Active fault detection method for energy storage system and energy storage system

Abstract

The application provides a kind of active fault detection method of energy storage system and energy storage system.The active fault detection method of energy storage system includes: the step of making the state of charge of energy storage battery reach the first preset value;The discharge time acquisition step that makes the energy storage battery discharge to the state of charge reach the second preset value with constant current a, cut off discharge and obtain discharge time T, wherein the second preset value is less than the first preset value;Judge whether the discharge time T is less than or equal to the preset discharge time t, if yes, determine that the energy storage battery exists hidden fault or its service life appears serious recession, if not, determine that the energy storage battery is normal.The technical scheme of the application can judge whether the energy storage battery exists hidden fault or its service life appears serious recession.

Description

Technical Field

[0001] This invention relates to the field of energy storage battery technology, and more specifically, to an active fault detection method and energy storage system for an energy storage system. Background Technology

[0002] Microgrids are the primary application area for energy storage systems. The roles of energy storage systems in microgrids include: 1) Improving the stability of distributed energy sources. Distributed energy sources, such as solar and wind power, are affected by external environmental factors like sunlight and wind speed, resulting in random power generation. Energy storage systems can balance these fluctuations and stabilize output within the microgrid; 2) Improving power quality for users. When a microgrid is connected to other grids, its power quality must meet national standards. Parameters such as power factor, voltage mismatch, and voltage sag must meet standard values. Energy storage systems can quickly provide power buffering, supporting both active and reactive power, and stabilizing voltage fluctuations; 3) Peak shaving and frequency regulation. In a microgrid, energy storage can absorb excess power generated by distributed energy sources during off-peak hours and release power during peak load periods, thereby reducing the operational and maintenance burden on the grid. Therefore, energy storage systems need to operate continuously. However, with the increase in the number of charge-discharge cycles, their lifespan degradation, internal faults, and battery consistency issues become increasingly prominent. Furthermore, energy storage systems cannot be moved after operation at the project site, making it difficult to verify their reliability.

[0003] The inventors have developed a battery fault diagnosis method for battery packs. After the battery pack has undergone multiple charging, discharging operations, and faults, the method uses remote monitoring data (stored data) to diagnose the battery pack. Specifically, the method uses the highest voltage value Vmax and the lowest voltage value Vmin of the series modules of the battery pack to perform an overall diagnosis of the battery pack and screen out faulty battery packs.

[0004] The above method involves screening faulty batteries based on stored data after a battery pack malfunctions. However, the dangers of charging and discharging are far greater than those of static batteries, whether they are power batteries or energy storage batteries. The diagnostic method for static batteries cannot predict malfunctions. Faulty batteries can only be identified after a malfunction occurs during the charging and discharging process. If the battery malfunction is not apparent, it is impossible to actively identify and determine the malfunction.

[0005] In existing technologies, most batteries, either during initial production or after a period of operation, suffer from internal or external welding defects or manufacturing flaws, such as external poor soldering or internal faults within individual cells. Under normal charging and discharging conditions (constant current charging and discharging), the energy storage system can still operate normally despite these faults, meaning the faults are difficult to detect (i.e., the energy storage battery has hidden faults). Only after a period of vibration during transportation or operation will these faults become apparent or cause a significant decline in the battery's lifespan. The method known to the inventor can only identify faults after they have occurred and become apparent. If the fault is not apparent, it cannot be actively identified and judged, and hidden faults are difficult to detect, which can easily lead to the failure of the entire energy storage system. Summary of the Invention

[0006] The main objective of this invention is to provide an active fault detection method and an energy storage system for an energy storage system. The active fault detection method for the energy storage system can determine whether there are hidden faults in the energy storage battery or whether its service life has seriously declined.

[0007] To achieve the above objectives, the present invention provides an active fault detection method for an energy storage system, comprising: a step of bringing the state of charge of the energy storage battery to a first preset value; a step of discharging the energy storage battery with a constant current a until its state of charge reaches a second preset value, stopping the discharge, and obtaining a discharge time T, wherein the second preset value is less than the first preset value; and a step of determining whether the discharge time T is less than or equal to a preset discharge time t. If so, the energy storage battery is determined to have a hidden fault or its service life has seriously declined; if not, the energy storage battery is determined to be normal.

