A self-protection method for a lithium battery charger and the charger itself.

Abstract

This invention discloses a self-protection method and charger for a lithium battery charger, relating to the field of battery charging control technology. It includes: S1: performing time-domain and frequency-domain analysis on the collected input voltage and current data to obtain feature data; S2: using the feature data as input to a multi-dimensional safety boundary model to obtain the corresponding instantaneous maximum allowable output power; S3: adjusting the actual output power in real time based on the instantaneous maximum allowable power through coordinated control of a feedforward loop and a feedback loop. This invention establishes a triple protection mechanism of switch junction temperature threshold, capacitor safe power limit, and battery safe power limit. When the input voltage is abnormal, it can adaptively adjust the output power, thereby not only ensuring the safe operation of key components of the charger but also avoiding the risk of overvoltage or undervoltage of the battery, improving the reliability and safety of the charger under abnormal operating conditions such as grid fluctuations.

Description

Technical Field

[0001] This invention relates to the field of battery charging control technology, specifically to a self-protection method for a lithium battery charger and the charger itself. Background Technology

[0002] With the rapid development of portable electronic devices (such as smartphones, laptops, and power tools), as well as electric vehicles and energy storage systems, lithium batteries have become one of the most important energy storage devices due to their advantages such as high energy density, long cycle life, and low self-discharge rate. The performance and reliability of lithium battery chargers, as key equipment for ensuring battery safety and extending battery life, are of paramount importance.

[0003] Chinese invention patent application CN119765532A discloses an anti-backflow monitoring and control power supply for new energy vehicles. This power supply controls the charging and discharging of the new energy vehicle power supply and the voltage slope during power-on. It dynamically adjusts the operating mode of the new energy vehicle power supply based on the power management system status and external conditions. It blocks the backflow current from the downstream energy storage capacitor of the new energy vehicle power supply, providing overvoltage protection, anti-self-oscillation, and short-circuit protection safety measures. It also isolates different power paths to prevent current backflow, ensuring the safety and stability of the new energy vehicle power supply. Furthermore, it ensures that the new energy vehicle power supply meets predetermined performance indicators during design and operation, and provides data support for the optimization and fault diagnosis of the new energy vehicle power supply through real-time monitoring. This allows the power management system to control the entire charging and discharging process, preventing current backflow.

[0004] When the AC / DC adapter at the charger's front end is malfunctioning or the mains voltage is unstable, the voltage input to the charger may be abnormally high or low. In this situation, traditional input overvoltage or undervoltage protection circuits, due to their inherent threshold hysteresis and response characteristics, will be unable to completely shut down the system when the voltage fluctuates near the critical threshold. This forces the charger to operate under abnormal voltage conditions undesigned for extended periods. While the aforementioned technical solutions can prevent current backflow during this process, the resulting abnormal operating conditions not only disrupt the stable operation of the internal DC / DC conversion circuit, affecting the charger's lifespan, but also overwhelm the output voltage feedback control loop, causing slow response or even temporary loss of control, thus leading to overvoltage or undervoltage phenomena in the battery. Summary of the Invention

[0005] The purpose of this invention is to provide a self-protection method for a lithium battery charger and a charger in order to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a self-protection method for a lithium battery charger, comprising:

[0007] S1: Acquire feature data: Perform time-domain and frequency-domain analysis on the collected input voltage and current data to acquire feature data;

[0008] S2: Risk Assessment: Using the aforementioned feature data as input to the multidimensional safety boundary model, the output obtains the corresponding instantaneous maximum permissible output power, including:

[0009] S2.1: Construction of Multidimensional Safety Boundary Model: Based on the aforementioned feature data, construct thermal boundaries, capacitance boundaries, and battery boundaries, including:

[0010] S2.1.1: Set thermal boundary: Determine the junction temperature threshold of the switching transistor based on the transient thermal impedance of the switching transistor, the switching loss corresponding to the main harmonic frequency, and the heat generation energy;

[0011] S2.1.2: Set capacitor boundaries: Determine the upper limit of the safe power of the capacitor based on the rated ripple current life curve, voltage ripple amplitude and equivalent series resistance of the capacitor.

[0012] S2.1.3: Set battery boundaries: Combine the battery surface temperature and voltage ripple amplitude to set a ripple prediction value, and determine the upper limit of the battery's safe power based on the ripple prediction value;

[0013] S2.2: Determine the instantaneous maximum allowable power: Determine the instantaneous maximum allowable power based on the junction temperature threshold of the switching transistor, the upper limit of the safe power of the capacitor, and the upper limit of the safe power of the battery;

[0014] S3: Capacitive power control: Based on the instantaneous maximum allowable power, the actual output power is adjusted in real time through the coordinated control of the feedforward loop and the feedback loop.

[0015] Furthermore, feature data is obtained, including:

[0016] S1.1: High-frequency sampling: Input voltage and input current are acquired by voltage and current sensors set on the input path of the charger;

[0017] S1.2: Feature extraction: Perform time-domain and frequency-domain analysis on the input voltage to obtain the voltage ripple amplitude, variation trend and main harmonic frequencies;

[0018] S1.3: Source impedance estimation: Based on the comparison between the input current and the current change threshold, the current change time period is determined, and the source impedance within the current change time period is determined based on the current difference and voltage difference within the current change time period.

[0019] Furthermore, the junction temperature threshold of the switching transistor is determined, including:

[0020] S2.1.1.1: Constructing a loss model: Based on the set ripple influence coefficient, on-resistance, and effective current value, determine the conduction loss of the MOSFET. At the same time, based on the set main harmonic frequency, turn-on energy, and turn-off energy, determine the switching loss of the MOSFET.

[0021] S2.1.1.2: Thermal impedance network modeling: The conduction loss and switching loss of the MOSFET are combined with the set junction-to-case thermal resistance data and case-to-ambient thermal resistance data to determine the predicted junction temperature of the semiconductor chip. At the same time, a safety margin is determined based on the predicted junction temperature and the maximum allowable junction temperature.

