Estimation of remaining useful life of capacitors

Abstract

The invention relates to a method for determining a value representing the remaining useful life RUL of a capacitor, the method comprising the following operations: - repeating a plurality of iterations 1 to k, k being an integer greater than 1: acquiring (301) an environmental measurement representing the environment of the capacitor in the current iteration; - calculating (307) at least one aging model based on previous environmental measurements acquired in previous iterations 1 to k-1 before the current iteration and based on the environmental measurement received in iteration k; - determining (308-311) a value representing the RUL of the capacitor based on the at least one calculated aging model.

Description

Technical Field

[0001] The present invention relates to the estimation of the remaining useful life of capacitors, in particular but not exclusively electrolytic capacitors. Background Art

[0002] Capacitors are well-known devices that are capable of storing electrical energy by accumulating positive and negative charges in an anode and a cathode separated by a dielectric component.

[0003] Electrolytic capacitors are used in power converters such as motor drives and Uninterruptible Power Systems (UPS).

[0004] Electrolytic capacitors are one of the most critical electronic components. A large number of failures in static converters are due to electrolytic capacitors, as explained in the following literature:

[0005] -A.Lahyani,P.Venet,G.Grellet,&P.J.Viverge,Failure prediction ofelectrolytic capacitors during operation of a switch-mode power supply.IEEETransactions on power electronics,1998,13(6),1199-1207;

[0006] -USof AD of Defense, "Military Handbook: Reliability Prediction of Electronic Equipment: MIL-HDBK-217F:2 December 1991". Department of defense, 1991;

[0007] -S.Yang, A.Bryant, P.Mawby, D.Xiang, and P.Tavner, "An industry-based survey of reliability in power electronic converters", in 2009 IEEE EnergyConversion Congress and Exposition, 2009, p.3151-3157.

[0008] In some power converter applications, it is recommended to replace electrolytic capacitors regularly to avoid unexpected downtime of the entire power converter product due to failure of the electrolytic capacitors.

[0009] In UPS products such as the Schneider Electric Galaxy series, it is recommended to replace the electrolytic capacitors every five years to avoid unexpected downtime of the entire UPS product due to failure of the electrolytic capacitors.

[0010] However, in practice, many capacitors are replaced before their remaining useful life expires.

[0011] Therefore, there is a need for a method and a tool that allows monitoring of environmental conditions and / or prediction of the remaining useful life RUL of capacitors in order to plan maintenance in a timely manner and to warn the operator / user when a capacitor change is required.

[0012] A real capacitor can be considered as a resistor connected in series with a capacitor (called capacitance C), which is called equivalent series resistance (ESR).

[0013] Prior art solutions propose to evaluate RUL based on ESR and C, such as described in detail in the following documents:

[0014] -P.Venet, H.Darnand and G.Grellet, "Detection of faults of filtercapacitors in a converter.Application to predictive maintenance", inProceedings of Intelec 93:15th International Telecommunications EnergyConference,1993,vol.2,p.229-234vol.2;

[0015] -P.Venet,F.Perisse,G.Grellet,&G.Rojat.Condensateurintelligent.Demande de brevet FR 99 10 292,1999;

[0016] -K.-W.Lee, M.Kim, J.Yoon, SBLee, and J.-Y.Yoo, "Condition monitoring ofDC-link electrolytic capacitors in adjustable-speed drives", IEEETrans.Ind.Appl., vol.44, n°5, p.1606-1613, 2008;

[0017] -K.Abdennadher, P.Venet, G.Rojat, J.-M.Rétif and C.Rosset, "A real-timepredictive-maintenance system of aluminum electrolytic capacitors used inuninterrupted power supplies", IEEE Trans.Ind.Appl., vol.46, n°4, p.1644-1652, 2010.

[0018] In the prior art solutions, in a preliminary phase, the RUL of the capacitors is estimated by building an aging model for each capacitor version. The aging model is built offline and besides the time (several months), it requires many measurements, special equipment, many calculations and hardware components, which makes the solution complex, expensive and not suitable for industrial applications.

[0019] When a new version of a capacitor is introduced, the aging model for that capacitor needs to be built again to be able to estimate the RUL.

[0020] Figure 1 A method of estimating the RUL of a capacitor according to the prior art is shown.

[0021] The method comprises a preliminary stage 100 of calculating / building an aging model.

[0022] The preliminary stage 100 includes the following steps:

[0023] - In step 101 , an accelerated aging test is performed on the capacitor based on certain values ​​such as the maximum temperature value and the maximum voltage value of the capacitor to determine the evolution of the ESR and C value over time;

[0024] - In step 102, capacitor parameters are obtained. These parameters are specific to the capacitor version;

[0025] - In step 103, an ESR aging model and a C aging model are constructed based on the ESR and C values ​​and based on the capacitor parameters. Based on these models and based on the current ESR or C value, the RUL can be directly determined;

[0026] - The constructed ESR and C models are stored in a storage device associated with the version of the capacitor at step 104. Therefore, steps 101 to 104 need to be performed for each capacitor version, which is time consuming and expensive.

[0027] According to the prior art, the current stage 110 of estimating the RUL of a given version of a capacitor comprises the following steps:

[0028] - In step 111 , based on the current measurement of the values, the current values ​​(also called indices) of ESR and C are determined;

[0029] - In step 112, the ESR and C models corresponding to the capacitor version are retrieved from the storage device;

[0030] - In step 113, the current ESR and C values ​​(also called indexes) are compared with the retrieved model respectively to extract two RUL values;

[0031] - In step 114 , the capacitor RUL is determined based on the two extracted RUL values.

