Device for electrically interconnecting a fuel cell stack and a high-voltage battery

Abstract

The present invention relates to a device (1) for electrically interconnecting at least one fuel cell stack (2) and at least one high-voltage battery (3), for supplying electrical power to consumers connected to the high-voltage battery (3). The invention is characterized in that the fuel cell stack (2) and the high-voltage battery (3) are interconnected with each other via at least one diode (7) blocking the flow of current in the direction of the fuel cell stack (2) and at least one switch (6) for opening and closing the connection. According to the method, a switch (6) is controlled depending on the voltage of the at least one fuel cell stack (2) on the one hand and the at least one high-voltage battery (3) on the other hand.

Description

Technical Field

[0001] The present invention relates to an apparatus for electrically interconnecting at least one fuel cell stack and at least one high-voltage battery in a fuel cell system of the type more particularly defined by the preamble of claim 1. Further, the present invention relates to a method for operating such an apparatus.

Background Art

[0002] The distribution of energy in a fuel cell system is usually carried out via a so-called Fuel Cell Interface comprising at least one DC converter or DC / DC converter. These interfaces are often provided in the area of the fuel cell or its housing itself. Basically, such a structure is known from Patent Document 1. In this connection, Patent Document 2 can also be referred to.

Patent Document 1

Patent Document 2

[0003] A power system optimized in terms of safety and equipped with such a fuel cell interface is described in Patent Document 3. Here, behind the DC converter, and thus between the DC converter and the battery, an emergency cut-off mechanism for the battery by means of a battery protection switch is realized. The fuel cell itself is arranged on the opposite side of the DC converter and is equipped with an emergency discharge device.

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, the problem of the present invention is basically to further simplify this structure of the fuel cell interface (FCI) which is basically known from the prior art.

Means for Solving the Problem

[0005] According to the present invention, this problem is solved by the device having the features of claim 1, here particularly the features of the characterizing part of claim 1. Advantageous forms and further developments of the device are obtained from the dependent claims subordinate thereto.

[0006] The device according to the present invention eliminates the need for the conventional DC / DC converter described in the prior art as a boost converter / buck converter in the interconnection of the high-voltage battery and the fuel cell stack. A simple fuel cell power interface can be realized by at least one diode that blocks the flow of current from the high-voltage battery to the fuel cell stack, and by at least one switch, particularly a contactor, for the connection between the high-voltage battery and the fuel cell stack. The device or fuel cell power interface according to the present invention solves the above-mentioned problems in a very cost-effective way that does not require a converter or a pre-charge circuit. Furthermore, by eliminating the converter, current ripple acting on the fuel cell stack, which cannot be avoided when using a converter, does not occur. Since current ripple places a great burden on the fuel cell stack, eliminating the DC / DC converter also increases the life of the fuel cell stack. Furthermore, by eliminating the converter, the power distribution efficiency can be made relatively low. Therefore, the overall efficiency can be improved.

[0007] The very simple interconnection of the device according to the present invention enables, in addition to an increase in the efficiency and life of the fuel cell stack, a reduction in weight compared to current concepts and implementations, and a unique interface, reducing the effort in adapting the fuel cell stack. Furthermore, by eliminating the DC / DC converter, reduction of installation space and cost can be achieved.

[0008] The present invention realizes the advantage of having very strong competitiveness in terms of reducing weight, cost, and installation space, as well as improving the efficiency and lifespan of a fuel cell system equipped with a fuel cell power interface according to the present invention. Therefore, a very advantageous development form of the present invention contemplates that the interconnection is performed without a converter.

[0009] The device according to the present invention is suitable for both truck applications and stationary fuel cell systems. In particular, when used in a mobile system such as a truck, according to a very advantageous development form, it can be contemplated that emergency stop equipment for at least one fuel cell stack is provided. Such emergency stop equipment can, for example, disconnect the fuel cell stack from the high-voltage battery and preferably short-circuit it during an accident to prevent danger.

