Grid-connected and off-grid switching method and energy storage system

Abstract

The invention discloses a grid-connected and off-grid switching method and an energy storage system, and the method comprises the steps: obtaining a first phase sequence of a three-phase power grid connected with a three-phase energy storage inverter and a second phase sequence of the three-phase energy storage inverter in an off-grid mode when the three-phase power grid connected with the three-phase energy storage inverter operates normally; controlling the first phase sequence of the three-phase energy storage inverter to be synchronized with the second phase sequence of the three-phase energy storage inverter so as to realize pre-synchronization of the phase sequences; when the connection of the three-phase power grid is abnormal, the synchronized three-phase energy storage inverter is controlled to be switched from the grid-connected control loop to the off-grid control loop, so that the smooth switching of the grid-connected and off-grid mode is realized, and the impact on the load in the switching process is reduced. By means of the mode, the three-phase energy storage inverter can be switched from the grid-connected mode to the off-grid mode under different phase sequences, the phase sequences of the three-phase energy storage inverter do not need to be fixed, the system complexity of the three-phase energy storage inverter is reduced, and the power distribution flexibility of the three-phase energy storage inverter is improved.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to grid-connected and off-grid switching methods and energy storage systems. Background Technology

[0002] In energy storage systems, the charging and discharging of power is typically controlled by a three-phase energy storage inverter. Energy storage systems generally include grid-connected and off-grid modes. In grid-connected mode, the three-phase energy storage inverter is connected to the three-phase power grid; in off-grid mode, the three-phase energy storage inverter outputs electrical energy that meets the load conditions to the corresponding load through three-phase off-grid connection.

[0003] Existing energy storage systems typically require switching between grid-connected and off-grid modes when experiencing abnormal fluctuations in the three-phase power grid. While three-phase energy storage inverters have both positive and negative phase sequences when connected to the three-phase power grid, incorrect wiring can lead to inconsistencies in phase sequence between grid-connected and off-grid modes. This causes the energy storage system to malfunction, preventing the switching between grid-connected and off-grid modes. Users must manually correct the three-phase power grid phase sequence and restart the system, resulting in complex and inflexible operation. Summary of the Invention

[0004] To address the aforementioned technical issues, this application provides a grid-connected / off-grid switching method and an energy storage system.

[0005] To address the aforementioned issues, this application provides a first technical solution: a grid-connected / off-grid switching method applied to a three-phase energy storage inverter. The grid-connected / off-grid switching method includes: when the three-phase power grid connected to the three-phase energy storage inverter is operating normally, acquiring the first phase sequence of the three-phase energy storage inverter connected to the three-phase power grid and the second phase sequence of the three-phase energy storage inverter in off-grid mode; controlling the synchronization of the first phase sequence of the three-phase energy storage inverter with the second phase sequence of the three-phase energy storage inverter; and when the three-phase power grid connection is abnormal, controlling the synchronized three-phase energy storage inverter to switch from the grid-connected control loop to the off-grid control loop.

[0006] Optionally, the above-mentioned synchronization of the first phase sequence of the three-phase energy storage inverter with the second phase sequence of the three-phase energy storage inverter includes: determining whether the first phase sequence and the second phase sequence are the same; and updating the second phase sequence to be synchronized with the first phase sequence in response to the difference between the first phase sequence and the second phase sequence.

[0007] Optionally, obtaining the first phase sequence of the three-phase energy storage inverter connected to the three-phase power grid includes: obtaining grid voltage data of the three-phase energy storage inverter connected to the three-phase power grid; performing coordinate transformation on the grid voltage data to obtain orthogonal voltage data of the three-phase energy storage inverter; and obtaining the first phase sequence of the three-phase energy storage inverter based on the orthogonal voltage data.

[0008] Optionally, the aforementioned quadrature voltage data includes the first voltage component and the second voltage component of the aforementioned grid voltage data under different coordinate axes; obtaining the first phase sequence of the aforementioned three-phase energy storage inverter based on the aforementioned quadrature voltage data includes: obtaining the second voltage component at the zero-crossing moment of the aforementioned first voltage component in the positive direction; determining the first phase sequence of the aforementioned three-phase energy storage inverter as positive sequence in response to the aforementioned second voltage component being less than a preset value; and determining the first phase sequence of the aforementioned three-phase energy storage inverter as negative sequence in response to the aforementioned second voltage component being greater than or equal to a preset value.

[0009] Optionally, updating the second phase sequence to be synchronized with the first phase sequence includes: when the first phase sequence is positive and the second phase sequence is negative, updating the second phase sequence to positive so that the second phase sequence is synchronized with the first phase sequence; and when the first phase sequence is negative and the second phase sequence is positive, updating the second phase sequence to negative so that the second phase sequence is synchronized with the first phase sequence.

[0010] Optionally, the second phase sequence includes the A-phase signal, B-phase signal, and C-phase signal output by the three-phase energy storage inverter in the off-grid mode; updating the second phase sequence to be synchronized with the first phase sequence in response to the difference between the first phase sequence and the second phase sequence includes: swapping the B-phase signal and the C-phase signal of the second phase sequence in response to the difference between the first phase sequence and the second phase sequence, so that the second phase sequence is synchronized with the first phase sequence.

