Direct-current charging pile direct-current contactor state monitoring and life prediction system and method

Abstract

The present application relates to the technical field of charging pile monitoring and prediction, and discloses a DC charging pile DC contactor state monitoring and service life prediction system and method; comprising: a feature map drawing module for drawing a coil current waveform graph; a waveform feature extraction module for extracting waveform current features; a dynamic feature extraction module for extracting dynamic execution features; a health score early warning module for determining whether to enter a service life prediction mode; a service life attenuation prediction module for determining whether to issue a replacement warning prompt; the present application can comprehensively reflect the performance degradation of the DC contactor from the perspective of multi-physical field coupling, avoids the limitations of single feature parameters reflecting certain side information in the degradation process, realizes the organic integration of multiple source heterogeneous features in the DC contactor, prevents misjudgment and missed judgment caused by single feature abnormal fluctuation or incomplete local feature information coverage, and improves the accuracy of health state evaluation.

Description

Technical Field

[0001] This invention relates to the field of charging pile monitoring and prediction technology, and more specifically, to a system and method for monitoring the condition and predicting the lifespan of DC contactors in DC charging piles. Background Technology

[0002] In the actual operation of DC charging piles, DC contactors need to frequently perform high-current switching operations. During long-term service, their contact systems will inevitably experience degradation phenomena such as material wear, arc erosion, and contact welding. These degradation phenomena have gradual and cumulative characteristics. If they are not identified and warned in time, they may cause the contactor to suddenly fail during charging, thereby causing safety accidents such as charging interruption and equipment damage. Therefore, it is necessary to accurately monitor and predict the operating status and service life of DC contactors.

[0003] Reference patent application CN122084960A discloses a multi-dimensional method and system for assessing damage to DC contactors in charging piles. The method includes: a host acquiring the current current value, current temperature, and previous temperature during the charging process of the DC contactor, as well as the voltage sequence and / or current sequence during the previous disconnection process, and historical charging and disconnection data; obtaining a disconnection damage score based on the voltage transient characteristics of the voltage sequence and / or the current drop characteristics of the current sequence; obtaining the current drift degree based on the difference between the current current value and the current compensation current value; obtaining the temperature rise rate deviation of the contact resistance based on the deviation between the actual temperature rise rate and the expected temperature rise rate; analyzing historical charging and disconnection data to obtain cumulative operating load data; and comprehensively analyzing the above four indicators to assess the damage status of the DC contactor. When performing condition monitoring and life prediction, existing DC contactors typically select only one or a few characteristic parameters to characterize their current health status. However, the performance degradation of a DC contactor is a complex process involving the coupling of multiple physical fields. Relying on only one or a few characteristic parameters to characterize its health status cannot comprehensively reflect the true performance degradation of the DC contactor from multiple different dimensions, resulting in low accuracy of its health status assessment results and a tendency to produce misjudgments and omissions.

[0004] In view of this, the present invention proposes a system and method for monitoring the condition and predicting the lifespan of DC contactors in DC charging piles to solve the above problems. Summary of the Invention

[0005] To overcome the aforementioned deficiencies of the prior art and to achieve the above objectives, the present invention provides the following technical solution: a DC charging pile DC contactor condition monitoring and life prediction system, applied to a charging control platform, comprising: The feature graph drawing module is used to set the sampling frequency and monitoring period, collect the coil current and status signals of the DC contactor during the monitoring period. The status signals include conduction signals and disconnection signals. The coil current waveform is drawn with the coil current as the vertical axis and time as the horizontal axis. The waveform feature extraction module is used to extract waveform current features from the coil current waveform diagram. The waveform current features include feature parameters, vibration energy, and steady-state current deviation rate. The dynamic feature extraction module is used to set the prediction period and extract the dynamic execution features of the DC contactor during the prediction period. The dynamic execution features include the resistance change rate and the ratio of action times consumed. The health score early warning module is used to import waveform current characteristics and dynamic execution characteristics into the health status scoring model, calculate the health status score, determine the early warning level based on the health status score, and determine whether to enter the life prediction mode. The lifespan degradation prediction module is used to calculate the predicted remaining lifespan of the DC contactor using a lifespan degradation model in lifespan prediction mode, and to determine whether to issue a replacement warning based on the predicted remaining lifespan and the warning level.

[0006] Furthermore, the method for drawing the coil current waveform is as follows: Arrange the currents of coil A sequentially according to the order of data acquisition to generate a current sequence; Plot the A coil currents in the current sequence as current curves with time as the horizontal axis and coil current as the vertical axis. The moment when the state signal is on is recorded as the moment when the auxiliary contact is on, and the moment when the state signal is off is recorded as the moment when the auxiliary contact is off. Mark the points where the auxiliary contact is on and off on the current curve, and draw the coil current waveform.

[0007] Furthermore, the method for extracting feature parameters is as follows: Identify the maximum value of the coil current from the coil current waveform diagram, record it as the current peak value, and multiply the current peak value by a preset mutation coefficient to calculate the current mutation value; In the coil current waveform diagram, the coil current at the next moment is subtracted from the coil current at the previous moment to calculate the current change value. The stage with a positive current change value is recorded as the rising stage, and the stage with a negative current change value is recorded as the falling stage. Starting from the second moment, the moment when the current change value first changes from the rising phase to the falling phase and the absolute value of the current change value is greater than the current sudden change value is recorded as the moment of completion of conduction, and the duration between the moment the auxiliary contact is turned on and the moment of completion of conduction is recorded as the pull-in duration. After the conduction is completed, the moment when the current change value first changes from the falling phase to the rising phase and the current change value is greater than the current sudden change value is recorded as the disconnection completion moment, and the duration between the auxiliary contact disconnection moment and the disconnection completion moment is recorded as the release duration. The characteristic parameters are calculated by subtracting the hold-in time from the release time and dividing the difference by the hold-in time.

