Vehicle electrical system with an insulation monitor and DC charging station with an insulation monitor on the charging station side

Abstract

Vehicle electrical system (VES) with an insulation monitor (IM), two supply potentials (V+, V-) and a ground potential (PE), wherein the supply potentials (V+, V-) are DC voltage potentials and wherein a filter capacitor (C1', C2') is connected between each of the two supply potentials (V+, V-) and the ground potential (PE), wherein the insulation monitor (IM) is connected to the ground potential (PE) and the supply potentials (V+, V-) and is equipped with an evaluation device (A) which is configured to output an error signal (S) when the actual voltage change rate of at least one voltage between the supply potentials on the one hand and the ground potential is greater than a predetermined maximum voltage change rate, wherein the evaluation device (A) is configured to output an error signal when the actual voltage change rate of a first voltage between a first of the supply potentials (V+) and the ground potential (PE) is substantially the inverse of the actual voltage change rate of a second voltage between a second of the supply potentials (V-) and the ground potential (PE).

Description

[0001] Vehicles with electric drive, meaning purely electric vehicles and hybrid vehicles, have a battery. It is known to transfer electrical power to the battery via a charging station to charge it. High voltages of at least 400 volts are preferably applied for this purpose. If a floating battery (i.e., one not connected to ground) is used, the voltage is applied via two supply potentials (positive and negative supply potentials). To protect against electric shock, the ground potential of the charging station is also connected to the ground potential (e.g., the chassis potential) of the vehicle. As a further safety measure, insulation monitors are used that detect the insulation of the supply potentials from the ground potential and disconnect the supply potentials if the insulation is too weak (i.e., the insulation resistance is too low).For this purpose, the insulation is determined by an active resistance measurement, during which the charging process is interrupted.

[0002] The publication EP 3 147 679 A1 describes the determination of insulation resistance by measuring a discharge curve and comparing this discharge curve with predefined sequences ("patterns") that are linked to individual insulation resistances. In one embodiment, a voltage ramp is used at the beginning of the charging process. One objective is to determine the insulation status without having to interrupt operation to measure such a charging curve.

[0003] This problem is solved by the subject matter of the independent claims. Further properties, features, embodiments and modes of operation are described in the dependent claims, the description and the figure.

[0004] Therefore, a vehicle electrical system with an isolation monitor is proposed, wherein the vehicle electrical system further comprises two supply potentials and a ground potential. The two supply potentials are part of a high-voltage (HV) electrical system. The ground potential is galvanically isolated from the supply potentials. The ground potential is, for example, the chassis potential. As mentioned, there is galvanic isolation between the ground potential on the one hand and the supply potential on the other. However, cylindrical capacitors are provided, which are connected between the ground potential and the two supply potentials. A first cylindrical capacitor thus connects the first of the two supply potentials to the ground potential, and a second cylindrical capacitor connects the second supply potential to the ground potential. The cylindrical capacitors serve for interference suppression, i.e., for diverting interference signals (generated by switching operations in the vehicle electrical system) to the ground potential.For example, a charger or inverter has electronic switches that are pulsed open and closed to act as a control element for power or current. DC-DC converters are also pulsed and can generate such disturbances in the DC voltage potentials. Since these Cy capacitors thus serve as filters and divert high-pass signals from the supply potentials to ground potential, they are also called filter capacitors.

[0005] After the two supply potentials are connected to ground via their respective filter capacitors, these capacitors form a capacitive voltage divider. According to the procedure described here, the voltage drop across at least one of the filter capacitors serves as an indicator of a fault. While a constant voltage can exist between the supply potentials, such as the 400 volts of a battery, a fault in the insulation between the supply potential and ground causes one of the supply potentials to shift relative to ground. For example, if a rupture creates an insulation fault between the positive supply potential and ground, this leads to a discharge of the Cy capacitor. In other words, such a fault results in a voltage change between the supply potential and ground.The voltage between the supply potentials remains constant; however, the potential shift relative to ground (since the supply potentials are not galvanically connected to ground) results in a voltage shift that indicates an insulation fault. It is evident that the voltage of the supply potential relative to ground can be measured, and thus an insulation problem can be detected, while the voltage between the supply potentials remains constant as energy is supplied to or drawn from the vehicle's electrical system. The insulation resistance measurement described here can therefore be performed during operation, particularly during charging.

[0006] The system is designed to detect a fault, i.e., generate a fault signal, when a voltage changes between at least one of the supply potentials and ground, and the associated rate of change exceeds a limit, such as a maximum voltage change rate. This rate of change corresponds to the discharge of a filter capacitor via an insulation fault. The discharge current flows from the improperly insulated supply potential to ground. This shifts the supply potentials relative to ground, and this shift is detected. Specifically, this shift can be detected before a person touches the ground potential and becomes connected to a supply potential via the insufficient insulation resistance, potentially resulting in a dangerous electric shock.