[0011] Optionally, the above-mentioned grid-connected / off-grid switching method further includes: when the three-phase energy storage inverter is in off-grid mode, determining the current second phase sequence; determining whether the connection between the three-phase energy storage inverter and the three-phase power grid is abnormal; in response to the normal connection between the three-phase power grid and the grid, obtaining the first phase sequence of the three-phase energy storage inverter connected to the grid; controlling the first phase sequence of the three-phase energy storage inverter to synchronize with the second phase sequence of the three-phase energy storage inverter, so as to switch the synchronized three-phase energy storage inverter from the off-grid control loop to the grid-connected control loop.

[0012] Optionally, determining whether the connection between the three-phase energy storage inverter and the three-phase power grid is abnormal includes: obtaining the voltage magnitude and voltage limit of the three-phase energy storage inverter; and determining whether the connection between the three-phase energy storage inverter and the three-phase power grid is abnormal based on the relationship between the voltage magnitude and the voltage limit.

[0013] Optionally, when the three-phase power grid connection is abnormal, the control of the synchronized three-phase energy storage inverter to switch from the grid-connected control loop to the off-grid control loop includes: obtaining the voltage magnitude and voltage limit of the three-phase energy storage inverter; determining whether the connection between the three-phase energy storage inverter and the three-phase power grid is abnormal based on the relationship between the voltage magnitude and the voltage limit; and controlling the three-phase energy storage inverter to switch from the grid-connected control loop to the off-grid control loop in response to the abnormal three-phase power grid connection.

[0014] To address the aforementioned issues, this application provides a second technical solution: an energy storage system comprising a processor and a memory connected to the processor, wherein the memory stores program instructions; the processor executes the program instructions stored in the memory to implement the above-described grid-connected / off-grid switching method.

[0015] This application provides a grid-connected / off-grid switching method and an energy storage system. The grid-connected / off-grid control method can obtain the first phase sequence of the three-phase grid connected to the three-phase energy storage inverter and the second phase sequence of the three-phase energy storage inverter in off-grid mode when the three-phase grid is operating normally. It then controls the synchronization of the first and second phase sequences of the three-phase energy storage inverter to achieve pre-synchronization of the phase sequence. In the event of an abnormal three-phase grid connection, the synchronized three-phase energy storage inverter is switched from the grid-connected control loop to the off-grid control loop, achieving a smooth switching between grid-connected and off-grid modes and reducing the impact on the load during the switching process. Through this method, the three-phase energy storage inverter of this application can switch from grid-connected mode to off-grid mode under different phase sequences without fixing the phase sequence of the three-phase energy storage inverter, reducing the system complexity of the three-phase energy storage inverter and improving its power distribution flexibility. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0017] Figure 1 This is a flowchart illustrating the first embodiment of the on-grid / off-grid handover method provided in this application;

[0018] Figure 2 This is a flowchart illustrating the second embodiment of the on-grid / off-grid handover method provided in this application;

[0019] Figure 3 This is a flowchart illustrating the third embodiment of the on-grid / off-grid handover method provided in this application;

[0020] Figure 4 This is a flowchart illustrating the fourth embodiment of the on-grid / off-grid handover method provided in this application;

[0021] Figure 5 This is a flowchart illustrating the fifth embodiment of the on-grid / off-grid handover method provided in this application;

[0022] Figure 6 This is a schematic diagram of the structure of an embodiment of the energy storage system provided in this application;

[0023] Figure 7 This is a schematic diagram of another embodiment of the energy storage system provided in this application;

[0024] Figure 8 This is a schematic diagram of an embodiment of the computer-readable storage medium provided in this application. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0027] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0028] To ensure that the three-phase energy storage inverter can switch between grid-connected and off-grid modes normally, the existing grid-connected and off-grid switching methods usually fix the phase sequence of the three-phase energy storage inverter in grid-connected and off-grid modes, for example, fix it to positive sequence or negative sequence, and adjust the wiring phase sequence in grid-connected mode to be consistent with the wiring phase sequence in off-grid mode, resulting in poor power distribution flexibility.

[0029] In view of this, the embodiments of this application first propose a grid-connected / off-grid switching method, which is applied to a three-phase energy storage inverter. The three-phase energy storage inverter is suitable for various phase sequence combinations in off-grid and grid-connected modes. The three-phase energy storage inverter is used to achieve seamless switching between off-grid control loop and grid-connected control loop under different phase sequences, and ensures that the electrical connection between the three-phase energy storage inverter and the load is not interrupted during the switching process. The power distribution method is simple and has low complexity.

[0030] Specifically, please see Figure 1 , Figure 1 This is a flowchart illustrating the first embodiment of the on-grid / off-grid handover method provided in this application. Figure 1 As shown, the on-grid / off-grid handover method includes the following steps:

[0031] Step S11: Obtain the first phase sequence and second phase sequence of the three-phase energy storage inverter in different modes.

[0032] Specifically, a three-phase energy storage inverter can include off-grid mode and grid-connected mode. In grid-connected mode, the three-phase energy storage inverter is connected to the three-phase power grid and can be used to supply power to the three-phase power grid. In off-grid mode, the three-phase energy storage inverter outputs power that meets the load conditions to the corresponding load through three-phase off-grid connection. The first phase sequence of the three-phase energy storage inverter can be the phase sequence of either off-grid mode or grid-connected mode, and the second phase sequence can be the phase sequence of the other of either off-grid mode or grid-connected mode.