[0022] S2.1.1.3: Determine thermal boundary limits: Based on the voltage ripple amplitude and the device's rated operating voltage, set a dynamic correction factor, and determine the upper power limit where the junction temperature does not exceed the safety limit by using ambient temperature, maximum allowable junction temperature, junction-to-case thermal resistance, case-to-ambient thermal resistance, and the dynamic correction factor. Specifically:

[0023]

[0024] in: For the maximum allowable thermal boundary power, For ambient temperature, To achieve the thermal resistance of the junction to the shell, For the thermal resistance from the shell to the environment, For safety reasons, This is a dynamic correction factor;

[0025] S2.1.1.4: Dynamic Power Limitation: The safety margin is compared with the margin intervention threshold, and a power adjustment strategy is determined based on the comparison result, specifically as follows:

[0026] When the safety margin is less than the margin intervention threshold, the corresponding power is reduced according to the maximum allowable thermal boundary power; otherwise, no power adjustment is made.

[0027] Furthermore, based on the on-resistance and turn-on energy corresponding to the main harmonic frequency, a ripple influence coefficient is set. At the same time, based on the instantaneous current within a preset time window, the effective value of the current is determined. The ripple influence coefficient, the effective value of the current, and the on-resistance are combined to determine the conduction loss of the MOSFET.

[0028] By turning the MOSFET on and off, the turn-on energy and turn-off energy of the MOSFET are obtained, and the switching loss of the MOSFET is determined based on the turn-on energy and turn-off energy.

[0029] Furthermore, based on the safety margin and the margin intervention threshold, a margin difference is obtained, and the upper limit of safe operating power is determined using the margin difference and the maximum allowable thermal boundary power, specifically:

[0030]

[0031] in: To adjust the allowable power, As a margin intervention threshold, For the maximum allowable thermal boundary power, For safety margin.

[0032] Furthermore, the upper limit of the safe power of the capacitor is determined, including:

[0033] S2.1.2.1: Determine the actual ripple current: Based on the equivalent series resistance at different temperatures, set the temperature coefficient, and based on the temperature coefficient, the measured surface temperature of the capacitor, and the equivalent series resistance under the nominal temperature of 25℃, determine the equivalent series resistance at the actual operating temperature. At the same time, based on the equivalent series resistance and the voltage ripple amplitude, obtain the actual ripple current.

[0034] S2.1.2.2: Determining the safety boundary: Based on the rated ripple current corresponding to the main harmonic frequency, a safety threshold is set, and the actual ripple current is compared with the safety threshold. Based on the comparison result, the safety state of the capacitor is determined, specifically as follows:

[0035] When the actual ripple current is greater than the safety threshold, the corresponding capacitor safety status is out of limit, and the upper limit of the capacitor safety power is determined; otherwise, the corresponding capacitor safety status is safe.

[0036] S2.1.2.3: Power Limitation: Based on the rated ripple current, set the maximum allowable ripple current, and determine the upper limit of the capacitor's safe power based on the maximum allowable ripple current and the actual ripple current.

[0037] Furthermore, the upper limit of the battery's safe power output is determined, including:

[0038] S2.1.3.1: Obtain ripple prediction: Based on the comparison between the battery surface temperature and the reference temperature, set a temperature compensation coefficient, and determine the ripple prediction value based on the temperature compensation coefficient and the voltage ripple amplitude value.

[0039] S2.1.3.2: Boundary Determination: Based on the battery ripple limit corresponding to the battery type, a ripple safety margin is set. Simultaneously, the ripple safety margin is compared with the predicted ripple value, and the battery safety state is determined based on the comparison result. Specifically:

[0040] When the predicted ripple value is greater than the ripple safety margin, the corresponding battery safety status is out of limit, and the upper limit of the battery safety power is determined based on the predicted ripple value, the ripple safety margin, and the current system output power; otherwise, the corresponding battery safety status is safe.

[0041] Furthermore, the actual output power is adjusted in real time, including:

[0042] S3.1: Determine the operating mode: Based on the output current and output voltage corresponding to the instantaneous maximum allowable power, the on-resistance of the MOSFET and the duty cycle limit, determine the safe voltage range. Simultaneously, compare the real-time input voltage with the safe voltage range, and determine the corresponding operating mode based on the comparison result. Specifically:

[0043] When the real-time input voltage is within the safe voltage range, it switches to the normal constant power mode; otherwise, it switches to the capacitive band operation mode.

[0044] S3.2: Feedforward control: Based on the proportional gain coefficient of the PWM controller and the voltage change trend, set the duty cycle adjustment amount, and determine the adjusted duty cycle of the controller based on the duty cycle adjustment amount and the current duty cycle of the controller;

[0045] S3.3: Feedback control: Set the output current setting value based on the instantaneous maximum allowable power and the current output voltage.

[0046] Furthermore, the set values ​​set during the switching process between the conventional constant power mode and the capacitive band operation mode are smoothed using a ramp function, including:

[0047] W1: Smooth switching: Based on the target current value in the conventional constant power mode, determine the current difference between the output current setpoint and the target current value, and determine the single-step current adjustment amount based on the current difference and the total number of adjustment steps.

[0048] W2: System Monitoring: Based on the current actual output power corresponding to the aforementioned capacitive operating mode, the instantaneous maximum allowable power is adjusted to obtain the adjusted instantaneous maximum allowable power, specifically:

[0049]

[0050] in: This is the adjusted instantaneous maximum allowable power. This represents the current actual output power. As a margin intervention threshold, For safety margin.

[0051] A charger that uses the self-protection method of a lithium battery charger as described in any one of the above-mentioned methods.

