Charging method with monitoring that takes into account overvoltage protection measures on the charging station side

Abstract

A DC voltage charging method with monitoring is described, in which a vehicle-side traction battery (B1, B2) is charged by a vehicle-external charging voltage source (SQ) via a vehicle-side charging circuit. The traction battery (B1, B2) has a rated voltage of at least 500 V. First, in a test step, it is detected whether the charging voltage source (SQ) has an overvoltage protection unit including a voltage limiting element (E) arranged between a charging voltage potential of the charging voltage source (SQ) and a ground potential and configured to transition to a conductive state from a voltage below the rated voltage. If it is detected in the test step that the charging voltage source (SQ) does not have the overvoltage protection unit (E), a DC voltage is transmitted from the charging voltage source (SQ) to the traction battery (B1, B2). If it is detected in the test step that the charging voltage source (SQ) has the overvoltage protection unit (E), at least one DC voltage charging mode for transmitting a DC voltage from the charging voltage source (SQ) to the traction battery (B1, B2) is blocked. Also described is a vehicle-side charging circuit configured to perform the method.

Description

[Technical field]

[0001] It is known to equip vehicles with an electric drive, whereby a charging station is provided for charging a storage device in the form of a battery on the vehicle side, said charging station being connected to the vehicle via a cable.

[0002] Due to the high charging or traction power required, electric drives and accumulators are designed for rated voltages in the high-voltage range, i.e. for voltages well above 60 V. In addition to 400 V systems for vehicles, there are now also 800 V systems for vehicles. Furthermore, there are corresponding charging stations that are configured according to charging standards. One of these standards is the CHAdeMO standard, whose versions provide for charging voltages of up to 500 V DC.

[0003] Nowadays, many vehicles use 800V vehicle-side batteries, but the charging voltage may differ from the vehicle-side voltage depending on the standard, for example a maximum DC voltage of 500V as the charging voltage. Therefore, the objective of the present invention is to provide a means for enabling safe charging operation even when the charging voltage is different.

[0004] This problem is solved by the subject matter of the independent claims. Further characteristics, features, embodiments and advantages emerge from the respective dependent claims, the description and the figures.

[0005] In charging standards such as the CHAdeMO charging standard, it has been recognized that in the case where a charging station outputs a first DC voltage for charging and a battery is charged on the vehicle side with a second DC voltage higher than the first DC voltage, problems can occur in the event of an insulation error of the high voltage potential (second DC voltage) with respect to ground, so that safety measures are provided on the charging station side. This is done in particular by charging stations according to the CHAdeMO charging standard 1.0 and the CHAdeMO charging standard 2.0 having an overvoltage protection element in the form of a varistor that protects the high voltage potential with respect to ground. The overvoltage protection element starts to conduct at a predefined threshold voltage or a predefined voltage value above the maximum charging voltage in case of an excessively high voltage with respect to ground occurring, for example due to an error or a flash surge.

[0006] However, in the case where the accumulator is charged with a rated voltage higher than the maximum charging voltage (in particular the threshold voltage or a predetermined voltage value), this safety measure means that, if an insulation error occurs on one side of the high voltage potential with respect to ground, the other high voltage potential with respect to ground has a voltage that starts the conduction of the overvoltage protection element. This causes an undesirable high current flow. In other words, if an insulation error occurs on one side with respect to ground in the high voltage part that provides the second DC voltage, a strong asymmetry of the potential of the second DC voltage with respect to ground occurs, which causes a high voltage with respect to ground on one side, which activates the overvoltage protection of the charging station (conducts).

[0007] Specifically, in an exemplary DC voltage system that has a voltage of +400V or -400V with respect to ground under fault-free conditions, if an insulation error occurs on one side with respect to ground, a voltage of 0V or 800V will be generated, which will result in a high voltage of 800V causing the overvoltage protection unit to trip.

[0008] Activation of the overvoltage protection unit may result in high ground currents, which, due to the low internal resistance of the accumulator, may be so high that it cannot be guaranteed that the ground is not damaged. This is particularly the case in charging stations where the ground cable has a relatively small cross-sectional area (relative to the cross-sectional area of ​​the high-voltage lines of the charging station). Thus, due to the high current flow caused by the asymmetric shift, the ground may be damaged (as a result of an insulation error to the ground), and if no ground potential terminal is provided, an insulation error remains on the vehicle side, especially in the case of a small ground cross-sectional area, which makes it impossible to eliminate dangerously high contact potentials on the chassis of the vehicle and thus leads to incorrect error identification.

[0009] Therefore, for a traction battery with a rated voltage greater than the voltage (threshold voltage) at which the voltage limiting element of the charging station starts to conduct, i.e. a high voltage at which the overvoltage protection of the charging station would be activated (and further dangers would be caused) in the event of an insulation error on one side of the high voltage potential with respect to ground, it is proposed to first check whether the charging station has an overvoltage protection that can be conducted. If the charging station has an overvoltage protection, at least one DC voltage charging mode is actively prevented. If it is detected that the charging station does not have an overvoltage protection (so that the above-mentioned problems do not exist), the otherwise prevented DC voltage charging mode here is permitted and a DC voltage is transmitted according to this DC voltage charging mode. The checking step is configured to check whether the charging voltage source has an overvoltage protection including a voltage limiting element arranged between the charging voltage potential of the charging voltage source and ground potential and configured to transition to a conducting state from a voltage (threshold voltage) below the rated voltage. The overvoltage protection is also called a critical overvoltage protection. This is because the overvoltage protection unit becomes active if a ground insulation error occurs, in particular when a vehicle is connected whose on-board power grid has a rated voltage higher than the trip voltage of the overvoltage protection unit.