[0032] Therefore, determining the capacitor RUL lacks flexibility because the model needs to be calculated and stored for each capacitor version.

[0033] What is needed is a method of determining the RUL of a capacitor that requires less computing power and is more flexible than prior art solutions. Summary of the invention

[0034] It is an object of the present invention to alleviate at least some of the above disadvantages.

[0035] A first aspect of the invention relates to a method for determining a value representative of a remaining useful life RUL of a capacitor, the method comprising the following operations:

[0036] - Repeat multiple iterations 1 to k, where k is an integer greater than 1:

[0037] Obtain an environmental measurement representing an environment of the capacitor in the current iteration;

[0038] - calculating at least one aging model based on previous environmental measurements acquired in previous iterations 1 to k-1 before the current iteration k and based on environmental measurements received in iteration k;

[0039] - determining a value representative of the RUL of the capacitor based on at least one calculated aging model.

[0040] According to some embodiments, environmental measurements may include:

[0041] -Temperature measurement near the capacitor;

[0042] - a voltage measurement representing the value of the voltage at the terminals of the capacitor; and / or

[0043] -Current measurement that represents the value of the current flowing through the capacitor.

[0044] As a supplement, for each iteration, the core temperature of the capacitor may be determined based on the measured ambient temperature in the vicinity of the capacitor, and the aging model may be calculated based on the core temperature, based on the current value and / or based on the voltage value.

[0045] According to some embodiments, the method may further include: for each iteration i, estimating the equivalent series resistance ESR i value and / or capacitor C i The value, i is comprised between 1 and k, and the at least one aging model may represent the evolution of the ESR value of the capacitor from iteration 1 to k and / or the evolution of the C value of the capacitor from iteration 1 to k.

[0046] As a complement, the first aging model may represent the evolution of the ESR value of the capacitor from iteration 1 to k, and the second aging model represents the evolution of the C value of the capacitor from iteration 1 to k.

[0047] As a complement, the ESR value and / or the C value may be obtained by filtering the value of the voltage at the terminals of the capacitor and the value of the current flowing through the capacitor.

[0048] As a complement, the C value may be obtained by applying a bandpass filter at a low frequency, and / or the ESR value may be obtained by applying a bandpass filter at an intermediate frequency.

[0049] Additionally, the low frequency may include 120 Hz and the middle frequency may include 15 kHz; or the low frequency may include 300 Hz and the middle frequency may include 4 kHz.

[0050] According to some embodiments, the aging model may include at least one impedance value and time for each iteration, the impedance value being determined based on the current value and the voltage value, and for each iteration i, the impedance value being adjusted based on a temperature value corresponding to iteration i and based on a reference condition.

[0051] As a supplement, the temperature value can be the capacitor T c,i The core temperature, for each iteration i, is based on a temperature measurement T representing the ambient temperature near the capacitor amb,i The core temperature T c,i .

[0052] In addition, the core temperature T c,i It can be calculated as follows:

[0053]

[0054] Among them, I RMS,i is the RMS value of the current flowing through the capacitor at iteration i;

[0055] R th is the thermal resistance of the capacitor; and

[0056] ESR i is the equivalent series resistance value of the capacitor at iteration i.

[0057] Additionally or alternatively, for each iteration i, the impedance value may include the ESR i Value and / or C i value, and can be based on the core temperature T c,i To adjust the ESR i Value and / or C i value to determine the adjusted value ESR based on the following equation, for example i,adjusted and / or C i,adjusted :

[0058]

[0059]

[0060] Among them, β1, β2, β3, β4 and β5 are constants.

[0061] As a complement, the method may also comprise a preliminary stage of determining β1 , β2 , β3 , β4 and β5 by varying the temperature conditions during a test period and performing current and voltage measurements during the test period.

[0062] According to some embodiments, the aging model may include at least one impedance value and time for each iteration, the impedance value being determined based on the current value and the voltage value, and for each iteration i, the time may be adjusted based on the temperature value, current value and / or voltage value corresponding to iteration i and based on a reference condition.

[0063] As a supplement, the following factor K can be used T,i , K I,i , K V and K TI,i The time for each iteration i can be adjusted by one or more combinations of:

[0064]

[0065]

[0066]

[0067]

[0068] Where T0 is the reference temperature, T x,i is the core temperature of the capacitor at iteration i, K r It depends on I RMSx,i The factor I RMS0 is the reference value of the current flowing through the capacitor, I RMSx,i is the actual value of the current flowing through the capacitor at iteration i, ΔT0 is the predefined value of the core temperature increase, V0 is the reference value of the voltage at the capacitor, V x,i is the actual value of the voltage at the capacitor at iteration i, n is a predefined integer, E a is the activation energy of the capacitor and kb is the Boltzmann constant.

[0069] According to some embodiments, at least one aging model may be updated in each iteration i based on a previous aging model determined in iteration i-1 and based on environmental measurements acquired in iteration i, and a value representing the RUL may be determined after each iteration i, i being between 1 and k.

[0070] According to some embodiments, the value representing the capacitor RUL may be determined by extrapolating a value of at least one aging model and by comparing the extrapolated value with at least one predetermined threshold value.

[0071] According to some embodiments, the value representing the RUL of the capacitor may be:

[0072] - the ratio between the RUL of the capacitor calculated based on the aging model and the end of life estimated based on the aging model; or

[0073] - The ratio between the RUL of the capacitor calculated based on the aging model and the predetermined end of life.

