DE102016009346A1 - Coolant circuit coupling to a circuit arrangement with fuel cell stack and high-voltage battery for a motor vehicle - Google Patents

Abstract

The invention relates to a circuit arrangement (10) for a motor vehicle, comprising: a fuel cell stack (11), a high-voltage battery (13), a power electronic energy converter (12), via which the fuel cell stack (11) with the high-voltage battery (13) electrically coupled using a common potential connection (16), an insulation monitoring device (14) adapted to monitor an insulation resistance between the circuit arrangement (10) and a ground potential (20) operatively electrically isolated therefrom, and a coolant circuit (15). for cooling the fuel cell stack (11). The coolant circuit (15) is electrically coupled to the common potential connection (16), wherein the insulation monitoring device (14) between the common potential connection (16) and the ground potential (20) is connected. In order to improve the measurement accuracy of an insulation resistance in a high-voltage network comprising the circuit arrangement (10), it is accordingly proposed to place the coolant circuit (15) on the common potential connection (16) and to place the insulation monitoring device (14) on the common potential connection (16) ,

Description

The invention relates to a circuit arrangement for a motor vehicle according to the preamble of claim 1. Furthermore, the invention relates to a method for operating a circuit arrangement for a motor vehicle according to the preamble of patent claim 5.

An electric high-voltage system is operated in a motor vehicle for safety reasons as a so-called IT network (Isolated Terra). Under a high-voltage network here is an electrical network with an operating voltage greater than or equal to 60 volts when operating with DC and greater than or equal to 30 volts when operating with an AC voltage. To ensure that the insulation state between the isolated high-voltage network and a surrounding ground potential, the potential of the vehicle body (vehicle chassis) is maintained in a motor vehicle, a monitoring of the isolation state is mandatory, which is usually permanently checked by a so-called iso-guard. However, a reliable function of the iso-monitor in the high-voltage network is disturbed by voltage fluctuation within the high-voltage network. With increasing voltage fluctuations in this case the disturbances are higher. In a high-voltage network with a fuel cell system, typically two energy sources are installed, namely a fuel cell stack and a high-voltage battery. However, a high-voltage network with a fuel cell system is less tolerant of interference, since firstly the electrical insulation resistance between the high-voltage network and the surrounding ground potential, ie the potential of the electrically conductive vehicle body, is reduced and secondly an electrical source in the form of a fuel cell naturally has high voltage fluctuations.

In this context is from the DE 10 2014 103 117 A1 a method of monitoring insulation resistance in a vehicle propulsion system, the method comprising: circulating a coolant in a coolant system fluidly coupled to a fuel cell stack forming at least part of the vehicle propulsion system, wherein the coolant provides thermal management within the fuel cell stack; wherein the coolant provides electrical isolation between the fuel cell stack and a vehicle driving value; Closing at least one contactor in an electrical system comprising a stack voltage and a battery voltage; Measuring a first isolation value, a second isolation value, the stack voltage, and the battery voltage. The method further comprises opening the at least one contactor to the electrical system; Measuring a first negative isolation value; Calculating a stack insulation resistance using the first insulation value, the second insulation value, the first negative insulation value, the stack voltage, and the battery voltage; Calculating a coolant conductivity value; and indicating that the coolant in the coolant system must be replaced when the coolant amenity value crosses a threshold.

Furthermore, from the JP 2007 305377 A a fuel cell system in which an increase in the ionic conductivity of the cooling water is to be securely suppressed. For this purpose, a fuel cell to pantograph plates, which collect the electrical energy generated by a fuel cell stack, which are generated by supplying an oxidizing agent and a fuel to the respective individual cells of the fuel cell stack. At the fuel cell, a cooling water pipe for introducing the cooling water into the fuel cell is connected. The cooling water pipe has an insulating pipe part which is connected to the fuel cell and has a conductive pipe part which adjoins the insulating pipe part. Between the fuel cell and the conductive pipe part, a potential difference is generated by a power supply device or an inverter.

It is an object of the present invention to achieve the influence of the coolant circuit on the insulation monitoring of the high-voltage network with simpler means. This object is achieved by a circuit arrangement having the features of patent claim 1 and by a method having the features of patent claim 5. Advantageous developments of the present invention are the subject matter of the dependent claims.

The invention is based on a circuit arrangement for a motor vehicle, which comprises a fuel cell stack, a high-voltage battery, a power electronic energy converter, an insulation monitoring device and a coolant circuit. About the power electronic energy converter, the fuel cell stack is electrically coupled to the high-voltage battery using a common potential connection. In particular, it is precisely just a single common potential within the entire high-voltage network of the motor vehicle. The insulation monitoring device is designed to monitor an insulation resistance between the circuit arrangement and an operationally electrically isolated earth potential. In this case, the potential which is given by the vehicle body of the motor vehicle is considered as earth potential in a motor vehicle. Of the Coolant circuit is used to cool the fuel cell stack, wherein as the coolant of the coolant circuit preferably water, especially water with a very low electrical conductivity, is used. The power electronic energy converter is preferably designed as a DC-DC converter (DC / DC converter). In particular, the power electronic energy converter is designed as a non-galvanic energy converter.

