Off-grid operation method of energy storage system, energy storage system and electric equipment

Abstract

The embodiment of the invention relates to the technical field of energy storage, and provides an off-grid operation method of an energy storage system, the energy storage system and electric equipment, and the operation method comprises the steps: determining whether the grid connection of the energy storage system is powered down or not; under the condition of grid-connected power failure of the energy storage system, port voltage and port current of a load of the energy storage system at the grid-connected power failure moment are obtained, the port voltage of the load is the voltage of one end, connected with a filter of the energy storage system, of the load, and the port current of the load is the current of one end, connected with the filter of the energy storage system, of the load; the arc extinguishing current of the energy storage system is obtained, whether the off-line power-on moment of the energy storage system is reached or not is determined according to the size of the arc extinguishing current, and the arc extinguishing current is the current flowing through the filter; and under the condition that the off-grid power-on moment is reached, off-grid power generation is controlled, and the energy storage system is controlled to operate in an off-grid operation mode based on the port voltage and the port current of the load. The method determines whether to start off-grid according to the magnitude of the arc extinguishing current, thereby avoiding impact caused by direct start.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to an off-grid operation method for an energy storage system, an energy storage system, and electrical equipment. Background Technology

[0002] In existing technologies, the power conversion system (PCS) is a key component of energy storage systems, primarily responsible for converting the direct current (DC) power from batteries into alternating current (AC) power to supply the grid or local loads, and vice versa. The switching of the PCS between grid-connected and off-grid modes is a crucial component of energy storage system operation, especially when grid faults occur or a proactive switch to off-grid mode is required; the smoothness and safety of this switching are paramount.

[0003] In the grid-connected to off-grid switching control strategy of energy storage converters, when the grid is disconnected or a switching command is issued, the control mode of the PCS needs to be switched from current source control (grid-connected mode) to voltage source control (off-grid mode). However, existing technologies cannot guarantee the continuity of output voltage and frequency during the grid-connected to off-grid transition process, resulting in significant transient impact problems and poor adaptability of control parameters. Summary of the Invention

[0004] This application provides an off-grid operation method for an energy storage system, an energy storage system, and electrical equipment, which at least solves the problems of existing technologies being unable to guarantee the continuity of output voltage and frequency during the grid-to-off-grid transition process, and having significant transient impacts and poor adaptability of control parameters.

[0005] According to some embodiments of this application, one aspect of this application provides an off-grid operation method for an energy storage system. The energy storage system includes an electrically connected load and a filter. The method includes: determining whether the grid connection of the energy storage system has failed; when the grid connection of the energy storage system fails, acquiring the port voltage and port current of the load of the energy storage system at the time of grid failure, wherein the port voltage of the load is the voltage at the end connected to the filter of the energy storage system, and the port current of the load is the current at the end connected to the filter of the energy storage system; acquiring the arc extinguishing current of the energy storage system, and determining whether the off-grid power-on time of the energy storage system has been reached based on the magnitude of the arc extinguishing current, wherein the arc extinguishing current is the current flowing through the filter; and when the off-grid power-on time has been reached, controlling off-grid power generation, and controlling the energy storage system to operate in off-grid operation mode based on the port voltage and port current of the load.

[0006] In some embodiments, determining whether the off-grid power-on time of the energy storage system has been reached based on the magnitude of the arc-extinguishing current includes: determining whether the arc-extinguishing current is less than or equal to a preset current; if the arc-extinguishing current is less than or equal to the preset current, determining that the off-grid power-on time of the energy storage system has been reached; if the arc-extinguishing current is greater than the preset current, determining that the off-grid power-on time of the energy storage system has not been reached.

[0007] In some embodiments, the energy storage system includes an energy storage converter, which includes power semiconductor devices. Controlling the energy storage system to operate in off-grid mode based on the port voltage and port current of the load includes: using the port voltage and port current of the load as initial values, performing proportional-integral calculations to obtain control signal parameters for the semiconductor devices in the energy storage converter; generating a control signal based on the control signal parameters, the control signal parameters including the duty cycle of a control signal that controls the semiconductor devices to turn on or off; and using the control signal to control the semiconductor devices to turn on or off, thereby controlling the energy storage system to operate in the off-grid mode.

[0008] In some embodiments, using the port voltage and port current of the load as initial values, proportional-integral calculations are performed to obtain the control signal parameters of the semiconductor device in the energy storage converter. This includes: obtaining the amplitude and phase angle of the port voltage of the load at the time of grid-connected power failure, and obtaining the voltage amplitude and voltage phase angle; obtaining the amplitude and phase angle of the port voltage of the load at the time of grid-connected power failure, and obtaining the current amplitude and current phase angle; and performing proportional-integral calculations based on the voltage amplitude, voltage phase angle, current amplitude, and current phase angle to obtain the control signal parameters of the semiconductor device in the energy storage converter.

[0009] In some embodiments, proportional-integral (PI) calculations are performed based on the voltage amplitude, voltage phase angle, current amplitude, and current phase angle to obtain the control signal parameters of the semiconductor device in the energy storage converter. This includes: performing coordinate transformation and positive / negative sequence separation processing on the port voltage and port current of the load based on the voltage amplitude, voltage phase angle, current amplitude, and current phase angle to obtain positive-sequence data and negative-sequence data, wherein the positive-sequence data includes positive-sequence voltage and positive-sequence current, and the negative-sequence data includes negative-sequence voltage and negative-sequence current; performing PI decoupling calculations based on the positive-sequence data to obtain a first calculated voltage, and performing PI decoupling calculations based on the negative-sequence data to obtain a second calculated voltage; and determining the control signal parameters of the semiconductor device in the energy storage converter based on the first calculated voltage and the second calculated voltage.

[0010] In some embodiments, coordinate transformation and positive / negative sequence separation processing are performed on the port voltage and port current of the load according to the voltage amplitude, voltage phase angle, current amplitude, and current phase angle to obtain positive-sequence data and negative-sequence data. This includes: transforming the port voltage and port current of the load from three-phase stationary coordinates to two-phase stationary coordinates according to the voltage amplitude, voltage phase angle, current amplitude, and current phase angle to obtain initial conversion voltage and initial conversion current; determining the coordinate transformation angle based on an off-grid phase-locked loop; and transforming the initial conversion voltage and initial conversion current from the two-phase stationary coordinates to two-phase rotating coordinates based on the coordinate transformation angle and performing the positive / negative sequence separation processing to obtain the positive-sequence data and the negative-sequence data.

[0011] In some embodiments, the coordinate transformation angle includes a positive angle and a negative angle. Based on the coordinate transformation angle, the initial conversion voltage and the initial conversion current are converted from the two-phase stationary coordinates to a two-phase rotating coordinate system and the positive-negative sequence separation process is performed to obtain the positive-sequence data and the negative-sequence data. This includes: based on the positive angle, converting the initial conversion voltage and the initial conversion current from the two-phase stationary coordinates to a two-phase rotating coordinate system and performing the positive-negative sequence separation process to obtain the positive-sequence data. The positive-sequence data includes a first positive-sequence voltage, a second positive-sequence voltage, a first positive-sequence current, and a second positive-sequence current. The first positive-sequence voltage is the positive-sequence voltage of the first coordinate axis of the two-phase rotating coordinate system, and the second positive-sequence voltage is the positive-sequence voltage of the second coordinate axis of the two-phase rotating coordinate system. The sequence current is the positive sequence current of the first coordinate axis of the two-phase rotating coordinate system, and the second positive sequence current is the positive sequence current of the second coordinate axis of the two-phase rotating coordinate system. Based on the negative angle, the initial conversion voltage and the initial conversion current are converted from the two-phase stationary coordinate system to the two-phase rotating coordinate system and the positive and negative sequence separation process is performed to obtain the negative sequence data. The negative sequence data includes a first negative sequence voltage, a second negative sequence voltage, a first negative sequence current, and a second negative sequence current. The first negative sequence voltage is the negative sequence voltage of the first coordinate axis of the two-phase rotating coordinate system, the second negative sequence voltage is the negative sequence voltage of the second coordinate axis of the two-phase rotating coordinate system, the first negative sequence current is the negative sequence current of the first coordinate axis of the two-phase rotating coordinate system, and the second negative sequence current is the negative sequence current of the second coordinate axis of the two-phase rotating coordinate system.

[0012] In some embodiments, performing proportional-integral decoupling calculation based on the positive-sequence data to obtain a first calculated voltage, and performing proportional-integral decoupling calculation based on the negative-sequence data to obtain a second calculated voltage, includes: acquiring a first positive-sequence set voltage, a second positive-sequence set voltage, a first negative-sequence set voltage, and a second negative-sequence set voltage; performing proportional-integral decoupling calculation based on the first positive-sequence set voltage, the second positive-sequence set voltage, and the positive-sequence voltage to obtain a first positive-sequence calculated current and a second positive-sequence calculated current, and performing proportional-integral decoupling calculation based on the first negative-sequence set voltage, the second negative-sequence set voltage, and the negative-sequence voltage to obtain a first negative-sequence calculated current and a second negative-sequence calculated current; determining the first calculated voltage based on the first positive-sequence calculated current and the second positive-sequence calculated current, and determining the second calculated voltage based on the first negative-sequence calculated current and the second negative-sequence calculated current.

[0013] In some embodiments, determining the first calculated voltage based on the first positive-sequence calculated current and the second positive-sequence calculated current, and determining the second calculated voltage based on the first negative-sequence calculated current and the second negative-sequence calculated current, includes: performing the proportional-integral decoupling calculation based on the first positive-sequence calculated current and the second positive-sequence calculated current to obtain the first calculated voltage, wherein the first calculated voltage includes a first sub-voltage and a second sub-voltage, wherein the first sub-voltage is the positive-sequence voltage of the first coordinate axis of the two-phase rotating coordinate system, and the second sub-voltage is the positive-sequence voltage of the second coordinate axis of the two-phase rotating coordinate system; performing the proportional-integral decoupling calculation based on the first negative-sequence calculated current and the second negative-sequence calculated current to obtain the second calculated voltage, wherein the second calculated voltage includes a third sub-voltage and a fourth sub-voltage, wherein the third sub-voltage is the negative-sequence voltage of the first coordinate axis of the two-phase rotating coordinate system, and the fourth sub-voltage is the negative-sequence voltage of the second coordinate axis of the two-phase rotating coordinate system.

[0014] In some embodiments, determining the control signal parameters of the semiconductor device in the energy storage converter based on the first calculated voltage and the second calculated voltage includes: controlling the energy storage converter to perform pulse width modulation waveform calculation based on the first calculated voltage and the second calculated voltage to obtain the control signal parameters of the semiconductor device in the energy storage converter.

[0015] In some embodiments, the method further includes: disconnecting the grid-connected switch in the event of a grid-connected power failure of the energy storage system, the grid-connected switch being connected between the grid and the filter.

[0016] In some embodiments, when the grid connection of the energy storage system fails, acquiring the port voltage and port current of the load of the energy storage system at the time of the grid connection failure includes: determining whether an off-grid operation enable command exists when the grid connection of the energy storage system fails; acquiring the port voltage and port current of the load of the energy storage system at the time of the grid connection failure when the off-grid operation enable command exists, and controlling the energy storage converter in the energy storage system to stop inverting when the grid connection fails; and controlling the energy storage system to shut down when the off-grid operation enable command does not exist.

