ENERGY STORAGE SYSTEM AND METHOD FOR CONTROLLING GROUNDING STRUCTURE OF ENERGY STORAGE SYSTEM

Abstract

An energy storage system according to an embodiment of the present invention includes a photovoltaic (PV) system and a battery system, and is an energy storage system interlocked with a power grid, and includes: a power converter (PCS) interlocked with the power grid and selectively connected to at least one of the photovoltaic power generation system and the battery system; a first switch selectively connecting the photovoltaic power generation system to a DC side of the power converter; a second switch selectively connecting the battery system to the DC side of the power converter; and a control device that controls the first switch and the second switch according to a state of the photovoltaic power generation system and a state of the battery system, to control the grounding structures of one or more of the photovoltaic power generation system, the battery system, and the power converter.

Description

[Technical field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0181167, filed with the Korean Intellectual Property Office on December 17, 2021, and all of the contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to an energy storage system and a method for controlling a ground structure of an energy storage system, and more particularly to an energy storage system including a solar power generation system and a battery system, and a method and device for controlling a ground structure in the energy storage system. [Background technology]

[0003] An energy storage system (ESS) is a system that connects new renewable energy, batteries that store power, and existing grid power. In recent years, smart grids and new renewable energy have become more widespread, and as the efficiency and stability of the power system are emphasized, the demand for energy storage systems is increasing to regulate power supply and demand and improve power quality. Depending on the purpose of use, the output and capacity of the energy storage system vary, and multiple battery systems can be connected to each other to form a large-capacity energy storage system.

[0004] Among ESS systems, ESS systems that are connected to PV (Photovoltaic) systems are changing from AC-coupled to DC-coupled systems. In DC-coupled ESS systems, the PV system and battery system are DC voltage, while the grid is AC voltage, making a power conversion device essential.

[0005] Meanwhile, PV systems and battery systems generally use different grounding methods due to system efficiency or safety issues. In this case, the type of grounding method to be used in an energy storage system in which a PV system and a battery system are linked is a matter of choosing between system efficiency and safety, which causes difficulties in system operation in that one of system efficiency and safety must be given up. Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE PRESENT EMBODIMENT In order to solve the above problems, an object of the present invention is to provide an energy storage system including a solar power generation system and a battery system.

[0007] Another object of the present invention to solve the above problems is to provide a method for controlling the ground structure of such an energy storage system.

[0008] Another object of the present invention to solve the above problems is to provide a control device for controlling a grounding structure of an energy storage system. [Means for solving the problem]

[0009] To achieve the above object, an energy storage system according to one embodiment of the present invention includes a photovoltaic (PV) system and a battery system, and is an energy storage system interlocked with a power grid, the energy storage system including: a power converter (PCS) interlocked with the power grid and selectively connected to at least one of the photovoltaic power generation system and the battery system; a first switch selectively connecting the photovoltaic power generation system to a DC side of the power converter; a second switch selectively connecting the battery system to the DC side of the power converter; and a control device that controls the first switch and the second switch according to a state of the photovoltaic power generation system and a state of the battery system to control the grounding structures of one or more of the photovoltaic power generation system, the battery system, and the power converter.

[0010] The energy storage system may further include a first ground fault detector that detects a ground fault in the solar power generation system.

[0011] The first ground fault detector can be selectively connected to the first switch and the solar power generation system via a third switch located between the solar power generation system and the first switch.

[0012] The first ground fault detector may include a Ground Fault Detection Interrupter (GFDI).

[0013] The energy storage system may further include a second ground fault detector configured to detect a ground fault in one or more of the solar power generation system, the battery system, and the power conversion device.

[0014] The second ground fault detector may be located between a DC conversion device included in the battery system and the second switch, or may be located between the first switch, the second switch, and the power conversion device.

[0015] The second ground fault detector may include an Insulation Monitoring Device (IMD).

[0016] When the battery system is charging, the control device can control the operation of one or more of the first switch, the second switch, and the third switch to apply a floating ground structure to the battery system, the solar power generation system, and the power conversion device.

[0017] When the battery system is in a resting state after charging, the control device can control the operation of one or more of the first switch, the second switch and the third switch depending on the position of the second ground fault detector, thereby adjusting the grounding structure for the battery system, the solar power generation system, and the power conversion device.

[0018] When the battery system is discharging or in a hibernating state after discharging, the control device can control the operation of one or more of the first switch, the second switch and the third switch to apply a grounding structure to the solar power generation system and a floating ground structure to the battery system and the power conversion device.

[0019] When the second ground fault detector is located between the DC conversion device and the second switch, the control device can control the operation of one or more of the first switch, the second switch and the third switch to always apply a floating ground structure to the battery system.

[0020] The battery system may include a plurality of battery racks; and a DC conversion device that performs DC conversion in conjunction with the plurality of battery racks.

[0021] The DC converter may include multiple individual DC / DC converters each associated with an individual battery rack or a central DC / DC converter associated with multiple battery racks.

[0022] In order to achieve another object of the present invention, a method for controlling a grounding structure of an energy storage system according to one embodiment of the present invention includes a photovoltaic (PV) system, a battery system, and a power conversion device (PCS) selectively connected to at least one of the photovoltaic power generation system and the battery system, and is a method for controlling a grounding structure of an energy storage system interlocked with a power grid, the method including the steps of: checking a state of the battery system and a state of the photovoltaic power generation system; and controlling, according to the state of the photovoltaic power generation system and the state of the battery system, a first switch that selectively connects the photovoltaic power generation system to a DC side of the power conversion device, and a second switch that selectively connects the battery system to the DC side of the power conversion device, to control the grounding structures of one or more of the photovoltaic power generation system, the battery system, and the power conversion device.

[0023] The energy storage system may further include a first ground fault detector that detects a ground fault in the solar power generation system; a second ground fault detector that is located between a DC converter included in the battery system and the second switch, or between the first switch, the second switch, and the power conversion device, and detects a ground fault in one or more of the solar power generation system, the battery system, and the power conversion device; and a third switch that selectively connects the first ground fault detector to the first switch and the solar power generation system.

[0024] The first ground fault detector may include a Ground Fault Detection Interrupter (GFDI), and the second ground fault detector may include an Insulation Monitoring Device (IMD).

