Power battery multi-stage dynamic charging control method based on ultrasonic monitoring feedback

Abstract

The invention relates to the technical field of battery charging control, and particularly provides a power battery multi-stage dynamic charging control method based on ultrasonic monitoring feedback, which comprises the following steps: constructing a safe charging boundary constraint of a power battery, and generating a multi-stage charging strategy under the safe charging boundary constraint; when the SOC value of the power battery is charged to the SOC switching point, the next stage of charging is switched; in the charging process of each stage, the lithium precipitation risk state of the power battery is monitored by adopting an ultrasonic technology, characteristic values are monitored in advance, and the lithium precipitation risk is evaluated; and when the risk of lithium precipitation occurs, entering the next stage of charging in advance and dynamically adjusting the SOC switching point. According to the method, the lithium precipitation risk is detected and fed back in real time in the charging process, charging control is dynamically and adaptively carried out, and collaborative optimization of charging efficiency and safety is achieved.

Description

Technical Field

[0001] This invention relates to the field of battery charging control technology, and more specifically, to a multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback. Background Technology

[0002] Fast charging technology for lithium-ion batteries needs to strike a balance between increasing charging speed and suppressing the risk of lithium plating. Currently, constant current (CC) charging remains the basic charging method widely used in the industry, which switches to constant voltage (CV) mode after charging with a constant current to the cutoff voltage. However, the selection of current intensity in the single constant current stage faces a dilemma: higher current can shorten charging time, but it is prone to inducing lithium dendrite growth; lower current, while relatively safe, significantly reduces charging efficiency.

[0003] To address this contradiction, researchers proposed a multi-stage constant current charging strategy (Multi-stage CC), which attempts to balance speed and safety by gradually reducing the current intensity during charging. However, such improvements still have fundamental flaws: First, stage switching relies on static thresholds: preset voltage or time thresholds cannot adapt to dynamic conditions such as battery aging and temperature fluctuations, leading to a mismatch between the threshold and the actual lithium plating critical point; second, there is a lack of real-time safety feedback. Existing methods only indirectly infer lithium plating risk through external electrical signals (voltage / current), which lacks sufficient sensitivity to microscopic lithium deposition and makes it difficult to trigger stage switching in a timely manner.

[0004] In the field of lithium plating monitoring technology, current mainstream methods have serious limitations: (1) destructive detection (such as SEM observation after battery disassembly after cycling) cannot be used for real-time control of the charging process; (2) indirect electrochemical models (such as lithium plating prediction based on dQ / dV curves or impedance spectra) rely on macroscopic parameter fitting, and there is a lag in the identification of early micron-sized lithium dendrites. In recent years, ultrasonic detection technology has been attempted to be introduced into the field of lithium plating risk status assessment of lithium-ion batteries due to its advantages such as non-invasiveness and high spatiotemporal resolution. The propagation characteristics of ultrasound inside the battery can sensitively reflect changes in the electrode-electrolyte interface, including local acoustic impedance abrupt changes caused by lithium dendrite growth. However, current ultrasonic detection is mostly used for offline diagnosis or laboratory research after cycling, and a real-time mapping relationship between ultrasonic signal characteristics and charging control parameters has not yet been established, resulting in a break in the "monitoring-decision" chain.

[0005] Therefore, it is necessary to deeply couple high-sensitivity ultrasonic lithium plating monitoring with multi-segment charging dynamic control, and develop and build an adaptive charging system based on real-time feedback, which is the key breakthrough to overcome the above-mentioned technical difficulties. Summary of the Invention

[0006] To overcome the shortcomings and deficiencies of the existing technology, the purpose of this invention is to provide a multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback. This method detects and provides feedback on the risk of lithium plating in real time during the charging process, and dynamically and adaptively controls the charging, thereby achieving synergistic optimization of charging efficiency and safety.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: a multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback, which constructs a safe charging boundary constraint for the power battery and generates a multi-stage charging strategy under the safe charging boundary constraint; when the SOC value of the power battery is charged to the SOC switching point, the charging is switched to the next stage; during the charging process of each stage, ultrasonic technology is used to monitor the lithium plating risk state of the power battery, monitor characteristic values ​​in advance, and assess the lithium plating risk; when the lithium plating risk occurs, the charging is switched to the next stage in advance and the SOC switching point is dynamically adjusted.

