Traction power grid and method for insulation resistance monitoring in a traction power grid

Abstract

The invention relates to a traction network for a motor vehicle, comprising a high-voltage battery, having a first measuring device for detecting the voltage of the high-voltage battery, a measuring device for detecting the voltage between a positive high-voltage line and ground and a further measuring device for detecting the voltage between a negative high-voltage line and ground, the insulation resistance between the positive high-voltage line and ground being equal to the insulation resistance between the negative high-voltage line and ground or being balanced by a separate balancing resistor, the traction network further having a measuring resistor which is connected to the positive high-voltage line by means of a first switching element and to the negative high-voltage line by means of a second switching element, the traction network further having an insulation monitor device which is designed to carry out an insulation monitoring by comparing the voltage between the positive high-voltage line and ground with the voltage between the negative high-voltage line and ground in the vehicle stationary state, to calculate the insulation resistance in the driving operation by closing one of the first switching element and the second switching element, respectively, and to a method for insulation monitoring.

Description

Technical Field

[0001] This invention relates to a traction power grid for motor vehicles and a method for monitoring insulation resistance in the traction power grid. Background Technology

[0002] The known method for calculating the insulation resistance in a traction power grid, according to ECE-R100 or SAE J1766, involves connecting a grounded measuring resistor to the positive high-voltage line via a switching element or to the negative high-voltage line via another switching element. The voltage between the corresponding high-voltage line and ground changes due to the connected measuring resistor, and this voltage change can be used to calculate the insulation resistance. Here, after the switch is closed, a certain time must be waited until C... Y The capacitor has completed reverse charging.

[0003] Therefore, the insulation resistance can be calculated as follows:

[0004] or

[0005]

[0006] Among them, U B This is the operating voltage or, in the traction power grid, the voltage of the high-voltage battery. An imbalance caused by the connection of the measuring resistor—that is, a difference in voltage between the two high-voltage lines and ground—causes C to... Y The capacitor is charged to varying degrees, causing C to... Y The energy content of a capacitor increases due to its relationship with the square of the voltage. This is relevant in the design of capacitors. Y The size of the capacitor is taken into account and its dimensions are limited.

[0007] A high-voltage system is known from EP 3 637 114 A1, comprising a high-voltage battery and a DC / DC converter, wherein, when the DC / DC converter is activated, the high-voltage system has two voltage levels connected to two different currents, wherein the high-voltage system has a first measuring device for detecting the voltage of the high-voltage battery and a second measuring device for detecting the voltage at the output terminal of the DC / DC converter, wherein the high-voltage system has an insulation resistance measuring device designed to perform insulation resistance measurement only when the DC / DC converter is deactivated, wherein the high-voltage system also has a third measuring device for detecting the voltage between the positive high-voltage line and ground and a fourth measuring device for detecting the voltage between the negative high-voltage line and ground, wherein the high-voltage system has an insulation monitoring device designed to monitor the insulation resistance based on data from the first to fourth measuring devices, at least when the DC / DC converter is activated.

[0008] A traction electrical grid in an electric or hybrid vehicle is known from DE 10 2017 220 982 A1, comprising at least one high-voltage battery connected to at least one high-voltage component via positive and negative high-voltage lines, wherein at least one Y capacitor is connected to the positive high-voltage line and at least one Y capacitor is connected to the negative high-voltage line. Here, the Y capacitor is associated with at least one switching element, wherein the at least one switching element can be controlled by at least one control unit, wherein the control unit is designed to disconnect at least one Y capacitor from a ground connection or its associated high-voltage line according to at least one operating state, and / or the Y capacitors of a Y capacitor pair are associated with a common switching element arranged between a common connection point between the Y capacitor and ground, wherein the common switching element can be controlled by at least one control unit, wherein the control unit is designed to disconnect the Y capacitor from the ground connection according to at least one operating state. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to create a traction electrical grid for motor vehicles, wherein the size of the Y capacitor is further simplified, and a corresponding method is provided.

[0010] This technical problem is solved by having a traction electrical network for motor vehicles and a method for monitoring insulation resistance in the traction electrical network for motor vehicles. Other advantageous embodiments of the invention are derived from the dependent claims.

