Thermal runaway protection method and system for immersed liquid-cooled battery energy storage system

Abstract

The invention relates to the technical field of safety of electrochemical energy storage systems, and discloses a thermal runaway protection method and system for an immersed liquid-cooled battery energy storage system, and the method comprises the steps: monitoring a vibration signal of the surface of a box body through a vibration sensor array arranged outside a sealed box body; a hydraulic hammer impact event caused by thermal runaway in the sealed box body is judged, and an impact area is positioned according to the difference of vibration signals of all sensors in the vibration sensor array; the sealed box body is subjected to pressure relief through the pressure relief device; and activating an enhanced cooling program of the cooling loop. A set of heat management system is designed, the vibration sensor array is arranged on the outer wall of the box body, the signal characteristics of the vibration sensor array are analyzed, then pressure relief is conducted through the multi-stage pressure relief channel, and finally the cooling loop circulation flow is increased and the reinforced cooling medium is introduced at the same time. And the immersed liquid-cooled battery energy storage system is helped to really get rid of thermal runaway and recover to a safe state.

Description

Technical Field

[0001] This invention relates to the field of safety technology for electrochemical energy storage systems, and more specifically, to a method and system for thermal runaway protection of immersion liquid-cooled battery energy storage systems. Background Technology

[0002] With the development of battery energy storage systems, immersion liquid cooling technology has become a key direction for improving the energy density and thermal safety of energy storage systems. This technology completely immerses the battery module in insulating coolant, and achieves efficient and uniform heat dissipation through the high specific heat capacity of the liquid and direct contact, thereby significantly suppressing the temperature difference between cells and the formation of hot spots.

[0003] However, while the full immersion feature provides extremely high heat dissipation efficiency and fire resistance, it also introduces a physical risk that is easily overlooked. When a battery cell inside the enclosure experiences rapid thermal runaway, the large amount of high-temperature gas generated instantaneously expands and collapses rapidly in the nearly incompressible coolant, triggering a powerful transient pressure shock wave. This phenomenon is also known as the hydraulic hammer effect caused by local overpressure. The destructive mode of this thermal runaway differs from slow pressure accumulation; the resulting shock wave has extremely high peak pressure and propagates extremely quickly. Existing safety designs for immersion systems mostly focus on thermal management and fire suppression, such as installing simple mechanical pressure relief valves or linking fire sprinklers. These are passive response measures against static or quasi-static pressure rises and combustion, and cannot effectively identify, buffer, or dissipate this millisecond to second-level dynamic hydraulic hammer impact. Ultimately, the shock wave may cause mechanical structural damage to adjacent battery cells, electrical connection failure, or even rupture of the sealed enclosure, thereby triggering a series of catastrophic chain reactions. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application designs a thermal management system. By arranging a vibration sensor array on the outer wall of the enclosure and analyzing its signal characteristics, then using multi-stage pressure relief channels for pressure relief, and finally by simultaneously increasing the circulation flow of the cooling circuit and introducing enhanced cooling medium, the immersion liquid-cooled battery energy storage system can truly escape thermal runaway and return to a safe state.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention discloses a method for thermal runaway protection in an immersed liquid-cooled battery energy storage system. The immersed liquid-cooled battery energy storage system includes a sealed enclosure, a battery module placed inside the sealed enclosure, and a cooling circuit for circulating insulating coolant. The method includes:

[0007] Vibration signals on the surface of the sealed enclosure are monitored by an array of vibration sensors located outside the enclosure. Predetermined characteristic quantities of the vibration signals are extracted. When the predetermined characteristic quantities exceed a preset threshold, it is determined that a hydraulic hammer impact event caused by thermal runaway has occurred inside the sealed enclosure. If a hydraulic hammer impact event is determined to have occurred, the impact area is located based on the difference in vibration signals of each sensor in the vibration sensor array.

[0008] The pressure relief device is used to relieve pressure on the sealed box. The pressure relief device includes multiple pressure relief channels with different response thresholds. When the pressure inside the sealed box reaches the corresponding response threshold, the pressure relief channels of different levels are opened in sequence.

[0009] Based on the identified impact zone, an enhanced cooling process is activated in the cooling circuit. This enhanced cooling process includes increasing the circulation flow rate of the cooling circuit and introducing enhanced cooling medium into the cooling circuit.

[0010] Furthermore, methods for locating the impact zone include:

[0011] Spectral analysis of the vibration signal is performed to extract the signal energy within a predetermined characteristic frequency band as a predetermined characteristic quantity;

[0012] The location of the impact zone is determined based on the arrival time difference of the predetermined characteristic quantities received by sensors at different positions in the vibration sensor array.

[0013] Furthermore, the multi-stage pressure relief channel includes at least one low-pressure guide channel and at least one high-pressure main relief channel;

[0014] The response threshold corresponding to the low-pressure guide channel is the first-level pressure threshold, and the response threshold corresponding to the high-pressure main venting channel is the second-level pressure threshold. The second-level pressure threshold is greater than the first-level pressure threshold.

[0015] When the pressure inside the sealed enclosure reaches the first-level pressure threshold, the low-pressure guide channel is opened.

[0016] When the pressure inside the sealed enclosure reaches the second-level pressure threshold, the high-pressure main venting channel is opened.

