A full-condition equivalent test system and method for a capacitor for direct current transmission

Abstract

The present application relates to the technical field of capacitor testing, and particularly relates to a full working condition equivalent testing system and method for a capacitor used in direct current transmission. The method comprises the following steps: applying a single frequency AC component on the capacitor to obtain a single frequency loss baseline inherent to the capacitor under single frequency excitation; determining harmonic coupling loss according to the single frequency loss baseline; screening out strong interactive harmonic pairs according to the harmonic coupling loss, and re-measuring additional loss under the conditions of respectively applying controlled thermal gradient disturbance and mechanical resonance excitation to calibrate thermal field gain factor and mechanical vibration gain factor; and evaluating total loss under full working condition based on the thermal field gain factor and the mechanical vibration gain factor to obtain full working condition testing data. The present application realizes accurate evaluation and contribution decomposition of the loss characteristics of the capacitor under multiple physical fields and full working conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of capacitor testing, in particular to a full working condition equivalent test system and method for capacitors used in direct current transmission. BACKGROUND

[0002] In actual power grid operation, capacitors used in direct current transmission not only bear direct current voltage, but also need to face various harmonic voltages and currents generated by power electronic devices and nonlinear loads. These harmonic components, through nonlinear interaction, cause additional losses in the capacitor, form local hot spots, accelerate the aging of insulation materials, and even cause equipment failure and system accidents in severe cases. However, the existing capacitor test methods mainly have the following technical defects: most of the traditional capacitor test systems use single frequency or simple superposition test methods, which cannot truly simulate the complex harmonic environment existing in the actual power grid. These test systems can usually only provide fundamental wave or a few harmonic components, and the amplitude and phase of each harmonic component cannot be accurately controlled, resulting in significant differences between the test results and the performance of the capacitor under actual working conditions. In fact, under complex harmonic environment, there is obvious nonlinear interaction effect between different frequency components. This effect causes a significant proportion of additional losses in total losses. The existing analysis methods cannot decompose and quantify this nonlinear interaction, resulting in incomplete and inaccurate evaluation of capacitor loss characteristics. SUMMARY

[0003] Based on this, the present application provides a full working condition equivalent test system and method for capacitors used in direct current transmission to solve at least one of the above technical problems.

[0004] To achieve the above purpose, a full working condition equivalent test method for capacitors used in direct current transmission includes the following steps:

[0005] Step S1: Apply a single frequency alternating current component to the capacitor, obtain the inherent loss tangent value of the capacitor under single frequency excitation, and generate a single frequency loss baseline;

[0006] Step S2: Select a harmonic combination according to the single frequency loss baseline; difference operation is performed between the theoretical superposition loss in the single frequency loss baseline and the actual total power loss of the test capacitor when the harmonic combination is injected synchronously, and the positive part is determined as the harmonic coupling loss;

[0007] Step S3: According to the harmonic coupling loss, strong interactive harmonic pairs are selected, and they are used as excitation sources to re-measure the additional loss under the conditions of applying controlled thermal gradient disturbance and mechanical resonance excitation to calibrate the thermal field gain factor and the mechanical vibration gain factor;

[0008] Step S4: based on the thermal field gain factor and the mechanical vibration gain factor, the total loss of the full working condition test is evaluated, and compared with the preset standard loss value, if the loss deviation value is within the preset range, the test result is locked and packaged into the full working condition test data, if the loss deviation value is not within the preset range, the test calibration request is executed, and the subsequent test process is automatically suspended, and all excitation outputs are immediately cut off.

[0009] The application also provides a capacitor full working condition equivalent test system for DC power transmission, which executes the capacitor full working condition equivalent test method for DC power transmission as described above, and comprises:

[0010] The inherent loss acquisition module is used for applying a single frequency AC component to the capacitor, obtaining the inherent loss tangent value of the capacitor under single frequency excitation, and generating a single frequency loss baseline.

[0011] The harmonic coupling analysis module is used for selecting a harmonic combination according to the single frequency loss baseline; and performing difference operation on the theoretical superimposed loss in the single frequency loss baseline and the actual total power loss of the tested capacitor when the harmonic combination is synchronously injected, and determining the positive part of the difference operation as the harmonic coupling loss.

[0012] The multi-working condition test module is used for screening strong interactive harmonics according to the harmonic coupling loss, and taking the strong interactive harmonics as excitation sources to re-measure the additional loss under the conditions of applying controlled thermal gradient disturbance and mechanical resonance excitation, so as to calibrate the thermal field gain factor and the mechanical vibration gain factor.

[0013] The full working condition verification control module is used for evaluating the total loss of the full working condition test based on the thermal field gain factor and the mechanical vibration gain factor, and comparing the total loss with the preset standard loss value, if the loss deviation value is within the preset range, the test result is locked and packaged into the full working condition test data, if the loss deviation value is not within the preset range, the test calibration request is executed, and the subsequent test process is automatically suspended, and all excitation outputs are cut off.

[0014] The application has the following beneficial effects:

[0015] On the one hand, the single frequency loss baseline is generated by the variable step frequency sweeping method, and on this basis, the harmonic coupling loss is accurately calculated by applying multi-frequency synchronous excitation, the application can effectively reveal and quantify the ignored nonlinear interaction between harmonics in the traditional test method; further, by performing difference operation on the measured coupling loss and the theoretical superimposed loss, the additional loss caused by the nonlinear characteristics of the medium can be accurately stripped, avoiding the evaluation error caused by simple linear superposition of single frequency test results, and significantly improving the accuracy of capacitor loss evaluation in complex power grid harmonic environment.

[0016] On the other hand, the application innovatively introduces controlled thermal gradient disturbance and mechanical resonance excitation, and derives thermal field gain factor and mechanical vibration gain factor respectively, so as to decouple and quantify the coupling effect of electric-thermal-mechanical multi-physical field; wherein, through regional temperature control and multi-axial vibration excitation, the complex stress of the capacitor due to uneven heat dissipation and external vibration in actual operation can be truly simulated, the limitation that the traditional test method can only be tested in a single and ideal environment is solved, and the test result can more comprehensively reflect the real performance degradation law of the capacitor under full working conditions.

[0017] On the other hand, the application obtains the total loss under full working conditions by comprehensively evaluating the basic loss, interaction loss and coupling amplification loss, and compares it with the standard value to form a closed-loop verification and evaluation mechanism. The application captures the key performance bottleneck of the capacitor under actual working conditions by decomposing the total loss into basic loss, interaction loss and coupling amplification loss, so as to more accurately evaluate the operation margin and service life of the capacitor. In addition, after evaluating the total loss under full working conditions, accurate data support can be provided for the design optimization, state maintenance and power grid harmonic control of the capacitor, effectively guaranteeing the long-term safe and stable operation of the entire direct current transmission system. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The figure is a schematic flow chart of the steps of the equivalent test method for the capacitor for direct current transmission according to the application.