[0010] If the rated voltage of the traction battery is below the maximum charging voltage or is lower than the threshold voltage at which the overvoltage protection unit becomes active, the above-mentioned error is unlikely to occur regardless of the presence or absence of an overvoltage protection unit on the charging station side, so the inspection step can be skipped. Even if an insulation error occurs on one side, the voltage here is small, so that the vehicle does not apply a voltage at the charging station that would trip the overvoltage protection unit (i.e., cause the voltage limiting element to transition to an active state).

[0011] Thus, in a test step, it is detected whether the charging station is provided with a voltage-limiting element that may be conducted if an insulation error on the vehicle side results in a corresponding voltage at the charging station (i.e. a voltage of high voltage potential with respect to ground). Thus, since the corresponding voltage-limiting elements are defined in the charging standard, e.g. the CHAdeMO charging standard, a test can be imposed only for the standard for which the charging station is built to conclude whether a critical voltage-limiting element is present. If a critical voltage-limiting element is present, it can be configured to inhibit at least one DC voltage charging mode. The DC voltage charging mode here is in particular a direct charging mode that can be used, for example when the battery is deeply discharged and the maximum charging voltage is suitable for charging the accumulator. Furthermore, the DC voltage charging mode can be a mode in which a galvanic non-isolated converter is used to transfer the charging power from the charging station to the accumulator on the vehicle side.

[0012] Advantageously, the transmission of the DC voltage is interrupted by tripping a safety device, in particular a pyrofuse or a cut-off switch, if the comparison shows that the deviation is greater than the set tolerance value and that this deviation exists for a set period of time. A pyrofuse in this context should be understood as a switch, since it can be opened by the signal control in the same way as a switch. In particular, the interruption is performed if the comparison shows that the deviation is greater than the set tolerance value and, after the comparison, a further comparison step (for plausibility check) is performed, in which further comparison step shows that the deviation is still greater than the set tolerance value after the set duration has elapsed. In this case, in other words, the transmission of the DC voltage is interrupted by tripping a safety device, i.e. a pyrofuse or a cut-off switch, if, after a debouncing period (corresponding to the set duration), the comparison shows that the deviation is still greater than the set tolerance value. If the comparison shows that the deviation here is greater than a set error limit but the pyrofuse is not directly tripped when the error limit is reached, then it can be configured so that only the charging circuit is stopped or the reclosable switch is opened.

[0013] At least one cut-off switch or pyrofuse can be configured to trip only if the deviation exceeds not only the error limit but also a tolerance value (greater than the error limit) over a specifically set debouncing period, where the pyrofuse is tripped only if the tolerance value is exceeded above (and not only a smaller error limit). The error limit indicates when an error has been identified that leads to activation of the above-mentioned overvoltage protector, and the tolerance value indicates when an actual danger to the user also occurs (due to a possible contact current exceeding the tolerance limit, i.e. a contact current that may be dangerous for humans).

[0014] Further described is a vehicle-side charging circuit configured to perform the method described herein. The charging circuit has a direct voltage conductor terminal with two contacts, each having a different polarity. The first contact is connected to a coupling point via a safety device. In this case, the safety device can be configured as an electric fuse or a melting fuse or a pyro-fuse. The first contact is connected to the coupling point via the safety device. A first direct charging path without a converter is connected to the coupling point. The first charging path has a switch connecting the coupling point to a first battery terminal of the charging circuit. If the switch is open, no current flows in the first charging path. A second charging path is connected to the coupling point. The second charging path has a voltage converter. The second charging path is thus configured to transmit power in a voltage-converted state via the voltage converter. Via the second charging path, the coupling point is connected to a second battery terminal of the charging circuit.

[0015] According to an embodiment, the voltage converter has at least one switch of the inverter as an operating switch and at least one winding as an operating inductance, as described above in the framework of the method, the winding being part of an electric machine that is controlled by the inverter. This allows the inverter and the electric machine to be used for two functions, namely, on the one hand, for running or regeneration, and on the other hand, for voltage conversion. A corresponding control device can be provided, which is controllably connected to the inverter to selectively perform one of the two above-mentioned functions.

[0016] The second contact of the DC voltage terminal is connected to the second battery terminal of the charging circuit, preferably via a diode. The forward direction of the diode is configured to allow current flow from the second battery terminal to the second contact. If the second contact has the negative polarity of the DC voltage charging terminal and the first contact has the positive polarity of the DC voltage charging terminal, the forward direction of the diode is toward the DC voltage charging terminal. In other words, in this case, the blocking direction of the diode of the DC voltage is away from the DC voltage terminal. If the second contact is associated with a positive polarity, the forward direction of the diode points away from the second contact or the DC voltage charging terminal, and the blocking direction points toward the DC voltage charging terminal.

[0017] Furthermore, the charging circuit on the vehicle side can be configured to have a control device connected to control the switch. The control device is further controllably connected to at least one switch to which at least one of the two battery terminals is connected. If the battery terminals are each connected (to the remaining circuit) via a switch, then the two battery terminals are each connected to the remaining circuit via one switch. In this case, one switch can be provided between the first battery terminal and a point where the two charging paths join again. The other switch can be provided between the second battery terminal and the diode. The control device can further be controllably connected to the voltage converter. The control device is preferably configured to perform a test step and to selectively control the switch and the DC voltage converter for transmission or transmission prevention depending on the result of the test step. That is, the control device is configured to realize at least two states by means of the switch and the DC voltage converter, namely transmission as a first state and transmission prevention as a second state.

