Fuel cell system and method for controlling a heating current for temperating a fuel cell stack of a fuel cell system

Abstract

The invention relates to a fuel cell system (100), the fuel cell system (100) comprising a fuel cell stack (10) for generating an output voltage and a step-up converter (30) for increasing the output voltage of the fuel cell stack (10), the step-up converter having at least one converter unit (31a, 31b, 31c, 31d), the converter unit (31a, 31b, 31c, 31d) comprises at least one coil (33) and a controllable switch (34) for increasing the output voltage of the fuel cell stack (10), the controllable switch (34) having a variable resistance. Furthermore, the fuel cell system (100) comprises a control device (50) which is designed to control the controllable switch (34) of the at least one converter unit (31a, 31b, 31c, 31d) in such a way that an electrical resistance of the controllable switch (34) of the at least one converter unit (31a, 31b, 31c, 31d) is set in order to control a heating current for controlling the temperature of at least the fuel cell stack (10).

Description

Background Art

[0001] Fuel cell stacks, especially in mobile applications, may be subject to ambient temperatures below freezing. In order to avoid damage to the fuel cell stack during startup in this temperature range, the fuel cell stack may be heated.

[0002] It is known to provide a warm-up phase before the normal operation of a fuel cell system, wherein, for example, the efficiency of the fuel cell system is disadvantageously deteriorated during this warm-up phase, in order to increase the waste heat generation of the fuel cell stack of the fuel cell system. This waste heat can be used to heat the fuel cell stack.

[0003] DE 10 2012 218 584 A1 also discloses an additional load resistor with a fixed resistance value arranged between the electrical contacts of the fuel cell assembly, wherein the additional load resistor can be switched on as the only or at least substantially the only electrical consumer by means of a switching element at least during a heating phase of the fuel cell arrangement. Disadvantageously, the current flowing through the load resistor is dependent on the fixed resistance value of the load resistor. Summary of the invention

[0004] The invention relates to a fuel cell system according to the features of claim 1 and a method according to the features of claim 7 .

[0005] Further features and details of the invention are derived from the respective dependent claims, the description and the drawings. Features and details described in connection with the battery stack according to the invention naturally also apply to the production method according to the invention and vice versa, so that the disclosures concerning the various aspects of the invention always refer to each other or can refer to each other.

[0006] According to a first aspect, the present invention shows a fuel cell system, wherein the fuel cell system includes a fuel cell stack for generating an output voltage. In addition, the fuel cell system includes a boost converter for increasing or for increasing and stabilizing the output voltage of the fuel cell stack, wherein the boost converter has at least one converter unit, wherein at least one converter unit includes at least one coil and a controllable switch for increasing the output voltage of the fuel cell stack, wherein the controllable switch has or is configured as a variable resistor or a variable resistance value, in particular a resistor that is continuously variable at least in sections or a resistor that is substantially continuously variable at least in sections. In addition, the fuel cell system includes a control device, wherein the control device is configured to control or manipulate at least one controllable switch of at least one converter unit in such a way that the variable resistance or the variable resistance value of the controllable switch of at least one converter unit is adjusted for controlling the heating current, in particular below the minimum input voltage of the boost converter, so as to temperature-control at least the fuel cell stack.

[0007] A fuel cell stack may have a plurality of interconnected fuel cells for generating an output voltage.

[0008] The fuel cell system can be used, for example, in a motor vehicle, for example in a fuel cell motor vehicle.

[0009] The output voltage generated by the fuel cell stack may be converted and / or stabilized to a higher voltage by a boost converter.

[0010] In particular, the coil and the controllable switch (electrically or electrically) of the at least one converter unit are arranged between a first electrical contact, preferably a positive pole, of the fuel cell stack and a second electrical contact, preferably a negative pole, of the fuel cell stack. Furthermore, at least one converter unit can have a freewheeling diode.

