A method for multi-section power distribution of a direct-current charging pile of an electric vehicle

Abstract

This invention discloses a method for multi-segment power allocation in DC charging piles for electric vehicles, belonging to the field of electric vehicle charging technology. The method includes: after the DC charging pile communicates with the electric vehicle battery management system, acquiring the initial state of charge, terminal voltage, and temperature of the power battery; dividing the charging process into sequentially connected first, second, and third charging stages based on the initial state of charge and configuring corresponding power allocation strategies; in the first charging stage, calculating the maximum acceptable charging current based on the initial internal resistance and polarization voltage and setting an upper limit for the output current; in the second charging stage, monitoring the rate of change of terminal voltage and the rate of change of temperature in real time, and dynamically adjusting the step size of the output voltage increment; in the third charging stage, gradually reducing the output power until charging terminates based on the rate of voltage drop when the state of charge reaches the saturation threshold. This invention achieves close tracking of charging parameters and the real-time state of the battery, improving charging safety and efficiency.

Description

Technical Field

[0001] This invention relates to the field of electric vehicle charging technology, specifically to a method for multi-segment power allocation in a DC charging pile for electric vehicles. Background Technology

[0002] When DC charging stations for electric vehicles rapidly charge power batteries, the power distribution method directly affects battery life and charging safety. To balance charging speed and battery protection, segmented charging is widely adopted, typically dividing the process into fixed stages such as constant current and constant voltage based on the state of charge. In the constant current stage, charging is often based on a preset maximum current rate, failing to fully consider the battery's initial polarization state and internal resistance differences. This can easily lead to excessive polarization voltage in the early stages of charging, limiting the acceptable current margin. After entering the constant voltage or similar variable voltage stage, the output voltage adjustment is mostly based on a preset fixed step size, failing to detect the rate of change of battery terminal voltage and temperature in real time. When the terminal voltage rises rapidly or the temperature rises abnormally, the fixed step voltage increment may lead to voltage overshoot or increased heat accumulation, accelerating battery aging. In the power reduction stage at the end of charging, constant voltage reduction or direct step-wise power reduction methods are commonly used, with the determination based mostly on the state of charge threshold, without considering the actual drop characteristics of the battery terminal voltage. The rate of voltage drop at the battery terminal reflects the degree of polarization relaxation and lithium-ion diffusion equilibrium within the battery. Ignoring this dynamic information may lead to a mismatch between the power reduction process and the battery's actual accepting capacity, resulting in prolonged charging time or the risk of localized lithium plating. Therefore, it is necessary to address how to dynamically adjust the voltage adjustment step size based on the real-time trends of battery terminal voltage and temperature during charging, and how to adaptively determine the power reduction magnitude using the voltage drop rate information. Summary of the Invention

[0003] The purpose of this invention is to provide a multi-segment power allocation method that can dynamically adjust the voltage increment according to the real-time voltage and temperature change rate of the battery, and adaptively reduce power based on the terminal voltage drop rate, so as to improve the safety and charging efficiency of the charging process.

[0004] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a method for multi-segment power allocation in a DC charging pile for electric vehicles. After establishing a communication connection between the DC charging pile and the electric vehicle battery management system, the initial state of charge (SOC), initial terminal voltage, and initial temperature of the power battery are collected. Based on the numerical range of the SOC, the entire charging process is divided into a first charging stage, a second charging stage, and a third charging stage, which are sequentially connected, and a first power allocation strategy, a second power allocation strategy, and a third power allocation strategy are configured respectively. By dividing the stages based on the initial SOC, the charging start stage is matched with the actual state of the battery, avoiding the application of excessive initial current to batteries with high SOC, and fully utilizing the battery's acceptable capacity when the SOC is low, thereby improving overall charging efficiency.

[0005] In the first charging stage, the maximum acceptable charging current of the power battery at the current moment is calculated based on the initial internal resistance and initial polarization voltage of the power battery, and the upper limit of the output current of the DC charging pile is set according to the maximum acceptable charging current. Preferably, the initial internal resistance value is obtained by querying a pre-stored internal resistance mapping table based on the initial state of charge value, and the initial polarization voltage value is obtained by querying a pre-stored polarization voltage mapping table based on the initial temperature value. Based on the difference between the initial terminal voltage value and the preset safe terminal voltage upper limit, combined with the sum of the initial internal resistance value and the initial polarization voltage value, the maximum acceptable charging current value is determined. The safe terminal voltage upper limit is dynamically corrected by the current temperature value of the power battery. For every preset temperature gradient increase in the current temperature value, the safe terminal voltage upper limit is correspondingly reduced by a preset voltage correction amount. In this stage, the current is constrained by the battery's own acceptable capacity. Under the premise of ensuring the safe terminal voltage boundary, the charging current is made close to the battery's actual tolerance limit, thereby accelerating the initial charging speed and suppressing the risk of overheating.

[0006] During the second charging phase, the rate of change of the terminal voltage and the rate of change of the temperature of the power battery are monitored in real time. Based on the real-time comparison of the rates of change of the terminal voltage and the rate of change of the temperature, the output voltage increment step size of the DC charging pile is dynamically adjusted. As a technical solution of this invention, the current terminal voltage value and the current temperature value are continuously collected at a preset sampling period, and the rates of change of the terminal voltage and the rate of change of the temperature are calculated respectively. The output voltage increment at the current sampling moment is obtained by multiplying the ratio of the rate of change of the terminal voltage to the rate of change of the temperature by a preset voltage increment reference value. When both the rate of change of the terminal voltage and the rate of change of the temperature are positive, the output voltage increment is set to a positive value, and the output voltage of the DC charging pile is increased by this increment based on the current output voltage value. When either the rate of change of the terminal voltage or the rate of change of the temperature is negative, the output voltage increment is set to a negative value, and the increment is decreased based on the current output voltage value. The voltage increment reference value is dynamically determined by the ratio of the terminal voltage value at the start of the second charging phase to the rated voltage value of the power battery; the larger this ratio, the smaller the voltage increment reference value. By adjusting the voltage step size through a closed-loop control of the coordinated change rate of terminal voltage and temperature, the growth rate of polarization voltage and the rate of temperature rise can be effectively balanced, avoiding lithium plating or a sudden temperature rise due to excessively rapid voltage rise, thus making the charging process smooth and stable.

