EP1820246A2

EP1820246A2 - Electric traction drive for vehicle with fault-current protection in the dc intermediate circuit

Info

Publication number: EP1820246A2
Application number: EP05801404A
Authority: EP
Inventors: Martin Trunk; Arndt Wagner
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2004-11-30
Filing date: 2005-11-11
Publication date: 2007-08-22
Also published as: WO2006058824A2; DE102004057694A1; WO2006058824A3; CN101069333B; CN101069333A; US20090015973A1

Abstract

The invention relates to a fault-current protective circuit which is preferably integrated into a vehicle on-board supply system, especially a multiple-voltage on-board supply system, on the high voltage side, and operates without current measurement. The fault current is determined in an evaluation logic system by evaluating two voltages. Said two voltages are voltages that fall on two high-impedance resistances located respectively between a connection between the battery and the generator and earth. If the evaluation logic system detects a fault current, the two connections between the battery and the generator and or the on-board supply system are cut. In addition, in conjunction with a dual-voltage on-board supply system comprising two partial on-board supply systems connected by means of a DC voltage converter, a voltage-dependent circuit can be mounted in parallel to the DC voltage converter, said parallel circuit being used to ground the high voltage side in the event of error.

Description

Wiring system with higher voltage

The invention relates to a vehicle electrical system with higher voltage according to the preamble of the main claim. In particular, it comprises a fault current protection circuit and is used in a vehicle electrical system.

State of the art

It is known that in electrical circuits that are suitable for higher voltages, a protection circuit is installed, which responds to accidental contact with the live parts of the circuit and the usually existing energy storage separates from the rest of the network. Associated residual current monitors usually work with a current transformer that measures occurring fault currents. All current-carrying conductors are routed through the current transformer and the differential current is measured. If this is not equal to zero, the circuit breaker or the circuit breaker is opened.

An example of such fault current monitoring in vehicles, which is used in particular in such vehicle electrical systems in which electrical voltages are present, which can be life-threatening to the human body when touched, with voltages greater than 65 volts, is shown in FIG. According to this example for the

Use of a residual current protection circuit is a generator 1, for example, a three-phase generator for generating voltage available. The output voltage of the generator or the alternator is rectified by means of an inverter 2 and via lines 3 and 4 and a switch 5 of the battery. 6 fed. The inverter 2 is designed for three phases bridge circuit with, for example, six PWM inverters.

The current flowing in the lines 3, 4 current is measured in a current measuring device, wherein for current measurement, for example, a current transformer 7 is used, which determines the differential current. A control device 8 evaluates the measured current and disconnects the switch 5 if the measured differential current exceeds predeterminable values. The switching process is triggered by corresponding control signals that are generated by the control device 8.

Since all current-carrying conductors must be routed through the current transformer 7, a relatively large and expensive current transformer is needed. In addition, the space for the current transformer from the position is not very flexible, since it must be arranged so that all current-carrying conductors are detected. The fault current shutdown after evaluation of the output signals of a summation current transformer or a forward converter is therefore quite complex.

The electrical system according to FIG. 1 can also be designed as a partial on-board network of a two-voltage on-board electrical system, for example as a high-voltage side of a two-voltage on-board electrical system. The connection to the low voltage part is then made via a DC-DC converter, which is connected to the generator, for example. An example of such a two-voltage electrical system is described in DE 41 38 943 C1. In this known two-voltage on-board network, which is shown schematically in FIG. 2, the DC-DC converter 26, which is arranged between the two partial on-board networks, is part of a complicated charging / disconnecting module that is supplied as a function of power

Signals, for example, depending on the measured currents, the connection between the two sub-board networks interrupts and thus prevents repercussions from one electrical system to another in the event of a fault. The first sub-board network includes a generator 27, a battery 28 and consumer 29, the second sub-board network, a battery 30 and consumer 31, for example, a starter. In both sub-board networks, the negative pole of the batteries 28 and 30 is grounded. The parenthesized reference numerals will be explained in conjunction with FIGS. 3 and 4, respectively. A fault current detection is difficult to implement in such a vehicle electrical system. In electrical home installations today so-called residual current circuit breakers are installed, which provide increased safety against dangerous electric shock. Such residual current circuit breakers, which are also referred to as RCD, always trigger when a connection between the neutral and the protective conductor is made. By switching off the power behind the circuit breaker part of the circuit hazards are avoided. Known residual current protective devices are designed so that they require only a low tripping current for tripping and have a relatively short switch-off time.

Advantages of the invention

The vehicle electrical system according to the invention with a higher voltage with a residual current circuit having the features of claim 1 has the advantage that a residual current cutoff is realized without current measurement, which is particularly useful in a vehicle electrical system and particularly advantageous in one

Vehicle electrical system with a subarea, which is at a higher voltage, can be used.

