Method for operating a charging system for a vehicle with a galvanically non-isolated charger

Abstract

Method for operating a vehicle (1) with a charging system (3), which charging system (3) has an on-board electrical system (2), a measuring device for determining the impedance (ZHV) of the on-board electrical system (2), and a galvanically non-isolated charger (9), which charger (9) is part of the on-board electrical system (2), in which method an impedance (ZHV) of the on-board electrical system (2) is determined by the measuring device and a switching frequency (fsw) of the galvanically non-isolated charger (9) is set as a function of the determined impedance (ZHV).

Description

[0001] The invention relates to a method for operating a charging system for a vehicle, in particular an electric or hybrid vehicle, having an on-board electrical system and a non-galvanically isolated charger. Furthermore, the invention relates to a charging system for a vehicle comprising an on-board electrical system and a non-galvanically isolated charger. A further subject matter is a vehicle having such a charging system.

[0002] Along with the electrification and hybridization of vehicle powertrains, the need for adequate battery charging infrastructure is growing. Not only fast charging of vehicles, but also a safe charging process is of paramount importance. Currently, electric and hybrid vehicles typically use galvanically isolated chargers, so that the circuits of the charging station and the vehicle's electrical system are potential-free.

[0003] Components installed in the vehicle electrical system, particularly their Y-capacitances, can cause fault currents to flow in every high-voltage component of the vehicle electrical system. These currents pose a danger to passengers ("electric shock") if they touch the vehicle's ground. Due to aging effects, for example, of the Y-capacitances, the fault currents can change over the service life. These fault currents pose an increased risk, particularly when using non-galvanically isolated chargers. Safe charging with non-galvanically isolated chargers is virtually impossible without additional protective measures.

[0004] DE 11 2016 003 586 T5 shows a charger in which a boost operation is started or stopped depending on a connection voltage.

[0005] DE 10 2017 123 783 A1 shows a high-voltage system for a vehicle in which main contactors are closed depending on an impedance

[0006] DE 10 2019 202 465 A1 shows a method for operating a battery system.

[0007] DE 10 2016 218 304 B3 shows a device for voltage conversion.

[0008] WO 2021 / 099 102 A1 shows a method for determining a condition value of a traction battery.

[0009] LIANG-RUI, C. et al.: Design of Sinusoidal Current Charger with Optimal Frequency Tracker for Li-ion Battery. The 2010 International Power Electronics Conference - ECCE ASIA -, 2010, pp. 1484-1489. doi: 10.1109 / IPEC.2010.5544521 demonstrate a sinusoidal current charger for a lithium-ion battery.

[0010] LIANG-RUI, C. et al.: Improving battery charging performance by using sinusoidal current charging with the minimum AC impedance frequency. 2010 IEEE International Conference on Sustainable Energy Technologies (ICSET), 2010, pp. 1–4. doi: 10.1109 / ICSET.2010.5684431 demonstrate a sinusoidal current charger with improved performance.

[0011] Against this background, the task now arises to develop a method that enables safe operation of a charging system with a galvanically non-isolated charger over a longer operating period.

[0012] To achieve this objective, a method is proposed for operating a charging system for a vehicle, in particular an electric or hybrid vehicle, having an on-board electrical system and a galvanically non-isolated charger, wherein an impedance of the on-board electrical system is determined, and a switching frequency of the galvanically non-isolated charger is adjusted as a function of the determined impedance. With the method according to the invention, a switching frequency of the galvanically non-isolated charger can be adjusted as a function of the determined impedance in such a way that fault currents are minimized. By determining the impedance, changes in the impedance (for example due to aging phenomena) can influence the selection of the switching frequency of the charger. The switching frequency can therefore be adjusted even in the event of changes in the impedance in such a way that fault currents are reduced.This enables safe operation of the charging system even when components of the on-board electrical system exhibit increased leakage currents due to aging effects and / or failure (or defect). This enables safe operation of the charging system with the non-galvanically isolated charger over a longer operating period. The method according to the invention can also simplify the maintenance of a vehicle's on-board electrical system, since the switching frequency of the charger can be automatically adjusted after a component has been replaced using the method according to the invention so that the fault current is as low as possible. Automated frequency downlinking can reduce the costs of a charging system compared to manual frequency downlinking and thus offer commercial advantages for electric and hybrid vehicles.