[0008] Furthermore, the method for extracting vibrational energy is as follows: In the coil current waveform diagram, the coil current located between the moment the auxiliary contact turns on and the moment the conduction is completed is recorded as the target current. The target current is de-DC biased and windowed to obtain the time-domain current. Perform a fast Fourier transform on the time-domain current to obtain the amplitude, and then summarize the amplitudes of all frequencies to generate a spectrum array. Starting with a preset lower frequency limit and ending with a preset upper frequency limit, the frequencies in the spectrum array located between the preset lower and upper frequency limits are recorded as target frequencies. The vibration energy is calculated by summing the squares of the amplitudes of all target frequencies.

[0009] Furthermore, the method for extracting the steady-state current deviation rate is as follows: In the coil current waveform diagram, the steady-state start time is obtained by extending the completion time of conduction backward by a preset impact time, and the steady-state end time is obtained by pushing back the time of auxiliary contact disconnection backward by a preset impact time. The time period between the steady-state start time and the steady-state end time is recorded as the steady-state time period. During the steady-state period, after removing the maximum and minimum values ​​of the coil current, the remaining coil currents are summed and averaged to calculate the real-time steady-state current. Find the rated steady-state current of the coil in the DC contactor, take the absolute value of the difference between the real-time steady-state current and the rated steady-state current, and divide it by the rated steady-state current to calculate the steady-state current deviation rate.

[0010] Furthermore, the method for extracting the rate of change of resistance is as follows: A1: Periodically check the status signal of the auxiliary contact based on the completion of one prediction cycle; A2: If the status signal of the auxiliary contact is a conducting signal, execute A3-A5; if the status signal of the auxiliary contact is a disconnected signal, repeat A1-A2. A3: Measure the real-time voltage of the circuit where the main contact is located, record it as the terminal voltage, and initialize the DC test current; A4: A constant current source is used to introduce a DC test current into the circuit where the main contacts of the DC contactor are located, and a differential amplifier is used to measure the voltage across the two ends of the circuit where the DC test current flows through the main contacts, which is recorded as the test voltage. A5: Subtract the test voltage from the terminal voltage, divide the difference by the DC test current, and calculate the resistance change rate.

[0011] Furthermore, when extracting the action consumption ratio, within a prediction period, a valid action is defined as the DC contactor completing one sequence of "coil energization - auxiliary contact conduction signal - coil de-energization - auxiliary contact disconnection signal". The number of valid actions of the DC contactor is counted and recorded as the real-time action count. The rated electrical life of the DC contactor is then retrieved, and the real-time action count is divided by the rated electrical life count to calculate the action consumption ratio.

[0012] Furthermore, the warning levels include recommended inspection level, planned replacement level, and immediate deactivation level; The method for determining whether to enter lifetime prediction mode is as follows: When the health status score is greater than the first warning score threshold, the warning level will be set to the recommended inspection level, and the system will be entered into life prediction mode. When the health status score is less than or equal to the first warning score threshold and the health status score is greater than the second warning score threshold, the warning level will be set to the planned replacement level, and the system will be determined to enter the life prediction mode. When the health status score is less than or equal to the second warning score threshold, the warning level will be set to the immediate shutdown level, and the life prediction mode will not be entered.

[0013] Furthermore, the method for determining whether to issue a replacement warning is as follows: When the predicted remaining lifetime is greater than or equal to the remaining lifetime threshold, it is determined that no replacement warning will be issued. When the predicted remaining lifetime is less than the remaining lifetime threshold, a replacement warning is issued. When the warning level of the DC contactor is the immediate shutdown level, a replacement warning prompt is issued.

[0014] A method for monitoring the condition and predicting the lifespan of DC contactors in DC charging piles is applied to a charging control platform. It is implemented based on a system for monitoring the condition and predicting the lifespan of DC contactors in DC charging piles, and includes: SS1: Set the sampling frequency and monitoring period, collect the coil current and status signal of the DC contactor during the monitoring period, and plot the coil current waveform with the coil current as the vertical axis and time as the horizontal axis. SS2: Extract waveform current features from the coil current waveform diagram. The waveform current features include characteristic parameters, vibration energy, and steady-state current deviation rate. SS3: Set the prediction period and extract the dynamic execution characteristics of the DC contactor during the prediction period. The dynamic execution characteristics include the resistance change rate and the ratio of action times consumed. SS4: Import waveform current characteristics and dynamic execution characteristics into the health status scoring model, calculate the health status score, determine the warning level based on the health status score, and determine whether to enter the life prediction mode. SS5: In life prediction mode, the predicted remaining life of the DC contactor is calculated using the life decay model, and a replacement warning is issued based on the predicted remaining life and the warning level.