[0010] According to a very advantageous development form, the emergency stop equipment in the device according to the present invention may be configured as an explosive actuator or may include an explosive actuator and may be connected to an external communication interface. Such an explosive actuator can be connected, for example, to a collision sensor of a vehicle equipped with this device. During an accident, for example, when the airbag is activated, a signal can be transmitted to the device according to the present invention in the above-mentioned advantageous development form through this sensor system to activate the explosive actuator, connect the poles of the fuel cell stack, and thus short-circuit it.

[0011] Here, a further very advantageous form of the device according to the present invention contemplates that the control mechanism of the switch is connected to an external communication interface and the switch is configured particularly as a line switch or a contactor. This connection may be different, in particular, from the connection of the explosive actuator in the above-mentioned form. Here, this switch is typically realized as a battery protection switch configured as a contactor, and connects and disconnects the two poles of the electrical connection according to the control signal of the external communication interface.

[0012] Here, a particularly preferred form of the device according to the present invention contemplates equipment for detecting the voltages of the fuel cell stack and the high-voltage battery. These pieces of equipment, each arranged on the fuel cell stack side and the high-voltage battery side of the switch, enable the voltages of the fuel cell stack and the high-voltage battery to be detected independently of each other when the switch is open. Furthermore, an ammeter can also be made part of the device.

[0013] Here, in this structure, according to a very advantageous development, it may be contemplated that the control mechanism of the switch, or an external control mechanism connected by a communication interface, is designed to operate the switch according to the voltages detected by the equipment for detecting the voltages of the fuel cell stack and the high-voltage battery. The voltages are ultimately used for the control of the switch, which also simplifies and makes the control efficient accordingly.

[0014] Here, a further very advantageous form of the device according to the present invention further contemplates that at least one electrical connection protected via a fuse for auxiliary units of the fuel cell system, i.e., for example, an air conveyance mechanism or a hydrogen recirculation blower, etc., is provided between the diode and the battery connection. Thus, power can also be directly supplied to these components via the device and be protected by the fuses in the device. According to an advantageous embodiment, in order to keep the structure simple and compact, the consumer device itself may be connected via the battery connection or in parallel with the high-voltage battery.

[0015] Here, the entire device can be integrated into a common housing configured to be attached particularly to the fuel cell, i.e., the fuel cell stack. Thus, the fuel cell power interface is incorporated into the structure of the fuel cell stack, particularly its housing, thereby reducing the labor of cable wiring work and realizing a single efficient interface module by the device according to the present invention.

[0016] Here, the method according to the present invention serves to operate such a device in any of the above-described configurations. Here, according to the present invention, it is contemplated that the switch is controlled in accordance with the voltage of at least one fuel cell stack on the one hand and the voltage of at least one high-voltage battery on the other hand. Here, these voltages, which are measured in any case, enable the implementation of a very simple and efficient control.

[0017] Here, according to a highly preferred form of the method, it may be contemplated that the switch is closed before the voltage of the fuel cell stack reaches the voltage of the high-voltage battery. Here, the diode prevents the flow of current in the direction of the fuel cell stack. When the voltage of the fuel cell stack rises, the current begins to flow to the high-voltage battery or the consumer device. Protection of the fuel cell stack by the diode can eliminate the pre-charge of the high-voltage intermediate circuit. The simple interconnection by the device according to the present invention results in a simple self-regulating system.

[0018] Further advantageous forms of the device and its method of operation according to the present invention are also obtained from the exemplary embodiments, which will be described in more detail below with reference to the drawings.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0020] Device 1 functions as a fuel cell power interface and, referring to the illustration of FIG. 1, is disposed between the suggested fuel cell stack 2 and the high voltage battery denoted by reference number 3. Device 1 can be disposed, in particular, within a housing 4 which is not specifically shown here but merely suggested, and the housing 4 is designed, in particular, to be connected to the fuel cell stack 2. Device 1 as a fuel cell power interface is also suitable for truck applications and stationary fuel cell systems. In contrast to the state of the art, in this novel concept, a DC / DC converter (boost converter) is not used to convert the voltage between the fuel cell stack 2 and the high voltage battery 3.