[0007] Preferably, during the second charging phase, the internal temperature field of the power battery is also estimated: the current Joule heat power value is calculated based on the surface temperature of the power battery and the output current value of the DC charging pile. Combined with the heat dissipation power value calculated using the temperature difference between the surface and ambient temperatures and the heat dissipation coefficient, the internal accumulated heat value is obtained. Then, the internal temperature rise value is calculated based on the heat capacity value. The surface temperature value and the internal temperature rise value are added to generate an estimated internal temperature value. When the estimated internal temperature value exceeds a preset safe temperature threshold, the output current value of the DC charging pile is reduced until the estimated internal temperature value falls below the safe temperature threshold. The heat dissipation coefficient increases with the increase of the power battery surface temperature. By estimating and limiting the internal temperature in real time, localized overheating inside the battery can be prevented, improving the thermal safety margin during high-power charging.

[0008] In the third charging stage, the output power of the DC charging pile is gradually reduced based on the voltage drop rate at which the battery's state of charge reaches a preset saturation threshold, until the battery's state of charge reaches the charging termination threshold. Specifically, when the current state of charge reaches the preset saturation threshold, the saturation terminal voltage value is recorded. The terminal voltage value is continuously collected at subsequent times, and the drop rate relative to the saturation terminal voltage value is calculated. The step reduction range of the DC charging pile's output power value is determined based on the magnitude of the drop rate. The step reduction range is positively correlated with the drop rate, and the output power value is gradually reduced at fixed time intervals according to this step reduction range until the state of charge reaches the charging termination threshold. This stage utilizes the terminal voltage drop characteristics to dynamically match the power reduction rhythm, avoiding overcharging at the end and reducing energy loss and gas evolution side reactions when the battery approaches saturation, thus extending cycle life.

[0009] As a further improvement of the present invention, the charging stages are divided as follows: the initial state of charge (SOC) value is compared with preset low-level and high-level boundary values; when the initial SOC value is less than or equal to the low-level boundary value, the entire charging process is divided into a first charging stage, a second charging stage, and a third charging stage connected sequentially; when the initial SOC value is greater than the low-level boundary value and less than the high-level boundary value, the entire charging process is divided into a second charging stage and a third charging stage connected sequentially, with the second charging stage as the initial stage; when the initial SOC value is greater than or equal to the high-level boundary value, the entire charging process is directly set to the third charging stage, with the third charging stage as the initial stage. This allows unnecessary stages to be skipped based on the battery's initial state, reducing conversion losses and optimizing the total charging time.

[0010] Preferably, the configured power allocation strategies are as follows: a constant current charging strategy is configured for the first charging stage, and the constant current value of the constant current charging strategy is set to a preset percentage of the maximum acceptable charging current value; a variable voltage incremental charging strategy is configured for the second charging stage, and the output voltage increment is determined in real time by the weighted ratio of the terminal voltage change rate and the temperature change rate; a constant voltage drop power strategy is configured for the third charging stage, and the output power value gradually decreases at fixed time intervals until the output power value drops to a preset termination power value. The three strategies work together to form an adaptive power allocation covering the entire charging range, from constant current rapid energy replenishment to variable voltage fine adjustment, and then to constant voltage drop power termination, achieving a balance between charging efficiency and battery protection.

[0011] Preferably, before the start of the first charging stage, a step of preprocessing the polarization voltage of the power battery is included: after establishing a communication connection between the DC charging pile and the electric vehicle battery management system, the resting time value of the power battery is collected; based on the resting time value, the pre-stored polarization voltage decay curve is queried to obtain the current residual polarization voltage value; a pre-charge elimination current value is calculated based on the current residual polarization voltage value, the direction of which is opposite to the current polarization voltage direction of the power battery; the DC charging pile is controlled to output a pre-charge current with the pre-charge elimination current value, and after a predetermined duration, the terminal voltage value is collected again as the preprocessed initial terminal voltage value. By actively eliminating the residual polarization voltage, the interference of polarization voltage on the initial internal resistance estimation and the maximum acceptable current calculation can be reduced, improving the accuracy of the current setting in the first charging stage.

[0012] Furthermore, the first charging stage also includes a step for real-time monitoring of the lithium plating risk of the power battery: The current negative electrode potential value of the power battery is collected in real time and compared with a preset lithium plating critical potential value; when the current negative electrode potential value is lower than the lithium plating critical potential value, the potential difference is calculated and an output current derating coefficient is generated accordingly, with the output current derating coefficient being positively correlated with the potential difference value; the current output current value of the DC charging pile is multiplied by the output current derating coefficient to obtain the drated output current value for continued charging; when the current negative electrode potential value rises back above the lithium plating critical potential value, the output current value of the DC charging pile is gradually restored to the upper limit of the output current value. Based on direct monitoring and dynamic derating of the negative electrode potential, lithium plating can be fundamentally prevented, ensuring fast charging safety.

[0013] Furthermore, the third charging stage also includes a step of correcting the estimated state of charge (SOC) value of the power battery: at the start of the third charging stage, the open-circuit voltage value of the power battery is collected, and a corrected initial SOC value is obtained based on the SOC-open-circuit voltage mapping curve; using this corrected initial SOC value as a reference, the output current value of the DC charging pile is calculated by ampere-hour integration to generate an ampere-hour integrated SOC increment value; simultaneously, the terminal voltage value and temperature value are collected in real time, and the SOC-open-circuit voltage mapping curve is queried to obtain the SOC estimate value corresponding to the current open-circuit voltage estimate value; the SOC deviation value between the ampere-hour integrated SOC increment value and the SOC estimate value is calculated; when the absolute value of the SOC deviation value is greater than a preset deviation correction threshold, the current SOC estimate value is replaced with the weighted average of the ampere-hour integrated SOC increment value and the SOC estimate value, and this weighted average value is used as the corrected current SOC value to participate in the output power reduction control of the third charging stage. This correction mechanism integrates ampere-hour integral and open-circuit voltage mapping to eliminate accumulated errors, making the end-charge cutoff control more precise and preventing overcharging or undercharging.

