Method and computing unit for checking an intermediate circuit capacitance in a DC network, converter arrangement and drive system

Abstract

The invention relates to a method for checking an intermediate circuit capacitance (121, 122, 123) in a DC network, in particular in a vehicle, wherein the intermediate circuit capacitance (121, 122, 123) is connected in parallel to a DC voltage source (110) and a converter circuit (130), wherein a discharge circuit (180) for discharging the intermediate circuit capacitance (121, 122, 123) is connected in parallel to the intermediate circuit capacitance (121, 122, 123), wherein the discharge circuit (180) comprises a consumer unit (181) and a switching element (182), comprising closing the switching element (182) of the discharge circuit (180) for a predetermined time interval when a predetermined condition is met;Determining a voltage difference of a DC voltage in the DC network resulting from the closing of the switching element (182), in particular determining a voltage difference of a first voltage value of the DC voltage before closing the switching element (182) and a second voltage value of the DC voltage after closing the switching element (182); and checking whether a fault and / or wear of the DC link capacitance (121, 122, 123) is present depending on the determined voltage difference.

Description

[0001] The present invention relates to a method for checking an intermediate circuit capacitance in a DC network, e.g. in a vehicle, a computing unit and a computer program for carrying it out, as well as a power converter arrangement and a drive system. Background of the invention

[0002] DC link capacitors in power converter arrangements (so-called inverters), such as those used in (motor) vehicles, can consist of capacitors connected in a DC link in parallel to a DC voltage source, for example, a vehicle battery or a DC electrical system, and in parallel to the DC voltage terminals of a power converter circuit (especially with half-bridges). For example, a power converter arrangement with such a DC link can be used to convert a voltage between the DC voltage source and an electric machine that can be operated with multiphase AC voltage. For example, a primary DC link can be provided in such a power converter arrangement, with one or more DC link capacitors connected in parallel to the DC voltage terminals of the power converter circuit.are connected to the individual half-bridges of the converter circuit. Furthermore, on the DC side, connected loads may also contain capacitances, particularly in the form of one or more intermediate circuit capacitors, forming a kind of secondary or distributed intermediate circuit.

[0003] Such intermediate circuit capacitance is crucial for the correct and optimal functioning of the respective device. For example, intermediate circuit capacitance can filter fluctuations in the DC voltage, smooth the DC voltage, and reduce electromagnetic interference (EMI). It is therefore important to be able to detect faults or signs of wear in the intermediate circuit capacitance, such as a reduction in the capacitance of the capacitors. Disclosure of the invention

[0004] According to the invention, a method for checking the intermediate circuit capacitance in a DC network, e.g., in a vehicle, a computing unit and a computer program for carrying out this method, as well as a power converter arrangement and a drive system with the features of the independent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0005] The DC link capacitance is connected in parallel to a DC voltage source, particularly a vehicle battery, and in parallel to the DC terminals of a power converter circuit in the DC network. For example, the DC link capacitance can be composed of several individual capacitances, e.g., in a power converter arrangement and / or in loads connected to the DC network.

[0006] A power converter circuit, as used here, is a circuit with an AC voltage side and a DC voltage side, designed to convert current between the two. The power converter circuit comprises a plurality of half-bridges, each with a high-side switching element and a low-side switching element. The DC voltage side is formed by the upper (high-side) and lower (low-side) DC terminals of the half-bridges, and the AC voltage side by the center taps of the half-bridges. The switching elements can, in particular, include semiconductor switches that can be opened (non-conducting) and closed (conducting) according to a control signal. The semiconductor switches can include MOSFETs or IGBTs, for example, gallium nitride (GaN) or silicon carbide (SiC) FETs.

[0007] The DC power supply can be a low-voltage or a high-voltage system. High-voltage and low-voltage systems can be coupled in the vehicle via a suitable DC-DC converter. The nominal voltage level of the high-voltage system (hereinafter also referred to as high-voltage level) can be significantly higher than a permissible touch voltage, particularly 60 V, for example, up to several hundred volts. For instance, current electric vehicles frequently use high-voltage levels of 400 V or 800 V. The nominal voltage level of the low-voltage system can correspond to typical vehicle low voltages of, for example, 12 V or 24 V.