[0052] Compared with the prior art, the beneficial effects of the present invention are:

[0053] Firstly, this invention uses a multi-dimensional safety boundary model that includes thermal boundary, capacitance boundary, and battery boundary to monitor the junction temperature of the switching transistor, the capacitor ripple current, and the battery ripple voltage in real time. This ensures that key components operate within a safe range, thereby avoiding problems such as overheating, overload, or battery damage.

[0054] Secondly, this invention adaptively adjusts the output power based on the characteristics of input voltage fluctuations and real-time risk assessment, thereby avoiding the hysteresis problem of traditional protection circuits and ensuring stable operation under abnormal input conditions, reducing the risk of frequent system shutdown or loss of control.

[0055] Thirdly, this invention can quickly respond to input changes through coordinated control between the feedforward loop and the feedback loop, thereby reducing the stress on power devices and capacitors, extending the life of the charger, and reducing the performance degradation of the battery caused by voltage fluctuations.

[0056] Fourthly, this invention uses a ramp function to smooth out the conventional constant power mode and capacitive band operation mode, thereby avoiding the impact of sudden current changes on the system and battery and ensuring a smooth transition during the charging process. Attached Figure Description

[0057] Figure 1 This is a flowchart illustrating the self-protection method in this invention;

[0058] Figure 2 This is the junction temperature prediction curve for the MOSFET in this invention;

[0059] Figure 3 This is a loss analysis diagram of the MOSFET in this invention;

[0060] Figure 4 This is the equivalent series resistance-temperature characteristic curve of the capacitor in this invention;

[0061] Figure 5 This is the capacitor ripple current lifetime curve in this invention;

[0062] Figure 6 This is a diagram showing the relationship between temperature and compensation coefficient in this invention. Detailed Implementation

[0063] 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.

[0064] When the AC / DC adapter at the charger's front end is malfunctioning or the mains voltage is unstable, the voltage input to the charger may be abnormally high or low. In this case, traditional input overvoltage or undervoltage protection circuits, due to their inherent threshold hysteresis and response characteristics, will be unable to completely shut down the system when the voltage fluctuates near the critical threshold. This forces the charger to operate under abnormal voltage conditions undesigned for extended periods. Such abnormal conditions not only disrupt the stable operation of the internal DC / DC conversion circuit, affecting the charger's lifespan, but also overwhelm the output voltage feedback control loop, causing slow response or even temporary loss of control, resulting in overvoltage or undervoltage of the battery. The technical solution of this application, however, performs time-domain and frequency-domain analysis on the real-time acquired input voltage and current data to obtain corresponding characteristic data and constructs a multi-dimensional safety boundary model including thermal, capacitance, and battery boundaries. This model determines the corresponding instantaneous maximum allowable output power. Simultaneously, through coordinated control between the feedforward and feedback loops, the actual output power is dynamically adjusted, and during the adjustment process, the adjusted actual output power is limited based on the instantaneous maximum allowable output power. By establishing a triple protection mechanism of switch junction temperature threshold, capacitor safe power limit and battery safe power limit, the output power can be adaptively adjusted when the input voltage is abnormal. This not only ensures the safe operation of the charger's key components, but also avoids the risk of battery overvoltage or undervoltage, and improves the charger's reliability and safety under abnormal operating conditions such as grid fluctuations.

[0065] Example 1

[0066] refer to Figures 1-6 This embodiment provides a self-protection method for a lithium battery charger, which includes the following steps:

[0067] Step S1: Acquire feature data. This involves real-time acquisition of input voltage and current data using an analog-to-digital converter, followed by time-domain and frequency-domain analysis of the acquired data to obtain the corresponding feature data. Specifically:

[0068] Step S1.1: High-frequency sampling. This involves setting up a voltage sensor (e.g., a resistor divider network) and a current sensor (e.g., a precision sampling resistor and operational amplifier circuit) on the input path of the charger (before the DC-DC converter). Specifically, the voltage sensor is electrically connected to one ADC pin of the MCU / DSP, and the current sensor is electrically connected to another ADC pin of the MCU / DSP.

[0069] In the specific implementation process, the input voltage and input current monitored by the voltage sensor and the current sensor are synchronously sampled through the ADC pin in the MCU / DSP according to a fixed sampling rate.

[0070] Step S1.2: Feature Extraction. Based on the input voltage data obtained in Step S1.1, time-domain analysis is performed on the input voltage within a preset time period to obtain the voltage ripple amplitude and its changing trend. Specifically:

[0071]

[0072] in: This refers to the voltage ripple amplitude. The maximum input voltage within a preset time period. The minimum input voltage within a preset time period. The trend of voltage change The input voltage at time t within a preset time period. The input voltage at time t-1 within a preset time period. This represents the time difference.

[0073] Furthermore, the input voltage within a preset time period is analyzed in the frequency domain using Fast Fourier Transform (FFT). In this embodiment, the input voltage is converted from the "time-amplitude" domain to the "frequency-energy" domain using FFT, and the corresponding main frequency data is determined from the input voltage data converted to the "frequency-energy" domain, that is, the main harmonic frequencies corresponding to the input voltage ripple are obtained.

[0074] Step S1.3: Source Impedance Estimation. This involves setting a current surge threshold based on the acquired input voltage and current data. Specifically, based on the input current data within a preset time period, the current difference between different time intervals within that preset time period is obtained. This current difference is then compared with the current surge threshold, and the corresponding current surge time period is determined based on the comparison result.

[0075] When the obtained current difference is less than the current sudden change threshold, the time period corresponding to the current difference is not a current sudden change time period. Conversely, when the obtained current difference is not less than the current sudden change threshold, the time period corresponding to the current difference is a current sudden change time period.

[0076] Furthermore, based on the determined current abrupt change time period, the input voltage data within that time period is obtained, and the corresponding voltage difference is determined based on the input voltage data within that time period. In this embodiment, the corresponding source impedance is obtained based on the corresponding current difference and voltage difference within the current abrupt change time period, specifically:

[0077]

[0078] in: The source impedance during the period of sudden current change. This represents the voltage difference during the period of sudden current change. This represents the current difference during the period of sudden current change.

