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 electric drives, in which a charging station is provided for charging a storage device in the form of a battery on the vehicle side, and which is 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 configured in accordance with charging standards. One such standard is the CHAdeMO standard, the versions of which provide for charging voltages of up to 500 V DC.

[0003] Today, many vehicles use 800V vehicle-side batteries, but the charging voltage can differ from the vehicle-side voltage depending on the standard, for example, a maximum DC voltage of 500V as the charging voltage. Therefore, the object 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 can be obtained from the respective dependent claims, the description and the figures.

[0005] Charging standards such as the CHAdeMO Charging Standard recognize that when a charging station outputs a first DC voltage for charging and a vehicle battery is charged with a second DC voltage higher than the first DC voltage, a problem can occur if an insulation error occurs in the high-voltage potential (second DC voltage) relative to ground. This is achieved by charging stations, particularly those compliant with the CHAdeMO Charging Standard 1.0 and CHAdeMO Charging Standard 2.0, including an overvoltage protection element in the form of a varistor that protects the high-voltage potential relative to ground. The overvoltage protection element begins to conduct at a predetermined threshold voltage or a predetermined voltage value above the maximum charging voltage if an excessively high voltage relative to ground occurs, for example, due to a fault or a flash surge.

[0006] However, in cases where the battery is charged at a rated voltage greater than the maximum charging voltage (especially a threshold voltage or a predetermined voltage), if an insulation error occurs on one side of the high-voltage potential relative to ground, the other high-voltage potential relative to ground may have a voltage that triggers the overvoltage protection element to conduct, resulting in an undesirable high current flow. In other words, if an insulation error occurs on one side of the high-voltage part providing the second DC voltage relative to ground, a strong asymmetry in the potential of the second DC voltage relative to ground may occur, resulting in a high voltage relative to ground on one side that triggers the overvoltage protection element of the charging station to become conductive.

[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 occur, which will result in a high voltage of 800V and a condition that will trip the overvoltage protection unit.

[0008] Due to the low internal resistance of the battery, activation of the overvoltage protection unit can generate high ground currents that can be so high that it is no longer possible to guarantee that the ground is not damaged. This is particularly the case in charging stations where the ground cable has a relatively small cross-section (compared to the cross-section of the high-voltage lines in the charging station). Therefore, a high current flow due to an asymmetric shift can damage the ground (as a result of an insulation error relative to the ground), and if no ground potential terminal is provided, an insulation error will remain on the vehicle side, especially if the ground cross-section is small, which can make it impossible to eliminate dangerously high contact potentials on the vehicle chassis and therefore lead 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 begins to conduct, i.e., a high voltage at which the overvoltage protection of the charging station would be activated (and further danger would be caused) in the event of an insulation error on one side of the high-voltage potential relative 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 blocked. If it is detected that the charging station does not have an overvoltage protection (and therefore the above-mentioned problem does not exist), the DC voltage charging mode that would otherwise be blocked is permitted, and 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 that includes a voltage-limiting element that is arranged between the charging voltage potential of the charging voltage source and ground potential and that is configured to transition to a conduction-enabled state at a voltage (threshold voltage) below the rated voltage. This overvoltage protection is also referred to as a critical overvoltage protection. This is because the overvoltage protection unit becomes active if a ground insulation error occurs, especially when a vehicle is connected that has an onboard electrical grid with a rated voltage higher than the trip voltage of the overvoltage protection unit.

[0010] If the rated voltage of the traction battery is lower than the maximum charging voltage or the threshold voltage at which the overvoltage protection unit becomes active, the above-mentioned error is unlikely to occur, regardless of whether or not there is 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 the vehicle will 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 the test step, it is determined whether the charging station is equipped with a voltage-limiting element that may be activated if a corresponding voltage (i.e., a voltage with a high voltage potential relative to ground) occurs at the charging station due to an insulation error on the vehicle side. Therefore, since corresponding voltage-limiting elements are defined in charging standards, such as the CHAdeMO charging standard, it is possible to conclude whether a critical voltage-limiting element is present by performing a test only for the standard for which the charging station is built. If a critical voltage-limiting element is present, at least one DC voltage charging mode can be inhibited. 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 storage battery. Furthermore, the DC voltage charging mode can be a mode in which a galvanic non-isolated converter is used to transfer charging power from the charging station to the storage battery on the vehicle side.