[0008] A power converter assembly is an arrangement comprising a power converter circuit and other components advantageous for operation, such as an intermediate circuit capacitor. A power converter assembly can also be designed as a device with a housing, in which case it is technically referred to as an inverter, which, for example, is located in a vehicle between an electric motor and a vehicle battery. The DC and AC voltage connections are brought out of the housing.

[0009] The invention offers particular advantages in power converter arrangements for controlling an electric machine, especially in vehicles, for example as a drive or traction drive, since large currents flow here and thus the discharge of the DC link capacity is particularly relevant to safety.

[0010] Furthermore, a discharge circuit for actively discharging the DC link capacitance is connected in parallel to the DC link capacitance, specifically in parallel to the DC terminals of the converter circuit. The discharge circuit includes a load unit, for example, one or more electrical resistors. It also includes a switching element, such as a semiconductor switch, for example, a MOSFET or an IGBT. The load unit and the switching element are advantageously connected in series. The discharge circuit may also include other elements, such as a current sensing unit or a current sensor. The discharge circuit is primarily intended as a safety measure to enable the rapid discharge of the energy stored in the DC link capacitance in the event of an emergency or safety risk, such as an accident.The discharge circuit can be particularly useful in order to meet special safety requirements in the (motor) vehicle sector, such as those specified in the ISO 26262 standard or, in particular, by the so-called "Automotive Safety Integrity Level" (ASIL), a safety requirement level for safety-related systems in motor vehicles specified by ISO 26262.

[0011] In this procedure, the switching element of the discharge circuit is closed, i.e., switched to a conducting state, for a predetermined time interval when a predefined condition is met. The resulting voltage difference (i.e., voltage drop) of a DC voltage in the DC network, particularly a DC voltage across the intermediate circuit capacitance, is determined. It is particularly advantageous to determine a voltage difference between a first DC voltage value, especially immediately before the switching element closes, and a second DC voltage value, especially immediately after the switching element closes. For example, the voltage values ​​can be measured directly or calculated using other (measured) values. A voltage measuring unit is particularly advantageous for determining the voltage difference.A voltage sensor is used, which is already integrated into the DC network to determine the DC voltage. Depending on this specific voltage difference, it is checked whether there is a fault and / or wear in the DC link capacitance.

[0012] Closing the switching element of the discharge circuit represents a special test switching state, which is particularly useful for determining the current state of the DC link capacitance. Closing the switching element conveniently generates a current flow through the load unit. By appropriately selecting the time interval, especially if the time interval does not exceed a predetermined maximum value, and if the size or resistance value of the load unit is not very small, especially if the resistance value does not fall below a predetermined minimum value, it can be ensured that this current flow is generated primarily from the DC link capacitance and not, or at least hardly, from the DC voltage source.

[0013] The voltage difference in the DC network that occurs during the test switching state when the switching element closes is particularly characteristic of the current state of the DC link capacitance. Specifically, the value of this voltage difference differs between a fault-free or wear-free DC link capacitance and a faulty or worn DC link capacitance. Therefore, the current value of the voltage difference provides a useful indication of whether the DC link capacitance is functioning correctly or whether a fault or deterioration of the DC link capacitance exists compared to the fault-free and wear-free state.

[0014] The invention thus provides a simple, cost-effective, and flexible way to check the DC link capacitance for faults or signs of wear. The DC voltage is conveniently measured during the regular operation of the DC network anyway, so no additional measurement effort is required to check the DC link capacitance. Furthermore, the discharge circuit is already provided as a safety measure in many DC networks, so no additional circuit is needed to check the DC link capacitance.

[0015] To check a DC link capacitance for faults or wear using conventional methods, the current capacitance value can be measured at the beginning of each operating cycle. However, this may require an additional measuring circuit, such as one with additional current and voltage sensors, which can be costly. Furthermore, the use of such additional components can increase space requirements, which may not always be available depending on the inverter topology. Moreover, transmitting the measured signals from the additional circuitry to the control system can be complex due to the need for isolation and interference immunity.

[0016] In contrast, the invention allows the DC link capacitance to be checked particularly efficiently using the components already present in the DC network, especially without requiring an additional measuring circuit or additional current and voltage sensors. Costs for checking the DC link capacitance can thus be kept to a minimum. Furthermore, no installation space is required for additional components, so that a potentially limited installation space in the DC network does not pose an obstacle to implementing the invention. Moreover, the invention allows for the particularly advantageous detection of a reduction in the DC link capacitance value due to a fault or wear, without determining a specific capacitance value or a specific value for the total DC link capacitance.