[0019] The implementation, functional features and advantages of the application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0020] The technical method of the application will be described clearly and completely below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0021] In addition, the accompanying drawings are only schematic diagrams of the application, and are not necessarily drawn to scale. The same reference signs in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some block diagrams shown in the drawings are functional entities, which do not necessarily correspond to physically or logically independent entities. The functional entities can be implemented in the form of software, or in one or more hardware modules or integrated circuits, or in different network and / or processor methods and / or microcontroller methods.

[0022] It should be understood that, although terms such as "first" and "second" can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to differentiate one element from another. For example, without departing from the scope of the example embodiments, a first element can be termed a second element, and similarly, a second element can be termed a first element. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0023] To achieve the above object, please refer to Figure 1 The application provides a full-condition equivalent test method for capacitors for direct current transmission, comprising the following steps:

[0024] Step S1: Apply a single-frequency AC component to the capacitor to obtain the inherent loss tangent value of the capacitor under single-frequency excitation, and generate a single-frequency loss baseline;

[0025] In the embodiment of the application, before the test starts, first, the test environment is set to a reference state, that is, the temperature of each part of the capacitor shell is stabilized at 40.0°C by the regional temperature control unit, and it is ensured that the piezoelectric actuator array is in a silent and vibration-free state. On this basis, a rated DC bias voltage is applied to the capacitor by a programmable AC / DC power supply, and a small AC signal component of a specific single frequency is superimposed. The preset harmonic frequency range (for example, 3 to 50 harmonics) is scanned point by point, and after stable operation at each frequency point, the loss tangent value corresponding to the frequency is collected by a high-precision loss measuring bridge. All collected "frequency-loss tangent value" data pairs are finally integrated into a lookup table, that is, a single-frequency loss baseline.

[0026] In one implementation manner of the embodiment of the application, it is assumed that the rated DC voltage of the capacitor is 800 kV. First, 800 kV DC bias is applied, and then a 150 Hz (3rd harmonic) AC component with an amplitude of 1% of the rated voltage is superimposed. After the working condition is stabilized for 3 minutes, the loss tangent value at this frequency is collected as 0.00012. Subsequently, the 150 Hz signal is removed, and a 250 Hz (5th harmonic) AC component is applied. After stabilization, the loss tangent value is collected as 0.00018. In this way, the test of all concerned frequency points is completed, and the generated single-frequency loss baseline data example is {(150 Hz, 0.00012), (250 Hz, 0.00018), (350 Hz, 0.00025),...}.

[0027] Step S2: selecting a harmonic combination according to the single-frequency loss baseline; performing difference operation on the theoretical superimposed loss in the single-frequency loss baseline and the actual total power loss of the capacitor obtained when the harmonic combination is synchronously injected, and determining the positive part as the harmonic coupling loss;

[0028] In the embodiment of the present application, a pair of harmonic frequencies to be studied, i.e., a harmonic combination, is selected from the single-frequency loss baseline. The respective basic loss values corresponding to the pair of frequencies are found from the single-frequency loss baseline, and the two values are added to obtain the theoretical superimposed loss without considering the interaction. Subsequently, the power supply is controlled to simultaneously superimpose the alternating components of the pair of harmonic frequencies on the same DC bias, and the actual total power loss of the capacitor at this time is measured. The actual total power loss is subtracted from the theoretical superimposed loss, and the difference is determined as the harmonic coupling loss caused by the interaction between the harmonics if the difference is positive.

[0029] In one implementation of the embodiment of the present application, the harmonic combination (150 Hz, 250 Hz) is selected. It is assumed that according to the single-frequency loss baseline and the capacitor parameters, the power loss under the excitation of the single frequency of 150 Hz is calculated as 1.2 W, and the power loss under the excitation of the single frequency of 250 Hz is calculated as 1.8 W. Then, the theoretical superimposed loss is:

[0030] 1.2 W+1.8 W=3.0 W;

[0031] Subsequently, the alternating components of 150 Hz and 250 Hz are synchronously injected into the capacitor, and the actual total power loss of 3.5 W is measured. Then, the harmonic coupling loss is calculated as follows:

[0032] Harmonic coupling loss=3.5 W-3.0 W=0.5 W;

[0033] Therefore, the interaction between the harmonics of 150 Hz and 250 Hz produces an additional loss of 0.5 W.

[0034] Step S3: screening out strong interaction harmonic pairs according to the harmonic coupling loss, and using the strong interaction harmonic pairs as excitation sources to re-measure the additional loss under the conditions of respectively applying a controlled thermal gradient disturbance and a mechanical resonance excitation to calibrate the thermal field gain factor and the mechanical vibration gain factor;

[0035] In the embodiment of the present application, the harmonic coupling loss calculated in the previous step is compared with the theoretical superposition loss. If the harmonic coupling loss is greater than a certain percentage (for example, 15%) of the theoretical superposition loss, the harmonic pair is determined to be a strong interactive harmonic pair. One strong interactive harmonic pair is selected as a fixed electrical excitation source, and its harmonic coupling loss in the reference environment is recorded as the interactive reference loss. First, a controlled thermal gradient disturbance (for example, top hot and bottom cold) is applied, and the new additional loss is measured under the condition of the thermal disturbance, which is recorded as the thermal disturbance additional loss. The ratio of the thermal disturbance additional loss to the interactive reference loss is the thermal field gain factor. Then, the reference temperature is restored, a controlled mechanical resonance excitation is applied, and the additional loss is measured, and the mechanical vibration gain factor is calculated.

[0036] In one implementation of the embodiment of the present application, for the harmonic combination (150 Hz, 250 Hz), the harmonic coupling loss is 0.5 W, and the theoretical superposition loss is 3.0 W. Because 0.5 W>(3.0 W*15%), that is, 0.5 W>0.45 W, it is determined to be a strong interactive harmonic pair. The harmonic coupling loss of 0.5 W is the interactive reference loss.

[0037] 1. Thermal field calibration: The electrical excitation is applied, and a temperature difference of 20°C is generated at the top and bottom of the capacitor. The additional loss (thermal disturbance additional loss) is measured to be 0.8 W. The thermal field gain factor is: 0.8 W / 0.5 W=1.6.

[0038] 2. Mechanical vibration calibration: The reference temperature is restored, and mechanical vibration is applied by the piezoelectric actuator array. The additional loss (mechanical vibration additional loss) is measured to be 0.6 W. The mechanical vibration gain factor is: 0.6 W / 0.5 W=1.2.

[0039] Step S4: Based on the thermal field gain factor and the mechanical vibration gain factor, the total loss of the full working condition test is evaluated, and a loss deviation value is compared with a preset standard loss value. If the loss deviation value is within the preset range, the test result is locked and packaged into full working condition test data. If the loss deviation value is not within the preset range, a test calibration request is executed, and the subsequent test process is automatically suspended, and all excitation outputs are immediately cut off.