[0074] According to some embodiments, the method may further include:

[0075] - comparing the value representing the RUL with a predetermined threshold; and

[0076] - Raise alerts based on comparisons.

[0077] According to some embodiments, the RUL of a capacitor may be determined for a reference condition, and the value of RUL is expressed as:

[0078] - is derived directly from the RUL of the capacitor; or

[0079] - is derived from the actual RUL (denoted by RULx) obtained by adjusting the RUL of the capacitor (denoted by RUL0) to the actual conditions.

[0080] As a supplement, the reference condition can be set by the user.

[0081] A second aspect of the invention relates to a non-transitory computer-readable storage medium having stored thereon a computer program, the computer program comprising instructions which, when executed by a processor, perform the steps of the method according to the first aspect of the invention.

[0082] A third aspect of the invention relates to a device for determining a value representing a remaining useful life RUL of a capacitor, the device comprising a memory and a processor, the processor being configured to:

[0083] - Repeat multiple iterations 1 to k, where k is an integer greater than 1:

[0084] acquiring, via at least one sensor or at least one communication interface, an environmental measurement representative of an environment of the capacitor in a current iteration;

[0085] - calculating at least one aging model based on previous environmental measurements acquired in previous iterations 1 to k-1 before the current iteration k and based on environmental measurements received in iteration k;

[0086] - determining a value representative of the RUL of the capacitor based on at least one calculated aging model.

[0087] Further objects, aspects, effects and details of the present invention are described in the following detailed description of a number of exemplary embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] By way of example only, embodiments of the present disclosure will be described with reference to the accompanying drawings, in which:

[0089] Figure 1 A method according to the prior art is shown;

[0090] Figure 2 represents an apparatus according to some embodiments of the present invention;

[0091] Figure 3 is a flow chart illustrating steps of a method according to some embodiments of the present invention;

[0092] Figure 4 is a diagram illustrating application of two filters to environmental measurements taken from a capacitor environment according to some embodiments of the present invention;

[0093] Figure 5shows the adjustment of characteristic values ​​ESR and C based on predetermined environmental conditions according to some embodiments of the present invention;

[0094] Figure 6 illustrates time-based adjustments to predetermined environmental conditions according to some embodiments of the present invention;

[0095] Figure 7 shows the calculation of a model for characteristic values ​​ESR and C according to some embodiments of the present invention;

[0096] Figure 8 shows the calculation of RUL value according to some embodiments of the present invention; and

[0097] Fig. 9 It shows execution Figure 3 A flowchart of the operation of step one is shown. DETAILED DESCRIPTION

[0098] refer to Figure 2 , shows a device 200 for estimating the RUL of a capacitor 206 (hereinafter referred to as "capacitor RUL") according to some embodiments of the present invention. The device 200 can be integrated in a system including a capacitor. For example, the capacitor 206 can be integrated in a larger device 207 such as a converter. There is no additional limitation to the device 207, which can be any device that integrates a capacitor.

[0099] The device 200 may include at least one sensor 201 configured to obtain an environmental measurement representative of the environment of the capacitor 206 at the current time.

[0100] Alternatively, and preferably, the device may include a communication interface 204 configured to communicate with one or more remote sensors 208 located near the capacitor 206 (e.g., inside the device 207). For example, in most converters that include a capacitor, an ambient temperature sensor is inherently integrated. Otherwise, one can be added at low cost. It should be noted that the external sensor 208 can be located outside the equipment 207.

[0101] Sensors 201 and 208 are configured to acquire environmental measurements related to capacitor 206 .

[0102] Thus, environmental measurements may be acquired by device 200 via sensor 201 and / or via communication interface 204 .

[0103] Sensors 201 and / or 208 may be, for example, temperature sensors, current sensors, and / or voltage sensors. However, there is no additional limitation on the type of sensor, and these examples are given for illustrative purposes. The ripple current i of capacitor 206 CIt can be derived by an algorithm based on the input and output currents of the converter and the switching state. Alternatively, a direct measurement of the ripple current i C Sensors 201 and / or 208.

[0104] The device 200 may further comprise a user interface 209 for interacting with a user. In particular, the user interface 209 may allow the user to set a reference condition or select a value representing the RUL of the capacitor among a plurality of possible values.

[0105] The device 200 may also include a processor 202 and a memory 203, which are configured to execute Figure 3 The steps of the method are shown.

[0106] Figure 3 is a flow chart showing the steps of a method according to some embodiments of the present invention. Figure 3 In the following, iteration k is mentioned, k being an integer greater than or equal to 1. There is no additional restriction on the duration between consecutive iterations. These durations may be fixed (environmental measurements are performed at a given frequency, such as once every 1000 hours), or may vary (e.g. triggered by event detection).

[0107] At step 301, the device 200 acquires (measured via the sensor 201 or received from the external sensor 208 via the communication interface 204) environmental measurements representing the environment of the capacitor 207 at the current time. The environmental measurements may include environmental characteristics, such as the ambient temperature around the capacitor 206, the voltage at the terminals of the capacitor 206 or the terminals of the equipment 207, and the current flowing through the capacitor 206 (hereinafter referred to as "ripple current") or the current flowing through the equipment 207. When the current flowing through the equipment or the voltage at the equipment is measured, the ripple current or capacitor voltage may be derived from the measured value(s) based on the architecture of the equipment 207 integrating the capacitor 206.

