WO2018192190A1 - Chained energy storage method and system, energy storage power station, and energy storage system - Google Patents

Abstract

A chained energy storage method and system, an energy storage power station, and an energy storage system. The method comprises: acquiring battery cell state data and past cell data (S100); selecting cascade utilization batteries according to the battery cell state data and the past cell data (S110); and reusing the cascade utilization batteries according to a planning strategy preset by an energy storage power station (S120). After selecting the cascade utilization batteries, the step of classifying the batteries according to cascade utilization value can also be comprised. By means of the technical solution, the operation of dismantling and restructuring batteries is omitted, and the initial investment for battery cascade utilization is reduced to a great extent. Moreover, in the present technical solution, the past data of battery cells are taken into consideration, and thus the cascade utilization life of batteries can be accurately estimated so as to estimate the value thereof.

Description

Chain energy storage method, system and energy storage power station and energy storage system Technical field

The invention relates to the field of energy storage technology, in particular to a chain energy storage method, a system, an energy storage power station and an energy storage system.

Background technique

At present, energy storage technology research and industrial development are very rapid, and the construction of national energy storage power station projects is accelerating. At present, energy storage equipment mostly uses battery energy storage technology, and adopts the ladder utilization technology of the battery, so that the utilization rate of the battery is higher and the return on investment is higher.

At the same time, traditional fuel vehicles, as large consumers of oil resources and polluting the environment, are constantly being hit by new clean energy vehicles. Taking electric vehicles as an example, electric vehicles can replace “zero emissions” and “low noise” with electricity, which is an important means to solve energy and environmental problems. With the shortage of petroleum resources and the development of battery technology, electric vehicles began to be gradually applied in the world. It is a common consensus that a new generation of energy-saving and environmentally-friendly vehicles represented by electric vehicles is an inevitable trend in the development of the automobile industry. However, the performance of the power battery is attenuated as the number of uses increases. When the performance of the power battery drops to 80% of the original performance, the standard of use of the electric vehicle will not be met. As the number of electric vehicles increases, power battery components that cannot meet the standards for electric vehicle use will appear in large numbers.

The eliminated batteries can usually be used in energy storage power stations. The conventional method will disassemble the batteries and classify and evaluate the performance of the batteries according to the test results, and then reorganize the battery modules according to the energy storage requirements. However, this disassembly test and evaluation process is very difficult.

In view of this, the present invention has been specifically proposed.

Summary of the invention

In order to solve the above problems in the prior art, in order to solve the technical problem of how to reduce the use of the battery disassembly test and accurately evaluate the battery utilization of the ladder, a chain energy storage method is provided. In addition, a chain energy storage system and an energy storage power station and an energy storage system are also provided.

In order to achieve the above object, according to an aspect of the present invention, the following technical solutions are provided:

A chain energy storage method, the method comprising:

Obtain battery cell status data and battery history data;

Selecting a battery using the ladder according to the battery state data and the battery historical data;

The use of the battery by the ladder is reused according to a preset planning strategy of the energy storage power station.

Preferably, the battery state data and the battery history data comprise: battery charging power data and historical data recorded in the power station, battery charging power data and historical data on the device to be charged, and the device to be charged The charging power data and historical data of the battery in the charging state of the charging post and the discharging power data and historical data of the battery during the moving of the device to be charged.

Preferably, after the selecting the ladder to utilize the battery, the method further comprises:

The batteries are classified according to the value of the ladder use.

Preferably, the method further includes:

Obtaining an identification code of the battery;

The classifying the battery according to the value of the ladder use includes:

Obtaining life cycle data of the battery by using the identification code;

Obtaining characteristic data of the battery according to the life cycle data;

The battery is classified according to the characteristic data.

Preferably, the acquiring the battery cell state data and the cell history data comprises: acquiring the battery cell state data and the cell history data by using a CAN communication protocol.

Preferably, the reusing the battery comprises:

Encapsulating the battery to obtain a chain link;

The chain energy storage device is constructed by using the chain links.

In order to achieve the above object, according to another aspect of the present invention, the following technical solutions are provided:

A chain energy storage system, the system comprising:

Obtaining a module for acquiring battery cell state data and cell history data;

And selecting a module, configured to select a battery for the ladder according to the battery state data and the historical data of the battery; and reuse a module for reusing the battery using the ladder according to a preset planning strategy of the energy storage power station .