[0017] Furthermore, the outlet of the low-pressure guide channel is connected to a guide pipe to direct the released initial gas-liquid mixture to a designated area within the sealed enclosure.

[0018] Furthermore, the cooling medium is enhanced to be a perfluorinated compound with phase change endothermic properties;

[0019] Methods for introducing enhanced cooling media into a cooling circuit include: when activating an enhanced cooling program, injecting a perfluorinated compound stored in a separate tank into the cooling circuit, causing it to mix with the circulating insulating coolant.

[0020] Furthermore, methods for activating enhanced cooling procedures in the cooling circuit include:

[0021] Increase the drive power of the circulating pump in the cooling circuit to improve the total system circulation flow;

[0022] The valves in the cooling circuit are adjusted synchronously to increase the proportion of flow through the branch where the positioning impact area is located.

[0023] Furthermore, after depressurizing the sealed housing using the pressure relief device, a cascading fault diagnosis step is also included:

[0024] The vibration signal characteristics and the internal pressure of the sealed enclosure are continuously monitored after the discharge. If neither of them drops below their respective safety thresholds within the preset observation time window, it is determined that a multi-cell cascade thermal runaway has occurred, and a system-level emergency shutdown and fault isolation are performed.

[0025] Furthermore, the decision conditions for activating the enhanced cooling procedure that activates the cooling circuit also include:

[0026] The rate of change of coolant temperature corresponding to the located impact area was found to exceed the change threshold.

[0027] Furthermore, the placement of the vibration sensor array is determined based on the structural vibration modal analysis of the sealed housing under the characteristic frequency band of hydraulic hammer impact.

[0028] Secondly, the present invention discloses a thermal runaway protection system for an immersion liquid-cooled battery energy storage system, used to implement the thermal runaway protection method for the immersion liquid-cooled battery energy storage system, the system comprising: a vibration monitoring module, a graded pressure relief module, an enhanced cooling control module, and a central controller.

[0029] The vibration monitoring module includes a vibration sensor array disposed outside the sealed housing and an analysis unit connected thereto. The analysis unit is configured to perform vibration signal characteristic analysis, preset threshold comparison and impact area location.

[0030] A graded pressure relief module includes a pressure relief device connected to a sealed housing, the pressure relief device including multi-stage pressure relief channels with different response thresholds;

[0031] The enhanced cooling control module includes a drive and valve unit for increasing the circulation flow of the cooling circuit, an independent storage tank for storing the enhanced cooling medium, and an injection unit connecting the cooling circuit and the independent storage tank.

[0032] The central controller, which communicates with the vibration monitoring module, the graded pressure relief module, and the enhanced cooling control module, is configured to, after determining that a hydraulic hammer impact event has occurred inside the sealed housing and locating the impact area, control the graded pressure relief module to depressurize the sealed housing, and control the enhanced cooling control module to execute the enhanced cooling program according to the located impact area.

[0033] Compared with related technologies, the present invention has the following beneficial effects:

[0034] This invention, by arranging a vibration sensor array on the outer wall of the enclosure and analyzing its signal characteristics, shifts the sensing object from the transient pressure inside the coolant, which is difficult to monitor reliably, to the vibration of the enclosure structure that is inevitably excited by this pressure and reliably transmitted. This enables reliable detection and localization of hydraulic hammer impact events. After obtaining the localization information, a multi-stage pressure relief channel based on different response thresholds is used as the core buffer mechanism. Different levels of pressure relief actions are triggered sequentially according to the impact intensity, transforming a steep destructive pressure peak into a phased pressure release process acceptable to the management system. Finally, by simultaneously increasing the circulation flow of the cooling circuit and introducing enhanced cooling medium, not only is the cooling capacity enhanced spatially, but a higher heat capacity intervention medium is also introduced at the energy transfer level. This allows the system to apply a targeted and enhanced cooling attack to the thermal runaway region while releasing the mechanical impact, aiming to suppress the electrochemical reaction rate from the energy source, thereby terminating the continuous pressure source of the hydraulic hammer and helping the submerged liquid-cooled battery energy storage system truly escape thermal runaway and return to a safe state.

[0035] This invention analyzes the signal energy within a predetermined characteristic frequency band and uses the spatiotemporal information of a sensor array for positioning. This enables the system to accurately extract the unique spectrum of hydraulic hammer impact from complex background vibration noise. By comparing the arrival order of signals from multiple sensors, the abstract impact event is transformed into specific three-dimensional coordinates within the chamber. This provides an indispensable spatial reference for subsequent precise control measures in all related areas, improving the targeting and efficiency of the entire system's actions and avoiding the resource waste and potential disturbances caused by traditional all-domain response.

[0036] This invention uses perfluorinated compounds with phase change endothermic properties as an enhanced cooling medium. The phase change process of perfluorinated compounds can absorb a huge amount of latent heat under near-constant temperature conditions. Thus, when cooling thermally runaway battery cells, the surface and surrounding temperature can be quickly suppressed below the critical point of the material's thermal runaway reaction. This method of actively grabbing heat through medium phase change improves both speed and efficiency compared to the traditional approach of simply increasing convection heat transfer. Attached Figure Description

[0037] Figure 1This is a schematic flowchart illustrating the steps of the thermal runaway protection method for an immersed liquid-cooled battery energy storage system provided by the present invention.

