Self-protection method of lithium battery charger and charger

Abstract

The invention discloses a self-protection method of a lithium battery charger and the charger, and relates to the technical field of battery charging control. Comprising the following steps: S1, carrying out time domain and frequency domain analysis on collected input voltage and current data to obtain characteristic data; s2, taking the feature data as the input of a multi-dimensional security boundary model, and outputting to obtain corresponding instantaneous maximum allowable output power; and S3, according to the instantaneous maximum allowable power, real-time adjustment is carried out on the actual output power through cooperative control of a feed-forward loop and a feedback loop. Through the established triple protection mechanism of the switching tube junction temperature threshold, the capacitor safety power upper limit and the battery safety power upper limit, the output power can be adaptively adjusted when the input voltage is abnormal, so that the safe operation of key components of the charger can be ensured, the overvoltage or undervoltage risk of the battery can be avoided, and the safety of the battery is ensured. And the reliability and the safety of the charger under abnormal working conditions such as power grid fluctuation are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery charging control, in particular to a self-protection method of a lithium battery charger and the charger. BACKGROUND

[0002] With the rapid development of portable electronic devices (such as smart phones, notebook computers, power tools) and electric vehicles, energy storage systems and other fields, lithium batteries have become one of the most important energy storage devices due to their high energy density, long cycle life and low self-discharge rate. As a key device to ensure battery safety and prolong battery life, the performance and reliability of the lithium battery charger are crucial.

[0003] The Chinese patent application with the publication number CN119765532A discloses a reverse flow prevention and control power supply for new energy vehicles, which controls the charging and discharging of the new energy vehicle power supply and the voltage slope during power-on, and dynamically adjusts the working mode of the new energy vehicle power supply according to the power management system state and external conditions; blocks the reverse current of the new energy vehicle power supply rear-stage energy storage capacitor, provides safety measures such as overvoltage protection, prevents self-oscillation, and short-circuit protection, and isolates different power supply paths to prevent current reverse flow and ensure the safety and stability of the new energy vehicle power supply; ensures that the new energy vehicle power supply can meet the 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, realizes the control of the entire current charging and discharging steps through the power management system, and can prevent current reverse flow.

[0004] When the AC / DC adapter at the front end of the charger has poor performance or the grid voltage is unstable, the voltage input to the charger may be abnormally high or low. At this time, the traditional input overvoltage or undervoltage protection circuit will not be able to completely shut down the system due to its inherent threshold hysteresis and response characteristics when the voltage fluctuates near the critical threshold, thereby forcing the charger to work under abnormal voltage conditions for a long time. Although the above technical solution can prevent the current reverse flow problem caused during this process, the abnormal working condition caused by it not only disturbs the stable operation of the internal DC / DC conversion circuit and affects the service life of the charger, but also overwhelms the feedback control loop of the output voltage, causing its response to be slow and even temporarily out of control, thereby causing the battery to overvoltage or undervoltage. SUMMARY

[0006] The present application relates to the technical field of battery charging control, in particular to a self-protection method of a lithium battery charger and the charger.

[0007] To achieve the above-mentioned purpose, the present application provides the following technical scheme: a self-protection method of a lithium battery charger, comprising:

[0008] S1: acquiring feature data: time domain and frequency domain analysis of the collected input voltage and current data to obtain feature data;

[0009] S2: risk assessment: inputting the feature data into a multi-dimensional safety boundary model to output the corresponding instantaneous maximum allowed output power, including:

[0010] S2.1: multi-dimensional safety boundary model construction: constructing a thermal boundary, a capacitance boundary, and a battery boundary according to the feature data, including:

[0011] S2.1.1: setting the thermal boundary: determining the switching tube junction temperature threshold according to the switching tube transient thermal impedance, the switching loss corresponding to the main harmonic frequency, and the heat generation energy;

[0012] S2.1.2: setting the capacitance boundary: determining the upper limit of the capacitor safety power according to the rated ripple current life curve of the filter capacitor, the voltage ripple amplitude, and the capacitor equivalent series resistance;

[0013] S2.1.3: setting the battery boundary: combining the battery surface temperature and the voltage ripple amplitude to set the ripple prediction value, and determining the upper limit of the battery safety power according to the ripple prediction value;

[0014] S2.2: determining the instantaneous maximum allowed power: determining the instantaneous maximum allowed power according to the switching tube junction temperature threshold, the capacitor safety power upper limit, and the battery safety power upper limit;

[0015] S3: band power control: adjusting the actual output power in real time according to the instantaneous maximum allowed power through the cooperative control of the feedforward loop and the feedback loop.

[0016] Further, acquiring feature data includes:

[0017] S1.1: high-frequency sampling: acquiring input voltage and input current through voltage sensors and current sensors arranged on the input path of the charger;

[0018] S1.2: feature extraction: time domain and frequency domain analysis of the input voltage to obtain the voltage ripple amplitude, the trend, and the main harmonic frequency;

[0019] S1.3: source impedance estimation: determining the current mutation time period according to the comparison between the input current and the current mutation threshold, and determining the source impedance in the current mutation time period according to the current difference and the voltage difference in the current mutation time period.