[0008] Furthermore, the energy storage battery includes multiple cells, each numbered i, where i can be from 1 to n, and n is an integer greater than 1. After determining that the energy storage battery has a hidden fault or its service life has severely degraded, the active fault detection method of the energy storage system also includes: obtaining the voltage Vi of each cell i at the time of discharge cutoff; determining whether each voltage Vi is less than or equal to the sum of the energy storage battery's termination voltage and voltage fluctuation value; if so, cell i is determined to be abnormal and replaced; if not, cell i is determined to be fault-free.

[0009] Furthermore, the discharge time acquisition step includes: discharging the energy storage battery with a constant current a using an energy storage converter and recording the initial time T1; determining whether the state of charge of the energy storage battery is less than or equal to a second preset value; if so, controlling the energy storage battery to stop discharging using the energy storage converter and recording the cutoff time T2; if not, continuing the discharge step; wherein, the discharge time T = cutoff time T2 - initial time T1.

[0010] Furthermore, the step of bringing the state of charge of the energy storage battery to a first preset value includes: powering on the energy storage system; determining whether the state of charge of the energy storage battery is less than or equal to the first preset value; if so, performing the step of determining whether the state of charge of the energy storage battery is equal to the first preset value; if not, performing the step of discharging the energy storage battery, and performing the step of determining whether the state of charge of the energy storage battery is less than or equal to the first preset value after discharging for a period of time.

[0011] Furthermore, the step of bringing the state of charge of the energy storage battery to a first preset value also includes: determining whether the state of charge of the energy storage battery is equal to the first preset value; if so, performing the discharge time acquisition step; if not, performing the charging step of the energy storage battery, and performing the step of determining whether the state of charge of the energy storage battery is equal to the first preset value after charging for a period of time.

[0012] Furthermore, before the discharge time acquisition step and after the step of bringing the state of charge of the energy storage battery to a first preset value, the active fault detection method of the energy storage system also includes: the microgrid controller issuing a standby command to the energy storage converter; disconnecting the electrical connection between the control energy storage battery and the microgrid; and connecting the energy storage battery, the energy storage converter, and the load in sequence to form a test circuit.

[0013] Furthermore, after determining that the energy storage battery is normal, the active fault detection method for the energy storage system also includes: the microgrid controller issuing a standby command to the energy storage converter; using the microgrid controller to control the test circuit to disconnect; and using the microgrid controller to connect the energy storage battery to the microgrid.

[0014] Furthermore, after determining that the energy storage battery is normal, the active fault detection method of the energy storage system also includes: a periodic inspection judgment step to determine whether the difference between the current time and the end time of the last detection is greater than or equal to the detection cycle. If so, a step to make the state of charge of the energy storage battery reach a first preset value is executed. If not, a preset time delay is executed, and then the periodic inspection judgment step is executed.

[0015] According to another aspect of the present invention, an energy storage system is provided, employing the above-described active fault detection method for the energy storage system. The energy storage system includes: an energy storage converter, an energy storage battery, a load, and a first switch connected sequentially to form a test circuit for detecting whether the energy storage battery is faulty. The energy storage converter is used for AC / DC conversion with the power grid and for controlling the charging and discharging power of the energy storage battery. The first switch is configured to be controlled and connected to a microgrid controller to control whether the test circuit is closed. The energy storage system also includes a microgrid controller and a second switch controlled and connected to the microgrid controller. The second switch is located between the energy storage converter and the microgrid, and both the energy storage converter and the first switch are controlled and connected to the microgrid controller.

[0016] Furthermore, the energy storage system also includes a battery management system connected to the energy storage battery control, a microgrid controller connected to the battery management system, and the battery management system used to collect the voltage Vi of each cell i.