[0033] In a three-phase energy storage inverter, electromotive force is induced by cutting the windings of phases A, B, and C during operation, thereby generating signals between different phases, such as phase A, phase B, and phase C signals. Depending on the phase order of phases A, B, and C, the first and second phase sequences can include positive and negative sequences. A positive sequence means phase A leads phase B by 120 degrees, and phase B leads phase C by 120 degrees; a negative sequence means phase A leads phase C by 120 degrees, and phase C leads phase B by 120 degrees.

[0034] Step S12: Synchronize the first phase sequence of the three-phase energy storage inverter with the second phase sequence of the three-phase energy storage inverter.

[0035] After obtaining the first and second phase sequences of the three-phase energy storage inverter, the first and second phase sequences of the three-phase energy storage inverter are synchronized. Specifically, when the first and second phase sequences are different, synchronization can be achieved by updating the first phase sequence to the same sequence as the second phase sequence, or by updating the second phase sequence to the same sequence as the first phase sequence. For example, when the first phase sequence is positive and the second phase sequence is negative, synchronization can be achieved by switching the first phase sequence to negative or the second phase sequence to positive.

[0036] Step S13: Control the three-phase energy storage inverter to switch between the grid-connected control loop and the off-grid control loop.

[0037] When the first and second phase sequences of the three-phase energy storage inverter are synchronized (e.g., both are positive or both are negative), the inverter is controlled to switch from the grid-connected control loop to the off-grid control loop, or vice versa. Because the first and second phase sequences are synchronized, the connection between the three-phase energy storage inverter and the load does not need to be disconnected during the switching process, allowing for flexible phase sequence settings during power distribution and improving distribution flexibility.

[0038] In this embodiment of the application, the phase sequence of the three-phase energy storage inverter in off-grid mode and grid-connected mode can be identified by the above method to obtain the first phase sequence and the second phase sequence. By synchronizing the first phase sequence with the second phase sequence, the three-phase energy storage inverter can switch between off-grid mode and grid-connected mode under different phase sequences. There is no need to fix the phase sequence of the three-phase energy storage inverter, which reduces the system complexity of the three-phase energy storage inverter and improves the power distribution flexibility of the three-phase energy storage inverter.

[0039] In one embodiment, please refer to Figure 2 , Figure 2 This is a flowchart illustrating the second embodiment of the on-grid / off-grid handover method provided in this application. Figure 2 As shown, in this embodiment, the on-grid / off-grid handover method includes the following steps:

[0040] Step S21: When the three-phase grid connected to the three-phase energy storage inverter is operating normally, obtain the first phase sequence of the three-phase grid connected to the three-phase energy storage inverter and the second phase sequence of the three-phase energy storage inverter in off-grid mode.

[0041] Specifically, when the three-phase grid connected to the three-phase energy storage inverter is operating normally, the three-phase energy storage inverter operates in grid-connected mode. The voltage phase sequence when the three-phase energy storage inverter is connected to the three-phase grid is the first phase sequence, which can include either a positive or negative sequence. At this time, a second phase sequence can be set for the three-phase energy storage inverter in off-grid mode. For example, the second phase sequence can be set to either a positive or negative sequence.

[0042] Step S22: Synchronize the first phase sequence of the three-phase energy storage inverter with the second phase sequence of the three-phase energy storage inverter.

[0043] After obtaining the first and second phase sequences of the three-phase energy storage inverter, the first and second phase sequences of the three-phase energy storage inverter are synchronized. Specifically, when the first and second phase sequences are different, synchronization can be achieved by updating the first phase sequence to the same sequence as the second phase sequence, or by updating the second phase sequence to the same sequence as the first phase sequence. For example, when the first phase sequence is positive and the second phase sequence is negative, synchronization can be achieved by adjusting the second phase sequence to positive; or, when the first phase sequence is negative and the second phase sequence is positive, synchronization can be achieved by adjusting the second phase sequence to negative; or, when both the first and second phase sequences are positive or negative, no adjustment is made to the first or second phase sequence.

[0044] Step S23: When the three-phase power grid connection is abnormal, control the synchronized three-phase energy storage inverter to switch from the grid-connected control loop to the off-grid control loop.

[0045] The grid-connected / off-grid control method in this embodiment can monitor parameters such as voltage, current, or power when the three-phase grid is connected to the three-phase energy storage inverter to determine whether the three-phase grid connection is normal. When unstable fluctuations occur in the parameters of the three-phase grid, an abnormal connection is determined, and the synchronized three-phase energy storage inverter is controlled to switch from the grid-connected control loop to the off-grid control loop, thus switching the three-phase energy storage inverter from grid-connected mode to off-grid mode, and continuing to supply power to the load in off-grid mode.

[0046] In this embodiment, the grid-connected / off-grid control method can obtain the first phase sequence of the three-phase grid connected to the three-phase energy storage inverter and the second phase sequence of the three-phase energy storage inverter in off-grid mode when the three-phase grid is operating normally. It then controls the first phase sequence of the three-phase energy storage inverter to synchronize with the second phase sequence, achieving pre-synchronization of the phase sequence. When the three-phase grid connection is abnormal, it controls the synchronized three-phase energy storage inverter to switch from the grid-connected control loop to the off-grid control loop, achieving a smooth switching between grid-connected and off-grid modes and reducing the impact on the load during the switching process. Through this method, the three-phase energy storage inverter of this application can switch from grid-connected mode to off-grid mode under different phase sequences without fixing the phase sequence of the three-phase energy storage inverter, reducing the system complexity of the three-phase energy storage inverter, eliminating the need for manual wiring adjustments, and improving the power distribution flexibility of the three-phase energy storage inverter.