[0015] The technical advantages of the DC charging pile DC contactor condition monitoring and life prediction system and method of the present invention are as follows: (1): This invention extracts waveform current features reflecting instantaneous dynamic changes from coil current waveform diagrams and dynamic execution features reflecting cumulative degradation trends from long-term service processes. It can comprehensively reflect the performance degradation of DC contactors from the perspective of multi-physics field coupling, avoiding the limitation of a single feature parameter reflecting information from one aspect of the degradation process. It realizes the organic integration of multi-source heterogeneous features in DC contactors, prevents misjudgment and omission caused by abnormal fluctuations of a single feature or incomplete coverage of local feature information, and improves the accuracy of DC contactor health status assessment.

[0016] (2): This invention uses a dual early warning mechanism that calculates health status scores and predicts remaining lifespan to independently analyze the actual operating health status of the DC contactor at the current moment and its safe service life at future moments. This not only achieves the dual analysis effect of status monitoring and lifespan prediction, avoiding the one-sidedness of single-dimensional analysis and early warning operations, but also enables the early detection of potential abnormal faults of the DC contactor, thereby allowing targeted maintenance operations to be carried out before the fault occurs, avoiding the lag problem caused by real-time status monitoring and lifespan prediction methods. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the DC charging pile DC contactor condition monitoring and life prediction system provided in Embodiment 1 of the present invention. Figure 2 This is a logic diagram of the DC charging pile DC contactor condition monitoring and life prediction system provided in Embodiment 1 of the present invention. Figure 3 This is a flowchart illustrating the DC contactor condition monitoring and life prediction method for DC charging piles provided in Embodiment 2 of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: Please refer to Figures 1-2 As shown in this embodiment, the DC charging pile DC contactor condition monitoring and life prediction system is applied to a charging control platform and includes: The feature graph drawing module sets the sampling frequency and monitoring period, collects the coil current and status signals of the DC contactor during the monitoring period. The status signals include conduction signals and disconnection signals. The coil current waveform is plotted with the coil current as the vertical axis and time as the horizontal axis. The coil current is a direct reflection of the electromagnetic mechanism's operating characteristics of a DC contactor. The variation pattern of the coil current signal is closely related to physical processes such as the movement of the iron core and the closing of the contacts. Therefore, by collecting the coil current of a DC contactor in the starting state, we can provide the prerequisites for monitoring the actual state of the DC contactor and predicting its lifespan.

[0020] A DC contactor consists of main contacts and auxiliary contacts. The main contacts are the core actuators of the DC contactor and are directly connected in series in the main circuit of the controlled equipment. The auxiliary contacts are not directly connected to the main circuit, but are used in the control circuit to implement various control logic or transmit status signals.

[0021] The status signal is a result of the actual working state of the auxiliary contacts in a DC contactor. By collecting the status signal of the auxiliary contacts, signal support can be provided to determine whether the main contacts of the DC contactor are in the closed or open state. Specifically, the status signals include on signals and off signals; the on signal indicates that the auxiliary contact is currently energized and conducting, and the main contact is in the closed state; conversely, the off signal indicates that the auxiliary contact is currently de-energized and disconnected, and the main contact is in the released state.

[0022] When acquiring the coil current signal and status signal of a DC contactor, the sampling frequency must be set first so that the sampling frequency can provide a time scale constraint for the acquisition of the coil current signal and status signal, ensuring that the acquired coil current signal and status signal can maintain continuity and synchronization on the time line. Specifically, when setting the sampling frequency, it is necessary to take into account the requirements of the Nyquist theorem, that is, in order to recover the highest frequency signal from the digital signal, the sampling frequency must be greater than twice that frequency. At the same time, it is also necessary to take into account the cutoff frequency of the anti-aliasing filter actually used, and coordinate with the hardware parameters of the anti-aliasing filter. Therefore, when setting the sampling frequency, the cutoff frequency of the anti-aliasing filter is used as the reference frequency, and the sampling frequency is set to a standard of being greater than or equal to twice the reference frequency. In this embodiment, it can be found that the cutoff frequency of the anti-aliasing filter is 45kHz. At this time, the sampling frequency is set to 100kHz.

[0023] The monitoring cycle is the duration of collecting coil current signals and status signals from a DC contactor. This ensures that the number of times the coil current signals and status signals are collected remains within a reasonable range, and also guarantees a sufficient and reliable amount of valid data. When setting the monitoring cycle, it is also necessary to consider the time taken from the coil being energized to the main contact closing, and the time taken from the coil breaking point to the main contact releasing, to ensure that the monitoring cycle can meet the requirements of one complete closing and releasing process, and that there is still some remaining time.

[0024] In this embodiment, it can be found that the duration of the coil energizing process to the main contact closing is 30ms-80ms, and the duration of the coil breaking process to the main contact releasing process is 40ms-100ms. Therefore, the monitoring period is set to 200ms.

[0025] When collecting coil current and status signals, the starting time of the DC contactor is taken as the starting time, the sampling frequency is taken as the frequency standard, and one monitoring cycle is taken as the duration standard. The coil current and status signals are continuously collected at A time points. Among them, the time when the status signal changes corresponds to only two time points, namely the time when the auxiliary contact is open and the time when the auxiliary contact is closed.

[0026] The coil current waveform is a graphic representation of the changes in current on the coil during the monitoring period, which provides a basis for the subsequent extraction of relevant features. The method for drawing the coil current waveform is as follows: The coil current is filtered by a 50Hz notch filter to eliminate power frequency interference, and the A coil currents are arranged in sequence according to the order of acquisition time to generate a current sequence. Plot the A coil currents in the current sequence as current curves with time as the horizontal axis and coil current as the vertical axis. The moment when the state signal is on is recorded as the moment when the auxiliary contact is on, and the moment when the state signal is off is recorded as the moment when the auxiliary contact is off. Mark the points where the auxiliary contact is on and off on the current curve, and draw the coil current waveform.