[0020] Further, determining the switching tube junction temperature threshold includes:

[0021] S2.1.1.1: Constructing loss model: according to the set ripple influence coefficient, on-resistance and current effective value, the on-state loss of the MOSFET tube is determined, and according to the set main harmonic frequency, turn-on energy and turn-off energy, the switching loss of the MOSFET tube is determined;

[0022] S2.1.1.2: Thermal impedance network modeling: the on-state loss and switching loss of the MOSFET tube are combined with the set junction-to-case thermal resistance data and case-to-environment thermal resistance data to determine the junction temperature prediction value of the semiconductor chip, and according to the junction temperature prediction value and the maximum allowed junction temperature, the safety margin is determined;

[0023] S2.1.1.3: Determine the thermal boundary limit: according to the voltage ripple amplitude and the rated operating voltage of the device, set the dynamic correction coefficient, and through the environmental temperature, the maximum allowed junction temperature, the junction-to-case thermal resistance, the case-to-environment thermal resistance and the dynamic correction coefficient, the upper limit of the power is determined, which is that the junction temperature does not exceed the safety limit, which is:

[0024]

[0025] Wherein: is the maximum allowed thermal boundary power, is the environmental temperature, is the junction-to-case thermal resistance, is the case-to-environment thermal resistance, is the safety factor, is the dynamic correction coefficient;

[0026] S2.1.1.4: Dynamic power limit: compare the safety margin with the margin intervention threshold, and according to the comparison result, determine the power adjustment strategy, which is:

[0027] When the safety margin is less than the margin intervention threshold, the corresponding power is reduced according to the maximum allowed thermal boundary power; otherwise, the power is not adjusted.

[0028] Further, according to the on-resistance and turn-on energy corresponding to the main harmonic frequency, the ripple influence coefficient is set, and according to the instantaneous current in the preset time window, the current effective value is determined, and the ripple influence coefficient, current effective value and on-resistance are combined to determine the on-state loss of the MOSFET tube;

[0029] Through the on and off of the MOSFET tube, the turn-on energy and turn-off energy of the MOSFET tube are obtained, and according to the turn-on energy and turn-off energy, the switching loss of the MOSFET tube is determined.

[0030] Further, according to the safety margin and the margin intervention threshold, a margin difference value is obtained, and a safety working power upper limit is determined according to the margin difference value and the maximum allowed thermal boundary power, specifically:

[0031]

[0032] Wherein: is the adjusted allowed power, is the margin intervention threshold, is the maximum allowed thermal boundary power, is the safety margin.

[0033] Further, a battery safety power upper limit is determined, including:

[0034] S2.1.2.1: Determine the actual ripple current: according to the equivalent series resistance under different temperatures, set the temperature coefficient, and according to the temperature coefficient, the actual working temperature of the capacitor surface measured temperature and the equivalent series resistance under the condition of 25℃ temperature nominal, determine the equivalent series resistance under the condition of actual working temperature, and according to the equivalent series resistance and voltage ripple amplitude, the actual ripple current is obtained;

[0035] S2.1.2.2: Determine the safety boundary: according to the rated ripple current corresponding to the main harmonic frequency, set the safety threshold, and compare the actual ripple current with the safety threshold, and according to the comparison result, determine the capacitor safety state, specifically:

[0036] When the actual ripple current is greater than the safety threshold, the corresponding capacitor safety state is over limit, and the capacitor safety power upper limit is determined; otherwise, the corresponding capacitor safety state is safe;

[0037] S2.1.2.3: Power limit: according to the rated ripple current, set the allowed maximum ripple current, and according to the allowed maximum ripple current and the actual ripple current, determine the capacitor safety power upper limit.

[0038] Further, the battery safety power upper limit is determined, including:

[0039] S2.1.3.1: Obtain ripple estimation: according to the comparison between the battery surface temperature and the reference temperature, set the temperature compensation coefficient, and according to the temperature compensation coefficient and the voltage ripple amplitude, determine the ripple prediction value;

[0040] S2.1.3.2: Boundary determination: according to the battery ripple limit value corresponding to the battery type, set the ripple safety margin, and compare the ripple safety margin with the ripple prediction value, and according to the comparison result, determine the battery safety state, specifically:

[0041] When the ripple prediction value is greater than the ripple safety margin, the corresponding battery safety state is over-limit, and a battery safety power upper limit is determined according to the ripple prediction value, the ripple safety margin and the current system output power; otherwise, the corresponding battery safety state is safe.

[0042] Further, the actual output power is adjusted in real time, including:

[0043] S3.1: determining a running mode: according to the output current and the output voltage corresponding to the instantaneous maximum allowable power, the on-resistance of the MOSFET tube and the duty cycle limit, a safe voltage range is determined, and the real-time input voltage is compared with the safe voltage range, and according to the comparison result, the corresponding running mode is determined, specifically:

[0044] When the real-time input voltage is in the safe voltage range, the conventional constant power mode is switched to; otherwise, the tolerance running mode is switched to;

[0045] S3.2: feedforward control: according to the proportional gain coefficient of the PWM controller and the voltage change trend, the duty cycle adjustment amount is set, and according to the duty cycle adjustment amount and the current controller duty cycle, the adjusted duty cycle of the controller is determined;

[0046] S3.3: feedback control: according to the instantaneous maximum allowable power and the current output voltage, the output current set value is set.

[0047] Further, the set value set in the switching process of the conventional constant power mode and the tolerance running mode is smoothed by a ramp function, including:

[0048] W1: smooth switching: according to the target current value in the conventional constant power mode, the current difference value between the output current set value and the target current value is determined, and according to the current difference value and the total adjustment step number, the single-step current adjustment amount is determined;

[0049] W2: system monitoring: according to the corresponding current actual output power in the tolerance running mode, the instantaneous maximum allowable power is adjusted to obtain the adjusted instantaneous maximum allowable power, specifically:

[0050]

[0051] Wherein: is the adjusted instantaneous maximum allowable power, is the current actual output power, is the margin intervention threshold, is the safety margin.

[0052] A charger uses the self-protection method of the lithium battery charger.

[0053] Compared with the prior art, the application has the beneficial effects that:

[0054] Firstly, the application can ensure that the key components work within the safe range by monitoring the junction temperature of the switch tube, the capacitor ripple current and the battery ripple voltage in real time through the multi-dimensional safety boundary model comprising the thermal boundary, the capacitance boundary and the battery boundary, thereby avoiding the problems of overheating, overloading or battery damage.