[0018] The charging voltage source can be a charging station which is stationarily installed and in particular connected to a supply grid, but also can be another vehicle which is used to charge the traction battery described herein.

[0019] The checking step is configured such that a signal is received which reflects whether or not the above-mentioned overvoltage protection unit (which is active below 500V or conductive to ground) is present in the charging voltage source. This is particularly related to the charging standard to which the charging voltage source is configured, so that the signal can reflect the charging standard to which the charging voltage source is configured here. From this, it can be concluded whether or not the charging voltage source has the above-mentioned overvoltage protection unit. In particular, the signal can represent whether or not the charging voltage source is configured in accordance with the CHAdeMO standard 2.0 series. Here, the "CHAdeMO standard 2.0 series" refers to the CHAdeMO standard in which the charging voltage source is provided with an overvoltage protection unit (with respect to the voltage between the charging voltage potential and ground) which is active from a voltage (threshold voltage) of about 500V, in particular from a voltage (threshold voltage) of less than 800V, 700V or 600V. Active here means that the overvoltage protection becomes conductive when a corresponding voltage (threshold voltage) is reached, and in particular forms a conductive path between the high voltage potential and ground. A control device or other device can be provided on the vehicle network side, which is arranged to receive the corresponding signals and evaluate them accordingly.

[0020] When a signal representative of the CHAdeMO standard 2.0 series is received, at least one DC voltage mode is blocked. When a signal representative of the CHAdeMO standard is received, or in general when a signal representative of a charging standard without the above-mentioned overvoltage protection unit is received, a DC voltage is transmitted from the charging voltage source to the traction battery in the above-mentioned DC voltage mode.

[0021] To receive such a signal, the charging circuit may comprise a signal receiver. The signal receiver is configured to receive a signal representative of a standard to which the configuration of the charging station complies (e.g. by implementing a corresponding data transmission protocol). The control unit may be configured to receive the signal from the signal receiver and evaluate whether the signal is representative of a charging standard for which an overvoltage protector with a voltage limiting element for the charging station is envisaged. The signal receiver may be wirelessly or cabled. The signal receiver and the control unit may be configured as a common device.

[0022] In addition to the means for excluding the charging standard in order to determine whether an overvoltage protection unit with a voltage limiting element is present, i.e. based on an information signal transmitted from the charging station to the charging circuit on the vehicle side, a test signal can also be used to determine whether an overvoltage protection unit with a voltage limiting element is present. The test signal can be configured to trip the voltage limiting element (i.e. to bring it into a conducting state) in order to determine whether an overvoltage protection unit with a voltage limiting element is present in accordance with a corresponding signal response to the test signal. The test signal can also be configured as a signal for actively measuring the impedance of the charging voltage source in order to determine an impedance in accordance with a corresponding signal response to the test signal and to determine from this impedance whether an overvoltage protection unit with a voltage limiting element is present. Thus, an embodiment is obtained in which a characteristic of the voltage limiting element is determined, and a conclusion is made that a voltage limiting element is present if the characteristic is determined and that a voltage limiting element is not present if a determination result indicating the absence of the characteristic is indicated. As the characteristic of the voltage limiting element, a characteristic that allows conduction from a threshold voltage and a characteristic that has an impedance within an impedance interval that is typical for a voltage limiting element, in particular a characteristic that has a capacitance within a typical capacitance interval, are suitable here. Another electrical characteristic characteristic of a voltage-limiting element may also be determined. If the characteristic occurs, a conclusion is made that a voltage-limiting element is present. If the determination indicates that the characteristic does not occur, a conclusion is made that a (potentially critical) voltage-limiting element is not present in the charging station.

[0023] It can therefore be arranged that in the test step it is detected whether the charging voltage source has an overvoltage protection. This is detected or determined by applying a test signal to the charging voltage potential and to the ground potential (i.e. to where the voltage-limiting element would be connected if it were present). The obtained signal response, i.e. the signal response resulting from the test signal, is detected. Based on the signal response it is determined whether the charging voltage source has an overvoltage protection. In other words, it is proposed to detect or determine the electrical characteristics typical for the voltage-limiting element by applying a test signal and detecting a corresponding signal response. The characteristics are obtained from an evaluation of how the signal response to the test signal behaves or whether a signal response occurs or not. As test signal a test voltage above a threshold voltage can be applied. The obtained signal response is detected as a current flow (above a set current threshold). In this case the current flow is the result of the test voltage being applied to the voltage-limiting element, which current flow brings the current-limiting element into a conducting state. Here the polarity of the test voltage and the polarity of the charging voltage potential are respected, in particular the absolute value of the test voltage above the absolute value of the threshold voltage is applied. This detects the characteristic of the voltage limiting element (if a voltage limiting element is present) to become conductive when a voltage above the current threshold is applied to the voltage limiting element. The test voltage may be derived from the traction battery or a DC voltage converter connected to the traction battery, and the test signal generator is connectable to the traction battery or a DC voltage converter connected to the traction battery.

