Insulation error detection based on ac voltage components of an activation signal in the DC voltage side of an ac voltage charging circuit

Abstract

The invention relates to a method for sensing an insulation error in a vehicle charging circuit (FL). This circuit has a DC voltage side (GS), which is insulated with respect to a protective conductor potential (PE), an AC voltage side and a controlled rectifier (PFC) via which the DC voltage side (GS) is connected to the AC voltage side (WS). The controlled rectifier (PFC) is operated in a clocked manner according to an activation signal (AS). The following steps are also provided: sensing a voltage (S1, S2, S3) that occurs between DC voltage potentials (U+, U-) of the DC voltage side (GS) or between a DC voltage potential (U-) of the DC voltage side (GS) and the protective conductor potential (PE) and outputting an insulation error signal (IF) if the voltage (S1, S2, S3) contains a DC voltage component (WK) that partly or completely corresponds to the activation signal (AS), and has a signal strength that is above a predefined threshold (SW). The invention also relates to a corresponding vehicle charging circuit (FL).

Description

[0001] Description

[0002] Insulation fault detection based on AC voltage components of a control signal in the DC side of an AC charging circuit

[0003] Vehicles with electric traction drive have a traction battery that supplies electrical energy for the drive. To charge this battery, charging circuits are used with a rectifying unit that can provide DC voltage from an external AC voltage source to charge the battery. The rectifying unit is typically a controlled rectifier, which can also be designed as an (active) power factor correction filter.

[0004] Due to the high traction power and high charging power, the rated voltage of the vehicle's drive system and the traction battery is often well above 60 volts, making insulation necessary. Corresponding on-board electrical systems or charging circuits therefore have insulation to isolate the on-board electrical system potentials from a protective conductor potential or from a chassis potential of the on-board electrical system. Especially during charging, when an external AC voltage source with a correspondingly high rated voltage is connected to the vehicle, it is important to ensure that no harmful contact voltage potential is present on the chassis or on-board electrical system components. It must be ensured that the insulation is functional.

[0005] It is an object of the invention to show a possibility with which insulation faults can be reliably detected.

[0006] This object is achieved by the subject matter of the independent claims. Further properties, features, embodiments, and advantages emerge from the dependent claims, the description, and the figure. It is proposed to operate a controlled rectifier according to a control signal that is oriented, for example, to target operating parameters of the vehicle charging circuit (output voltage, output power, output current, etc.). In a DC voltage section or in a DC voltage side of the vehicle charging circuit or in a vehicle electrical system connected to it, a check is carried out to determine whether an AC voltage component similar to the control signal occurs there. If this is the case, or if the signal strength of this AC voltage component (which is similar to the control signal or is a part thereof) is above a threshold value, then an insulation fault is assumed.

[0007] In the event of an insulation fault, the AC voltage resulting from the operation of the rectifier is transmitted with significantly greater intensity or with significantly less attenuation than with functioning insulation, so that an insulation fault can be determined based on the detection of AC voltage components on the DC side. In particular, it can be examined whether a voltage between a chassis or protective conductor potential and a DC voltage potential contains the AC voltage component or the control signal with a signal strength that exceeds a threshold value. Alternatively, the voltage between the two DC voltage potentials (on the DC side) can be observed to determine whether an AC voltage signal similar to the control signal or the relevant AC voltage component with a signal strength that exceeds a threshold value.The control signal corresponds to the pulse signal (PMW) that operates the controlled rectifier. The AC voltage component, which partially or completely corresponds to the control signal, is similar to the control signal. In other words, the AC voltage component partially or completely corresponds to the switching signal of the controlled rectifier. Since the switching signal, i.e., the switching pulses in the power path, correspond to the control signal (and vice versa), the AC voltage component under investigation partially or completely corresponds to both the control signal and the switching signal of the rectifier's power path.

[0008] A method for detecting an insulation fault in a vehicle charging circuit therefore provides for the clocked operation of the controlled rectifier according to a control signal. The vehicle charging circuit comprises a DC voltage side and an AC voltage side. The DC voltage side is connected to the AC voltage side via a controlled rectifier of the vehicle charging circuit. The DC voltage side, or at least a portion thereof, is insulated from a protective conductor potential. In particular, at least a portion of the DC voltage side is insulated from the protective conductor potential or the chassis potential. A further portion of the DC voltage side can be provided that is not insulated from the protective conductor potential.

[0009] A device can be provided on the DC side that transmits DC voltage or DC current between the two sections while still providing galvanic isolation. The insulation fault to be detected exists between a DC voltage potential on the DC side, particularly a section of the DC side that is galvanically isolated, and the protective conductor potential or the chassis potential. The insulation fault can be present in the charging circuit or in a circuit or component connected to it (an on-board electrical system, a section of the on-board electrical system, a battery, etc.), whereby the insulation fault equally affects the charging circuit.Therefore, insulation faults caused by the charging circuit and insulation faults caused by a connected circuit or component are both referred to as insulation faults in the charging circuit, since causes outside the charging circuit also affect the charging circuit. Therefore, all insulation faults that affect the charging circuit are referred to as "insulation faults in the charging circuit."

[0010] A protective conductor potential can be provided within the vehicle charging circuit, which is connected (within the charging circuit) to the chassis potential. In particular, an AC voltage connection can be provided to which an external AC voltage source or AC current source can be connected, wherein this AC voltage connection has a protective conductor potential. This potential of the connection is preferably connected to the chassis potential of the vehicle in which the vehicle charging circuit is located. As mentioned, due to the equipotentiality, the two terms "protective conductor potential" and "chassis potential" can be interchanged.