[0025] The step of controlling the grounding structure of one or more of the solar power generation system, the battery system, and the power conversion device may include a step of controlling the operation of one or more of the first switch, the second switch, and the third switch to apply a floating grounding structure to the battery system, the solar power generation system, and the power conversion device when the battery system is charging.

[0026] The step of controlling the grounding structure of one or more of the solar power generation system, the battery system, and the power conversion device may include a step of controlling the operation of one or more of the first switch, the second switch, and the third switch depending on the position of the second ground fault detector when the battery system is in a resting state after charging, thereby adjusting the grounding structure for the battery system, the solar power generation system, and the power conversion device.

[0027] The step of controlling the grounding structure of one or more of the solar power generation system, the battery system, and the power conversion device may include a step of controlling the operation of one or more of the first switch, the second switch, and the third switch when the battery system is discharging or in a resting state after discharging to apply a grounding structure to the solar power generation system and a floating ground structure to the battery system and the power conversion device.

[0028] The step of controlling the grounding structure of one or more of the solar power generation system, the battery system, and the power conversion device may include a step of controlling the operation of one or more of the first switch, the second switch, and the third switch to always apply a floating grounding structure to the battery system when the second ground fault detector is located between the DC conversion device and the second switch.

[0029] In order to achieve the above-mentioned another object, a ground structure control device for an energy storage system according to one embodiment of the present invention is provided, which is located in an energy storage system that includes a photovoltaic (PV) system, a battery system, and a power conversion device (PCS) selectively connected to at least one of the photovoltaic power generation system and the battery system, and is connected to a power grid, and includes at least one processor; a memory that stores at least one instruction executed through the at least one processor, the at least one instruction including an instruction to check a state of the battery system and a state of the photovoltaic power generation system; and an instruction to control a first switch that selectively connects the photovoltaic power generation system to a DC side of the power conversion device, and a second switch that selectively connects the battery system to a DC side of the power conversion device, depending on the state of the photovoltaic power generation system and the state of the battery system, thereby controlling the ground structure of one or more of the photovoltaic power generation system, the battery system, and the power conversion device.

[0030] The energy storage system may further include a first ground fault detector that detects a ground fault in the solar power generation system; a second ground fault detector that is located between a DC converter included in the battery system and the second switch, or between the first switch, the second switch, and the power conversion device, and detects a ground fault in one or more of the solar power generation system, the battery system, and the power conversion device; and a third switch that selectively connects the first ground fault detector to the first switch and the solar power generation system.

[0031] The instructions for controlling the grounding structure of one or more of the solar power generation system, the battery system, and the power conversion device may include instructions for controlling operation of one or more of the first switch, the second switch, and the third switch to apply a floating grounding structure to the battery system, the solar power generation system, and the power conversion device when the battery system is charging.

[0032] The instructions for controlling the grounding structure of one or more of the solar power generation system, the battery system, and the power conversion device may include instructions for controlling the operation of one or more of the first switch, the second switch, and the third switch depending on the position of the second ground fault detector when the battery system is in a resting state after charging, to adjust the grounding structure for the battery system, the solar power generation system, and the power conversion device.

[0033] The instructions for controlling the grounding structures of one or more of the solar power generation system, the battery system, and the power conversion device may include instructions for controlling the operation of one or more of the first switch, the second switch, and the third switch when the battery system is discharging or in a resting state after discharging to apply a grounding structure to the solar power generation system and a floating ground structure to the battery system and the power conversion device. Effect of the Invention

[0034] According to the above-described embodiments of the present invention, it is possible to minimize PID generated in a solar power generation system and prevent a decrease in efficiency of the solar power generation system.

[0035] In addition, it is possible to monitor ground faults in the DC-Coupled energy storage system connected to the entire PV system, and by floating the battery system through which a large fault current flows in the event of an accident, it is possible to minimize the fault current and the spread of the fault.

[0036] That is, the embodiment of the present invention can ensure both efficiency and stability at the same time as compared to the existing technology. [Brief description of the drawings]

[0037] [Figure 1]1 is a block diagram of an example of a PV system-connected DC-Coupled energy storage system to which the present invention can be applied. [Figure 2a] FIG. 1 is a schematic diagram of a PV system-connected DC-Coupled energy storage system having a typical floating ground structure. [Figure 2b] FIG. 1 is a conceptual diagram showing a method of operating a DC-Coupled energy storage system connected to a PV system having a typical floating ground structure. [Figure 3a] FIG. 1 is a schematic diagram of a PV system-connected DC-Coupled energy storage system having a general grounding structure. [Figure 3b] FIG. 1 is a conceptual diagram showing a method of operating a PV system-connected DC-Coupled energy storage system having a general grounding structure. [Figure 4a] 1 is a configuration example of an energy storage system having a grounding structure according to a first embodiment of the present invention. [Figure 4b] 4 is another configuration example of the energy storage system having the grounding structure according to the first embodiment of the present invention. [Diagram 5] FIG. 2 is a conceptual diagram showing a method of operating an energy storage system having a grounding structure according to the first embodiment. [Figure 6] FIG. 11 is a configuration diagram of an energy storage system having a grounding structure according to a second embodiment of the present invention. [Figure 7] FIG. 11 is a conceptual diagram of an example of a method for operating an energy storage system having a grounding structure according to a second embodiment of the present invention. [Figure 8] FIG. 11 is a conceptual diagram of another example of a method for operating an energy storage system having a grounding structure according to the second embodiment of the present invention. [Figure 9] FIG. 4 is a flow chart of a method for controlling a ground structure of an energy storage system according to an embodiment of the present invention. [Figure 10] FIG. 4 is a detailed flow chart of a method for controlling a grounding structure of an energy storage system according to an embodiment of the present invention. [Figure 11]FIG. 2 is a block diagram of a ground structure control device of an energy storage system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Since the present invention can be modified in various ways and has various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, it is understood that this is not intended to limit the present invention to the specific embodiment, but includes all modifications, equivalents, and alternatives within the spirit and technical scope of the present invention. Similar reference numerals are used for similar components while describing each drawing.

[0039] Terms such as first, second, A, B, etc. may be used to describe various components, but the components should not be limited by these terms. The terms are used only to distinguish one component from another. For example, a first component may be named a second component, and similarly, a second component may be named a first component, without departing from the scope of the present invention. The term "and / or" includes a combination of multiple associated listed items or any of multiple associated listed items.