[0017] In this context, the term "wear-free" should be understood to mean, in particular, that there is no wear or at least minimal wear, or that while wear is present, it remains within an acceptable range typical for the service life of the DC network. Conversely, the term "wear-prone" should be understood in this context to mean that any existing wear exceeds the acceptable, typical range. If the inspection determines that no wear is present or that the situation is wear-free, this should be understood to mean, in particular, that any existing wear does not exceed an acceptable limit. Conversely, if it is determined that wear is present or that the situation is wear-prone, this should be understood to mean, in particular, that the existing wear exceeds this acceptable limit.

[0018] According to one embodiment, checking for a fault and / or wear involves comparing the measured voltage difference with a reference value. Depending on the result of this comparison, it is determined whether a fault and / or wear of the DC link capacitance is present. The reference value specifically characterizes the voltage difference of the DC network that occurs when the switching element closes, assuming a fault-free and wear-free DC link capacitance. For example, if the actual voltage difference deviates from the reference value by more than a predetermined amount, a fault and / or wear can be inferred.

[0019] According to one embodiment, a DC voltage value in the DC network is determined before the switching element closes. Depending on this specific voltage value and the resulting voltage difference, it is checked whether a fault and / or wear of the DC link capacitance is present. For example, this could be the first voltage value explained above, determined particularly immediately before closing, which is also used to determine the voltage difference. However, a further, third voltage value can also be determined or measured at a time before the switching element closes and thus before the test switching state is brought about. The voltage difference resulting from the closing of the switching element can vary depending on the current DC voltage value before the switching element closes. The current voltage value, or...The current operating point of the DC network before generating the test switching state can therefore be particularly useful as a reference point for checking the DC link capacitance.

[0020] According to one embodiment, the comparison value is determined depending on the specified voltage value, as well as on at least one reference voltage value and at least one reference voltage difference associated with that reference voltage value. In particular, at least one pair of such a reference voltage value and a reference voltage difference associated with that reference voltage value is predefined and stored, for example, in a storage unit of a control unit that controls the DC network. A respective reference voltage difference characterizes, in particular, a voltage difference occurring in the DC network when the switching element closes, assuming a fault-free and wear-free intermediate circuit capacitance, provided that the DC voltage in the network has the respective, associated reference voltage value before the switching element closes.Based on the current, determined voltage value, the reference voltage differences can be calibrated to determine the valid comparison value for the current operating point.

[0021] According to one embodiment, the determined voltage value is compared with at least one reference voltage value. Depending on the result of this comparison and the at least one associated reference voltage difference, the comparison value is determined, in particular by interpolation and / or extrapolation. Depending on the difference between the current voltage value and the reference voltage values, the comparison value can expediently be determined by interpolation and / or extrapolation of the associated reference voltage differences. If the voltage difference is generally not linearly related to the voltage value, at least two pairs of a reference voltage value and an associated reference voltage difference can be specified in order to precisely determine the comparison value for the current operating point by interpolation / extrapolation.

[0022] According to one embodiment, the at least one reference voltage value and the at least one associated reference voltage difference are each predetermined values ​​from a manufacturing and / or configuration phase of the DC network. For example, the reference value pairs can be measured during a manufacturing process or theoretically determined during a computer-implemented simulation of the DC network to be manufactured. Alternatively or additionally, according to one embodiment, the at least one reference voltage value and the at least one associated reference voltage difference are each determined or measured values ​​from a prior check of the DC link capacitance. The reference value pairs can thus be determined online during the regular operation of the DC network.For example, the reference value pairs can be determined during initial commissioning and / or in various start-up processes of the DC network. It is also conceivable that the reference value pairs, consisting of the reference voltage value and the reference voltage difference, can be learned using self-learning systems, e.g., by means of a neural network or machine learning.

[0023] According to one embodiment, depending on the specific voltage difference, it is further checked whether a fault and / or wear of the discharge circuit is present. Particularly advantageously, the discharge circuit itself can also be tested for faults. If, in the test switching state, no or at least no significant voltage difference occurs in the DC network when the switching element closes, especially if the voltage difference is below a predetermined minimum value, and if, furthermore, no or at least very little current flows through the load unit, especially if the current through the load unit is below a predetermined minimum value, this indicates that the switching element and / or a gate driver for controlling the switching element are faulty, defective, or worn.