[0014] The technical effects and advantages provided by the present invention in the above technical solution are as follows: In the second charging phase, the current terminal voltage and temperature values ​​of the power battery are collected in real time. The rate of change of terminal voltage and the rate of change of temperature are calculated, and the output voltage increment at the current moment is determined by multiplying the weighted ratio of the two by the voltage increment reference value. When both the rate of change of terminal voltage and the rate of change of temperature are positive, the output voltage increment is set to a positive value, and the DC charging pile increases the current output voltage by this increment. When either rate of change is negative, the output voltage increment is set to a negative value, and the current output voltage is decreased by this increment. The voltage increment reference value is dynamically determined by the ratio of the initial terminal voltage of the second phase to the rated voltage; the larger the ratio, the smaller the reference value. Thus, the step adjustment of the output voltage is directly related to the battery's voltage rise rate and temperature rise rate. When the voltage rises rapidly or the temperature rises too quickly, the voltage increase is automatically reduced or even the voltage is reversed, suppressing over-polarization and thermal runaway tendencies. This ensures that the charging voltage is always close to the battery's real-time accepting capacity, balancing charging speed and safety margin.

[0015] In the third charging stage, the voltage drop rate at which the state of charge reaches a preset saturation threshold is monitored in real time. The drop rate is calculated from the difference between the saturation voltage and the voltage at subsequent times. The step reduction in output power is determined based on this drop rate, which is positively correlated with the drop rate. Power is gradually reduced at fixed time intervals. A smaller voltage drop rate indicates faster internal polarization reduction and better power handling capacity, resulting in a smaller power reduction and more efficient use of the battery's acceptable power. A larger voltage drop rate indicates that the battery is nearing full charge and side reactions are increasing, leading to a larger power reduction and a rapid decrease in charging power. By directly driving the power reduction step by the voltage drop rate, the lag and overcharging risk associated with solely relying on state of charge for power reduction are eliminated. This avoids lithium plating or overvoltage during the final charging stage and effectively shortens the final charging time. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0017] Figure 1 This is a flowchart of the multi-segment power allocation method for DC charging piles for electric vehicles; Figure 2 This is a flowchart for calculating the maximum acceptable charging current of a DC charging pile; Figure 3 This is a flowchart of the DC charging pile output power step reduction control based on the terminal voltage drop rate. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0019] See Figure 1 This invention provides a method for multi-segment power allocation in a DC charging pile for electric vehicles. After establishing a communication connection between the DC charging pile and the electric vehicle battery management system, the initial state of charge (SOC), initial terminal voltage, and initial temperature of the electric vehicle's power battery are collected. Based on the numerical range of the initial SOC, the entire charging process is divided into a first charging stage, a second charging stage, and a third charging stage, and a first power allocation strategy, a second power allocation strategy, and a third power allocation strategy are configured respectively. In the first charging stage, the maximum acceptable charging current of the power battery at the current moment is calculated based on the initial internal resistance and initial polarization voltage of the power battery, and the upper limit of the output current of the DC charging pile is set based on the maximum acceptable charging current. In the second charging stage, the rate of change of the terminal voltage and the rate of change of the temperature of the power battery are monitored in real time, and the output voltage increment step of the DC charging pile is dynamically adjusted based on the real-time comparison results of the rate of change of the terminal voltage and the rate of change of the temperature. In the third charging stage, the output power of the DC charging pile is gradually reduced based on the rate of voltage drop when the SOC of the power battery reaches a preset saturation threshold, until the SOC of the power battery reaches the charging termination threshold.

[0020] Example 1: In practical implementation, the controller of the DC charging pile pre-stores preset low-level boundary values ​​and preset high-level boundary values. After establishing a communication connection between the DC charging pile and the electric vehicle battery management system, it collects the initial state of charge (SOC), initial terminal voltage, and initial temperature values ​​of the power battery. The controller of the DC charging pile compares the collected SOC values ​​with the low-level and high-level boundary values.

[0021] When the initial state of charge (SBC) value is less than or equal to the lower boundary value, the DC charging pile controller divides the entire charging process into three sequentially connected charging stages: the first, second, and third charging stages, and determines the execution order of these stages. When the initial SBC value is greater than the lower boundary value but less than the higher boundary value, the DC charging pile controller divides the entire charging process into two sequentially connected charging stages: the second and third charging stages, and sets the second charging stage as the initial stage; in this case, the first charging stage is not generated. When the initial SBC value is greater than or equal to the higher boundary value, the DC charging pile controller directly sets the entire charging process to the third charging stage and sets the third charging stage as the initial stage; in this case, the first and second charging stages are not generated.

[0022] After determining the charging stages, the DC charging pile controller configures a power allocation strategy for each stage. A constant current charging strategy is configured for the first charging stage, with the constant current value set as a preset percentage of the maximum acceptable charging current. The maximum acceptable charging current is calculated based on the initial internal resistance and initial polarization voltage, and the preset percentage is determined based on the battery's chemical system and safety boundaries, and can be stored in the DC charging pile's memory. A variable voltage incremental charging strategy is configured for the second charging stage, with the output voltage increment determined in real-time by a weighted ratio of the terminal voltage change rate and the temperature change rate. The terminal voltage change rate is obtained by dividing the difference between the current terminal voltage value and the terminal voltage value at the previous sampling time by the sampling time interval, and the temperature change rate is obtained by dividing the difference between the current temperature value and the temperature value at the previous sampling time by the sampling time interval. The weighting coefficients in the weighted ratio are calibrated using previous battery test data and stored in the DC charging pile's controller. A constant voltage drop power strategy is configured for the third charging stage, with the output power value gradually decreasing at fixed time intervals. The fixed time interval can be a preset cycle value for the DC charging pile controller. The increment of each decrease is determined based on the rate at which the terminal voltage of the power battery falls back after reaching a preset saturation threshold in its state of charge. The output power value decreases continuously until it reaches a preset termination power value. The preset termination power value corresponds to the charging termination threshold of the power battery. When the output power value drops to the termination power value, the DC charging pile stops outputting power.

[0023] Example 2: In specific implementation, refer to Figure 2The controller of a DC charging pile pre-stores an internal resistance mapping table and a polarization voltage mapping table in its internal memory. The internal resistance mapping table is a table that corresponds to the state of charge (SOC) as an input parameter and the internal resistance of the power battery as an output parameter. It is generated by performing AC impedance tests or DC internal resistance tests on battery samples of the same model as the power battery under different SOC conditions to obtain raw data points. After linear interpolation or spline interpolation, the raw data points are processed to form an internal resistance mapping table covering the entire SOC range and stored. The polarization voltage mapping table is a table that corresponds to the temperature as an input parameter and the polarization voltage of the power battery as an output parameter. It is generated by performing pulse charge-discharge tests on battery samples of the same model as the power battery under different temperature conditions, recording the polarization voltage value when the voltage tends to steady state after the pulse ends to obtain raw data points. After interpolation, the raw data points are processed to form a polarization voltage mapping table covering the entire temperature range and stored.