[0011] The boost converter may include a plurality of converter units each having at least one coil and a controllable switch for increasing the output voltage of the fuel cell stack. In other words, the boost converter may be implemented in a multi-phase manner. Therefore, the boost converter may have good efficiency in a wide power range and the filter cost may be kept particularly low. In the case of a plurality of converter units, the heating current for regulating the temperature of at least the fuel cell stack may be distributed, preferably evenly distributed to a plurality of converter units. The so-called details and / or features and / or explanations and / or implementations of at least one converter unit and / or a converter unit or its components may also be transferred to another converter unit or a plurality of converter units, and vice versa. The coil and / or the controllable switch may be particularly understood as a component. In particular, at least one converter unit and another converter unit or a plurality of converter units may be constructed identically or substantially identically. Therefore, the boost converter may be particularly simple and / or cost-effective.

[0012] A boost converter can also be understood as a DC / DC converter (direct current / direct current converter).

[0013] The expression “wherein the controllable switch has a variable resistance” may also be understood as the controllable switch including a resistor having a variable resistance value.

[0014] Preferably, the controllable switch of at least one converter unit has a resistance that is continuously variable at least in sections or a resistance that is substantially continuously variable at least in sections. Therefore, the variable resistance of the controllable switch of at least one converter unit can be freely set and the heating current for temperature control of at least the fuel cell stack can be controlled particularly advantageously. The region in which the controllable switch of at least one converter unit has a resistance that is continuously variable at least in sections or a resistance that is substantially continuously variable at least in sections can be understood as a resistance variation region of the controllable switch of at least one converter unit. In addition, the controllable switch of at least one converter unit can have a blocking region and / or a conducting region, wherein in particular the controllable switch has a maximum resistance in the blocking region and a minimum resistance in the conducting region. In particular, the increase in the output voltage of the fuel cell stack is achieved by (directly) switching back and forth between the blocking region (resistance maximum value) and the conducting region (resistance minimum value) of the controllable switch, in particular repeatedly switching back and forth, of the resistance of the controllable switch of at least one converter. The resistance variation region of the controllable switch of at least one converter unit is particularly located between the blocking region and the conducting region of the controllable switch of at least one converter unit. For example, the controllable switch can be a transistor, in particular a MOSFET transistor or a thyristor, in particular a GTO transistor, which has a blocking region and a saturation region as a conducting region, wherein the transistor, in particular a MOSFET transistor or a thyristor, in particular a GTO transistor, has a continuously variable resistance or at least a substantially continuously variable resistance in sections in the linear region.

[0015] A variable resistance of a controllable switch of at least one converter unit of a step-up converter may be understood to be a resistor, in particular an ohmic resistor.

[0016] The control device can at least control the controllable switch of at least one converter unit in such a way that the resistance of the controllable switch of at least one converter unit or the resistance value of the controllable switch can be adjusted or can be adjusted. Therefore, the heating current for temperature control of at least the fuel cell stack can be adjusted. For example, when a MOSFET transistor is used as a controllable switch, the control device can control the gate-source voltage (Gate-Source-Spannung) of the MOSFET transistor in order to adjust the resistance of the controllable switch of at least one converter unit or the resistance value of the controllable switch. Adjusting the resistance or resistance value of the controllable switch of at least one converter unit can be understood in particular as changing the resistance or resistance value of the controllable switch, for example, between at least one first resistance value and a second resistance value and / or within the resistance change range of the controllable switch of at least one switch unit.

[0017] In addition, the control device can control the controllable switch of another converter unit or the corresponding controllable switches of multiple other converter units in addition to the controllable switch of at least one converter unit in such a way that the resistance of the controllable switch of the corresponding converter unit or the resistance value of the controllable switch can be adjusted or capable of adjustment, preferably independently of each other, for temperature control of at least the fuel cell stack.

[0018] The control device can in particular have a microcontroller at least for controlling a controllable switch of at least one converter unit or for correspondingly controlling controllable switches of a plurality of converter units of the boost converter. Additional circuits can thus be omitted. In addition, the control device can have a heating current distributor, wherein the heating current distributor is designed to calculate the required target heating current for each of the plurality of converter units. In particular, a heating current or a target heating current for the output capacitor of the fuel cell system or the boost converter is predefined or calculated taking into account the load current.