[0038] Figure 2 This invention provides a data processing flowchart for a thermal runaway protection system in an immersion liquid-cooled battery energy storage system. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] Please see Figure 1 As shown, this embodiment provides a thermal runaway protection method for an immersed liquid-cooled battery energy storage system. An immersed liquid-cooled battery energy storage system typically includes a sealed enclosure, battery modules housed within the sealed enclosure, and a cooling circuit for circulating insulating coolant. The complete process of this protection method includes steps one through three, which will be described in detail below:

[0042] Step 1: Vibration signals on the surface of the sealed enclosure are monitored by a vibration sensor array set outside the enclosure. Predetermined characteristic quantities of the vibration signals are extracted. When the predetermined characteristic quantities exceed a preset threshold, it is determined that a hydraulic hammer impact event caused by thermal runaway has occurred inside the sealed enclosure. The impact area is located based on the differences in vibration signals from each sensor in the vibration sensor array.

[0043] In this embodiment, the vibration sensor array specifically refers to a piezoelectric accelerometer network. Its placement is not arbitrary. For example, the placement of the vibration sensor array is determined based on the structural vibration modal analysis of the sealed housing under the characteristic frequency band corresponding to the hydraulic hammer impact event.

[0044] Specifically, during the system design phase, the first few natural vibration modes of the sealed box in a predetermined characteristic frequency band (e.g., set to 50-2000Hz, which can be adjusted multiple times) can be calculated using finite element analysis software. The sensors are then preferentially installed at the antinodes (where the dynamic strain is the greatest) of the vibration modes, such as the center of the box side plate or the intersection of the reinforcing ribs. This arrangement ensures the highest sensitivity to the excitation of hydraulic hammer impact events.

[0045] External vibration monitoring is used instead of internal pressure sensing because: if internal pressure sensors are used, they may face serious challenges such as sealing failure, corrosion, and signal drift due to long-term immersion in coolant, resulting in low reliability. Monitoring the vibration of the enclosure structure caused by internal pressure impacts is an indirect but highly reliable and long-life sensing method. Not only does the sensor not need to be in contact with the coolant, but it also has low maintenance costs.

[0046] In practical use, when a battery cell experiences an internal short circuit and enters the initial stage of thermal runaway, the instantaneously generated high-temperature gas forms a violent pressure wave (hydraulic hammer) in the coolant. This mechanical impact is transmitted to the outer wall through the enclosure structure, triggering specific vibrations. This vibration signal is captured by a vibration sensor array located outside the sealed enclosure. The characteristic quantities of the vibration signal are then analyzed. If the value exceeds a preset threshold (since this embodiment discusses the situation in the initial stage of thermal runaway, the analysis result will inevitably exceed the preset threshold), it is determined that a hydraulic hammer impact event caused by thermal runaway has occurred inside the sealed enclosure.

[0047] Among them, the characteristic quantity of the vibration signal (denoted as R) is the core quantitative indicator used to judge the event. In this embodiment, the relative energy ratio within a predetermined characteristic frequency band is used as the characteristic quantity R, which is defined as: the ratio of the total energy E of the current signal within the predetermined characteristic frequency band to the average energy E1 of the system in the same frequency band under the reference normal state, that is, R=E / E1. This characteristic quantity is chosen because the impact energy of the hydraulic hammer is concentrated in the mid-to-high frequency band, while the vibration energy of pumps, fans and other normal operating equipment is mainly distributed in the low frequency band.

[0048] It is important to understand that the preset threshold is the threshold value for judging whether the feature quantity R is abnormal, and the setting of this threshold N can follow the principles of statistical learning and adaptation.

[0049] For example, during the initial learning process, such as after the system's first commissioning or major overhaul, the system should operate stably for at least 24 hours under typical charge and discharge conditions, collecting vibration data from all sensors. For each sensor, calculate the characteristic quantity R of its data per second, obtaining a set of samples {R1, R2, ..., Rm}. Calculate the arithmetic mean μ and standard deviation σ of this sample set. The initial threshold N can be set as N = μ + k × σ. Here, k is a safety factor, which can be selected according to the requirements for the system's false alarm rate. Typically, k can be set between 3 and 5, which means that under the assumption of a normal distribution, the probability of R exceeding N during normal operation is extremely low.

[0050] The online adaptive phase refers to the periodic (usually weekly) inclusion of new feature quantity R samples that are not identified as events and are under normal operating conditions into the historical data pool after the system is running. μ and σ are recalculated on a rolling basis, and the threshold N is fine-tuned. This allows the system to adapt to the slow drift of background vibration caused by seasonal changes and equipment aging.

[0051] Specifically, when analyzing whether the characteristic quantity of the vibration signal exceeds the preset threshold, it is necessary to first collect the original acceleration signal a acquired by each sensor in the vibration sensor array, and perform hardware anti-aliasing filtering and digitization. In the analysis unit, the continuous data window with a length of T (which can be set to 0.1 seconds in this embodiment) is processed: the DC component is removed, a Hanning window is added, and then the frequency spectrum A(f) of the signal is obtained by fast Fourier transform. Then, the energy E of the data window T in the predetermined characteristic frequency band [f1,f2] is calculated.

