Energy storage system and method for controlling grounding structure of energy storage system

Abstract

An energy storage system includes a photovoltaic (PV) system and a battery system connected to a power grid. The energy storage system may include: a power conversion system (PCS) configured to be connected to the power grid and selectively connected to at least one of the PV system and the battery system; a first switch selectively connecting a direct current (DC) link between the PV system and the power conversion system; a second switch selectively connecting the battery system and the DC link between the power conversion system; and a controller configured to control the grounding structure of at least one of the PV system, the battery system, and the power conversion system by controlling the first and second switches based on the states of the PV system and the battery system.

Description

Technical Field

[0001] This application claims priority and benefit to Korean Patent Application No. 10-2021-0181167, filed on December 17, 2021, with the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to energy storage systems and methods for controlling the grounding configuration of energy storage systems, and more specifically, to energy storage systems including photovoltaic systems and battery systems, and methods and apparatus for controlling the grounding configuration in energy storage systems. Background Technology

[0003] Energy storage systems involve renewable energy, batteries for storing electricity, and electricity itself. In recent years, with the increasing prevalence of smart grids and renewable energy, and the growing emphasis on power system efficiency and stability, the demand for energy storage systems for power supply and demand control and power quality improvement has been growing. Depending on their intended use, energy storage systems can have different outputs and capacities. To configure large-capacity energy storage systems, multiple battery systems can be connected.

[0004] In energy storage systems, the systems connected to photovoltaic (PV) systems are changing from AC-coupled systems to DC-coupled systems. In a DC-coupled energy storage system (ESS), the PV and battery systems operate at DC voltage, but the power grid operates at AC voltage, thus requiring power conversion equipment.

[0005] Meanwhile, due to system efficiency or safety concerns, photovoltaic (PV) systems and battery systems typically use different grounding methods. In energy storage systems where PV and battery systems are interlocked, the choice of which grounding method to use becomes a matter of selecting between system efficiency and safety, thus creating a dilemma in system operation where one must sacrifice either system efficiency or safety. Summary of the Invention

[0006] [Technical Issues]

[0007] Embodiments of this disclosure provide an energy storage system including a photovoltaic (PV) system and a battery system.

[0008] Embodiments of this disclosure also provide a method for controlling the grounding configuration of an energy storage system.

[0009] Embodiments of this disclosure also provide an apparatus for controlling the grounding configuration of an energy storage system.

[0010] [Technical Solution]

[0011] To achieve the objectives of this disclosure, an energy storage system is provided, comprising a photovoltaic (PV) system and a battery system connected to a power grid. The energy storage system may include: a power conversion system (PCS) configured to be connected to the power grid and selectively connected to at least one of the PV system and the battery system; a first switch selectively connecting a direct current (DC) link between the PV system and the power conversion system; a second switch selectively connecting the battery system and the DC link between the power conversion system; and a controller configured to control the grounding structure of at least one of the PV system, the battery system, and the power conversion system by controlling the first and second switches based on the states of the PV system and the battery system.

[0012] The energy storage system may further include: a first ground fault detector configured to detect ground faults in the photovoltaic system.

[0013] The first ground fault detector can be selectively connected to the first switch and the photovoltaic system via a third switch placed between the first switch and the photovoltaic system.

[0014] The first ground fault detector may include a ground fault detection interrupter (GFDI).

[0015] The energy storage system may further include: a second ground fault detector configured to detect a ground fault in at least one of the photovoltaic system, the battery system, and the power conversion system.

[0016] The second ground fault detector can be located between the DC converter included in the battery system and the second switch, or between the first switch, the second switch and the power conversion system.

[0017] The second ground fault detector may include an insulation monitoring device (IMD).

[0018] The controller can be configured to control the operation of at least one of the first, second, and third switches when the battery system is charging, in order to apply the floating grounding structure to the battery system, photovoltaic system, and power conversion system.

[0019] The controller can be configured to control the operation of at least one of the first, second, and third switches based on the location of the second ground fault detector when the battery system is in a resting state after charging, in order to adjust the grounding structure of the battery system, photovoltaic system, and power conversion system.

[0020] The controller can be configured to control the operation of at least one of the first, second, and third switches when the battery system is discharging or in a resting state after discharge, so as to apply a grounded grounding structure to the photovoltaic system and a floating grounding structure to the battery system and the power conversion system.

[0021] The controller can be configured to control one or more of the first, second, and third switches to always apply the floating grounding structure to the battery system when the second ground fault detector is located between the DC converter and the second switch.

[0022] The battery system may include: a plurality of battery racks; and one or more DC converters configured to perform DC conversion in conjunction with the plurality of battery racks.

[0023] One or more DC converters may include: multiple individual DC / DC converters, each of which interacts with a separate battery rack; or a central DC / DC converter that interacts with multiple battery racks.

[0024] According to another embodiment of this disclosure, a method for controlling the grounding configuration of an energy storage system includes a photovoltaic (PV) system, a battery system, and a power conversion system (PCS), the PCS being selectively connected to at least one of the PV system and the battery system, wherein the energy storage system is connected to a power grid. The method may include: checking the state of the battery system and the state of the PV system; and controlling the grounding configuration of at least one of the PV system, the battery system, and the PCS by controlling a first switch and a second switch according to the state of the PV system and the state of the battery system, wherein the first switch selectively connects the PV system and the DC link of the PCS, and the second switch selectively connects the battery system and the DC link of the PCS.

[0025] The energy storage system may further include: a first ground fault detector configured to detect ground faults in the photovoltaic system; a second ground fault detector configured to detect ground faults in at least one of the photovoltaic system, the battery system, and the power conversion system, wherein the second ground fault detector is located between a DC converter included in the battery system and a second switch, or between the first switch, the second switch, and the power conversion system; and a third switch selectively connecting the first ground fault detector to the first switch and the photovoltaic system.

[0026] 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).

[0027] Controlling the grounding structure of at least one of the photovoltaic system, battery system, and power conversion system may include: controlling the operation of at least one of the first switch, second switch, and third switch during battery system charging to apply the floating grounding structure to the battery system, photovoltaic system, and power conversion system.

[0028] Controlling the grounding structure of at least one of the photovoltaic system, battery system, and power conversion system may include: when the battery system is in a resting state after charging, controlling the operation of at least one of the first switch, second switch, and third switch according to the location of the second ground fault detector to adjust the grounding structure of the battery system, photovoltaic system, and power conversion system.

