Apparatus and method for controlling operation of energy storage system

Abstract

Disclosed is an apparatus for controlling operation of an energy storage system, the energy storage system comprising a battery and an inverter and connected to an electrical power grid, the apparatus comprising at least one processor; and a memory configured to store at least one instruction executed by the at least one processor, where the at least one instruction includes: an instruction to set a power price linking mode according to a selection of an operator or a user when power can be supplied from the power grid; setting an instruction of reference power of an inverter of the energy storage system according to the power price link mode; and an instruction to transmit the set reference power of the inverter to the inverter, in which charging and discharging of the energy storage system are controlled according to the price of the power supplied by the power grid in the power price link mode.

Description

Technical Field

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0086958, filed on July 5, 2023, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an apparatus and method for controlling the operation of an energy storage system, and more particularly to an apparatus and method for controlling the operation of a DC-coupled energy storage system. Background Art

[0003] Energy storage systems (ESS) involve renewable energy, batteries that store electricity, and the power grid. In recent years, with the increasing adoption of smart grids and renewable energy, and the increasing emphasis on grid efficiency and stability, there has been a growing demand for energy storage systems to control power supply and demand and improve power quality. Energy storage systems may have varying output and capacity depending on their intended use. To configure large-capacity energy storage systems, multiple battery systems can be connected.

[0004] ESSs linked to photovoltaic (PV) systems are evolving from AC-coupled ESSs to DC-coupled energy storage systems. In DC-coupled ESSs, the PV and battery systems operate on DC voltage, while the grid operates on AC voltage, requiring power conversion equipment (e.g., inverters).

[0005] Meanwhile, in the case where the power environment in the photovoltaic system and the power grid linked to the DC-coupled energy storage system changes in various ways, it is necessary to consider how to make the system operate in an optimal state in response to these changes. Summary of the Invention

[0006] Technical issues

[0007] To solve one or more problems in the related art, embodiments of the present disclosure provide an apparatus for controlling the operation of an energy storage system.

[0008] In order to solve one or more problems in the related art, embodiments of the present disclosure further provide a method for controlling the operation of an energy storage system.

[0009] To solve one or more problems in the related art, embodiments of the present disclosure also provide an energy storage system using the method for controlling operation of the energy storage system.

[0010] Technical Solution

[0011] To achieve the purpose of the present disclosure, a device for controlling the operation of an energy storage system, which includes a battery and an inverter and is connected to an electric power grid, may include: 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 set an electricity price linkage mode according to the selection of an operator or user when electricity can be supplied from the electric power grid; an instruction to set a reference power of an inverter of the energy storage system according to the electricity price linkage mode; and an instruction to send the set reference power of the inverter to the inverter.

[0012] Here, in the power price linked mode, charging and discharging of the energy storage system may be controlled according to the price of power provided by the power grid.

[0013] In more detail, in the power price linked mode, during battery discharge, the battery discharge amount can be set to the highest when the power selling price is the highest, and during battery charging, the battery charge amount can be set to the highest when the power purchasing price is the lowest.

[0014] Instructions for setting the reference power of the inverter of the energy storage system according to the power price linkage mode may include: instructions for determining to perform discharge of the battery when the power purchase price exceeds the price setting point; and instructions for calculating the discharge power to be used during the battery discharge and determining the reference power of the inverter.

[0015] Here, the discharge power to be used during battery discharge may be determined according to the ratio of the power selling price at the time of discharge to the maximum power selling price.

[0016] The instructions for setting the reference power of the inverter of the energy storage system according to the power price linkage mode may include: an instruction for determining to perform charging of the battery when the power purchase price is lower than the price setting point; and an instruction for calculating the charging power to be used during battery charging and determining the reference power of the inverter.

[0017] The charging power to be used during battery charging may be determined according to the ratio of the lowest power purchasing price collected within a certain period of time to the power purchasing price at the time of charging.

[0018] Here, the price set point may be set to an average value of prices for purchasing electric power from the electric power grid over a certain period of time, or the price set point may be set by a user.

[0019] The instruction to set the power price linking mode may include an instruction to set the power price linking mode as a default mode in advance.

[0020] The at least one instruction may further include an instruction to select one of a plurality of grid-connected operation modes other than the default mode and the power price linked mode.

[0021] The plurality of grid-connected operation modes other than the default mode and the power price linked mode may include at least one of a self-consumption maximization mode, a user-defined mode, an emergency mode, a battery usage maximization mode, and a battery protection mode.

[0022] The at least one instruction may further include an instruction to select one of a plurality of off-grid operating modes when power cannot be supplied from the power grid, wherein the plurality of off-grid operating modes are operating modes that operate the energy storage system using at least one of a generator operating algorithm and a backup algorithm.

[0023] According to another embodiment of the present disclosure, a method for controlling the operation of an energy storage system including a battery and an inverter and connected to a power grid may include: setting a power price linkage mode according to an operator or user's selection when power can be supplied from the power grid; setting a reference power for an inverter of the energy storage system according to the power price linkage mode; and transmitting the set reference power for the inverter to the inverter. In the power price linkage mode, charging and discharging of the energy storage system may be controlled based on the price of power provided by the power grid.

[0024] Here, in the power price linked mode, during battery discharge, the battery discharge amount may be set to the highest when the power selling price is the highest, and during battery charge, the battery charge amount may be set to the highest when the power purchasing price is the lowest.

[0025] Setting the reference power of the inverter of the energy storage system according to the power price linking mode may include: determining to perform discharge of the battery when the power purchase price exceeds the price setting point; and calculating the discharge power to be used during battery discharge and determining the reference power of the inverter.

[0026] Here, the discharge power to be used during battery discharge may be determined according to the ratio of the power selling price at the time of discharge to the highest power selling price collected within a certain period of time.

[0027] Setting the reference power of the inverter of the energy storage system according to the power price linking mode may include: determining to perform charging of the battery when the power purchase price is lower than the price setting point; and calculating the charging power to be used during battery charging and determining the reference power of the inverter.

[0028] The charging power to be used during battery charging may be determined according to the ratio of the lowest power purchasing price collected within a certain period of time to the power purchasing price at the time of charging.