[0079] Step S2: Risk Assessment. The ripple amplitude, trend, and main harmonic frequencies obtained in Step S1.2, and the source impedance obtained in Step S1.3, are used as inputs to the constructed multidimensional safety boundary model. The output is the corresponding instantaneous maximum allowable output power. Details are as follows:

[0080] Step S2.1: Construction of the multidimensional safety boundary model. This involves constructing the thermal boundary, capacitance boundary, and battery boundary by obtaining the ripple amplitude, variation trend, main harmonic frequencies, and source impedance. Details are as follows:

[0081] Step S2.1.1: Set the thermal boundary. This involves determining the corresponding junction temperature threshold of the switching transistor based on its transient thermal impedance and the switching losses and heat generation corresponding to the main harmonic frequencies. Specifically:

[0082] Step S2.1.1.1: Construct a loss model. Based on the main harmonic frequency obtained in step S1.2 and the transient thermal impedance curve in the current device datasheet, determine the on-resistance and turn-on energy corresponding to the main harmonic frequency. Simultaneously, based on the ripple amplitude obtained in step S1.2 and the set rated operating voltage of the device, determine the corresponding ripple influence coefficient, specifically:

[0083]

[0084] in: Ripple influence coefficient The rated operating voltage of the device. This represents the voltage ripple amplitude.

[0085] Furthermore, by acquiring all instantaneous current magnitudes within a preset time window, the corresponding effective current value is determined, specifically as follows:

[0086]

[0087] in: This is the effective value of the current. The total number of sampling points. Let k be the instantaneous current value at the kth sampling point. This is the index for the sampling points.

[0088] In this embodiment, based on the obtained on-resistance, ripple influence coefficient, and effective current value, the amount of heat generated by the current flowing through the MOSFET in the on-state is determined, specifically as follows:

[0089]

[0090] in: For conduction loss, For on-resistance, Ripple influence coefficient This is the effective value of the current.

[0091] In the specific implementation process, the effective current value is 3.1A, the on-resistance is 0.045Ω, the ripple influence coefficient is 0.18, and the corresponding on-loss is 520mW.

[0092] Furthermore, the changes in drain-source voltage are monitored using a high-voltage differential probe, and the changes in drain current are monitored using a current Rogowski coil. Both the high-voltage differential probe and the current Rogowski coil are used to monitor the drain current changes simultaneously, and the high voltage differential is connected to an oscilloscope to obtain the corresponding drain-source voltage and drain current magnitudes. In other words, by controlling the on / off state of the MOSFET, the turn-off transient waveform of the MOSFET is captured, and the corresponding turn-off energy is obtained.

[0093] In this embodiment, based on the obtained main harmonic frequency, turn-on energy, and turn-off energy, the energy loss of the corresponding MOSFET during the switching transition process is determined, specifically as follows:

[0094]

[0095] in: For switching losses, To activate the energy, To shut off the energy, The dominant harmonic frequency.

[0096] In the specific implementation process, the turn-on energy is 2.5μJ, the turn-off energy is 2.8μJ, the dominant harmonic frequency is 125kHz, and the corresponding switching loss is 662mW.

[0097] Step S2.1.1.2: Thermal Impedance Network Modeling. The DS18B20 digital temperature sensor is positioned at the center of the device's air inlet, 5 cm from the outer casing, and the corresponding ambient temperature data is acquired at a sampling rate of 1 Hz. Simultaneously, based on the junction-to-case thermal resistance data in the current device datasheet, the corresponding junction-to-case thermal resistance and case-to-ambient thermal resistance data are determined.

[0098] In this embodiment, based on the obtained external ambient temperature data, junction-to-case thermal resistance data, and the conduction loss and switching loss obtained in step S2.1.1.1, the actual operating temperature of the corresponding semiconductor chip is determined, specifically as follows:

[0099]

[0100] in: This is the predicted junction temperature value. For ambient temperature, For conduction loss, For switching losses, To achieve the thermal resistance of the junction to the shell, The thermal resistance from the shell to the environment.

[0101] In the specific implementation process, the conduction loss is 520mW, the switching loss is 662mW, and the corresponding total loss is 1182 mW. Meanwhile, the junction-to-case thermal resistance is 1.5℃ / W, the case-to-ambient thermal resistance is 15℃ / W, the ambient temperature is 65℃, and the corresponding predicted junction temperature is 84.5℃.

[0102] Furthermore, based on the obtained predicted junction temperature and the maximum allowable junction temperature set in the current device datasheet, the corresponding safety margin is determined, specifically as follows:

[0103]

[0104] in: For safety margin, The maximum allowable junction temperature, This is the predicted junction temperature.

[0105] In the actual implementation process, the maximum allowable junction temperature set in the current device datasheet is 125℃, and the predicted junction temperature is 84.5℃, so the corresponding safety margin is 32.4%.

[0106] Step S2.1.1.3: Determine the thermal boundary limit. Specifically, based on the voltage ripple amplitude obtained in step S1.2 and the set rated operating voltage of the device, determine the corresponding dynamic correction coefficient, as follows:

[0107]

[0108] in: This is a dynamic correction factor. This refers to the voltage ripple amplitude. This is the device's rated operating voltage.

[0109] In this embodiment, based on the obtained ambient temperature, maximum allowable junction temperature, junction-to-case thermal resistance, case-to-ambient thermal resistance, and dynamic correction factor, the corresponding power limit for the junction temperature not exceeding the safety limit is determined, specifically as follows:

[0110]

[0111] in: For the maximum allowable thermal boundary power, For ambient temperature, To achieve the thermal resistance of the junction to the shell, For the thermal resistance from the shell to the environment, For safety reasons, This is a dynamic correction coefficient.