[0017] By applying the technical solution of this invention, the energy storage battery can be disconnected from the microgrid by controlling the energy storage converter (PCS) and the second switch through the microgrid controller, thus avoiding affecting the operation of the microgrid when fault detection of the energy storage battery is performed. Furthermore, a load connected in series with the energy storage battery is provided on the test circuit. This load can absorb the power during the energy storage system test, providing test conditions for the energy storage system. The microgrid controller can connect the energy storage battery to the load by closing the first switch, forming an independent test circuit. Then, the microgrid controller controls the energy storage battery to charge and discharge through the energy storage converter. During the charging and discharging of the energy storage battery, the following active fault detection method for the energy storage system is used to detect faults. In this way, not only can faults in the energy storage battery be effectively detected, but the operation of the microgrid can also be avoided. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0019] Figure 1 A flowchart illustrating an embodiment of the active fault detection method for an energy storage system according to the present invention is shown;

[0020] Figure 2 Another flowchart illustrating an embodiment of the active fault detection method for an energy storage system according to the present invention is shown; and

[0021] Figure 3 A schematic diagram of an embodiment of the energy storage system of the present invention is shown. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] like Figure 3As shown, an embodiment of the present invention provides an energy storage system that employs the following active fault detection method for energy storage systems. The energy storage system includes an energy storage converter, an energy storage battery, a load, and a first switch connected sequentially to form a test circuit for detecting whether the energy storage battery is faulty. The energy storage converter is used for AC / DC conversion with the power grid and for controlling the charging and discharging power of the energy storage battery. The first switch is configured to be controlled and connected to a microgrid controller to control whether the test circuit is closed. The energy storage system also includes a microgrid controller and a second switch controlled and connected to the microgrid controller. The second switch is located between the energy storage converter and the microgrid, and both the first switch and the energy storage converter are controlled and connected to the microgrid controller.

[0024] In the above technical solution, by controlling the energy storage converter (PCS) and the second switch through the microgrid controller, the energy storage battery can be disconnected from the microgrid to avoid affecting the operation of the microgrid when the energy storage battery is being fault-detected. Furthermore, a load connected in series with the energy storage battery is provided on the test circuit. This load can absorb the power during the energy storage system test, providing test conditions for the energy storage system. The microgrid controller can connect the energy storage battery to the load by closing the first switch, forming an independent test circuit. Then, the microgrid controller controls the energy storage battery to charge and discharge through the energy storage converter. During the charging and discharging of the energy storage battery, the following active fault detection method for the energy storage system is used to detect faults. In this way, not only can faults in the energy storage battery be effectively detected, but the operation of the microgrid can also be avoided.

[0025] Furthermore, by using the aforementioned energy storage system for fault detection, and through the coordinated control of the microgrid controller, the energy storage system can automatically perform fault testing. It can also automatically and safely disconnect from the microgrid and then enter the test loop, improving the testing convenience of the energy storage system. There is no need for manual on-site connection of the test loop to test the energy storage battery, thus solving the problem of difficult on-site testing of energy storage systems in projects.

[0026] Preferably, in an embodiment of the present invention, both the first switch and the second switch are circuit breakers.

[0027] Preferably, in an embodiment of the present invention, the load must have the ability to support the energy storage battery at least 4C discharge.

[0028] Preferably, in an embodiment of the present invention, the battery management system adopts an STM32f4 series microcontroller, and the microgrid controller adopts an ARM-A53 controller.

[0029] like Figure 3 As shown in the embodiments of the present invention, the energy storage system further includes a battery management system (BMS) connected to the energy storage battery control, and a microgrid controller connected to the battery management system. The battery management system is used to collect the voltage Vi of each cell i.

[0030] With the above settings, the battery management system can obtain the voltage Vi of each cell i and transmit the obtained data to the microgrid controller, so that the microgrid controller can analyze and process the voltage data and issue control commands to protect the energy storage battery.

[0031] like Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a method for active fault detection in an energy storage system. Using the aforementioned energy storage system for detection, the method includes: a step of bringing the state of charge (SOC) of the energy storage battery to a first preset value; a step of discharging the energy storage battery at a constant current 'a' until its SOC reaches a second preset value, stopping the discharge, and obtaining a discharge time 'T', wherein the second preset value is less than the first preset value; and a step of determining whether the discharge time 'T' is less than or equal to a preset discharge time 't'. If so, the energy storage battery is determined to have a hidden fault or its lifespan has severely declined; otherwise, the energy storage battery is determined to be normal.

