energy storage charging integrated system.

[0004] For the entire photovoltaic energy storage charging integrated system, system configuration not only includes energy storage configuration, but also includes multiple aspects such as photovoltaic capacity configuration and the number of charging piles configuration. How to allocate the area ratio of each component of the system has been rarely studied. Usually, the area or volume of the photovoltaic energy storage charging integrated system is relatively clear. Therefore, taking the area of modular equipment as a variable, comprehensively considering various factors such as policy, environment, market, and system residual value, and uniformly and reasonably planning the configuration relationship of photovoltaic, energy storage, and charging in the system is very necessary. Summary of the Invention

[0005] To solve the problems existing in the background art, based on the prior art, a configuration method for a photovoltaic energy storage charging integrated system based on area modularization is provided. By combining various factors such as policy, environment, market, and system residual value, the photovoltaic-energy storage-charging of the photovoltaic energy storage charging integrated system is optimized and configured to obtain a photovoltaic-energy storage-charging configuration plan with the optimal overall benefits of the photovoltaic energy storage charging integrated system under conditions such as a specific environment and a fixed area.

[0006] The integrated solar energy storage and charging system provided by the present invention includes:

[0007] An energy supply device, which includes a solar photovoltaic panel, a busbar device, and an energy supply converter;

[0008] An energy storage device, which includes but is not limited to feasible small-scale distributed energy storage forms such as electrochemical energy storage batteries and tank-type compressed air energy storage;

[0009] A charging device, which includes but is not limited to device forms such as charging piles for energy replenishment of electric vehicles;

[0010] An intelligent control unit, which integrates devices for information collection, information analysis, and strategy execution within the system.

[0011] The optimization configuration method for the integrated solar energy storage and charging system provided by the present invention is as follows:

[0012] Based on equipment selection, establish the relationship between the energy supply device, energy storage device, and charging device in the integrated solar energy storage and charging system and their usage areas; according to the equipment characteristics and regional characteristics, obtain the energy supply output characteristics of the energy supply device, charge and discharge characteristics of the energy storage device, and charging load characteristics of the charging device per unit area; construct an optimization configuration model with the optimal benefit of the integrated solar energy storage and charging system as the objective function under multi-factor constraints; solve the optimization configuration model to obtain the corresponding configuration schemes for the energy supply device, energy storage device, and charging device.

[0013] The system and optimization configuration method provided by the present invention have the following advantages:

[0014] 1. The integrated solar energy storage and charging system and its optimization configuration method provided by the present invention are provided with an energy supply device, an energy storage device, a charging device, and an intelligent control unit. The energy supply device includes a solar photovoltaic panel, a busbar device, and an energy supply converter; the energy storage device includes but is not limited to feasible small-scale distributed energy storage forms such as electrochemical energy storage batteries and tank-type compressed air energy storage; the charging device includes but is not limited to device forms such as charging piles for energy replenishment of electric vehicles; the intelligent control unit is the integration of the control part within the integrated solar energy storage and charging system, integrating control modules with multiple functions such as communication and information processing of the integrated solar energy storage and charging system. By equipping feasible small-scale distributed energy storage forms in addition to electrochemical energy storage batteries, such as tank-type compressed air energy storage, etc., the construction flexibility of the integrated solar energy storage and charging system is improved, adapting to different application scenarios and terrain conditions, and helping to promote the development of the construction of the integrated solar energy storage and charging system.

[0015] 2. The integrated energy storage, charging and photovoltaic system and its optimized configuration method provided by the present invention consider the energy storage configuration, photovoltaic capacity configuration and charging configuration of the system in association with the land area, which is more reasonable and effective for obtaining the optimal revenue configuration plan of the integrated energy storage, charging and photovoltaic system under a specific area.

[0016] 3. The integrated energy storage, charging and photovoltaic system and its optimized configuration method provided by the present invention consider the salvage value of each component device of the system in the revenue when constructing the system revenue model, and consider the recovery cost of the salvage value of each component device of the system in the cost, which makes the establishment of the revenue model closer to the actual situation. Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram of the integrated energy storage, charging and photovoltaic system in the embodiment of the present invention.

[0018] Figure 2 It is a configuration flow chart of the integrated energy storage, charging and photovoltaic system based on area modularization.

