WO2018210494A1

WO2018210494A1 - Method for operating an on-board power supply system

Info

Publication number: WO2018210494A1
Application number: PCT/EP2018/059285
Authority: WO
Inventors: Nils Draese; Mirko Schinzel
Original assignee: Robert Bosch Gmbh
Priority date: 2017-05-18
Filing date: 2018-04-11
Publication date: 2018-11-22
Also published as: DE102017208425A1

Abstract

The invention relates to a method for operating an on-board power supply system (200), comprising a number of consumers (212), wherein at least some of the consumers (212) are switched on selectively in each case via a switching element (214), wherein a limitation of the current flowing through the switching element (214) is carried out.

Description

Description title

Method for operating a vehicle electrical system

The invention relates to a method for operating a vehicle electrical system and such a vehicle electrical system. The invention particularly relates to a method for operating a vehicle electrical system, in which the electrical system is started up.

State of the art

Under a vehicle electrical system is to be understood in particular in the automotive use, the totality of all electrical components in a motor vehicle. Thus, both electrical consumers and sources of supply, such as. Generators or electrical storage, z. As batteries includes. In the motor vehicle care must be taken that electrical energy is available in such a way that the motor vehicle can be started at any time and sufficient power is ensured during operation. But even when parked, electrical consumers should still be operable for a reasonable period of time, without a subsequent start being impaired. Under an IVlehrspannungsbordnetz means an electrical system with several subnets, which have a different supply voltage. These subnets are coupled or connected to each other via coupling elements, such as DC-DC converters.

Document EP 2 721 704 B1 describes a method for connecting multi-voltage networks. In this, a DC-DC converter is provided which couples a first vehicle electrical system with a first vehicle electrical system voltage with a second vehicle electrical system with a second vehicle electrical system voltage. In the method, a charging means increases the second vehicle electrical system voltage before connecting an energy store for feeding the second vehicle electrical system. The presented method allows by simple measures in the reverse operation of a DC-DC converter, in particular a bidirectional throttle buck converter, a charge of an energy storage on the primary side.

After commissioning of the motor vehicle, the electrical system must be started up. It must be ensured that consumers are adequately supplied within the shortest possible time.

48 V electrical systems are currently being started up using a process that corresponds to the process of starting high-voltage on-board electrical systems. In this case, the current level of the electrical system is brought to the target voltage in total in a current-limited operation. It should be noted that vibrations and disturbances are automatically reduced by the flow-limited operation. It should be noted that the electrical system can only be started up as a whole. If the startup fails because a component is defective, the vehicle electrical system can not continue to operate.

With the help of novel power distributors, it is now possible to separate individual consumers via electronic security functions from the electrical system. This can happen as part of a malfunction within a sub-board network or else on the basis of an extended energy management.

In contrast to an existing 12 V electrical system, however, many consumers can not be switched on easily in an active 48 V electrical system. Since many high-power consumers are equipped with capacitive input circuits, a resonance circuit between the battery, the inductance of the wiring harness and the capacity of the load may form. This resonant circuit leads to overvoltages that are above the maximum permissible limits.

Furthermore, when the switch is closed, an inductive voltage divider is created, through which the voltage at the switching unit or switch unit breaks. Due to the resulting voltage dip, the supply of other consumers connected to the switching unit is no longer guaranteed. The following requirements result from the connection of loads with capacitive input circuit to an active 48 V electrical system:

The peak or peak current during the connection of the load must be limited in order not to trigger any fuse functions

- Do not overload the input circuit of the consumer.

By switching on the active electrical system must not be excessively excited to vibrate to avoid interference with other consumers. The voltage in the active vehicle electrical system must not break too much to avoid failures and disturbances. During connection, a diagnosis for a short circuit, i. H. a hard or soft short circuit, the relevant board network branch take place.

DISCLOSURE OF THE INVENTION Against this background, a method according to claim 1 and electrical system according to claim 10 are presented. Embodiments emerge from the dependent claims and from the description.

The proposed method is used to operate a vehicle electrical system, this being used in particular during the startup of the electrical system. It is provided in the method, the consumers in the electrical system, at least some of the consumers in the electrical system to selectively control. In the selection of consumers who are started up in this special way, for example, the safety relevance but also the susceptibility to error of the individual consumers can be taken into account.

