DE10314360B4 - Power supply for a vehicle - Google Patents

Abstract

Power supply for a vehicle in which at least two voltage circuits with different voltage levels are connected to supply a voltage on-board network and / or for an electric vehicle drive, and in which at least one energy source is provided for energy supply, characterized in that the energy source is an energy converter which as a fuel cell stack (1) is formed from series-connected fuel cell elements (3), and that the fuel cell stack (1) has a multiple voltage tap (2), via which the respective voltage levels provided for the voltage circuits can be tapped, and via which the the consumers assigned to the voltage circuits can be supplied.

Description

The invention relates to a power supply for a vehicle in which at least two voltage circuits with different voltage levels are connected to supply a voltage on-board network and / or for an electric vehicle drive, and in which at least one energy source is provided for energy supply.

The increasing electrification of components in motor vehicles, with high-current consumers, such as air conditioning units, windscreen drives, window regulator motors, and the realization of technical innovations, such as hybrid drive, drive-by-wire systems, crankshaft starter generators, electric valve train, leads to a constantly increasing demand for electrical power Voltage systems of motor vehicles. On the other hand, in today's standard 14 V voltage on-board systems, the aim is to keep the line currents below 200 A in order to limit ohmic power losses. For future Bordnetze therefore sources of power with higher voltage levels will be in demand. In particular, to supply the high-current, or high-power consumers, a vehicle electrical system is now favored, for example, with a 36 V (nominal voltage) -Energiespeicher at a charging voltage of 42V. In addition to conventional electrochemical batteries, more and more powerful capacitor banks (SuperCaps, UltraCaps) will be used as energy storage. Due to the ongoing development of fuel cells, also in vehicle technology, fuel cell stacks will play an important role as energy converters in vehicles in the future. A fuel cell stack (stack) consists of several fuel cells connected in series, each separated by a so-called bipolar plate. Fuel cell stacks are discussed as an energy source for electric vehicle drives, but also come as auxiliary equipment, as so-called APU (Auxiliary Power Unit) systems, for example, to the electrical system supply, in question.

Many electrical consumers in vehicles, such as incandescent lamps, displays, instrument cluster, control units, but are designed for the conventional 14 V 12 V battery power and not or only with great effort to a 42 V electrical system customizable. Therefore, voltage circuits with multiple voltage circuits, in particular a two-voltage on-board network with a 42 V high-voltage circuit and a 14 V low-voltage circuit, have already been proposed. Examples of such two-voltage systems are the DE 101 19 985 A1 and the DE 100 28 748 A1 called.

The voltage circuits of such multi-voltage systems are usually connected via one or more unidirectional or bidirectional DC / DC converters (DC / DC converters) in order to transfer electrical powers, for example between the 14 V and 42 V sides, or the voltage levels For example, to charge the 12 V battery on the 14 V side via a generator located on the 42 V side.

The problem with multiple-voltage on-board networks is their relatively high costs in terms of costs, design and operation. In particular, DC / DC converters with their associated peripherals, d. H. Water or air cooling and multiple electrical connections are costly. The required components reduce the available installation space in the vehicle when integrated into the vehicle electrical system, cause noise by pumps or fans for cooling, which is particularly disturbing in stationary operation and worsens the energy balance due to the converter efficiency of typically 85-95%.

From the DE 101 02 243 A1 a three-voltage on-board network is known, with a first voltage on-board network, which has a fuel cell stack, which acts as an energy source for an electric vehicle drive, and a second, 42 V electrical system, with a 36 V energy storage and a third, 14 V electrical system, with a 12 V energy storage. The first electrical system is connected to the second electrical system and the second electrical system with the third electrical system via a respective DC / DC converter. For safety reasons, the first bidirectional DC / DC converter is galvanically isolated from the second voltage on-board network because of the high nominal voltage of the fuel cell stack (> 60 V). The energy stores are charged via the fuel cell stack and can in turn load each other via the second DC / DC converter. The second and third on-board power supply high-current and low-current consumers and support the fuel cell system with the electric drive as well as associated auxiliary equipment. The 36 V memory is preferably realized by three series-connected 12 V batteries. To save space, it is proposed to combine the 36 V energy storage and the 12 V energy storage in a two-voltage battery in which the 36 V memory receives a tap at 12 V.

