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

Abstract

The embodiment of the application 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 an electric equipment, the operation method comprises the following steps: determining whether the grid connection of the energy storage system is powered off; in the case that the grid connection of the energy storage system is powered off, acquiring the port voltage and the port current of a load of the energy storage system at the grid connection power-off moment, the port voltage of the load being the voltage of one end of the load connected with a filter of the energy storage system, and the port current of the load being the current of one end of the load connected with the filter of the energy storage system; acquiring an arc extinguishing current of the energy storage system, and determining whether the off-grid power-on moment of the energy storage system is reached according to the size of the arc extinguishing current, the arc extinguishing current being the current flowing through the filter; in the case that the off-grid power-on moment is reached, controlling off-grid power generation, and controlling the energy storage system 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 size of the arc extinguishing current, so that the impact caused by direct starting is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage, and in particular to an off-grid operation method of an energy storage system, the energy storage system, and an electrical equipment. BACKGROUND

[0002] In the prior art, a power conversion system (PCS) is a key component of an energy storage system, which is mainly responsible for converting direct current of a battery into alternating current to supply a power grid or a local load, or vice versa. Switching of the PCS between grid-connected and off-grid modes is an important part of operation of the energy storage system, and smoothness and safety of the switching are crucial, especially when the power grid fails or needs to be actively switched to the off-grid mode.

[0003] In the grid-connected switching off-grid control strategy of the power conversion system, when the power grid is disconnected or a switching instruction is issued, the control mode of the PCS needs to be converted from current source control (grid-connected mode) to voltage source control (off-grid mode). However, the prior art cannot guarantee continuity of output voltage and frequency in the grid-connected to off-grid process, and there are significant transient impact problems and poor control parameter adaptability. SUMMARY

[0004] Embodiments of the present application provide an off-grid operation method of an energy storage system, the energy storage system, and an electrical equipment, at least for solving the problem that the prior art cannot guarantee continuity of output voltage and frequency in the grid-connected to off-grid process, and there are significant transient impact problems and poor control parameter adaptability.

[0005] According to some embodiments of the present application, an off-grid operation method of an energy storage system is provided in an aspect of the embodiments of the present application, the energy storage system comprising a load and a filter connected electrically, and the method comprising: determining whether a grid-connected power supply of the energy storage system is disconnected; in the case that the grid-connected power supply of the energy storage system is disconnected, acquiring a port voltage and a port current of the load of the energy storage system at a grid-connected disconnection time, the port voltage of the load being a voltage of one end of the load connected with the filter of the energy storage system, and the port current of the load being a current of one end of the load connected with the filter of the energy storage system; acquiring an arc extinguishing current of the energy storage system, and determining whether an off-grid power supply time of the energy storage system is reached according to a size of the arc extinguishing current, the arc extinguishing current being a current flowing through the filter; in the case that the off-grid power supply time of the energy storage system is reached, controlling off-grid power generation, and controlling the energy storage system to operate in an off-grid operation mode based on the port voltage and the port current of the load.

[0006] In some embodiments, determining whether the off-grid online time of the energy storage system is reached according to the magnitude of the arc extinguishing current comprises: determining whether the arc extinguishing current is less than or equal to a preset current; determining that the off-grid online time of the energy storage system is reached when the arc extinguishing current is less than or equal to the preset current; and determining that the off-grid online time of the energy storage system is not reached when the arc extinguishing current is greater than the preset current.

[0007] In some embodiments, the energy storage system comprises an energy storage converter, the energy storage converter comprises power semiconductor devices, 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, which comprises: taking the port voltage and the port current of the load as initial values, performing proportional integral calculation to obtain control signal parameters of the semiconductor devices in the energy storage converter; generating a control signal according to the control signal parameters, the control signal parameters comprising a duty cycle of the control signal for controlling the semiconductor devices to turn on or off; and controlling the semiconductor devices to turn on or off using the control signal to control the energy storage system to operate in the off-grid operation mode.

[0008] In some embodiments, taking the port voltage and the port current of the load as initial values, performing proportional integral calculation to obtain control signal parameters of the semiconductor devices in the energy storage converter comprises: obtaining the amplitude and phase angle of the port voltage of the load at the grid-connected power-off time to obtain a voltage amplitude and a voltage phase angle; obtaining the amplitude and phase angle of the port voltage of the load at the grid-connected power-off time to obtain a current amplitude and a current phase angle; and performing proportional integral calculation according to the voltage amplitude, the voltage phase angle, the current amplitude, and the current phase angle to obtain the control signal parameters of the semiconductor devices in the energy storage converter.

[0009] In some embodiments, performing proportional integral calculation according to the voltage amplitude, the voltage phase angle, the current amplitude, and the current phase angle to obtain the control signal parameters of the semiconductor devices in the energy storage converter comprises: performing coordinate conversion and positive and negative sequence separation processing on the port voltage and the port current of the load according to the voltage amplitude, the voltage phase angle, the current amplitude, and the current phase angle to obtain positive sequence data and negative sequence data, the positive sequence data comprising a positive sequence voltage and a positive sequence current, and the negative sequence data comprising a negative sequence voltage and a negative sequence current; performing proportional integral decoupling calculation according to the positive sequence data to obtain a first calculation voltage, and performing proportional integral decoupling calculation according to the negative sequence data to obtain a second calculation voltage; and determining the control signal parameters of the semiconductor devices in the energy storage converter according to the first calculation voltage and the second calculation voltage.

[0010] In some embodiments, the coordinate conversion and positive and negative sequence separation processing of the port voltage and the port current of the load according to the voltage amplitude, the voltage phase angle, the current amplitude and the current phase angle to obtain positive sequence data and negative sequence data comprises: converting the port voltage and the port current of the load from three-phase static coordinates to two-phase static coordinates according to the voltage amplitude, the voltage phase angle, the current amplitude and the current phase angle to obtain initial converted voltage and initial converted current; determining a coordinate conversion angle based on an off-grid phase-locked loop; converting the initial converted voltage and the initial converted current from the two-phase static coordinates to two-phase rotating coordinates based on the coordinate conversion angle and performing the positive and negative sequence separation processing to obtain the positive sequence data and the negative sequence data.

[0011] In some embodiments, the coordinate conversion angle comprises a positive direction angle and a negative direction angle, and the converting the initial converted voltage and the initial converted current from the two-phase static coordinates to two-phase rotating coordinates based on the coordinate conversion angle and performing the positive and negative sequence separation processing to obtain the positive sequence data and the negative sequence data comprises: converting the initial converted voltage and the initial converted current from the two-phase static coordinates to two-phase rotating coordinates based on the positive direction angle and performing the positive and negative sequence separation processing to obtain the positive sequence data, the positive sequence data comprising 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 being a positive sequence voltage of a first coordinate axis of the two-phase rotating coordinates, the second positive sequence voltage being a positive sequence voltage of a second coordinate axis of the two-phase rotating coordinates, the first positive sequence current being a positive sequence current of the first coordinate axis of the two-phase rotating coordinates, and the second positive sequence current being a positive sequence current of the second coordinate axis of the two-phase rotating coordinates; converting the initial converted voltage and the initial converted current from the two-phase static coordinates to two-phase rotating coordinates based on the negative direction angle and performing the positive and negative sequence separation processing to obtain the negative sequence data, the negative sequence data comprising 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 being a negative sequence voltage of the first coordinate axis of the two-phase rotating coordinates, the second negative sequence voltage being a negative sequence voltage of the second coordinate axis of the two-phase rotating coordinates, the first negative sequence current being a negative sequence current of the first coordinate axis of the two-phase rotating coordinates, and the second negative sequence current being a negative sequence current of the second coordinate axis of the two-phase rotating coordinates.

[0012] In some embodiments, the proportional-integral decoupling calculation according to the positive sequence data to obtain a first calculation voltage and the proportional-integral decoupling calculation according to the negative sequence data to obtain a second calculation voltage comprises: obtaining a first positive sequence setting voltage, a second positive sequence setting voltage, a first negative sequence setting voltage and a second negative sequence setting voltage; performing the proportional-integral decoupling calculation according to the first positive sequence setting voltage, the second positive sequence setting voltage and the positive sequence voltage to obtain a first positive sequence calculation current and a second positive sequence calculation current, and performing the proportional-integral decoupling calculation according to the first negative sequence setting voltage, the second negative sequence setting voltage and the negative sequence voltage to obtain a first negative sequence calculation current and a second negative sequence calculation current; determining the first calculation voltage according to the first positive sequence calculation current and the second positive sequence calculation current, and determining the second calculation voltage according to the first negative sequence calculation current and the second negative sequence calculation current.

[0013] In some embodiments, the proportional-integral decoupling calculation according to the first positive sequence calculation current and the second positive sequence calculation current to obtain the first calculation voltage and the proportional-integral decoupling calculation according to the first negative sequence calculation current and the second negative sequence calculation current to obtain the second calculation voltage comprises: performing the proportional-integral decoupling calculation according to the first positive sequence calculation current and the second positive sequence calculation current to obtain the first calculation voltage, the first calculation voltage comprising a first sub-voltage and a second sub-voltage, the first sub-voltage being a positive sequence voltage of a first coordinate axis of a two-phase rotating coordinate, and the second sub-voltage being a positive sequence voltage of a second coordinate axis of the two-phase rotating coordinate; and performing the proportional-integral decoupling calculation according to the first negative sequence calculation current and the second negative sequence calculation current to obtain the second calculation voltage, the second calculation voltage comprising a third sub-voltage and a fourth sub-voltage, the third sub-voltage being a negative sequence voltage of the first coordinate axis of the two-phase rotating coordinate, and the fourth sub-voltage being a negative sequence voltage of the second coordinate axis of the two-phase rotating coordinate.

[0014] In some embodiments, the determination of the control signal parameter of the semiconductor device in the energy storage converter according to the first calculation voltage and the second calculation voltage comprises: controlling the energy storage converter to perform a pulse width modulation calculation according to the first calculation voltage and the second calculation voltage to obtain the control signal parameter of the semiconductor device in the energy storage converter.

[0015] In some embodiments, the method further comprises: in the case of grid-connected power-off of the energy storage system, disconnecting a grid-connected side switch connected between the grid and the filter.