[0008] Preferably, the monitoring of the lithium plating risk status of the power battery using ultrasonic technology refers to: using an ultrasonic detection device to output ultrasonic signals that propagate inside the power battery; collecting the echo signals of the ultrasonic waves; extracting the main reflected wave signal from the echo signals; and calculating monitoring characteristic values ​​based on the main reflected wave signal, including: time-of-flight rate of change ΔTOF and peak-to-peak decay rate. A pp and envelope area ratio S env Each monitoring characteristic value is compared with its corresponding threshold to assess the risk of lithium plating.

[0009] Preferably, before charging the power battery, an ultrasonic detection device outputs an ultrasonic signal that propagates inside the power battery to collect the echo signal of the ultrasonic wave. The main reflected wave signal before charging is extracted from the echo signal. Based on the main reflected wave signal before charging, the ultrasonic wave reflection time before charging is obtained. t ref The amplitude difference between the highest and lowest points of the main reflected wave signal The envelope curve was obtained by performing a Hilbert transform on the main reflected wave signal before charging. The envelope area is obtained by integration within the target time window. ; During each stage of the charging process, the time-of-flight change rate ΔTOF and the peak-to-peak decay rate are... A pp and envelope area ratio S env The calculation method is as follows: The ultrasonic wave reflection time at the current moment is obtained based on the peak value of the main reflected wave signal at the current moment. t curThe time-of-flight rate of change ΔTOF is calculated as follows: ; Extract the amplitude difference between the highest and lowest points of the main reflected wave signal at the current moment. Peak-to-peak attenuation rate A pp The calculation is as follows: ; The envelope curve is obtained by performing a Hilbert transform on the main reflected wave signal at the current moment. The envelope area is obtained by integration within the target time window. envelope area ratio S env The calculation is as follows: .

[0010] Preferably, after acquiring the echo signal of the ultrasonic wave, the echo signal is bandpass filtered to remove noise, and high-frequency interference is removed by four-level decomposition and reconstruction using the db4 wavelet basis function to extract the main reflected wave signal and locate the peak value of the main reflected wave signal.

[0011] Preferably, the lithium plating risk is assessed to obtain a lithium plating risk level; the lithium plating risk level includes low risk (representing no lithium plating risk), medium risk (representing moderate lithium plating risk), and high risk (representing high lithium plating risk). The method for assessing the risk level of lithium plating is as follows: Each monitoring characteristic value corresponds to a low-risk threshold T1 and a medium-risk threshold T2. If one or more monitoring characteristic values ​​are greater than or equal to the medium-risk threshold T2, the lithium plating risk level is determined to be high risk. Otherwise, if one or more monitoring characteristic values ​​are greater than or equal to the low-risk threshold T1, the lithium plating risk level is determined to be medium risk. If all monitoring characteristic values ​​are less than the low-risk threshold T1, the lithium plating risk level is determined to be low risk. When the lithium plating risk level is medium risk and the current stage is not the last stage, the charging will be moved to the next stage in advance and the SOC switching point will be dynamically adjusted; when the lithium plating risk level is medium risk and the current stage is the last stage, or when the lithium plating risk level is high risk, the charging will be cut off immediately.

[0012] Preferably, both the low-risk threshold T1 and the medium-risk threshold T2 are updated iteratively based on the aging state of the power battery.

[0013] Preferably, the dynamic adjustment of the SOC switching point means that when the lithium plating risk level is determined to be medium risk, all SOC switching points that have not yet been reached are adjusted forward and saved.