[0017] According to some embodiments of this application, another aspect of this application provides an energy storage system, which is operated using any of the off-grid operation methods of the energy storage system described herein. The energy storage system includes: an off-grid side, an energy storage converter, a filter, and a grid-connected side connected thereto; and a load electrically connected to the filter and the grid-connected side, respectively.

[0018] In some embodiments, the system further includes a grid-connected switch, wherein a first terminal of the grid-connected switch is electrically connected to the filter and the load, and a second terminal of the grid-connected switch is electrically connected to the grid-connected side.

[0019] In some embodiments, the energy storage converter further includes power semiconductor devices.

[0020] In some embodiments, the semiconductor device is an insulated gate bipolar transistor.

[0021] According to some embodiments of this application, another aspect of this application provides an electrical device including any of the described energy storage systems.

[0022] The technical solution provided in this application has at least the following advantages: Considering the arc-extinguishing current, the decision to initiate off-grid operation is determined based on the magnitude of the arc-extinguishing current, thereby avoiding the impact caused by direct start-up. Furthermore, the voltage at the load power supply port is collected through a sampling circuit, and this information is used to initialize the off-grid parameters, preventing the impact caused by direct off-grid operation. Adjusting the PI parameters corresponding to the grid-to-off-grid transition achieves a smooth grid-to-off-grid conversion, solving the problems of existing technologies that cannot guarantee the continuity of output voltage and frequency during grid-to-off-grid transitions, and that exhibit significant transient impacts and poor adaptability of control parameters. Attached Figure Description

[0023] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the drawings in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 A schematic flowchart of an off-grid operation method for an energy storage system provided in an embodiment of this application is shown.

[0025] Figure 2 A schematic diagram of the PI algorithm flow for off-grid operation of an energy storage system provided in an embodiment of this application is shown.

[0026] Figure 3 A flowchart illustrating another off-grid operation method for an energy storage system provided in an embodiment of this application is shown.

[0027] Figure 4 A schematic diagram illustrating the effect of an off-grid operation method for an energy storage system provided in an embodiment of this application is shown.

[0028] Figure 5 A schematic diagram of the structure of an energy storage system provided in an embodiment of this application is shown;

[0029] Figure 6 A schematic diagram of another energy storage system provided in an embodiment of this application is shown.

[0030] The above figures include the following reference numerals:

[0031] 01. Off-grid side; 02. Energy storage converter; 03. Filter; 04. Grid-connected side; 05. Load; 06. Grid-connected side switch. Detailed Implementation

[0032] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0033] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0034] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0035] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0036] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0037] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0038] In the accompanying drawings corresponding to the embodiments of this application, the thickness and area of ​​the layers are enlarged for better understanding and ease of description. When describing a component (such as a layer, film, region, or substrate) on or on the surface of another component, the component may be "directly" located on the surface of the other component, or there may be a third component between the two components. Conversely, when describing a component on the surface of another component, or when another component is formed or disposed on the surface of a component, it indicates that there is no third component between the two components. Furthermore, when describing a component as being "generally" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a portion of the edge of the entire surface.

[0039] In the description of the embodiments of this application, when a component "includes" another component, other components are not excluded unless otherwise stated, and other components may be further included. Furthermore, when a component such as a layer, film, region, or plate is referred to as being "on / located" on another component, it can be "directly on" the other component (i.e., located on the surface of the other component with no other components between them), or another component may be present therein. Moreover, when a component such as a layer, film, region, or plate is "directly located" on another component, or when a component such as a layer, film, region, or plate is located on the surface of another component, it indicates that no other components are located therein.

[0040] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "part" is also intended to include the plural form unless the context clearly indicates otherwise. Components include layers, films, regions, or plates, etc.

[0041] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0042] As described in the background section, in traditional grid-connected energy storage systems, the power conversion system (PCS) typically serves as the core energy conversion device, responsible for converting the direct current (DC) from the battery into alternating current (AC) to supply the grid or local loads. This grid-connected operation mode ensures efficient energy management and stable power delivery in most situations and at most times. However, when the grid experiences a fault or unexpected power outage, the PCS needs to quickly switch to off-grid mode to prevent system shutdown and ensure a continuous power supply to local loads.

[0043] Existing PCS grid-connected to off-grid switching technologies mainly include the following implementation methods: Direct switching: Once a grid fault is detected, the inverter immediately shuts down and switches to off-grid mode. While this method reacts quickly, the voltage output by the inverter may differ significantly in phase and amplitude from the grid voltage before the power outage, causing instantaneous voltage fluctuations that can impact local loads and the PCS itself, potentially even damaging the equipment. Pre-charge switching: After a power outage, the PCS's filter capacitors are charged through a pre-charge circuit, gradually bringing its voltage closer to the grid voltage before the outage, before the inverter is started to enter off-grid mode. While this method can mitigate the switching impact to some extent, it increases the switching delay time, which may not meet the requirements of applications with extremely high power continuity requirements, such as hospital operating rooms and data centers. Software control: This method uses software algorithms to predict the voltage change trend after a grid outage and attempts to smooth the transition by adjusting the inverter's output parameters. However, this method is limited by the accuracy and response speed of the algorithm, making it difficult to adjust in real time at the instant of a grid outage.

[0044] The main problem with the aforementioned existing technologies in practical applications is the poor consistency of voltage phase and amplitude during switching, which causes a significant difference between the inverter output voltage and the grid voltage during switching. This difference not only directly affects the normal operation of the local load but may also cause damage to internal inverter components, reducing system reliability and lifespan.

[0045] Specifically, traditional switching technologies cannot guarantee that the output voltage will match the grid voltage in phase and amplitude at the moment of power failure when the inverter restarts after a grid disconnection. This results in voltage jumps, which in turn impact the PCS and its connected local loads. The impact of voltage jumps is particularly significant in the presence of filter capacitors and local loads, potentially leading to equipment damage or system instability, thus reducing the overall performance of the energy storage system and the user experience.

[0046] In summary, existing PCS grid-connected to off-grid switching technologies have drawbacks when dealing with abnormal grid conditions, including large voltage fluctuations during switching, high potential impact risks, and difficulty in real-time response in applications requiring high reliability.

[0047] To address the problems of existing technologies failing to guarantee the continuity of output voltage and frequency during grid-connected to off-grid transitions, as well as significant transient impacts and poor adaptability of control parameters, embodiments of this application provide an off-grid operation method for an energy storage system, an energy storage system, and electrical equipment.

[0048] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0049] Embodiments of this application provide an off-grid operation method for an energy storage system, wherein the energy storage system includes an electrically connected load and a filter, such as... Figure 1 As shown, the above method includes the following steps:

[0050] Step S101: Determine whether the grid connection of the above-mentioned energy storage system has been lost;

[0051] Step S102: In the event of a grid-connected power failure of the energy storage system, obtain the port voltage and port current of the load of the energy storage system at the time of the grid-connected power failure. The port voltage of the load is the voltage at the end where the load is connected to the filter of the energy storage system, and the port current of the load is the current at the end where the load is connected to the filter of the energy storage system.

[0052] Step S103: Obtain the arc extinguishing current of the energy storage system and determine whether the off-grid power-on time of the energy storage system has been reached based on the magnitude of the arc extinguishing current. The arc extinguishing current is the current flowing through the filter.

[0053] Step S104: When the above-mentioned off-grid power-on time is reached, control the off-grid power generation, and control the above-mentioned energy storage system to operate in off-grid operation mode based on the port voltage and port current of the above-mentioned load.

[0054] When the grid-connected power supply to the energy storage system suddenly fails, directly switching to off-grid mode may cause sudden changes in current and voltage, impacting the system and potentially damaging inverters and other equipment. Through steps S102 and S103, this method can accurately grasp the instantaneous state of the grid-connected power failure and monitor the arc-extinguishing current, ensuring that off-grid generation is only restarted after the arc-extinguishing current has dropped to a safe level. This avoids equipment damage caused by instantaneous high current and ensures a smooth transition of the system from grid-connected to off-grid mode.

[0055] Step S101 promptly detects grid connection failure events, and step S104 immediately controls the energy storage system to enter off-grid mode when the conditions are met. This method reduces switching delays by monitoring in real time and switching quickly at appropriate times, enabling the energy storage system to provide a stable power supply to local loads more quickly, thus improving the system's response speed and reliability.

[0056] In step S104, the energy storage system is controlled to enter off-grid mode based on the port voltage and current of the load at the time of power failure. This control strategy ensures that the output voltage and frequency in off-grid mode match the operating conditions before the power failure. This helps maintain the normal operation of the local load, avoids load interruption or anomalies caused by grid fluctuations, and improves the user satisfaction and practicality of the entire energy storage system.

[0057] By acquiring real-time information on the load's port voltage and current, as well as the arc-extinguishing current, this control method can more precisely adjust the operating parameters of the energy storage system, such as voltage output, frequency, and phase. This is crucial for improving the overall efficiency of the system in off-grid mode. Furthermore, proper parameter adjustment can extend equipment lifespan and reduce maintenance costs.

[0058] In summary, this method achieves seamless switching of the energy storage system from grid-connected to off-grid mode through a series of precise steps. This not only improves system stability but also optimizes power output, providing strong support for the continuous operation of the load. Technically, this embodiment achieves precise control of the grid-to-off-grid switching process by detecting the grid-connected status and the voltage and current at the load port, avoiding voltage and current surges caused by direct switching. In principle, a voltage sampling circuit monitors the load port voltage in real time, ensuring that the voltage phase and amplitude during off-grid operation are consistent with the grid state before the switch, thus ensuring a smooth transition. In terms of effectiveness, the technology in this embodiment ensures rapid and stable operation of the inverter in off-grid mode, avoiding impacts on local loads and the inverter, and improving system stability and safety. In other embodiments, voltage and current prediction algorithms can be added to further optimize the switching process and solve the problem of smooth switching during grid fluctuations.

[0059] The off-grid operation method of the energy storage system described in this application takes into account the arc-extinguishing current issue. It determines whether to initiate off-grid operation based on the magnitude of the arc-extinguishing current, thereby avoiding the impact caused by direct start-up. Furthermore, it uses a sampling circuit to collect the voltage at the load power supply port and initializes the off-grid parameters with this information, preventing impact caused by direct off-grid operation. By adjusting the PI parameters corresponding to the grid-to-off-grid transition, it achieves a smooth grid-to-off-grid conversion, solving the problems of existing technologies that cannot guarantee the continuity of output voltage and frequency during grid-to-off-grid transitions, and suffer from significant transient impacts and poor control parameter adaptability.

[0060] In some embodiments, determining whether the off-grid power-on time of the energy storage system has been reached based on the magnitude of the arc-extinguishing current includes the following steps:

[0061] Step S1031: Determine whether the arc extinguishing current is less than or equal to the preset current;

[0062] Step S1032: When the arc extinguishing current is less than or equal to the preset current, determine the time when the energy storage system is powered off the grid.

[0063] Step S1033: If the arc extinguishing current is greater than the preset current, determine that the off-grid power-on time of the energy storage system has not been reached.

[0064] In power systems, controlling the arc-extinguishing current is crucial for ensuring the safe shutdown and restart of electrical equipment. Step S1031 sets a preset current threshold to ensure that the energy storage system will only activate off-grid mode when the arc-extinguishing current drops to a sufficiently low level. This effectively avoids potential risks such as overvoltage and overcurrent surges that may arise from sudden mode switching under high current conditions, thereby improving the safety and reliability of system operation.

