Method for determining the remaining lifetime of a capacitor unit and converter arrangement used in an intermediate circuit capacitor

Abstract

The invention relates to a method for determining the remaining lifetime of a capacitor unit (121, 122, 123) used in an intermediate circuit capacitor (120), wherein the intermediate circuit capacitor (120) is connected between a DC voltage source (110) and a power converter circuit (130) and comprises a plurality of capacitor units (121, 122, 123), comprising the steps of: determining the power dissipation of each individual capacitor unit (121, 122, 123) of the plurality of capacitor units; determining the temperature value of each capacitor unit (121, 122, 123) of the plurality of capacitor units depending on the determined power dissipation of the individual capacitor units; and determining the remaining lifetime of each capacitor unit (121, 122, 123) depending on the determined temperature value of the respective capacitor unit and on a voltage value of the respective capacitor unit.

Description

[0001] The present invention relates to a method for determining the remaining lifetime of a capacitor unit used in an intermediate circuit capacitor, a computing unit and a computer program for carrying it out, as well as a power converter arrangement. Background of the invention

[0002] In power electronics applications, e.g. in power converter arrangements (e.g. inverters or converters), DC link capacitors can be used as energy storage devices to supply the fast transient switching currents required by power modules or switching elements, e.g. MOSFETs, IGBTs, etc., and to produce an almost constant DC voltage for transient loads.

[0003] To meet the increasing power demands of electric drives in electromobility, for example, while keeping the resulting currents low, a design for high voltages (>60 V DC, for example, from approximately 400 V DC up to 1.2 kV DC) can be implemented. To comply with electrical safety requirements in the high-voltage range, metallized film capacitors in through-hole technology (THT) can be used for the DC link capacitors.

[0004] High-voltage power electronics products, such as power converter assemblies in the automotive sector, can be designed for wide DC link voltage ranges, e.g., between 450 V and 900 V DC. Regardless of the design or selection of DC link capacitors, significant voltage stresses can occur due to varying voltage levels and voltage fluctuations throughout the product's service life.

[0005] In addition to voltage fluctuations, current ripples can lead to a temperature increase at the capacitor's internal hotspot. Since the switching of the respective power module is usually controlled according to the product's load requirements, these temperature changes can result in significant thermal stresses over its lifetime.

[0006] For DC link capacitors, the rated service life in hours can be specified by a manufacturer or supplier, or in a datasheet, in conjunction with reference values, such as a reference temperature and a rated voltage. For example, the rated service life might be specified as 100,000 hours at a reference temperature of 85°C and a rated voltage of 900 V DC. However, if voltage or temperature loads are higher than these reference values, the expected service life may be shorter than the specified rated service life. Disclosure of the invention

[0007] According to the invention, a method for determining the remaining service life of a capacitor unit used in an intermediate circuit capacitor, a computing unit and a computer program for carrying out the method, as well as a power converter arrangement with the features of the independent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0008] The invention presents a way to determine the remaining lifetime of a capacitor unit in an intermediate circuit capacitor more precisely.

[0009] The DC link capacitance can consist of one or more capacitor units, particularly those connected in parallel, each of which can be designed as individual, discrete capacitor elements or capacitor components. These capacitor units are also referred to as DC link capacitors. The DC link capacitance is connected between two potentials of a DC voltage source, for example, a DC electrical system or a (vehicle) battery. The DC voltage network can be a low-voltage network or a high-voltage network, whereby the nominal voltage level of such a high-voltage network can be significantly higher than 60 V, for example, from approximately 400 V to 1.2 kV DC. The DC link capacitance can be part of a power converter circuit (so-called inverter).The power converter circuit can be designed, in particular, to convert direct current (DC) voltage into alternating current (AC) voltage and vice versa, with the AC voltage being applied, in particular, to an electric machine. Specifically, the power converter circuit can comprise a number of half-bridges consisting of two series-connected (semiconductor) switching elements, e.g., MOSFETs or IGBTs. The power converter circuit with the capacitor units is used, in particular, in a technical device or in a higher-level product, for example, in a vehicle.

[0010] The invention provides a way to regularly determine the remaining service life or residual service life of individual discrete capacitor units of the intermediate circuit capacitance online, i.e. during operation, of the corresponding technical device.

[0011] For this purpose, the current power dissipation of each individual capacitor unit within the multitude of capacitor units is determined. These individual power dissipations characterize, in particular, the heat dissipation of each capacitor unit. Estimating the individual power dissipations is especially advantageous without performing a voltage measurement, and specifically without measuring the voltage drop across the individual capacitor units. Therefore, high-precision voltage measuring instruments are not required.

