Vehicle electrical systems with coupling via a DC-DC converter

Abstract

Motor vehicle (1) with an electrical high-voltage electrical system (2) in which a first high-voltage voltage (9) is provided during operation, and with an electrical low-voltage electrical system (3) in which a low-voltage voltage (13) is provided during operation, wherein the high-voltage electrical system (2) and the low-voltage electrical system (3) are coupled via a converter device (4) which has: - a high-voltage connection (10) for receiving the first high-voltage voltage (9) of the high-voltage on-board network (2), - a low-voltage connection (15) for supplying the low-voltage voltage (13) to the low-voltage on-board network (3), - a DC-DC converter (16) for generating the low-voltage voltage (13), characterized in that the converter device (4) comprises a converter stage (17) distinct from the DC-DC converter (16), which is designed to convert the first high-voltage voltage (9) into a lower second high-voltage voltage (19), wherein the high-voltage terminal (10) is connected to the converter stage (17), and an output (18) of the converter stage (17) is connected to the DC-DC converter (16), and the DC-DC converter (16) is connected to the low-voltage terminal (15), and the DC-DC converter (16) is designed to generate the low-voltage voltage (13) from the second high-voltage voltage (19), and wherein the high-voltage electrical system (2) includes a high-voltage battery (5) and an electric drive unit (6) with a power converter (7) and an electric motor (8) and the converter device (4) has a connection (25) to which a vehicle component (24) is connected to the converter device (4), the connection (25) being electrically connected to the output (18) of the converter stage (17).

Description

[0001] The invention relates to a motor vehicle with a converter device. The converter device enables the high-voltage electrical system of the motor vehicle to be coupled with a low-voltage electrical system of the motor vehicle in order to transfer electrical power, at least from the high-voltage electrical system to the low-voltage electrical system. For this purpose, the converter device comprises a DC-DC converter.

[0002] A motor vehicle with a converter device of the type mentioned is known, for example, from DE 10 2010 001 239 A1. According to this patent, the high-voltage electrical system of the motor vehicle can have at least one high-power consumer, for example, an electric air conditioning compressor, an electric heating system, or an electric motor. The low-voltage electrical system is coupled to the high-voltage electrical system via a converter device, which can be designed as a buck converter.

[0003] Today's high-voltage electrical systems operate at voltages ranging from 150 to 475 volts. To continue meeting the increasing power demands of these high-power consumers, a higher voltage level than the aforementioned 775 volts is currently being considered. This would necessitate that all components, i.e., the aforementioned high-power consumers, supplied by the high-voltage system, be designed for the new, higher voltage level. Another disadvantage of increasing the high-voltage voltage is that the high-voltage input of the converter unit would also need to be adapted. A switching element is typically provided at the high-voltage input to switch the high-voltage voltage for the voltage conversion. For safety reasons, the blocking voltage of this switching element is higher than the aforementioned 475 volts, for example, 650 volts.Switching elements with such a blocking voltage are readily available and inexpensive in the prior art. Furthermore, these switching elements exhibit a low through-resistance Rdson, which is available in a range down to 65 milliohms.

[0004] If one attempts to provide a high-voltage electrical system with a higher high voltage than currently common, the blocking voltage of the switching elements must also be increased accordingly. However, there are currently only a few semiconductor-based switching elements with a suitable blocking voltage. Furthermore, these switching elements have not yet been developed to the point where they exhibit a low through-resistance (Rdson). Switching elements with a sufficiently high blocking voltage for the higher high voltages exhibit a through-resistance up to 70 times greater. This results in an unacceptably high power loss in these switching elements during the conversion of the high voltage to the low voltage.

[0005] Furthermore, the increase in high-voltage voltage also results in the described necessity to redesign the high-performance components accordingly, for example, by increasing the blocking voltage.

[0006] Further motor vehicles with high-voltage and low-voltage electrical systems and intermediate converter devices are known from DE 10 2010 001 238 A1 and DE 10 2013 206 298 A1.

[0007] German patent DE 10 2008 047 502 A1 describes a motor vehicle in which a fuel cell stack and a high-voltage battery are each connected to a high-voltage intermediate circuit via a DC-DC converter. A 12V electrical system can be supplied from the high-voltage intermediate circuit via a further DC-DC converter.