According to the invention, the circuit arrangement is further developed in that the coolant circuit is electrically coupled to the common potential connection, wherein the insulation monitoring device is connected between the common potential connection and the ground potential.

The invention is based on the finding that the insulation resistance arising from a fuel cell system is largely determined by the cooling system, especially by the coolant circuit, which is also referred to as the coolant line. The inventors have also recognized that all components with potentially influential isolation values, that is, components that introduce small electrical isolation resistances into the high-voltage network, should not couple to potentials that are connected in series with the isolation monitor (iso-monitor). In other words, the insulation paths to be monitored by the insulation monitoring device should not be separated by one or more voltage sources with variable voltage. By explicitly contacting the coolant circuit as part of the cooling system with the common potential connection, disturbances due to voltage fluctuations of the fuel cell stack can be reduced. Therefore, it is proposed according to the invention to place the coolant circuit (coolant line) at a common potential, namely the potential of the common potential connection. This type of connection thus minimizes the disruptive influence of voltage fluctuations on the insulation monitoring. As a result, a reliable insulation measurement can be achieved, which makes it possible to lower an absolute limit value of the insulation value at which an insulation fault is reported by the insulation monitoring device. As a result, the requirements for the insulation monitoring device can be reduced, for example with regard to operational safety, costs and cross-project applicability.

According to an advantageous embodiment of the circuit arrangement is provided that the negative pole of the high-voltage battery and the negative terminal of the fuel cell stack is electrically connected to the common potential connection or the positive pole of the high-voltage battery and the positive pole of the fuel cell stack is electrically connected to the common potential connection.

It can preferably be provided that the insulation monitoring device is electrically coupled to the negative pole of the high-voltage battery or the positive pole of the high-voltage battery. An internal test voltage of the insulation monitoring device can thus be temporarily coupled to one of the two poles of the high-voltage battery, for example via a switching device.

According to an advantageous development, it is provided that the insulation monitoring device is set up to display an insulation fault exclusively as a function of an insulation resistance determined between the common potential connection and the ground potential. It goes without saying that in the described insulation monitoring device with a test voltage not only the insulation resistance against only a high-voltage potential, so for example against the positive pole of the high-voltage battery or against the negative pole of the high-voltage battery can be measured. In principle, the insulation resistances of the remaining potentials are always measured as well. Thus, variable voltage sources in series with an isolation path and the test voltage of the insulation monitoring device cause variable measurement voltages which no longer unequivocally correlate with the isolation resistance of the isolation path, resulting in measurement errors. However, if the measured insulation resistances of the residual potentials are of subordinate magnitude (high resistance) to an insulation resistance to the common potential connection, voltage fluctuations of the sources involved are also of secondary importance.

The invention is further based on a method for operating a circuit arrangement for a motor vehicle, wherein the circuit arrangement comprises a fuel cell stack, a high-voltage battery and a power electronic energy converter. In this case, the fuel cell stack is electrically coupled to the high-voltage battery using a common potential connection. The method comprises monitoring an insulation resistance between the circuit arrangement and an operationally electrically isolated ground potential by means of an insulation monitoring device. According to the invention, the method is developed by cooling the fuel cell stack by means of a coolant circuit, wherein the coolant circuit is electrically coupled to the common potential connection, and wherein the insulation monitoring device is connected between the common potential connection and the ground potential.

The embodiments and advantages shown for the circuit arrangement according to the invention apply mutatis mutandis to the inventive method. Consequently, corresponding device features and vice versa can be provided for device features.

Further advantages, features and details of the invention will become apparent from the following description of a preferred embodiment and from the drawings. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or in the figures alone can be used not only in the respectively specified combination but also in other combinations or in isolation, without the scope of To leave invention.

Showing:

1 in a simplified schematic representation of an electrical equivalent circuit diagram of an exemplary generic circuit arrangement, and

2 in a simplified schematic representation of a preferred embodiment according to the invention with the corresponding complex equivalent resistors.