[0007] The vehicle electrical system described here therefore comprises an insulation monitor, two supply potentials, and a ground potential, with a filter capacitor connected between each of the two supply potentials and the ground potential. The supply potentials are DC voltage potentials, such as V+ and V-. The insulation monitor is connected to the ground potential and the supply potentials. The insulation monitor is configured for voltage measurement, specifically for measuring the voltage between ground potential and one of the supply potentials, or for measuring the voltages between ground potential and the two supply potentials. The insulation monitor includes an evaluation unit. This unit is configured to output an error signal if the actual voltage change rate exceeds a predefined maximum voltage change rate.Here, the actual voltage change rate refers to at least one of the two voltages between the supply potentials and ground, i.e., at least one voltage between the supply potentials on the one hand and the ground potential on the other.

[0008] It should be noted that if an insulation fault occurs in the first supply potential, the voltage between this supply potential and ground decreases, and this voltage change can be detected. However, this is accompanied by a change in the voltage relative to ground of an unaffected supply potential, namely an increase, because the filter capacitor connected to the unaffected supply potential charges to the same extent as the filter capacitor connected to the affected supply potential discharges. Therefore, by monitoring only one of the two supply potentials, both insulations of the two supply potentials can be monitored.

[0009] The vehicle electrical system may also include a battery, in particular a high-voltage battery with a nominal voltage of at least 60 volts, and especially of substantially 400, 600, or 800 volts. This battery is connected to the supply potentials. The battery may be located in a housing that is connected to ground, with galvanic isolation between the battery or the supply potentials on the one hand and ground potential on the other. As mentioned, filter capacitors are connected between the supply potentials on the one hand and ground potential on the other. The insulation monitor may also be configured to detect insulation resistances between the supply potentials and ground by measuring resistance. Preferably, this latter function is deactivated when the vehicle electrical system is charging. The charging station may be configured to perform the insulation monitoring.

[0010] The evaluation device is preferably configured to output a fault signal when the rate of change of a first voltage between one of the two supply potentials and ground is essentially the inverse of the rate of change of a second voltage between the second supply potentials and ground. The first and second voltages together constitute the essentially constant supply voltage. If one of the two voltages drops, this could be due to an insulation fault or a break in the connection to the battery. To detect this fault, it is checked whether one of the two voltages changes, but the total voltage remains constant. Since the two voltages together constitute the supply voltage, it is checked whether the first voltage drops by the same amount as the second voltage rises, or vice versa.If this is the case, an insulation fault affecting one of the two supply potentials can be inferred. It can also be determined whether the magnitude of the voltage change rate of the first voltage corresponds to the magnitude of the voltage change rate of the second voltage, and if so, the fault signal is then output. The fault detection described in this paragraph can be implemented as the previously mentioned detection method, or the fault detection described above can be performed first, and a fault signal can only be output if the condition described in this paper is also met.In other words, the evaluation device can be configured to output a fault signal if the actual voltage change rate is greater than a predetermined maximum voltage change rate, or if the actual voltage change rate of the first voltage is the inverse of the actual voltage change rate of the second voltage (and exceeds a limit). It can also be configured to output a fault signal if the actual voltage change rate is greater than a predetermined maximum voltage change rate and, furthermore, if the voltage change rate of the first voltage is essentially the inverse of the voltage change rate of the second voltage (or if the magnitudes of the voltage change rates are essentially the same). In the latter case, this provides plausibility that an insulation fault is present.

[0011] Furthermore, the system may be configured to consider the ratio of the first to the second voltage. This ratio indicates whether the two supply potentials are symmetrical with respect to ground or whether an asymmetry exists. Therefore, it may be configured to output an error signal if an asymmetry of the supply potentials with respect to ground is detected that exceeds a predefined limit. The evaluation device may thus be configured to output an error signal if the ratio of a first voltage between one of the supply potentials and ground to a second voltage between a second of the supply potentials and ground exceeds an upper limit or falls below a lower limit. The latter can also be referred to as the detection of an asymmetry.The evaluation unit can therefore be configured to output an error signal if the actual voltage change rate exceeds a predefined maximum voltage change rate and an asymmetry is detected. Alternatively, the evaluation unit can be configured to output an error signal if the actual voltage change rate exceeds a predefined maximum voltage change rate or if an asymmetry is detected. Furthermore, the detection of asymmetry can be logically linked to the detection of whether the voltage change rates of the first voltage and its inverse (in this case, the second voltage) are essentially equal. The inverse of a value is the value with the opposite sign.