[0019] Description of the Reference Numerals:

[0020] 1, energy supply device; 2, solar photovoltaic panel; 3, busbar device; 4, energy supply converter; 5, energy storage device; 6, charging device; 7, intelligent control unit. Detailed Embodiments

[0021] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific examples described herein are part of the embodiments of the present invention, but not all of the embodiments, and are not intended to limit the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0022] In this application, the term "comprising", "including" or any other variant thereof is intended to cover a non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "comprising a..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0023] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0024] Embodiment 1

[0025] As Figure 1 shown, a photovoltaic energy storage and charging integrated system provided in this embodiment includes: an energy supply device 1, an energy storage device 5, a charging device 6, and an intelligent control unit 7 of the system. In the energy supply device 1, a solar photovoltaic panel 2 converts solar energy into electrical energy through a busbar device 3 and an energy supply converter 4, and supplies the electrical energy to the energy storage device 5 for energy storage or to the charging device 6 for charging; the energy stored in the energy storage device 5 can come from the energy supply device 1 or the power grid, and at the same time, the energy stored in the energy storage device 5 can be used for the charging device 6 or the power grid; the intelligent control unit 7 analyzes the information collected, obtains a control signal, and adjusts the working states of the devices in the system.

[0026] In this embodiment, the form of the energy supply converter 3 is determined according to the matching with the solar photovoltaic panel 2, including but not limited to one or more of a DC / DC converter, a DC / AC converter, an AC / DC converter, an AC / AC converter and their combinations.

[0027] In this embodiment, the energy storage device 5 selects an energy storage form according to the environmental terrain where the system is located, including but not limited to feasible small-scale distributed energy storage forms such as electrochemical energy storage batteries and tank-type compressed air energy storage.

[0028] In this embodiment, the intelligent control unit 7 includes a host computer, sensors, an intelligent monitoring system, etc. The intelligent control unit 7 is an integration of the control modules of the entire system, including information collection, information transmission, information analysis, device working condition adjustment, etc.

[0029] The operation logic of the photovoltaic energy storage and charging integrated system of this embodiment will be elaborated in detail below.

[0030] In this embodiment, in the energy supply device 1, the solar photovoltaic panel 2 converts solar energy into electrical energy, which is collected through the busbar device 3, and then converted through the energy supply converter 4, and supplied to the energy storage device 5 to realize energy storage or directly supplied to the charging device 6 for use; the energy stored in the energy storage device 5 can come from the solar photovoltaic panel 2 or the power grid, and at the same time, the energy stored in the energy storage device 5 can be used for the charging device 6 or the power grid through energy release conversion.

[0031] In this embodiment, the charging device 6 is used to meet the charging load, and its energy source can be the energy storage device 5 or through the energy supply device 1.

[0032] In this embodiment, the intelligent control unit 7 includes a host computer and sensors. The intelligent control unit 7 analyzes the information collected, including the energy supply output P supply of the energy supply device 1, the energy storage margin E storage of the energy storage device 5, and the working state (energy storage power P charge or energy release power P discharge) The charging power P of the charging device 6 charge ; Send control signals to adjust the operating states of the devices in the system, mainly including the energy storage or release of the energy storage device 5 and the energy transmission relationship between the energy storage device 5 and the power grid, thereby realizing the efficient and stable operation of the system.

[0033] The optimization configuration method of the integrated solar energy storage and charging system of this embodiment will be elaborated in detail below.

[0034] According to Figure 2 the logic of the system optimization configuration method shown, it will be elaborated in detail:

[0035] Based on the device selection, establish the relationship between the energy supply device 1, the energy storage device 5, the charging device 6 in the system and their usage areas.

[0036] According to the device characteristics and regional characteristics, obtain the energy supply output characteristics of the energy supply device 1 per unit area, the charge and discharge characteristics of the energy storage device 5 per unit area, and the charging load characteristics of the charging device 6 per unit area.

[0037] According to the energy supply output characteristics of the energy supply device 1, the charge and discharge characteristics of the energy storage device 5, and the charging load characteristics of the charging device 6, construct an optimization configuration model with the optimal benefit of the integrated solar energy storage and charging system as the objective function under multi-factor constraints.

[0038] Solve the optimization configuration model to obtain the corresponding configuration schemes for the energy supply device 1, the energy storage device 5, and the charging device 6.