[0047] Optionally, please see Figure 3 , Figure 3 This is a flowchart illustrating the third embodiment of the on-grid / off-grid handover method provided in this application. Figure 3 As shown, step S12 or step S22 may include the following steps:

[0048] Step S31: Determine whether the first phase sequence and the second phase sequence are the same.

[0049] Specifically, in this embodiment, the first phase sequence is the phase sequence of the three-phase energy storage inverter in grid-connected mode, and the second phase sequence is the phase sequence of the three-phase energy storage inverter in off-grid mode. The first phase sequence can be obtained by identifying the phase sequence of the signals of the three-phase energy storage inverter under the grid-connected control loop, and the second phase sequence is usually the default phase sequence of the three-phase energy storage inverter under the off-grid control loop.

[0050] After obtaining the first phase sequence and the second phase sequence, it can be determined whether the first phase sequence and the second phase sequence are the same. If the first phase sequence and the second phase sequence are the same, for example, both the first phase sequence and the second phase sequence are positive or negative, then proceed to step S23; if the first phase sequence and the second phase sequence are different, then proceed to step S22.

[0051] Step S32: In response to the difference between the first phase sequence and the second phase sequence, update the second phase sequence to be synchronized with the first phase sequence.

[0052] When the first phase sequence and the second phase sequence are different, the second phase sequence is updated to be synchronized with the first phase sequence. For example, when the three-phase energy storage inverter is in grid-connected mode, the second phase sequence in off-grid mode can be updated to be synchronized with the first phase sequence; when the three-phase energy storage inverter is in off-grid mode, the second phase sequence in off-grid mode can be updated to be synchronized with the first phase sequence.

[0053] When the first phase sequence and the second phase sequence are the same, the step of switching the three-phase energy storage inverter from the first control loop to the second control loop is executed. For example, when the three-phase energy storage inverter is in grid-connected mode, the first phase sequence and the second phase sequence are synchronized, and the three-phase energy storage inverter is switched from the grid-connected control loop to the off-grid control loop; when the three-phase energy storage inverter is in off-grid mode, the first phase sequence and the second phase sequence are synchronized, and the three-phase energy storage inverter is switched from the off-grid control loop to the grid-connected control loop. Through the above method, the grid-connected and off-grid switching method of this embodiment can realize automatic switching between off-grid mode and grid-connected mode under different phase sequences, without fixing the phase sequence of the three-phase energy storage inverter, reducing the system complexity of the three-phase energy storage inverter, and improving the power distribution flexibility of the three-phase energy storage inverter.

[0054] Optionally, please see Figure 4 , Figure 4 This is a flowchart illustrating the fourth embodiment of the on-grid / off-grid handover method provided in this application. Figure 4 As shown, in this embodiment, step S11 includes:

[0055] Step S41: Obtain the grid voltage data of the three-phase energy storage inverter.

[0056] The grid-connected / off-grid switching method in this embodiment can identify the first phase sequence of the three-phase energy storage inverter by recognizing the grid voltage data when the three-phase energy storage inverter is connected to the three-phase grid. Specifically, when the three-phase grid connected to the three-phase energy storage inverter is operating normally, the grid voltage data during the operation of the three-phase energy storage inverter can be directly obtained.

[0057] Step S42: Perform coordinate transformation on the grid voltage data to obtain the quadrature voltage data of the three-phase energy storage inverter.

[0058] The grid voltage data refers to the voltage data of the three-phase energy storage inverter in grid-connected mode. This grid voltage data can include phase A, phase B, and phase C voltage data. By performing coordinate transformations on the phase A, phase B, and phase C voltage data, orthogonal voltage data for the three-phase energy storage inverter is obtained. The orthogonal voltage data uses one of the phase A, phase B, or phase C voltage data as a reference, transforming the other two data into components perpendicular to it. Coordinate transformation methods include, but are not limited to, Clark and Park transformations, and are not specifically limited here.

[0059] Step S43: Based on the quadrature voltage data, obtain the first phase sequence of the three-phase energy storage inverter.

[0060] After obtaining the quadrature voltage data of the three-phase energy storage inverter, the first phase sequence of the three-phase energy storage inverter can be determined as positive or negative based on the quadrature voltage data.

[0061] In this embodiment, grid voltage data of the three-phase energy storage inverter is obtained, and coordinate transformation is performed on the grid voltage data to obtain orthogonal voltage data of the three-phase energy storage inverter. Based on the orthogonal voltage data, the first phase sequence of the three-phase energy storage inverter is obtained. When the first phase sequence and the second phase sequence are different, the second phase sequence is updated to be synchronized with the first phase sequence. This enables the three-phase energy storage inverter to switch between grid-connected mode and off-grid mode under different phase sequences without fixing the phase sequence of the three-phase energy storage inverter, reducing the system complexity of the three-phase energy storage inverter and improving the power distribution flexibility of the three-phase energy storage inverter.

[0062] Furthermore, the quadrature voltage data includes the first voltage component and the second voltage component of the grid voltage data under different coordinate axes. Step S43 includes: acquiring the second voltage component at the zero-crossing moment of the first voltage component in the positive direction; determining the first phase sequence of the three-phase energy storage inverter as positive sequence in response to the second voltage component being less than a preset value; and determining the first phase sequence of the three-phase energy storage inverter as negative sequence in response to the second voltage component being greater than or equal to a preset value.