Preferably, the battery state data and the battery history data comprise: battery charging power data and historical data recorded in the power station, battery charging power data and historical data on the device to be charged, and the device to be charged The charging power data and historical data of the battery in the charging state of the charging post and the discharging power data and historical data of the battery during the moving of the device to be charged.

Preferably, the system further comprises:

A classification module for classifying the batteries according to the value of the ladder use.

Preferably, the obtaining module is further configured to acquire an identifier of the battery;

The classification module includes:

a first obtaining submodule, configured to acquire lifecycle data of the battery by using the identifier;

a second obtaining submodule, configured to obtain characteristic data of the battery according to the life cycle data;

a classification sub-module for classifying the battery according to the characteristic data.

Preferably, the obtaining module comprises:

And a third obtaining submodule, configured to acquire the battery cell state data and the cell history data by using a CAN communication protocol.

Preferably, the reuse module comprises:

a packaging module for packaging the battery to obtain a link;

Constructing a module for constructing a chain energy storage device by using the link.

In order to achieve the above object, according to still another aspect of the present invention, the following technical solutions are provided:

An energy storage power station comprising any of the above chain energy storage systems.

In order to achieve the above object, according to still another aspect of the present invention, the following technical solutions are provided:

An energy storage system, the system comprising a power grid and the energy storage power station; wherein the power grid is connected to the energy storage power station; wherein the chain energy storage system is used for processing a battery, obtaining a battery for the ladder, and The ladder uses a battery for an energy storage power station.

Preferably, the above grid is a medium voltage grid.

Preferably, the energy storage power station includes a link, the link includes an AC/DC bidirectional inverter; and the AC/DC bidirectional inverter is connected to the ladder using a battery.

Preferably, the chain energy storage system comprises a three-phase line, each of the three-phase lines comprises a plurality of links in series; each phase line is connected in parallel with the grid by a reactor, or is isolated A transformer is coupled in series with the grid; wherein phase voltages of the respective phase lines are matched to voltages of the grid.

Preferably, the three-phase line is a star structure or a triangular structure.

Embodiments of the present invention provide a chain energy storage method and system, and an energy storage power station and an energy storage system. The method includes acquiring battery cell state data and battery historical data; selecting a battery for the ladder according to the battery state data and the battery historical data; and reusing the battery by the step according to a preset planning strategy of the energy storage power station. Through the technical scheme, the eliminated batteries are detected, the batteries are screened out, and then the batteries are classified, and then the batteries are reused according to the preset planning strategy of the energy storage station and the results of the battery classification. How to reduce the disassembly test of the battery using the ladder and accurately evaluate the technical problem of using the battery in the ladder, eliminating the disassembly and reorganization of the battery, which greatly saves the upfront investment of the battery ladder utilization, and the technology The solution considers the historical data of the battery cells, so that the battery life of the battery can be accurately evaluated and the value can be evaluated.

DRAWINGS

1 is a schematic flow chart of a chain energy storage method according to an embodiment of the present invention;

2 is a schematic structural view of a link according to an embodiment of the present invention;

3 is a schematic structural view of another link according to an embodiment of the present invention;

4 is a schematic structural view of still another link according to an embodiment of the present invention;

5 is a schematic diagram of a chain energy storage device with a triangular topology constructed by a link according to an embodiment of the present invention;

6 is a schematic diagram of a chain energy storage device with a star topology constructed by a link link applied to a power grid according to an embodiment of the present invention;

7 is a schematic structural view of a chain energy storage system according to an embodiment of the present invention;

FIG. 8 is a schematic structural diagram of a chain energy storage system according to another embodiment of the present invention; FIG.

9 is a schematic structural view of an energy storage power plant according to an embodiment of the present invention;

FIG. 10 is a schematic structural view of an energy storage system according to an embodiment of the present invention.

detailed description

Preferred embodiments of the present invention are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention, and are not intended to limit the scope of the present invention.

At present, when dealing with the eliminated batteries, the conventional method will disassemble the battery and classify and evaluate the performance of the battery according to the test results, and then reorganize the battery module according to the energy storage requirements. This disassembly test and evaluation process Very difficult. To this end, it is necessary to solve the technical problem of how to eliminate the use of the battery disassembly test process and accurately evaluate the commercial value of the battery.