[0012] Another possibility is that the fault can be transmitted, for example to an external device such as a charging station. Therefore, the insulation monitor and / or the evaluation unit can have a signal output configured to transmit an externally receivable request signal, which results in an insulation test request. This insulation monitor or evaluation unit can thus be configured to communicate with an external charging station in order to transmit a request signal to the charging station. Upon receiving a request signal, the charging station is configured to perform an insulation test, in which, for example, the insulation resistance of the charging station's supply potentials relative to its ground is measured and evaluated. This evaluation can also result in the charging station being deactivated if the insulation resistance is faulty.Therefore, the vehicle's detection of an insulation problem is intended to trigger an insulation check at the charging station. The request signal can, for example, correspond to the fault signal emitted by the evaluation unit.

[0013] It can be specifically configured that the insulation monitor is set up to output a request signal via its signal output when the evaluation unit emits a fault signal. This triggers an insulation check by the external charging station when the fault signal is emitted. In this case, as soon as the vehicle electrical system's insulation monitor detects a fault or generates a fault signal, the charging station's insulation monitor (receiving the request signal) is immediately stopped to perform an insulation measurement. The charging station's insulation monitor can directly process the request signal and interpret it as a command, thereby triggering an insulation measurement at the charging station.

[0014] Alternatively, the insulation monitor can be configured to output the request signal via its signal output with a predefined delay. This prevents momentary measurement errors by the vehicle's electrical system's insulation monitor. Specifically, the insulation monitor can be configured to output the request signal only if the fault signal persists for a predefined minimum duration. With a delayed request signal, there is a time separation between fault detection by the charging station and fault detection in the vehicle's electrical system. This time separation ensures that if an insulation fault is detected simultaneously at both the charging station and the vehicle, the two insulation monitors do not interfere with each other.In particular, it is ensured that an insulation test performed by the charging station's insulation monitor will not interfere with the operation of the vehicle's electrical system's insulation monitor. The vehicle's electrical system's insulation monitor, or its evaluation unit, may include a delay element or may be configured to monitor the fault signal over a period of time, determine the relevant voltage(s) multiple times, and / or evaluate the voltage(s) for a minimum duration.

[0015] The two supply potentials and the ground potential are connected to respective contacts of a DC charging interface. The DC charging interface of the vehicle's electrical system can be designed as a charging socket, for example, according to a standard for charging sockets. The DC charging interface is therefore a conductive interface with plug contacts.

[0016] Preferably, the two supply potentials are connected to the respective contacts of the DC charging interface via switches. In other words, the two supply potentials and the ground potential are switchably connected to the contacts of the DC charging interface, particularly via two switches connected to the supply potentials. The insulation monitor is connected to the switches for control purposes. Therefore, the insulation monitor can open the switches, for example, when a fault occurs, thus disconnecting the connection to the DC charging interface or the relevant contacts. The insulation monitor is thus configured to open the switches when a fault signal is present. In particular, the insulation monitor is configured to open the switches when a fault signal persists for at least a predetermined duration.

[0017] In addition to the vehicle's electrical system, a DC charging station is also described. This station features an insulation monitor with a signal input. The signal input is configured to receive a signal. This signal represents an insulation test request and can be, in particular, a fault signal or the requested signal itself. The insulation monitor is configured to perform an insulation test when an insulation test request is received. Specifically, an insulation test is only performed if the insulation test request persists for a minimum duration.

[0018] Furthermore, the insulation monitor on the charging station side may be configured to perform the insulation test with a delay after receiving the insulation request. Specifically, the insulation monitor on the charging station side is configured to perform the insulation test with a minimum delay. This minimum delay may be predefined.

[0019] The DC charging station has a socket or cable with contacts through which the DC voltage can be supplied. Like a vehicle's electrical system, the DC charging station may also have filter capacitors, particularly to suppress interference from switched-mode components within the charging station. The principle is the same as in a vehicle's electrical system. When the charging station is connected, the voltage distribution is as described above, with a voltage shift relative to ground occurring if a one-sided insulation fault occurs. The DC charging station therefore also has two supply potentials and a ground potential, which is galvanically isolated from the charging station's supply potentials.

[0020] The Fig. Figure 1 serves to illustrate the objects according to the invention within the framework of an exemplary consideration of one embodiment. In the Fig. Figure 1 shows a DC charging station LS connected to a vehicle electrical system FB via a DC charging interface LB. The diagram shows the supply potentials V+ and V- of the vehicle electrical system FB, which, due to the connection with the charging station LS, correspond to the supply potentials V+ and V- of the vehicle electrical system. Furthermore, a ground potential PE exists on both the vehicle electrical system side and the charging station side, whereby the ground potential is galvanically isolated from the supply potentials V+ and V-.