These advantages are achieved by a circuit in which both connecting lines between the battery and the inverter or the generator connected to the inverter are connected via at least one high-impedance resistor to ground and the voltage drop across these two resistors voltage is measured. With the help of a Auswertelogik the two voltages are checked for a fault current and in case of error, so when detected fault current both lines using a generated by the Auswertelogik shutdown signal, the associated switches is separated, separated.

Further advantages of the invention are achieved by the measures specified in the dependent claims. A particular advantage is that only by evaluating the measured voltage drop across the two resistors, ie without further measuring device or without further sensors, an over- and / or a

Undervoltage monitoring can be performed. In order to prevent rapid load changes from causing potential shifts, additional capacitors can be connected in parallel with the two resistors. By means of a plausibility check, that is to say a comparison of the two measuring voltages, a distinction can be made between a load change and occurring fault currents in an advantageous manner. - A -

The response threshold at which the evaluation logic emits a switch-off signal or a drive signal can advantageously be adjusted to any desired fault currents, advantageously such a limit value is less than 30 mA. The shutdown can be done very quickly.

In an embodiment of a vehicle electrical system with a higher voltage than two-voltage electrical system, an advantageous coupling of the two sub-systems is possible, which ensures that in the event of a fault on the high-voltage side, ie in the sub-board network, which is at the higher voltage, the high-voltage side is forced hard to ground. This advantage is achieved by connecting the two electrical systems coupled via a DC-DC converter by means of a parallel to the DC-DC converter switching element, the switching element preferably monitors the voltage between the negative high voltage terminal of the DC-DC converter and the electrical system and keeps this within certain limits. Advantageously, the switching element is a voltage-dependent resistor, a Zener diode or a switching element which is controlled by the voltage difference between the negative voltage terminal and ground.

With this circuit, which is not the FI circuit, it can be ensured that the maximum permissible insulation voltage between high voltage and low voltage range is not exceeded, or with such a circuit, the system can be designed for a significantly lower isolation voltage and thus a Protection of the electrical system components or components are obtained.

drawing

FIG. 1 shows a known and currently conventional residual current protection circuit, and FIG. 2 shows a known two-voltage on-board electrical system. Both known circuits are described in detail in the section "prior art". FIG. 3 shows a block diagram for an electrical system with a residual-current-protection circuit according to the invention and FIG. 4 shows the possibility of connecting two partial-voltage systems located at different voltage levels. The explanation of the circuit shown in Figure 3 and Figure 4 is given in the following description. description

In Figure 3, the essential for understanding the invention components of a vehicle electrical system or a sub-electrical system, preferably the

High voltage vehicle electrical system shown together with a residual current circuit according to the invention.

In detail, FIG. 3 shows a vehicle electrical system or a sub-electrical system with an electric machine 10, for example a three-phase starter-generator 10 or an electric machine for a hybrid on-board network, which is connected to an inverter 11 in the usual way , From the inverter 11, which is constructed as a bridge circuit with, for example, six pulse inverters, lead two lines 12, 13 via a switch 14 to the battery 15. About these connecting lines between the battery 15 and the inverter 11 and the electric machine 10 is in normal regenerative operation the electric machine 10, the battery 15 is charged. If a starter-generator is used as the electric machine 10, the electric machine can operate as a starter in the starting case, that is to say as an electric motor and be supplied with electrical power via the inverter 11 from the battery 15.

Between the line 12 and ground, in particular vehicle or body ground 40, a parallel connection of a resistor 16, a capacitor 17 and a voltmeter 18 is provided in the embodiment of Figure 3. Between the line 13 and ground are a resistor 19, a capacitor 20 and a

Voltmeter 21 connected in parallel. The two capacitors 17 and 20 are not essential.

Both the voltmeter 18, which measures the voltage drop across the resistor 16 and the voltmeter 21, which determines the voltage drop across the resistor 19, are connected to the evaluation logic 24 and provide the latter with the measured variables which are to be evaluated. The associated connections between the voltmeters 18 and 21 are indicated at 22 and 23, respectively. If the evaluation logic 24 detects a fault current by evaluating the voltages, it sends control signals to the switch 14 via a connection 25 and actuates the latter and disconnects the battery. This will be the electrical system de-energized. Upon reaching specifiable conditions that indicate a fault, so both connecting lines 12, 13 between the battery 15 and the inverter 11 and the connected to the inverter 11 generator 10 is interrupted and ensures residual current protection.

The exemplary embodiment according to the invention according to FIG. 3 is characterized in that a fault current cut-off is possible which requires no current measurement. It is essential that high-voltage lines in the electrical system can be on which are much higher voltages than 12 volts. In a vehicle electrical system for a hybrid vehicle, the voltage on the high-voltage side is, for example, 65 volts and more, but under certain conditions significantly higher voltages of up to 288 volts may be present. Under these conditions protection by means of FI wiring is absolutely necessary. In a 12/42 vehicle electrical system such protection may also be appropriate.