[0012] Depending on the specific power losses of the individual capacitor units, a current temperature value for each unit within the group of capacitor units is determined. Particularly useful is determining the current maximum temperature or hotspot temperature of the respective capacitor unit. Since the individual capacitors are primarily heat sources that interact with each other, the current temperature value of each capacitor unit can be estimated particularly effectively based on the current power losses and the associated heat output of the other capacitor units. In this way, the current temperature value can be estimated computationally without actually measuring the temperature.In particular, there is no need to install a temperature sensor that measures the internal (hotspot) temperature of the capacitor unit, the housing temperature of the capacitor unit, or an external temperature around the capacitor unit.

[0013] The remaining service life of each capacitor unit is determined based on its specific temperature and voltage values. Comparing the current temperature with reference values ​​and / or constants or parameters that correlate capacitor temperature with its associated lifespan consumption allows for a particularly useful estimation of the remaining service life of each capacitor unit.

[0014] For example, the remaining service life of a capacitor can be determined based on its current temperature and voltage by referencing a rated service life at a reference temperature and voltage. The voltage of the capacitor can be measured, calculated, or estimated, particularly depending on the ripple current. Estimating the voltage based on the ripple current without high-precision voltage measurement is especially useful. However, if there is no load, the ripple will be zero, but voltage stress may still be present, contributing to aging. In this case, the voltage can be determined by a non-high-precision DC link voltage measurement, which is typically available during normal operation.

[0015] The present invention thus proposes a method for continuous online lifetime prediction of DC link capacitors, particularly for use in high-voltage electronics, to enable effective lifetime prediction and, if desired, to take appropriate measures. Lifetime prediction can be particularly advantageously performed regularly during operation, especially by one or more algorithms that continuously perform calculations, for example, during the operation of the respective technical device using the current voltage and hotspot temperatures. The algorithms can be implemented, for example, in an internal or central control unit of the respective technical device, such as a microcontroller, a (micro)processor, a control unit, etc.In this way, continuous online condition monitoring and associated limitations or protective measures, as well as predictive maintenance, can be implemented in the power electronics.

[0016] The invention enables, in particular, a more up-to-date and accurate determination of the expected service life than would be possible during a design or development phase, especially by taking into account real voltage and temperature loads. Service life prediction makes it possible, in particular, to define limits or protective measures online or continuously in order to meet product service life requirements and / or to prevent failures or damage to DC link capacitors during operation.

[0017] The proposed lifetime determination method does not require an additional voltage sensing or measuring unit that would need to be highly accurate across the entire DC link voltage range, in addition to the DC link voltage measurement that is typically already part of the design for control and protection functions. Furthermore, a temperature measuring unit is not required at an internal point, at the hotspot point, or on a housing or external point of the DC link capacitors. The proposed lifetime determination can be particularly advantageously performed using lookup tables (LUTs) or characteristic curves, which can be derived, for example, from electrical system simulations and from thermal 3D finite element method (FEM) simulations.This allows for significantly shorter computation times, reduced computational effort, and higher accuracy compared to purely analytical models. For example, frequency-, temperature-, and aging-dependent Z- (impedance) and ESR (equivalent series resistance) LUTs can be used to represent capacitor losses more accurately. For this purpose, inputs can be derived as feedback from various computational modules.

[0018] Determining power losses, temperature, and remaining service life can each be performed by a separate determination or calculation module, with each module executing corresponding functions or algorithms. The individual determination modules can, for example, be executed periodically or continuously in specific time steps or determination steps. These time steps are denoted by the letter 'n' in the following. Advantageously, results from the preceding, most recently executed determination step n-1 can be fed back into the current determination step n.

[0019] According to one embodiment, the power losses of the individual capacitor units are determined depending on a ripple current of the individual capacitor units and / or on a resistance value of the individual capacitor units, in particular an equivalent series resistance (ESR). Furthermore, other parameters or values ​​can be included in the calculation of the power losses, e.g., an (electrical) impedance value and / or an age-dependent capacitance value of the individual capacitor units.

[0020] In particular, the current power loss P loss,i [n] of the corresponding capacitor unit i in the current determination step n depending on the ripple current i ripple,i [n] and the equivalent resistance value ESR i[n] of this capacitor unit i can be determined according to the following formula (1): Ploss,i[n]=iripple,i2[n]⋅ESRi[n]

[0021] Here, 'i' can take values ​​from 1 to N, where N denotes the total number of capacitor units of the intermediate circuit capacitance.

