DE102016224721A1 - The fuel cell system - Google Patents

Abstract

The invention relates to a fuel cell system, preferably in a vehicle, comprising at least one fuel cell, a leading to the fuel cell supply line for an oxidant, preferably air, a low voltage network, operable with a low voltage, a high voltage network, operable with a high voltage that is higher than the low voltage a first compressor in the supply line and a first electric motor in the low-voltage network for driving the first compressor, and a second compressor in the supply line downstream of the first compressor and a second electric motor in the high-voltage network for driving the second compressor.

Description

The present technology relates to a fuel cell system, preferably in a vehicle, and a method of controlling a fuel cell system.

Fuel cell systems comprise at least one fuel cell, in particular a stack of several fuel cells. To the fuel cell leads a supply line for the oxidant. The oxidizing agent is in particular air. In the technology considered here, the oxidizing agent is compressed before being fed into the fuel cells.

US 2011/0097632 A1 shows a 2-stage compression of the air. In this case, a first compressor is driven via an exhaust gas turbine. A second, in series compressor is operated by an electric motor.

It is a preferred object of the technology disclosed herein to reduce or eliminate at least one disadvantage of a previously known solution or to suggest an alternative solution. Other preferred objects may result from the beneficial effects of the technology disclosed herein. In particular, it is an object of the technology disclosed herein to provide a fuel cell system and a corresponding method that enable operation of the fuel cell with very high efficiency. The object (s) is / are solved by the subject matter of the independent claims. The dependent claims are preferred embodiments.

The technology disclosed herein relates to a fuel cell system having at least one fuel cell. The fuel cell system is intended, for example, for mobile applications such as motor vehicles, in particular for providing the energy for at least one electric drive machine for locomotion of the motor vehicle. In its simplest form, a fuel cell is an electrochemical energy converter that converts fuel and oxidant into reaction products, producing electricity and heat. The fuel cell includes an anode and a cathode separated by an ion-selective or ion-permeable separator. The anode is supplied with fuel. Preferred fuels are: hydrogen, low molecular weight alcohol, biofuels, or liquefied natural gas. The cathode is supplied with oxidant. Preferred oxidizing agents are, for example, air, oxygen and peroxides. The ion-selective separator can be designed, for example, as a proton exchange membrane (PEM). Preferably, a cation-selective polymer electrolyte membrane is used. Materials for such a membrane are, for example: Nafion®, Flemion® and Aciplex®.

A fuel cell system preferably comprises, in addition to the at least one fuel cell, peripheral system components (BOP components) which can be used during operation of the at least one fuel cell. As a rule, several fuel cells are combined to form a fuel cell stack or stack.

The problem is solved by a fuel cell system. The fuel cell system is located in particular in a vehicle. The fuel cell system comprises at least one fuel cell. Preferably, a plurality of fuel cells are combined to form a fuel cell stack. For the sake of simplicity, this is usually referred to as a fuel cell, although the stack of multiple fuel cells can always be used.

The fuel cell system includes a supply line for the oxidant. The supply leads to the fuel cell. The oxidizing agent is in particular ambient air.

Furthermore, the fuel cell system comprises a low-voltage network and a high-voltage network. The low voltage network can be operated with a low voltage. The high voltage network can be operated with a high voltage. Both voltage networks can be supplied at least indirectly via the same energy source, in particular the fuel cell. Via corresponding means for voltage transformation it is achieved that the two voltage networks are operated with different voltage.

In addition, the fuel cell system comprises a first compressor in the supply line and a first electric motor in the low-voltage network. The first compressor is arranged in the supply line for compressing the oxidizing agent. The first electric motor is drive-connected to the first compressor. The first electric motor is operated with the low voltage from the low voltage grid.

Downstream of the first compressor, the fuel cell system includes a second compressor in the supply line. The second compressor is preferably arranged in the supply line so that it can further compress the oxidizing agent compressed by the first compressor. The second compressor is thus preferably in series with the first compressor. A second electric motor drive-connected to the second compressor is located in the high-voltage network. The second electric motor is with the High voltage operated from the high voltage network.

In a preferred embodiment, it is provided that the oxidizing agent is compressed only via the two compressors described. In an alternative embodiment, however, the fuel cell system can also have further compressors in series connection or parallel circuits.

The high voltage in the high voltage network is higher than the low voltage in the low voltage network. When comparing the voltages or in terms of size to the voltages are preferably always considered nominal voltages.

In the context of the invention it has been recognized that a very energy-efficient compression of the oxidizing agent is possible when the first compressor, and thus the compressor designed for the lower power, is driven via the low-voltage network. The second compressor, and thus the compressor designed for higher performance, can be operated more energy-efficiently with the higher voltage than with the lower voltage.

