EP4175845A1

EP4175845A1 - Identifying an unbalanced load in a high-voltage system and response thereto

Info

Publication number: EP4175845A1
Application number: EP21743377.0A
Authority: EP
Inventors: Tobias Aurand; Markus Zimmer
Original assignee: Mercedes Benz Group AG
Current assignee: Mercedes Benz Group AG
Priority date: 2020-07-01
Filing date: 2021-06-25
Publication date: 2023-05-10
Also published as: CN115835973A; US20240036078A1; DE102020006919A1; WO2022002800A1

Abstract

According to a method for determining information about an electric unbalanced load in a vehicle having an at least partially electrified drive train and having at least one high-voltage system (1), a variable characterizing an energy quantity of a Y capacitor (C1, C2) of the high-voltage system (1) is determined. Furthermore, a threshold value relating to a capacitance of the Y capacitor (C1, C2) is provided. Finally, the information about the electric unbalanced load is determined by comparing the characterizing variable determined with the threshold value provided.

Description

Determining an unbalanced load in a high-voltage system and reacting to it

The present invention relates to a method for determining information about an unbalanced electrical load of a vehicle with an at least partially electrified drive train, which has at least one high-voltage system. The present invention also relates to a method for reacting to such information about the unbalanced electrical load. The invention also relates to a corresponding high-voltage system for an electrically drivable motor vehicle and an electrically drivable motor vehicle with such a high-voltage system. x and Y capacitors

In simplified terms, there are two types of capacitors in electrical drive systems, so-called X-capacitors and so-called Y-capacitors. While the X capacitors are switched between the HV potentials (i.e. between HV + and HV-) and there act as a buffer, Y capacitors are switched from each of the HV potentials to vehicle ground and act as so-called "interference suppression capacitors". In addition, many components (especially the HV battery) form so-called parasitic Y capacitors due to their design principles, i.e. a capacitance is formed between the respective HV potentials and the vehicle ground.

While HV vehicles are so-called II or IT network systems from the point of view of the energy distribution systems and are therefore per-se safe with regard to dangers from electrical current or electrical voltage when touched, only the energy stored in the Y capacitors remains Hazard source to be taken into account in the event of a first failure, since when touching an HV potential (either HV + or HV-) the total energy of all Y capacitors connected to this potential is diverted through the body. The problem of variable Y capacitors arises in particular in the commercial vehicle sector. It is customary there to equip a base vehicle with different superstructures, such as a crane, cooling system, etc. If necessary, the superstructures are removed, rebuilt or additionally set up. This changes the total Y capacity of the vehicle, which results from the sum of all Y individual capacities of the superstructures. So when “Y capacitance” or “Y capacitor” is mentioned in the following document, this usually means the sum of all parasitic or discretely effective Y capacitances or Y capacitors per HV potential according to vehicle mass.

In order to minimize the associated dangers and probabilities of damage to health, there are standards and regulations that regulate and limit the maximum amount of energy that can be stored in Y-capacitors. This means that strict compliance with these limits is relevant for approval. If, for whatever reason, these limits cannot be adhered to, the vehicle can either not be approved (preventing entry into the market) or extremely significant constructive measures must be taken to prevent possible contact with the HV potential. This is technically possible, but very time-consuming, i.e. corresponding measures are associated with constructive complexity (and thus maintenance unfriendliness) and the associated negative effects on the vehicle weight as well as considerable additional costs. So this is to be avoided.

Energy in the capacitor

Furthermore, the steadily increasing system voltage of the electrical drive systems (especially in the commercial vehicle sector) exacerbates the problem considerably, since the amount of energy stored in a capacitor (constant size) increases with the square of the capacitor voltage. That means it applies where W is the stored energy, C is the capacitance of the capacitor and U is the aforementioned voltage across the capacitor. In concrete terms, this means that if the system voltage in the HV system increases from 400V to 800V, the sum of the capacities permitted per HV potential is only a quarter of the previous value. This is unfavorable because the higher voltage level is often associated or must be associated with shorter switching times of semiconductor components in order to limit the thermal switching losses that occur during switching. Shorter switching times result however, conversely to so-called steeper switching edges, these lead to more interference that must be diverted (see above "Y capacitors are interference suppression capacitors") and thus there is a tendency towards the need for larger Y capacitors. This means that there is a doubly unfavorable, contrary development.

Insulation resistances in HV systems

As already mentioned above, HV systems are so-called II or IT systems, ie they have no relation to the vehicle mass (cf. a flashlight, here the system only relates to the plus or minus pole of the flashlight batteries, but not to any ground potential). Ideally, the HV potentials can therefore be referred to as undefined or "floating" with regard to the vehicle mass. This is deliberate and forms the basis of the first failure safety mentioned above.