Therefore, an embodiment of the present invention provides a chain energy storage method. As shown in Figure 1, the method includes:

S100: Obtain battery cell state data and cell history data.

The battery state data and the battery historical data specifically include: battery charging power data and historical data recorded in the power station, battery charging power data and historical data on the device to be charged, and the battery on the device to be charged are charged in the charging pile. The charging power data and historical data in the state and the discharging power data and historical data of the battery during the movement of the device to be charged.

The embodiment of the present invention can more accurately evaluate the battery life of the battery by considering the historical data of the battery core.

Preferably, the above method can acquire battery cell state data and cell history data through a CAN communication protocol.

In practical applications, the state data of each cell is uploaded in the CAN communication protocol and stored in the cloud. Among them, each battery (or battery pack (PACK)) can find all the battery history data. The cloud can be an OSS (Operational Support System) server or a server cluster, but is not limited to this.

When the battery is a battery in the power station, the charging power data (ie, the data on the charging power curve) and the historical data of the battery are recorded in real time, and the charging power data and the historical data are uploaded to the cloud for storage, and then the subsequent analysis.

When the battery is a battery applied to a device to be charged (such as an electric car, an electric bicycle, etc.), the charging power data and historical data of the battery in the charging state of the charging post are recorded in real time, and the charging power data and historical data are uploaded to the cloud. Perform storage for subsequent analysis. If the device to be charged is moving (for example: the electric car is driving In the process, the discharge power data and historical data of the battery are recorded in real time, and the discharge power data and historical data are uploaded to the cloud for storage, and then the subsequent analysis is performed.

S110: Select a battery using the ladder according to the battery state data and the battery historical data.

Here, after the battery is lowered to a predetermined level in SOH (the percentage of the full charge capacity of the battery relative to the rated capacity), it is defined as a step-by-step battery.

For example, in the case of an electric vehicle, when the performance of the power battery drops to 80% of the original performance, the standard of use of the electric vehicle cannot be met. At this time, the battery is characterized as a ladder.

In an optional embodiment, after the stepping battery is used, the method further includes: classifying the battery according to the value of the ladder.

In the specific implementation process, the battery can be classified by the identification code of the battery, and the foregoing classifying the battery according to the use value of the ladder may include:

S111: Obtain a life cycle data of the battery by using an identification code.

Among them, the battery life cycle data is all data from the time the battery is put into use to the end of life. Taking an electric vehicle as an example, the life cycle data of the battery can be all data from the time the electric vehicle is put into use to the battery during the retirement of the electric vehicle.

S112: Obtain characteristic data of the battery according to the life cycle data.

The battery characteristic data may be data on how long the battery can be used, battery health data, data for value evaluation, and the like.

S113: classify the battery according to the characteristic data.

S120: Reusing the battery by the ladder according to the preset planning strategy of the energy storage power station.

This step applies the battery to different occasions according to the preset planning strategy of the energy storage power station. Preferably, step S120 may include encapsulating the battery to obtain a link; and using the link to construct a chain energy storage device. More preferably, the link system obtained by the embodiment of the present invention can also be used to combine the control system and the reactance device to obtain the required chain energy storage device.

By adopting the above technical solution, the embodiment of the present invention considers the battery cell state data and the battery core historical data, and determines whether the battery uses the battery for the ladder, and when the battery uses the battery for the ladder, according to the value of the ladder, the battery is used. Classification, and reuse of batteries according to the preset planning strategy of the energy storage power station. This eliminates the disassembly and reorganization of the battery. This has largely saved the upfront investment in battery ladder utilization. Moreover, the technical solution of the present application considers the historical data of the battery cells, so that the ladder life of the battery can be accurately evaluated, thereby evaluating the value of the battery.

The topology of the chain energy storage device constructed by implementing the chain energy storage method provided by the embodiment of the present invention may be: a star type or a triangle type structure inside the chain energy storage device. According to the voltage level of the medium-voltage grid connected to the medium-voltage network, each phase line includes n links (ie, energy storage units), and the n links are connected in series on the AC output side of the grid. After matching the grid voltage, the series reactors are directly connected to the grid. Each link includes a battery and a DC/.../AC conversion module, as shown in Figure 2. In practical applications, n links can be connected in series. The chain energy storage equipment can be connected in parallel to the grid through reactors, or can be connected in series to the grid through an isolating transformer.