[0055] Secondly, the application can avoid the hysteresis problem of the traditional protection circuit and still operate stably under abnormal input conditions by adaptively adjusting the output power according to the input voltage fluctuation characteristics and real-time risk assessment, thereby reducing the risk of frequent shutdown or loss of control of the system.

[0056] Thirdly, the application can quickly respond to input changes through the cooperative control between the feedforward loop and the feedback loop, thereby reducing the stress of the power device and the capacitor, prolonging the service life of the charger, and reducing the performance degradation of the battery caused by voltage fluctuation.

[0057] Fourthly, the application can avoid the impact of current mutation on the system and the battery and ensure smooth transition of the charging process by smoothing the conventional constant power mode and the tolerance operation mode through the ramp function. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 It is a flowchart of the self-protection method in the application;

[0060] Figure 2 It is a junction temperature prediction curve of the MOSFET tube in the application;

[0061] Figure 3 It is a loss analysis diagram of the MOSFET tube in the application;

[0062] Figure 4 It is an equivalent series resistance-temperature characteristic curve of the capacitor in the application;

[0063] Figure 5 It is a capacitor ripple current life curve in the application;

[0064] Figure 6 It is a relationship diagram between temperature and compensation coefficient. DETAILED DESCRIPTION

[0066] With reference to the accompanying drawings, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments of the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work fall within the scope of the present application.

[0067] When the AC / DC adapter at the front end of the charger has poor performance or the grid voltage is unstable, the voltage input to the charger may be abnormally high or low. At this time, the traditional input overvoltage or undervoltage protection circuit will not be able to completely shut down the system due to its inherent threshold hysteresis and response characteristics when the voltage fluctuates near the critical threshold, thereby forcing the charger to work under abnormal voltage conditions for a long time. Such abnormal working conditions not only disturb the stable operation of the internal DC / DC conversion circuit and affect the service life of the charger itself, but also overwhelm the feedback control loop of the output voltage, causing its response to be delayed or even temporarily out of control, thereby causing the battery to be overvoltage or undervoltage. The technical solution of the present application obtains corresponding feature data by analyzing the input voltage and current data collected in real time in time domain and frequency domain, and constructs a multi-dimensional safety boundary model containing thermal boundary, capacitance boundary and battery boundary, determines the corresponding instantaneous maximum allowable output power, dynamically adjusts the actual output power through the cooperative control between the feedforward loop and the feedback loop, and limits the adjusted actual output power according to the instantaneous maximum allowable output power. Thus, through the three protection mechanisms of the established switching tube junction temperature threshold, the upper limit of the capacitor safety power and the upper limit of the battery safety power, the output power can be adaptively adjusted when the input voltage is abnormal, thereby not only ensuring the safe operation of the key components of the charger, but also avoiding the risk of overvoltage or undervoltage of the battery, and improving the reliability and safety of the charger under abnormal working conditions such as grid fluctuation.

[0068] Embodiment 1

[0069] Reference Figures 1-6 The present embodiment provides a self-protection method for a lithium battery charger, which comprises the following steps:

[0070] Step S1: Obtain feature data. That is, the input voltage and current data are collected in real time by an analog-to-digital converter, and the collected input voltage and current data are analyzed in time domain and frequency domain to obtain corresponding feature data. Specifically as follows:

[0071] Step S1.1: High-frequency sampling. That is, a voltage sensor (such as a resistance voltage dividing network) and a current sensor (such as a precision sampling resistor and an operational amplifier circuit) are arranged on the input path of the charger (before the DC-DC converter). Specifically, the arranged voltage sensor is electrically connected to an ADC pin of the MCU / DSP, and the arranged current sensor is electrically connected to another ADC pin of the MCU / DSP.

[0072] In the process of specific implementation, according to the fixed sampling rate, the input voltage and the input current monitored by the voltage sensor and the current sensor are synchronously sampled through the ADC pins in the MCU / DSP.

[0073] Step S1.2: Feature extraction. That is, the input voltage in the preset time period is analyzed in the time domain according to the input voltage data obtained in step S1.1, and the voltage ripple amplitude and the change trend are obtained, specifically:

[0074]

[0075] Among them: is the voltage ripple amplitude, is the maximum input voltage in the preset time period, is the minimum input voltage in the preset time period, is the change trend of the voltage, is the input voltage at the t-th moment in the preset time period, is the input voltage at the t-1-th moment in the preset time period, is the time difference.

[0076] Further, the input voltage in the preset time period is analyzed in the frequency domain by fast Fourier transform. In this embodiment, the input voltage is converted from the "time-amplitude" domain to the "frequency-energy" domain by fast Fourier transform, and the corresponding main frequency data is determined from the input voltage data converted to the "frequency-energy" domain, that is, the main harmonic frequency corresponding to the input voltage ripple is obtained.

[0077] Step S1.3: Source impedance estimation. That is, according to the obtained input voltage and input current data, a current mutation threshold is set. That is, according to the input current data in the preset time period, the current difference in different time periods in the preset time period is obtained, and the obtained current difference is compared with the current mutation threshold, and according to the comparison result, the corresponding current mutation time period is determined, specifically:

[0078] When the obtained current difference value is less than the current mutation threshold value, the time period corresponding to the current difference value is not the current mutation time period. Conversely, when the obtained current difference value is not less than the current mutation threshold value, the time period corresponding to the current difference value is the current mutation time period.