[0029] Here, the price set point may be set to an average value of prices for purchasing electric power from the electric power grid over a certain period of time, or the price set point may be set by a user.

[0030] Setting the power price linking mode may include setting the power price linking mode as a default mode in advance.

[0031] The method may further include selecting one of a plurality of grid-connected operation modes other than the default mode and the power price linked mode.

[0032] The plurality of grid-connected operation modes other than the default mode and the power price linked mode may include at least one of a self-consumption maximization mode, a user-defined mode, an emergency mode, a battery usage maximization mode, and a battery protection mode.

[0033] The method may further include selecting one of a plurality of off-grid operation modes when power cannot be supplied from the power grid, wherein the plurality of off-grid operation modes are operation modes for operating the energy storage system using at least one of a generator operation algorithm and a backup algorithm.

[0034] The plurality of off-grid operation modes are operation modes in which the energy storage system is operated using at least one of a generator operation algorithm and a backup algorithm.

[0035] According to another embodiment of the present disclosure, an energy storage system includes a battery and is connected to an electric power grid, and the energy storage system may include: an operation control device, which is configured to set an electricity price linkage mode according to the selection of an operator or user when electricity can be supplied from the electric power grid, set a reference power of an inverter of the energy storage system according to the electricity price linkage mode, and send the set reference power of the inverter to the inverter; and an inverter, which is configured to perform charge / discharge control on the battery according to the reference power received from the operation control device, wherein, in the electricity price linkage mode, charging and discharging of the energy storage system are controlled according to the price of electricity provided by the electric power grid.

[0036] In the power price linked mode, during battery discharge, the battery discharge amount may be set to the highest when the power selling price is the highest, and during battery charge, the battery charge amount may be set to the highest when the power purchasing price is the lowest.

[0037] The operation control device can determine to perform discharge of the battery and calculate the discharge power to be used during battery discharge and determine the reference power of the inverter when the electricity purchase price exceeds the price setting point, and the operation control device can determine to perform charging of the battery and calculate the charging power to be used during battery charging and determine the reference power of the inverter when the electricity purchase price is lower than the price setting point.

[0038] Here, the discharge power to be used during battery discharge may be determined according to the ratio of the power selling price at the time of discharge to the highest power selling price collected within a certain period of time.

[0039] Furthermore, the charging power to be used during battery charging may be determined based on the ratio of the lowest power purchasing price collected within a certain period of time to the power purchasing price at the time of charging.

[0040] The battery and inverter are connected to the renewable energy generation system via a direct current (DC) link.

[0041] Beneficial effects

[0042] According to an embodiment of the present disclosure, in an energy storage system, particularly an energy storage system linked to a photovoltaic system in the form of DC coupling, the system can operate in an optimal state by appropriately responding to various changes in the power environment, such as changes in the price of electricity provided by the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a block diagram of a PV system-linked DC-coupled energy storage system to which the present invention may be applied.

[0044] Figure 2 is an example of an operation control method of an energy storage system according to an embodiment of the present invention.

[0045] Figure 3 4 is a flow chart of a method for selecting an off-grid mode of an energy storage system according to an embodiment of the present invention.

[0046] Figure 4 4 is a flow chart of a method for selecting a grid-connected mode for an energy storage system according to an embodiment of the present invention.

[0047] Figure 5 is a flowchart of a method for calculating inverter reference power in an energy storage system according to an embodiment of the present invention.

[0048] Figure 6 is a conceptual diagram of the operation of an energy storage system based on the power price linking mode according to an embodiment of the present invention.

[0049] Figure 7 is a flowchart of an operating method in an electricity price linked mode according to an embodiment of the present invention.

[0050] Figure 8 is an example of a power price fluctuation graph for explaining charging and discharging operations of an energy storage system based on a power price linking mode according to an embodiment of the present invention.

[0051] Figure 94 is a flowchart of an operation control method of an energy storage system based on an electricity price linking mode according to an embodiment of the present invention.

[0052] Figure 10 is a block diagram of an operation control device for an energy storage system according to an embodiment of the present invention.

[0053] 100: Battery

[0054] 300: Operation control device (gateway)

[0055] 400: Power conversion device / inverter

[0056] 600: Power grid

[0057] 700: Photovoltaic (PV) systems DETAILED DESCRIPTION

[0058] The present invention can be modified in various ways 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 present invention is not intended to be limited to these specific embodiments. On the contrary, the present invention should cover all modifications, equivalents, and alternatives that fall within the spirit and technical scope of the present invention. Throughout the description of the drawings, similar reference numerals refer to similar elements.

[0059] It will be understood that although various elements may be described herein using terms such as first, second, A, B, etc., these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element may be referred to as a second element, and similarly, a second element may also be referred to as a first element without departing from the scope of the present invention. As used herein, the term "and / or" includes any combination of a plurality of associated listed items or a plurality of associated listed items.

[0060] It will be understood that when an element is referred to as being "coupled" or "connected" to another element, it can be directly coupled or connected to the other element or other elements or intervening elements may be present. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, there are no intervening elements.

[0061] The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the present 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 will be further understood that the terms "comprises," "comprising," "containing," and / or "having" when used herein specify the presence of stated features, integers, steps, operations, constituent elements, components, and / or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, constituent elements, components, and / or combinations thereof.

[0062] 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 to which the present invention belongs. It will 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 the relevant art and should not be interpreted in an idealized or overly formal sense unless so explicitly defined herein.

[0063] Some terms used herein are defined below.

[0064] State of Charge (SOC) refers to the current state of charge of the battery, expressed in percentage points [%), and State of Health (SOH) may be the current condition of the battery compared to its ideal or original condition, expressed in percentage points [%).

[0065] The power limit refers to the limit of power that can be output from the battery, which is preset by the battery manufacturer based on the battery condition. Depending on whether charging or discharging is applied, the power limit can be a charging power limit or a discharging power limit.

[0066] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0067] Figure 1 is a block diagram of a PV system-linked DC-coupled energy storage system to which the present invention may be applied.

[0068] Figure 1 An example of a DC-coupled system is shown, in which the output terminal of a photovoltaic (PV) system (700) and the output terminal of a battery (100) are connected to a DC link, and the DC link and the DC terminal of an inverter (400) are connected. The AC link of the inverter (400) is connected to a power grid (700) and can receive power from the power grid (700) or provide power to the power grid (700). The AC link of the inverter (400) is also connected to a load, and power supplied from the PV system (700) or the battery (100) can be provided to the load.

