A direct current charging pile charging control system and method for electric vehicles

Abstract

The application discloses a kind of electric vehicle direct current charging pile charging control system and method, it is related to electric vehicle direct current charging control technical field.The method includes: obtaining the initial voltage fluctuation sequence of charging pile output end, generates the transient impact coefficient of charging handshake moment in combination with the handshake signal of vehicle end battery management system;According to the transient impact coefficient dynamic correction soft start length, obtain the corrected slow rise time window;Collect vehicle end battery polarization voltage decay sequence in slow rise time window, according to adjacent difference value judges decay trend and generates current polarization depth value;According to current polarization depth value, adjust current charging stage target output current rising slope;After adjustment, track the current difference sequence between charging pile output current and vehicle end request current, according to current difference value change quantity updates PWM duty cycle adjustment step size.The scheme can match the transient impact characteristics of charging handshake, improve current tracking accuracy and charging process stability.

Description

Technical Field

[0001] This invention relates to the field of DC charging control technology for electric vehicles, specifically to a DC charging control system and method for electric vehicles. Background Technology

[0002] During the charging handshake phase, DC charging piles for electric vehicles typically establish output voltage and current according to a preset fixed soft-start duration. After the vehicle's battery management system interacts with the charging pile via the handshake signal, the charging pile starts power output based on preset parameters. During charging, battery polarization is often sensed through terminal voltage sampling or state of charge estimation, and the current rise slope is generally determined by a fixed curve or lookup table. For closed-loop output current regulation, the charging pile adjusts the output current by changing the PWM duty cycle, commonly using fixed step size adjustment or proportional-integral control. A fixed soft-start duration cannot adapt to differences in vehicle models, battery states, and transient voltage surges during the handshake. When the voltage overshoot or undershoot is large at the moment of handshake, a fixed soft-start duration may cause the current to build up too quickly, further increasing the output voltage surge and battery polarization; conversely, when the transient surge is small, a fixed soft-start duration may slow down the startup process, delaying power establishment after the handshake. The polarization voltage decay process is affected by charging history, temperature, state of charge, and battery aging, and the decay trend is not always monotonic. Existing methods for determining polarization depth based on voltage difference or a fixed slope are prone to misinterpreting non-continuous decay as continuous or complete decay, leading to inappropriate selection of the current rise slope and increasing the risk of intensified battery polarization or lithium plating. The vehicle-side requested current dynamically changes with the battery state, and the difference between the charging pile output current and the requested current is affected by sampling delay, line impedance, and load fluctuations. A fixed PWM duty cycle adjustment step size is insufficient to quickly approximate the current when the difference is large or suppress overshoot when the difference is small, resulting in output current tracking lag or fluctuations. A charging control scheme is needed that dynamically determines the soft-start time window based on the transient impact of the charging handshake, evaluates the polarization decay trend and polarization depth within this time window, and coordinates the current rise slope with the PWM duty cycle adjustment step size. Summary of the Invention

[0003] This invention provides a charging control system and method for electric vehicle DC charging piles. Based on the transient impact coefficient at the charging handshake moment, the soft start duration is dynamically corrected. Within the corrected soft start time window, the current polarization depth value is calculated according to the polarization voltage decay trend. The target output current rise slope is adjusted according to the current polarization depth value. At the same time, the PWM duty cycle adjustment step size is updated according to the change in the difference between the output current and the vehicle-side requested current. This improves the adaptability of charging handshake transient impact matching, current slope selection, and current tracking adjustment.

[0004] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a charging control method for a DC charging pile for electric vehicles, comprising: acquiring an initial voltage fluctuation sequence at the output end of the charging pile, and generating a transient impact coefficient at the charging handshake moment based on the handshake signal between the initial voltage fluctuation sequence and the vehicle-side battery management system; dynamically correcting the soft-start duration of the charging pile based on the transient impact coefficient to obtain a corrected soft-start time window; within the soft-start time window, acquiring a polarization voltage decay sequence of the vehicle-side battery at a fixed sampling period; determining the decay trend based on adjacent differences in the polarization voltage decay sequence, and generating a current polarization depth value of the vehicle-side battery based on the decay trend; adjusting the target output current rise slope of the charging pile in the current charging stage based on the current polarization depth value; after the target output current rise slope is adjusted, tracking the current difference sequence between the output current of the charging pile and the requested current of the vehicle-side battery in real time, and updating the PWM duty cycle adjustment step size of the charging pile according to the change in current difference in the current difference sequence. This method corrects the soft-start time window by using the transient impact coefficient, which can reduce the impact of voltage oscillations on the battery during the charging handshake; it identifies the current polarization depth by using the polarization voltage decay trend, which can make the output current rise slope adapt to the actual polarization state of the battery; and it improves the current tracking speed and stability by dynamically updating the PWM duty cycle adjustment step size by using the change in current difference.

[0005] Preferably, when generating the transient impact coefficient for the charging handshake moment, the pre-sampled voltage value before the handshake signal rising edge trigger moment and the post-sampled voltage value after the handshake signal rising edge trigger moment in the initial voltage fluctuation sequence are extracted and formed into a transient comparison sequence in chronological order; the voltage overshoot extreme points and voltage undershoot extreme points in the transient comparison sequence are identified, and a first difference between the voltage overshoot extreme point and the steady-state voltage value and a second difference between the steady-state voltage value and the voltage undershoot extreme point are calculated. The ratio of the first difference to the second difference is set as the transient impact coefficient. Characterizing the degree of transient impact through the relative relationship between voltage overshoot and undershoot is beneficial to improving the accuracy of impact identification.