[0079] Further, according to the determined current mutation time period, the input voltage data in the current mutation time period is obtained, and according to the input voltage data in the current mutation time period, the corresponding voltage difference value is determined. In the embodiment, according to the corresponding current difference value and the voltage difference value in the current mutation time period, the corresponding source impedance size is obtained, specifically:

[0080]

[0081] Among them: is the source impedance in the current mutation time period, is the voltage difference value in the current mutation time period, is the current difference value in the current mutation time period.

[0082] Step S2: risk assessment. That is, the ripple amplitude, change trend and main harmonic frequency obtained in step S1.2 and the source impedance size obtained in step S1.3 are taken as the input of the constructed multi-dimensional safety boundary model, and the corresponding instantaneous maximum allowed output power is obtained. The output is obtained. Specifically as follows:

[0083] Step S2.1: multi-dimensional safety boundary model construction. That is, through the obtained ripple amplitude, change trend, main harmonic frequency and source impedance size, the thermal boundary, capacitance boundary and battery boundary are constructed. Specifically as follows:

[0084] Step S2.1.1: set the thermal boundary. That is, according to the transient thermal impedance size of the switch tube and the switch loss and heat energy corresponding to the main harmonic frequency, the corresponding switch tube junction temperature threshold is determined. Specifically as follows:

[0085] Step S2.1.1.1: construct a loss model. That is, according to the main harmonic frequency obtained in step S1.2 and the transient thermal impedance curve in the current device manual, the on-resistance and turn-on energy corresponding to the main harmonic frequency are determined. At the same time, according to the ripple amplitude obtained in step S1.2 and the set device rated working voltage, the ripple influence coefficient is determined, specifically:

[0086]

[0087] Among them: is the ripple influence coefficient, is the device rated working voltage, is the voltage ripple amplitude.

[0088] Further, the corresponding current effective value is determined by all the instantaneous current values obtained within the preset time window, specifically:

[0089]

[0090] Wherein: is the current effective value, is the total number of sampling points, is the instantaneous current value of the kth sampling point, is the sampling point index.

[0091] In this embodiment, the heat energy generated by the current through the MOSFET tube in the on state is determined according to the obtained on-resistance, ripple influence coefficient and current effective value, specifically:

[0092]

[0093] Wherein: is the on-state loss, is the on-resistance, is the ripple influence coefficient, is the current effective value.

[0094] In the process of specific implementation, the current effective value is 3.1A, the on-resistance is 0.045Ω, and the ripple influence coefficient is 0.18, so the corresponding on-state loss is 520mW.

[0095] Further, the change of drain-source voltage is monitored by the high-voltage differential probe, and the change of drain current is monitored by the current Rogowski coil. At the same time, the high-voltage differential probe and the current Rogowski coil are connected with the oscilloscope to obtain the corresponding drain-source voltage and drain current through the oscilloscope. That is, by controlling the on and off of the MOSFET tube, the off transient waveform of the MOSFET tube is captured, and the corresponding off energy is obtained.

[0096] In this embodiment, the energy loss of the corresponding MOSFET tube in the switching transition process is determined according to the obtained main harmonic frequency, turn-on energy and turn-off energy, specifically:

[0097]

[0098] Wherein: is the switching loss, is the turn-on energy, is the turn-off energy, is the dominant harmonic frequency.

[0099] In the process of specific implementation, the turn-on energy is 2.5 μJ, the turn-off energy is 2.8 μJ, and the dominant harmonic frequency is 125 kHz, so the corresponding switching loss is 662 mW.

[0100] Step S2.1.1.2: thermal impedance network modeling. That is, the DS18B20 digital temperature sensor is arranged in the center of the equipment air inlet, and is arranged at a position 5 cm away from the shell. The corresponding external environment temperature data is obtained at a sampling rate of 1 Hz. At the same time, according to the junction-to-ambient thermal resistance data in the current device manual, the corresponding junction-to-ambient thermal resistance data and the shell-to-environment thermal resistance data are determined.

[0101] In this embodiment, according to the obtained external environment temperature data and the junction-to-ambient thermal resistance data, the turn-on loss and the switching loss obtained in step S2.1.1.1, the actual working temperature of the semiconductor chip is determined, specifically:

[0102]

[0103] Wherein: is the junction temperature prediction value, is the environment temperature, is the turn-on loss, is the switching loss, is the junction-to-ambient thermal resistance, is the shell-to-environment thermal resistance.

[0104] In the process of specific implementation, the turn-on loss is 520 mW, the switching loss is 662 mW, the total loss is 1182 mW, the junction-to-ambient thermal resistance is 1.5 ℃ / W, the shell-to-environment thermal resistance is 15 ℃ / W, and the environment temperature is 65 ℃, so the corresponding junction temperature prediction value is 84.5 ℃.

[0105] Further, according to the obtained junction temperature prediction value and the maximum allowed junction temperature set in the current device manual, the safety margin is determined, specifically:

[0106]

[0107] Wherein: is the safety margin, is the maximum allowed junction temperature, is the junction temperature prediction value.

[0108] In the process of specific implementation, the maximum allowed junction temperature set in the current device manual is 125 ℃, and the junction temperature prediction value is 84.5 ℃, so the corresponding safety margin is 32.4%.

[0109] Step S2.1.1.3: determining the thermal boundary limit. That is, according to the voltage ripple amplitude obtained in step S1.2 and the set device rated operating voltage, the corresponding dynamic correction coefficient is determined, specifically:

[0110]

[0111] Wherein: is the dynamic correction coefficient, is the voltage ripple amplitude, is the device rated operating voltage.

[0112] In this embodiment, according to the obtained ambient temperature, the maximum allowed junction temperature, the junction-to-case thermal resistance, the case-to-ambient thermal resistance and the dynamic correction coefficient, the corresponding power upper limit that the junction temperature does not exceed the safety limit is determined, specifically:

[0113]

[0114] Wherein: is the maximum allowed thermal boundary power, is the ambient temperature, is the junction-to-case thermal resistance, is the case-to-ambient thermal resistance, is the safety factor, is the dynamic correction coefficient.