[0112] In the specific implementation process, the junction-to-case thermal resistance is 1.5℃ / W, the case-to-ambient thermal resistance is 15℃ / W, the ambient temperature is 65℃, the maximum allowable junction temperature is 125℃, the safety factor is 0.75, the dynamic correction factor is 0.8, and the corresponding maximum allowable thermal boundary power is 2.18W.

[0113] Step S2.1.1.4: Dynamic Power Limitation. This involves comparing the safety margin obtained in step S2.1.1.2 with the set margin intervention threshold (the specific setting is based on actual data, and therefore not specifically described in this embodiment, e.g., 20%), and determining the corresponding power adjustment strategy based on the comparison result. Specifically:

[0114] When the obtained safety margin is less than the margin intervention threshold, the corresponding power will be reduced to ensure that the adjusted power does not exceed the set maximum allowable thermal boundary power. Otherwise, no power adjustment will be made, and the current power will be maintained for continued operation.

[0115] In this embodiment, the margin difference between the margin intervention threshold and the safety margin is combined with the maximum allowable thermal boundary power obtained in step S2.1.1.3 to determine the corresponding safe operating power upper limit, specifically:

[0116]

[0117] in: To adjust the allowable power, As a margin intervention threshold, For the maximum allowable thermal boundary power, For safety margin.

[0118] refer to Figure 2 and Figure 3 It can be seen that the predicted junction temperature remains stable between the derating threshold of 84.5℃ and the maximum allowable junction temperature of 125℃. Meanwhile, the periodic fluctuations in switching losses cause the junction temperature to show a regular change of ±3℃.

[0119] Step S2.1.2: Set capacitor boundaries. This involves combining the rated ripple current lifetime curve of the filter capacitor with the voltage ripple amplitude and equivalent series resistance of the capacitor obtained in step S1.2 to determine the corresponding upper limit of the capacitor's safe power. Specifically:

[0120] Step S2.1.2.1: Determine the actual ripple current. This involves determining the equivalent series resistance at the nominal temperature of 25℃ based on the reference parameters provided in the equipment manufacturer's specifications. Simultaneously, the equivalent series resistance at 25℃, 50℃, and 85℃ is measured in the temperature control chamber. The corresponding temperature-equivalent series resistance curve is then obtained by fitting the curve using the least squares method. Based on the slope of the temperature-equivalent series resistance curve, a corresponding temperature coefficient is set. Specifically:

[0121]

[0122] in: For temperature coefficient, This is the equivalent series resistance at a reference temperature of 25°C. The measured value of the equivalent series resistance at ambient temperature. The ambient temperature.

[0123] In the specific implementation process, the equivalent series resistance at the 25℃ reference temperature is 0.085Ω, while the corresponding equivalent series resistances at 50℃, 85℃, and 105℃ are 0.078Ω, 0.077Ω, and 0.035Ω, respectively. Therefore, the corresponding temperature coefficients are 0.00165 / ℃, 0.00157 / ℃, and 0.00196 / ℃, respectively. In other words, the final obtained temperature coefficient is 0.00713 / ℃.

[0124] Furthermore, by mounting an NTC thermistor or using infrared thermometry, the actual measured temperature of the capacitor surface is obtained. Simultaneously, based on the determined temperature coefficient and the equivalent series resistance under the nominal temperature condition of 25°C, the true impedance characteristics of the capacitor under the current operating conditions are determined. Specifically:

[0125]

[0126] in: This is the equivalent series resistance at the actual operating temperature. This is the measured temperature of the capacitor surface. For temperature coefficient, This is the equivalent series resistance at a reference temperature of 25°C.

[0127] Furthermore, based on the equivalent series resistance at the actual operating temperature and the voltage ripple amplitude obtained in step S1.2, the corresponding actual ripple current is determined, specifically as follows:

[0128]

[0129] in: This is the actual ripple current. This refers to the voltage ripple amplitude. This is the equivalent series resistance at the actual operating temperature.

[0130] Step S2.1.2.2: Determine the safety boundary. That is, based on the major harmonic frequencies determined in step S1.2, determine the corresponding rated ripple current from the equipment manufacturer's specifications. In this embodiment, based on the determined rated ripple current, a corresponding safety threshold is set, specifically 0.8 times the rated ripple current is set as the safety threshold.

[0131] Furthermore, the actual ripple current obtained is compared with the set safety threshold, and the corresponding capacitor safety state is determined based on the comparison result, specifically:

[0132] When the actual ripple current is greater than the safety threshold, the corresponding capacitor is in an out-of-limit safety state. In this case, the upper limit of the capacitor's safe power is determined through the next step, S2.1.2.3, power limitation. Conversely, when the actual ripple current is not greater than the safety threshold, the corresponding capacitor is in a safe safety state.

[0133] Step S2.1.2.3: Power Limitation. Based on the rated ripple current obtained from the manufacturer's specifications, 0.8 times the rated ripple current is set as the corresponding maximum allowable ripple current. Simultaneously, the maximum allowable ripple current is combined with the current system's output power and the actual ripple current obtained in step S2.1.2.1 to determine the corresponding upper limit of the capacitor's safe power. Specifically:

[0134]

[0135] in: This is the upper limit of the safe power of the capacitor. This represents the current system output power. This is the actual ripple current. The maximum allowable ripple current.

[0136] During the actual implementation, the current system output power is 60W, the actual ripple current is 12.99A, the maximum allowable ripple current is 2.56A, and the corresponding upper limit of the safe power of the capacitor is 2.33W.

[0137] refer to Figure 4 and Figure 5 It can be seen that the equivalent series resistance of the capacitor is relatively stable in the temperature range of 25℃-85℃, but drops sharply to 0.035Ω at 105℃. At the same time, the actual ripple current reaches 14.12A at 25℃, far exceeding the allowable value of 2.56A, exceeding it by 452%. Although the decrease in the equivalent series resistance of the capacitor at high temperature will lead to a further increase in ripple current, the difference between its maximum allowable ripple current value and the actual value decreases.