[0006] Preferably, when dynamically correcting the soft-start duration based on the transient impact coefficient, the correction coefficient interval of the transient impact coefficient is located, and the duration scaling factor of the initial soft-start duration is determined based on the correction coefficient interval; the duration scaling factor is multiplied by the initial soft-start duration to obtain the temporary buffer duration; it is then checked whether the temporary buffer duration is within the preset system-allowed buffer duration range. If the temporary buffer duration exceeds the system-allowed buffer duration range, the boundary value of the system-allowed buffer duration range is set as the corrected soft-start time window. The correction coefficient interval consists of multiple continuous and non-overlapping numerical intervals, each corresponding to a different duration scaling factor, thereby enabling graded adjustment of the soft-start duration and avoiding exceeding the system-allowed range.

[0007] Preferably, when generating the current polarization depth value of the vehicle-side battery, the difference between every two adjacent sampling points in the polarization voltage decay sequence is calculated, and all adjacent differences are arranged in chronological order to form a difference trend sequence. The number of positive and negative changes between adjacent differences in the difference trend sequence is counted, and the decay trend type of the polarization voltage decay sequence is determined based on the number of positive and negative changes. When the decay trend type is a continuous decay type, the difference between the maximum and minimum polarization voltage values ​​in the polarization voltage decay sequence is set as the current polarization depth value. When the decay trend type is a non-continuous decay type, the difference between the polarization voltage value of the last sampling point and the polarization voltage value of the initial sampling point in the polarization voltage decay sequence is multiplied by a preset correction coefficient to obtain the current polarization depth value. By distinguishing between continuous decay and non-continuous decay, the interference of polarization voltage fluctuations on the polarization depth calculation results can be reduced.

[0008] Preferably, when adjusting the target output current rise slope, the initial set slope value of the charging pile in the current charging stage is obtained, and a slope restriction coefficient of the initial set slope value is determined based on the current polarization depth value; the slope restriction coefficient is multiplied by the initial set slope value to obtain the candidate output current rise slope; the state of charge value of the vehicle battery at the current moment is obtained, and the maximum allowable slope value corresponding to the charge interval in the preset slope constraint table is queried based on the charge interval in which the state of charge value is located; the candidate output current rise slope is compared with the maximum allowable slope value, and the smaller value is set as the target output current rise slope. Through the dual constraints of polarization depth and state of charge, damage to the battery caused by excessively rapid current rise can be prevented.

[0009] Preferably, when tracking the current difference sequence between the output current of the charging pile and the requested current of the vehicle in real time, the first instantaneous current value of the charging pile output terminal and the second instantaneous current value sent by the vehicle battery management system are collected synchronously according to a predetermined tracking sampling interval; the difference between the first instantaneous current value and the second instantaneous current value at the same sampling moment is calculated to obtain the instantaneous current difference; the instantaneous current differences of multiple consecutive sampling moments are arranged in the order of collection to form an original current difference sequence; the original current difference sequence is subjected to sliding filtering to remove outlier difference points in the original current difference sequence to obtain the current difference sequence, thereby filtering out instantaneous disturbances and improving the stability of the current difference sequence.

[0010] Preferably, when updating the PWM duty cycle adjustment step size of the charging pile, the latest current difference value and the historical current difference value from the previous moment are extracted from the current difference value sequence, and the absolute value of the difference between the latest current difference value and the historical current difference value is calculated and set as the current difference change amount; the current PWM duty cycle of the charging pile is obtained, and the step size correction direction of the current PWM duty cycle is determined according to the current difference change amount; a candidate PWM duty cycle adjustment step size is calculated according to the step size correction direction and a preset step size increment value; it is detected whether the candidate PWM duty cycle adjustment step size exceeds a preset step size upper limit value. If it does, the step size upper limit value is set as the updated PWM duty cycle adjustment step size. The step size correction direction is determined by the positive or negative sign of the current difference change amount. When the current difference change amount is positive, the step size correction direction is increasing; when the current difference change amount is negative, the step size correction direction is decreasing. This allows for adaptive adjustment of the PWM adjustment step size according to the current difference change trend, improving the current tracking response speed and suppressing overshoot.

[0011] This invention also provides a charging control system for an electric vehicle DC charging pile, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of the aforementioned electric vehicle DC charging pile charging control method. This system can perform functions such as charging handshake impact recognition, soft-start time correction, polarization voltage decay analysis, current slope adjustment, current difference tracking, and PWM duty cycle adjustment step size update, enabling dynamic matching of the charging process with the vehicle's battery status and improving the charging safety and adaptability of the DC charging pile.

[0012] The technical effects and advantages provided by the present invention in the above technical solution are as follows:

[0013] The transient impact coefficient at the charging handshake moment is jointly generated by the initial voltage fluctuation sequence and the handshake signal from the vehicle's battery management system. Specifically, a transient comparison sequence is constructed using the pre-sampled voltage values ​​before and after the rising edge of the handshake signal, identifying voltage overshoot and undershoot extreme points. The first difference between the overshoot extreme point and the steady-state voltage value, and the second difference between the steady-state voltage value and the undershoot extreme point are calculated. The ratio of the first difference to the second difference is used as the transient impact coefficient. A duration scaling factor is determined based on the correction coefficient range of the transient impact coefficient, and the initial soft-start duration is dynamically corrected to obtain the corrected soft-start time window. This method allows the soft-start time to adaptively change with the actual degree of transient impact during the handshake. When the transient impact is large, the soft-start process is extended to suppress the impact of excessively rapid current build-up on the battery and power devices; when the transient impact is small, the soft-start process is shortened, allowing the charging power to quickly enter a stable build-up state, thus matching the handshake characteristics of different vehicles and battery states. Within the corrected slow-start time window, the polarization voltage decay sequence of the vehicle-side battery is collected at a fixed sampling period. The difference between adjacent sampling points is calculated, and the number of positive and negative changes in the difference trend sequence is counted. The decay trend type is determined based on the number of positive and negative changes. Under the continuous decay type, the difference between the maximum and minimum polarization voltage values ​​in the polarization voltage decay sequence is taken as the current polarization depth value. Under the non-continuous decay type, the polarization voltage difference between the last sampling point and the initial sampling point is multiplied by a preset correction coefficient to obtain the current polarization depth value. A slope limit coefficient is determined based on the current polarization depth value, and multiplied by the initially set slope value to obtain the candidate output current rise slope. At the same time, the smaller value is taken as the target output current rise slope, which is combined with the maximum allowable slope value corresponding to the current state of charge range of the vehicle-side battery. This method can distinguish between continuous and non-continuous decay, avoid misjudging non-continuous decay as complete polarization decay, and the current rise slope is limited by both polarization depth and state of charge, reducing the risk of battery polarization aggravation and lithium plating. After the target output current rise slope is adjusted, the current difference sequence between the charging pile output current and the vehicle-side requested current is tracked in real time. The PWM duty cycle adjustment step size is updated according to the change in current difference. When the change in current difference is positive, the step size is increased to quickly approach the requested current; when the change in current difference is negative, the step size is decreased to suppress overshoot. This allows the PWM duty cycle adjustment step size to be dynamically adjusted with the change in current difference, improving the output current tracking accuracy and charging process stability. Attached Figure Description