[0108] Preferably, in step 301, multiple measurements of the same environmental characteristic are obtained. For example, multiple changes in capacitor voltage and / or ripple current over a given period of time are obtained. Temperature is a less variable environmental characteristic and can be represented by a single value (e.g., an instantaneous value or an average value over a period of time). There is no limit to the measurement frequency and the number of measurements performed for each iteration of the method according to the present invention. For example, measurements can be performed at a regular frequency or continuously between two iterations k and k+1. For illustrative purposes, environmental measurements can be obtained every 10 seconds, or a continuous signal can be obtained as environmental measurements.

[0109] At least some of the environmental measurements may be filtered by at least one filter at step 302. For example, an impedance Z corresponding to the ratio between the capacitor voltage and the ripple current may be filtered. Alternatively, and preferably, due to easier implementation, the capacitor voltage and the ripple current may be filtered separately, and then the impedance Z may be calculated based on the filtered values.

[0110] Figure 4 The evolution of the impedance 300 of the capacitor 206 with frequency is shown according to some embodiments of the present invention.

[0111] By applying a bandpass filter 401 in low frequencies (e.g., between 0 and 1 kHz or 2 kHz, more generally, less than a few kHz) to the impedance Z, the capacitance C of the capacitor 206 can be calculated. In fact, at low frequencies, the capacitor 206 has a capacitive characteristic, so the low-frequency bandpass filter 401 allows the capacitance value C of the capacitor 206 to be estimated. Figure 4 As shown, the low frequency band pass filter 401 can exclude frequencies higher than 1 kHz, and in particular exclude frequencies higher than 2 kHz. This is given for illustrative purposes and does not limit the scope of the present invention. The low frequency band pass filtering can be a band pass filtering centered on a low frequency (e.g., 120 Hz).

[0112] By applying the intermediate frequency bandpass filter 402 to the impedance Z, the ESR of the capacitor 206 can be estimated. In fact, at the intermediate frequency, the capacitor 206 has a resistive characteristic, so the intermediate frequency bandpass filter 402 allows the capacitor's ESR to be estimated. Figure 4 As shown, the intermediate frequency bandpass filter 402 may only allow frequencies between 5 kHz and 800 kHz. This is given for illustrative purposes and does not limit the scope of the present invention.

[0113] Alternatively, bandpass filters (low frequency and medium frequency) can be applied to the ripple current and the measured voltage, respectively, and the impedance can then be calculated based on the filtered ripple current and the filtered voltage. In this embodiment, the ripple current signal and the measured voltage signal are filtered, and then the filtered signals can be processed to calculate a root mean square RMS value for each signal or to obtain an image of an effective value, such as the peak value of each filtered signal or the average value within a half cycle (e.g., the positive half cycle) of each filtered signal. 1 / 2πf.C then corresponds to the ratio or image of the RMS values ​​when filtered by the first filter, and ESR corresponds to the ratio or image of the RMS values ​​when filtered by the second filter.

[0114] A low-pass filter can also be applied to the measured voltage signal to extract the DC voltage value U DC .

[0115] The filter may be a digital filter stored in the memory 203 , or may be an electronic circuit of the device 200 .

[0116] For iteration k, the ripple current i C Filter the voltage u and calculate the RMS value U rms and I rms Afterwards, the following table can be obtained, which is given as an example:

[0117]

[0118] Because the current flowing through capacitor 206 is alternating, the RMS value is calculated.

[0119] In this table, temperature T may be the core temperature T determined based on the temperature measurements performed in iteration k. c,k , as described below.

[0120] In this example, k is equal to 7, and the environmental measurement of row 7 has been acquired in step 301 and filtered in step 302, before rows 1 to 6 have been acquired in previous iterations. According to the above table, environmental measurements are acquired at regular time intervals (such as once every 5000 hours), or more frequently (or continuously), and then weighted and averaged to obtain a single value for each time interval between two iterations.

[0121] The low frequency bandpass filtering enables the calculation of C, and the medium frequency bandpass filtering enables the calculation of ESR. Specific values ​​are given below for illustration purposes only. The low frequency bandpass filtering can be performed around 120 Hz, and the medium frequency bandpass filtering can be performed around 15 kHz. Alternatively, the low frequency bandpass filtering can be performed at 300 Hz, and the medium frequency bandpass filtering can be performed at 4 kHz. However, from Figure 4 It can be seen from Figure 1 that ESR and C cannot be directly obtained using these filtered values ​​because 300 Hz and 4 kHz correspond to the frequencies of mixed characteristics (both capacitive characteristics and resistive characteristics). However, ESR and C can be estimated by using a system of equations of two equations with two unknown parameters (ESR and C). There is no additional restriction on the system of equations, which can represent the impedance Z filtered by two different filters based on C and ESR, respectively.

[0122] Return to reference Figure 3 The method according to some embodiments of the present invention further comprises a step 303 of obtaining parameters related to the version of the capacitor. Some of the parameters may be denoted as β j , where j varies between 1 and n, and n is an integer equal to or greater than 1. th 、E a 、Tmax、U0、I RMS0Other parameters of γ1..3 can also be obtained in step 303. th is the thermal resistance of the capacitor. E a is the activation energy of the capacitor. U0 is the maximum voltage allowed by the capacitor, and I RMS0 is the maximum RMS value of the current allowed by the capacitor. These other parameters can be obtained directly from the manufacturer data sheet. For a given capacitor, step 303 can only be performed once and does not need to be repeated like other steps.