[0019] By configuring the control device to control at least the controllable switch of at least one converter unit or in particular the controllable switches of corresponding converter units of a plurality of converter units respectively in such a way that the variable resistance of the controllable switch of at least one converter unit or the variable resistance of the controllable switch of corresponding converter units of a plurality of converter units can be set or can be set, no additional circuit costs in the form of separate switching elements and separate load resistors are required. In addition, it is particularly advantageous to adjust the temperature of at least the fuel cell stack, in particular below the minimum input voltage of the boost converter, because the heating current can be freely adjusted. In addition, the heating current can be adjusted even when the output voltage of the fuel cell stack is very low, for example during the accelerated operation of the fuel cell system. As a result, the accelerated operation of the fuel cell system can be kept particularly impaired and at the same time particularly short in time.

[0020] Furthermore, controlling the controllable switch by the control device may be understood to mean controlling or actuating the controllable switch by the control device.

[0021] Controlling the heating current may be controlling and / or regulating the heating current.

[0022] It can be advantageous that in the fuel cell system according to the invention the control device is configured to at least temporarily non-clockwise control the controllable switch of at least one converter unit so as to adjust the resistance of the controllable switch for controlling the heating current for temperature control of at least the fuel cell stack. Thus, the control of the controllable switch can be achieved particularly simply. The expression "non-clockwise control" should be expressed as follows: the resistance of the controllable switch of at least one converter unit does not (directly) switch back and forth, in particular repeatedly switch back and forth, at least temporarily, for example at least for (1) second, between the blocking region and the conducting region of the controllable switch. In addition, the control device is particularly configured to at least temporarily non-clockwise control the controllable switch of at least one converter unit at least in a first voltage region. The first voltage region is, for example, from 0V (volts) to the minimum input voltage of the boost converter.

[0023] It can be advantageous that in the fuel cell system according to the present invention, the control device has a regulating unit so as to regulate the heating current for regulating the temperature of at least one fuel cell stack to a target heating current by controlling the controllable switch of at least one converter unit. Therefore, the temperature regulation of at least the fuel cell stack can be particularly advantageous. The regulating unit can have a current measuring unit for detecting the heating current or part of the heating current of the controllable switch of at least one converter unit flowing through the boost converter. The current measuring unit can in particular have at least one measuring resistor and / or an operational amplifier for detecting the heating current or part of the heating current of the controllable switch of at least one converter unit flowing through the boost converter. Therefore, the current measuring unit can be configured particularly simply. In addition, the regulating unit can include a current regulating unit for controlling the controllable switch of at least one converter unit or the resistance of the controllable switch of at least one converter unit, wherein the control of the controllable switch is in particular based on the detected heating current or part of the heating current and based on a predeterminable or predetermined target heating current. In particular, the current regulating unit can include an operational amplifier or the resistance of the controllable switch of at least one converter unit. Therefore, the current regulating unit can be configured particularly simply. The target heating current can be predefined by the operating system, for example.

[0024] It can be advantageous if, in the fuel cell system according to the invention, the controllable switch with variable resistance of at least one converter unit is a transistor, in particular a MOSFET transistor, or a thyristor, in particular a GTO transistor. The controllable switch can thus be designed particularly simply.

[0025] It can be advantageous that in the fuel cell system according to the invention, the control device is also configured to at least temporarily control the controllable switch of at least one converter unit in a clocked manner, in particular between the conducting state and the blocking state of the controllable switch, in order to increase the output voltage of the fuel cell stack and / or control the heating current for temperature control of at least the fuel cell stack. Therefore, the fuel cell system can be configured particularly simply. The expression "clocked control" should be expressed as follows: the resistance of the controllable switch of at least one converter unit is switched back and forth (directly) between the blocking region of the controllable switch, in particular the maximum resistance, and the conducting region of the controllable switch, in particular the minimum resistance, in order to at least increase the output voltage of the fuel cell stack (by means of the coil of at least one converter unit). In addition, the control device is particularly configured to at least temporarily control the controllable switch of at least one converter unit in a clocked manner, at least in a second voltage region different from the first voltage region. The second voltage region is, for example, from the minimum input voltage of the boost converter to the upper voltage limit.