[0013] Advantageous embodiments and further developments of the invention can be found in the dependent claims and the description with reference to the drawings.

[0014] The impedance of the vehicle electrical system is preferably an impedance of a high-voltage part of the vehicle electrical system. The high-voltage part is preferably designed for a voltage greater than or equal to 400 V, particularly preferably greater than or equal to 800 V. In an advantageous embodiment of the present invention, it is provided that the impedance is determined as a function of a voltage response, in particular a step response, of the vehicle electrical system. The voltage response can be evaluated to determine the impedance of the vehicle electrical system, in particular a capacitive impedance. The impedance is preferably the impedance of one or more Y-capacitors of the vehicle electrical system. Alternatively, it can be provided that the impedance is determined by means of a bridge circuit or that the impedance is determined by frequency matching.

[0015] An advantageous embodiment of the invention provides that an impedance parameter is determined to adjust the switching frequency. Preferably, a capacitance, particularly a Y capacitance, is determined. It has been found that changes in the capacitance, particularly the Y capacitance, of the vehicle electrical system contribute significantly to changes in the impedance of the vehicle electrical system. In this respect, it is possible to use the determined capacitance to adjust the switching frequency.

[0016] According to an advantageous embodiment of the present invention, the switching frequency is selected depending on a characteristic map that specifies a relationship between the impedance of the vehicle electrical system or an impedance parameter, in particular a capacitance, and a fault current for different switching frequencies. The characteristic map makes it possible to assign a switching frequency to an impedance determined by the control unit that results in the lowest possible fault current. According to a variant of this embodiment, the characteristic map is stored in a memory unit of the control device. The characteristic map can be stored in the memory unit, for example, as a database or table and / or as a mathematical algorithm or function.

[0017] An advantageous embodiment of the method provides that the switching frequency is selected such that a minimal fault current is generated in the charging system. Such a target switching frequency can reduce compensating currents between the vehicle electrical system and a charging station caused by fault currents.

[0018] According to an advantageous embodiment of the present invention, the actual switching frequency of the non-galvanically isolated charger is adjusted to the selected switching frequency. A control loop can be used to adjust the switching frequency to the desired switching frequency.

[0019] The object is further achieved by a charging system for a vehicle, in particular an electric or hybrid vehicle, comprising an on-board electrical system and a galvanically non-isolated charger, wherein a switching frequency of the galvanically non-isolated charger can be adjusted by a control device as a function of an impedance of the on-board electrical system.

[0020] The charging system according to the invention achieves the same advantages as have already been described in connection with the method according to the invention.

[0021] The vehicle electrical system preferably comprises a battery, in particular a high-voltage battery.

[0022] Furthermore, the on-board electrical system can include an inverter, in particular a pulse-controlled inverter, for controlling a traction drive and / or a DC-DC converter. The on-board electrical system, in particular its aforementioned components, can include capacitors, in particular Y capacitors.

[0023] According to an advantageous embodiment of the present invention, the charging system comprises a measuring device, in particular a sensor arrangement, for determining the impedance. The measuring device can be configured such that the vehicle electrical system can be excited with a pulse and a voltage response can be measured, in particular excited with a step function and a step response can be measured. According to a variant of the embodiment, the measuring device comprises one or more voltage measuring sensors and / or one or more current sensors.

[0024] According to a preferred embodiment, the control device comprises a memory unit in which a characteristic map is stored. Based on the characteristic map, an automated selection of a switching frequency can be performed that results in the lowest possible fault current. The characteristic map can be stored, for example, as a database or table and / or as a mathematical algorithm or mathematical function.

[0025] In an advantageous embodiment of the present invention, the non-galvanically isolated charger is a component of the vehicle electrical system. In such an embodiment, the charger's switching frequency can be adjusted exclusively by vehicle components. The vehicle can regulate the optimal switching frequency for achieving a low fault current itself, i.e., independently of an external charging station connected to the vehicle electrical system. According to a preferred variant of this embodiment, the vehicle electrical system is designed such that the non-galvanically isolated charger can be replaced with a galvanically isolated charger if necessary.