However, since all insulation materials used in reality have a resistance - albeit a very high one - there is also a high-resistance connection of both HV potentials to the vehicle ground in such systems. These undesirable and purely parasitic resistances, which are not built in as a component, are called insulation resistances.

Since these insulation resistances must not fall below a certain value, because otherwise the protective character of the II or IT systems is no longer given, the insulation resistances are measured by means of an insulation measuring device, which is called an insulation monitor. Admittedly, compliance is also certain

Insulation resistance limits relevant to approval, but irrelevant for this invention.

As can be seen in Fig. 1, the resistors Riso_HV + and Riso_HV- represent a voltage divider over the HV voltage. In the course of a vehicle's life, there is usually a change in the insulation resistance, mainly due to the aging or deterioration of the insulation materials. While the insulation resistances of a new vehicle are usually approximately the same in both potentials and also usually deteriorate to the same extent, it can nonetheless occur (and does so in practice) that the insulation resistance of one of the potentials changes faster than that of the others Potential, which then leads to an “unbalanced load” or “imbalance” of the insulation resistance.

In other words, in an ideal new vehicle, in which both insulation resistances are the same, the HV voltage is evenly divided over the voltage divider, i.e. the voltage of each of the HV potentials according to vehicle mass is of the same magnitude. If the "unbalanced load" described above occurs, this shifts the resistance ratio and thus also the distribution of the HV voltage, i.e. the voltage of one HV potential according to vehicle mass is larger than the absolute value of the other potential according to mass.

Insulation resistors and Y capacitors

If you connect the two topics mentioned above, Y capacitors and insulation resistors, the right part of the circuit diagram of Fig. 1 results.

You can see that the Y capacitors are parallel to the insulation resistors (i.e. connected in parallel) and that they are charged to the voltage that is set by the voltage divider of the insulation resistors.

This is also where the problem to be improved by the invention lies. If the ratio of the insulation resistances to one another shifts due to changes (see aging), the voltage across the capacitors will also shift. Due to the generally relatively high insulation resistance in such systems and the "relatively" low legally prescribed switch-off threshold when the insulation resistance falls below the limit, extreme "unbalanced loads" can result in almost the entire voltage of the HV system being applied to one of the two capacitors.

This means that for the design case of the maximum Y capacitances (quasi) the maximum HV voltage occurring in the system must be used, since in the worst case this can almost completely drop across the Y capacitors of a potential. Since, as mentioned above, the voltage with the square is included in the energy stored in the capacitor, this is considerably disadvantageous and means that for systems with a system voltage of up to 850V, for example, not 425V can be used for the calculation (ideal system) but the full 850V.

The resulting maximum Y capacitance per potential is then so low that either compliance with EMC standards is not possible, with considerable thermal Losses due to longer switching times (possibly technically limited or sometimes impossible) are to be expected, the system voltage is reduced (counteracts the idea of powerful 850V systems for commercial vehicles) or, as mentioned above, considerable constructive and thus expensive and payload-reducing measures have to be taken.

As mentioned above, it can therefore be advantageous to provide the highest possible Y capacitances in a high-voltage system for an electrically drivable motor vehicle. In this way, for example, thermal losses can be reduced, switching times reduced or higher system voltages used. On the other hand, as described, component aging can lead to an unbalanced load, in which different voltages are applied to the Y capacitances of different high-voltage potential connections of the high-voltage system. In the worst case, the entire system voltage is on one potential side of the high-voltage system. For safety reasons, however, the maximum amount of energy that can be stored in the Y capacitors is limited. Due to the unbalanced load, compromises have to be made in the design of the Y capacitors in order to still be able to map the limit case of maximum unbalanced load. Ultimately, this limits the maximum capacity of the Y capacitors.

Against this background, it is an object of the present invention to specify an improved concept for a high-voltage system of an electrically drivable motor vehicle.

This object is achieved by the respective subject matter of the independent claims. Advantageous further developments and preferred embodiments are the subject matter of the dependent claims.

The improved concept is based on the idea of determining an unbalanced load based on the amount of energy in a Y capacitor. The unbalanced load can be reacted to by reducing the amount of energy.

According to the improved concept, a method for determining a first piece of information about an unbalanced electrical load of a vehicle with an at least partially electrified drive train, which has at least one high-voltage system, is specified. A quantity characterizing an amount of energy in the Y capacitor of the high-voltage system is first determined. Furthermore, a first threshold value is provided in relation to a capacitance of the Y-capacitor. Finally, the first information about the unbalanced electrical load is determined by comparing the determined characterizing variable with the provided first threshold value.