[0052] It's important to understand that the predetermined characteristic frequency bands [f1, f2] originate from experimental analysis and data calibration of the system itself. During the system development phase, a continuous frequency range can be identified by comparing and analyzing known hydraulic hammer impact events with the vibration signal spectra collected under numerous normal operating conditions. The selection criterion for this range is that the average energy of the impact signal within this range is consistently and significantly higher than the energy of the background operating noise, thus maximizing the differentiation between fault signals and daily interference. The lower limit f1 of the range is typically set above a frequency point that effectively filters out major low-frequency operating noise (such as the pump fundamental frequency and its main harmonics, usually below 50Hz) to avoid strong background noise; the upper limit f2 can be determined based on the effective range of vibration transmission in the housing structure.

[0053] E is obtained by summing the squares of the spectral amplitudes at all discrete frequency points within the frequency band, and can be expressed by the formula: E=Σ|A(fn)| 2 Where fn represents a discrete frequency point, the summation range covers all frequency points that satisfy f1≤fn≤f2, and |A(fn)| is the spectral amplitude at frequency fn. (The formula uses the square of the amplitude to represent the contribution of the frequency component to the total signal energy, which is also a common and fundamental method for calculating bandwidth energy in digital signal processing).

[0054] By summing the energy of all frequency components within the predetermined characteristic frequency band through the above operations, the total energy E of the frequency band can be obtained. Then, the energy E of the data window within the predetermined characteristic frequency band is calculated, and the corresponding E1 of the sensor is called to calculate the current characteristic quantity R.

[0055] Next, R is compared with the current preset threshold N of the sensor. If R > N, an initial trigger signal is generated. To eliminate transient interference, more continuous data windows (e.g., three consecutive data windows, or 0.3 seconds) need to be collected for further confirmation. If more than a preset proportion (which can be set to 2 / 3 in this embodiment) of data windows satisfy R > N during this period, it is finally determined that a hydraulic hammer impact event caused by thermal runaway has occurred in the area covered by the sensor.

[0056] Once an impact event is confirmed, the impact area is immediately located based on the differences in the signals from each sensor in the vibration sensor array.

[0057] For example, the method for locating the impact area includes: performing spectral analysis on the vibration signal and extracting the signal energy within a predetermined characteristic frequency band as a predetermined characteristic quantity; determining the location of the impact area based on the arrival time difference of the predetermined characteristic quantity received by sensors at different positions in the vibration sensor array. In this embodiment, the location can be based on the principle of vibration wave arrival time difference.

[0058] Specifically, first, from all the initially triggered sensors, determine the sensor S0 that reaches the threshold first, and record its trigger time as t0. Then select the other two sensors S1 and S2 that also trigger, and their trigger times are t1 and t2 respectively (t1, t2>t0).

[0059] The propagation speed v of the vibration wave in the box material is known (it can be obtained through experiments or material handbooks). Let the impact source point be i, and the coordinates of each sensor position are known. According to wave theory, the following relationships exist: distance (S1,i) - distance (S0,i) = v × (t1 - t0); distance (S2,i) - distance (S0,i) = v × (t2 - t0).

[0060] Using the above hyperbolic equations and a mature hyperbolic intersection positioning algorithm, the two-dimensional or three-dimensional coordinates of the impact source P in the box coordinate system can be calculated, thus realizing the positioning of the impact area.

[0061] Here's a calculation example: Assume a box 2m long and 1m wide, with sensors S1 at coordinates (0, 0.5), S2 at (1, 0.5), and S3 at (2, 0.5). If S1 triggers first, followed by S2 after 20 microseconds, and S3 after 35 microseconds, and given v = 5000m / s, the impact point can be calculated to be approximately 0.1 meters in front of sensor S1, in the middle of the box's depth.

[0062] In the implementation of step one, an external vibration sensor array is used to monitor whether a hydraulic hammer impact event caused by thermal runaway occurs inside the sealed box, and to provide the location information of the impact area for the next step.

[0063] Step two: Depressurize the sealed box using a pressure relief device. The pressure relief device includes multi-stage pressure relief channels with different response thresholds. When the pressure inside the sealed box reaches the corresponding response threshold, the pressure relief channels of different stages are opened sequentially.

[0064] After locating the impact zone, the pressure relief device depressurizes the sealed housing. This device includes at least two stages of pressure relief channels with different response thresholds. Because the hydraulic hammer pressure rises extremely rapidly (milliseconds), the response speed and control complexity of electric valves are unreliable under extreme conditions. Mechanical pressure relief valves, however, can meet the response speed requirements by relying on preset springs or diaphragms, and are reliable and maintenance-free. Therefore, in this embodiment, a two-stage mechanical pressure relief valve assembly can be used as a typical implementation.

[0065] For example, the multi-stage pressure relief channel includes at least one low-pressure guide channel and at least one high-pressure main relief channel; the response threshold corresponding to the low-pressure guide channel is the first-level pressure threshold, and the response threshold corresponding to the high-pressure main relief channel is the second-level pressure threshold, the second-level pressure threshold being greater than the first-level pressure threshold; when the pressure inside the sealed chamber reaches the first-level pressure threshold, the low-pressure guide channel is opened to release accumulated gas and reduce the pressure rise rate; when the pressure inside the sealed chamber reaches the second-level pressure threshold, the high-pressure main relief channel is opened.