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

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

[0014] Further described is a vehicle-side charging circuit configured to perform the methods described herein. The charging circuit includes a DC 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, 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, which does not include a converter, is connected to the coupling point. The first charging path includes a switch connecting the coupling point to a first battery terminal of the charging circuit. When the switch is open, no current flows through the first charging path. A second charging path is connected to the coupling point. The second charging path includes a voltage converter. Thus, the second charging path is configured to transmit power in a voltage-converted form via the voltage converter. The coupling point is connected to a second battery terminal of the charging circuit via the second charging path.

[0015] According to one embodiment, the voltage converter, as described above in the method, has at least one switch of the inverter as an operating switch and at least one winding as an operating inductance. The winding is part of an electric machine controlled by the inverter. This allows the inverter and the electric machine to be used for two functions: on the one hand, for traction 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 functions.

[0016] The second contact of the DC voltage terminal is preferably connected to the second battery terminal of the charging circuit via a diode. The forward direction of the diode is configured to allow current to 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 DC voltage blocking direction of the diode 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] The vehicle-side charging circuit may further include a control device connected to control the switch. The control device may be further controllably connected to at least one switch connected to at least one of the two battery terminals. When the battery terminals are each connected to the remaining circuit via a switch, each of the two battery terminals may be connected to the remaining circuit via a separate switch. In this case, one switch may be provided between the first battery terminal and a point where the two charging paths converge again. The other switch may be provided between the second battery terminal and the diode. The control device may further be controllably connected to the voltage converter. The control device is preferably configured to perform a test step and selectively control the switch and the DC voltage converter to transmit or prevent transmission depending on the result of the test step. That is, the control device is configured to use the switch and the DC voltage converter to realize at least two states, i.e., a first state of transmission and a second state of prevention of transmission.

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

[0019] The checking step is configured to receive a signal that indicates whether the charging voltage source has an overvoltage protection unit (which is activated or conductive to ground when the voltage drops below 500 V). This is particularly related to the charging standard to which the charging voltage source conforms, so the signal can reflect the charging standard to which the charging voltage source conforms. From this, it can be concluded whether the charging voltage source has the overvoltage protection unit. In particular, the signal can indicate whether the charging voltage source conforms to the CHAdeMO Standard 2.0 series. Here, the term "CHAdeMO Standard 2.0 series" refers to a CHAdeMO standard in which the charging voltage source is provided with an overvoltage protection unit (relating to the voltage between the charging voltage potential and ground) that is activated at a voltage (threshold voltage) of approximately 500 V, in particular below 800 V, 700 V, or 600 V. Active here means that the overvoltage protection becomes conductive when a corresponding voltage (threshold voltage) is reached, thereby forming a conductive path between the high voltage potential and ground. A control device or other device may be provided on the vehicle network side, which is configured to receive the corresponding signal and evaluate it accordingly.

[0020] When a signal representing a CHAdeMO 2.0 series standard is received, at least one DC voltage mode is blocked. When a signal representing a CHAdeMO standard is received, or in general when a signal representing a charging standard without the above-mentioned overvoltage protection is received, 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 have a signal receiver. The signal receiver is configured to receive a signal representing 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 represents a charging standard that assumes an overvoltage protector with a voltage limiting element for the charging station. The signal receiver may be connected wirelessly or with a cable. 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 to determine whether an overvoltage protector 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 protector with a voltage-limiting element is present. The test signal can be configured to trip the voltage-limiting element (i.e., to transition it to a conductive state) based on a corresponding signal response to the test signal to determine whether an overvoltage protector with a voltage-limiting element is present. The test signal can also be configured as a signal for actively measuring the impedance of the charging voltage source to calculate an impedance based on a corresponding signal response to the test signal and determine whether an overvoltage protector with a voltage-limiting element is present from the impedance. 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. Suitable characteristics of the voltage-limiting element here include a characteristic that enables conduction from a threshold voltage and a characteristic that has an impedance within a typical impedance interval for a voltage-limiting element, particularly a characteristic that has a capacitance within a typical capacitance interval. Another electrical characteristic characteristic of a voltage-limiting element may be determined. If the characteristic is present, a voltage-limiting element is concluded to be present. If the determination indicates that the characteristic is not present, a (potentially critical) voltage-limiting element is not present in the charging station.