According to the improved concept, a method for reacting to a first piece of information about an unbalanced electrical load of a vehicle with an at least partially electrified drive train, which has at least one high-voltage system, is specified. In this case, a first measure is initiated as a function of the first information, as a result of which an amount of energy in a Y capacitor relating to the unbalanced load is reduced.

According to the improved concept, a high-voltage system for an electrically drivable motor vehicle with a Y capacitor is also specified. The high-voltage system has an analysis device for determining a quantity characterizing an amount of energy of a Y-capacitor of the high-voltage system and for providing a first threshold value in relation to a capacitance of the Y-capacitor. In addition, the high-voltage system has a computing device for determining the first information about the unbalanced electrical load by comparing the determined variable with the first threshold value provided.

According to the improved concept, an electrically drivable motor vehicle with a high-voltage system according to the improved concept is also specified.

A first high-voltage potential connection (e.g. HV +) can be connected to a first output of a high-voltage battery of the high-voltage system, for example, and the second high-voltage potential connection (HV-) can be connected to a second connection of the high-voltage battery, which has an opposite polarity compared to the first connection of the high-voltage battery having.

In general, the high-voltage system does not have a direct ground connection and is therefore floating, so to speak, so that the first high-voltage potential connection and the second high-voltage potential connection essentially only have one potential difference that represents the voltage in the high-voltage system. However, since the high-voltage system can nevertheless be connected with high resistance via Y capacitors and insulation resistors to, for example, a vehicle ground connection of the motor vehicle, this usually results in a ground reference for the high-voltage system. As a result, one can also speak of HV + for the first high-voltage potential connection and HV- for the second high-voltage potential connection, for example, without having to refer directly to a ground or zero position or even a symmetrical one To imply potential difference to this. To simplify understanding, this wording is retained and, accordingly, an opposite polarity continues to be assumed without restricting the high voltage.

According to the method or in a high-voltage system according to the improved concept, a quantity characterizing a quantity of energy of a Y-capacitor of the high-voltage system is determined. This characterizing variable can be the actual amount of energy or a variable from which the amount of energy can be clearly determined. The characterizing variable can therefore be rated as a proxy for the actual amount of energy in the Y-capacitor. If necessary, the Y capacitor forms the sum of several Y individual capacitors.

In the method, a first threshold value in relation to a capacitance of the Y capacitor is also provided. This means that the first threshold value is made available practically as a function of the capacitance of the Y capacitor. Since the first threshold value is used to assess the unbalanced load, it is necessary that it depends on the size of the capacitance of the Y-capacitor. Namely, the more Y-capacitance is built into the vehicle, the lower the unbalanced load may be. This is immediately evident, since the unbalanced load represents the voltage division ratio of the voltages on the Y capacitors to the high-voltage potential connections. A high unbalanced load leads to a correspondingly high partial voltage on the corresponding Y capacitor and thus to a correspondingly high energy content. A high unbalanced load can therefore not pose a risk with a small capacity, while it certainly does with a higher capacity. The first threshold value can be provided by means of a look-up table or an analytical function.

Ultimately, in the method according to the improved concept, the first information about the electrical unbalanced load is determined by comparing the determined characterizing variable with the first threshold value provided. The comparison result thus leads to the first information item, which can be binary, for example, depending on whether the characterizing variable is greater or less than the first threshold value. This first information can then be used to react accordingly automatically by initiating suitable measures and, in the simplest case, only warning the driver.

In an advantageous embodiment of the method according to the invention, ie in the improved concept, it can be provided that the amount of energy characterizing variable is a voltage or partial voltage of the high-voltage system or a related variable, a ratio of voltages of the high-voltage system or a ratio of insulation resistances of the high-voltage system. If the total voltage of the high-voltage system is known, a certain voltage value is obtained on a Y-capacitor in an initial state (eg with given insulation resistances). If this voltage or the voltage value changes, the voltage to the other high-voltage potential also changes in accordance with the voltage division ratio. If the capacity is known, the respective individual voltage can be converted into the corresponding amount of energy. If the voltage rises above a certain voltage threshold value, the energy in the capacitor also rises above a corresponding energy threshold value. If the voltage drops, this is a sign that the voltage on the Y capacitor increases correspondingly to the other high-voltage potential. So a drop in voltage also means an unbalanced load and possibly a danger.