[0021] Device 1 as a cost-effective and space-saving fuel cell power interface can efficiently connect the fuel cell stack 2 to the high voltage battery 3 to charge the high voltage battery 3 or supply current to the application shown here as the consumer device or main consumer device 5. The fuel cell power interface according to FIG. 1 includes a switch 6, in particular a battery safety switch, which is formed from contacts for switching the two poles of the connection between the fuel cell stack 2 and the high voltage battery 3. Further, the fuel cell power interface includes at least one diode 7 and a connection 14 for an external power supply of the auxiliary unit. These are protected via fuses within device 1 which are not shown in detail. Further, two interfaces 8, 9 are provided for external communication. Further, there are devices 10, 11 for detecting the voltages on the fuel cell stack 2 side and the high voltage battery 3 side respectively, and an ammeter 12.

[0022] In the case of mobile applications, device 1 further includes a pyrotechnic locking device as an emergency stop device 13. The pyrotechnic locking device is required to short-circuit the circuit for the fuel cell stack 2 when it is necessary to disconnect the high voltage battery 3 from the fuel cell stack 2 in case of an accident. The emergency stop device 13 is connected to one of the external communication interfaces 9 and can be controlled via the external communication interface 9, for example when generating a signal for activating an airbag.

[0023] Switch 6 is configured in the form of two synchronous switching switches or contacts, one for each pole. Hereinafter, these are represented as "one" switch 6, but both are meant in each case. Switch 6 is required to switch on the high-voltage battery 3 at the start of the fuel cell stack 2. Diode 7 protects the fuel cell stack 2 by preventing current from flowing back into the fuel cell stack 2.

[0024] As long as the voltage on the fuel cell stack 2 side is lower than the voltage on the high-voltage battery 3 side, switch 6 is closed. Here, diode 7 protects the fuel cell stack 2 from negative current. Current flows to the high-voltage battery 3 or the consumer device 5 only when the voltage on the fuel cell stack 2 side has risen. By protecting the fuel cell stack 2 with diode 7, the pre-charge of the HV intermediate circuit can be omitted.

[0025] By interconnecting the fuel cell stack 2 and the high-voltage battery 3 via the fuel cell power interface of device 1, a self-regulating fuel cell system is obtained. The self-regulation of a fuel cell system with consumer devices is shown below using the example of truck applications.

[0026] Here, assume a high-voltage battery 3 with a short-term maximum output of 400 kW and a constant internal resistance of 80 mOhm. The assumed drive unit includes two drive mechanisms, each with a continuous power of 230 kW (total 460 kW) and a peak power of 330 kW (total 660 kW). As the fuel cell stack 2, two fuel cell stacks connected in series, each with 245 individual fuel cells, are assumed. Four different scenarios are considered below in this regard.

[0027] The first scenario describes a truck operating at a constant speed of 80 - 100 km / h in a fuel cell system. For this, the truck requires one drive unit with a drive power of approximately 120 kW. For ease of understanding, in Figure 2, the current flow i is shown in a very simplified manner. The current i 2 represents the current from the fuel cell stack 2, and the current i 3 represents the current from or to the high - voltage battery 3 depending on whether it is being charged or discharged, and the current i 5 represents the current to the consumer device 5. The circles V shown represent the respective associated voltages. Figure 3 shows the polarization curve profile of a supposed structure having two fuel cell stacks 2 connected in series. The polarization curve is represented by the reference number 15. Further, three simplified characteristic curves 16 of the high - voltage battery 3 are shown for different states of charge. Here, the battery characteristic curve with the reference number 16.1 represents a 10% charge level, the battery characteristic curve with the reference number 16.5 represents a 50% charge level, and the battery characteristic curve with the reference number 16.9 represents a 90% charge level. The characteristic curves 16 are shown such that the high - voltage battery 3 is charged on the right side of the graph and supplies power to the consumer device 5 on the left side of the graph. To supply the corresponding 120 kW of power to the drive mechanism, the following states occur according to Figure 3.