[0029] Controlling the grounding structure of at least one of the photovoltaic system, battery system, and power conversion system may include: controlling the operation of at least one of the first switch, second switch, and third switch when the battery system is discharging or in a resting state after discharge, to apply a grounded grounding structure to the photovoltaic system and a floating grounding structure to the battery system and power conversion system.

[0030] The grounding structure for controlling at least one of the photovoltaic system, battery system, and power conversion system may include: when a second ground fault detector is located between the DC converter and the second switch, controlling one or more of the first switch, the second switch, and the third switch to always apply the floating grounding structure to the battery system.

[0031] According to another embodiment of this disclosure, an apparatus for controlling a grounding configuration is provided, the apparatus being positioned in an energy storage system including a photovoltaic (PV) system, a battery system, and a power conversion system (PCS), the power conversion system (PCS) being selectively connected to at least one of the PV system and the battery system, wherein the energy storage system is connected to a power grid, the apparatus including: at least one processor; and a memory configured to store at least one instruction executed by the at least one processor; wherein the at least one instruction includes: an instruction to check the state of the battery system and the state of the PV system; and an instruction to control the grounding configuration of at least one of the PV system, the battery system, and the power conversion system by controlling a first switch and a second switch according to the state of the PV system and the battery system, wherein the first switch selectively connects the DC link of the PV system and the power conversion system, and the second switch selectively connects the DC link of the battery system and the power conversion system.

[0032] The energy storage system may further include: a first ground fault detector configured to detect ground faults in the photovoltaic system; a second ground fault detector configured to detect ground faults in at least one of the photovoltaic system, the battery system, and the power conversion system, wherein the second ground fault detector is located between a DC converter included in the battery system and a second switch, or between the first switch, the second switch, and the power conversion system; and a third switch selectively connecting the first ground fault detector to the first switch and the photovoltaic system.

[0033] 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).

[0034] Instructions for controlling the grounding structure of at least one of the photovoltaic system, battery system, and power conversion system may include instructions to perform the following operations: while the battery system is charging, control the operation of at least one of the first switch, second switch, and third switch to apply the floating grounding structure to the battery system, photovoltaic system, and power conversion system.

[0035] Instructions for controlling the grounding structure of at least one of the photovoltaic system, battery system, and power conversion system may include instructions to perform the following operations: when the battery system is in a resting state after charging, control the operation of at least one of the first switch, second switch, and third switch according to the position of the second ground fault detector to adjust the grounding structure of the battery system, photovoltaic system, and power conversion system.

[0036] The instructions for controlling the grounding structure of at least one of the photovoltaic system, battery system, and power conversion system may include instructions to perform the following operations: when the battery system is discharging or in a resting state after discharge, control the operation of at least one of the first switch, second switch, and third switch to apply a grounded grounding structure to the photovoltaic system and a floating grounding structure to the battery system and power conversion system.

[0037] [Beneficial Effects]

[0038] According to embodiments of this disclosure, the efficiency reduction of a photovoltaic system can be prevented by minimizing the PID generated in the photovoltaic system.

[0039] In addition, grounding faults in DC-coupled energy storage systems linked to photovoltaic systems can be monitored, and in the event of an accident, by applying floating grounding to the battery system through which large fault currents flow, the spread of fault current and fault can be minimized.

[0040] In other words, compared with the prior art, the embodiments of the present invention can simultaneously ensure efficiency and stability. Attached Figure Description

[0041] Figure 1 This is a block diagram of an example of a DC-coupled energy storage system linked to a PV system to which this invention can be applied.

[0042] Figure 2a This is a diagram of a DC-coupled energy storage system linked to a PV system with a typical floating grounding structure.

[0043] Figure 2b This is a conceptual diagram illustrating the operation of a DC-coupled energy storage system linked to a PV system with a typical floating ground structure.

[0044] Figure 3a This is a conceptual diagram of a DC-coupled energy storage system linked to a PV system with a typical grounded grounding structure.

[0045] Figure 3b This is a conceptual diagram illustrating the operation of a DC-coupled energy storage system linked to a PV system with a typical grounded grounding structure.

[0046] Figure 4a This is a configuration example of an energy storage system with a grounded structure according to a first embodiment of the present invention.

[0047] Figure 4b This is another configuration example of an energy storage system with a grounded structure according to the first embodiment of the present invention.

[0048] Figure 5 This is a conceptual diagram illustrating the operation method of an energy storage system with a grounded structure according to a first embodiment of the present invention.

[0049] Figure 6 This is a configuration example of an energy storage system with a grounded structure according to a second embodiment of the present invention.

[0050] Figure 7 This is a conceptual diagram illustrating an exemplary operation method of an energy storage system with a grounded structure according to a second embodiment of the present invention.

[0051] Figure 8 This is a conceptual diagram illustrating another exemplary operating method of an energy storage system with a grounded structure according to a second embodiment of the present invention.

[0052] Figure 9 This is an operation flowchart of a method for controlling the grounding configuration of an energy storage system according to an embodiment of the present invention.

[0053] Figure 10This is a detailed operation flowchart of a method for controlling the grounding configuration of an energy storage system according to an embodiment of the present invention.

[0054] Figure 11 This is a block diagram of a device for controlling the grounding structure of an energy storage system according to an embodiment of the present invention. Detailed Implementation

[0055] This invention can be modified in various forms and has various embodiments, and specific embodiments thereof are shown by way of example in the accompanying drawings and will be described in detail below. However, it should be understood that the invention is not intended to be limited to the specific embodiments, but rather, the invention should cover all modifications, equivalents, and substitutions falling within the spirit and scope of the invention. Throughout the description of the accompanying drawings, the same reference numerals refer to the same elements.

[0056] It should be understood that while terms such as first, second, A, B, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, a first element may be referred to as a second element without departing from the scope of the invention, and similarly, a second element may be referred to as a first element. As used herein, the term "and / or" includes a combination of or any one of the associated listed items.

[0057] It should be understood that when a component is described as "coupled" or "connected" to another component, it can be directly coupled or connected to the other component, or there may be intermediate components. Conversely, when a component is described as "directly coupled" or "directly connected" to another component, there are no intermediate components.