[0022] According to one embodiment, the ripple current of each capacitor unit is dependent on an electrical frequency (f el [n]) and / or from a switching frequency (f sw [n]) of a switching element or several switching elements of the power converter circuit and / or of a phase angle between a phase voltage and a phase current (φ[n]) and / or of the phase current (i ph [n]) and / or a modulation index (m[n]). For example, in a B6 bridge inverter topology, the ripple current i ripple[n] of the corresponding capacitor unit in the respective current determination step [n] as a function depending on these quantities according to the following formula (2): iripple[n]=f(fel[n],fsw[n],φ[n],iph[n],m[n])

[0023] According to one embodiment, the ripple current and / or resistance of each capacitor unit are determined using a predefined lookup table (LUT) or characteristic map. To avoid using a voltage measurement, which would need to be very precise specifically for capturing high-frequency ripple, it is particularly advantageous to use a LUT specific to the respective technical device or converter topology to determine the ripple current as a function of specific parameters, especially according to the formula (2) above. Equation (2) applies in particular to a B6 bridge inverter, especially for motor drive applications in the automotive sector. However, it is advantageous to determine and derive a corresponding ripple current LUT for each specific converter type and each specific application.The respective table can be derived, for example, using a system simulation and / or a thermal 3D FEM simulation, such as during a manufacturing or configuration phase. A corresponding table for the resistance value of the capacitor units can also be derived in the same way.

[0024] According to one embodiment, the ripple current of the individual capacitor units and / or the resistance value of the individual capacitor units are determined as a function of a recently determined temperature of the individual capacitor units and / or a recently determined remaining lifetime of the individual capacitor units. In particular, the respective values ​​determined in the last determination step [n-1] can thus be fed back to the current determination step [n]. The current resistance value can be particularly conveniently determined using the corresponding table as a function of the last determined temperature and the last determined remaining lifetime.

[0025] According to one embodiment, the power losses, in particular the resistance values, of the individual capacitor units are determined depending on the rated lifetime of each capacitor unit, and in particular depending on a lifetime parameter or aging parameter that depends on the rated lifetime of the individual capacitor units and, furthermore, in particular on the last determined remaining lifetime. Advantageously, the resistance values ​​can be read from the corresponding (lookup) table or characteristic curve depending on the lifetime parameter, or read or interpolated using a resistance-lifetime parameter diagram.

[0026] For example, the lifetime or aging parameter L fb for a corresponding capacitor unit in the current determination step [n] depending on the nominal service life L rthis capacitor unit and depending on the remaining lifetime L determined for this capacitor unit in the current step [n] e [n] can be determined as follows: Lfb[n]=mean(1−Le[n]Lr)

[0027] The aging parameter is thus determined, in particular, as a cumulative average or mean value, which is especially saturated between 0 and 1. The aging parameter L can expediently be defined as... fb [n] can be used as a feedback value in the next determination step [n+1] or the value determined in the last step [n-1] can be coupled into the current step [n].

[0028] According to one embodiment, the temperature value of each capacitor unit is further determined depending on an initial temperature value of the respective capacitor unit and / or on a thermal impedance value of the individual capacitor units. The initial temperature value can, in particular, correspond to a temperature value at the time of initial commissioning or at the beginning of the service life of the respective capacitor unit. Using the thermal impedance values ​​and the power losses of the individual capacitor units, the heat input from the individual capacitor units as heat sources into the respective capacitor unit can be estimated.

[0029] According to one embodiment, the temperature value of each capacitor unit is determined as a sum of the products of the specific power losses of the individual capacitor units, multiplied by the time-dependent change in the respective thermal impedance value of each capacitor unit. Specifically, for each capacitor unit, the corresponding product of the respective power loss and the respective impedance change of that capacitor unit is determined. All these products are then summed.

[0030] It is advisable to use the current (hotspot) temperature value T hs,i [n] of the respective capacitor unit i in the calculation step [n] is determined according to the following formula: {Ths,i[n]=T0,i,n=0Ths,i[n]+=∑mM(Ploss,m[n]*dZth,mdt),n>0

[0031] Here, 'i' can take values ​​between 1 and N, where N is the total number of capacitors connected in parallel, and 'm' can take values ​​between 1 and M, where M is the total number of heat sources. P loss,m [n] denotes the time-dependent power loss of the heat source 'm'. Z th,m denotes the thermal impedance value and can in particular be a Z obtained for the hotspot point with the active heat source 'm'. th -curve. T 0,i denotes the original temperature value or the initial hotspot temperature of the respective capacitor unit 'i'. The convolution operation is indicated by '*'. dt denotes the computation time step (discrete time intervals, e.g., 1 second). In particular, all capacitor units of the DC link capacitance are part of the M heat sources. M is therefore generally equal to or greater than N. M may be greater than N if there are high thermal cross-effects from other heat sources (e.g., FETs, copper components / layers, transformers, etc.) on the DC link capacitors. In this case, the respective power dissipation for these heat sources can also be determined.