[0026] It can be advantageous that, in the fuel cell system according to the invention, the boost converter comprises at least one further converter unit having at least one coil and a controllable switch for increasing the output voltage of the fuel cell stack, wherein the control device is configured to control the controllable switch of at least one converter and the controllable switch of at least one further converter independently of each other, in particular for controlling a heating current for temperature control of at least the fuel cell stack. With the aid of at least one further converter unit, the boost converter can have good efficiency over a wide power range, and the filter costs can be kept particularly low. Advantageously, by independently controlling the controllable switch of at least one converter unit and the controllable switch of at least one further converter unit, the controllable switch of at least one converter unit can be switched from continuous operation to clocked operation and the controllable switch of at least one further converter unit can be switched from continuous operation to clocked operation with a time delay. The clocked operation of the controllable switch can be understood in particular as the clocked operation of the controllable switch of the converter unit of the boost converter of the fuel cell stack. For example, the resistance of the controllable switch of the converter unit can be switched back and forth (directly), in particular repeatedly, between a blocking region, in particular a maximum resistance, and a conducting region, in particular a minimum resistance, of the controllable switch by means of a control device, so as to at least increase the output voltage of the fuel cell stack (by means of the coil of at least one converter unit). The non-clocked operation of the controllable switch can be understood in particular as a continuous operation of the controllable switch of the converter unit of the boost converter of the fuel cell stack. In particular, in the continuous operation of the controllable switch of the converter unit, the resistance of the controllable switch is in the variable resistance region of the controllable switch. Continuous operation can also be understood as linear operation.

[0027] According to a second aspect, the invention discloses a method for controlling a heating current for temperature control of a fuel cell stack of a fuel cell system, wherein the fuel cell system is designed according to the invention. The method comprises as a step activating the fuel cell stack for generating an output voltage at the fuel cell stack. Furthermore, the method comprises as a step controlling, in particular non-clockwise controlling, a controllable switch of at least one converter unit of a boost converter of the fuel cell system so that the resistance of the controllable switch of at least one converter unit is adjusted for controlling a heating current for temperature control of at least the fuel cell stack.

[0028] The method steps described above and below can, as far as this is technically sensible, be carried out individually, together, once, several times, in parallel in time and / or in any order relative to one another.

[0029] In particular, before the fuel cell stack is activated, the fuel cell stack is deactivated, i.e., for example, no hydrogen and oxygen are supplied. In the deactivated state, the quiescent voltage is short-circuited, in particular as an output voltage, at the terminals of the fuel cell stack. The short-circuit can be realized, for example, by means of a switchable load-reducing resistor or a controllable switch of at least one converter unit of the step-up converter. In order to reduce the quiescent current consumption, it is sufficient to actuate only one controllable switch.

[0030] In order to activate the fuel cell stack, in particular a reducing agent and an oxidizing agent are supplied to the fuel cell stack and, if necessary, short circuits at the connections of the fuel cell stack are eliminated.

[0031] It can be advantageous if, in the method according to the invention, the control device has a regulating unit, wherein the heating current for controlling the temperature control of at least the fuel cell stack is regulated to a target heating current by means of the regulating unit by controlling a controllable switch of at least one converter unit. The temperature control of the fuel cell stack can thus be carried out particularly advantageously.