[0011] The controlled rectifier has switching elements that are controlled by a switching signal external to the switch. In other words, the switches have a control input via which it can be set whether the switch is closed or not in the power path. The controlled rectifier is, in particular, a semiconductor rectifier and has electronic semiconductor switches, i.e., semiconductor switches that have a control input such as a base, a gate, or similar. The control inputs of the semiconductor switches are controlled by a control signal, which may originate from a control device. Rectifiers are generally referred to as rectifying units, such as rectifier circuits with controllable switches such as (single- or multi-phase) full-wave rectifiers or power factor correction filters, which, in addition to a rectifier circuit, also have working inductances.The charging circuit is in particular an AC charging circuit configured to convert an AC charging voltage into a DC voltage (in the DC voltage side).

[0012] The controlled rectifier is designed to controllably rectify an alternating voltage present on the alternating side and to output the rectified voltage to the direct side. The direct side can be referred to as the secondary side, while the alternating side is the primary side. The voltage can be detected on the direct side (secondary side) as described, and an error signal can be output if the voltage contains an alternating voltage component that partially or completely corresponds to the control signal (primary side). In this case, power is transferred from the primary side to the secondary side (forward operation); the signal is generated on the primary side and detected on the secondary side. A galvanically isolating DC-DC converter can be connected to the direct side of the rectifier.

[0013] The terms "secondary side" and "primary side" refer to the direction of power flow in forward operation and are used in the same way for reverse operation (in a bidirectional charging circuit). In reverse operation, power is transferred from the secondary side to the primary side. In forward operation, the reverse is true.

[0014] The vehicle charging circuit can be bidirectional. The method can also be applied to a circuit in which power is transferred from the secondary side to the primary side of the rectifier. The method can also be used for a reverse-operating, bidirectional charging circuit (reverse operation). On the secondary side (or in the DC-DC converter connected to the secondary side of the rectifier), the clocked operation is carried out according to the control signal, in particular by a circuit that rectifies in forward operation and operates as a chopper (or clocked switching) in reverse operation. This circuit can be part of the secondary side of the rectifier or the DC-DC converter. On the primary side (relative to the rectifier), an alternating voltage is generated, which is generated by the rectifier in reverse operation. In reverse operation, the rectifier generates an alternating current on the AC voltage side.

[0015] A voltage is present on the AC side. An insulation fault signal is generated if the voltage contains an AC component that partially or completely corresponds to the control signal (from the secondary side of the rectifier or the optional DC-DC converter). In particular, the fault signal is only generated if the signal strength exceeds a predetermined threshold. In other words, on the side where clocked operation according to a control signal is carried out in forward operation, the voltage can be measured in reverse operation and checked for the presence of AC components (in order to generate an insulation fault signal if the signal strength exceeds the threshold).This side is preferably the AC side of the vehicle charging circuit (especially for forward operation) and can also be the rectifier in reverse operation, but also a DC-DC converter connected to the DC side of the rectifier.

[0016] On the side where the voltage is applied in forward operation, which is analyzed for AC components (to emit an insulation fault signal if necessary), clocked operation is carried out in reverse operation according to a control signal. This side is the DC side of the vehicle charging circuit, for example, the DC side of the rectifier or the DC-DC converter (especially the side facing away from the rectifier). This refers to forward operation. In reverse operation, this refers in particular to the AC side of the rectifier, or also to its DC side, or to the side of the DC-DC converter connected downstream of the rectifier, which side faces the rectifier.

[0017] One embodiment provides that the vehicle charging circuit has a DC voltage side that is insulated from a protective conductor potential, an AC voltage side, and a controlled rectifier via which the DC voltage side is connected to the AC voltage side. The vehicle charging circuit is bidirectional. In a reverse operating mode, also referred to as output mode, feedback mode, or supply mode, the rectifier is operated to convert power or voltage from the DC voltage side into AC voltage. In this mode, the rectifier functions as a converter. The rectifier is operated in a clocked manner according to a control signal to generate an AC voltage on the AC voltage side. The control signal is configured to generate, in addition to the conversion, a potential difference with respect to the protective conductor potential, which corresponds to a test AC signal.A voltage is detected that exists between DC potentials of the DC side or between a DC potential of the DC side and the protective conductor potential. In particular, the method detects the voltage on one side of a galvanically isolating DC-DC converter or another galvanically isolating unit that has another, opposite side connected to the controlled rectifier. An insulation fault signal is emitted (and / or a disconnection is performed and / or operation of the charging circuit is interrupted) if the voltage contains an AC component that partially or completely corresponds to the test AC signal and that has a signal strength that exceeds a predetermined threshold.

[0018] This specifically generates a test signal on the primary side that corresponds to an alternating voltage relative to the protective potential, and it is checked whether the (changing) potential offset represented by this test signal is present on the secondary side with a minimum signal strength. This means that the method can also be used in reverse operation. A suitably equipped vehicle charging circuit has a signal generator that is designed to generate the test signal and control the rectifier (in converter mode) accordingly. A corresponding vehicle charging circuit also has a voltmeter that measures the potential offset (e.g., voltage, power, or current) relative to the protective conductor potential on the secondary side, as well as an evaluation unit that compares this value with a threshold value and is designed to emit an insulation fault signal (only) if the threshold value is exceeded.