Of course, the total voltage between ground and the respective high-voltage potential does not necessarily have to be considered for the voltage analysis, because a partial voltage (e.g. at a corresponding voltage divider) of the high-voltage system can also be representative of the respective total voltage. Alternatively, however, a variable related to the voltage can also be determined as a characterizing variable. If necessary, a current could, for example, be such a related variable, or else an arbitrary variable that can be translated into a voltage value with a predetermined function or relation.

In addition, the quantity characterizing the amount of energy can also be a ratio of voltages in the high-voltage system. In particular, it can be the ratio of the total voltages from ground to the respective high-voltage potential. The latter stress ratio represents the unbalanced load directly, so that in this case an actual unbalanced load can be compared with an unbalanced load limit value. Analogously to this, a ratio of insulation resistances of the high-voltage system can also be determined directly as a characterizing variable. It is particularly advantageous if the respective insulation resistances represent the total resistances from ground to the respective high-voltage potential connection. This ratio of the insulation resistance also directly represents the unbalanced load.

In a further development of the method, an additional step is provided, namely the determination of a second item of information about the electrical unbalanced load by means of Comparison of the determined variable with a provided second threshold value different from the first threshold value with regard to the capacitance of the Y-capacitor. This means that the specific characterizing variable is compared with two different threshold values. This results in two different comparison results which lead to the first information item and to the second information item. These two pieces of information can then be used for a cascade of reactions. If necessary, a comparison with a third threshold value etc. can of course also take place.

As mentioned above, the method according to the invention can, in accordance with the improved concept, provide that a reaction is made to the first information about the unbalanced electrical load. In particular, a first measure should be initiated as a function of the first information in order to reduce an amount of energy in a Y capacitor relating to the unbalanced load. The first information can be obtained by a method as described above. The first information is not only obtained and, if necessary, made available, but an adequate response also takes place here.

A possible reaction as the first measure can be an automatic shutdown of the entire high-voltage system. This automatic shutdown of the high-voltage system has the consequence that, for example, the high-voltage connections of the high-voltage system are disconnected from the high-voltage battery. At this point in time the voltages are still applied to the capacitors, but discharge can take place via active and / or passive discharge devices, or the insulation resistors also represent a very high-resistance connection can be purposefully discharged through additional measures.

A first measure as a reaction to an undesired unbalanced load can also be a decoupling of a sub-network from the high-voltage system. For example, a cooling system of a vehicle body can be separated from the high-voltage system as a sub-network. This reduces the total Y capacitance, which also reduces the amount of energy in the entire Y capacitor.

As an alternative or in addition, a voltage on the Y capacitor can also be reduced as a first measure. With the reduction of the voltage by means customary for a person skilled in the art, the energy in the Y-capacitor is also reduced. This can be done under for example a reduction of the system voltage or the energy consumption but also a limitation of the maximum charging voltages or system voltage serve as measures.

As an alternative or in addition, an insulation resistance at the Y-capacitor can also be reduced, in particular by introducing, removing, switching on or switching back one or more correction resistors. In any case, a resistor is added to the existing insulation resistance or separated from it in such a way that the unbalanced load or imbalance is reduced. This means that the amount of energy in the respective Y-capacitor cannot exceed a predetermined maximum.

In a further development of the method according to the invention, it can also be provided that a second measure, in particular a warning, is initiated as a function of the second information, whereby the amount of energy of the Y-capacitor relating to the unbalanced load is not reduced. While the amount of energy in the Y capacitor is reduced with the first measure, this is not the case with the second measure. This is particularly advantageous for purely precautionary measures in which the driver is warned in advance of an impending danger, for example. Of course, further measures can also be initiated here, if necessary, depending on further threshold values. In this way, a cascade of measures can be implemented with regard to reactions to an unbalanced load.

In a particularly advantageous embodiment of the method, provision is made that the provision of the first threshold value includes determining a total capacitance of the Y capacitor and determining the first threshold value as a function of the total capacitance. The total capacity can in particular be determined automatically. It is thus possible to determine the current total capacitance of the Y-capacitor at certain points in time and to adapt the threshold value (s) according to the total capacitance. This means that it is always possible to react to aging of the entire Y-capacitor, for example.

Further advantages, features and details of the invention emerge from the following description of preferred exemplary embodiments and on the basis of the drawings. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures are can be used not only in the respectively specified combination, but also in other combinations or on their own, without departing from the scope of the invention.

In the figures show:

1 shows a schematic representation of an exemplary embodiment of a high-voltage system according to the improved concept;

2 shows a schematic representation of an alternative embodiment of a high-voltage system according to the improved concept; and

3 shows a schematic representation of a further exemplary embodiment of a high-voltage system according to the improved concept.

