Method for determining a maximum permissible charge level when charging a traction battery of a battery electric vehicle at a charging station

Abstract

The invention relates to a method for determining a maximum permissible charge level (L). max ) when charging a traction battery of a battery electric vehicle, in particular a truck, at a charging station, wherein the vehicle has a continuous braking system which is based at least partly on recuperation braking while charging the traction battery, and wherein the maximum permissible charge level (L max ) depending on the terrain height profile (G) around the charging station, such that sufficient charging capacity is reserved in the traction battery for the recuperation energy potentially generated when driving downhill sections in the terrain around the charging station at a target speed and using only the continuous braking system.

Description

[0001] The invention relates to a method for determining a maximum permissible charge level when charging a traction battery of a battery-electric motor vehicle at a charging station, and to a method based thereon for charging the traction battery of such a motor vehicle. STATE OF THE ART

[0002] In the prior art, continuous braking systems for battery-electric vehicles, particularly trucks or buses, are commonly used. These systems are based, at least in part, on the principle of regenerative braking, whereby the recovered energy is fed into the vehicle's traction battery. To reliably ensure the operational readiness of such a continuous braking system, a portion of the traction battery's charging capacity must always be reserved during driving to absorb energy from the system. This unfortunately limits the vehicle's range. Therefore, in the prior art, additional braking resistors are often integrated into the continuous braking system to convert some of the energy generated during electromechanical braking into waste heat.On the downside, the use of such braking resistors increases the complexity of the continuous braking system and imposes design constraints regarding the dissipation of the resulting waste heat.

[0003] The performance of the continuous braking system is also subject to legal regulations in the relevant jurisdictions; in particular, the UN ECE-R13 standard applies in the European Union. This standard defines various homologation scenarios, such as the Type IIA test for trucks and buses, according to which the continuous braking effect of a regenerative braking system (without using the service brakes) must ensure the ability to drive down a 6 km downhill stretch with a 7% gradient at an average speed of only 30 km / h (+ / - 5 km / h). In practice, the recuperation energy generated during this process can amount to up to 10% of the total charging capacity of the traction battery, and it is therefore common practice to limit the charge level of the traction battery accordingly when charging at a charging station. REVELATION OF THE INVENTION

[0004] The invention relates to a method for determining a maximum permissible charge level when charging a traction battery of a battery-electric vehicle at a charging station, wherein the vehicle has a continuous braking system that is at least partially based on recuperation braking while charging the traction battery, and wherein the maximum permissible charge level is determined as a function of the terrain elevation profile around the charging station, such that a sufficient charging capacity is reserved in the traction battery for the recuperation energy that may potentially occur when driving downhill sections in the terrain around the charging station at a target speed and using only the continuous braking system.

[0005] The idea of ​​the invention is to optimize the charge level of the traction battery during charging in such a way that, on the one hand, sufficient charging capacity, particularly in compliance with legal regulations, is always available for the continuous braking system during driving, and on the other hand, the vehicle's range is maximized. To this end, the invention takes the terrain elevation profile around the charging station into account in detail, as this significantly influences the charge level during driving. Thus, the energy consumption of the drive system when driving on level or uphill sections leads to a decrease in the charge level, whereas on downhill sections, recuperation energy is usually generated, the absorption of which into the traction battery increases the charge level.The basic idea of ​​the invention is to predict the charging profile and, based on this, to determine a maximum permissible (initial) charge level when charging the traction battery at a charging station. If, for example, an incline must be encountered immediately after leaving the charging station, the charge capacity released during this process can be allocated to the portion reserved for the continuous braking system, thus allowing a correspondingly higher charge level during charging at the station. This is because, particularly in accordance with the legal regulations of the aforementioned EU standard, it is only necessary to ensure that sufficient charge capacity is available for the continuous braking system when subsequently driving downhill.Therefore, it may be permissible in particular to fully charge the traction battery at the charging station, resulting in a significant increase in the vehicle's range compared to the prior art approach, which provides for maintaining a fixed buffer of typically up to 10% of the total charging capacity.

[0006] According to the invention, the prediction of the charge level profile is based on the assumption that traversing downhill sections in the terrain around the charging station is carried out at a suitably selected target speed and using only the continuous braking system. The target speed can, in particular, be the average speed of 30 km / h prescribed in the aforementioned EU standard (Type IIA test).

