Energy storage inverter cabinet and energy storage system

Abstract

The utility model provides an energy storage inverter cabinet and an energy storage system, the energy storage inverter cabinet comprises a cabinet body and an inverter cabin arranged on the cabinet body; a plurality of mounting racks and energy storage converters detachably arranged on the mounting racks are arranged in the inversion cabin, and the mounting racks are sequentially arranged in the height direction of the cabinet body. The energy storage inverter cabinet provided by the utility model can realize convenient disassembly and assembly of each energy storage converter, so that the number and model of the energy storage converters can be set and adjusted according to the power distribution requirements of the direct current battery cabinet, and therefore, the energy storage inverter cabinet can better adapt to the application requirements of different electric quantities and different users, and has higher suitability.

Description

Technical Field

[0001] The utility model relates to the technical field of energy storage equipment, and in particular to an energy storage inverter cabinet. At the same time, the utility model also relates to an energy storage system provided with the energy storage inverter cabinet. Background Art

[0002] The battery energy storage system is an energy storage system that uses large energy storage batteries to store and release electricity. The industrial and commercial energy storage system can supplement and enrich the needs of the power system and consumers from different aspects because of its high integration, flexible installation and wide range of applications.

[0003] The current industrial and commercial energy storage system is usually composed of multiple energy storage battery clusters integrated into the structure of energy storage cabinets or energy storage containers. Among them, the energy storage battery cluster is generally composed of multiple battery cells assembled in series into modules, and then multiple modules are combined into battery packs, and finally multiple battery packs are installed on a fixed stand to form a modular energy storage device. In addition, the existing industrial and commercial energy storage system often adopts the design of outdoor energy storage cabinets, which are flexible and convenient to install and maintain, have a wide range of application scenarios, and can be modularly expanded according to the actual application scenarios. At the same time, it can be specifically divided into two technical solutions: integrated energy storage system design and distributed energy storage system design.

[0004] The design of the integrated energy storage system is an all-in-one (integrated) idea, which integrates all components such as the battery system, battery management system, thermal management system, fire protection system, energy management system, energy storage inverter, control system and convergence system in an outdoor cabinet. In the design of distributed energy storage systems, the entire energy storage system generally consists of two parts: the DC side system (DC battery cabinet) includes battery systems, battery management systems, thermal management systems, fire protection systems and other components, and its output DC is connected to the AC side system. The AC side system mainly includes inverter cabinets (energy storage inverters and convergence systems and other components) and control cabinets (energy management systems and control systems and other components), and its output is AC power connected to the user-side power grid.

[0005] Existing distributed energy storage systems usually use multiple DC battery cabinets, equipped with an inverter cabinet and a control cabinet to adapt to customer application needs. However, since the structures of the inverter cabinet and the control cabinet are generally fixed, the adaptation range of the existing distributed energy storage system is limited. For example, when there are fewer DC battery cabinets, the inverter cabinet has a large number of energy storage converters in the inverter cabinet, which causes a waste of inverter cabinet functions and cannot meet the application needs of different power levels. At the same time, both of them also have the problem of occupying a large area. Utility Model Content

[0006] In view of this, the utility model aims to provide an energy storage inverter cabinet, which can better adapt to application requirements of different power quantities.

[0007] In order to achieve the above object, the technical solution of the utility model is implemented as follows:

[0008] An energy storage inverter cabinet comprises a cabinet body and an inverter cabin arranged on the cabinet body;

[0009] The inverter cabin is provided with a plurality of mounting frames and an energy storage converter detachably arranged on each of the mounting frames, and each of the mounting frames is arranged in sequence along the height direction of the cabinet.

[0010] Furthermore, each of the energy storage converters is inserted into the corresponding mounting frame.

[0011] Furthermore, the cabinet is provided with a control cabin and a junction cabin; the junction cabin is used to merge the alternating current converted by the inverter cabin, and the control cabin is used to control the normal operation of the junction cabin and the inverter cabin.

[0012] Furthermore, the inverter cabin and the merge cabin are located on the same side of the control cabin, and the inverter cabin and the merge cabin are arranged up and down along the height direction of the cabinet.