[0058] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should be further understood that, when used herein, the terms “comprises,” “comprising,” “includes,” “including,” and / or “having” specify the presence of the stated features, integers, steps, operations, constituent elements, components, and / or combinations thereof, but do not exclude the presence or addition of one or more other features, integers, steps, operations, constituent elements, components, and / or combinations thereof.

[0059] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. It should be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning consistent with their meaning in the context of their relevant field, and should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0060] The following are definitions of some of the terms used in this article.

[0061] Nominal capacity refers to the capacity [Ah] of a battery as defined by the battery manufacturer during development.

[0062] State of charge (SOC) refers to the current state of a battery's charge, expressed as a percentage (%), while state of health (SOH) can be the current condition of a battery compared to its ideal or original state, expressed as a percentage (%).

[0063] A battery rack is a system of the smallest single structure assembled by connecting modules in series or parallel, as specified by the battery manufacturer. It can be monitored and controlled by a battery management system (BMS). A battery rack may include several battery modules and battery protection units or any other protection devices.

[0064] A battery bank refers to a large-scale battery rack system configured by connecting several racks in parallel. A battery bank BMS can monitor and control several BMSs, each managing a battery rack.

[0065] A battery segment controller (BSC) is the highest-level device that controls a battery system that includes one or more battery cell hierarchies.

[0066] Battery power limit refers to the maximum amount of electricity that can be output from a battery, which is preset by the battery manufacturer based on battery conditions. Rack power limit can refer to the output power limit ([kW]) set for a rack class and can be set based on the battery's state of charge (SOC) and temperature.

[0067] Depending on whether the application is charging or discharging, the power limit can be either a charging power limit or a discharging power limit. Furthermore, depending on the battery system architecture, a rack power limit or a battery bank power limit can be defined.

[0068] Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0069] Figure 1 This is a block diagram of a DC-coupled energy storage system according to an embodiment of the present invention.

[0070] In DC-coupled energy storage systems, a DC / DC converter 500 capable of individually controlling the DC voltage / current of each battery system is required. Because the DC / DC converter is integrated into the battery system, a DC / AC converter for connection to the photovoltaic system is no longer needed, thus improving efficiency. Furthermore, as in existing energy storage systems, protection control of the battery system can be performed via the DC / DC converter for each battery system. Moreover, even when battery racks differ in SOC, SOH, and capacity, the amount of battery power can be controlled based on the characteristics of each individual battery system.

[0071] Figure 1 An example of a DC-coupled system is shown, in which the output of a photovoltaic (PV) 700 is connected to the output of a DC / DC converter 500 and the input of a PCS 400.

[0072] In an energy storage system (ESS), batteries are used to store energy or electricity. Typically, multiple battery modules can form a battery rack, and multiple battery racks can form a battery bank. Here, depending on the device or system in which the batteries are used, the battery rack can be referred to as a battery pack. Figure 1 The batteries #1, #2, ..., #N shown can be battery packs or battery racks.

[0073] Here, a Battery Management System (BMS) 100 can be installed for each battery. The BMS 100 can monitor the current, voltage, and temperature of each battery pack (or battery rack) to be managed, and calculate the battery's state of charge (SOC) based on the monitoring results to control charging and discharging. Figure 1 In a system where each battery is a battery rack, the BMS can be a rack BMS (RBMS).

[0074] The Battery Segment Controller (BSC) 200 can be located in each battery segment, each battery segment including multiple batteries, peripheral circuits, and devices for monitoring and controlling objects such as voltage, current, temperature, and circuit breakers.

[0075] The power conversion / regulation system (PCS) 400 installed in each battery segment controls the power supplied from the external source and the power supplied from the battery segment to the external source, thereby controlling the charging and discharging of the batteries. The power conversion system may include a DC / AC inverter. The output of the DC / DC converter 500 can be connected to the PCS 400, and the PCS 400 can be connected to the power grid 600. Here, the PCS 400 typically operates in constant power mode. The power management system (PMS) 300 connected to the PCS can control the output of the PCS based on the monitoring and control results of the battery management system or the battery segment controller.

[0076] exist Figure 1In the energy storage system, 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 converter #N. The output of the DC / DC converter corresponding to each battery is connected to PCS 400 via a DC link.

[0077] A DC / DC converter can be a bidirectional converter, where the input of the DC / DC converter is connected to the battery (battery cell, battery rack, or battery pack) and the output of the DC / DC converter can be connected to the load when the conversion is performed from battery to load. As examples of DC / DC converters, various types of converters can be used, such as full-bridge converters, half-bridge converters, and flyback converters.

[0078] Meanwhile, communication between the BMS, BSC 200, PMS 300, and PCS 400 can be achieved via Controller Area Network (CAN) or Ethernet (via Ethernet). Figure 1 (As indicated by the dotted line in the text) to achieve this.

[0079] according to Figure 1 In the embodiment of the invention shown, the BSC 200, responsible for overall control of the battery region, can report the status of each battery to the PMS 300. Here, the status of each battery can include information such as its state of charge (SOC), state of health (SOH), voltage, and temperature. The BSC 200 can provide the power management system 300 with information such as the maximum power limit (P_battery_limit) and actual power (P_battery_real) for each battery. During system operation, the power management system 300, responsible for controlling the entire ESS system, can issue charging or discharging commands (via P_pcs_reference) to the power conversion system 400.

[0080] Here, the BSC 200 determines the output reference of each DC / DC converter based on the state of each battery. In embodiments according to the invention, the output reference of individual DC / DC converters can be set in different ways depending on droop mode or constant power (CP) mode.

[0081] When controlling the output of a DC / DC converter based on droop mode, the BSC can set the droop curve for each DC / DC converter before operating the system, taking into account the state of each battery, and provide the set droop curve to the converter. Simultaneously, when the DC / DC converter operates in CP mode, a power reference for each DC / DC converter can be determined during system operation and provided to the corresponding converter.

[0082] During the actual operation of the energy storage system, the power management system delivers charging and discharging commands to the power conversion system and battery segment controller. Here, the power management system can monitor the status of the photovoltaic system (PV), the grid, and the batteries in real time, and determine the operating mode and output baseline of the corresponding components in the system based on the operating commands received from the upper-level system—such as the EMS (Energy Management System).

[0083] At the same time, although Figure 1 The illustration shows a system in which a corresponding DC / DC converter is applied to each battery rack, but the invention can also be applied to a system in which a central DC / DC converter is connected to multiple battery racks.