[0016] In some embodiments, in the case of grid-connected power-off of the energy storage system, the port voltage and the port current of the load of the energy storage system at the grid-connected power-off moment are acquired, comprising: in the case of grid-connected power-off of the energy storage system, determining whether an off-grid operation enabling instruction exists; in the case that the off-grid operation enabling instruction exists, acquiring the port voltage and the port current of the load of the energy storage system at the grid-connected power-off moment, and controlling the energy storage converter in the energy storage system to stop inverting; in the case that the off-grid operation enabling instruction does not exist, controlling the energy storage system to shut down.

[0017] According to some embodiments of the present application, another aspect of the embodiments of the present application provides an energy storage system, which is applied to any one of the off-grid operation methods of the energy storage system, and the energy storage system comprises: an off-grid side, an energy storage converter, a filter and a grid-connected side connected in sequence; and a load, which is electrically connected with the filter and the grid-connected side respectively.

[0018] In some embodiments, further comprising: a grid-connected side switch, a first end of the grid-connected side switch being electrically connected with the filter and the load respectively, and a second end of the grid-connected side switch being electrically connected with the grid-connected side.

[0019] In some embodiments, the energy storage converter further comprises a power semiconductor device.

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

[0021] According to some embodiments of the present application, another aspect of the embodiments of the present application provides a power utilization device, which comprises any one of the energy storage systems.

[0022] The technical solutions provided by the embodiments of the present application have at least the following advantages: considering the problem of arc extinguishing current, whether to start off-grid operation is determined according to the size of the arc extinguishing current, so as to avoid the impact caused by direct starting. The sampling circuit is used to realize the collection of the port voltage of the load, and the information is used to initialize the off-grid parameters, so as to avoid the impact caused by direct off-grid operation; the PI parameters corresponding to the grid-connected to off-grid operation are adjusted, the smooth grid-connected to off-grid operation is realized, and the problems that the continuity of the output voltage and frequency cannot be guaranteed in the grid-connected to off-grid operation process in the prior art, and there are significant transient impact and poor adaptability of control parameters are solved. BRIEF DESCRIPTION OF DRAWINGS

[0023] One or more embodiments are illustrated by way of example in the figures that form a part of this disclosure and which are shown by way of illustration in the accompanying drawings and are not intended to limit the scope of the embodiments unless otherwise specifically indicated, the figures do not constitute a limiting factor in terms of proportion; in order to more clearly illustrate the technical solutions in the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly introduced below, obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0024] Figure 1 A flowchart of a method for off-grid operation of an energy storage system is shown according to an embodiment of the present application;

[0025] Figure 2 A PI algorithm flowchart of off-grid operation of an energy storage system is shown according to an embodiment of the present application;

[0026] Figure 3 A flowchart of another method for off-grid operation of an energy storage system is shown according to an embodiment of the present application;

[0027] Figure 4 An effect diagram of a method for off-grid operation of an energy storage system is shown according to an embodiment of the present application;

[0028] Figure 5 A structural diagram of an energy storage system is shown according to an embodiment of the present application;

[0029] Figure 6 Another structural diagram of an energy storage system is shown according to an embodiment of the present application.

[0030] Among the above drawings, the following reference signs are included:

[0031] 01, off-grid side; 02, energy storage converter; 03, filter; 04, grid-connected side; 05, load; 06, grid-connected side switch. DETAILED DESCRIPTION

[0032] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0033] Reference to“an embodiment” herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase“in an embodiment” in various places in the specification are not necessarily referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. As will be apparent to those of ordinary skill in the art, embodiments described herein can be combined with other embodiments in accordance with the application.

[0034] In the description of the embodiments of the application, the term“and / or” only means an association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can mean that A exists, A and B exist, and B exists. In addition, the character“ / ” herein generally means that the front and rear associated objects are in an“or” relationship.

[0035] In the description of the embodiments of the application, the term“a plurality of” refers to two or more (including two), and similarly, “a plurality of groups” refers to two or more groups (including two groups), and “a plurality of pieces” refers to two or more pieces (including two pieces).

[0036] In the description of the embodiments of the application, the technical terms“center”,“longitudinal”,“transverse”,“length”,“width”,“thickness”,“upper”,“lower”,“front”,“rear”,“left”,“right”,“vertical”,“horizontal”,“top”,“bottom”,“inner”,“outer”,“clockwise”,“counterclockwise”,“axial”,“radial”,“circumferential” and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the embodiments of the application.

[0037] In the description of the embodiments of the application, unless otherwise explicitly specified and limited, the technical terms“mounting”,“connection”,“connection”,“fixing” and the like should be understood broadly, for example, can be fixedly connected, or can be detachably connected, or can be integrated; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the embodiments of the application can be understood according to the specific circumstances.

[0038] In the drawings corresponding to the embodiments of the present application, the thickness and area of a layer are exaggerated for clarity and ease of description. When it is described that a component (such as a layer, a film, a region, or a substrate) is "on" or "at" another component, the component can be "directly" on the surface of the other component, or a third component can be present between the two components. Conversely, when it is described that a component is "on" the surface of another component, or a component forms or is provided on the surface of another component, it means that there is no third component between the two components. In addition, when it is described that a component is "formed substantially 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 partial edge of the entire surface.

[0039] In the description of the embodiments of the present application, when a certain component "includes" another component, unless otherwise specified, other components can also be included, and other components can also be further included. In addition, when a layer, a film, a region, or a plate, and the like, are referred to as "on / over" another component, it can be "directly on" another component (i.e., between the surface of another component and another component, there is no other component), or another component can be present therebetween. In addition, when a layer, a film, a region, a plate, and the like, are "directly on" another component, or when a layer, a film, a region, a plate, and the like, are on the surface of another component, it means that there is no other component therebetween.

[0040] The terms used in the description of various described embodiments herein are only used to describe specific embodiments, and are not intended to be limiting. As used in the description of various described embodiments and the appended claims, "the part" is also intended to include the plural, unless the context clearly indicates otherwise. Among them, the components include layers, films, regions, or plates, and the like.

[0041] The embodiments of the present application will be described in detail below with reference to the accompanying drawings. However, those of ordinary skill in the art can understand that in the embodiments of the present application, many technical details are presented in order to enable the reader to better understand the present application. However, the technical solutions claimed by the present application can be implemented even without these technical details and various changes and modifications based on the following embodiments.

[0042] As introduced in the background, in the traditional grid-connected energy storage system, the energy storage converter (PCS) is usually used as the core device for energy conversion, which is responsible for converting the direct current of the battery into alternating current, and then supplying it to the power grid or local load. This grid-connected operation mode can guarantee efficient energy management and stable power transmission in most cases and scenarios. However, when the power grid fails or is unexpectedly powered off, the PCS needs to quickly switch to an off-grid mode to avoid system stoppage and ensure continuous power supply to the local load.

[0043] The existing PCS grid-connected and off-grid switching technology mainly includes the following implementation methods: direct switching method: once the power grid failure is detected, immediately stop and switch to off-grid state. Although this method reacts quickly, there may be a significant difference between the voltage and the grid voltage before the power failure in the switching moment, resulting in instantaneous voltage fluctuation, which may impact the local load and the PCS itself, and even cause equipment damage in severe cases. Pre-charge switching method: after power failure, the filter capacitor of the PCS is charged through the pre-charge circuit, so that its voltage gradually approaches the voltage of the power grid before power failure, and then the inverter is started to enter the off-grid mode. This method can reduce the switching impact to some extent, but it increases the switching delay time, which may not meet the requirements of some applications with high requirements for power continuity, such as hospital operating rooms, data centers, etc. Software control method: use software algorithm to predict the voltage trend after power failure, and try to adjust the output parameters of the inverter to smooth the transition, but this method is limited by the accuracy and response speed of the algorithm, and it is difficult to adjust in real time at the moment of power failure.

[0044] The main problem faced by the above existing technology in actual application is the poor consistency of voltage phase and amplitude in the switching moment, which leads to a large difference between the output voltage of the inverter and the grid voltage at the time of switching. This difference not only directly affects the normal operation of the local load, but also may cause the internal devices of the inverter to be impacted, reducing the system reliability and life.

[0045] Specifically, after the power grid is disconnected, the inverter restarts and cannot guarantee the consistency of the output voltage and the grid voltage phase and amplitude at the moment of power failure, resulting in voltage jump, which further impacts the PCS and the local load connected thereto. Especially in the presence of filter capacitors and local loads, the impact of voltage jump is more significant, which may cause damage to the equipment or instability of the system, reducing the overall performance and user experience of the energy storage system.

[0046] In summary, the existing PCS grid-connected and off-grid switching technology has defects such as large voltage fluctuation in the switching moment, high potential impact risk, and difficulty in real-time response in high reliability demand scenarios when dealing with abnormal power grid conditions.

[0047] To solve the problem that the existing technology cannot guarantee the continuity of output voltage and frequency during grid-connected to off-grid switching, and there is a significant transient impact and poor control parameter adaptability, embodiments of the present application provide an off-grid running method of an energy storage system, an energy storage system and an electrical equipment.

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

[0049] Embodiments of the present application provide a method for off-grid operation of an energy storage system, the energy storage system comprising a load and a filter connected electrically, as shown in Figure 1 The method comprises the following steps:

[0050] Step S101, determining whether the grid of the energy storage system is powered off;

[0051] Step S102, in the case that the grid of the energy storage system is powered off, acquiring the port voltage and the port current of the load of the energy storage system at the grid power-off moment, the port voltage of the load being the voltage at one end of the load connected to the filter of the energy storage system, and the port current of the load being the current at one end of the load connected to the filter of the energy storage system;

[0052] Step S103, acquiring the arc extinguishing current of the energy storage system, and determining whether the off-grid power-on moment of the energy storage system is reached according to the size of the arc extinguishing current, the arc extinguishing current being the current flowing through the filter;

[0053] Step S104, in the case that the off-grid power-on moment is reached, controlling off-grid power generation, and controlling the energy storage system to operate in an off-grid operation mode based on the port voltage and the port current of the load.

[0054] When the grid power of the energy storage system is suddenly powered off, directly switching to the off-grid mode may cause a sudden change in current and voltage, causing an impact on the system, and even damaging the inverter and other equipment. Through steps S102 and S103, this method can accurately grasp the instantaneous state of grid power-off, and monitor the arc extinguishing current, ensuring that off-grid power generation is started only after the arc extinguishing current drops to a safe level. This can avoid damage to equipment caused by instantaneous high current, and ensure smooth transition of the system from grid to off-grid mode.