[0065] High arc-extinguishing currents can lead to accelerated wear and tear on electrical equipment (such as switches and contactors) and even cause malfunctions. Through steps S1032 and S1033, this method allows the off-grid mode to be activated only when the arc-extinguishing current drops to a safe range, thereby reducing the electrical stress on the equipment, extending its service life, and reducing maintenance and replacement costs.

[0066] The magnitude of the arc-extinguishing current directly affects the energy storage system's ability to smoothly switch from grid-connected to off-grid mode. By monitoring in real time and determining whether the appropriate off-grid power-on time has been reached based on a preset current threshold, this control strategy can more accurately grasp the switching timing, avoid unnecessary delays, and ensure the smoothness and efficiency of the switching process.

[0067] Reducing switching delays and impacts caused by arc-extinguishing current helps improve the overall performance of energy storage systems, especially for applications with high requirements for power supply continuity and quality (such as hospitals and data centers). This optimization not only enhances system stability and controllability but also further improves user satisfaction and trust.

[0068] In summary, by monitoring the arc-extinguishing current and determining the off-grid power-on time of the energy storage system based on a preset threshold, the safety, reliability, and performance of the system during the switchover from grid-connected to off-grid mode can be significantly improved. Technically, this embodiment ensures that off-grid operation is initiated only when the current drops to a safe level by monitoring the arc-extinguishing current, avoiding the risk of equipment damage due to excessive current. In principle, the monitoring and control of the arc-extinguishing current is based on the current change after the grid-connected switch is disconnected, and a threshold is set to determine whether it is safe to start off-grid mode. In terms of effectiveness, the technology in this embodiment can effectively prevent damage to the inverter or load due to excessive current during the switching process, ensuring the safe startup of the system in off-grid mode. In other embodiments, the timing of off-grid startup can be optimized by dynamically adjusting the preset current threshold according to different load conditions and grid environment, solving the problem of safe switching under different operating conditions.

[0069] In some embodiments, the energy storage system includes an energy storage converter, which includes power semiconductor devices. Controlling the energy storage system to operate in off-grid mode based on the port voltage and port current of the load includes the following steps:

[0070] Step S201: Using the port voltage and port current of the load as initial values, perform proportional-integral calculations to obtain the control signal parameters of the semiconductor device in the energy storage converter.

[0071] Step S202: Generate a control signal according to the above control signal parameters, wherein the control signal parameters include the duty cycle of the control signal that controls the semiconductor device to be turned on or off;

[0072] Step S203: The above-mentioned control signal is used to control the semiconductor device to be turned on or off, so as to control the energy storage system to operate in the above-mentioned off-grid operation mode.

[0073] The proportional-integral calculation in step S201 is based on the actual voltage and current values ​​of the load port. This means that the generation of the control signal will be closer to the actual needs, thereby ensuring that the voltage and current output of the energy storage converter in off-grid mode are more stable and accurate, reducing unnecessary fluctuations and errors, and improving the quality of power.

[0074] The control signal generated in step S202, especially the duty cycle parameter, allows for highly flexible control of the conduction time of semiconductor devices, providing a powerful tool for power management of energy storage systems. In off-grid mode, precise control of power semiconductor devices helps achieve maximum energy utilization efficiency while reducing unnecessary power consumption and heat loss, thus improving the overall energy efficiency of the system.

[0075] Dynamically adjusting control signal parameters based on load conditions enables a smooth transition between grid-connected and off-grid modes, avoiding system oscillations and instability that may result from hard switching. This is crucial for protecting the internal components of the energy storage system, such as capacitors and transformers, and ensuring that external loads are not affected.

[0076] The ability to rapidly generate and execute control signals enables energy storage systems to react quickly upon detecting a grid outage, reducing the delay between detection and response. This is crucial for applications requiring immediate power supply, such as industrial production lines and emergency power systems, ensuring a rapid and seamless switch to off-grid mode during grid failures and providing uninterrupted power support.

[0077] A stable and efficient power supply is one of the key factors in ensuring user satisfaction. By precisely controlling power semiconductor devices, energy storage systems can continuously provide high-quality power in off-grid mode. Even in the event of a grid outage, users can enjoy virtually imperceptible power services, greatly enhancing the user experience.

[0078] In summary, this control strategy, through refined power management, rapid mode switching, and smooth voltage and current control, not only improves the operating efficiency and reliability of the energy storage system but also ensures the continuity and quality of power supply. Technically, this embodiment uses a proportional-integral (PI) controller to precisely control the power semiconductor devices of the energy storage converter, ensuring stable inverter output in off-grid mode. In principle, PI calculations based on the voltage and current at the load port allow for real-time adjustment of the semiconductor device's on-time, i.e., duty cycle, to maintain stable output voltage and frequency. Effectively, the technology in this embodiment ensures rapid response and stable operation of the inverter in off-grid mode, avoiding voltage or frequency fluctuations caused by improper control and improving the system's power quality. In other embodiments, fuzzy control or adaptive control algorithms can be introduced to further optimize control signal generation and address stable control issues under complex load and grid environments.

[0079] In some embodiments, using the port voltage and port current of the load as initial values, proportional-integral calculations are performed to obtain the control signal parameters of the semiconductor devices in the energy storage converter, including the following steps:

[0080] Step S2011: Obtain the amplitude and phase angle of the port voltage of the load at the time of the grid-connected power failure, and obtain the voltage amplitude and voltage phase angle;

[0081] Step S2012: Obtain the amplitude and phase angle of the port voltage of the load at the time of the grid-connected power failure, and obtain the current amplitude and current phase angle;

[0082] Step S2013: Based on the voltage amplitude, voltage phase angle, current amplitude, and current phase angle, proportional-integral calculations are performed to obtain the control signal parameters of the semiconductor device in the energy storage converter.

[0083] Specifically, in steps S2011 and S2012, the voltage amplitude, phase angle, and current amplitude and phase angle at the load port at the moment of grid-connected power failure are obtained. This step ensures that when the energy storage system switches from grid-connected mode to off-grid mode, the output voltage and current remain consistent with the state before the power failure, thereby avoiding sudden phase changes. This precise synchronization helps reduce power disturbances during the switching process, ensuring stable operation of the load unaffected by mode switching.

[0084] By utilizing the voltage and current information at the moment of grid connection failure to perform PI calculations, control signal parameters suitable for the current load conditions can be quickly generated. This mechanism enables the energy storage system to rapidly adjust its operating mode, shortening the transition time from grid-connected to off-grid mode and improving the system's agility to grid changes.

[0085] In step S2013, the PI control algorithm calculates the most suitable control signal parameters based on the acquired voltage and current parameters, including but not limited to the on-time (duty cycle) of the semiconductor device. By optimizing the control strategy, the energy storage system can utilize the electrical energy stored in the battery more efficiently, while reducing energy loss during the conversion process and improving the overall energy efficiency of the system.

[0086] PI controllers can smoothly adjust the operating state of semiconductor devices based on voltage and current trends, avoiding voltage spikes or current surges that may occur during switching. This ability to reduce surges is extremely beneficial for protecting sensitive components inside energy storage converters, such as capacitors and inductors, and for extending the lifespan of power semiconductor devices.

[0087] By precisely controlling semiconductor devices to ensure the stability and accuracy of output voltage and current, this method helps improve power quality in off-grid environments. It benefits both sensitive electronic devices and applications with stringent power continuity requirements, such as medical equipment and data center servers, ensuring the safe operation of end-user equipment.

[0088] In summary, this control strategy, by capturing load state information at the moment of grid-connected power failure, quickly and accurately adjusts the operating mode of the energy storage converter. This not only achieves seamless switching from grid-connected to off-grid mode but also significantly improves system efficiency, stability, and safety. Technically, this embodiment provides accurate initial values ​​for off-grid mode control by precisely measuring the voltage and current phase at the moment of grid-connected power failure, ensuring a smooth switching process. In principle, using the amplitude and phase angle information of voltage and current for PI calculations, the inverter output can be precisely controlled to match its state before grid disconnection. In terms of effectiveness, the technology in this embodiment ensures rapid and stable operation of the inverter in off-grid mode, avoiding voltage or frequency surges caused by switching, thus improving system stability and safety. In other embodiments, voltage and current prediction algorithms can be added to further optimize control signal generation and address the issue of smooth switching during grid fluctuations.

[0089] In some embodiments, the control signal parameters of the semiconductor device in the energy storage converter are obtained by proportional-integral calculation based on the voltage amplitude, voltage phase angle, current amplitude, and current phase angle, including the following steps:

[0090] Step S301: Based on the voltage amplitude, voltage phase angle, current amplitude and current phase angle, perform coordinate transformation and positive / negative sequence separation on the port voltage and port current of the load to obtain positive sequence data and negative sequence data. The positive sequence data includes positive sequence voltage and positive sequence current, and the negative sequence data includes negative sequence voltage and negative sequence current.

[0091] Step S302: Perform proportional-integral decoupling calculation based on the above positive sequence data to obtain the first calculated voltage, and perform proportional-integral decoupling calculation based on the above negative sequence data to obtain the second calculated voltage;

[0092] Step S303: Determine the control signal parameters of the semiconductor device in the energy storage converter based on the first calculated voltage and the second calculated voltage.

[0093] Specifically, step S301 effectively distinguishes the fundamental positive-sequence and negative-sequence components of voltage and current through coordinate transformation (e.g., from the abc three-phase stationary coordinate system to the dq rotating coordinate system) and positive-negative-sequence separation. This operation simplifies the complexity of the control system, improves control accuracy, optimizes the current path within the semiconductor device, and enhances energy conversion efficiency.

[0094] The separated positive-sequence data is used to guide the normal operation of semiconductor devices, while the negative-sequence data reflects the asymmetry of the power grid or the imbalance of the load. Through the decoupled PI calculation in step S302, these negative-sequence components can be compensated or eliminated in a targeted manner, thereby reducing harmonic interference in the system, purifying the quality of the output power, and having a direct benefit to improving the purity of power.

[0095] The rapid response capability of PI decoupling calculation means that the system can quickly adapt to instantaneous changes in the power grid or load, whether it is a small fluctuation in grid-connected mode or a large-scale adjustment during off-grid switching. This rapid response mechanism helps improve the system's flexibility and adaptability, ensuring the continuity and stability of power supply.

[0096] The PI controller is designed with the system's dynamic characteristics in mind. Its proportional-integral action effectively suppresses oscillations in the system, especially during grid switching, maintaining a stable output from the power converter and avoiding drastic voltage and current fluctuations. By using the control signal parameters determined in step S303, the system can better cope with various operating conditions, enhancing overall stability.

[0097] The entire control process not only considers the efficiency of power conversion but also takes into account the system's response speed and stability. Through precise calculation and control, the energy storage converter can efficiently convert electrical energy, providing high-quality power to local loads in off-grid operation mode, while reducing equipment losses and noise, and improving the overall performance of the system.

[0098] In summary, the complex PI control strategy employing coordinate transformation and positive / negative sequence separation not only improves the accuracy of semiconductor device control in energy storage systems but also significantly enhances system stability and response speed, thereby achieving efficient, stable, and high-quality power conversion. Technically, this embodiment converts three-phase voltage and current into easily controllable positive and negative sequence components through coordinate transformation and positive / negative sequence separation, improving control accuracy. In principle, using coordinate transformation and positive / negative sequence separation technology simplifies the complex three-phase system into two independent systems, facilitating PI decoupling calculations and obtaining precise control signal parameters. In terms of effectiveness, the technology in this embodiment ensures rapid and stable operation of the inverter in off-grid mode. By precisely controlling the positive and negative sequence components, it avoids voltage or frequency surges caused by switching, improving system stability and safety. In other embodiments, higher-order mathematical models, such as Clarke transforms or Parker transforms, can be introduced to further optimize the coordinate transformation process and solve the problem of precise control under nonlinear loads and grid environments.