[0032] According to one embodiment, the thermal impedance value of each capacitor unit is determined using a predefined lookup table (LUT) or characteristic map. This table can also be derived, for example, using system simulation and / or a thermal 3D FEM simulation, such as during a manufacturing or configuration phase.

[0033] According to one embodiment, the remaining service life of the respective capacitor unit is further determined depending on a last determined remaining service life (L). e [n-1]) of the respective capacitor unit and / or a rated lifetime (L r ) especially at a reference temperature (T ref ) and a nominal voltage (U r ) the respective capacitor unit and / or a reference temperature (T ref ) of the respective capacitor unit and / or of a nominal voltage (U r) of the respective capacitor unit and / or of a voltage value of the respective capacitor unit (U) c ) and / or a voltage-related constant (α) of the respective capacitor unit and / or a temperature-related constant (β) of the respective capacitor unit and / or a base value for a temperature-dependent acceleration (B) of the respective capacitor unit. The rated lifetime L r can in particular refer to the reference temperature T ref and to the nominal voltage U r This could refer to something else. For example, the nominal service life could be a value specified by a manufacturer.

[0034] The voltage value U cThe voltage of each capacitor unit can be determined based on its ripple current, power dissipation, and equivalent resistance, thus eliminating the need for voltage measurement. When the inverter is unloaded and there is no associated ripple current, the typical DC link voltage measurement, which is already present, can be used to determine the voltage value. Above the rated voltage, the voltage applied to the capacitors can lead to aging without generating significant heat at the hotspot. However, this condition is rare and not dominant compared to the aging effects at elevated hotspot temperatures above the reference / rated temperature.

[0035] For example, the remaining lifespan L e [n] in the current determination step [n] according to the following formula: Le[n]=M−1M⋅Le[n−1]+1M⋅(Lr⋅B(Tref−Ths[n]β)⋅(UrUc[n])α)

[0036] Here, L denotes r the rated service life in hours (h) at the reference temperature T ref in °C and at the nominal voltage U r in volts. With T hs The specific hotspot temperature of the respective intermediate circuit capacitor unit is denoted in °C. U c The DC link capacitor voltage is denoted in volts. α is the dimensionless, voltage-related empirical constant, and β is the temperature-related empirical constant in °C. B is the base value for the temperature-dependent acceleration, which can be, for example, B = 2. The subscript n denotes the current time step or measurement step. M denotes the number of time steps or measurement steps up to the current step n.

[0037] According to one embodiment, the determination of the power losses of the individual capacitor units, the determination of the temperature of the respective capacitor unit, and the determination of the remaining service life of the respective capacitor unit are each carried out at predetermined, in particular regular, time intervals. For example, the respective determinations can be carried out at regular, predetermined times and repeated periodically. For example, the individual functions or algorithms for the respective determinations can run periodically or continuously in a specific time step, e.g., every second or at a lower or higher frequency, for example, depending on the temperature-related constant and / or the service life or aging parameter.

[0038] The invention is suitable for a wide variety of technical applications. It is particularly suitable for use in the automotive sector, where the power converter circuit is used to control an electric motor in a vehicle, for example, as a drive or traction motor. The process can be carried out, for example, by an in-vehicle computing unit, such as a microcontroller, processor, or control unit, or by an external, remote computing unit, such as a server or a cloud computing system, for example, for remote vehicle monitoring.

[0039] A computing unit according to the invention, e.g. a control unit of a power converter arrangement, is, in particular in terms of programming, equipped to carry out a method according to the invention.

[0040] A power converter arrangement according to the invention comprises a power converter circuit, an intermediate circuit capacitor with a plurality of capacitor units connected in parallel to the power converter circuit, and a computing unit according to the invention.

[0041] Implementing a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, as this incurs particularly low costs, especially if an executing control unit is already available for other tasks. Finally, a machine-readable storage medium is provided with a computer program stored on it as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical, and electrical storage media, such as hard drives, flash memory, EEPROMs, DVDs, etc. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or wireless (e.g., via a WLAN network, a 3G, 4G, 5G, or 6G connection, etc.).