[0069] Here, a photovoltaic system is used as an example of a power generation system using renewable energy, and the present invention can be applied to power generation systems utilizing various renewable energy sources (renewable energy) such as wind energy, geothermal energy, biomass energy, and ocean energy, as well as photovoltaic systems. Therefore, in this specification, the photovoltaic system can be understood as one of the renewable energy power generation systems, and the amount of PV power generated can also be interpreted as the amount of renewable energy power generated.

[0070] The battery (100) is used to store electrical energy. Generally, a plurality of battery packs may form a battery rack, and a plurality of battery racks may form a battery bank. Here, the battery pack may be referred to as a battery module depending on the device or system in which the battery is used.

[0071] In DC-coupled energy storage systems, a DC / DC converter is required that can individually control the DC voltage and current of each battery system. Since the DC / DC converter is placed within the battery system, a DC / AC converter for connecting to the photovoltaic system is no longer necessary, improving efficiency. Furthermore, by incorporating a DC / DC converter into each battery system, not only can existing battery systems be protected and controlled, but battery power can also be controlled by taking into account the characteristics of each battery system, even if there are differences in SOC, SOH, and capacity between battery racks.

[0072] Here, a battery management system (BMS) may be installed for each battery. The BMS can monitor the current, voltage, and temperature of each battery rack (or group), calculate the state of charge (SOC) based on the monitoring results, and control charging and discharging.

[0073] A photovoltaic (PV) system (700) may include a plurality of unidirectional solar modules connected in series and parallel, capable of generating electricity. The output end of the PV system (700) is connected to a battery (100) and an inverter (400) via a DC link. A reverse current prevention device may be placed on the DC link (700) connected to the PV system to prevent reverse current from flowing to the solar modules.

[0074] The inverter (400) may also be referred to as a power conditioning system (PCS) and controls the power supplied from the outside and the power supplied from the battery to the outside. The inverter (400) may generally be implemented in the form of a DC / AC inverter. At the same time, the inverter (400) may include a power management system (PMS), and the power management system may report the monitoring results of the BMS to the gateway (300) and receive information about the inverter reference power from the gateway (300) to control the inverter output.

[0075] Meanwhile, the inverter (400) can be connected to the network by using a controller area network (CAN) or Ethernet ( Figure 1The gateway (300) is connected to the gateway (300) for communication with the inverter (400) (indicated by a dotted line). The gateway (300) can perform energy management system (EMS) functions, monitor the inverter (400), provide the user with information about the operation of the energy storage system received from the PMS in the inverter, and send control commands related to energy or power use to the inverter (400). Therefore, the gateway (300) can include a user interface. Here, the gateway (300) can be understood as an example of an operation control device of the energy storage system according to the present invention.

[0076] In this specification, the energy storage system may be understood as a concept including a battery (100) and an inverter (400), or a concept including a battery (100), an inverter (400) and a gateway (300).

[0077] Meanwhile, the command related to energy or power usage may include information on the power usage pattern and operation mode of the energy storage system, and the PMS may operate according to the power usage pattern and operation mode received from the gateway (300).

[0078] More specifically, the inverter (400) operates substantially according to the power usage mode received from the gateway. For example, the operating state of the inverter may vary depending on whether the power usage mode is set to passive mode or active mode. In active mode, the inverter charges the battery with the highest priority, and as the highest priority, energy is used to charge the battery to the charging limit. Passive mode refers to a mode in which the battery power is naturally determined according to the power situation of the grid and the PV system.

[0079] More specifically, if the power usage mode is set to passive mode, the power generated by the PV system = 7 kW, the power to be consumed by the load = 3 kW, the battery charging limit power (BAT Ch Limit) = 2 kW, and the grid export power limit = 0 W, then 3 kW of power generated by the PV system is supplied to the load, and 2 kW is used to charge the battery. Due to the set grid export power limit, the remaining 2 kW of power cannot be supplied to the grid, and this information is fed back to the PV system, causing it to reduce its power generation by the remaining power. Here, the export power limit refers to the limit of power that can be exported to the grid.

[0080] On the other hand, if the power usage mode is set to active mode, the power generated by the PV system = 2 kW, the power to be consumed by the load = 3 kW, the battery charging limit power (BAT Ch Limit) = 7 kW, and the grid transmission limit power = 0 W, then the 2 kW of power generated by the PV system and the 5 kW of power supplied from the grid are all used to charge the battery. In addition, the remaining 3 kW of power supplied from the grid can be supplied to the load.

[0081] At the same time, the inverter (400) may also receive information about the operation mode of the energy storage system from the gateway and control the output of the inverter according to the operation mode. According to a preferred embodiment of the present invention, an energy storage system including a battery and connected to an electric power grid may include: an operation control device configured to: when power can be supplied from the electric power grid, set an electric power price linking mode according to a selection of an operator or a user, set a reference power of an inverter of the energy storage system according to the electric power price linking mode, and send the set reference power of the inverter to the inverter; and an inverter configured to perform charge / discharge control on the battery according to the reference power received from the operation control device.

[0082] Here, in the power price linked mode, during battery discharge, the battery discharge amount is set to the highest when the power selling price is the highest, and during battery charge, the battery charge amount is set to the highest when the power purchasing price is the lowest.

[0083] An operation control device, such as a gateway (300), can determine to perform discharge of a battery when the power purchase price exceeds a price set point, calculate the discharge power to be used during battery discharge and determine a reference power of an inverter, and can determine to perform charge of the battery when the power purchase price is lower than the price set point, calculate the charge power to be used during battery charging and determine a reference power of an inverter.

[0084] The discharge power to be used during battery discharge is determined according to the ratio of the power selling price at the time of discharge to the maximum power selling price.

[0085] Furthermore, the charging power to be used during battery charging is determined according to the ratio of the lowest power purchasing price collected within a certain period of time to the power purchasing price at the time of charging.

[0086] Figure 2 is an example of an operation control method of an energy storage system according to an embodiment of the present invention.