[0014] 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.

[0015] Figure 1This is a flowchart of the charging control method for DC charging piles for electric vehicles;

[0016] Figure 2 This is a flowchart for determining the polarization voltage decay trend type and calculating the polarization depth;

[0017] Figure 3 This is a schematic diagram of the initial voltage fluctuation sequence and overshoot / undershoot extreme values ​​during the charging handshake.

[0018] Figure 4 This is a schematic diagram of the polarization voltage decay sequence and its maximum and minimum values;

[0019] Figure 5 This is a probability density distribution diagram of the initial voltage fluctuation sequence and the polarization voltage decay sequence. Detailed Implementation

[0020] 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.

[0021] See Figure 1 This invention provides a charging control method for DC charging piles for electric vehicles. The charging pile acquires the initial voltage fluctuation sequence at its output terminal and generates a transient impact coefficient for the charging handshake moment based on the handshake signal between the initial voltage fluctuation sequence and the vehicle-side battery management system. Based on the transient impact coefficient, the soft-start duration of the charging pile is dynamically corrected to obtain a corrected soft-start time window. Within the corrected soft-start time window, the polarization voltage decay sequence of the vehicle-side battery is acquired at a fixed sampling period. Based on the adjacent differences in the polarization voltage decay sequence, the decay trend of the polarization voltage decay sequence is determined, and the current polarization depth value of the vehicle-side battery is generated based on the decay trend. Based on the current polarization depth value, the target output current rise slope of the charging pile in the current charging stage is adjusted. After the target output current rise slope is adjusted, the current difference sequence between the output current of the charging pile and the requested current of the vehicle-side battery is tracked in real time. The PWM duty cycle adjustment step size of the charging pile is updated according to the change in the current difference in the current difference sequence.

[0022] In practice, the initial voltage fluctuation sequence at the charging pile output is acquired by a voltage sensor at the charging pile output. The vehicle-side battery management system communicates with the charging pile via a handshake signal, which has a rising edge trigger time. The charging pile controller detects the transition time of the handshake signal level from low to high, obtaining the rising edge trigger time. The charging pile controller extracts the pre-sampled voltage value before the rising edge trigger time of the handshake signal from the initial voltage fluctuation sequence, and extracts the post-sampled voltage value after the rising edge trigger time of the handshake signal from the initial voltage fluctuation sequence. The charging pile controller arranges the pre-sampled and post-sampled voltage values ​​in chronological order to form a transient comparison sequence.

[0023] In practical implementation, the charging pile controller identifies voltage overshoot and undershoot extreme points in the transient comparison sequence. The voltage overshoot extreme point is the sampling point in the transient comparison sequence where the voltage value is higher than the adjacent sampling points and has the largest voltage value. The voltage undershoot extreme point is the sampling point in the transient comparison sequence where the voltage value is lower than the adjacent sampling points and has the smallest voltage value. The charging pile controller acquires the steady-state voltage value, which is the average voltage value at the charging pile output terminal when it enters a steady state after the charging handshake is completed. The charging pile controller calculates the first difference between the voltage overshoot extreme point and the steady-state voltage value, and the second difference between the steady-state voltage value and the voltage undershoot extreme point. The charging pile controller sets the ratio of the first difference to the second difference as the transient impact coefficient. The transient impact coefficient is calculated according to the following formula:

[0024]

[0025] in, This represents the transient impact coefficient, which is a dimensionless parameter. The range of values ​​for is a dimensionless value greater than 0; This represents the first difference between the voltage overshoot extreme point and the steady-state voltage value, expressed in volts. It is obtained by calculating the difference between the voltage sample value corresponding to the voltage overshoot extreme point and the steady-state voltage value. The range of values ​​for is non-negative. This represents the second difference between the steady-state voltage value and the voltage undershoot extreme point, expressed in volts. It is obtained by calculating the difference between the steady-state voltage value and the voltage sample value corresponding to the voltage undershoot extreme point. The range of values ​​is non-negative.

[0026] In practice, the charging pile controller pre-stores a correction coefficient interval table. This table contains multiple consecutive and non-overlapping numerical intervals, each corresponding to a duration scaling factor. The charging pile controller searches for the correction coefficient interval to which the transient impact coefficient falls, determines the numerical interval into which the transient impact coefficient falls, and reads the duration scaling factor corresponding to that interval. The correction coefficient intervals consist of multiple consecutive and non-overlapping numerical intervals, with different intervals corresponding to different duration scaling factors, all of which are greater than zero.