[0042] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0043] The invention is schematically illustrated in the drawing using exemplary embodiments and is described below with reference to the drawing. Brief description of the drawings Fig. Figure 1 schematically shows a drive system with an intermediate circuit capacity, which can form the basis of an embodiment of the method according to the invention, in a circuit diagram-like view. Fig. Figure 2 schematically shows an embodiment of a method according to the invention as a block diagram. Fig. Figure 3 schematically shows a diagram of an expected lifetime plotted against a quotient of stress values, which can be determined in the course of an embodiment of a method according to the invention. Fig. Figure 4 schematically shows a diagram of a resistance value plotted against a lifetime parameter, which can be determined in the course of an embodiment of a method according to the invention. Fig. Figure 5 schematically shows a diagram of a capacity value plotted against a lifetime parameter, which can be determined in the course of an embodiment of a method according to the invention. embodiment(s) of the invention

[0044] Fig. Figure 1 shows a drive system 100 schematically and in circuit diagram form, which can be used, for example, as a drive system in a vehicle.

[0045] The drive system 100 comprises a DC voltage source 110, for example a vehicle battery, a multiphase electric machine 150, and a power converter circuit 130 for rectifying or alternating current between the DC voltage source 110 and the electric machine 150. The power converter circuit 130 has a plurality of half-bridges (here three), each comprising a high-side switching element 141 and a low-side switching element 142. The individual switching elements 141 and 142 can each be configured, for example, as a metal-oxide-semiconductor field-effect transistor (MOSFET) or an insulated-gate bipolar transistor (IGBT). A control unit 160 is provided for controlling the power converter circuit 130, in particular for controlling the individual switching elements of the power converter circuit 130.

[0046] Fig. Figure 1 shows, purely as an example, a three-phase electric machine 150 and a corresponding three-phase converter circuit 130; however, the electric machine and the converter circuit can also have more than three phases.

[0047] A DC link capacitor 120 is connected to the DC side of the converter circuit 130, wherein this DC link capacitor 120 comprises a plurality of parallel-connected capacitor units 121, 122, 123. In Fig. Figure 1 shows three such intermediate circuit capacitors 121, 122, 123 by way of example, however, more or fewer than three intermediate circuit capacitors may also be provided.

[0048] The power converter circuit 130, the control unit 160 and one or more or all of the intermediate circuit capacitors 121, 122, 123 can be part of a power converter arrangement (e.g. so-called inverter or converter) which structurally forms a device and in particular has a housing with connections in which the aforementioned components are arranged.

[0049] In order to determine online (i.e., during operation) the remaining service life of the individual capacitor units 121, 122, 123 of the intermediate circuit capacitance, the control unit 160 is configured, particularly by means of software, to carry out an embodiment of a method according to the invention, as described below with regard to Fig. 2 is explained.

[0050] Fig. Figure 2 shows the embodiment of the method according to the invention schematically as a block diagram.

[0051] In step 210, a current power loss P is calculated. foss[n] of the individual capacitor units 121, 122, 123 of the DC link capacitance 120 is determined. In step 220, a current temperature value T is determined for each of the capacitor units 121, 122, 123. hs [n] determined, in particular a current hotspot temperature, depending on the power losses P determined in step 210 loss [n] of the individual capacitor units 121, 122, 123. In a step 230, a remaining lifetime or residual lifetime L is determined for each of the capacitor units 121, 122, 123. e [n] determined, each depending on the respective temperature value T determined in step 220 hs [n] of the respective capacitor unit.

[0052] These individual process steps 210, 220, 230 can each be performed by a separate determination or calculation module, whereby these modules can each execute corresponding functions or algorithms. The individual determination modules can, for example, be executed periodically or continuously in specific time steps or determination steps n, e.g., every second or at a higher or lower frequency.

[0053] Advantageously, results from the previous, most recently performed determination step [n-1] can be used in a current determination step [n], or results from the current determination step [n] can be fed back into the next determination step [n+1]. For example, the temperature values ​​T determined in step 220 can be used in the current determination step [n]. hs[n] of the individual capacitor units 121, 122, 123 are fed back for a subsequent determination step [n+1], indicated by reference numeral 226. Furthermore, the lifetimes L determined in step 230 can be e [n] of the individual capacitor units or one of the respective lifetime L e [n] dependent lifetime or aging parameter L fb [n], for a subsequent determination step [n+1], indicated by reference numeral 236, as explained in detail below.

[0054] In step 210, the power loss is determined as a function of the ripple current and electrical resistance (ESR) of the corresponding capacitor unit. For this purpose, in step 212, the ripple current and the ESR are each determined using a corresponding predefined lookup table (LUT). To avoid using a voltage measurement, which would need to be particularly precise for capturing high-frequency ripple, an LUT specific to the existing converter topology is derived from a system simulation to obtain the ripple current as a function of certain parameters. If no load / ripple current is present, voltage stress can still contribute to aging. In this case, for example, a typical, non-high-precision measurement of the DC link voltage, which is already intended for regular operation, can be performed instead of the LUT.