[0027] It should be noted that the status signal of the auxiliary contact can accurately reflect the actual action time of the main contact; since the auxiliary contact and the main contact maintain mechanical linkage, the moment when the auxiliary contact is turned on is the moment when the main contact is turned on, and the moment when the auxiliary contact is turned off is the moment when the main contact is turned off.

[0028] The waveform feature extraction module extracts waveform current features from the coil current waveform diagram. The waveform current features include feature parameters, vibration energy, and steady-state current deviation rate. The coil current fluctuation diagram contains a large number of different types of features. These features can represent the current change characteristics, vibration change characteristics, and conduction and disconnection time change characteristics of the DC contactor from different perspectives. Therefore, it is necessary to extract the waveform current features from the coil current waveform diagram to provide direct parameters for subsequent monitoring and life prediction of the DC contactor.

[0029] Specifically, waveform current characteristics include characteristic parameters, vibration energy, and steady-state current deviation rate.

[0030] The characteristic parameter reflects the degree of sluggishness caused by wear of the main contact. With the ablation or mechanical jamming of the main contact, the extension of the release time of the main contact is usually greater than the extension of the pull-in time. Therefore, the larger the characteristic parameter, the more sluggish the response of the main contact when it is turned on and off, and the more severe the wear of the main contact. The method for extracting feature parameters is as follows: The maximum value of the coil current is identified from the coil current waveform and recorded as the current peak value. This peak value is then multiplied by a preset mutation coefficient to calculate the current mutation value. The preset mutation coefficient is used to determine the magnitude of change between the coil current at a given moment and the coil current at the previous moment. This magnitude of change serves as the basis for identifying when the main contacts complete their conduction and disconnection actions. The preset mutation coefficient is not a fixed absolute value. To adapt to the differences in operating current of different DC charging piles and ensure the algorithm's adaptability under both light and heavy load conditions, the preset mutation coefficient is adjustable. In this embodiment, the preset mutation coefficient is 10%. In the coil current waveform diagram, the coil current at the next moment is subtracted from the coil current at the previous moment to calculate the current change value. The phase in which the current change is positive is called the rising phase, and the phase in which the current change is negative is called the falling phase. Starting from the second moment, the moment when the current change value first changes from the rising phase to the falling phase and the absolute value of the current change value is greater than the current sudden change value is recorded as the moment of completion of conduction, and the duration between the moment the auxiliary contact is turned on and the moment of completion of conduction is recorded as the pull-in duration. After the conduction is completed, the moment when the current change value first changes from the falling phase to the rising phase and the current change value is greater than the current sudden change value is recorded as the disconnection completion moment, and the duration between the auxiliary contact disconnection moment and the disconnection completion moment is recorded as the release duration. The characteristic parameters are calculated by subtracting the release duration from the hold duration and comparing the result with the hold duration. The formula for calculating the characteristic parameters is: ; In the formula, For feature parameters, To release duration, This refers to the absorption time.

[0031] Vibration energy is an energy value that reflects the intensity of mechanical collision at the moment the main contact is engaged. When the surface of the main contact is uneven or the spring is fatigued, the high-frequency vibration energy during engagement will increase significantly, which can be used as an indicator of early wear failure of the main contact. The method for extracting vibrational energy is as follows: In the coil current waveform diagram, the coil current between the moment the auxiliary contact turns on and the moment the conduction is completed is recorded as the target current. The target current is subjected to DC bias removal and windowing processing to obtain the time-domain current. In this embodiment, during DC bias removal, the arithmetic mean of the target current is calculated, and then each target current is subtracted from the arithmetic mean so that the current signal can fluctuate around the zero axis. This is to eliminate the large current rise trend caused by the coil inductance and avoid the useful signal being overwhelmed by a huge DC component near 0Hz in the FFT spectrum. The windowing processing can be multiplied by a Hanning window or a Hamming window. This is to force the beginning and end of the data segment to be zero, solve the spectrum leakage problem caused by data truncation, and improve the amplitude accuracy of frequency domain analysis. Perform a fast Fourier transform on the time-domain current to obtain the amplitude, and then summarize the amplitudes of all frequencies to generate a spectrum array. Starting with a preset lower frequency limit and ending with a preset upper frequency limit, the frequencies in the spectrum array located between the preset lower and upper frequency limits are recorded as target frequencies. The vibration energy is calculated by summing the squares of the amplitudes of all target frequencies.

[0032] In this embodiment, the preset lower frequency limit and the preset upper frequency limit are used as the basis for filtering the amplitude of the target frequency participating in the vibration energy calculation. Essentially, it is a bandpass filter window used to accurately avoid the power frequency and current ramp interference at the bottom and cut off the power electronic switching noise at the top. For example, the preset lower frequency limit is 1kHz and the preset upper frequency limit is 5kHz.