In the embodiment of Figure 3, both connecting lines 12, 13 are connected via at least one high-resistance resistor 16 and 19 to ground. This creates a voltage divider which sets the ground potential 40 between the potentials of the lines 12 and 13. Now flows from a fault current from the line 12 or the line 13 to ground 40 from, "warps" the voltage divider, the ratio of means of the

Voltmeter 18 and 21 measured voltages changes and thus the fault current is detected. For fault current detection, the two measured voltages, for example, the evaluation logic 24 are supplied and the fault current detection in the evaluation logic 24 are performed. One way of error detection is, for example, by comparing the determined

Voltage ratio with a limit and an error detection when reaching or exceeding this limit. In the event of a fault then a shutdown via the switch 14 takes place, wherein the battery is disconnected from the rest of the electrical system.

The vehicle electrical system shown in FIG. 3 can also be a high-voltage network of a vehicle located at an elevated voltage of, for example, 288 volts relative to the usual vehicle electrical system voltage of 12 volts, which is connected to the usual vehicle electrical system, for example via a voltage converter. The high-voltage network has in the embodiment shown in Figure 3 no low-impedance connection to the vehicle ground. To prevent the potential the high-voltage network drifts away uncontrolled, the high-resistance resistors 16 and 19 and the capacitors 17, 20 are provided. If these are the same in pairs, the net is kept symmetrical to the vehicle mass. It is essential that the values of the resistors are so high that no significant loss caused by the resistors, so there is no relevant current from the

Line 12 via the resistor 16 and of the line 13 via the resistor 19 to ground. Expedient values for the resistors 16 and 19 are for example 2 megohms.

If a person touches one of the ladder 12 or 13 and touches the Fahrzeugbzw. Body ground, resulting in a fault current in turn leads to a significant potential shift. This potential shift can be evaluated according to the invention. The person behaves like a resistor, which is connected in parallel to resistor 16 or 19. In this case, the voltage divider is thus also "warped", this can be used for error detection.

So that fast load changes, d. H. rapid changes in the electrical system load do not lead to potential shifts, the capacitors 17, 20 connected in parallel to the resistors 16, 19. If the two voltages, which are at the resistors 16, 19 are falling or measured, can be clearly on the existence of one

Close fault current. It is necessary to measure both voltages. A plausibility check makes it possible to distinguish between load changes, ie between rapidly changing loads on the electrical system and fault currents.

The evaluation logic 24, which detects the fault current from the comparison of the two voltages can be set to almost any fault current, usually to a fault current of less than 30 milliamps (mA). When the set fault current is reached, the evaluation logic 24 outputs a corresponding signal to the switch 15 and opens it.

In a vehicle with a two-voltage electrical system should, if no other protective measures are taken, for safety reasons, the high-voltage system must be potential-free to earth, for example to the housing and additionally designed touch-safe. This means that a potential separation between the high voltage and the low voltage electrical system must be ensured. this applies especially since in the low voltage electrical system with a nominal voltage of usually 12 volts, the vehicle body is the negative pole. At the same time, the high voltage electrical system, which is for example up to 288 volts and possibly more, very high impedance connected to the body potential, so that the voltage potentials can not drift arbitrarily. This voltage connection is obtained by the symmetry resistors 16, 19 and / or the capacitors 17, 20. Assuming these facts, it can be seen from the two measured voltages or voltage drops across the resistors 17, 19 by comparing the voltages with each other whether the overall system is in order.

If there is no fault and the voltage potentials are within predeterminable limits, the ratio of the resistance values of the resistors 16 and 19 will be the same as the ratio of the two measured voltages. Flows through contact or other fault in the electrical system of the power in the high-voltage electrical system completely or partially on the vehicle body, the resistor voltage divider warps accordingly as through the two resistors 16, 19 different currents flow. The then adjusting change in the ratio of the two voltage drops can be detected in the evaluation logic 8 and a response to be triggered. This reaction may consist, for example, in the shutdown of the high voltage. Such a reaction is triggered, for example, when the displacement of the voltage divider reaches predeterminable values. These values can again be selected relatively freely.

FIG. 4 illustrates an embodiment of the two-voltage on-board electrical system according to FIG. 2, in which the coupling of the two subnetworks is implemented via the DC-DC converter 32. The first part of the electrical system includes a generator 33 including the inverter, not shown separately, a battery 34 and consumer 35, the second electrical system a battery 36 and consumer 37th Das

Low voltage electrical system (12 / 14V) is grounded with the negative pole of batteries 36 grounded. The high voltage electrical system is, however, connected as a controlled floating traction network, for coupling to the low voltage electrical system in addition to the DC converter 32 is still a switching element 38 is parallel to the DC-DC converter and this switching element is a voltage-dependent switching element, the voltage between the negative High-voltage connection (B-) and the wiring material monitored and keeps within certain limits.