[0055] At the in Fig. In the B6 bridge inverter topology shown in 1, the ripple current can be calculated, for example, according to formula (2) explained above as a function of the electrical frequency (f). el [n]), the switching / PWM frequency (f sw [n]), of the phase angle (φ[n]) between phase voltage and phase current (i ph [n]), of the phase current (i ph [n]) and the modulation index (m[n]). These quantities f el [n], f sw [n], φ[n], i ph [n] and modulation index (m[n]) are determined in step 211. In particular, a corresponding ripple current LUT can be derived from system simulations for each specific converter type and application.

[0056] For example, for each of the physical capacitor units 121, 122, 123, the respective ripple current can be determined using LUTs with respect to the electrical impedance value Z(f,T). hs ,L fb) are determined, which are derived from laboratory measurements. With T hs Here, the feedback temperature value from the previous determination step [n-1] is denoted, indicated by the reference symbol 226. With L fb Here, the feedback lifetime or aging parameter from the previous determination step [n-1] is denoted, indicated by the reference symbol 236. This temperature and aging feedback allows different impedances for the different capacitors 121, 122, 123 to be calculated from the LUTs. Based on the actual impedances of the different capacitors 121, 122, 123, imbalances or distributions of the ripple current can be calculated according to the current division principle. The calculated ripple current per capacitor is denoted by i. ripple,idenoted, where 'i' can take values ​​from 1 to N, where N is the total number of capacitors 121, 122, 123 connected in parallel, with a DC link capacitance of 120. The equivalent resistance value ESR( f ,T hs ,L jb ) can be used for each of the capacitor units 121, 122, 123 by means of temperature and aging feedback depending on the last determined hotspot temperature value T hs and the last determined lifetime parameter L fb be determined.

[0057] The power loss P loss,i [n] is calculated in step 210 for each physical capacitor 121, 122, 123, for example, according to formula (1) explained above, using ESR LUTs derived from laboratory measurements. The actual ESR value of each physical capacitor 121, 122, 123 may differ due to varying temperature and aging effects.

[0058] Depending on the ripple current, power loss and equivalent resistance value of each capacitor unit 121, 122, 123, a voltage value U can also be determined in step 210. c [n] of each capacitor unit 121, 122, 123 are determined. These individual voltage values ​​U c [n] can be used in process step 230, indicated by reference numeral 216, as will be explained later.

[0059] The power losses P determined in step 210 loss [n] of the individual capacitor units 121, 122, 123 are provided, indicated by the reference numeral 215, and used in process step 220. In step 220, the respective temperature value T hs,i [n] of the respective capacitor unit further depends on an initial temperature value T 0, i for initial commissioning or at the beginning of the service life of the respective capacitor unit and depending on a thermal impedance value Z th,mof the individual capacitor units. In step 221, the impedance values ​​Z are determined. th,m the individual capacitor units 121, 122, 123 are determined, for example with the help of a corresponding lookup table or with the help of Z th -curves. These Z th -Curves can be created for the hotspot points of the intermediate circuit capacitors 121, 122, 123 from 3D FEM models and simulations taking into account various heat sources.

[0060] In step 220, the T hs,i [n] values ​​for each physical capacitor 121, 122, 123 based on the P loss,mThe [n] values ​​of all capacitors 121, 122, 123 and, if applicable, other heat sources are calculated according to formula (4) explained above. Since all capacitors are also part of the heat sources, the value M is equal to or greater than N. M can be greater than N if there are high thermal cross-effects from other heat sources (e.g., FETs, Cu components / layers, transformers, etc.) on the DC link capacitors 121, 122, 123. In this case, the corresponding power losses for these heat sources can be determined and taken into account in formula (4).

[0061] The individual hotspot temperatures T determined in step 220 hs [n] are fed back or fed back for the next determination step [n+1], indicated by the reference symbol 226, in order to determine the equivalent resistance values ​​ESR( in the next determination step [n+1] f ,T hs ,L jb ) or the impedance values ​​Z(f,T) hs ,L fb) to be able to determine. Furthermore, the determined hotspot temperatures T hs [n] provided for process step 230, indicated by reference numeral 225.