[0008] German patent DE 10 2007 024 567 A1 discloses a motor vehicle in which a fuel cell stack and a high-voltage battery are coupled to electric motors via an integrated circuit unit. This circuit unit may include DC-DC converters and a power converter.

[0009] The invention is based on the objective of meeting the growing power demands of high-performance consumers in a high-voltage electrical system.

[0010] The problem is solved by the subject matter of the independent patent claim. Advantageous further developments of the invention are given by the features of the dependent patent claims.

[0011] The invention provides a motor vehicle with a converter device. As described, the converter device has a high-voltage connection for receiving a first high-voltage voltage from a high-voltage electrical system and a low-voltage connection for supplying a low-voltage voltage to a low-voltage electrical system. A DC-DC converter is provided for generating the low-voltage voltage.

[0012] To provide a higher initial high-voltage voltage in the high-voltage electrical system, the invention provides an additional converter stage, separate from the DC-DC converter, designed to convert the initial high-voltage voltage of the high-voltage electrical system into a lower second high-voltage voltage. The DC-DC converter is designed to generate the low-voltage voltage from the second high-voltage voltage. The second high-voltage voltage is, in particular, less than 90 percent of the initial high-voltage voltage. In other words, the initial high-voltage voltage is converted or reduced by the converter stage to the second high-voltage voltage, and then the second high-voltage voltage is converted to the low-voltage voltage by the DC-DC converter. In the context of the invention, "high-voltage voltage" is understood to mean, in particular, an electrical voltage greater than 60 volts.A low-voltage voltage is, in particular, an electrical voltage that is less than 60 volts. The first high-voltage voltage is, in particular, greater than 600 volts, for example, in the range of 600 volts to 1,000 volts. The second high-voltage voltage is, in particular, less than 600 volts, for example, 475 volts. Thus, the DC-DC converter can advantageously be a conventional DC-DC converter known from the prior art, designed for operation at a high-voltage voltage such as is currently common in the prior art. In other words, the DC-DC converter does not need to be modified to switch a higher high-voltage voltage. The described electrical voltages are defined, in particular, with respect to the respective ground potentials of the high-voltage and low-voltage electrical systems.

[0013] The converter device comprises the DC-DC converter and the converter stage. The high-voltage connection is connected to the converter stage. An output of the converter stage is connected to the DC-DC converter. The DC-DC converter is connected to the low-voltage connection.

[0014] To operate a vehicle component with the second high-voltage supply, the converter device has a connection to which the vehicle component is connected. This connection is electrically linked to the output of the converter stage.

[0015] The invention also includes optional further developments whose features provide additional advantages.

[0016] According to a further development, the converter stage for transmitting the second high-voltage voltage is galvanically connected to the DC-DC converter. This has the advantage that the converter stage and the DC-DC converter are at the same potential, meaning that no drift of the electrical potential can occur, as is possible with galvanic isolation.

[0017] One further development involves designing the converter stage as a buck converter or step-down converter. In other words, no bidirectional conversion from the second high-voltage voltage back to the first high-voltage voltage is provided. This further development has the advantage that the converter stage can be implemented with minimal circuitry.

[0018] According to a further development, the converter stage includes a switching element for switching the first high-voltage voltage, wherein the switching element's reverse voltage is lower than the first high-voltage voltage. For example, the switching element can be a transistor, in particular a MOSFET (metal-oxide semiconductor field-effect transistor). Reverse voltage is defined as the electrical voltage that can drop across or be applied to the switching element without causing it to become electrically conductive and / or be destroyed. This further development offers the advantage that the switching element can be selected independently of the value of the first high-voltage voltage. In particular, even with a high value of the first high-voltage voltage, for example, greater than 600 volts, a switching element can be used that, as described above, has a forward resistance Rdson of less than 100 milliohms.

[0019] According to further development, the DC-DC converter also includes a switching element for switching the second high-voltage voltage. This switching element also has a blocking voltage, which is lower than that of the first high-voltage voltage. In other words, the DC-DC converter does not need to be designed to completely block the electrical voltage between the high-voltage and low-voltage electrical systems. The switching element of the DC-DC converter can also be a transistor, particularly a MOSFET. Switching the voltage means that a current flowing through or across the switching element can be interrupted by opening the switching element or by transferring the switching element to an electrically blocking state, at which point the electrical voltage driving the current drops across the switching element.