[0032] It can be advantageous that in the method according to the invention, the controllable switch of at least one converter unit is at least temporarily controlled in a non-clocked manner or operated in continuous operation by a control device in order to set the resistance of the controllable switch for controlling a heating current for temperature control of at least the fuel cell stack, and wherein, after the non-clocked control of the controllable switch, the controllable switch of at least one converter unit is controlled in a clocked manner or operated in a clocked manner by the control device in a manner such that at least the output voltage of the fuel cell stack is increased. Thus, in a first voltage range, for example from 0 V (volts) to the minimum input voltage of the boost converter, the controllable switch of at least one converter unit can be used for a temperature control phase, in particular a heating phase, of the fuel cell system. Furthermore, in a second voltage range, for example from the minimum input voltage of the boost converter to an upper voltage limit, the controllable switch of at least one converter unit can be used to increase and / or stabilize the output voltage of the boost converter. It can be advantageous that in the method according to the invention, the controllable switch of at least one converter unit is clocked by the control device when the output voltage of the fuel cell stack exceeds a certain voltage threshold value and / or the fuel cell stack exceeds a certain temperature threshold value. For example, the determined voltage threshold value may be a minimum input voltage of the step-up converter. The minimum input voltage of the step-up converter is in particular a voltage, starting from which the step-up converter with the voltage boosting function can be started, in particular for control reasons.

[0033] It can be advantageous that in the method according to the invention the fuel cell system comprises at least one further converter unit with at least one coil and a controllable switch for increasing the output voltage of the fuel cell stack, wherein the corresponding controllable switches of at least two converter units of the boost converter of the fuel cell system are controlled, in particular independently of one another, so that the resistance of the controllable switch of the corresponding converter unit is set for controlling a heating current for temperature control of at least the fuel cell stack. The heating current can be distributed via the further converter units with controllable switches and, for example, starting from the output voltage of the fuel cell system, one of the two controllable switches can be used to increase the output voltage, while the controllable switch of the further converter unit is still used for temperature control of at least the fuel cell stack. It can be advantageous that in the method according to the invention the controllable switch of at least one converter unit is switched from continuous operation or linear operation to clocked operation and the controllable switch of at least one further converter unit is switched from continuous operation or linear operation to clocked operation with a time delay. Thus, advantageously, a controllable switch is switched from continuous operation or linear operation to clocked operation after the other controllable switches, and interference caused by the simultaneous switching of a plurality of controllable switches can be prevented in an improved manner. The (corresponding) switch from continuous operation to clocked operation can in particular be such a switch that the controllable switches are clocked or operated in a clocking manner that is itself slowly increasing (so-called soft start).

[0034] It can be advantageous if, in the method according to the invention, the resistance of the controllable switch of at least one converter unit is adjusted as a function of the voltage, in particular the output voltage of the fuel cell stack and / or the minimum input voltage of the step-up converter, and / or the temperature, in particular the temperature of the fuel cell stack, and / or the anode gas quantity and / or the cathode gas quantity and / or the aging of the fuel cell system, for controlling the heating current for temperature control of at least the fuel cell stack. Temperature control of at least the fuel cell stack can therefore be particularly advantageous.

[0035] The method according to the second aspect of the invention thus has the same advantages as have been described for the fuel cell system according to the first aspect of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Further measures for improving the invention are shown below in the description of some exemplary embodiments of the invention, which are schematically shown in the drawings. All features and / or advantages highlighted by the claims, the description or the drawings, including structural details, spatial arrangements and method steps, are important to the invention both individually and in various combinations. It should be noted that the drawings have only descriptive features and are not to be understood as limiting the invention in any way.

[0037] The accompanying drawings schematically show:

[0038] Figure 1 : Circuit diagram of the fuel cell system, and

[0039] Figure 2 : a method, and

[0040] Figure 3 : a method.