[0063] Specifically, after performing coordinate transformation on the grid voltage data, the first voltage component and the second voltage component of the grid voltage data in a two-dimensional coordinate system are obtained. The grid voltage data may include the A-phase voltage data U. a Phase B voltage data U b And C-phase voltage data U c The first voltage component U a Second voltage component U β The calculation formula is as follows:

[0064]

[0065] In this embodiment, the direction in which the sine wave of the first voltage component crosses zero at 0° is considered positive, and the direction in which the sine wave of the first voltage component crosses zero at 180° is considered negative. This embodiment obtains the second voltage component corresponding to the zero-crossing moment of the first voltage component at angle 0, and determines the relationship between the second voltage component and a preset value. When the second voltage is less than the preset value, the first phase sequence of the three-phase energy storage inverter is positive; when the second voltage component is greater than or equal to the preset value, the first phase sequence of the three-phase energy storage inverter is negative. The preset value can be 0.

[0066] In this application, by obtaining the second voltage component at the zero-crossing moment of the first voltage component in the positive direction, and determining the first phase sequence of the three-phase energy storage inverter as positive when the second voltage component is less than a preset value; and determining the first phase sequence of the three-phase energy storage inverter as negative when the second voltage component is greater than or equal to the preset value; and updating the second phase sequence to be synchronized with the first phase sequence when the first phase sequence and the second phase sequence are different, the three-phase energy storage inverter can switch between the first mode and the second mode under different phase sequences, without the need to fix the phase sequence of the three-phase energy storage inverter, thereby reducing the system complexity of the three-phase energy storage inverter and improving the power distribution flexibility of the three-phase energy storage inverter.

[0067] Optionally, step S32 includes: when the first phase sequence is positive and the second phase sequence is negative, updating the second phase sequence to positive so that the second phase sequence is synchronized with the first phase sequence; when the first phase sequence is negative and the second phase sequence is positive, updating the second phase sequence to negative so that the second phase sequence is synchronized with the first phase sequence.

[0068] Specifically, when the first phase sequence is positive and the second phase sequence is negative, the second phase sequence is updated to positive so that the second phase sequence is the same as the first phase sequence. The three-phase energy storage inverter performs power distribution control in positive sequence in both off-grid and grid-connected modes. This allows the three-phase energy storage inverter to seamlessly switch between off-grid and grid-connected modes in the event of power outages or grid fluctuations, without disconnecting the connection between the three-phase energy storage inverter and the load during the switching process.

[0069] Optionally, the second phase sequence includes the A-phase signal, B-phase signal, and C-phase signal output by the three-phase energy storage inverter in off-grid mode; step S22 includes: in response to the difference between the first phase sequence and the second phase sequence, swapping the B-phase signal and the C-phase signal of the second phase sequence to synchronize the second phase sequence with the first phase sequence.

[0070] Specifically, the three-phase energy storage inverter can obtain phase A, phase B, and phase C signals by sequentially sampling phases A, C, and B. After obtaining the first phase sequence of the three-phase energy storage inverter through phase sequence identification, it is determined whether the first phase sequence and the second phase sequence are the same. If the first phase sequence and the second phase sequence are different, the second phase sequence can be synchronized by swapping the B phase signal and the C phase signal of the second phase sequence, thereby switching the second phase sequence from positive sequence to negative sequence, or vice versa.

[0071] In one embodiment, please refer to Figure 5 , Figure 5 This is a flowchart illustrating the fifth embodiment of the on-grid / off-grid handover method provided in this application. Figure 5 As shown, the on-grid / off-grid handover method also includes the following steps:

[0072] Step S51: When the three-phase energy storage inverter is in off-grid mode, determine the current second phase sequence of the three-phase energy storage inverter.

[0073] Specifically, when the three-phase power grid connected to the three-phase energy storage inverter is operating normally, the three-phase energy storage inverter operates under the grid-connected control loop; when the three-phase power grid connection is abnormal, the three-phase energy storage inverter can be controlled to switch from the grid-connected control loop to the off-grid control loop through the method of any of the above embodiments.

[0074] When the three-phase energy storage inverter is under the off-grid control loop, the current second phase sequence of the three-phase energy storage inverter is determined. The second phase sequence is the electrical signal phase sequence under the current control loop. The second phase sequence can be positive or negative.

[0075] Step S52: Determine whether the connection between the three-phase energy storage inverter and the three-phase power grid is abnormal.

[0076] After determining the current second phase sequence of the three-phase energy storage inverter, it is necessary to further determine whether the connection between the three-phase energy storage inverter and the three-phase power grid is abnormal. Specifically, this can be done by monitoring the voltage, current, and other electrical signals on the connection side between the three-phase energy storage inverter and the three-phase power grid to determine whether the connection between the three-phase energy storage inverter and the three-phase power grid is abnormal.

[0077] Step S53: In response to the normal connection of the three-phase power grid, obtain the first phase sequence of the three-phase energy storage inverter connected to the three-phase power grid.