[0099] In some embodiments, based on the voltage amplitude, voltage phase angle, current amplitude, and current phase angle, coordinate transformation and positive / negative sequence separation are performed on the port voltage and port current of the load to obtain positive-sequence data and negative-sequence data, including the following steps:

[0100] Step S3011: Based on the voltage amplitude, voltage phase angle, current amplitude and current phase angle, the port voltage and port current of the load are converted from three-phase stationary coordinates to two-phase stationary coordinates to obtain the initial conversion voltage and initial conversion current.

[0101] Step S3012: Determine the coordinate transformation angle based on the off-grid phase-locked loop;

[0102] Step S3013: Based on the coordinate transformation angle, the initial conversion voltage and the initial conversion current are converted from the two-phase stationary coordinates to the two-phase rotating coordinates and the positive and negative sequence separation process is performed to obtain the positive sequence data and the negative sequence data.

[0103] Specifically, the voltage at the aforementioned ports of the load is as follows: Figure 2 As shown in the figure, Va, Vb, and Vc represent the port voltage values ​​in three directions of the three-phase stationary coordinate system, respectively. The aforementioned port currents of the load are as follows: Figure 2 As shown in the figure, Ia, Ib and Ic are the current values ​​of the port current in the three directions of the three-phase stationary coordinate system. The three-phase stationary coordinate system is the abc coordinate system, the two-phase stationary coordinate system is the αβ coordinate system, and the two-phase rotating coordinate system is the dq coordinate system. Figure 2VF_PLL in the code represents an off-grid phase-locked loop, and θ is the coordinate transformation angle. When the separation is in positive sequence, the coordinate transformation angle is θ; when the separation is in negative sequence, the coordinate transformation angle is -θ. Positive sequence data includes... Figure 2 In the data, Vd+, Vq+, Id+, and Iq+ represent the positive sequence voltage components along the d-axis and q-axis, respectively, while Id+ and Iq+ represent the positive sequence current components along the d-axis and q-axis, respectively. Negative sequence data includes... Figure 2 In the figure, Vd-, Vq-, Id-, and Iq- are the negative sequence voltage components of the d-axis and q-axis, respectively, and Id- and Iq- are the negative sequence current components of the d-axis and q-axis, respectively.

[0104] In step S3011, by transforming the voltage and current from the three-phase stationary coordinate system to the two-phase stationary coordinate system, the complexity of subsequent control algorithms can be simplified. Compared with a three-phase system, the control system design in the two-phase coordinate system is simpler and requires less computation, which helps to improve the real-time response speed and overall computational efficiency of the control system. In step S3012, the coordinate transformation angle determined based on the off-grid phase-locked loop ensures the synchronization of voltage and current signals with the inverter output. Phase-locked loop technology can track and adapt to the frequency and phase changes of the grid or inverter output, making the generation of control signals more accurate, which is conducive to achieving high-quality voltage and current control and improving power conversion efficiency. Step S3013, through further coordinate transformation (from a two-phase stationary to a two-phase rotating coordinate system) and positive and negative sequence separation processing, can effectively distinguish between positive and negative sequence components. The positive sequence component reflects the balance and symmetry state of the three-phase power system, while the negative sequence component is related to system imbalance and power disturbances. After separating the positive and negative sequences, the control system can optimize the positive sequence component in a targeted manner, while suppressing or eliminating the negative sequence component, thereby improving the quality of the output power and reducing the adverse effects on sensitive loads.

[0105] By separating positive and negative sequences, the robustness of the control system to grid fluctuations and load changes can be enhanced. For energy storage systems, especially in off-grid mode, this processing helps the system better cope with complex operating conditions such as nonlinear loads and unbalanced conditions, improving system stability and reliability, and ensuring that power output is not affected by external interference.

[0106] The separated positive-sequence and negative-sequence data provide crucial information for energy management. Based on this data, the control system can optimize energy allocation, reduce energy losses, and improve overall system performance. Optimizing positive-sequence data can improve energy conversion efficiency, while suppressing negative-sequence data helps reduce system losses and improve power quality.

[0107] In summary, through coordinate transformation and positive / negative sequence separation, this control strategy achieves precise control of the load port voltage and current in the energy storage system. This not only simplifies the control algorithm and improves computational efficiency but also effectively improves power quality and enhances the system's stability and robustness under complex operating conditions. Technically, this embodiment achieves precise control of the positive and negative sequence components in a three-phase system through coordinate transformation and positive / negative sequence separation, improving the inverter's response speed and stability in off-grid mode. In principle, using phase-locked loop (PLL) technology to determine the coordinate transformation angle allows for real-time tracking of grid or load frequency changes, ensuring that the transformed voltage and current are synchronized with the system frequency, thus obtaining accurate positive and negative sequence components. In terms of effectiveness, the technology in this embodiment ensures rapid and stable operation of the inverter in off-grid mode. By precisely controlling the positive and negative sequence components, it avoids voltage or frequency surges caused by switching, improving system stability and safety. In other embodiments, higher-order mathematical models, such as Clarke transforms or Park transforms, can be introduced to further optimize the coordinate transformation process and solve the problem of precise control under nonlinear loads and grid environments.

[0108] In some embodiments, the coordinate transformation angles described above include positive angles and negative angles. Figure 2 Based on the coordinate transformation angle mentioned above, the initial conversion voltage and the initial conversion current are converted from the two-phase stationary coordinates to the two-phase rotating coordinates and the positive and negative sequence separation process is performed to obtain the positive sequence data and the negative sequence data, including the following steps:

[0109] Step S401: Based on the aforementioned positive angle, the aforementioned initial conversion voltage and the aforementioned initial conversion current are converted from the aforementioned two-phase stationary coordinates to two-phase rotating coordinates and the aforementioned positive and negative sequence separation processing is performed to obtain the aforementioned positive sequence data. The aforementioned positive sequence data includes a first positive sequence voltage, a second positive sequence voltage, a first positive sequence current, and a second positive sequence current. The aforementioned first positive sequence voltage is the positive sequence voltage of the first coordinate axis of the aforementioned two-phase rotating coordinates, the aforementioned second positive sequence voltage is the positive sequence voltage of the second coordinate axis of the aforementioned two-phase rotating coordinates, the aforementioned first positive sequence current is the positive sequence current of the first coordinate axis of the aforementioned two-phase rotating coordinates, and the aforementioned second positive sequence current is the positive sequence current of the second coordinate axis of the aforementioned two-phase rotating coordinates.

[0110] Step S402: Based on the aforementioned negative angle, the aforementioned initial conversion voltage and the aforementioned initial conversion current are converted from the aforementioned two-phase stationary coordinates to two-phase rotating coordinates and the aforementioned positive and negative sequence separation processing is performed to obtain the aforementioned negative sequence data. The aforementioned negative sequence data includes a first negative sequence voltage, a second negative sequence voltage, a first negative sequence current, and a second negative sequence current. The aforementioned first negative sequence voltage is the negative sequence voltage of the first coordinate axis of the aforementioned two-phase rotating coordinates, the aforementioned second negative sequence voltage is the negative sequence voltage of the second coordinate axis of the aforementioned two-phase rotating coordinates, the aforementioned first negative sequence current is the negative sequence current of the first coordinate axis of the aforementioned two-phase rotating coordinates, and the aforementioned second negative sequence current is the negative sequence current of the second coordinate axis of the aforementioned two-phase rotating coordinates.

[0111] Specifically, such as Figure 2 As shown, the above positive angle is Figure 2 In the middle θ, the above negative angle is Figure 2 In the figure, the first coordinate axis can be either the d-axis or the q-axis, and the second coordinate axis can be either the q-axis or the d-axis. In this embodiment, the first coordinate axis is the d-axis and the second coordinate axis is the q-axis. The first positive sequence voltage is Vd+, the second positive sequence voltage is Vq+, the first positive sequence current is Id+, the second positive sequence current is Iq+, the first negative sequence voltage is Vd-, the second negative sequence voltage is Vq-, the first negative sequence current is Id-, and the second negative sequence current is Iq-.

[0112] In particular, the coordinate transformation and positive / negative sequence separation processes in steps S401 and S402 effectively decompose the energy in the three-phase system into positive and negative sequence components. Positive sequence energy represents the useful, balanced energy flow in the system, while negative sequence energy contains components that cause system imbalance and energy waste. This decoupling allows the control system to independently and precisely manage each part of the energy, optimizing energy utilization efficiency.

[0113] Separating positive and negative sequence components in a two-phase rotating coordinate system provides a faster dynamic response because the control equations in a rotating coordinate system typically have better decoupling properties. This allows the control system to adjust the inverter output more quickly to adapt to transient changes in the load or power grid, improving the overall system flexibility and response speed. Independent control of the positive and negative sequence components effectively reduces power quality problems caused by the negative sequence component, such as voltage fluctuations and current distortion. By suppressing the negative sequence component and optimizing the positive sequence component, the quality of the output power can be significantly improved, meeting the requirements of high-precision loads. The introduction of positive and negative angles, and the separation of positive and negative sequence components in a two-phase rotating coordinate system, significantly reduces the complexity of the control algorithm compared to direct control in a complex three-phase coordinate system. This reduces the resources required for real-time computation and improves the computational efficiency and real-time performance of the control system.

[0114] By implementing positive-sequence and negative-sequence separation control in a rotating coordinate system, the system can better suppress imbalances and disturbances, improving its stability and reliability under various operating conditions. This is especially beneficial for energy storage inverters, reducing internal shocks caused by grid anomalies or load surges and protecting the equipment from damage. The separation of positive-sequence and negative-sequence data provides a foundation for optimizing energy conversion strategies. The control system can adjust the inverter output based on positive-sequence data to achieve efficient energy transfer, while simultaneously using negative-sequence data feedback to take measures to suppress or compensate for non-ideal conditions, thereby maximizing energy conversion efficiency and reducing losses.

[0115] In summary, by utilizing coordinate transformation and positive / negative sequence separation technologies, energy storage systems can achieve more refined and efficient energy management and control. This method not only improves power quality and reduces control complexity but also enhances the system's stability and reliability under complex operating conditions. Technically, this embodiment separates the positive and negative sequence components by converting voltage and current to a rotating coordinate system, improving the inverter's control accuracy in off-grid mode. In principle, using the positive and negative angles of the rotating coordinate system for coordinate transformation converts voltage and current in the three-phase stationary coordinate system into components in the rotating coordinate system, facilitating positive and negative sequence separation. In terms of effectiveness, the technology in this embodiment ensures rapid and stable operation of the inverter in off-grid mode. By precisely controlling the positive and negative sequence components, it avoids voltage or frequency surges caused by switching, improving system stability and safety. In other embodiments, higher-order mathematical models, such as Clarke transform or Parker transform, can be introduced to further optimize the coordinate transformation process and solve the problem of precise control under nonlinear loads and grid environments.

[0116] In some embodiments, proportional-integral decoupling calculation is performed based on the above-mentioned positive-sequence data to obtain a first calculated voltage, and proportional-integral decoupling calculation is performed based on the above-mentioned negative-sequence data to obtain a second calculated voltage, including the following steps:

[0117] Step S3021: Obtain the first positive sequence setting voltage, the second positive sequence setting voltage, the first negative sequence setting voltage, and the second negative sequence setting voltage;

[0118] Step S3022: Based on the first positive sequence setting voltage, the second positive sequence setting voltage, and the positive sequence voltage, perform the above proportional-integral decoupling calculation to obtain the first positive sequence calculated current and the second positive sequence calculated current; and based on the first negative sequence setting voltage, the second negative sequence setting voltage, and the negative sequence voltage, perform the above proportional-integral decoupling calculation to obtain the first negative sequence calculated current and the second negative sequence calculated current.