[0041] In the following figures, the same reference numerals are used even for the same technical features of different exemplary embodiments. DETAILED DESCRIPTION

[0042] Figure 1 A circuit diagram of a fuel cell system 100 is disclosed. The fuel cell system 100 includes a fuel cell stack 10 for generating an output voltage. In addition, the fuel cell system 100 includes a boost converter 30 for increasing the output voltage of the fuel cell stack 10, wherein the boost converter 30 has at least one converter unit 31a, wherein at least one converter unit 31a includes at least one coil 33 and a controllable switch 34 for increasing the output voltage of the fuel cell stack 10, wherein the controllable switch 34 has a variable resistor, in particular a resistor that is continuously variable at least in sections or a resistor that is substantially continuously variable at least in sections. In addition, the fuel cell system 100 includes a control device 50, wherein the control device is configured to control the controllable switch 34 of at least one converter unit 31a at least in such a way that the variable resistor of the controllable switch 34 of at least one converter unit 31a is set to control a heating current for temperature control of at least the fuel cell stack 10. Advantageously, in Figure 1 The boost converter 30 shown in the figure includes three other converter units 31b, 31c and 31d, which are optional, that is, additional, each having a coil 33 and each having a controllable switch 34. In addition, each converter unit 31a, 31b, 31c, 31d additionally has a freewheeling diode. The controllable switches 34 of the four converter units 31a, 31b, 31c, 31d can be transistors with a blocking region, a linear region as a resistance change region, and a saturation region as a conducting region. In addition, it is conceivable that the controllable switch 34 of at least one converter unit 31a and the controllable switches 34 of the other converter units 31b, 31c, 31d can be controlled independently of each other. Therefore, the controllable switches 34 can be switched to the clocking operation in sequence by means of the corresponding coils 33 to increase the output voltage of the fuel cell stack 10.

[0043] Advantageously, in Figure 1Optionally, i.e. additionally, in the fuel cell system 100 shown, the control device 50 is constructed to at least temporarily non-clockwise control a controllable switch 34 of at least one converter unit 31a, 31b, 31c, 31d in order to adjust the resistance of the controllable switch 34 for controlling a heating current for temperature control of at least the fuel cell stack 10, for example during a heating phase of the fuel cell system 100.

[0044] Advantageously, in Figure 1 The control device 50 shown in the figure optionally, that is, additionally includes a regulating unit 51, so as to regulate the heating current for temperature control of at least the fuel cell stack 10 to a target heating current by controlling the controllable switch 34 of at least one converter unit 31a, 31b, 31c, 31d. The regulating unit 51 may have a current measuring unit 52 for detecting the heating current or part of the heating current flowing through the controllable switch 34 of at least one converter unit 31a of the boost converter 30. In particular, the current measuring unit 52 may have at least one measuring resistor 54 and / or an operational amplifier for detecting the heating current or part of the heating current flowing through the controllable switch of at least one converter unit of the boost converter. In addition, the regulating unit 51 includes a current regulating unit 53 for controlling the controllable switch 34 of at least one converter unit 31a or the resistance of the controllable switch 34 of at least one converter unit 31a.

[0045] Advantageously, in Figure 1 In the fuel cell system 100 shown, the control device 50 is optionally, that is, additionally, also configured to at least temporarily clock-control the controllable switch 34 of at least one converter unit 31a, 31b, 31c, 31d, in particular to control between a conducting state and a blocking state of the controllable switch 34, in order to increase the output voltage of the fuel cell stack 10 and / or to control a heating current for temperature control of at least the fuel cell stack 10. Therefore, the control device 50 can be used not only for non-clock-controlled but also for clock-controlled control of at least the controllable switch 34 of the at least one converter unit 31a and additionally the controllable switch 34 of the other converter units 31b, 31c, 31d.