In the context of the present application, various concepts are presented in order to enable economic implementation of the requirements listed above. One possibility is to use a linear switching element, e.g. B. a planar mosfet with current feedback to realize the pre-charging of the load with a defined current level and limited excitation of the resonant circuit. In this variant, however, it should be noted that the implementation of the linear operation on the one hand means a high peak power dissipation, on the other hand, special circuit breakers and a special control are needed only for the Vorladezweck.

Another embodiment provides a clocked connection of the load. The clocked operation of an intelligent switching element, the load is driven by a pulsed current, so that in this way a limitation of the current is achieved. In particular, the current is limited by a clocking operation, in one embodiment via a maximum current limitation. The limitation of the current gradient happens in this case via the parasitic inductance of the wiring harness. The advantage of this method is that it does not cause any significant increase in costs due to special components.

Due to a reduced current level, the amount of energy stored in the harness inductance is severely limited:

The aim is therefore to reduce the energy W _pa r, which leads to disturbances and damage.

In order to avoid additional disturbances or damages by the cyclic operation, special control strategies and unloading circuits are possible:

By an internal DC link capacitor (C _e i _n ) also a freewheeling element is created, in which the current can be stored from the harness inductance. This avoids an avalanche load on the switch as much as possible. Increasing the input capacitance also reduces the frequency at which the harness swings to frequencies below the E MV-related range. By choosing an input con- sators with significant internal loss resistance also reduces the quality of the resonant circuit.

To prevent the repeated cycling of the current periodically stimulates the cable harness to vibrate, on the one hand, the distance between two clocks can be chosen so large that the oscillation has dropped to an uncritical level. This is z. 1 ms.

In order to limit the thermal load of the switch and the freewheel in the first few clock cycles, it is also possible to choose the period longer at the beginning to allow a cooling of the semiconductor.

The low switching frequency also leads to a, typically on average, very low high-frequency interference spectrum, which is advantageous in terms of EMC (electromagnetic compatibility).

The goal is to pre-load other on-board power supply units and loads through the switch unit only when the main on-board power supply is in a stable state, ie. H. the lithium-ion battery is switched on hard. This makes it possible to realize an optimized wave-like run-up of on-board networks.

After a certain, in particular small number of clock cycles, it is also possible to check whether a countervoltage builds up at the output. If a stable reverse voltage has built up, a hard short circuit can be ruled out. In this case, further cycles can be released for a final pre-charge. In addition, the distance between the clocks can be reduced, since the load for the freewheel has dropped sharply by the built counter voltage.

Another possibility is the evaluation of the required number of clock processes to allow a diagnosis of the connected load or the sub-board network.

Depending on the harness inductance, different boundary conditions apply for the selection of the cut-off current during pre-charging operation. So the power level should be so small be chosen that the voltage across the capacitor does not drop so low that the supply of other consumers is at risk.

Since the frequency with which the oscillation between C _e i _n , harness and battery is formed, is very low, it is also possible to realize a targeted anti-vibration control of the switch. This can be done by measuring the input voltage V, _n . The next switch-on pulse of the switch can then ideally take place at the time at which the oscillation of the input voltage V, _{n has} a local maximum.

The input capacitor may be exposed during normal operation by the Bordnetzwelligkeit a high RMS load. In order to prevent this load, it is useful to connect the capacitor in the form of an active attenuator, for example an attenuator with resistor R, capacitor C and diode D, which is also referred to as RCD snubber. In this case, the inverse diode of a MOSFET of the switching element can be used in the example in order to derive switch-off and glitches at any time into the capacitor. During clocked precharging of the load, the mosfet can be driven to provide a backup function through the capacitor, such as a 100 iF capacitor.

The creation of a freewheeling path via the input capacitor freewheeling via the ground line of the switching unit is no longer mandatory. This makes it possible to realize a secured mass concept. In this case, a thermal overload of the switching unit is avoided by an uncontrolled flow of current to ground.

The presented vehicle electrical system is set up to carry out the method described here. This vehicle electrical system comprises a number of consumers, all of which, or at least some of them selectively, can each be started up via an intelligent power switch, for example an electronic power distribution unit (ePDU). Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

Brief description of the drawings

Figure 1 shows in a block diagram a load in a vehicle electrical system, which is powered up in a conventional manner, together with curves of electrical quantities.

FIG. 2 shows in a further block diagram a load in a vehicle electrical system which is started up by means of a linear switching element, together with curves of electrical quantities.