[0040] In the embodiment of the present application, a specific target full condition is first defined, including all harmonic components, thermal gradient and mechanical vibration conditions, and the predicted total loss under the target condition, i.e. the full condition test total loss, is calculated. The total loss is composed of three parts: the sum of all single-frequency losses (basic loss), the sum of all harmonic pairs of reference interaction losses (interaction loss), and the additional loss (coupling amplification loss) generated by the thermal field gain factor and the mechanical vibration gain factor amplifying the interaction loss. Subsequently, the full condition test total loss is compared with a preset standard loss value provided by the manufacturer or determined based on historical data, and a loss deviation value is calculated. If the deviation value is within the allowable range (for example, less than 5% of the standard value), the test is passed, and the analysis graph containing each loss component is packaged as full condition test data. If the deviation exceeds the range, it is determined that the current test needs to be calibrated, a test calibration request is triggered immediately, and the subsequent process is automatically suspended and all excitation outputs are cut off to ensure safety.

[0041] In one implementation of the embodiment of the present application, it is assumed that the target full condition contains (150Hz, 250Hz) harmonics, a 20°C temperature difference and 1g, 100Hz vibration.

[0042] The full condition test total loss is evaluated as follows:

[0043] The basic loss is 3.0W;

[0044] The interaction loss is 0.5W;

[0045] The coupling amplification loss is interaction loss x (thermal field gain factor-1) + interaction loss x (mechanical vibration gain factor-1) = 0.5W x (1.6-1) + 0.5W x (1.2-1) = 0.3W + 0.1W = 0.4W;

[0046] The full condition test total loss is 3.0W + 0.5W + 0.4W = 3.9W.

[0047] It is assumed that the preset standard loss value of the capacitor is 4.0W. The loss deviation value is |3.9W-4.0W|=0.1W.

[0048] The preset allowable range is 5% of the standard value, i.e. 4.0W x 5%=0.2W.

[0049] Since 0.1W is within the preset range (±0.2W), it is determined that the test is passed, the current test result is locked, and is packaged as full condition test data.

[0050] It should be noted that if the deviation exceeds the range, it is determined that the current test needs to be calibrated, a test calibration request is triggered immediately, and the subsequent process is automatically suspended and all excitation outputs are cut off to ensure safety.

[0051] When the prediction deviation is not less than 5% of the total loss, a calibration request flag is generated and written into the tail of the current test cycle;

[0052] After the calibration request flag takes effect, a parameter rollback action is triggered, the test process returns to step S1, and the single-frequency loss baseline is re-generated at half of the original frequency interval;

[0053] After the parameter rollback action is completed, the calibration request flag and the current prediction deviation are packaged into a calibration log frame and pressed into the system maintenance queue in order;

[0054] After the system maintenance queue is filled, the subsequent test process is suspended, and all excitation outputs are cut off.

[0055] Preferably, step S1 comprises the following steps:

[0056] Step S11: An AC component with an initial frequency of 50 Hz and an amplitude of 1% of the rated voltage is superimposed on the preset rated DC bias voltage;

[0057] Step S12: The AC component is applied to the capacitor, and the first loss tangent value is collected and recorded as the first frequency loss point;

[0058] Step S13: The 50 Hz is used as the step increment frequency of the AC component to replace the frequency of the AC component in turn and perform frequency point scanning, taking the first frequency loss point as the reference; wherein, after each replacement, the transient forced air cooling is applied to the lead terminals of the capacitor;

[0059] Step S14: The loss tangent value is collected at each frequency point, and the loss change rate is calculated by subtracting the loss value of the previous frequency point;

[0060] Step S15: The loss change rate is compared with the preset response threshold; if it is less than the preset response threshold, the frequency point is marked as a flat frequency point; if it is greater than the preset response threshold, the frequency point is marked as a sensitive frequency point, and the frequency scanning step is reduced to 5 Hz;

[0061] Step S16: All flat frequency points and sensitive frequency points and their corresponding loss tangent values are connected in frequency order to draw a single-frequency loss baseline.

[0062] In one implementation manner of the embodiment of the application, it is assumed that the rated DC voltage of the capacitor is 800 kV. The power supply output is set to a DC voltage of 800 kV, and at the same time, a sinusoidal AC voltage with a frequency of 50 Hz and a peak-to-peak value of 16 kV (i.e., an amplitude of 8 kV, which is 1% of 800 kV) is superimposed.

[0063] In one implementation of the embodiment, after applying the voltage containing 50Hz AC component and stabilizing for 3 minutes, the loss measurement bridge acquires and records the resulting tan delta value as 0.00008. This data point (50Hz, 0.00008) is stored as the first frequency loss point.

[0064] In the embodiment, the frequency scan is automatically performed starting from the frequency of the first frequency loss point (50Hz) with an initial step size of 50Hz. After each frequency point measurement is completed, the power supply removes the AC component at the current frequency and replaces it with the AC component at the next frequency point (current frequency + 50Hz). In the gap of each frequency switching, the cooling unit located near the capacitor lead terminals is controlled to perform a short (e.g. 10 seconds) forced air cooling to quickly eliminate the local heat accumulation generated by the previous frequency point test, ensuring that the thermal initial conditions of each measurement are substantially consistent.

[0065] In one implementation of the embodiment, after the 50Hz point measurement is completed, the AC component is switched to 100Hz. During the switching process, the lead terminals are subjected to 10 seconds of forced air cooling. After the 100Hz point measurement is completed, it is switched to 150Hz and forced air cooling is performed again, and so on.

[0066] In one implementation of the embodiment, assuming that the loss value measured at 100Hz is 0.00010, and the loss value of the previous frequency point (50Hz) is 0.00008. Then the loss change rate at 100Hz is calculated as follows:

[0067] Loss change rate = (0.00010 - 0.00008) / 0.00008 = 0.25, i.e. 25%.

[0068] In one implementation of the embodiment, the preset response threshold is 20%. The loss change rate calculated at 100Hz is 25%, which is greater than 20%, so 100Hz is marked as a sensitive frequency point, and the next test frequency point is automatically set to 105Hz instead of the originally planned 150Hz.

[0069] It should be noted that the setting of the preset response threshold is determined according to the estimated loss peak region of the dielectric polarization relaxation time constant of the capacitor dielectric material, in order to improve the capture accuracy of the characteristic frequency.

[0070] In the embodiment of the present application, after the adaptive step scanning of the entire preset frequency range (e.g. up to 2500 Hz) is completed, all the marked flat frequency points and sensitive frequency points and their corresponding tan delta data are sorted in ascending order of frequency. Finally, these discrete data points are connected by a smooth curve to form an intuitive atlas, which is the final single-frequency loss baseline.

[0071] In one implementation of the embodiment of the present application, suppose the final data point sequence is {(50Hz, 0.00008), (100Hz, 0.00010), (105Hz, 0.00011), (110Hz, 0.00013),..., (150Hz, 0.00020),...}. These data points are plotted into a curve with frequency as the horizontal axis and tan delta as the vertical axis. The data point density around 100Hz is obviously higher than that in other areas, accurately depicting the sensitive area characteristics of the loss.