[0084] exist Figure 1 In the DC-coupled energy storage system shown, the grounding structure is determined based on whether the negative power line of the PV system is grounded. Furthermore, the grounding fault monitoring method varies depending on the grounding structure, and the consequences of an accident also depend on how the grounding structure manifests itself.

[0085] Grounding systems can be categorized into grounded (grounded-to-ground) systems and ungrounded (floating-to-ground) systems. When a single-wire ground fault occurs, the grounding system may damage equipment due to the flow of fault current. Conversely, in an ungrounded system, no fault current occurs when a single-wire ground fault occurs, and current only flows when a ground fault occurs again.

[0086] Figure 2a This is a configuration diagram of a DC-coupled energy storage system linked to a PV system with a typical floating grounding structure.

[0087] Figure 2a The energy storage system includes a battery system 10, a DC / DC converter 50, a PV system 70, and a power conversion system 40 interconnected with them, and has a floating grounding structure. Typically, a floating grounding (or ungrounded) structure is recommended in battery systems to ensure safety in the event of a grounding fault.

[0088] The connection between the PV system 70 and the power conversion system 40 can be controlled by switch 1 (SW1), and the PV system 70 is typically disconnected from the DC link at night. The connection between the battery system 10, including the DC / DC converter 50, and the power conversion system 40 is made by switch 2 (SW2), and this connection is typically kept ON during normal system operation.

[0089] exist Figure 2aIn this system architecture, neither the positive nor negative terminals of the PV system and battery system are connected to ground. This type of grounding structure, where the positive and negative terminals of the power lines are not connected to ground, is called a floating ground (or ungrounded). To monitor grounding faults in this system architecture, insulation monitoring devices—such as insulation monitoring devices (IMDs)—can be used to monitor insulation resistance and grounding faults. An IMD is a device used to measure and monitor the insulation resistance values ​​between the positive terminal and ground and between the negative terminal and ground, and can be located on the DC power lines of the power conversion system 40, such as... Figure 2a As shown.

[0090] As a ground fault monitoring device, the IMD detects insulation resistance and ground faults based on the open / closed state of switch 1. However, in this configuration, the limitations described below may occur.

[0091] Figure 2b This is a conceptual diagram illustrating the operation of a DC-coupled energy storage system linked to a PV system with a typical floating ground structure.

[0092] Figure 2b The diagram illustrates the status of the corresponding components (Power Conversion System (PCS), PV System, and Battery System) according to the operating state of an 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. Here, the Power Conversion System 40, PV System 70, and Battery System 10 are all in a floating ground state, and the insulation resistance can be measured by the IMD, allowing for the monitoring of ground faults.

[0093] However, when switch 1 is disconnected at night to isolate the PV system from the DC link, grounding faults occurring within the PV system cannot be detected. Furthermore, potential-induced degradation (PID) can occur in the solar cells of a PV system with floating grounding, leading to gradual system deterioration. As degradation progresses, the amount of energy generated by the solar cells decreases, and consequently, system efficiency declines.

[0094] For this reason, negative grounding is primarily used to prevent potential-induced degradation (PID) in PV systems, which adversely affects power generation efficiency.

[0095] Figure 3a This is a conceptual diagram of a DC-coupled energy storage system linked to a PV system with a typical grounded grounding structure.

[0096] Figure 3aThe energy storage system includes a battery system 10, a DC / DC converter 50, a PV system 70, and a power conversion system 40 interconnected with them, and has a negative grounding structure between the single-pole grounding structure and the negative grounding structure. A negative grounding structure refers to a structure where the negative (-) end of the power line is connected to ground. Figure 3a In this configuration, the negative terminals of the PV system and the battery system are connected to ground via a switch.

[0097] The connection between the PV system 70 and the power conversion system 40 can be controlled by switch 1 (SW1), and the PV system 70 is typically disconnected from the DC link at night. The connection between the battery system 10, including the DC / DC converter 50, and the power conversion system 40 is made via switch 2 (SW2), and this connection is typically kept ON during normal system operation. Furthermore, in Figure 3a In the system, the negative terminals of the battery system and the PV system are selectively connected to ground via switch 3 (SW3).

[0098] In this system architecture, insulation and ground fault monitoring devices, such as IMD, residential current monitoring (RCM) devices, and ground fault detection interrupters (GFDI) for monitoring ground faults, can be used to monitor insulation resistance and ground faults.

[0099] An IMD (Insulation Displacement Device) is a device used to measure and monitor the insulation resistance between the positive terminal and ground, and between the negative terminal and ground. For example... Figure 3a As shown, the IMD can be located on the DC power line of the power conversion system 40, or between the battery rack and the DC / DC converter. The RCM is a device used to detect leakage current by monitoring whether the sum of the currents flowing through each of the positive and negative power lines is zero, and it is located on... Figure 3a The battery rack is located between the DC / DC converter. Furthermore, a GFDI is a device that connects the power line to ground and blocks current when the current flowing from the power line to ground exceeds a reference value.

[0100] At the same time, even in this negative grounding structure, the limitations described below may occur.

[0101] Figure 3b This is a conceptual diagram illustrating the operation of a DC-coupled energy storage system linked to a PV system with a typical grounded grounding structure.

[0102] Figure 3bThe diagram illustrates the states of the corresponding components (Power Conversion System (PCS), PV System, and Battery System) according to the operating state of an energy storage system with a grounded structure. Here, when the battery is charging or in a resting state after charging, switch 1 is closed, and the PV System is connected to the Battery System and the power grid. Here, switch 3 is also closed, and the negative terminals of the Power Conversion System 40, PV System 70, and Battery System 10 are grounded. If a ground fault occurs under these conditions, a fault current will be generated.

[0103] Subsequently, after the PV system's power generation ceases, switches 1 and 3 are opened, causing the power conversion system 40, PV system 70, and battery system 10 to all be in a floating ground state. Here, because PV system 70 is in a floating ground state, PID (Power Injection Degradation) occurs, ultimately reducing PV power generation efficiency. Furthermore, due to the opening of switch 1, insulation degradation and grounding faults cannot be detected.

[0104] Therefore, choosing the right grounding method in energy storage systems, including PV and battery systems, becomes a choice between system efficiency and safety. Ultimately, system efficiency and safety are a trade-off, determined by the system designer's choice, which can lead to problems regardless of the option chosen.

[0105] To address this issue, the present invention aims to ensure both the stability and efficiency of a DC-coupled energy storage system linked to a PV system by operating the energy storage system by changing the grounding mode according to the battery's operating state.