[0013] Furthermore, along the length direction of the cabinet, the junction cabin, the inverter cabin and the control cabin are arranged in sequence.

[0014] Furthermore, the control cabin includes a plurality of relays, each of which corresponds to each of the energy storage inverters; each of the relays is used to control the on / off between the corresponding energy storage inverter and the high-voltage box in the energy storage DC battery cabinet.

[0015] Furthermore, a heater is provided at the bottom of the control cabin, and the heater is used to preheat the control cabin when the temperature is low to prevent failure of components in the control cabin due to the low temperature; and / or, an emergency stop button is provided on the door of the control cabin for cutting off the electrical connection between each of the energy storage inverters and the high-voltage box in the energy storage DC battery cabinet in the event of an emergency failure.

[0016] Furthermore, a detachable lifting ring is provided on the top of the cabinet, and the lifting ring is used for lifting the cabinet with an external lifting device; and / or, a plurality of cooling fans are provided on the door of the inverter cabin.

[0017] Furthermore, a socket and a decorative plate for covering the socket are provided at the bottom of the cabinet, and the socket is used for a forklift to be inserted into the cabinet.

[0018] Compared with the prior art, the utility model has the following advantages:

[0019] The energy storage inverter cabinet described in the utility model can realize convenient disassembly and assembly of each energy storage inverter by providing a plurality of mounting frames arranged in sequence along the height direction of the cabinet body, and each energy storage inverter is detachably mounted on the corresponding mounting frame, so that the number and model of the energy storage inverter can be set and adjusted according to the power distribution requirements of the DC battery cabinet, so as to better adapt to the application requirements of different power quantities and different users, making it more adaptable.

[0020] In addition, each energy storage converter is installed on the corresponding mounting frame, which is simple to operate and easy to take and put. The cabinet is equipped with a control cabin and a junction cabin, which can integrate the inverter cabin, junction cabin and control cabin into one, so as to achieve high integration of the AC side of the distributed energy storage system, thereby reducing the floor space. By locating the inverter cabin and the junction cabin on the same side of the control cabin, and arranging the inverter cabin and the junction cabin up and down along the height direction of the cabinet, it is conducive to adapting to the situation where the power distribution demand in the energy storage DC battery cabinet is small, avoiding the waste of the functions of the inverter cabin, the junction cabin and the control cabin.

[0021] In addition, by adopting a design in which the junction compartment, inverter compartment and control compartment are arranged in sequence, it is conducive to adapting to the situation where the power distribution demand in the energy storage DC battery cabinet is large. By setting up multiple relays, and each relay is used to control the on and off between the corresponding energy storage converter and the high-voltage box in the energy storage DC battery cabinet, it is conducive to independent control of a single energy storage converter, and then it is conducive to the precise removal of a single fault without affecting the overall operation of the energy storage system.

[0022] Another object of the utility model is to provide an energy storage system, comprising an energy storage DC battery cabinet, and an energy storage inverter cabinet as described above connected to the energy storage DC battery cabinet;

[0023] The energy storage inverter cabinet is used to convert the direct current transmitted by the energy storage DC battery cabinet into alternating current and supply it to the user-side power grid.

[0024] The energy storage system described in the utility model and the above-mentioned energy storage inverter cabinet have the same beneficial effects as compared with the traditional technology, and will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation on the present invention. In the accompanying drawings:

[0026] Figure 1 A schematic diagram of the structure of an energy storage inverter cabinet according to an embodiment of the utility model;

[0027] Figure 2 for Figure 1A schematic diagram of the internal structure of the structure shown;

[0028] Figure 3 Another structural schematic diagram of the energy storage inverter cabinet according to an embodiment of the utility model;

[0029] Figure 4 It is a topological diagram of the working principle of the energy storage inverter cabinet described in the embodiment of the utility model;

[0030] Figure 5 It is a communication control topology diagram of the energy storage inverter cabinet described in the embodiment of the utility model;

[0031] Description of reference numerals:

[0032] 1. Cabinet; 11. Inverter cabin; 111. Mounting frame; 112. Energy storage converter; 12. Merger cabin; 13. Control cabin; 14. Lifting ring; 15. Emergency stop button; 16. Cooling fan; 17. Decorative panel. DETAILED DESCRIPTION

[0033] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0034] In the description of the present invention, it should be noted that if there are terms such as "upper", "lower", "inner", "outer" and the like indicating orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, if there are terms such as "first" and "second", they are also used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0035] In addition, in the description of the present invention, unless otherwise clearly defined, the terms "installation", "connection", "connection" and "connector" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood in combination with specific circumstances.