[0123] These parameters can be obtained directly from the manufacturer's data sheet, or can be obtained during a preliminary phase. For example, during a preliminary phase, the parameters can be calculated, for example, during a test period in a laboratory. j The value is a constant that allows the ESR and C values ​​to be adjusted based on ambient or core temperature, as described below.

[0124] Value β j In step 303, it can be obtained:

[0125] - obtained from the manufacturer's data sheet;

[0126] - obtained from a training session (such as a training session of a day) during which, for a given core temperature (eg 25°C or a maximum temperature value), the value ESR described below adjusted , C adjusted is considered fixed and during the training period, the ESR, C and core temperature T c The main goal is to obtain the effect of varying temperature over the course of a day (or more generally, a period of time short enough that aging does not affect the ESR and C values) on the estimated values ​​of ESR and C, so that β j The value can be determined based on, for example, the following formula:

[0127]

[0128]

[0129] This may be performed after commissioning of the equipment 207 and during normal operation;

[0130] - obtained from a training period (such as a training period of a day), for example before commissioning of the equipment 207, for a given core temperature (eg 25°C or a maximum temperature value), the value ESR described below adjusted , C adjusted is considered fixed and controls the core temperature T c Measuring ESR and C at different temperatures allows β to be estimated according to the above formula j value.

[0131] At step 304, the value ESR is derived from the impedance values ​​obtained from the two filters as described above. k and C k .

[0132] In step 305, the value ESR k and C k and the previous value ESR i and C i A first adjustment is made, i varies between 1 and k-1. Alternatively, the first adjustment is applied only to the value ESR k and C k , and ESR i and C i The adjusted value of (i varies between 1 and k-1) has been pre-stored in the memory 203. The same principle applies to the second adjustment of step 306.

[0133] As an example, the first adjustment can be a measurement adjustment (meaning an adjustment of the values ​​of ESR and C calculated based on environmental measurements). This enables measurements performed at different times and under different conditions to be adjusted to similar predetermined conditions (e.g. temperature conditions). In fact, the value ESR i and C i (i varies between 1 and k) is temperature dependent, and the core temperature of the capacitor varies with some of the environmental measurements (such as the ambient temperature T amb,k and / or ripple current i C,k The first adjustment value ESR k,adjusted and C k,adjusted It can be calculated as follows:

[0134]

[0135]

[0136] As mentioned above, β has been obtained in step 303. k Value. c,k is the core temperature, which can be obtained from the measured ambient temperature T amb Export. For example, T c,k It can be calculated as follows:

[0137]

[0138] Among them, I RMS,k is based on the ripple current signal i measured or determined for iteration k C,k The calculated RMS value, R th is the thermal resistance of capacitor 206. Figure 5Indicates the value ESR on the curve representing the time-varying value ESR and C i and C i (i varies between 1 and k, in the above example k is equal to 7). Figure 5 In the example, the value of ESR i and C i is adjusted to a reference temperature corresponding to the maximum temperature. The maximum temperature can be obtained from the manufacturer's data sheet. Alternatively, the reference temperature can be set to any temperature value, such as 25°C, for example. The constant β discussed above j Depends on the reference temperature.

[0139] For example, to adjust the value ESR of the reference mark 500 based on the formula given above i , to obtain the adjusted value ESR i,adjusted 501. For example, based on the formula given above (in this example, the reference temperature is the maximum temperature value), the value C of reference mark 502 is adjusted. i , to obtain the adjustment value C i,adjusted 503.

[0140] In step 306, the adjustment value ESR k,adjusted and C k,adjusted A second adjustment is applied. In this exemplary embodiment, the second adjustment corresponds to time compression. It should be noted that this is given for illustrative purposes, and alternatively, the first adjustment may correspond to time compression and the second adjustment may correspond to measurement adjustment (adjustment of the values ​​ESR and C). It should be noted that the reference temperature T0 of the first and second adjustments may be different. For example, even when the reference temperature for measurement adjustment is a temperature such as 20°C or 25°C, the reference temperature T0 for the second adjustment (time compression) is preferably the maximum rated temperature. This also applies to the reference values ​​ΔT0, I RMS,0 , ESR0 and V0, which are preferably at their maximum rated values ​​for the second adjustment. This allows for a time scale that is as compressed as possible.

[0141] It can be considered that the ambient conditions are maintained between two iterations: the conditions between k-1 and k therefore correspond to the core temperature T c,k-1 (or the ambient temperature T measured at time k-1 x,k-1 ), ripple current i c,k-1 (e.g., like this, or a ripple current filtered by a low-frequency bandpass filter) and / or the applied voltage u k-1 Alternatively, the temperature may be measured continuously between iterations k-1 and k (or measured at a given frequency greater than the frequency of iteration k), and the average temperature may be used as the ambient condition. Alternatively, and preferably, the following factor K is calculated for each measurement instant:T (possibly multiple times per iteration), then the average K can be calculated for iteration i T,i This principle can be extended to the applied voltage and ripple current or their corresponding factor K I,i and K V,i .

[0142] For example, it is proposed to calculate the factor K based on the following formula T,i , K I,i , K V,i :

[0143] Based on information given by the manufacturer:

[0144] -For the temperature factor K T,i :

[0145]

[0146] - For the current factor K I,i :

[0147]

[0148] Among them, K r is a predetermined empirical safety factor:

[0149] If I RMSx,i ≤I RMS0 , then K r =2;

[0150] If I RMSxi，i >I RMS0 , then K r =4.