[0119] Step S3023: Determine the first calculated voltage based on the first positive sequence calculated current and the second positive sequence calculated current, and determine the second calculated voltage based on the first negative sequence calculated current and the second negative sequence calculated current.

[0120] Specifically, such as Figure 2 As shown, the first positive sequence set voltage is Vd+ * The first positive sequence setting voltage is Vq+, which is typically set to 0. The second positive sequence setting voltage is Vq+. * That is, the positive sequence setting voltage on the q-axis; the first negative sequence setting voltage is Vd-. * The negative sequence setting voltage on the d-axis is typically set to 0, and the second negative sequence setting voltage is Vq-. * This refers to the negative sequence setting voltage on the q-axis, which is typically set to 0. The first positive sequence setting voltage Vd+ is... * The aforementioned second positive sequence setting voltage Vq+ * The first positive sequence voltage, Vd+, and the second positive sequence voltage, Vq+, are input into the PI algorithm for decoupling calculation to obtain the first positive sequence calculated current, Id+. * Second positive sequence current Iq+ * Similarly, the first negative sequence setting voltage Vd- * The aforementioned second negative sequence setting voltage Vq- * The first negative sequence voltage, Vd-, and the second negative sequence voltage, Vq-, are input into the PI algorithm for decoupling calculation to obtain the first negative sequence calculated current, Id-. * Second negative sequence current Iq- * .

[0121] In step S3022, proportional-integral decoupling calculations are used to calculate the first positive-sequence current and the second positive-sequence current, as well as the first negative-sequence current and the second negative-sequence current, based on the set voltage and the actual measured positive-sequence and negative-sequence voltages. This decoupling control method enables precise current control, ensuring that the current remains consistent with the set voltage, thereby optimizing the energy transfer process and reducing energy loss.

[0122] Through the dynamic adjustment function of the proportional-integral (PI) controller, the system can respond quickly to voltage changes and adjust the current output in a timely manner. This dynamic adaptability is particularly important for handling unstable operating conditions such as grid fluctuations or load abrupt changes, helping the system quickly reach a new steady state and improving overall stability. Performing PI decoupling calculations on positive-sequence and negative-sequence data separately means that the system can independently manage these two types of energy flows. Positive-sequence control optimizes symmetrical and balanced energy transmission in the system, while negative-sequence control can compensate for or eliminate imbalances in the system, such as voltage asymmetry and current distortion, significantly improving the quality of output power and reducing the impact on sensitive loads. Effective control of the negative-sequence component can reduce internal system stress, such as reducing inverter switching losses and lowering thermal stress during power conversion, thereby extending equipment lifespan, reducing failure rates, and improving overall system reliability.

[0123] The calculated voltage obtained through proportional-integral (PI) decoupling can guide the inverter to more precisely control the energy conversion process, reducing energy waste and improving efficiency. This is especially important for energy storage systems, where high-efficiency energy conversion not only reduces energy loss but also enhances the system's economic benefits. Unlike traditional control methods that may suffer from mutual interference, PI decoupling control strengthens the system's robustness to various disturbances, maintaining high-quality and stable output power even in complex and variable grid environments. This is crucial for ensuring the long-term reliable operation of the system.

[0124] In summary, this control strategy achieves refined current control in the energy storage system through independent proportional-integral (PI) decoupling calculations of positive-sequence and negative-sequence data, enhancing the system's adaptability and robustness to grid changes. Technically, this embodiment achieves precise control of positive-sequence and negative-sequence currents through PI decoupling calculations, improving the inverter's response speed and stability in off-grid mode. In principle, using set positive-sequence and negative-sequence voltages as references, PI decoupling calculations yield a calculated current matching the set voltages, thus obtaining a corresponding calculated voltage for controlling the switching on and off of power semiconductor devices. In terms of effectiveness, the technology in this embodiment ensures rapid and stable operation of the inverter in off-grid mode. By precisely controlling the positive-sequence and negative-sequence components, it avoids voltage or frequency surges caused by switching, improving system stability and safety. In other embodiments, higher-order control algorithms, such as sliding mode control or predictive control, can be introduced to further optimize the current control process and solve stability control problems under complex load and grid environments.

[0125] In some embodiments, determining the first calculated voltage based on the first positive-sequence calculated current and the second positive-sequence calculated current, and determining the second calculated voltage based on the first negative-sequence calculated current and the second negative-sequence calculated current, includes the following steps:

[0126] Step S30231: Based on the first positive sequence calculated current and the second positive sequence calculated current, perform the proportional-integral decoupling calculation to obtain the first calculated voltage. The first calculated voltage includes a first sub-voltage and a second sub-voltage. The first sub-voltage is the positive sequence voltage of the first coordinate axis of the two-phase rotating coordinate system, and the second sub-voltage is the positive sequence voltage of the second coordinate axis of the two-phase rotating coordinate system.

[0127] Step S30232: Based on the first negative sequence calculated current and the second negative sequence calculated current, perform the proportional-integral decoupling calculation to obtain the second calculated voltage. The second calculated voltage includes a third sub-voltage and a fourth sub-voltage. The third sub-voltage is the negative sequence voltage of the first coordinate axis of the two-phase rotating coordinate system, and the fourth sub-voltage is the negative sequence voltage of the second coordinate axis of the two-phase rotating coordinate system.

[0128] Specifically, such as Figure 2 As shown, the first positive sequence current Id+ is calculated. * Second positive sequence current Iq+ * The input is fed into the PI algorithm for decoupling calculation to obtain the first sub-voltage Vdp and the second sub-voltage Vqp, and the first negative sequence calculated current Id is then used. * Second negative sequence current Iq- * The input is fed into the PI algorithm for decoupling calculation to obtain the third sub-voltage Vdn and the fourth sub-voltage Vqn.

[0129] This process enables the inverter to indirectly control the output voltage through precise current regulation. Specifically, it uses a first calculated voltage (including first and second sub-voltages) obtained from a first positive-sequence calculated current and a second positive-sequence calculated current, and a second calculated voltage (including third and fourth sub-voltages) obtained from a first negative-sequence calculated current and a second negative-sequence calculated current, ensuring a high degree of consistency between the output voltage and the desired setpoint. This precise current-voltage relationship regulation helps improve the efficiency and quality of power conversion.

[0130] Separating the control of positive-sequence and negative-sequence voltages means that the system can independently manage symmetrical positive-sequence voltages and asymmetrical negative-sequence voltages. Positive-sequence voltage control focuses on maintaining stable system operation, while negative-sequence voltage control emphasizes compensating for grid imbalances and protecting the inverter from non-ideal conditions. This independent control capability makes the system's power management more flexible and efficient. Through proportional-integral decoupling calculations, the system can quickly respond to current changes, thereby adjusting the voltage output more rapidly and reducing the transition time during grid switching, load changes, and other situations. This rapid response capability is crucial for improving the continuity and stability of the system's power supply.

[0131] The precise generation of the first and second calculated voltages helps optimize voltage regulation strategies, reduce voltage fluctuations and distortions, and ensure that the quality of output power meets high standards, which is crucial for the stable operation of sensitive loads. Independent control of positive and negative sequence voltages enhances the system's resistance to external disturbances, such as grid imbalances and harmonic pollution, thereby improving system robustness and reliability. For energy storage inverters, this means maintaining stable operation and reducing failure rates even in complex grid environments. Refined voltage control strategies enable the system to manage the energy conversion process more intelligently, reducing losses during energy conversion, improving the overall energy conversion efficiency of the energy storage system, thereby optimizing system energy consumption, reducing costs, and enhancing economic efficiency.

[0132] In summary, the process of determining the calculated voltage through proportional-integral (PI) decoupling calculation based on positive-sequence and negative-sequence currents not only improves the accuracy of energy storage system control but also enhances the system's anti-interference capability and power quality management. Technically, this embodiment achieves precise control of positive-sequence and negative-sequence voltages through decoupling calculations, improving the inverter's response speed and stability in off-grid mode. In principle, by using the first and second positive-sequence calculated currents for PI decoupling calculations, a first sub-voltage and a second sub-voltage matching the calculated current can be obtained, thus yielding the first calculated voltage. Similarly, by using the first and second negative-sequence calculated currents for PI decoupling calculations, a third and a fourth sub-voltage matching the calculated current can be obtained, thus yielding the second calculated voltage. In terms of effectiveness, the technology in this embodiment ensures rapid and stable operation of the inverter in off-grid mode. By precisely controlling the positive-sequence and negative-sequence voltages, it avoids voltage or frequency surges caused by switching, improving system stability and safety. In other embodiments, the voltage control process can be further optimized by introducing higher-order mathematical models, such as Clark transform or Park transform, to solve the problem of precise control under nonlinear loads and power grid environments.

[0133] In some embodiments, determining the control signal parameters of the semiconductor device in the energy storage converter based on the first calculated voltage and the second calculated voltage includes: controlling the energy storage converter to perform pulse width modulation waveform calculation based on the first calculated voltage and the second calculated voltage to obtain the control signal parameters of the semiconductor device in the energy storage converter.

[0134] The control signal parameters include, for example: Figure 2 The values ​​shown are Duty_va, Duty_vb, and Duty_vc. Duty represents the duty cycle.

[0135] Specifically, pulse width modulation (PWM) waveform calculation can precisely adjust the on-time and off-time of semiconductor devices (such as IGBTs) based on the calculated first calculated voltage (positive-sequence voltage component) and second calculated voltage (negative-sequence voltage component), thereby achieving precise control of the output power of the energy storage converter. This improved control precision is crucial for maintaining the power demand of the grid or local loads, helping to avoid power surplus or shortage. By optimizing the PWM waveform mode, switching losses and dead time during power conversion can be reduced, thus improving the overall efficiency of power conversion. This high-efficiency energy conversion capability means less energy waste and greater economic and environmental benefits for energy storage systems.

[0136] The precise definition of control signal parameters ensures that the energy storage converter can provide stable and high-quality voltage and frequency output in both grid-connected and off-grid modes. This is crucial for supporting sensitive loads and ensuring the stable operation of the power grid. Controlling the first and second calculated voltages effectively filters out harmonics and negative sequence components in the power grid, improves the quality of output power, reduces electromagnetic interference, and ensures the safe operation of equipment in the power system.

[0137] The rapid response characteristics of PWM waveform calculation enable energy storage converters to quickly adjust their output under conditions of grid fluctuations and load changes, reducing transient time and power fluctuations, and enhancing the system's dynamic response and flexibility. By accurately calculating PWM waveforms, overvoltage and overcurrent phenomena caused by improper control can be avoided, protecting the inverter and related equipment from damage, thereby enhancing the overall reliability and durability of the system. Efficient and precise PWM control reduces thermal stress and mechanical wear on equipment, lowering the frequency of maintenance and replacement of inverters and other power electronic components, and helping to reduce system operating and maintenance costs.