[0024] Furthermore, as the test signal, an excitation signal for impedance measurement can be applied. As the excitation signal, an alternating voltage signal (or an alternating current signal) having multiple simultaneous frequency components (e.g. noise) or an alternating voltage signal (or an alternating current signal) having a frequency component whose frequency varies over time ("sweeping") is suitable. In particular, a signal response obtained in association with the test signal is detected as a signal representative of the impedance of the charging voltage source. If an alternating voltage signal is the excitation signal, the signal response can be detected as a current signal. If an alternating current signal is the excitation signal, the signal response can be detected as a voltage signal.

[0025] The test voltage is preferably applied by a current limiter, so that only a limited current flows even if the voltage limiting element is conductive. Current limiting of the test signal can preferably be achieved simply by a switchable series resistor (current limiting resistor connected in series) or by correspondingly controlling a DC-to-voltage converter to form a test signal with a limited current intensity. The test signal can be limited to a maximum current intensity of less than 1 A, less than 100 mA, less than 10 mA or less than 1 mA. The series resistor (current limiting resistor) can be provided as a switchable resistor, in particular as a series circuit of a resistive element and a switch. The switch is preferably closed temporarily (during the test step).

[0026] A test signal generator may be provided on the vehicle side (e.g. in the charging circuit). The test signal generator is configured to generate a test signal. The test signal generator is preferably connected (on the output side) to the charging voltage potential and to the ground potential. This is used to apply the test signal to the respective potential. The test signal generator is connectable (in particular on the input side) to the traction battery and to a DC voltage converter or a low voltage source connected to the traction battery. Furthermore, a detection device may be provided which is configured to detect a signal response generated by the test signal. The detection device is connectable on the input side, preferably in a signal-transmitting manner or by a voltage divider or capacitive coupling, to the charging voltage potential and / or to the ground potential. The test signal generator and the detection device together preferably form a detection module which actively detects or measures an electrical characteristic of the voltage-limiting element. A control device may be downstream of the detection device or the detection module, or the detection device or the detection module may be part of the control device or part of a common device.

[0027] According to an embodiment, the vehicle-side charging circuit, through which the DC voltage is transmitted, has a first charging path that is direct and without a converter and a second charging path. The second charging path leads via a voltage converter. The voltage converter can be configured as a dedicated voltage converter or can be formed from a winding of the electric machine as the operating inductance of the voltage converter and a switch of the inverter as the operating switch of the voltage converter, where the inverter and the winding belong to a drive on the vehicle side, in particular a traction drive. The winding is in particular a winding, in particular a stator winding, of an electric machine of an electric drive of the vehicle. The method is preferably configured to select whether the transmission takes place via the first charging path or via the second charging path. This concerns the transmission of the DC voltage from the charging voltage source to the traction battery or the transmission of the DC voltage via the vehicle-side charging circuit. The selecting step can be configured such that the first path or the second path is provided depending on the state of charge or the clamp voltage of the traction battery to be charged. If the difference between the charging voltage and the traction battery voltage is greater than a set margin, the second charging path is selected because it has a voltage converter that can adapt the voltage. If the difference is small, the first (direct) charging path can be selected.

[0028] The voltage converter used according to the method is in particular a DC voltage converter, preferably a step-up converter, although other types of converters are also conceivable. The voltage converter can have at least one dedicated operating switch and at least one dedicated operating inductance as converter element, and can be configured to perform the conversion by clocking the operating switch together with the inductance. In this case, the operating switch and the operating inductance only have the task of voltage conversion and are not configured to realize functions, in particular in the drive or traction drive of the vehicle. Alternatively, a switch of the inverter is used to realize the converter, in particular the operating switch of the converter, in which case one or more switches of the inverter can be used. Additionally, a winding of the electric machine, in particular a winding of the electric machine of the traction drive, can be used as the operating inductance. Both the switch of the inverter as the operating switch and at least one winding of the electric machine as the operating inductance can be used. This makes it possible to realize the converter without a dedicated output element. In particular, if the switch of the inverter is used as the operating switch and at least one winding of the electric machine is used as the operating inductance, the drive control of the inverter can be configured to drive the inverter together with the operating inductance as the converter. The corresponding control device or inverter control therefore has two functional parts, namely a drive control of the inverter for generating a rotating field in the electric machine and a drive control of at least one switch of the inverter as an operating switch of the voltage converter.

[0029] A further aspect of the approach described herein is isolation monitoring to determine the degree of symmetry of the charging voltage potential with respect to the ground potential. The charging voltage potential is electrically isolated with respect to the ground potential in error-free operation. If the degree of isolation is approximately the same, then the symmetry of the charging voltage potential with respect to the ground potential is obtained. For charging voltage potentials of +400V and -400V (i.e., charging voltage of 800V), the ground potential should be approximately 0V, since the ground potential should have approximately equal insulation resistance for the two charging voltage potentials. If an isolation error occurs in any of the charging voltage potentials with respect to the ground potential, the ground potential will shift with respect to the charging voltage potential. In particular, the voltage between the charging voltage potential with isolation error and the ground potential is much smaller than in error-free operation. An insulation error pulls the corresponding charging voltage potential down to ground potential, which results in a very low voltage between these potentials, i.e., much smaller than 1 / 2 the charging voltage, whereas the voltage between the charging voltage potential and ground potential without an insulation error can be much larger than 1 / 2 the charging voltage, in particular close to the total charging voltage. Such a high voltage between the charging voltage potential and ground potential without an insulation error will cause the tripping of the overvoltage protection unit on the charging voltage source side, if the voltage at which the overvoltage protection unit is activated (threshold voltage) is smaller than the charging voltage.