[0014] Preferably, the construction of the safe charging boundary constraint of the power battery refers to: simulating the change curve of the negative electrode voltage of the power battery with the SOC value under different charging rates based on a pseudo two-dimensional electrochemical model, determining the critical SOC value at which the negative electrode voltage first drops to 0V for each charging rate, establishing the mapping relationship between the maximum allowable charging current and the SOC value through polynomial fitting, constructing the safe charging boundary surface, and thus obtaining the safe charging boundary constraint; The multi-stage charging strategy refers to: under the constraint of the safe charging boundary, taking the shortest total charging time as the objective function, and using an optimization algorithm to obtain a charging strategy that includes multi-stage constant current charging current values ​​and corresponding SOC switching points; in the stages before and after the charging process, the charging current value decreases sequentially and forms a monotonically increasing relationship with the SOC switching point.

[0015] Preferably, the polynomial fitting adopts a quadratic or cubic polynomial form, and the fitting coefficients are solved by the least squares method or the weighted least squares method, and the critical SOC value is corrected by laboratory calibration.

[0016] Preferably, the objective function of the optimization algorithm simultaneously optimizes the total charging time and energy loss in a weighted form; wherein, the energy loss is calculated by integrating the polarization voltage.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. Achieving dynamic adaptability of battery charging control: Compared with the traditional multi-segment constant current charging strategy that relies on static voltage or time threshold, this invention introduces an ultrasonic real-time monitoring mechanism for the first time. It can dynamically adjust the charging strategy according to the acoustic characteristics of the current state of the power battery, overcome the inherent limitation of mismatch between static threshold and actual working conditions (such as aging and temperature changes), and greatly improve the flexibility and safety of the charging process. 2. Constructing a highly reliable safety charging boundary model: This invention simulates the negative electrode voltage change under different charging rates using a pseudo-two-dimensional electrochemical model. Combined with actual ultrasonic monitoring experiments, it double-confirms the lithium plating critical point under different charging rate-SOC combinations. This effectively avoids the bias caused by traditional predictions based on experience or simplified models, and constructs a safety boundary model with a solid physical foundation and sufficient experimental verification, providing an accurate basis for optimizing charging strategies. 3. Achieve synergistic optimization of charging efficiency and safety: Under the safety boundary constraints obtained by fitting, a multi-segment optimal constant current curve is designed using a gradient optimization algorithm, which significantly shortens the charging time; at the same time, a real-time ultrasonic signal feedback mechanism is used to identify potential lithium plating risks and switch stages in advance, achieving dual protection of charging efficiency and battery life. 4. Breakthrough realization of closed-loop linkage of "monitoring-decision-control": This invention deeply integrates ultrasonic signal feature extraction, lithium plating risk assessment model and charging control strategy to form a complete feedback closed loop of "monitoring-decision-execution", truly realizing intelligent charging control based on microstructure changes and improving the depth and timeliness of the system's perception of the internal state of the battery; 5. Possesses good engineering scalability and deployment prospects: The proposed method relies on non-contact ultrasonic monitoring, which has universal adaptability to different types of cell structures. Moreover, the constructed charging boundary can be dynamically updated during operation, adapting to the personalized needs of batteries in different batches, aging states and usage environments, and has good engineering portability and commercial potential. 6. Promoting the transformation of ultrasound technology from a diagnostic tool to a control method: Traditional ultrasound monitoring is mostly used for offline diagnosis of battery health status. This invention introduces it into the real-time control of charging strategy for the first time, explores and establishes the mapping relationship between ultrasound characteristics and charging control parameters, and lays the technical foundation for the integrated development of ultrasound sensing and control in future intelligent battery systems. Attached Figure Description

[0018] Figure 1 This is a flowchart of the multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback according to the present invention. Figure 2 This is a graph showing the variation of the negative electrode voltage of the power battery with the SOC value under different charging rates according to the present invention. Figure 3 This is a schematic diagram of the safe charging boundary surface of the present invention. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0020] Example 1 This embodiment presents a multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback, the process of which is as follows: Figure 1 As shown, it can be used for scenarios where the power battery is removed and charged separately, or for scenarios where the power battery is charged in place.