[0138] In summary, PWM waveform calculation based on the first and second calculated voltages can significantly improve the power control accuracy of the energy storage converter, thereby improving power conversion efficiency and power quality. Technically, this embodiment achieves precise control of power semiconductor devices by performing PWM waveform calculation based on the calculated voltage, improving the inverter's response speed and stability in off-grid mode. In principle, using the first and second calculated voltages as references for PWM waveform calculation yields control signal parameters that match the calculated voltages, used to control the on / off state of the power semiconductor devices. Effectively, the technology in this embodiment ensures rapid and stable operation of the inverter in off-grid mode. By precisely controlling the power semiconductor devices, it avoids voltage or frequency surges caused by switching, improving system stability and safety. In other embodiments, higher-order control algorithms, such as sliding mode control or predictive control, can be introduced to further optimize control signal generation and solve stable control problems under complex load and grid environments.

[0139] In some specific embodiments, such as Figure 2 As shown, firstly, the port voltages Va, Vb, and Vc of the load, and the port currents Ia, Ib, and Ic of the load are obtained. Va, Vb, and Vc represent the voltage values ​​in the three directions of the three-phase stationary coordinate system, and Ia, Ib, and Ic represent the current values ​​in the three directions of the three-phase stationary coordinate system. Then, the port voltages and currents of the load are transformed from the three-phase stationary coordinate system abc to the two-phase stationary coordinate system αβ. Next, based on the off-grid phase-locked loop VF_PLL and the coordinate transformation angle θ, the two-phase stationary coordinate system αβ is transformed to the rotating coordinate axis dq, and positive and negative sequence separation is performed. Specifically, the coordinate transformation angle is θ when the separation is positive sequence, and -θ when the separation is negative sequence. After coordinate transformation and separation of positive and negative sequences, positive and negative sequence data are obtained. The positive sequence data includes the positive sequence voltage components Vd+ and Vq+ along the d and q axes, and the positive sequence current components Id+ and Iq+ along the d and q axes. The negative sequence data includes the negative sequence voltage components Vd− and Vq− along the d and q axes, and the negative sequence current components Id− and Iq− along the d and q axes. Then, the first positive sequence setting voltage Vd+ is... * The aforementioned second positive sequence setting voltage Vq+ * The first positive sequence voltage, Vd+, and the second positive sequence voltage, Vq+, are input into the PI algorithm for decoupling calculation to obtain the first positive sequence calculated current, Id+. * Second positive sequence current Iq+ * Similarly, the first negative sequence setting voltage Vd- * The aforementioned second negative sequence setting voltage Vq- *The first negative sequence voltage, Vd-, and the second negative sequence voltage, Vq-, are input into the PI algorithm for decoupling calculation to obtain the first negative sequence calculated current, Id-. * Second negative sequence current Iq- * The first positive sequence current Id+ is calculated. * Second positive sequence current Iq+ * The input is fed into the PI algorithm for decoupling calculation to obtain the first sub-voltage Vdp and the second sub-voltage Vqp, and the first negative sequence calculated current Id is then used. * Second negative sequence current Iq- * The inputs are fed into the PI algorithm for decoupling calculation to obtain the third sub-voltage Vdn and the fourth sub-voltage Vqn. Based on the first sub-voltage Vdp, the second sub-voltage Vqp, the third sub-voltage Vdn, and the fourth sub-voltage Vqn, PWM waveform calculation is performed to obtain the duty cycles Duty_va, Duty_vb, and Duty_vc of the aforementioned semiconductor devices in the energy storage converter.

[0140] In some embodiments, the method further includes: disconnecting the grid-connected switch when the grid connection of the energy storage system fails, wherein the grid-connected switch is connected between the grid connection and the filter.

[0141] Specifically, disconnecting the grid-connected switch can quickly isolate the energy storage system from the grid, preventing the system from continuing to supply power to an unstable grid during grid faults or power outages. This prevents potential damage to the energy storage inverter, battery, and other power electronic components caused by overvoltage, overcurrent, or other abnormal conditions. When the grid experiences a fault or power outage, disconnecting the grid-connected switch prevents the energy storage system from accidentally becoming a power source, reducing the risk of maintenance personnel or users coming into contact with live lines and ensuring personnel safety during maintenance or emergencies. If the connection between the energy storage system and the grid is not disconnected during a grid outage, the energy in the energy storage system may be fed back into the grid, potentially interfering with the grid's recovery process and posing safety hazards to grid workers. Disconnecting the grid-connected switch effectively prevents backfeeding. After a grid outage, disconnecting the grid-connected switch creates conditions for the energy storage system to smoothly switch from grid-connected mode to off-grid mode. At the moment of grid disconnection, by disconnecting the grid-connected switch, the system can quickly switch to off-grid control mode, maintaining continuous power supply to local loads and achieving seamless power supply transition. Disconnecting the grid-connected switch allows the energy storage system to focus on managing the energy demand of local loads. Through precise control strategies in off-grid mode, it ensures efficient energy utilization, avoids unnecessary energy waste, and helps extend the system's lifespan. In the event of grid instability or power outages, disconnecting from the grid reduces the impact of external grid fluctuations on the energy storage system, preventing external interference and thus improving the system's stability and controllability in off-grid conditions.

[0142] In summary, disconnecting the grid-connected switch is a crucial measure to ensure the safe and stable operation of the energy storage system during grid anomalies. It protects equipment and personnel while enabling rapid system response and optimized energy management. Technically, this embodiment achieves a safe switchover between grid-connected and off-grid modes by disconnecting the grid-connected switch, avoiding electrical surges during grid restoration. In principle, immediately disconnecting the grid-connected switch upon detecting a grid failure prevents current surges during grid restoration, protecting the inverter and load. Effectively, the technology in this embodiment ensures rapid and stable inverter operation in off-grid mode. By disconnecting the grid-connected switch, it avoids electrical surges during grid restoration, improving system stability and safety. In other embodiments, the safety and reliability of switching can be further enhanced by increasing the switch's arc-extinguishing capability or optimizing the switch's control strategy, addressing the issue of smooth switching during grid fluctuations.

[0143] In some embodiments, when the grid connection of the energy storage system fails, obtaining the port voltage and port current of the load of the energy storage system at the time of grid connection failure includes the following steps:

[0144] Step S1021: In the event of a grid-connected power failure of the aforementioned energy storage system, determine whether an off-grid operation enable command exists.

[0145] Step S1022: When the off-grid operation enable command is present, obtain the port voltage and port current of the load of the energy storage system at the time of grid power failure, and control the energy storage converter in the energy storage system to stop inverting.

[0146] Step S1023: If the above-mentioned off-grid operation enable command is not available, control the above-mentioned energy storage system to shut down.

[0147] When a power outage occurs, the system can react immediately by quickly detecting the presence or absence of an off-grid operation enable command. If the enable command is present, the system will rapidly acquire the voltage and current information at the load port, providing the necessary data for subsequent switching from grid-connected mode to off-grid mode. If the enable command is absent, the system will enter a safety shutdown procedure to avoid invalid or dangerous operating states. Acquiring the voltage and current information at the load port during a grid-connected power outage provides accurate reference data for the energy storage converter when switching from grid-connected to off-grid mode. This helps the inverter start operating in a state close to the actual load demand at the moment of switching, reducing power fluctuations and potential equipment impacts caused by mode switching, and achieving a smoother and safer mode transition.

[0148] After confirming the existence of the off-grid operation enable command, promptly stopping the inverter's grid-connected inverter function can prevent attempts to supply power to the grid when it is disconnected, thereby reducing the risk of system failure and damage and improving the overall reliability of the energy storage system. Determining the load state at the moment of grid disconnection, i.e., the port voltage and current, helps the system take appropriate protective measures, such as adjusting the inverter's output parameters to protect the load from voltage or frequency surges, while ensuring that the inverter is not damaged by sudden load changes.

[0149] If the off-grid operation enable command is not available, the system will automatically shut down to prevent the energy storage system from accidentally becoming a power source during grid failures. This reduces the risk of electric shock for personnel during maintenance or inspection and ensures operator safety. Accurately acquiring load data at the moment of grid connection failure allows the energy storage system to better understand and meet the actual needs of local loads when entering off-grid mode, thereby optimizing energy allocation, improving energy utilization efficiency, and reducing energy waste.

[0150] In summary, the execution of this series of steps helps the energy storage system respond quickly and accurately to abnormal grid conditions, ensuring the safety, reliability, and efficiency of system operation. Technically, this embodiment achieves intelligent control of the grid-to-off-grid switching process by detecting off-grid operation enable commands, avoiding unnecessary switching operations. In principle, when a grid-connected power outage occurs, the system checks the off-grid operation enable command. If present, it acquires the voltage and current at the load port and stops the inverter's grid-connected inverter operation, preparing to enter off-grid mode; if absent, it controls the inverter to shut down, avoiding switching operations when off-grid operation is not required, thus protecting the inverter and load. In terms of effectiveness, the technology in this embodiment ensures rapid and stable operation of the inverter in off-grid mode. By intelligently detecting the off-grid operation enable command, unnecessary switching operations are avoided, improving system stability and safety. In other embodiments, further optimization of the switching process can be achieved by adding more control logic, such as load type judgment or grid state prediction, to solve the problem of safe switching under different operating conditions.

[0151] In some embodiments, such as Figure 2As shown, the grid-connected to off-grid switching function occurs when a grid off-grid event occurs and the inverter needs to operate off-grid to supply the load, or when the grid has not experienced a power outage but the control system actively requests the inverter to operate off-grid. Its control process mainly includes judging the grid and control commands, controlling the disconnection of the grid-connected switch to avoid grid recovery causing voltage fluctuations during off-grid operation, sampling the load supply port voltage after the switch is disconnected, and switching off-grid loop control parameters. After entering off-grid operation, it starts with the load supply port voltage amplitude and phase angle. The main factors affecting the switching time include relay action time, grid-connected switch arc extinguishing time, mode switching time, and load type.

[0152] In other embodiments, such as Figure 3 As shown, the specific steps of an off-grid operation method for an energy system are as follows: First, determine whether a power outage event has occurred. If no power outage event has occurred, maintain grid-connected operation. If a power outage event has occurred, disconnect the grid-connected side switch and determine the off-grid operation enable command (i.e., determine whether off-grid operation can proceed normally). If the off-grid operation enable command does not exist, it indicates an off-grid power outage fault, and shutdown is performed. If the off-grid operation enable command exists, enter the grid-connected to off-grid transition process. Use an inverter to stop the inverter and disconnect the inverter switch. The inverter is the energy storage converter, and the inverter switch is the switch for the energy storage converter. Determine whether the arc-extinguishing current decreases after the grid-connected side switch is disconnected. If the arc-extinguishing current does not decrease, continue waiting for the arc-extinguishing current to decrease. Sample the voltage amplitude and phase angle at the load port and initialize the off-grid parameters (control phase-locked loop, off-grid loop control parameters, etc.). Engage the inverter switch, open the waveform, and enter off-grid operation. The relay switch in the energy storage converter is a blocking switch on the AC side to prevent grid connection and off-grid operation from conflicting.

[0153] Depend on Figure 3 As can be seen, the grid-connected to off-grid switching function occurs when a grid off-grid event occurs and the inverter needs to operate off-grid to supply the load, or when the grid has not experienced a power outage but the control system actively requests the inverter to operate off-grid. Its control process mainly includes judging the grid and control commands, controlling the disconnection of the grid-connected switch to avoid grid recovery causing voltage fluctuations during off-grid operation, sampling the load supply port voltage after the switch is disconnected, and switching the off-grid loop control parameters. Upon entering off-grid operation, it starts with the load supply port voltage amplitude and phase angle as the starting point. Details are as follows: Figure 3 As shown, the main factors affecting switching time include relay operating time, grid-connected switch arc extinguishing time, mode switching time, and load type. The arc extinguishing current is as follows: Figure 5 The current in filter 03 mentioned above.

