Electrical variable detection method for inverter aging test

Abstract

The invention relates to the technical field of inverters, and particularly discloses an electrical variable detection method for an inverter aging test, which comprises the following steps: periodically acquiring THD of output voltage of an inverter in a UPS system, and if the THD at the current moment is greater than a preset THD threshold, acquiring future THD and historical THD; generating future coordinate points based on the future THD, and fitting the future coordinate points to obtain a future curve; generating historical coordinate points based on the historical THD, and fitting the historical coordinate points to obtain a historical curve; a judgment value K is calculated based on the historical curve and the future curve, and if the judgment value K is smaller than a preset judgment value threshold value, it is judged that the inverter in the UPS system is aged; and judging the aging degree of the inverter according to the future THD and the historical THD. According to the invention, the accuracy degree of aging detection of the inverter in the UPS system is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inverters, in particular to an electric variable detection method for inverter aging test. BACKGROUND

[0002] An inverter is a power electronic device that can convert direct current into alternating current. Its core function is to solve the adaptation problem of direct current power supply and most alternating current electrical equipment. It converts unstable direct current into alternating current with waveform, voltage and frequency meeting the electrical standard through the high-frequency on-off of semiconductor switching devices, combined with filtering, voltage stabilizing and other circuits, and is widely used in solar photovoltaic power generation systems, vehicle power supply, emergency backup power, outdoor camping power supply and other scenes.

[0003] In the UPS system, the load often has burst characteristics. For example, when the server group of a data center starts or switches operation, it will generate a large current impact in an instant. This current mutation will introduce short-term irregular components in the voltage waveform, causing abnormal harmonic analysis results. The actual measured harmonic content will rise significantly in this case, but this rise is not caused by the aging of the inverter itself or long-term deterioration of power quality, but by short-term interference caused by load transient behavior. This kind of false harmonic can interfere with the judgment of the health status of the inverter. SUMMARY

[0004] The purpose of the present application is to provide an electric variable detection method for inverter aging test, which solves the above technical problems.

[0005] The purpose of the present application can be achieved by the following technical solutions: The electric variable detection method for inverter aging test comprises the following steps: Periodically obtain the THD of the inverter output voltage in the UPS system. If the THD at the current time is greater than the preset THD threshold, then take the current time as the starting point, select n THD in the time axis order and the reverse time axis order respectively, and mark them as future THD and history THD respectively, n is a preset number; Generate future coordinate points based on future THD, and obtain future curve f(t) his based on fitting of the future coordinate points, t represents time; generate history coordinate points based on history THD, and obtain history curve f(t) fut based on fitting of the history coordinate points; Calculate the judgment value K based on the history curve and the future curve. If the judgment value K is less than the preset judgment value threshold, it is determined that the inverter in the UPS system exists aging. The calculation formula of the judgment value K is: ; Where [F1, F2] represents the future curve f(t) histhe definition domain of the history curve f(t) his the definition domain of the history curve f(t) judging the aging degree of the inverter according to the future THD and the history THD.

[0006] As a further scheme of the present application, the generating of the history coordinate point and the future coordinate point comprises: generating a future coordinate point (tj', THDj'), tj' representing the difference between the time stamp of the jth selected future THD and the time stamp of the 1st selected future THD, and THDj representing the jth selected future THD. generating a history coordinate point (ti, THDi), ti representing the difference between the time stamp of the ith selected history THD and the time stamp of the nth selected history THD, and THDi representing the ith selected history THD.

[0007] As a further scheme of the present application, in the process of calculating the judging value, F1 and H1 are both 0, and F2 and H2 are tn' and tn respectively.

[0008] As a further scheme of the present application, judging the aging degree of the inverter according to the future THD and the history THD comprises: taking both the future THD and the history THD as the judging THD, and sorting the judging THD according to the time axis order; grouping the judging THD, the difference between any two judging THD in the group being less than a preset difference threshold, and the position of the judging PHD in the group in the sorting being adjacent to the position of at least one judging THD in the same group in the sorting; calculating the mean value of the judging PHD in the group as the group value of the group, and if the variance of the group value is less than a preset variance threshold, then weighted summing the group values to obtain the aging value L of the inverter, and judging the aging degree of the inverter according to the aging value L.

[0009] As a further scheme of the present application, judging the aging degree of the inverter according to the aging value L comprises: setting aging value thresholds L1 and L2, and L1 being less than L2; if L if L1≤L if L2

[0010] As a further scheme of the present application, in the process of calculating the aging value L, if the variance of the group value is greater than or equal to a preset variance threshold, the following steps are executed: The grouping values are sorted in ascending order, the first grouping value in the sorting is removed, the variance of the remaining grouping values is calculated, and it is judged whether to execute the step of calculating the aging value L.