[0072] Preferably, step S2 comprises the following steps:

[0073] Step S21: At the beginning of the current test period, the first harmonic frequency and the second harmonic frequency are selected in turn based on the single-frequency loss baseline; wherein the first harmonic frequency is greater than the second harmonic frequency;

[0074] Step S22: The first harmonic frequency and the second harmonic frequency are taken as a harmonic combination;

[0075] Step S23: Obtain the tan delta of each single frequency corresponding to the harmonic combination, calculate the linear superposition equivalent loss, and obtain the theoretical superposition loss;

[0076] Step S24: In the current test period, control the power supply to superimpose the harmonic combination on the DC bias to inject two-frequency AC components into the capacitor, and measure the actual total power loss of the capacitor after the injection is stable;

[0077] Step S25: Perform a difference operation on the actual total power loss and the theoretical superposition loss, and the positive part of the result is determined as the harmonic coupling loss.

[0078] In the embodiment of the present application, when the test control system enters the current test period, an automatic harmonic pair traversal program is started. Based on all the frequency points recorded in the single-frequency loss baseline, the program generates harmonic frequency pairs that need to be tested according to the preset rules. To ensure the systematicness and non-repeatability of the traversal, the program selects a frequency as the first harmonic frequency (fi) in turn, and selects a frequency less than fi as the second harmonic frequency (fj) from the frequency points.

[0079] In one implementation of the embodiment of the present application, suppose the frequency points contained in the single-frequency loss baseline are {150 Hz, 250 Hz, 350 Hz,...}. At the beginning of a test cycle, the program first selects 350 Hz as the first harmonic frequency, and then selects 250 Hz and 150 Hz as the second harmonic frequencies in turn, thereby generating the frequency pairs to be tested (350 Hz, 250 Hz) and (350 Hz, 150 Hz). In the next cycle, the program selects 250 Hz as the first harmonic frequency, and selects 150 Hz as the second harmonic frequency, thereby generating the frequency pair to be tested (250 Hz, 150 Hz).

[0080] In one implementation of the embodiment of the present application, after 350 Hz and 250 Hz are selected, a harmonic combination is generated, and the data content of the harmonic combination is {f1: 350, f2: 250}. The combination is sent to the test sequence queue for execution.

[0081] In the embodiment of the present application, after the harmonic combination is received, the two frequency values in the combination are immediately used as indexes to query the single-frequency loss baseline data, and the loss tangent values of the two frequencies under the action of the single frequency are extracted respectively (tan(δ1) and tan(δ2)). and Subsequently, based on the known parameters such as the rated voltage (U_rated) and the capacitance (C) of the capacitor, the power loss (P1 and P2) of each frequency under the action of the single frequency is calculated respectively by using the formula Finally, the two power loss values are added to obtain the total loss under the assumption of no interaction, that is, the theoretical superposition loss.

[0082] In the embodiment of the present application, the two frequency values in the harmonic combination are sent to the programmable AC / DC power supply. While maintaining the rated DC bias voltage, the arbitrary waveform generator in the power supply accurately synthesizes a composite waveform containing the two frequency AC components, and applies the composite waveform to the capacitor. Similarly, a preset stabilization time (for example, 3 minutes) is waited to ensure that the capacitor reaches a new electro-thermal balance. After stabilization, a high-precision power analyzer or a loss measurement bridge performs a comprehensive measurement to directly obtain the total active power consumed by the capacitor under the dual-frequency excitation, and the value is recorded as the actual total power loss.

[0083] In one implementation of the embodiment of the present application, the data of the previous step is calculated as follows:

[0084] The actual total power loss is 5.0 W; the theoretical superposition loss is 4.3 W; and the harmonic coupling loss is 5.0 W-4.3 W=0.7 W.

[0085] The positive value of 0.7W is determined as the harmonic coupling loss generated by the harmonic combination of (350Hz, 250Hz), and is stored in association with the harmonic combination.

[0086] In another implementation of the embodiment of the application, two frequency values in the harmonic combination are taken as input, and the measured loss response is taken as output, to construct a double-frequency input response data pair.

[0087] Based on the Volterra series expansion method, the second-order Volterra kernel function representing the nonlinear interaction of the two frequency components is extracted from the double-frequency input response data pair, to generate a second-order interaction kernel function.

[0088] The second-order interaction kernel function is evaluated at the two frequencies in the harmonic combination, and the result is directly determined as the harmonic coupling loss.

[0089] Preferably, the calibration of the thermal field gain factor in step S3 includes:

[0090] When the harmonic coupling loss is greater than 15% of the theoretical superposition loss, the harmonic pair is determined as a strong interaction harmonic pair; otherwise, it is determined as a weak interaction harmonic pair, and the weak interaction harmonic pair is removed.

[0091] The strong interaction harmonic pair is taken as the excitation source electrical signal, and the frequency values of the harmonic pair are taken as the interaction reference loss.

[0092] A thermal gradient disturbance is applied in the capacitor shell area when the excitation source electrical signal is applied; wherein the thermal gradient disturbance sets the target temperature of the top of the capacitor to 70°C and the target temperature of the bottom to 50°C, and the heating power is monitored and adjusted in real time until the temperature difference between the top and the bottom is stabilized at 20°C±1°C.

[0093] The total power loss of the capacitor under thermal excitation is re-measured under the condition of maintaining the thermal gradient disturbance and the excitation source electrical signal.

[0094] The difference between the total power loss under thermal excitation and the corresponding theoretical superposition loss in the strong interaction harmonic pair is calculated to obtain the additional loss under thermal disturbance.

[0095] The ratio of the additional loss under thermal disturbance to the interaction reference loss is calculated to obtain the thermal field gain factor.

[0096] In one implementation of the embodiment, a threshold value of 15% is built into the logic. If the calculated harmonic coupling loss is greater than 15% of the theoretical superposition loss, the harmonic combination is marked as a strong interactive harmonic pair and is retained in the subsequent test sequence. Conversely, if it is less than or equal to 15%, it is marked as a weak interactive harmonic pair. For the harmonic combination (350Hz, 250Hz), the harmonic coupling loss is 0.7W and the theoretical superposition loss is 4.3W. Calculation: 4.3W x 15% = 0.645W. Since 0.7W > 0.645W, the combination is determined to be a strong interactive harmonic pair and is added to the thermal field gain factor calibration task queue.

[0097] In one implementation of the embodiment, a strong interactive harmonic pair is extracted from the task queue and its corresponding frequency values (e.g. 350Hz and 250Hz) are set as the fixed electrical excitation for subsequent tests, i.e. the excitation source electrical signal. For example, (350Hz, 250Hz) is selected as the excitation source electrical signal. At the same time, its interactive reference loss is locked at 0.7W. This value of 0.7W represents the additional loss purely due to electrical interaction and is the "zero point" for measuring the impact of subsequent physical field disturbances.

[0098] In the embodiment, while the excitation source electrical signal is continuously applied, the sub-region temperature control unit is started, which sends instructions to the heating / cooling modules at the top and bottom of the capacitor according to the pre-set thermal gradient disturbance scheme. Real-time temperature data is fed back by the multiple temperature sensors arranged at the top and bottom of the shell, forming a closed-loop PID control loop. The power of the top heating module and the bottom cooling module is continuously adjusted until the average temperature at the top stabilizes at 70°C ± 0.5°C and the average temperature at the bottom stabilizes at 50°C ± 0.5°C, thereby ensuring that the temperature difference between the two is accurately maintained within the target range of 20°C ± 1°C.