[0040] When a component is referred to as being "coupled" or "connected" to another component, it should be understood that the component may be directly coupled or connected to the other component, but that there may be other components in between. In contrast, when a component is referred to as being "directly coupled" or "directly connected" to another component, it should be understood that there are no other components in between.

[0041] The terms used in this application are merely used to describe certain embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless the context clearly indicates otherwise. In this application, the terms "include" or "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and are not intended to preclude the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0042] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Terms as defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant art, and should not be interpreted as having an ideal or overly formal meaning unless expressly defined in this application.

[0043] Some terms used in this specification are defined as follows:

[0044] Nominal capacity (Nominal Capa.) refers to the set capacity [Ah] of a battery that is set by the battery manufacturer at the time of development.

[0045] SOC (State of Charge) is the current charged state of the battery expressed as a percentage [%], and SOH (State of Health) is the current deterioration state of the battery expressed as a percentage [%].

[0046] A battery rack is a system with the smallest single structure that can connect pack units set by the battery manufacturer in series / parallel and be monitored and controlled through a BMS. It can consist of multiple battery modules and one BPU or protection device.

[0047] A battery bank can refer to a large-scale collection of battery rack systems consisting of multiple racks connected in parallel. The battery bank BMS can monitor and control the rack BMS (RBMS) of each battery rack.

[0048] A BSC (Battery System Controller) is a device that performs top-level control of a battery system including a bank-based battery system, and can also be used as a control device in a battery system having a multi-bank level structure.

[0049] Power limit refers to the output limit preset by the battery manufacturer according to the battery condition. Rack power limit refers to the output limit (in kW) set at the rack level, and can be set based on the battery's SOC and temperature.

[0050] The power limit can be divided into a charge power limit and a discharge power limit depending on whether the battery is charging or discharging. Also, a rack power limit for each rack and a bank power limit for each bank can be defined depending on the structure of the battery system.

[0051] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0052] FIG. 1 is a block diagram of an example of a PV system-connected DC-Coupled energy storage system to which the present invention can be applied.

[0053] In a DC-Coupled energy storage system, a DC / DC converter 500 capable of individually controlling the DC voltage / current for each battery system 100 is essential. Since a DC / DC converter is provided in the battery system, a DC / AC converter used for linking with the solar power system is no longer necessary, and efficiency is increased. In addition, by applying a DC / DC converter to each battery system, not only can the existing battery system be protected and controlled, but also the battery power can be controlled taking into account the characteristics of each individual battery system, even if differences in SOC, SOH, and capacity occur between battery racks.

[0054] FIG. 1 shows an example of a DC coupled system in which an output side of a PV (Photovoltaic; solar power generation system) 700 is connected to an output side of a DC / DC converter 500 and an input side of a PCS 400 .

[0055] Batteries that serve to store power in an energy storage system may be embodied in the form of a battery rack made up of a number of battery modules, and a number of battery racks made up of a battery bank. Here, the battery rack may be called a battery pack depending on the device or system in which the battery is used. Battery #1, battery #2, ..., battery #N shown in FIG. 1 may be in the form of a battery pack or battery rack.

[0056] At this time, each battery 100 may be provided with a Battery Management System (BMS). The BMS may monitor the current, voltage, and temperature of each battery rack (or pack) under its management, calculate a Status Of Charge (SOC) based on the monitoring results, and control charging and discharging. In the system of FIG. 1, when each battery is a battery rack, the BMS may be a rack BMS (RBMS).

[0057] Each battery section, which is composed of a number of batteries and peripheral circuits, devices, etc., is provided with a Battery Section Controller (BSC) 200, which can monitor and control control targets such as voltage, current, temperature, circuit breakers, etc.

[0058] In addition, a power conversion / conditioning system (PCS) 400 provided for each battery section controls power supplied from the outside and power supplied from the battery section to the outside, and may include a DC / AC inverter. In addition, an output of the DC-DC converter 500 may be connected to the PCS 400, and the PCS 400 may be connected to a grid 600. The PCS 400 usually operates in a constant power mode. A power management system (PMS) / energy management system (EMS) 300 connected to the PCS may control the output of the PCS based on the monitoring and control results of the BMS or BSC.

[0059] 1, battery #1 is connected to DC-DC converter #1, battery #2 is connected to DC-DC converter #2, and battery #N is connected to DC-DC #N. The output of the DC-DC converter corresponding to each battery is connected to PCS 400 via a DC link.

[0060] The DC-DC converter may be a bidirectional converter, and when conversion is performed in the direction from the battery to the load, the input of the DC-DC converter may be connected to the battery (battery unit, battery rack, or battery pack), and the output of the DC-DC converter may be connected to the load. As examples of the DC-DC converter, various types of converters such as a full-bridge converter, a half-bridge converter, and a flyback converter may be used.

[0061] Meanwhile, communication using a Controller Area Network (CAN) or Ethernet (shown by dotted lines in FIG. 1) can be performed between the BMS, BSC 200, PMS 300, and PCS 400.

[0062] According to an embodiment of the present invention shown in FIG. 1, the BSC 200 in charge of the overall control of the battery section can report the status of each battery to the PMS 300. Here, the status of each battery can include information such as the SOC (Status Of Charge), SOH (Status Of Health), voltage, temperature, etc. of each battery. The BSC 200 can provide information such as the limit power (P_battery_limit) and actual power (P_battery_real) of each battery to the PMS 300. The PMS 300 in charge of the control of the entire ESS system issues a charge or discharge command (through P_pcs_reference) to the PCS 400 during actual system operation.

[0063] Here, the BSC 200 determines the output reference for each individual DC / DC converter taking into account the state of each battery. In an embodiment of the present invention, the output reference of each individual DC / DC converter can be set in different manners depending on whether the mode is droop or constant power (CP).

[0064] When the output of the DC / DC converter is controlled by the droop mode, the BSC can set a droop curve for each DC / DC converter considering the state of each battery before the system operation and provide it to the converter, whereas when the DC / DC converter operates in the CP mode, the BSC can determine the power reference of each DC / DC converter during the system operation and provide it to the converter.