[0011] The traction electrical grid for motor vehicles includes a high-voltage battery. The traction electrical grid has a first measuring device for detecting the voltage of the high-voltage battery, a measuring device for detecting the voltage between the positive high-voltage line and ground, and a further measuring device for detecting the voltage between the negative high-voltage line and ground. Furthermore, the insulation resistance between the positive high-voltage line and ground is equal to or balanced by a balancing resistor with the insulation resistance between the negative high-voltage line and ground. The traction electrical grid also has a grounding measuring resistor, which can be connected to the positive high-voltage line via a first switching element and to the negative high-voltage line via a second switching element. The traction electrical grid also has an insulation monitoring device designed to perform insulation monitoring when the vehicle is stationary by comparing the voltage between the positive high-voltage line and ground with the voltage between the negative high-voltage line and ground. During operation, the insulation resistance is calculated by closing one of the first and second switching elements, respectively. This allows for a larger Y capacitor design because it avoids imbalances that could lead to contact with live parts when the vehicle is stationary, whereas during operation, imbalances can be measured because contact can be eliminated. For the measurement and calculation of insulation resistance during operation, please refer to the prior art in the introduction, or ECE-R100 or SAE J1766. For further possibilities of drawing conclusions about insulation faults from pure voltage comparisons, please refer to EP 3 637 114 A1. Therefore, for example, if an AC voltage is measured between the high-voltage line and ground, an insulation fault in the AC section can be inferred. Finally, the measures in DE10 2017 220 982 A1 can be used supplementarily. If a subsequent comparison reveals a difference between the two voltages being compared when the vehicle is stationary, this can be interpreted as an insulation fault.

[0012] In one embodiment, the insulation monitoring device is designed to form a ratio between voltages, wherein an insulation fault is inferred if the voltage exceeds a first threshold or falls below a second threshold. For example, the first threshold is between 1.1 and 1.2, and the second threshold is between 0.8 and 0.9. If an insulation fault is determined, the traction power grid is shut off and actively discharged. Additionally, the Y capacitor may be actively discharged. Similarly, if an excessively low insulation resistance is calculated, the traction power grid is switched to a safe state, and then the traction power grid is shut off and the Y capacitor is actively discharged when the vehicle is stationary.

[0013] Since voltage comparison is only qualitative when the vehicle is stationary, while insulation resistance is calculated very accurately when the vehicle is in motion, it is preferable to adapt the threshold for comparison when the vehicle is stationary based on the calculated insulation resistance, so as to take into account small deviations in the balance.

[0014] The design of the method is completely based on the previous implementation method. Attached Figure Description

[0015] The invention will now be described in more detail with reference to preferred embodiments. In the accompanying drawings:

[0016] Figure 1 A schematic block diagram of the traction power grid is shown.

[0017] Figure 2 A schematic measurement circuit according to ECE-R100 (prior art) is shown, and

[0018] Figure 3 An exemplary reverse charging curve is shown in a measurement according to ECE-R100 (prior art). Detailed Implementation

[0019] Before describing the traction power grid according to the present invention, the problem of voltage imbalance measured by ECE-R100 should be briefly explained first, wherein, Figure 2 A schematic measurement circuit is shown and Figure 3 The voltage curve is illustrated schematically. For example, if switching element S1 is closed, the insulation resistance generated between the positive high-voltage line and ground decreases, resulting in a decrease in the insulation resistance R between the negative high-voltage line and ground. iso A voltage divider with insulation resistance R iso The voltage drop across the capacitor increases, with the voltage dropping and rising exponentially due to the reverse charging process in the Y capacitor. Therefore, in extreme cases, almost all the voltage of the battery U0 exists across the Y capacitor for a short period of time, resulting in a very high energy content.

[0020] exist Figure 1 The diagram shows a traction grid 1, which includes a high-voltage battery 2, an inverter 4, and a motor 5. Furthermore, the traction system 1 has two contactors S, by which the high-voltage battery 2 can be current-isolated from the rest of the traction grid 1 at all poles. A pre-charge resistor R is also shown. V and pre-charge relay S V A semiconductor switch can also be used instead of the contactor S. The high-voltage system 1 also has a first measuring device M1, which measures the voltage U_2b of the high-voltage battery 2. Y capacitors C for interference suppression are arranged between the positive high-voltage line 7 and ground, and between the negative high-voltage line 8 and ground, respectively. YFurthermore, an insulation resistance R_iso_2b_P is formed between the positive high-voltage line 7 and ground. Correspondingly, an insulation resistance R_iso_2b_N is formed between the negative high-voltage line 8 and ground. When the two insulation resistances R_iso_2b_P and R_iso_2b_N are not equal, discrete balancing resistors R_sym_2b_P and R_sym_2b_N are connected between the high-voltage lines 7 and 8 and ground, so that the two parallel circuits form insulation resistances of equal magnitude. In addition, a measuring device M3 is provided to detect the voltage U_2b_P between the positive high-voltage line 7 and ground. Correspondingly, another measuring device M4 is provided to detect the voltage U_2b_N between the negative high-voltage line 8 and ground. Finally, insulation resistances R_iso_1-R_iso_3 are formed between the three phase lines of the motor 5 and ground. Furthermore, the traction power grid 1 has an insulation monitoring device 10, which is integrated, for example, in the engine control equipment or battery management control equipment 11.