FIG. 3 shows in a block diagram a load in a vehicle electrical system which is started up in accordance with an embodiment of the presented method, together with courses of electrical quantities.

FIG. 4 shows in a block diagram a load in a vehicle electrical system which is started up in accordance with a further embodiment of the presented method.

Embodiments of the invention

The invention is schematically illustrated by means of embodiments in the drawings and will be described in detail below with reference to the drawings.

FIG. 1 shows in a block diagram a greatly simplified vehicle electrical system, which is designated overall by the reference numeral 10. The illustration shows a power supply 1 1, for example, a lithium-ion battery, a load or a consumer 12 and a switching element 14. The illustration also shows a first Lei In the switching element 14, a driver 30, a switch 32 with parallel-connected first diode 34, a second capacitor 36 and a second diode 38 are provided. The second capacitance 36 and the second diode 38 are connected to an internal ground potential 40 within the switching element 14. This internal ground potential is connected via a Zuleitungsinduktivität 42 with the central electrical system ground. The load 12 is shown with a resistor 50 and a third capacitor 52.

The task of the circuit element 14 is to connect or disconnect the load 12 to the vehicle electrical system 10 within the vehicle electrical system 10.

When connecting the load 12 by closing the switch 32, it comes through the discharged capacitive input circuit, exemplified by the

Capacitance 52 and the resistor 50, the load 12 to a resonant circuit between the energy storage 11, the inductance of the wiring harness and the capacitance 52 of the load 12. This resonant circuit leads to overvoltages, especially in a 48 V electrical system, which is above the maximum allowable limits lie.

In the illustration, three signal curves are reproduced on the right side, which illustrate the connection of the load 12 in the electrical system 10. A first curve 60 shows the course of the current through the switch 32, a second curve 62 shows the curve of the voltage at an input V, _n 64, and a third curve 66 shows the curve of the voltage at the load 12. The curves 60, 62 , 66 illustrate that there is a swing in the current flow (first curve 60), which causes the voltage at the input V, _n 64 (second curve 62) also oscillates and reaches values up to 60 V. The voltage on the load 12 also oscillates (third curve 66) and reaches values up to 80 V. This can cause damage to the load 12.

FIG. 2 shows in a block diagram a greatly simplified vehicle electrical system, which is denoted overall by the reference numeral 100. The diagram shows an energy supply 1 1 1, for example a lithium-ion battery, a load or a consumer. The illustration also shows a first line inductance 120, a first line resistance 122, a second line inductance or supply line inductance 124 and a second line resistance 126. In the switching element 1 14, a drive 130, a switch 132 with parallel connected first diode 134, a second capacitor 136, a second diode 138 and a linear current limiter 139 are provided. The second capacitor 136 and the second diode 138 are connected within the switching element 1 14 to an internal ground potential 140. This internal ground potential 140 is connected via the supply line inductance 124 to the central vehicle electrical system. The load 12 is represented by a resistor 150 and a third capacitor 152.

The linear current limiter 139 together with the switch 132 represents a linear switching element, with which the pre-charging of the load 1 12 can be realized with a defined current level and limited excitation of the resonant circuit. The linear current limiter 139 can also be implemented directly in the switch 132.

In the illustration, three waveforms are reproduced on the right side, which illustrate the connection of the consumer 112 in the electrical system 100.

A first curve 160 shows the course of the current through the switch 132. A second curve 162 shows the curve of the voltage at an input V, _n 164 and a third curve 166 shows the profile of the voltage at the load 112. The curves 160, 162 , 166 show that there is only a slight swing in the current (first curve 160) and that the values for the voltages (second and third curves 162, 166) remain within a permissible range.

However, it should be noted that the implementation of linear operation brings a high peak power dissipation. Furthermore, special power switches are required when the linear operation is implemented within the switch 132.

FIG. 3 shows in a block diagram a greatly simplified vehicle electrical system, which is designated overall by the reference numeral 200. The illustration shows an energy supply 21 1, for example a lithium-ion battery, a load or a consumer. The illustration also shows a first line inductance 220, a first line resistance 222, a second line inductance 224, and a second line resistance 226. The load 212 is represented by a resistor 250 and a capacitor 252.

In the switching element 214 are a flip-flop 260, a timer 262, a comparator 264, a limit switch 266, a current measuring element 268, a switch 270, a first diode 272, a second diode 274, a first capacitor 276, 278 and a second one Capacity 278 provided. The first and second capacitors and the second diode 274 are connected to an internal ground potential 280 within the switching element 214. This internal ground potential is connected via a Zuleitungsinduktivität 254 with the central electrical system ground.