[0065] During actual operation of the energy storage system, the PMS transmits charge and discharge commands to the PCS and BSC. At this time, the PMS monitors the status of the photovoltaic power system (PV), grid, and battery in real time, and determines the operation mode and output reference of the components in the system based on the operation command received from the higher-level system, the Energy Management System (EMS).

[0066] Meanwhile, FIG. 1 shows an example of a system in which a separate DC / DC converter is applied to each battery rack, but the present invention can also be applied to a system in which a central DC / DC converter commonly connected to multiple battery racks is applied.

[0067] In the DC Coupled Energy Storage System explained in Figure 1, the grounding structure is determined by whether the negative power line of the PV system is grounded or not. The method of monitoring a ground fault varies depending on the grounding structure, and the impact of the fault appears in different forms depending on the grounding structure.

[0068] The structure of grounding-related systems can be broadly divided into grounding systems and floating systems. In a grounding system, a fault current flows when a single-line ground fault occurs, which can damage equipment. In contrast, in a floating system, a fault current does not flow when a single-line ground fault occurs, but current flows when a ground fault occurs again.

[0069] FIG. 2a is a schematic diagram of a PV system-connected DC-Coupled energy storage system having a typical floating ground structure.

[0070] The energy storage system in Fig. 2a includes a battery system 10, a DC / DC converter 50, a PV system 70, and a power conversion system 40 linked thereto, and has a floating earth structure. In general, a floating earth (non-grounded) structure is recommended for battery systems to ensure safety in the event of a ground fault.

[0071] The connection between the PV system 70 and the power conversion system 40 can be controlled through switch 1 (SW1), but the PV system 70 is usually isolated from the DC grid at night. The connection between the battery system 10 including the DC / DC converter 50 and the power conversion system 40 is made through switch 2 (SW2), which is usually kept in the on state when the system is operating normally.

[0072] In the system structure of Fig. 2a, the positive and negative terminals of the PV system and the battery system are not connected to ground. Such a ground structure in which the positive and negative terminals of the power line are not connected to ground is called floating (or ungrounded) ground. In order to monitor ground faults in such a system structure, insulation resistance and ground faults can be monitored using an insulation monitoring device such as an IMD (Insulation Monitoring Device). The IMD is a device that measures and monitors the insulation resistance value between the positive terminal and ground and between the negative terminal and ground, and can be located on the DC power line of the power conversion system 40 as shown in Fig. 2a.

[0073] The IMD, which is a ground fault monitoring device, detects insulation resistance and ground faults depending on the open / close state of switch 1, but such a structure has limitations as described below.

[0074] FIG. 2b is a conceptual diagram showing a method of operating a PV system-connected DC-Coupled energy storage system having a typical floating ground structure.

[0075] 2b shows the state of each component (power converter, PV system, battery system) according to the operating state of the energy storage system with a floating ground structure. When the system is charging, switch 1 is closed and the PV system is connected to the battery system and the power grid. At this time, the power converter 40, PV system 70, and battery system 10 are all in a floating state, and the insulation resistance can be measured by the IMD, and a ground fault can be monitored.

[0076] However, when switch 1 is opened at night to separate the PV system from the DC system, it is not possible to detect a ground fault occurring in the system. In addition, PID (potential induced degradation) occurs in the solar cells in the floating PV system, causing gradual system degradation. As degradation progresses, the amount of energy generated by the solar cells decreases, ultimately resulting in a decrease in system efficiency.

[0077] For this reason, negative grounding is mainly used in PV systems to prevent potential induced degradation (PID), which adversely affects power generation efficiency.

[0078] FIG. 3a is a schematic diagram of a PV system-connected DC-Coupled energy storage system having a typical grounding structure.

[0079] The energy storage system of Fig. 3a includes a battery system 10, a DC / DC converter 50, a PV system 70, and a power conversion system 40 linked thereto, and has a negative grounding structure among one-pole grounding structures. The negative grounding structure refers to a structure in which the negative (-) terminal of the power line is connected to the ground. It can be seen from Fig. 3a that the negative terminal of the PV system and the negative terminal of the battery system can be connected to the ground via a switch.

[0080] The connection between the PV system 70 and the power conversion system 40 can be controlled through switch 1 (SW1), but the PV system 70 is usually isolated from the DC grid at night. The connection between the battery system 10 including the DC / DC converter 50 and the power conversion system 40 is made through switch 2 (SW2), which is usually kept on when the system is operating normally. The system of Fig. 3a further selectively connects the negative terminals of the battery system and the PV system to ground through switch 3 (SW3).

[0081] In such a system structure, insulation and ground fault monitoring devices such as IMD, RCM (Residential Current Monitoring), and GFDI (Ground Fault Detection Interrupter) can be used to monitor insulation resistance and ground faults in order to monitor ground faults.

[0082] The IMD is a device that measures and monitors the insulation resistance between the positive terminal and ground and between the negative terminal and ground, and can be located on the DC power line of the power conversion system 40 or between the battery rack and the DC / DC converter as shown in Fig. 3a. The RCM is a device that monitors whether the sum of the currents flowing through the positive power line and the negative power line is zero to detect whether leakage current occurs, and is located between the battery rack and the DC / DC converter in Fig. 3a. The GFDI is a device that is connected between the power line and ground, and cuts off the current when the current flowing from the power line to the ground is equal to or greater than a reference value.

[0083] On the other hand, even such a negative grounding structure has limitations, as will be explained below.

[0084] FIG. 3b is a conceptual diagram showing a method of operating a PV system-connected DC-Coupled energy storage system having a typical grounding structure.

[0085] FIG. 3b shows the state of each component (power conversion device, PV system, battery system) according to the operating state of an energy storage system having a grounding structure. Here, when the battery is being charged and in a standby state after charging, switch 1 is in a closed state, and the PV system is connected to the battery system and the power grid. Switch 3 is also in a closed state, and the negative electrodes of the power conversion device 40, PV system 70, and battery system 10 are in a grounded state. If a ground fault occurs in this state, a fault current will be generated.

[0086] Then, after the PV system finishes generating power, switch 1 and switch 3 are opened, and the power converter 40, the PV system 70, and the battery system 10 are all in a floating ground state. At this time, since the PV system 70 is in a floating ground state, PID occurs, and as a result, the PV power generation efficiency decreases. In addition, since switch 1 is open, insulation reduction and ground faults cannot be detected.