[0033] The steady-state current deviation rate is a value that reflects whether the coil core is in place. If the core is not tightly attracted due to foreign objects or residual magnetism, the steady-state current will deviate from the rated value. The method for extracting the steady-state current deviation rate is as follows: In the coil current waveform diagram, the steady-state start time is obtained by extending the completion time of conduction backward by a preset impact duration, and the steady-state end time is obtained by pushing back the time of auxiliary contact disconnection backward by a preset impact duration. The time period between the steady-state start time and the steady-state end time is recorded as the steady-state period. The preset impact duration is used to eliminate the impact spike effect caused by the moment the main contact closes and the negative impact of the falling edge before power-off, ensuring that all coil currents can remain in a stable and smooth state during the steady-state period. The preset impact duration is usually the sampling interval of several consecutive coil currents. In this embodiment, the preset impact duration is 10ms. During the steady-state period, after removing the maximum and minimum values ​​of the coil current, the remaining coil currents are summed and averaged to calculate the real-time steady-state current. The rated steady-state current of the coil in the DC contactor is found by looking up the technical parameter table. The absolute value of the difference between the real-time steady-state current and the rated steady-state current is taken and compared with the rated steady-state current to calculate the steady-state current deviation rate. The formula for calculating the steady-state current deviation rate is: ; In the formula, The steady-state current deviation rate, For real-time steady-state current, This is the rated steady-state current.

[0034] By analyzing and extracting features from the coil current waveform, some features that monitor the operating status and predict the lifespan of the DC contactor can be extracted from the coil current waveform. This achieves the logic of "analyzing the changing trend from the graph and extracting potential features from the changing trend", thus achieving the effect of combining graphs and data.

[0035] The dynamic feature extraction module sets the prediction period and extracts the dynamic execution features of the DC contactor during the prediction period. The dynamic execution features include the resistance change rate and the ratio of action times consumed. During long-term service, the main contacts of a DC contactor will experience material wear and arc erosion due to frequent switching operations, resulting in a gradual increase in contact resistance. At the same time, each switching operation of the main contacts is the most direct indicator of the mechanical life consumption of the DC contactor. Therefore, it is necessary to collect dynamic execution characteristics that can reflect contact resistance and cumulative number of operations.

[0036] The prediction period is a time limit used to collect the dynamic execution characteristics of a DC contactor, ensuring that the dynamic execution characteristics can be collected within a reasonable and accurate time period. Specifically, since the change in the resistance of the main contact is a relatively slow physical process, too short an acquisition interval is not conducive to acquiring the range of change in the resistance of the main contact. Each conduction and disconnection operation of the main contact requires a certain amount of time, and the acquisition of a large number of cumulative actions depends on a certain time span. Furthermore, the duration of the prediction cycle also needs to take into account the maintenance and continuous operation of the actual DC charging pile. Therefore, when setting the prediction cycle, the preset cycle duration is at least 12 hours. In this embodiment, the prediction period is 24 hours.

[0037] Dynamic execution characteristics include resistance change rate and action consumption ratio.

[0038] The resistance change rate refers to the magnitude of the change in contact resistance of the main contacts of a DC contactor within a predicted cycle. The resistance change rate can reflect the degree of oxidation, ablation, or contamination on the surface of the main contacts. The method for extracting the rate of change of resistance is as follows: A1: Periodically check the status signal of the auxiliary contact based on the completion of one prediction cycle; A2: If the status signal of the auxiliary contact is a conducting signal, the main contact is in a reliable closed conducting state, then execute A3-A5; if the status signal of the auxiliary contact is a closed signal, the main contact is in an unreliable released closed state, then repeat A1-A2. A3: Measure the real-time voltage of the circuit where the main contact is located, record it as the terminal voltage, and initialize the DC test current (the DC test current is much smaller than the rated operating current of the circuit where the main contact is located, and will not cause additional temperature rise or damage to the main contact; for example, the DC test current is 1A). A4: A constant current source is used to introduce a DC test current into the circuit where the main contacts of the DC contactor are located, and a differential amplifier is used to measure the voltage across the two ends of the circuit where the DC test current flows through the main contacts, which is recorded as the test voltage. A5: Calculate the resistance change rate by subtracting the terminal voltage from the test voltage and comparing it with the DC test current; The formula for calculating the rate of change of resistance is: ; In the formula, The rate of change of resistance, Terminal voltage, For testing voltage, This is the DC test current.

[0039] The number of actuations consumption ratio is a data reflecting the cumulative mechanical fatigue damage during the continuous engagement and disengagement of the main contacts. Even if all electrical parameters are normal, the closer the number of actuations is to the rated number, the mechanical structure is at risk of metal fatigue failure. In this embodiment, when extracting the action consumption ratio, within a prediction period, a valid action is defined as the DC contactor completing one "coil energization - auxiliary contact conduction signal - coil de-energization - auxiliary contact disconnection signal" sequence. The number of valid actions of the DC contactor is counted and recorded as the real-time action count. The rated electrical life count of the DC contactor is retrieved from the technical parameter table, and the real-time action count is compared with the rated electrical life count to calculate the action consumption ratio. The formula for calculating the action number consumption ratio is: ; In the formula, The ratio of action counts to total actions consumed. For real-time action count, The rated electrical life cycles.

[0040] The health score early warning module imports waveform current characteristics and dynamic execution characteristics into the health status scoring model, calculates the health status score, determines the early warning level based on the health status score, and determines whether to enter the life prediction mode. The health status scoring model is a weighted scoring model based on multi-feature fusion. This health status scoring model can comprehensively and weightedly evaluate waveform current characteristics and dynamic execution characteristics, and give a specific score that reflects the true health status of the DC contactor at the current moment. It can overcome the limitations of evaluating health status with a single feature.