In a high-voltage electrical system of a fuel cell drive, there are typically two electrical sources, namely a fuel cell stack (fuel cell stack), which in the illustration according to FIG 1 is represented by a voltage source having a first voltage U ₁ and a high-voltage battery, which is represented by a voltage source having a second voltage U ₂ . Since the two voltage sources do not have exactly the same voltage behavior, the voltage sources must be coupled via a converter. This converter acts like a serially connected voltage source with a third voltage U _1-2 . All insulation resistors operating in such a high-voltage network can be considered together. There are corresponding insulation resistances R _{ISO, 1} , R _{ISO, 2} , R _{ISO, 3} from the three potentials I, II, III shown here. Capacitors connected in parallel must not be neglected in insulation monitoring, for example in neighboring areas between the high-voltage network and a housing, but also explicitly used so-called Y capacitors for interference suppression. These capacities are in the 1 as capacities C _{Y, 1} , C _{Y, 2} , C _{Y, 3} shown. These each between the potentials I, II, III and a ground potential, also referred to as Ground 20 effective electrical couplings interfere in particular then the insulation measurement by an insulation guard 14 when the first voltage U ₁ or the second voltage U ₂ change, since then different currents through the capacitances C _{Y, 1} , C _{Y, 2} , C _{Y, 3} the current through the "isolation path" (equal fault current), which through an insulation guard 14 is recorded, is in addition enlarge.

A significant proportion of the insulation resistance of the coolant section of a fuel cell system is represented here by the resistance R _{ISO, 3} . This coolant line typically consists of an inlet and a return. Both are currently connected via a common media distribution unit to the fuel cell stack. In the current variant, the media manifold unit is located at the positive end of the fuel cell stack, and the negative side of the fuel cell stack is only electrically coupled through air / creepage paths via the grounded housing. This coupling can be assumed to be negligibly high impedance compared to the coolant line (about a factor of 100).

At an assumed, sufficiently constant second voltage U ₂ , but provided with significant voltage fluctuations first voltage U ₁ , the advantageous connection of the coolant line at the common potential I is proposed. That is, the coolant line can touch any potential of the stack within the fuel cell stack system (arrangement of the distributor plates, interconnection of cell groups et cetera), but it should be placed in the input (inlet) or outlet (return), the coolant line to the common potential, according to hereinafter described preferred embodiment as shown in the 2 on the negative pole.

According to a preferred embodiment of the invention, a circuit arrangement comprises 10 a fuel cell stack 11 , a power electronic energy converter 12 , a high-voltage battery 13 and an isolation guard 14 , The fuel cell stack 11 includes a first fuel cell connector 11a , which with a first energy converter connection 12a of the energy converter 12 is electrically connected, and a second fuel cell connection 11b on, which with a second energy converter connection 12b of the energy converter 12 is electrically connected. Furthermore, the high-voltage battery 13 a first battery connection 13a which is electrically conductive with a third energy converter connection 12c of the energy converter 12 connected, as well as a second battery connection 13b which is electrically conductive with a fourth energy converter connection 12d of the energy converter 12 is electrically connected. The first energy converter connection 12a and the second Power transformer connection 12b are a primary side of the energy converter 12 assigned to which energy from the fuel cell stack 11 is fed. The third energy converter connection 12c and the fourth energy converter connection 12d are a secondary side of the energy converter 12 associated with providing the fuel cell stack 11 related electrical energy on the side of the high-voltage battery 13 serves. The second fuel cell connection 11b and the second battery connector 13b as well as the second energy converter connection 12b and the third energy converter connection 12c are via a common electrical connection 16 electrically connected to each other and thus are at the electrical potential 1 ,

A first insulation monitor connection 14a of the isolation guard 14 is electrically conductive with the common electrical connection 16 connected, a second insulation monitor connection 14b of the isolation guard 14 is one with the earth potential 20 leading conductor, for example, the vehicle body of the motor vehicle connected. A third insulation monitor connection 14c of the isolation guard 14 is with the first battery connection 13a electrically connected, which according to the preferred embodiment by the positive pole of the high-voltage battery 13 given is.

The circuit arrangement 10 further includes a coolant line 15 Part of one for cooling the fuel cell stack 11 provided cooling system. With coolant line in this case the actual coolant circuit consisting of the preferably liquid coolant, in particular water, and the refrigerant line leading system is called. Electrically supplied components of the cooling system, for example, electrically driven pumps and the like, however, do not belong to the coolant circuit according to the invention. The coolant line 15 is on the common connection 16 placed, whereby between the coolant distance 15 and the common connection 16 a potential equalization is produced. A production of an electrical contact can be realized, for example, by a pipe section of the coolant circuit.

The contribution of the principle existing insulation resistance R _{ISO, 3} can generally be neglected, since this plays a minor role. Because, as described above, provides the coolant line 15 the insulation-determining resistance component of the insulation resistance R _{ISO, 1} represents.

Here are now the through the coolant line 15 additionally introduced insulation resistance R _{ISO, 1} and the insulation resistance R _Iso1 at a potential, namely the potential I, which in the measurement of a voltage variation of the first voltage U, is subjected. To the operation of the insulation guard 14 to illustrate, its internal structure is exemplified by a signal generator 141 , a measuring resistor 142 , a measuring device 143 and a switch 144 shown. The operating principle is based on the fact that by means of the signal generator 141 an electrical signal, preferably a square wave signal, between the first insulation monitor terminal 14a and the second isolation guard connection 14b or between the third insulation guard connection 14c and the second isolation guard connection 14b is created and one in consequence by the measuring resistor 142 flowing measuring current through the measuring device 143 is detected.