[0087] Therefore, in an energy storage system including a PV system and a battery system, the choice of which grounding method to use is a matter of choosing between system efficiency and safety. In the end, system efficiency and safety are in a trade-off relationship and are determined by the system designer's choice, and no matter which method is selected, problems will occur.

[0088] In order to solve this problem, the present invention aims to ensure both the stability and efficiency of a DC-Coupled energy storage system connected to a PV system by operating the energy storage system by changing the grounding mode according to the operating state of the battery.

[0089] FIG. 4a shows a configuration example of an energy storage system having a grounding structure according to a first embodiment of the present invention.

[0090] The energy storage system according to an embodiment of the present invention includes a battery system 100, a DC / DC converter 500, a PV system 700, and a power conversion system 400 linked thereto, and may include a number of switches for controlling the connections of these components.

[0091] The connection between the PV system 700 and the power conversion system 400 may be controlled through a first switch S1. A Ground Fault Detection Interrupter (GFDI) may be located between the first switch and the PV system (including a plurality of PV panels) as a device for detecting a ground fault. The connection of the GFDI with the first switch and the PV system may be controlled through a third switch.

[0092] A connection control between the battery system 100 including the DC / DC converter 500 and the power conversion system 400 may be performed through the second switch S2. An IMD may be disposed between the second switch S2 and the DC / DC converter as a device for monitoring or detecting a ground fault. In this embodiment, the DC / DC converter 500 is in the form of a rack DC / DC converter, and a separate DC / DC converter is connected and used for each battery rack.

[0093] In this embodiment, the PV system applies a floating ground structure only when the battery is being charged to minimize the occurrence of PID, and applies a negative grounding structure in other operating modes to eliminate PID that occurs in the floating ground structure.

[0094] In addition, in the case of a battery system, a floating ground structure is applied in the entire operation mode, thereby minimizing the possibility of fault current flowing in the event of a ground fault, thereby ensuring system stability.

[0095] FIG. 4b shows another example of the configuration of an energy storage system having a grounding structure according to the first embodiment of the present invention.

[0096] The energy storage system of the embodiment of FIG. 4b also includes a battery system 100, a DC / DC converter 500, a PV system 700 and a power conversion device 400 associated therewith, and may include a number of switches to control the connections of these components.

[0097] The connection between the PV system 700 and the power conversion system 400 may be controlled through a first switch S1. A Ground Fault Detection Interrupter (GFDI) may be located between the first switch and the PV system (including a plurality of PV panels) as a device for detecting a ground fault. The connection of the GFDI with the first switch and the PV system may be controlled through a third switch.

[0098] A connection control between the battery system 100 including the DC / DC converter 500 and the power conversion system 400 may be performed through the second switch S2. An IMD may be disposed between the second switch S2 and the DC / DC converter as a device for detecting a ground fault. Here, the DC / DC converter 500 is in the form of a central DC / DC converter and is used in parallel connection with a plurality of battery racks.

[0099] Except for the form of the DC / DC converter, the configuration of the energy storage system according to this embodiment is the same as the configuration of the energy storage system according to FIG. 4a, and the system operation is also the same.

[0100] FIG. 5 is a conceptual diagram showing a method of operating the energy storage system having the grounding structure according to the first embodiment.

[0101] According to the method for operating an energy storage system having a grounded structure according to the first embodiment of the present invention, the battery system 100 is always operated in a floating grounded structure.

[0102] Specifically, in a battery charging state, the first switch S1 and the second switch S2 are connected, and the third switch S3 is opened, so that the battery system 100, the PV system 700, and the PCS 400 are all operated in a floating ground state. At this time, a PID may occur in the PV system 700. In this case, a ground fault may be detected by an IMD located on the battery system side.

[0103] When the PV system 700 is generating power and the battery is in a resting state, the third switch S3 is closed, i.e., connected, and the PV system and the PCS 400 are operated in a grounded structure, so the second switch S2 is opened to separate the battery system 100 from the DC system. In this case, the PV system 700 and the PCS 400 detect a ground fault using a Ground Fault Detection Interrupter (GFDI) located between the first switch and the PV system. Also, the battery system can detect a ground fault using an IMD located between the second switch S2 and the DC / DC converter.

[0104] In addition, in a battery discharging state, the first switch S1 is opened and the second switch S2 is connected to transfer power from the battery to the grid. At this time, the third switch is kept connected, i.e., closed, so that the PV system 700 maintains a grounded structure. The connection state of these switches is the same even in a hibernation state, and by operating the PV system in a grounded structure as much as possible, it is possible to eliminate the PID phenomenon that occurs during battery charging.

[0105] Meanwhile, the embodiment of FIG. 5 can be applied to either an energy storage system including a rack DC / DC converter or a central DC / DC converter.

[0106] FIG. 6 is a configuration diagram of an energy storage system having a grounding structure according to a second embodiment of the present invention.

[0107] The energy storage system having the grounding structure according to the second embodiment of the present invention also includes a battery system 100, a DC / DC converter 500, a PV system 700 and a power conversion system 400 linked thereto, and may include a number of switches for controlling the connections of these components.

[0108] The connection between the PV system 700 and the power conversion system 400 may be controlled through a first switch S1. A Ground Fault Detection Interrupter (GFDI) may be located between the first switch and the PV system (including multiple PV panels) as a device for detecting a ground fault. The connection of the GFDI with the first switch and the PV system may be controlled through a third switch.

[0109] The connection between the battery system 100 including the DC / DC converter 500 and the power conversion system 400 can be controlled through the second switch S2. In the grounding structure according to the second embodiment, the IMD is located between the first switch S1, the second switch S2, and the PCS 400.

[0110] FIG. 7 is a conceptual diagram of an example of a method for operating an energy storage system having a grounding structure according to the second embodiment of the present invention.

[0111] According to the operating method of the energy storage system shown in FIG. 7, the battery system 100 is operated in a grounded structure in a standby state after charging, and is operated in a floating ground structure in other operating modes.

[0112] Specifically, in a battery charging state, the first switch S1 and the second switch S2 are connected, and the third switch S3 is opened, so that the battery system 100, the PV system 700, and the PCS 400 are all operated in a floating ground state. At this time, PID may occur in the PV system 700. In this case, a ground fault may be detected by an IMD located between the first switch S1, the second switch S2, and the PCS 400.