[0151] Where ΔT0 is the core temperature increase at the maximum rated temperature, and I RMS0 This indicates the maximum temperature change due to current variation (self-heating) that the capacitor can support without degradation. ΔT0 may be equal to 10° C. Preferably, this value may be predetermined.

[0152] - For voltage factor K V,i :

[0153]

[0154] Wherein, V0 is the rated voltage obtained in step 303, V x,i is the operating voltage actually applied at time i (measured voltage), and n is a predetermined empirical safety factor. n may for example be comprised between 2 and 5. This parameter may be obtained in step 303 , for example from a manufacturer data sheet or a technical description.

[0155] Once the factor K is calculated T,i , K I,i , K V,i , then two consecutive iterations can be performed with each interval Δtime between i and i+1 x,i time (in the example above, the interval is fixed to 5000 hours) to obtain Δtime 0,i :

[0156]

[0157] As with other symbols, the index "0" refers to reference (eg, extreme) environmental conditions, while "x" refers to actual environmental conditions.

[0158] An alternative formula based on Arrhenius's law that is more accurate than the manufacturer's formula above can be used to determine K T,i .K I,i , which can be denoted as K TI,i :

[0159]

[0160]

[0161] Where E a is the activation energy and kb is the Boltzmann constant, T x,i is the ambient temperature near the capacitor at time i, T0 is the reference or maximum temperature,

[0162] in,

[0163] Figure 6 The ESR obtained after the above step 306 on the curve representing the time-varying values ​​ESR and C is shown in FIG. i,adjusted and C i,adjusted (i varies between 1 and k, in the above example, k is equal to 7) to obtain the normalized value ESR i,adjusted,norm and C i,adjusted,norm .

[0164] Value ESR i,adjusted and C i,adjusted is adjusted in time to a common time reference. For example, the value ESR referenced at 600 is adjusted based on the formula given above i,Tmax To obtain the normalized value ESR i,adjusted,norm 601. For example, based on the formula given above, the C referenced as 602 is adjusted. i,adjusted To obtain the normalized value C i,adjusted,norm 603.

[0165] In step 307, based on the adjusted value ESR i,adjusted,norm and C i,adjusted,norm The evolution model of ESR and C is established. There is no additional restriction on the manner of establishing the evolution model. For example, the identification may include a least squares criterion. For example, the model may be determined according to the least squares criterion so that the model and the adjusted value ESR i,adjusted,norm and C i,adjusted,norm The difference between is minimal. The model may be built by updating the model built in the previous iteration k-1, or may be calculated based on all measurements acquired (and optionally adjusted) between iterations 1 and k.

[0166] like Figure 7 As shown, the model ESR model (t) can be a predetermined form ESR model (t) = α1 + α2e α 3 t , and the evolution model C model (t) may be a predetermined form C model (t) = α4 + α5t. This means that the evolution model is assumed to have the above form, and the evolution model is established by determining the optimal values ​​of the coefficients α1, α2, α3, α4 and α5. There is no additional restriction on the form of the model, which may be different from Figure 7 Different than shown.

[0167] Thus, the coefficients α1, α2, α3, α4 and α5 are calculated and updated in each new iteration k. Thus, the evolution model (or aging model) can be updated in each iteration, becoming more and more accurate. The larger k is, the more accurate the evolution model is. Alternatively, the model is updated only when the minimum index k is reached. min For the previous iterations 1 to k min -1, the measured or adjusted value is stored for final processing.

[0168] At step 308 , based on the determined model, the ESR and C curves may be extrapolated over times corresponding to iterations 1 to k.

[0169] The model has been built in step 307 and the ESR has been extrapolated in step 308 model (t) and C model After the (t) curve, the method may further include a step of estimating the RUL value 309. To this end, one or more criteria may be fixed to determine the time corresponding to the end of the life of the capacitor 206.

[0170] The criteria could be, for example:

[0171] - the ESR value doubles compared to its initial value; and / or

[0172] -C value decreased by 20% compared to its initial value.

[0173] When the standard is met, a time corresponding to the end of the life of the capacitor according to the standard can be derived.

[0174] There are no additional restrictions on the criteria used to estimate the end of life. For example, different thresholds than those given above may be used.

[0175] The RUL value can then be calculated by calculating the difference between the estimated end of life (compression or under extreme conditions) and the compression time of the current iteration k. The "compression time" refers to the time of iteration k, such as Figure 6 shown.

[0176] refer to Figure 8 , a curve 800 of the ESR evolution model and a curve 803 of the C evolution model are shown. Thresholds 801 and 804 are represented as described above (twice the initial ESR value and 80% of the initial C value).

[0177] Then, two RUL values ​​RUL can be calculated ESR,k 802 and RUL C,k 805 (they correspond to the differences mentioned above).

[0178] Then, in step 310, based on the RUL value RUL ESR,k 802 and RUL C,k 805 to calculate the capacitor RUL. For example, the RUL value RUL can be selected ESR,k 802 and RUL C,k The minimum value among 805 is taken as the capacitor RUL. Alternatively, the RUL value RUL can be calculated ESR,k 802 and RUL C,k The average of 805 is used as the capacitor RUL. Other calculations can be applied to the RUL value RUL ESR,k 802 and RUL C,k 805 is to determine the capacitor RUL.

[0179] Due to the steps 305 and 306 of adjusting the reference environmental conditions (eg extreme environmental conditions), a capacitor RUL for such reference environmental conditions is obtained, which is denoted as RUL0 (or RUL 0,k because it is determined for iteration k).