[0138] Step S2.1.3: Set battery boundaries. This involves combining the battery surface temperature with the voltage ripple amplitude obtained in step S1.2 to determine the corresponding ripple prediction value. Based on this ripple prediction value, the corresponding upper limit of the battery's safe power is then determined. Details are as follows:

[0139] Step S2.1.3.1: Obtain ripple prediction. This involves acquiring the battery surface temperature in real time using an NTC thermistor or infrared thermometer, comparing it to a reference temperature of 25°C, and setting a corresponding temperature compensation coefficient based on the comparison result. Specifically:

[0140]

[0141] in: This is the temperature compensation coefficient. This refers to the surface temperature of the battery.

[0142] During the actual implementation, the battery surface temperature is 40℃, and the corresponding temperature compensation coefficient is 1.075.

[0143] Furthermore, the obtained voltage ripple amplitude value is combined with the set temperature compensation coefficient to determine the corresponding ripple prediction value, specifically:

[0144]

[0145] in: This is the predicted ripple value. This represents the peak-to-peak value of the voltage fluctuation on the input side of the power module. This is the temperature compensation coefficient.

[0146] During the actual implementation, the peak-to-peak voltage fluctuation on the input side of the power module is 1.2V, and the corresponding ripple prediction value is 258mV.

[0147] Step S2.1.3.2: Boundary determination. This involves setting a corresponding ripple safety margin based on the battery type and its corresponding ripple limit recorded in the battery datasheet. Specifically, the ripple safety margin is 0.8 times the battery ripple limit.

[0148] Furthermore, the obtained ripple prediction value is compared with the set ripple safety margin, and the corresponding battery safety state is determined based on the comparison result, specifically:

[0149] When the obtained ripple prediction value is greater than the ripple safety margin, the corresponding battery safety state is out of limit. In this case, the ratio between the ripple prediction value and the ripple safety margin obtained in step S2.1.3.1 is combined with the current system output power to determine the corresponding upper limit of battery safety power. Conversely, when the obtained ripple prediction value is not greater than the ripple safety margin, the corresponding battery safety state is safe.

[0150] In this embodiment, the corresponding upper limit of battery safe power is obtained by using the ripple prediction value, ripple safety margin, and current system output power, specifically:

[0151]

[0152] in: This is the upper limit of the battery's safe power. This represents the current system output power. To provide a safety margin for ripple, This is the predicted value for ripple.

[0153] In the actual implementation process, the current system output power is 40W, the ripple safety margin is 50mV, and the ripple prediction value is 258mV, so the corresponding upper limit of the battery safe power is about 7.75W.

[0154] refer to Figure 6 It can be seen that the temperature compensation coefficient increases from 1 at 25℃ to 1.175 at 60℃. At the same time, the compensation coefficient increases by 5% for every 10℃ increase, which can accurately track temperature changes.

[0155] Step S2.2: Determine the instantaneous maximum allowable power. This involves combining the maximum allowable thermal boundary power obtained in step S2.1.1.3, the upper limit of the capacitor's safe power obtained in step S2.1.2.3, and the upper limit of the battery's safe power obtained in step S2.1.3.2 to determine the corresponding instantaneous maximum allowable power. Specifically:

[0156]

[0157] in: The instantaneous maximum permissible power, For the maximum allowable thermal boundary power, This is the upper limit of the battery's safe power. This is the upper limit of the safe power of the capacitor.

[0158] In the specific implementation process, the maximum allowable thermal boundary power is 2.18W, the upper limit of the safe power of the capacitor is 2.33W, and the upper limit of the safe power of the battery is 7.75W. Therefore, the corresponding instantaneous maximum allowable power is 2.18W.

[0159] Step S3: Capacitive power control. Based on the instantaneous maximum allowable power obtained in step S2.2, the actual output power is adjusted in real time through the coordinated control of the feedforward loop and the feedback loop. Specifically:

[0160] Step S3.1: Determine the operating mode. Based on the instantaneous maximum allowable power obtained in step S2.2, determine the corresponding output current. Simultaneously, based on the output current and voltage corresponding to the instantaneous maximum allowable power, the on-resistance of the MOSFET, and its duty cycle limit, determine the corresponding safe voltage range. Specifically:

[0161]

[0162] in: Minimum input voltage, The output voltage of the power supply system. This is the output current corresponding to the instantaneous maximum allowable power. This is the on-resistance of the MOSFET. The upper limit of the duty cycle allowed by the controller. Maximum input voltage, This is the lower limit of the duty cycle allowed by the controller.

[0163] Furthermore, the corresponding real-time input voltage is obtained through the power input terminal. Simultaneously, the obtained real-time input voltage is compared with the determined safe voltage range, and based on the comparison result, the corresponding operating mode is determined. Specifically:

[0164] When the real-time input voltage is within the safe voltage range, it switches to the normal constant power mode. Conversely, when the real-time input voltage is not within the safe voltage range, it switches to the capacitive band operation mode.

[0165] Step S3.2: Feedforward Control. This involves comparing the voltage change trend obtained in step S1.2 with a set change threshold (the specific threshold is set based on actual data, and therefore not specifically described in this embodiment, e.g., 20V / ms), and adjusting the PWM duty cycle based on the comparison result. Specifically:

[0166] When the obtained voltage change trend is greater than the change threshold, the PWM duty cycle is adjusted by the controller. Conversely, when the obtained voltage change trend is not greater than the change threshold, the PWM duty cycle is not adjusted.

[0167] In this embodiment, the proportional gain coefficient of the PWM controller is combined with the voltage change trend obtained in step S1.2 to obtain the corresponding duty cycle adjustment amount, specifically:

[0168]

[0169] in: This is the duty cycle adjustment amount. This is the proportional gain coefficient. This represents the trend of voltage change.