[0011] As a further scheme of the present application: in the process of calculating the aging value L, the weight of the grouping value is proportional to the target time, and the target time represents the mean of the time stamps of all THD determinations in the grouping.

[0012] As a further scheme of the present application: if it is determined that there is no aging of the inverter in the UPS system, the mean of the historical THD is used to replace the future THD, and the replacement is called when the THD greater than the preset THD threshold appears next time.

[0013] The present application has the following advantages: 1) The present application realizes comparison of the data change trend by simultaneously selecting the future and historical harmonic data for fitting curve analysis, thereby effectively distinguishing the short-term fluctuation caused by load transient from the long-term trend caused by degradation of the inverter itself, avoiding misjudgment caused by occasional interference in the traditional method, and making the aging judgment result more reliable. 2) The present application introduces the curve area difference as the judgment basis in the calculation process, thereby ensuring the rationality of the determination logic; when the load suddenly changes, the difference between the curves before and after is large, i.e., the judgment value is large; while in the aging case, the trend of the historical and future data is close, and the curve difference is relatively small, i.e., the judgment value is small, thereby accurately identifying the aging phenomenon of the inverter and improving the accuracy and applicability of the detection. 3) The present application determines the aging value by grouping the determination data and combining the variance and the weighting method, so that the final result can comprehensively reflect the overall change trend of the inverter at different time points. This method can still obtain a stable aging evaluation when the data fluctuates, avoiding the interference of a single abnormal point on the overall conclusion, thereby making the aging degree judgment more stable and continuous. BRIEF DESCRIPTION OF DRAWINGS

[0014] The present application will be further described below with reference to the accompanying drawings.

[0015] Figure 1 is a structural schematic diagram of the electrical variable detection method for inverter aging test of the present application. DETAILED DESCRIPTION

[0016] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described, obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work are within the protection scope of the present application.

[0017] Please refer to Figure 1 The present application is an electric variable detection method for inverter aging test, comprising the following steps: In the continuous running process, the output voltage waveform is sampled and the harmonic component is extracted, so as to obtain the harmonic distortion rate value at the current time. In this process, the harmonic distortion rate as a parameter for measuring the distortion degree of the voltage waveform can reflect the difference between the non-fundamental wave component and the fundamental wave component in the voltage waveform. When the harmonic distortion rate at the current time is detected to be greater than a preset threshold, the time is taken as a key starting point for subsequent processing. THD, i.e. total harmonic distortion rate, is an index for measuring the proportion of harmonic component in the voltage or current waveform relative to the fundamental wave component. It reflects the waveform distortion degree by comparing the relationship between the fundamental wave energy and the harmonic energy. The higher the value, the greater the degree of deviation of the waveform from the ideal sine wave. The calculation method of THD is not described here; On the basis of the starting point, a plurality of harmonic distortion rate values are selected as future reference data in time sequence and a plurality of harmonic distortion rate values are selected as historical reference data in reverse time sequence. The future harmonic distortion rate obtained in this way reflects the change trend of the voltage waveform distortion in a period of time after the current time, and the historical harmonic distortion rate reflects the change trend of the voltage waveform distortion in a period of time before the current time. Both of them are developed in time sequence, which can characterize the characteristic evolution of the voltage waveform in different periods under the same reference framework. The number selected is limited by a pre-set parameter to ensure the consistency and comparability of the future data and the historical data in quantity, thereby providing a complete data basis for subsequent fitting and analysis. It can be understood that the future THD is obtained after at least n THDs are obtained from the current time. Because the future n THDs cannot be predicted at the current time, subsequent steps need to be performed after the time reaches the length required to obtain at least n THDs.

[0018] The future coordinate points are generated based on the future THD, and the future curve f(t) is obtained by fitting the future coordinate points fut , t represents time; the historical coordinate points are generated based on the historical THD, and the historical curve f(t) his is obtained by fitting the historical coordinate points. It can be understood that the fitting method includes but is not limited to a cubic spline interpolation method. In a preferred embodiment of the present application, the generated historical coordinate point and future coordinate point include: The generated future coordinate point (tj', THDj') represents the difference between the timestamp of the jth selected future THD and the timestamp of the 1st selected future THD, and THDj represents the jth selected future THD. The generated historical coordinate point (ti, THDi) represents the difference between the timestamp of the ith selected historical THD and the timestamp of the nth selected historical THD, and THDi represents the ith selected historical THD.