[0021] The first step is to construct a safe charging boundary constraint for the power battery, and under the safe charging boundary constraint, generate a multi-stage charging strategy; when the SOC value of the power battery is charged to the SOC switching point, switch to the next stage of charging.

[0022] Specifically, firstly, safe charging boundary constraints are constructed: based on a pseudo-two-dimensional electrochemical model, the variation curves of the negative electrode voltage of the power battery with the SOC value under different charging rates are simulated, such as... Figure 2As shown, the critical SOC value (i.e., state of charge) at which the negative electrode voltage first drops to 0V for each charging rate is determined. A mapping relationship between the maximum allowable charging current and the SOC value is established through polynomial fitting, constructing a safe charging boundary surface, as shown below. Figure 3 As shown; the polynomial fitting adopts the form of a quadratic or cubic polynomial, and the fitting coefficients are solved by the least squares method or the weighted least squares method, and the critical SOC value is corrected by laboratory calibration; then, the safe charging boundary constraints are obtained according to the safe charging boundary surface. Subsequently, a multi-stage charging strategy is generated: under the constraints of the safe charging boundary, with the shortest total charging time as the objective function, an optimization algorithm is used to solve for the charging strategy that includes the constant current charging current values ​​of multiple stages and the corresponding SOC switching points; the objective function of the optimization algorithm simultaneously optimizes the total charging time and energy loss in a weighted form; wherein, the energy loss is calculated by integrating the polarization voltage. During the charging process, the charging current value decreases sequentially at each stage and exhibits a monotonically increasing relationship with the SOC switching point. For example, this embodiment generates a five-stage constant current charging process, with the constant current charging current values ​​for each stage being: 4.9C → 4.2C → 3.8C → 3.6C → 3.5C, where C is a standardized rate unit. The SOC switching points between the stages are 33%, 49%, 56%, and 67%, respectively. In practical applications, the number of constant current charging stages is not limited to five stages; for example, it can be four, six, seven, or even more stages.

[0023] The second step involves using ultrasonic technology to monitor the lithium plating risk status of the power battery. The ultrasonic detection device outputs an ultrasonic signal (e.g., a 2MHz frequency-modulated pulse) that propagates inside the power battery, and the echo signal is received. When applied to scenarios where the power battery is removed and charged separately, existing ultrasonic detection devices can be used to detect both sides of the power battery. When used for scenarios where the power battery is charged in situ, a small, lightweight patch-type ultrasonic transducer can be selected. This transducer is placed between adjacent battery cells or on the surface of the cell casing using thermally conductive / acoustic coupling adhesive, without occupying additional battery pack space or requiring significant modifications to the battery module structure.

[0024] Before charging the power battery, an ultrasonic detection device outputs an ultrasonic signal that propagates inside the power battery to collect the echo signal. The main reflected wave signal before charging is extracted from the echo signal. Based on the main reflected wave signal before charging, the ultrasonic reflection time before charging is obtained. t ref The amplitude difference between the highest and lowest points of the main reflected wave signal The envelope curve was obtained by performing a Hilbert transform on the main reflected wave signal before charging. The integral is obtained within the target time window. .

[0025] During each stage of the charging process, ultrasonic technology is used to monitor the lithium plating risk status of the power battery. Ultrasonic echo signals are collected, and noise is removed by 2–5 MHz bandpass filtering. High-frequency interference is removed by four-level decomposition and reconstruction using the db4 wavelet basis function. The main reflected wave signal is extracted and its peak value is located. Monitoring characteristic values ​​are calculated based on the main reflected wave signal, including: time-of-flight rate of change ΔTOF and peak-to-peak decay rate. A pp and envelope area ratio S env The calculation method is as follows: The ultrasonic wave reflection time at the current moment is obtained based on the peak value of the main reflected wave signal at the current moment. t cur The time-of-flight rate of change ΔTOF is calculated as follows: ; Extract the amplitude difference between the highest and lowest points of the main reflected wave signal at the current moment. Peak-to-peak attenuation rate A pp The calculation is as follows: ; The envelope curve is obtained by performing a Hilbert transform on the main reflected wave signal at the current moment. The integral is obtained within the target time window. envelope area ratio S env The calculation is as follows: .