[0170] Furthermore, based on the current duty cycle of the controller and the amount of duty cycle adjustment, the adjusted duty cycle of the controller is determined, specifically as follows:

[0171]

[0172] in: This is the adjusted duty cycle. This is the current duty cycle. This is the duty cycle adjustment amount.

[0173] Step S3.3: Feedback Control. This involves combining the instantaneous maximum allowable power obtained in step S2.2 with the current output voltage to obtain the corresponding output current setpoint, specifically:

[0174]

[0175] in: Set the output current value. The output voltage of the power supply system. This represents the instantaneous maximum permissible power.

[0176] Furthermore, based on the obtained output current setting value, the currently obtained current value is reduced until the current is reduced to the output current setting value.

[0177] This embodiment also provides a charger that uses the self-protection method of the above-mentioned lithium battery charger.

[0178] Example 2

[0179] This embodiment provides a self-protection method for a lithium battery charger. The specific implementation method is the same as in Embodiment 1, except that when switching between the normal constant power mode and the capacity-band operation mode, or when adjusting the current based on the output current setting in the capacity-band operation mode, a ramp function is used to smooth the setting value to restore the normal charging mode. The invention will be illustrated below with specific examples of this embodiment.

[0180] In this embodiment, the set value is processed using a ramp function and restored to the normal charging mode, as detailed below:

[0181] Step W1: Smooth Switching. This involves combining the output current setting value obtained in step S3.3 with the output voltage and output power of the power supply system to determine the corresponding operating mode, namely, capacitive control mode. Simultaneously, based on the target current value corresponding to the conventional constant power mode, the current difference between the output current setting value and the target current value is determined.

[0182] Furthermore, the difference between the output current setpoint and the target current value is combined with the total number of adjustment steps to determine the corresponding single-step current adjustment amount, specifically:

[0183]

[0184] in: This is the single-step current adjustment amount. The current difference between the output current setpoint and the target current value. This represents the total number of adjustment steps.

[0185] In this embodiment, the system thermal time constant is set as the ramp time constant, and the ramp time constant is combined with the control cycle. That is, the total number of adjustment steps is set according to the ratio between the ramp time constant and the control cycle.

[0186] In other words, the current magnitude is adjusted based on the determined single-step current adjustment amount.

[0187] Step W2: System Monitoring. This involves acquiring the corresponding voltage ripple amplitude, main harmonic frequencies, and the actual operating temperature of the internal chips of the semiconductor devices using a high-voltage differential probe, spectrum analysis module, and K-type thermocouples to determine the corresponding operating power. Simultaneously, the determined operating power is compared with the instantaneous maximum allowable power obtained in step S2.2, and the instantaneous maximum allowable power is adjusted based on the comparison result, specifically as follows:

[0188] When the actual operating power exceeds the instantaneous maximum allowable power, the operating power is adjusted via the capacity power control in step S3 until the actual operating power is no greater than the instantaneous maximum allowable power. Conversely, when the actual operating power is no greater than the instantaneous maximum allowable power, no adjustment is made to the operating power.

[0189] Furthermore, when switching from capacitive band operation mode to regular constant power mode, the instantaneous maximum allowable power is adjusted based on the current actual output power corresponding to the current capacitive band operation mode, to obtain the adjusted instantaneous maximum allowable power, specifically:

[0190]

[0191] in: This is the adjusted instantaneous maximum allowable power. This represents the current actual output power. As a margin intervention threshold, For safety margin.

[0192] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended embodiments and their equivalents.

Claims

1. A self-protection method for a lithium battery charger, characterized in that, Including: S1: Acquire feature data: Perform time-domain and frequency-domain analysis on the collected input voltage and current data to acquire feature data; S2: Risk Assessment: Using the aforementioned feature data as input to the multidimensional safety boundary model, the output obtains the corresponding instantaneous maximum permissible output power, including: S2.1: Construction of Multidimensional Safety Boundary Model: Based on the aforementioned feature data, construct thermal boundaries, capacitance boundaries, and battery boundaries, including: S2.1.1: Setting Thermal Boundaries: Based on the transient thermal impedance of the switching transistor, the switching losses corresponding to the main harmonic frequencies, and the heat generation energy, determine the junction temperature threshold of the switching transistor, including: S2.1.1.1: Constructing a loss model: Based on the set ripple influence coefficient, on-resistance, and effective current value, determine the conduction loss of the MOSFET. At the same time, based on the set main harmonic frequency, turn-on energy, and turn-off energy, determine the switching loss of the MOSFET. S2.1.1.2: Thermal impedance network modeling: The conduction loss and switching loss of the MOSFET are combined with the set junction-to-case thermal resistance data and case-to-ambient thermal resistance data to determine the predicted junction temperature of the semiconductor chip. At the same time, a safety margin is determined based on the predicted junction temperature and the maximum allowable junction temperature. S2.1.1.3: Determine thermal boundary limits: Based on the voltage ripple amplitude and the device's rated operating voltage, set a dynamic correction factor, and determine the upper power limit where the junction temperature does not exceed the safety limit by using ambient temperature, maximum allowable junction temperature, junction-to-case thermal resistance, case-to-ambient thermal resistance, and the dynamic correction factor. Specifically: ； in: For the maximum allowable thermal boundary power, For ambient temperature, To achieve the thermal resistance of the junction to the shell, For the thermal resistance from the shell to the environment, For safety reasons, S2.1.1.4: Dynamic power limitation: The safety margin is compared with the margin intervention threshold, and a power adjustment strategy is determined based on the comparison result, specifically as follows: When the safety margin is less than the margin intervention threshold, the corresponding power is reduced according to the maximum allowable thermal boundary power; otherwise, no power adjustment is made. Based on the safety margin and the margin intervention threshold, the margin difference is obtained, and the upper limit of safe operating power is determined by the margin difference and the maximum allowable thermal boundary power, specifically: ； in: To adjust the allowable power, As a margin intervention threshold, For the maximum allowable thermal boundary power, For safety margin; S2.1.2: Set capacitor boundaries: Determine the upper limit of the safe power of the capacitor based on the rated ripple current life curve, voltage ripple amplitude and equivalent series resistance of the capacitor. S2.1.3: Set battery boundaries: Combine the battery surface temperature and voltage ripple amplitude to set a ripple prediction value, and determine the upper limit of the battery's safe power based on the ripple prediction value; S2.2: Determine the instantaneous maximum allowable power: Based on the junction temperature threshold of the switching transistor, the upper limit of the safe power of the capacitor, and the upper limit of the safe power of the battery, determine the instantaneous maximum allowable power; S3: Capacitive power control: Based on the instantaneous maximum allowable power, the actual output power is adjusted in real time through the coordinated control of the feedforward loop and the feedback loop.