[0099] In another implementation of the embodiment, when the top temperature is monitored to be 68°C and the bottom temperature is 52°C. The PID controller will increase the PWM duty cycle of the top heating wire while reducing the drive current of the bottom Peltier cooling plate until the sensor readings reach the target values of 70°C and 50°C respectively and remain stable within ± 0.5°C.

[0100] In one implementation of the embodiment, when it is confirmed that the thermal gradient has stabilized and the excitation source electrical signal is still continuously applied, a new power loss measurement is triggered by the power analyzer. Assuming that under the stable temperature difference of 70°C at the top and 50°C at the bottom, the power analyzer measures the total power loss of the capacitor to be 5.4W, this value is recorded as the thermal excitation total power loss.

[0101] In one implementation of the embodiment of the application, the thermal agitation total power loss is 5.4 W, and the corresponding theoretical superposition loss is 4.3 W. Then the additional loss under thermal agitation is calculated as follows:

[0102] The additional loss under thermal agitation = 5.4 W - 4.3 W = 1.1 W.

[0103] In one implementation of the embodiment of the application, the additional loss under thermal agitation is 1.1 W, and the cross-reference loss is 0.7 W. Then the thermal field gain factor is calculated as follows:

[0104] Thermal field gain factor = 1.1 W / 0.7 W ≈ 1.57.

[0105] This result shows that the temperature difference of 20°C amplifies the cross additional loss of the harmonic (350 Hz, 250 Hz) by about 57%.

[0106] Preferably, applying the thermal gradient disturbance in the capacitor shell region further comprises:

[0107] setting a first temperature control time sequence for the upper region of the capacitor shell, with the target temperature fluctuating between 60°C and 80°C in a sinusoidal law at a frequency of 0.1 Hz;

[0108] setting a second temperature control time sequence for the lower region of the capacitor shell, with the target temperature fluctuating between 60°C and 40°C in an inverse sinusoidal law at a frequency of 0.1 Hz;

[0109] the phase difference between the first temperature control time sequence and the second temperature control time sequence is fixed at 180 degrees;

[0110] synchronously recording the temperature difference value and the corresponding thermal agitation total power loss at each control sampling point in the first temperature control time sequence and the second temperature control time sequence to form a dynamic loss sequence.

[0111] In the embodiment of the application, a dynamic target temperature instruction sequence, i.e., the first temperature control time sequence, is sent to the regional temperature control unit. The target temperature of the upper region of the capacitor shell is no longer a fixed value, but fluctuates in a sinusoidal law between 60°C and 80°C with 70°C as the center. The frequency of the sinusoidal fluctuation is set to 0.1 Hz, i.e., the period is 10 seconds.

[0112] In one implementation of the embodiment of the application, the target temperature of the first temperature control time sequence can be described by the following formula:

[0113] ;

[0114] wherein t is time (seconds), π is the ratio of the circumference of a circle to its diameter. In At 0s, the target temperature is 70°C; At t=2.5s, the target temperature reaches its peak of 80°C; at t=7.5s, it reaches its trough of 60°C.

[0115] In this embodiment of the invention, a second temperature control sequence is simultaneously set for the lower region of the housing, in conjunction with the temperature control timing of the upper region. This timing sequence instructs the target temperature of the lower region to vary sinusoidally between 40°C and 60°C, centered at 50°C, with a fluctuation frequency of 0.1Hz. Crucially, the phase of this timing sequence is set to be completely opposite to the first temperature control sequence.

[0116] In one implementation of this invention, the target temperature of the second temperature control sequence is... It can be described by the following formula:

[0117] ;

[0118] exist At 2.5s, when the upper temperature reaches its peak of 80°C, the lower temperature reaches its trough of 40°C; =7.5s, when the lower part temperature reaches its peak of 60°C, the upper part temperature reaches its trough of 60°C.

[0119] In another implementation of this invention, the generation of the two timing sequences can be represented as follows:

[0120] and ,

[0121] in . Equivalent to This perfectly achieves phase reversal control. This means that when the upper region is in the fastest heating phase, the lower region is in the fastest cooling phase.

[0122] In this embodiment of the invention, at each sampling moment during the entire cycle of dynamic thermal gradient perturbation, two actions are performed simultaneously: First, the instantaneous values ​​of the temperature sensors at the top and bottom of the casing are read, and the instantaneous temperature difference (ΔT(t)) is calculated; second, the power analyzer is triggered to collect the instantaneous total thermal shock power loss at this moment (ΔT(t)). For each pair (ΔT(t), The data is stored as a record point in a sequence. After one or more complete temperature fluctuation cycles are completed, this sequence containing a large number of instantaneous data points constitutes the dynamic loss sequence.

[0123] It should be noted that this dynamic loss sequence is different from the single thermal field gain factor obtained by the previous static test, which can reveal the response characteristics of the loss to the dynamic temperature difference, including the existing delay effect (hysteresis loop). For example, when the temperature difference is also 30°C, the loss measured during the heating process is different from that measured during the cooling process.

[0124] Preferably, calibrating the machine vibration gain factor in step S3 comprises:

[0125] Restore the capacitor to the reference temperature, apply a mechanical resonance excitation of 10Hz to 2000Hz through the piezoelectric actuator array, and dynamically identify the mechanical resonance frequency point;

[0126] Apply a constant amplitude mechanical vibration to the capacitor shell centered on the mechanical resonance frequency point, and synchronously inject an excitation source electrical signal during the vibration duration, and read the additional loss under machine vibration;

[0127] Calculate the ratio of the additional loss under machine vibration to the cross-reference loss to obtain the machine vibration gain factor.

[0128] In an implementation manner of the embodiment of the application, after completing the calibration of the thermal field gain factor, first stop heating and start the cooling system, restore the overall temperature of the capacitor to the reference temperature, for example, 25°C±1°C. After the temperature is stable, the test control system starts the piezoelectric actuator array connected with the capacitor base. The control signal generator outputs a linear sweep signal to drive the actuator array to generate mechanical vibration linearly increasing from 10Hz to 2000Hz, and the sweep rate is set to 10Hz / s. In this process, a plurality of acceleration sensors installed at key positions of the capacitor shell monitor the vibration response in real time.

[0129] In an implementation manner of the embodiment of the application, a logarithmic sweep is performed from 10Hz to 2000Hz, and when the excitation frequency reaches 455Hz, the vibration acceleration amplitude monitored by the sensor reaches a maximum value of 3.5g, which is much higher than the response at other frequencies. Therefore, 455Hz is determined and stored as the mechanical resonance frequency point of the capacitor.

[0130] In an implementation manner of the embodiment of the application, the piezoelectric actuator array is instructed to vibrate the capacitor at a frequency of 455Hz and an acceleration amplitude of 1g. At the same time, an excitation source electrical signal of (350Hz, 250Hz) is applied to the capacitor. After stabilization, the measured total power loss is 5.1W. The corresponding theoretical superposition loss is 4.3W. Therefore, the additional loss under machine vibration is calculated as follows:

[0131] The additional loss under machine vibration = 5.1W-4.3W = 0.8W.