[0180] At step 311, an output is issued based on capacitor RUL. The output may be a health status value that is transmitted to a remote entity for display to an operator, or that is displayed on the device, or that is used to compare to a threshold to issue an alarm based on the comparison.

[0181] The health status can be calculated as follows:

[0182] - capacitor RUL and Figure 8 End of life shown (when ESR model (t) curve and / or C model (t) the time when the curve reaches the threshold);

[0183] - The ratio between the capacitor RUL and a predetermined end of life (such as that given by the manufacturer's data sheet).

[0184] The ratio is preferred because the capacitor RUL has been determined for given reference environmental conditions.

[0185] For example, when the health status value is below a predefined alarm threshold (such as 10% or 5%), an alarm may be issued at step 310 .

[0186] The reference condition may be set by a user of the device 200 via the user interface 209. The user may also set an alarm threshold and may select a value to be output at step 311 from a set of multiple possible values ​​(eg, may select between the two possible ratios mentioned above).

[0187] Before performing step 311, a step 312 of adjusting the capacitor RUL from the reference environmental conditions to the actual environmental conditions may optionally be performed. In fact, the capacitor RUL calculated in step 310 has been calculated for the reference environmental conditions and does not represent the actual environmental conditions to which the capacitor is exposed.

[0188] The same principles may be used as used for compressing the time in step 306. In order to adjust the time from the reference conditions to the actual conditions, the influence of each environmental condition may be taken into account (ambient temperature, ripple current and applied voltage).

[0189] RUL x =RUL0.K T .K I .K V ;

[0190] For example, K T,k ,K I,k and K V,k (the value of the last iteration k) can be used as K T ,K I and K V .

[0191] RUL x represents the capacitor value under actual conditions. In step 310, this value can be used instead of RUL0. RUL x(rather than indicating a ratio) it also indicates that the value corresponds to the current conditions.

[0192] According to different embodiments:

[0193] - for each iteration 1 to k, repeat steps 301 to 312; or

[0194] - For iterations 1 to k min , repeating steps 301 to 306 and storing the measured or adjusted values ​​in a memory, and steps 301 to 312 may be iterated for the next iteration; or

[0195] - iterate steps 301 to 306 and store the measured or adjusted values ​​in a memory and execute steps 307 to 312 based on a user request via a user interface; or

[0196] iterate steps 301 to 306 and store the measured or adjusted values ​​in a memory and once k reaches a predetermined value, execute steps 307 to 312; or

[0197] - iterate steps 301 to 307 and store the latest (updated) version of the model in a memory and perform steps 308 to 312 based on a user request via a user interface; or

[0198] - Iterate steps 301 to 307 and store the latest (updated) version of the model in memory, and once k reaches a predetermined value, execute steps 308 to 312.

[0199] Fig. 9 is a flow chart illustrating the operation of performing the above step 303 according to some embodiments of the present invention.

[0200] Specifically, it means that the obtained value β j operation.

[0201] As described above, the following operations may be performed during a given period, such as a period of one day, which is short enough that time does not affect the parameters ESR and C during the period. Thus, the period may be comprised between a few hours and a few days (eg, up to a week).

[0202] At step 900, capacitor 206 is at a given temperature T (eg, core temperature). As described above, this temperature may be controlled or may depend on conditions of normal operation.

[0203] At step 901, ESR and C are calculated as described above and stored in association with a given temperature.

[0204] For different temperature values, steps 900 and 901 are repeated.

[0205] In step 902, a reference temperature (such as 20°C, 25°C or a maximum temperature) is defined. We assume that the reference temperature is defined as 20°C, denoted as T20. The ESR and C values ​​are calculated by dividing ESR by T20 and C T20 And normalized, ESR T20 and C T20 are the ESR and T values ​​at the reference temperature.

[0206] In step 903, the curve depending on T To obtain the values ​​β1, β2 and β3, for example, In addition, the curve depends on T To obtain the values ​​β1, β2, and β3,

[0207] The least squares method can be used to determine β j value.

[0208] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the specific forms set forth herein. On the contrary, the present invention is limited only by the appended claims, and within the scope of these appended claims, other embodiments besides the specific embodiments described above are equally possible.

[0209] In addition, although exemplary embodiments have been described above with some exemplary combinations of components and / or functions, it should be understood that alternative embodiments may be provided by different combinations of components and / or functions without departing from the scope of the present disclosure. In addition, it is specifically contemplated that specific features described separately or as part of an embodiment may be combined with other separately described features or parts of other embodiments.

Claims

1. A method for determining a value representing a remaining useful life RUL of a capacitor (206), the method comprising the following operations: - Repeat multiple iterations 1 to k, where k is an integer greater than 1: Obtain an environmental measurement representing an environment of the capacitor in the current iteration; - calculating at least one aging model based on previous environmental measurements acquired in previous iterations 1 to k-1 before the current iteration and based on environmental measurements received in iteration k; - determining a value representative of the RUL of the capacitor based on at least one calculated aging model, in, The aging model comprises at least one impedance value and a time for each iteration, the impedance value being determined based on the current value and the voltage value, and wherein, for each iteration i, the time is adjusted based on the temperature value, the current value and / or the voltage value corresponding to the iteration i and based on a reference condition.

2. The method according to claim 1, wherein: The environmental measurements include: - temperature measurement in the vicinity of the capacitor (206); - a voltage measurement representing the value of the voltage at the terminals of the capacitor; and / or -Current measurement that represents the value of the current flowing through the capacitor.