[0027] In practice, the charging pile controller multiplies the duration scaling factor by the initial soft-start duration to obtain the temporary buffer duration. The initial soft-start duration is the soft-start time set for the charging pile before dynamic correction. The temporary buffer duration represents the corrected soft-start time.

[0028] In practice, the charging pile controller checks whether the temporary buffer duration is within the preset system-allowed buffer duration range. The system-allowed buffer duration range is pre-stored in the charging pile controller. The lower limit of the system-allowed buffer duration range is the minimum allowable soft-start time for the charging pile's power devices, and the upper limit is the maximum allowable time for the vehicle-side battery management system to wait for the charging pile's output current. If the temporary buffer duration is less than the lower limit of the system-allowed buffer duration range, the charging pile controller sets the lower limit as the corrected soft-start time window. If the temporary buffer duration is greater than the upper limit of the system-allowed buffer duration range, the charging pile controller sets the upper limit as the corrected soft-start time window. If the temporary buffer duration is within the system-allowed buffer duration range, the charging pile controller uses the temporary buffer duration as the corrected soft-start time window.

[0029] See Figure 3 In the graph, the vertical axis represents the output voltage of the charging pile in volts, and the horizontal axis represents time in milliseconds. The blue solid line represents the initial voltage fluctuation sequence collected from the charging pile output. The gray dashed line represents the steady-state voltage value of the charging pile output when it enters a steady state after the charging handshake is completed, which is approximately 500 volts. The vertical black dashed line represents the trigger moment of the rising edge of the handshake signal, at 0 milliseconds. The red dot marks the voltage overshoot extreme point in the transient comparison sequence, with a voltage value of approximately 507 volts, which appears shortly after the trigger moment of the rising edge of the handshake signal. The green square marks the voltage undershoot extreme point, with a voltage value of approximately 492 volts, located not far after the voltage overshoot extreme point.

[0030] Before the rising edge of the handshake signal triggers, the initial voltage fluctuation sequence fluctuates smoothly around the steady-state voltage value with small amplitude. After the trigger, a significant overshoot peak appears, followed by a rapid drop to the undershoot peak, exhibiting a typical transient impact phenomenon. The difference between the voltage overshoot peak and the steady-state voltage value (first difference) and the difference between the steady-state voltage value and the undershoot peak (second difference) are used to calculate the transient impact coefficient. This transient impact coefficient is a dimensionless parameter and is a key basis for the dynamic correction of the soft-start duration.

[0031] In specific implementation, please refer to Figure 2 The polarization voltage decay sequence is obtained by acquiring the polarization voltage of the vehicle-side battery at a fixed sampling period within a corrected soft-start time window. Each sampling point in the polarization voltage decay sequence corresponds to a sampling time and the polarization voltage value acquired at that sampling time. The fixed sampling period is the polarization voltage sampling time interval preset by the charging pile controller, and the sampling time interval remains constant.

[0032] In practice, the charging pile controller calculates the difference between every two adjacent sampling points in the polarization voltage decay sequence. Two adjacent sampling points include the preceding and following sampling points, and the adjacent difference is obtained by subtracting the polarization voltage value of the preceding sampling point from the polarization voltage value of the following sampling point. The charging pile controller arranges all adjacent differences obtained in the polarization voltage decay sequence according to the chronological order of sampling time, forming a difference trend sequence. Each element in the difference trend sequence is an adjacent difference, which can be positive, negative, or zero.

[0033] In practice, the charging pile controller counts the number of positive and negative changes between adjacent differences in the difference trend sequence. The number of positive and negative changes between adjacent differences is the number of times the sign of the next adjacent difference differs from the sign of the previous adjacent difference. If the sign of the next adjacent difference is opposite to that of the previous adjacent difference, it is counted as one positive and negative change. If the signs of all adjacent differences in the difference trend sequence are the same, the number of positive and negative changes is zero. The charging pile controller determines the attenuation trend type of the polarization voltage attenuation sequence based on the number of positive and negative changes. If the number of positive and negative changes is zero, the attenuation trend type of the polarization voltage attenuation sequence is a continuous attenuation type. If the number of positive and negative changes is greater than zero, the attenuation trend type of the polarization voltage attenuation sequence is a non-continuous attenuation type.

[0034] In practice, when the attenuation trend of the polarization voltage decay sequence is continuous attenuation, the charging pile controller searches for the maximum and minimum polarization voltage values ​​within the sequence. The maximum polarization voltage value is the largest value in the sequence, and the minimum polarization voltage value is the smallest. The charging pile controller calculates the difference between the maximum and minimum polarization voltage values ​​and sets this difference as the current polarization depth value.

[0035] In practical implementation, when the attenuation trend of the polarization voltage decay sequence is a non-continuous decay type, the charging pile controller acquires the polarization voltage value of the last sampling point and the polarization voltage value of the initial sampling point in the polarization voltage decay sequence. The last sampling point is the latest sampling point in the polarization voltage decay sequence, and the initial sampling point is the earliest sampling point in the polarization voltage decay sequence. The charging pile controller calculates the current polarization depth value based on the polarization voltage value of the last sampling point, the polarization voltage value of the initial sampling point, and a preset correction coefficient. The current polarization depth value is calculated according to the following formula:

[0036]

[0037] in, This represents the current polarization depth value, which is expressed in volts. The value of is a real number; This represents the polarization voltage value at the last sampling point in the polarization voltage decay sequence. The unit is volt. It is obtained by reading the sampled data of the last sample point in the polarization voltage decay sequence; This represents the polarization voltage value at the initial sampling point in the polarization voltage decay sequence. The unit is volt. It is obtained by reading the sampling data of the initial sampling point in the polarization voltage decay sequence; This indicates the preset correction factor. For dimensionless parameters, The value range is from 0.5 to 1.5. The data is obtained by offline battery polarization testing, recording polarization voltage decay data under different polarization depths and temperatures, using the average value of the ratio of the actual polarization depth to the voltage difference at the end as the correction coefficient, and storing the correction coefficient in the charging pile controller.