[0055] Step S101 detects the grid power-off event in time, and step S104 controls the energy storage system to enter the off-grid mode immediately when the conditions are met. This method reduces switching delay by monitoring in real time and switching quickly at the appropriate time, so that the energy storage system can provide stable power supply for local loads more quickly, improving the response speed and reliability of the system.

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

[0057] By acquiring the real-time information of the port voltage and port current of the load and the arc extinguishing current, the control method can more finely adjust the operating parameters of the energy storage system, such as voltage output, frequency, phase, etc., which is crucial for improving the overall efficiency of the system in off-grid mode. In addition, reasonable parameter adjustment can prolong the service life of the equipment and reduce maintenance costs.

[0058] In summary, this method realizes seamless switching of the energy storage system from grid-connected to off-grid mode through a series of precise steps, not only improving the stability of the system, but also optimizing the power output, providing a strong guarantee for the continuous operation of the load. Technically, this embodiment realizes precise control of the grid-connected to off-grid switching process by detecting the grid-connected state and the voltage and current of the load port, avoiding voltage and current impact caused by direct switching. In principle, real-time monitoring of the load port voltage using a voltage sampling circuit ensures that the voltage phase and amplitude during off-grid operation are consistent with the grid state before switching, thus smoothly transitioning. In terms of effect, the technology in this embodiment can ensure that the inverter operates stably and quickly in off-grid mode, avoiding impact on the local load and the inverter, improving the stability and safety of the system. In other embodiments, a voltage and current prediction algorithm can be added to further optimize the switching process and solve the problem of smooth switching during grid fluctuations.

[0059] The above-mentioned off-grid operation method of the energy storage system of the present application takes into account the problem of arc extinguishing current, determines whether to start off-grid according to the size of the arc extinguishing current, thereby avoiding the impact caused by direct start. And through the sampling circuit to realize the collection of the load power supply port voltage, and initialize this information to off-grid parameters, avoid the impact caused by direct off-grid operation; adjust the PI parameters corresponding to the grid-connected to off-grid conversion, realize the smooth grid-connected to off-grid conversion, solve the problem that the existing technology cannot guarantee the continuity of output voltage and frequency during grid-connected to off-grid conversion, and there is significant transient impact and poor control parameter adaptability.

[0060] In some embodiments, determining whether the off-grid power-up time of the energy storage system is reached according to the size of the above-mentioned arc extinguishing current includes the following steps:

[0061] Step S1031, determining whether the above-mentioned arc extinguishing current is less than or equal to the preset current;

[0062] Step S1032, in the case where the above-mentioned arc extinguishing current is less than or equal to the above-mentioned preset current, determining that the off-grid power-up time of the energy storage system is reached;

[0063] Step S1033, in the case where the above-mentioned arc extinguishing current is greater than the above-mentioned preset current, determining that the off-grid power-up time of the energy storage system is not reached.

[0064] In power systems, the control of arc extinction current is crucial for ensuring the safe shutdown and restart of electrical equipment. Step S1031 sets a pre-set current threshold to ensure that the energy storage system only starts the off-grid mode when the arc extinction current drops to a sufficiently low level. This effectively avoids potential risks such as over-voltage and over-current shock that may occur during sudden mode switching under high current conditions, thereby improving the safety and reliability of system operation.

[0065] High arc extinction current can cause accelerated wear and tear of electrical equipment such as switches, contactors, etc., and even cause failure. Through steps S1032 and S1033, this method allows the off-grid mode to be started only when the arc extinction current drops to a safe range, thereby reducing the electrical stress on the equipment, prolonging the service life of the equipment, and reducing maintenance and replacement costs.

[0066] The size of the arc extinction current directly affects the ability of the energy storage system to smoothly switch from grid-connected mode to off-grid mode. By monitoring in real time and based on the pre-set current threshold to determine whether the appropriate off-grid power-up time has been reached, this control strategy can more accurately grasp the switching opportunity, avoid unnecessary delays, and ensure the smoothness and efficiency of the switching process.

[0067] Reducing switching delays and shocks caused by arc extinction current helps to improve the overall performance of the energy storage system, especially for applications that require high continuity and quality of power supply (such as hospitals, data centers, etc.). This optimization measure not only enhances the stability and controllability of the system, but also further improves user satisfaction and reliability.

[0068] In summary, by monitoring the arc extinction current and determining the off-grid power-up time of the energy storage system based on the pre-set threshold, the safety, reliability and performance of the system during the grid-connected to off-grid mode switching process can be significantly improved. Technically, this embodiment monitors the arc extinction current to ensure that the off-grid operation is started only when the current drops to a safe level, avoiding the risk of equipment damage due to excessive current. In principle, the monitoring and control of arc extinction current is based on the current change after the grid-connected switch is turned off, and a threshold is set to determine whether the off-grid mode can be safely started. In terms of effect, the technology in this embodiment can effectively prevent damage to the inverter or load caused by excessive current during the switching process, ensuring safe startup of the system in off-grid mode. In other embodiments, the threshold of the pre-set current can be dynamically adjusted to optimize the timing of off-grid startup according to different load conditions and grid environments, solving the problem of safe switching under different working conditions.

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

[0070] Step S201, the above-mentioned load port voltage and port current as the initial value, proportional integral calculation, get the control signal parameters of the above-mentioned semiconductor device in the above-mentioned energy storage converter;

[0071] Step S202, according to the control signal parameters to generate control signal, the control signal parameters include control the duty cycle of the control signal of the semiconductor device conduction or off;

[0072] Step S203, using the control signal to control the semiconductor device conduction or off, to control the energy storage system above the off-grid operation mode operation.

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

[0074] The control signal generated by step S202, especially the duty cycle parameter in it, can very flexibly control the conduction time of the semiconductor device, which provides a powerful tool for power management of the energy storage system. In off-grid mode, accurate control of power semiconductor devices helps to achieve maximum energy utilization efficiency, while reducing unnecessary power consumption and heat loss, improving the overall energy efficiency of the system.

[0075] Based on the dynamic adjustment of control signal parameters based on load state, smooth transition between grid-connected and off-grid modes can be achieved, avoiding system oscillation and instability that may be caused by hard switching. This is crucial for protecting internal components of the energy storage system, such as capacitors, transformers, etc., and ensuring that external loads are not affected.

[0076] The ability to quickly generate and execute control signals enables the energy storage system to respond quickly after detecting grid power failure, reducing the delay time from detection to response. This is extremely important for situations that require immediate power supply, such as industrial production lines, emergency power systems, etc., ensuring that the off-grid mode can be switched to seamlessly in the event of a power grid failure, providing uninterrupted power support.

[0077] Stable and efficient power supply is one of the key factors to ensure user satisfaction. By precisely controlling power semiconductor devices, the energy storage system can continuously provide high-quality electric energy in off-grid mode, so that users can enjoy almost imperceptible power service even in the event of a power grid failure, greatly improving user experience.

[0078] In summary, this control strategy improves the efficiency and reliability of the energy storage system through fine power management, fast response mode switching, and smooth voltage and current control, while ensuring the continuity and quality of power supply. Technically, the embodiment uses a proportional-integral (PI) controller to accurately control the power semiconductor devices of the energy storage converter, ensuring stable output of the inverter in off-grid mode. In principle, based on the voltage and current at the load port, PI calculation is performed to adjust the conduction time of the semiconductor devices, i.e., the duty cycle, to maintain the stability of the output voltage and frequency. In terms of effect, the technology in this embodiment can ensure that the inverter quickly responds and operates stably in off-grid mode, avoiding voltage or frequency fluctuations caused by improper control, and improving the power quality of the system. In other embodiments, fuzzy control or adaptive control algorithms can be introduced to further optimize the generation of control signals, solving the problem of stable control under complex load and grid environment.

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

[0080] Step S2011, obtaining the amplitude and phase angle of the port voltage of the load at the grid-connected power-off moment to obtain the voltage amplitude and voltage phase angle;

[0081] Step S2012, obtaining the amplitude and phase angle of the port voltage of the load at the grid-connected power-off moment to obtain the current amplitude and current phase angle;

[0082] Step S2013, performing proportional-integral calculation based on the voltage amplitude, voltage phase angle, current amplitude, and current phase angle to obtain the control signal parameters of the above-mentioned semiconductor devices in the above-mentioned energy storage converter.

[0083] Specifically, in steps S2011 and S2012, the voltage amplitude, phase angle, current amplitude, and phase angle of the load port at the grid-connected power-off moment are obtained. This step ensures that the output voltage and current remain consistent with the state before power failure when the energy storage system switches from grid-connected mode to off-grid mode, thereby avoiding sudden changes in phase. This precise synchronization helps reduce power disturbances during the switching process and ensures stable operation of the load without being affected by mode switching.

[0084] Using the voltage and current information at the grid-connected power-off moment for PI calculation can quickly generate control signal parameters suitable for the current load condition. This mechanism enables the energy storage system to quickly adjust its operating mode, shortening the transition time from grid-connected to off-grid mode and improving the system's agility in response to grid changes.

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

[0086] The PI controller can smoothly adjust the operating state of the semiconductor devices according to the voltage and current trends, avoiding voltage spikes or current surges that may occur during switching. This ability to reduce impact is extremely beneficial for protecting sensitive components within the energy storage inverter, such as capacitors, inductors, etc., as well as extending the service life of power semiconductor devices.

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

[0088] In summary, this control strategy captures the load state information at the instant of grid drop-out, quickly and accurately adjusts the operating mode of the energy storage inverter, not only achieving seamless switching from grid-connected to off-grid mode, but also significantly improving the system's operating 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 instant of grid drop-out, ensuring smooth switching. In principle, using the amplitude and phase angle information of voltage and current for PI calculation can accurately control the inverter output to match the state before the grid is disconnected. In terms of effect, the technology in this embodiment can ensure the stable operation of the inverter in off-grid mode, avoiding voltage or frequency mutations caused by switching, and improving the stability and safety of the system. In other embodiments, by adding a voltage and current prediction algorithm, the generation of control signals can be further optimized to solve the problem of smooth switching during grid fluctuations.