The above link may have other structures. For example, as shown in FIG. 3, the link includes a battery and an H-bridge inverter module. Among them, the battery provides DC+ and DC-voltage to provide DC input to the H-bridge inverter module, and after the inverter, the output pulse AC AC1, AC2; T1, T2, T3 and T4 in the H-bridge inverter module are IGBT modules. For another example, the link may also adopt a structure as shown in FIG. 4, and the link includes an H-bridge converter, a DC/DC module, and a battery. Among them, T1, T2, T3 and T4 in the H-bridge inverter module are respectively IGBT modules. The battery provides DCB+, DCB- as input to DC/DC, and then DC/DC converts DCB+, DCB- into DC+, DC- to provide input to the H-bridge inverter module. T1, T2, T3, and T4 invert the DC power on the DC+ and DC- sides into pulsed AC, and output them from AC1 and AC2, respectively.

FIG. 5 exemplarily shows a schematic diagram of a chain type energy storage device of a triangular topology constructed by the method provided by the embodiment of the present invention applied to a power grid. Among them, the number of links (A1, A2, ... An-1, An, B1, B2, ... Bn-1, Bn, C1, C2, ... Cn-1, Cn) is 3n, and the number of energy storage units is 3n. Each link can be constructed as shown in Figures 2, 3, and 4. Taking the structure shown in FIG. 4 as an example, each link includes an energy storage unit, a DC/DC unit, and an H-bridge converter. Among them, the H-bridge converter acts as an inverter unit. The energy storage unit includes a battery, a DC/DC bidirectional inverter directly connected to the battery, and a DC/AC inverter module connected to the DC/DC bidirectional inverter. 3n energy storage units are connected in series on the AC output side, and after matching the grid voltage, the series reactor L is directly connected to the grid. FIG. 6 exemplarily shows a schematic diagram of a chain energy storage device with a star topology constructed by the method provided by the embodiment of the present invention applied to a power grid. Each of the links may adopt the structure as shown in FIG. 2, FIG. 3 and FIG. 4, and details are not described herein again.

The invention will now be described in detail with reference to a preferred embodiment. Take the power battery of an electric car as an example.

S200: Embed state data and historical data of the battery cell and the identification code into the CAN communication protocol, and upload to the OSS (Operation Support System) server.

S201: Determine whether the battery uses the battery according to the battery state data and the battery historical data. If yes, execute S202; otherwise, execute S203.

S202: Obtain a life cycle data of the battery by using an identification code.

S203: Continue to apply the battery.

S204: Obtain characteristic data of the battery according to the life cycle data.

S205: Classify the battery according to the characteristic data and according to the value of the ladder utilization.

S206: According to a preset planning strategy of the energy storage power station and a result of battery classification, the battery is packaged to obtain a link.

According to the preset planning strategy of the energy storage power station and the result of the battery classification, this step selects the battery that meets the requirements for direct packaging and obtains the link.

S207: Using the link to build a chain energy storage device.

For example, this step can combine chain links, control systems, reactances and other equipment to obtain the required chain energy storage equipment.

The battery can be directly used for the medium voltage grid by the embodiment of the present invention. By adopting the above technical solution, the life of the battery can be accurately evaluated, thereby evaluating the commercial value of the energy storage system; the disassembly and reorganization of the battery can be omitted, and the upfront investment of the battery ladder utilization is largely saved.

The embodiment of the invention also provides a chain energy storage system. The chain energy storage system can perform the above chain energy storage method. FIG. 7 is a schematic structural diagram of an embodiment. The chain energy storage system 70 of the present embodiment includes an acquisition module 72, a selection module 74, and a reuse module 76. The obtaining module 72 is configured to acquire battery cell state data and cell history data. The selection module 74 is configured to select a battery using the ladder according to the battery state data and the battery historical data. The reuse module 76 is configured to reuse the battery of the ladder according to the preset planning strategy of the energy storage power station.

The battery state data and the battery historical data include: battery charging power data and historical data recorded in the power station, battery charging power data and historical data on the device to be charged, and the battery on the device to be charged are in the charging state of the charging pile. The charging power data and historical data under and the discharge power data and historical data of the battery during the movement of the device to be charged.