[0087] refer to Figure 2 The energy storage system may perform system initialization for operation (S210). During the system initialization process, a gateway ID and droop parameters may be received from the gateway, and grid code values, inverter selection information when multiple inverters are included, and inverter parallel operation setting information may be received from the application.

[0088] After the initial system setup is complete, the system checks whether it is connected to the grid, that is, whether it is in a grid-connected state (S220). If it is in a grid-connected state, data related to each device is read and obtained (S230). This data may include data related to the inverter, battery, backup box, and application. The backup box may be a switchgear that monitors the grid status and switches the system from grid-connected to off-grid if any abnormality occurs.

[0089] Afterwards, the system may check whether the system is off-grid (S240) or on-grid (S250) to identify and respond to abnormal situations occurring in the power grid. Figure 2 In the example, if the grid is in an off-grid state due to an abnormality, the state flag (StateFlag) is set to "2", and if in a grid-connected state, the state flag (StateFlag) is set to "1".

[0090] If the system is off-grid (Yes in S240 ), the off-grid mode selection algorithm ( S300 ) may be executed, and if the system is on-grid (Yes in S250 ), the on-grid mode selection algorithm ( S500 ) may be executed. In neither off-grid nor on-grid situations, the system is considered non-operating, and the ESS reference power (WEssRef) value to be sent by the gateway to the inverter is set to "0" ( S260 ). In other words, since it does not correspond to any operating mode at this stage, the ESS reference power is set to 0 to prevent battery charging and discharging.

[0091] Subsequently, grid power may be calculated using information on values ​​of current and power flowing in a link connected to the grid ( S270 ).

[0092] The energy storage system may calculate reference power of the inverter using information such as the calculated grid power, the battery power reference, the battery limit power, and the grid limit power ( S700 ).

[0093] The energy storage system may check the communication cycle ( S280 , S221 ), and if the system is operating (No in S290 ), the above process may be repeated according to the communication cycle.

[0094] Figure 3 4 is a flow chart of a method for selecting an off-grid mode of an energy storage system according to an embodiment of the present invention.

[0095] exist Figure 3 In the Figure 2 The off-grid mode selection algorithm or method (S300) is briefly described in the flowchart of the overall operation control method.

[0096] If the system is determined to be in an off-grid state due to a grid failure, etc., it may be checked whether a generator can be connected (S310). If the generator can be connected (Yes in S310), a generator connection algorithm may be executed (S321) to connect the system to the generator, and the system may operate in a generator operation mode.

[0097] To prevent diesel generator overload caused by a sudden increase in load power demand when operating off-grid, the generator can be operated within a wider range of permissible frequency and voltage. If the generator is overloaded, it becomes difficult to maintain the rated frequency and voltage, potentially reducing the generator's service life or causing insufficient fuel supply. Therefore, to extend the generator's service life and save fuel costs, the generator's rotational speed can be increased to increase the voltage. It is desirable for the gateway to operate the generator within this permissible range of frequency and voltage.

[0098] If the generator cannot be connected, a determination is made as to whether Mode 3 is in effect (S330), and a backup algorithm may be executed (S322). Mode 3 may be defined as backup mode. When a grid failure occurs, the currently operating mode may be automatically switched to backup mode, and the battery may respond to the load by discharging to supply the power required by the load. A minimum SOC value may be set and controlled in relation to the maximum dischargeable capacity. The minimum SOC value may be set to, for example, 20%.

[0099] For example, assuming PV generated power = 4 kW, load demand power = 7 kW, and BAT SOC = 50%, if a grid fault occurs while operating in the default mode (e.g., MSC (Maximum Self-Consumption) mode), the grid relay is closed. Then, the entire 4 kW of PV generated power will be supplied to the load, and the battery will be additionally discharged to supply the remaining 3 kW of required power to the load.

[0100] Figure 4 4 is a flow chart of a method for selecting a grid-connected mode for an energy storage system according to an embodiment of the present invention.

[0101] exist Figure 4 In the Figure 2 The overall operation control method is briefly described in the flowchart of the grid connection mode selection algorithm or method (S500).

[0102] If it is determined that the system is in the grid-connected state, it is first checked whether one of the operation modes has been selected by the user (S510). If an operation mode has been selected, a process for checking which mode has been selected is performed (S520, S530).

[0103] If the selected mode is Mode 1, the operations according to Mode 1 can be performed (S540), and if the selected mode is Mode 2, the operations according to Mode 2 can be performed (S550).

[0104] In this embodiment, Mode 1 can be a power price linkage mode, where the DC-coupled system operates by controlling the charging and discharging of the energy storage system according to the price of the power provided by the power grid. In other words, in a manner of automatically controlling the charging / discharging power according to the ratio of the grid price, even if the user does not set the charging / discharging power, the control device (e.g., gateway) can perform charging / discharging in response to the price. At the same time, in the present invention, the power price linkage mode can be set by the user's selection when using the energy storage system, but can also be preset as the default mode by the system administrator, operator, user, etc.

[0105] Here, the default value for determining the price setting point for charging or discharging can be set as the average value of the power price aggregated over a certain period of time and can be changed by the user. In addition, according to an embodiment of the present invention, in the power price linkage mode, when the power selling price is the highest, the discharge amount of the battery is set to the highest, and when the power purchase price is the lowest, the charge amount of the battery is set to the highest.

[0106] At the same time, in this embodiment, Mode 2 can include one or more of a maximum self-consumption (MSC) mode, a user-defined mode, an emergency preparation mode, a battery usage maximization mode, and a battery protection mode.

[0107] In the maximum self-consumption (MSC) mode, according to the PV power generation amount and the power demand of the load, the surplus power is charged to the battery and sold to the grid, or the power can be supplied to the load through battery discharge and by purchasing power from the power grid.

[0108] More specifically, in the MSC mode, when PV>LOAD, the PV power generation amount is used for the load, the surplus power is charged to the battery, and if there is still residual power, the energy can be sold to the grid. When PV<LOAD, the PV power generation amount is used for the load, the power is supplied to the load through battery discharge, and if the load still requires more power, power can be purchased and supplied from the grid. In other words, in the MSC mode, the system is operated such that the power purchased from the grid is minimized. In addition, battery charging and discharging can be performed through droop control using the DC voltage determined by PV and LOAD.