[0024] According to one embodiment, the predetermined time interval is determined depending on the voltage value of the DC voltage of the DC network and / or depending on the state of charge of the DC voltage source and / or depending on the rated current of the switching element of the discharge circuit and / or on the rated current of the load unit of the discharge circuit and / or a pulse power of the load unit. In particular, the time interval is determined depending on the current voltage value of the DC network, the current state of charge of the DC voltage source, and the rated current of the switching element, and furthermore, in particular, depending on the rated current or pulse power of the load unit, such that the current flow through the load unit after the closing of the switching element is generated mainly from the DC link capacitance and not, or at least hardly, from the DC voltage source.

[0025] According to one embodiment, the specified condition includes the requirement that an electrical machine connected to the converter circuit, in particular an electrical machine connected to the AC side of the converter circuit, is at a standstill. In this case, the converter circuit can be used, in particular, to convert currents or voltages between the DC voltage source and the electrical machine, for example, to drive the electrical machine using electrical energy from the DC voltage source or to feed electrical energy generated by the electrical machine into the DC voltage source. When the electrical machine is at a standstill, the inspection for faults or wear can be carried out, in particular, without distorting the result of the inspection and without impairing the operation of the electrical machine.Furthermore, it is also possible to initiate the check of the DC link capacity during a drive mode of the converter circuit, whereby in particular the effects of the DC link voltage ripple on the voltage drop are compensated or filtered.

[0026] According to one embodiment, a predefined action is taken if, during the inspection, a fault and / or wear of the DC link capacitance is determined or detected. For example, such an action could involve outputting a fault signal to a control unit that manages the DC network and / or to a safety unit or safety logic. Furthermore, as a measure, the power converter circuit could, for example, be prevented from starting or being controlled. Other predefined measures could include, for example, bringing the DC network or a vehicle equipped with the DC network into a safe state, issuing a fault message to the vehicle's driver, creating an entry in a fault memory, etc.

[0027] A computing unit according to the invention, e.g. a control unit, a microprocessor or microcontroller of a power converter arrangement and / or a vehicle, is, in particular in terms of programming, equipped to carry out a method according to the invention.

[0028] 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. The computer program can, in particular, be part of microcontroller code. Suitable 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.

[0029] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0030] 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 which may form the basis of an embodiment of the method according to the invention, in a circuit diagram-like view. Fig. Figure 2 schematically shows currents in the drive system according to Fig. 1 in a test switching state according to an embodiment of the invention. Fig. Figure 3 schematically shows an embodiment of the method according to the invention as a block diagram. Fig. Figure 4 schematically shows diagrams of a voltage and a current plotted against time, which can be determined in the course of an embodiment of the method according to the invention. embodiment(s) of the invention

[0031] In Fig. Figure 1 is a drive system in which the invention can be advantageously applied, shown schematically and in circuit diagram form, and designated overall by 100. The drive system 100 can, for example, be used as a drive system in a vehicle. The drive system 100 has a power converter circuit 130 for rectifying or alternating current between a DC voltage source 110, which is connected to a DC voltage side of the power converter circuit 130, and a multiphase electric machine 150, which is connected to an AC voltage side of the power converter circuit 130. The DC voltage source 110 can, for example, be designed as a vehicle battery.

[0032] The power converter circuit 130 has a plurality of half-bridges 131, 132, 133 (here three), each of which has a high-side switching element 141, 142 or 143 and a low-side switching element 144, 145 or 146, each of which can be designed, for example, as a metal-oxide-semiconductor field-effect transistor (MOSFET) or an insulated-gate bipolar transistor (IGBT).

[0033] 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. For this purpose, a gate driver 161 is provided for each of the switching elements 141, 142, 143, 144, 145 and 146 to control the gate connection of the respective switching element.

[0034] In Fig. Figure 1 shows, purely by way of example, a three-phase electric machine 150 with the phase windings or phases 151, 152 and 153 (U, V, W) and a corresponding three-phase converter circuit 130, however it is understood that the electric machine and the converter circuit can also have more than three phases.

