High-voltage electrical system and switching device

Abstract

The invention relates to a high-voltage on-board electrical system (100) for an electric or hybrid vehicle, comprising a high-voltage battery (20), a traction converter (30), a distribution box (40), and at least one first auxiliary device (53), the first auxiliary device (53) comprising at least one first buffer capacitor (C1), characterized in that a circuit device (70) having a protective diode (75) is arranged in a power line from the high-voltage battery (20) or the distribution box (40) to the first auxiliary device (53), the protective diode (75) being installed in the circuit for supplying power to the first auxiliary device (30) in such a way that it is connected in the forward direction and does not impair the normal operation of the circuit.

Description

[0001] The invention relates to a high-voltage electrical system for an electric or hybrid vehicle and a circuit device for a high-voltage electrical system.

[0002] In vehicles with electric or hybrid drive systems, the high-voltage electrical system is crucial for the operation of various vehicle components. The high-voltage electrical system consists of a high-voltage battery, a drive system with an electric motor, DC / DC converters (direct current converters), buffer capacitors, power electronics, compressors, air conditioning inverters, and, if applicable, fuel cells. The high-voltage battery is the main energy source of the electric vehicle and stores the electrical energy used to power the vehicle. The traction inverter converts the battery's direct current into alternating current for the electric motor. This electric motor then drives the vehicle's wheels. The DC / DC converter converts the battery's high-voltage direct current into the low-voltage direct current required to operate the vehicle's auxiliary consumers and accessories.In addition, electric vehicles often use electrically powered compressors to operate the air conditioning system. The air conditioning inverter converts the direct current of the high-voltage electrical system into the alternating current required to operate the air conditioning and other AC consumers. In hybrid vehicles or vehicles with extended range, fuel cells can also serve as an additional energy source. These are connected to the high-voltage electrical system via DC / DC converters.

[0003] The high-voltage electrical system is separated from the low-voltage electrical system, which supplies the lighting, radio, on-board computer, and other small consumers. This separation serves the safety of passengers and the vehicle and minimizes potential hazards associated with high voltage.

[0004] The switching frequency of a traction inverter refers to the frequency at which the inverter converts the battery's DC voltage into a modulated AC voltage to power the electric motor at a variable frequency. This conversion is achieved by rapidly switching semiconductor switches on and off, typically transistors such as IGBTs (insulated gate bipolar transistors) or MOSFETs (metal-oxide-semiconductor field-effect transistors).

[0005] The traction inverter receives the DC voltage from the high-voltage battery and modulates the DC voltage by rapidly switching the semiconductor switches on and off. This creates an AC voltage with variable frequency and amplitude. This frequency variability can be used to adjust the speed of the electric motor and thus the vehicle's control. The switching frequency is the frequency at which the semiconductor switches are switched on and off. It is measured in Hertz (Hz) and indicates how often this switching process occurs per second.

[0006] A higher switching frequency typically enables more precise control of the output voltage and frequency, reduces harmonics, and improves the efficiency of the electric motor. To ensure efficient power transmission while keeping losses low, many modern traction inverters operate at high switching frequencies in the range of several kilohertz (typically in the range of 2 kHz to 20 kHz or more).

[0007] However, for very high power levels of several hundred kW, as required for commercial vehicles or buses, the switching frequency may be limited for reasons of performance and heat dissipation, which may lead to lower switching frequencies.

[0008] However, the drive system's impact on the high-voltage electrical system, particularly from the traction converter and the electric motor, leads to various electrical phenomena. For example, the low clock frequency of the traction converter, which converts the battery's DC voltage into AC voltage for the electric motor, can impact the high-voltage electrical system. Low frequencies can lead to voltage transients that can affect other components of the high-voltage system. Furthermore, high electrical power for the drive, especially during acceleration, can require rapid changes in current and also lead to transient voltage fluctuations.

[0009] The feedback also depends on the battery's performance, including its internal resistance. A battery with low internal resistance can help minimize the feedback on the high-voltage electrical system. A low internal resistance results in a lower voltage drop across the battery when high currents flow. This reduces the likelihood of voltage fluctuations in the high-voltage electrical system. The internal resistance also influences the battery's ability to handle rapid load changes. A low internal resistance helps minimize voltage spikes that can be caused by rapid load changes in the high-voltage electrical system.

[0010] Transient voltages are short-term voltage fluctuations that can be caused by rapid changes in the electrical system, such as the switching on and off of the semiconductor switches of the traction inverter. These transients can affect other electrical components in the vehicle if they are not adequately absorbed or dampened.