[0036] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0037] Embodiment 1

[0038] The present embodiment relates to an energy storage inverter cabinet, which can realize convenient disassembly and assembly of each energy storage inverter 112, and then can set and adjust the number and model of the energy storage inverter 112 according to the power distribution requirements of the DC battery cabinet, so that it can be compatible with multiple configuration schemes and has higher product adaptability.

[0039] In terms of overall structure, Figures 1 to 3 As shown, the energy storage inverter cabinet of this embodiment includes a cabinet body 1 and an inverter cabin 11 disposed on the cabinet body 1. The inverter cabin 11 is provided with a plurality of mounting frames 111 and an energy storage converter 112 detachably disposed on each mounting frame 111, and each mounting frame 111 is arranged in sequence along the height direction of the cabinet body 1.

[0040] Specifically, as an exemplary structure, Figure 2 As shown, in this embodiment, each energy storage converter 112 is inserted and installed on the corresponding mounting frame 111. Therefore, the disassembly and assembly operation of each energy storage converter 112 can be made simpler, and each energy storage converter 112 can be easily taken and placed.

[0041] In addition, in this embodiment, as a preferred implementation form, a control cabin 13 and a junction cabin 12 are provided on the cabinet 1. The junction cabin 12 is used to merge the AC power converted by the inverter cabin 11, and output the AC power to connect with the user-side power grid. The control cabin 13 is used to control the normal operation of the junction cabin 12 and the inverter cabin 11.

[0042] It is understandable that by arranging the control cabin 13 and the junction cabin 12 on the cabinet 1, the inverter cabin 11, the junction cabin 12 and the control cabin 13 can be integrated into one, so as to achieve high integration of the AC side of the distributed energy storage system, thereby reducing the occupied area.

[0043] At this time, see Figure 1 and Figure 2 As shown, in this embodiment, as a preferred implementation form, the junction cabin 12, the inverter cabin 11 and the control cabin 13 are arranged in sequence along the length direction of the cabinet 1. The advantage of such an arrangement is that it is conducive to adapting to the situation where the power distribution demand in the energy storage DC battery cabinet is large.

[0044] Furthermore, in this embodiment, see Figure 3 As shown, as a preferred implementation form, the inverter cabin 11 and the merge cabin 12 are located on the same side of the control cabin 13, and the inverter cabin 11 and the merge cabin 12 are arranged up and down along the height direction of the cabinet 1. In this way, it is possible to adapt to the situation where the power distribution demand in the energy storage DC battery cabinet is small, and avoid wasting the functions of the inverter cabin 11, the merge cabin 12 and the control cabin 13.

[0045] It is worth mentioning that in the specific structure, if the design form of arranging the junction cabin 12, the inverter cabin 11 and the control cabin 13 in sequence is adopted, six mounting frames 111 are preferably arranged in the inverter cabin 11, that is, six energy storage inverters 112 can be disassembled and assembled to adapt 1 to 6 branches (the energy storage DC battery cabinet has 1 to 6 battery clusters that need to be adapted to the energy storage inverter 112) and are used in parallel. The number of branches is large, which is conducive to meeting the large power distribution demand in the energy storage DC battery cabinet.

[0046] If the inverter cabin 11 and the junction cabin 12 are located on the same side of the control cabin 13, and the inverter cabin 11 and the junction cabin 12 are arranged up and down along the height direction of the cabinet 1, three mounting frames 111 are preferably provided in the inverter cabin 11, that is, three energy storage inverters 112 can be disassembled and assembled to adapt 1 to 3 branches (the energy storage DC battery cabinet has 1 to 3 battery clusters that need to be adapted to the energy storage inverter 112) for parallel use. The number of branches is small, which is conducive to meeting the situation where the power distribution demand in the energy storage DC battery cabinet is small.

