Two-stage insulated high-voltage on-board electrical system with potential island and resistance discharge

Abstract

The invention relates to a high-voltage on-board electrical system, comprising a ground potential (M) and a high-voltage potential (HV), which is insulated from the ground potential (M) by means of a two-stage insulation, said two-stage insulation comprising a first insulation device (I1), which insulates the high-voltage potential (HV) from a potential island (PI), and a second insulation device (I2), which insulates the high-voltage potential (HV) from the potential island (PI). The second insulation means insulates the potential island (PI) from the ground potential (M). The potential island (PI) is connected to the ground (M) via a discharge element (R) which is designed to generate a current below a hazard threshold and above a sensitivity threshold of the insulation monitor (IM) in the event of an insulation fault of the two-stage insulation.

Description

Background Art

[0001] As is known, vehicles are equipped with electric traction drives, wherein a high-voltage on-board electrical system is used to transmit energy. Such a high-voltage on-board electrical system operates with a high voltage in order to be able to meet the high power requirements during traction.

[0002] Especially when charging with DC voltage, high voltages are used, in some cases up to 800 V or even more, which can pose a high risk. In order to avoid danger due to contact voltages, the high voltage potential is insulated with respect to the ground potential of the vehicle (chassis, etc.).

[0003] If double insulation or reinforced insulation is to be provided between a high voltage area and a low voltage area (referenced to ground), the high voltage potential is insulated by means of a first insulating device and then insulated again by a second insulating device to provide two levels of insulation relative to ground potential. For example, a first optocoupler with a high voltage potential on the input side and a second optocoupler with a ground reference on the output side can be connected in series in a transmission chain, thereby producing double insulation between the high voltage potential and ground potential. It has been recognized that an insulation fault in one of the insulation levels cannot be identified because the other insulation level prevents the flow of current required to detect the insulation fault. Summary of the invention

[0004] It is therefore an object of the present invention to provide a possibility for insulating a high-voltage onboard electrical system with increased safety.

[0005] This object is achieved by a high-voltage onboard electrical system according to claim 1. Further properties, features, embodiments and advantages are revealed from the dependent claims and the drawings.

[0006] It is proposed to insulate the high voltage potential from the ground potential in a two-stage manner by means of two consecutive insulating devices. A (conductive) potential island is provided between the insulating devices. The insulating devices are connected via the potential island. In order to be able to detect an insulation fault in one of the insulating devices, it is proposed to connect the potential island to the ground potential of the onboard electrical system (or the high voltage potential or another high voltage potential) via a discharge element. If a fault occurs in the first insulating device, a current flow (Strom flux) is generated through the discharge element, which current flow can be detected by the insulation monitor. At the same time, excessively high contact currents due to failure of the first insulating device can also be avoided by the discharge element, wherein the resistor limits the contact current to a harmless level.

[0007] Therefore, a high-voltage on-board electrical system (hereinafter referred to as: on-board electrical system) having a ground potential and a high-voltage potential is described. A plurality of high-voltage potentials may also be provided in the on-board electrical system, which are preferably insulated relative to the ground as described herein. The high-voltage potential is insulated relative to the ground potential by means of two-stage insulation. This insulation may correspond to double insulation or reinforced insulation, which may also be called "double insulation" or "reinforced insulation" (provided that the reinforced insulation is two-stage). The two-stage insulation has a first insulating device. The first insulating device insulates the high-voltage potential from the potential island. The insulating device extends between the conductor to which the high-voltage potential is applied and the potential island. The second insulating device of the two-stage insulation insulates the potential island from the ground potential. In this case, the ground potential may correspond to the chassis potential or the ground potential of the vehicle ground terminal, or it may be a potential electrically connected thereto. The potential of the potential island may be regarded as an indicator of fault-free operation of the insulation device. In other words, the potential of the potential island may be used to detect faults in the two-stage insulation or the insulation device. Therefore, the potential island may be regarded as a voltage sensor or a potential sensor between two insulation devices. In order to be able to detect the insulation state, the potential of the potential island is evaluated. According to the invention, a discharge element is used in this case, which connects the potential island to ground potential (or another potential electrically connected thereto). (Alternatively, the discharge element can connect the potential island to the high voltage potential of the on-board electrical system or another high voltage potential to detect insulation faults in the second insulation device).