A disadvantage is that although space is saved by the two-voltage battery, but a reduction in the cost of DC / DC converters is not provided or due to the special interconnection is not possible - at least no reference is given in this regard. An additional voltage tap on an electrochemical battery is also problematic because the electrochemical balance of the battery would be severely impaired. To compensate, both voltage sides (14 V and 42 V) would have to be loaded evenly, if necessary by applying artificial electrical loads, which, however, does not appear to be energetically practicable. Therefore, an additional voltage tap on an electrochemical battery is possibly conceivable for (load-free) diagnostic purposes.

The document DE 198 27 045 A1 relates to a device for measuring voltage at more than two identical voltage source units with contacting means for voltage tapping and evaluation unit connected to the contacting means, wherein a plurality of contacting means are structurally combined in a contacting unit.

Object of the present invention is therefore to improve the known power supplies for voltage supply systems with multiple voltage levels so that they are easier and cheaper feasible in terms of cost, construction and operation.

The object is achieved in conjunction with the preamble of claim 1, characterized in that the energy source is an energy converter, as a fuel cell stack. is formed from series-connected fuel cell elements, and that the fuel cell stack has a Mehrfachspannungsabgriff over which the voltage levels provided for the respective voltage levels can be tapped, and over which the voltage circuits associated consumers can be supplied.

Due to the multiple voltage tap on the fuel cell stack, the use of a DC / DC converter can be omitted. Fuel cell stacks are made up of a number of individual fuel cell elements which, depending on the type, supply individual voltages between 0.5 V-1.1 V, modularly constructed in series circuits. For the automotive industry stacks are already designed and made available with the respective desired voltages in a compact design. These stacks can be easily provided with a multiple voltage tap to provide the vehicle with different voltage levels without having to switch DC-DC converters. Depending on the application, as APU or for vehicle propulsion fuel cells of different types are preferred. The multiple voltage tap can be adapted to the various stacks in question. Fuel cells react far less critically to the Mehrfachspannungsabgriff compared to electrochemical storage, since the fuel, or fuel, is supplied from the outside and thereby avoid energy imbalances, or compensate more easily. Due to the multiple tap, can be dispensed with the use of multiple batteries in multi-voltage on-board networks. The power supply is possible from an energy source. This saves costs, installation space and weight. The omission of the DC / DC converter in the multi-voltage electrical system, including its wiring, control and cooling, further components and space and integration costs are saved. Degradation of efficiency, due to the required during the voltage conversion primary energy and noise, caused by additional cooling devices are avoided.

Preferred embodiments of the invention are described in the subclaims 2 to 9.

According to a preferred embodiment of the invention, the fuel cell stack has a distribution device for distributing the fuel cell fuel in the fuel cell stack.

By the distribution device, a very uniform distribution of the supplied fuel in the fuel cell stack can be ensured, so that in the power requirement by the Mehrfachspannungsabgriff always the electrochemical balance of the cell system is maintained, which has a favorable effect on the efficiency and the life of the stack. Since the fuel cell fuel is usually gaseous, the distribution device can particularly advantageously have a controllable flow system, through which the fuel cell stack can be flowed through by a gaseous fuel cell fuel. In principle, however, a distribution system is also conceivable with which a liquid fuel can be distributed within the stack.

According to a further preferred embodiment of the invention, the fuel cell stack is designed as a power source for supplying a two-voltage on-board network, and the Mehrfachspannungsabgriff on the fuel cell stack has a first Abgriffpol at a first voltage level, a second Abgriffpol at a second voltage level and a third Abgriffpol for a common ground connection on.