[0011] Buffer capacitors are frequently used in devices connected to the high-voltage electrical system of electric vehicles to stabilize DC voltage sources and supply short-term power peaks. Buffer capacitors are typically designed as electrolytic capacitors. Capacitors have the ability to absorb charge and quickly release it again. Buffer capacitors in high-voltage electrical systems of electric vehicles have low impedance, allowing these capacitors to respond effectively to voltage changes and thus contribute to stabilizing the electrical system. In particular, they can respond very quickly to voltage changes, such as those that can occur during transient events—i.e., short-term changes in a system. In this context, low impedance means that both the ohmic resistance and the imaginary part of the impedance are low.

[0012] The low impedance of the buffer capacitors enables a rapid response to voltage changes. This is generally beneficial for stabilizing the vehicle electrical system and providing short-term power. However, when transient voltages occur, bidirectional compensating currents can flow through the buffer capacitors, which essentially depend on the capacitance of the respective buffer capacitor. This is due to the capacitors' ability to absorb and release charge. These currents can flow in both directions and override the normal operating current of the connected devices. The bidirectional compensating currents can lead to an increase in the total current, especially during sudden voltage transients. This can cause fuses designed for normal operating current to blow because the total current exceeds a threshold.Blowing fuses can create an unsafe condition in the vehicle because it can impair the proper functioning of the affected electrical components.

[0013] Although there are various approaches to minimizing voltage transients, in commercial vehicles such as trucks and buses, the clock frequency of the traction converter cannot be increased due to the high power requirements. Likewise, interference suppression measures in the form of interference suppression networks based on passive components reach their limits due to space, weight, and cost.

[0014] The invention is therefore based on the object of creating possibilities for reducing bidirectional compensating currents in electrical devices connected to a high-voltage electrical system of a vehicle with electric or hybrid drive, which are easy to implement and ensure safe operation of the high-voltage electrical system.

[0015] This object is achieved according to the invention with regard to a high-voltage vehicle electrical system by the features of patent claim 1 and with regard to a circuit device by the features of claim 7. The further claims relate to preferred embodiments of the invention.

[0016] The present invention effectively prevents or reduces bidirectional compensating currents in a high-voltage electrical system. The invention is particularly advantageous for high-power traction systems, since the traction converter has low clock frequencies and thus transient voltages cannot be completely smoothed. This is particularly the case for commercial vehicles such as trucks or buses, but also for sports vehicles with high drive system power, which can amount to several hundred kW.

[0017] According to a first aspect, the invention provides a high-voltage electrical system for an electric or hybrid vehicle, comprising a high-voltage battery, a traction converter, a distribution box, and at least one first auxiliary device. The first auxiliary device comprises at least one first buffer capacitor. A circuit device comprising a protective diode is arranged in a power line from the high-voltage battery or the distribution box to the first auxiliary device. The protective diode is incorporated into the circuit for supplying power to the first auxiliary device in such a way that it is normally switched in the reverse direction and does not impair the normal operation of the circuit.

[0018] In a further development, a second auxiliary device and / or a third auxiliary device or more auxiliary devices are provided, wherein the auxiliary devices each comprise a DC / DC converter and / or a compressor and / or an air conditioning inverter.

[0019] In a further embodiment, it is provided that the circuit device comprises a resistor connected in parallel to the protective diode.

[0020] Advantageously, the switching device is arranged in a separate device, the distribution box or in one of the auxiliary devices.

[0021] In particular, the high-voltage electrical system is designed for the operation of commercial vehicles or sports vehicles with high power outputs in the range above 100 kW and includes a traction converter with low clock frequencies.

[0022] According to a second aspect, the invention provides a circuit device for a high-voltage electrical system of an electric or hybrid vehicle, comprising a high-voltage battery, a traction converter, a distribution box, and at least one first auxiliary device. The first auxiliary device comprises at least one first buffer capacitor. The circuit device comprises a protective diode, wherein the protective diode is incorporated into the circuit for supplying power to the first auxiliary device in such a way that it is normally switched in the reverse direction and does not impair the normal operation of the circuit.

[0023] In a further development, it is provided that a second auxiliary device and / or a third auxiliary device can be connected to the circuit device by means of a series connection, wherein any number of auxiliary devices can also be connected, wherein the auxiliary devices each comprise a DC / DC converter and / or a compressor and / or an air conditioning inverter.