[0030] Such asymmetries can be identified by (absolute) comparison of the voltage difference of the charging voltage potential with respect to the ground potential with a set rated value. If the absolute value of the voltage difference (in the positive or negative direction) deviates from the rated value by more than a set safety margin, this deviation corresponds to a identified asymmetry, and an insulation error can be identified by this. Thus, for example, for a charging voltage of 800 V, the rated value may be 400 V (or more than ½ of the charging voltage, i.e. about 500 V), where an asymmetry occurs if the voltage between the charging voltage potential and the ground potential is much smaller than the rated value (in which case the corresponding charging voltage potential has an error) or if the corresponding voltage is much larger than the rated value (in which case the other charging voltage potential has an insulation error). Alternatively or in combination, the absolute value of the voltage difference between one charging voltage potential and the ground potential can be compared with the voltage difference between another charging voltage potential and the ground potential, thereby directly detecting the asymmetry. If the comparison indicates that there is a deviation that is greater than a set error limit or safety margin, an insulation error signal is output. If not, then no insulation error signal is output, or a signal is output indicating that no insulation error exists.

[0031] Furthermore, it can be configured that the voltage converter is stopped if the comparison shows that the deviation is greater than a set error limit. The voltage converter can be stopped in particular by switching its operating switch to a permanently open state. This prevents the converter from continuing to operate and outputting a converted DC voltage in the event of an insulation error. The error limit here corresponds to a deviation at which it can be concluded that a dangerously high contact voltage may be present, meaning that a contact voltage that is not permissible according to high voltage safety standards may be present on the chassis of the vehicle.

[0032] In another embodiment, if a small deviation is detected, the charging or transmission of the DC voltage continues or at least one charging mode remains permitted, whereas if the deviation is large as described above, the transmission of the DC voltage is interrupted or prevented. To distinguish between these, a tolerance value is used below which no danger is assumed and above which a potential danger can be assumed. A safety distance can be provided between the tolerance value and the above-mentioned error limit. If the deviation does not exceed the tolerance value, an insulation indication signal can be output, which indicates that the insulation must be checked, but that no dangerous insulation error is present. On the other hand, if the above-mentioned error limit is exceeded, an error signal is output, which preferably indicates a critical insulation error, which indicates that the transmission process should be interrupted within the framework of the charging process.

[0033] If an error limit is exceeded or if the deviation is greater than a set tolerance value, preferably by at least one safety value, a safety device, in particular a pyrofuse, can be configured to trip. Alternatively or in combination with this, a disconnect switch can also be tripped, in particular by opening the disconnect switch. Disconnection here therefore preferably only takes place if the deviation actually indicates a dangerous touch voltage or if touch voltages that are not permissible according to standards for high voltage safety may be present on the vehicle chassis. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 is a diagram for explaining an exemplary embodiment of the procedure described herein.

[0035] FIG. 1 is used to explain an exemplary embodiment of the procedure described herein.

[0036] In Fig. 1, an exemplary vehicle-side charging circuit is shown with battery terminals B+, B- connected to a battery circuit. In the illustrated embodiment, the battery circuit comprises two batteries B1, B2 (each configured as a high-voltage accumulator) connected in series, which are connected to one another via a cut-off switch device, in particular configured as a pyrofuse. The battery circuit can generally comprise two accumulators (high-voltage accumulators) connected in series, in which case the pyrofuse, in general a fuse or a cut-off switch, is likewise connected in series. It is also possible for two accumulators to be connected in series directly with one another, in which case the cut-off switch, i.e. a fuse or in particular a pyrofuse, can also be connected (in series), so that the resulting series-connected circuit is connected to the battery terminals. A central arrangement between the two high-voltage accumulators is shown.

[0037] A first battery terminal B+ and a second battery terminal B- are connected to the battery circuit (B1, SB, B2). The polarity can be seen from the reference symbols. Optionally, a switch S5 connected to a further charging circuit is connected in series with the first battery terminal B+. A further optional switch S6 connects the second battery terminal B- to the remaining charging circuit. Furthermore, a current measuring device 1 can be provided between the second battery terminal B- and the switch S6. The measuring device can also be provided directly behind the switch S6.

[0038] The illustrated switches S5 and S6 are used for the controlled connection of the two battery terminals B+, B- to an inverter I, which is configured as a traction inverter and has three half-bridges, each of which has a neutral point, which serves as a phase terminal for three windings W of the electric machine. Furthermore, three current measuring devices 2, 3, 4 are shown, which are arranged between the electric machine or its windings W and the phase terminals of the inverter I.

[0039] The windings W are interconnected in a star-connected circuit, with a switch S3 connected to the star-connection point.

[0040] The inverter I has two DC voltage terminals connected to a positive rail or a negative rail. The positive DC voltage terminal of the inverter I is connected to a potential rail that connects the switch S5 (leading to the first battery terminal B+) to the switch S2. The second DC voltage terminal of the inverter I is connected to a potential rail (negative potential rail) that connects the switch S6 or the second battery terminal B- to the diode D on the one hand and to the switch S1 on the other hand. The diode D is connected in series with the switch S4. A switching diode circuit is obtained with the diode D and the switch S4. The switch S1 is connected in parallel to the diode circuit. In the closed state, the switch S1 bridges the diode circuit. In particular, the switch S1 can be closed if it is determined that there is no critical overvoltage protection on the charging station side. In this case, the possibility of a reverse energy supply from the battery terminals B+, B- to the contacts K+, K- of the illustrated DC voltage charging terminals arises.