[0109] User-defined modes include a mode in which the user directly sets the details of the charge / discharge plan and operates the system, a mode in which the system operates according to a mode selected by the user from among multiple operating modes provided by the system, and the like. In the mode in which the user directly sets the details of the charge / discharge plan and operates the system, the system operates according to the charge / discharge schedule directly specified by the user. Furthermore, the user can check grid electricity prices, determine a charge / discharge plan, and input it into the app to operate the system.

[0110] Emergency Readiness Mode is a mode in which the system waits with the battery fully charged in the event of a planned power outage, such as a hurricane or typhoon, as announced in advance. For example, if the weather forecast for the next day is abnormal, the battery can be charged to 100% using PV power and power from the grid to prepare for the event.

[0111] Furthermore, the battery usage maximization mode maximizes battery usage. In this mode, if PV power generation is available, the power generated by the PV system is used to charge the battery. If the PV power generation is less than the full battery capacity, the difference can be charged from the grid. On the other hand, if PV power generation is not available, the battery can be fully discharged and used to power the load, and any remaining energy can be sold to the grid. Both charging the battery with grid power and selling electricity to the grid are permitted only in regions where such activities are permitted.

[0112] Battery conservation mode can also be used in areas where grid power purchase and sale are permitted. Battery conservation mode is a mode that limits battery usage as much as possible based on a comparison of PV power generation and load power demand when battery life needs to be extended while power can be supplied from the grid.

[0113] On the other hand, if any operation mode is not selected, an operation of a mode set as a default may be performed ( S511 ).

[0114] The default mode is a mode selected by default when the user does not make a mode selection. According to an embodiment of the present invention, the MSC mode among the power price linked mode described above as mode 1 or mode 2 may be set as the default mode.

[0115] Figure 5 The present invention is a flowchart of a method for calculating inverter reference power in an energy storage system according to an embodiment of the present invention.

[0116] Figure 5The operation method shown in FIG. 4 can be executed by an operation control device of the energy storage system, such as a gateway. However, the operation subject of the operation method of the energy storage system according to the embodiment of the present invention is not limited to the gateway.

[0117] The operation control device may transmit EMS data to the inverter and receive PMS data from the inverter ( S710 ). In other words, the operation control device may collect information required to calculate the reference power of the inverter.

[0118] By utilizing the fact that the power (WLoad) supplied to the load is determined ( S720 ) from the grid power and the inverter reference power (WInvRef), the operation control device may calculate the inverter reference power (WInvRef) as (WInvRef=WGrid−WLoad) ( S730 ).

[0119] Next, the inverter reference power is checked to see if it is less than the grid export lower limit (WGridLowLim) (S740). If so, the inverter reference power is set to the grid export lower limit (S741). This is because if there is a limit range for the amount of power exported to the grid depending on the country or region, power export outside of this range is not allowed.

[0120] Likewise, it is checked whether the inverter reference power exceeds the grid purchase upper limit (WGridUpLim) ( S750 ), and if so, the inverter reference power is set to the grid purchase upper limit ( S751 ).

[0121] Figure 6 is a conceptual diagram of the operation of an energy storage system based on the power price linking mode according to an embodiment of the present invention.

[0122] The power price linked mode according to an embodiment of the present invention is a mode of controlling charging and discharging of an energy storage system according to the power price provided by the power grid.

[0123] See also Figure 6 , the price set point (Price Set Point; λ) defined in the electricity price link model grid,Set ) is a value that determines whether the battery in the energy storage system will be charged or discharged. When the power price of the grid exceeds the price set point, the energy storage system can perform battery discharge, and when the power price of the grid is lower than the price set point, the energy storage system can perform battery charging. The default value of the price set point can be set to the power purchase price (λ) collected during a certain period of time. grid,buy ) and can be changed by the user. For example, the price set point can be set to the average of the electricity purchase prices collected over a certain period of time (e.g., 24 hours).

[0124] In the power price linked mode, the battery discharge amount when discharging the battery can be determined according to the power selling price ratio. Therefore, when the power selling price to the power grid is the highest, the discharge amount of the energy storage system can be set to the highest.

[0125] The discharge amount of the battery determined by the power selling price rate may be defined as the following Formula 1.

[0126] [Formula 1]

[0127] In formula 1, P Dchset (t) represents the real-time discharge power of the battery, P max Indicates the battery's discharge limit power or maximum discharge power, λ grid,sell (t) represents the real-time electricity selling price to the grid, and λ grid,sellMax Indicates the maximum electricity selling price.

[0128] In other words, in the electricity price link mode according to an embodiment of the present invention, the discharge power when the battery is discharged can be determined based on the ratio of the electricity selling price at the time of discharge to the maximum electricity selling price collected within a certain period of time, and can be calculated by considering the discharge limit power of the battery.

[0129] At the same time, according to an embodiment of the present invention, the battery charge capacity can be determined according to the power purchase price ratio in the power price link mode. Therefore, when the price for purchasing electricity from the power grid is the lowest, the energy storage system charge capacity can be set to the highest.

[0130] Under the operation according to the power price link mode, the charge amount of the battery determined according to the power purchase price ratio may be defined as the following Formula 2.

[0131] [Formula 2]

[0132] In formula 2, P chset (t) represents the real-time charging power of the battery, P max Indicates the battery's charging limit power or maximum charging power, λ grid,buy (t) represents the real-time electricity purchase price, and λ grid,buyMin Indicates the lowest electricity purchase price within a certain period of time.

[0133] In other words, in the electricity price link mode according to an embodiment of the present invention, the charging power when charging the battery can be determined based on the ratio of the lowest electricity purchase price collected within a certain period of time to the electricity purchase price at the time of charging, and can be calculated by considering the charging limit power of the battery.

[0134] Figure 7 is a flowchart of an operating method in an electricity price linked mode according to an embodiment of the present invention.

[0135] Figure 7 The operation method shown in FIG. 4 can be executed by an operation control device of the energy storage system, such as a gateway. However, the operation subject of the operation method of the energy storage system according to the embodiment of the present invention is not limited to the gateway.