[0019] The clocked operation of the controlled rectifier according to the control signal provides that the switches of the rectifier are opened or closed according to the control signal. The control signal is preferably clocked to achieve a desired rectification or a desired output current or a desired output voltage. In particular, the rectifier is clocked to correct a power factor or to generate (compensating) reactive power, and in particular to reduce harmonics. Therefore, the control signal can also be designed according to a desired reactive power signal or equalization signal.

[0020] To determine whether an AC voltage component sufficiently similar to the control signal is passing from the AC side to the DC side with a signal strength that exceeds a threshold value, a voltage on the DC side is detected. This voltage can be between DC potentials on the DC side (either in a galvanically isolated area of ​​the DC side or in a galvanically non-isolated area of ​​the DC side). Alternatively, the voltage can be present between a DC potential on the DC side and the protective conductor potential, in particular between the protective conductor potential and a DC potential of a galvanically isolated or non-galvanically isolated section of the DC side. The DC potentials on the DC side are power potentials, i.e.carry the power delivered by the rectifier (as a power signal) as direct voltage.

[0021] An insulation fault signal is emitted when the voltage (in the DC side as shown) contains an AC component that is similar to the control signal or its AC signal components. The AC component is similar to the control signal with a similarity measure that exceeds a predetermined threshold. A correlation, for example, or a spectral comparison with one or more frequency bands or individual frequencies can be used as a similarity measure. The similarity between the AC component and the control signal does not refer to the amplitude, but only to the curve or to AC signal parameters (frequency, spectrum, aperiodic AC voltage components, etc.). An insulation fault signal is emitted when the AC component in the voltage corresponds to the control signal in terms of its curve or with regard to at least one frequency.The AC voltage component can partially correspond to the control signal if the AC voltage component has one or more predetermined AC voltage components of the control signal. The AC voltage component can also completely correspond to the control signal, in which case the curve of the AC voltage component corresponds to the curve of the control signal. If there are several individual switches in the rectifier, the control signal corresponds in particular to the totality of all individual switching signals. For comparison with the AC voltage component, the control signal can be represented by at least one frequency component of the control signal, by the repetition frequency of switching edges, by the duty cycle of edges or states in the control signal, or by switching times of the switches in the rectifier, or by other characteristics of the operation of a controlled rectifier.It can be checked whether the AC voltage component has a minimum degree of similarity to the control signal, with or without taking into account the absolute switching times in the control signal. Furthermore, when determining the similarity or whether the AC voltage component is partially or completely contained in the switching signal, only one switching frequency or only a plurality of frequencies of the control signal can be considered. This frequency or frequencies correspond to the AC voltage component. If one or more frequencies are now searched for as an AC voltage component, a check is carried out to determine whether this AC voltage component is contained in the control signal. This corresponds to checking whether the AC voltage component (with one or more frequencies partially contained in the control signal, which also contains further frequency components) is contained or partially corresponds to this control signal.

[0022] Furthermore, the insulation fault signal is emitted when these

[0023] AC voltage component that partially or completely corresponds to the control signal (in particular with regard to its waveform or with regard to at least one frequency component), and if it is given that the AC voltage component is contained in the control signal with a signal strength that lies above a predetermined threshold. This avoids false positive insulation fault signals that can occur with real, functioning insulation, since slight ohmic, inductive, or capacitive coupling across the insulation cannot be ruled out. Furthermore, the insulation fault signal can only be emitted if the further condition is met that the signal strength is continuously present in the AC voltage component with the signal strength above the predetermined threshold for at least a period of time.In other words, the emission of the insulation fault signal can be de-energized, in particular according to a predetermined period of time during which the AC component in the voltage is present with the signal strength above the threshold value (continuous).

[0024] The voltage can be detected in a section of the DC side that is not galvanically isolated from the rectifier or from the AC connection, or in a section of the DC side that is galvanically insulated from the rectifier. The vehicle charging circuit can have a galvanically isolating unit, in particular a unit via which the DC voltage from the rectifier is transferred to a section of the DC side that is galvanically isolated from the DC-DC converter. This galvanically isolating unit can be provided as a galvanically isolating DC-DC converter. The voltage can thus be detected on one side of a galvanically isolating unit (or a DC-DC converter) that points away from the rectifier and is galvanically isolated from it. This unit has a further, opposite side that is connected to the controlled rectifier.The voltage can thus be detected on the side of the galvanically isolating unit facing away from the rectifier (i.e., a galvanically isolated section). The galvanically isolating unit thus has a first side connected to the controlled rectifier and, in particular, is not galvanically isolated from the rectifier or the AC voltage connection, and a second side that is galvanically isolated from the AC voltage connection or the rectifier.

[0025] Alternatively, the voltage can be detected on the side of the galvanically isolating unit (in particular a DC-DC converter) that is galvanically connected to the rectifier. The voltage can in particular be detected in an intermediate circuit that connects the rectifier to the galvanically isolating unit (e.g. a DC-DC converter). This results in particular in a voltage that exists between the DC voltage potentials. When detecting a voltage that exists between a DC voltage potential and the protective conductor potential, this is preferably detected on the second side of the galvanically isolating unit or in a section of the DC voltage side that is galvanically isolated from the rectifier or the AC voltage connection.As mentioned, preferably at a voltage that is present between the DC voltage potential, this voltage is preferably detected in an area that is not galvanically isolated from the rectifier or from the AC voltage connection.