[0035] Current sensors 171, 172, 173 are provided to detect current values ​​of phase currents of phases 151, 152, and 153 of the electric machine 150, respectively. The following is an example: Fig. 1 Sensor 171 shown is provided to measure a phase current I U to detect the U-phase 151. Sensor 172 is intended, for example, to detect a phase current I. V to detect the V-phase 152 and sensor 173 is intended, for example, to measure a phase current I W to detect the W-phase 153. Furthermore, a voltage measuring unit 175 is provided to measure a voltage value V. DCto detect the DC voltage side. The individual current and voltage values ​​are transmitted from the respective sensors 171, 172, 173 and 175 to the control unit 160.

[0036] An intermediate circuit capacitor arrangement 120 comprises a plurality of intermediate circuit capacitors 121, 122, 123. In Fig. Figure 1 shows three such intermediate circuit capacitors 121, 122, 123 as examples; however, more or fewer than three intermediate circuit capacitors can also be provided. For example, the intermediate circuit capacitor arrangement 120 can be constructed by connecting discrete capacitors in parallel, or capacitor elements (e.g., so-called "bobbins") can be combined as a lumped capacitor (so-called "brake capacitor"). The converter circuit 130, the control unit 160, and this intermediate circuit capacitor arrangement 120 can form a single structural unit or device, which is referred to as a converter arrangement or inverter. The voltage measuring unit 175 can also be part of this converter arrangement.

[0037] The intermediate circuit capacitor arrangement 120 is part of an intermediate circuit. The DC voltage source 110 and this intermediate circuit are part of a DC voltage network. The intermediate circuit capacitors 121, 122, 123 of the intermediate circuit capacitor arrangement 120 together form an intermediate circuit capacitance, which is monitored in embodiments of the invention. It is also conceivable that the intermediate circuit may include other elements besides the intermediate circuit capacitor arrangement 120, e.g., loads. Any input capacitances of these loads can then, together with the intermediate circuit capacitors 121, 122, 123, form the intermediate circuit capacitance.

[0038] A discharge circuit 180 is provided as a safety measure to enable the rapid discharge of energy stored in the DC link capacitor in the event of an emergency or safety risk, such as an accident. For this purpose, the discharge circuit 180 is connected in parallel to the DC link capacitor and comprises a load unit 181, e.g., at least one resistor, a switching element 182, and a current sensing unit or current sensor 183. The switching element 182 can, for example, be a semiconductor switch, such as a MOSFET or IGBT. The control unit 160 is also provided for controlling the switching element 182, and for this purpose, a gate driver 165 is provided to control the gate terminal of the switching element 182. The discharge circuit 180 can also be part of the power converter arrangement.The discharge circuit 180, for example, is designed to meet safety requirements according to the ISO 26262 standard, in particular according to the so-called “Automotive Safety Integrity Level” (ASIL).

[0039] The intermediate circuit capacitance is of great importance for the correct and optimal functioning of the drive system 100. Therefore, faults or signs of wear in the intermediate circuit capacitance should be detected as quickly as possible. For this purpose, the control unit 160 is configured, particularly in terms of its programming, to carry out an embodiment of a method according to the invention, as described below in general terms with regard to the Fig. 2 and Fig. 3 will be explained.

[0040] Fig. Figure 2 shows the drive system 100 accordingly. Fig. 1, wherein current flows are schematically represented which can be generated in the course of the embodiment of the method according to the invention.

[0041] Fig. Figure 3 shows the embodiment of the method according to the invention as a schematic block diagram.

[0042] As in Fig. As shown in Figure 3, a predefined condition is met in step 310, whereupon a check of the DC link capacity is performed. For example, this condition is met when the electric machine 150 is at standstill.

[0043] If the condition is met, a special test switching state is generated in step 320, whereby the switching element 182 of the discharge circuit 180 is closed or switched to a conducting state for a predetermined time interval Δt. The individual switching elements 141, 142, 143, 144, 145, 146 of the half-bridges 131, 132, 133 are open or in a non-conducting state during the predetermined time interval Δt.