[0115] In the process of specific implementation, 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 allowed junction temperature is 125℃, the safety factor is 0.75, and the dynamic correction coefficient is 0.8. The corresponding maximum allowed thermal boundary power is 2.18W.

[0116] Step S2.1.1.4: dynamic power limit. That is, the safety margin obtained in step S2.1.1.2 is compared with the set margin intervention threshold (according to the actual data, the specific setting is not described in this embodiment, for example, 20%), and the corresponding power adjustment strategy is determined according to the comparison result. Specifically:

[0117] When the obtained safety margin is less than the margin intervention threshold, the corresponding power is reduced to make the adjusted power not exceed the set maximum allowed thermal boundary power. Otherwise, the power is not adjusted and the current power continues to run.

[0118] In this embodiment, the margin difference between the margin intervention threshold and the safety margin is combined with the maximum allowed thermal boundary power obtained in step S2.1.1.3 to determine the corresponding safety working power upper limit, specifically:

[0119]

[0120] wherein: is the adjusted allowed power, is the margin intervention threshold, is the maximum allowed thermal boundary power, is the safety margin.

[0121] Referring to Figure 2 and Figure 3 It can be seen that the junction temperature prediction value is always stable between the 84.5℃ load reduction threshold and the 125℃ maximum allowed junction temperature, and the periodic fluctuation of the switching loss causes the junction temperature to present a regular change of ±3℃.

[0122] Step S2.1.2: Set the capacitor boundary. That is, according to the rated ripple current life curve of the filter capacitor, combine it with the voltage ripple amplitude and the equivalent series resistance of the capacitor obtained in step S1.2 to determine the corresponding upper limit of the capacitor safety power. The specific process is as follows:

[0123] Step S2.1.2.1: Determine the actual ripple current. That is, according to the reference parameters provided in the equipment manufacturer's specification, determine the size of the equivalent series resistance under the temperature nominal condition of 25℃. At the same time, measure and obtain the size of the equivalent series resistance under the temperature of 25℃, 50℃ and 85℃ in the temperature control box, and through the least square method, fit to obtain the corresponding temperature-equivalent series resistance curve, and set the corresponding temperature coefficient according to the slope size in the temperature-equivalent series resistance curve, which is:

[0124]

[0125] wherein: is the temperature coefficient, is the equivalent series resistance at the reference temperature of 25℃, is the measured value of the equivalent series resistance at the ambient temperature, is the ambient temperature.

[0126] In the process of specific implementation, the equivalent series resistance at the reference temperature of 25℃ is 0.085Ω, and the equivalent series resistance at the temperatures of 50℃, 85℃ and 105℃ is 0.078Ω, 0.077Ω and 0.035Ω respectively, so the corresponding temperature coefficients are: 0.00165 / ℃, 0.00157 / ℃ and 0.00196 / ℃. That is, the finally obtained temperature coefficient is 0.00713 / ℃.

[0127] Further, by attaching NTC thermistor or infrared temperature measurement, the corresponding capacitor surface measured temperature is obtained, and according to the determined temperature coefficient and the corresponding equivalent series resistance size at 25℃ temperature nominal condition, the real impedance characteristics of the capacitor under the current working condition are determined, specifically:

[0128]

[0129] Wherein: is the equivalent series resistance at the actual working temperature, is the capacitor surface measured temperature, is the temperature coefficient, is the equivalent series resistance at 25℃ reference temperature.

[0130] Further, according to the equivalent series resistance at the actual working temperature obtained and the voltage ripple amplitude obtained in step S1.2, the corresponding actual ripple current is determined, specifically:

[0131]

[0132] Wherein: is the actual ripple current, is the voltage ripple amplitude, is the equivalent series resistance at the actual working temperature.

[0133] Step S2.1.2.2: Determine the safety boundary. That is, according to the main harmonic frequency determined in step S1.2, the corresponding rated ripple current is determined from the equipment manufacturer's specification book. In this embodiment, according to the determination of the rated ripple current, the corresponding safety threshold is set, that is, 0.8 times of the rated ripple current is set as the safety threshold.

[0134] Further, the obtained actual ripple current is compared with the set safety threshold, and according to the comparison result, the corresponding capacitor safety state is determined, specifically:

[0135] When the obtained actual ripple current is greater than the safety threshold, the corresponding capacitor safety state is over-limit, and at this time, the corresponding capacitor safety power upper limit is determined through the next step S2.1.2.3 power limitation. Conversely, when the obtained actual ripple current is not greater than the safety threshold, the corresponding capacitor safety state is safe.

[0136] Step S2.1.2.3: power limitation. That is, according to the rated ripple current obtained from the manufacturer's specification, 0.8 times the rated ripple current is set as the corresponding allowed maximum ripple current, and the allowed maximum ripple current is combined with the output power of the current system and the actual ripple current obtained in step S2.1.2.1 to determine the corresponding capacitor safe power upper limit, which is:

[0137]

[0138] Wherein: is the capacitor safe power upper limit, is the current system output power, is the actual ripple current, is the allowed maximum ripple current.

[0139] In the process of specific implementation, the current system output power is 60W, the actual ripple current is 12.99A, and the allowed maximum ripple current is 2.56A, so the corresponding capacitor safe power upper limit is 2.33W.

[0140] Referring 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 it sharply decreases to 0.035Ω at 105℃. At the same time, the actual ripple current reaches 14.12A at 25℃, which is 452% higher than the allowed value of 2.56A. Although the decrease of the equivalent series resistance of the capacitor at high temperature will lead to further increase of the ripple current, the difference between the allowed maximum ripple current values is actually reduced.