[0132] In one implementation of the embodiment of the application, the additional loss due to mechanical vibration is 0.8 W, while the cross-reference loss is 0.7 W. Then the mechanical vibration gain factor is calculated as follows:

[0133] Mechanical vibration gain factor = 0.8 W / 0.7 W ≈ 1.14.

[0134] This result shows that, under the condition of 455 Hz resonance frequency and 1 g amplitude, the mechanical vibration amplifies the cross-reference additional loss of the pair of harmonics (350 Hz, 250 Hz) by about 14%. This mechanical vibration gain factor will be stored and used together with the thermal field gain factor for the final full-condition loss evaluation.

[0135] Preferably, the dynamic identification of the mechanical resonance frequency point comprises:

[0136] A first sweep excitation sequence is independently generated for the piezoelectric actuator in the X-axis direction, with the excitation frequency being logarithmically increased from 10 Hz to 2000 Hz;

[0137] A second sweep excitation sequence is independently generated for the piezoelectric actuator in the Y-axis direction, with the excitation frequency being inversely logarithmically decreased from 2000 Hz to 10 Hz, and the starting point of the second sweep excitation sequence being aligned in time with the center point of the first sweep excitation sequence;

[0138] The response amplitude of the capacitor shell is captured by the acceleration sensor;

[0139] At each frequency step of the first sweep excitation sequence, if the acceleration response amplitude in the X-axis direction exceeds a preset threshold, the current excitation frequency and the response amplitude are pressed into the X-axis resonance candidate stack as a data pair;

[0140] At each frequency step of the second sweep excitation sequence, if the acceleration response amplitude in the Y-axis direction exceeds a preset threshold, the current excitation frequency and the response amplitude are pressed into the Y-axis resonance candidate stack as a data pair;

[0141] After the two sweep sequences are all executed, all data pairs in the X-axis resonance candidate stack and the Y-axis resonance candidate stack are compared, and the frequency point with the maximum response amplitude is determined as the mechanical resonance frequency point.

[0142] In one implementation of the embodiment of the application, it is assumed that the entire sweep process lasts for 100 seconds. The frequency of the first sweep excitation sequence is generated by the formula , where is the time from 0 to 100 seconds. At = 50 s, the frequency is about 141 Hz, while at = 90 s, the frequency has reached about 1012 Hz, embodying the characteristics of logarithmic scanning.

[0143] In the embodiment of the present application, a second sweep excitation sequence is generated independently for the piezoelectric actuator sub-array in Y-axis direction to control the vibration in this direction. The excitation frequencies in this sequence are set in a "inverse logarithm" manner, i.e. decreasing from 2000Hz to 10Hz, scanning densely in high frequency band and sparsely in low frequency band. In order to optimize the test procedure and stagger the excitation peaks in the two axial directions, the start time of the second sweep excitation sequence is set precisely to align with the center time of the first sweep excitation sequence.

[0144] In one implementation of the embodiment of the present application, the total time length of the first sweep excitation sequence is 100 seconds, and the center point is = 50 seconds. Therefore, the second sweep excitation sequence starts at = 50 seconds, also lasts for 100 seconds, and ends at = 150 seconds. This timing arrangement avoids the simultaneous high frequency or low frequency excitation in the two axial directions, which helps to reduce the instantaneous power demand on the power supply.

[0145] In the embodiment of the present application, during the entire sweep excitation process, the two orthogonal acceleration sensors arranged on the capacitor shell and used to measure the vibrations in X-axis and Y-axis directions work continuously. The sensors convert the captured vibration signals into voltage signals, and after signal conditioning and high-speed ADC sampling, the vibration response amplitudes (usually in g, i.e. gravitational acceleration) corresponding to the current excitation frequencies are extracted in real time through fast Fourier transform (FFT) or digital filtering, etc.

[0146] In the embodiment of the present application, during the execution of the first sweep excitation sequence, the response amplitude of the X-axis acceleration sensor is compared with a preset response threshold (e.g. 0.5g) in real time. This threshold is used to preliminarily screen out meaningful vibration peaks and ignore small background vibrations.

[0147] In one implementation of the embodiment of the present application, when the X-axis excitation frequency scans to 125Hz, the X-axis sensor measures a response amplitude of 0.8g, which is greater than the threshold of 0.5g. A data pair (125Hz, 0.8g) is immediately generated and pushed into the X-axis resonance candidate stack.

[0148] In the embodiment of the present application, the processing method for the X-axis is exactly the same, and during the execution of the second sweep excitation sequence (t=50s to 150s), the response amplitude of the Y-axis acceleration sensor is compared with the same response threshold. If it exceeds the threshold, the current Y-axis excitation frequency and the response amplitude are packaged into a data pair and pushed into the Y-axis resonance candidate stack.

[0149] In another implementation of the embodiment of the application, when the Y-axis excitation frequency is scanned to 455 Hz (at this time t≈118 s), the Y-axis sensor measures a response amplitude of 3.5 g, which is much greater than the threshold of 0.5 g. The data pair (455 Hz, 3.5 g) is generated and pressed into the Y-axis resonance candidate stack.

[0150] It should be noted that, in order to avoid strong coupling interference of the two axial excitations at the same time point, the starting time of the second sequence is set to the center point of the first sequence, i.e., starting at t=50 s. In this way, when the X-axis excitation is scanned to the medium frequency band, the Y-axis excitation starts to scan from the high frequency, achieving staggered excitation in time.

[0151] In the embodiment of the application, after the entire sweep frequency process (to t=150 s) is completed, all data pairs in the X-axis resonance candidate stack and the Y-axis resonance candidate stack are traversed, and the response amplitudes in each data pair are compared to find the global maximum value. After the maximum response amplitude is found, the excitation frequency in the data pair is extracted and finally determined as the main mechanical resonance frequency point of the entire capacitor structure under the test condition.

[0152] Preferably, the total loss under the full working condition in step S4 is evaluated based on the thermal field gain factor and the mechanical vibration gain factor, and includes:

[0153] The loss values of all corresponding harmonics are extracted and accumulated from the single-frequency loss baseline to generate a basic loss component;

[0154] All harmonic pairs are traversed from the harmonic coupling loss, and the corresponding harmonic additional loss is accumulated to generate an interaction loss component;

[0155] The coupling amplification loss component is calculated according to the thermal field gain factor and the mechanical vibration gain factor;

[0156] The basic loss component, the interaction loss component, and the coupling amplification loss component are combined in numerical order, so as to evaluate the total loss under the full working condition.

[0157] In one implementation of the embodiment of the application, it is assumed that the harmonic list of the target working condition is {150 Hz, 250 Hz, 350 Hz}. It is found from the single-frequency loss baseline that the power loss corresponding to 150 Hz is 1.2 W; the power loss corresponding to 250 Hz is 1.8 W; and the power loss corresponding to 350 Hz is 2.5 W. The basic loss component is calculated as follows:

[0158] The basic loss component=1.2 W+1.8 W+2.5 W=5.5 W.