[0008] If the potential island is not properly insulated with respect to the high voltage potential, the discharge element generates a current flow which can be used as a signal for a two-pole insulation fault. The discharge element is designed in such a way that the magnitude of the current it generates is sufficient to be detected by the insulation monitor. Furthermore, the discharge element is dimensioned to ensure that in the event of a fault in the two-pole insulation, no dangerous touch current is generated or only a contact current below a dangerous threshold is generated, in particular a contact current below the dangerous threshold with a predetermined safety factor. The potential island is therefore connected to ground potential via the discharge element, which is arranged to generate a current below the dangerous threshold and at the same time above a sensitivity threshold of the insulation monitor in the event of an insulation fault in the first or second insulation device.

[0009] The discharge element comprises in particular a resistor. Embodiments described with a resistor as a discharge element can generally be embodied with a discharge element, as described below. For the sake of simplicity, the term "discharge element" is also referred to as the term "resistance" in the following text and in particular in the description of the figures or in the title. The discharge element may have one or more resistor elements connected to each other. The discharge element may also be or contain an ohmic element, a capacitive element and / or an inductive element. The discharge element may also be formed by a high-pass filter, a low-pass filter or a bandpass filter, which may also have an ohmic element. Therefore, the discharge element can be designed to be frequency selective, so as to form a certain frequency-dependent transmission behavior, for example, depending on the application or depending on the signal generated (or expected) due to the insulation fault. Instead of a linear element, or in combination with a linear element, the discharge element can have at least one nonlinear element, for example an element with an actual impedance depending on the voltage applied to the element, such as a Zener diode, a varistor, a gas discharge tube, a spark gap, a protection diode, a thyristor circuit, a DIAC and / or a four-layer diode. The discharge element can thus be constructed so that a current flow recognized by the insulation monitor only occurs from a certain signal strength or voltage. This avoids erroneous (false-positive) insulation fault detection.

[0010] For example, the danger threshold may come from a wired charging standard for electric vehicles. Similarly, the sensitivity threshold (from which the insulation monitor must react) may also come from a high-voltage technical standard. In addition or in combination therewith, the danger threshold may also be designed such that a current, a voltage or a power (flowing through the device) is generated for the first and / or second insulation device within the rated current, the rated voltage or the rated power (or the rated pulse power) of the insulation device (or both insulation devices). Therefore, the danger threshold may be designed instead of or in combination with the above definition so that when an insulation fault occurs in (one of the devices), the other insulation device is not damaged, in particular its insulation performance or insulation resistance is maintained. This ensures that in the event of an insulation fault, the insulation device without fault can maintain its insulation performance due to the current generated by the resistor. In other words, the resistor is designed so that the current flowing through the resistor does not cause damage to the insulation device without fault or the insulation resistance of the insulation device does not (significantly) decrease. By the resistance value or by the transmission behavior of the discharge element, a chain failure (Folgefehler) (in other insulation devices) caused by an insulation fault in the insulation device is avoided. The transmission behavior of the discharge element is provided to generate a current flow through the discharge element detectable by the insulation monitor. The transmission behavior of the discharge element is provided to generate a current flow through the discharge element that is in particular above a sensitivity threshold of the insulation monitor or other safety device.

[0011] The value of the resistor element provided as a discharge element is preferably at least 75 kilo-ohms, 80 kilo-ohms or 85 kilo-ohms. In combination therewith or as an alternative, the value of the resistor element is preferably not more than 150 kilo-ohms, 120 kilo-ohms or 100 kilo-ohms. The discharge element may have a transmission behavior corresponding to such a resistor element.