[0136] refer to Figure 7 , the operation control device may monitor the electricity purchase price, that is, the price for purchasing electricity by the user or consumer (λ grid,buy If the electricity purchase price is lower than the price set point (Yes in S541 ), the battery charging in the system may be determined and the charging power (WEssChaSet) may be calculated ( S543 ). Here, the charging power may be defined according to Formula 2 above. In other words, according to an embodiment of the present invention, in the electricity price linked mode, the battery charging capacity may be determined based on the electricity purchase price ratio. Therefore, when the price for purchasing electricity from the power grid is the lowest, the energy storage system charging capacity may be set to the highest.

[0137] After that, it is checked whether the energy storage system can be charged by receiving power from the grid (S545). This is because when charging the ESS (or battery), whether it is allowed to charge only by the power supplied from the PV system or whether it is allowed to charge the ESS by the power supplied from the grid varies depending on the country and region. If Figure 7 If the value of the parameter “GridtoESS_ENA” in step S545 is “0”, the ESS cannot be charged using grid power.

[0138] If the ESS cannot be charged by receiving power from the grid (Yes in S545 ), the ESS reference power (WEssRef) is set to "WEssRef = min(Wpv, WEssChaLim, WEssChaSet)" ( S546 ). In other words, the minimum value among the PV power generation, the battery charge limit power, and the set battery charge power value is set as the ESS reference power.

[0139] On the other hand, if the ESS can be charged by receiving power from the grid (No in S545), the smaller of the charging power when purchasing power from the grid and the battery charging limit may be set as the reference power of the ESS (WEssRef = min(WEssChaSet, WEssChaLim)) (S547). For example, if the ESS can be charged using grid power, the PV power generation amount = 1 kW, the battery charging limit = 2 kW, and the calculated and set battery charging power = 3 kW, the battery charging power may be determined to be 2 kW, which is the minimum of these values, and in addition to the 1 kW of PV power generation, an additional 1 kW of power required to charge the battery may be introduced from the grid.

[0140] In a certain way, when the electricity purchase price (λ grid,buy ) exceeds the price set point (Yes in S542 ), battery discharge in the system may be determined, ESS discharge power (WEssDiscSet) may be calculated ( S544 ), and the calculated discharge power may be compared with the discharge limit of the battery, and the smaller value may be set as a reference power of the ESS ( S548 ).

[0141] Here, the discharge power can be defined according to the above formula 1. In other words, in the power price linked mode, the battery discharge power can be determined according to the power selling price ratio. Therefore, when the power selling price to the grid is the highest, the energy storage system discharge capacity can be set to the highest.

[0142] After that, the system can set the power usage mode to active mode (PWR_pri=1) to ensure that the battery maintains the ESS reference power value and the process can be terminated. Figure 7 The ESS reference power used in the flowchart may be understood to have the same or similar meaning as the inverter reference power used in other parts of this specification.

[0143] At the same time, despite Figure 7 Although not shown, the power price linkage mode according to the present invention can operate within the SOC operating range agreed with the DR (demand response) plan. Here, demand response (DR) refers to changing grid power usage by controlling power resources to meet demand response requests.

[0144] For example, the control device according to the present invention can receive a DR signal from a utility company (or a virtual power plant (VPP)) in real time, operate according to a DR command when the DR signal changes from 0 to 1, and operate the system by switching back to the electricity price link mode when the DR signal changes from =1 to 0.

[0145] Figure 8is an example of a power price fluctuation graph for explaining charging and discharging operations of an energy storage system based on a power price linking mode according to an embodiment of the present invention.

[0146] Figure 8 Graph 1 is a graph showing examples of the power selling price and the power purchasing price that vary within 24 hours, and shows an example in which the price setting point of the power price linking pattern according to the present invention is set to 32 cents.

[0147] The energy storage system according to the present invention can determine to perform discharge in a time period when the electricity purchase price exceeds the price set point. Figure 8 In the figure, the electricity purchase price exceeds the price set point during the time period from 16:00 to 20:00. Therefore, the energy storage system can perform battery discharge during this time period.

[0148] exist Figure 8 In the example, the maximum electricity selling price is 30 cents, and for example, assuming that PV power generation = 0kW, load demand = 7kW, and BAT discharge limit power = 7kW, the discharge power in each time segment can be calculated according to the above formula 1. More specifically, the discharge power in each time segment can be calculated as 16h: 7kW (5 / 30) = 1.17kW, 17h: 7kW (7 / 30) = 1.63kW, 18h: 7kW (10 / 30)=2.33kW, 19h: 7kW (28 / 30)=6.53kW, 20h: 7kW (30 / 30) = 7 kW. Therefore, the energy storage system according to the present invention can supply power to the load by discharging the battery at 6.53 kW at 19:00, for example, and purchase the remaining 0.47 kW required by the load from the grid and supply it to the load.

[0149] Figure 9 4 is a flowchart of an operation control method of an energy storage system based on an electricity price linking mode according to an embodiment of the present invention.

[0150] The operation control device of an energy storage system according to an embodiment of the present invention can first check whether the energy storage system is in a state where it can supply power from the power grid (S910). If the power price linkage mode is set by the operator or user (Yes in S920) while the power can be supplied from the power grid, the reference power of the energy storage system's inverter can be set according to the power price linkage mode. More specifically, the power purchase price is compared with the price set point to determine whether the battery should be discharged or charged (S921), and the inverter reference power is determined by calculating the discharge power or charge power (S922). The power price linkage mode can also be pre-set as a default mode by the operator or user.

[0151] In the power price linked mode, the charging and discharging of the energy storage system can be controlled according to the electricity price provided by the power grid. In other words, in the power price linked mode, during battery discharge, when the electricity selling price is the highest, the battery discharge amount can be set to the highest, and during battery charging, when the electricity purchasing price is the lowest, the battery charge amount can be set to the highest.

[0152] More specifically, the discharge power to be used during battery discharge is determined based on the ratio of the electricity selling price during discharge to the highest electricity selling price collected during a certain period. Furthermore, the charge power to be used during battery charging is determined based on the ratio of the lowest electricity purchasing price collected during a certain period to the electricity purchasing price during charging.

[0153] Furthermore, the price set point may be set to an average value of prices for purchasing electric power from the electric power grid during a certain period of time, or may be set by a user.