[0023] Therefore, in the testing step, it can be configured to detect whether the charging voltage source has an overvoltage protection unit. This is detected or determined by applying test signals to the charging voltage potential and to ground potential (i.e., to the location where the voltage-limiting element would be connected if present). The resulting 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 unit. In other words, it is proposed to detect or determine typical electrical characteristics of the voltage-limiting element by applying test signals and detecting corresponding signal responses. The characteristics are obtained by evaluating how the signal response to the test signal behaves or whether a signal response occurs or not. A test voltage above a threshold voltage can be applied as the test signal. The resulting 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 causes the current-limiting element to switch to a conductive state. Here, the polarity of the test voltage and the polarity of the charging voltage potential are observed, and in particular, a test voltage with an absolute value above the absolute value of the threshold voltage is applied. This detects the characteristic of the voltage limiting element (if 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 may be connectable to the traction battery or a DC voltage converter connected to the traction battery.

[0024] Furthermore, an excitation signal for impedance measurement can be applied as the test signal. An AC voltage signal (or an AC current signal) having multiple simultaneous frequency components (e.g., noise) or an AC voltage signal (or an AC current signal) having frequency components whose frequency varies over time ("swept") is suitable as the excitation signal. A signal response obtained in a state associated with the test signal is detected as a signal representing the impedance of the charging voltage source. When an AC voltage signal is the excitation signal, the signal response can be detected as a current signal. When an AC current signal is the excitation signal, the signal response can be detected as a voltage signal.

[0025] Preferably, the test voltage is applied by a current limiting element, so that even if the voltage-limiting element is conductive, only a limited current flows. Current limiting of the test signal can be preferably achieved simply by a switchable series resistor (a current-limiting resistor connected in series) or by appropriately driving a DC-to-voltage converter to generate a test signal with a limited current intensity. The test signal can be limited to a maximum current intensity of 1 A or less, 100 mA or less, 10 mA or less, or 1 mA or less. The series resistor (current-limiting resistor) can be implemented 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 ground potential, thereby applying the test signal to each potential. The test signal generator may be connected (especially on the input side) to the traction battery and to a DC voltage converter or low-voltage source connected to the traction battery. Furthermore, a detection device may be provided that is configured to detect a signal response generated by the test signal. The detection device may be connected on the input side, preferably in a signal-transmitting manner or via a voltage divider or capacitive coupling, to the charging voltage potential and / or ground potential. The test signal generator and the detection device together preferably form a detection module that actively detects or measures the electrical characteristics 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 a common device.

[0027] In one embodiment, the vehicle-side charging circuit through which the DC voltage is transmitted has a first direct charging path without a converter and a second charging path. The second charging path is connected via a voltage converter. The voltage converter can be a dedicated voltage converter or can be formed by 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 vehicle-side drive, in particular a traction drive. The winding is in particular a winding, in particular a stator winding, of the electric machine of the vehicle's electric drive. The method preferably includes selecting whether the transmission takes place via the first charging path or the second charging path. This applies to the transmission of DC voltage from the charging voltage source to the traction battery or the transmission of DC voltage via the vehicle-side charging circuit. The selecting step can be configured so 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 in the method is particularly a DC voltage converter, preferably a step-up converter, although other types of converters are also possible. The voltage converter can have at least one dedicated operating switch and at least one dedicated operating inductance as a 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 implement functions, particularly in a vehicle drive or traction drive. Alternatively, a switch of the inverter can be used to implement the converter, particularly the operating switch of the converter, in which case one or more switches of the inverter can be used. Additionally, a winding of an electric machine, particularly a winding of an electric machine of a 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 allows the converter to be realized without a dedicated output element. In particular, if a 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 inverter drive control can be configured to drive and control the inverter together with the operating inductance as a converter. The corresponding control device or inverter control therefore has two functional parts: 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, which determines the degree of symmetry of the charging voltage potential with respect to ground potential. The charging voltage potential is electrically isolated with respect to ground potential during error-free operation. If the degree of isolation is approximately the same, then symmetry of the charging voltage potential with respect to ground potential is achieved. For charging voltage potentials of +400V and −400V (i.e., a charging voltage of 800V), the ground potential should be approximately 0V, because the ground potential should have approximately equal insulation resistance for the two charging voltage potentials. If an isolation error occurs in either of the charging voltage potentials with respect to ground potential, the ground potential will shift with respect to the charging voltage potential. In particular, the voltage between the charging voltage potential with an isolation error and ground potential is much smaller than in error-free operation. An insulation error pulls the corresponding charging voltage potential down to ground potential, resulting in a very low voltage between these potentials, i.e., a voltage much smaller than half the charging voltage, while the voltage between the charging voltage potential and ground potential without an insulation error can be much larger than half 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 overvoltage protection unit on the charging voltage source side to trip if the voltage at which the overvoltage protection unit is activated (threshold voltage) is smaller than the charging voltage.