[0007] For example, to determine the maximum permissible charge level, the route through the terrain around the charging station is considered, based on a specific route selection for the subsequent journey of the vehicle. If, for instance, a charging station at a motorway service station is used for charging during long-distance transport, the considered terrain elevation profile may be limited to the elevation profile of the further course of the motorway. However, such a procedure carries the risk that, in the event of an (unforeseen) change in route selection, the traction battery will only have a suboptimal charge level, in particular such that when driving downhill, the necessary charging capacity for the continuous braking system is not available. Therefore, in a further embodiment of the method according to the invention, it is provided to consider the route through the terrain around the charging station for which the greatest charging capacity must be reserved.For this purpose, the maximum permissible charge level must be determined for a suitable majority of possible routes, whereby the minimum found serves as a guideline for the charging process at the charging station.

[0008] Preferably, calculations are performed to predict the charge level of the traction battery while driving in the area around the charging station, based on a predicted speed profile of the vehicle. In addition to assuming a target speed when driving downhill, speeds are also specified or predicted for level or uphill sections. For example, the traffic volume in the area around the charging station can be taken into account, such that the predicted speed profile is adjusted accordingly. Traffic volume data is preferably obtained from real-time data sources, such as online service providers like Google Maps, TomTom, or Here Maps, which provide real-time traffic data based on mobile network data analysis.

[0009] The calculations for predicting the charge level preferably include a model for predicting the driving resistance encountered when traversing the terrain around the charging station, as well as a model of the vehicle's continuous braking system and powertrain. This model is used to predict the corresponding recuperation energy and electric drive energy profiles based on the driving resistance profile. Based on the predicted speed profile, the expected driving resistances in the different terrain sections are first calculated, along with the resulting torque and braking torque at the wheels. Using the continuous braking system and powertrain model, the recuperation energy and drive energy demand are calculated from these torques, from which the charge level of the traction battery is predicted.

[0010] The invention further relates to a method for charging a traction battery of a battery-electric vehicle at a charging station, wherein the vehicle has a continuous braking system that uses at least partial recuperation braking, wherein the following steps are carried out: - Recording the terrain elevation profile around the charging station and / or data on traffic volume in the area around the charging station, - Determining the maximum permissible load level using the method according to one of the aforementioned embodiments based on the recorded terrain elevation profile and / or the recorded traffic data, and - Charging the traction battery to the maximum permissible charge level.

[0011] This ensures that the vehicle's range is maximized while complying with the legally required minimum performance of the continuous braking system.

[0012] Furthermore, the invention relates to a control unit for a battery-electric vehicle, wherein the control unit is configured to carry out the methods according to the invention. The invention also relates to a computer program product comprising program code stored on a computer-readable medium for carrying out the methods according to one of the aforementioned embodiments. The computer program product can, in particular, be stored on and executed by the control unit of a battery-electric vehicle. Alternatively, the method can be carried out in the cloud, with the control unit and / or a user receiving a specification for the maximum permissible charge level. EXAMPLES OF THE INVENTION

[0013] Exemplary embodiments of the invention are illustrated in more detail with reference to the following figures. It shows Fig. 1. Exemplary progressions of the predicted charge level, and Fig. 2 a schematic representation of the inventive method for determining the maximum permissible charge level.

[0014] Fig. Figure 1 shows exemplary curves of the predicted charge level L of a traction battery of a battery-electric vehicle, in this case a truck, as a function of the driving time t while traversing the terrain around a considered charging station. The dashed line represents the case where the traction battery is fully charged at the charging station, i.e., to a charge level of L = 100%. Following the charging station, the route initially includes flat or uphill sections, during which drive energy is consumed, thus decreasing the charge level. Between times t1 and t2, a downhill section is traversed, during which recuperation energy is generated and fed back into the traction battery, thus increasing the charge level.According to the invention, the prediction is based on the assumption that the downhill section is traversed using only the vehicle's continuous braking system and at a constant target speed. In this case, with an initial charge level of L = 100% (dashed line), there would not be sufficient charging capacity in the traction battery to fully absorb the energy recuperated when traversing the downhill section using the continuous braking system. Rather, the prediction indicates that the maximum charge level will be exceeded by the value ΔL, and according to the invention, this value is used as a correction factor to determine the maximum permissible charge level L. max to be determined when charging at the charging station: L max= 100% - ΔL. The corresponding course of the charge level is shown by the solid line, whereby in this scenario it is ensured that the energy generated by the continuous braking system can be fully fed into the traction battery, but also that the range of the vehicle is maximized, since at the end of the downhill section at time t2 there is a charge level of L = 100%.