[0019] The determination value K is calculated based on the historical curve and the future curve, and if the determination value K is less than a preset determination value threshold, it is determined that the inverter in the UPS system is aging, and the calculation formula of the determination value K is: ; Where [F1, F2] represents the domain of the future curve f(t) fut , and [H1, H2] represents the domain of the historical curve f(t) his ; It should be noted that in the process of calculating the determination value, by integrating the difference between the historical curve and the future curve within their respective domain ranges, the overall area difference between the two curves can be obtained, which can reflect the consistency of the harmonic distortion rate change trend in different time periods. If the difference between the two curves is large, it means that the change after the current time is significantly discontinuous from the previous change, which is often caused by transient mutation of external load. On the contrary, if the difference between the two curves is small, it means that the future change trend is continuous with the past change trend, and the current increase is not an isolated phenomenon, but is related to the history, so it can be explained that the inverter may be aging, and thus the size of the area difference is used as a basis for judgment, which embodies the principle of distinguishing external interference and device state by comparing the consistency of trends in different periods.

[0020] In another preferred embodiment of the present application, if it is determined that the inverter in the UPS system is not aging, the mean value of the historical THD is used to replace the future THD, and the next time the THD greater than the preset THD threshold appears, it is called.

[0021] In the case where it is determined that the inverter does not exist aging, the mean value of the historical harmonic distortion rate is used to replace the future harmonic distortion rate, so as to avoid that the abnormality is directly brought into the subsequent judgment process due to the future data itself containing load transient interference; the mean value of the historical harmonic distortion rate can represent the overall level in a long time range, and is more stable than the data at a single moment, when the mean value is used to replace the future data, it is equivalent to resetting the future data as a reference point consistent with the existing trend, so that when the harmonic distortion rate exceeding the preset threshold appears next time, the new future data will be collected and analyzed again, avoiding that the continuity interference caused by the last abnormality on the result, so as to ensure that the subsequent judgment is established on the basis of relative stability, and the trend comparison can be re-performed when the new judgment condition appears, so that the continuity and rationality of the aging judgment can be maintained.

[0022] According to the future THD and the historical THD, the aging degree of the inverter is judged. In another preferred embodiment of the present application, the aging degree of the inverter is judged according to the future THD and the historical THD, which comprises: The future THD and the historical THD are both used as the judgment THD, and the judgment THD is sorted in time sequence; The judgment THD is grouped, the difference between any two judgment THDs in the group is less than a preset difference threshold, and the position of the judgment PHD in the group in the sorting is adjacent to the position of at least one judgment THD in the same group in the sorting; The mean value of the judgment PHD in the group is calculated as the group value of the group, if the variance of the group value is less than a preset variance threshold, the aging value L of the inverter is obtained by weighted summation of the group values, and the aging degree of the inverter is judged according to the aging value L; It should be noted that in the process of judging the aging degree of the inverter, the grouping step is added because a single judgment harmonic distortion rate may be affected by instantaneous fluctuations or local abnormalities, and single-point data cannot fully represent the overall trend. Arranging the judgment harmonic distortion rate in time sequence and grouping can ensure that the data difference in the same group is within the preset range, and the data in adjacent positions can reflect the continuity in time. The group formed in this way can reduce the interference of isolated abnormal points on the overall judgment to a certain extent. The mean value of each data in the group as the group value can comprehensively reflect the overall level of the time period. The stability of the group value is judged by using the variance, if the group value changes little internally, it means that the data consistency in the group is good, which can be used as a reliable basis. By weighted summation of these group values, the aging value can be obtained, so that the result can reflect the overall change of different time periods and maintain continuity and stability.

[0023] It should be noted that in the process of calculating the aging value L, the weight of the grouping value is proportional to the target time, which represents the mean of the time stamps of all the THD determinations in the grouping.

[0024] Specifically, the weight can be set according to historical experience, such as when the number of groupings is how many, the weight of the grouping value of each grouping is how many, for example, 5 groupings, the groupings are sorted in chronological order, and the weights of the five groupings are 0.1, 0.15, 0.2, 0.25, and 0.3, respectively, which satisfies the total weight of 1 and the weight of the grouping value being proportional to the target time.

[0025] In one preferred case of the embodiment, determining the aging degree of the inverter according to the aging value L includes: Setting aging value thresholds L1 and L2, and L1 is less than L2; If L < L1, it is determined that the aging degree of the inverter is low; If L1≤L < L2, it is determined that the aging degree of the inverter is general; If L2 < L, it is determined that the aging degree of the inverter is high.

[0026] The aging value thresholds L1 and L2 can be set according to experience; In another preferred case of the embodiment, in the process of calculating the aging value L, if the variance of the grouping values is greater than or equal to a preset variance threshold, the following steps are performed: The grouping values are sorted in ascending order, the first grouping value in the sorting is removed, the variance of the remaining grouping values is calculated, and it is determined whether to perform the step of calculating the aging value L.