[0041] On the side of the diode circuit D, S4 or the switch S1 opposite the inverter or opposite the second battery terminal B-, a second (negative) contact K- is provided. The second (negative) contact K- belongs to a DC voltage charging terminal which also has a first (positive) contact K+. The first contact K+ is connected to the connection point V via an (optional) safety device F1. The safety device F1 is configured as an additional safety device, but may also be configured as an electronic or pyro fuse.

[0042] A node V, which is connected to the neutral point of the winding W via a switch S3, is further connected via a switch S2 to a positive potential rail, which leads to the positive battery terminal B+ or to a switch S5.

[0043] Thus, the switches S5 and S6 form an all-polarity disconnect switch on the charging circuit side for a controlled isolation of the battery terminals B+, B-. The switch SB (particularly configured as a pyrofuse) is part of the battery circuit connected to the battery terminals. It also serves to isolate the battery circuit or the batteries B1 and B2, so that in the open state, the potential resulting from the sum of the two voltages of the batteries B1 and B2 is not applicable.

[0044] There is a first charging path from the connection point V (seen from the first contact K+) directly to the first battery terminal B+ via the switch S2 (and optionally via the switch S5). The charging path does not have a converter. From the connection point V, a second charging path also leads to the battery terminal (B+) via the (optional) switch S3, the winding W and the inverter I. The second charging path has a voltage converter, since at least one of the windings W can form a voltage converter together with at least one of the switches I or with any half-bridge of the inverter I. The control unit C is arranged to drive and control the switches of the inverter I, so that a DC voltage conversion function for the second charging path is provided. The connection point V is protected against the first contact K+ of the DC voltage charging terminal via a safety device F1. Alternatively or in combination, the safety device F1 can be connected in front of the second contact K-.

[0045] The DC voltage charging terminal contacts K+, K- form the opposite end of the charging circuit to the battery terminals B+, B-, so that B+, B- on the one hand and K+, K- on the other form either end of the charging circuit.

[0046] It is shown here that a voltage source SQ is connected to the charging circuit via contacts K+, K-. The voltage source SQ is connected via optional switching elements S7, S8, which are provided with all polarities. The voltage source SQ is a charging voltage source, in particular formed from a DC voltage charging station or from a vehicle which delivers charging energy. The switches S7, S8 serve as self-safety devices for the voltage source SQ.

[0047] The control unit C is furthermore drivably connected to the switches of the charging circuit and, optionally, to the disconnection switches of the battery circuit (B1, SB, B2). The control unit C is configured to detect whether the voltage source SQ has an overvoltage protection designed or configured to conduct current when a voltage corresponding to the sum of the rated voltages (or the minimum operating voltages) of the accumulators B1 and B2 with respect to ground potential occurs at one of the contacts K+, K-. If said voltage occurs or if the test step indicates that this is the case, the control device C is configured to trip or open at least one of the switches S1, S2, S4, S5, S6 or SB, or to prevent at least one direct voltage charging mode by opening at least one of the switches. In this case, the switch S3 can also be opened.

[0048] At least one further of the switches may be opened if a current flow exceeding a (predetermined) error limit is further determined based on the overvoltage protection unit, the error limit representing a current value at which an error occurring based on the current flow is identified.

[0049] If one of the switches is configured as a one-time opening switch, for example as a pyrofuse, it is preferably only opened if the above-mentioned conditions are met and it is determined that the current flowing (through element E) based on the overvoltage protection exceeds a tolerance value. The tolerance value is greater than the error limit. The tolerance value indicates a threshold at which the current flow can be dangerous for humans. The error limit indicates at what current flow an error related to the current flow based on the overvoltage protection of the charging station is detected and is lower than the tolerance value. Thus, if the tolerance value is exceeded, another switch can be opened that is not opened when the error limit is exceeded. If the current is between the tolerance value and the error limit, limited charging can take place, i.e. one DC voltage charging state can be prevented and the other DC voltage charging state can be allowed. The two DC voltage charging states can be distinguished by the charging path used in each case. The control device C is configured to make the distinction.

[0050] According to one embodiment, the control device C is configured to drive and control the switch of the inverter in the open state when it is detected that the charging voltage source SQ has an overvoltage protection unit including a voltage limiting element E arranged between the charging voltage potential of the charging voltage source SQ and the ground potential GND and configured to transition to a conductive state from a voltage (threshold voltage) below the rated voltage. For this purpose, the control device C can have a signal input side or a receiving device by means of which it is possible to transmit information to the control device C reflecting whether the charging voltage source SQ has an overvoltage protection unit including a voltage limiting element E configured to transition to a conductive state from a voltage (threshold voltage) below the rated voltage (or whether the charging voltage source SQ is connected to said overvoltage protection unit). Here, the rated voltage means the rated voltage of the entire battery circuit, i.e. the sum of the rated voltages of the accumulator B1 and the accumulator B2.

[0051] Means are shown for connecting the signal receiver EM to the control device C. The signal receiver EM is configured to receive a signal RA corresponding to or representative of information as to whether or not the charging voltage source (charging station) is configured in accordance with the CHAdeMO standard 2.0 series (or which standard the charging voltage source or the charging station is configured in accordance with).