It is preferably provided that the high voltage is at least 2 times, preferably at least 3 times, particularly preferably at least 4 times, the low voltage. It has been shown that these voltage differences of the two voltage grids allow a very energy-efficient operation of the two electric motors in view of the required performance of the compressor.

Furthermore, it is preferably provided that the low voltage is at most 100 volts (V), preferably at most 75 V, particularly preferably at most 48 V. Additionally or alternatively, the high voltage is preferably at least 200 V. In particular, the high voltage is between 200 V and 1000 V. These voltages are particularly suitable for the operation of the fuel cell system in a road vehicle.

The fuel cell system preferably includes a bypass conduit for the oxidant. The bypass line bypasses the second compressor. In particular, the bypass line branches off between the first compressor and the second compressor. Downstream of the second compressor, the bypass line opens again into the supply line for the oxidizing agent. It is provided a controllable valve that allows opening and closing of the bypass line. In particular, the valve, for example as a throttle valve, designed for a stepped or stepless change in the volume flow through the bypass line.

The bypass line thus makes it possible to pass the oxidant completely or partially past the second compressor. This is particularly useful in the partial load range of the fuel cell, since not the full compressor capacity of both compressors is necessary here.

Particularly preferably, the second compressor has an air-bearing compressor wheel. This air bearing requires a minimum speed of the compressor wheel, otherwise the air cushion does not build up in the air bearing. Without the bypass line, the oxidant would always flow through the second compressor and drive the compressor wheel. Under certain circumstances, however, the minimum speed of the air bearing is not reached, resulting in an increased load on the bearing. By using the bypass line, this disadvantageous effect can be avoided.

Furthermore, an exhaust pipe preferably leads away from the fuel cell. In particular for the exhaust pipe into the environment. In the exhaust pipe is preferably a turbine. The turbine is driven by the exhaust gas and is drive-connected to the first compressor. Depending on the pressure in the exhaust pipe, the turbine can take over the drive of the first compressor partially or completely and the power of the first electric motor can be reduced accordingly partially or completely.

In a preferred embodiment, the second compressor is operated exclusively via the second electric motor. In an alternative variant, it is also possible to additionally or completely drive the second compressor via a further turbine of the exhaust gas line.

The rated power of the second compressor is preferably at least 1.5 times, in particular at least twice, more preferably at least 2.5 times, the rated power of the first compressor. In particular, the rated capacity of the compressor is the possible continuous output of the compressor, which can be provided during normal operation without significant time restriction, without significantly affecting the life of the compressor. The first compressor preferably has a rated power between 2 kW and 10 kW.

The use of the second compressor with a higher power than the first compressor, in particular allows the use of the second compressor in a relatively high power range of the fuel cell. In the lower power range, in particular the described bypass line is used to compress the first compressor Pass oxidant past the second compressor.

It is preferably provided to use the same coolant circuit both for cooling the first compressor and the second compressor.

The technology disclosed herein further includes a vehicle. The vehicle is in particular a road vehicle. The vehicle includes the fuel cell system described herein and at least two electrical systems. The two on-board networks are the low-voltage network for the operation of the first electric motor and the high-voltage network for the operation of the second electric motor.

Furthermore, the vehicle comprises at least one electric drive machine. The electric drive machine is drive-connected with at least one wheel of the vehicle thus serves to propel the vehicle. The prime mover is preferably operated with the high-voltage network. Thus, the already existing in the vehicle high-voltage network is preferably used for the operation of the second compressor. Furthermore, it is preferably provided that the low-voltage network is not only used to drive the first compressor, but also for other components of the vehicle. These other components are for example: peripheral system components of the fuel cell system, such as coolant pump or control units, or other electrical components of the vehicle, such as lighting, control units, audio systems, comfort systems, etc.

Preferably, the prime mover is an electric motor, which can regenerate electrical energy by recuperation to an energy storage device.

Likewise, the vehicle disclosed herein may include a plurality of electric drive machines.

Further, the technology disclosed herein includes a method of controlling a fuel cell system. Preferably, the fuel cell system is controlled, which has been described in detail here. In particular, it is a fuel cell system in the vehicle.

In the method, a compression of an oxidizing agent, preferably air, with at least two, in particular connected in series, compressors. The first compressor is driven by a first electric motor. The second compressor is driven by a second electric motor. The first electric motor is operated with a low voltage and the second electric motor with a high voltage. The high voltage is higher than the low voltage. Furthermore, the compressed oxidizing agent is supplied to at least one fuel cell, in particular to a fuel cell stack.