[0047] In addition, in this embodiment, as a preferred implementation form, the control cabin 13 includes a plurality of relays, each relay corresponding to each energy storage converter 112. Each relay is used to control the on / off between the corresponding energy storage converter 112 and the high voltage box in the energy storage DC battery cabinet.

[0048] It should be noted that there are multiple high-voltage boxes in the energy storage DC battery cabinet in this embodiment, and the multiple high-voltage boxes correspond one-to-one to the multiple battery clusters in the energy storage DC battery cabinet, and are arranged one-to-one to each energy storage inverter 112.

[0049] To this end, by setting up multiple relays, and each relay is used to control the on / off connection between the corresponding energy storage inverter 112 and the high-voltage box in the energy storage DC battery cabinet, it is beneficial to achieve independent control of a single energy storage inverter 112, and then it is beneficial to achieve accurate removal of a single fault without affecting the overall operation of the energy storage system.

[0050] Furthermore, in this embodiment, as a preferred implementation form, a heater is provided at the bottom of the control cabin 13, and the heater is used to preheat the control cabin 13 when the temperature is low, so as to prevent the components in the control cabin 13 from failing due to the low temperature.

[0051] Also, see Figure 1 As shown, as a preferred implementation form, an emergency stop button 15 is provided on the door of the control cabin 13 of this embodiment for cutting off the electrical connection between each energy storage inverter 112 and the high-voltage box in the energy storage DC battery cabinet in the event of an emergency failure, so as to ensure the overall safety of the energy storage system.

[0052] Continue to see Figure 1As shown, in this embodiment, as a preferred implementation form, a plurality of cooling fans 16 are provided on the door of the inverter cabin 11 to facilitate heat dissipation of the inverter cabin 11, and the number and arrangement of the cooling fans 16 can be set and adjusted accordingly according to actual heat dissipation requirements.

[0053] In addition, as a preferred implementation form, a detachable lifting ring 14 is provided on the top of the cabinet 1 of this embodiment. The lifting ring 14 is used for lifting the cabinet 1 with an external lifting device to facilitate the movement of the energy storage inverter cabinet.

[0054] At the same time, as a preferred implementation form, in this embodiment, a socket and a decorative plate 17 for covering the socket are provided at the bottom of the cabinet 1, and the socket is used for a forklift to insert the cabinet 1 to further improve the mobility of the energy storage inverter cabinet.

[0055] It is still necessary to mention that the various structures not mentioned in the energy storage inverter cabinet of this embodiment can refer to the relevant structural parts of the common energy storage inverter cabinet in the prior art. For example, it also includes an energy management system, etc. Moreover, the junction cabin 12 is used to realize the junction of the AC output side of the inverter cabin 11, and the number of junction loops is synchronized with the number of energy storage inverters 112. After the junction, the 400V AC power is output and connected to the user's power grid side.

[0056] Among them, the control cabin 13 is the brain of all components on the entire AC control side (including EMS, control circuit, temperature control module and fire protection module, etc.), responsible for coordinating the normal operation of the control system as a whole, such as being responsible for the control of the entire switching state of the system, the operating state of each energy storage inverter 112 and the thermal management system.

[0057] Also, see Figure 1 and Figure 2 As shown, taking the case where there are 6 energy storage inverters 112 (PCS) in the cabinet 1 as an example, it can support six branches in parallel. The 6 energy storage inverters 112 are equipped with a control cabin 13 (that is, a control communication host). The control cabin 13 is used to aggregate the communications of all branches and output them to the EMS (battery management system). At the same time, the control cabin 13 can control the energy storage inverter 112 of each branch.