[0038] Optionally, preset correction coefficients can be stored in the non-volatile memory of the charging pile controller and read by the charging pile controller when calculating the current polarization depth value.

[0039] See Figure 4 In the graph, the horizontal axis represents time in seconds, and the vertical axis represents polarization voltage in volts. The curve in the graph represents the polarization voltage decay sequence collected by the charging pile controller at a fixed sampling period within the corrected soft-start time window. The polarization voltage decay sequence shows a continuous downward trend, with the curve gradually decreasing from approximately 100 volts at the initial sampling point to approximately 4 volts, reflecting the decay process of the polarization voltage over time.

[0040] In the diagram, the blue dot marks the initial sampling point, located at time 0 seconds with a polarization voltage of approximately 100 volts; the red square marks the last sampling point, located at time 50 seconds with a polarization voltage of approximately 4 volts. The green triangle and orange inverted triangle indicate the maximum and minimum polarization voltage values ​​in the polarization voltage sequence, respectively. The maximum polarization voltage value corresponds to the initial sampling point, and the minimum polarization voltage value corresponds to the lowest point in the polarization voltage sequence, located close to the minimum sampling voltage value at time 50 seconds.

[0041] According to the description of the above embodiment, the decay trend type of the polarization voltage decay sequence is a continuous decay type, that is, the sign of adjacent differences in the sequence does not change from positive to negative. Therefore, the difference between the maximum polarization voltage value and the minimum polarization voltage value is used as the current polarization depth value. In the figure, the maximum polarization voltage value is approximately 100 volts, the minimum polarization voltage value is approximately 4 volts, and the difference between the two is approximately 96 volts, which is used as the current polarization depth value to reflect the polarization state of the vehicle-side battery.

[0042] In practice, the charging pile controller obtains the initial set slope value of the charging pile in the current charging stage. The initial set slope value is the preset output current rise slope of the charging pile when polarization is not considered in the current charging stage, and it is stored in the charging stage parameter table of the charging pile controller. The charging pile controller determines the slope limitation coefficient of the initial set slope value based on the current polarization depth value. The slope limitation coefficient is a dimensionless value greater than 0 and less than or equal to 1. The charging pile controller stores a slope limitation coefficient mapping table, which contains multiple polarization depth intervals and the slope limitation coefficient corresponding to each polarization depth interval. The charging pile controller searches for the polarization depth interval in which the current polarization depth value is located and reads the slope limitation coefficient corresponding to that interval. The slope limitation coefficient mapping table was obtained through offline testing. In the offline test, different output current rise slopes were applied to the vehicle-end battery under different polarization depth conditions, and the changes in AC internal resistance and temperature rise of the vehicle-end battery were recorded. The ratio of the maximum output current rise slope when the rate of change of AC internal resistance of the vehicle-end battery does not exceed the preset AC internal resistance change rate threshold and the temperature rise does not exceed the preset temperature rise threshold to the initial set slope value was used as the slope limitation coefficient for the corresponding polarization depth range.

[0043] In practice, the charging pile controller multiplies the slope limit coefficient by the initially set slope value to obtain the candidate output current rise slope. The candidate output current rise slope is calculated according to the following formula:

[0044]

[0045] in, This indicates the rise slope of the candidate output current, and the unit of the rise slope of the candidate output current is amperes per second. The value of is a positive number; This represents the initial slope value, expressed in amperes per second. This is obtained by reading the parameter table of the current charging stage from the charging pile controller. The value of is a positive number; This represents the slope limiting coefficient. For dimensionless parameters, The value of is greater than 0 and less than or equal to 1. It is obtained by looking up the slope constraint coefficient corresponding to the current polarization depth value in the slope constraint coefficient mapping table.

[0046] In practice, the charging pile controller obtains the current state of charge (SOC) value of the vehicle-side battery. This SOC value, representing the percentage of the battery's remaining capacity to its rated capacity, is sent to the charging pile controller via the vehicle-side battery management system. The charging pile controller then queries a pre-defined slope constraint table to determine the maximum permissible slope value for each SOC range, based on the range it falls within. This table, stored in the charging pile controller, contains multiple SOC ranges and their corresponding maximum permissible slope values. Each SOC range consists of multiple consecutive, non-overlapping percentage intervals. The maximum permissible slope value for each SOC range is pre-determined by the vehicle-side battery management system based on the battery's current temperature, health status, and permissible rate of change of charging current, and is then sent to the charging pile controller.

[0047] In practice, the charging pile controller compares the rising slope of the candidate output current with the maximum allowable slope value. If the rising slope of the candidate output current is less than the maximum allowable slope value, the charging pile controller sets the rising slope of the candidate output current as the target rising slope of the output current. If the rising slope of the candidate output current is greater than the maximum allowable slope value, the charging pile controller sets the maximum allowable slope value as the target rising slope of the output current. If the rising slope of the candidate output current is equal to the maximum allowable slope value, the charging pile controller sets either the rising slope of the candidate output current or the maximum allowable slope value as the target rising slope of the output current. The target rising slope of the output current is used to adjust the output current of the charging pile during the current charging phase.

[0048] In practice, the charging pile controller synchronously acquires the first instantaneous current value at the charging pile output terminal and the second instantaneous current value sent by the vehicle-side battery management system according to a predetermined tracking sampling interval. The predetermined tracking sampling interval is stored in the charging pile controller and is shorter than the closed-loop control cycle of the charging pile output current. The first instantaneous current value at the charging pile output terminal is acquired by a current sensor at the charging pile output terminal, and the second instantaneous current value sent by the vehicle-side battery management system is received through the communication bus between the charging pile and the vehicle-side battery management system. Synchronous acquisition means that the charging pile controller reads the first and second instantaneous current values ​​at the same sampling moment.