In an alternative embodiment, the chain energy storage system may further include a classification module. The classification module is used to classify the battery according to the value of the ladder.

In a preferred embodiment, the obtaining module 72 in the above embodiment is further configured to acquire an identification code of the battery. The foregoing classification module may specifically include a first acquisition submodule, a second acquisition submodule, and a classification submodule. The first obtaining submodule is configured to obtain life cycle data of the battery by using the identification code. The second acquisition sub-module is configured to obtain characteristic data of the battery according to the life cycle data. The classification sub-module is used to classify the battery based on the characteristic data.

In a preferred implementation, the obtaining module 72 may further include a third acquiring submodule. The third acquisition submodule is configured to acquire battery cell state data and cell history data through a CAN communication protocol.

In a preferred embodiment, the foregoing reuse module 76 may specifically include a package module and a build module. The package module is used to package the battery to obtain a link. The building module is used to build chain energy storage equipment by using chain links.

The chain energy storage system will be described in detail below with reference to FIG. 8 in a preferred embodiment.

In the chain energy storage system 80 of this embodiment, a chain type energy storage device with a star topology is taken as an example, and a three-phase line is connected in parallel to the power grid through the reactor L, and a plurality of links in each phase line are connected in series. . Each link can adopt the structure shown in Figures 2, 3, and 4.

In this embodiment, the link is connected to the acquisition module 82 via the CAN bus. The acquisition module 82 obtains battery state data and battery history data of the battery in the link. Acquisition module 82 then transmits the data to selection module 84. The selection module 84 selects the battery using the ladder according to the battery state data and the battery historical data. Finally, the reuse module 86 reuses the battery of the ladder according to a preset planning strategy of the energy storage power station.

In this embodiment, by analyzing the battery cell state data and the battery historical data, the battery is selected by the ladder, and the preset utilization strategy of the energy storage power station is used to reuse the battery. The elimination of the battery disassembly, testing and reorganization work saves the upfront investment of the battery ladder utilization, and can more accurately evaluate the ladder life and commercial value of the battery PACK.

Herein, the related descriptions of the chain energy storage system embodiment in the process of solving the technical problem can refer to the related description of the chain energy storage method embodiment, and details are not described herein again.

In addition, an energy storage power station embodiment is also provided. As shown in FIG. 9, the energy storage power station 90 of this embodiment includes a chain energy storage system 91, and the chain energy storage system 91 can be any of the above chain energy storage systems.

Here, the description of the energy storage power station can be referred to the relevant description in the embodiment of the chain energy storage method, and details are not described herein again.

In addition, the present invention also provides an embodiment of an energy storage system. As shown in FIG. 10, the energy storage system 100 of this embodiment includes a power grid 101 and an energy storage power station 102; wherein the energy storage power station 102 includes a chain energy storage system 103 and is connected to the power grid 101; wherein, the chain energy storage system 103 is used for processing the battery, obtaining a battery for the ladder, and applying the battery to the energy storage station 103.

In the above embodiment, the power grid is preferably a medium voltage grid.

The chain energy storage system comprises a three-phase line, each of the three-phase lines comprises a plurality of series connected links; each phase line is connected in parallel with the medium-voltage network through a reactor, or through an isolating transformer and a medium-voltage piezoelectric The net phase is connected in series; wherein the phase voltage of each phase line matches the voltage of the medium voltage grid.

Among them, the three-phase line can be set to a star structure or a triangular structure. Those skilled in the art can set according to the actual situation on site, and can also set each phase line to be composed of N links according to the voltage level. Where N takes a positive integer.

The energy storage power station includes a link, and the link includes an AC/DC bidirectional inverter; the AC/DC bidirectional inverter is connected to the ladder by a battery.

In this embodiment, the ladder battery is directly disconnected from the AC/DC bidirectional inverter without being disassembled, and constitutes an energy storage unit, that is, a link. The energy storage unit is connected in series on the AC output side, and is connected to the grid (especially the medium voltage grid) after matching the grid voltage. Wherein, the phase lines can be connected in parallel with the medium-voltage grid through the reactor or in series with the medium-voltage grid through the isolation transformer.

For a detailed description of the chain energy storage system, reference may be made to the foregoing description of the chain energy storage system embodiment, and details are not described herein.