[0012] The rated voltage of the high-voltage on-board electrical system is preferably designed to be higher than 60V, in particular at least 200V, at least 400V or higher. The rated voltage of the high-voltage on-board electrical system is preferably more than 600V, for example from 650V to 900V, or in particular from 700V to 850V. Therefore, the rated voltage of the on-board electrical system can be about 800V, 820V or 850V. The additional word "about" here means that the tolerance does not exceed 2%, 5% or 10%. The discharge element can have a transmission behavior corresponding to such a resistance element.

[0013] The resistor element as a discharge element generates a current above the sensitivity threshold in the event of an insulation fault, since the resistance value preferably corresponds to a value of 80 kilo-ohms with a deviation of no more than 20% or 10%. This is particularly true in conjunction with an onboard electrical system with a rated voltage of 800 V. At other rated voltages, the resistance value can also assume other values, wherein the resistance value is preferably adjusted proportionally to the coefficient of variation of the rated voltage. The discharge element can have a transmission behavior corresponding to such a resistor element.

[0014] The rated voltage of the on-board electrical system can also be 400 V. In this case, the resistor is set so that in the event of an insulation fault a current above the sensitivity threshold is generated because the resistor value corresponds to the value of 40 kilo-ohms with a deviation of no more than 20% or 10%. Therefore, at different rated voltages, the resistor value may be 80 kilo-ohms (rated voltage 800 V) or 40 kilo-ohms (rated voltage 400 V). The tolerance of these data does not exceed 20% or 10%.

[0015] The on-board electrical system preferably has an insulation monitor. The insulation monitor monitors the insulation of the high voltage potential relative to the ground potential. In particular, the insulation monitor has a sensitivity threshold, which corresponds to a sensitivity threshold for determining a resistance value (taking into account the high voltage). In particular, the resistance-dependent sensitivity threshold corresponds to the insulation monitor, which is part of the on-board electrical system.

[0016] The insulation monitor is connected to the ground potential and the high voltage potential to obtain the insulation between them. In this case, the insulation monitor is arranged to measure the insulation resistance between the high voltage potential and the ground potential. This can be done actively by applying a test voltage and measuring the current caused, or by injecting a test current and determining the voltage generated. The insulation monitor can be arranged to relate the test current and the voltage generated or the test voltage and the current generated to each other to obtain the insulation resistance. In addition, in a simpler embodiment, the insulation monitor can apply a determined test voltage (or indicate a determined test current), so that the current generated or the voltage generated is the variable used to directly or indirectly obtain the insulation resistance. The discharge element described in this article ensures that the insulation fault is detected only in the first insulation device (the second insulation device functions normally), because due to the working mode of the insulation monitor (and due to the resistance value), the resistance is significantly helpful for fault identification.

[0017] In order to redirect the load generated by the pulse voltage to the first insulating device in a targeted manner, a Cy capacitor can be connected in parallel between the first insulating device on the one hand and the second insulating device on the other hand. For example, the value of the Cy capacitor can be in the interval of 100pF to 2nF. The capacitance value of the Cy capacitor is preferably at least 100pF, 500pF or 700pF, or 1nF or 2nF respectively. In addition, it can also be specified that the capacitance value of the capacitor does not exceed 50nF, 20nF, 10nF, 5nF or 2nF. The Cy capacitor forms a capacitive voltage divider, and its end is connected to the ground potential and the high voltage potential. The connection point between the capacitors in the capacitive voltage divider is connected to the potential island. The voltage division of the capacitive voltage divider does not necessarily have to be 1:1, but can also be 1:2, 1:3, 1:4 or 1:5. In particular, in this case, the first capacitor (connecting the potential island to the high voltage potential) can be greater than the second capacitor, for example, with a coefficient of at least 2, 3, 4 or 5. In one specific embodiment, for example, the capacitance of the first Cy capacitor is 20 nF and the capacitance of the second capacitor is 5 nF. Other embodiments provide that the second capacitor is larger than the first capacitor (wherein the voltage division may be 2:1, 3:1, 4:1 or 5:1). In particular, if a resistor connects the potential island to the high voltage potential, the second capacitor may be larger than the first capacitor.