[0026] According to an advantageous embodiment of the present invention, the non-galvanically isolated charger is provided as part of an external charging station. One advantage of this embodiment is that a charger does not need to be provided in the vehicle's electrical system, thereby reducing the vehicle's complexity and, if necessary, the vehicle's weight. According to an advantageous variant of the embodiment, the charging station is designed such that the non-galvanically isolated charger can be replaced with a galvanically isolated charger if necessary.

[0027] The invention further relates to a vehicle, in particular an electric or hybrid vehicle, comprising a charging system as described above. In order for the vehicle's battery to be charged safely and without danger, potential sources of error in battery charging must be reduced. By setting an optimal switching frequency of the charger, fault currents can be minimized, thus enabling safe battery charging. Further details and advantages of the invention will be explained below with reference to the exemplary embodiment illustrated in the drawings. Herein: Fig. 1. a schematic representation of an embodiment of a vehicle according to the invention; and Fig. 2 an embodiment of the charging system according to the invention in a schematic block diagram; and Fig. 3 a flowchart of an embodiment of the method according to the invention.

[0028] In Fig. Figure 1 shows a vehicle 1 configured as an electric or hybrid vehicle according to an exemplary embodiment of the present invention. The vehicle 1 has an on-board electrical system 2, which is part of a charging system 3 according to an exemplary embodiment of the present invention.

[0029] An embodiment of such a charging system 3 is shown in Fig. 2. As an external component, the charging system 3 comprises a charging station 4 connected to a power grid. The charging station 4 can be connected to the on-board electrical system 2 of the vehicle 1 via a charging cable 5 in order to charge a battery 6 of the vehicle 1.

[0030] The battery 6 is part of the vehicle electrical system 2 of the charging system 3. The vehicle electrical system 2 further comprises a galvanically non-isolated charger 9, which can be connected to the charging station 4 via the charging cable 5. The battery 6 is arranged in a high-voltage part 10 of the vehicle electrical system, which is operated with a higher voltage. This higher voltage is preferably in a range greater than or equal to 400 V, preferably greater than or equal to 800 V. In the exemplary embodiment, a DC-DC converter 8 coupled to the charger 9 is additionally provided, which can optionally convert the output voltage of the charger 9 to a higher or lower voltage, for example in order to Fig. 2 not shown component. In the high-voltage part 10 of the vehicle electrical system 2, in addition to the battery 6, there is also an inverter 7 for controlling a Fig. 2 not shown traction drive of the vehicle 1.

[0031] In the vehicle electrical system 2, in particular in the high-voltage part 10 of the vehicle electrical system 2, several Y-capacitors Cy are provided, which can divert high-frequency interference signals to the vehicle ground GND as interference suppression capacitors. The capacitance of the Y-capacitors Cy changes over their operating life and thus has a direct impact on fault currents generated in the vehicle electrical system. These fault currents can cause an electric shock if they come into contact with the vehicle ground GND and thus pose a danger to persons. In order to enable safe operation of the charging system 3 with the galvanically non-isolated charger 9, the charging system 3 is therefore Fig. 1 special measures have been taken.

[0032] Thus, the charging system is operated according to a method in which an impedance ZHV of the vehicle electrical system 2, in particular of the high-voltage part 10, is determined and a switching frequency fsw of the galvanically non-isolated charger 9 is determined as a function of the determined impedance Z HV The method according to the invention is carried out by means of a control device 11 of the charging system 3 and will be described below with reference to the illustration in Fig. 3 will be explained in more detail.

[0033] A first method step of the method according to the invention includes a measuring step 100 in which the impedance ZHV of the vehicle electrical system 2, in particular of the high-voltage part 10, is determined. Measuring devices, in particular sensor arrangements, can be used to determine the impedance ZHV. The impedance ZHV can be determined via an impedance measurement. For example, the impedance ZHV can be determined as a function of a voltage response, in particular a step response, of the vehicle electrical system 2. For this purpose, a measuring device can excite the vehicle electrical system with a pulse in order to measure a voltage response, in particular with a step function in order to measure a step response.