[0024] After establishing a communication connection between the DC charging pile and the electric vehicle battery management system, the DC charging pile controller collects the initial state of charge (SOC), initial terminal voltage, and initial temperature of the power battery. Using the collected SOC as a lookup index, the controller traverses the internal resistance mapping table to obtain the corresponding internal resistance value of the power battery, and uses this internal resistance value as the initial internal resistance value. Similarly, using the collected initial temperature as a lookup index, the controller traverses the polarization voltage mapping table to obtain the corresponding polarization voltage value of the power battery, and uses this polarization voltage value as the initial polarization voltage value.

[0025] Optionally, when the initial state of charge (SOC) value does not directly fall into a discrete SOC value stored in the internal resistance mapping table, the initial internal resistance value is calculated using nearest neighbor interpolation or linear interpolation based on the internal resistance values ​​corresponding to the two SOC values ​​adjacent to the initial SOC value in the internal resistance mapping table. Similarly, when the initial temperature value does not directly fall into a discrete temperature value stored in the polarization voltage mapping table, the initial polarization voltage value is calculated using nearest neighbor interpolation or linear interpolation based on the polarization voltage values ​​corresponding to the two temperature values ​​adjacent to the initial temperature value in the polarization voltage mapping table.

[0026] The controller of a DC charging station calculates the maximum acceptable charging current based on the read initial terminal voltage value, the preset upper limit of the safe terminal voltage, the initial internal resistance value, and the initial polarization voltage value. The formula for calculating the maximum acceptable charging current value is as follows: ; in, This is the maximum acceptable charging current value, in amperes. This is the upper limit of the safe terminal voltage, in volts. This is the initial terminal voltage value, in volts; This is the initial internal resistance value, in ohms; This is the initial polarization voltage value, in volts.

[0027] In practice, the upper limit of the safe terminal voltage is not a fixed constant, but a variable dynamically adjusted based on the current temperature of the power battery. The controller of the DC charging pile stores a reference temperature value, a preset temperature gradient value, and a preset voltage correction amount. The reference temperature value is a reference temperature within the normal operating temperature range of the power battery, for example, it can be set to 25 degrees Celsius. The preset temperature gradient value is a temperature interval, for example, it can be set to 5 degrees Celsius. The preset voltage correction amount is the decrease in the upper limit of the safe terminal voltage for each increase in temperature gradient, for example, it can be set to 0.02 volts. The parameter values ​​are determined by fitting the relationship between the terminal voltage safety boundary and temperature after conducting overcharge tolerance tests on the power battery at different temperatures.

[0028] The controller of the DC charging pile collects the current temperature value of the power battery in real time during the charging process. The controller subtracts the current temperature value from a reference temperature value to obtain the temperature difference. The controller divides the temperature difference by a preset temperature gradient value and rounds down to obtain the number of temperature gradients. The controller multiplies the number of temperature gradients by a preset voltage correction amount to obtain the total voltage correction amount. The controller subtracts the total voltage correction amount from the stored reference safe terminal voltage upper limit value to obtain the real-time safe terminal voltage upper limit value, which is used to calculate the maximum acceptable charging current value mentioned above. The reference safe terminal voltage upper limit value is the highest allowable terminal voltage of the power battery at the reference temperature value, determined according to the power battery's chemical system and the manufacturer's specifications.

[0029] Optionally, when the current temperature value is lower than the reference temperature value, the temperature gradient number is set to zero, the upper limit of the safety terminal voltage remains at the reference upper limit of the safety terminal voltage, and no upward adjustment is performed.

[0030] The maximum acceptable charging current value calculated through the above process is used by the controller of the DC charging pile to set the constant current value in the constant current charging strategy of the first charging stage, that is, to set the constant current value to a preset percentage of the maximum acceptable charging current value to ensure charging safety.

[0031] Example 3: In specific implementation, after the charging process enters the second charging stage, the controller of the DC charging pile initiates a timed sampling mechanism to continuously collect the current terminal voltage and temperature values ​​of the power battery at a preset sampling period. The preset sampling period is a fixed time interval, which is determined based on the communication rate of the battery management system and the computing power of the controller. A typical value can be configured as 100 milliseconds or 200 milliseconds, and the data is stored in the non-volatile memory of the DC charging pile. The controller of the DC charging pile has a built-in shift register or circular buffer to save the terminal voltage and temperature values ​​at the previous sampling time.

[0032] At each sampling moment, the DC charging pile controller obtains the current terminal voltage and temperature values ​​from the battery management system, and then reads the terminal voltage and temperature values ​​from the previous sampling moment from the shift register. The controller calculates the difference between the current and previous terminal voltage values ​​to obtain the terminal voltage difference. The controller divides this difference by the sampling time interval to generate the terminal voltage change rate. The terminal voltage time interval is the difference between the timestamp of the current sampling moment and the timestamp of the previous sampling moment. In an implementation using a fixed sampling period, the terminal voltage time interval is equal to a preset sampling period.

[0033] The controller of the DC charging pile calculates the difference between the temperature value at the current sampling time and the temperature value at the previous sampling time to obtain the temperature difference value. The controller divides the temperature difference value by the sampling time interval to generate the temperature change rate. The temperature time interval is also the difference between the timestamp of the current sampling time and the timestamp of the previous sampling time. In an implementation using a fixed sampling period, the temperature time interval is equal to the preset sampling period.

[0034] The controller of the DC charging pile calculates the ratio of the rate of change of terminal voltage to the rate of change of temperature, obtaining the rate of change ratio. This rate of change ratio is then multiplied by a preset voltage increment reference value to calculate the output voltage increment at the current sampling moment. The voltage increment reference value is determined at the start of the second charging phase and is dynamically updated during the duration of the second charging phase.

[0035] The calculation of the output voltage increment is based on the following formula: ; in, The output voltage increment at the current sampling moment, in volts; This is the rate of change of terminal voltage, measured in volts per second. This is the rate of temperature change, expressed in degrees Celsius per second. This is the reference value for voltage increment, in volts.

[0036] After obtaining the output voltage increment at the current sampling moment, the controller of the DC charging pile determines the rate of change of the terminal voltage. Positive and negative and the rate of temperature change The sign of the output voltage increment is determined by the rate of change of both the terminal voltage and the temperature. When both are positive, the DC charging pile controller maintains a positive sign for the output voltage increment, and the output voltage is set to the sum of the current output voltage value and the output voltage increment. When either the terminal voltage or temperature is negative, the controller sets the output voltage increment to a negative sign. Even if the value calculated based on the rate of change ratio is positive, it is forcibly negative, and the output voltage is set to the sum of the current output voltage value and the negative output voltage increment, effectively reducing the output voltage.