[0089] In some embodiments, the proportional integral calculation is performed based on the above-mentioned voltage amplitude, voltage phase angle, current amplitude, and current phase angle to obtain the control signal parameters of the above-mentioned semiconductor devices in the above-mentioned energy storage inverter, including the following steps:

[0090] Step S301, according to the above-mentioned voltage amplitude, voltage phase angle, current amplitude, and current phase angle, coordinate conversion and positive and negative sequence separation processing are performed on the above-mentioned port voltage and the above-mentioned port current of the above-mentioned load to obtain positive sequence data and negative sequence data, the above-mentioned positive sequence data includes positive sequence voltage and positive sequence current, and the above-mentioned negative sequence data includes negative sequence voltage and negative sequence current;

[0091] Step S302, according to the above positive sequence data, the proportional integral decoupling calculation is carried out to obtain the first calculation voltage, and according to the above negative sequence data, the proportional integral decoupling calculation is carried out to obtain the second calculation voltage;

[0092] Step S303, according to the above first calculation voltage and the above second calculation voltage, the control signal parameters of the semiconductor devices in the energy storage converter are determined.

[0093] Specifically, step S301 can effectively distinguish the fundamental positive sequence component and the negative sequence component in the voltage and current through coordinate conversion (such as conversion from abc three-phase static coordinate system to dq rotating coordinate system) and positive and negative sequence separation. This operation simplifies the complexity of the control system and also improves the accuracy of the control, so that the path of the current in the semiconductor device is more optimized, which is beneficial to improve the efficiency of the electric energy conversion.

[0094] The separated positive sequence data is used to guide the normal operation of the semiconductor device, and the negative sequence data reflects the asymmetry of the power grid or the imbalance of the load. Through the decoupling PI calculation in step S302, these negative sequence components can be compensated or eliminated, thereby reducing the harmonic interference in the system and purifying the quality of the output electric energy, which has a direct benefit for improving the purity of the electric energy.

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

[0096] The design of the PI controller considers the dynamic characteristics of the system, and its proportional integral action can effectively suppress the oscillation in the system, especially in the process of grid switching, which can maintain the stable output of the electric energy converter and avoid the violent fluctuation of voltage and current. Through the control signal parameters determined in step S303, the system can better cope with various working conditions, and the overall stability is strengthened.

[0097] The whole control process not only considers the efficiency of electric energy conversion, but also takes into account the response speed and stability of the system. Through accurate calculation and control, the energy storage converter can efficiently convert electric energy and provide high-quality power for local loads in off-grid operation mode, while reducing the loss and noise of the equipment and improving the overall performance of the system.

[0098] In summary, the complex PI control strategy using coordinate conversion and positive and negative sequence separation processing not only improves the precision of semiconductor device control in the energy storage system, but also significantly enhances the stability and response speed of the system, thereby realizing efficient, stable and high-quality electric energy conversion. In terms of technology, the embodiment converts three-phase voltage and current into positive and negative sequence components for easy control through coordinate conversion and positive and negative sequence separation processing, thereby improving the accuracy of control. In principle, the complex three-phase system can be simplified into two independent systems using coordinate conversion and positive and negative sequence separation technology, which facilitates PI decoupling calculation and thus obtains accurate control signal parameters. In terms of effect, the technology in the embodiment can ensure that the inverter operates stably and quickly in off-grid mode, and by accurately controlling the positive and negative sequence components, it avoids voltage or frequency mutations caused by switching, thereby improving the stability and safety of the system. In other embodiments, higher-order mathematical models such as Clark transformation or Park transformation can be introduced to further optimize the coordinate conversion process and solve the problem of accurate control under nonlinear load and grid environment.

[0099] In some embodiments, the port voltage and the port current of the load are subjected to coordinate conversion and positive and negative sequence separation processing according to the voltage amplitude, the voltage phase angle, the current amplitude and the current phase angle, to obtain positive sequence data and negative sequence data, including the following steps:

[0100] Step S3011, converting the port voltage and the port current of the load from three-phase stationary coordinates to two-phase stationary coordinates according to the voltage amplitude, the voltage phase angle, the current amplitude and the current phase angle, to obtain initial converted voltage and initial converted current;

[0101] Step S3012, determining a coordinate conversion angle based on an off-grid phase-locked loop;

[0102] Step S3013, converting the initial converted voltage and the initial converted current from the two-phase stationary coordinates to two-phase rotating coordinates based on the coordinate conversion angle and performing the positive and negative sequence separation processing, to obtain the positive sequence data and the negative sequence data.

[0103] Specifically, the port voltage of the load is indicated by Va, Vb and Vc in Figure 2 , Va, Vb and Vc are voltage values of the port voltage in three directions of three-phase stationary coordinates, and the port current of the load is indicated by Ia, Ib and Ic in Figure 2 , Ia, Ib and Ic are current values of the port current in three directions of three-phase stationary coordinates, the three-phase stationary coordinates are abc coordinates, the two-phase stationary coordinates are αβ coordinates, and the two-phase rotating coordinates are dq coordinates. Figure 2Vd+, Vq+, Id+, Iq+ in the positive sequence data include Vd+, Vq+ respectively as the positive sequence voltage components of d-axis and q-axis, Id+, Iq+ respectively as the positive sequence current components of d-axis and q-axis, the negative sequence data include Figure 2 Vd+, Vq+, Id+, Iq+ in the positive sequence data include Vd+, Vq+ respectively as the positive sequence voltage components of d-axis and q-axis, Id+, Iq+ respectively as the positive sequence current components of d-axis and q-axis, the negative sequence data include Figure 2 Vd+, Vq+, Id+, Iq+ in the positive sequence data include Vd+, Vq+ respectively as the positive sequence voltage components of d-axis and q-axis, Id+, Iq+ respectively as the positive sequence current components of d-axis and q-axis, the negative sequence data include

[0104] In step S3011, the voltage and current in the three-phase stationary coordinate system are converted to the two-phase stationary coordinate system, which can simplify the complexity of the subsequent control algorithm. Compared with the three-phase system, the control system design in the two-phase coordinate system is simpler and the calculation amount is less, which helps to improve the real-time response speed and overall calculation efficiency of the control system. In step S3012, the coordinate conversion angle determined based on the off-grid phase-locked loop ensures the synchronization of the voltage and current signals with the inverter output. The 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 and conducive to achieving high-quality control of voltage and current and improving power conversion efficiency. In step S3013, through further coordinate transformation (from two-phase stationary to two-phase rotating coordinate system) and positive and negative sequence separation processing, the positive and negative sequence components can be effectively distinguished. The positive sequence component reflects the balance and symmetry state in the three-phase power system, while the negative sequence component is related to system imbalance and power disturbance. After separating the positive and negative sequences, the control system can optimize the positive sequence component and suppress or eliminate the negative sequence component, thereby improving the quality of output power and reducing the adverse effects on sensitive loads.

[0105] Through positive and negative sequence separation processing, 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 can help the system better cope with complex working conditions such as nonlinear loads and unbalanced conditions, improve the stability and reliability of the system, and ensure that the power output is not disturbed by external interference.

[0106] The separated positive and negative sequence data provide important information for energy management. Based on these data, the control system can optimize energy distribution, reduce energy loss, and improve the overall performance of the system. Optimization of positive sequence data can improve energy conversion efficiency, while suppression of negative sequence data can help reduce system loss and improve power quality.

[0107] In summary, through coordinate transformation and positive and negative sequence separation processing, the control strategy realizes accurate control of the load port voltage and current in the energy storage system, not only simplifies the control algorithm, improves the calculation efficiency, but also effectively improves the power quality, enhances the stability and robustness of the system under complex working conditions. In terms of technology, the embodiment realizes accurate control of the positive and negative sequence components in the three-phase system through coordinate transformation and positive and negative sequence separation processing, improves the response speed and stability of the inverter in off-grid mode. In principle, the phase-locked loop technology is used to determine the coordinate transformation angle, which can track the frequency change of the grid or load in real time, ensure that the transformed voltage and current are synchronized with the system frequency, and thus obtain accurate positive and negative sequence components. In terms of effect, the technology in the embodiment can ensure that the inverter operates stably and quickly in off-grid mode, and through accurate control of the positive and negative sequence components, it avoids voltage or frequency mutation caused by switching, improves the stability and safety of the system. In other embodiments, higher-order mathematical models such as Clark transformation or Park transformation can be introduced to further optimize the coordinate transformation process and solve the problem of accurate control under nonlinear load and grid environment.

[0108] In some embodiments, the coordinate transformation angle includes a positive angle and a negative angle (θ+θ-) Figure 2 The initial transformed voltage and the initial transformed current are converted from the two-phase static coordinates to two-phase rotating coordinates based on the coordinate transformation angle, and the positive and negative sequence separation processing is performed to obtain the positive sequence data and the negative sequence data, including the following steps:

[0109] Step S401, based on the positive angle, the initial transformed voltage and the initial transformed current are converted from the two-phase static coordinates to two-phase rotating coordinates and the positive and negative sequence separation processing is performed to obtain the positive sequence data, the positive sequence data including the first positive sequence voltage, the second positive sequence voltage, the first positive sequence current and the second positive sequence current, the first positive sequence voltage being the positive sequence voltage of the first coordinate axis of the two-phase rotating coordinates, the second positive sequence voltage being the positive sequence voltage of the second coordinate axis of the two-phase rotating coordinates, the first positive sequence current being the positive sequence current of the first coordinate axis of the two-phase rotating coordinates, and the second positive sequence current being the positive sequence current of the second coordinate axis of the two-phase rotating coordinates;

[0110] Step S402, based on the above negative angle, the initial conversion voltage and the initial conversion current are converted from the above two-phase static coordinate to two-phase rotating coordinate and the positive and negative sequence separation processing is carried out, and the above negative sequence data is obtained, the above negative sequence data includes first negative sequence voltage, second negative sequence voltage, first negative sequence current and second negative sequence current, the above first negative sequence voltage is the negative sequence voltage of the first coordinate axis of the above two-phase rotating coordinate, the above second negative sequence voltage is the negative sequence voltage of the second coordinate axis of the above two-phase rotating coordinate, the above first negative sequence current is the negative sequence current of the first coordinate axis of the above two-phase rotating coordinate, and the above second negative sequence current is the negative sequence current of the second coordinate axis of the above two-phase rotating coordinate.

[0111] Specifically, as shown in Figure 2 the above positive angle is Figure 2 in θ, the above negative angle is Figure 2 in -θ, the first coordinate axis can be d-axis or q-axis, and the second coordinate axis can correspond to q-axis or d-axis, and in the embodiment, the first coordinate axis is d-axis and the second coordinate axis is q-axis, for example, 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] Among them, the coordinate transformation and positive and negative sequence separation processing in steps S401 and S402 effectively decompose the energy in the three-phase system into positive and negative sequences. The positive sequence energy represents the useful and balanced energy flow in the system, while the negative sequence energy contains the components that cause system imbalance and energy waste. This decoupling enables the control system to independently and accurately manage each part of the energy, optimizing energy utilization efficiency.