[0062] In step 230, the remaining service life L is determined. e [n] of the individual capacitor units 121, 122, 123 each further dependent on a last determined remaining lifetime L e [n-1], of a nominal lifetime L r at a reference temperature T ref and a nominal voltage U r , from the reference temperature T ref , from the nominal voltage U r , from the voltage value U determined in step 210 c , from a voltage-related constant α, from a temperature-related constant β, and from a base value B for a temperature-dependent acceleration of the respective capacitor unit. In particular, the remaining lifetime L can be determined. e[n] can be determined according to formula (5) explained above. The quantities L r , T ref , U r α, β, and B can be read in in one step 231. From the algorithm's perspective, these quantities are L r , T ref , U r , α, β and B are in particular configuration parameters that specify the respective type of intermediate circuit capacitor.

[0063] The remaining lifetimes L determined in this way in step 230 e [n] of the individual capacitor units 121, 122, 123 are provided, indicated by the reference numeral 235. Depending on the lifetimes L e[n] For example, a predefined measure can be implemented to prevent a defect or failure of the individual capacitor units. For example, such a measure could involve issuing an error message to the vehicle's driver and creating an entry in a fault memory when the specified service life of a particular capacitor unit reaches a predefined threshold.

[0064] Furthermore, depending on the specific lifespans L e [n] in step 230 for each of the capacitor units 121, 122, 123 the current lifetime or aging parameter L fb [n] is determined, in particular according to formula (3) explained above. To determine the aging effect in Z(f,T) hs ,L jb ) and ESR( f ,T hs ,L jb To take this specific parameter L into account, fb[n] is fed back as lifetime or aging feedback value for the next determination step [n+1], indicated by reference numeral 236.

[0065] The empirical constants α, β, and B can be derived, for example, from literature data or from a lifetime diagram, whereby such a lifetime diagram can be provided by a manufacturer or supplier, for example, in a data sheet, as shown below in relation to Fig. 3 will be explained.

[0066] Fig. Figure 3 schematically shows a diagram 300 of an expected lifetime L e plotted against the quotient U of a capacitor unit c / U r of the voltage value U c and the nominal voltage U r In Fig. The three curves are different: 310, 320, 330 and 340 for different hotspot temperature values ​​T. hsThe capacitor unit is shown. Curve 310, for example, is valid for a hotspot temperature of 85°C, curve 320 for a hotspot temperature of 105°C, curve 330 for a hotspot temperature of 125°C, and curve 340 for a hotspot temperature of 135°C. Diagram 300 can be provided, for example, by a manufacturer or supplier of the capacitor unit. From this diagram 300, the constants α, β, and B can be derived for step 231. If this extraction is not possible with a small fitting error, the parameters may be voltage-dependent and / or temperature-dependent.

[0067] The following refers to Fig. Section 4 explains how, in step 212, the equivalent resistance value depends on the traceable lifetime parameter L. fb [n] can be determined. Fig. Figure 4 schematically shows a diagram 400 of the equivalent resistance value of a capacitor unit plotted against the lifetime parameter L. fb of the capacitor unit. BoL (Beginning of Life) denotes the beginning of the capacitor unit's service life, which may correspond, for example, to the initial commissioning of the capacitor unit. EoL (End of Life) denotes the end of the capacitor unit's service life, at which point a defect or failure of the capacitor unit is expected.

[0068] As explained above, the aging feedback value L fb According to equation (3), the impedance and ESR curves or values ​​in the corresponding LUTs can be calculated as a cumulative mean and are saturated between 0 and 1. These values ​​can be derived from laboratory characterization measurements, which may also involve accelerated aging. Therefore, the actual impedance and ESR values ​​from the LUTs can be compared with the actual L fbThe ESR value can be derived from the BoL value. Furthermore, the ESR value can also be determined by linear interpolation between the BoL value and the EoL value. If the expected lifetime L e When the value reaches zero, the ESR value of the intermediate circuit capacitor reaches its end-of-life (EoL) value. Therefore, if, as in Fig. 4 shows the value of the lifetime parameter L fb As the value increases from zero, the ESR value increases by the same amount. If the lifetime parameter L fb For example, if it takes the value 0.2 (20% increase towards EoL), the ESR value increases by 20% from its BoL value towards the EoL value.

[0069] Similarly, the capacity value C(L) can also be determined in the same way fb ) of the capacitor unit depending on the lifetime parameter L fb will be determined as follows with regard to Fig. 5 is explained. Fig.Figure 5 schematically shows a diagram 500 of the capacitance value C of a capacitor unit plotted against the lifetime parameter L. fb of the capacitor unit. The actual capacitance C(L fb ) can, for example, be determined using a corresponding lookup table depending on the actual L fb -value can be derived. Furthermore, the capacity C(L) can be determined. fb The capacity can also be derived by linear interpolation in diagram 500 between the BoL and EoL values. The EoL capacity value can, for example, correspond to a capacity loss of 5%.

