DE102022201188A1 - AC charging circuit on the vehicle side with high-pass fault protection impedance between rectifier star point and protective conductor - Google Patents

Abstract

A vehicle-side AC charging circuit (LS) is described with a rectifier circuit (PFC) that is multi-phase and has a star point (SP) on the DC side, which is connected to a neutral conductor connection (N) of the AC charging circuit (LS). The AC charging circuit (LS) is equipped with a fault protection impedance (ZY) via which the star point (SP) is connected to a protective conductor connection (PE) of the AC charging circuit (LS). The fault protection impedance (ZY) is designed as a high-pass filter.

Description

Vehicles with an electric drive have a high-voltage traction battery that feeds the drive and can be charged by an AC charging circuit. For the charging process, an external charging current source (alternating current) is connected to an on-board alternating current charging circuit, to which in turn the traction battery is connected. Due to the high high-voltage voltages, which can be well over 60 V, special protective measures are required to protect against excessive contact voltages on the vehicle. One of these measures is the use of a protective conductor, which connects a protective conductor potential of the charging current source to a protective conductor potential of the vehicle or the vehicle's electrical system. If an insulation fault occurs, the protective conductor is used to divert the resulting fault current in order to avoid a dangerous contact current.

It is an object of the invention to indicate a possibility with which a touch current can be reduced, which reduces the potentially dangerous touch current in the event of a faulty protective conductor connection or generally in the event of an insulation fault.

This object is achieved by the AC charging circuit on the vehicle side according to claim 1. Further properties, features, embodiments and advantages result from the dependent claims as well as the description and the figures.

It is proposed to provide a fault protection impedance in a polyphase (particularly three-phase) AC charging circuit, via which a star point of a rectifier circuit of the AC charging circuit is connected to a protective conductor connection of the charging circuit. In a multi-phase rectifier circuit, in particular in a controlled multi-phase rectifier circuit, AC components can arise as a result of asymmetries, which are not completely output to a chassis potential using the fault protection impedance proposed here, but can be fed back to the connected charging current source via the neutral conductor connection of the charging circuit. If the protective conductor connection of the vehicle's charging circuit is not or not correctly connected to the protective conductor potential of the charging current source, then touching the chassis potential could otherwise result in these AC components being conducted to the protective conductor potential (earth) via the user who is touching them. The fault protection impedance provides a return path for high frequency AC components that has a low impedance, thereby reducing touch currents through a user to ground potential. It should be noted that the AC components fed back by the fault protection impedance have a frequency that is higher than the fundamental frequency of the AC current supplied by the charging station, especially in the case of switching rectifiers whose switching frequency defines the frequency of the AC components that can be fed back by the fault protection impedance. This is also the case with unswitched rectifier circuits. As a result of the multi-phase nature, asymmetrical AC components can arise whose frequency is above the fundamental frequency of the AC current which is applied to the rectifier circuit. These are at least partially returned to the charging station by means of the fault protection impedance from the star point. For this purpose, the fault protection impedance is designed as a high-pass filter in order to feed back the asymmetrical, higher-frequency components from the chassis potential (= earth potential on the vehicle side) via the neutral conductor.

Therefore, an on-vehicle AC charging circuit equipped with a multi-phase rectifier circuit is proposed. The rectifier circuit is, in particular, of three-phase design in order to be able to be connected to a three-phase supply network (alternating current).

The rectifier circuit has a (free) star point on the DC side. The rectifier circuit has, in particular, a direct current side and an alternating current side, with the star point being located on the direct current side. This star point connects potentials of the multiple phases of the rectifier circuit. The star point is connected in particular to a neutral conductor connection of the AC charging circuit, preferably indirectly, direct connections also being possible. On the AC side, the rectifier circuit has a number of phases which are connected to phases of a multi-phase AC connection of the charging circuit. The charging circuit also includes a protective conductor connection. The neutral conductor connection, the protective conductor connection and the phase connections can be designed as contacts of a common charging socket. This charging socket is preferably set up to be contacted from the outside and can in particular be designed according to a standard for conductive AC charging.