[0032] In the above technical solution, the discharge capacity of the energy storage battery is detected by discharging the energy storage battery with a constant current a and judging whether the discharge time T of the energy storage battery meets the requirements (that is, comparing the discharge time T of the energy storage battery with the preset discharge time t). This allows the determination of whether the energy storage battery has hidden faults or whether its service life has seriously declined. It can also effectively verify whether the cells in the energy storage battery have good consistency.

[0033] Furthermore, if the discharge time T is less than or equal to the preset discharge time t, it indicates that the consistency of the multiple cells in the energy storage battery is poor, and there is a case where a cell reaches the termination voltage in advance. Further judgment can be made to screen out the abnormal cells.

[0034] It should be noted that in the embodiments of the present invention, the discharge current a≥2C (where C is the battery charge-discharge capacity ratio, a measure of the discharge speed, and 1C refers to the current required to discharge the entire capacity of the battery in 1 hour), which allows the energy storage battery to discharge with a large current.

[0035] It should be noted that in the embodiments of the present invention, the first preset value and the second preset value are empirical values. Since the differences between the individual cells of the energy storage battery are more obvious when the battery capacity is low, and the short-board cells (abnormal cells that cause hidden faults in the energy storage battery) have a more significant impact on the output power of the energy storage battery, the first preset value and the second preset value can be selected according to the above situation. The first preset value is preferably 30%, and the second preset value is preferably 20%. In this way, the energy storage battery can be subjected to high current discharge when the capacity is low, which can quickly test the continuous power output capability of the energy storage battery, thereby testing the overall performance of the energy storage battery and discovering hidden faults in the energy storage battery.

[0036] The first preset value is greater than the discharge cutoff capacity of the energy storage battery (when the capacity of the energy storage battery reaches the discharge cutoff capacity, the energy storage battery will stop discharging).

[0037] In one embodiment, the first preset value can also be a value greater than 30%. Even when the energy storage battery is not at a low capacity, discharging the energy storage battery will affect the output power of the energy storage battery due to the short circuit cell. This can also help determine whether there is a hidden fault in the energy storage battery.

[0038] It should be noted that in the embodiments of the present invention, the preset discharge time t is an empirical value obtained by normal battery cells through a large number of charge and discharge tests. For example, if the difference between the first preset value and the second preset value is 10%, and the discharge is carried out at a discharge rate of 2C, then t is 0.04h.

[0039] It should be noted that in the embodiments of the present invention, hidden faults refer to the fact that most batteries may have problems with poor welding or poor battery manufacturing process, such as external poor welding or internal faults of individual cells, at the beginning of production or after a period of operation. Under normal charging and discharging conditions (constant current charging and discharging), the energy storage system can still operate normally with the above-mentioned faults, that is, the faults are difficult to show (i.e., the energy storage battery has hidden faults), and the faults will only become apparent after a period of vibration or operation such as transportation.

[0040] It should be noted that, in the embodiments of the present invention, severe degradation of the lifespan of the energy storage battery means that the lifespan of the energy storage battery is less than 80% of the initial lifespan.

[0041] like Figure 2As shown in the embodiments of the present invention, the energy storage battery includes multiple cells, each numbered i, where i can be from 1 to n, and n is an integer greater than 1. After determining that the energy storage battery has a hidden fault or its service life has seriously declined, the active fault detection method of the energy storage system further includes: obtaining the voltage Vi of each cell i at the time of discharge cutoff; determining whether each voltage Vi is less than or equal to the sum of the termination voltage and voltage fluctuation value of the energy storage battery; if so, cell i is determined to be abnormal and replaced; if not, cell i is determined to be fault-free.

[0042] By setting up the above, the problematic cell that is closest to the termination voltage can be identified among all the cells, and the problematic cell can be screened out and replaced, thus eliminating abnormal cells. This can effectively extend the service life of the energy storage system, effectively avoid cell failures during daily operation of the energy storage battery, and improve the safety performance and health index of the energy storage system.