It is thus compared to the comparator 264 which compares the current through the switch 270 with a value provided by the limit 266.

If the limit is exceeded, the flip-flop 260 is set and the switch 270 is opened. The switch 270 is thus closed for a first period. After opening the switch 270 this is closed again after a second period of time. The first period is, for example, Ι ΟΟμβ and is dependent on the measured current. The second period is typically given and may vary. Thus, the second period at the beginning of the startup, for example, to 5 ms, for example. Depending on the first period, set and then gradually or continuously, for example, to 1 ms, and possibly also depending on the first period, reduced.

The clocked operation obtained in this way limits the current, in this case via a maximum current limitation. The maximum value is predetermined by the value of the limit switch 266. It takes into account how much the consumer 212 can be charged.

In the illustration, three waveforms are reproduced on the right side, which illustrate the connection of the consumer 212 in the electrical system 200. A first curve 260 shows the course of the current through the switch 270. A second curve 262 shows the profile of the voltage at an input V, _n 264, and a third curve 266 shows the profile of the voltage at the consumer 212. The curves 260, 262, 266 illustrate that the current moves primarily at an OA level, until it increases in stages to short current peaks 270 (first curve 260) and the voltage across the load 212 (third curve 266). A significant swinging or even overshooting can not be determined.

FIG. 4 shows in a block diagram a greatly simplified vehicle electrical system, which is denoted overall by the reference numeral 300. The illustration shows a power supply 31 1, for example a lithium-ion battery, a load or a load 312 and a switching element 314. The illustration also shows a first line inductance 320, a first line resistance 322, a second line inductance 324 and a second one Line resistance 326. The load 312 is represented by a resistor 350 and a capacitor 352.

In the switching element 314 are a flip-flop 360, a clock 362, a comparator 364, a limit switch 366, a current measuring element 368, a switch 370, a first diode 372, a second diode 374, a first capacitor 376, 378 and a second one Capacity 378 provided. The first and the second capacitance as well as the second diode 374 are connected within the switching element 314 to an internal ground potential 380. This internal ground potential is connected via a Zuleitungsinduktivität 354 with the central electrical system ground. Furthermore, a mosfet 390 with parallel resistor 392 is shown. In this case, the inverse diode of the Mosfet 390 is used to derive switch-off and glitches on the capacitor, the first capacitor, 376 in the capacitance-larger capacitor, the second capacitor, 378. This takes into account that the input capacitor, the second capacitance, 378 is exposed in normal operation by the Bordnetzwelligkeit a high RMS current load. To prevent this load, the capacitor is connected in the form of an active RCD snubber.

As a result, overvoltage pulses which are generated when the switch 370 is switched off by the onboard power inductors 320, 324 and 354 can decay through the parallel path of the transistor 390, the capacitor 378 and the diode 374. In operating conditions where active suppression of the input voltage Vm 391 is required, for example to reduce voltage dips due to the switching on of loads, the transistor 390 may be driven to allow bidirectional current measurement.

Claims

claims

A method of operating a vehicle electrical system (100, 200, 300) having a number of consumers, wherein at least some of the consumers (112, 212, 312) are selectively connected via a switching element (114, 214, 314), respectively a limitation of the current flowing through the switching element (114, 214, 314) is made.

2. The method of claim 1, wherein the limitation of the current via the use of a linear switching element is achieved.

3. The method of claim 1, wherein the limitation of the current via a clocked operation of the switching element (114, 214, 314) is achieved.

4. The method of claim 3, wherein the switching element via a comparator (264), which compares a measured current with a predetermined value, is driven.

5. The method of claim 4, wherein when the predetermined value is exceeded after a first period, a switch (270) of the switching element (114, 214, 314) is opened and this switch (270) is closed again after a predetermined second period.

6. The method of claim 5, wherein the second period of time is set variable depending on the first period.

7. The method according to any one of claims 3 to 6, wherein a vibration-inhibiting control by the switching element (114, 214, 314) is made.

The method of any one of claims 1 to 7, wherein said some consumers (264) are powered up in turn

9. The method according to any one of claims 1 to 7, wherein the some consumers (264) are started up at the same time.

10. Vehicle electrical system, which is set up to carry out a method according to one of claims 1 to 9.