As mentioned, the AC charging circuit is equipped with a fault protection impedance. About this is the star point of the rectifier circuit connected to the protective conductor connection. The star point is connected directly or indirectly to the neutral conductor connection in order to at least partially derive the AC components of the potential of the protective conductor connection via the fault protection impedance. The fault protection impedance is designed as a high-pass filter. The star point is connected in series to the protective conductor connection via the fault protection impedance. In this case, the fault protection impedance can connect the star point to the protective conductor connection directly or indirectly (in particular switched). The fault protection impedance can be designed in one piece as a serially connected capacitor, but can also be in the form of an RC circuit connected in series between the star point and the protective earth connection. In particular, the fault protection impedance is connected between the neutral conductor terminal and the protective conductor terminal. The fault protection impedance is preferably connected between the protective earth connection and a connection point via which the star point of the rectifier is connected to a connection impedance which connects the connection point to the neutral connection.

The AC charging circuit preferably has an intermediate circuit capacitor circuit which is connected in parallel to two DC voltage outputs of the rectifier circuit (DC side). The intermediate circuit capacitor circuit can be in one piece, i.e. it can comprise an intermediate circuit capacitor which connects the two DC voltage outputs, or it can comprise two intermediate circuit capacitors which are connected to one another via a connection point of the intermediate circuit capacitor circuit. In this case, this connection point can be connected directly or preferably in a switched manner to the neutral point. In particular, the connection point of the intermediate circuit capacitor circuit can be connected to one end of the fault protection impedance (directly or via a switch), while the other end of the fault protection impedance is connected to the protective earth terminal. The intermediate circuit capacitor circuit can be designed for a total voltage of at least 300 or 350 V or for an operating voltage of no more than 900 or 1000 V. In a multi-part intermediate circuit capacitor circuit, the individual intermediate circuit capacitors are designed for such a voltage divided by the number of series-connected capacitors in the intermediate circuit capacitor circuit.

As mentioned, the intermediate circuit capacitor circuit can include a series connection of two intermediate circuit capacitors. These are connected in series via a connection point (the intermediate circuit capacitor circuit). This connection point is connected to the neutral point of the rectifier either directly or via an intermediate circuit switch. A control unit that controls the intermediate circuit switch is preferably set up to close the switch when charging is taking place and to open it when an error occurs, in particular when an error occurs that reflects a faulty protective conductor connection of the charging circuit.

The fault protection impedance can be connected in different ways. The fault protection impedance can be connected directly to the neutral point. Alternatively, the fault protection impedance can be connected to the star point via an intermediate circuit switch. The fault protection impedance can be connected directly to a connection point of two serial intermediate circuit capacitors (in particular the previously mentioned connection point of the intermediate circuit capacitor circuit). Furthermore, the fault protection impedance can be connected to the connection point of the intermediate circuit capacitor circuit via an intermediate circuit switch. This applies in particular to one end of the fault protection impedance, the other end being connected to the protective conductor connection. This also applies to a series connection of the fault protection impedance and a connection switch connected in series thereto, with this series connection then taking the place of the fault protection impedance. In other words, the fault protection impedance can also be switched (by a switch connected upstream of the impedance).

According to further embodiments, the star point is connected to the neutral conductor connection via a connection impedance. The connection point can be connected directly to the neutral conductor connection via the connection impedance, or further elements such as a (disconnecting) switch, a fuse or the like can be provided in this connection.

The connection impedance can be designed as an ohmic resistor, as a capacitor or as a series connection or parallel connection thereof.

For example, the star point is connected to the protective conductor connection via the fault protection impedance and a connection switch that is connected in series to this. In this case, the connection switch can be provided between the fault protection impedance and the protective conductor connection. The connection switch can also be provided between the fault protection impedance and a connection point via which the star point is connected to a connection impedance which leads to the neutral conductor connection.

The fault protection impedance can be connected to the neutral point via an intermediate circuit switch. The fault protection impedance can also be connected to the connection point of two serial intermediate circuit capacitors of the intermediate circuit capacitor circuit via an intermediate circuit switch. In addition, a control device can be provided in particular, which is connected to the intermediate circuit switch in a driving manner. The control device is preferably set up to provide the intermediate circuit switch in the open state when there is a fault in the AC charging circuit, or when there is a fault in a component that is provided in an on-board branch that is connected to the DC side of the rectifier circuit. In particular, the control device is set up to provide the intermediate circuit switch in the closed state if there is no error state.

In this case, the error state reflects in particular a faulty protective conductor connection of the AC charging circuit. The faulty protective conductor connection can result from a defective charging cable between the charging circuit and the external AC power source, or it can be caused by a faulty protective conductor connection of the external charging source itself.