[0058] At the same time, the cabinet 1 is also provided with a switch circuit breaker and an electric meter. The switch circuit breaker is located in the junction compartment 12 of the cabinet 1, including 6 branch DC circuit breakers, 1 AC junction circuit breaker and 1 control circuit molded case circuit breaker. The electric meter is installed in the junction compartment 12 to measure the amount of electricity charged and discharged on the AC side of the system (energy storage inverter cabinet).

[0059] Specifically, the DC circuit breaker on the DC side (energy storage DC battery cabinet) is the intermediate protection for the energy storage DC battery cabinet and the energy storage inverter cabinet of this embodiment, and is located between each high-voltage box and each energy storage converter 112 in the energy storage DC battery cabinet. The confluence circuit breaker on the AC side (energy storage inverter cabinet) is on the AC output side, confluences the AC side of the six-branch energy storage converter 112, and connects it to the power grid. The control circuit breaker is in the control cabin 13, and provides power supply protection for each control circuit.

[0060] The cabinet 1 is also provided with a copper busbar and cables. The copper busbar is used to connect the modules of the energy storage converter 112 and the busbar circuit breaker to transmit the busbar current to the busbar circuit breaker, and then to the power grid through the busbar circuit breaker. The energy storage converter 112 and the DC circuit breaker on the DC side (energy storage DC battery cabinet) are connected one-to-one by cables.

[0061] In addition, the cabinet 1 is also equipped with a UPS power supply (uninterruptible power supply), a switching power supply, an EMS (battery management system), a relay, a surge protector, an IO module and a terminal block assembly, which can all refer to the common structural parts in the existing energy storage system.

[0062] The energy storage inverter cabinet of this embodiment, by providing a plurality of mounting frames 111 arranged in sequence along the height direction of the cabinet body 1, and each energy storage inverter 112 is detachably mounted on the corresponding mounting frame 111, it is possible to realize convenient disassembly and assembly of each energy storage inverter 112, so that the number and model of the energy storage inverter 112 can be set and adjusted according to the power distribution requirements of the energy storage DC battery cabinet, so as to better adapt to the application requirements of different power quantities and different users, making it more adaptable.

[0063] Embodiment 2

[0064] This embodiment relates to an energy storage system, which includes an energy storage DC battery cabinet and an energy storage inverter cabinet in Embodiment 1 connected to the energy storage DC battery cabinet. The energy storage inverter cabinet is used to convert the DC power transmitted by the energy storage DC battery cabinet into AC power and supply it to the user-side power grid.

[0065] It is worth mentioning that the various structures not mentioned in the energy storage DC battery cabinet of this embodiment can refer to the relevant structural parts of the energy storage DC battery cabinet known to those skilled in the art, such as a battery system, and a battery management system (BMS), a thermal management system and a fire protection system connected to the battery system.

[0066] See also Figure 4As shown, the AC side system (i.e., the energy storage inverter cabinet) includes an inverter cabin 11, a junction cabin 12, and a control cabin 13. Among them, the inverter cabin 11 and the junction cabin 12 include multiple energy storage converters 112 (PCS), DC circuit breakers, and AC junction circuit breakers. The control cabin 13 mainly includes equipment for receiving and controlling the status of components such as each PCS, each high-voltage box, and each circuit breaker.

[0067] Figure 5 It is the internal communication topology of the AC side system (i.e., energy storage inverter cabinet). Among them, the AC side control communication is mainly divided into three parts, namely PCS, auxiliary components and EMS. The PCS part is composed of multiple PCS modules, which are connected to the corresponding high-voltage box in the DC side (energy storage DC battery cabinet) through CAN communication to form a data transmission channel. The PCS module summarizes the collected information and its own information to the communication controller.

[0068] Auxiliary components include UPS, temperature and humidity controller, fire protection system, communication controller, liquid cooling system and IO module, etc. UPS provides emergency power to the control and communication part, and needs to feedback its own operating status to the energy management system EMS in real time. The temperature and humidity controller monitors the internal temperature and humidity of the AC side system (i.e., the energy storage inverter cabinet) and feeds back to the EMS in real time. It has internal control functions and can automatically start heat dissipation, dehumidification and heating according to environmental conditions.