[0078] Specifically, when an anomaly is detected in the three-phase grid connection, the three-phase energy storage inverter remains in the off-grid control loop. When a normal three-phase grid connection is detected, the first phase sequence of the three-phase energy storage inverter connected to the three-phase grid can be further obtained. The first phase sequence can be either positive or negative. This can be achieved by monitoring electrical signals or voltage data from the voltage and current signals on the connection side between the three-phase energy storage inverter and the three-phase grid, or by further sampling the signals on the connection side after confirming a normal connection. No specific limitation is made here.

[0079] Step S54: Synchronize the first phase sequence of the three-phase energy storage inverter with the second phase sequence of the three-phase energy storage inverter, so as to switch the synchronized three-phase energy storage inverter from the off-grid control loop to the grid-connected control loop.

[0080] After obtaining the first phase sequence of the three-phase energy storage inverter, it is determined whether the first phase sequence and the second phase sequence are the same. When the first phase sequence and the second phase sequence are the same, they are synchronized, and the three-phase energy storage inverter can be directly switched from the off-grid control loop to the grid-connected control loop. When the first phase sequence and the second phase sequence are different, the second phase sequence is updated to be synchronized with the first phase sequence, so that the synchronized three-phase energy storage inverter can be switched from the off-grid control loop to the grid-connected control loop. In a possible implementation, the second phase sequence may include phase A signal, phase B signal, and phase C signal. When the first phase sequence and the second phase sequence are different, the second phase sequence can be synchronized with the first phase sequence by swapping the phase B signal and the phase C signal of the second phase sequence.

[0081] Specifically, before synchronizing the first phase sequence of the three-phase energy storage inverter with the second phase sequence of the three-phase energy storage inverter, the three-phase energy storage inverter is first controlled to exit the off-grid control loop before phase sequence synchronization is performed. After phase sequence synchronization, it re-enters the off-grid control loop and switches the synchronized three-phase energy storage inverter from the off-grid control loop to the grid-connected control loop.

[0082] Through the above method, the grid-connected / off-grid switching method of this embodiment monitors the connection between the three-phase energy storage inverter and the three-phase power grid in off-grid mode. When the connection to the three-phase power grid is confirmed to be normal, the first phase sequence of the three-phase power grid is obtained. After synchronizing the first phase sequence with the second phase sequence, the three-phase energy storage inverter is switched from the off-grid control loop to the grid-connected control loop. This allows the three-phase energy storage inverter to switch from off-grid mode to grid-connected mode without interrupting the power supply to the load, achieving a smooth switching between grid-connected and off-grid modes and reducing the impact on the load during the switching process. Furthermore, adaptive switching between off-grid and grid-connected modes can be achieved under different phase sequences. The operation is simple, reducing the system complexity of the three-phase energy storage inverter and improving its power distribution flexibility.

[0083] Optionally, step S52 above further includes: obtaining the voltage modulus and voltage limit of the three-phase energy storage inverter; and determining whether the connection between the three-phase energy storage inverter and the three-phase power grid is abnormal based on the relationship between the voltage modulus and voltage limit.

[0084] The voltage magnitude value of the three-phase energy storage inverter is obtained. The voltage magnitude value is the instantaneous phase voltage value of the three-phase energy storage inverter, which can be obtained from the quadrature voltage data of the three-phase energy storage inverter. For example, the first voltage component U of the three-phase energy storage inverter can be obtained by performing coordinate transformation on the voltage data of the three-phase energy storage inverter under off-grid control loop. a Second voltage component U β The first voltage component U of the three-phase energy storage inverter is obtained. α Second voltage component U β Then, the voltage magnitude V can be calculated using the following formula. m :

[0085]

[0086] The voltage limits of a three-phase energy storage inverter are used to indicate the range of values ​​of the three-phase power grid to which the inverter is connected. For example, the voltage limits may include the upper and lower limits of the grid voltage. After obtaining the voltage magnitude and voltage limits, the voltage magnitude is compared with the voltage limits to determine their magnitude relationship. This relationship is then used to determine whether the three-phase grid connection is abnormal. Specifically, if the voltage magnitude is greater than or equal to the lower limit of the grid voltage and less than or equal to the upper limit of the grid voltage, the three-phase grid connection is considered normal; if the voltage magnitude is less than the lower limit of the grid voltage or greater than the upper limit of the grid voltage, the three-phase grid connection is considered abnormal.

[0087] Due to an abnormal three-phase grid connection of the three-phase energy storage inverter, the inverter is under off-grid control. By continuously monitoring the connection status of the three-phase grid through the above steps, it can be determined whether the connection has been restored. When the current voltage magnitude of the three-phase energy storage inverter is greater than or equal to the lower limit voltage of the grid and less than or equal to the upper limit voltage of the grid, it is determined that the connection of the three-phase grid has been restored to normal. The grid-connected and off-grid control method of this embodiment can control the three-phase energy storage inverter, after phase sequence synchronization, to switch from the off-grid control loop to the grid-connected control loop. The switching is rapid and does not require interruption of the connection between the three-phase energy storage inverter and the load, thus improving the practicality of the three-phase energy storage inverter.

[0088] In one embodiment, step S23 may include the following steps: obtaining the voltage magnitude and voltage limit of the three-phase energy storage inverter; determining whether the connection between the three-phase energy storage inverter and the three-phase power grid is abnormal based on the relationship between the voltage magnitude and voltage limit; and controlling the three-phase energy storage inverter to switch from the grid-connected control loop to the off-grid control loop in response to the abnormal connection of the three-phase power grid.