[0049] In practice, the charging pile controller calculates the difference between the first and second instantaneous current values ​​at the same sampling moment to obtain the instantaneous current difference. The instantaneous current difference is the value obtained by subtracting the second instantaneous current value from the first instantaneous current value, and it can be positive, negative, or zero. The charging pile controller arranges the instantaneous current differences from multiple consecutive sampling moments in the order of sampling to form an original current difference sequence. The order of elements in the original current difference sequence is consistent with the order of sampling moments, and the number of elements in the original current difference sequence is determined by the number of samples within the tracking sampling interval.

[0050] In practice, the charging pile controller performs a sliding filter on the original current difference sequence to remove outlier points, resulting in the current difference sequence. The sliding filter uses a median filter with a window length of 5. The charging pile controller sequentially extracts five consecutive instantaneous current differences from the original current difference sequence to form a sliding window. It calculates the median of these five instantaneous current differences within the sliding window. Instantaneous current differences whose absolute value differs from the median is greater than a preset outlier threshold are identified as outlier points and removed from the original current difference sequence. The median is then used to replace the outlier points. The preset outlier threshold is stored in the charging pile controller and is determined based on the measurement noise amplitude of the current sensor, set to three times the current sensor's measurement noise amplitude. The sliding window moves point by point on the original current difference sequence according to the sampling time sequence, traversing the original current difference sequence to obtain the final current difference sequence.

[0051] In practice, the charging pile controller extracts the latest current difference and the historical current difference from the previous moment in the current difference sequence. The latest current difference is the current difference with the latest sampling time in the current difference sequence, and the historical current difference is the current difference with a sampling time earlier than the latest current difference and adjacent to it. The charging pile controller calculates the absolute value of the difference between the latest current difference and the historical current difference, and sets this absolute value as the change in current difference. The change in current difference is a non-negative value.

[0052] In practice, the charging pile controller obtains the current PWM duty cycle adjustment step size of the charging pile. This current step size is stored in the PWM modulation module of the charging pile controller and represents the maximum allowable duty cycle value to change each time the PWM duty cycle is updated. The charging pile controller determines the step size correction direction of the current PWM duty cycle based on the change in current difference. The step size correction direction is determined by the sign of the change in current difference. Since the change in current difference is the absolute value of the difference, the charging pile controller also obtains the relationship between the latest current difference and the historical current difference. When the latest current difference is greater than the historical current difference, the sign of the change in current difference is positive, and the step size correction direction is increasing; when the latest current difference is less than the historical current difference, the sign of the change in current difference is negative, and the step size correction direction is decreasing.

[0053] In practical implementation, the charging pile controller calculates the candidate PWM duty cycle adjustment step size based on the step size correction direction and the preset step size increment value. The candidate PWM duty cycle adjustment step size is calculated according to the following formula:

[0054]

[0055] in, Indicates the step size for adjusting the duty cycle of the candidate PWM. The unit is duty cycle percentage. The value of is a positive number; This indicates the current PWM duty cycle adjustment step size of the charging pile. The unit is duty cycle percentage. It is obtained by reading the current PWM duty cycle adjustment step size stored in the PWM modulation module of the charging pile controller. The value of is a positive number; This represents the step size correction direction coefficient. For dimensionless parameters, The value can be +1 or -1, and when the step size correction direction is the increasing direction... The value is +1, when the step size correction direction is the decreasing direction. The value is -1; This represents the preset step increment value. The unit is duty cycle percentage. The value of is a positive number. It is obtained by reading the PWM step size increment configuration parameters stored in the charging pile controller. The settings are based on PWM resolution and current loop response accuracy. Not less than the minimum duty cycle change corresponding to the PWM resolution.

[0056] In practice, the charging pile controller detects whether the candidate PWM duty cycle adjustment step size exceeds a preset upper limit. This preset upper limit is stored in the charging pile controller and is determined based on the maximum allowable duty cycle change of the PWM modulation module. If the candidate PWM duty cycle adjustment step size exceeds the preset upper limit, the charging pile controller sets the upper limit as the updated PWM duty cycle adjustment step size. If the candidate PWM duty cycle adjustment step size does not exceed the preset upper limit, the charging pile controller uses the candidate PWM duty cycle adjustment step size as the updated PWM duty cycle adjustment step size.

[0057] In practical implementation, the electric vehicle DC charging pile charging control system includes a memory, a processor, and a computer program stored in the memory and running on the processor. The memory and processor are connected via a data bus and an address bus. The memory is divided into a program storage area and a data storage area. The program storage area stores the computer program, and the data storage area stores the data generated during the charging control process. The processor reads the computer program instructions from the program storage area in the memory and executes the corresponding control steps according to the computer program instructions.

[0058] In practical implementation, a combination of non-volatile and volatile memory is used. Non-volatile memory is used to retain the computer program, parameter tables, and control logic data after the charging pile is powered off, while volatile memory is used to temporarily store intermediate variables and sampled data during computer program execution. Data generated during charging control includes initial voltage fluctuation sequences, transient comparison sequences, polarization voltage decay sequences, difference trend sequences, original current difference sequences, current difference sequences, current polarization depth values, target output current rise slope, and PWM duty cycle adjustment step sizes. The processor accesses the data storage area in the memory via the address bus, writes intermediate calculation results to the data storage area, and reads intermediate calculation results from the data storage area in subsequent steps.

[0059] In practical implementation, when the processor executes the computer program, it generates the transient impact coefficient at the charging handshake moment, dynamically corrects the soft-start duration, acquires the polarization voltage decay sequence within the soft-start time window, generates the current polarization depth value, adjusts the target output current rise slope, tracks the current difference sequence, and updates the PWM duty cycle adjustment step size. The processor obtains the initial voltage fluctuation sequence through the voltage sensor at the charging pile output end, and obtains the handshake signal and the second instantaneous current value through the communication interface between the charging pile and the vehicle-side battery management system.