[0052] Furthermore, for this purpose, further means are provided, the aim of which is to actively (by excitation with the signal TS) determine, by means of a test signal TS, a characteristic characteristic of a voltage-limiting element E, for example a characteristic of being above (and not below) a threshold voltage or of having an impedance characteristic of the element E. Shown is a test signal generator T, having an input I connected on the one hand to the potential of one of the traction batteries B1, B2 or the battery terminals B+, B- or to the (output) potential of a voltage converter I, W (charging voltage potential) and on the other hand to the ground potential GND. The test signal generator T applies the test signal TS to the two potentials.

[0053] In a simple embodiment, the test signal generator TG may correspond to a current-limiting resistor connected in series between the potentials B+, B- or the (output) potential of a voltage converter and the point V. Via the connection V1 or the connection V2, the test signal generator TG or its input I can be connected to a charging voltage potential (of a battery or a DC-voltage converter). The output O of the test signal generator TG can be connected in particular via a detection device M to one of the contacts K+ or K- (or to the point V). If the detection device M is an ammeter, this can detect whether the application of the test signal results in a (DC) current flow or not. If a current flow occurs, the presence of the voltage-limiting element E is presumed, and if no current flow occurs, the absence of the voltage-limiting element E is presumed. An embodiment is shown in which the test signal generator TG forms a voltage above the threshold voltage of the element E. It is also possible to provide a test signal generator TG which emits a test signal suitable for an impedance measurement, the signal response then being detected by a measuring device. The control unit C or other units (T, M, ...) can be configured to determine whether an impedance characteristic of the element E is present or not, for the determination and evaluation of the impedance based on the signal response (and possibly the test signal). If the impedance is present, the presence of the voltage-limiting element E is presumed, and if the impedance is not present, the absence of the voltage-limiting element E is presumed. In the case of a test signal suitable for impedance measurements, the test signal generator TG can be a low-voltage device (with an operating voltage below 60 V), in particular having a supply voltage input I configured for a supply voltage below 60 V.

[0054] If the control unit C determines that there is no voltage limiting element E or any such overvoltage protection in the connected charging energy source (i.e. in the circuit to the right of the contacts K+, K-), it is configured to close the switches S5, S6, S2, S7, S8, S4 and / or S1 in order to enable the DC voltage charging mode. In particular, the switch S1 connected in parallel to the switching diode circuit (series circuit of the diode D and the switch S4) can be configured to be opened, thereby preventing transmission.

[0055] In particular, if in the test step it is detected that the charging voltage source does not have an overvoltage protection unit, a method can be configured to be executed to check whether an insulation error occurs in particular with respect to ground potential in the charging circuit. If it is detected that an insulation error is affecting only one of the two HV potentials (B+ or K+ or B- or K-), the opposite HV potential not affected by the insulation error is considered to be at full HV potential with respect to ground. If such a potential shift is detected, an insulation error is presumed. An insulation error can also be identified by detecting (e.g. with the current measuring device 1) a current flow that exceeds an error limit in particular.

[0056] If an insulation error is identified when using the second charging path, or if an error is generally identified in the second charging path, the controller switches the converter to an inactive state by opening or keeping open all switches of the inverter.

[0057] It can then be checked whether a current flows due to an insulation error that is greater than a defined limit value. The defined limit value can in particular be the sustained current load capacity of the ground conductor used. The limit value can correspond to a tolerance limit. Furthermore, the defined limit value can correspond to a standard limit contact current value for high-voltage charging, for example a direct current of 100 mA, 40 mA, 20 mA or 10 mA. This can in particular be done by detecting the current flowing through one of the two battery terminals B+, B-. In particular, the current measuring device 1 can be used to determine whether a current flows due to an insulation error that is greater than a defined limit value.

[0058] A closed switch can be kept closed as long as the error current does not exceed a defined limit value. If the limit value is exceeded, the switch is opened. In particular, if the limit value is exceeded, the switch SB of the battery circuit is driven towards opening, in particular by the control unit C. If the switch SB is a pyrofuse, it is only ignited by the control unit C if the error current is greater than the defined limit value, even if the DC-DC converter I,W is inactive. The limit value can correspond to the tolerance value mentioned at the beginning (or to a set error limit).

[0059] The pyrofuse or another non-reclosable switch in the illustrated circuit therefore does not open in any case when an insulation error occurs or when critical overvoltage protection is present, but only if the fault current is greater than a limit value reflecting a contact current that is dangerous for humans, despite the voltage transformer being interrupted, which can be defined by a limit value stated in the standard minus in particular a safety margin.

Claims

1. A DC voltage charging method with monitoring, in which a vehicle-side traction battery (B1, B2) is charged via a vehicle-side charging circuit using a charging voltage source (SQ) external to the vehicle, comprising: The traction batteries (B1, B2) have a rated voltage of at least 500 V; First, in an inspection step, it is detected whether the charging voltage source (SQ) has an overvoltage protection unit including a voltage limiting element (E) that is provided between a charging voltage potential of the charging voltage source (SQ) and a ground potential (GND) and is configured to transition to a conductive state from a threshold voltage below the rated voltage; If it is detected in the inspection step that the charging voltage source (SQ) does not have the overvoltage protection unit (E), a DC voltage is transmitted from the charging voltage source (SQ) to the traction battery (B1, B2), if it is detected in the checking step that the charging voltage source (SQ) has the overvoltage protection unit (E), then at least one DC voltage charging mode for the transmission of a DC voltage from the charging voltage source (SQ) to the traction batteries (B1, B2) is prevented. DC voltage charging method with monitoring.