A multi-phase circuit breaker device can be provided which, on the AC side, connects the rectifier to a multi-phase AC connection, in particular a multi-phase phase connection. In this case, for example, there can be three phase connections in the AC connection, which are connected to individual phases of the AC side of the rectifier via individual isolating switch elements of the isolating switch device. The AC charging circuit preferably has a voltage measuring device drivingly connected to the circuit breaker device. Furthermore, the measuring device has two voltage potential inputs that are connected to the neutral conductor connection and the protective conductor connection. In other words, the voltage measuring device is equipped to detect the voltage between the neutral conductor connection and the protective conductor connection. Alternatively or in combination with this, the voltage measuring device is designed to detect voltages between the phase connections of the AC connection, or to detect a voltage between at least one of the phase connections and the neutral conductor connection. The voltage measuring device is set up to close the isolating switch device only if at least one of these voltages is not greater than a predetermined voltage limit. The voltage measuring device is preferably set up so that it otherwise controls the disconnector device in the open state. The voltage limit can be 20, 30 or 50 V, for example.

The rectifier circuit is preferably designed as a serial rectifier. The star point then corresponds to the free star point of the Vienna rectifier. The Vienna rectifier has a multi-phase design and has one switching cell per phase. Each switching cell comprises two half-bridges (switchable or non-switchable), each having two switching elements that are connected to one another via a connection point. The connection point of one of the half-bridges of each cell is connected (via an inductor) to a phase connection. The second half-bridge includes two switching elements connected via a connection point of this half-bridge. The connection points of the second half-bridges of the switching cells are connected to one another and form the star point, which is referred to as the free star point. In other words, the Vienna rectifier has a number of switching cells which have half bridges which each have a connection point via which the switching elements of the half bridge are connected to one another, these connection points being connected to one another and forming the neutral point. Switching elements are switching elements controlled by external signals, such as transistors or thyristors, as well as diodes whose switching state is controlled by the voltage applied to them (and are therefore not switched by a control signal to a control input).

The rectifier circuit can be designed according to a three-phase AC voltage of 230 V rms voltage at a frequency of 50 Hz.

Furthermore, the rectifier circuit can be designed for an output voltage with such an AC input voltage of 600 to 800 V, in particular from 700 to 750 V. Based on an output voltage of the rectifier circuit of 700 to 750 V, the fault protection impedance can have a capacitance of 250 to 400 nF be designed, in particular with a fault protection impedance, which is designed as a capacitor with a capacity of less than 800 nF. In particular, the fault protection impedance is greater than 10, 50 or 100 nF. If the charging circuit is designed for an input voltage with a different frequency, this capacitance must be multiplied by a factor that corresponds to 50 Hz divided by the other frequency. If the rectifier circuit is designed for a different AC voltage, the capacitance value must be multiplied by a factor of the line-to-line AC voltage divided by the line-to-line AC voltage of a corresponds to a three-phase alternating current system with an effective voltage of 230 V. In one embodiment (for a three-phase AC voltage of 230 V effective voltage at 50 Hz), the fault protection impedance can be designed as a capacitor with 300 nF, 320 nF, 350 nF, 360 nF or 400 nF, in particular with a capacitance of at least 150 nF, 200 nF or 300 nF and not exceeding 500 nF, 450 nF or 400 nF.

The 1 and 2 serve to explain in more detail exemplary embodiments of the circuit described here.

The 1 FIG. 1 shows an external AC charging voltage source SQ with three phases, which is connected via a cable K to a charging connection LA of the AC charging circuit LS. For connection to an external charging station (alternating current), the charging circuit LS thus includes three phase connections L1, L2, L3, a neutral conductor connection N and a protective conductor connection PE. These can be combined in a common charging socket (in the vehicle). The charging socket can be designed according to a standard for charging electric vehicles with alternating current.

The charging circuit LS also includes a rectifier circuit PFC, which is connected to the phase connections L1 to L3 on the AC side. On the DC side, the rectifier circuit has two DC voltage outputs HV+, HV-, between which the rectified DC voltage is generated. In addition, the rectifier circuit PFC has a star point SP or a relevant connection. An intermediate circuit capacitor circuit with two intermediate circuit capacitors ZK connected via a connection point V is connected downstream of the rectifier circuit PFC. The resulting intermediate circuit capacitor circuit is connected in parallel to the DC voltage outputs HV+, HV-.