[0089] Specifically, in this embodiment, the voltage magnitude can be obtained by performing coordinate transformation on the grid voltage data of the three-phase energy storage inverter under the grid-connected control loop. The voltage limits include the upper limit voltage and the lower limit voltage of the three-phase grid. By comparing the voltage magnitude with the voltage limits, if the voltage magnitude is greater than or equal to the lower limit voltage and less than or equal to the upper limit voltage, the three-phase grid connection is determined to be normal; if the voltage magnitude is less than the lower limit voltage or greater than the upper limit voltage, the three-phase grid connection is determined to be abnormal.

[0090] When an abnormal connection is detected between the three-phase energy storage inverter and the three-phase power grid, the three-phase energy storage inverter is controlled to exit the grid-connected control loop and switch to the off-grid control loop, so that the three-phase energy storage inverter can continue to output off-grid voltage to the load without interrupting the power supply to the load.

[0091] In this embodiment, when the three-phase energy storage inverter operates under the grid-connected control loop, the first phase sequence and the second phase sequence of the three-phase energy storage inverter can be obtained and synchronized to achieve pre-synchronization of the phase sequence. When it is determined that the grid connection of the three-phase energy storage inverter is abnormal based on the relationship between the voltage magnitude and the voltage limit, the three-phase energy storage inverter is controlled to switch from the grid-connected control loop to the off-grid control loop to achieve adaptive switching between off-grid mode and grid-connected mode under different phase sequences. The operation is simple, the system complexity of the three-phase energy storage inverter is reduced, and the power distribution flexibility of the three-phase energy storage inverter is improved.

[0092] Through the above methods, the grid-connected / off-grid switching method of this application embodiment can be applied to various phase sequence situations of three-phase power grids and three-phase off-grid operation. It can control the three-phase energy storage inverter to switch between grid-connected and off-grid operations under different connection conditions without fixing the phase sequence. When the three-phase power grid connected to the three-phase energy storage inverter is operating normally, the phase sequence can be pre-synchronized by acquiring the first and second phase sequences. This allows the three-phase energy storage inverter to directly switch between grid-connected and off-grid operations based on the pre-synchronized first and second phase sequences when abnormal situations such as three-phase power grid fluctuations occur. The switching process is smooth, reducing the impact on the load during the switching process without interrupting power supply. Furthermore, the grid-connected / off-grid switching method of this embodiment can be applied to different phase sequences, improving the adaptability and flexibility of the three-phase energy storage inverter to the three-phase power grid, reducing switching operations by grid personnel, and improving the user experience. The grid-connected / off-grid switching method of this embodiment can execute the process from detecting a three-phase power grid abnormality to completing the mode switching within 10ms, quickly switching the mode of the three-phase energy storage inverter without interrupting the connection between the three-phase energy storage inverter and the load, thus improving the practicality of the three-phase energy storage inverter.

[0093] Please see Figure 6 , Figure 6 This is a schematic diagram of an embodiment of the energy storage system provided in this application. Figure 6 As shown, the energy storage system of this embodiment includes an interconnected memory 52 and a processor 51. The processor 51 can also be referred to as a CPU (Central Processing Unit). The processor 51 may be an integrated circuit chip with signaling processing capabilities. The processor 51 can also be a general-purpose processor, a digital signaling processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components. The general-purpose processor can be a microprocessor or any conventional processor.

[0094] The memory 52 can be a memory module, TF card, etc., and can store all information in the energy storage system, including the input raw data, computer program, intermediate running results, and final running results. It stores and retrieves information according to the location specified by the controller. With the memory, the string matching prediction device has a memory function and can ensure normal operation. The memory of the string matching prediction device can be classified according to its purpose into main memory (RAM) and auxiliary memory (external storage), or it can be classified into external memory and internal memory. External storage is usually magnetic media or optical discs, which can store information for a long time. RAM refers to the storage components on the motherboard, used to store currently executing data and programs, but it is only used for temporary storage of programs and data; the data will be lost when the power is turned off.

[0095] In the several embodiments provided in this application, it should be understood that the disclosed methods and apparatus can be implemented in other ways. For example, the device implementations described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between devices or units through some interfaces, and may be electrical, mechanical, or other forms.

[0096] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0097] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0098] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, system server, or network device, etc.) or processor to execute all or part of the steps of the methods of the various embodiments of this application.

[0099] Please see Figure 7 , Figure 7 This is a schematic diagram of another embodiment of the energy storage system provided in this application. Figure 7 As shown, the energy storage system in this embodiment further includes a three-phase energy storage inverter, a three-phase power grid, a three-phase off-grid connection, relays, and a load. A processor is connected to the three-phase energy storage inverter and is used to switch the operating mode of the three-phase energy storage inverter using any of the on-grid / off-grid switching methods described in the above embodiments. The three-phase energy storage inverter is connected to both the three-phase power grid and the three-phase off-grid connection via relays. Under the on-grid control loop, the three-phase energy storage inverter can charge and discharge the three-phase power grid via relays, and / or discharge the load via relays. Under the off-grid control loop, the three-phase energy storage inverter can connect to the three-phase off-grid connection via relays and discharge the load.

[0100] This application also proposes a computer-readable storage medium storing program instructions that can be executed by a processor to implement the on-grid / off-grid handover method as described in any of the above embodiments.