[0024] In a further embodiment, it is provided that the circuit device comprises a resistor connected in parallel to the protective diode.

[0025] Advantageously, the switching device is arranged in a separate device, the distribution box or in one of the auxiliary devices.

[0026] In particular, the circuit device is designed for a high-voltage electrical system for the operation of commercial vehicles or sports vehicles with high power in the range above 100 kW.

[0027] The invention is explained in more detail below with reference to embodiments shown in the drawing.

[0028] It shows: Fig. 1 a schematic representation of a high-voltage electrical system according to the state of the art; Fig. 2 a schematic representation of a first embodiment of a high-voltage electrical system according to the invention; Fig. 3 a schematic representation of a second embodiment of a high-voltage electrical system according to the invention; Fig. 4 a representation of the temporal course of the total electrical current of an electrical device connected to a high-voltage vehicle electrical system according to the state of the art; Fig. 5 a representation of the time course of the total electrical current of an electrical device connected to the high-voltage electrical system according to the invention.

[0029] Additional features, aspects and advantages of the invention or embodiments thereof will become apparent from the detailed description taken in conjunction with the claims.

[0030] Fig. 1 shows a high-voltage electrical system 100 according to the prior art for an electric vehicle or a hybrid vehicle. In particular, the electric vehicle or hybrid vehicle is designed as a commercial vehicle, such as a truck or a bus, or as a high-performance sports vehicle. The high-voltage electrical system 100 comprises a high-voltage battery 20, a traction converter 30, a distribution box 40, and at least one first auxiliary device 53. In particular, the high-voltage electrical system 100 comprises a second auxiliary device 55 and / or a third auxiliary device 57. The auxiliary devices 53, 55, 57 can each comprise, in particular, a DC / DC converter, compressors, or air conditioning inverters.

[0031] The first slave device 53 comprises a first buffer capacitor C1, the second slave device 55 comprises a second buffer capacitor C2 and the third slave device 57 comprises a third buffer capacitor C3.

[0032] The distribution box 40 comprises an assembly or housing responsible for distributing electrical energy to the traction converter 30 and the auxiliary devices 53, 55, 57. The distribution box 40 serves as a central point where the high-voltage lines of the various electrical systems are brought together. The distribution box may contain safety devices such as high-voltage fuses and disconnectors to interrupt the electrical energy in the event of a fault or hazard and to protect the vehicle. The main purpose of the distribution box is to distribute the high voltage from the high-voltage battery 20 to various parts of the vehicle. These are the traction converter 30, the auxiliary devices 53, 55, 57 with the buffer capacitors C1, C2, C3, and possibly other electrical components.The distribution box 40 may also contain integrated control electronics to monitor, control, and regulate the power distribution. This enables precise control of the high-voltage electrical system 100 according to the vehicle's operating conditions.

[0033] The traction inverter 30 receives the DC voltage from the high-voltage battery 20 and modulates the DC voltage by rapidly switching semiconductor switches on and off. This creates an AC voltage with variable frequency and amplitude. This frequency variability can be used to adjust the speed of the electric motor and thus the vehicle's control. The clock frequency is the frequency at which the semiconductor switches are switched on and off. It is measured in Hertz (Hz) and indicates how often this switching process occurs per second.

[0034] A higher switching frequency generally allows for more precise control of the output voltage and frequency, reduces harmonics, and improves the efficiency of the electric motor. However, at very high power levels of several hundred kW, such as those required for commercial vehicles or buses, the switching frequency may be limited for performance and heat dissipation reasons, which can lead to lower switching frequencies.

[0035] However, repercussions from the drive system on the high-voltage electrical system 100, particularly from the traction converter 30 and the electric motor, lead to various electrical phenomena. For example, the low clock frequency of the traction converter 30 can lead to voltage transients that can affect other components of the high-voltage system 100. Furthermore, high electrical power for the drive, especially during acceleration, can require rapid changes in current intensity and also lead to transient voltage fluctuations.

[0036] The buffer capacitors C1, C2, and C3 in the auxiliary devices 53, 55, and 57 of the high-voltage electrical system 100 serve to stabilize DC voltage sources and provide short-term power peaks. When sudden changes in power demand occur, these capacitors C1, C2, and C3 can briefly provide additional charge to minimize voltage dips. The buffer capacitors C1, C2, and C3 are typically designed as electrolytic capacitors. The buffer capacitors C1, C2, and C3 have a low impedance, allowing them to respond effectively to voltage changes and thus contribute to stabilizing the high-voltage electrical system 100. In particular, they can respond very quickly to voltage changes such as those that can occur during transient events. In this context, low impedance means that both the ohmic resistance and the imaginary part of the impedance are low.