With an assumed, high-resistance value of R _Iso2 , according to a particularly preferred embodiment, the insulation _measurement can be provided in a first switch position S1 shown. Here is the signal generator 141 in series with the measuring resistor 142 between the potential I and the earth potential 20 connected. As a result, further disturbances due to voltage changes of the second voltage U _{2 can} be avoided.

The embodiment is merely illustrative of the invention and is not limitative of it. Thus, other components that are different from the coolant circuit and that can contribute to a significant reduction in the measured insulation values can not be specifically coupled to potentials that are in series with the insulation monitor 14 are connected without departing from the spirit of the invention.

Thus, a specific coolant connection to a fuel cell system has been proposed above, which enables a reduction in the measurement result falsification of insulation resistances due to voltage fluctuations in the fuel cell system.

LIST OF REFERENCE NUMBERS

10

circuitry

11

fuel cell stack

11a

first fuel cell connection

11b

second fuel cell connection

12

power electronic energy converter

12a

first energy converter connection

12b

second energy converter connection

12c

third energy converter connection

12d

fourth energy converter connection

13

High-voltage battery

13a

first battery connection

13b

second battery connection

14

insulation monitors

14a

first insulation monitor connection

14b

second insulation monitor connection

14c

third insulation monitor connection

141

signal generator

142

measuring resistor

143

gauge

144

switch

15

Coolant path

16

common electrical connection

20

ground

C _{Y, 1} , C _{Y, 2} , C _{Y, 3} , C _{Y, 3 '}

capacity

R _{ISO, 1} ; R _{ISO, 1 '} ; R _{ISO, 2} ; R _{ISO, 3} ; R _{ISO, 3 '}

insulation resistance

S1; S2

switch position

U ₁

first tension

U ₂

second tension

U _1-2

third tension

I; II; III

potential

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102014103117 A1 [0003]
• JP 2007305377 A [0004]

Claims (5)

Circuit arrangement ( 10 ) for a motor vehicle, comprising: - a fuel cell stack ( 11 ), - a high-voltage battery ( 13 ), - a power electronic energy converter ( 12 ) over which the fuel cell stack ( 11 ) with the high-voltage battery ( 13 ) using a common potential connection ( 16 ) is electrically coupled, - an insulation monitoring device ( 14 ), which is designed to provide an insulation resistance between the circuit arrangement ( 10 ) and one of them operatively electrically isolated ground potential ( 20 ), and - a coolant circuit ( 15 ) for cooling the fuel cell stack ( 11 ), characterized in that the coolant circuit ( 15 ) electrically connected to the common potential connection ( 16 ), wherein the insulation monitoring device ( 14 ) between the common potential connection ( 16 ) and the earth potential ( 20 ) is switched. Circuit arrangement according to Claim 1, characterized in that the negative pole of the high-voltage battery ( 13 ) and the negative pole of the fuel cell stack ( 11 ) with the common potential connection ( 16 ) is electrically connected or the positive pole of the high-voltage battery ( 13 ) and the positive pole of the fuel cell stack ( 11 ) with the common potential connection ( 16 ) is electrically connected. Circuit arrangement ( 10 ) according to one of the preceding claims, characterized in that the insulation monitoring device ( 14 ) with the negative terminal of the high-voltage battery ( 13 ) or the positive pole of the high-voltage battery ( 13 ) is electrically coupled. Circuit arrangement ( 10 ) according to one of the preceding claims, characterized in that the insulation monitoring device ( 14 ) is adapted to an insulation fault exclusively as a function of one between the common potential connection ( 16 ) and the earth potential ( 20 ) indicated insulation resistance. Method for operating a circuit arrangement ( 10 ) for a motor vehicle, the circuit arrangement comprising a fuel cell stack ( 11 ), a high-voltage battery ( 13 ) and a power electronic energy converter ( 12 ), wherein the fuel cell stack ( 11 ) with the high-voltage battery ( 13 ) using a common potential connection ( 16 ) is electrically coupled, by - monitoring an insulation resistance between the circuit arrangement ( 10 ) and one of them operatively electrically isolated ground potential ( 20 ) by means of an insulation monitoring device ( 14 ), characterized by - cooling the fuel cell stack by means of a coolant circuit ( 15 ), wherein the coolant circuit ( 15 ) electrically connected to the common potential connection ( 16 ), and wherein the insulation monitoring device ( 14 ) between the common potential connection ( 16 ) and the earth potential ( 20 ) is switched.

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