[0141] Step S2.1.3: set the battery boundary. That is, the battery surface temperature and the voltage ripple amplitude obtained in step S1.2 are combined to determine the corresponding ripple prediction value, and the corresponding battery safe power upper limit is determined according to the obtained ripple prediction value. The specific is as follows:

[0142] Step S2.1.3.1: obtain ripple estimation. That is, the battery surface temperature is obtained in real time by NTC thermistor or infrared temperature measurement, and the battery surface temperature is compared with the reference temperature of 25℃. According to the comparison result, the corresponding temperature compensation coefficient is set, which is:

[0143]

[0144] Wherein: is the temperature compensation coefficient, is the battery surface temperature.

[0145] In the process of specific implementation, the battery surface temperature is 40℃, and the corresponding temperature compensation coefficient is 1.075.

[0146] Further, the obtained voltage ripple amplitude is combined with the set temperature compensation coefficient to determine the corresponding ripple prediction value, specifically:

[0147]

[0148] Among them: is the ripple prediction value, is the voltage fluctuation peak-to-peak value of the power module input side, is the temperature compensation coefficient.

[0149] In the process of specific implementation, the voltage fluctuation peak-to-peak value of the power module input side is 1.2V, and the corresponding ripple prediction value is 258mV.

[0150] Step S2.1.3.2: Boundary determination. That is, according to the battery type recorded in the battery specification book and the corresponding battery ripple limit value, the corresponding ripple safety margin is set, specifically, the ripple safety margin is 0.8 times the battery ripple limit value.

[0151] Further, the obtained ripple prediction value is compared with the set ripple safety margin, and the corresponding battery safety state is determined according to the comparison result, specifically:

[0152] When the obtained ripple prediction value is greater than the ripple safety margin, the corresponding battery safety state is over-limit, and at this time 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 battery safety power upper limit. On the contrary, when the obtained ripple prediction value is not greater than the ripple safety margin, the corresponding battery safety state is safe.

[0153] In this embodiment, the battery safety power upper limit is obtained by the ripple prediction value, the ripple safety margin and the current system output power, specifically:

[0154]

[0155] Among them: is the battery safety power upper limit, is the current system output power, is the ripple safety margin, is the ripple prediction value.

[0156] In the process of specific implementation, the current system output power is 40W, the ripple safety margin is 50mV, and the ripple prediction value is 258mV, so the corresponding battery safe power upper limit is about 7.75W.

[0157] Reference Figure 6 It can be seen that the temperature compensation coefficient increases from 1 at 25℃ to 1.175 at 60℃, and the compensation coefficient increases by 5% per 10℃ increase, which can accurately track temperature changes.

[0158] Step S2.2: Determine the instantaneous maximum allowable power. That is, the maximum allowable thermal boundary power obtained in step S2.1.1.3, the capacitor safe power upper limit obtained in step S2.1.2.3 and the battery safe power upper limit obtained in step S2.1.3.2 are combined to determine the corresponding instantaneous maximum allowable power, which is:

[0159]

[0160] Wherein: is the instantaneous maximum allowable power, is the maximum allowable thermal boundary power, is the battery safe power upper limit, is the capacitor safe power upper limit.

[0161] In the process of specific implementation, the maximum allowable thermal boundary power is 2.18W, the capacitor safe power upper limit is 2.33W, and the battery safe power upper limit is 7.75W, so the corresponding instantaneous maximum allowable power is 2.18W.

[0162] Step S3: Tolerance power control. That is, according to the instantaneous maximum allowable power obtained in step S2.2, the actual output power is adjusted in real time through the cooperative control of the feedforward loop and the feedback loop. The specific is as follows:

[0163] Step S3.1: Determine the running mode. That is, according to the instantaneous maximum allowable power obtained in step S2.2, the output current corresponding thereto is determined, and according to the output current corresponding to the instantaneous maximum allowable power, the output voltage, the on-resistance of the MOSFET tube and the duty cycle limit, the corresponding safe voltage range is determined, which is:

[0164]

[0165] Wherein: is the minimum input voltage, is the output voltage of the power supply system, is the output current corresponding to the instantaneous maximum allowable power, is the on-resistance of the MOSFET tube, an upper limit of the duty cycle allowed by the controller, a maximum input voltage, a lower limit of the duty cycle allowed by the controller.

[0166] Further, through the power input terminal, the corresponding real-time input voltage is obtained, and the obtained real-time input voltage is compared with the determined safe voltage range, and the corresponding operation mode is determined according to the comparison result, specifically:

[0167] When the real-time input voltage is in the safe voltage range, the normal constant power mode is switched to. Conversely, when the real-time input voltage is not in the safe voltage range, the tolerance operation mode is switched to.

[0168] Step S3.2: feedforward control. That is, the voltage change trend obtained in step S1.2 is compared with the set change threshold (which is set according to actual data, so it is not specifically described in this embodiment, for example, 20V / ms), and the duty cycle of the PWM is adjusted according to the comparison result, specifically:

[0169] When the obtained voltage change trend is greater than the change threshold, the duty cycle of the PWM is adjusted by the controller. Conversely, when the obtained voltage change trend is not greater than the change threshold, the duty cycle of the PWM is not adjusted.

[0170] In this embodiment, according to the proportional gain coefficient of the PWM controller, the voltage change trend obtained in step S1.2 is combined to obtain the corresponding duty cycle adjustment amount, specifically:

[0171]

[0172] Wherein: is the duty cycle adjustment amount, is the proportional gain coefficient, is the voltage change trend.

[0173] Further, according to the current duty cycle of the controller and the duty cycle adjustment amount, the adjusted duty cycle of the controller is determined, specifically:

[0174]

[0175] Wherein: is the adjusted duty cycle, is the current duty cycle, is the duty cycle adjustment amount.