Claims

[1] Method for determining a remaining lifetime of a capacitor unit (121, 122, 123) used in an intermediate circuit capacitor (120), wherein the intermediate circuit capacitor (120) is connected in parallel on the DC side of a power converter circuit (130) and comprises a plurality of capacitor units (121, 122, 123), comprising the steps: Determine (210) the power loss of each of the individual capacitor units (121, 122, 123) of the plurality of capacitor units; Determining (220) a temperature value of a respective capacitor unit (121, 122, 123) of the plurality of capacitor units depending on the determined power losses of the individual capacitor units; and Determining (230) the remaining lifetime of each capacitor unit (121, 122, 123) depending on the determined temperature value of each capacitor unit and on a voltage value of each capacitor unit. [2] Method according to claim 1, wherein determining (210) the power losses of the individual capacitor units (121, 122, 123) further comprises: Determining the power losses of the individual capacitor units depending on a ripple current (211) of the individual capacitor units and / or on a resistance value (212) of the individual capacitor units, in particular on an equivalent resistance value. [3] Method according to claim 2, wherein determining (210) the power losses of each of the individual capacitor units (121, 122, 123) further comprises: Determining (211) the ripple current of the individual capacitor units (121, 122, 123) depending on an electrical frequency and / or a switching frequency of a switching element (141, 142, 123) of the converter circuit (130) and / or a phase angle between a phase voltage and a phase current and / or the phase current and / or a modulation index. [4] Method according to claim 2 or 3, wherein determining (210) the power losses of the individual capacitor units (121, 122, 123) further comprises: Determine (211, 212) the ripple current of the individual capacitor units and / or the resistance value of the individual capacitor units using a given table. [5] Method according to any one of claims 2 to 4, wherein determining (210) the power losses of the individual capacitor units (121, 122, 123) further comprises: Determine (211, 212) the ripple current of the individual capacitor units and / or the resistance value of the individual capacitor units, each depending on a last determined temperature (226) of the individual capacitor units and / or on a last determined remaining lifetime (236) of the individual capacitor units. [6] Method according to any one of claims 2 to 5, wherein determining (210) the power losses of the individual capacitor units (121, 122, 123) further comprises: Determining (210) the power losses, in particular determining (212) the resistance values, of the individual capacitor units, each depending on a rated lifetime of the individual capacitor units, in particular depending on a lifetime parameter (236) that depends on the rated lifetime of the individual capacitor units. [7] Method according to one of the preceding claims, wherein the determination (220) of the temperature value of the respective capacitor unit (121, 122, 123) is further dependent on an initial temperature value of the respective capacitor unit and / or on a thermal impedance value of the individual capacitor units. [8] Method according to claim 7, wherein determining (220) the temperature value of the respective condenser unit (121, 122, 123) comprises: Determining the temperature value of each capacitor unit depending on a sum of products of the determined power losses of the individual capacitor units multiplied by a time change of the respective thermal impedance value of the individual capacitor units. [9] Method according to claim 7 or 8, wherein determining (220) the temperature value of the respective condenser unit (121, 122, 123) further comprises: Determine (221) the thermal impedance value of each capacitor unit using a given table. [10] Method according to any of the preceding claims, wherein determining (230) the remaining lifetime of the respective capacitor unit (121, 122, 123) comprises: Determining the remaining lifetime further depending on a last determined remaining lifetime of the respective capacitor unit and / or on a nominal lifetime of the respective capacitor unit and / or on a reference temperature of the respective capacitor unit and / or on a nominal voltage of the respective capacitor unit and / or on a voltage-related constant of the respective capacitor unit and / or on a temperature-related constant of the respective capacitor unit and / or on a base value for a temperature-dependent acceleration of the respective capacitor unit. [11] Method according to one of the preceding claims, wherein the determination (210) of the power losses of the individual capacitor units, the determination (220) of the temperature value of the respective capacitor unit and the determination (230) of the remaining lifetime of the respective capacitor unit are each carried out at predetermined time intervals. [12] Computing unit (160) configured to perform all process steps of a process according to any of the preceding claims. [13] Power converter arrangement comprising a power converter circuit (130), an intermediate circuit capacitor (120) with a plurality of capacitor units (121, 122, 123) connected in parallel to the power converter circuit (130), and a computing unit (160) according to claim 12. [14] Computer program that causes a computing unit (160) to perform all the process steps of a method according to any one of claims 1 to 11 when executed on the computing unit (160). [15] Machine-readable storage medium with a computer program stored thereon according to claim 14.

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