[0026] According to one embodiment, the AC voltage component is an alternating signal that occurs during normal, unmodified operation of the rectifier. In other words, this embodiment provides for the AC voltage component to result from the operation of the rectifier, i.e., from the rectifying function of the rectifier. In particular, the AC voltage component can be an alternating signal that is determined, by the function of the controlled rectifier, to generate a (compensating) reactive power component or to reduce harmonics. The AC voltage component can thus be based on the intended operation of the rectifier. In this case, it is only necessary to detect whether the signal strength of the AC component, which results from the intended operation of the rectifier, is above the threshold value.In this case, the control signal is generated by the intended operation of the rectifier. In particular, the control signal is generated according to a regulation or control, which in turn is based on a target operating parameter of the vehicle charging circuit. Target operating parameters are considered to be parameters that are necessary for the intended operation of the rectifier, for example operating parameters such as target voltage, target power, target power factor or target reactive power or even target harmonic upper limit. Target operating parameters are therefore considered to be parameters that result from the rectifying operation or from operation as a power factor correction filter for the rectifier. The target operating parameters relate in particular to the operation of the vehicle charging circuit for transmitting a target power or for generating a target direct current or a target voltage on the DC side of the vehicle charging circuit.Alternatively, or in combination with this, the regulation or control is carried out according to the target operating parameters of the rectifier designed as a power factor correction filter. These target operating parameters relate in particular to a target reactive power, a target harmonic limit, a target power factor, or similar operating parameters that characterize operation as a power factor correction filter (PFC). If the rectifier is designed as a power factor correction filter, it may have working impedances such as working inductances connected to the switches.

[0027] In particular, the rectifier's switches are connected to the AC voltage terminal via working inductors in order to specifically correct a power factor (by generating reactive power). If an alternating signal is used as the AC voltage component, which occurs anyway during normal operation of the rectifier, i.e., which characterizes the rectifier's operation as a rectifier itself or as a power factor correction filter, then this signal can already be used for insulation fault detection. In other words, the AC voltage component, which characterizes the rectifying function in the rectifier or the function as a power factor correction filter, can be used to check whether this occurs in the voltage with a signal strength above the specified threshold.This corresponds to considering the alternating voltage component that occurs anyway as a test signal to check the insulation.

[0028] Alternatively, or in combination, the control signal can be modulated with a test signal. The test signal can then correspond to the AC voltage signal. Furthermore, the AC voltage signal can correspond not only to the test signal, but also to the AC signal resulting from the operation of the rectifier as a rectifier itself or as a power factor correction filter. In this case, the switching signals for the rectifier's switches can already be modulated with the test signal, or the test signal can be indexed into the DC voltage side of the rectifier. Thus, the rectifier can be operated not only according to the operating parameters, but also according to the test signal.The control signal can be modulated with the test signal in such a way that the modulation by the test signal results in a modulated voltage between the DC potential, or in such a way that the test signal results in a modulated voltage between the protective conductor potential and one of the DC potentials. If the control signal is modulated with the test signal in such a way that a modulated output voltage results (preferably in a non-galvanically isolated section of the DC side), the test signal is preferably a signal with a frequency significantly below the switching frequency of the rectifier (which results from operation as a rectifier or as a power factor correction filter). For example, modulation with a frequency of less than 10 Hz can be provided by the test signal, in which case the DC signal output by the rectifier is also modulated with this voltage.Since the frequency differs significantly from the expected ripple frequency on the DC side of the rectifier, the relevant AC component can be easily detected. If the control signal is modulated with the test signal in such a way that a voltage is created between the protective conductor potential and one of the DC potentials, which is modulated according to the test signal, then a test signal with a frequency can be used that is preferably significantly higher than the switching frequency of the switching elements of the rectifier, whereby this switching frequency is determined by the function as a rectifier or as a power factor correction filter. In particular, the frequency of the test signal is below 1 kHz and preferably below a frequency of an insulation monitor test signal that is actively fed in for insulation monitoring. This serves to separate the present method from the operation of active insulation monitors.The test signal is generated, for example, by a test signal generator.

[0029] The test signal can, for example, be an alternating signal with a predetermined spectrum, for example with a spectrum that essentially has only a frequency component, or can correspond to a square wave signal that, in particular, has a specific edge frequency (inverse of the pulse duration). The test signal can be provided as a noise signal, in particular as a pseudo-noise signal. This enables interference-free recognition or detection in the voltage that is detected in the DC voltage side. The test signal can also have a signal component of a frequency that constitutes no more than a minor portion of the unmodulated control signal. In other words, the alternating signal can have a signal component in the frequency range dominated by the unmodulated control signal that lies below a threshold value.In other words, the spectrum of the test signal preferably differs significantly from the spectrum of the unmodulated (i.e., resulting from closed-loop or closed-loop control) control signal. In particular, a large portion of the test signal's power is preferably located in a spectral range in which the power of the control signal is below a threshold value or at least 20, 30, or 40 decibels below the power of the frequency range with the highest power.

[0030] The control signal is preferably modulated with a test frequency, i.e., with a test signal frequency that is (within a predetermined margin) below or above the frequency resulting from the rectifier's operation in the rectifying function or when functioning as a power factor correction filter. In particular, the test frequency (test signal frequency) is below or above the frequency that, during clocked operation of the rectifier according to the target operating parameters, is assigned to the largest power component within the AC component of the voltage. The test signal frequency thus differs from the frequency corresponding to the largest AC power component in the DC voltage (of the galvanically non-isolated region) or the galvanically isolated region of the DC voltage side.The test frequency is therefore a frequency that differs sufficiently from the frequencies that occur during normal operation of the rectifier (as a rectifying unit or as a power factor correction filter).