[0066] Specifically, in this embodiment, the first-level pressure threshold M1 of the low-pressure guide channel can be set to 30% to 50% of the design pressure-bearing capacity of the sealed enclosure. This setting follows two clear engineering boundaries: the lower limit must be higher than the maximum pressure fluctuation peak that may occur during normal operation and charging / discharging of the system to ensure that accidental opening does not occur under normal operating conditions; the upper limit must be lower than the critical damage pressure that the cell module structure can withstand to ensure that the guide channel has been activated before the pressure reaches the damage threshold. A typical design practice is to take a safety factor as a reference for the upper limit based on the cell module's ultimate withstand voltage test data.

[0067] In this embodiment, the second-stage pressure threshold M2 of the high-pressure main relief channel can be set to 60% to 80% of the design pressure-bearing capacity of the sealed enclosure. Its setting also follows clear engineering constraints: the lower limit must be higher than the first-stage pressure threshold M1 of the low-pressure guide channel to ensure a progressive pressure response sequence between the two relief channels; the upper limit must be lower than the ultimate pressure-bearing capacity of the sealed enclosure structure design and leave sufficient safety margin to ensure that even if the low-pressure guide channel's relief capacity is insufficient, causing the pressure to continue to rise, the enclosure structure remains within an absolutely safe pressure-bearing range after the high-pressure main relief channel is opened. In engineering practice, M2 is usually determined by dividing the ultimate pressure value obtained from the enclosure burst test by a safety factor and then reversing the result.

[0068] By introducing a quantifiable reference system of design bearing capacity percentage, and clarifying that M1 and M2 are subject to multiple constraints such as damage threshold, operational fluctuation threshold, hierarchical progression relationship, and structural safety margin, those skilled in the art can clearly understand that these two thresholds are not arbitrarily selected parameters, but rather executable values ​​calculated based on the physical characteristics of the system itself, following a clear engineering design logic.

[0069] Since direct discharge may spray high-temperature flammable materials onto the healthy battery cells, in order to prevent the high-temperature, high-speed gas-liquid mixture released from the low-pressure guide channel from directly impacting the surface of the adjacent battery module and causing electrical short circuits or secondary thermal runaway, a safe flow guiding design is implemented for the channel in this embodiment.

[0070] For example, the outlet of the low-pressure guide channel is connected to a guide pipe to direct the initial gas-liquid mixture released into a designated area within the sealed enclosure to avoid direct impact on adjacent battery modules.

[0071] In this embodiment, the designated area refers to the internal area of ​​the enclosure that is predetermined during the system design phase based on the internal spatial layout of the sealed enclosure, the installation position of the battery module, the outlet position of the low-pressure guide channel, and the flow path of the discharged material, and is used to receive the initial gas-liquid mixture flow discharged from the low-pressure guide channel.

[0072] The determination of the designated area should at least meet the following requirements: First, the designated area should maintain a sufficient distance from the battery module and its electrical connection components to avoid direct impact from the discharged fluid; Second, the designated area should have sufficient liquid buffer space or be equipped with a buffer structure for energy absorption and flow guidance so that the initial gas-liquid mixture discharged can be decelerated, cooled and dispersed within the area; Third, the designated area should not affect the normal circulation of coolant within the sealed enclosure.

[0073] Specifically, the outlet of the low-pressure guide channel is not directly open, but is connected to a guide pipe. The end of the pipe extends and is fixed to a designated area, such as an empty liquid corner inside the box away from all battery modules, or a specially designed small buffer cavity with energy-absorbing material on its inner wall.

[0074] In this way, the initial release is directed to a designated area, where it is slowed down, cooled, and dissolved in the liquid, completely preventing the release itself from becoming a new source of risk.

[0075] After the pressure relief device is activated, the system does not stop working, but instead enters the interlocking fault diagnosis step.

[0076] For example, the vibration signal characteristics and the internal pressure of the sealed enclosure are continuously monitored after the discharge. If neither of them drops below their respective safety thresholds within a preset observation time window, it is determined that a multi-cell cascade thermal runaway has occurred, and a system-level emergency shutdown and fault isolation are performed.

[0077] Specifically, the change trends of two key parameters after venting are continuously monitored: one is the vibration signal characteristic quantity R; the other is the internal pressure value P read by the pressure transmitter on the top of the enclosure.

[0078] Another observation time window is set. This observation time window can be pre-calibrated through a single-point thermal runaway controlled test. Specifically, in multiple thermal runaway samples that have not experienced chain diffusion, the time required from the start of pressure relief device depressurization to the recovery of both the vibration signal characteristic quantity R and the internal pressure P of the chamber to stability is recorded. A safety margin is added to the statistical results to determine the preset observation time.

[0079] In this embodiment, the observation time window can be set to 30 seconds. If R and P both show a rapid decrease and stabilize below the safety threshold within 30 seconds, it is determined that the single-point thermal runaway has been controlled.

[0080] If R or P does not decrease within 30 seconds, or even continues to rise, it is determined that a multi-cell cascading thermal runaway has occurred. At this time, the system will go beyond the current local control strategy and execute the highest level of system-level emergency shutdown and fault isolation, including: cutting off the charging and discharging circuit of the battery cluster, activating the alarm for the entire enclosure, and uploading the fault information to the cloud monitoring center.