[0113] In the two-phase rotating coordinate system, the positive and negative sequence separation can provide faster dynamic response speed, because the control equation in the rotating coordinate system usually has better decoupling properties, which makes the control system can adjust the output of the inverter faster to adapt to the transient changes of the load or power grid, improve the flexibility and response speed of the whole system. Independent control of positive and negative sequence components can effectively reduce the power quality problems caused by negative sequence components, such as voltage fluctuation and current distortion. By suppressing negative sequence components and optimizing positive sequence components, the quality of output power can be significantly improved to meet the needs of high-precision loads. The introduction of positive and negative angles and the positive and negative sequence separation in the two-phase rotating coordinate system greatly reduces the complexity of the control algorithm compared to direct control in the complex three-phase coordinate system, reduces the resources required for real-time calculation, and improves the calculation efficiency and real-time performance of the control system.

[0114] By separating positive and negative sequences in the rotating coordinate system, the system can better suppress imbalances and disturbances, improving its stability and reliability under various operating conditions. Especially for energy storage inverters, this can reduce internal shocks caused by abnormal grid or load changes, protecting equipment from damage. The separation of positive and negative sequence data provides a basis for optimizing energy conversion strategies. The control system can adjust the inverter's output based on positive sequence data to achieve efficient energy transmission, while negative sequence data feedback allows for measures to suppress or compensate for non-ideal conditions, maximizing energy conversion efficiency and reducing losses.

[0115] In summary, by using coordinate transformation and positive and negative sequence separation technology, the energy storage system can achieve more precise and efficient energy management and control. This method not only improves power quality and reduces control complexity, but also enhances the stability and reliability of the system when facing complex operating conditions. Technically, this embodiment achieves separation of positive and negative sequence components by converting voltage and current to the rotating coordinate system, improving control accuracy of the inverter in off-grid mode. In principle, using the positive and negative angles of the rotating coordinate system for coordinate transformation can convert voltage and current in the three-phase stationary coordinate system into components in the rotating coordinate system, facilitating positive and negative sequence separation processing. In terms of effect, the technology in this embodiment ensures that the inverter operates stably and quickly in off-grid mode, avoiding voltage or frequency mutations caused by switching by precisely controlling positive and negative sequence components, improving system stability and safety. In other embodiments, higher-order mathematical models such as Clark or Park transformations can be introduced to further optimize the coordinate transformation process and solve the problem of precise control under nonlinear load and grid conditions.

[0116] In some embodiments, the proportional-integral decoupling calculation according to the above positive sequence data obtains a first calculated voltage, and the proportional-integral decoupling calculation according to the above negative sequence data obtains a second calculated voltage, including the following steps:

[0117] Step S3021, obtaining 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;

[0118] Step S3022, performing the proportional-integral decoupling calculation according to 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 the proportional-integral decoupling calculation according to 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;

[0119] Step S3023, according to the above-mentioned first positive sequence calculation current and the above-mentioned second positive sequence calculation current, determine the above-mentioned first calculation voltage, and according to the above-mentioned first negative sequence calculation current and the above-mentioned second negative sequence calculation current, determine the above-mentioned second calculation voltage.

[0120] Specifically, as shown in the figure, Figure 2 The first positive sequence setting voltage is Vd+ * , the positive sequence setting voltage on the d-axis, generally set to 0, the second positive sequence setting voltage is Vq+ * , 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, generally set to 0, the second negative sequence setting voltage is Vq- * , the negative sequence setting voltage on the q-axis, generally set to 0. The first positive sequence setting voltage Vd+ * , the above-mentioned second positive sequence setting voltage Vq+ * , the first positive sequence voltage is Vd+, the second positive sequence voltage is Vq+ input to the PI algorithm for decoupling calculation, get the first positive sequence calculation current Id+ * and the second positive sequence calculation current Iq+ * . Similarly, the first negative sequence setting voltage Vd- * , the above-mentioned second negative sequence setting voltage Vq- * , the first negative sequence voltage is Vd-, the second negative sequence voltage is Vq- input to the PI algorithm for decoupling calculation, get the first negative sequence calculation current Id- * and the second negative sequence calculation current Iq- * .

[0121] Among them, in step S3022, by proportional integral decoupling calculation, according to the setting voltage and the actual measurement of the positive sequence voltage, negative sequence voltage, respectively calculate the first positive sequence calculation current and the second positive sequence calculation current, and the first negative sequence calculation current and the second negative sequence calculation current. This decoupling control method can realize accurate control of current, ensure that the current and the setting voltage remain consistent, so as to optimize the energy transmission process and reduce energy loss.

[0122] Through the dynamic adjustment function of the proportional-integral (PI) controller, the system can quickly respond to voltage changes and timely adjust the current output. This dynamic adaptability is particularly important for handling unstable conditions such as grid fluctuations or load surges, helping the system quickly reach a new steady state and improving overall stability. PI decoupling calculations are performed on positive and negative sequence data separately, meaning the system can independently manage these two types of energy flow. Positive sequence control optimizes symmetric and balanced energy transmission in the system, while negative sequence control can compensate for or eliminate unbalanced factors such as voltage asymmetry and current distortion, significantly improving the quality of output power and reducing the impact on sensitive loads. Effective control of negative sequence components can reduce internal stress in the system, such as reducing switch losses in inverters and reducing thermal stress during energy conversion, thereby extending the service life of equipment, reducing failure rates, and improving the overall reliability of the system.

[0123] The calculated voltage obtained through proportional-integral decoupling calculation can guide the inverter to more accurately control the energy conversion process, reduce energy waste during conversion, and improve energy conversion efficiency. Especially for energy storage systems, high-efficiency energy conversion not only reduces energy loss but also improves the economic efficiency of the system. Unlike the mutual interference that may exist in traditional control methods, proportional-integral decoupling control can enhance the robustness of the system to various disturbances, maintaining high-quality and stable output power even in complex and changing grid environments, which is crucial for ensuring long-term reliable operation of the system.

[0124] In summary, this control strategy achieves fine control of current in the energy storage system through independent proportional-integral decoupling calculation of positive and negative sequence data, enhancing the adaptability and robustness of the system to grid changes. Technically, this embodiment achieves precise control of positive and negative sequence currents through proportional-integral decoupling calculation, improving the response speed and stability of the inverter in off-grid mode. In principle, using the set positive and negative sequence voltages as references for PI decoupling calculation, the calculated current matching the set voltage can be obtained, and the corresponding calculated voltage can be obtained to control the conduction and turn-off of power semiconductor devices. In terms of effect, the technology in this embodiment can ensure that the inverter operates stably and quickly in off-grid mode, and through precise control of positive and negative sequence components, it avoids voltage or frequency mutations caused by switching, improving the stability and safety of the system. 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 the problem of stable control in 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] Separate control of positive and negative sequence voltages means that the system can independently manage symmetric positive sequence voltages and asymmetric negative sequence voltages. Positive sequence voltage control focuses on maintaining stable operation of the system, while negative sequence voltage control focuses on compensating for imbalances in the power grid 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 calculation, the system can quickly respond to current changes, thereby more quickly adjusting voltage output and reducing transition time in situations such as grid switching and load changes. This fast response capability is crucial for improving the continuity and stability of the system's power supply.

[0131] The accurate generation of the first and second calculated voltages helps to optimize voltage regulation strategies, reduce voltage fluctuations and distortions, and ensure that the quality of output power meets high standard requirements, which is crucial for the stable operation of sensitive loads. Independent control of positive and negative sequence voltages can enhance the system's ability to resist external disturbances, such as grid imbalance and harmonic pollution, thereby improving the system's robustness and reliability. For energy storage inverters, this means that they can still maintain stable operation in complex grid environments and reduce failure rates. The refined voltage control strategy enables the system to more intelligently manage the energy conversion process, reduce energy conversion losses, and improve the energy conversion efficiency of the entire energy storage system, thereby optimizing system energy consumption, reducing costs, and enhancing economic efficiency.

[0132] In summary, the process of performing proportional-integral decoupling calculation based on positive and negative sequence currents to determine the calculated voltages not only improves the accuracy of energy storage system control, but also enhances the system's anti-interference ability and power quality management. Technically, the embodiment achieves accurate control of positive and negative sequence voltages through decoupling calculation, improving the response speed and stability of the inverter in off-grid mode. In principle, using the first and second positive sequence currents for PI decoupling calculation can obtain the first and second sub-voltages that match the calculated currents, thereby obtaining the first calculated voltage; similarly, using the first and second negative sequence currents for PI decoupling calculation can obtain the third and fourth sub-voltages that match the calculated currents, thereby obtaining the second calculated voltage. In terms of effect, the technology in the embodiment can ensure that the inverter operates stably and quickly in off-grid mode, and through accurate control of positive and negative sequence voltages, it avoids voltage or frequency mutations caused by switching, improving the stability and safety of the system. In other embodiments, higher-order mathematical models such as Clark or Park transformations can be introduced to further optimize the voltage control process and solve the problem of accurate control in nonlinear load and grid environments.

[0133] In some embodiments, determining the control signal parameters of the semiconductor devices in the energy storage converter according to the first calculated voltage and the second calculated voltage comprises: controlling the energy storage converter to perform pulse width modulation (PWM) firing calculation according to the first calculated voltage and the second calculated voltage to obtain the control signal parameters of the semiconductor devices in the energy storage converter.

[0134] wherein the control signal parameters include Duty_va, Duty_vb, and Duty_vc as shown in Figure 2 Duty is the duty cycle.

[0135] Specifically, the pulse width modulation (PWM) firing calculation can accurately adjust the on-time and off-time of semiconductor devices (such as IGBTs) based on the first calculated voltage (positive sequence voltage component) and the second calculated voltage (negative sequence voltage component), thereby achieving precise control of the output power of the energy storage converter. This improvement in control accuracy is crucial for maintaining the power needs of the grid or local loads, helping to avoid situations of power excess or deficiency. By optimizing the PWM firing mode, switching losses and dead-time during energy conversion can be reduced, thereby improving the overall efficiency of energy conversion. This high-efficiency energy conversion capability means less energy waste, higher economic efficiency, and environmental friendliness for the energy storage system.