[0031] The AC voltage signal has a frequency of essentially 50 Hz, 60 Hz, 150 Hz, or 180 Hz, whereby the frequency does not deviate by more than 2%, 5%, or 10% from 50 Hz, 60 Hz, 150 Hz, or 180 Hz. This is particularly the case when the voltage corresponds to between a protective conductor potential and a DC voltage potential. Alternatively, the control signal is modulated with a test signal whose frequency is less than 20 Hz, 10 Hz, 5 Hz, or 2 Hz. The frequency does not deviate by more than 2%, 5%, or 10% from 20 Hz, 10 Hz, 5 Hz, or 2 Hz. Another aspect is that the frequency of the AC voltage signal or the test signal is below 1 kHz. If an (active) insulation monitor is provided in the on-board network whose test signal is at 1 kHz or above, this ensures that the process is not affected by the active insulation monitor, and vice versa.

[0032] The voltage can be detected at one side of a galvanically isolating unit (e.g., a DC-DC converter) connected to the controlled rectifier. This can, in particular, correspond to a galvanically non-isolated section of the DC side of the charging circuit. The side of the galvanically isolating unit connected to the controlled rectifier is galvanically conductively connected to it. If the controlled rectifier is also not galvanically isolating, then the voltage is detected in a region of the DC side that is not galvanically isolated (from the protective conductor potential). In particular, the voltage is detected at this point if this corresponds to the voltage between two DC potentials.In this case, the control signal is preferably modulated with a test signal whose frequency is below the mains frequency of the AC voltage connection or the AC voltage side of the rectifier. For example, when the voltage is detected at this point, the control signal can be modulated with a test signal whose frequency is no more than 10 Hz, 5 Hz, 2 Hz, or 1 Hz. The frequency does not deviate by more than 2%, 5%, or 10% from 5 Hz, 2 Hz, or 1 Hz, in particular from 10 Hz. If an insulation fault is detected according to the method, it can be provided that a vehicle-side connection is interrupted, or that an interruption signal is emitted, which causes a vehicle-external charging source to interrupt the connection to the vehicle-side charging circuit.A method for operating the vehicle charging circuit described here therefore provides that the method mentioned here for detecting an insulation fault is carried out, and that a vehicle-side connection is interrupted when an insulation fault is detected and / or an interruption signal is transmitted to a source external to the vehicle or to a controller thereof. Furthermore, an interruption signal can be transmitted to a higher-level controller (on the vehicle or external to the vehicle, in particular in the charging source external to the vehicle) to initiate an interruption (through indirect control).

[0033] Furthermore, a vehicle charging circuit is described, in particular a vehicle charging circuit as described with reference to the method. The vehicle charging circuit has a DC voltage side that is insulated from a protective conductor potential. In particular, the vehicle charging circuit has a section of a DC voltage side that is insulated from a protective conductor potential. The vehicle charging circuit can further have a section of the DC voltage side that is not galvanically isolated from the protective conductor potential. In this case, the state in which the relevant units are galvanically isolated from one another is referred to as "isolated". The vehicle charging circuit further has an AC voltage side and a controlled rectifier. The DC voltage side is connected to the AC voltage side via the rectifier.As also mentioned with reference to the method, the AC voltage side can have an AC voltage connection. This AC voltage connection can correspond to the AC voltage connection described here. A control device is provided which is connected to the rectifier in a controlling manner. The control device is preferably part of the vehicle charging circuit. The control device is configured to operate the rectifier in a clocked manner according to a control signal. The control device is in particular configured to output a control signal to the rectifier which implements a control or regulation (as described here). The control device is further preferably configured to output such a control signal to the rectifier, which enables the rectifier to perform the function of a controlled rectifier or to perform the function of a power factor correction filter.As mentioned, both functions are linked to specific operating parameters that are available as target values ​​(or that are used as specifications for control or regulation).

[0034] An insulation fault detection unit of the vehicle charging circuit is configured to detect a voltage. This voltage is present between the DC potentials of the DC side (in particular in a non-galvanically isolated section or also in a galvanically isolated section). The voltage can also be present between a DC potential of the DC side and the protective conductor potential (of the AC side), preferably in a galvanically isolated section of the DC side or also in a non-galvanically isolated section of the DC side. Potentials that are galvanically isolated from the rectifier or from the protective conductor potential or from the AC side or the AC connection are referred to as galvanically isolated.Galvanically isolated is a component that is electrically insulated from the AC side, the rectifier, the AC terminal and / or the rectifier.

[0035] The insulation fault detection unit has a detection unit configured to receive the voltage. The insulation fault detection unit, and in particular the detection unit, thus has at least one signal-transmitting connection that leads to the aforementioned potentials. The detection unit is configured to receive the voltage. In particular, the detection unit is configured to receive a signal that corresponds to the voltage and that, in particular, reproduces the waveform. The detection unit is not necessarily configured to receive the voltage with the amplitude present at the aforementioned potentials. This also applies to the insulation fault detection unit. In particular, a voltage divider or a digital-to-analog converter can be provided, which is connected upstream of the insulation fault detection unit or its input.

[0036] The detection unit is configured to detect a signal strength of the alternating voltage component present in the voltage. The alternating voltage component corresponds in particular to the alternating voltage component mentioned with reference to the method. This also applies to the voltage. The alternating voltage component corresponds partially or completely to the control signal, in particular as described above with reference to the method.