[0154] Meanwhile, if the energy storage system is in a state capable of supplying power from the power grid, but the power price linking mode is not selected, and another grid connection mode is selected (Yes in S940), then the inverter reference power according to the selected grid connection mode may be calculated (S941). Here, the grid connection operation mode other than the power price linking mode may include one or more of a self-consumption maximization mode, a user-defined mode, an emergency mode, a battery usage maximization mode, and a battery protection mode.

[0155] However, if the energy storage system is in a state capable of supplying power from the power grid, but the power price linking mode is not selected and another grid connection mode is not selected (No in S940), a default mode may be set, and the inverter reference power according to the default mode may be calculated (S950). Figure 9 If the power price linking mode is preset as the default mode in the flowchart, step S950 is not required.

[0156] Meanwhile, returning to step 910, if power cannot be supplied from the power grid to the energy storage system (No in S910), an off-grid mode is selected (S930), and an inverter reference power according to the selected off-grid mode can be calculated (S931). The off-grid mode can be a mode for operating the energy storage system using one of a generator operation algorithm and a backup algorithm.

[0157] Thereafter, information on the inverter reference power calculated according to each mode may be transmitted to the inverter ( S970 ), and may be utilized in charging and discharging of the battery.

[0158] Figure 10 is a block diagram of an operation control device for an energy storage system according to an embodiment of the present invention.

[0159] An operation control device (300) for an energy storage system may include at least one processor (310), a memory (320) storing at least one instruction executed by the processor, and a transceiver (330), the transceiver being a communication module connected to a network and performing communication. Here, the operation control device (300) may be a gateway located in the energy storage system.

[0160] Here, at least one processor may be referred to as a control unit, a controller, a micro control unit (MCU), etc., and may include 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 may be executed.

[0161] At the same time, at least one instruction executed by the processor may include: an instruction to set an electricity price linkage mode according to the selection of an operator or user when electricity can be supplied from the power grid; an instruction to set a reference power of an inverter of the energy storage system according to the electricity price linkage mode; and an instruction to send the set reference power of the inverter to the inverter.

[0162] Here, in the power price linked mode, charging and discharging of the energy storage system may be controlled according to the price of power provided by the power grid.

[0163] In more detail, in the power price linked mode, during battery discharge, the battery discharge amount can be set to the highest when the power selling price is the highest, and during battery charging, the battery charge amount can be set to the highest when the power purchasing price is the lowest.

[0164] Instructions for setting the reference power of the inverter of the energy storage system according to the power price linkage mode may include: instructions for determining to perform discharge of the battery when the power purchase price exceeds the price setting point; and instructions for calculating the discharge power to be used during the battery discharge and determining the reference power of the inverter.

[0165] Here, the discharge power to be used during battery discharge may be determined according to the ratio of the power selling price at the time of discharge to the maximum power selling price.

[0166] The instructions for setting the reference power of the inverter of the energy storage system according to the power price linkage mode may include: an instruction for determining to perform charging of the battery when the power purchase price is lower than the price setting point; and an instruction for calculating the charging power to be used during battery charging and determining the reference power of the inverter.

[0167] The charging power to be used during battery charging may be determined according to the ratio of the lowest power purchasing price collected within a certain period of time to the power purchasing price at the time of charging.

[0168] Here, the price setting point may be set to an average value of prices for purchasing electric power from the electric power grid over a certain period of time, or the price setting point may be set by a user.

[0169] The instruction to set the power price linking mode may include an instruction to set the power price linking mode as a default mode in advance.

[0170] The at least one instruction may further include an instruction to select one of a plurality of grid-connected operating modes other than the default mode and the power price linked mode.

[0171] Additionally, the at least one instruction may further include an instruction to select one of a plurality of grid-connected operation modes other than the default mode and the power price linked mode.

[0172] The plurality of grid-connected operation modes other than the default mode and the power price linked mode may include at least one of a self-consumption maximizing mode, a user-defined mode, an emergency mode, a battery usage maximizing mode, and a battery protection mode.

[0173] The at least one instruction may further include an instruction to select one of a plurality of off-grid operating modes when power cannot be supplied from the power grid, wherein the plurality of off-grid operating modes are operating modes that operate the energy storage system using at least one of a generator operating algorithm and a backup algorithm.

[0174] The operation control device (300) may further include an input interface device (340), an output interface device (350), a storage device (360), etc. The respective components included in the operation control device (300) may be connected via a bus (370) to communicate with each other.

[0175] In addition, the memory (or storage device) (320, 330) can be configured as at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory can be configured as at least one of a read-only memory (ROM) and a random access memory (RAM).

[0176] The operation of the method according to an embodiment of the present invention can be implemented as a computer-readable program or code on a computer-readable recording medium. Computer-readable recording media include all types of recording devices in which computer system-readable data is stored. In addition, computer-readable recording media can be distributed among network-connected computer systems to store and execute computer-readable programs or codes in a distributed manner.

[0177] Although some aspects of the present invention are described in the context of an apparatus, they may also be described in terms 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 represent a corresponding block or item or feature of a corresponding apparatus. Some or all of the method steps may be performed by (or using) hardware devices 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.

[0178] In the foregoing, the present invention has been described with reference to exemplary embodiments thereof, but those skilled in the art will appreciate that the present invention can be modified and altered in various ways within the scope without departing from the spirit and scope of the invention described in the appended claims.

Claims

1. A device for controlling the operation of an energy storage system, the energy storage system comprising a battery and an inverter and connected to an electric power grid, the device comprising: at least one processor; as well as a memory configured to store at least one instruction executed by the at least one processor, The at least one instruction includes: an instruction to set a power price linking mode according to a selection of an operator or a user when power can be supplied from the power grid; an instruction to set a reference power of the inverter of the energy storage system according to the power price linkage mode; and Sending an instruction to set the reference power of the inverter to the inverter, Wherein, in the electricity price linked mode, the charging and discharging of the energy storage system is controlled according to the price of electricity provided by the power grid.

2. The device according to claim 1, wherein Under the electricity price linking mode, During battery discharge, when the electricity selling price is the highest, the discharge amount of the battery is set to the highest, and During battery charging, when the power purchasing price is lowest, the charge amount of the battery is set to be highest.