[0159] In one implementation of the embodiment of the application, based on the harmonic list {150Hz, 250Hz, 350Hz}, the harmonic pairs are generated: (150Hz, 250Hz), (150Hz, 350Hz), (250Hz, 350Hz). The harmonic coupling loss of (150Hz, 250Hz) is 0.5W; the harmonic coupling loss of (150Hz, 350Hz) is 0.6W; the harmonic coupling loss of (250Hz, 350Hz) is 0.7W;

[0160] Then the interaction loss component is calculated as follows:

[0161] Interaction loss component = 0.5W + 0.6W + 0.7W = 1.8W.

[0162] In one implementation of the embodiment of the application, it is assumed that the target working condition sets a temperature difference of 20°C and a vibration of 1g resonance frequency. The corresponding thermal field gain factor is 1.6 and the machine vibration gain factor is 1.14. The interaction loss component is 1.8W. Then the coupling amplification loss component is calculated as follows: coupling amplification loss component = 1.8W x (1.6-1) + 1.8W x (1.14-1) = 1.8W x 0.6 + 1.8W x 0.14 = 1.08W + 0.252W = 1.332W.

[0163] In the embodiment of the application, after all the loss components are calculated, the three components, the basic loss component, the interaction loss component and the coupling amplification loss component, are arithmetically summed to obtain the final result, which is the accurate evaluation value of the total loss of the capacitor under the target full working condition, i.e. the full working condition test total loss.

[0164] Preferably, in step S4, if the loss deviation value is within the preset range, the test result is locked and packaged into the full working condition test data, which comprises:

[0165] The loss deviation value is calculated by the preset standard loss value of the capacitor and the full working condition test total loss;

[0166] When the loss deviation value is less than 5% of the full working condition test total loss, the test state is marked as a verification pass flag at the tail of the current test period;

[0167] After the verification pass flag takes effect, the current test result is locked to construct a full working condition effect matrix, so as to be packaged into the full working condition test data.

[0168] In the embodiment of the present application, after the total loss under all conditions is evaluated, a preset standard loss value for the capacitor under the same or similar conditions is called from the internal database or external file. The standard value can be provided by the manufacturer or set based on a large amount of historical test data or authoritative simulation results. The calculation unit performs subtraction operation on the total loss under all conditions evaluated and the preset standard loss value, and takes the absolute value, and the difference is determined as the loss deviation value.

[0169] In one implementation of the embodiment of the present application, the loss deviation value is 0.332 W. The tolerance threshold is calculated: 8.632 W x 5% = 0.4316 W. Since 0.332 W < 0.4316 W, the condition is met, and the state bit Test_Status is set to 0x01 (representing "pass") at the tail of the current period.

[0170] In the embodiment of the present application, once the system detects that the pass flag is set, it will immediately trigger the final data packaging program. The program will lock all the key data obtained in the current evaluation period to prevent it from being modified by subsequent operations. Then, the program will organize these data in a structured manner to construct an all-condition effect matrix. The matrix clearly shows the contribution of each harmonic, each physical field disturbance and their interaction to the total loss in the form of a multi-dimensional array or nested data structure. Finally, this matrix together with the basic information of the test (such as capacitor model, test time, target condition parameters, etc.) is packaged into an independent and portable digital file, which is the final delivered all-condition test data.

[0171] In another implementation of the embodiment of the present application, the all-condition effect matrix can be constructed as follows:

[0172] The absolute values of the harmonic coupling loss, thermal effect loss and mechanical effect loss are taken as the first column data of the matrix;

[0173] The respective loss contribution rates are taken as the second column data of the matrix;

[0174] The harmonic frequency, temperature gradient and mechanical vibration frequency used in the test are taken as the third column data of the matrix;

[0175] The three columns of data are combined into a structured data, which is determined as the all-condition effect matrix.

[0176] Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, the scope of the present application is defined by the appended claims rather than the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the application file are intended to be included in the present application.

[0177] The foregoing is considered as illustrative only of the principles of the application. Numerous modifications and changes will readily occur to those skilled in the art, and it is intended to embrace all such modifications and changes that fall within the scope of the application. Accordingly, the application is not to be restricted in scope to the specific embodiments disclosed herein but is to be accorded the full scope that the principles and novel features request appropriately granted.

Claims

1. A full duty cycle equivalent test method for capacitors used in HVDC power transmission, characterized by, Comprising the following steps: Step S1: Apply a single frequency AC component on the capacitor, obtain the inherent loss tangent value of the capacitor under single frequency excitation, generate a single frequency loss baseline, step S1 includes the following steps: Step S11: superimpose an AC component with an initial frequency of 50Hz and an amplitude of 1% of the rated voltage on the preset rated DC bias voltage; Step S12: apply an AC component to the capacitor and collect the first loss tangent value, denoted as the first frequency loss point; Step S13: Take the first frequency loss point as the reference, increase the frequency of the AC component by 50Hz as the step size, and perform frequency point scanning in turn by replacing the frequency of the AC component; wherein, after each replacement, the outgoing terminals of the capacitor are immediately subjected to instantaneous forced air cooling; Step S14: Collect the loss tangent value at each frequency point and subtract the loss value at the previous frequency point to calculate the loss change rate; Step S15: Compare the loss change rate with the preset response threshold; if it is less than the preset response threshold, mark the frequency point as a flat frequency point; if it is greater than the preset response threshold, mark the frequency point as a sensitive frequency point, and reduce the frequency scanning step size to 5Hz; Step S16: Connect all flat frequency points and sensitive frequency points and their corresponding loss tangent values in frequency order to draw a single frequency loss baseline; Step S2: Select a harmonic combination according to the single frequency loss baseline; difference the theoretical superimposed loss in the single frequency loss baseline and the actual total power loss of the test capacitor when the harmonic combination is injected synchronously, and the positive part determines the harmonic coupling loss; Step S3: According to the harmonic coupling loss, select the strong interactive harmonic pair, and take it as the excitation source to re-measure the additional loss under the conditions of applying controlled thermal gradient disturbance and mechanical resonance excitation to mark the thermal field gain factor and the mechanical vibration gain factor; Step S4: Based on the thermal field gain factor and the mechanical vibration gain factor, evaluate the total loss under all working conditions, and compare it with the preset standard loss value to obtain the loss deviation value, if the loss deviation value is within the preset range, lock the test result and package it into the full working condition test data, if the loss deviation value is not within the preset range, execute the test calibration request, and automatically suspend the subsequent test process, immediately cut off all excitation outputs.

2. The full duty cycle equivalent test method for a DC power transmission capacitor of claim 1, wherein, Step S2 includes the following steps: Step S21: At the beginning of the current test period, select a first harmonic frequency and a second harmonic frequency in turn based on the single frequency loss baseline; wherein, the first harmonic frequency is greater than the second harmonic frequency; Step S22: Take the first harmonic frequency and the second harmonic frequency as the harmonic combination; Step S23: Obtain the single frequency loss tangent value corresponding to the harmonic combination, calculate the linear superimposed equivalent loss, and obtain the theoretical superimposed loss; Step S24: During the current test period, control the power supply to synchronously superimpose the harmonic combination on the DC bias to inject AC components of two frequencies into the capacitor, and measure the actual total power loss of the capacitor after the injection is stable; Step S25: Difference the actual total power loss and the theoretical superimposed loss, and the positive part determines the harmonic coupling loss.