[0021] In addition, traction power grid 1 has a measuring resistance R mess and a first switching element S1 and a second switching element S2, wherein the measuring resistance R mess It is fixedly grounded and can be connected to the positive high-voltage line 7 via the first switching element S1 and to the negative high-voltage line 8 via the second switching element S2. The insulation monitoring device 10 receives the measurement results from the three measuring devices M1, M3, and M4 and generates control signals for the two switching elements S1 and S2.

[0022] Before driving begins or while the vehicle is stationary during charging, the insulation monitoring device compares two voltages, U_2b_P and U_2b_N, for example, by forming a ratio between the two voltages and comparing this ratio to a threshold. In a fault-free state, this ratio should be 1, because the insulation resistance is balanced or neutralized. Conversely, if the ratio is greater than a first threshold or less than a second threshold, an insulation fault is inferred. The traction power grid 1 is then shut off and actively discharged. Additionally, Y capacitor C can be used. Y The system actively discharges and notifies the driver. Conversely, if no insulation fault is identified, the vehicle can be driven away. During driving, the insulation resistance is calculated according to ECE-R100 by closing the primary switching element S1 and using the voltage change to calculate the insulation resistance between the positive high-voltage line 7 and ground. Correspondingly, the insulation resistance between the negative high-voltage line 8 and ground can then be determined based on the voltage change by closing the second switching element S2. The insulation resistance determined in this way is stored and can be used to adapt thresholds. If the insulation resistance calculation indicates an insulation fault, the driver is warned and the traction power grid is shut off when the vehicle is stationary.

[0023] List of reference numerals

[0024] 1 Traction power grid

[0025] 2 high-voltage batteries

[0026] 4 inverters

[0027] 5 motors

[0028] 7 Positive High Voltage Line

[0029] 8 negative high voltage lines

[0030] 10 Insulation monitoring device

[0031] 11 Battery Management and Control Equipment

Claims

1. A traction electrical grid (1) for a motor vehicle, comprising a high-voltage battery (2), wherein, The traction power grid (1) has a first measuring device M1 for detecting the voltage of the high-voltage battery (2), a measuring device M3 for detecting the voltage between the positive high-voltage line (7) and ground, and an additional measuring device M4 for detecting the voltage between the negative high-voltage line (8) and ground, wherein the insulation resistance between the positive high-voltage line (7) and ground is... Insulation resistance between the negative high-voltage line (8) and ground Equal, or through discrete balancing resistors and balancing resistor Balance, wherein the traction power grid (1) also has a grounded measuring resistance. , wherein the measuring resistance The traction power grid (1) is capable of being connected to the positive high-voltage line (7) via a first switching element S1 and to the negative high-voltage line (8) via a second switching element S2. The traction power grid (1) also includes an insulation monitoring device (10), which is designed to detect the voltage between the positive high-voltage line (7) and ground when the vehicle is stationary. The voltage between the negative high-voltage line (8) and ground Insulation monitoring is performed by comparison, wherein, during operation, the insulation resistance is calculated by closing one of the first switching element S1 and the second switching element S2 respectively. and insulation resistance .

2. The traction power grid according to claim 1, characterized in that, The insulation monitoring device (10) is designed to be formed in the voltage and the voltage The ratio between the two thresholds, where an insulation fault is inferred if the threshold exceeds the first threshold or falls below the second threshold.

3. The traction power grid according to claim 2, characterized in that, The insulation monitoring device (10) is designed to monitor the insulation resistance based on the calculated insulation resistance. and insulation resistance To adapt to the first threshold and the second threshold.

4. A method for monitoring insulation resistance in the traction power grid of a motor vehicle, wherein, The traction power grid (1) has a first measuring device M1 for detecting the voltage of the high-voltage battery (2), a measuring device M3 for detecting the voltage between the positive high-voltage line (7) and the ground, and an additional measuring device M4 for detecting the voltage between the negative high-voltage line (8) and the ground, wherein the insulation resistance between the positive high-voltage line (7) and the ground is... Insulation resistance between the negative high-voltage line (8) and ground Equal, or through discrete balancing resistors and balancing resistor Balance, wherein the traction power grid (1) also has a grounded measuring resistance. , wherein the measuring resistance The traction power grid (1) is capable of being connected to the positive high-voltage line (7) via a first switching element S1 and to the negative high-voltage line (8) via a second switching element S2. The traction power grid (1) also includes an insulation monitoring device (10), which monitors the voltage when the vehicle is stationary. With voltage Insulation monitoring is performed by comparison, wherein, during operation, the insulation resistance is calculated by closing one of the first switching element S1 and the second switching element S2 respectively. and insulation resistance .

5. The method according to claim 4, characterized in that, The insulation monitoring device (10) generates the voltage. and the voltage The ratio between the two thresholds, where an insulation fault is inferred if the threshold exceeds the first threshold or falls below the second threshold.

6. The method according to claim 5, characterized in that, The insulation monitoring device (10) calculates the insulation resistance. and insulation resistance To adapt to the first threshold and the second threshold.

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