[0037] Optionally, when the terminal voltage change rate is zero, the controller of the DC charging pile sets the output voltage increment to zero, and the output voltage of the DC charging pile remains unchanged. When the temperature change rate is zero, to avoid division by zero, the controller of the DC charging pile sets the output voltage increment to zero, and the output voltage of the DC charging pile remains unchanged.

[0038] At the start of the second charging phase, the DC charging pile controller acquires the current terminal voltage value and uses it as the starting terminal voltage value for the second charging phase. The controller reads the rated voltage value of the power battery from its memory; this rated voltage value is a nominal parameter provided by the battery manufacturer. The controller calculates the ratio of the starting terminal voltage value to the rated voltage value of the power battery, obtaining the starting voltage ratio. Based on the starting voltage ratio, the controller determines the initial value of the voltage increment reference value. The larger the starting voltage ratio, the smaller the initial value of the voltage increment reference value; the two follow a monotonically decreasing mapping relationship. This mapping relationship is stored in the controller in the form of a lookup table, and the corresponding values ​​in the table are obtained through step charging tests on battery samples under different initial charging conditions. In the subsequent process of the second charging phase, the controller periodically updates the voltage increment reference value based on the ratio of the current terminal voltage value to the rated voltage value of the power battery in the same manner as at the start, with the period being the same as the sampling period.

[0039] Example 4: In specific implementation, during the second charging phase, the controller of the DC charging pile simultaneously estimates and monitors the internal temperature field of the power battery. The controller collects the surface temperature value of the power battery in real time through the battery management system and obtains the output current value of the DC charging pile from its own output monitoring circuit. Using the collected surface temperature and output current values, the controller calculates the Joule thermal power value of the power battery at the current moment. The Joule thermal power value originates from the irreversible heat generated by the current flowing through the ohmic internal resistance of the battery, and its value is equal to the square of the output current value multiplied by the ohmic internal resistance value of the power battery. The ohmic internal resistance value of the power battery is related to the state of charge and temperature. The controller of the DC charging pile can retrieve the ohmic internal resistance value of the power battery online from a pre-stored internal resistance mapping table based on the current state of charge and surface temperature value.

[0040] The controller of the DC charging pile iteratively updates the internal accumulated heat value of the power battery at fixed calculation cycles. Within each calculation cycle, the controller multiplies the Joule thermal power value obtained in the current cycle by the cycle duration to obtain the Joule thermal increment for that cycle. Simultaneously, the controller calculates the heat dissipation power value for the current cycle and multiplies it by the cycle duration to obtain the heat dissipation reduction for that cycle. Finally, the controller adds the Joule thermal increment for the current cycle to the internal accumulated heat value stored at the end of the previous cycle, and then subtracts the heat dissipation reduction for the current cycle to obtain the updated current internal accumulated heat value.

[0041] The controller of the DC charging station reads the heat capacity value of the power battery from its memory. The heat capacity value of the power battery is a preset constant, measured in joules per degree Celsius. It is obtained through experimental calibration by inputting known heat and measuring the temperature rise under adiabatic conditions and is stored in the DC charging station's read-only memory. The controller then divides the current accumulated internal heat value by the heat capacity value of the power battery to calculate the internal temperature rise of the battery.

[0042] The controller of the DC charging pile adds the real-time surface temperature value of the power battery to the calculated internal temperature rise value to generate the estimated internal temperature value of the power battery. The estimated internal temperature value represents the estimated temperature of the highest temperature region inside the power battery cell.

[0043] The controller of the DC charging pile compares the generated internally estimated temperature value with a preset safe temperature threshold. The safe temperature threshold is determined based on the thermal shrinkage temperature limit of the battery separator and the decomposition temperature limit of the electrolyte, and is written into the controller parameter table after a safety margin is allowed. Typical values ​​can be set to 55 degrees Celsius or 60 degrees Celsius. When the internally estimated temperature value exceeds the safe temperature threshold, the controller of the DC charging pile executes output current limiting control. The controller gradually reduces the output current setting of the DC charging pile with a preset current drop-off step size. After each reduction, it waits for a stabilization period, re-collects the surface temperature value, and iteratively updates the internally estimated temperature value until the internally estimated temperature value falls below the safe temperature threshold. Once the internally estimated temperature value falls below the safe temperature threshold and remains below it for a hysteresis period, the controller maintains the current output current value, and the second charging phase continues.

[0044] The heat dissipation power value is calculated by the controller of the DC charging pile in the following way: The controller obtains the ambient temperature value through the battery management system or through a temperature sensor installed at the air inlet of the DC charging pile. The controller calculates the difference between the surface temperature of the power battery and the ambient temperature to obtain the surface ambient temperature difference. The controller reads a preset heat dissipation coefficient from the memory and multiplies the surface ambient temperature difference by the heat dissipation coefficient to obtain the heat dissipation power value.

[0045] The heat dissipation coefficient is not a fixed constant, but a variable that increases with the increase of the surface temperature of the power battery. In practice, the functional relationship between the heat dissipation coefficient and the surface temperature is stored in the controller of the DC charging pile in the form of a lookup table. The heat dissipation coefficient mapping table is obtained by calibrating the heat dissipation power of the power battery pack under natural cooling or forced air cooling conditions at different surface temperature values. During the test, the power battery pack is placed in a constant temperature environment, heated to different surface temperatures, and the rate of temperature decrease of the battery pack over time is recorded. The heat dissipation power value at the corresponding surface temperature value is calculated based on the equivalent heat capacity of the battery pack. The heat dissipation power value is divided by the corresponding surface ambient temperature difference to obtain the heat dissipation coefficient value at the corresponding surface temperature value. During the charging process, the controller of the DC charging pile uses the currently collected surface temperature value of the power battery as an index to look up the heat dissipation coefficient mapping table and obtain the corresponding heat dissipation coefficient value for real-time calculation of the heat dissipation power value. The resolution of the heat dissipation coefficient mapping table matches the sampling accuracy of the surface temperature value, and the temperature step between adjacent temperature index entries is no greater than 1 degree Celsius.