[0021] An insulation monitor IM of the vehicle electrical system comprises an evaluation unit A. The insulation monitor IM is connected to the supply potentials and to the ground potential PE, enabling it to monitor and measure the voltage across the filter capacitors C1' and C2' in the vehicle electrical system. For this purpose, the insulation monitor includes voltage sensing devices M1 and M2 for detecting the voltages of the supply potentials V+ and V- relative to ground potential PE. The voltage sensing devices M1 and M2 are connected to the evaluation unit A to output the detected voltage(s) (as a value) to it.

[0022] The DC charging station also includes (symmetrically arranged) filter capacitors C1 and C2, which, when the vehicle's electrical system is connected, add to the filter capacitors C1' and C2'. The DC charging station LS is powered by an AC voltage source Q, such as a public power grid, and the DC charging station LS has a rectifier GR. The rectifier GR is connected to the AC voltage source Q and can thus generate the supply potentials V+ and V-. The rectifier GR does not connect the ground potential PE to the supply potentials V+ and V-; within the rectifier GR and also within the charging station LS, the ground potential PE is galvanically isolated from the supply potentials V+ and V-. Rather, the ground potential PE of the DC charging station LS is connected to a housing of the charging station and / or to an earth potential or earthing terminal of the power grid.of the AC voltage source Q. The ground potential PE of the DC charging station LS can also be connected to an earth potential PE of an earthing of the DC charging station LS.

[0023] It is shown that the insulation monitor IM of the vehicle electrical system can output a signal S indicating a detected fault. Furthermore, a request signal AF can be transmitted to the DC charging station LS, as indicated by the arrow. For this purpose, the insulation monitor IM includes a signal output SA (e.g., a radio interface) which can transmit the request signal AF. The insulation monitor LI of the DC charging station LS is equipped with a signal input E. This input is configured to receive signals from the signal output SA of the insulation monitor IM of the vehicle electrical system FB. If the insulation monitor LI of the DC charging station LS detects a signal from the vehicle electrical system's insulation monitor IM via signal input E, then the DC charging station, or rather its insulation monitor LI, can perform its own insulation measurement.The signal S of the insulation monitor IM of the vehicle electrical system FB triggers an insulation measurement, which is carried out by the insulation monitor LI of the DC charging station LS.

[0024] Switches S1 and S2 are used to disconnect the DC voltage interface LB of the vehicle's electrical system. In the event of a fault, this allows the DC voltage interface to be de-energized, particularly if the insulation monitor IM detects a fault. This disconnects a high-voltage battery B of the vehicle's electrical system FB from the charging interface LB.

Claims

[1] Vehicle electrical system (VES) with an insulation monitor (IM), two supply potentials (V+, V-) and a ground potential (PE), wherein the supply potentials (V+, V-) are DC voltage potentials and wherein a filter capacitor (C1', C2') is connected between each of the two supply potentials (V+, V-) and the ground potential (PE), wherein the insulation monitor (IM) is connected to the ground potential (PE) and the supply potentials (V+, V-) and is equipped with an evaluation device (A) which is configured to output an error signal (S) when the actual voltage change rate of at least one voltage between the supply potentials on the one hand and the ground potential is greater than a predetermined maximum voltage change rate, wherein the evaluation device (A) is configured to output an error signal when the actual voltage change rate of a first voltage between a first of the supply potentials (V+) and the ground potential (PE) is substantially the inverse of the actual voltage change rate of a second voltage between a second of the supply potentials (V-) and the ground potential (PE). [2] Vehicle electrical system (VES) according to claim 1, wherein the evaluation device (A) is configured to output an error signal when a ratio of a first voltage between a first of the supply potentials (V+) and the ground potential (PE) to a second voltage between a second of the supply potentials (V-) and the ground potential (PE) exceeds an upper limit or falls below a lower limit. [3] Vehicle electrical system (FET) according to one of the preceding claims, wherein the insulation monitor (IM) has a signal output (SA) configured to emit an externally receivable request signal that represents an insulation test request. [4] Vehicle electrical system (FB) according to claim 3, wherein the insulation monitor (IM) is configured to output the request signal (AF) via the signal output (SA) when the evaluation device (A) outputs an error signal (S). [5] Vehicle electrical system (FB) according to claim 4, wherein the isolation monitor (IM) is configured to output the request signal (AF) via the signal output (SA) with a predetermined delay. [6] Vehicle electrical system (FOS) according to one of the preceding claims, wherein the two supply potentials (V+, V-) and the ground potential (PE) are connected to respective contacts of a DC charging interface (LA). [7] Vehicle electrical system (FB) according to claim 6, wherein the two supply potentials (V+, V-) are connected via switches (S1, S2) to the respective contacts of a DC charging interface (LB), and the insulation monitor (IM) is connected to the switches (S1, S2) in a controlling manner and is configured to open the switches (S1, S2) when a fault signal is present.

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