[0030] Such asymmetry can be identified by comparing the (absolute) voltage difference between the charging voltage potential and 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 detected asymmetry, which can identify an insulation error. Thus, for example, for an 800V charging voltage, the rated value may be 400V (or more than half the charging voltage, i.e., approximately 500V). An asymmetry occurs when the voltage between the charging voltage potential and ground potential is significantly smaller than the rated value (in which case the corresponding charging voltage potential has an error) or significantly 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 ground potential can be compared with the voltage difference between another charging voltage potential and ground potential, thereby directly detecting the asymmetry. If the comparison indicates a deviation greater than a set error limit or safety margin, an insulation error signal is output. If not, no insulation error signal is output, or a signal is output indicating that no insulation error exists.

[0031] Furthermore, the voltage converter can be configured to be deactivated if the comparison indicates that the deviation is greater than a set error limit. The voltage converter can be deactivated, in particular, by switching its operating switch to a permanently open state. This prevents the converter from continuing to operate and output 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 vehicle chassis.

[0032] In another embodiment, if a small deviation is detected, charging or transmission of DC voltage continues or at least one charging mode remains permitted, while if the deviation is large as described above, the transmission of DC voltage is interrupted or blocked. To distinguish between these cases, a tolerance value is used below which no danger is expected and above which a potential danger can be expected. A safety distance can be set between the tolerance value and the error limit described above. If the deviation does not exceed the tolerance value, an insulation indication signal can be output, which indicates that the insulation should be checked, but that no dangerous insulation error exists. On the other hand, if the error limit described above is exceeded, an error signal is output, preferably indicating 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 pyro-fuse, can be configured to trip. Alternatively or in combination, a disconnect switch can also be tripped, in particular by opening the disconnect switch. Thus, disconnection here preferably only occurs if the deviation actually indicates a dangerous touch voltage or if touch voltages that are not permissible according to high-voltage safety standards may be present on the vehicle chassis. [Brief explanation of the drawings]

[0034] [Figure 1] 1A-1C are diagrams for explaining exemplary embodiments of the procedures described herein.

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

[0036] FIG. 1 shows an exemplary vehicle-side charging circuit with battery terminals B+ and B- connected to a battery circuit. In the illustrated embodiment, the battery circuit includes two series-connected batteries B1 and B2 (each configured as a high-voltage accumulator), which are connected to each other via a disconnecting switch device, particularly configured as a pyrofuse. The battery circuit can generally include two series-connected accumulators (high-voltage accumulators), in which case a pyrofuse, typically a fuse or disconnecting switch, is also connected in series. Two accumulators can also be directly connected in series with each other, in which case a disconnecting switch, i.e., a fuse or particularly 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] The battery circuit (B1, SB, B2) is connected to a first battery terminal B+ and a second battery terminal B-. The polarity can be seen from the reference symbols. Optionally, a switch S5, which is connected to another 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 after 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 with a neutral point that serves as a phase terminal for one of the three windings W of the electric machine. Also shown are three current measuring devices 2, 3, 4, which are arranged between the electric machine or its windings W and the phase terminals of the inverter I.

[0039] The windings W are connected to each other as a star-connected circuit, and a switch S3 is 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 (which is connected 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 the switch S1 on the other hand. The diode D is connected in series with the switch S4. The diode D and the switch S4 form a switching diode circuit. The switch S1 is connected in parallel with the diode circuit. In the closed state, the switch S1 bridges the diode circuit. In particular, if it is determined that there is no critical overvoltage protection on the charging station side, the switch S1 can be closed. In this case, there is a possibility of energy being supplied back from the battery terminals B+ and B- to the contacts K+ and K- of the DC voltage charging terminals shown in the figure.

[0041] On the side of the diode circuit D, S4 or the switch S1 opposite the inverter or the second battery terminal B-, a second (negative) contact K- is provided. This 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 fuse or a pyro-fuse.