[0081] In addition, the safety threshold corresponding to the vibration signal characteristic quantity R can be determined based on the vibration data under normal operating conditions of the system. Since the preset threshold N for event determination has been determined based on the vibration samples under normal operating conditions in the previous text, in this embodiment, the safety threshold corresponding to R can be preset by combining the statistical distribution of the characteristic quantity R under normal operating conditions and the fallback requirement after the event is resolved, and preferably is lower than the preset threshold N for hydraulic hammer impact event determination.

[0082] The safety threshold corresponding to the internal pressure P of the sealed enclosure can be preset according to the pressure fluctuation range of the enclosure under normal operating conditions. Specifically, it can be the upper limit of the stable pressure range under normal operation, or determined by adding an allowable fluctuation margin to the upper limit.

[0083] In the implementation of step two, by utilizing a two-stage mechanical pressure relief design, the sharp pressure impact that could cause structural damage is transformed into a relatively gentle and controllable pressure release process, realizing intelligent pressure management with lead buffering followed by main release, thus buying valuable time for the root cause suppression in step three.

[0084] Step 3: Based on the identified impact area, activate the enhanced cooling program of the cooling circuit. The enhanced cooling program includes increasing the circulation flow rate of the cooling circuit and introducing enhanced cooling medium into the cooling circuit to enhance the cooling of the identified impact area and suppress the development of thermal runaway.

[0085] In addition to relying on the hydraulic hammer impact event determination in step one, the activation of the enhanced cooling process can also introduce multi-condition fusion judgment to improve accuracy.

[0086] Another key condition is that the rate of change of coolant temperature corresponding to the located impact area exceeds a threshold value. In this embodiment, the threshold value is used to distinguish between the abnormal rapid temperature rise caused by thermal runaway and the normal fluctuation of coolant temperature during normal system operation. It can be preset based on the statistical results of the coolant temperature change rate under normal operating conditions and the local temperature rise characteristics in the early thermal runaway samples. Specifically, under normal system charging and discharging, circulating cooling, and ambient temperature fluctuation conditions, coolant temperature data output by temperature sensors near the location area can be collected, the rate of change of temperature per unit time can be calculated, and the upper limit of the temperature change rate fluctuation under normal operating conditions can be determined accordingly. Based on this, combined with the characteristic range of local rapid temperature rise in the early thermal runaway test or historical calibration data, a value higher than the upper limit of normal operating fluctuation and capable of reflecting the abnormal temperature rise trend is selected as the threshold value.

[0087] In this embodiment, the change threshold can be set as follows: the temperature sensor near the positioning area detects a temperature rise exceeding 1°C per second. When both the "vibration characteristic quantity R exceeds the limit" and the "local temperature rise rate exceeds the change threshold" conditions are met simultaneously, the enhanced cooling program is activated with the highest priority. This avoids false starts caused by interference from a single vibration signal, ensuring high confidence in the action. This method can also effectively filter out background noise (such as equipment operating vibration) that does not match the spectral characteristics of the hydraulic hammer, and is insensitive to individual sensor differences and installation differences.

[0088] When the enhanced cooling program is activated, the first step is to increase the circulation flow rate of the cooling circuit, which can be achieved through coordinated control steps. For example, the drive power of the circulation pump in the cooling circuit is increased to increase the total system circulation flow rate; the valves in the cooling circuit are simultaneously adjusted to increase the flow distribution ratio through the branch where the positioning impact area is located.

[0089] Specifically, increasing the total system flow requires increasing the drive power of the main circulating cooling pump to an overload state within a few seconds. In this embodiment, the motor speed can be increased to 120% of the rated value by a frequency converter, thereby increasing the total circulating flow of the coolant to more than 150% of the normal value.

[0090] Directional flow distribution can be achieved by adjusting the opening of an electric proportional valve or three-way valve near the impact zone in the cooling circuit, thereby altering the flow distribution in the branch. The ultimate goal is to increase the proportion of flow passing through the branch containing the impact zone. In this embodiment, this proportion can be set to increase the average distribution from the usual level to allow that area to receive more than 30% of the total flow. This pump-valve coordinated control ensures that the enhanced cooling capacity is precisely directed to the thermal runaway source area that most needs cooling, rather than being uniformly diluted throughout the system, thus improving cooling efficiency.

[0091] However, simply increasing the flow rate (convective heat transfer) is sometimes insufficient to keep up with the heat generation rate when dealing with extremely high-power heat sources such as thermal runaway. Therefore, it is necessary to introduce an enhanced cooling medium into the cooling circuit. For example, the enhanced cooling medium is a perfluorinated compound with phase change endothermic properties. The method of introducing the enhanced cooling medium into the cooling circuit includes: when activating the enhanced cooling program, injecting the perfluorinated compound stored in a separate tank into the cooling circuit, allowing it to mix with the circulating insulating coolant.

[0092] Specifically, in this embodiment, a perfluorinated compound (such as perfluorohexanone or similar fluorinated ketones) with phase change endothermic properties can be selected as the enhanced cooling medium. This medium has high insulation, inertness (non-combustible), and undergoes a liquid-gas phase change in the range of 40°C to 60°C, absorbing a large amount of latent heat.