The advantageous embodiments and subclaims described in the context of the disclosed fuel cell system and the disclosed vehicle accordingly find advantageous application to the method disclosed here.

In particular, it is envisaged not to operate the second electric motor and thus the second compressor up to a fuel cell power of 50%, preferably 40%, particularly preferably 30%. In particular, only the first compressor is used in this power range. The first compressor is driven by the first electric motor and / or the turbine.

The fuel cell power refers to the rated power of the fuel cell, in particular to the rated power of the fuel cell stack. In particular, the rated power of the fuel cell is the possible continuous power of the fuel cell, which can be provided during a normal operation without significant time limitation, without significantly affecting the life of the fuel cell.

Furthermore, within the scope of the method it is preferably provided that, up to a fuel cell output of 50%, preferably 40%, particularly preferably 30%, the oxidizing agent is compressed only with the first compressor, with a compression ratio of up to 2.5, preferably up to 2, more preferably up to 1.5. The first compressor is designed especially for these compression ratios. For operation of the fuel cell system in the higher power range, the second compressor will use in addition to the first compressor.

Furthermore, it is preferably provided that, up to a fuel cell output of 50%, preferably 40%, particularly preferably 30%, the entire volume flow of the oxidizing agent is conducted past the second compressor. This passing of the oxidizing agent takes place in particular with the described bypass line.

Preferably, from a fuel cell power of 30%, preferably 40%, particularly preferably 50%, both compressors are operated.

In the described method, other factors, such as, for example, temperatures in the environment or in the Fuel cell system, considered. Depending on these further factors, conditions may arise in which, for example, both compressors are already operated at a fuel cell power of less than 30% or in which, for example, only the first compressor of a fuel cell power is operated above 50%. Thus, the use of the compressors does not have to be assigned to the defined fuel cell outputs in all operating states.

• 1 eine schematische Ansicht des offenbarten Brennstoffzellensystems, und
• 2 eine schematische Ansicht des Brennstoffzellensystems, integriert in ein Fahrzeug.

The technology disclosed herein will now be explained with reference to the figures. Show it:

• 1 a schematic view of the disclosed fuel cell system, and
• 2 a schematic view of the fuel cell system, integrated into a vehicle.

The 1 and 2 show in purely schematic representations of a fuel cell system 1 ,

The fuel cell system 1 includes at least one fuel cell 2 , in particular a fuel cell stack with a plurality of fuel cells 2 , To the at least one fuel cell 2 leads a supply line 3 for an oxidizer, here air from the environment.

Furthermore, the fuel cell system comprises 1 a low voltage network 4 and a high voltage network 5 , The two voltage networks 4 . 5 are shown here purely schematically. In particular, both are voltage network 4 . 5 directly or indirectly with electrical energy from the fuel cell 2 provided. Corresponding means for transformation provide for the different voltages in the low-voltage network 4 and high voltage network 5 ,

In the supply line 3 there is a first compressor 6 for compacting the oxidizing agent. Downstream and in series with the first compressor 6 is in the supply line 3 a second compressor 8th arranged.

The first compressor 6 is with a first electric motor 7 drive-connected. The second compressor 8th is with a second electric motor 9 drive-connected. The first electric motor 7 will be powered by the low voltage grid 4 operated. The second electric motor 9 will be powered from the high voltage grid 5 operated.

Between the first compressor 6 and the second compressor 8th branches from the supply line 3 a bypass line 10 from. The bypass line 10 bypasses the second compressor 8th and opens downstream of the second compressor 8th in the supply line 3 , In or on the bypass line 10 there is a controllable valve 11 , preferably designed as a throttle valve.

In the supply line 3 are preferably an air filter 14 and / or a charge air cooler 15 and / or a humidifier 16 , The air filter 14 is upstream of the first compressor 6 arranged. The intercooler 15 is downstream of the second compressor 8th , in particular between the second compressor 8th and the humidifier 16 , The bypass line 10 in particular opens between the second compressor 8th and the intercooler 15 in the supply line 3 , The humidifier 16 is in particular between the intercooler 15 and the fuel cell 2 arranged.

Furthermore, the fuel cell system includes 1 preferably an exhaust pipe 12 that from the fuel cell 2 leads away. The exhaust pipe 12 leads in particular the cathode exhaust air of the fuel cell 2 from. Preferably, the exhaust pipe leads 12 through the humidifier 16 , In the humidifier 16 is the relatively dry supply air in the supply line 3 with the relatively humid exhaust air in the exhaust pipe 12 moistened.