3. The device according to claim 1, wherein The instruction for setting the reference power of the inverter of the energy storage system according to the power price linkage mode includes: determining an instruction to execute discharge of the battery when the electric power purchase price exceeds a price set point; and An instruction to calculate discharge power to be used during battery discharge and determine the reference power of the inverter.

4. The device according to claim 3, wherein The discharge power to be used during battery discharge is determined according to the ratio of the power selling price at the time of discharge to the highest power selling price collected within a certain period of time.

5. The device according to claim 3, wherein The instruction for setting the reference power of the inverter of the energy storage system according to the power price linkage mode includes: determining an instruction to execute charging of the battery when the electric power purchasing price is lower than the price set point; and An instruction to calculate charging power to be used during battery charging and determine the reference power of the inverter.

6. The device according to claim 5, wherein The charging power to be used during battery charging is determined based on a ratio of the lowest power purchasing price collected within a certain period of time to the power purchasing price at the time of charging.

7. The device according to claim 2, wherein The price set point is set to an average value of prices for purchasing electric power from the electric power grid over a certain period of time, or the price set point is set by a user.

8. The device according to claim 1, wherein The instructions for setting the electricity price linking mode include: An instruction to set the power price linking mode as a default mode in advance.

9. The device according to claim 8, wherein The at least one instruction further comprises: Instructions for selecting one of a plurality of grid-connected operating modes other than the default mode and the power price linked mode.

10. The device according to claim 9, wherein The plurality of grid-connected operation modes other than the default mode and the power price linked mode include: At least one of a self-consumption maximizing mode, a user-defined mode, an emergency mode, a battery usage maximizing mode, and a battery protection mode.

11. The device according to claim 1, wherein The at least one instruction further comprises: instructions for selecting one of a plurality of off-grid operating modes when power cannot be supplied from the power grid, and The multiple off-grid operation modes are operation modes for operating the energy storage system using at least one of a generator operation algorithm and a backup algorithm.

12. A method for controlling operation of an energy storage system, the energy storage system comprising a battery and an inverter and connected to an electric power grid, the method comprising: When power can be supplied from the power grid, setting a power price linking mode according to a selection of an operator or a user; setting a reference power of the inverter of the energy storage system according to the power price linking mode; as well as sending the set reference power of the inverter to the inverter, Wherein, in the electricity price linked mode, the charging and discharging of the energy storage system is controlled according to the price of electricity provided by the power grid.

13. The method according to claim 12, wherein: Under the electricity price linking mode, During battery discharge, when the electricity selling price is the highest, the discharge amount of the battery is set to the highest, and During battery charging, when the power purchasing price is lowest, the charge amount of the battery is set to be highest.

14. The method according to claim 12, wherein: Setting the reference power of the inverter of the energy storage system according to the power price linkage mode includes: determining to perform discharging of the battery when the electric power purchase price exceeds a price set point; and Discharge power to be used during battery discharge is calculated and the reference power of the inverter is determined.

15. The method according to claim 14, wherein The discharge power to be used during battery discharge is determined according to the ratio of the power selling price at the time of discharge to the highest power selling price collected within a certain period of time.

16. The method according to claim 14, wherein Setting the reference power of the inverter of the energy storage system according to the power price linkage mode includes: determining to execute charging of the battery when the electric power purchasing price is lower than the price set point; and Charging power to be used during battery charging is calculated and the reference power of the inverter is determined.

17. The method according to claim 16, wherein The charging power to be used during battery charging is determined according to the ratio of the lowest power purchasing price collected within a certain period of time to the power purchasing price at the time of charging.

18. The method according to claim 13, wherein The price set point is set to an average value of prices for purchasing electric power from the electric power grid over a certain period of time, or the price set point is set by a user.

19. The method according to claim 12, wherein: Setting the electricity price linking mode includes: The power price linking mode is set as a default mode in advance.

20. The method according to claim 19, further comprising: One of a plurality of grid-connected operation modes other than the default mode and the power price linked mode is selected.

21. The method according to claim 20, wherein The plurality of grid-connected operation modes other than the default mode and the power price linked mode include: At least one of a self-consumption maximizing mode, a user-defined mode, an emergency mode, a battery usage maximizing mode, and a battery protection mode.

22. The method according to claim 12, further comprising: selecting one of a plurality of off-grid operation modes when power cannot be supplied from the power grid, The multiple off-grid operation modes are operation modes for operating the energy storage system using at least one of a generator operation algorithm and a backup algorithm.

23. An energy storage system comprising a battery and connected to an electric power grid, the system comprising: an operation control device configured to, when power can be supplied from the power grid, set a power price linkage mode according to a selection of an operator or user, set a reference power of the inverter of the energy storage system according to the power price linkage mode, and transmit the set reference power of the inverter to the inverter; as well as an inverter configured to perform charge / discharge control on the battery according to the reference power received from the operation control device, Wherein, in the electricity price linked mode, the charging and discharging of the energy storage system is controlled according to the price of electricity provided by the power grid.

24. The energy storage system according to claim 23, wherein: Under the electricity price linking mode, During battery discharge, when the electricity selling price is the highest, the discharge amount of the battery is set to the highest, and During battery charging, when the power purchasing price is lowest, the charge amount of the battery is set to be highest.

25. The energy storage system according to claim 23, wherein: The operation control device determines to perform discharge of the battery when the power purchase price exceeds a price set point, calculates discharge power to be used during battery discharge and determines the reference power of the inverter, and wherein the operation control device determines to perform charging of the battery when the electric power purchasing price is lower than the price setting point, calculates charging power to be used during battery charging, and determines the reference power of the inverter.

26. The energy storage system according to claim 25, wherein: The discharge power to be used during battery discharge is determined according to the ratio of the power selling price at the time of discharge to the highest power selling price collected within a certain period of time.

27. The energy storage system according to claim 25, wherein: The charging power to be used during battery charging is determined according to the ratio of the lowest power purchasing price collected within a certain period of time to the power purchasing price at the time of charging.

28. The energy storage system according to claim 23, wherein: The battery and the inverter are connected to a renewable energy generation system via a DC link.

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