[0044] By closing the switching element 182 of the discharge circuit 180 during the test switching state, a discharge current flow I is initiated. Dis generated by the load 181. The time interval Δt is expediently chosen such that damage to the load 181 and the switching element 182 is avoided. The discharge current I Dis can be composed according to the following formula (1): IC=IDis−IBatt

[0045] This is I Batt a current supplied by the DC voltage source 110, which in Fig. 2 is indicated by arrow 210. Furthermore, I C a current supplied by the intermediate circuit capacitance, which in Fig. 2 is indicated by the arrow 220. The current I C According to the following formula (2), in particular, is a sum of currents supplied by the individual intermediate circuit capacitors 121, 122, 123: IC=IC1+IC2+…+IC3

[0046] Here, I denotes C1 for example, a current supplied by capacitor 121, which in Fig. 2 is indicated by arrow 221. I C2 For example, this refers to a current supplied by capacitor 122, which in Fig. 2 is indicated by the arrow 222, and I C3 denotes a current supplied by capacitor 123, in Fig. 2 indicated by arrow 223.

[0047] If the specified time interval Δt is chosen appropriately, in particular if the time interval Δt does not exceed a specified maximum value, and if the size or resistance value of the consumer 181 is not very small, in particular if the resistance value does not fall below a specified minimum value, it can be achieved, due to the impedance of cables and conductor tracks, that the discharge current I DisThe consumer 181 is mainly supplied or generated by the intermediate circuit capacitance and not, or at least hardly, by the DC voltage source 110.

[0048] In step 330, the current voltage value of the DC voltage in the DC network is determined both essentially immediately before and essentially immediately after the closing of the switching element 182, in particular by means of the voltage measuring unit 175 in parallel with the DC voltage source 110 and the DC link capacitance. Depending on the voltage values ​​determined in this way, the DC link capacitance is checked, as explained below. The current of the discharge current I Dis can be detected using the current sensor 183, however, this current is not usefully required for checking the DC link capacity.

[0049] Using the voltage measuring unit 175, a first voltage value U is determined.OC1 the DC voltage immediately before closing the switching element 182 as well as a second voltage value U DC2 the DC voltage immediately after the closing of the switching element 182. A voltage difference ΔU resulting from the closing of the switching element 182. DC (Voltage drop) is defined as the difference between the first voltage value U and the second voltage value U. DC1 and the second voltage value U DC2 certainly.

[0050] This voltage difference ΔU, which arises from the closing of the switching element DC is characteristic of the current state of the DC link capacitance. The value of the voltage difference ΔU DC In a fault-free or wear-free case, the DC link capacitance differs from the specific value of the voltage difference ΔU. DC In the case of a faulty or worn DC link capacitance, the voltage difference ΔU is determined by the current value.DC Therefore, it is checked whether the DC link capacitance is functioning correctly or whether a fault or deterioration of the DC link capacitance exists compared to the fault-free and wear-free state. For this purpose, the specific current voltage difference ΔU is measured. DC compared with a reference value that characterizes a fault- and wear-free case of the DC link capacitance. Since the specific value of the voltage difference ΔU DC However, since in general it may depend on the specific value of the DC voltage in the DC network before the closing of the switching element 182, it is first expedient to calibrate the reference value to the current operating point of the DC network.

[0051] For this purpose, in step 340, depending on the determined first voltage value U, DC1The reference value to be used is determined immediately before the closing of the switching element 182. A memory unit of the control unit 160 stores a multitude of pairs, each consisting of a reference voltage value and a corresponding reference voltage difference. These individual reference voltage differences each characterize a voltage difference of the DC voltage in the DC network that occurs when the switching element 182 closes, assuming a fault-free and wear-free intermediate circuit capacitance, provided the DC voltage has the respective corresponding reference voltage value before the closing of the switching element 182. The determined, current first voltage value U DC1 is compared with the reference voltage values. Depending on a difference in the current first voltage value U DC1The current comparison value is determined from the reference voltage values ​​by interpolation or extrapolation of the associated reference voltage differences.

[0052] The individual pairs of reference voltage values ​​and their corresponding reference voltage differences can be determined, for example, during the manufacturing and / or configuration phase of the DC network, e.g., through measurements and / or calculations using a computer-implemented simulation of the DC network to be manufactured. Alternatively or additionally, the reference value pairs can also be determined online during the regular operation of the DC network, e.g., during prior checks of the DC link capacitance. Furthermore, the reference value pairs can also be learned using self-learning systems, e.g., via a neural network or machine learning.