[0039] According to Figure 2 the flowchart of the system optimization configuration method shown, the specific steps are as follows:

[0040] (1) According to the composition characteristics of the integrated solar energy storage and charging system, decompose the system into three main components: the energy supply device 1, the energy storage device 5, and the charging device 6. At the same time, combined with the device and system regional characteristics, obtain the parameters per unit area of each component of the system.

[0041] a. The relationship between the energy supply device 1 and its floor area S solar including the necessary device accessories such as the solar photovoltaic panel 2, the busbar device 3, and the energy supply converter 4. Combined with the device characteristics and regional characteristics, obtain the unit energy supply output characteristics P supply_unit of the energy supply device 1 per unit area, the unit initial cost C inv_supply_unit of the energy supply device 1, the unit operation and maintenance cost C O_supply_unit of the energy supply device 1, and the unit recovery cost C eol_supply_unit of the energy supply device 1; the P supply_unit value, the C inv_supply_unit value, the C O_supply_unit value, the C eol_supply_unitThe value can be obtained according to the market conditions after the equipment selection is determined.

[0042] b. The relationship between the energy storage device 5 and its floor area S storage According to the size, upper and lower limits of the capacity, and charge and discharge characteristics of the energy storage device 5, the energy storage characteristic E charge_unit and the energy release characteristic E discharge_unit of the energy storage device 5 per unit area are obtained, as well as the unit initial cost C inv_storage_unit of the energy storage device 5, the unit operation and maintenance cost C O_storage_unit of the energy storage device 5, and the unit recovery cost C eol_storage_unit .

[0043] c. The relationship between the charging device 6 and its floor area S charge According to the size and charging characteristics of the charging device 6, the charging characteristic P charge_unit of the charging device 6 per unit area is obtained, as well as the unit initial cost C inv_charge_unit of the charging device 6, the unit operation and maintenance cost C O_charge_unit of the charging device 6, and the unit recovery cost C eol_charge_unit .

[0044] (2) Based on the equipment characteristics and regional characteristics, define the full life cycle N life of the integrated solar energy storage and charging system, and establish the system revenue model INC.

[0045] a. The revenue model INC refers to the total revenue of the integrated solar energy storage and charging system minus the total system cost LCC during the full life cycle.

[0046] b. During the full life cycle of the system,

[0047] LCC = C inv + C O + C eol ; (1)

[0048] LCC is the total system cost; C inv is the initial investment cost of the system; C O is the operation and maintenance cost of the system; C eol system salvage recovery cost;

[0049] Where:

[0050] C inv = C inv_supply_unit * S solar + C inv_storage_unit * S storage + C inv_charge_unit * S charge (2)

[0051] C O = CO_supply_unit *S solar +C O_storage_unit *S storage +C O_charge_unit *S charge (3)

[0052] C eol =C eol_supply_unit *S solar +C eol_storage_unit *S storage +C eol_charge_unit *S charge (4)

[0053] c. During the entire life cycle of the system, the total revenue includes the revenue from selling electricity to the power grid, I electric , the charging revenue, I charge and the residual value R of the integrated PV - energy storage - charging system valve ;

[0054] Then the system revenue model INC = I electric +I charg +R valve -C inv -C O -C eol (5)

[0055] (3) Define the constraint conditions of multiple factors in the system revenue model

[0056] a. System area constraint: The system area S total , is greater than or equal to the sum of the areas of each part of the system for PV, energy storage, and charging, that is, it satisfies the relationship

[0057] S solar +S storage +S charge ≤S total (6)

[0058] b. Energy supply output curve constraint: Under the PV area S solar , combined with the changes in light intensity and light direction in the area where the integrated PV - energy storage - charging system is located, the upper limit of the PV capacity configuration of the system is obtained, that is, the maximum energy supply output curve is P supply_max ; Then the energy supply output characteristics of the energy supply device should satisfy the relationship

[0059] S solar *P supply_unit ≤P supply_max (7)

[0060] c. Energy storage constraint condition: The area of the energy storage area is S storage, based on the device characteristics of the energy storage device, determine the power of the energy storage system and the SOC constraint, and obtain the upper limit of the capacity configuration of the system energy storage device, the upper limit of the energy storage characteristics E charge_max and the upper limit of the energy release characteristics E discharge_max , then the energy storage characteristics and energy release characteristics of the energy storage device should respectively satisfy the relational expressions

[0061] S storage *E charge_unit ≤E charge_max (8)

[0062] S storage *E discharge_unit ≤E discharge_max (9)

[0063] d. Charging load constraint conditions. According to the load demand within the mapped range around the system, including but not limited to load forms such as electric vehicles, after data processing, obtain the upper limit of the charging load P of the integrated photovoltaic energy storage and charging system charge_max , then the charging characteristics of the charging device should satisfy the relational expression

[0064] P charge_max ≤S solar *P supply_unit (10)

[0065] (4) Under the multi-factor constraint conditions, taking the maximum value of the system revenue model INC as the objective function, solve to obtain the corresponding configuration schemes of the energy supply device, energy storage device, and charging device.