In the figures, identical elements or elements with identical functions are identified by identical reference symbols.

In FIG. 1, an exemplary embodiment of a high-voltage system 1 for an electrically drivable motor vehicle (hereinafter also referred to as "HV vehicles") is shown schematically. The high-voltage system 1 has two high-voltage potential connections HV1, HV2 (hereinafter also referred to as "HV potentials") with opposite polarity (e.g. HV + and HV-) and a vehicle ground connection M (hereinafter also referred to as "vehicle ground").

In a high-voltage system 1 of this type, in particular in an electrical drive system, there can be, in simplified terms, two types of capacitors, namely X-capacitors and Y-capacitors. While the X capacitors can be connected between the HV potentials HV1, HV2 in order to perform a buffer function, Y capacitors can be connected from each of the HV potentials HV1, HV2 to vehicle ground M in order to act, for example, as interference suppression capacitors. In addition, many components, especially the high-voltage battery, form parasitic Y (partial) capacitors due to their design principles. A (total) capacity is thus formed between the respective HV potentials HV1, HV2 and the vehicle mass M. While HV vehicles are so-called II or IT network systems from the point of view of an energy distribution system and are therefore per se first-fault-proof with regard to dangers from electrical current or electrical voltage when touched, the energy stored in the Y-capacitors remains in the event of a first failure Considerable source of danger, since when touching an HV potential HV1, HV2, the total energy of all Y capacitors connected to this potential is diverted through the body. The entirety of the Y capacitors including the parasitic Y capacitors is shown schematically in FIG. 1 as a first Y capacitor C1 between the first HV potential HV1 and vehicle ground M and as a second Y capacitor C2 between the second HV potential HV2 and vehicle ground M shown.

In order to reduce the dangers associated with touching an HV potential HV1, HV2 or the probability of damage to health, the maximum amount of energy that can be stored in Y capacitors can be limited. Constructive measures to avoid possible touching of the HV potentials HV1, HV2 may be technically possible, but are in any case associated with a high degree of structural complexity and thus maintenance unfriendliness as well as negative effects on the vehicle weight and considerable additional costs. According to the improved concept, this is avoided.

It should also be noted that a higher system voltage exacerbates the problem outlined above, as the amount of energy stored in a capacitor increases with the square of the capacitor voltage. Specifically, this means that if the system voltage increases from 400V to 800V, the sum of the capacities permitted per HV potential HV1, HV2 is only a quarter of the previous value.

This is unfavorable because the higher voltage level is often associated with shorter switching times of semiconductor components in order to limit thermal switching losses that occur during switching. Conversely, however, shorter switching times lead to steeper switching edges, which in turn lead to more interference, which in turn has to be countered with interference suppression capacitors, which leads to the need for larger Y capacitors.

As already mentioned above, high-voltage systems of motor vehicles are II or IT systems, that is, they have no relation to vehicle mass M, so that the HV potentials with regard to vehicle mass M are ideally regarded as undefined or "floating" be able. However, since all insulation materials used in reality have a finite electrical resistance have, there is also a high-resistance connection of both HV potentials HV1, HV2 to vehicle ground M in such systems. These undesirable and not built-in as a component, but purely parasitic resistances are also referred to as insulation resistances. In FIG. 1, these are shown schematically as a first insulation resistance RI1 between the first HV potential HV1 and vehicle ground M and as a second insulation resistance RI2 between the second HV potential HV2 and vehicle ground M.

Since the insulation resistances R11, RI2 must not fall below a certain value, because otherwise the protective character of the II or IT systems is no longer given, the insulation resistances R11, RI2 are measured using an insulation measuring device.

As can be seen from Fig. 1, the insulation resistors R11, RI2 represent a voltage divider over the entire HV voltage between the HV potentials HV1, HV2 Aging or deterioration of the insulation materials. While in a new vehicle the insulation resistances R11, RI2 at both HV potentials HV1, HV2 are usually approximately the same and also usually deteriorate to the same extent, it can still happen that one of the insulation resistances R11, RI2 changes faster than the other , which leads to a so-called unbalanced load or "imbalance" of the insulation resistances R11, RI2.

In an ideal new vehicle, in which both insulation resistances R11, RI2 are the same, the HV voltage is evenly divided over the voltage divider, so that the voltages U 1, U2 between the respective HV potentials HV1, HV2 and vehicle ground M are of the same magnitude are. If the unbalanced load described above occurs, this shifts the resistance ratio and thus also the division of the HV voltage, so that one of the voltages U1, U2 is greater than the other.