[0106] Figure 4a This is a configuration example of an energy storage system with a grounded structure according to a first embodiment of the present invention.

[0107] An energy storage system according to an embodiment of the present invention may include a battery system 100, a DC / DC converter 500, a PV system 700, a power conversion system 400 interconnected with the battery system 100, the DC / DC converter 500 and the PV system 700, and a plurality of switches connecting them.

[0108] The connection between the PV system 700 and the power conversion system 400 can be controlled via the first switch S1. A ground fault detection interrupter (GFDI) can be placed between the first switch and the PV system (including multiple PV panels) as a device for detecting ground faults. The connection between the GFDI and the first switch and the PV system can be controlled via the third switch S3.

[0109] The connection control between the battery system 100, including the DC / DC converter 500, and the power conversion system 400 can be performed via the second switch S2. An IMD can be positioned between the second switch S2 and the DC / DC converter as a device for monitoring or detecting ground faults. In this embodiment, the DC / DC converter 500 is in the form of a rack-type DC / DC converter, wherein corresponding DC / DC converters are connected and used for each battery rack.

[0110] This embodiment minimizes the occurrence of PID by applying a floating ground structure to the PV system only when the battery is being charged, and eliminates the PID generated by the floating ground structure by applying a negative ground structure to the PV system in other operating modes.

[0111] Furthermore, by applying a floating grounding structure to the battery system in all operating modes, the possibility of fault current flow in the event of a ground fault can be minimized and the stability of the system can be ensured.

[0112] Figure 4b This is another configuration example of an energy storage system with a grounded structure according to the first embodiment of the present invention.

[0113] according to Figure 4b The energy storage system of the embodiment may also include a battery system 100, a DC / DC converter 500, a PV system 700, a power conversion system 400 interconnected with the battery system 100, the DC / DC converter 500 and the PV system 700, and a plurality of switches connecting them.

[0114] The connection between the PV system 700 and the power conversion system 400 can be controlled via the first switch S1. A ground fault detection interrupter (GFDI) can be placed between the first switch and the PV system (including multiple PV panels) as a device for detecting ground faults. The connection between the GFDI and the first switch and the PV system can be controlled via the third switch S3.

[0115] The connection control between the battery system 100, including the DC / DC converter 500, and the power conversion system 400 can be performed via the second switch S2. The IMD can be positioned between the second switch S2 and the DC / DC converter as a device for monitoring or detecting ground faults. In this embodiment, the DC / DC converter 500 is in the form of a central DC / DC converter connected to multiple battery racks.

[0116] Besides the shape of the DC / DC converter, the configuration of the energy storage system according to this embodiment and according to Figure 4a Their energy storage systems have the same configuration and operate in the same way.

[0117] Figure 5 This is a conceptual diagram illustrating the operation method of an energy storage system with a grounded structure according to a first embodiment of the present invention.

[0118] According to the operation method of the energy storage system with a grounding structure according to the first embodiment of the present invention, the battery system 100 always operates using a floating grounding structure.

[0119] Specifically, during battery charging, the first switch S1 and the second switch S2 are closed, and the third switch S3 is open, causing all components of the battery system 100, PV system 700, and PCS 400 to operate in a floating ground condition. Here, a PID (Power Injection Point) may occur in the PV system 700. In this case, ground fault detection can be performed using an IMD (In-Mechanism Displacement Device) located on the battery system side.

[0120] When the PV system 700 is generating power and the battery is in a dormant state, the third switch S3 closes, i.e., connects, allowing the PV system and PCS 400 to operate in a grounded configuration, and the second switch S2 opens to isolate the battery system 100 from the DC link. Here, the PV system 700 and PCS 400 can detect ground faults using a Ground Fault Detection Interruptor (GFDI) located between the first switch and the PV system. Additionally, the battery system can detect ground faults using an IMD located between the second switch S2 and the DC / DC converter.

[0121] Furthermore, during battery discharge, the first switch S1 is open and the second switch S2 is closed, allowing power to be transferred from the battery to the power grid. Here, the third switch remains connected, i.e., closed, ensuring the PV system 700 maintains a grounded structure. During battery rest, these switches maintain the same connection state, and by operating the PV system in a grounded structure for as long as possible, the PID phenomenon that occurs during battery charging can be eliminated.

[0122] at the same time, Figure 5 The embodiments can be applied to any energy storage system that includes rack-mounted DC / DC converters or central DC / DC converters.

[0123] Figure 6 This is a configuration example of an energy storage system with a grounded structure according to a second embodiment of the present invention.

[0124] The energy storage system with a grounded structure according to a second embodiment of the present invention may include a battery system 100, a DC / DC converter 500, a PV system 700, a power conversion system 400 interconnected with the battery system 100, the DC / DC converter 500 and the PV system 700, and a plurality of switches connecting them.

[0125] The connection between the PV system 700 and the power conversion system 400 can be controlled via the first switch S1. A ground fault detection interrupter (GFDI) can be placed between the first switch and the PV system (including multiple PV panels) as a device for detecting ground faults. The connection between the GFDI and the first switch and the PV system can be controlled via the third switch S3.

[0126] The connection control between the battery system 100, including the DC / DC converter 500, and the power conversion system 400 can be performed via 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.

[0127] Figure 7 This is a conceptual diagram illustrating an exemplary operation method of an energy storage system with a grounded structure according to a second embodiment of the present invention.

[0128] according to Figure 7 The energy storage system shown in the figure operates with a grounded grounding structure in the resting state after charging, and with a floating grounding structure in other operating modes.

[0129] Specifically, during battery charging, the first switch S1 and the second switch S2 are closed, and the third switch S3 is open, causing all components of the battery system 100, PV system 700, and PCS 400 to operate in a floating grounded state. Here, a PID (Power Injection Device) may occur in the PV system 700. In this case, ground fault detection can be performed using an IMD (Integrated Device Distributed) placed between the first switch S1, the second switch S2, and the PCS 400.

[0130] When the battery is fully charged and at rest, and the PV system 700 is generating power, the third switch S3 closes, i.e., connects, so that the PV system, PCS 400, and battery system 100 all operate in a grounded configuration. This is because the IMD is positioned between the first switch S1, the second switch S2, and PCS 400.