[0046] Example 5: In specific implementation, refer to Figure 3Once the charging process enters the third charging stage, the DC charging pile's controller initiates a continuous monitoring process for the battery's state of charge (SOC). The controller obtains the current SOC value of the battery in real time through the battery management system and compares it with a preset saturation threshold. The preset saturation threshold is a reference value for SOC approaching a fully charged state, set according to the battery's chemical characteristics. A typical value can be set to 85% or 90% of the SOC value and is stored in the DC charging pile's non-volatile memory.

[0047] When the controller of the DC charging pile determines that the current state of charge has reached a preset saturation threshold, the controller records the current terminal voltage value of the power battery, marks this terminal voltage value, and stores it as the saturation terminal voltage value. The saturation terminal voltage value is stored in a dedicated register address in the internal random access memory of the DC charging pile controller.

[0048] During the period after the current state of charge (SOC) reaches a preset saturation threshold, the controller of the DC charging pile continuously collects the terminal voltage value of the power battery at a preset monitoring cycle. Each collected terminal voltage value is transmitted to the controller of the DC charging pile, which calculates the rate of decline of each collected terminal voltage value relative to the saturation terminal voltage value. The rate of decline is calculated by subtracting the current collected terminal voltage value from the saturation terminal voltage value, and then dividing by the cumulative duration from the moment the current SOC reaches the preset saturation threshold to the moment of the current collection. The cumulative duration is recorded by a built-in timer in the controller of the DC charging pile.

[0049] The controller of the DC charging pile determines the step reduction magnitude of the output power value based on the calculated fallback rate. There is a positive correlation between the step reduction magnitude and the fallback rate; the larger the fallback rate, the larger the step reduction magnitude. This positive correlation is stored in the controller of the DC charging pile as a function mapping. This function mapping is obtained by performing a third-stage charging simulation test on a battery sample of the same model as the power battery, recording the optimal power step reduction magnitude under different fallback rate conditions that prevents overcharging and ensures acceptable charging time, and then fitting the data. In practical implementation, this function mapping can be implemented using a piecewise linear mapping table, with the fallback rate as the index input and the step reduction magnitude as the output value.

[0050] After determining the step reduction range, the controller of the DC charging pile gradually reduces the output power value of the DC charging pile at fixed time intervals according to this step reduction range. The fixed time interval is a preset time constant, determined based on the data update rate of the battery management system and the response time of the power module; a typical value can be set to 500 milliseconds or 1 second. At the end of each fixed time interval, the controller of the DC charging pile subtracts the step reduction range from the current output power value to obtain the updated output power value, and writes the updated output power value into the power module's power setpoint register, controlling the power module to output according to the updated output power value. The controller of the DC charging pile continuously monitors the current state of charge (SOC). When the current SOC reaches the charging termination threshold, the controller of the DC charging pile directly sets the output power value to zero, and the charging process terminates. The charging termination threshold is the SOC corresponding to a fully charged battery, usually set to 100%.

[0051] Optionally, after the DC charging pile establishes a communication connection with the electric vehicle battery management system and before the start of the first charging phase, the controller of the DC charging pile performs a preprocessing step on the polarization voltage of the power battery. The controller of the DC charging pile collects the resting time value of the power battery through the battery management system. The resting time value is the duration from the end of the last charge / discharge process to the current communication connection establishment time, which is recorded and provided by the timer inside the battery management system. The controller of the DC charging pile has a pre-stored polarization voltage decay curve. The polarization voltage decay curve is a correlation curve with resting time as the independent variable and residual polarization voltage as the dependent variable. This correlation curve is obtained by performing voltage rebound tests on battery samples of the same model as the power battery under different resting times. In the test, the battery sample is charged or discharged to a specific state of charge and then rested. The change of the battery sample terminal voltage over time is continuously recorded, the polarization voltage component is separated, and decay data with time as the horizontal axis is formed. The decay data is fitted to an exponential decay function or a high-order polynomial decay function and then stored as the polarization voltage decay curve.

[0052] The controller of the DC charging pile uses the collected resting time value as an index to query the polarization voltage decay curve and obtain the residual polarization voltage value of the power battery under the current resting conditions, which is recorded as the current residual polarization voltage value. The controller then calculates the pre-charge elimination current value based on this current residual polarization voltage value. The direction of the pre-charge elimination current value is opposite to the direction of the current polarization voltage of the power battery; that is, when the residual polarization voltage is positive, the pre-charge elimination current is the discharge direction current; when the residual polarization voltage is negative, the pre-charge elimination current is the charging direction current. The amplitude of the pre-charge elimination current value is calculated by dividing the absolute value of the current residual polarization voltage value by the ohmic internal resistance value of the power battery. The ohmic internal resistance value of the power battery is obtained by querying an internal resistance mapping table based on the current temperature value and the current state of charge value.

[0053] The controller of the DC charging pile controls the power module of the DC charging pile to output a pre-charging current to the power battery according to the calculated pre-charging elimination current value, and simultaneously starts the pre-charging timer. When the pre-charging timer reaches the predetermined duration, the controller of the DC charging pile stops the pre-charging current output. The predetermined duration is determined by the time constant characteristics of the polarization voltage decay curve, and is taken as the duration corresponding to the polarization voltage decaying to less than 10% of the initial value, with a typical value ranging from tens of seconds to several minutes. After the pre-charging is completed, the controller of the DC charging pile collects the terminal voltage value of the power battery again through the battery management system, and uses the collected terminal voltage value as the preprocessed initial terminal voltage value, which is used to replace the initial terminal voltage value collected in step one in the calculation of the maximum acceptable charging current value in the subsequent first charging stage.

[0054] Optionally, during the first charging phase, the DC charging pile controller synchronously performs real-time monitoring of the lithium plating risk of the power battery. The DC charging pile controller collects the current negative electrode potential value of the power battery in real time through the battery management system. The current negative electrode potential value is obtained by the reference electrode measurement link built into the battery management system, or estimated by the battery management system based on the negative electrode half-cell open-circuit voltage curve and the current state of charge value. The DC charging pile controller compares the collected current negative electrode potential value with the preset lithium plating critical potential value. The preset lithium plating critical potential value is the thermodynamic equilibrium potential value of metallic lithium plating on the negative electrode surface, which is determined with reference to the standard electrode potential of the lithium metal electrode and combined with temperature correction. The typical value is 0 volts relative to the lithium reference electrode scale and is stored in the controller parameter table of the DC charging pile.