[0069] The fire protection system includes a DC side (energy storage DC battery cabinet) and an AC side (i.e., energy storage inverter cabinet). They transmit the information collected by the smoke sensor and the combustible gas sensor to the EMS, which determines whether to execute the fire protection action and returns it to the fire protection system for action. The communication controller receives the DC side and its own information from the PCS and transmits it to the EMS, which issues charging and discharging instructions and controls the charging and discharging power. The liquid cooling system mainly consists of a liquid cooler and related pipelines. The liquid cooler sends the relevant temperature information to the EMS, which controls the temperature of the liquid cooler to ensure that the DC side battery system is at a suitable operating temperature.

[0070] The IO module is divided into two parts: DI (input) and DO (output). The DI input collects the status of each control switch on the DC side and the AC side and feeds it back to the EMS. The EMS receives the data parameters communicated from other parts and outputs the DO signal to the IO module. The IO module triggers the control relay according to the DO signal, thereby achieving the function of controlling the DC side high-voltage box, the AC side energy storage converter 112 and the control switch. Controlling the high-voltage box and the energy storage converter 112 through the DO output can more accurately cut off the fault circuit without affecting the system operation.

[0071] The energy storage system of this embodiment can reduce the occupied area by setting the energy storage inverter cabinet in the first embodiment, and is conducive to adapting to the application requirements of different power quantities and different users, that is, it can be compatible with multiple configuration schemes, so that it can have high product adaptability.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An energy storage inverter cabinet, characterized in that: It comprises a cabinet body and an inverter cabin arranged on the cabinet body; The inverter cabin is provided with a plurality of mounting frames and an energy storage converter detachably arranged on each of the mounting frames, and each of the mounting frames is arranged in sequence along the height direction of the cabinet.

2. The energy storage inverter cabinet according to claim 1, characterized in that: Each of the energy storage converters is plugged into the corresponding mounting frame.

3. The energy storage inverter cabinet according to claim 1, characterized in that: The cabinet is provided with a control cabin and a confluence cabin; The junction cabin is used to merge the alternating current converted by the inverter cabin, and the control cabin is used to control the normal operation of the junction cabin and the inverter cabin.

4. The energy storage inverter cabinet according to claim 3 is characterized in that: The inverter cabin and the merge cabin are located on the same side of the control cabin, and the inverter cabin and the merge cabin are arranged up and down along the height direction of the cabinet.

5. The energy storage inverter cabinet according to claim 3 is characterized in that: Along the length direction of the cabinet, the junction cabin, the inverter cabin and the control cabin are arranged in sequence.

6. The energy storage inverter cabinet according to claim 3 is characterized in that: The control cabin includes a plurality of relays, each of the relays corresponding to each of the energy storage converters; Each relay is used to control the on / off connection between the corresponding energy storage converter and the high-voltage box in the energy storage DC battery cabinet.

7. The energy storage inverter cabinet according to claim 3 is characterized in that: A heater is provided at the bottom of the control cabin, and the heater is used to preheat the control cabin when the temperature is low, so as to prevent the components in the control cabin from failing due to the low temperature; and / or, The hatch of the control cabin is provided with an emergency stop button for cutting off the electrical connection between each of the energy storage converters and the high-voltage box in the energy storage DC battery cabinet in the event of an emergency failure.

8. The energy storage inverter cabinet according to claim 1, characterized in that: The top of the cabinet is provided with a detachable lifting ring, and the lifting ring is used for lifting the cabinet with an external lifting device; and / or, A plurality of cooling fans are arranged on the door of the inverter cabin.

9. The energy storage inverter cabinet according to any one of claims 1 to 8, characterized in that: The bottom of the cabinet is provided with a socket and a decorative plate for covering the socket, and the socket is used for a forklift to be inserted into the cabinet.

10. An energy storage system, characterized in that: It comprises an energy storage DC battery cabinet, and an energy storage inverter cabinet according to any one of claims 1 to 9 connected to the energy storage DC battery cabinet; The energy storage inverter cabinet is used to convert the direct current transmitted by the energy storage DC battery cabinet into alternating current and supply it to the user-side power grid.

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