[0136] The precise definition of the control signal parameters ensures that the energy storage converter can provide stable and high-quality voltage and frequency output in grid-connected or off-grid modes, which is crucial for supporting sensitive loads and stable operation of the grid. The control of the first calculated voltage and the second calculated voltage can effectively filter out harmonics and negative sequence components in the grid, improve the quality of output power, reduce electromagnetic interference, and ensure the safe operation of equipment in the power system.

[0137] The fast response characteristics of the PWM firing calculation enable the energy storage converter to quickly adjust its output in the event of grid fluctuations, load changes, and other situations, reducing transition time and power fluctuations, enhancing the dynamic response capability and flexibility of the system. By accurately calculating the PWM firing, overvoltage, overcurrent, and other 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 accurate PWM control reduces the thermal stress and mechanical wear of the equipment, reduces the maintenance and replacement frequency of inverters and other power electronic components, and helps to reduce the operating and maintenance costs of the system.

[0138] In summary, according to the first calculated voltage and the second calculated voltage, the PWM wave calculation can significantly improve the power control accuracy of the energy storage converter, improve the power conversion efficiency and power quality. In terms of technology, the embodiment realizes the accurate control of the power semiconductor device by calculating the PWM wave according to the calculated voltage, and improves the response speed and stability of the inverter in the off-grid mode. In principle, by using the first calculated voltage and the second calculated voltage as a reference, the PWM wave calculation can obtain control signal parameters matched with the calculated voltage for controlling the conduction and turn-off of the power semiconductor device. In terms of effect, the technology in the embodiment can ensure the stable operation of the inverter in the off-grid mode, and by accurately controlling the power semiconductor device, the voltage or frequency mutation caused by switching is avoided, and the stability and safety of the system are improved. In other embodiments, higher-order control algorithms such as sliding mode control or predictive control can be introduced to further optimize the generation of control signals and solve the stable control problem in complex load and grid environment.

[0139] In some specific embodiments, as shown in Figure 2 , first, the port voltages Va, Vb and Vc of the load and the port currents Ia, Ib and Ic of the load are obtained, wherein Va, Vb and Vc are the voltage values of the port voltages in three directions of the three-phase stationary coordinate, and Ia, Ib and Ic are the current values of the port currents in three directions of the three-phase stationary coordinate. Then, the port voltage and the port current of the load are converted from the three-phase stationary coordinate abc to the two-phase stationary coordinate αβ, and then converted from the two-phase stationary coordinate αβ to the rotating coordinate axis dq according to the off-grid phase-locked loop VF_PLL and the coordinate conversion angle θ, and the positive and negative sequence separation is performed. When separating as positive sequence, the coordinate conversion angle is θ, and when separating as negative sequence, the coordinate conversion angle is -θ. After coordinate conversion and positive and negative sequence separation, positive sequence data and negative sequence data are obtained, the positive sequence data includes positive sequence voltage components Vd+, Vq+ of d-axis and q-axis, and positive sequence current components Id+, Iq+ of d-axis and q-axis, and the negative sequence data includes negative sequence voltage components Vd-, Vq- of d-axis and q-axis, and negative sequence current components Id-, Iq- of d-axis and q-axis. Then, the first positive sequence set voltage Vd+ * , the second positive sequence set 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+ * and the second positive sequence calculated current Iq+ * . Similarly, the first negative sequence set voltage Vd- * , the second negative sequence set 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 calculation current Id- * and the second negative sequence calculation current Iq- * The first positive sequence calculation current Id+ * and the second positive sequence calculation current Iq+ * are input 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 calculation current Id- * and the second negative sequence calculation current Iq- * are input into the PI algorithm for decoupling calculation to obtain the third sub-voltage Vdn and the fourth sub-voltage Vqn. According to the first sub-voltage Vdp, the second sub-voltage Vqp, the third sub-voltage Vdn and the fourth sub-voltage Vqn, PWM wave generation calculation is performed to obtain the duty ratios Duty_va, Duty_vb and Duty_vc of the above semiconductor devices in the energy storage converter.

[0140] In some embodiments, the above method further comprises: in the case of grid-connected power failure of the above energy storage system, disconnecting a grid-side switch connected between the grid and the filter.

[0141] Specifically, disconnecting the grid-side switch can quickly isolate the connection between the energy storage system and the grid, avoid the energy storage system continuing to supply power to the unstable grid in the event of grid failure or power failure, and prevent abnormal conditions such as overvoltage and overcurrent that may be caused thereby from causing damage to the energy storage inverter, the battery and other power electronic components. When the grid fails, disconnecting the grid-side switch can avoid the energy storage system becoming an accidental power source, reducing the risk of maintenance personnel or users coming into contact with live lines and ensuring the safety of personnel in maintenance or emergency situations. When the grid is powered off, if the connection between the energy storage system and the grid is not disconnected, the energy in the energy storage system may be sent back to the grid, which not only may interfere with the process of the grid returning to normal operation, but also may pose a safety hazard to grid workers. Disconnecting the grid-side switch effectively prevents the occurrence of reverse power transmission. After the grid-connected power failure event occurs, disconnecting the grid-side switch creates conditions for the energy storage system to smoothly switch from grid-connected mode to off-grid mode. At the moment the grid is disconnected, by disconnecting the grid-side switch, the system can quickly switch to off-grid control mode to maintain continuous power supply to local loads, achieving seamless connection of power supply. The disconnection of the grid-side switch enables the energy storage system to focus on managing the energy needs of local loads, ensuring efficient use of energy through precise control strategies in off-grid mode, avoiding unnecessary energy waste, and also helping to extend the service life of the energy storage system. In the case of unstable or power failure of the grid, disconnecting the connection with the grid can reduce the impact of external grid fluctuations on the energy storage system, avoid the operation of the energy storage system being disturbed by external interference, and thus improve the stability and controllability of the system in off-grid state.

[0142] In summary, the operation of disconnecting the grid-side switch is an important measure to ensure the safe and stable operation of the energy storage system during grid anomalies, which not only protects the safety of equipment and personnel, but also realizes the fast response and energy management optimization of the system. Technically, the embodiment realizes safe switching between grid-connected and off-grid modes by disconnecting the grid-side switch, avoiding electrical shock when the grid recovers. In principle, when a grid-connected power failure event is detected, the grid-side switch is immediately disconnected, which can prevent current shock when the grid recovers, protecting the inverter and load. In terms of effect, the technology in the embodiment can ensure that the inverter operates stably and quickly in off-grid mode, and by disconnecting the grid-side switch, it avoids electrical shock when the grid recovers, improving the stability and safety of the system. In other embodiments, the safety and reliability of switching can be further improved by increasing the arc extinguishing capacity of the switch or optimizing the control strategy of the switch, solving the problem of smooth switching during grid fluctuations.

[0143] In some embodiments, in the case of grid-connected power failure of the above-mentioned energy storage system, the port voltage and port current of the load of the above-mentioned energy storage system at the grid-connected power failure moment are obtained, including the following steps:

[0144] Step S1021, in the case of grid-connected power failure of the above-mentioned energy storage system, determining whether an off-grid operation enabling instruction exists;

[0145] Step S1022, in the case that the off-grid operation enabling instruction exists, obtaining the port voltage and port current of the load of the above-mentioned energy storage system at the grid-connected power failure moment, and controlling the energy storage converter in the above-mentioned energy storage system to stop inverting;

[0146] Step S1023, in the case that the off-grid operation enabling instruction does not exist, controlling the above-mentioned energy storage system to shut down.

[0147] When a power failure event occurs in the grid, the system can immediately respond by quickly detecting the existence or nonexistence of the off-grid operation enabling instruction. If the enabling instruction exists, the system will quickly obtain the voltage and current information of the load port, providing necessary data for subsequent switching from grid-connected mode to off-grid mode; if the enabling instruction does not exist, the system will enter a safe shutdown program to avoid invalid or dangerous operating states. Obtaining the voltage and current information of the load port at the grid-connected power failure moment can provide accurate reference data for the energy storage converter when switching from grid-connected to off-grid mode. This helps the inverter start running in a state close to the actual load demand at the switching moment, reducing electrical energy fluctuations and potential equipment shocks caused by mode switching, and achieving smoother and safer mode conversion.

[0148] After confirming the existence of the off-grid operation enabling instruction, the grid-connected inversion function of the inverter is stopped in time, which can avoid continuing to attempt to supply power to the grid in the case of power grid disconnection, thereby reducing the risk of system failure and damage and improving the overall reliability of the energy storage system. Determining the load state, i.e., the port voltage and current, at the grid-connected power-off moment helps the system take appropriate protective measures, such as adjusting the output parameters of the inverter, to protect the load from voltage or frequency mutations, while ensuring that the inverter will not be damaged due to sudden load changes.

[0149] In the absence of the off-grid operation enabling instruction, the system will automatically shut down, avoiding the energy storage system from accidentally becoming a power source during power grid failure, reducing the risk of electric shock when personnel are performing maintenance or inspection, and ensuring the safety of operating personnel. Accurate acquisition of load data at the grid-connected power-off moment enables the energy storage system to better understand and meet the actual needs of local loads when entering off-grid mode, thereby optimizing energy distribution, 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 when facing abnormal grid conditions, ensuring the safety, reliability, and efficiency of system operation. Technically, the present embodiment realizes intelligent control of the grid-connected-to-off-grid process by detecting the off-grid operation enabling instruction, avoiding unnecessary switching operations. In principle, when a grid-connected power-off event occurs, the system checks for the off-grid operation enabling instruction. If it exists, the voltage and current of the load port are acquired, and the grid-connected inversion of the inverter is stopped, preparing to enter off-grid mode. If it does not exist, the inverter is controlled to shut down, avoiding switching operations when off-grid operation is not needed, protecting the inverter and the load. In terms of effect, the technology in the present embodiment can ensure that the inverter runs quickly and stably in off-grid mode, avoiding unnecessary switching operations by intelligently detecting the off-grid operation enabling instruction, thereby improving the stability and safety of the system. In other embodiments, more control logic, such as load type judgment or power grid state prediction, can be added to further optimize the switching process and solve the problem of safe switching under different working 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 4An effect diagram of an off-grid operation method for an energy storage system is shown in FIG. 6. Figure 4 As shown in FIG. 6, curve a is the inverter port AB phase line voltage waveform, and curve b is the inverter port BC phase line voltage waveform. First, the inverter is started in parallel operation mode, and then the inverter receives a switching off-grid instruction or the off-grid operation condition is met, the inverter disconnects the grid-side switch, and after a certain time delay, the port voltage phase angle is used as the initial phase angle to generate waves and slowly start the off-grid voltage output.