As can be seen in Fig. 1, the Y capacitors C1, C2 are parallel to the respective insulation resistors R11, RI2 and are therefore charged to the respective voltage U 1, U2, which is divided by the voltage divider of the insulation resistors R11,

RI2 adjusts. If the ratio of the insulation resistances R11, RI2 shifts to one another, the voltage U 1, U2 across the capacitors C1, C2 also shifts. Due to the generally relatively high insulation resistances R11, RI2 in such Systems, with extreme unbalanced loads it can happen that almost the entire voltage of the high-voltage system 1, i.e. a voltage of the amount | U 1 | + | U2 |, is present. This means that for the design case of the maximum Y capacitors C1, C2 without the improved concept, the maximum HV voltage that occurs in the system must be used, since in the worst case it can almost completely drop across one of the Y capacitors C1, C2.

Since, as mentioned above, the voltage with the square is included in the energy stored in the capacitor, this would be considerably disadvantageous and lead to the fact that for systems with a system voltage of up to 850V, for example, not 425V but the full 850V can be used for the calculation. The resulting maximum Y capacitance per HV potential HV1, HV2 would then be so low that EMC requirements could not be met, considerable thermal losses would have to be accepted due to longer switching times, the system voltage would have to be reduced or, as mentioned above, considerable structural engineering and therefore cost-intensive and payload-reducing measures would have to be taken.

According to a high-voltage system 1, as shown in FIG. 1, this problem can be solved in that a maximum “unbalanced load limit” that is permissible in the system is specified and this is used for the design. When this limit is reached, the high-voltage system 1 can be switched off, for example, and / or other risk-reducing measures can be taken.

For example, in the high-voltage system 1, a voltage (of which a setpoint or reference value is known), the ratio of the voltages U1, U2 of the two HV potentials HV1, HV2 to vehicle mass M, is used as a variable that characterizes the amount of energy in a Y capacitor The ratio of partial voltages of the high-voltage system 1 or the ratio of the insulation resistances is determined. This can be done, for example, by means of insulation resistance measurements

Insulation resistance ratio measurement, a voltage ratio measurement, one or more voltage measurements or other suitable measures are carried out. If the preset ratio is now violated or a threshold value of the characterizing variable is exceeded or not reached, this leads to a corresponding comparison result, which is also referred to here as the first information regarding the electrical unbalanced load. This first information is possibly only provided by the vehicle. According to a further development, there is a reaction to the first information. For example, there is only one warning (for example, “maximum drive to the end of the current journey” warning). If necessary, however, the high-voltage system 1 is (partially) switched off automatically. In a cascade process, the characterizing variable can, however, also be compared with one or more further threshold values in order to obtain a second, third, etc. piece of information. A sequence of measures can be initiated on the basis of this additional information. For example, a (partial) shutdown with advance warning can take place if the characterizing variable initially exceeds / falls below a first threshold value and then a second threshold value.

With an 850V system and a permitted "unbalanced load limit" of 1: 3, for example, the full voltage of 850V would no longer have to be used to design and thus limit the Y capacitors C1, C2, but only ³ Å of it, i.e. 637V. Since, as mentioned, the voltage is included in the calculation as a square, this results in a factor of 1.78 by which the Y capacitors C1, C2 may be larger than without this measure.

The improved concept therefore makes it possible to actively ensure compliance with the specified limit values in accordance with a maximum amount of energy, but at the same time to use larger Y capacitors C1, C2 than would otherwise be possible.

For this purpose, for example, a fixed unbalanced load limit value can be defined in the design, compliance with which is then monitored by means of a monitoring unit 2. However, this is particularly disadvantageous in the commercial vehicle segment, where there are a large number of different configurations of the HV system, since a static unbalanced load limit would always have to be based on the worst-case vehicle configuration, so that, as a result, base vehicles with only a low Y-capacity are too much would have to drive to the workshop early or be taken out of service. For example, if a base vehicle has a Y-capacitance of 400 nF per vehicle, a maximum equipped vehicle can definitely have 900 nF. Since W _capacitor = ¹ CU ² applies, one should allow a higher voltage (and thus unbalanced load) on the Y capacitors of the respective potentials in the base vehicle due to the smaller capacitance than in the vehicle with maximum equipment.