[0055] When the controller of the DC charging pile determines that the current negative electrode potential is lower than the lithium plating critical potential, the controller calculates the potential difference between the current negative electrode potential and the lithium plating critical potential. The formula for calculating the potential difference is: ; in, This is the potential difference value, in volts. This is the critical potential for lithium deposition, expressed in volts. This represents the current negative electrode potential value, in volts.

[0056] The controller of the DC charging pile calculates the potential difference value. Calculate the output current derating factor. The output current derating factor is positively correlated with the potential difference; the larger the potential difference, the smaller the output current derating factor, and the more significant the derating effect. The mapping relationship between the output current derating factor and the potential difference is stored in the controller of the DC charging pile in the form of a lookup table. The mapping relationship is determined by combining the test data of the negative electrode potential deviating from the equilibrium potential under different charging rates with the allowable current amplitude under lithium plating boundary conditions. The output current derating factor ranges from 0 to 1. When the potential difference is zero, the output current derating factor is 1, meaning no derating.

[0057] The controller of the DC charging pile multiplies the current output current value of the DC charging pile by the output current derating factor to generate the drated output current value, and writes the drated output current value into the current setpoint register of the power module, controlling the power module to continue charging the power battery with the drated output current value.

[0058] During the derating charging process, the DC charging pile controller continuously collects the current negative electrode potential value and compares it with the lithium plating critical potential value. When the DC charging pile controller determines that the current negative electrode potential value has risen above the lithium plating critical potential value, the controller executes the output current recovery process. The output current recovery process uses a preset current recovery step size to gradually increase the output current value at a fixed step period until the output current value recovers to the upper limit of the output current set in the first charging stage. After each current step increase, the DC charging pile controller waits for one monitoring cycle and confirms that the negative electrode potential value is still above the lithium plating critical potential value before proceeding with the next step increase. If the negative electrode potential value falls below the lithium plating critical potential value again during the recovery process, the output current derating process is re-executed.

[0059] Optionally, during the third charging phase, the DC charging pile controller synchronously corrects the estimated state of charge (SOC) value of the power battery. At the start of the third charging phase, the DC charging pile controller requests the open-circuit voltage value of the power battery from the battery management system. The open-circuit voltage value is obtained by either pausing power output for a short measurement window, waiting for the power battery terminal voltage to relax and stabilize, and then reading the terminal voltage value as the open-circuit voltage value, or by the battery management system estimating the open-circuit voltage value online based on the current terminal voltage value, current value, and internal resistance value using a built-in battery model.

[0060] The controller of a DC charging pile pre-stores a state-of-charge (POC)-open-circuit voltage (OPC) mapping curve. This curve represents the correspondence between open-circuit voltage and POC values. Data points corresponding to the OOC and POC are obtained through low-rate charge-discharge tests on battery samples of the same model as the power battery. These data points are then interpolated and fitted to generate a continuous curve, which is stored in the DC charging pile's read-only memory (ROM). The controller uses the acquired OOC value as a lookup index to perform a table lookup or interpolation search on the OOC-OPC mapping curve to obtain the corresponding POC value. This POC value is then used as the initial POC value for correction.

[0061] The controller of the DC charging pile initiates the ampere-hour integral calculation process based on the corrected initial state of charge value. In this process, the controller integrates the output current value of the DC charging pile over time, divides the integral result by the rated capacity of the power battery, and obtains the ampere-hour integral state of charge increment. The sign of the ampere-hour integral state of charge increment is determined by the direction of the output current; the charging direction is a positive increment.

[0062] During the third charging phase, the DC charging pile's controller collects the terminal voltage and temperature values ​​of the power battery in real time. Based on the collected terminal voltage and temperature values, the controller queries the state-of-charge (POC)-open-circuit voltage (OPV) mapping curve and uses a temperature compensation algorithm to obtain the estimated POC value corresponding to the current estimated open-circuit voltage. The temperature compensation algorithm is used to eliminate the influence of temperature on the open-circuit voltage. The compensation parameters are obtained by calibrating the offset of the open-circuit voltage curve under different temperature conditions and stored in the DC charging pile's controller.

[0063] The controller of a DC charging station calculates the state-of-charge (SOC) deviation between the ampere-hour integrated SOC increment and the estimated SOC. The SOC deviation is the difference between the absolute value of the ampere-hour integrated SOC increment and the absolute value of the estimated SOC. The controller compares the absolute value of the SOC deviation with a preset deviation correction threshold. This threshold is set based on battery capacity degradation tolerance and estimation accuracy requirements; a typical value is 3% or 5% of the SOC value, and it is stored in the controller parameter table of the DC charging station.

[0064] When the controller of the DC charging pile determines that the absolute value of the state of charge (SOC) deviation is greater than the deviation correction threshold, the controller replaces the current SOC estimate with a weighted average of the ampere-hour integral SOC increment and the SOC estimate. In the calculation of the weighted average, the sum of the weighting coefficients for the ampere-hour integral SOC increment and the SOC estimate is 1. The specific values ​​of these weighting coefficients are determined based on the statistical variance of the ampere-hour integral cumulative error and the open-circuit voltage lookup error. When the ampere-hour integral cumulative duration is short, a larger ampere-hour integral weight is used; when the ampere-hour integral cumulative duration is long, a larger open-circuit voltage lookup weight is used. The transition relationship of the weighting coefficients with the cumulative duration is stored in a lookup table. The controller of the DC charging pile uses the weighted average as the corrected current SOC value and applies this corrected current SOC value to the logic for controlling the reduction of output power in the third charging stage. This includes comparing the current SOC value with a preset saturation threshold and determining whether the current SOC value has reached the charging termination threshold.

[0065] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for multi-section power distribution of a direct current charging pile of an electric vehicle, characterized in that, The method includes: After establishing a communication connection between the DC charging pile and the electric vehicle battery management system, the initial state of charge, initial terminal voltage, and initial temperature of the electric vehicle's power battery are collected. Based on the numerical range of the initial state of charge value, the entire charging process is divided into a first charging stage, a second charging stage, and a third charging stage that are connected sequentially, and a first power allocation strategy, a second power allocation strategy, and a third power allocation strategy are configured respectively. In the first charging stage, the maximum acceptable charging current value of the power battery at the current moment is calculated based on the initial internal resistance value and the initial polarization voltage value of the power battery, and the upper limit value of the output current of the DC charging pile is set based on the maximum acceptable charging current value. During the second charging phase, the rate of change of the terminal voltage and the rate of change of the temperature of the power battery are monitored in real time, and the output voltage increment step of the DC charging pile is dynamically adjusted based on the real-time comparison results of the rate of change of the terminal voltage and the rate of change of the temperature. In the third charging stage, the output power of the DC charging pile is gradually reduced according to the rate at which the terminal voltage falls back when the state of charge of the power battery reaches a preset saturation threshold, until the state of charge of the power battery reaches the charging termination threshold.