[0015] Fig. Figure 2 shows a schematic representation of the inventive method for determining the maximum permissible charge level L max When charging the traction battery of a battery-electric vehicle, particularly a truck, at a charging station. The associated calculation module 100 can, for example, be executed on a control unit of the vehicle. Determining the maximum permissible charge level L maxThe calculation is based on the terrain elevation profile G around the charging station, with the relevant data being obtained primarily from online map services. Additional input parameters, such as vehicle data F, are passed to the calculation module 100. These parameters include, for example, the vehicle's weight, the weight of the load or the maximum permissible load, and the number of axles. Furthermore, data concerning the current traffic volume T in the area around the charging station are taken into account.

[0016] From these input variables around the charging station, a predicted speed profile V of the vehicle is generated when driving through the terrain. This speed profile V specifically corresponds to the conditions of the homologation scenario for the Type IIA test of the EU standard UN ECE-R13, i.e., that all downhill sections are driven at a target speed of 30 km / h using only the continuous braking system. It may be possible to predict a separate speed profile V for each suitable route through the terrain around the charging station, ultimately selecting the route for which the greatest charging capacity in the traction battery is to be reserved. In addition to the aforementioned assumptions regarding driving on downhill sections, the traffic volume T is preferably also taken into account for the predicted speed profile V.

[0017] Based on the speed profile V, model 10 predicts the corresponding course of the driving resistance encountered when driving on the terrain around the charging station, from which the drive and braking torques M applied to the wheels are determined. Using model 20 of the continuous braking system and the vehicle's drivetrain, corresponding curves of recuperation energy and electrical drive energy are predicted, which in turn determine the charge level L. If the continuous braking system is only partially based on recuperation braking and also has additional braking resistance, model 20 performs an appropriate distribution of the required braking torques. Based on the predicted charge level L, the maximum permissible charge level L during charging at the charging station is determined. maxdetermined in such a way that sufficient charging capacity is reserved in the traction battery for the recuperation energy potentially generated when driving downhill sections in the terrain around the charging station at the target speed and using only the continuous braking system.

Claims

[1] Method for determining a maximum permissible charge level (L max ) when charging a traction battery of a battery electric vehicle at a charging station, wherein the vehicle has a continuous braking system that is based at least partly on recuperation braking while charging the traction battery, and wherein the maximum permissible charge level (L max ) depending on the terrain height profile (G) around the charging station, such that sufficient charging capacity is reserved in the traction battery for the recuperation energy potentially generated when driving downhill sections in the terrain around the charging station at a target speed and using only the continuous braking system. [2] Method according to claim 1, wherein to determine the maximum permissible charge level (L max ) the route through the area around the charging station is considered, - which is intended for the subsequent journey of the motor vehicle, or - for which the largest loading capacity must be reserved. [3] Method according to claim 1 or 2, wherein calculations are performed to predict the course of the charge level (L) of the traction battery when driving on the terrain around the charging station based on a predicted speed profile (V) of the motor vehicle. [4] Method according to claim 3, wherein the calculations comprise a model (10) for predicting the course of the driving resistance occurring when driving on the terrain around the charging station, and wherein a model (20) of the continuous braking system and the drive train of the motor vehicle is used to predict associated courses of the recuperation energy and the electric drive energy. [5] Method according to claim 3 or 4, wherein the calculations take into account the traffic volume (T) in the area around the charging station, such that the predicted speed profile (V) is adapted to the traffic volume (T). [6] Method for charging a traction battery of a battery electric vehicle at a charging station, wherein the vehicle has a continuous braking system which uses at least partial recuperation braking, wherein the following steps are carried out: - Recording the terrain elevation profile around the charging station and / or data on traffic volume in the area around the charging station, - Determining the maximum permissible charge level (L max ) by means of the method according to one of the aforementioned claims based on the recorded terrain elevation profile and / or the recorded traffic data, and - Charging the traction battery to the maximum permissible charge level (L max ). [7] Control unit for a battery-electric motor vehicle wherein the control unit is configured to carry out the method according to one of claims 1 to 5 and / or the method according to claim 6. [8] Computer program product comprising program code stored on a computer-readable medium for performing the method according to any one of claims 1 to 5 and / or the method according to claim 6.

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