[0042] The 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 in turn leads to the positive battery terminal B+ or to a switch S5.

[0043] Switches S5 and S6 therefore form a charging circuit-side, all-polarity disconnect switch for controlled isolation of battery terminals B+ and B-. Switch SB (particularly configured as a pyrofuse) is part of the battery circuit connected to the battery terminals. This switch SB also serves to isolate the battery circuit or batteries B1 and B2, so that in the open state, the potential resulting from the sum of the two voltages of batteries B1 and B2 cannot be applied.

[0044] A first charging path exists from the node V (seen from the first contact K+) directly to the first battery terminal B+ via switch S2 (and optionally via switch S5). This charging path does not include a converter. A second charging path also leads from the node V to the battery terminal B+ via (optional) switch S3, winding W, and inverter I. The second charging path includes 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 one of the half-bridges of the inverter I. A control unit C is configured to drive and control the switches of the inverter I, thereby providing a DC voltage conversion function for the second charging path. The node 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+ and K- form the opposite end of the charging circuit from the battery terminals B+ and B-, so B+ and B- on one side and K+ and K- on the other side form two ends of the charging circuit.

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

[0047] The control unit C is further drivably connected to the switches of the charging circuit and, optionally, to the disconnection switches of the battery circuits (B1, SB, B2). The control unit C is configured to detect whether the voltage source SQ has an overvoltage protection section designed or configured to conduct current when a voltage corresponding to the sum of the rated voltages (or minimum operating voltages) of the accumulators B1 and B2 with respect to ground potential appears at one of the contacts K+, K-. If this voltage appears 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 DC voltage charging mode by opening at least one of the switches. In this case, the switch S3 can also be opened.

[0048] If the overvoltage protection unit further determines that the current flow exceeds a (predetermined) error limit, at least one other of the switches can be opened, where the error limit represents a current value at which an error is identified based on the current flow.

[0049] If one of the switches is configured as a one-time open switch, e.g., a pyro-fuse, the switch is preferably opened only when the above-mentioned conditions are met and the current flowing (through element E) based on the overvoltage protection unit exceeds a tolerance value. The tolerance value is greater than the error limit. The tolerance value indicates a threshold at which the current flow may be dangerous to humans. The error limit indicates the current flow level at which an error related to the current flow based on the overvoltage protection unit of the charging station is detected and is lower than the tolerance value. Thus, if the tolerance value is exceeded, another switch that is not opened when the error limit is exceeded can be opened. If the current is between the tolerance value and the error limit, limited charging can be performed, i.e., one DC voltage charging state can be blocked and the other DC voltage charging state can be allowed. The two DC voltage charging states can be distinguished by the charging path used. The control device C is configured to make this distinction.

[0050] According to one embodiment, the control device C is configured to drive the inverter switch in an 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 ground potential GND and configured to transition to a conductive state at a voltage below the rated voltage (threshold voltage). For this purpose, the control device C can have a signal input or receiving device by which it can transmit information to the control device C reflecting whether the charging voltage source SQ has (or is connected to) an overvoltage protection unit including a voltage-limiting element E configured to transition to a conductive state at a voltage below the rated voltage (threshold voltage). 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 representing information on whether 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 charging station is configured in accordance with).

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

[0053] In a simple design, the test signal generator TG can correspond to a current-limiting resistor connected in series between point V and potentials corresponding to B+, B- or the (output) potential of a voltage converter. Via connection V1 or connection V2, the test signal generator TG or its input I can be connected to the charging voltage potential (of the accumulator or DC-voltage converter). The output O of the test signal generator TG can be connected to one of contacts K+ or K- (or point V), in particular, via a detection device M. If the detection device M is an ammeter, this can detect whether or not a (DC) current flow occurs upon application of the test signal. If a current flow occurs, the presence of the voltage-limiting element E is inferred; if no current flow occurs, the absence of the voltage-limiting element E is inferred. In an embodiment shown, the test signal generator TG generates a voltage above the threshold voltage of element E. It is also possible to provide a test signal generator TG that emits a test signal suitable for impedance measurement, with the signal response 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), and in particular can have 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 other such overvoltage protection element 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 to enable the DC voltage charging mode. In particular, the switch S1 connected in parallel to the switching diode circuit (series circuit consisting of the diode D and the switch S4) can be configured to be opened, thereby preventing transmission.