[0037] The low impedance of the buffer capacitors C1, C2, and C3 enables a rapid response to voltage changes. This is generally advantageous for stabilizing the high-voltage vehicle electrical system 100 and providing short-term energy. However, when voltage transients occur, bidirectional compensating currents can flow through the buffer capacitors C1, C2, and C3. These compensating currents essentially depend on the capacitance of the respective buffer capacitor C1, C2, and C3, i.e., on the ability of the buffer capacitors C1, C2, and C3 to accept and release charge. These compensating currents can flow in both directions and superimpose the normal operating current of the connected auxiliary devices 53, 55, and 57. The bidirectional compensating currents can lead to an increase in the total current, especially during sudden voltage transients.This may cause fuses designed for normal operating current to blow because the total current exceeds a threshold. Blowing fuses may create an unsafe condition in the vehicle, as it may impair the proper functioning of the affected electrical components.

[0038] Fig. Figure 2 shows a high-voltage vehicle electrical system 100 according to the invention with a first embodiment of a switching device 70 connected to the distribution box 40. The auxiliary devices 53, 55, 57 with the buffer capacitors C1, C2, and C3 are connected in series to the distribution box 40. According to the invention, the switching device 70 has a protective diode 75.

[0039] The protective diode 75 is an electronic component that allows current flow in one direction and blocks it in the opposite direction. The circuit device 70 is a protective circuit for protecting the auxiliary devices 53, 55, 57 from the occurrence of compensating currents caused by transient voltages in the high-voltage vehicle electrical system. The circuit device 70 according to the invention prevents or reduces the bidirectional compensating currents by arranging the protective diode 75 in the power line between the distribution box 40 and at least one of the auxiliary devices 53, 55, 57. This ensures that the compensating current between the distribution box 40 or a power line in the high-voltage vehicle electrical system 100 and the respective buffer capacitor C1, C2, C3 is essentially unidirectional and directed toward the respective auxiliary device 53, 55, 57.The negative amplitude of the compensating currents is therefore at most as large as the operating direct current of the respective auxiliary device 53, 55, 57.

[0040] For example, when switching electrical loads, such as turning the semiconductor switches of the traction inverter on and off, sudden voltage transients can occur across the buffer capacitors C1, C2, and C3 in the auxiliary electrical devices 53, 55, and 57. The protective diode 75 is installed in the circuit in such a way that it is normally forward-biased and does not affect the normal operation of the circuit. In this state, the protective diode 75 has very low resistance and does not block the flow of current. This does not affect the normal operation of the circuit. Its main function is triggered when a transient undervoltage occurs in the high-voltage vehicle electrical system.In this case, the protective diode 75 blocks and thus prevents a transient current flow from the connected auxiliary devices 53, 55, 57 to the high-voltage vehicle electrical system and thus a current that can be many times the actual operating current and thus lead to the triggering of a safety device.

[0041] The specification of the protective diode 75 depends on the respective high-voltage vehicle electrical system 100 and is determined in particular by its blocking voltage and response time.

[0042] Furthermore, the switching device 70 prevents the formation of resonant currents. These can be excited by the feedback of the traction converter 30 on the high-voltage electrical system 100 and form between existing inductances and the buffer capacitors C1, C2, and C3. Depending on the damping, the resonant currents can exceed the operating current of the auxiliary devices 53, 55, 57 many times over and cause overvoltages in addition to overcurrents. These overvoltages can lead to irreversible damage to the auxiliary devices 53, 55, 57 because they are not necessarily detected by a safety device or, when resonant currents occur, the safety device does not trip quickly enough to prevent overvoltages and, in particular, to adequately protect semiconductor components.

[0043] Fig. 3 shows a high-voltage vehicle electrical system 100 according to the invention with a second embodiment of a circuit device 70, in which an additional ohmic resistor 77 is connected in parallel with the protective diode 75. In this way, a central passive discharge of all auxiliary devices 53, 55, 57 can be enabled. However, the behavior of the protective diode 75 is not affected by this.

