Method and control unit for fast charging of a battery-powered electric vehicle

Abstract

The present invention relates to a method for fast charging a battery-powered electric vehicle, in which, in a first step, a respective fast-charging map is created depending on a respective aging state (1), wherein a maximum value of a fast-charging current (2) is assigned to a battery temperature and a state of charge by means of the respective fast-charging map, in which, in a second step, a maximum fast-charging current is set by determining the aging state, the battery temperature, and the state of charge of the battery in the vehicle, and a maximum fast-charging current value is calculated by interpolating the respective maximum values ​​of the fast-charging current, which are obtained from the two fast-charging maps whose respective aging states are adjacent to the determined aging state, with the determined battery temperature and the determined state of charge of the battery.and the electric vehicle is charged at a charging station with the maximum fast-charging current. Furthermore, a control unit is presented with which the procedure can be carried out.

Description

[0001] The present invention relates to a method for fast charging a battery-powered electric vehicle, in which the charging process is controlled based on temperature, state of charge, and cell aging of the battery. Furthermore, a control unit with which the method can be implemented is presented.

[0002] For battery-powered electric vehicles, a maximum fast-charging capacity and charging time are often cited as key selling points, typically determined based on a predefined usage profile. Depending on actual usage by the owner or driver of the electric vehicle, with faster charging being used more frequently than predicted, a control system adjusts the maximum fast-charging capacity and, consequently, the predicted charging time. For example, it is common practice to set an upper limit for the amount of charge that can be absorbed via fast charging and to prevent further charging once this limit is exceeded.Intensive use of fast charging at the beginning of a vehicle's lifespan can, under certain circumstances, lead to a drastically increased fast charging time. Depending on how such a prediction is implemented, this reduction is at best indicated or reflected in the charging behavior regarding fast charging performance only when the warranty expires (EOW). Once reduced, performance values ​​would then remain constant until the battery's end of life (EOL). This leads, on the one hand, to misleading expectations on the part of the owner, and on the other hand, to the unpredictability of such a performance reduction based on the reduced fast charging values. This unpredictability, therefore, makes it impossible to predict the validity period of previously stated or...displayed fast charging values ​​as well as a forecast of the residual value reduction of the vehicle resulting from the performance reduction.

[0003] German patent application DE 10 2019 212 762 A1 discloses a method for charging the battery of an electric vehicle. A maximum charging energy is determined from a characteristic map based on the battery's aging state.

[0004] German patent application DE 10 2009 058 263 A1 describes a further method for charging an electric vehicle battery. The battery's state of aging and temperature are determined. Depending on the state of aging and temperature, the charging process can be switched off if the battery's state of charge exceeds a limit. Furthermore, the state of aging or the temperature can lead to a limitation of the charging current.

[0005] The publication DE 10 2019 000 813 A1 discusses an alternative method for charging an electric vehicle battery, in which a maximum state of charge is selected based on the battery's aging and temperature. This involves the use of characteristic curves where the state of aging is plotted against temperature and state of charge.

[0006] Against this background, it is an object of the present invention to propose a method for fast charging a battery-powered electric vehicle, in which a charging current requested by a charging controller during fast charging is selected according to the battery's condition with respect to temperature, state of charge, and current state of aging. Furthermore, a control unit with which the method can be carried out is to be presented.

[0007] To solve the aforementioned problem, a method for fast charging a battery-powered electric vehicle is proposed, in which, in a first step, a specific fast-charging map is created depending on the battery's state of aging. This fast-charging map assigns a maximum fast-charging current value to a given battery temperature and state of charge. In a second step, a maximum fast-charging current is set by... • the vehicle's aging state, battery temperature, and battery charge level are determined, and • a maximum fast charging current value is calculated by interpolating the respective maximum values ​​of the fast charging current, which are obtained from the two fast charging characteristic maps, whose assigned respective aging state borders on the determined aging state, to the determined battery temperature and the determined state of charge of the battery,

[0008] The electric vehicle is charged at a charging station with the maximum fast charging current.

[0009] The interpolation of the respective maximum values ​​of the fast charging current is performed, for example, as a linear interpolation. Other suitable interpolation methods are also conceivable.

[0010] The method according to the invention thus advantageously provides, for the entire lifespan of the battery, an optimal maximum charging current value for the current state of the battery's aging, ensuring that the battery is charged within the predicted fast-charging time. This deviates from a prior art approach that potentially makes fast charging dependent on the actual state of the battery's aging at the end of a warranty period. Advantageously, during vehicle operation, fast charging is aligned with the current state of the battery's aging at every point in time. Therefore, current fast charging is independent of any previously unknown driver behavior, as the end of the warranty period does not lead to changes in the predicted fast-charging time.Furthermore, fast charging is in principle possible even after the warranty period has expired, provided that excessive use has not previously led to a drastic reduction in fast charging capability. Moreover, the inventive method provides the driver with predictable maximum fast charging performance at all times, thus advantageously allowing the driver to conserve battery life and increase the vehicle's residual value by reducing restrictions on fast charging.

[0011] It is conceivable that the method according to the invention is implemented as a software extension and integrated into an existing vehicle system.

[0012] In one embodiment of the method according to the invention, the maximum value of the fast-charging current is defined in the respective fast-charging maps for a given battery temperature and state of charge, in accordance with a safety specification for the battery cells. This represents the maximum possible fast-charging current for each aging state according to the safety specifications and ensures the battery's safety over its entire operating period between the start of operation and the end of its service life. The maximum charging current available from the charging station is limited to the maximum value of the fast-charging current in order to comply with the safety specifications.