[0131] Furthermore, during battery discharge, the first switch S1 is disconnected to transfer power from the battery to the grid. Here, the third switch remains connected, i.e., closed, so that the PV system 700 maintains a grounded grounding structure. Simultaneously, a floating grounding structure is applied to both the PCS 400 and the battery system 100.

[0132] In the battery resting state after discharge, the connection states of the first switch (S1), the second switch (S2), and the third switch (S3) are the same as the connection states in the battery discharge state. Furthermore, by operating the PV system in a grounded structure for as long as possible, the PID phenomenon that occurs during battery charging can be eliminated.

[0133] at the same time, Figure 7 The illustrated embodiments can be applied to any energy storage system that includes rack-mounted DC / DC converters or central DC / DC converters.

[0134] In this embodiment, except when the battery system is in a resting state after being fully charged (where a grounded grounding structure is applied to the battery system), system stability can be ensured by applying a floating grounding structure to the battery. System stability can be ensured by minimizing the possibility of fault current flow in the event of a ground fault.

[0135] In addition, besides minimizing PID occurrences by applying a grounded grounding structure to the PV system while the battery is being charged.

[0136] Figure 8 This is a conceptual diagram illustrating another exemplary operating method of an energy storage system with a grounded structure according to a second embodiment of the present invention.

[0137] according to Figure 8 The energy storage system shown in the diagram operates with the battery system 100 always operating in a floating grounded structure.

[0138] Specifically, during battery charging, the first switch S1 and the second switch S2 are closed and the third switch S3 is open, causing all components of the battery system 100, PV system 700, and PCS 400 to operate in a floating ground state. Here, a PID (Power Injection Point) may occur in the PV system 700. In this case, ground fault detection can be performed using an IMD (In-Mechanism for Grounding) located between the first switch S1, the second switch S2, and PCS 400.

[0139] After the battery is fully charged and in a resting state, and while the PV system 700 is generating power, the third switch S3 remains open, allowing each component to maintain the same operation and state as when the battery is charging. In other words, the battery system 100, PV system 700, and PCS 400 all operate using a floating ground state. Therefore, the resulting PID (Processing Identifier) ​​may increase in the PV system 700 compared to other embodiments, and consequently, the time required to remove the PID may decrease.

[0140] Furthermore, during battery discharge, the first switch S1 is disconnected to transfer power from the battery to the power grid. Here, the third switch is kept in the connected (closed) state, making the PV system 700 a grounded structure. A floating grounding structure is applied to both the PCS 400 and the battery system 100 in some way.

[0141] The connection states of the first switch (S1), the second switch (S2), and the third switch (S3) are the same as the connection states during battery discharge, even in the resting state after discharge. Furthermore, by operating the PV system in a grounded grounding structure, the PID phenomenon that occurs during battery charging can be eliminated.

[0142] at the same time, Figure 8 The embodiments shown can be applied to any energy storage system that includes rack-mounted DC / DC converters or central DC / DC converters.

[0143] In this embodiment, system stability can be ensured by always applying a floating grounding structure to the battery system, and thus, the possibility of fault current flow in the event of a ground fault is minimized.

[0144] In the grounding structure according to the second embodiment of the present invention, the IMD is positioned between the first switch S1, the second switch S2, and the PCS 400. Therefore, according to Figure 7 and Figure 8 The second embodiment of the operation method of the energy storage system with a grounded grounding structure described herein allows for the application of the grounded grounding structure to the entire battery system, photovoltaic system, and power conversion system when the battery is in a resting state after charging and the PV is generating electricity, or the application of the floating grounding structure to the entire battery system, photovoltaic system, and power conversion system.

[0145] Figure 9 This is an operation flowchart of a method for controlling the grounding configuration of an energy storage system according to an embodiment of the present invention.

[0146] Figure 9 The embodiments illustrate the sequence of operations in a method for controlling a grounded structure in an energy storage system, 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 PV system and the battery system, wherein the energy storage system is interconnected with the power grid.

[0147] The method for controlling the grounding configuration of an energy storage system according to an embodiment of the present invention can be performed by a PMS or EMS in the energy storage system, but can also be performed by any type of controller located in or interconnected with the energy storage system.

[0148] refer to Figure 9 The controller can check the status of the battery system and the photovoltaic system (S910).

[0149] The controller can control the grounding structure of at least one of the photovoltaic system, battery system, and power conversion system by controlling the first and second switches according to the state of the photovoltaic system and the battery system (S920). Here, the first switch can selectively connect the DC link of the photovoltaic system and the power conversion system, and the second switch can selectively connect the DC link of the battery system and the power conversion system.

[0150] Figure 10 This is a detailed operation flowchart of a method for controlling the grounding configuration of an energy storage system according to an embodiment of the present invention.

[0151] refer to Figure 10 The controller can check the status of the battery system and the photovoltaic system, more specifically, check whether the battery system is charging (S911), and when the battery system is charging, control the operation of at least one of the first switch, the second switch, and the third switch to apply the floating grounding structure to the battery system, the photovoltaic system, and the power conversion system (S921). Here, the controller controls the first switch S1 and the second switch S2 to connect, that is, close, and the third switch S3 to open.

[0152] When the battery system is in a resting state after charging and the photovoltaic system is generating electricity ("Yes" in S913), the controller can control the operation of at least one of the first switch, second switch, and third switch according to the location of the second ground fault detector to adjust the grounding structure of the battery system, photovoltaic system, and power conversion system (S923). Here, depending on the location of the second ground fault detector (i.e., IMD), the battery system, photovoltaic system, and power conversion system can have different grounding structures, and the operation of the first switch, second switch, and third switch can also be controlled according to each grounding structure.

[0153] Specifically, when the IMD is positioned between the second switch S2 and the DC / DC converter, and when the battery is in a resting state after charging and the PV is generating power, the third switch S3 becomes closed, i.e., connected, and thus the PV system and PCS operate in a grounded structure. Furthermore, the second switch (S2) is disconnected to isolate the battery system 100 from the DC link, and the battery system 100 operates using a floating grounded structure.

[0154] On the other hand, when the IMD is positioned 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 electricity, the grounded grounding structure can be applied to the entire battery system, photovoltaic system, and power conversion system, or the floating grounding structure can be applied to the entire battery system, photovoltaic system, and power conversion system.