[0028] When the charge level of the high-voltage battery 3 is 90%, a voltage of 740 V is generated. Here, the power of 120 kW used by the consumer device is obtained from 40 kW supplied from the high-voltage battery 3 and 80 kW supplied from the fuel cell stack 2. This is shown in the table of Figure 4. When the charge level of the high-voltage battery 3 is 50%, the voltage is 685 V. Here, the high-voltage battery 3 is charged at 80 kW, which means that the fuel cell stack 2 generates 200 kW. At a charge level of 10%, the voltage is 610 V. Here, the charging power of the high-voltage battery becomes 190 kW. Therefore, the charging of the high-voltage battery 3 is automatically adjusted. When the high-voltage battery 3 has a low charging power, the high-voltage battery 3 is supplied with high power by the fuel cell stack 2. As the charge level of the high-voltage battery 3 increases, the fuel cell stack 2 decreases its generated power. By reducing the power of the fuel cell stack 2, its efficiency, and ultimately its lifespan also increase simultaneously. The table in Figure 4 clearly shows these three states.

[0029] In the second scenario, the truck is stopped. Therefore, the drive mechanism does not consume energy, and all the energy of the fuel cell stack 2 can be used to charge the high-voltage battery 3. In the graph of Figure 3, it is to the right of the zero line. Here, the table is omitted. At a charge level of 90%, a voltage of approximately 750 V is generated, whereby the high-voltage battery 3 is charged at approximately 70 kW. When the high-voltage battery 3 has a charge level of 50%, a voltage of 690 V is generated, and the high-voltage battery 3 is charged at 180 kW. At a rather low charge level of 10%, a voltage of approximately 620 V is generated, and the high-voltage battery 3 is charged at 280 kW.

[0030] The third scenario describes a consumption of 460 kW at the continuous output of the drive mechanism, and the fourth scenario describes 660 kW regarding the peak power of the drive mechanism. Both scenarios 3 and 4 are summarized in the table of Figure 5.

[0031] Here, in Scenario 3, it should be noted that when the charge level of the high-voltage battery 3 is low, specifically only when the charge level is 10%, the continuous power cannot be fully drawn. In Scenario 4, it shows that the maximum power of 660 kW can be drawn only when the charge level of the high-voltage battery 3 is 50%. On the other hand, if the charge level of the high-voltage battery 3 is too high or too low, the maximum performance of the fuel cell system is limited.

Claims

1. An apparatus (1) for electrically interconnecting at least one fuel cell stack (2) and at least one high-voltage battery (3), wherein in said apparatus (1) for supplying power to a consumer device connected to the side of said high-voltage battery (3), said fuel cell stack (2) and said high-voltage battery (3) are interconnected to each other via at least one diode (7) that blocks the flow of current in the direction of said fuel cell stack (2), and at least one switch (6) for opening and closing said connection, said interconnection is made without a converter, the control mechanism of said switch (6) is connected to an external communication interface (8), and said switch (6) is configured as a line switch or contact, in particular for both poles of said connection, devices (10, 11) are provided for detecting the voltages of said fuel cell stack (2) and said high-voltage battery (3), the control mechanism of said switch (6), or an external control mechanism connected to said external communication interface (8), is designed to operate said switch (6) in response to the voltages detected by said devices (10, 11) for detecting the voltages of said fuel cell stack (2) and said high-voltage battery (3), and the control mechanism of said switch (6), or the external control mechanism connected to said external communication interface (8), is designed to close said switch (6) before the voltage of said fuel cell stack (2) reaches the voltage of said high-voltage battery (3), said apparatus (1).

2. The apparatus (1) according to claim 1, characterized in that an emergency stop device (13) is provided for said at least one fuel cell stack (2).

3. The apparatus (1) according to claim 2, characterized in that said emergency stop device (13) comprises an explosive actuator and is connected to an external communication interface (9).

4. At least one electrical connection (14) protected via at least one fuse for an auxiliary unit of a fuel cell system is provided between said diode (7) and said high-voltage battery (3), and a consumer device (5) is connected via the battery connection of said apparatus (1). The apparatus (1) according to any one of claims 1 to 3.

5. A method of operating the apparatus (1) according to any one of claims 1 to 3, wherein on the one hand, the switch (6) is controlled in response to the voltage of the at least one fuel cell stack (2) and on the other hand, the voltage of the at least one high-voltage battery (3), and the switch (6) is closed before the voltage of the fuel cell stack (2) reaches the voltage of the high-voltage battery (3).

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