[0013] In another embodiment of the method according to the invention, the maximum value of the fast-charging current is defined in the respective fast-charging maps for a given battery temperature and state of charge, based on test series results, to maximize battery longevity. Safety requirements for the battery cells are observed in this process. Aligning the determination of the maximum fast-charging current with regard to battery longevity generally results in a longer fast-charging time compared to a fast-charging time determined solely based on safety requirements. On the other hand, this approach increases the battery's longevity and thus the residual value of the vehicle.

[0014] In a further embodiment of the method according to the invention, each battery capacity value is assigned to a specific aging state from the following list: commissioning, start of power consumption, end of warranty, restriction to constant currents, end of operation. For example, the battery capacity value is set to 100% upon commissioning. A drop or loss in capacity to 80% is assigned to the end of the warranty, and a drop to 50% is assigned to the end of operation. This results, for example, in a first fast-charging map for the aging state of a vehicle commissioning with a virtually new battery, and a second fast-charging map for the aging state at the end of the warranty.It is conceivable to derive a fast-charging map corresponding to the start of power degradation from the first and second fast-charging maps – possibly using linear interpolation. It is further conceivable to select the aging state for a third fast-charging map to restrict it to uniform currents. Thus, a total of three fast-charging maps are considered to model battery power degradation, which can be described as a 3D power degradation strategy.

[0015] This makes it conceivable to perform an interpolation according to the invention for calculating the maximum fast charging current value between the second fast charging map for the aging state at the end of the warranty and the third fast charging map for the aging state when restricted to uniform currents, thereby making fast charging possible even for an aging state extending beyond the end of the warranty.

[0016] In a further embodiment of the method according to the invention, during the first step, respective fast-charging maps are created for a multitude of aging states between commissioning and the end of operation. This multitude results from a predetermined distribution of the aging states according to the capacity loss of the battery cells. For example, the distribution is chosen to be in five-percent increments between the capacity at commissioning and the capacity at the end of operation.

[0017] Furthermore, a control unit is claimed, wherein the control unit in a charging system comprising the control unit, a charging station and a battery-powered electric vehicle with a battery containing battery cells is designed to • In a first step, to create a respective fast charging map depending on a respective state of aging, whereby a maximum value of a fast charging current is assigned to a battery temperature and a state of charge by the respective fast charging map, • in a second step, set a maximum fast charging current by ◯ in the vehicle the aging state, battery temperature and battery charge level are determined and ◯ a maximum fast charging current value is calculated by interpolating the respective maximum values ​​of the fast charging current, which are obtained from the two fast charging characteristic maps, whose assigned respective aging state borders on the determined aging state, to the determined battery temperature and the determined state of charge of the battery, • and to charge the electric vehicle at the charging station with the maximum fast charging current.

[0018] In one embodiment of the control unit according to the invention, it is configured to first determine the maximum value of the fast charging current for a given battery temperature and state of charge in the respective fast charging maps in accordance with a safety specification for battery cells of the battery.

[0019] In another embodiment of the control unit according to the invention, it is configured to first determine the maximum value of the fast charging current for a given battery temperature and state of charge in the respective fast charging maps according to test series results in order to maximize the longevity of the battery, while adhering to safety requirements for the battery cells of the battery.

[0020] In a further embodiment of the control unit according to the invention, the respective aging state from the following list is assigned to each capacity value of the battery: commissioning, start of power consumption, end of warranty, restriction to uniform currents, end of operation.

[0021] In a further embodiment of the control unit according to the invention, it is configured to create respective fast-charging maps for a multitude of aging states between commissioning and the end of operation during the first step, wherein the multitude results from a predetermined distribution of the aging states according to a capacity loss of battery cells of the battery.

[0022] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0023] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0024] The figures are described in a coherent and comprehensive manner. Identical components are assigned the same reference symbols. Fig. Figure 1 shows a performance reduction scheme of a battery for an embodiment of the method according to the invention. Fig. Figure 2 shows a variable power reduction scheme of a battery for a further embodiment of the method according to the invention.

[0025] In Fig. Figure 1 shows a performance degradation scheme 10 of a battery for an embodiment of the method according to the invention. The abscissa represents the battery's state of health (SOH). The ordinate represents a fast-charging current 2. For initial commissioning 11 of the battery, an aging state with a capacity value of 100% is assumed for a virtually new battery. A warranty end 13 is defined when the capacity value drops to 80% compared to the new battery. Prior to this, a decline in the battery's performance 12 is expected. During operation, the performance decreases further until an aging state is reached with a restriction to uniform currents 14. Finally, when the capacity value drops to 50% compared to the new battery, operation ends 15. A linear interpolation according to the invention between maximum values ​​of the fast-charging current 2, e.g.,A maximum fast charging current value is obtained from the respective fast charging maps at the beginning of a power consumption 12 of the battery and the end of the warranty 13 or between the respective fast charging maps at the end of the warranty 13 and the aging state with a restriction to uniform currents 14 for a current battery temperature and a current state of charge.

[0026] In Fig.Figure 2 shows a variable power reduction scheme 20 of a battery for a further embodiment of the method according to the invention. Depending on the behavior of a driver of a battery-powered electric vehicle with regard to the frequency of use of a fast-charging function, an aging state 22 with regard to the onset of a power reduction 12 or an aging state 24 with regard to the restriction to uniform currents 14 is shifted. For example, with increased use of fast charging compared to a normal profile of an electric vehicle manufacturer, the battery will age faster and thus the aging state 22 corresponding to the onset of a power reduction 12 will occur at an earlier operating time than would be the case with more gentle use of the fast-charging function.The inventive method advantageously sets a fast charging current 2 corresponding to the current aging state 1 of the battery for charging at a charging station at each operating time and displays a current fast charging time to the driver based on this. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2019 212 762 A1

[0003] DE 10 2009 058 263 A1

[0004] DE 10 2019 000 813 A1

[0005]

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