[0155] Simultaneously, when the battery system is discharging or in a resting state after discharge ("Yes" in S912), the controller can control the operation of at least one of the first, second, and third switches to apply a grounded (ground-based) grounding structure to the photovoltaic system and a floating grounding structure to both the battery system and the power conversion system. Here, the first switch S1 is open and the second switch S2 is closed, allowing power to be transferred from the battery to the grid. The third switch remains connected, i.e., closed, so that the PV system maintains a grounded grounding structure.

[0156] Figure 11 This is a block diagram of a device for controlling the grounding structure of an energy storage system according to an embodiment of the present invention.

[0157] The device for controlling the grounding structure of an energy storage system according to embodiments of the present invention may be a PMS 300 or EMS included in the energy storage system, but may also be any type of control device located in or interconnected with the energy storage system. Here, the energy storage system may include a photovoltaic (PV) system, a battery system, and a power conversion system (PCS) selectively connected to at least one of the PV system and the battery system, wherein the energy storage system is connected to the power grid.

[0158] The apparatus for controlling the grounding structure may include at least one processor 310, a memory 320 for storing at least one instruction executed by the processor, and a transceiver 330 connected to a network to perform communication.

[0159] At least one instruction may include: an instruction to check the state of the battery system and the state of the photovoltaic system; and an instruction to control the grounding structure of at least one of the photovoltaic system, the battery system, and the power conversion system by controlling a first switch and a second switch according to the state of the photovoltaic system and the state of the battery system, wherein the first switch selectively connects the DC link of the photovoltaic system and the power conversion system, and the second switch selectively connects the DC link of the battery system and the power conversion system.

[0160] The energy storage system may further include: a first ground fault detector configured to detect ground faults in the photovoltaic system; a second ground fault detector configured to detect ground faults in at least one of the photovoltaic system, the battery system, and the power conversion system, wherein the second ground fault detector is located between a DC converter included in the battery system and a second switch, or between the first switch, the second switch, and the power conversion system; and a third switch selectively connecting the first ground fault detector to the first switch and the photovoltaic system.

[0161] The instructions for controlling the grounding structure of at least one of the photovoltaic system, battery system, and power conversion system include instructions to perform the following operations: while the battery system is charging, control the operation of at least one of the first switch, second switch, and third switch to apply the floating grounding structure to the battery system, photovoltaic system, and power conversion system.

[0162] The instructions for controlling the grounding structure of at least one of the photovoltaic system, battery system, and power conversion system include instructions to perform the following operations: when the battery system is in a resting state after charging, control the operation of at least one of the first switch, second switch, and third switch according to the position of the second ground fault detector to adjust the grounding structure of the battery system, photovoltaic system, and power conversion system.

[0163] The instructions for controlling the grounding structure of at least one of the photovoltaic system, battery system, and power conversion system include instructions to perform the following operations: when the battery system is discharging or in a resting state after discharge, control the operation of at least one of the first switch, second switch, and third switch to apply a grounded grounding structure to the photovoltaic system and a floating grounding structure to the battery system and power conversion system.

[0164] The means for controlling the grounding structure of the energy storage system may further include an input interface 340, an output interface 350, and a storage device 360. Each component included in the means for controlling the grounding structure may be connected to communicate with each other via a bus 370.

[0165] Processor 310 can execute program instructions stored in at least one of memory 320 and storage device 360. Here, processor may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor that executes methods according to embodiments of the present invention thereon. Memory (or storage device) may consist of at least one of volatile storage media and non-volatile storage media. For example, memory may include at least one of read-only memory (ROM) and random access memory (RAM).

[0166] According to the embodiments of the present invention described above, costs can be reduced by minimizing the number of ground fault detection devices by selecting the optimal grounding structure in each operating mode. Furthermore, by installing devices capable of detecting ground faults in each of the PV system and battery system, system stability can be ensured by minimizing areas where ground faults cannot be detected using existing systems.

[0167] The operation of the method according to embodiments of the present invention can be implemented as a computer-readable program or code on a computer-readable recording medium. The computer-readable recording medium includes all types of recording devices that store data readable by a computer system. Furthermore, the computer-readable recording medium can be distributed across network-connected computer systems, thereby storing and executing the computer-readable program or code in a distributed manner.

[0168] While some aspects of the invention have been described in the context of apparatus, they may also refer to the description of a corresponding method, where a block or apparatus corresponds to a method step or feature of a method step. Similarly, aspects described in the context of a method may also refer to features of a corresponding block or item or corresponding apparatus. Some or all of the method steps may be performed by (or using) hardware devices—such as, for example, microprocessors, programmable computers, or electronic circuits. In some embodiments, one or more of the most important method steps may be performed by such apparatus.

[0169] The invention has been described above with reference to exemplary embodiments thereof; however, those skilled in the art will recognize that the invention may be modified and altered in various ways without departing from the spirit and scope of the invention as described in the appended claims.

Claims

1. An energy storage system comprising a photovoltaic (PV) system and a battery system and connected to a power grid, the energy storage system comprising: A power conversion system (PCS) configured to be connected to the power grid and selectively connected to at least one of the photovoltaic system and the battery system; A first switch selectively connects the photovoltaic system and the DC link of the power conversion system; A second switch selectively connects the battery system and the DC link of the power conversion system; A controller configured to control the grounding structure of at least one of the photovoltaic system, the battery system, and the power conversion system by controlling the first switch and the second switch based on the state of the photovoltaic system and the state of the battery system; as well as A first ground fault detector, configured to detect ground faults in the photovoltaic system. The first ground fault detector is selectively connected to the first switch and the photovoltaic system via a third switch placed between the first switch and the photovoltaic system.

2. The energy storage system according to claim 1, wherein, The first ground fault detector includes a ground fault detection interrupter (GFDI).

3. The energy storage system according to claim 1, further comprising: A second ground fault detector is configured to detect a ground fault in at least one of the photovoltaic system, the battery system, and the power conversion system.

4. The energy storage system according to claim 3, wherein, The second ground fault detector is located between the DC converter included in the battery system and the second switch, or between the first switch, the second switch and the power conversion system.

5. The energy storage system according to claim 3, wherein, The second ground fault detector includes an insulation monitoring device (IMD).

6. The energy storage system according to claim 1, wherein, The controller is configured to control the operation of at least one of the first switch, the second switch, and the third switch during the charging of the battery system, so as to apply the floating grounding structure to the battery system, the photovoltaic system, and the power conversion system.