[0043] It should be noted that in the embodiments of the present invention, the battery termination voltage is related to the battery type and voltage level. In this embodiment, a lithium battery is used, and its termination voltage is 3.2V.

[0044] It should be noted that in the embodiments of the present invention, the voltage fluctuation value is set to 0.2V. In this way, abnormal cells that are close to the termination voltage can be identified, and the voltage of the cells can be prevented from dropping to the termination voltage.

[0045] Specifically, in embodiments of the present invention, a battery management system is used to obtain the voltage Vi of each cell i at the point of discharge cutoff.

[0046] like Figure 2 As shown, in an embodiment of the present invention, the discharge time acquisition step includes: discharging the energy storage battery with a constant current a using an energy storage converter and recording the initial time T1; determining whether the state of charge of the energy storage battery is less than or equal to a second preset value; if so, controlling the energy storage battery to stop discharging using the energy storage converter and recording the cutoff time T2; if not, executing the discharge step; wherein, the discharge time T = cutoff time T2 - initial time T1. In this way, the discharge time T of the energy storage battery from the start of discharge at the first preset value until it discharges to the second preset value can be obtained, which facilitates determining whether the discharge time T of the energy storage battery meets the requirements, thereby improving the detection accuracy.

[0047] like Figure 2As shown, in an embodiment of the present invention, the step of bringing the state of charge of the energy storage battery to a first preset value includes: powering on the energy storage system; determining whether the state of charge of the energy storage battery is less than or equal to the first preset value; if so, performing the step of determining whether the state of charge of the energy storage battery is equal to the first preset value; if not, performing the step of discharging the energy storage battery, and performing the step of determining whether the state of charge of the energy storage battery is less than or equal to the first preset value after discharging for a period of time.

[0048] By setting the above, the state of charge (SOC) of the energy storage battery can be made to reach or below the first preset value, which makes it easier for the energy storage battery to start discharging at the first preset value, thereby improving the detection accuracy.

[0049] It should be noted that, in the embodiments of the present invention, powering on the energy storage system means starting the energy storage system so that the battery management system, energy storage converter and microgrid controller are powered.

[0050] It should be noted that in the embodiments of the present invention, the discharge time period is a preset value, which can be 1 second, 2 seconds, 1 minute, etc.

[0051] After the energy storage system is powered on, the active fault detection method also includes using a microgrid controller to detect whether there are significant operational faults in the energy storage system, i.e., whether the energy storage system can operate normally. If it can operate normally, the step of judging whether the state of charge of the energy storage battery has reached a first preset value is executed. If the energy storage system cannot operate normally, there is a safety hazard in the energy storage system, and the active detection mode cannot be performed. In this way, the safety of the energy storage system can be guaranteed.

[0052] like Figure 2 As shown, in an embodiment of the present invention, the step of bringing the state of charge of the energy storage battery to a first preset value further includes: determining whether the state of charge of the energy storage battery is equal to the first preset value; if so, performing a discharge time acquisition step; if not, performing charging of the energy storage battery, and performing the step of determining whether the state of charge of the energy storage battery is equal to the first preset value after charging for a period of time, until the state of charge of the energy storage battery is replenished to the first preset value.

[0053] By setting the above parameters, the state of charge (SOC) of the energy storage battery can reach a first preset value, which facilitates the subsequent discharge of the energy storage battery at the first preset value, thereby improving the detection accuracy.

[0054] It should be noted that in the embodiments of the present invention, the charging time period is a preset value, which can be 1 second, 2 seconds, 1 minute, etc.

[0055] like Figure 2As shown, in an embodiment of the present invention, before the discharge time acquisition step and after the step of bringing the state of charge of the energy storage battery to a first preset value, the active fault detection method of the energy storage system further includes: the microgrid controller issuing a standby command to the energy storage converter; disconnecting the electrical connection between the control energy storage battery and the microgrid; and connecting the energy storage battery, the energy storage converter, and the load end to end in sequence to form a test circuit.