[0026] Each monitoring characteristic value is compared with its corresponding threshold to assess the risk of lithium plating.

[0027] Time-of-flight rate of change ΔTOF, peak-to-peak decay rate A pp and envelope area ratio S env This is clearly evident during lithium plating: Time-of-flight rate of change ΔTOF: When lithium plating occurs, the metallic lithium deposited on the surface of the negative electrode of the power battery changes the elastic modulus and density distribution of the internal materials of the power battery, thereby changing the speed of sound; due to the propagation speed of ultrasound... (E is the elastic modulus, ρ is the density) Lithium metal deposition reduces the local sound velocity in the propagation path, causing a delay in echo arrival time and an increase in the time-of-flight rate of change ΔTOF. Peak-to-peak attenuation rate A ppLithium plating and gas formation lead to surface roughening and increased porosity of the negative electrode in power batteries, enhancing scattering and absorption effects, accelerating energy attenuation of ultrasonic waves along the propagation path, reducing echo signal amplitude, and decreasing peak-to-peak value; peak-to-peak attenuation rate A pp This is a direct manifestation of the increased acoustic impedance mismatch caused by lithium plating; Envelope area ratio S env Lithium plating-induced multiple scattering also causes the echo energy to diffuse over time, reducing the overall envelope area and decreasing the envelope area ratio. S env decline.

[0028] Simultaneously, the time-of-flight change rate ΔTOF and peak-to-peak decay rate are used. A pp and envelope area ratio S env The reason why this monitoring characteristic value is used to assess the risk level of lithium plating is: I. Strong complementarity: The time-of-flight rate of change ΔTOF reflects the change in propagation speed (sensitive to changes in structural / material elasticity), while the peak-to-peak decay rate... A pp Ratio of envelope area S env It reflects changes in attenuation and scattering characteristics (sensitive to structural defects and interface conditions); the combination of these three can comprehensively capture changes in the internal mechanical characteristics of the power battery. 2. High real-time performance: Compared with electrical signals such as voltage and temperature, acoustic features are more sensitive to the mechanical / structural micro changes in the early stage of lithium plating, and can provide early warning of risks hundreds of milliseconds to several seconds in advance; 3. Easy to calibrate: All three monitoring characteristics can obtain reference values ​​under the initial safe state and be judged by the relative change, without relying on absolute sound speed or amplitude, thereby reducing the consistency requirements between different cells; IV. Embeddable in control loop: The monitoring feature extraction computation is low and can run in real time on BMS or edge computing unit to realize dynamic correction and strategy optimization of safety boundary during charging.

[0029] Therefore, the time-of-flight change rate ΔTOF and the peak-to-peak decay rate are selected. A pp and envelope area ratio S env As a core acoustic health indicator, it can detect risks such as lithium plating and gas production, and directly feed back to the multi-stage charging strategy optimization module to dynamically adjust the charging current, thereby improving charging speed while ensuring safety.

[0030] The lithium plating risk is assessed to obtain a lithium plating risk level; the lithium plating risk level includes low risk (representing no lithium plating risk), medium risk (representing moderate lithium plating risk), and high risk (representing high lithium plating risk); the lithium plating risk level assessment method is as follows: Each monitoring characteristic value corresponds to a low-risk threshold T1 and a medium-risk threshold T2. The low-risk threshold T1 and medium-risk threshold T2 are set according to the lithium plating determination requirements. Both the low-risk threshold T1 and medium-risk threshold T2 are updated online iteratively based on the aging state of the power battery. If one or more monitoring characteristic values ​​are greater than or equal to the medium-risk threshold T2, the lithium plating risk level is determined to be high risk; otherwise, if one or more monitoring characteristic values ​​are greater than or equal to the low-risk threshold T1, the lithium plating risk level is determined to be medium risk; if all monitoring characteristic values ​​are less than the low-risk threshold T1, the lithium plating risk level is determined to be low risk. When the lithium plating risk level is low, maintain normal charging at the current stage; when the lithium plating risk level is medium and the current stage is not the last stage, advance to the next stage of charging and dynamically adjust the SOC switching point; when the lithium plating risk level is medium and the current stage is the last stage, immediately cut off charging and determine that there are obvious defects inside the power battery, making it unsuitable for the application scenario of power batteries, and consider its secondary use in the future; when the lithium plating risk level is high, immediately cut off charging.