[0060] In practical implementation, when the processor generates the transient impulse coefficient at the charging handshake moment, it calls the initial voltage fluctuation sequence and the handshake signal rising edge trigger time stored in memory. The processor extracts the pre-sampled voltage value before the handshake signal rising edge trigger time and the post-sampled voltage value after the handshake signal rising edge trigger time from the initial voltage fluctuation sequence, forming a transient comparison sequence in chronological order. The processor identifies the voltage overshoot and undershoot extreme points in the transient comparison sequence, reads the steady-state voltage value from the data storage area, calculates the first difference and the second difference, and calculates the transient impulse coefficient. The processor stores the transient impulse coefficient in the data storage area.

[0061] In practice, when the processor performs dynamic adjustment of the soft-start duration, it reads the transient impact coefficient and the initial soft-start duration from the data storage area, and reads the adjustment coefficient interval table stored in the program storage area. The processor finds the adjustment coefficient interval in which the transient impact coefficient falls, obtains the duration scaling factor, calculates the temporary buffer duration, and reads the system's allowed buffer duration range. The processor compares the temporary buffer duration with the system's allowed buffer duration range and stores the adjusted soft-start time window in the data storage area.

[0062] In practical implementation, when the processor completes the acquisition of the polarization voltage decay sequence within the soft-start time window, it reads the corrected soft-start time window from the data storage area, controls the sampling circuit to acquire the polarization voltage of the vehicle-end battery according to a fixed sampling period, forms the polarization voltage decay sequence, and writes it into the data storage area. When the processor completes the generation of the current polarization depth value, it reads the polarization voltage decay sequence, calculates the adjacent differences and forms a difference trend sequence, counts the number of positive and negative changes, determines the decay trend type, calculates the current polarization depth value according to the decay trend type, and writes the current polarization depth value into the data storage area.

[0063] In practice, when the processor completes the adjustment of the target output current rise slope, it reads the current polarization depth value and the initial set slope value from the data storage area, and reads the slope limit coefficient mapping table and slope constraint table from the program storage area. The processor determines the slope limit coefficient based on the current polarization depth value, calculates the candidate output current rise slope, obtains the current state of charge value of the vehicle-side battery and queries the maximum allowable slope value, compares these values, generates the target output current rise slope, and writes the target output current rise slope into the data storage area.

[0064] In practical implementation, when the processor completes current difference sequence tracking, it synchronously collects the first instantaneous current value from the charging pile output and the second instantaneous current value sent by the vehicle-side battery management system according to a predetermined tracking sampling interval, calculates the instantaneous current difference, and forms the original current difference sequence. The processor performs sliding filtering on the original current difference sequence to obtain the current difference sequence and writes it into the data storage area. When the processor completes PWM duty cycle adjustment step size update, it reads the latest current difference value and historical current difference value from the current difference sequence, calculates the change in current difference value, obtains the current PWM duty cycle adjustment step size, determines the step size correction direction, calculates candidate PWM duty cycle adjustment step sizes, checks whether the candidate PWM duty cycle adjustment step size exceeds the step size upper limit, writes the updated PWM duty cycle adjustment step size into the data storage area, and sends it to the PWM modulation module.

[0065] See Figure 5 In the graph, the horizontal axis represents voltage values ​​in volts, and the vertical axis represents probability density. The graph shows three curves: the initial voltage fluctuation sequence (blue solid line), the transient comparison sequence (red dashed line), and the polarization voltage decay sequence (green dotted line). The main peaks of both the initial voltage fluctuation sequence and the transient comparison sequence are concentrated in the 480-520 volt range, and the curves of the two sequences largely overlap. This indicates that the transient comparison sequence is formed by arranging the voltage samples before and after the rising edge of the handshake signal in the initial voltage fluctuation sequence in chronological order, reflecting the transient voltage change characteristics before and after the charging handshake moment. Within this range, the probability density peak of the initial voltage fluctuation sequence is slightly higher than that of the transient comparison sequence, indicating that the transient comparison sequence fluctuates slightly after data filtering and processing.

[0066] The probability density distribution of the polarization voltage decay sequence is significantly different from the previous two sequences. Its peak is concentrated in the low voltage range of 0 volts to 50 volts. The probability density in this range shows a right-skewed distribution, gradually decaying to zero, and is far away from the high voltage region of the initial voltage fluctuation sequence and the transient comparison sequence. This indicates that the polarization voltage decay sequence is a voltage decay sequence formed by collecting the polarization voltage of the vehicle battery with a fixed sampling period within the corrected slow start time window. It reflects the polarization effect of the vehicle battery in the early stage of charging, and its lower voltage range is significantly different from the initial voltage fluctuation sequence, which is convenient for subsequent judgment and calculation of polarization depth.

[0067] 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 charging control method for a DC charging pile for electric vehicles, characterized in that, The method includes: The initial voltage fluctuation sequence at the output of the charging pile is obtained, and the transient impact coefficient at the charging handshake moment is generated based on the handshake signal between the initial voltage fluctuation sequence and the vehicle-side battery management system. Based on the transient impact coefficient, the soft start time of the charging pile is dynamically corrected to obtain the corrected soft start time window; Within the slow-start time window, the polarization voltage decay sequence of the vehicle-side battery is collected at a fixed sampling period; Based on the adjacent differences in the polarization voltage decay sequence, the decay trend of the polarization voltage decay sequence is determined, and the current polarization depth value of the vehicle battery is generated based on the decay trend. Based on the current polarization depth value, adjust the target output current rise slope of the charging pile in the current charging stage; After the target output current rise slope is adjusted, the current difference sequence between the output current of the charging pile and the requested current at the vehicle end is tracked in real time. The PWM duty cycle adjustment step size of the charging pile is updated according to the change in current difference in the current difference sequence.