[0066] Considering the device characteristics of the energy supply device, energy storage device, charging device, etc., numerical methods can be used to solve for the maximum value of the system revenue model, and the corresponding photovoltaic area is S solar 、the energy storage area is S storage 、the charging pile area is S charge , and the numerical methods include but are not limited to numerical solution methods such as the small-range traversal method or the dichotomy method.

[0067] According to the areas of each region of the system, obtain the preliminary configuration results of the energy supply device, energy storage device, and charging device, and round up and down in combination with device selection.

[0068] Verify the preliminary system configuration results obtained with the revenue model INC to obtain the optimal configuration schemes of the integrated photovoltaic energy storage and charging system, energy supply device, energy storage device, and charging device.

[0069] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A method for configuring an integrated photovoltaic storage and charging system based on area modularization, characterized in that: The method comprises: Based on equipment selection, establish the relationship between the energy supply device, energy storage device and charging device and their usage area in the integrated photovoltaic storage and charging system; According to the equipment characteristics and regional characteristics, the energy supply output characteristics of the energy supply device, the charge and discharge characteristics of the energy storage device and the charging load characteristics of the charging device are obtained per unit area; According to the energy output characteristics of the energy supply device, the charge and discharge characteristics of the energy storage device and the charging load characteristics of the charging device, an optimization configuration model is constructed under multi-factor constraints with the optimal benefit of the photovoltaic storage and charging integrated system as the objective function; The optimization configuration model is solved to obtain the optimal area solutions of the corresponding energy supply device, energy storage device, and charging device.

2. The method for configuring an integrated photovoltaic storage and charging system based on area modularization according to claim 1, characterized in that: The total system cost LCC of the integrated photovoltaic storage and charging system during its entire life cycle is: LCC= C inv + C O + C eol ; (1) The system return INC model is: INC=I electric +I charg +R valve -C inv -C O -C eol (5) Where: LCC is the total system cost; C inv is the initial investment cost of the system; C O is the system operation and maintenance cost; C eol The system residual value recovery cost; INC is the system income; I electric is the revenue from selling electricity to the grid, I charge is the charging benefit, R valve is the system residual value.

3. The method for configuring an integrated photovoltaic storage and charging system based on area modularization according to claim 2, characterized in that: The initial investment cost of the system is C inv , System operation and maintenance cost C O , System residual value recovery cost C eol The calculation method is: C inv =C inv_supply_unit *S solar +C inv_storage_unit *S storage +C inv_charge_unit *S charge (2) C O =C O_supply_unit *S solar +C O_storage_unit *S storage +C O_charge_unit *S charge (3) C eol =C eol_supply_unit *S solar +C eol_storage_unit *S storage +C eol_charge_unit *S charge (4) Where: C inv_supply_unit is the unit initial cost of the energy supply device; S solar is the floor space of the energy supply device; C inv_storage_unit is the unit initial cost of the energy storage device; S storage is the floor space of the energy storage device; C inv_charge_unit is the unit initial cost of the charging device; S charge The floor space of the charging device; C O_supply_unit is the unit operation and maintenance cost of the energy supply device; C O_storage_unit is the unit operation and maintenance cost of the energy storage device; C O_charge_unit is the unit operation and maintenance cost of the charging device; Unit recovery cost of energy supply device C eol_supply_unit ; C eol_storage_unit is the unit recovery cost of the energy storage device; C eol_charge_unit The unit recovery cost of the charging device 6 is .