Due to the fact that the fuel cell stack with the multiple voltage tap is designed as an energy source for supplying the two-voltage on-board network, the on-board network has a permanent, high-performance supply with two voltage levels which can be operated independently of the operation of a conventional internal combustion engine with generator (alternator) and battery , Particularly advantageous is the use of Mehrfachspannungsabgriffs in the favored for the future 14 V / 42 V network, as this network already numerous innovations are in development, the power supply can be improved by the fuel cell stack with the multiple tap. Similarly, the first tap pole may be at 14V and the second tap pole may be at 42V. Typically, 3-10 kW power can be provided in a 42 V voltage circuit with a fuel cell APU. As a result, the functionality of the high-power consumers of the high-voltage circuit of the two-voltage electrical system, such as auxiliary heating and air conditioning and new electronic systems is improved. The two-voltage on-board network is cheaper by eliminating a DC / DC converter in cost and construction. The power supply in a multi-voltage vehicle electrical system is thus more cost effective and effective.

According to a further preferred embodiment of the invention, the fuel cell stack is designed as an energy source for supplying an electric vehicle drive and a voltage on-board network, and has the Mehrfachspannungsabgriff on the fuel cell stack a first Abgriffpol for the vehicle drive and at least a second Abgriffpol at a voltage level of the onboard electrical system , The tapping pole for the voltage on-board network can be 14 V.

In an electric vehicle, one or more fuel cell stacks may be used to power the electric drive and the on-board power supply. With the multiple tap at the corresponding voltage levels, both consumer complexes (drive and vehicle electrical system) can be fed from one energy source without the aid of DC / DC converters. Preferably, the tap for the vehicle drive is 200-350 V. The tap for the electrical system can be at 14 V in the case of a conventional electrical system. But it is also a tap at a higher voltage or multiple taps for a multi-voltage electrical system, for example, at 14 V and 42 V conceivable.

According to a further preferred embodiment of the invention, the fuel cell stack is formed in a solid oxide construction.

Solid oxide fuel cells are particularly advantageous in an auxiliary power system (APU) for board power supply of a two-voltage electrical system in conjunction with conventional fuels (gasoline, diesel) can be used. In such an APU system is preferably a fuel cell stack based on a solid oxide technology, short SOFC (Solid Oxide Fuel Cell), in question. SOFCs are high-temperature fuel cells in which the gaseous fuel required for the oxidation process or fuel (hydrogen, carbon monoxide, methane and others) is generated by a chemical reaction at a high operating temperature (700-1400 ° C). This can be implemented directly in the cell, but preferably with the aid of an upstream reformer. The electrochemical use of the gaseous fuel in the fuel cell stack for electricity production proceeds at similarly high temperatures (650-850 ° C). Fossil fuels (diesel, gasoline, natural gas) can also be considered as fuels for generating the reformate to be fed into the cells, so that the existing supply infrastructure (filling stations) can be used.

According to a further preferred embodiment of the invention, the fuel cell stack is formed in a polymer electrolyte membrane construction.

Polymer electrolyte membrane fuel cells, short PEMFC, are particularly advantageous for mobile use in vehicles with electric drive. Compared to SOFC systems, they already work at low temperatures (60-100 ° C) and therefore have shorter startup times. However, such systems require as pure as possible hydrogen, which must be carried in a special tank or possibly generated in an upstream reforming process. Like the SOFCs, PEMFCs are particularly suitable for arranging the multiple voltage tap. However, other fuel cells are also suitable in principle.

Further details of the invention will become apparent from the following detailed description and the accompanying drawings, in which preferred embodiments of the invention are illustrated, for example.

Show it

1 : A schematic representation of a fuel cell stack with a multiple tap and with a fuel distribution device and

2 The fuel cell stack with a second embodiment of the fuel distribution device.

A power supply for a vehicle consists essentially of a fuel cell stack 1 at which a multiple voltage tap 2 is arranged. The fuel cell stack 1 is advantageous for supplying a 14 V / 42 V two-voltage electrical system in a solid oxide construction designed as a SOFC stack. In this case, the fuel, for example a hydrogen-containing reformate, is generated in a reforming process and the stack 1 fed. By a series connection of a sufficient number of cell elements 3 , for example 50, becomes the stack 1 educated. At the fuel cell stack 1 are three tap poles 4 . 5 . 6 arranged. The voltage levels result from the number of switched cells 3 according to the addition of the individual voltages. The first tap pole 4 is at 14 V, ie the voltage level of the conventional electrical system and serves to supply the "normal current" consumer (lighting, etc). The second tap pole 5 is 42 V and is used to supply the high-performance consumers (for example, an electric front / rear window heater or an electric air conditioner). The two voltage taps 4 . 5 (Positive poles) have an identical mass passing through the third tap pole 6 is pictured.