[0113] After the battery is fully charged, when the PV system 700 generates power in a hibernation state, the third switch S3 is closed, i.e., connected, and the PV system, the PCS 400, and the battery system 100 are all operated in a grounded structure because the IMD is located between the first switch S1, the second switch S2, and the PCS 400.

[0114] In addition, in the battery discharging state, the first switch S1 is opened to transfer power from the battery to the grid. At this time, the third switch is kept connected, i.e., closed, so that the PV system 700 maintains a grounded structure. At this time, a floating ground structure is applied to the PCS 400 and the battery system 100.

[0115] The connection states of the first switch S1, the second switch S2, and the third switch S3 are the same in both the hibernation state and the discharge state, and the PV system is operated as a grounded structure as much as possible to eliminate the PID phenomenon that occurs when the battery is charged.

[0116] Meanwhile, the embodiment of FIG. 7 can be applied to either an energy storage system including a rack DC / DC converter or a central DC / DC converter.

[0117] In this embodiment, when the battery system is in a resting state after being fully charged, the floating ground structure is applied except when the battery system is grounded, thereby ensuring system stability. The possibility of a fault current flowing in the event of a ground fault can be minimized, ensuring system stability.

[0118] PV systems can also employ grounding techniques to minimize the occurrence of PID, except when the battery is being charged.

[0119] FIG. 8 is a conceptual diagram of another example of a method for operating an energy storage system having a grounding structure according to the second embodiment of the present invention.

[0120] According to the operating method of the energy storage system shown in FIG. 8, the battery system 100 is always operated in a floating ground structure.

[0121] Specifically, in a battery charging state, the first switch S1 and the second switch S2 are connected, and the third switch S3 is opened, so that the battery system 100, the PV system 700, and the PCS 400 are all operated in a floating ground state. At this time, PID may occur in the PV system 700. In this case, a ground fault may be detected by an IMD located between the first switch S1, the second switch S2, and the PCS 400.

[0122] Even when the PV system 700 generates power in a resting state after the battery is fully charged, the third switch S3 remains open, and each component maintains its operation and state in a battery charging state. That is, the battery system 100, the PV system 700, and the PCS 400 are all operated in a floating ground state. Therefore, compared to other embodiments, the PV system 700 may generate more PID, and therefore the time required to remove the PID may be reduced.

[0123] In addition, in the battery discharging state, the first switch S1 is opened to transfer power from the battery to the grid. At this time, the third switch is kept connected, i.e., closed, so that the PV system 700 has a grounding structure. At this time, a floating ground structure is applied to the PCS 400 and the battery system 100.

[0124] The connection states of the first switch S1, the second switch S2, and the third switch S3 are the same in both the hibernation state and the discharge state, and the PV system is operated in a grounded structure, thereby eliminating the PID phenomenon that occurs when the battery is charged.

[0125] Meanwhile, the embodiment of FIG. 8 can be applied to any energy storage system including a rack DC / DC converter or a central DC / DC converter.

[0126] In this embodiment, in the case of a battery system, by always applying a floating ground structure, the possibility of fault current flowing in the event of a ground fault can be minimized, thereby ensuring system stability.

[0127] In the grounding structure according to the second embodiment of the present invention, the IMD is located between the first switch S1, the second switch S2, and the PCS 400. Therefore, according to the method of operating the energy storage system having the grounding structure according to the second embodiment described with reference to Figures 7 and 8, when the battery is in a resting state after charging and the PV is generating power, a grounding structure may be applied to all of the battery system, the solar power generation system, and the power conversion device, or a floating ground structure may be applied to all of the battery system, the solar power generation system, and the power conversion device.

[0128] FIG. 9 is a flow chart of a method for controlling a ground structure of an energy storage system according to an embodiment of the present invention.

[0129] The embodiment of FIG. 9 illustrates an operational sequence in a method for controlling a grounding structure in an energy storage system that interfaces with a power grid and includes a photovoltaic (PV) system, a battery system, and a power conversion system (PCS) selectively connected to at least one of the photovoltaic (PV) system and the battery system.

[0130] The ground structure control method of the energy storage system according to this embodiment can be performed by a PMS or EMS in the energy storage system, but can also be performed by any form of control device located in or connected to the energy storage system.

[0131] Referring to FIG. 9, the control device checks the state of the battery system and the state of the solar power generation system (S910).

[0132] Depending on the state of the solar power generation system and the state of the battery system, a first switch that selectively connects the solar power generation system to the DC side of the power conversion device, and a second switch that selectively connects the battery system to the DC side of the power conversion device are controlled to control the grounding structures of one or more of the solar power generation system, the battery system, and the power conversion device (S920).

[0133] FIG. 10 is a detailed flow diagram of the ground structure control method for the energy storage system according to an embodiment of the present invention.

[0134] 10, the control device checks the state of the battery system and the state of the solar power generation system, and checks whether the battery system is being charged (S911), and if it is being charged, controls the operation of one or more of the first switch, the second switch, and the third switch to apply a floating ground structure to the battery system, the solar power generation system, and the power conversion device (S921). At this time, the control device controls the first switch S1 and the second switch S2 to be connected, i.e., closed, and the third switch S3 to be opened.

[0135] When the battery system transitions to a rest state after charging and the solar power system is generating power (Yes in S913), the operation of one or more of the first switch, the second switch, and the third switch is controlled according to the position of the second earth fault detector to adjust the grounding structure for the battery system, the solar power generation system, and the power conversion device (S923). At this time, depending on the position of the second earth fault detector, i.e., the IMD, different grounding structures for the battery system, the solar power generation system, and the power conversion device can be applied, and the operation of the first switch, the second switch, and the third switch can also be controlled according to each grounding structure.

[0136] Specifically, when the IMD is located between the second switch S2 and the DC / DC converter, when the battery is in a resting state after charging and the PV is generating power, the third switch S3 is closed, i.e., connected, and the PV system and PCS operate in a grounded structure, and the second switch S2 is opened to isolate the battery system 100 from the DC system and operate it in a floating ground structure.

[0137] In contrast, when the IMD is located between the first switch S1, the second switch S2, and the PCS, when the battery is in a resting state after charging and the PV is generating power, a grounded structure or a floating ground structure can be applied to the battery system, the solar power generation system, and the power conversion device.