[0037] The insulation fault detection unit further comprises a comparator. This comparator is configured to compare the signal strength with a predetermined threshold value. The comparator is configured to output an insulation fault signal if the signal strength is greater than the threshold value. The comparator is configured not to output an insulation fault signal if the signal strength is not greater than the threshold value. Outputting no insulation fault signal is equivalent to outputting a signal indicating that no insulation fault is present. Finally, an insulation fault detection unit configured to carry out the method can be provided. Such an insulation fault detection unit is configured like the insulation fault detection unit described above.Such an insulation fault detection unit can be configured outside the vehicle charging circuit or can be configured as part of the vehicle charging circuit. The insulation fault detection unit has, in particular, an input that can be connected to the relevant potentials. Furthermore, the insulation fault detection unit can have an input to which the control signal can be input, or a signal that characterizes the control signal. In this way, the insulation fault detection unit can determine whether or not the control signal is present in the voltage with a signal strength that exceeds the threshold value.In the former case, the insulation fault detection unit would report an insulation fault or a corresponding signal, and in the latter case, the insulation fault detection unit would not report an insulation fault or would not issue a corresponding insulation fault signal.

[0038] The options described here are used to detect an insulation fault in a vehicle charging circuit. If the insulation fault exists outside the vehicle charging circuit, for example in a connected vehicle electrical system, and the insulation fault is present in the connected vehicle electrical system, then the insulation fault also exists in the vehicle charging circuit due to this connection. The detection of an insulation fault in a vehicle charging circuit is therefore synonymous with the detection of an insulation fault that affects the vehicle charging circuit and which does not necessarily have its cause in the vehicle charging circuit. Rather, the cause of the insulation fault can also lie in a connected circuit (vehicle electrical system) or connected component, so that the insulation fault also affects the vehicle charging circuit and thus also represents an insulation fault in the vehicle charging circuit.Figure 1 serves to explain embodiments by way of example and symbolically shows a circuit which is intended to serve as an explanation.

[0039] Figure 1 shows a vehicle charging circuit FL with an AC voltage side that includes an AC voltage connection WA, WA'. The AC voltage connection is composed of a protective conductor connection WA' and a (exemplary) four-part / four-wire AC current connection WA, which can include three phase connections and a neutral conductor connection. The vehicle charging circuit FL shown further comprises a rectifier PFC, which is an interface between a DC voltage side GS and an AC voltage side WS of the vehicle charging circuit FL. In the illustrated embodiment, a galvanically isolating DC-DC converter GW (also an example of a galvanically isolating unit) is connected with a first side 1 to the DC voltage side of the rectifier PFC. The DC-DC converter GW has a second side 2, which is galvanically isolated from the first side 1.The second side 2 is connected to an on-board power supply connection, which has contacts B+ and B-, i.e., two DC potential contacts with different potentials. A component (battery) external to the charging circuit or an on-board power supply external to the charging circuit can be connected to these. Insulation faults here affect the charging circuit and are therefore detected as described herein.

[0040] An AC voltage source WQ external to the vehicle charging circuit FL is connected to the vehicle charging circuit, in particular to the terminals WA and WA'. The rectifier PFC is a controlled rectifier that converts the power signal of the AC voltage terminal WA (alternating current) into a DC voltage. This DC voltage exists between the potentials Z+ and Z-, whereby these potentials are the potentials of an intermediate circuit. The intermediate circuit connects the rectifier PFC to the DC-DC converter GW and has an intermediate circuit capacitor ZK, which serves to smooth or support the voltage between Z+ and Z-, i.e., a DC voltage. The rectifier PFC is controlled by a control signal AS generated by a control device C.Particularly when the PFC rectifier is designed as a power factor correction filter, this generates an alternating signal, which is present as a ripple voltage in the voltage between Z+ and Z- in the intermediate circuit. The DC-DC converter following the intermediate circuit or the PFC rectifier is galvanically isolated, so that with fault-free insulation (of the DC-DC converter GW or other components connected to the charging circuit), this essentially does not occur on the second side of the DC-DC converter GW. The insulation refers to the insulation between the DC voltage potentials U- / U+ on the second side of the DC-DC converter, i.e., in a galvanically isolated section of the DC voltage side GS from the protective conductor potential PE or GND.If the insulation (between the DC potentials of a galvanically isolated section of the DC side and the protective conductor potential PE) is defective, the alternating signal generated during control in the PFC rectifier is transferred to a voltage S1 between the protective conductor potential PE and one of the DC potentials U- or U+. A corresponding voltage S1 is shown between the PE potential and the U- potential, which contains an AC voltage component resulting from the control of the GR rectifier.

[0041] The signal strength of this AC voltage component is used to detect whether or not an insulation fault is present. The AC voltage component is only transmitted to a galvanically isolated section of the DC side if the insulation between the protective conductor potential PE and a DC potential U+ or U- of a galvanically isolated section of the DC side is defective or has an insufficient insulation resistance.

[0042] The entire alternating signal can be checked as an alternating voltage component on the direct voltage side GS for insulation fault detection, or only a part of it, in particular only an alternating voltage component that makes up a part or only a spectrum of the alternating signal that originates overall from the control of the rectifier PFC.