Heretofore, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the drawings, but it is obvious to those skilled in the art that the scope of the present invention is obviously not limited to the specific embodiments. The embodiment was chosen and described in order to best explain the principles of the invention, The embodiments of the present invention may omit some of the above technical features and solve only some of the technical problems existing in the prior art. Moreover, the described technical features can be combined in any combination. Those skilled in the art can make equivalent changes or substitutions to the related technical features without departing from the principles of the present invention, and the technical solutions after the modifications or replacements fall within the scope of the present invention.

Claims (18)

A chain energy storage method, characterized in that the method comprises: Obtain battery cell status data and battery history data; Selecting a battery using the ladder according to the battery state data and the battery historical data; The use of the battery by the ladder is reused according to a preset planning strategy of the energy storage power station. The chain energy storage method according to claim 1, wherein the battery state data and the battery history data comprise: battery charging power data and historical data recorded in the power station, and the device to be charged Battery charging power data and historical data, charging power data and historical data of the battery in the charging state of the charging device, and discharging power data and history of the battery during the moving of the device to be charged data. The chain energy storage method according to claim 1, further comprising: after the selecting the use of the battery by the ladder: The batteries are classified according to the value of the ladder use. The chain energy storage method according to claim 3, wherein the method further comprises: Obtaining an identification code of the battery; The classifying the battery according to the value of the ladder use includes: Obtaining life cycle data of the battery by using the identification code; Obtaining characteristic data of the battery according to the life cycle data; The battery is classified according to the characteristic data. The chain energy storage method according to claim 1, wherein the acquiring the battery cell state data and the cell history data comprises: acquiring the battery cell state data and the cell history through a CAN communication protocol data. The chain energy storage method according to claim 1, wherein said reusing said battery comprises: Encapsulating the battery to obtain a chain link; The chain energy storage device is constructed by using the chain links. A chain energy storage system, characterized in that the system comprises: Obtaining a module for acquiring battery cell state data and cell history data; And selecting a module, configured to select a battery using the ladder according to the battery state data and the historical data of the battery; Reusing module for utilizing the ladder according to a preset planning strategy of the energy storage power station The battery is reused. The chain energy storage system according to claim 7, wherein said battery state data and said battery core history data comprise: battery charging power data and historical data recorded in the power station, and on the device to be charged Battery charging power data and historical data, charging power data and historical data of the battery in the charging state of the charging device, and discharging power data and history of the battery during the moving of the device to be charged data. The chain energy storage system according to claim 7, wherein the system further comprises: A classification module for classifying the batteries according to the value of the ladder use. The chain energy storage system according to claim 9, wherein the acquisition module is further configured to acquire an identification code of the battery; The classification module includes: a first obtaining submodule, configured to acquire lifecycle data of the battery by using the identifier; a second obtaining submodule, configured to obtain characteristic data of the battery according to the life cycle data; a classification sub-module for classifying the battery according to the characteristic data. The chain energy storage system according to claim 7, wherein the acquisition module comprises: And a third obtaining submodule, configured to acquire the battery cell state data and the cell history data by using a CAN communication protocol. The chain energy storage system according to claim 7, wherein the reuse module comprises: a packaging module for packaging the battery to obtain a link; Constructing a module for constructing a chain energy storage device by using the link. An energy storage power plant comprising the chain energy storage system of any of the preceding claims 7-12. An energy storage system, characterized in that the system comprises a power grid and an energy storage power plant according to claim 13; wherein the power grid is connected to the energy storage power station; the chain energy storage system is used for The battery is processed to obtain a ladder using the battery, and the ladder is used for the energy storage station. The energy storage system of claim 14 wherein said grid is medium Piezoelectric mesh. The energy storage system according to claim 14, wherein said energy storage power station comprises a link, said link comprising an AC/DC bidirectional inverter; said AC/DC bidirectional inverter and said step Connected with a battery. The energy storage system according to claim 16, wherein said chain energy storage system comprises a three-phase line, each of said three-phase lines comprising a plurality of links in series; each phase line passes The reactor is connected in parallel with the grid or in series with the grid via an isolating transformer; wherein the phase voltages of the respective phase lines match the voltage of the grid. The energy storage system according to claim 17, wherein said three-phase line is a star structure or a triangular structure.

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