[0041] The health status score is a specific score reflecting the health status of the main contacts of a DC contactor at a given moment after mechanical wear and metal fatigue. Different health status scores correspond to different health usage states of the main contacts. The higher the health status score, the less mechanical wear of the main contacts and the better the health usage state; conversely, the lower the score, the worse the health usage state. The calculation method for the health status score is as follows: After assigning corresponding proportional coefficients to the characteristic parameters, vibration energy, steady-state current deviation rate, resistance change rate, and action number consumption ratio in sequence, the data are imported into the health status scoring model to calculate the health status score. The expression for the health status scoring model is: ; In the formula, Rate your health status. Vibrational energy, , , , , These are the proportional coefficients for characteristic parameters, vibration energy, steady-state current deviation rate, resistance change rate, and the ratio of action frequency consumption, respectively. , , , , Both are greater than 0 and less than 1, and , , , , The sum of these parameters is 1; all the above parameters are dimensionless pure numbers, eliminating the influence of different dimensions.

[0042] For example, It is 0.3. It is 0.15. It is 0.2. It is 0.25. It is 0.1.

[0043] The warning level is a specific level determined by the health status score to provide an early warning on the current health status of the main contacts of the DC contactor. It can serve as a numerical basis for judging whether the DC charging pile will have abnormal phenomena and provide necessary theoretical support for the charging control platform. The warning levels include the recommended inspection level, the planned replacement level, and the immediate discontinuation level; the health status scores corresponding to the recommended inspection level, the planned replacement level, and the immediate discontinuation level decrease in that order.

[0044] The method for determining the warning level is as follows: The health status score is compared with the preset first warning score threshold and the second warning score threshold respectively, and the first warning score threshold is greater than the second warning score threshold. When the health status score is greater than the first warning score threshold, it indicates that the main contact wear of the DC contactor is relatively mild. At this time, the health status of the DC contactor is good, and the warning level is determined to be the recommended inspection level. When the health status score is less than or equal to the first warning score threshold and the health status score is greater than the second warning score threshold, it indicates that the main contact wear of the DC contactor is moderate. At this time, the health status of the DC contactor is generally good, and the warning level is determined to be the planned replacement level. When the health status score is less than or equal to the second warning score threshold, it indicates that the main contacts of the DC contactor are severely worn. In this case, the health status of the DC contactor is poor, and the warning level is set to the immediate shutdown level.

[0045] The first and second early warning scoring thresholds refer to the critical values ​​of the health status scores corresponding to the warning levels of recommended inspection, planned replacement, and immediate discontinuation, respectively, thus providing precise numerical basis for determining different warning levels. Specifically, the first and second early warning scoring thresholds are obtained by averaging the critical values ​​of health status scores for the recommended inspection and planned replacement levels, as well as the critical values ​​of health status scores for the planned replacement and immediate discontinuation levels, collected from a large number of historical data. For example, the first early warning scoring threshold is 80, and the second early warning scoring threshold is 65.

[0046] The life prediction mode is a working mode used to predict the number of safe service life cycles of the DC contactor's engagement and disengagement operations. It can provide guidance and suggestions on the remaining service life cycles of the DC contactor to the charging control platform, thereby helping operation and maintenance personnel to replace the DC contactors of DC charging piles in advance and avoiding the lag problem caused by replacing the DC contactor after it fails. Specifically, when determining whether to enter the life prediction mode, it is necessary to consider whether the DC contactor can continue to be used. Therefore, when the warning level of the DC contactor is the recommended inspection level or the planned replacement level, the DC contactor can still be used, and it is determined to enter the life prediction mode; when the warning level of the DC contactor is the immediate shutdown level, the DC contactor cannot continue to be used, and it is determined not to enter the life prediction mode.

[0047] The lifespan degradation prediction module, in lifespan prediction mode, calculates the predicted remaining lifespan of the DC contactor using a lifespan degradation model, and determines whether to issue a replacement warning based on the predicted remaining lifespan and the warning level. In the life prediction mode, the remaining safe service life of the DC contactor from the current moment needs to be calculated using the life decay model, so as to give the predicted number of times the DC contactor can be safely used for engagement and disengagement operations.

[0048] The life decay model and the health status scoring model are essentially the same. Both are weighted scoring models based on multi-feature fusion, which can provide a calculation basis for predicting the remaining life of DC contactors. Specifically, the expression for the lifetime decay model is: ; In the formula, To predict remaining lifespan, Based on the attenuation coefficient, This is the dynamic performance degradation coefficient. The static performance degradation coefficient is used. When a DC contactor performs an opening and closing action, regardless of the operating conditions, it will generate irreversible mechanical wear and electrical ablation. This loss is cumulative. Moreover, the above parameters are all dimensionless pure numbers to eliminate the influence of different dimensions. In this embodiment, the basic attenuation coefficient, dynamic performance attenuation coefficient, and static performance attenuation coefficient are all obtained by fitting a large amount of life test data of the same model of DC contactor under standard operating conditions; for example, the basic attenuation coefficient is 0.0005, the dynamic performance attenuation coefficient is 0.02, and the static performance attenuation coefficient is 0.15.

[0049] The replacement early warning is a notification message that indicates whether or not to replace the DC contactor corresponding to the predicted remaining lifespan. This allows the charging control platform to send replacement information to the operation and maintenance personnel in advance, thereby achieving the effect of replacing the DC contactor in advance and avoiding the lag caused by replacing it after the DC contactor has failed at the end of its service life.