Furthermore, the fuel cell stack 1 a distribution facility 7 . 7 ' for the distribution of a gaseous fuel. The distribution facility 7 is in a first embodiment ( 1 ) in a so-called "up-stream" design. The fuel is delivered through a central feeder 9 via an adjustable flow system 8th in an upper feeder 10 and a lower feeder 11 fed. After the known functional principle of fuel cells, by oxidation of hydrogen with (air) oxygen to water vapor in the cells 3 Electricity released. The use of reformates in a SOFC stack produces additional exhaust gases at an operating temperature of several hundred degrees. To exhaust the exhaust gases or unburned fuel is an outlet 12 intended. Depending on the load is in the area of the tapping poles 4 . 5 Consumed a lot of fuel. Through the flow system 8th the different consumption is continuously balanced.

A second embodiment with an alternative distribution system 7 ' in a so-called "down-stream" design is in 2 shown. In this embodiment, the fuel is via a separate upper feed 13 in the stack 1 directed. Fuel can then be out of the stack 1 about a derivative 14 the flow system 8th are fed and via the lower feeder 11 again in a cycle the stack 1 be supplied. Excess unburned fuel, or exhaust gas, can via an outlet 15 of the flow system 8th directly or via the outlet 12 of the stack 1 be derived.

LIST OF REFERENCE NUMBERS

1

Fuel Cell Stack

2

Mehrfachspannungsabgriff

3

fuel cell elements

4

Tap pole (first positive pole)

5

Tap pole (second positive pole)

6

Tap pole (ground)

7, 7 '

distribution facility

8th

flow system

9

central feeder

10

upper feeder

11

lower feeder

12

Drain the stack

13

separate upper feeder

14

derivation

15

Drainage of the flow system

Claims (9)

Power supply for a vehicle in which at least two voltage circuits with different voltage levels are connected to supply a voltage on-board network and / or for an electric vehicle drive, and in which at least one energy source is provided for energy supply, characterized in that the energy source is an energy converter, as a fuel cell stack ( 1 ) of series-connected fuel cell elements ( 3 ), and that the fuel cell stack ( 1 ) a multiple voltage tap ( 2 ), via which the respective voltage levels provided for the voltage circuits can be tapped, and via which the consumers assigned to the voltage circuits can be supplied. Power supply according to claim 1, characterized in that the fuel cell stack ( 1 ) a distribution facility ( 7 . 7 ' ) for distributing the fuel cell fuel in the fuel cell stack ( 1 ) having. Power supply according to claim 2, characterized in that the distribution device ( 7 . 7 ' ) an adjustable flow system ( 8th ) over which the fuel cell stack ( 1 ) With a gaseous fuel cell fuel can flow. Power supply according to one of claims 1 to 3, characterized in that the fuel cell stack ( 1 ) is designed as an energy source for supplying a two-voltage on-board network, and that the multiple voltage tap ( 2 ) on the fuel cell stack ( 1 ) a first tap pole ( 4 ) at a first voltage level, a second tap pole ( 5 ) at a second voltage level and a third tap pole ( 6 ) for a common ground connection. Power supply according to claim 4, characterized in that the first voltage level of the two-voltage on-board network is 14 V, and in that the second voltage level is 42 V. Power supply according to one of claims 1 to 5, characterized in that the fuel cell stack ( 1 ) is designed as an energy source for supplying an electric vehicle drive and a voltage on-board network, and that the multiple voltage tap ( 2 ) on the fuel cell stack ( 1 ) has a first Abgriffpol for the vehicle drive and at least one second Abgriffpol at a voltage level of the onboard electrical system. Power supply according to claim 6, characterized in that the Abgriffpol for the voltage on-board network is 14 V. Power supply according to one of claims 1 to 7, characterized in that the fuel cell stack ( 1 ) is formed in a solid oxide construction. Power supply according to one of claims 1 to 7, characterized in that the fuel cell stack ( 1 ) is formed in a polymer electrolyte membrane construction.

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