2. The self-protection method for a lithium battery charger according to claim 1, characterized in that, The feature data obtained includes: S1.1: High-frequency sampling: Input voltage and input current are acquired by voltage and current sensors set on the input path of the charger; S1.2: Feature extraction: Perform time-domain and frequency-domain analysis on the input voltage to obtain the voltage ripple amplitude, variation trend and main harmonic frequencies; S1.3: Source impedance estimation: Based on the comparison between the input current and the current change threshold, the current change time period is determined, and the source impedance within the current change time period is determined based on the current difference and voltage difference within the current change time period.

3. The self-protection method for a lithium battery charger according to claim 1, characterized in that, Based on the on-resistance and turn-on energy corresponding to the main harmonic frequency, a ripple influence coefficient is set. At the same time, based on the instantaneous current within a preset time window, the effective value of the current is determined. The ripple influence coefficient, the effective value of the current, and the on-resistance are combined to determine the conduction loss of the MOSFET. By turning the MOSFET on and off, the turn-on energy and turn-off energy of the MOSFET are obtained, and the switching loss of the MOSFET is determined based on the turn-on energy and turn-off energy.

4. The self-protection method for a lithium battery charger according to claim 1, characterized in that, The upper limit of the safe power of the capacitor is determined, including: S2.1.2.1: Determine the actual ripple current: Based on the equivalent series resistance at different temperatures, set the temperature coefficient, and based on the temperature coefficient, the measured surface temperature of the capacitor, and the equivalent series resistance under the nominal temperature of 25℃, determine the equivalent series resistance at the actual operating temperature. At the same time, based on the equivalent series resistance and the voltage ripple amplitude, obtain the actual ripple current. S2.1.2.2: Determining the safety boundary: Based on the rated ripple current corresponding to the main harmonic frequency, a safety threshold is set, and the actual ripple current is compared with the safety threshold. Based on the comparison result, the safety state of the capacitor is determined, specifically as follows: When the actual ripple current is greater than the safety threshold, the corresponding capacitor safety status is out of limit, and the upper limit of the capacitor safety power is determined; otherwise, the corresponding capacitor safety status is safe. S2.1.2.3: Power Limitation: Based on the rated ripple current, set the maximum allowable ripple current, and determine the upper limit of the capacitor's safe power based on the maximum allowable ripple current and the actual ripple current.

5. A self-protection method for a lithium battery charger according to claim 1, characterized in that, The upper limit of the battery's safe power is determined, including: S2.1.3.1: Obtain ripple prediction: Based on the comparison between the battery surface temperature and the reference temperature, set a temperature compensation coefficient, and determine the ripple prediction value based on the temperature compensation coefficient and the voltage ripple amplitude value. S2.1.3.2: Boundary Determination: Based on the battery ripple limit corresponding to the battery type, a ripple safety margin is set. Simultaneously, the ripple safety margin is compared with the predicted ripple value, and the battery safety state is determined based on the comparison result. Specifically: When the predicted ripple value is greater than the ripple safety margin, the corresponding battery safety status is out of limit, and the upper limit of battery safety power is determined based on the predicted ripple value, the ripple safety margin and the current system output power. Conversely, the corresponding battery safety status is safe.

6. The self-protection method for a lithium battery charger according to claim 1, characterized in that, Real-time adjustment of actual output power includes: S3.1: Determine the operating mode: Based on the output current and output voltage corresponding to the instantaneous maximum allowable power, the on-resistance of the MOSFET and the duty cycle limit, determine the safe voltage range. Simultaneously, compare the real-time input voltage with the safe voltage range, and determine the corresponding operating mode based on the comparison result. Specifically: When the real-time input voltage is within the safe voltage range, it switches to the normal constant power mode; otherwise, it switches to the capacitive band operation mode. S3.2: Feedforward control: Based on the proportional gain coefficient of the PWM controller and the voltage change trend, set the duty cycle adjustment amount, and determine the adjusted duty cycle of the controller based on the duty cycle adjustment amount and the current duty cycle of the controller; S3.3: Feedback control: Set the output current setting value based on the instantaneous maximum allowable power and the current output voltage.

7. A self-protection method for a lithium battery charger according to claim 6, characterized in that, The set values ​​set during the switching process between the conventional constant power mode and the capacitive band operation mode are smoothed using a ramp function, including: W1: Smooth switching: Based on the target current value in the conventional constant power mode, determine the current difference between the output current setpoint and the target current value, and determine the single-step current adjustment amount based on the current difference and the total number of adjustment steps. W2: System Monitoring: Based on the current actual output power corresponding to the aforementioned capacitive operating mode, the instantaneous maximum allowable power is adjusted to obtain the adjusted instantaneous maximum allowable power, specifically: ； in: This is the adjusted instantaneous maximum allowable power. This represents the current actual output power. As a margin intervention threshold, For safety margin.

8. A charger, characterized in that, A self-protection method for a lithium battery charger as described in any one of claims 1-7 was used.

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