In order to ensure maximum vehicle availability, however, it is advantageous to combine the unbalanced load limit value or a threshold value with regard to the amount of energy in one The variable characterizing the respective Y-capacitor, for example during the manufacture of the vehicle, if the capacities of the built-in Y-capacitors C1, C2 are known, to be programmed individually into the vehicle or to be calculated dynamically in the vehicle. The latter can take place, for example, in that each component of the high-voltage system 1 sends information about the Y capacitors assigned to it or contained by it to a computing unit of the high-voltage system 1, the computing unit sums up all capacities in terms of potential and then the unbalanced load limit value or threshold value for the vehicle's own system voltage calculated. Alternatively, a look-up table can be stored in the arithmetic unit or at another location, which has Y capacitors for the components of the high-voltage system 1. With regard to possible subsequent changes to the components, the described dynamic calculation of the unbalanced load limit is particularly advantageous.

Specifically, (new) commercial vehicles are often sold after 3 years at the end of depreciation and converted by the next owner. For the high-voltage system, this can mean, for example, that a second battery is installed, a crane is replaced by a cooling body, or the like. This results in considerable changes in the high-voltage system and thus in the Y capacitances in the system. The aforementioned dynamic calculation of the unbalanced load limit or the limit value or limit values is therefore recommended.

A further exemplary embodiment of a high-voltage system 1 for an electrically drivable motor vehicle is shown schematically in FIG. 2. The high-voltage system 1 of FIG. 2 is based on that of FIG. 1.

In the high-voltage system 1 of FIG. 2, it is possible to actively influence the insulation resistances and thus the voltages U1, U2 or their ratio. This can be achieved by inserting switchable or controllable resistors R1, R2 between the respective HV potential HV1, HV2 and vehicle ground M by means of respective switching devices S1, S2, and thus via targeted control or switching on and / or off the resistors R1 , R2 the unbalanced load ratio is actively influenced. In Fig. 2, for the sake of clarity, only one resistor R1, R2 is shown. In fact, however, several switchable or controllable resistors and optionally one or more non-variable resistors can also be represented as a result. As an alternative or in addition, it is possible not only to compensate or control the insulation resistances in terms of potential but also to introduce a resistance, fixed or switchable, on both HV potentials HV1, HV2, which is selected so that even when a predefined warning threshold is reached, for example 500 W / V or until a predefined switch-off threshold, for example 100 W / V, is reached, such an unbalanced load cannot occur at any point in time. Making these resistors switchable has the advantage that when the resistors are switched off, the actual insulation resistances R11, RI2 can still be reliably determined.

In particular, it can be provided that, from the start, switchable resistors between the high-voltage potentials HV1 and HV2 on the one hand and vehicle ground M on the other hand are introduced into a base vehicle. There is no limit to the number of resistances that can be used. For example, further switchable resistors R1, R1 ″, etc. could be connected in parallel to the resistor R1. The same applies to the switchable resistance R2. The individual resistors could preferably be connected individually or in groups in parallel to the respective insulation resistance RI1, RI2. This allows the parallel resistance to the insulation resistance to be changed and thus the total resistance of the vehicle ground to the respective high-voltage connection HV1, HV2. Depending on the configuration and / or age, an unbalanced load can be compensated for by simply connecting or disconnecting the corresponding resistors.

As an alternative or in addition to a switch-off threshold, one or more warning thresholds can be provided via which the driver or third party can be informed that a corresponding unbalanced load is present and that a visit to the workshop may be necessary in order to avoid a forced switch-off.

Alternatively or additionally, especially in the case of very high unbalanced insulation resistance loads, a maximum charging voltage of the high-voltage battery and subsequently the maximum possible voltage on the Y-capacitors C1, C2 can be limited so that it is possible to continue driving or to the workshop. Optionally, a temporary partial connection of the high-voltage system 1 can be used to destroy energy to a certain extent, for example by means of a heater or an air-conditioning system or the like. As a result, the battery voltage is lowered and the system voltage is thus reduced to such an extent that the entire high-voltage system 1 can be operated, since then the total voltage and thus the then extreme voltage The unbalanced load voltages on the Y capacitors C1, C2 are low enough to adhere to the limits.

Provision can also be made to predict both insulation resistances R11, RI2 or voltages U 1, U2, for example by means of an extrapolation method, in order to issue a warning at an early stage.

The points explained with regard to FIG. 2 can be provided independently or in combination with the monitoring and, if necessary, disconnection, as explained with regard to FIG. 1.

In Fig. 3, a further exemplary embodiment of a high-voltage system 1 for an electrically drivable motor vehicle is shown schematically.

In the embodiment of FIG. 3, a slot P1, P2 for manually inserting correction resistors RK1, RK1 between vehicle ground M and the respective HV potential HV1, HV2, for example in a workshop, is provided for each HV potential HV1, HV2. Together with diagnostic routines, a worker could be supported in restoring the balance of the insulation resistances so that the specified requirements for the maximum energy in the Y capacitors C1, C2 can be met.