[0031] Dynamic adjustment of SOC switching points means that when the lithium plating risk level is determined to be medium risk, all SOC switching points that have not yet been reached are adjusted forward so that the start and end points of subsequent stages match the new charging state, and the new SOC switching points are saved for retrieval and use in future charging.

[0032] For example, the SOC switching point between the second and third stages is 33%. The constant current charging current value in the second stage is 3.8C, and in the third stage it is 2.6C. During charging, if the ultrasonic monitoring assesses a medium-risk level for lithium plating when charging reaches the second stage (SOC = 28%), the system directly switches to the third stage with a constant current charging current of 2.6C. Simultaneously, the originally planned subsequent SOC switching points are adjusted based on this early switching, meaning any unreached SOC switching points are moved forward to match the start and end points of the SOC values ​​in subsequent stages with the new charging state. This ensures that when early risk signals appear, the charging strategy can reduce the rate in real time and enter a more conservative stage earlier, thereby reducing the time spent charging at high rates and lowering the risk of lithium plating and thermal runaway.

[0033] The charging control method of the present invention was compared with the traditional constant current charging method, and the experimental data results are shown in Table 1.

[0034] Table 1. Experimental data of the charging control method of the present invention and the traditional constant current charging method.

[0035] As shown in Table 1, the charging control method of this invention achieves an average charging time of 22 minutes to increase the State of Charge (SOC) from 0% to 80%, significantly shorter than the 35 minutes of the traditional constant current charging method, resulting in an approximately 37% improvement in charging efficiency. Regarding safety, the lithium plating event rate of this invention is only 0.8%, far lower than the 5.2% of the traditional constant current charging method, effectively reducing the risk to the power battery under high charging rates. Furthermore, in terms of cycle life, the capacity retention rate of this invention after 500 charge-discharge cycles is 92.3%, higher than the 86.7% of the traditional constant current charging method, indicating that this invention not only improves charging speed and safety but also significantly enhances the lifespan of the power battery.

[0036] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback, characterized in that: A safe charging boundary constraint for the power battery is constructed, and a multi-stage charging strategy is generated under the safe charging boundary constraint. When the SOC value of the power battery is charged to the SOC switching point, the charging is switched to the next stage. During the charging process of each stage, ultrasonic technology is used to monitor the lithium plating risk state of the power battery, monitor characteristic values ​​in advance, and assess the lithium plating risk. When the lithium plating risk occurs, the charging is switched to the next stage in advance and the SOC switching point is dynamically adjusted.

2. The multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback according to claim 1, characterized in that: The monitoring of lithium plating risk status of power batteries using ultrasonic technology refers to: using an ultrasonic detection device to output ultrasonic signals that propagate inside the power battery; collecting the echo signals of the ultrasonic waves; extracting the main reflected wave signal from the echo signals; and calculating monitoring characteristic values ​​based on the main reflected wave signal, including: time-of-flight rate of change ΔTOF and peak-to-peak decay rate. A pp and envelope area ratio S env Each monitoring characteristic value is compared with its corresponding threshold to assess the risk of lithium plating.