[0020] According to a further development, a connection is provided to supply an external vehicle component with the second high-voltage voltage. "External" in this context means that the component is different from the converter device. For example, one of the described high-power consumers of a high-voltage electrical system, such as an air conditioning compressor, can be connected to this connection. This further development offers the advantage that even when a higher value is set for the first high-voltage voltage, a high-power consumer designed for operation at the second high-voltage voltage can still be connected via the additional connection. This allows the vehicle to be manufactured without having to adjust the high-power consumer to the new value for the first high-voltage voltage of the high-voltage electrical system.

[0021] According to a further development, the converter stage is housed in a separate enclosure, distinct from the DC-DC converter's enclosure. This makes the converter stage advantageously available as a retrofit component that can be connected to the DC-DC converter without additional development effort.

[0022] An alternative design proposes arranging the converter stage and the DC-DC converter in a single housing, which then incorporates the described high-voltage and low-voltage connections. This offers the advantage that no complex shielding is required in the connection area between the converter stage and the DC-DC converter. The shielding can then be provided by the shared housing. This shared housing preferably also includes the aforementioned connection for attaching the external vehicle component.

[0023] The motor vehicle also has a high-voltage electrical system, in which the first high-voltage voltage is provided during operation. Furthermore, the motor vehicle has a low-voltage electrical system, in which a low-voltage voltage is provided during operation. The high-voltage voltage is higher than the low-voltage voltage and, for example, higher than 600 volts. The low-voltage voltage is, in particular, lower than 60 volts; for example, it is 14 volts or 12 volts. In the motor vehicle according to the invention, the high-voltage and low-voltage electrical systems are coupled via a converter device, which represents one embodiment of the converter device according to the invention.

[0024] The high-voltage electrical system includes a high-voltage battery and an electric drive unit with a power converter and an electric motor.

[0025] According to a further development, an output of the converter stage of the converter device, at which the converter stage generates a second high-voltage voltage during operation, is connected to a vehicle component of the motor vehicle. The second high-voltage voltage is, as described, lower than the first high-voltage voltage. The vehicle component is, in particular, an air conditioning compressor. The second high-voltage voltage is also, in particular, higher than 60 volts. The air conditioning compressor thus represents a high-voltage component or, as described at the outset, a high-power consumer. The air conditioning compressor does not necessarily have to be designed for operation on the vehicle's high-voltage electrical system, i.e., for operation at the first high-voltage voltage. The air conditioning compressor is therefore preferably designed only for a supply voltage lower than the first high-voltage voltage.

[0026] The motor vehicle according to the invention is preferably designed as a motor vehicle, in particular as a passenger car.

[0027] An embodiment of the invention is described below. The single figure (Fig.) shows a schematic representation of an embodiment of the motor vehicle according to the invention.

[0028] The embodiment described below is a preferred embodiment of the invention. In this embodiment, the described components each represent individual features of the invention that can be considered independently of one another. Each of these features further develops the invention independently and can therefore be considered part of the invention individually or in a combination other than that shown. Furthermore, the described embodiment can also be supplemented by other features of the invention already described.

[0029] The figure shows a motor vehicle 1, which could be, for example, a car, in particular a passenger car. A high-voltage electrical system 2 and a low-voltage electrical system 3 are shown. The electrical systems 2 and 3 are connected or coupled to each other via a converter device 4. The high-voltage electrical system 2 can, for example, include a high-voltage battery 5 and an electric drive unit 6 with a power converter 7 and an electric motor 8. The power converter 7 can, for example, be an active inverter to generate a multi-phase, in particular three-phase, alternating voltage from a first high-voltage voltage 9 of the high-voltage electrical system 2 for operating the electric motor 8. The first high-voltage voltage 9 can, for example, be generated by the high-voltage battery 5. The high-voltage electrical system 2 can be connected to a high-voltage terminal 10 of the converter device 4.

[0030] The low-voltage electrical system 3 can, for example, include a battery 11 and electrical loads 12, which are represented in the figure by a single element. The battery 11 can generate a low-voltage voltage 13 in the low-voltage electrical system 3.