[0176] Step S3.3: feedback control. That is, the instantaneous maximum allowable power obtained in step S2.2 and the current output voltage are combined to obtain the corresponding output current set value, which is specifically:

[0177]

[0178] wherein: is the output current set value, is the output voltage of the power supply system, is the instantaneous maximum allowable power.

[0179] Further, according to the obtained output current set value, the current value obtained at present is decreased until the current is decreased to the output current set value.

[0180] The embodiment also provides a charger using the self-protection method of the lithium battery charger.

[0181] Embodiment 2

[0182] The embodiment provides a self-protection method of a lithium battery charger, and the specific implementation method is the same as that of embodiment 1, and the difference is that when the normal constant power mode and the tolerance operation mode are switched or the current value is adjusted according to the output current set value in the tolerance operation mode, the set value is processed by a ramp function to be smoothed to restore to the normal charging mode. The application is illustrated by combining the specific implementation of the embodiment.

[0183] In the embodiment, the set value is processed by a ramp function and restored to the normal charging mode, which is specifically as follows:

[0184] Step W1: smooth switching. That is, the output current set value obtained in step S3.3 is combined with the output voltage and output power of the power supply system to determine the corresponding operation mode, which is the tolerance operation mode. At the same time, according to the corresponding target current value in the normal constant power mode, the current difference value between the output current set value and the target current value is determined.

[0185] Further, the current difference value between the output current set value and the target current value is combined with the total adjustment step number set to determine the size of the single-step current adjustment amount, which is specifically:

[0186]

[0187] wherein: is the single-step current adjustment amount, is the current difference value between the output current set value and the target current value, is the total adjustment step number.

[0188] In the embodiment, the system thermal time constant is set as the ramp time constant, and the ramp time constant is combined with the control period. That is, according to the size of the ratio between the ramp time constant and the control period, the corresponding total adjustment steps are set.

[0189] That is, the current size is adjusted according to the determined single-step current adjustment amount.

[0190] Step W2: System monitoring. That is, through the high-voltage differential probe, the spectrum analysis module and the K-type thermocouple, the corresponding voltage ripple amplitude, the main harmonic frequency and the actual working temperature of the internal chip of the semiconductor device are collected to determine the corresponding running power. At the same time, the determined running power is compared with the instantaneous maximum allowable power obtained in step S2.2, and the instantaneous maximum allowable power is adjusted according to the comparison result, specifically:

[0191] When the actual running power is greater than the instantaneous maximum allowable power, the running power is adjusted through the step S3 tolerance power control until the actual running power is not greater than the instantaneous maximum allowable power. Conversely, when the actual running power is not greater than the instantaneous maximum allowable power, the running power is not adjusted.

[0192] Further, when switching from the tolerance running mode to the conventional constant power mode, the instantaneous maximum allowable power is adjusted according to the current actual output power corresponding to the current tolerance running mode, and the adjusted instantaneous maximum allowable power is obtained, specifically:

[0193]

[0194] Wherein: is the adjusted instantaneous maximum allowable power, is the current actual output power, is the margin intervention threshold, is the safety margin.

[0195] Although the embodiments of the present application have been shown and described, it can be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended embodiments and their equivalents.

Claims

1. A self-protection method of a lithium battery charger, characterized in that, Comprise: S1: obtain characteristic data: time domain and frequency domain analysis of the collected input voltage and current data, obtain characteristic data; S2: risk assessment: the characteristic data as the input of the multi-dimensional safety boundary model, output the corresponding instantaneous maximum allowable output power, comprising: S2.1: multi-dimensional safety boundary model construction: according to the characteristic data, construct thermal boundary, capacitance boundary and battery boundary, comprising: S2.1.1: set the thermal boundary: according to the transient thermal impedance of the switch tube, the switch loss and the heat energy corresponding to the main harmonic frequency, determine the switch tube junction temperature threshold; S2.1.2: set the capacitance boundary: according to the rated ripple current life curve of the filter capacitor, the voltage ripple amplitude and the capacitance equivalent series resistance, determine the upper limit of the capacitor safety power; S2.1.3: set the battery boundary: combine the battery surface temperature and the voltage ripple amplitude, set the ripple prediction value, and determine the upper limit of the battery safety power according to the ripple prediction value; S2.2: determine the instantaneous maximum allowable power: according to the switch tube junction temperature threshold, the capacitor safety power upper limit and the battery safety power upper limit, determine the instantaneous maximum allowable power; S3: band power control: according to the instantaneous maximum allowable power, through the cooperative control of feedforward loop and feedback loop, real-time adjust the actual output power.

2. The self-protection method of a lithium battery charger according to claim 1, wherein, Obtain characteristic data, comprising: S1.1: high frequency sampling: through the voltage sensor and current sensor set on the charger input channel, collect input voltage and input current; S1.2: feature extraction: time domain and frequency domain analysis of the input voltage, obtain the voltage ripple amplitude, trend and main harmonic frequency; S1.3: source impedance estimation: according to the comparison between the input current and the current mutation threshold, determine the current mutation time period, and according to the current difference and voltage difference in the current mutation time period, determine the source impedance in the current mutation time period.