7. The energy storage system according to claim 4, wherein, The controller is configured to, when the battery system is in a resting state after charging, control the operation of at least one of the first switch, the second switch, and the third switch according to the location of the second ground fault detector, in order to adjust the grounding structure of the battery system, the photovoltaic system, and the power conversion system.

8. The energy storage system according to claim 1, wherein, The controller is configured to control the operation of at least one of the first switch, the second switch, and the third switch when the battery system is discharging or in a resting state after discharge, so as to apply a grounded grounding structure to the photovoltaic system and a floating grounding structure to the battery system and the power conversion system.

9. The energy storage system according to claim 4, wherein, The controller is configured to: When the second ground fault detector is positioned between the DC converter and the second switch. Control one or more of the first switch, the second switch, and the third switch to always apply the floating grounding structure to the battery system.

10. The energy storage system according to claim 1, wherein, The battery system includes: Multiple battery racks; and One or more DC converters, the one or more DC converters being configured to perform DC conversion in conjunction with the plurality of battery racks.

11. The energy storage system according to claim 10, wherein, The one or more DC converters include: Multiple individual DC / DC converters, each interacting with a separate battery rack; or A central DC / DC converter that interacts with the plurality of battery racks.

12. A method for controlling the grounding configuration of an energy storage system, the energy storage system comprising a photovoltaic (PV) system, a battery system, and a power conversion system (PCS), the power conversion system (PCS) being selectively connected to at least one of the PV system and the battery system, wherein, The energy storage system is connected to the power grid, and the method includes: Check the status of the battery system and the photovoltaic system; and The grounding structure of at least one of the photovoltaic system, the battery system, and the power conversion system is controlled by controlling a first switch and a second switch according to the states of the photovoltaic system and the battery system, wherein the first switch selectively connects the DC link of the photovoltaic system and the power conversion system, and the second switch selectively connects the DC link of the battery system and the power conversion system. The energy storage system further includes: A first ground fault detector, configured to detect ground faults in the photovoltaic system; and A third switch is placed between the first switch and the photovoltaic system, and the first ground fault detector is selectively connected to the first switch and the photovoltaic system.

13. The method according to claim 12, wherein, The energy storage system further includes: A second ground fault detector is configured to detect a ground fault in at least one of the photovoltaic system, the battery system, and the power conversion system, wherein the second ground fault detector is located between the DC converter included in the battery system and the second switch, or is located between the first switch, the second switch, and the power conversion system.

14. The method according to claim 13, wherein, The first ground fault detector includes a ground fault detection interrupter (GFDI).

15. The method according to claim 13, wherein, The second ground fault detector includes an insulation monitoring device (IMD).

16. The method according to claim 13, wherein, The grounding structure controlling at least one of the photovoltaic system, the battery system, and the power conversion system includes: When the battery system is charging, Controlling the operation of at least one of the first switch, the second switch, and the third switch to apply the floating grounding structure to the battery system, the photovoltaic system, and the power conversion system.

17. The method according to claim 13, wherein, The grounding structure controlling at least one of the photovoltaic system, the battery system, and the power conversion system includes: When the battery system is in a resting state after charging, The operation of at least one of the first switch, the second switch, and the third switch is controlled based on the location of the second ground fault detector to adjust the grounding structure of the battery system, the photovoltaic system, and the power conversion system.

18. The method according to claim 13, wherein, The grounding structure controlling at least one of the photovoltaic system, the battery system, and the power conversion system includes: When the battery system is discharging or in a resting state after discharging, The operation of at least one of the first switch, the second switch, and the third switch is controlled to apply a grounded grounding structure to the photovoltaic system and a floating grounding structure to the battery system and the power conversion system.

19. The method according to claim 15, wherein, The grounding structure controlling at least one of the photovoltaic system, the battery system, and the power conversion system includes: When the second ground fault detector is positioned between the DC converter and the second switch. Control one or more of the first switch, the second switch, and the third switch to always apply the floating grounding structure to the battery system.

20. An apparatus for controlling a grounding configuration, the apparatus being positioned in an energy storage system comprising a photovoltaic (PV) system, a battery system, and a power conversion system (PCS), the PCS being selectively connected to at least one of the PV system and the battery system, wherein, The energy storage system is connected to the power grid, and the device includes: At least one processor; and A memory configured to store at least one instruction executed by the at least one processor; Wherein, the at least one instruction includes: Instructions for checking the status of the battery system and the photovoltaic system; and Commands are used to control the grounding structure of at least one of the photovoltaic system, the battery system, and the power conversion system by controlling a first switch and a second switch according to the states of the photovoltaic system and the battery system, wherein the first switch selectively connects the DC link of the photovoltaic system and the power conversion system, and the second switch selectively connects the DC link of the battery system and the power conversion system. The energy storage system further includes: A first ground fault detector, configured to detect ground faults in the photovoltaic system; and A third switch is placed between the first switch and the photovoltaic system, and the first ground fault detector is selectively connected to the first switch and the photovoltaic system.

21. The apparatus according to claim 20, wherein, The energy storage system further includes: A second ground fault detector is configured to detect a ground fault in at least one of the photovoltaic system, the battery system, and the power conversion system, wherein the second ground fault detector is located between the DC converter included in the battery system and the second switch, or is located between the first switch, the second switch, and the power conversion system.

22. The apparatus according to claim 21, wherein, The instructions for controlling the grounding structure of at least one of the photovoltaic system, the battery system, and the power conversion system include instructions to perform the following operations: While the battery system is charging, Controlling the operation of at least one of the first switch, the second switch, and the third switch to apply the floating grounding structure to the battery system, the photovoltaic system, and the power conversion system.

23. The apparatus according to claim 21, wherein, The instructions for controlling the grounding structure of at least one of the photovoltaic system, the battery system, and the power conversion system include instructions to perform the following operations: When the battery system is in a resting state after charging, The operation of at least one of the first switch, the second switch, and the third switch is controlled based on the location of the second ground fault detector to adjust the grounding structure of the battery system, the photovoltaic system, and the power conversion system.

24. The apparatus according to claim 21, wherein, The instructions for controlling the grounding structure of at least one of the photovoltaic system, the battery system, and the power conversion system include instructions to perform the following operations: When the battery system is discharging or in a resting state after discharging, The operation of at least one of the first switch, the second switch, and the third switch is controlled to apply a grounded grounding structure to the photovoltaic system and a floating grounding structure to the battery system and the power conversion system.

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