[0031] The voltages 9 and 13 mentioned above can, for example, be referenced to a ground potential 14 for the high-voltage network 2 and a ground potential 14' for the low-voltage electrical system 3. The electrical consumers 12 can, for example, be at least one of the following: a direction indicator, a brake booster, a power steering system, or a radio. The low-voltage electrical system 3 can be connected to the converter device 4 via a low-voltage output 15.

[0032] The first high-voltage voltage 9 is a DC voltage and can, for example, have a value greater than 600 volts. In this example, we can assume that the first high-voltage voltage 9 has a value of 850 volts. The low-voltage voltage 13 is a DC voltage and can have a value less than 60 volts. In this example, we can assume that the low-voltage voltage 13 has a value of 12 volts.

[0033] The converter device 4 allows electrical energy to be transferred from the high-voltage electrical system 2 to the low-voltage electrical system 3. For this purpose, the converter device 4 comprises a DC-DC converter 16 and a converter stage 17. The high-voltage connection 10 is connected to the converter stage 17. An output 18 of the converter stage 17 is connected to the DC-DC converter 16. The DC-DC converter 16 is connected to the low-voltage output 15. The converter stage 17 generates a second high-voltage voltage 19 from the first high-voltage voltage 9. The second high-voltage voltage 19 is converted into the low-voltage voltage 13 by the DC-DC converter 16. The second high-voltage voltage 19 is a DC voltage and has a value greater than 60 volts. The second high-voltage voltage 19 is lower than the first high-voltage voltage 9. In this example, it can be assumed that the second high-voltage voltage 19 has a value of 475 volts.

[0034] The converter stage 17 can generate the second high-voltage voltage 19 from the first high-voltage voltage 9 by comprising a switching element 20, an inductor element 21, and a current valve 22. The current valve 22 can be formed by another switching element or a diode. By periodically switching the switching element 20, a buffer capacitor 23 can be charged to the second high-voltage voltage 19 via the inductor element 21. If the current valve 22 also has a switching element, the switching elements 20 and 22 are switched alternately. A circuit with a corresponding switching function can be provided for this purpose. The inductor element 21 can, for example, be based on an electrical coil and a soft magnetic coil core. The switching element 20 and the optional switching element for the current valve 22 can each be, for example, a transistor, in particular a MOSFET.

[0035] The DC-DC converter 16 can be designed in a manner known per se. In particular, it can be a DC-DC converter of a type also used in motor vehicles that have a high-voltage electrical system which is operated exclusively with the second high-voltage voltage 19, i.e., which does not have a voltage level greater than the second high-voltage voltage 19.

[0036] The motor vehicle 1 may also be equipped with a vehicle component 24, which is operated using the second high-voltage voltage 19 in the motor vehicle. The vehicle component 24 may, for example, be an air conditioning compressor. To operate the vehicle component 24 with the second high-voltage voltage 19, the converter device 4 may have a connection 25 to which the vehicle component 24 is connected. The connection 25 may be electrically connected to the output 18 of the converter stage 17.

[0037] In the converter device 4, the blocking voltage of the switching element 20 can be lower than the first high-voltage voltage 9. The switching element 20 only needs to be capable of blocking or switching a voltage corresponding to the difference between the first high-voltage voltage 9 and the second high-voltage voltage 19. Similarly, components of the DC-DC converter 16 can be designed such that the blocking voltage of, for example, a switching element of the DC-DC converter 16 is lower than the first high-voltage voltage 9. The DC-DC converter 16 is specifically designed to operate at the second high-voltage voltage 19, but not at the first high-voltage voltage 9. In other words, the operating voltage of the DC-DC converter 16 is lower than the first high-voltage voltage 9.

[0038] By placing converter stage 17 upstream of the DC-DC converter 16, the circuit of the currently known DC-DC converter is extended, for example, to allow operation at 475 volts. Converter stage 17 can be galvanically connected to the DC-DC converter 16. Converter stage 17 is preferably designed as a buck converter. This interconnected converter stage 17, which is particularly easy to implement technically, converts the input voltage at the high-voltage input 10, i.e., the first high-voltage voltage 9, from the first high-voltage voltage 9 (e.g., 850 volts) to the already known high-voltage range, namely the second high-voltage voltage (e.g., 475 volts). A tap for supplying power to a vehicle component, such as an air conditioning compressor, can then be provided via this voltage level within the device. This tap is implemented via terminal 25.This allows the second high-voltage voltage 19 to be routed externally, i.e., outside the converter device 4. The DC-DC converter 16 is provided as the second converter stage, converting the second high-voltage voltage 19 into the low-voltage voltage 13, for example, from 475 volts to 12 volts. This technology is already known and can be derived from the prior art. Therefore, this part of the converter stage can be adopted entirely from an existing solution.