[0154] in, Figure 4This is a schematic diagram illustrating the effect of an off-grid operation method for an energy storage system, such as... Figure 4 As shown, curve a represents the voltage waveform of phase line AB at the inverter port, and curve b represents the voltage waveform of phase line BC at the inverter port. Initially, the inverter starts up and operates in grid-connected mode. Then, when the inverter receives a switch-off-grid command or the off-grid operation conditions are met, the inverter disconnects the grid-side switch. After a certain delay, it generates waveforms with the port voltage phase angle as the initial phase angle, and slowly starts up to output the off-grid voltage.

[0155] In addition, energy storage systems are equipped with arc-extinguishing devices. These devices are used to extinguish the electric arc (i.e., arc-extinguishing current) caused by a sudden interruption of current during the operation of switching equipment (such as circuit breakers, contactors, relays, etc.). Arc-extinguishing devices can take many forms, depending on the type of equipment, power rating, voltage rating, and intended operating environment. Below are some common types and principles of arc-extinguishing devices:

[0156] 1. Magnetic arc extinguishing utilizes the principle of magnetic fields to guide and lengthen the electric arc, causing it to cool and extinguish rapidly under the influence of the magnetic field. This device is commonly used in high-voltage circuit breakers, where a built-in permanent magnet or electromagnet generates a magnetic field to accelerate the extinguishing of the arc.

[0157] 2. Gas blowout arc extinguishing: This method extinguishes the electric arc by blowing gas (such as air, SF6 gas, etc.) into the arc area. The gas blowing in accelerates arc cooling and disrupts the arc's continuity, making it less likely to reignite. Gas blowout arc extinguishing is widely used in medium- and high-voltage switchgear.

[0158] 3. Vacuum arc extinguishing: In switchgear operating in a vacuum environment, the electric arc cannot be sustained due to the lack of a dielectric medium and thus extinguishes naturally. Vacuum arc extinguishing devices are commonly used in medium and low voltage circuit breakers, utilizing vacuum (or very low pressure) to rapidly extinguish the arc.

[0159] 4. Composite arc extinguishing technology: Modern high-voltage and ultra-high-voltage circuit breakers often employ a combination of multiple arc extinguishing technologies, such as magnetic blowing and air blowing, or air blowing and vacuum technology, to improve arc extinguishing efficiency and meet the requirements of higher breaking capacity and faster breaking speed.

[0160] 5. Electronic arc extinguishing: In some precision electronic devices, such as solid-state relays, electronic control technology is used to extinguish arcs. This typically involves fast-switching circuits and software control, adjusting circuit parameters such as voltage, current, or frequency to control and quickly extinguish the arc.

[0161] To rapidly reduce the arc-extinguishing current, some embodiments employ a multi-stage arc-extinguishing design with multiple breaks, each equipped with a dedicated arc-extinguishing device. Through multiple arc segmentations and cooling, the current decrease is accelerated. Simultaneously, magnetic blowout technology utilizes a built-in permanent magnet to generate a magnetic field, guiding the arc to cool and extinguish more quickly. Alternatively, optimizing the connection between the inverter and the grid reduces unnecessary cable lengths, and employing low-inductance switches and connectors reduces the contribution of inductance in the circuit, minimizing back electromotive force and current oscillations at the moment of disconnection, thereby accelerating the reduction of the arc-extinguishing current.

[0162] In other embodiments, to rapidly reduce the arc-extinguishing current, the intelligent control system can pre-trigger the arc-extinguishing device the instant before the grid disconnection. Even if the grid is not completely de-energized, the arc-extinguishing device is already prepared. Once a grid disconnection signal is detected, the arc-extinguishing function is immediately activated, significantly shortening the arc-extinguishing preparation time. By monitoring current changes in the circuit and the status of the arc-extinguishing device, the switching speed is dynamically adjusted to ensure that the circuit is disconnected at the optimal time, avoiding additional arcs or current peaks caused by improper disconnection speed. Alternatively, an arc-extinguishing status monitoring function can be integrated into the control software. Once an arc-extinguishing requirement is detected, the software immediately sends a command to the hardware. After the hardware responds, the software can adjust the inverter's operating state in real time, reducing dependence on the current at the instant of grid disconnection, thereby accelerating the reduction of the arc-extinguishing current.

[0163] In other embodiments, the energy storage converter can switch between grid-connected and off-grid modes based on real-time commands. To ensure a smooth transition during the switch from grid-connected to off-grid operation, the energy storage converter can be started using a soft-switching mechanism.

[0164] Before the PCS switches to off-grid mode, the voltage phase angle at the current load port is acquired via a phase-locked loop (PLL) circuit, and this is used to initialize the inverter's off-grid parameters. Simultaneously, the BMS checks the battery's state of charge to ensure sufficient energy to support the inverter's soft-start process. Once the PCS enters off-grid mode, the inverter's output power is initially set to zero or extremely low to avoid impacting the load and the inverter itself. Employing a soft-start control strategy, the inverter's output power gradually increases according to a predetermined slope or curve. This process can be divided into the following three stages:

[0165] Phase 1, Voltage Pre-charge: The inverter (i.e., energy storage converter) is set to output a small, constant power to charge the filter capacitor of the local load, gradually establishing a voltage that matches the load. The load voltage rise is monitored until a certain percentage (e.g., 90%) of the target voltage is reached.

[0166] Phase Two, Power Ramp-up: Once the voltage pre-charge is complete, the inverter begins to gradually increase its output power according to actual load demand. The power ramp-up rate should be optimized based on system parameters (such as inverter capacity, battery status, and load characteristics) and safety guidelines.

[0167] Phase 3, Full Power Operation: When the inverter output power approaches or reaches the predetermined power in off-grid mode, the control system monitors the stability of the load and the operating status of the inverter. After completing the soft-start process, the inverter enters full power operation and outputs power stably according to load demand.

[0168] During the soft-start process, key parameters such as inverter temperature, battery SOC (state of charge), and load power demand are continuously monitored to ensure that the inverter and battery system operate within safe limits. If any abnormalities are detected, such as inverter overheating or battery SOC falling below the threshold, the control system should immediately adjust the output power or even pause the soft-start process to avoid potential risks.

[0169] The soft-start control algorithm should comprehensively consider the inverter's maximum output capacity, the battery's discharge characteristics, and the load's power requirements. Based on system characteristics and experimental data, optimize parameters such as the power ramp-up rate and voltage pre-charge time during soft start-up to ensure the smoothest possible startup process.

[0170] By adopting a soft-start control strategy, the PCS can gradually and smoothly increase its output power when starting in off-grid mode, effectively avoiding the impact on the load and the inverter itself, and improving the overall stability and safety of the energy storage system.

[0171] According to some embodiments of this application, another aspect of this application provides an energy storage system that operates using any of the above-described off-grid operation methods for energy storage systems, such as... Figure 5 As shown, the energy storage system includes: an off-grid side 01, an energy storage converter 02, a filter 03, and a grid-connected side 04 connected thereto; and a load 05, which is electrically connected to the filter 03 and the grid-connected side 04 respectively.

[0172] Technically, this embodiment provides an energy storage system integrating off-grid operation methods. By optimizing the grid-connected / off-grid switching control strategy, the system's stability and security are improved. In principle, the energy storage converter, filter, and grid-connected side in the energy storage system form a complete power conversion and transmission path through electrical connections. The load is electrically connected to the filter and grid-connected side, enabling it to receive power from the energy storage system. In terms of effectiveness, the technology in this embodiment ensures rapid and stable operation of the inverter in off-grid mode. By optimizing the control strategy, voltage and current surges during switching are avoided, improving system stability and security. In other embodiments, the overall performance of the energy storage system can be further optimized by adding more functional modules, such as an energy management system or a communication module, to address the issue of stable operation in complex grid environments.

[0173] In some embodiments, such as Figure 6 As shown, the energy storage system further includes a grid-connected switch 06, the first end of which is electrically connected to the filter 03 and the load 05 respectively, and the second end of which is electrically connected to the grid-connected side 04.

[0174] Technically, this embodiment achieves safe switching between grid-connected and off-grid modes by adding a grid-connected side switch, avoiding electrical surges during grid restoration. In principle, when a grid-connected power outage occurs, disconnecting the grid-connected side switch prevents current surges during grid restoration, protecting the inverter and load; in grid-connected mode, closing the grid-connected side switch ensures normal connection between the inverter and the grid. Effectively, the technology in this embodiment ensures rapid and stable operation of the inverter in off-grid mode. By adding a grid-connected side switch, it avoids electrical surges during grid restoration, improving system stability and safety. In other embodiments, optimizing the switch control strategy can further enhance switching safety and reliability, addressing the issue of smooth switching during grid fluctuations.

[0175] In some embodiments, the energy storage converter further includes power semiconductor devices.

[0176] Technically, this embodiment achieves high-efficiency energy conversion of the inverter by using power semiconductor devices, thereby improving the system's energy conversion efficiency and stability. In principle, power semiconductor devices, such as IGBTs, can achieve high-efficiency energy conversion of the inverter by controlling their on / off states, meeting the power demands in off-grid mode. In terms of effectiveness, the technology in this embodiment ensures rapid and stable operation of the inverter in off-grid mode. By using power semiconductor devices, it improves the system's energy conversion efficiency and stability, meeting the power demands in off-grid mode. In other embodiments, energy conversion efficiency can be further improved by optimizing the control strategy of the power semiconductor devices, addressing the issue of stable operation under high loads or grid fluctuations.

[0177] In some embodiments, the semiconductor device described above is an insulated gate bipolar transistor.

[0178] Technically, this embodiment achieves high-efficiency energy conversion in the inverter by using an insulated-gate bipolar transistor (IGBT), improving the system's energy conversion efficiency and stability. In principle, the IGBT, as a power semiconductor device, possesses advantages such as high switching speed, low conduction loss, and high reliability. By controlling its on / off state, the inverter's high-efficiency energy conversion can be achieved, meeting the power demands in off-grid mode. In terms of effect, the technology in this embodiment ensures the inverter operates quickly and stably in off-grid mode. By using IGBTs, the system's energy conversion efficiency and stability are improved, meeting the power demands in off-grid mode. In other embodiments, energy conversion efficiency can be further improved by optimizing the IGBT control strategy, addressing the issue of stable operation under high load or grid fluctuations.

[0179] According to some embodiments of this application, another aspect of this application provides an electrical device including any of the above-described energy storage systems.

[0180] Technically, this embodiment provides an electrical device with an integrated and optimized off-grid operation method. By optimizing the grid-connected to off-grid switching control strategy, the stability and safety of the device are improved. In principle, the energy storage system in the electrical device forms a complete power conversion and transmission path through electrical connections, capable of receiving power from the grid or the off-grid side to supply power to the load. In terms of effectiveness, the technology in this embodiment ensures the inverter operates quickly and stably in off-grid mode. By optimizing the control strategy, voltage and current surges during the switching process are avoided, improving the stability and safety of the device. In other embodiments, the overall performance of the electrical device can be further optimized by adding more functional modules, such as an energy management system or a communication module, to solve the problem of stable operation in complex grid environments.