In the exhaust pipe 12 there is a preferably used turbine 13. The turbine 13 is with the first compressor 6 drive-connected. Depending on the pressure in the exhaust pipe 12 can the turbine 13 the drive of the first compressor 6 partially or completely from the first electric motor 7 take.

2 shows the integration of the fuel cell system 1 in a vehicle 17 , The vehicle 17 includes in addition to the fuel cell system 1 bikes 19 and at least one electric drive machine 18 to drive the wheels 19 , In particular, it is provided that the drive machine 18 with electrical energy from the high-voltage grid 5 is operated.

The foregoing description of the present invention is for illustrative purposes only, and not for the purpose of limiting the invention. Various changes and modifications are possible within the scope of the invention without departing from the scope of the invention and its equivalents

LIST OF REFERENCE NUMBERS

1

The fuel cell system

2

Fuel cell, in particular fuel cell stack

3

supply

4

Low-voltage grid

5

High Voltage Power

6

first compressor

7

first electric motor

8th

second compressor

9

second electric motor

10

bypass line

11

controllable valve

12

exhaust pipe

13

turbine

14

air filter

15

Intercooler

16

humidifier

17

vehicle

18

electric drive machine

19

bikes

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

• US 2011/0097632 A1 [0003]

Claims (14)

Fuel cell system (1), preferably in a vehicle comprising At least one fuel cell (2), A supply line (3) leading to the fuel cell (2) for an oxidizing agent, preferably air, A low voltage network (4), operable with a low voltage, A high voltage network (5) operable with a high voltage higher than the low voltage, • a first compressor (6) in the supply line (3) and a first electric motor (7) in the low-voltage network (4) for driving the first compressor (6), and • a second compressor (8) in the supply line (3), in particular downstream of the first compressor (6), and a second electric motor (9) in the high-voltage network (5) for driving the second compressor (8). Fuel cell system after Claim 1 , wherein the high voltage is at least 2 times, preferably at least 3 times, more preferably at least 4 times, the low voltage. Fuel cell system according to one of the preceding claims, wherein the low voltage is at most 100 V (volts), preferably at most 75 V, particularly preferably 48 V, and / or wherein the high voltage is at least 200 V, preferably 200 V to 1000 V. Fuel cell system according to one of the preceding claims, comprising a bypass line (10) for the oxidizing agent bypassing the second compressor (8) and a controllable valve (11) for opening and closing the bypass line (10). Fuel cell system according to one of the preceding claims comprising an exhaust line (12) which leads away from the fuel cell (2) and a turbine (13) in the exhaust line (12) for driving the first compressor (6). Fuel cell system according to one of the preceding claims, wherein the rated power of the second compressor (8) is at least 1.5 times, preferably at least 2 times, more preferably at least 2.5 times, the rated power of the first compressor (6) , Fuel cell system according to one of the preceding claims, wherein the first compressor (6) has a rated power between 2 kW (kilowatts) and 10 kW. Fuel cell system according to one of the preceding claims, wherein the second compressor (8) comprises an air-bearing compressor wheel. Vehicle (17), in particular road vehicle, with at least one fuel cell system (1) according to one of the preceding claims and at least two electrical systems, namely a low voltage network (4) for the operation of the first electric motor (7) and a high voltage network (5) for the operation of the second electric motor (9) and for the operation of an electric drive machine (18) for driving the vehicle (17). Method for controlling a fuel cell system (1), preferably according to one of Claims 1 to 8th comprising the following steps: • compressing an oxidizing agent, preferably air, with at least two compressors (6, 8) connected in series, each driven by an electric motor (7, 9), • operating the first electric motor (7) with a low voltage and second electric motor (9) having a high voltage, wherein the high voltage is higher than the low voltage, and • supplying the compressed oxidant to at least one fuel cell (2). Method according to Claim 10 , wherein up to a fuel cell power of 50%, preferably 40%, particularly preferably 30%, based on the rated power of the fuel cell (2), the second electric motor (9) is not operated. Method according to one of Claims 10 or 11 , wherein up to a fuel cell power of 50%, preferably 40%, more preferably 30%, based on the rated power of the fuel cell (2), the oxidizing agent is compressed only with the first compressor (6), with a compression ratio of up to 2.5, preferably up to 2, more preferably up to 1.5. Method according to one of Claims 10 to 12 , wherein up to a fuel cell power of 50%, preferably 40%, particularly preferably 30%, based on the rated power of the fuel cell (2), the entire volume flow of the oxidant is passed to the second compressor (8). Method according to one of Claims 10 to 13 , wherein from a fuel cell power of 30%, preferably 40%, particularly preferably 50%, based on the rated power of the fuel cell (2), both compressors (6, 8) are operated.

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