[0138] On the other hand, when the battery system is in a discharging or resting state after discharging (Yes in S912), the operation of one or more of the first switch, the second switch, and the third switch is controlled to apply a grounded structure to the photovoltaic power generation system, and a floating ground structure to the battery system and the power conversion device (S922). At this time, the first switch S1 is opened and the second switch S2 is connected, and power is transferred from the battery to the grid. The third switch is kept connected, i.e., closed, and the PV system maintains the grounded structure.

[0139] FIG. 11 is a block diagram of a ground structure control device of an energy storage system according to an embodiment of the present invention.

[0140] The ground structure control device 300 according to the embodiment of the present invention may be a PMS or EMS included in an energy storage system, but may be any type of control device located in or connected to the energy storage system. Here, the energy storage system includes a photovoltaic (PV) system, a battery system, and a power conversion system (PCS) selectively connected to at least one of the photovoltaic (PV) system and the battery system, and is connected to a power grid.

[0141] The ground structure control device 300 may include at least one processor 310, a memory 320 for storing at least one instruction executed by the processor, and a transceiver 330 for communicating with a network.

[0142] The at least one instruction may include an instruction to check a state of the battery system and a state of the solar power generation system; and an instruction to control a first switch that selectively connects the solar power generation system to a DC side of the power conversion device and a second switch that selectively connects the battery system to the DC side of the power conversion device according to the state of the solar power generation system and the state of the battery system, thereby controlling the grounding structures of one or more of the solar power generation system, the battery system, and the power conversion device.

[0143] The energy storage system may further include a first ground fault detector located between the solar power generation system and the first switch, detecting a ground fault in the solar power generation system; and a second ground fault detector located between a DC converter included in the battery system and the second switch, or between the first switch, the second switch, and the power conversion device, detecting a ground fault in one or more of the solar power generation system, the battery system, and the power conversion device; and a third switch selectively connecting the first ground fault detector to the first switch and the solar power generation system.

[0144] The instructions for controlling the grounding structure of one or more of the solar power generation system, the battery system, and the power conversion device may include instructions for controlling operation of one or more of the first switch, the second switch, and the third switch to apply a floating grounding structure to the battery system, the solar power generation system, and the power conversion device when the battery system is charging.

[0145] The instructions for controlling the grounding structure of one or more of the solar power generation system, the battery system, and the power conversion device may also include instructions for controlling the operation of one or more of the first switch, the second switch, and the third switch to adjust the grounding structure for the battery system, the solar power generation system, and the power conversion device depending on the position of the second ground fault detector when the battery system is in a resting state after charging.

[0146] The instructions for controlling the grounding structure of one or more of the solar power generation system, the battery system, and the power conversion device may also include instructions for controlling the operation of one or more of the first switch, the second switch, and the third switch when the battery system is discharging or in a rest state after discharging to apply a grounding grounding structure to the solar power generation system and a floating grounding structure to the battery system and the power conversion device.

[0147] The ground structure control device 300 of the energy storage system may further include an input interface device 340, an output interface device 350, a memory device 360, etc. Each component included in the ground structure control device 300 may be connected by a bus 370 to communicate with each other.

[0148] The processor 310 can execute program commands stored in at least one of the memory 320 and the storage device 360. Here, the processor can refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which the method according to the embodiment of the present invention is performed. The memory (or storage device) can be composed of at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory can be composed of at least one of a read only memory (ROM) and a random access memory (RAM).

[0149] According to the above-described embodiment of the present invention, it is possible to select an optimal grounding structure for each operation mode, thereby minimizing the number of ground fault detection devices and reducing costs. Furthermore, by providing devices capable of detecting ground faults in the PV system and the battery system, it is possible to minimize the areas that cannot be detected by the existing system and ensure system stability.

[0150] The operation of the method according to the embodiment of the present invention can be embodied as a computer readable program or code in a computer readable recording medium. The computer readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. In addition, the computer readable recording medium can be distributed to computer systems connected via a network, and the computer readable program or code can be stored and executed in a distributed manner.

[0151] Some aspects of the invention have been described in the context of an apparatus, but it may also be presented in terms of a corresponding method, where a block or apparatus corresponds to a method step or a feature of a method step. Similarly, aspects described in the context of a method may be presented in terms of a corresponding block or item or feature of a corresponding apparatus. Some or all of the method steps may be performed by (or using) a hardware apparatus, such as, for example, a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, one or more of the most important method steps may be performed by such an apparatus.

[0152] Although the present invention has been described with reference to preferred embodiments thereof, those skilled in the art will understand that various modifications and variations of the present invention can be made without departing from the spirit and scope of the present invention as set forth in the following claims. [Explanation of symbols]

[0153] 40 Power Conversion Systems 50 DC / DC Converter 70 PV systems 100 Battery System 200 Battery Section Controller (BSC) 300 Ground structure control device 310 Processor 320 Memory 330 Transmitting and Receiving Equipment 340 Input Interface Device 350 Output Interface Device 360 storage device 370 Bus 400 Power Conversion / Conditioning System (PCS) 400 Power Conversion System 500 DC / DC Converter 600 Grid 700 PV system

Claims

1. An energy storage system including a photovoltaic (PV) system and a battery system, the energy storage system being connected to a power grid, a power conversion system (PCS) that interfaces with the power grid and is selectively connected to at least one of the solar power generation system and the battery system; a first switch that selectively connects the solar power generation system to a DC side of the power conversion device; a second switch that selectively connects the battery system to a DC side of the power conversion device; a third switch located between the solar power generation system and the first switch; a first ground fault detector selectively connected to the first switch and the solar power generation system via the third switch, the first ground fault detector detecting a ground fault in the solar power generation system; and a control device that controls the first switch and the second switch according to a state of the solar power generation system and a state of the battery system to control one or more grounding structures of the solar power generation system, the battery system, and the power conversion device; When the battery system is being charged, the control device A floating ground structure is applied to the battery system, the solar power generation system, and the power conversion device by closing the first switch, closing the second switch, and opening the third switch. Energy storage systems.

2. The energy storage system of claim 1 , wherein the first ground fault detector includes a Ground Fault Detection Interrupter (GFDI).

3. The energy storage system of claim 1 , further comprising a second ground fault detector configured to detect a ground fault in one or more of the solar power generation system, the battery system, and the power conversion device.