4. The method for configuring an integrated photovoltaic storage and charging system based on area modularization according to claim 2, characterized in that: The constraints for solving the system revenue INC model include: System area constraint: System area S total , is greater than or equal to the sum of the areas of all parts of the system's light storage and charging. S solar +S storage +S charge ≤S total (6) Energy output curve constraint: In the photovoltaic area S solar Under this condition, the maximum energy output curve of the system is P supply_max , the energy output characteristics of the energy supply device should satisfy the relationship S solar *P supply_unit ≤P supply_max (7) Energy storage constraint: The area of ​​the energy storage area is S storage , energy storage characteristic upper limit E charge_max and the upper limit of energy release characteristics E discharge_max , the energy storage characteristics and energy release characteristics of the energy storage device satisfy the relationship S storage *E charge_unit ≤E charge_max (8) S storage *E discharge_unit ≤E discharge_max (9) Charging load constraint condition, negative upper limit P of the integrated photovoltaic storage and charging system charge_max Should satisfy the relationship P charge_max ≤S solar *P supply_unit (10)。 5. The method for configuring a photovoltaic storage and charging integrated system based on area modularization according to claim 1, characterized in that: The photovoltaic storage and charging integrated system includes an energy supply device on the power generation side, an energy storage device and a charging device on the power sales side, a power network and equipment load on the user side, and an intelligent control unit, and is characterized by: The energy supply device on the power generation side includes a solar photovoltaic panel, a converging device and an energy supply converter; When there is a solar energy supply unit in the energy supply unit, the confluence device is used to connect the photovoltaic components in order to achieve the confluence function and assist in completing the collection and transmission of solar energy supply information; The energy supply converter includes a power electronic converter used during the operation of the system, which is used to convert the electric energy generated by the solar photovoltaic panel into a form that can be used by the energy storage device or the charging device. The power electronic converter includes but is not limited to one or more of a DC / DC converter, a DC / AC converter, an AC / DC converter, and an AC / AC converter, and a combination thereof; The energy storage device includes, but is not limited to, electrochemical energy storage batteries, tank-type compressed air energy storage or other small distributed energy storage forms; The charging device includes, but is not limited to, a charging pile for replenishing energy for the electric vehicle; The intelligent control unit includes a communication and information processing module of the integrated photovoltaic storage and charging system.

6. The method for configuring an integrated photovoltaic storage and charging system based on area modularization according to claim 1, characterized in that: The relationship between the energy supply device, energy storage device and charging device of the integrated photovoltaic storage and charging system and their use area includes: The relationship between the energy supply device and the occupied area includes the solar photovoltaic panels, the confluence device and the necessary device accessories of the energy supply converter. Combined with the equipment characteristics and regional characteristics, the unit energy output characteristics, unit initial cost, unit operation and maintenance cost, and unit recovery cost of the energy supply device per unit area are obtained; The relationship between the energy storage device and the floor area is as follows: based on the size of the energy storage device, the upper and lower limits of the capacity, and the charge and discharge characteristics, the unit energy storage characteristics and energy release characteristics, unit initial cost, unit operation and maintenance cost, and unit recovery cost of the energy storage device per unit area are obtained; The relationship between the charging device and the floor area is obtained based on the size and charging characteristics of the charging device, and the unit charging characteristics, unit initial cost, unit operation and maintenance cost, and unit recovery cost of the charging device per unit area are obtained.

7. According to the method for configuring an integrated photovoltaic storage and charging system based on area modularization in claim 1, the optimal benefit of the integrated photovoltaic storage and charging system is an optimization configuration model of the objective function, characterized in that: Based on the full life cycle of the integrated photovoltaic storage and charging system life , construct the revenue model INC of the photovoltaic storage and charging integrated system; The revenue model INC of the integrated photovoltaic storage and charging system refers to the total revenue of the integrated photovoltaic storage and charging system minus the total cost during the entire life cycle; The total cost of the integrated photovoltaic, storage and charging system includes the initial investment cost of the integrated photovoltaic, storage and charging system, the operation and maintenance cost of the integrated photovoltaic, storage and charging system during its entire life cycle, and the residual value recovery cost of the integrated photovoltaic, storage and charging system; The total revenue of the integrated photovoltaic, storage and charging system includes the revenue from selling electricity to the power grid, the charging revenue and the residual value of the integrated photovoltaic, storage and charging system.

8. The method for configuring a photovoltaic storage and charging integrated system based on area modularization according to claim 1, characterized in that: The optimization configuration model with the optimal benefit as the objective function includes solving the benefit model of the integrated photovoltaic storage and charging system under the constraints, obtaining the regional area division corresponding to the integrated photovoltaic storage and charging system, and obtaining the optimal configuration results of the energy supply device, energy storage device, and charging device.

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