[0155] In addition, an arc extinguishing device is also provided in the energy storage system, which is used to extinguish the arc (i.e. arc current) generated by the sudden interruption of current during the operation of the switching device (such as circuit breaker, contactor, relay, etc.). The arc extinguishing device can have many forms, depending on the type of device, power level, voltage level and expected use environment. The following are some common arc extinguishing device types and principles:

[0156] 1. Magnetic blowout arc extinguishing, which uses magnetic field principle to guide and lengthen the arc, so that it is quickly cooled and extinguished under the action of magnetic field. This device is usually applied in high-voltage circuit breaker, through built-in permanent magnet or electromagnetic to generate magnetic field, accelerate the arc extinguishing.

[0157] 2. Gas blowout arc extinguishing, which blows gas (such as air, SF6 gas, etc.) into the arc area to extinguish the arc. The blowing of gas can accelerate the cooling of arc, and at the same time destroy the continuity of arc, so that it is not easy to reignite. Gas blowout arc extinguishing is widely used in medium and high voltage switching devices.

[0158] 3. Vacuum arc extinguishing, in the switching device under vacuum environment, the arc cannot be maintained due to the lack of medium, so it is naturally extinguished. Vacuum arc extinguishing device is usually used in low-voltage circuit breaker, which uses vacuum (or very low pressure) to quickly extinguish the arc.

[0159] 4. Composite arc extinguishing technology, modern high-voltage and ultra-high-voltage circuit breakers often use a combination of multiple arc extinguishing technologies, such as magnetic blow and gas blow combination, gas blow and vacuum technology combination, etc., to improve the arc extinguishing efficiency, meet higher breaking capacity and faster breaking speed requirements.

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

[0161] To make the arc extinguishing current drop quickly, some embodiments can also adopt a multi-stage arc extinguishing design, with multiple breaking points, each equipped with a dedicated arc extinguishing device, to accelerate the current drop through multiple divisions and cooling of the arc. At the same time, the magnetic blow technology is used to generate a magnetic field through the built-in permanent magnet to guide the arc to cool and extinguish quickly. Alternatively, the connection line between the inverter and the grid is optimized to reduce unnecessary cable length, and low-inductance designed switches and connectors are used to reduce the contribution of inductance in the circuit and reduce the reverse electromotive force and current oscillation during the breaking moment, thereby accelerating the drop of the arc extinguishing current.

[0162] In other embodiments, to make the arc extinguishing current drop quickly, the intelligent control system can trigger the arc extinguishing device in advance at the moment before the grid is disconnected, so that the arc extinguishing device is ready even before the grid is completely disconnected, and as soon as the signal of grid disconnection is detected, the arc extinguishing function is immediately started, greatly shortening the arc extinguishing preparation time. By monitoring the current change in the circuit and the state of the arc extinguishing device, the speed of the switch breaking is dynamically adjusted to ensure that the circuit is broken at the best time and to avoid additional arcs or current peaks caused by improper breaking speed. Alternatively, the arc extinguishing state monitoring function is integrated into the control software, and as soon as the arc extinguishing demand is detected, the software immediately sends instructions to the hardware, and after the hardware responds, the software can adjust the working state of the inverter in real time to reduce the dependence on the current at the moment of grid disconnection, thereby accelerating the drop of the arc extinguishing current.

[0163] In other embodiments, the energy storage converter can switch between grid-connected and off-grid modes according to real-time instructions. To ensure smooth transition of the energy storage converter during the switching from grid-connected to off-grid, the energy storage converter can be started in the form of soft switching.

[0164] Before the PCS switches to off-grid mode, the phase angle of the voltage at the load port is collected by the phase-locked loop (PLL) circuit, and this is used to initialize the off-grid parameters of the inverter. At the same time, the BMS checks the state of charge of the battery to ensure that there is enough energy to support the soft start process of the inverter. When the PCS enters off-grid mode, the output power of the inverter is initially set to zero or very low to avoid impact on the load and the inverter itself. A soft start control strategy is adopted, and the output power of the inverter gradually increases according to a predetermined slope or curve. This process can be divided into the following three stages:

[0165] Stage one, voltage pre-charging: set the inverter (i.e. energy storage converter) to output a small constant power to charge the local load's filter capacitor and gradually establish a voltage matching the load. Monitor the rise of the load voltage until it reaches a certain percentage (e.g. 90%) of the target voltage.

[0166] Phase 2: Power Ramp-Up: Once the voltage pre-charge is complete, the inverter starts to gradually increase the output power according to the actual load demand. The power ramp-up rate should be optimized based on system parameters (such as inverter capacity, battery state, 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 state of the inverter. After completing the soft start process, the inverter enters full power operation state and stabilizes the output according to the 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 a safe range. If any abnormal conditions are detected, such as inverter overheating or battery SOC below threshold, the control system should immediately adjust the output power or even suspend the soft start process to avoid potential risks.

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

[0170] By adopting the soft start control strategy, the PCS can gradually and smoothly increase the 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 the present application, another aspect of the embodiments of the present application provides an energy storage system, which is operated by any one of the above-mentioned off-grid operation methods, such as Figure 5 As shown in the figure, the above-mentioned energy storage system includes: off-grid side 01, energy storage converter 02, filter 03 and grid-connected side 04 connected in turn; load 05, which is electrically connected with the above-mentioned filter 03 and the above-mentioned grid-connected side 04 respectively.

[0172] In terms of technology, the embodiment provides a storage system integrated with an off-grid operation method, and optimizes the grid-connected and off-grid control strategy to improve the stability and safety of the system. In terms of principle, the storage converter, filter and grid-connected side in the storage system are electrically connected to form a complete electric energy conversion and transmission path, and the load is electrically connected with the filter and the grid-connected side to receive electric energy from the storage system. In terms of effect, the technology in the embodiment can ensure that the inverter operates stably and quickly in the off-grid mode, and through the optimization of the control strategy, the voltage and current impact in the switching process is avoided, and the stability and safety of the system are improved. In other embodiments, more functional modules such as an energy management system or a communication module can be added to further optimize the overall performance of the storage system and solve the stable operation problem in the complex power grid environment.

[0173] In some embodiments, as shown in Figure 6 The grid-connected side switch 06 is electrically connected with the filter 03 and the load 05 at the first end, and is electrically connected with the grid-connected side 04 at the second end.

[0174] In terms of technology, the embodiment realizes the safe switching between the grid-connected and off-grid modes by adding the grid-connected side switch, and avoids the electrical impact when the power grid recovers. In terms of principle, when the grid-connected power-off event occurs, the grid-connected side switch is opened to prevent the current impact when the power grid recovers, and to protect the inverter and the load; in the grid-connected mode, the grid-connected side switch is closed to ensure the normal connection of the inverter and the power grid. In terms of effect, the technology in the embodiment can ensure that the inverter operates stably and quickly in the off-grid mode, and through the addition of the grid-connected side switch, the electrical impact when the power grid recovers is avoided, and the stability and safety of the system are improved. In other embodiments, the control strategy of the switch can be optimized to improve the safety and reliability of the switching, and to solve the smooth switching problem when the power grid fluctuates.

[0175] In some embodiments, the storage converter further includes a power semiconductor device.

[0176] In terms of technology, the embodiment realizes high-efficiency energy conversion of the inverter by using the power semiconductor device, and improves the energy conversion efficiency and stability of the system. In terms of principle, the power semiconductor device, such as IGBT, can realize high-efficiency energy conversion of the inverter by controlling its conduction and disconnection, and meet the power demand in off-grid mode. In terms of effect, the technology in the embodiment can ensure that the inverter operates stably and quickly in off-grid mode, and improve the energy conversion efficiency and stability of the system by using the power semiconductor device, and meet the power demand in off-grid mode. In other embodiments, the energy conversion efficiency can be further improved by optimizing the control strategy of the power semiconductor device, and the stable operation problem in high load or power grid fluctuation can be solved.

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

[0178] In terms of technology, the embodiment realizes high-efficiency energy conversion of the inverter by using the insulated gate bipolar transistor (IGBT), and improves the energy conversion efficiency and stability of the system. In terms of principle, the IGBT as a power semiconductor device has the advantages of high switching speed, low conduction loss and high reliability, and can realize high-efficiency energy conversion of the inverter by controlling its conduction and disconnection, and meet the power demand in off-grid mode. In terms of effect, the technology in the embodiment can ensure that the inverter operates stably and quickly in off-grid mode, and improve the energy conversion efficiency and stability of the system by using the IGBT, and meet the power demand in off-grid mode. In other embodiments, the energy conversion efficiency can be further improved by optimizing the control strategy of the IGBT, and the stable operation problem in high load or power grid fluctuation can be solved.

[0179] According to some embodiments of the present application, another aspect of the present application provides a power utilization device comprising any of the above-mentioned energy storage systems.

[0180] In terms of technology, the embodiment provides a power utilization device integrated with an off-grid operation method, and improves the stability and safety of the device by optimizing the grid-connected and off-grid control strategy. In terms of principle, the energy storage system in the power utilization device forms a complete energy conversion and transmission path through electrical connection, and can receive power from the power grid or off-grid side to supply power to the load. In terms of effect, the technology in the embodiment can ensure that the inverter operates stably and quickly in off-grid mode, and improve the stability and safety of the device by optimizing the control strategy, and avoid voltage and current surges in the switching process. In other embodiments, more functional modules, such as energy management systems or communication modules, can be added to further optimize the overall performance of the power utilization device, and solve the stable operation problem in complex power grid environment.

[0181] The technical scheme of the application relates to the switching process of the energy storage system between grid-connected and off-grid modes. In the grid-connected mode, the inverter is connected to the power grid to supply power to the load. When a power grid outage event occurs, the system first detects the voltage and current on the grid side to determine whether it needs to enter the off-grid mode. If the off-grid operation enable instruction exists, the system will disconnect the grid side switch to avoid current impact when the power grid is restored. Then, the inverter stops grid-connected inversion, and the system obtains the voltage and current information of the load port through the voltage sampling circuit, initializes the off-grid parameters, including the wave angle and the starting voltage. After the arc extinguishing current drops to a safe level, the inverter restarts, taking the voltage amplitude and phase angle of the load port as the starting point, and enters the off-grid operation mode. During this process, the system adjusts the PI parameters corresponding to the grid-connected to off-grid to optimize the response speed and stability of the inverter, ensuring the stability of the output voltage and frequency to meet the load demand. In addition, the system also sets a relay switch to prevent electrical conflicts in the grid-connected and off-grid modes, ensuring the safety of the switching process. Through precise control and intelligent detection, the entire switching process realizes a smooth transition from grid-connected to off-grid, improves the stability and safety of the energy storage system, and meets the power demand of the electrical equipment when the power grid is disconnected.