[0044] The switching device 70 is conveniently housed in a separate device and can therefore be easily integrated into existing high-voltage vehicle electrical systems. It is also possible to integrate the switching device 70 into other components with the same current conduction, for example, into the distribution box 40 or directly into one of the auxiliary devices 53, 55, 57 to be protected.

[0045] In Fig. Figure 4 shows the time profile of the total current of an auxiliary unit 53 during an acceleration process of an electric or hybrid vehicle with a high-voltage electrical system 100 according to the prior art. The capacitance of the buffer capacitor C1 is 300 µF. It is clearly evident that the total current increases over time.

[0046] In Fig. Figure 5 shows the time profile of the total current in an auxiliary device 53 during an acceleration process of an electric or hybrid vehicle with a high-voltage electrical system 100 according to the invention, which includes the circuit device 70 with the protective diode 75 and the parallel 100 Ω resistor 77. The buffer capacitor C1 has a capacitance of 300 µF. The total current is virtually constant over time.

[0047] The present invention effectively prevents or reduces bidirectional compensating currents in a high-voltage electrical system. The invention is particularly advantageous for high-power traction systems, since the traction converter has low clock frequencies and thus transient voltages cannot be completely smoothed. This is particularly the case for commercial vehicles such as trucks or buses, but also for sports vehicles with high drive system power, which can amount to several hundred kW. Reference symbol 20 high-voltage battery 30 traction inverters 40 distribution box 53 first secondary device 55 second auxiliary device 57 third auxiliary device 70 Circuit device 75 Diode 77 Resistance 100 high-voltage electrical system C1 first buffer capacitor C2 second buffer capacitor C3 third buffer capacitor

Claims

[1] High-voltage electrical system (100) for an electric or hybrid vehicle with a high-voltage battery (20), a traction converter (30), a distribution box (40) and at least one first auxiliary device (53), wherein the first auxiliary device (53) comprises at least one first buffer capacitor (C1), characterized by in that a circuit device (70) with a protective diode (75) is arranged in a power line from the high-voltage battery (20) or the distribution box (40) to the first auxiliary device (53), wherein the protective diode (75) is installed in the circuit for supplying power to the first auxiliary device (30) in such a way that it is switched in the forward direction and does not impair the normal operation of the circuit. [2] High-voltage vehicle electrical system (100) according to claim 1, wherein a second auxiliary device (55) and / or a third auxiliary device (57) is / are provided, and wherein the auxiliary devices (53, 55, 57) each comprise a DC / DC converter and / or a compressor and / or an air conditioning inverter. [3] High-voltage vehicle electrical system (100) according to one of claims 1 to 2, wherein the circuit device (70) comprises a resistor (77) connected in parallel to the protective diode (75). [4] High-voltage vehicle electrical system (100) according to one of claims 1 to 3, wherein the circuit device (70) is arranged in a separate device, the distribution box (40) or in one of the auxiliary devices (53, 55, 57). [5] High-voltage electrical system (100) according to one of claims 1 to 4, wherein the high-voltage electrical system (100) is designed for the operation of commercial vehicles or sports vehicles with high power in the range of 100 to 100 kW and comprises a traction converter (30) with low clock frequencies. [6] Circuit device (70) for a high-voltage electrical system (100) of an electric or hybrid vehicle with a high-voltage battery (20), a traction converter (30), a distribution box (40) and at least one first auxiliary device (53), wherein the first auxiliary device (53) comprises at least one first buffer capacitor (C1), characterized by that the circuit device (70) comprises a protective diode (75), wherein the protective diode (75) is installed in the circuit for supplying power to the first auxiliary device (30) in such a way that it is switched in the forward direction and does not impair the normal operation of the circuit. [7] Circuit device (70) according to claim 6, wherein a second auxiliary device (55) and / or a third auxiliary device (57) is / are connectable to the circuit device (70) by means of a series circuit, and wherein the auxiliary devices (53, 55, 57) each comprise a DC / DC converter and / or a compressor and / or an air conditioning inverter. [8] Circuit device (70) according to one of claims 6 to 7, wherein the circuit device (70) comprises a resistor (77) connected in parallel to the protective diode (75). [9] Circuit device (70) according to one of claims 6 to 8, wherein the circuit device (70) is arranged in a separate device, the distribution box (40) or in one of the auxiliary devices (53, 55, 57). [10] Circuit device (70) according to one of claims 6 to 9, wherein the high-voltage electrical system (100) is designed for the operation of commercial vehicles or sports vehicles with high power in the range above 100 kW.

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