[0034] In the embodiment of the method, a parameter of the impedance ZHV, preferably a capacitance, particularly preferably a Y-capacitance, is further determined in measuring step 100.

[0035] Following measurement step 100, in a selection step 200, a switching frequency fsw is selected depending on a characteristic map that specifies a relationship between the impedance ZHV of the vehicle electrical system 2 or a parameter of the impedance ZHV, in particular a capacitance, and a fault current for different switching frequencies fsw. The switching frequency fsw is selected such that it is a switching frequency fsw that results in a minimal fault current. The characteristic map used in selection step 200 is preferably stored in a memory unit of the control device 11. The characteristic map can be stored in the memory unit, for example, as a database or table and / or as a mathematical algorithm or function.Following the selection step 200, in a control step 300, the switching frequency fsw of the galvanically non-isolated charger 9 is set to the target switching frequency 19, in particular, adjusted so that the fault current of the charging system 3 is reduced. A control loop can be used to control the galvanically non-isolated charger 9 in order to adjust an actual switching frequency of the galvanically non-isolated charger 9 to the selected switching frequency fsw.

Claims

[1] Method for operating a vehicle (1) with a charging system (3), which charging system (3) has an on-board electrical system (2), a measuring device for determining the impedance (ZHV) of the on-board electrical system (2), and a galvanically non-isolated charger (9), which charger (9) is part of the on-board electrical system (2), in which method an impedance (ZHV) of the on-board electrical system (2) is determined by the measuring device and a switching frequency (fsw) of the galvanically non-isolated charger (9) is set as a function of the determined impedance (ZHV). [2] Method according to one of the preceding claims, characterized by that the impedance (ZHV) is determined as a function of a voltage response of the vehicle electrical system (2). [3] Method according to claim 2, wherein the impedance (ZHV) is determined as a function of a step response of the vehicle electrical system (2). [4] Method according to one of the preceding claims, characterized bythat an impedance parameter (ZHV) is determined to set the switching frequency (fsw). [5] Method according to claim 4, in which a capacitance or a Y-capacitance is determined as a parameter of the impedance (ZHV). [6] Method according to one of the preceding claims, in which the charging system (3) is designed to be connected to a charging station (4) via a charging cable (5) for a charging process without galvanic isolation between the vehicle electrical system (2) and the charging station (4). [7] Method according to one of the preceding claims, characterized by that the switching frequency (fsw) is selected depending on a characteristic map which indicates a relationship between the impedance (ZHV) of the on-board network (2) or a parameter of the impedance (ZHV) and a fault current for different switching frequencies (fsw). [8] Method according to claim 7, characterized bythat the switching frequency (fsw) is selected such that a minimal fault current results in the charging system (3). [9] Method according to claim 8, characterized by that an actual switching frequency of the galvanically non-isolated charger (9) is adjusted to the selected switching frequency (fsw). [10] Vehicle (1) with a charging system (3) and a control device (11), which charging system (3) has an on-board electrical system (2), a measuring device and a galvanically non-isolated charger (9), which charger (9) is part of the on-board electrical system (2), which measuring device is designed to determine an impedance (ZHV) of the on-board electrical system (2), and in which vehicle (1) a switching frequency (fsw) of the galvanically non-isolated charger (9) can be set by the control device (11) as a function of the determined impedance (ZHV) of the on-board electrical system (2). [11] Vehicle (1) according to claim 10, characterized bythat the charging system (3) is designed to be connected to a charging station (4) via a charging cable (5) for a charging process without galvanic isolation between the on-board network (2) and the charging station (4). [12] Vehicle (1) according to claim 10 or 11, characterized by that the control device (11) has a memory unit in which a characteristic map is stored which indicates a relationship between the impedance (ZHV) of the vehicle electrical system (2) or a parameter of the impedance (ZHV), in particular a capacitance, and a fault current for different switching frequencies (fsw).

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