2. The charging control method for a DC charging pile for electric vehicles according to claim 1, characterized in that, The step of obtaining the initial voltage fluctuation sequence at the output of the charging pile and generating the transient impact coefficient at the charging handshake moment based on the initial voltage fluctuation sequence and the handshake signal of the vehicle-side battery management system includes: Extract the presampled voltage value in the initial voltage fluctuation sequence that is before the triggering time of the rising edge of the handshake signal, and extract the postsampled voltage value in the initial voltage fluctuation sequence that is after the triggering time of the rising edge of the handshake signal. The pre-sampled voltage values ​​and the post-sampled voltage values ​​are arranged in chronological order to form a transient comparison sequence; Identify voltage overshoot and voltage undershoot extreme points in the transient comparison sequence, and calculate the first difference between the voltage overshoot extreme point and the steady-state voltage value, and the second difference between the steady-state voltage value and the voltage undershoot extreme point; The ratio of the first difference to the second difference is set as the transient impact coefficient.

3. The electric vehicle DC charging pile charging control method according to claim 2, characterized in that, The step of dynamically correcting the soft-start time of the charging pile based on the transient impact coefficient to obtain the corrected soft-start time window includes: Locate the correction coefficient range in which the transient impact coefficient falls, and determine the duration scaling factor of the initial soft-start duration based on the correction coefficient range; Multiply the duration scaling factor by the initial soft-start duration to obtain the temporary buffer duration; The system detects whether the temporary buffer duration is within the preset system-allowed buffer duration range. If the temporary buffer duration exceeds the system-allowed buffer duration range, the boundary value of the system-allowed buffer duration range is set as the corrected soft-start time window.

4. The charging control method for a DC charging pile for electric vehicles according to claim 1, characterized in that, The step of determining the decay trend of the polarization voltage decay sequence based on the adjacent differences in the polarization voltage decay sequence, and generating the current polarization depth value of the vehicle-side battery based on the decay trend, includes: Calculate the difference between every two adjacent sampling points in the polarization voltage decay sequence, and form a difference trend sequence by arranging all adjacent differences in chronological order; The number of positive and negative changes between adjacent differences in the difference trend sequence is counted, and the decay trend type of the polarization voltage decay sequence is determined based on the number of positive and negative changes. When the attenuation trend type is a continuous attenuation type, the difference between the maximum polarization voltage value and the minimum polarization voltage value in the polarization voltage attenuation sequence is set as the current polarization depth value; When the attenuation trend type is a non-continuous attenuation type, the difference between the polarization voltage value of the last sampling point and the polarization voltage value of the initial sampling point in the polarization voltage attenuation sequence is multiplied by a preset correction coefficient to obtain the current polarization depth value.

5. The charging control method for a DC charging pile for electric vehicles according to claim 1, characterized in that, The step of adjusting the target output current rise slope of the charging pile in the current charging stage according to the current polarization depth value includes: Obtain the initial set slope value of the charging pile in the current charging stage, and determine the slope limit coefficient of the initial set slope value based on the current polarization depth value; Multiply the slope limiting coefficient by the initial set slope value to obtain the candidate output current rise slope; Obtain the state of charge (SOC) value of the vehicle battery at the current moment, and query the maximum allowable slope value corresponding to the SOC interval from a preset slope constraint table based on the SOC interval in which the SOC value is located. The candidate output current rise slope is compared with the maximum allowable slope value, and the smaller value is set as the target output current rise slope.

6. The charging control method for a DC charging pile for electric vehicles according to claim 1, characterized in that, The step of tracking the current difference sequence between the charging pile's output current and the vehicle's requested current in real time after the target output current's rising slope has been adjusted includes: According to the predetermined tracking sampling interval, the first instantaneous current value at the output end of the charging pile and the second instantaneous current value sent by the vehicle-side battery management system are collected simultaneously. The difference between the first instantaneous current value and the second instantaneous current value at the same sampling time is calculated to obtain the instantaneous current difference; The instantaneous current differences at multiple consecutive sampling times are arranged in the order of sampling to form the original current difference sequence; The original current difference sequence is subjected to sliding filtering to remove outlier difference points, thus obtaining the current difference sequence.

7. The electric vehicle DC charging pile charging control method according to claim 6, characterized in that, The step of updating the PWM duty cycle adjustment step size of the charging pile according to the change in current difference in the current difference sequence includes: Extract the latest current difference and the historical current difference from the previous moment in the current difference sequence, and calculate the absolute value of the difference between the latest current difference and the historical current difference, which is set as the change in current difference. Obtain the current PWM duty cycle of the charging pile, and determine the step size correction direction of the current PWM duty cycle based on the change in current difference; The candidate PWM duty cycle adjustment step size is calculated based on the step size correction direction and the preset step size increment value. Detect whether the candidate PWM duty cycle adjustment step size exceeds the preset step size upper limit. If it does, set the step size upper limit to the updated PWM duty cycle adjustment step size.

8. The charging control method for a DC charging pile for electric vehicles according to claim 3, characterized in that, The correction coefficient interval is a plurality of continuous and non-overlapping numerical intervals, and each correction coefficient interval corresponds to a different duration scaling factor.

9. A charging control method for a DC charging pile for electric vehicles according to claim 7, characterized in that, The step size correction direction is determined by the sign of the change in current difference. When the change in current difference is positive, the step size correction direction is increasing; when the change in current difference is negative, the step size correction direction is decreasing.

10. A charging control system for a DC charging pile for electric vehicles, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the electric vehicle DC charging pile charging control method according to any one of claims 1 to 9.

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