[0053] In step 350, the current voltage difference ΔU determined in step 330 is used. DC The current voltage difference ΔU is compared to the reference value determined in step 340. For example, tolerances of individual components of the DC link capacitor can also be taken into account. Depending on the result of this comparison, it is checked whether a fault and / or wear of the DC link capacitor is present. DC For example, if the current voltage difference ΔU lies within a predefined interval around the reference value, it can be determined in step 360 that there is no fault and no or minimal wear of the DC link capacitance, or that while wear is present, it does not exceed an acceptable limit. DCHowever, if the value deviates from the reference value by more than the specified interval, a conclusion can be drawn in step 370 regarding an existing error and / or existing wear, or unusual wear that exceeds the acceptable limit.

[0054] If in step 370 it is determined that there is a fault and / or wear of the DC link capacity, a predefined action can be carried out in step 380, e.g. the vehicle can be brought into a safe state, an error message can be issued to a driver of the vehicle, an entry can be created in a fault memory, etc.

[0055] The present invention thus provides a means of checking the DC link capacitance for faults or signs of wear in a simple, cost-effective, and flexible manner. The DC voltage is conveniently measured anyway during the regular operation of the DC network, so no additional measurement effort is required to check the DC link capacitance. Furthermore, the discharge circuit 180 is already provided as a safety measure in DC networks, so no additional circuit is conveniently required to check the DC link capacitance.

[0056] Furthermore, the discharge circuit 180 itself can also be checked for faults. If, in the test switching state, closing the switching element 182 does not result in any or at least no significant voltage difference in the DC network, or if the voltage difference is below a predetermined minimum value, and if, furthermore, no current or a current with a current intensity below a predetermined minimum value is detected by the current sensor 183, this indicates that the switching element 182 and / or the gate driver 165 of the switching element 182 are faulty or defective.

[0057] The voltage difference occurring when switching element 182 closes during the test switching state is therefore a particularly useful evaluation parameter for drawing conclusions about the current state of the DC link capacitance, as described below in relation to Fig. 4 is explained.

[0058] Fig. Figure 4a schematically shows a diagram 410 of the DC voltage U measured by means of the voltage measuring unit 175. DC plotted against time t, and in a corresponding manner a diagram 420 of the discharge current I measured by means of the current sensing unit 183 Dis plotted against time t. At a first time point t1, the switching element 182 of the discharge circuit 180 is closed, and at a second time point t2, after the predefined time interval Δt has elapsed, the switching element 182 is opened again. The time interval Δt can be, for example, 5 µs.

[0059] The discharge current I Dis In diagram 420, it is designated with the reference symbol 421. The current I supplied by the DC voltage source 110 Batt is designated with the reference numeral 422. As can be seen in diagram 420, the current I supplied by the DC voltage source 110 is Battalmost zero. As explained above, by appropriately choosing the time interval Δt and the resistance value of the load 181, it can be achieved that the discharge current I Dis The power is generated by the consumer 181 mainly through the intermediate circuit capacitance and not, or at least hardly, through the DC voltage source 110.

[0060] A section of the two diagrams 410 and 420 around the first time t1, at which the switching element 182 is closed, is in Fig. 4b shown enlarged.

[0061] Accordingly Fig. 4a shows Fig. 4b schematically a diagram 430 of the DC voltage U measured by means of the voltage measuring unit 175 DC plotted against time t and a diagram 440 of the discharge current I measured by means of the current sensing unit 183 Dis plotted against time t. In diagram 440, the discharge current I is shown. Disdesignated with reference numeral 441 and the current I supplied by the DC voltage source 110 Batt with reference number 442.

[0062] In diagram 430, for example, curve 431 represents the time course of the voltage U. DC for a fault-free and wear-free intermediate capacitance. Curve 432, for example, represents the time course of the voltage U. DC , when the capacitance value of the intermediate capacitance has reduced from its original value to 93%. Curve 433, for example, represents the time course of the voltage U. DC , when the capacitance value of the intermediate capacitance has reduced from its original value to 87%. Curve 434, for example, represents the time course of the voltage U. DC , if the capacity value of the intermediate capacity has decreased from the original value to 67%.

[0063] Reference numeral 435 denotes the voltage difference or voltage drop ΔU that occurs when the switching element 182 is closed. DC The fault- and wear-free intermediate capacitance is indicated for curve 431. Reference numeral 436 denotes the voltage difference ΔU that occurs when switching element 182 closes. DC This is indicated for curve 434, when the capacity value of the intermediate capacity has reduced from the original value to 67%.