[0018] The insulating device is in particular an insulating element of a component transmitted in an electrically isolated manner, such as a transformer or an optocoupler. In addition, the insulating device can also be provided by an insulating material, such as a cable insulation, an insulating material of a substrate or a circuit board, or a housing.

[0019] The potential island in the on-board electrical system is preferably not accessible from the outside, in particular, for example, it is covered with an insulating material. Only the connection to the discharge element of the potential island can leave the potential island in an electrically conductive manner, so this is preferably the only electrically conductive lead-out of the potential of the potential island. However, this connection and the discharge element are preferably also not accessible from the outside by an insulating cover. The discharge element and the potential island (in particular the cover) can be covered or encapsulated so that they cannot be contacted from the outside. Only the discharge path (Ableitung) leading from the discharge element, that is, the discharge path between the discharge element and the ground potential, can be contacted because it has the ground potential. Alternatively, the discharge path between the discharge element and the ground potential can also be covered by the housing (with the help of an insulating material).

[0020] A vehicle may be provided which is equipped with a high-voltage on-board electrical system, wherein a traction drive device of the vehicle and / or a vehicle-side high-voltage charging device are part of the on-board electrical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is used to exemplify the embodiments of the vehicle electrical system described herein. DETAILED DESCRIPTION

[0022] Figure 1 A high-voltage on-board electrical system is shown symbolically, in particular its high-voltage potential HV and ground potential M. The high-voltage potential HV shown in the figure does not have to be the only high-voltage potential of the on-board electrical system. On the contrary, there is preferably another high-voltage potential HV', which is only shown symbolically. This potential HV' can be insulated in the manner described in the present document, that is, in the same way as the high-voltage potential with the reference numeral HV. The potential HV can correspond to a positive high-voltage potential, and the potential HV' can correspond to a negative high-voltage potential. The on-board electrical system has a high voltage applied between the potentials HV and HV'.

[0023] The insulating device I1 insulates the high voltage potential HV from the potential island PI. The potential island PI itself is electrically conductive, as is the carrier of the high voltage potential HV.

[0024] The second insulating device I2 insulates the potential island relative to the ground potential M. The ground potential M can be the chassis potential of the vehicle. Conventionally, the high voltage potential HV (or high voltage potential HV-) is electrically isolated from the ground potential. The resistor R is provided to ensure that the insulation monitor IM can still detect a fault in the insulating device I1.

[0025] The resistor R connects the potential island PI to the ground potential M. Typically, the potential island PI is connected to the ground potential M via a resistor, but other components (diodes, fuses or similar components) may also be provided. It is important to provide a resistor between the potential island PI and the ground potential M so that, in the event of a fault in the insulation I1, a limited current flow occurs that is large enough to be recognized as an insulation fault by the insulation monitor IM.

[0026] The insulation monitor IM shown is connected to a high voltage potential HV and to a ground potential M. If the insulation device I1 fails, a current will flow through the resistor R, since the high voltage potential HV is also applied to the potential island PI due to the insulation fault. Therefore, the current through the resistor R can be reliably detected. In the absence of the resistor R, the insulation device I1 may fail, the potential island PI may carry the high voltage potential HV, but the insulation monitor IM still cannot detect the insulation fault, because the insulation device I2 between the potential PI and the potential M prevents the current flow required for detecting the insulation fault.

[0027] In addition, a capacitive voltage divider having two Cy capacitors C1 and C2 is provided. The internal connection point of the voltage divider, i.e. the connection point between C1 and C2, is connected to the potential island PI. The two ends of the voltage divider are connected to the potentials HV and M. Therefore, the capacitor C1 connects the potential HV to the potential of the potential island PI. The capacitor C2 connects the potential island PI to the ground potential M. Since the capacitors C1 and C2 exist between the ground potential and the high voltage potential, they are called Cy capacitors.