2. The method for multi-segment power allocation of a DC charging pile for electric vehicles according to claim 1, characterized in that, Based on the numerical range of the initial state of charge value, the entire charging process is divided into a first charging stage, a second charging stage, and a third charging stage, which are sequentially connected, including: The initial state of charge value is compared with a preset low-level boundary value and a preset high-level boundary value. When the initial state of charge value is less than or equal to the low-level boundary value, the entire charging process is divided into a first charging stage, a second charging stage, and a third charging stage that are connected in sequence. When the initial state of charge value is greater than the low-level boundary value and less than the high-level boundary value, the entire charging process is divided into a second charging stage and a third charging stage connected in sequence, and the second charging stage is set as the initial stage. When the initial state of charge value is greater than or equal to the high-level boundary value, the entire charging process is directly set as the third charging stage, and the third charging stage is set as the initial stage.

3. The method for multi-segment power allocation of a DC charging pile for electric vehicles according to claim 1, characterized in that, The configuration of the first power allocation strategy, the second power allocation strategy, and the third power allocation strategy includes: Configure a constant current charging strategy for the first charging stage, and set the constant current value of the constant current charging strategy to a preset percentage value of the maximum acceptable charging current value; A variable voltage incremental charging strategy is configured for the second charging stage, wherein the output voltage increment of the variable voltage incremental charging strategy is determined in real time by the weighted ratio of the terminal voltage change rate and the temperature change rate. A constant voltage drop power strategy is configured for the third charging stage. The output power value of the constant voltage drop power strategy gradually decreases at fixed time intervals until the output power value drops to a preset termination power value.

4. The method for multi-segment power allocation of a DC charging pile for electric vehicles according to claim 1, characterized in that, Based on the initial internal resistance and initial polarization voltage of the power battery, calculate the maximum acceptable charging current of the power battery at the current moment, including: The initial internal resistance value of the power battery under the initial state of charge is obtained by querying a pre-stored internal resistance mapping table based on the initial state of charge value. The initial polarization voltage value of the power battery at the initial temperature value is obtained by querying a pre-stored polarization voltage mapping table based on the initial temperature value. The maximum acceptable charging current value is calculated by dividing the difference between the initial terminal voltage value and the preset upper limit of the safe terminal voltage value by the sum of the initial internal resistance value and the initial polarization voltage value.

5. The method for multi-segment power allocation of a DC charging pile for electric vehicles according to claim 4, characterized in that, The upper limit of the safety terminal voltage is dynamically corrected by the current temperature value of the power battery. For every increase in the current temperature value by a preset temperature gradient, the upper limit of the safety terminal voltage is reduced by a preset voltage correction amount.

6. The method for multi-segment power allocation of a DC charging pile for electric vehicles according to claim 3, characterized in that, The output voltage increment of the variable voltage incremental charging strategy is determined in real time by the weighted ratio of the terminal voltage change rate to the temperature change rate, including: During the second charging phase, the current terminal voltage and current temperature of the power battery are continuously collected at a preset sampling period. The terminal voltage change rate is generated by dividing the difference between the current sampling time and the previous sampling time by the sampling time interval. The temperature change rate is generated by dividing the temperature difference between the current sampling time and the previous sampling time by the sampling time interval. The output voltage increment at the current sampling moment is calculated by multiplying the ratio of the terminal voltage change rate to the temperature change rate by a preset voltage increment reference value. When the terminal voltage change rate is positive and the temperature change rate is positive, the output voltage increment is set to a positive value, and the output voltage of the DC charging pile is increased by the output voltage increment based on the current output voltage value; When the terminal voltage change rate or the temperature change rate is negative, the output voltage increment is set to a negative value, and the output voltage of the DC charging pile is reduced by the output voltage increment based on the current output voltage value.

7. The method for multi-segment power allocation of a DC charging pile for electric vehicles according to claim 6, characterized in that, The voltage increment reference value is dynamically determined by the ratio of the terminal voltage value at the start of the second charging stage to the rated voltage value of the power battery. The larger the ratio, the smaller the voltage increment reference value.

8. The method for multi-segment power allocation of a DC charging pile for electric vehicles according to claim 1, characterized in that, The second charging stage also includes a step of estimating the internal temperature field of the power battery: The current Joule thermal power value of the power battery is calculated based on the surface temperature value of the power battery and the output current value of the DC charging pile. Based on the current Joule thermal power value and the heat dissipation power value of the power battery, calculate the internal cumulative heat value of the power battery; The internal temperature rise of the power battery is calculated based on the internal accumulated heat value and the heat capacity value of the power battery. The surface temperature value is added to the internal temperature rise value to generate the estimated internal temperature value of the power battery; When the internally estimated temperature value exceeds the preset safe temperature threshold, the output current value of the DC charging pile is reduced until the internally estimated temperature value falls back below the safe temperature threshold.

9. A method for multi-segment power allocation in a DC charging pile for electric vehicles according to claim 8, characterized in that, The heat dissipation power value is calculated by multiplying the difference between the surface temperature of the power battery and the ambient temperature by a preset heat dissipation coefficient, and the heat dissipation coefficient increases as the surface temperature of the power battery increases.

10. A method for multi-segment power allocation in a DC charging pile for electric vehicles according to claim 1, characterized in that, Based on the rate at which the terminal voltage falls back when the state of charge of the power battery reaches a preset saturation threshold, the output power of the DC charging pile is gradually reduced, including: The current state of charge of the power battery is monitored in real time. When the current state of charge reaches the preset saturation threshold, the terminal voltage value at the current moment is recorded as the saturation terminal voltage value. After the current state of charge value reaches the preset saturation threshold, the terminal voltage value at subsequent times is continuously collected, and the rate of decline of the terminal voltage value relative to the saturation terminal voltage value is calculated. Based on the magnitude of the fall rate, the step reduction range of the output power value of the DC charging pile is determined, and the step reduction range is positively correlated with the fall rate; According to the step reduction range, the output power value of the DC charging pile is gradually reduced at fixed time intervals until the current state of charge value reaches the charging termination threshold.

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