4. The second ground fault detector includes: Located between a DC converter included in the battery system and the second switch; or The energy storage system of claim 3 , located between the first switch, the second switch, and the power converter.

5. The energy storage system of claim 3 , wherein the second ground fault detector includes an Insulation Monitoring Device (IMD).

6. The control device includes: When the battery system is in a resting state after charging, 5. The energy storage system of claim 4, further comprising: controlling operation of one or more of the first switch, the second switch, and the third switch depending on a position of the second ground fault detector to adjust a grounding structure for the battery system, the solar power generation system, and the power conversion device.

7. The control device includes: When the battery system is discharging or in a resting state after discharging, 2. The energy storage system of claim 1, further comprising: controlling operation of one or more of the first switch, the second switch, and the third switch to apply a grounding structure to the solar power generation system and a floating ground structure to the battery system and the power conversion device.

8. The control device includes: When the second ground fault detector is located between the DC converter and the second switch, 5. The energy storage system of claim 4, further comprising: controlling the operation of one or more of the first switch, the second switch, and the third switch to always apply a floating ground structure to the battery system.

9. The battery system includes: A plurality of battery racks; and The energy storage system of claim 1 , further comprising a DC converter in communication with the plurality of battery racks for DC conversion.

10. The DC converter comprises:

10. The energy storage system of claim 9, comprising a plurality of individual DC / DC converters each associated with an individual battery rack or a central DC / DC converter associated with a plurality of battery racks.

11. A method for controlling a grounding structure of an energy storage system that is connected to a power grid, the energy storage system including a photovoltaic (PV) system, a battery system, and a power conversion system (PCS) selectively connected to at least one of the photovoltaic (PV) system and the battery system, the method comprising: checking the state of the battery system and the state of the solar power generation system; and Depending on the state of the solar power generation system and the state of the battery system, Controlling a first switch that selectively connects the solar power generation system and a DC side of the power conversion device; controlling a second switch that selectively connects the battery system and a DC side of the power conversion device; Controlling a third switch located between the solar power generation system and the first switch; A first ground fault detector is selectively connected to the first switch and the solar power generation system via the third switch, and the first ground fault detector detects a ground fault in the solar power generation system. a step of: when the battery system is charging, closing the first switch, closing the second switch, and opening the third switch. A method for controlling a ground structure of an energy storage system, comprising the step of applying a floating ground structure to the solar power generation system, the battery system, and the power conversion device.

12. The energy storage system includes:

12. The method for controlling the grounding structure of an energy storage system according to claim 11, further comprising a second ground fault detector located between a DC converter included in the battery system and the second switch, or located between the first switch, the second switch, and the power conversion device, for detecting a ground fault in one or more of the solar power generation system, the battery system, and the power conversion device.

13. The method for controlling a ground structure of an energy storage system according to claim 12 , wherein the first ground fault detector includes a Ground Fault Detection Interrupter (GFDI).

14. The method for controlling a ground structure of an energy storage system according to claim 12 , wherein the second ground fault detector includes an insulation monitoring device (IMD).

15. The step of controlling the ground structure of one or more of the solar power generation system, the battery system, and the power conversion device includes: When the battery system is in a resting state after charging, 13. The method for controlling the grounding structure of an energy storage system according to claim 12, comprising the step of controlling the operation of one or more of the first switch, the second switch, and the third switch depending on a position of the second ground fault detector to adjust the grounding structure for the battery system, the solar power generation system, and the power conversion device.

16. The step of controlling the ground structure of one or more of the solar power generation system, the battery system, and the power conversion device includes: When the battery system is discharging or in a resting state after discharging, 13. The method for controlling the ground structure of an energy storage system according to claim 12, comprising the step of controlling the operation of one or more of the first switch, the second switch, and the third switch to apply a grounding structure to the solar power generation system and a floating ground structure to the battery system and the power conversion device.

17. The step of controlling the ground structure of one or more of the solar power generation system, the battery system, and the power conversion device includes: When the second ground fault detector is located between the DC converter and the second switch, The method for controlling the ground structure of an energy storage system according to claim 14, comprising the step of controlling the operation of one or more of the first switch, the second switch, and the third switch to always apply a floating ground structure to the battery system.

18. 1. A ground structure control device located in an energy storage system that interfaces with a power grid, the energy storage system including a photovoltaic (PV) system, a battery system, and a power conversion system (PCS) selectively connected to at least one of the photovoltaic (PV) system and the battery system, the ground structure control device comprising: at least one processor; a memory for storing at least one instruction to be executed by said at least one processor; The at least one instruction: instructions for verifying a status of the battery system and a status of the solar power system; and Depending on the state of the solar power generation system and the state of the battery system, Controlling a first switch that selectively connects the solar power generation system and a DC side of the power conversion device; controlling a second switch that selectively connects the battery system and a DC side of the power conversion device; Controlling a third switch located between the solar power generation system and the first switch; A first ground fault detector is selectively connected to the first switch and the solar power generation system via the third switch, and the first ground fault detector detects a ground fault in the solar power generation system. A ground structure control device, the ground structure control device including instructions for applying a floating ground structure to the solar power generation system, the battery system, and the power conversion device by closing the first switch, closing the second switch, and opening the third switch when the battery system is charging.

19. The energy storage system includes: The ground structure control device of claim 18, further comprising a second ground fault detector located between a DC converter included in the battery system and the second switch, or located between the first switch, the second switch, and the power conversion device, for detecting a ground fault in one or more of the solar power generation system, the battery system, and the power conversion device.

20. The instructions for controlling the ground structure of one or more of the solar power generation system, the battery system, and the power conversion device include: When the battery system is in a resting state after charging, 20. The ground structure control device of claim 19, further comprising instructions for controlling operation of one or more of the first switch, the second switch, and the third switch depending on a position of the second ground fault detector to adjust the ground structure for the battery system, the solar power generation system, and the power conversion device.

21. The instructions for controlling the ground structure of one or more of the solar power generation system, the battery system, and the power conversion device include: When the battery system is discharging or in a resting state after discharging, The ground structure control device of claim 19, comprising instructions for controlling the operation of one or more of the first switch, the second switch, and the third switch to apply a grounding structure to the solar power generation system and a floating ground structure to the battery system and the power conversion device.

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