[0027] Under the premise that it has been determined that there is aging, if the variance of the grouping values is greater than or equal to a preset threshold, it indicates that the horizontal dispersion degree of different time periods is high, and directly summarizing the possibly low grouping may lower the overall result, causing underestimation of the aging degree. The grouping values are sorted in ascending order and the first grouping is removed, because this minimum grouping is more likely to correspond to short-term load reduction or local unaffected interval, and its representativeness for the overall aging trend is weak; by sorting, the lower limit value can be clearly identified and removed, so as to retain the main distribution that can better reflect the aging trend. Then, the variance of the remaining grouping values is recalculated for determining whether the stability required for the aging value calculation is possessed. This process avoids underestimating the aging degree in a conservative principle, and meets the control requirement of the deviation direction of the result under the safety-first orientation.

[0028] The above formulas are dimensionless values, and the formulas are obtained by collecting a large amount of data to simulate the most recent real situation. The preset parameters and thresholds in the formulas are set by a person skilled in the art according to the actual situation.

[0029] The above has been described in detail one embodiment of the present application, but the content is only the preferred embodiment of the present application, cannot be considered for limiting the scope of the present application. Any equivalent changes and improvements made in the scope of the present application, should still belong to the scope of the present application.

Claims

1. A method for detecting electrical variables in inverter aging tests, characterized in that, Includes the following steps: The THD of the inverter output voltage in the UPS system is periodically acquired. If the THD at the current moment is greater than the preset THD threshold, then n THDs are selected from the current moment in chronological order and in reverse chronological order, and recorded as future THD and historical THD respectively, where n is the preset number. Future coordinate points are generated based on future THD, and the future curve f(t) is obtained by fitting these future coordinate points. fut t represents time; historical coordinate points are generated based on historical THD, and the historical curve f(t) is obtained by fitting the historical coordinate points. his ; The judgment value K is calculated based on historical and future curves. If the judgment value K is less than the preset judgment value threshold, the inverter in the UPS system is determined to be aging. The formula for calculating the judgment value K is: ； Where [F1, F2] represent the future curve f(t). fut The domain of definition, [H1, H2], represents the historical curve f(t). his Domain; The aging level of the inverter can be determined by comparing the future THD with the historical THD.

2. The electrical variable detection method for inverter aging test according to claim 1, characterized in that, Generating historical and future coordinate points includes: Generate future coordinate points (tj', THDj'), where tj' represents the difference between the timestamp of the j-th selected future THD and the timestamp of the 1st selected future THD, and THDj represents the j-th selected future THD; Generate historical coordinate points (ti, THDi), where ti represents the difference between the timestamp of the i-th selected historical THD and the timestamp of the n-th selected historical THD, and THDi represents the i-th selected historical THD.

3. The electrical variable detection method for inverter aging test according to claim 1, characterized in that, During the calculation of the judgment value, F1 and H1 are both 0, and F2 and H2 are tn' and tn respectively.

4. The method for detecting electrical variables in inverter aging tests according to claim 1, characterized in that, Determining the aging level of an inverter based on future THD and historical THD includes: Both future THD and historical THD are used as THD for judgment, and the THDs are sorted in chronological order. The THDs are grouped, and the difference between any two THDs in a group is less than a preset difference threshold. The position of the PHD in the group in the sorting is adjacent to the position of at least one THD in the same group in the sorting. The mean value of the PHD in the group is calculated as the group value. If the variance of the group value is less than the preset variance threshold, the weighted sum of the group values ​​is used to obtain the aging value L of the inverter. The aging degree of the inverter is determined based on the aging value L.

5. The electrical variable detection method for inverter aging test according to claim 4, characterized in that, Determining the aging degree of an inverter based on its aging value L includes: Set aging value thresholds L1 and L2, with L1 being less than L2; If L < L1, then the inverter is considered to have a low degree of aging. If L1≤L<L2, then the inverter is considered to be of average aging level. If L2 < L, then the inverter is considered to be in a high aging state.

6. The method for detecting electrical variables in inverter aging tests according to claim 4, characterized in that, During the calculation of the aging value L, if the variance of the grouped values ​​is greater than or equal to the preset variance threshold, the following steps are performed: Sort the group values ​​in ascending order, remove the first group value in the sorted list, calculate the variance of the remaining group values, and determine whether to proceed with the step of calculating the aging value L.

7. The method for detecting electrical variables in inverter aging tests according to claim 4, characterized in that, In the process of calculating the aging value L, the weight of the group value is proportional to the target time, which represents the average of the timestamps of all THD determinations in the group.

8. The method for detecting electrical variables in inverter aging tests according to claim 1, characterized in that, If it is determined that the inverter in the UPS system does not have aging, the average historical THD is used to replace the future THD, and this value is invoked the next time a THD value greater than the preset THD threshold occurs.

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