3. The multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback according to claim 2, characterized in that: Before charging the power battery, an ultrasonic detection device outputs an ultrasonic signal that propagates inside the power battery to collect the echo signal. The main reflected wave signal before charging is extracted from the echo signal. Based on the main reflected wave signal before charging, the ultrasonic reflection time before charging is obtained. t ref The amplitude difference between the highest and lowest points of the main reflected wave signal The envelope curve was obtained by performing a Hilbert transform on the main reflected wave signal before charging. The envelope area is obtained by integration within the target time window. ; During each stage of the charging process, the time-of-flight change rate ΔTOF and the peak-to-peak decay rate are... A pp and envelope area ratio S env The calculation method is as follows: The ultrasonic wave reflection time at the current moment is obtained based on the peak value of the main reflected wave signal at the current moment. t cur The time-of-flight rate of change ΔTOF is calculated as follows: ； Extract the amplitude difference between the highest and lowest points of the main reflected wave signal at the current moment. Peak-to-peak attenuation rate A pp The calculation is as follows: ； The envelope curve is obtained by performing a Hilbert transform on the main reflected wave signal at the current moment. The envelope area is obtained by integration within the target time window. envelope area ratio S env The calculation is as follows: 。 4. The multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback according to claim 3, characterized in that: After acquiring the echo signal of the ultrasound, the echo signal is bandpass filtered to remove noise, and high-frequency interference is removed by four-level decomposition and reconstruction using the db4 wavelet basis function. The main reflected wave signal is then extracted and its peak value is located.

5. The multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback according to claim 2, characterized in that: Assess the risk of lithium plating and obtain the lithium plating risk level; The lithium plating risk levels include low risk (representing no lithium plating risk), medium risk (representing moderate lithium plating risk), and high risk (representing high lithium plating risk). The method for assessing the risk level of lithium plating is as follows: Each monitoring characteristic value corresponds to a low-risk threshold T1 and a medium-risk threshold T2. If one or more monitoring characteristic values ​​are greater than or equal to the medium-risk threshold T2, the lithium plating risk level is determined to be high risk. Otherwise, if one or more monitoring characteristic values ​​are greater than or equal to the low-risk threshold T1, the lithium plating risk level is determined to be medium risk. If all monitoring characteristic values ​​are less than the low-risk threshold T1, the lithium plating risk level is determined to be low risk. When the lithium plating risk level is medium risk and the current stage is not the last stage, the charging will be moved to the next stage in advance and the SOC switching point will be dynamically adjusted; when the lithium plating risk level is medium risk and the current stage is the last stage, or when the lithium plating risk level is high risk, the charging will be cut off immediately.

6. The multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback according to claim 5, characterized in that: Both the low-risk threshold T1 and the medium-risk threshold T2 are updated iteratively based on the aging state of the power battery.

7. The multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback according to claim 5, characterized in that: The dynamic adjustment of SOC switching points refers to: when the lithium plating risk level is determined to be medium risk, all SOC switching points that have not yet been reached are adjusted forward and saved.

8. The multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback according to claim 1, characterized in that: The construction of the safe charging boundary constraint for the power battery refers to: simulating the change curve of the negative electrode voltage of the power battery with the SOC value under different charging rates based on a pseudo two-dimensional electrochemical model, determining the critical SOC value at which the negative electrode voltage first drops to 0V for each charging rate, establishing the mapping relationship between the maximum allowable charging current and the SOC value through polynomial fitting, constructing the safe charging boundary surface, and thus obtaining the safe charging boundary constraint. The multi-stage charging strategy refers to: under the constraint of the safe charging boundary, taking the shortest total charging time as the objective function, and using an optimization algorithm to obtain a charging strategy that includes multi-stage constant current charging current values ​​and corresponding SOC switching points; in the stages before and after the charging process, the charging current value decreases sequentially and forms a monotonically increasing relationship with the SOC switching point.

9. The multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback according to claim 8, characterized in that: The polynomial fitting adopts a quadratic or cubic polynomial form, and the fitting coefficients are solved by the least squares method or the weighted least squares method. The critical SOC value is corrected by laboratory calibration.

10. The multi-stage dynamic charging control method for power batteries based on ultrasonic monitoring feedback according to claim 8, characterized in that: The objective function of the optimization algorithm simultaneously optimizes the total charging time and energy loss in a weighted manner.

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