[0093] Regarding the injection method of the cooling medium, an independent storage tank can be connected in parallel with the main cooling circuit via pipelines, with the connection controlled by a high-speed solenoid valve. Upon receiving an injection command, the solenoid valve opens, and the perfluorinated compound in the storage tank is rapidly injected into the main circulation pipeline under the action of pressure difference, instantly mixing with the existing insulating coolant (which can be mineral oil in this embodiment). When the mixed fluid flows through the thermally runaway battery cell, the perfluorinated compound rapidly undergoes a phase change and vaporizes, absorbing a huge amount of heat from the surface of the battery cell and the surrounding liquid, thereby achieving explosive and rapid cooling.

[0094] In the implementation of step three, heat dissipation is achieved by increasing the flow rate (convective heat transfer), and a heat absorption mechanism of latent heat of phase change is introduced by injecting a phase change medium. The combination of the two forms a three-dimensional cooling attack of enhanced convection and phase change heat absorption, which can quickly pull the temperature of the thermal runaway point back to the safe range, directly suppress and terminate the runaway chemical reaction of the battery cell, and fundamentally stop the generation of combustible gas and heat (only after this step is completed will the continuous pressure source of the hydraulic hammer truly disappear, and the system can get rid of thermal runaway and truly return to a safe state).

[0095] In summary, by arranging a vibration sensor array on the outer wall of the enclosure and analyzing its signal characteristics, the sensing target shifted from the transient pressure inside the coolant, which is difficult to monitor reliably, to the vibration of the enclosure structure that is inevitably excited by this pressure and reliably transmitted. This enabled reliable detection and localization of hydraulic hammer impact events. After obtaining the localization information, a multi-stage pressure relief channel based on different response thresholds was used as the core buffer mechanism. Different levels of pressure relief actions were triggered sequentially according to the impact intensity, transforming a steep, destructive pressure peak into a phased pressure release process acceptable to the management system. Finally, by simultaneously increasing the cooling circuit circulation flow and introducing enhanced cooling medium, not only was the cooling capacity enhanced spatially, but a higher heat capacity intervention medium was also introduced at the energy transfer level. This allowed the system to apply a targeted and enhanced cooling attack to the thermal runaway region while releasing the mechanical impact, aiming to suppress the electrochemical reaction rate from the energy source, thereby terminating the continuous pressure source of the hydraulic hammer and helping the submerged liquid-cooled battery energy storage system truly escape thermal runaway and return to a safe state.

[0096] Furthermore, by analyzing the signal energy within the predetermined characteristic frequency band and using the spatiotemporal information of the sensor array for positioning, the system can accurately extract the unique spectrum of hydraulic hammer impact from complex background vibration noise. By comparing the arrival order of signals from multiple sensors, the abstract impact event is transformed into specific three-dimensional coordinates within the box, providing an indispensable spatial reference for subsequent precise control measures in all areas. This improves the targeting and efficiency of the entire system's actions and avoids the resource waste and potential disturbances caused by traditional all-domain response.

[0097] Furthermore, by using perfluorinated compounds with phase change endothermic properties as an enhanced cooling medium, the phase change process of perfluorinated compounds can absorb a huge amount of latent heat under near-constant temperature conditions. Thus, when cooling thermally runaway battery cells, the surface and surrounding temperature can be quickly suppressed below the critical point of the material's thermal runaway reaction. This method of actively seizing heat through medium phase change improves both speed and efficiency compared to the traditional approach of simply increasing convective heat transfer.

[0098] Example 2

[0099] Please see Figure 2 As shown, this embodiment provides a thermal runaway protection system for an immersion liquid-cooled battery energy storage system, which is used to implement the thermal runaway protection method for an immersion liquid-cooled battery energy storage system disclosed in Embodiment 1. The system can be loaded as a subsystem into the immersion liquid-cooled battery energy storage system. The system includes: a vibration monitoring module, a graded pressure relief module, an enhanced cooling control module, and a central controller.

[0100] The vibration monitoring module includes a vibration sensor array located outside the sealed housing and an analysis unit connected thereto. The analysis unit is configured to perform vibration signal characteristic calculation, preset threshold comparison (whether the characteristic exceeds the preset threshold), and location of the impact area.

[0101] The graded pressure relief module includes a pressure relief device connected to a sealed housing, and the pressure relief device includes multi-stage pressure relief channels with different response thresholds.

[0102] The enhanced cooling control module includes a drive and valve unit for increasing the circulation flow of the cooling circuit, an independent storage tank for storing the enhanced cooling medium, and an injection unit connecting the cooling circuit and the independent storage tank.

[0103] The central controller is communicatively connected to the vibration monitoring module, the graded pressure relief module, and the enhanced cooling control module. The central controller is configured to, upon determining that a hydraulic hammer impact event has occurred inside the sealed enclosure and locating the impact area, control the graded pressure relief module to depressurize the sealed enclosure and, based on the located impact area, control the enhanced cooling control module to execute an enhanced cooling program.

[0104] Since this system uses the thermal runaway protection method for immersion liquid-cooled battery energy storage systems in Example 1, it has the same effect, which will not be repeated here.

[0105] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the aforementioned scope.