[0056] In the above technical solution, the microgrid controller issues a standby command to the energy storage converter, which stops the charging and discharging of the energy storage battery, thus avoiding interference with subsequent operations. Then, the second switch is used to disconnect the electrical connection between the energy storage battery and the microgrid, so that the energy storage system is completely disconnected from the grid, avoiding the generation of large inrush currents. This prevents subsequent tests from affecting the operation of the microgrid or prevents the microgrid from affecting subsequent tests. Finally, the first switch is closed to form a test loop with the energy storage battery, energy storage converter, and load. The load can be used to absorb the power during the energy storage system test, providing test conditions for the energy storage system test.

[0057] In one embodiment, the load can be manually connected to the energy storage battery on-site to form a test circuit for testing the energy storage battery.

[0058] like Figure 2 As shown in the embodiments of the present invention, after determining that the energy storage battery is normal, the active fault detection method of the energy storage system further includes: the microgrid controller issuing a standby command to the energy storage converter; using the microgrid controller to control the test circuit to disconnect; and using the microgrid controller to connect the energy storage battery to the microgrid.

[0059] In the above technical solution, after determining that the energy storage battery is normal, the microgrid controller sends a standby command to the energy storage converter to stop the energy storage battery from charging and discharging. The microgrid controller controls the first switch to open to disconnect the load from the energy storage battery. Then, the microgrid controller controls the second switch to close so that the energy storage battery can be connected to the microgrid, thereby enabling the energy storage system to continue to work.

[0060] like Figure 2 As shown in the embodiment of the present invention, after the step of determining that the energy storage battery is normal, the active fault detection method of the energy storage system further includes: a periodic inspection judgment step of determining whether the difference between the current time and the last detection end time is greater than or equal to the detection cycle; if so, then the step of making the energy storage battery state of charge reach a first preset value is executed; if not, then the preset time is delayed, and then the periodic inspection judgment step is executed.

[0061] In the above technical solution, by setting a fixed detection cycle, the energy storage system can be periodically diagnosed during normal operation. This proactively detects hidden faults within the energy storage system and identifies and replaces abnormal cells, thus preventing the entire system from failing due to a single cell failure. This improves the safety and stability of the energy storage system and enables unmanned management.

[0062] It should be noted that in the embodiments of the present invention, the detection cycle is a manually set value, which can be one year, one month, or one week.

[0063] In one embodiment, the diagnostic mode can also be entered by the software operator manually issuing a diagnostic command.

[0064] It should be noted that, in the embodiments of the present invention, the last detection end time refers to the time when the energy storage battery was determined to be normal during the last detection.

[0065] This embodiment improves the lifespan of the energy storage system by regularly inspecting and manually replacing abnormal cells, and can prevent cell failures from occurring during normal operation of the energy storage system.

[0066] It should be noted that the microgrid controller handles unified scheduling, data collection, and analysis without human intervention, which can significantly reduce manual operation and maintenance costs, enable autonomous fault detection of the energy storage system, and improve the overall safety and intelligence level of the energy storage system.

[0067] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: By controlling the energy storage converter (PCS) and the second switch through the microgrid controller, the energy storage battery can be disconnected from the microgrid to avoid affecting the operation of the microgrid when the energy storage battery is being fault-detected; and a load connected in series with the energy storage battery is also provided on the test circuit. The load can be used to absorb the power during the energy storage system test and provide test conditions for the energy storage system test. The microgrid controller can connect the energy storage battery with the load by closing the first switch to form an independent test circuit. Then, the microgrid controller controls the energy storage battery to charge and discharge through the energy storage converter. When the energy storage battery is charging and discharging, the following active fault detection method of the energy storage system is used to detect faults. In this way, not only can the faults of the energy storage battery be effectively detected, but the operation of the microgrid can also be avoided.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for active fault detection in an energy storage system, characterized in that, include: The steps to bring the state of charge of the energy storage battery to a first preset value; The step of obtaining the discharge time is to discharge the energy storage battery with a constant current a until its state of charge reaches a second preset value, cut off the discharge, and obtain the discharge time T, wherein the second preset value is less than the first preset value. Determine whether the discharge time T is less than or equal to the preset discharge time t. If yes, it is determined that the energy storage battery has a hidden fault or its service life has seriously declined. If no, it is determined that the energy storage battery is normal. The energy storage battery includes multiple cells, each numbered i, where i can be from 1 to n, and n is an integer greater than 1. After determining that the energy storage battery has a hidden fault or its service life has severely declined, the active fault detection method of the energy storage system further includes: Obtain the voltage Vi of each cell i at the point of discharge cutoff; Determine whether each voltage Vi is less than or equal to the sum of the battery's termination voltage and voltage fluctuation value. If yes, cell i is determined to be abnormal and replaced. If no, cell i is determined to be fault-free. The step of obtaining the discharge time includes: The energy storage battery is discharged with a constant current a using an energy storage converter, and the discharge steps at the initial time T1 are recorded. Determine whether the state of charge of the energy storage battery is less than or equal to the second preset value. If yes, execute the process of controlling the energy storage battery to stop discharging using the energy storage converter and record the cutoff time T2. If no, continue to execute the discharge step. Wherein, the discharge time T = cutoff time T2 - initial time T1.