[0043] An insulation fault detection unit IE shown as an example has a signal input E which is connected to the potentials PE and U-. Alternatively, the input can also be connected to the potentials PE and U+ or to the potentials U- and U+. A connection to the potentials Z+ and Z- is also conceivable. The voltages S1, S3 or S2 lying between these potentials are present at the input E, either as these voltages themselves or as a signal that represents these voltages. A detection unit ER is connected downstream of the input E of the insulation fault detection unit IE and detects an AC voltage component from this voltage (S1, S2 or S3) as shown above. A comparator V connected downstream of the detection unit ER determines whether the signal strength of the AC voltage component WK is greater than a threshold value SW or not.If the threshold is reached or exceeded, an insulation fault signal IF is output at a fault output FA of the insulation detection unit IE. If the threshold is not exceeded, no insulation fault signal IF is output.

[0044] Since the AC voltage component WK corresponds partially or completely to the control signal AS of the rectifier PFC, the determination unit ER knows which characteristics the AC voltage component WK to be detected has. This is symbolically represented by the dashed double arrow, which is intended to show that the control signal AS generates alternating signals that can be detected by the insulation fault determination unit IE (using component ER) when an insulation fault is present. The determination unit ER can thus be set to the characteristics of the control signal AS. Alternatively, the determination unit ER can have an input to which the control signal, an AC voltage component (which can be at least part of the control signal), or a signal that represents these signals can be input.In this way, the detection unit ER can compare the signal S1 (S2 or S3) with the AC voltage component WK to determine the signal strength of the AC voltage component WK. The illustration shows that the AC voltage signal WK is passed from the detection unit ER to the comparator. Alternatively, the signal strength of the AC voltage component WK can also be passed from the detection unit to the comparator V. In the former case, the comparator V is able to generate the signal strength of the AC voltage component from the AC voltage component WK originating from the detection unit ER in order to compare it with the threshold value SW.

[0045] The voltage containing the AC component WK in the event of an insulation fault can be the voltage S1 between a protective conductor potential PE and a potential U- (or U+) of a galvanically isolated section of the DC side GS. Furthermore, this voltage can also correspond to the intermediate circuit voltage S2, i.e., the voltage between DC potentials (power DC potentials) in a galvanically non-isolated section of the DC side GS. Finally, the voltage S3 can be used as the voltage to be tested for the AC component, with the voltage S3 existing between the potentials U+ and U- in a galvanically isolated section of the DC side GS.

[0046] The control signal AS can be based exclusively on the desired function of the rectifier (controlled rectification or function as a power factor correction filter). The control signal AS is generated exclusively according to the associated operating parameters, where these operating parameters include, for example, the desired output power of the rectifier, the output current of the rectifier, the output voltage of the rectifier, the reactive power of the rectifier, the desired power factor, and / or the frequency of the generated reactive power. In its function as a power factor correction filter, the rectifier can be operated as an active power factor correction filter to generate a desired reactive power that at least partially compensates for another reactive power to be compensated. This reduces undesirable interference with an external AC voltage source WQ.In other words, the control signal typically used for the GR rectifier can be used as the control signal, without further modification of this signal for other functions. This control signal, or signal components thereof, typical for operation can then be used as the AC voltage component to check whether faulty insulation is causing components of the control signal to be transmitted to the DC voltage side with a certain signal strength. This can be used to determine the faulty insulation condition.

[0047] Alternatively, the controller C can be configured for additional modulation in order to specifically generate a test signal that is not used for the normal operation of the rectifier (controlled rectification or power factor correction), but rather for the insulation fault detection described above. In this case, the control signal resulting from normal operation can be additionally modulated in order to generate a test signal that is applied between one of the DC voltage potentials Z+, Z-, U+, U- on the one hand and the protective conductor potential PE. Alternatively, the (remodulated) control signal can be modulated in such a way that a test signal is produced that is applied between DC voltage potentials on the DC side, for example a test signal voltage as an AC voltage in the voltage S2 in the intermediate circuit or S3 in a galvanically isolated section of the DC side.The intermediate circuit is not galvanically isolated and forms a galvanically non-isolated section of the DC voltage side GS. If the modulation is intended to generate a test signal between the protective conductor potential and another voltage, an AC voltage with a frequency of less than 1 kHz is preferably used as the test signal, preferably with a frequency that differs from the frequencies generated by the normal operation of the PFC rectifier. If the modulation generates a test signal that refers to a voltage between two DC voltage potentials (for example between Z- and Z+ or between U- and U+, i.e. voltages S2 or S3), then an AC voltage with a frequency below the fundamental frequency of the PFC rectifier control is preferably used as the test signal. A corresponding frequency can be, for example, approximately 10, 5, 2 or 1 Hz.

[0048] Finally, another on-board power supply can be connected to the B+ and B- terminals of the galvanically isolated section of the DC voltage side, for example, a battery B designed as a high-performance traction battery. This connected on-board power supply is not part of the charging circuit.

[0049] Figure 1 shows a protective conductor potential on the AC power source side, represented as ground potential GND. The vehicle charging circuit also includes a protective conductor potential, embodied as chassis potential. Although these potentials have different origins, they represent the same electrical potential because they are interconnected. To represent the different origins of the two potentials, the reference symbol GND is used for the protective conductor potential of the AC voltage source WQ.