[0046] Figure 2 A method for controlling a heating current for temperature control of at least one fuel cell stack 10 of a fuel cell system 100 is disclosed, for example Figure 1As described. Advantageously, the fuel cell system 100 is constructed according to the invention. The method comprises activating 320 the fuel cell stack 10 for generating an output voltage on the fuel cell stack 10 as a first step. In addition, the method comprises controlling 340, in particular at least temporarily non-clockwise controlling 340, a controllable switch 34 of at least one converter unit 31a, 31b, 31c, 31d of the boost converter 30 of the fuel cell system 100, so that the controllable switch 34 of at least one converter unit 31a, 31b, 31c, 31d is set to control, in particular to adjust, a heating current for temperature control of at least the fuel cell stack 10 as another step. In addition, it is conceivable to adjust the resistance of the controllable switch 34 of at least one converter unit 31a, 31b, 31c, 31d according to the voltage and / or temperature and / or the anode gas amount and / or the cathode gas amount and / or the aging of the fuel cell system 100 to control the heating current for temperature control of at least the fuel cell stack 10. Furthermore, in the case of a plurality of converter units 31a, 31b, 31d, 31d (see, for example Figure 1 ), the corresponding controllable switches 34 of the plurality of converter units 31a, 31b, 31c, 31d of the boost converter 30 of the fuel cell system 100 can be controlled independently of one another. In addition, in the case of the plurality of converter units 31a, 31b, 31c, 31d, it is conceivable that the controllable switch 34 of at least one converter unit 31a is first switched from continuous operation to clocked operation, and the other controllable switches 34 of the other converter units 31b, 31c, 31d are switched sequentially from continuous operation to clocked operation with a time delay.

[0047] Figure 3 A method for controlling a heating current for temperature control of at least one fuel cell stack 10 of a fuel cell system 100 is disclosed, as in particular in Figure 2 As has been said and described in . The fuel cell system 100 is in particular a fuel cell system 100 according to the present invention. The method comprises as a step activating 320 the fuel cell stack 10 for generating an output voltage on the fuel cell stack 10. Furthermore, in another step of the method, the controllable switch 34 of at least one converter unit 31a, 31b, 31c, 31d is at least temporarily controlled 341 non-clockwise by the control device 50 so as to adjust the resistance of the controllable switch 34 for controlling the heating current for temperature control of the fuel cell stack 10. In another step of the method, after the controllable switch 34 is controlled 341 non-clockwise, the controllable switch 34 of at least one converter unit 31a, 31b, 31c, 31d is at least temporarily controlled 342 clockwise by the control device 50 so as to at least increase the output voltage of the fuel cell stack 10.

Claims

1. A fuel cell system (100), wherein: The fuel cell system (100) comprises: - a fuel cell stack (10) for generating an output voltage, - a step-up converter (30) for increasing the output voltage of the fuel cell stack (10), wherein the step-up converter (30) has at least one converter unit (31a, 31b, 31c, 31d), wherein the at least one converter unit (31a, 31b, 31c, 31d) comprises at least one coil (33) and a controllable switch (34) for increasing the output voltage of the fuel cell stack (10), wherein the controllable switch (34) has a variable resistor, in particular a resistor that is continuously variable at least in sections or a resistor that is substantially continuously variable at least in sections, - A control device (50), wherein the control device is configured to control at least a controllable switch (34) of at least one converter unit (31a, 31b, 31c, 31d) so that a variable resistance of the controllable switch (34) of at least one converter unit (31a, 31b, 31c, 31d) is adjusted to control a heating current for temperature control of at least the fuel cell stack (10).

2. The fuel cell system (100) according to claim 1, It is characterized in that The control device (50) is configured to at least temporarily non-clockwise control a controllable switch (34) of at least one converter unit (31a, 31b, 31c, 31d) in order to adjust the resistance of the controllable switch (34) for controlling a heating current for temperature control of at least the fuel cell stack (10).

3. The fuel cell system (100) according to any one of the preceding claims, It is characterized in that The control device (50) has a regulating unit (51) for regulating the heating current for temperature control of at least the fuel cell stack (10) to a target heating current by controlling a controllable switch (34) of the at least one converter unit (31a, 31b, 31c, 31d).

4. The fuel cell system (100) according to any one of the preceding claims, It is characterized in that The controllable switch (34) having the variable resistor of the at least one converter unit (31a, 31b, 31c, 31d) is a transistor, in particular a MOSFET transistor, or a thyristor, in particular a GTO thyristor.

5. The fuel cell system (100) according to any one of the preceding claims, It is characterized in that The control device (50) is also configured to at least temporarily control a controllable switch (34) of at least one converter unit (31a, 31b, 31c, 31d) in a clocked manner, in particular to control the controllable switch (34) between an on state and a blocked state, in order to increase an output voltage of the fuel cell stack (10) and / or to control a heating current for temperature control of at least the fuel cell stack (10).