3. The full duty cycle equivalent test method for a DC power transmission capacitor of claim 1, wherein, The marking of the thermal field gain factor in step S3 includes: When the harmonic coupling loss is greater than 15% of the theoretical superposition loss, the harmonic pair is determined to be a strong interactive harmonic pair; otherwise, it is determined to be a weak interactive harmonic pair, and the weak interactive harmonic pair is removed; The strong interactive harmonic pair is taken as an excitation source electrical signal, and the frequency value of the harmonic pair is taken as an interactive reference loss; A thermal gradient disturbance is applied in the capacitor shell area when the excitation source electrical signal is applied; wherein the thermal gradient disturbance sets the target temperature of the top of the capacitor to 70°C and the target temperature of the bottom to 50°C, the heating power is monitored and adjusted in real time until the temperature difference between the top and the bottom is stabilized at 20°C±1°C; The thermal excitation total power loss of the capacitor is re-measured under the condition of maintaining the thermal gradient disturbance and the excitation source electrical signal; The difference between the thermal excitation total power loss and the corresponding theoretical superposition loss in the strong interactive harmonic pair is calculated to obtain the additional loss under thermal disturbance; The ratio of the additional loss under thermal disturbance to the interactive reference loss is calculated to obtain the thermal field gain factor.

4. The full duty cycle equivalent test method for a DC power transmission capacitor of claim 3, wherein, Applying a thermal gradient disturbance in the capacitor shell area further comprises: A first temperature control time sequence is set for the upper area of the capacitor shell, and the target temperature thereof fluctuates between 60°C and 80°C with a frequency of 0.1Hz in a sine law; A second temperature control time sequence is set for the lower area of the capacitor shell, and the target temperature thereof fluctuates between 60°C and 40°C with a frequency of 0.1Hz in an inverse sine law; The phase difference between the first temperature control time sequence and the second temperature control time sequence is fixed at 180 degrees; The temperature difference value and the corresponding thermal excitation total power loss are recorded synchronously at each control sampling point in the first temperature control time sequence and the second temperature control time sequence to form a dynamic loss sequence.

5. The full duty cycle equivalent test method for a DC power transmission capacitor of claim 1, wherein, The step S3 of calibrating the machine vibration gain factor comprises: The capacitor is restored to the reference temperature, a 10Hz to 2000Hz mechanical resonance excitation is applied through the piezoelectric actuator array, and the mechanical resonance frequency point is dynamically identified; A mechanical vibration with constant amplitude is applied to the shell of the capacitor with the mechanical resonance frequency point as the center frequency, the excitation source electrical signal is injected synchronously during the vibration duration, and the additional loss under machine vibration is read; The ratio of the additional loss under machine vibration to the interactive reference loss is calculated to obtain the machine vibration gain factor.

6. The full duty cycle equivalent test method for a power capacitor for HVDC power transmission as claimed in claim 5, wherein, The dynamic identification of the mechanical resonance frequency point comprises: A first sweep excitation sequence is independently generated for the piezoelectric actuator controlling the X-axis direction, and the excitation frequency is set to increase logarithmically from 10Hz to 2000Hz; A second sweep excitation sequence is independently generated for the piezoelectric actuator controlling the Y-axis direction, and the excitation frequency is set to decrease inversely logarithmically from 2000Hz to 10Hz, and the starting point of the second sweep excitation sequence is aligned in time with the center point of the first sweep excitation sequence; The response amplitude of the capacitor shell is captured by using an acceleration sensor; When the frequency steps in the first sweep excitation sequence, if the acceleration response amplitude in the X-axis direction exceeds a preset threshold, the current excitation frequency and the response amplitude are pressed into the X-axis resonance candidate stack as a data pair; When the frequency steps in the second sweep excitation sequence, if the acceleration response amplitude in the Y-axis direction exceeds a preset threshold, the current excitation frequency and the response amplitude are pressed into the Y-axis resonance candidate stack as a data pair; After the two sweep sequences are all executed, all data pairs in the X-axis resonance candidate stack and the Y-axis resonance candidate stack are compared, and the frequency point with the largest response amplitude is determined as the mechanical resonance frequency point.

7. The full duty cycle equivalent test method for a power capacitor for DC power transmission as recited in claim 1, wherein, The total loss in the full working condition test is evaluated based on the thermal field gain factor and the mechanical vibration gain factor in step S4, and includes: Extract and accumulate the loss values of all corresponding harmonics from the single-frequency loss baseline to generate a basic loss component; All harmonic pairs are traversed from the harmonic coupling loss, and the corresponding harmonic additional loss is accumulated to generate an interaction loss component; The coupling amplification loss component is calculated from the interaction loss component according to the thermal field gain factor and the mechanical vibration gain factor; The basic loss component, the interaction loss component, and the coupling amplification loss component are combined in numerical order to evaluate the total loss in the full working condition test.

8. The full duty cycle equivalent test method for a power capacitor for DC power transmission as recited in claim 1, wherein, If the loss deviation value is within the preset range in step S4, the test result is locked and encapsulated into full working condition test data, which includes: The loss deviation value is calculated by the preset capacitor standard loss value and the total loss in the full working condition test; When the loss deviation value is less than 5% of the total loss in the full working condition test, the test state is marked as a verification pass flag at the tail of the current test period; After the verification pass flag takes effect, the current test result is locked to construct a full working condition effect matrix, thereby encapsulating the full working condition test data.

9. A full duty cycle equivalent test system for capacitors used in HVDC power transmission, characterized by The full working condition equivalent test system for DC power transmission capacitors includes: The inherent loss acquisition module is used to apply a single-frequency AC component to the capacitor, obtain the inherent loss tangent value of the capacitor under single-frequency excitation, and generate a single-frequency loss baseline; The harmonic coupling analysis module is used to select a harmonic combination according to the single-frequency loss baseline; the theoretical superposition loss in the single-frequency loss baseline is subtracted from the actual total power loss of the test capacitor when the harmonic combination is injected synchronously, and the positive part is determined as the harmonic coupling loss; The multi-working condition test module is used to select strong interactive harmonic pairs according to the harmonic coupling loss, and to re-measure the additional loss under the conditions of applying controlled thermal gradient disturbance and mechanical resonance excitation to label the thermal field gain factor and the mechanical vibration gain factor; The full working condition verification control module is used to evaluate the total loss in the full working condition test based on the thermal field gain factor and the mechanical vibration gain factor, and compare it with the preset standard loss value to obtain the loss deviation value. If the loss deviation value is within the preset range, the test result is locked and encapsulated into full working condition test data. If the loss deviation value is not within the preset range, the test calibration request is executed, and the subsequent test process is automatically suspended to cut off all excitation outputs.

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