[0101] Please see Figure 8 , Figure 8 This is a schematic diagram of the structure of an embodiment of the computer-readable storage medium provided in this application. Figure 8 As shown, the computer-readable storage medium of this application stores program instructions 61 capable of implementing all the above methods. These program instructions 61 can be stored in the storage medium in the form of a software product, including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor to execute all or part of the steps of the methods of each embodiment of this application. The aforementioned storage devices include various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks, or battery systems such as computers, servers, mobile phones, and tablets.

[0102] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for switching between parallel and offline networks, characterized in that, The grid-connected / off-grid switching method, applied to three-phase energy storage inverters, includes: When the three-phase power grid connected to the three-phase energy storage inverter is operating normally, the first phase sequence of the three-phase energy storage inverter connected to the three-phase power grid and the second phase sequence of the three-phase energy storage inverter in off-grid mode are obtained; The first phase sequence of the three-phase energy storage inverter is synchronized with the second phase sequence of the three-phase energy storage inverter. When the three-phase power grid connection is abnormal, the synchronized three-phase energy storage inverter switches from the grid-connected control loop to the off-grid control loop.

2. The on-grid / off-grid handover method according to claim 1, characterized in that, The control of synchronizing the first phase sequence of the three-phase energy storage inverter with the second phase sequence of the three-phase energy storage inverter includes: Determine whether the first phase sequence and the second phase sequence are the same; In response to the difference between the first phase sequence and the second phase sequence, the second phase sequence is updated to be synchronized with the first phase sequence.

3. The on-grid / off-grid handover method according to claim 2, characterized in that, Obtaining the first phase sequence of the three-phase energy storage inverter connected to the three-phase power grid includes: Obtain the grid voltage data of the three-phase power grid to which the three-phase energy storage inverter is connected; The grid voltage data is subjected to coordinate transformation to obtain the quadrature voltage data of the three-phase energy storage inverter; Based on the orthogonal voltage data, the first phase sequence of the three-phase energy storage inverter is obtained.

4. The on-grid / off-grid handover method according to claim 3, characterized in that, The orthogonal voltage data includes the first voltage component and the second voltage component of the grid voltage data under different coordinate axes; obtaining the first phase sequence of the three-phase energy storage inverter based on the orthogonal voltage data includes: Obtain the second voltage component at the zero-crossing moment of the first voltage component in the positive direction; In response to the second voltage component being less than a preset value, the first phase sequence of the three-phase energy storage inverter is determined to be positive. In response to the second voltage component being greater than or equal to a preset value, the first phase sequence of the three-phase energy storage inverter is determined to be negative.

5. The on-grid / off-grid handover method according to claim 1 or 4, characterized in that, The step of updating the second phase sequence to be synchronized with the first phase sequence includes: When the first phase sequence is positive and the second phase sequence is negative, the second phase sequence is updated to positive to synchronize the second phase sequence with the first phase sequence. When the first phase sequence is negative and the second phase sequence is positive, the second phase sequence is updated to negative so that the second phase sequence is synchronized with the first phase sequence.

6. The on-grid / off-grid handover method according to claim 2, characterized in that, The second phase sequence includes the A-phase signal, B-phase signal, and C-phase signal output by the three-phase energy storage inverter in the off-grid mode; The step of updating the second phase sequence to be synchronized with the first phase sequence in response to a difference between the first and second phase sequences includes: In response to the difference between the first phase sequence and the second phase sequence, the B phase signal and the C phase signal of the second phase sequence are swapped to synchronize the second phase sequence with the first phase sequence.

7. The on-grid / off-grid handover method according to claim 1, characterized in that, The on-grid / off-grid handover method further includes: When the three-phase energy storage inverter is in off-grid mode, the current second phase sequence is determined; Determine whether the connection between the three-phase energy storage inverter and the three-phase power grid is abnormal; In response to the normal connection of the three-phase power grid, the first phase sequence of the three-phase energy storage inverter connected to the three-phase power grid is obtained; The first phase sequence of the three-phase energy storage inverter is synchronized with the second phase sequence of the three-phase energy storage inverter, so as to switch the synchronized three-phase energy storage inverter from the off-grid control loop to the grid-connected control loop.

8. The on-grid / off-grid handover method according to claim 7, characterized in that, Determining whether the connection between the three-phase energy storage inverter and the three-phase power grid is abnormal includes: Obtain the voltage modulus and voltage limit of the three-phase energy storage inverter; Based on the relationship between the voltage magnitude and the voltage limit, it is determined whether the connection between the three-phase energy storage inverter and the three-phase power grid is abnormal.

9. The on-grid / off-grid handover method according to claim 1, characterized in that, When the three-phase power grid connection is abnormal, the control of the synchronized three-phase energy storage inverter to switch from the grid-connected control loop to the off-grid control loop includes: Obtain the voltage modulus and voltage limit of the three-phase energy storage inverter; Based on the relationship between the voltage magnitude and the voltage limit, determine whether the connection between the three-phase energy storage inverter and the three-phase power grid is abnormal; In response to the three-phase grid connection anomaly, the three-phase energy storage inverter is controlled to switch from the grid-connected control loop to the off-grid control loop.

10. An energy storage system, characterized in that, Includes a processor and a memory connected to the processor, wherein, The memory stores program instructions; The processor is used to execute program instructions stored in the memory to implement the on-grid / off-grid switching method as described in any one of claims 1 to 9.

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