The slots P1, P2 can in principle be arranged at any points in the high-voltage system 1, preferably outside the high-voltage battery. For example, the slots P1, P2 can be located under a service flap, where, for example, fuses can also be located.

The worker can be supported by the vehicle or vehicle software in dimensioning the correction resistors RK1, RK1. In particular, it is also possible to monitor which of the insulation resistances RI1, RI2 is currently changing more rapidly in order to then undertake an overcompensation as a preventive measure.

Optionally, one or more safety resistors RS1, RS2 can be provided in series with the corresponding slot P1, P2 for each HV potential HV1, HV2. These can be viewed as a personal protection measure which, for example, covers the case that the HV potentials HV1, HV2 are accidentally bridged become or the like. The sum of the respective correction resistor RK1, RK2 with the respective safety resistors RS1, RS2 is in particular dimensioned such that the loss at the respective other HV potential HV1, HV2 can be corrected.

In a particularly simple implementation of the method according to the invention or the high-voltage system according to the invention, it can be provided that only a single voltage is measured at any one of the insulation resistors or the resistors connected in parallel as a variable characterizing the amount of energy of a Y capacitor. Since the total voltage of the high-voltage system and possibly also the configuration of the resistors connected in parallel to the insulation resistors is known, it is inevitable that conclusions can be drawn about the voltages on the two Y capacitors. An unbalanced load can thus be recognized if this single measured voltage value is compared with a threshold value or tolerance range. If such a threshold value is exceeded, adequate measures can be taken, for example to reduce the amount of energy in a Y-capacitor or simply to issue a warning.

List of reference symbols

1 high-voltage system

2 monitoring unit

HV1, HV2 high-voltage potential connections M ground connection

R11, RI2 insulation resistors C1, C2 Y capacitors in, U2 voltages S1, S2 switching devices R1, R2 resistors P1, P2 slots RK1, RK2 correction resistors RS1, RS2 safety resistors

Claims

1. A method for determining a first piece of information about an unbalanced electrical load of a vehicle with an at least partially electrified drive train, which has at least one high-voltage system (1)

- Determination of an amount of energy of a Y-capacitor (C1, C2) of the high-voltage system (1) characterizing variable,

- Providing a first threshold value in relation to a capacitance of the Y capacitor (C1, C2) and

Determination of the first information about the unbalanced electrical load by comparing the determined characterizing variable with the first threshold value provided.

2. The method according to claim 1, wherein the variable characterizing the amount of energy is a voltage (U1, U2) or partial voltage of the high-voltage system (1) or a related variable, a ratio of voltages (U1, U2) of the high-voltage system (1) or a ratio of insulation resistances (RI1, RI2) of the high-voltage system (1).

3. The method according to claim 1 or 2, with the further step of determining a second item of information about the unbalanced electrical load by comparing the determined characterizing variable with a provided second threshold value different from the first threshold value with regard to the capacitance of the Y-capacitor (C1, C2 ).

4. A method for reacting to a first piece of information about an unbalanced electrical load of a vehicle with an at least partially electrified drive train, which has at least one high-voltage system (1) - Initiation of a first measure as a function of the first information, as a result of which an amount of energy in a Y capacitor (C1, C2) relating to the unbalanced load is reduced.

5. The method according to claim 4, wherein the first information is obtained according to a method according to any one of claims 1 to 3.

6. The method according to claim 4 or 5, wherein the first measure is selected from: a) automatic shutdown of the entire high-voltage system, b) decoupling of a sub-network from the high-voltage system, c) reducing a voltage on the Y capacitor (C1, C2) or d) Reducing an insulation resistance on the Y capacitor (C1, C2), in particular by introducing, removing, connecting or disconnecting one or more correction resistors.

7. The method according to any one of claims 3 to 6, with the initiation of a second measure, in particular a warning, as a function of the second information, whereby the amount of energy of the Y capacitor (C1, C2) relating to the unbalanced load is not reduced.

8. The method according to any one of the preceding claims, wherein the provision of the first threshold value includes that a total capacitance of the Y-capacitor (C1, C2) is determined and the first threshold value is determined as a function of the total capacitance.

9. High-voltage system for an electrically drivable motor vehicle with a Y-capacitor, an analysis device for determining an amount of energy of a Y-capacitor (C1, C2) of the high-voltage system (1) characterizing variable and for providing a first threshold value in relation to a capacitance of the Y. -Capacitor (C1, C2) and a computing device for determining the first information about the electrical unbalanced load by comparing the determined variable with the provided first threshold value.

10. Electrically drivable motor vehicle with a high-voltage system according to claim 9.