[0050] The illustrated galvanically isolated section of the DC voltage side GS further comprises a capacitive voltage divider with the capacitors C1 and C2. The potential PE, i.e. in particular a chassis potential, is present at the junction point of this capacitive voltage divider. The voltage which contains the AC voltage component in the event of an insulation fault can also be the voltage S1 which lies between the junction point of the capacitive voltage divider C1, C2 and the potential U-, which is a DC voltage potential of a galvanically isolated section of the DC voltage side GS. The galvanically non-isolated section of the DC voltage side GS extends from the DC voltage side of the rectifier PFC to the first side 1 of the rectifier GW. A galvanically isolated section of the DC voltage side GS extends from the second side 2 to the terminals B+, B- of the charging circuit.The rectifier GW is designed to transfer power from the first side 1 to the second side 2 with galvanic isolation. The first side 1 is connected to the DC voltage side of the rectifier BFC, while the opposite side 2 is connected to the terminals B+, B- and has the potentials U- and U+.

Claims

Patent claims 1 . Method for detecting an insulation fault in a vehicle charging circuit (FL), the - a DC voltage side (DC) which is insulated from a protective conductor potential (PE), - an AC side and - has a controlled rectifier (PFC) through which the DC voltage side (GS) is connected to the AC voltage side (WS), with the steps: Clocked operation of the controlled rectifier (PFC) according to a control signal (AS); Detecting a voltage (S1, S2, S3) which is present between DC potentials (U+, U-) of the DC side (GS) or between a DC potential (U-) of the DC side (GS) and the protective conductor potential (PE) and; Emitting an insulation fault signal (IF) if the voltage (S1, S2, S3) contains an AC voltage component (WK) which corresponds partially or completely to the control signal (AS) and which has a signal strength which is above a predetermined threshold value (SW).

2. Method according to claim 1, wherein the voltage (S1, S2, S3) is detected at one side (2) of a galvanically isolating DC-DC converter (GW) or another galvanically isolating unit having a further, opposite side (1) connected to the controlled rectifier (PFC).

3. Method according to claim 1 or 2, wherein the control signal (AS) is generated according to a regulation or control which is carried out according to at least one desired operating parameter of the vehicle charging circuit (FL) or the control signal (AS) is generated according to a regulation or control which is carried out according to at least one desired operating parameter of theThe method according to claim 3, wherein the control signal (AS) is modulated with a test signal corresponding to the AC voltage component (WK). The method according to claim 4, wherein the test signal is generated as a noise signal, as a pseudo-noise signal, or as an AC signal with a signal component of a frequency that constitutes no more than a minor portion of the unmodulated control signal. The method according to claim 3, 4, or 5, wherein the control signal is modulated with a test frequency that lies below or above the frequency that is assigned to the largest power component in the AC component of the voltage during clocked operation of the rectifier (PFC) according to the target operating parameter.Method according to one of claims 3-6, wherein the AC voltage component (WK) has a frequency of 50 Hz, 60 Hz, 150 Hz, or 180 Hz with a maximum deviation of no more than 2%, 5%, or 10%, or the control signal (AS) is modulated with a test signal whose frequency is less than 20 Hz, 5 Hz, or 10 Hz with a maximum deviation of no more than 2%, 5%, or 10%, and / or the frequency of the AC voltage component (WK) is below 1 kHz. Method according to one of the preceding claims, wherein the voltage (S1, S2, S3) is detected on one side (1) of a galvanically isolating DC-DC converter (GW) or another galvanically isolating unit connected to the controlled rectifier (PFC).

9. The method according to claim 8, wherein the control signal (AS) is modulated with a test signal whose frequency is not more than 5 Hz, in particular not more than 2 Hz or 1 Hz.

10. A method for operating a vehicle charging circuit, comprising the steps of: executing the method according to any one of the preceding claims, and interrupting a vehicle-side connection when an insulation fault (IF) has been detected, or sending an interruption signal to a vehicle-external charging source (WQ) or a controller thereof.

11. Vehicle charging circuit (FL) with a DC voltage side (GS) which is insulated from a protective conductor potential (PE), an AC voltage side and a controlled rectifier (PFC) via which the DC voltage side (GS) is connected to the AC voltage side (WS), wherein a control device (C) is connected to the rectifier (PFC) in a control manner and is designed to operate it in a clocked manner according to a control signal (AS);an insulation fault detection unit (IE) which is configured to detect a voltage (S1, S2, S3) which is present between direct voltage potentials (U+, U-) of the direct voltage side (GS) or which is present between a direct voltage potential (U-) of the direct voltage side (GS) and the protective conductor potential (PE) and which has a detection unit (ER) which is configured to receive the voltage and is designed to detect a signal strength of the alternating voltage component (WK) present in the voltage, which corresponds partially or completely to the control signal (AS), wherein the insulation fault detection unit (IE) further has a comparator (V) which is configured to compare the signal strength with a predetermined threshold value (SW) and then output an insulation fault signal (IF) if the signal strength is greater than the threshold value (SW); 12. Method for detecting an insulation fault in a bidirectional vehicle charging circuit having a DC side which is insulated from a protective conductor potential, has an AC voltage side and has a controlled rectifier via which the DC voltage side is connected to the AC voltage side, wherein in a delivery mode the method comprises the steps of: clocked operation of the rectifier according to a control signal such that an AC voltage is generated on the AC voltage side, wherein the control signal is configured, in addition to this conversion, to generate a potential difference with respect to the protective conductor potential which corresponds to a test AC signal; Detecting a voltage that is present between DC potentials on the DC side or between a DC potential on the DC side and the protective conductor potential; Emitting an insulation fault signal if the voltage contains an AC component that partially or completely corresponds to the test AC signal and that has a signal strength that is above a predetermined threshold.

Images