[0182] Those skilled in the art can understand that the above embodiments are specific examples for implementing the application, and in actual application, various changes can be made in form and details without departing from the spirit and scope of the application. Any person skilled in the art can make various modifications and changes without departing from the spirit and scope of the application, therefore the protection scope of the application should be limited by the scope defined in the claims.

Claims

1. A method of off-grid operation of an energy storage system, the energy storage system comprising a load and a filter electrically connected, characterized in that, The method comprises: determining whether the grid of the energy storage system is powered off; in the case that the grid of the energy storage system is powered off, acquiring the port voltage and the port current of the load of the energy storage system at the grid power-off time, the port voltage of the load being the voltage at one end of the filter connected with the load of the energy storage system, and the port current of the load being the current at one end of the filter connected with the load 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 is reached according to the size of the arc extinguishing current, the arc extinguishing current being the current generated suddenly after the current is interrupted and flowing through the filter; in the case that the off-grid power-on time of the energy storage system is reached, controlling off-grid power generation, and controlling the energy storage system to operate in the off-grid operation mode based on the port voltage and the port current of the load; determining whether the off-grid power-on time of the energy storage system is reached according to the size of the arc extinguishing current, comprising: determining whether the arc extinguishing current is less than or equal to a preset current; in the case that 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 is reached; in the case that the arc extinguishing current is greater than the preset current, determining that the off-grid power-on time of the energy storage system is not reached; a multi-stage arc extinguishing design is adopted, a plurality of breaking points are provided, each of the breaking points is equipped with a dedicated arc extinguishing device, the arc extinguishing function is realized through multiple division and cooling of the arc, and the arc extinguishing current is reduced.

2. The off-grid method of operating an energy storage system of claim 1, wherein, The energy storage system comprises an energy storage converter, the energy storage converter comprises a power semiconductor device, and the energy storage system is controlled to operate in the off-grid operation mode based on the port voltage and the port current of the load, comprising: taking the port voltage and the port current of the load as initial values, performing proportional integral calculation to obtain control signal parameters of the semiconductor device in the energy storage converter; generating a control signal according to the control signal parameters, the control signal parameters comprising a duty cycle of the control signal for controlling the semiconductor device to be turned on or turned off; the semiconductor device is controlled to be turned on or turned off by using the control signal, so as to control the energy storage system to operate in the off-grid operation mode.

3. The off-grid method of operating an energy storage system of claim 2, wherein, taking the port voltage and the port current of the load as initial values, performing proportional integral calculation to obtain control signal parameters of the semiconductor device in the energy storage converter, comprising: acquiring the amplitude and the phase angle of the port voltage of the load at the grid power-off time to obtain a voltage amplitude and a voltage phase angle; acquiring the amplitude and the phase angle of the port voltage of the load at the grid power-off time to obtain a current amplitude and a current phase angle; performing proportional integral calculation according to the voltage amplitude, the voltage phase angle, the current amplitude and the current phase angle to obtain control signal parameters of the semiconductor device in the energy storage converter.

4. The off-grid method of operating an energy storage system of claim 3, wherein, performing proportional integral calculation according to the voltage amplitude, the voltage phase angle, the current amplitude and the current phase angle to obtain control signal parameters of the semiconductor device in the energy storage converter, comprising: According to the voltage amplitude, voltage phase angle, current amplitude and current phase angle, the port voltage and the port current of the load are subjected to coordinate conversion and positive and negative sequence separation processing to obtain positive sequence data and negative sequence data, the positive sequence data including positive sequence voltage and positive sequence current, and the negative sequence data including negative sequence voltage and negative sequence current; According to the positive sequence data, proportional integral decoupling calculation is performed to obtain a first calculation voltage, and according to the negative sequence data, proportional integral decoupling calculation is performed to obtain a second calculation voltage; According to the first calculation voltage and the second calculation voltage, a control signal parameter of the semiconductor device in the energy storage converter is determined.

5. The off-grid method of operating an energy storage system of claim 4, wherein, According to the voltage amplitude, voltage phase angle, current amplitude and current phase angle, the port voltage and the port current of the load are subjected to coordinate conversion and positive and negative sequence separation processing to obtain positive sequence data and negative sequence data, including: According to the voltage amplitude, voltage phase angle, current amplitude and current phase angle, the port voltage and the port current of the load are converted from three-phase static coordinates to two-phase static coordinates to obtain initial conversion voltage and initial conversion current; Based on an off-grid phase-locked loop, a coordinate conversion angle is determined; Based on the coordinate conversion angle, the initial conversion voltage and the initial conversion current are converted from the two-phase static coordinates to two-phase rotating coordinates and subjected to the positive and negative sequence separation processing to obtain the positive sequence data and the negative sequence data.

6. The off-grid method of operating an energy storage system of claim 5, wherein, The coordinate conversion angle includes a positive angle and a negative angle, and based on the coordinate conversion angle, the initial conversion voltage and the initial conversion current are converted from the two-phase static coordinates to two-phase rotating coordinates and subjected to the positive and negative sequence separation processing 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 static coordinates to two-phase rotating coordinates and subjected to the positive and negative sequence separation processing to obtain the positive sequence data, the positive sequence data including first positive sequence voltage, second positive sequence voltage, first positive sequence current and second positive sequence current, the first positive sequence voltage being positive sequence voltage of a first coordinate axis of the two-phase rotating coordinates, the second positive sequence voltage being positive sequence voltage of a second coordinate axis of the two-phase rotating coordinates, the first positive sequence current being positive sequence current of the first coordinate axis of the two-phase rotating coordinates, and the second positive sequence current being 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 static coordinates to two-phase rotating coordinates and subjected to the positive and negative sequence separation processing to obtain the negative sequence data, the negative sequence data including first negative sequence voltage, second negative sequence voltage, first negative sequence current and second negative sequence current, the first negative sequence voltage being negative sequence voltage of the first coordinate axis of the two-phase rotating coordinates, the second negative sequence voltage being negative sequence voltage of the second coordinate axis of the two-phase rotating coordinates, the first negative sequence current being negative sequence current of the first coordinate axis of the two-phase rotating coordinates, and the second negative sequence current being negative sequence current of the second coordinate axis of the two-phase rotating coordinates.

7. The off-grid method of operating an energy storage system of claim 4, wherein, The proportional integral decoupling calculation is performed according to the positive sequence data to obtain a first calculation voltage, and the proportional integral decoupling calculation is performed according to the negative sequence data to obtain a second calculation voltage, including: obtaining a first positive sequence setting voltage, a second positive sequence setting voltage, a first negative sequence setting voltage and a second negative sequence setting voltage; performing the proportional integral decoupling calculation according to the first positive sequence setting voltage, the second positive sequence setting voltage and the positive sequence voltage to obtain a first positive sequence calculation current and a second positive sequence calculation current, and performing the proportional integral decoupling calculation according to the first negative sequence setting voltage, the second negative sequence setting voltage and the negative sequence voltage to obtain a first negative sequence calculation current and a second negative sequence calculation current; determining the first calculation voltage according to the first positive sequence calculation current and the second positive sequence calculation current, and determining the second calculation voltage according to the first negative sequence calculation current and the second negative sequence calculation current.

8. The off-grid method of operating an energy storage system of claim 7, wherein, determining the first calculation voltage according to the first positive sequence calculation current and the second positive sequence calculation current, and determining the second calculation voltage according to the first negative sequence calculation current and the second negative sequence calculation current, including: performing the proportional integral decoupling calculation according to the first positive sequence calculation current and the second positive sequence calculation current to obtain the first calculation voltage, the first calculation voltage including a first sub-voltage and a second sub-voltage, the first sub-voltage being a positive sequence voltage of a first coordinate axis of a two-phase rotating coordinate, and the second sub-voltage being a positive sequence voltage of a second coordinate axis of the two-phase rotating coordinate; performing the proportional integral decoupling calculation according to the first negative sequence calculation current and the second negative sequence calculation current to obtain the second calculation voltage, the second calculation voltage including a third sub-voltage and a fourth sub-voltage, the third sub-voltage being a negative sequence voltage of the first coordinate axis of the two-phase rotating coordinate, and the fourth sub-voltage being a negative sequence voltage of the second coordinate axis of the two-phase rotating coordinate.

9. The off-grid method of operating an energy storage system of claim 4, wherein, determining the control signal parameter of the semiconductor device in the energy storage converter according to the first calculation voltage and the second calculation voltage, including: controlling the energy storage converter to perform pulse width modulation calculation according to the first calculation voltage and the second calculation voltage to obtain the control signal parameter of the semiconductor device in the energy storage converter.

10. The off-grid method of operating an energy storage system of any of claims 1-9, wherein, The method further includes: in the case of grid outage of the energy storage system, disconnecting a grid-side switch connected between the grid and the filter.

11. The off-grid method of operating an energy storage system of any of claims 1-9, wherein, in the case of grid outage of the energy storage system, obtaining a port voltage and a port current of a load of the energy storage system at a grid outage time, including: in the case of grid outage of the energy storage system, determining whether an off-grid operation enabling instruction exists; in the case that the off-grid operation enabling instruction exists, obtaining the port voltage and the port current of the load of the energy storage system at the grid outage time, and controlling an energy storage converter in the energy storage system to stop inverting; in the case that the off-grid operation enabling instruction does not exist, controlling the energy storage system to shut down.

12. An energy storage system characterized by, The off-grid operation method is applied to the energy storage system of any one of claims 1 to 11, and the energy storage system comprises: The off-grid side, the energy storage converter, the filter and the grid-connected side are connected in this order; A load is electrically connected to the filter and the grid-connected side, respectively.

13. The energy storage system of claim 12, wherein, Further comprising: A grid-connected side switch, a first end of the grid-connected side switch is electrically connected to the filter and the load, respectively, and a second end of the grid-connected side switch is electrically connected to the grid-connected side.

14. The energy storage system of claim 12, wherein, The energy storage converter further comprises a power semiconductor device.

15. The energy storage system of claim 14, wherein, The semiconductor device is an insulated gate bipolar transistor.

16. An electrical device, characterized by The energy storage system of any one of claims 12 to 15 is included.

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