[0181] The technical solution of this application relates to the switching process of an energy storage system between grid-connected and off-grid modes. In grid-connected mode, the inverter is connected to the grid to supply power to the load. When a grid outage occurs, the system first detects the voltage and current on the grid-connected side to determine whether it needs to enter off-grid mode. If the off-grid operation enable command exists, the system will disconnect the grid-connected side switch to avoid current surges when the grid recovers. Then, the inverter stops grid-connected inverter operation, and the system obtains the voltage and current information of the load port through a voltage sampling circuit to initialize the off-grid parameters, including the wave phase angle and starting voltage. After the arc-extinguishing current drops to a safe level, the inverter restarts, starting with the load port voltage amplitude and phase angle, and enters the off-grid operation mode. During this process, the system optimizes the inverter's response speed and stability by adjusting the PI parameters corresponding to the grid-connected to off-grid transition, ensuring stable output voltage and frequency to meet load requirements. In addition, the system is equipped with a relay switch to prevent electrical conflicts between grid-connected and off-grid modes, ensuring the safety of the switching process. The entire switching process, through precise control and intelligent detection, achieved a smooth transition from grid connection to off-grid, improving the stability and safety of the energy storage system and meeting the power needs of electrical equipment when the grid is disconnected.

[0182] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. An off-grid operation method for an energy storage system, the energy storage system comprising an electrically connected load and a filter, characterized in that, The method includes: Determine whether the grid connection of the energy storage system has been lost; In the event of a grid-connected power failure of the energy storage system, the port voltage and port current of the load of the energy storage system at the time of the grid-connected power failure are obtained. The port voltage of the load is the voltage at the end of the load connected to the filter of the energy storage system, and the port current of the load is the current at the end of the load connected to the filter of the energy storage system. The arc extinguishing current of the energy storage system is obtained, and the off-grid power-on time of the energy storage system is determined based on the magnitude of the arc extinguishing current. The arc extinguishing current is the current flowing through the filter. When the off-grid power-on time is reached, off-grid power generation is controlled, and the energy storage system is controlled to operate in off-grid mode based on the port voltage and port current of the load.

2. The off-grid operation method of the energy storage system according to claim 1, characterized in that, Determining whether the off-grid power-on time of the energy storage system has been reached based on the magnitude of the arc-extinguishing current includes: Determine whether the arc-extinguishing current is less than or equal to the preset current; When the arc extinguishing current is less than or equal to the preset current, the off-grid power-on time of the energy storage system is determined. If the arc extinguishing current is greater than the preset current, it is determined that the off-grid power-on time of the energy storage system has not been reached.

3. The off-grid operation method of the energy storage system according to claim 1, characterized in that, The energy storage system includes an energy storage converter, which includes power semiconductor devices. The system is controlled to operate in off-grid mode based on the port voltage and port current of the load, including: Using the port voltage and port current of the load as initial values, proportional-integral calculations are performed to obtain the control signal parameters of the semiconductor devices in the energy storage converter; A control signal is generated based on the control signal parameters, wherein the control signal parameters include the duty cycle of the control signal that controls the semiconductor device to be turned on or off; The control signal is used to control the semiconductor device to turn on or off, so as to control the energy storage system to operate in the off-grid operation mode.

4. The off-grid operation method of the energy storage system according to claim 3, characterized in that, Using the port voltage and port current of the load as initial values, proportional-integral calculations are performed to obtain the control signal parameters of the semiconductor devices in the energy storage converter, including: Obtain the amplitude and phase angle of the port voltage of the load at the time of the grid-connected power failure, and obtain the voltage amplitude and voltage phase angle; Obtain the amplitude and phase angle of the port voltage of the load at the time of grid power failure, and obtain the current amplitude and current phase angle; The control signal parameters of the semiconductor device in the energy storage converter are obtained by proportional-integral calculation based on the voltage amplitude, voltage phase angle, current amplitude, and current phase angle.

5. The off-grid operation method of the energy storage system according to claim 4, characterized in that, Based on the voltage amplitude, voltage phase angle, current amplitude, and current phase angle, proportional-integral calculations are performed to obtain the control signal parameters of the semiconductor devices in the energy storage converter, including: Based on the voltage amplitude, voltage phase angle, current amplitude, and current phase angle, coordinate transformation and positive / negative sequence separation are performed on the port voltage and port current of the load to obtain positive-sequence data and negative-sequence data. The positive-sequence data includes positive-sequence voltage and positive-sequence current, and the negative-sequence data includes negative-sequence voltage and negative-sequence current. A first calculated voltage is obtained by performing proportional-integral decoupling calculation based on the positive-sequence data, and a second calculated voltage is obtained by performing proportional-integral decoupling calculation based on the negative-sequence data. Based on the first calculated voltage and the second calculated voltage, the control signal parameters of the semiconductor device in the energy storage converter are determined.

6. The off-grid operation method of the energy storage system according to claim 5, characterized in that, Based on the voltage amplitude, voltage phase angle, current amplitude, and current phase angle, coordinate transformation and positive / negative sequence separation are performed on the port voltage and port current of the load to obtain positive-sequence data and negative-sequence data, including: Based on the voltage amplitude, voltage phase angle, current amplitude, and current phase angle, the port voltage and port current of the load are converted from three-phase stationary coordinates to two-phase stationary coordinates to obtain the initial conversion voltage and initial conversion current. Determine the coordinate transformation angle based on the off-grid phase-locked loop; Based on the coordinate transformation angle, the initial conversion voltage and the initial conversion current are converted from the two-phase stationary coordinates to the two-phase rotating coordinates and the positive and negative sequence separation process is performed to obtain the positive sequence data and the negative sequence data.

7. The off-grid operation method of the energy storage system according to claim 6, characterized in that, The coordinate transformation angle includes a positive angle and a negative angle. Based on the coordinate transformation angle, the initial conversion voltage and the initial conversion current are converted from the two-phase stationary coordinates to the two-phase rotating coordinates and the positive and negative sequence separation process is performed to obtain the positive sequence data and the negative sequence data, including: Based on the positive angle, the initial conversion voltage and the initial conversion current are converted from the two-phase stationary coordinates to the two-phase rotating coordinates and the positive and negative sequence separation process is performed to obtain the positive sequence data. The positive sequence data includes a first positive sequence voltage, a second positive sequence voltage, a first positive sequence current, and a second positive sequence current. The first positive sequence voltage is the positive sequence voltage of the first coordinate axis of the two-phase rotating coordinates, the second positive sequence voltage is the positive sequence voltage of the second coordinate axis of the two-phase rotating coordinates, the first positive sequence current is the positive sequence current of the first coordinate axis of the two-phase rotating coordinates, and the second positive sequence current is the positive sequence current of the second coordinate axis of the two-phase rotating coordinates. Based on the negative angle, the initial conversion voltage and the initial conversion current are converted from the two-phase stationary coordinates to the two-phase rotating coordinates and the positive and negative sequence separation process is performed to obtain the negative sequence data. The negative sequence data includes a first negative sequence voltage, a second negative sequence voltage, a first negative sequence current, and a second negative sequence current. The first negative sequence voltage is the negative sequence voltage of the first coordinate axis of the two-phase rotating coordinates, the second negative sequence voltage is the negative sequence voltage of the second coordinate axis of the two-phase rotating coordinates, the first negative sequence current is the negative sequence current of the first coordinate axis of the two-phase rotating coordinates, and the second negative sequence current is the negative sequence current of the second coordinate axis of the two-phase rotating coordinates.

8. The off-grid operation method of the energy storage system according to claim 5, characterized in that, Based on the positive-sequence data, a proportional-integral decoupled calculation is performed to obtain a first calculated voltage, and based on the negative-sequence data, a proportional-integral decoupled calculation is performed to obtain a second calculated voltage, including: Obtain the first positive sequence setting voltage, the second positive sequence setting voltage, the first negative sequence setting voltage, and the second negative sequence setting voltage; Based on the first positive sequence setting voltage, the second positive sequence setting voltage, and the positive sequence voltage, the proportional-integral decoupling calculation is performed to obtain the first positive sequence calculated current and the second positive sequence calculated current. Based on the first negative sequence setting voltage, the second negative sequence setting voltage, and the negative sequence voltage, the proportional-integral decoupling calculation is performed to obtain the first negative sequence calculated current and the second negative sequence calculated current. The first calculated voltage is determined based on the first positive-sequence calculated current and the second positive-sequence calculated current, and the second calculated voltage is determined based on the first negative-sequence calculated current and the second negative-sequence calculated current.

9. The off-grid operation method of the energy storage system according to claim 8, characterized in that, The calculation of the first calculated voltage is determined based on the first positive-sequence calculated current and the second positive-sequence calculated current, and the calculation of the second calculated voltage is determined based on the first negative-sequence calculated current and the second negative-sequence calculated current, including: Based on the first positive sequence calculated current and the second positive sequence calculated current, the proportional-integral decoupling calculation is performed to obtain the first calculated voltage. The first calculated voltage includes a first sub-voltage and a second sub-voltage. The first sub-voltage is the positive sequence voltage of the first coordinate axis of the two-phase rotating coordinate system, and the second sub-voltage is the positive sequence voltage of the second coordinate axis of the two-phase rotating coordinate system. Based on the first negative sequence calculated current and the second negative sequence calculated current, the proportional-integral decoupling calculation is performed to obtain the second calculated voltage. The second calculated voltage includes a third sub-voltage and a fourth sub-voltage. The third sub-voltage is the negative sequence voltage of the first coordinate axis of the two-phase rotating coordinate system, and the fourth sub-voltage is the negative sequence voltage of the second coordinate axis of the two-phase rotating coordinate system.

10. The off-grid operation method of the energy storage system according to claim 5, characterized in that, Based on the first calculated voltage and the second calculated voltage, the control signal parameters of the semiconductor devices in the energy storage converter are determined, including: Based on the first calculated voltage and the second calculated voltage, the energy storage converter is controlled to perform pulse width modulation waveform calculation to obtain the control signal parameters of the semiconductor device in the energy storage converter.

11. The off-grid operation method of the energy storage system according to any one of claims 1 to 10, characterized in that, The method further includes: In the event of a grid-connected power failure in the energy storage system, the grid-connected switch, which is connected between the grid and the filter, is disconnected.

12. The off-grid operation method of the energy storage system according to any one of claims 1 to 10, characterized in that, In the event of a grid-connected power outage of the energy storage system, the port voltage and port current of the load of the energy storage system at the time of the grid-connected power outage are obtained, including: In the event of a grid-connected power failure of the energy storage system, determine whether an off-grid operation enable command exists; When the off-grid operation enable command is present, the port voltage and port current of the load of the energy storage system are obtained at the time of grid-connected power failure, and the energy storage converter in the energy storage system is controlled to stop inverting. If the off-grid operation enable command is not available, the energy storage system is shut down.

13. An energy storage system, characterized in that, The energy storage system is operated using the off-grid operation method according to any one of claims 1 to 12, wherein the energy storage system comprises: The off-grid side, energy storage converter, filter, and grid-connected side are connected accordingly. The load is electrically connected to the filter and the grid-connected side, respectively.

14. The energy storage system according to claim 13, characterized in that, Also includes: A grid-connected switch, wherein the first terminal of the grid-connected switch is electrically connected to the filter and the load respectively, and the second terminal of the grid-connected switch is electrically connected to the grid side.

15. The energy storage system according to claim 13, characterized in that, The energy storage converter also includes power semiconductor devices.

16. The energy storage system according to claim 15, characterized in that, The semiconductor device is an insulated gate bipolar transistor.

17. An electrical appliance, characterized in that, Includes the energy storage system described in any one of claims 13 to 16.

Images