Furthermore, an EMC filter is shown, which has two capacitors C1, which are connected to one another via a connection point. This EMC filter is part of the on-board charging circuit LS. The outer ends of this EMC filter are connected to the DC voltage terminals HV+, HV- and the connection point is connected to the protective conductor terminal PE. A further on-board branch connection BS of the charging circuit LS, shown symbolically, can be connected to another branch branch, which has a further EMC filter, shown symbolically. The vehicle electrical system branch is connected to the on-board charging circuit LS. The EMC filter of the vehicle electrical system branch, which is connected to the charging circuit LS, also includes two series-connected capacitors C2, with the connection point between these capacitors also being connected to the protective conductor PE here. The vehicle electrical system branch shown, which is connected to the charging circuit LS via the interface BS, also has accumulator connections AA. A traction accumulator A is connected to this. This is a high-voltage traction battery with a nominal voltage of more than 400 V, in particular 800, 850, 900 or 1000 V, for example.

It can be seen that if the protective conductor connection is faulty, the energies of the intermediate circuit capacitors or the EMC filters, represented by C1 and C2, require a correct protective conductor connection in order to avoid touch voltages. An AC signal is transmitted to the intermediate circuit capacitor circuit ZK via the star point SP, which AC signal corresponds in particular to asymmetrical AC components. In the event of a faulty protective conductor connection, the fault protection impedance ZY is provided so that this is not (completely) transmitted to a user who is touching the chassis or the protective conductor potential of the vehicle. This is connected to the protective conductor connection PE. An embodiment is shown in which the fault protection impedance ZY is connected to the protective earth connection PE via a serial connection switch S2. An alternative is to place the switch S2 on the other side of the fault protection impedance, in particular between the fault protection impedance ZY and the illustrated connection point between the star point SP and a connection impedance ZN.

The embodiment shown provides a connection point V via which the intermediate circuit capacitors ZK are connected to one another. This connection point V of the intermediate circuit capacitor circuit is connected to the star point SP of the rectifier circuit PFC via a switch S1. An alternative embodiment provides a non-switched connection between the connection point V and the star point SP. In this case, the intermediate circuit switch can be in a different position, namely between the connection point V of the intermediate circuit capacitor circuit and the fault protection impedance ZY. This alternative intermediate circuit switch is identified by the reference symbol S1'. It is also shown that the fault protection impedance ZY is connected directly to the star point SP. Alternative embodiments provide that the fault protection impedance ZY is connected to the connection point V of the intermediate circuit capacitor circuit (via a switch or directly), while the star point SP can be connected to the connection point V directly or via a switch.

Also shown is a connection impedance ZN, which connects the end of the fault protection impedance facing away from the protective conductor PE to the neutral conductor N. The connection impedance can also be capacitive, can be implemented as a resistor or as a combination of at least one resistor and at least one capacitor. In particular, the connection impedance ZN is in the form of a resistor and a capacitor connected in series, but it can also be in the form of a resistor and a capacitor connected in parallel, with this parallel circuit connecting the star point SP to the neutral conductor connection N in series.

A controller C is also provided, which controls the switches S1 or S1′ and S2 shown. The controller C is set up to close the switch S1 or S1' when it is detected that there is a fault in the protective conductor connection. In this case, the switch S2 is preferably also closed. If there is no error in the protective conductor connection, switches S1 or S1' and S2 can be opened.

A voltage measuring device M of the charging circuit LS on the vehicle side detects the voltage present between the neutral conductor connection N and the protective conductor connection PE. If this is greater than a limit, which can be about 20, 30 or 50 V (in particular less than 60 V), then the voltage measuring device opens the isolating switch device TS, which is present between the phase terminals L1 to L3 and the rectifier circuit PFC. In general, the voltage measuring device M can be set up to provide the isolating switch device TS in an open state when there is no voltage at the phase connections L1 to L3 (among each other or with respect to potential N) and/or when there is also that between the neutral conductor connection N and the protective conductor connection PE no voltage present.