[0064] As can be seen in diagram 430, the voltage difference ΔU DC When switching element 182 closes at time t1, the intermediate capacitance increases steadily due to wear and tear and the decreasing capacitance value. This depends on the current voltage difference ΔU. DC Therefore, it is particularly effective to deduce the current state of the intermediate circuit capacity.

Claims

[1] Method for checking an intermediate circuit capacitance (121, 122, 123) in a DC network, in particular in a vehicle, wherein the intermediate circuit capacitance (121, 122, 123) is connected in parallel to a DC voltage source (110) and in parallel to a converter circuit (130), wherein a discharge circuit (180) for discharging the intermediate circuit capacitance (121, 122, 123) is connected in parallel to the intermediate circuit capacitance (121, 122, 123), wherein the discharge circuit (180) comprises a consumer unit (181) and a switching element (182), comprising the steps: Closing (320) of the switching element (182) of the discharge circuit (180) for a predetermined time interval when a predetermined condition (310) is met; Determining (330) a voltage difference of a DC voltage in the DC voltage network resulting from the closing of the switching element (182), in particular determining a voltage difference of a first voltage value of the DC voltage before the closing of the switching element (182) and a second voltage value of the DC voltage after the closing of the switching element (182); Check (350) whether there is a fault and / or wear of the intermediate circuit capacitance (121, 122, 123) depending on the determined voltage difference. [2] Method according to claim 1, wherein checking (350) whether there is a fault and / or wear of the intermediate circuit capacity (121, 122, 123) comprises: Comparing the determined voltage difference with a reference value; and determining whether there is a fault and / or wear of the DC link capacitance (121, 122, 123) depending on a result of this comparison. [3] Method according to claim 1 or 2, further comprising: Determining (330) a voltage value of the DC voltage in the DC voltage network before closing the switching element (182), furthermore checking (350) whether there is a fault and / or wear of the intermediate circuit capacitance (121, 122, 123) depending on the determined voltage value. [4] Method according to claims 2 and 3, further comprising: Determining (340) the comparison value depending on the determined voltage value as well as depending on at least one reference voltage value and on at least one associated reference voltage difference. [5] The method of claim 4, further comprising: Comparing the determined voltage value with at least one reference voltage value and Determining (340) the comparison value depending on a result of this comparison and depending on the at least one associated reference voltage difference, in particular by interpolation and / or extrapolation. [6] Method according to claim 4 or 5, wherein the at least one reference voltage value and the at least one associated reference voltage difference are each predetermined values ​​from a manufacturing and / or configuration phase of the DC network and / or certain values ​​from a previous verification of the DC link capacitance. [7] Method according to any of the foregoing claims, further comprising: Check (350) whether there is a fault and / or wear of the discharge circuit (180) depending on the determined voltage difference. [8] Method according to any of the foregoing claims, further comprising: Determining the specified time interval depending on a voltage value of the DC voltage in the DC network and / or depending on a state of charge of the DC voltage source and / or depending on a rated current of the switching element (182) of the discharge circuit (180) and / or on a rated current of the consumer unit (181) of the discharge circuit (180) and / or a pulse power of the consumer unit (181) of the discharge circuit (180). [9] Method according to one of the preceding claims, wherein the specified condition (310) comprises that an electrical machine (150) connected to the converter circuit (130) is at a standstill. [10] Method according to any of the foregoing claims, further comprising: Perform (380) a specified action if, during the inspection, it is determined that there is a fault and / or wear of the intermediate circuit capacity. [11] Computing unit (160) comprising a processor configured to perform the method according to any of the preceding claims. [12] Converter arrangement for controlling a multiphase electric machine (150), comprising: a power converter circuit (130) with a DC voltage side and an AC voltage side, which has a plurality of half-bridges (131, 132, 133) each with a high-side switching element (141, 142, 143) and a low-side switching element (144, 145, 146), an intermediate circuit capacity (121, 122, 123), and a computing unit (160) according to the preceding claim. [13] Drive system (100) comprising a converter arrangement according to the preceding claim and a multiphase electric machine (150) connected to the AC voltage side of the converter circuit (130). [14] Computer program comprising instructions which, when the program is executed by a computing unit, cause it to execute the method according to claims 1 to 10. [15] Computer-readable data carrier on which the computer program according to claim 14 is stored.

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