3. The method according to claim 2, wherein: For each iteration, a core temperature of the capacitor is determined based on a measured ambient temperature in the vicinity of the capacitor, and wherein the aging model is determined based on the core temperature, based on the current value and / or based on the voltage value.

4. The method according to any one of claims 1 to 3, comprising: For each iteration i, the equivalent series resistance ESR is estimated i value and / or capacitance C i The value, i, is comprised between 1 and k, wherein at least one aging model represents the evolution of the ESR value of the capacitor (206) from iterations 1 to k and / or the evolution of the C value of the capacitor (206) from iterations 1 to k.

5. The method according to claim 4, wherein: The first aging model represents the evolution of the ESR value of the capacitor (206) from iterations 1 to k, and the second aging model represents the evolution of the C value of the capacitor (206) from iterations 1 to k.

6. The method according to claim 2 or 3, wherein: The ESR value and / or the C value are obtained by filtering the value of the voltage at the terminals of the capacitor and the value of the current flowing through the capacitor.

7. The method according to claim 6, wherein: The C value is obtained by applying a bandpass filter at a low frequency, and / or the ESR value is obtained by applying a bandpass filter at an intermediate frequency.

8. The method according to claim 7, wherein: The low frequency comprises 120 Hz, and wherein the intermediate frequency comprises 15 kHz; or Wherein the low frequency comprises 300 Hz, and wherein the intermediate frequency comprises 4 kHz.

9. The method according to any one of claims 1 to 3, wherein: For each iteration i, the impedance value is adjusted based on the temperature value corresponding to iteration i and based on the reference conditions.

10. The method according to claim 9, wherein: The temperature value is the core temperature T of the capacitor (206) c,i , for each iteration i, based on a temperature measurement T representing the ambient temperature near the capacitor amb,i To calculate the core temperature T c,i .

11. The method according to claim 10, wherein: Among them, I RMS,i is the RMS value of the current flowing through the capacitor (206) at iteration i; R th is the thermal resistance of the capacitor; and ESR i is the equivalent series resistance value of the capacitor at iteration i.

12. The method according to claim 4, wherein: For each iteration i, the impedance value includes the ESR i Value and / or C i value, and where, according to the core temperature T c,i To adjust the ESR i Value and / or C i value to determine the value of the adjusted ESR based on the following equation i,adjusted and / or C i,adjusted : Among them, β1, β2, β3, β4 and β5 are constants.

13. The method of claim 12, further comprising a preliminary stage of determining β1, β2, β3, β4, and β5 by varying temperature conditions during a test period and performing current and voltage measurements during the test period.

14. The method according to claim 1, wherein: Based on the following factor K T,i , K I,i , K V and K TI,i The time for each iteration i can be adjusted by one or more combinations of: Where T0 is the reference temperature, T x,i is the core temperature of the capacitor at iteration i, K r It depends on I RMSx,i The factor I RMS0 is the reference value of the current flowing through the capacitor, I RMSx is the actual value of the current flowing through the capacitor at iteration i, ΔT0 is the predefined value of the core temperature increase, V0 is the reference value of the voltage at the capacitor, V x,i is the actual value of the voltage at the capacitor at iteration i, n is a predefined integer, E a is the activation energy of the capacitor and kb is the Boltzmann constant.

15. The method according to any one of claims 1 to 3, wherein: At least one aging model is updated in each iteration i based on a previous aging model determined in iteration i-1 and based on environmental measurements acquired in iteration i, and wherein a value representing the RUL is determined after each iteration i, i being between 1 and k included.

16. The method according to any one of claims 1 to 3, wherein: A value representative of the RUL of the capacitor is determined by extrapolating a value of at least one aging model and comparing the extrapolated value to at least one predetermined threshold value.

17. The method according to any one of claims 1 to 3, wherein: The value of RUL representing the capacitor is: - the ratio between the RUL of the capacitor calculated based on the aging model and the estimated end of life based on the aging model; or - The ratio between the RUL of the capacitor calculated based on the aging model and the predetermined end of life.

18. The method according to any one of claims 1 to 3, further comprising: - comparing the value representing the RUL with a predetermined threshold; as well as - issuing an alert based on said comparison.

19. The method according to any one of claims 1 to 3, wherein: The RUL of the capacitor is determined for reference conditions and where represents the value of RUL: - is derived directly from the RUL of the capacitor; or - is obtained by adjusting the RUL of the capacitor denoted by RUL0 to the actual conditions, denoted by RUL x The actual URL is derived.

20. The method according to claim 19, wherein: The reference condition is set by the user.

21. A non-transitory computer-readable storage medium having stored thereon a computer program, the computer program comprising instructions which, when executed by a processor, perform the steps of the method according to any one of claims 1 to 20.

22. A device for determining a value representing a remaining useful life RUL of a capacitor, the device comprising a memory and a processor, the processor being configured to: - Repeat multiple iterations 1 to k, where k is an integer greater than 1: acquiring, via at least one sensor or at least one communication interface, an environmental measurement representative of an environment of the capacitor in a current iteration; - calculating at least one aging model based on previous environmental measurements acquired in previous iterations 1 to k-1 before the current iteration and based on environmental measurements received in iteration k; - determining a value representative of the RUL of the capacitor based on at least one calculated aging model, in, The aging model comprises at least one impedance value and a time for each iteration, the impedance value being determined based on the current value and the voltage value, and wherein, for each iteration i, the time is adjusted based on the temperature value, the current value and / or the voltage value corresponding to the iteration i and based on a reference condition.

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