3. The self-protection method of a lithium battery charger according to claim 1, wherein, Determine the switch tube junction temperature threshold, comprising: S2.1.1.1: build loss model: according to the set ripple influence coefficient, on-resistance and current effective value, determine the on-resistance loss of MOSFET tube, and according to the set main harmonic frequency, turn-on energy and turn-off energy, determine the switch loss of MOSFET tube; S2.1.1.2: thermal impedance network modeling: combine the on-resistance loss and switch loss of the MOSFET tube with the set junction to shell thermal resistance data and shell to environment thermal resistance data, determine the junction temperature prediction value of the semiconductor chip, and according to the junction temperature prediction value and the maximum allowable junction temperature, determine the safety margin; S2.1.1.3: determine the thermal boundary limit: according to the voltage ripple amplitude and the rated working voltage of the device, set the dynamic correction coefficient, and through the environmental temperature, the maximum allowable junction temperature, the junction to shell thermal resistance, the shell to environment thermal resistance and the dynamic correction coefficient, determine the power upper limit that the junction temperature does not exceed the safety limit, specifically: ： wherein: Pmax is the maximum allowed thermal boundary power, Tambient is the ambient temperature, Rj-c is the junction to case thermal resistance, Rcase-ambient is the case to ambient thermal resistance, Fsafety is the safety factor, Fdyn is the dynamic correction factor; S2.1.1.4: Dynamic power limit: comparing the safety margin with the margin intervention threshold, and determining a power adjustment strategy according to the comparison result, specifically: When the safety margin is less than the margin intervention threshold, the corresponding power is reduced according to the maximum allowed thermal boundary power; otherwise, the power is not adjusted.

4. The self-protection method of a lithium battery charger according to claim 3, wherein, According to the conduction resistance and turn-on energy corresponding to the main harmonic frequency, a ripple influence coefficient is set, and according to the instantaneous current in the preset time window, the current effective value is determined, and the conduction loss of the MOSFET tube is determined by combining the ripple influence coefficient, current effective value and conduction resistance. The turn-on energy and turn-off energy of the MOSFET tube are obtained through the turn-on and turn-off of the MOSFET tube, and the switching loss of the MOSFET tube is determined according to the turn-on energy and turn-off energy.

5. The self-protection method of a lithium battery charger according to claim 3, wherein, According to the safety margin and the margin intervention threshold, a margin difference value is obtained, and a safety working power upper limit is determined by the margin difference value and the maximum allowed thermal boundary power, specifically: ： wherein: Pallow is the adjusted allowed power, Pmargin is the margin intervention threshold, Pmax is the maximum allowed thermal boundary power, Psafe is the safety margin.

6. The self-protection method of a lithium battery charger according to claim 1, wherein, The capacitor safety power upper limit is determined, including: S2.1.2.1: Determine the actual ripple current: set the temperature coefficient according to the equivalent series resistance at different temperatures, and determine the equivalent series resistance at the actual working temperature according to the temperature coefficient, the actual capacitor surface temperature and the equivalent series resistance at 25°C temperature nominal condition, and obtain the actual ripple current according to the equivalent series resistance and voltage ripple amplitude; S2.1.2.2: Determine the safety boundary: set the safety threshold according to the rated ripple current corresponding to the main harmonic frequency, and compare the actual ripple current with the safety threshold, and determine the capacitor safety state according to the comparison result, specifically: When the actual ripple current is greater than the safety threshold, the corresponding capacitor safety state is over limit, and the capacitor safety power upper limit is determined; otherwise, the corresponding capacitor safety state is safe; S2.1.2.3: Power limit: set the maximum allowed ripple current according to the rated ripple current, and determine the capacitor safety power upper limit according to the maximum allowed ripple current and the actual ripple current.

7. The self-protection method of a lithium battery charger according to claim 1, wherein, The battery safety power upper limit is determined, including: S2.1.3.1: Obtain the ripple estimation: set the temperature compensation coefficient according to the comparison between the battery surface temperature and the reference temperature, and determine the ripple prediction value according to the temperature compensation coefficient and the voltage ripple amplitude; S2.1.3.2: Boundary determination: set the ripple safety margin according to the battery ripple limit value corresponding to the battery type, and compare the ripple safety margin with the ripple prediction value, and determine the battery safety state according to the comparison result, specifically: When the ripple prediction value is greater than the ripple safety margin, the corresponding battery safety state is over limit, and the battery safety power upper limit is determined according to the ripple prediction value, the ripple safety margin and the current system output power; Otherwise, the corresponding battery safety state is safe.

8. The self-protection method of a lithium battery charger according to claim 1, wherein, The actual output power is adjusted in real time, including: S3.1: determining the running mode: according to the output current and output voltage corresponding to the instantaneous maximum allowable power, the on-resistance of the MOSFET tube and the duty cycle limit, the safe voltage range is determined, and the real-time input voltage is compared with the safe voltage range, and the corresponding running mode is determined according to the comparison result, specifically: When the real-time input voltage is in the safe voltage range, it is switched to the conventional constant power mode; otherwise, it is switched to the tolerance running mode; S3.2: feedforward control: according to the proportional gain coefficient of the PWM controller and the voltage change trend, the duty cycle adjustment amount is set, and the adjusted duty cycle of the controller is determined according to the duty cycle adjustment amount and the current controller duty cycle; S3.3: feedback control: according to the instantaneous maximum allowable power and the current output voltage, the output current set value is set.

9. The self-protection method of a lithium battery charger according to claim 8, wherein, Through the ramp function, the set value set in the switching process of the conventional constant power mode and the tolerance running mode is smoothed, including: W1: smooth switching: according to the target current value in the conventional constant power mode, the current difference value between the output current set value and the target current value is determined, and the single-step current adjustment amount is determined according to the current difference value and the total adjustment step number; W2: system monitoring: according to the corresponding current actual output power in the tolerance running mode, the instantaneous maximum allowable power is adjusted to obtain the adjusted instantaneous maximum allowable power, specifically: ； wherein: Pmax, adj is the adjusted instantaneous maximum allowed power, Pact is the current actual output power, Pmargin, int is the margin intervention threshold, Pmargin, safe is the safety margin.

10. A charger characterized by comprising: A self-protection method for a lithium battery charger according to any one of claims 1-9 is used.

Images