[0050] When determining whether to issue a replacement warning, it is necessary to combine the two different dimensions of predicted remaining lifespan and warning level to ensure the accuracy and rationality of the judgment result. Specifically, the method for determining whether to issue a replacement warning is as follows: The predicted remaining life is compared with a preset remaining life threshold. The preset remaining life threshold is the maximum value of the predicted remaining life corresponding to the issuance of a replacement warning, which can provide a suitable numerical basis for the early replacement of DC contactors. The preset remaining life threshold is obtained by collecting the average value of the maximum predicted remaining life corresponding to a large number of historical replacement warnings. For example, the preset remaining life threshold is 1000. When the predicted remaining life is greater than or equal to the remaining life threshold, it indicates that the DC contactor has performed a relatively large number of engagement and disengagement actions at the current moment, and therefore it is determined that no replacement warning will be issued. When the predicted remaining life is less than the remaining life threshold, it indicates that the DC contactor has a relatively small number of times it performs the engagement and disengagement actions at the current moment, and a replacement warning is issued. When the warning level of a DC contactor is the immediate shutdown level, the DC contactor cannot continue to be used, and a replacement warning is issued.

[0051] In this embodiment, after issuing a replacement warning, the charging control platform will send corresponding information to the operation and maintenance personnel of the DC charging pile, prompting them to replace the DC contactor of the DC charging pile in advance and in real time. This transforms the periodic preventive maintenance strategy of the DC charging pile into an on-demand maintenance strategy based on precise condition monitoring, thereby improving the operation and maintenance efficiency of the DC charging pile.

[0052] Example 2: Please refer to Figure 3 As shown, parts not described in detail in this embodiment are described in Embodiment 1. A method for monitoring the condition and predicting the lifespan of a DC contactor in a DC charging pile is provided and applied to a charging control platform. It is implemented based on a system for monitoring the condition and predicting the lifespan of a DC contactor in a DC charging pile, and includes: SS1: Set the sampling frequency and monitoring period, collect the coil current and status signal of the DC contactor during the monitoring period, and plot the coil current waveform with the coil current as the vertical axis and time as the horizontal axis. SS2: Extract waveform current features from the coil current waveform diagram. The waveform current features include characteristic parameters, vibration energy, and steady-state current deviation rate. SS3: Set the prediction period and extract the dynamic execution characteristics of the DC contactor during the prediction period. The dynamic execution characteristics include the resistance change rate and the ratio of action times consumed. SS4: Import waveform current characteristics and dynamic execution characteristics into the health status scoring model, calculate the health status score, determine the warning level based on the health status score, and determine whether to enter the life prediction mode. SS5: In life prediction mode, the predicted remaining life of the DC contactor is calculated using the life decay model, and a replacement warning is issued based on the predicted remaining life and the warning level.

[0053] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention 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 the present invention should be included within the scope of protection of the present invention.

Claims

1. A DC charging pile DC contactor condition monitoring and life prediction system, applied to a charging control platform, characterized in that, include: The feature graph drawing module is used to set the sampling frequency and monitoring period, collect the coil current and status signals of the DC contactor during the monitoring period. The status signals include conduction signals and disconnection signals. The coil current waveform is drawn with the coil current as the vertical axis and time as the horizontal axis. The waveform feature extraction module is used to extract waveform current features from the coil current waveform diagram. The waveform current features include feature parameters, vibration energy, and steady-state current deviation rate. Subtract the hold-in time from the release time, then divide the difference by the hold-in time to calculate the characteristic parameters. Find the rated steady-state current of the coil in the DC contactor, take the absolute value of the difference between the real-time steady-state current and the rated steady-state current, and divide it by the rated steady-state current to calculate the steady-state current deviation rate. The dynamic feature extraction module is used to set the prediction period and extract the dynamic execution features of the DC contactor during the prediction period. The dynamic execution features include the resistance change rate and the ratio of action times consumed. The health score early warning module is used to import waveform current characteristics and dynamic execution characteristics into the health status scoring model, calculate the health status score, determine the early warning level based on the health status score, and determine whether to enter the life prediction mode. The lifespan degradation prediction module is used to calculate the predicted remaining lifespan of the DC contactor using a lifespan degradation model in lifespan prediction mode, and to determine whether to issue a replacement warning based on the predicted remaining lifespan and the warning level.

2. The DC charging pile DC contactor condition monitoring and life prediction system according to claim 1, characterized in that, The method for drawing the coil current waveform is as follows: Arrange the currents of coil A sequentially according to the order of data acquisition to generate a current sequence; Plot the A coil currents in the current sequence as current curves with time as the horizontal axis and coil current as the vertical axis. The moment when the state signal is on is recorded as the moment when the auxiliary contact is on, and the moment when the state signal is off is recorded as the moment when the auxiliary contact is off. Mark the points where the auxiliary contact is on and off on the current curve, and draw the coil current waveform.

3. The DC charging pile DC contactor condition monitoring and life prediction system according to claim 2, characterized in that, The method for extracting feature parameters is as follows: Identify the maximum value of the coil current from the coil current waveform diagram, record it as the current peak value, and multiply the current peak value by a preset mutation coefficient to calculate the current mutation value; In the coil current waveform diagram, the coil current at the next moment is subtracted from the coil current at the previous moment to calculate the current change value. The stage with a positive current change value is recorded as the rising stage, and the stage with a negative current change value is recorded as the falling stage. Starting from the second moment, the moment when the current change value first changes from the rising phase to the falling phase and the absolute value of the current change value is greater than the current sudden change value is recorded as the moment of completion of conduction, and the duration between the moment the auxiliary contact is turned on and the moment of completion of conduction is recorded as the pull-in duration. After the conduction is completed, the moment when the current change value first changes from the falling phase to the rising phase and the current change value is greater than the current sudden change value is recorded as the disconnection completion moment, and the time between the auxiliary contact disconnection moment and the disconnection completion moment is recorded as the release time.