[0039] The additional converter stage 17 from the first high-voltage voltage 9 to the second high-voltage voltage 19 can be implemented cost-effectively and with optimized power losses. The resulting additional costs for providing the vehicle 1 with a voltage level defined by the first high-voltage voltage 9 can be more than offset by eliminating the need for a separate DC-DC converter for operating the vehicle component 24, in particular an air conditioning compressor. A conventional air conditioning compressor suitable for operation at the second high-voltage voltage 19 can still be used; therefore, no new development for an 850-volt air conditioning compressor is required.The second conversion stage in the form of the DC-DC converter 16 (for example from 475 volts to 12 volts) can be adopted from the already known, mass-produced DC-DC converter, thus further increasing economies of scale in production.

[0040] Overall, the converter device 4, through the described modular approach consisting of converter stage 17 and DC-DC converter 16 and the use at the voltage level of the second high-voltage voltage 19 for the operation of the vehicle component 24, can contribute to a large reuse of common parts in the development of the motor vehicle 1.

[0041] The converter stage 17 can be provided in its own housing, which is connected upstream of the DC-DC converter 16, or the converter stage 17 and the DC-DC converter 16 can be provided in a common housing.

[0042] Overall, the example shows how the invention can provide an 850V to 12V DC to DC converter with a 400V air conditioning compressor output.

Claims

[1] Motor vehicle (1) with a high-voltage electrical system (2) in which a first high-voltage voltage (9) is provided during operation, and with a low-voltage electrical system (3) in which a low-voltage voltage (13) is provided during operation, wherein the high-voltage electrical system (2) and the low-voltage electrical system (3) are coupled via a converter device (4) which comprises: - a high-voltage connection (10) for receiving the first high-voltage voltage (9) of the high-voltage on-board network (2), - a low-voltage connection (15) for supplying the low-voltage voltage (13) to the low-voltage on-board network (3), - a DC-DC converter (16) for generating the low-voltage voltage (13), characterized by , that the converter device (4) comprises a converter stage (17) distinct from the DC-DC converter (16), which is designed to convert the first high-voltage voltage (9) into a lower second high-voltage voltage (19), wherein the high-voltage terminal (10) is connected to the converter stage (17), and an output (18) of the converter stage (17) is connected to the DC-DC converter (16), and the DC-DC converter (16) is connected to the low-voltage terminal (15), and the DC-DC converter (16) is designed to generate the low-voltage voltage (13) from the second high-voltage voltage (19), and wherein the high-voltage electrical system (2) includes a high-voltage battery (5) and an electric drive unit (6) with a power converter (7) and an electric motor (8) and the converter device (4) has a connection (25) to which a vehicle component (24) is connected to the converter device (4), the connection (25) being electrically connected to the output (18) of the converter stage (17). [2] Motor vehicle (1) according to claim 1, wherein the converter stage (17) for transmitting the second high voltage voltage (19) is galvanically connected to the DC-DC converter (16). [3] Motor vehicle (1) according to one of the preceding claims, wherein the converter stage (17) is designed as a buck converter. [4] Motor vehicle (1) according to one of the preceding claims, wherein in the converter device (4) a blocking voltage of a switching element (20) of the converter stage (17) provided for switching the first high voltage (9) is smaller than the first high voltage (9). [5] Motor vehicle (1) according to one of the preceding claims, wherein a blocking voltage of a switching element of the DC-DC converter (16) provided for switching the second high voltage (19) is smaller than the first high voltage (9). [6] Motor vehicle (1) according to one of the preceding claims, wherein the converter stage (17) is arranged in a separate housing which is different from a housing of the DC-DC converter (16). [7] Motor vehicle (1) according to one of claims 1 to 5, wherein the converter stage (17) and the DC-DC converter (16) are arranged in a common housing. [8] Motor vehicle (1) according to one of the preceding claims, wherein the vehicle component (24) is designed as an air conditioning compressor (24).

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