The 2 is used for the exemplary representation of a rectifier circuit PFC, which is designed as a Vienna rectifier. The illustrated Vienna rectifier PFC includes three serial input inductances I1 to I3, which are intended for connection to three phase connections. A switching cell, which has two half-bridges HB1, HB2, is provided for each phase. The first half-bridge HB1 of each cell is connected to one of the inductances I1, in particular via a connection point within the half-bridge HB1. The half-bridge HB2 of each phase or switching cell of the rectifier includes two switching elements (here: diodes) that are connected to one another via a connection point. The star point SP results from connecting the connection points of all second half-bridges HB2, ie all half-bridges that are not connected to one of the inductances I1 to I3. The star point SP is also referred to as a free star point, since its potential is not fixed in relation to HV+ or HV-, but can be shifted with the switching states of the switching elements of the switching cells. Compensating currents between the various phases or switching cells of the Vienna rectifier result via the neutral point. However, due to asymmetries, an AC voltage component can also result, which can be present between the star point SP and a neutral conductor connection or neutral conductor potential. The fault protection impedance ZY according to the invention (see 1 ) is suitable for dissipating such currents (from the protective conductor connection) to the neutral conductor connection in order to prevent the chassis potential and thus the protective conductor connection on the charging circuit side from generating a dangerous voltage potential compared to the earth potential or protective conductor potential of the charging station in the event of a faulty protective conductor connection. Since these AC components have a high frequency compared to the zero frequency (i.e. they are at least a factor of 2 above the fundamental frequency of the AC voltages at the phase connections), a high-pass filter can be used as the fault protection impedance, which attenuates the fundamental frequency much more than the frequencies of the asymmetrical AC components.

Claims (11)

AC charging circuit (LS) on the vehicle side, with a rectifier circuit (PFC), which is multi-phase and has a star point (SP) on the DC side, which is connected to a neutral conductor connection (N) of the AC charging circuit (LS), the AC charging circuit (LS) is equipped with a fault protection impedance (ZY) via which the star point (SP) is connected to a protective conductor connection (PE) of the AC charging circuit (LS) and the fault protection impedance (ZY) is designed as a high-pass filter. Vehicle-side AC charging circuit (LS) according to claim 1 , wherein the rectifier circuit (PFC) has two DC voltage outputs (HV+, HV-) on the DC side, to which an intermediate circuit capacitor circuit is connected in parallel. Vehicle-side AC charging circuit (LS) according to claim 2 , wherein the intermediate circuit capacitor circuit comprises a series circuit of two intermediate circuit capacitors (ZK) which are connected to one another in the series circuit via a connection point (V) which is direct or is connected to the star point (SP) via an intermediate circuit switch (S1). AC charging circuit (LS) on the vehicle side according to one of the preceding claims, wherein the fault protection impedance (ZY) is connected directly to the star point (SP), is connected to the star point (SP) via an intermediate circuit switch (S1), is connected directly to a connection point (V ) of two serial intermediate circuit capacitors (ZK) or via an intermediate circuit switch (S1') to a connection point (V) of two serial intermediate circuit capacitors (ZK). AC charging circuit (LS) on the vehicle side according to one of the preceding claims, wherein the star point (SP) is connected to the neutral conductor connection (N) via a connecting impedance (ZN). Vehicle-side AC charging circuit (LS) according to claim 5 , The connection impedance (ZN) being designed as an ohmic resistor or as a capacitor or as a combination thereof. Vehicle-side AC charging circuit (LS) according to claim 5 or 6 , whereby the star point (SP) is connected to the protective earth connection (PE) via the fault protection impedance (ZY) and a serial connection switch (S2) for this. Vehicle-side AC charging circuit (LS) according to one of the preceding claims, wherein the fault protection impedance (ZY) is connected to the star point (SP) via an intermediate circuit switch (S1), or via an intermediate circuit switch (S1') to a connection point (V) of two serial intermediate circuit capacitors (ZK) and wherein the vehicle-side AC charging circuit (LS) also has a control device (C) which is connected to the intermediate circuit switch (S1, S1') in a driving manner and is set up to switch the intermediate circuit switch (S1, S1') in closed state when there is a fault in the AC charging circuit (LS) or in a component of an onboard branch connected to it, and is set up to provide the intermediate circuit switch (S1, S1 ') in the open state when there is no fault state. Vehicle-side AC charging circuit (LS) according to claim 8 , where the error state reflects a faulty protective conductor connection of the AC charging circuit (LS). Vehicle-side AC charging circuit (LS) according to one of the preceding claims, which has a multi-phase AC connection (L1, L2, L3) which is connected to the rectifier (PFC) on the AC side via a multi-phase disconnector device (TS), the AC charging circuit (LS ) also has a voltage measuring device (M) which is drivingly connected to the disconnector device (TS) and is signal-transmittingly connected to the neutral conductor terminal (N) and the protective conductor terminal (PE) and which is set up to be connected between the neutral conductor terminal (N) and the protective conductor terminal ( PE) present voltage and only close the circuit breaker device if this voltage is not greater than a predetermined voltage limit. Vehicle-side AC charging circuit (LS) according to one of the preceding claims, wherein the rectifier circuit (PFC) is designed as a Vienna rectifier and the star point (SP) corresponds to the free star point (SP) of the Vienna rectifier.

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