[0106] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for thermal runaway protection in an immersed liquid-cooled battery energy storage system, the immersed liquid-cooled battery energy storage system comprising a sealed enclosure, a battery module placed inside the sealed enclosure, and a cooling circuit for circulating insulating coolant, characterized in that, The method includes: Vibration signals on the surface of the sealed enclosure are monitored by an array of vibration sensors located outside the enclosure. Predetermined characteristic quantities of the vibration signals are extracted. When the predetermined characteristic quantities exceed a preset threshold, it is determined that a hydraulic hammer impact event caused by thermal runaway has occurred inside the sealed enclosure. If a hydraulic hammer impact event is determined to have occurred, the impact area is located based on the difference in vibration signals of each sensor in the vibration sensor array. The pressure relief device is used to relieve pressure on the sealed box. The pressure relief device includes multiple pressure relief channels with different response thresholds. When the pressure inside the sealed box reaches the corresponding response threshold, the pressure relief channels of different levels are opened in sequence. Based on the identified impact area, an enhanced cooling program is activated in the cooling circuit. This enhanced cooling program includes increasing the circulation flow rate of the cooling circuit and introducing enhanced cooling medium into the cooling circuit to enhance cooling of the identified impact area.

2. The thermal runaway protection method for an immersed liquid-cooled battery energy storage system according to claim 1, characterized in that, Methods for locating the impact area include: Spectral analysis of the vibration signal is performed to extract the signal energy within a predetermined characteristic frequency band as a predetermined characteristic quantity; The location of the impact zone is determined based on the arrival time difference of the predetermined characteristic quantities received by sensors at different positions in the vibration sensor array.

3. The thermal runaway protection method for an immersed liquid-cooled battery energy storage system according to claim 1, characterized in that, The multi-stage pressure relief channel includes at least one low-pressure guide channel and at least one high-pressure main relief channel; The response threshold corresponding to the low-pressure guide channel is the first-level pressure threshold, and the response threshold corresponding to the high-pressure main venting channel is the second-level pressure threshold. The second-level pressure threshold is greater than the first-level pressure threshold. When the pressure inside the sealed enclosure reaches the first-level pressure threshold, the low-pressure guide channel is opened. When the pressure inside the sealed enclosure reaches the second-level pressure threshold, the high-pressure main venting channel is opened.

4. The thermal runaway protection method for an immersed liquid-cooled battery energy storage system according to claim 3, characterized in that, The outlet of the low-pressure guide channel is connected to a guide pipe to direct the initial gas-liquid mixture released into a designated area within the sealed enclosure.

5. The thermal runaway protection method for an immersed liquid-cooled battery energy storage system according to claim 1, characterized in that, The enhanced cooling medium is a perfluorinated compound with phase change endothermic properties; Methods for introducing enhanced cooling media into a cooling circuit include: when activating an enhanced cooling program, injecting a perfluorinated compound stored in a separate tank into the cooling circuit, causing it to mix with the circulating insulating coolant.

6. The thermal runaway protection method for an immersed liquid-cooled battery energy storage system according to claim 1, characterized in that, Methods for activating enhanced cooling procedures that activate the cooling circuit include: Increase the drive power of the circulating pump in the cooling circuit to improve the total system circulation flow; The valves in the cooling circuit are adjusted synchronously to increase the flow distribution ratio through the branch where the positioning impact area is located.

7. The thermal runaway protection method for an immersed liquid-cooled battery energy storage system according to claim 1, characterized in that, After depressurizing the sealed housing using the pressure relief device, the process also includes a cascading fault diagnosis step: The vibration signal characteristics and the internal pressure of the sealed enclosure are continuously monitored after the discharge. If neither of them drops below their respective safety thresholds within the preset observation time window, it is determined that a multi-cell cascade thermal runaway has occurred, and a system-level emergency shutdown and fault isolation are performed.

8. The thermal runaway protection method for an immersed liquid-cooled battery energy storage system according to claim 1, characterized in that, The criteria for activating the enhanced cooling procedure that activates the cooling circuit also include: The rate of change of coolant temperature corresponding to the located impact area was found to exceed the change threshold.

9. The thermal runaway protection method for an immersed liquid-cooled battery energy storage system according to claim 1, characterized in that, The placement of the vibration sensor array is determined based on the structural vibration modal analysis of the sealed enclosure under the characteristic frequency band corresponding to the hydraulic hammer impact event.

10. A thermal runaway protection system for an immersed liquid-cooled battery energy storage system, used to implement the thermal runaway protection method for an immersed liquid-cooled battery energy storage system as described in any one of claims 1 to 9, characterized in that, The system includes: The vibration monitoring module includes a vibration sensor array disposed outside the sealed housing and an analysis unit connected thereto. The analysis unit is configured to perform vibration signal characteristic analysis, preset threshold comparison and impact area location. A graded pressure relief module includes a pressure relief device connected to a sealed housing, the pressure relief device including multi-stage pressure relief channels with different response thresholds; The enhanced cooling control module includes a drive and valve unit for increasing the circulation flow of the cooling circuit, an independent storage tank for storing the enhanced cooling medium, and an injection unit connecting the cooling circuit and the independent storage tank. The central controller, which communicates with the vibration monitoring module, the graded pressure relief module, and the enhanced cooling control module, is configured to, after determining that a hydraulic hammer impact event has occurred inside the sealed housing and locating the impact area, control the graded pressure relief module to depressurize the sealed housing, and control the enhanced cooling control module to execute the enhanced cooling program according to the located impact area.

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