2. In the inspection step, a signal (RA) indicating whether or not the charging voltage source (SQ) outside the vehicle is configured in compliance with the CHAdeMO standard 2.0 series is received from the charging voltage source (SQ) to detect whether or not the charging voltage source (SQ) has the overvoltage protection unit (E); When a signal (RA) representing the CHAdeMO standard 2.0 series is received, at least one DC voltage charging mode is blocked; When a signal (RA) representing the CHAdeMO standard 3.0 series is received, or when a signal (RA) representing a charging standard of the charging voltage source (SQ) that does not assume the overvoltage protection unit (E) is received, a DC voltage is transmitted from the charging voltage source (SQ) to the traction battery (B1, B2). The method of claim 1.

3. In the inspection step, a test signal (TS) is applied to the charging voltage potential and the ground potential (GND) to detect whether the charging voltage source (SQ) has the overvoltage protection unit (E); The obtained signal response (SA) is detected, and based on the signal response (SA), it is determined whether the charging voltage source (SQ) has the overvoltage protection unit (E). The method of claim 1.

4. A test voltage exceeding the threshold voltage is applied as the test signal (TS), and a resulting signal response (SA) is detected as a current flow generated by the test voltage. The method of claim 3.

5. An excitation signal for impedance measurement is applied as the test signal (TS), and a resulting signal response (SA) is detected as a signal representative of the impedance of the charging voltage source. The method of claim 3.

6. The vehicle-side charging circuit that transmits a DC voltage has a first direct charging path that does not include a converter and a second charging path that passes through a voltage converter (I, Q), The method includes a step of selecting between the first charging path and the second charging path for transmitting a DC voltage from the charging voltage source (SQ) to the traction battery (B1, B2), 6. The method according to any one of claims 1 to 5.

7. When a DC voltage is transmitted via the second charging path, the DC voltage is converted by the voltage converter (I, W); the voltage converter (W) converts the DC voltage using a dedicated operating switch and a dedicated operating inductance as converter elements or using at least one switch of an inverter (I) as an operating switch and at least one winding (W) of an electric machine as an operating inductance, whereby the inverter (I) and the electric machine form a traction drive on the vehicle side, The method of claim 6.

8. an insulation monitoring is performed before and / or during the transmission of a DC voltage to the traction batteries (B1, B2), which is configured in such a way that a voltage difference between one charging voltage potential and the ground potential (GND) is compared with a set nominal value or with another voltage difference between another charging voltage potential and the ground potential (GND), so that asymmetries of the two charging voltage potentials with respect to the ground potential, which give rise to the charging voltage, are identified, outputting an isolation error signal if the comparison indicates that a deviation greater than a set error limit has occurred, and not outputting an isolation error signal if the comparison indicates that the deviation does not exceed the set error limit.

8. A method for charging with direct voltage with monitoring according to any one of claims 1 to 7.

9. If the comparison indicates that the deviation is greater than a set error limit, the voltage converter (I, W) of the charging circuit is shut down. The DC voltage charging method with monitoring according to claim 8.

10. if the comparison indicates that the deviation is greater than a set tolerance value after the voltage converter (I, W) has been turned off, the transmission of DC voltage is interrupted; If, after the voltage converter (I, W) has been stopped, the comparison indicates that the deviation does not exceed a set tolerance value, the transmission of the DC voltage is performed or continued. The DC voltage charging method with monitoring according to claim 9.

11. The transmission of the DC voltage is interrupted by tripping a safety device, in particular a pyro-fuse (SB) or a cut-off switch, The DC voltage charging method with monitoring according to claim 10.

12. if the comparison indicates that the deviation is greater than the set tolerance value, a further comparison is performed at a set duration after the comparison, and if the further comparison indicates that the deviation is greater than the set tolerance value after the set duration has elapsed, the transmission of the DC voltage is interrupted by tripping the safety device, in particular the pyro-fuse (SB) or the cut-off switch. The DC voltage charging method with monitoring according to claim 11.

13. A vehicle-side charging circuit configured to carry out the method according to any one of claims 1 to 12, comprising: The charging circuit has a DC voltage charging terminal having two contacts (K+, K-) of different polarities, a first contact (K+) is connected to a node (V) via a safety device (F1); a first direct charging path not including a converter is connected to the node (V), the first charging path including a switch (S2), the node (V) being connected to a first battery terminal (B+) of the charging circuit via the switch (S2); a second charging path including a voltage converter (I, W) is connected to the node (V), the node (V) being connected to a second battery terminal (B-) of the charging circuit via the voltage converter (I, W); A second contact (K-) of the DC voltage terminal is connected to a second battery terminal (B-) of the charging circuit via a diode (D), the forward direction of the diode (D) being configured to allow a current to flow from the second battery terminal (B-) to the second contact (K-); The vehicle-side charging circuit has a control device (C) controllably connected to the switch (S2), at least one switch (S5, S6) to which at least one of the battery terminals is connected, and the voltage converter (I, W), and the control device (C) is configured to perform a test step and selectively control the switches (S2, S5, S6) and the DC voltage converter (I, W) for transmission or prevention of transmission depending on a result of the test step. Charging circuit on the vehicle side.

14. The charging circuit further includes a signal receiver (EM) for receiving a signal indicating whether the charging voltage source (SQ) is configured in compliance with the CHAdeMO standard 2.0 series; or The charging circuit further comprises a test signal generator (T) configured to generate a test signal (TS) and to apply the test signal (TS) to the charging voltage potential and the ground potential (GND), and a detection device (M) configured to detect a signal response (SA) generated by the test signal (TS).

14. A vehicle-side charging circuit according to claim 13.

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