6. The fuel cell system (100) according to any one of the preceding claims, It is characterized in that The boost converter (30) comprises at least one further converter unit (31a, 31b, 31c, 31d) having at least one coil (33) and a controllable switch (34) for increasing the output voltage of the fuel cell stack (10), wherein the control device (50) is configured to control the controllable switch (34) of the at least one converter unit (31a, 31b, 31c, 31d) and the controllable switch (34) of the at least one further converter unit (31a, 31b, 31c, 31d) independently of each other, in particular in order to control a heating current for temperature control of at least the fuel cell stack (10).

7. A method for controlling a heating current for temperature control of at least one fuel cell stack (10) of a fuel cell system (100), wherein: The fuel cell system (100) is configured according to any one of the preceding claims, wherein the method comprises: - activating (320) the fuel cell stack (10) for generating an output voltage on the fuel cell stack (10), - Controlling (340), in particular non-clockwise controlling, a controllable switch (34) of at least one converter unit (31a, 31b, 31c, 31d) of a boost converter (30) of the fuel cell system (100) so that the resistance of the controllable switch (34) of the at least one converter unit (31a, 31b, 31c, 31d) is adjusted to control a heating current for temperature control of at least the fuel cell stack (10).

8. The method according to claim 7, It is characterized in that The control device (50) has a regulating unit (51), wherein the heating current used to control the temperature of at least the fuel cell stack (10) is regulated to a target heating current by controlling (340) a controllable switch (34) of at least one converter unit (31a, 31b, 31c, 31d) with the help of the regulating unit (51).

9. The method according to any one of claims 7 or 8, It is characterized in that The control device (50) at least temporarily controls (341) a controllable switch (34) of at least one converter unit (31a, 31b, 31c, 31d) in a non-clockwise manner to adjust the resistance of the controllable switch (34) for controlling a heating current for temperature control of at least the fuel cell stack (10), and wherein, after the controllable switch (34) is controlled (341) in a non-clockwise manner, the control device (50) at least temporarily controls (342) the controllable switch (34) of at least one converter unit (31a, 31b, 31c, 31d) in a clockwise manner to at least increase the output voltage of the fuel cell stack (10).

10. The method according to claim 9, It is characterized in that When the output voltage of the fuel cell stack (10) exceeds a certain voltage threshold and / or the fuel cell stack exceeds a certain temperature threshold, the controllable switch (34) of at least one converter unit (31a, 31b, 31c, 31d) is controlled (342) in a clocked manner by the control device (50).

11. The method according to any one of claims 7 to 10, It is characterized in that The fuel cell system (10) comprises at least one further converter unit (31a, 31b, 31c, 31d) having at least one coil (33) and a controllable switch (34) for increasing the output voltage of the fuel cell stack (10), wherein the corresponding controllable switches (34) of at least two converter units (31a, 31b, 31c, 31d) of the boost converter (30) of the fuel cell system (100) are controlled, in particular independently of each other (340), so that the resistance of the controllable switches (34) of the corresponding converter units (31a, 31b, 31c, 31d) is adjusted to control a heating current for temperature control of at least the fuel cell stack (10).

12. The method according to claim 11, It is characterized in that A controllable switch (34) of at least one converter unit (31a, 31b, 31c, 31d) is switched from continuous operation to clocked operation and a controllable switch (34) of at least one other converter unit (31a, 31b, 31c, 31d) is switched from continuous operation to clocked operation with a time delay.

13. The method according to any one of claims 7 to 12, It is characterized in that The resistance of the controllable switch (34) of at least one converter unit (31a, 31b, 31c, 31d) is adjusted according to the voltage and / or temperature and / or the anode gas amount and / or the cathode gas amount and / or aging of the fuel cell system to control the heating current for temperature control of at least the fuel cell stack (10).

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