[0028] The capacitors C1 and C2 shown are implemented as dedicated capacitor components. Preferably, the capacitor C1 is larger than the capacitor C2 so as to specifically direct the voltage pulse load to the insulating device I2, especially to protect the insulating device I1 more or reduce its load. In this way, the pulse load can be concentrated on the insulating devices I1 and I2 that can be monitored by means of a resistor by means of a capacitive voltage divider. If the resistor is arranged between the potential island PI and the potential M, the insulating device I1 will be monitored so that the pulse load is preferably concentrated on the insulating device I1. If in an embodiment not shown, the resistor is located between the potential island PI and the high voltage potential HV, the pulse load is preferably concentrated on the insulating device I2. The insulating device connected in parallel with the capacitor with the lower capacitance value of the two capacitors obtains a higher pulse load. Preferably, this is also the one of the two insulating devices that can be monitored, that is, in the event of a fault, it will cause a current to flow through the resistor R (which can be identified as an insulation fault by the insulation monitor).

[0029] Therefore, if the resistor R connects the potential island PI to the ground potential M, the capacitor arranged between the high voltage potential HV and the potential island PI is preferably the smaller of the two capacitors. If the resistor R is arranged between the high voltage potential HV and the potential island PI, the capacitor C2 is preferably the smaller of the two capacitors. In this case, the capacitor C2 connects the potential island PI to the ground potential M.

Claims

1. A high-voltage on-board electrical system having a ground potential (M) and a high-voltage potential (HV), wherein the high-voltage potential is insulated from the ground potential (M) by means of two-stage insulation, wherein: The two-stage insulation comprises a first insulation device (I1) and a second insulation device (I2), wherein the first insulation device insulates the high voltage potential (HV) from a potential island (PI), and the second insulation device insulates the potential island (PI) from a ground potential (M), wherein the potential island (PI) is connected to the ground potential (M) via a discharge element (R), and the discharge element (R) is configured to generate a current lower than a danger threshold and higher than a sensitivity threshold of an insulation monitor (IM) when an insulation fault occurs in the two-stage insulation.

2. The high-voltage vehicle electrical system according to claim 1, wherein: The discharge element (R) is configured as a resistor element, the value of which is at least 75 kilohms, 80 kilohms or 85 kilohms, but not more than 120 kilohms or 100 kilohms.

3. The high-voltage vehicle electrical system according to claim 1 or 2, wherein: The rated voltage of the high-voltage on-board electrical system is 650V-900V or 700V-850V.

4. The high-voltage vehicle electrical system according to claim 1, wherein: The discharge element (R) is designed as a resistance element and is provided for generating a current above the sensitivity threshold when an insulation fault occurs, in that the resistance value of the resistance element corresponds to a value of 80 kilo-ohms with a deviation of no more than 20% or 10% and the rated voltage of the high-voltage onboard electrical system is 800 V, or wherein, The discharge element (R) is designed as a resistance element and is provided for generating a current above the sensitivity threshold when an insulation fault occurs, in that the resistance value of the resistance element corresponds to a value of 40 kilo-ohms with a deviation of no more than 20% or 10% and the rated voltage of the high-voltage onboard electrical system is 400 V.

5. The high-voltage on-board electrical system according to any one of the preceding claims, further comprising an insulation monitor (IM) for monitoring the insulation condition of the high-voltage potential relative to the ground potential (M).

6. The high-voltage vehicle electrical system according to claim 5, wherein: The insulation monitor (IM) is configured to actively monitor the insulation condition by applying a test voltage or by injecting a test current.

7. A high voltage on-board electrical system according to any one of the preceding claims, wherein: The first Cy capacitor (C1) connects the potential island (PI) to the high voltage potential (HV), and the second Cy capacitor (C2) connects the potential island (PI) to the ground potential (M).

8. The high-voltage vehicle electrical system according to claim 7, wherein: The capacitance of each of the Cy capacitors (C1, C2) is at least 100pF, 500pF or 700pF and does not exceed 50nF, 20nF, 10nF, 5nF or 2nF.

9. A high voltage on-board electrical system according to any one of the preceding claims, wherein: The insulating device (I1, I2) is arranged as an insulating barrier for an optocoupler, a transformer and / or cable insulation. 10 . The high-voltage on-board electrical system as claimed in claim 1 , which is part of a direct voltage charging section of an electric drive system of a vehicle.

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