2. The active fault detection method for an energy storage system according to claim 1, characterized in that, The steps to bring the state of charge of the energy storage battery to a first preset value include: Power on the energy storage system; If the state of charge of the energy storage battery is less than or equal to the first preset value, then the step of determining whether the state of charge of the energy storage battery is equal to the first preset value is executed; otherwise, the step of discharging the energy storage battery is executed, and after discharging for a period of time, the step of determining whether the state of charge of the energy storage battery is less than or equal to the first preset value is executed.

3. The active fault detection method for an energy storage system according to claim 2, characterized in that, The steps to bring the state of charge of the energy storage battery to the first preset value also include: If the state of charge of the energy storage battery is equal to the first preset value, the discharge time acquisition step is executed; otherwise, the energy storage battery is charged, and after charging for a period of time, the step of determining whether the state of charge of the energy storage battery is equal to the first preset value is executed.

4. The active fault detection method for an energy storage system according to any one of claims 1 to 3, characterized in that, Before the discharge time acquisition step, and after the step of bringing the state of charge of the energy storage battery to a first preset value, the active fault detection method of the energy storage system further includes: The microgrid controller sends a standby command to the energy storage converter; Disconnect the electrical connection between the control energy storage battery and the microgrid; Connect the energy storage battery, energy storage converter, and load sequentially to form a test circuit.

5. The active fault detection method for an energy storage system according to claim 4, characterized in that, After determining that the energy storage battery is normal, the active fault detection method of the energy storage system further includes: The microgrid controller sends a standby command to the energy storage converter; The test circuit is disconnected using a microgrid controller. A microgrid controller is used to electrically connect the energy storage battery to the microgrid.

6. The active fault detection method for an energy storage system according to any one of claims 1 to 3, characterized in that, After determining that the energy storage battery is normal, the active fault detection method of the energy storage system further includes: The periodic inspection judgment step determines whether the difference between the current time and the end time of the last detection is greater than or equal to the detection cycle. If yes, the step of making the state of charge of the energy storage battery reach the first preset value is executed. If no, the preset time is delayed, and then the periodic inspection judgment step is executed.

7. An energy storage system, characterized in that, The fault detection method of the energy storage system according to any one of claims 1 to 6 is used to detect faults, wherein the energy storage system comprises: An energy storage converter, an energy storage battery, a load, and a first switch are connected in sequence to form a test circuit for detecting whether the energy storage battery is faulty. The energy storage converter is used for AC / DC conversion with the power grid and for charging and discharging power control of the energy storage battery. The first switch is configured to be connected to a microgrid controller to control whether the test circuit is closed. The energy storage system also includes a microgrid controller and a second switch connected to the microgrid controller. The second switch is located between the energy storage converter and the microgrid, and both the energy storage converter and the first switch are connected to the microgrid controller.

8. The energy storage system according to claim 7, characterized in that, The energy storage system also includes a battery management system that is controlled and connected to the energy storage battery. The microgrid controller is controlled and connected to the battery management system. The battery management system is used to collect the voltage Vi of each cell i.

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