[0055] In particular, if the test step detects that the charging voltage source does not have an overvoltage protection unit, a method can be implemented to test whether an insulation error with respect to ground potential has occurred in the charging circuit. If an insulation error is detected in 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 inferred. In particular, an insulation error can also be identified by detecting a current flow (e.g., using a current measuring device 1) that exceeds an error limit.

[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 greater than a predetermined limit value flows due to an insulation error. The predetermined limit value can be, in particular, the sustained current load capacity of the ground conductor used. The limit value can correspond to a tolerance limit. Furthermore, the predetermined limit value can correspond to a standard limit contact current value for high-voltage charging, e.g., 100 mA, 40 mA, 20 mA, or 10 mA of DC current. This can be done, in particular, 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 flowing due to an insulation error exceeds the predetermined limit value.

[0058] The 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 to open, in particular by the control unit C. If the switch SB is a pyro-fuse, the control unit C will only fire the pyro-fuse if the error current is greater than the defined limit value, even if the DC-to-DC converter I,W is inactive. The limit value may correspond to the tolerance value (or a set error limit) mentioned at the beginning.

[0059] The pyrofuse or another non-reclosable switch in the illustrated circuit therefore does not always open in the event of an insulation error 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 to personnel, even though the voltage transformer is disconnected, which can be defined by a limit value stated in the standard minus, inter alia, 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 that is lower than 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 batteries (B1, B2), If it is detected in the checking 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 batteries (B1, B2) is blocked. DC voltage charging method with monitoring.

2. In the inspection step, a signal (RA) indicating whether the charging voltage source (SQ) outside the vehicle is configured in accordance with the CHAdeMO Standard 2.0 series is received from the charging voltage source (SQ) to detect whether 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 a 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 batteries (B1, B2).

2. The DC voltage charging method according to 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).

2. The DC voltage charging method according to claim 1.

4. A test voltage exceeding the threshold voltage is applied as the test signal (TS), and the resulting signal response (SA) is detected as a current flow formed by the test voltage.

4. The DC voltage charging method according to 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 representing the impedance of the charging voltage source; 4. The DC voltage charging method according to claim 3.

6. the vehicle-side charging circuit transmitting 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, W); The DC voltage charging method with monitoring includes a step of selecting between the first charging path and the second charging path for transmitting DC voltage from the charging voltage source (SQ) to the traction batteries (B1, B2).

2. The DC voltage charging method according to claim 1.

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 (I, 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 the inverter (I) as the operating switch and at least one winding (W) of the electric machine as the operating inductance, wherein the inverter (I) and the electric machine form a traction drive on the vehicle side; 7. The DC voltage charging method according to claim 6.

8. an insulation monitoring is performed before and / or during the transmission of a DC voltage to the traction batteries (B1, B2), the insulation monitoring being configured to compare a voltage difference between one charging voltage potential and the ground potential (GND) with a set nominal value or to compare it with another voltage difference between another charging voltage potential and the ground potential (GND), thereby identifying asymmetries of the two charging voltage potentials with respect to the ground potential that result in a charging voltage; 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. The DC voltage charging method with monitoring according to claim 1.

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 deactivated. 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) is stopped, the transmission of DC voltage is interrupted; After the voltage converter (I, W) has been stopped, if 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, another comparison is performed at a set duration after the comparison, and if the other 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 DC voltage charging 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, The first contact (K+) is connected to a node (V) via a safety device (F1), and a first direct charging path without a converter is connected to the node (V), the first charging path having a switch (S2), and the node (V) is connected to a first battery terminal (B+) of the charging circuit via the switch (S2), and a second charging path having a voltage converter (I, W) is connected to the node (V), and the node (V) is 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 charging terminal is connected to a second battery terminal (B-) of the charging circuit through a diode (D), the forward direction of the diode (D) being configured to allow 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) connected to at least one of the battery terminals, and the voltage converter (I, W), and the control device (C) is configured to perform a test step and selectively drive and control the switches (S2, S5, S6) and the voltage converter (I, W) to transmit or prevent transmission depending on the result of the test step. Vehicle charging circuit.

14. The charging circuit further comprises a signal receiver (EM) for receiving a signal indicating whether the charging voltage source (SQ) is configured in accordance 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 connected to the charging voltage potential and the ground potential (GND) to apply the test signal (TS) to each potential, and a detection device (M) configured to detect a signal response (SA) generated by the test signal (TS).

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

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