In Figure 4, three ways to implement the switching element 38 are indicated. In this case, the negative terminal of the high-voltage side (B-) either via a voltage-dependent resistor 38a whose value changes, for example, proportional to the voltage U, a Zener diode 38b or a switching element 38c, which is controlled by the voltage difference between (B) and ground, connected to the ground more or less high impedance. In principle, the positive high-voltage connection (B +) could also be connected to ground. Alternatively, one would also be

Connection to the 14V line between the DC-DC converter and the battery instead of the ground connection possible.

The function of the parallel to the DC-DC converter 32 switching element 38 in its embodiments is the following: Once the reference potential of

High voltage side exceeds a certain voltage to the vehicle mass, the value of the voltage-controlled resistor 38a decreases and the reference potential of the high voltage side is pulled back to ground, the course is continuous. If a zener diode 38b is used as the switching element 38, the reference potential of the high-voltage side 3 of the switching element, on the other hand, jumps

Mass pulled. If the voltage between the high voltage side reference potential and ground is approximately equal to zero, the two electrical systems are not or only very high impedance connected to each other.

In order to minimize interference from the high-voltage side to the 14V vehicle electrical system, it may be expedient to use an active switching element instead of a Zener diode or a voltage-dependent resistor. One possible embodiment shows 38c. Such a switching element 39 must at least consist of a unit for measuring voltage and a switch. To suppress glitches when switching, a network of coil, capacitor and resistor can be provided and placed in front of the switch. In the event of a fault, the switch can be closed and the high voltage side can be grounded.

Claims

claims

1. electrical system with higher voltage in a vehicle, in particular with a residual current circuit comprising at least one electric machine, an inverter and two connecting lines between the inverter and a battery, and the error protection circuit includes a switch for separating the two connections to the battery, and a Auswertelogik which opens the switch under predetermined conditions, characterized in that these conditions are voltages that drop across resistors (16), (19), wherein the resistor 16 between a first line (12) and ground and the resistor (19 ) is connected between a second line 13 and ground and the two lines (12) and (13) respectively corresponding terminals of the battery (15) with the

Connect the inverter (11) or the generator (10).

2. Residual current circuit according to claim 1, characterized in that parallel to the resistor (16) and / or parallel to the resistor (19) in each case a capacitor (17), (20) for preventing potential shifts during rapid load changes.

3. Residual current protection circuit according to claim 1 or 2, characterized in that at the two resistors (16), (19) falling voltage by means of a respective current meter (18), (21) is determined and the measured values via corresponding

Connections of the evaluation logic (24) are supplied.

4. Fault protection circuit according to one of the preceding claims, characterized in that the evaluation logic (24) from both supplied voltages forms a differential voltage and from the differential voltage, the fault current determines and on reaching a predetermined value for the fault current opens the switch (14).

5. Residual current protection circuit according to claim 4, characterized in that the predeterminable limit value of the current is selectable and is preferably 30 mA.

6. Residual current protection circuit according to one of the preceding claims, characterized in that it is part of a two-voltage on-board electrical system and is arranged on the higher voltage side of the electrical system.

7. Residual current circuit according to one of the preceding claims, characterized in that the values of the resistors 17, 19 are equal and preferably amount to two megohms.

8. Residual current protection circuit according to one of the preceding claims, characterized in that ratios of the sloping at the two resistors voltages are evaluated for fault current detection.

9. Residual current circuit according to one of the preceding claims, characterized in that run in the evaluation logic (24) plausibility checks, to distinguish between load change and fault current.

10. Residual current protection circuit according to one of the preceding claims, characterized in that in addition to the fault current detection over / undervoltage monitoring takes place.

11. Residual current protection circuit according to one of the preceding claims, characterized in that it is part of a vehicle electrical system of a hybrid vehicle.

12. On-board electrical system with higher voltage, with two sub-board networks, the one above the other

DC converter are in communication and with a protective circuit, characterized in that one of the sub-electrical systems is not or only very high impedance to ground and the protection circuit comprises a voltage-dependent circuit which is parallel to the DC-DC converter and not in case of failure Pulling on earth connected onboard electrical system.

13. Protection circuit according to claim 11, characterized in that the voltage-dependent circuit comprises at least one voltage-dependent resistor or a Zener diode.

14. Protection circuit according to claim 11, characterized in that the voltage-dependent circuit comprises at least one active switching element with a switch and a voltmeter.

15. Protection circuit according to claim 12, characterized in that it is part of a vehicle electrical system of a hybrid vehicle.