4. The DC charging pile DC contactor condition monitoring and life prediction system according to claim 3, characterized in that, The method for extracting vibrational energy is as follows: In the coil current waveform diagram, the coil current located between the moment the auxiliary contact turns on and the moment the conduction is completed is recorded as the target current. The target current is de-DC biased and windowed to obtain the time-domain current. Perform a fast Fourier transform on the time-domain current to obtain the amplitude, and then summarize the amplitudes of all frequencies to generate a spectrum array. Starting with a preset lower frequency limit and ending with a preset upper frequency limit, the frequencies in the spectrum array located between the preset lower and upper frequency limits are recorded as target frequencies. The vibration energy is calculated by summing the squares of the amplitudes of all target frequencies.

5. The DC charging pile DC contactor condition monitoring and life prediction system according to claim 4, characterized in that, The method for extracting the steady-state current deviation rate is as follows: In the coil current waveform diagram, the steady-state start time is obtained by extending the completion time of conduction backward by a preset impact time, and the steady-state end time is obtained by pushing back the time of auxiliary contact disconnection backward by a preset impact time. The time period between the steady-state start time and the steady-state end time is recorded as the steady-state time period. During the steady-state period, after removing the maximum and minimum values ​​of the coil current, the remaining coil currents are summed and averaged to calculate the real-time steady-state current.

6. The DC charging pile DC contactor condition monitoring and life prediction system according to claim 5, characterized in that, The method for extracting the rate of change of resistance is as follows: A1: Periodically check the status signal of the auxiliary contact based on the completion of one prediction cycle; A2: If the status signal of the auxiliary contact is a conducting signal, execute A3-A5; if the status signal of the auxiliary contact is a disconnected signal, repeat A1-A2. A3: Measure the real-time voltage of the circuit where the main contact is located, record it as the terminal voltage, and initialize the DC test current; A4: A constant current source is used to introduce a DC test current into the circuit where the main contacts of the DC contactor are located, and a differential amplifier is used to measure the voltage across the two ends of the circuit where the DC test current flows through the main contacts, which is recorded as the test voltage. A5: Subtract the test voltage from the terminal voltage, divide the difference by the DC test current, and calculate the resistance change rate.

7. The DC charging pile DC contactor condition monitoring and life prediction system according to claim 6, characterized in that, When extracting the action consumption ratio, within a prediction period, a valid action is defined as the DC contactor completing one "coil energization - auxiliary contact conduction signal - coil de-energization - auxiliary contact disconnection signal" sequence. The number of valid actions of the DC contactor is counted and recorded as the real-time action count. The rated electrical life of the DC contactor is then retrieved, and the real-time action count is divided by the rated electrical life count to calculate the action consumption ratio.

8. The DC charging pile DC contactor condition monitoring and life prediction system according to claim 7, characterized in that, The warning levels include the recommended inspection level, the planned replacement level, and the immediate deactivation level; The method for determining whether to enter lifetime prediction mode is as follows: When the health status score is greater than the first warning score threshold, the warning level will be set to the recommended inspection level, and the system will be entered into life prediction mode. When the health status score is less than or equal to the first warning score threshold and the health status score is greater than the second warning score threshold, the warning level will be set to the planned replacement level, and the system will be determined to enter the life prediction mode. When the health status score is less than or equal to the second warning score threshold, the warning level will be set to the immediate shutdown level, and the life prediction mode will not be entered.

9. The DC charging pile DC contactor condition monitoring and life prediction system according to claim 8, characterized in that, The method for determining whether to issue a replacement warning is as follows: When the predicted remaining lifetime is greater than or equal to the remaining lifetime threshold, it is determined that no replacement warning will be issued. When the predicted remaining lifetime is less than the remaining lifetime threshold, a replacement warning is issued. When the warning level of the DC contactor is the immediate shutdown level, a replacement warning prompt is issued.

10. A method for monitoring the condition and predicting the lifespan of a DC contactor in a DC charging pile, applied to a charging control platform, implemented based on the DC contactor condition monitoring and lifespan prediction system for DC charging piles as described in any one of claims 1-9, characterized in that... include: SS1: Set the sampling frequency and monitoring period, collect the coil current and status signal of the DC contactor during the monitoring period, and plot the coil current waveform with the coil current as the vertical axis and time as the horizontal axis. SS2: Extract waveform current features from the coil current waveform diagram. The waveform current features include characteristic parameters, vibration energy, and steady-state current deviation rate. SS3: Set the prediction period and extract the dynamic execution characteristics of the DC contactor during the prediction period. The dynamic execution characteristics include the resistance change rate and the ratio of action times consumed. SS4: Import waveform current characteristics and dynamic execution characteristics into the health status scoring model, calculate the health status score, determine the warning level based on the health status score, and determine whether to enter the life prediction mode. SS5: In life prediction mode, the predicted remaining life of the DC contactor is calculated using the life decay model, and a replacement warning is issued based on the predicted remaining life and the warning level.

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