Method for operating an electric drive system

Abstract

The invention relates to a method for operating an electric drive system of a motor vehicle (2), the motor vehicle having a buffer battery (2.8) and a fuel cell (2.6) for providing electric drive power. Route data are determined, and consumption data are subsequently predicted based on the route data. The invention is characterized in that, in order to optimize the operation of the fuel cell (2.6), the total energy requirement for the route is predicted based on the predicted consumption data, and then the average fuel cell power required to determine the total energy requirement over a constant power trajectory for the fuel cell (2.6) is determined together with the energy stored in the buffer battery (2.8) at the start of the route. A check is then performed to determine whether limit values ​​for the buffer battery (2.8) are violated when traveling the route using this power trajectory. If the limit values ​​are not violated, the fuel cell (2.6) is operated using the determined power trajectory. If the limit values ​​are violated, the power of the fuel cell (2.6) is changed in the area where the limit values ​​are violated and then adjusted to achieve an average fuel cell power over the entire route, thereby determining a new power trajectory. The check is then repeated using a new power trajectory until a power trajectory is determined without violating the limits of the fuel cell (2.6), and the fuel cell (2.6) is then operated according to this power trajectory.

Description

Technical Field

[0001] The invention relates to a method for operating an electric drive system of a motor vehicle. Background Art

[0002] Electric drive systems for motor vehicles, particularly commercial vehicles, having a buffer battery and at least one fuel cell are known from the prior art. Furthermore, it is known that very rapid and dynamic changes in fuel cell power are detrimental to the fuel cell's effective power and service life. Therefore, it is also known to optimize such electric drive systems in such a way that these problems can be remedied.

[0003] In this regard, DE 10 2017 213 088 A1, for example, describes a method for operating an electric drive system of a motor vehicle having at least one fuel tank for a fuel cell and at least one traction battery. Navigation data is read and processed to predict consumption data based on route information and thereby determine phases for operating and not operating the fuel cell. Optimization objectives can include, for example, optimizing the total range, power, or the number of fuel stations. Summary of the Invention

[0004] The object of the present invention is now to further improve this method.

[0005] Similar to such prior art methods, the method according to the present invention provides for determining route data, subsequently predicting consumption data based on this route data, and optimizing the operation of the fuel cell based on this data. According to the present invention, in order to optimize the operation of the fuel cell, the total energy requirement for the planned route is determined, i.e., based on the predicted consumption data. Subsequently, the average fuel cell power required to meet the total energy requirement, together with the energy stored in the buffer battery at the start time, is determined so that the vehicle can complete the route.

[0006] The average fuel cell power, or the following terms, which may also refer to driving zones and phases, refers to the average value in time units or route units. These units are essentially related to each other, so it is not important to focus on the route or the time required for the route.

[0007] The average fuel cell power required to complete the entire route, including any energy stored in buffer batteries, is assumed to be constant over the entire route and is set in a corresponding constant power trajectory for the power required by the fuel cell. The fuel cell is then operated according to this trajectory.

[0008] After determining this constant first power trajectory, a check is then performed to determine whether the buffer battery's limit values ​​are violated when completing the route with this power trajectory. Such limit values ​​can include, for example, excessively high buffer battery temperatures, excessive currents, excessive dynamic loads, and the like. According to a particularly advantageous embodiment of the method according to the present invention, in addition to other variables mentioned above as limit values ​​for the buffer battery, the state of charge of the buffer battery is used as a limit value. The state of charge will also be used hereinafter as an example to describe the method, but the method should not be limited to this state of charge.

[0009] If the prediction for a route with a determined, constant power trajectory for the fuel cell during the first startup does not violate the buffer battery's limit values, the method is terminated in this case, allowing operation to proceed with this constant power trajectory corresponding to the average fuel cell power. Conversely, if a limit violation occurs, the fuel cell power is varied by a constant value in the region where the limit violation occurs, again in the time or route region. This can be done, for example, by increasing or decreasing the power. If the limit value is, for example, the battery's state of charge, and the state of charge falls below a critical limit value, the fuel cell power is increased accordingly to ensure that there is enough energy to recharge the buffer battery and thus prevent the state of charge from falling below the critical limit value.

[0010] Since, in this exemplary case, the total power provided by the fuel cell is now increased by increasing the power until this time or point on the route is reached, the fuel cell power is now adjusted in time, or in the example just described, reduced, so that an average fuel cell power is again provided on average over the entire route. This effectively results in a new power trajectory for the fuel cell power, which, in the example just described, is such that it initially begins constantly at the value of the average fuel cell power, is then temporarily increased in the region where the exemplary limit values ​​for the state of charge are violated, and then continues constantly below the previously determined average fuel cell power.

[0011] This new power trajectory is then re-evaluated in the manner and method described above, with these steps being repeated until a power trajectory is determined without violating the buffer battery's limits, and this power trajectory is then used to operate the fuel cell. This allows for a simple and efficient determination of the average fuel cell power based on the average required energy demand per route or time unit, or based on the total required energy demand for the entire route, and for optimization of the average fuel cell power in the event of a violation of the fuel cell's limits. This is simple and effective. It protects the buffer battery by increasing resilience to critical states previously determined by prediction, and simultaneously stabilizes the fuel cell's power regulation via this trajectory, allowing the fuel cell to be operated at a largely constant power, which contributes both to the fuel cell's efficiency and, on the other hand, to its service life.

[0012] According to a particularly advantageous refinement of the method according to the present invention, the duration of the phase in which the fuel cell's power is adjusted is greater than the region in which the limit value is violated. This phase begins before the violation begins. This is possible because the optimization is based on a prediction and therefore does not have to wait until the limit value is actually violated. Therefore, it is possible to compensate for the limit value violation before it actually occurs, thereby avoiding it and, in particular, protecting the buffer battery and optimizing its service life. However, dynamic loading of the fuel cell is initially avoided. This means that if a limit value is violated, for example, by falling below a critical state of charge, the fuel cell is only "countered" by increasing its power very strongly and dynamically after the violation or the undershoot is measured. This dynamic loading is therefore necessary. However, this is precisely disadvantageous for the fuel cell. By selecting the compensation phase to be greater than the region in which the limit value is violated, the required power surge can be reduced in magnitude. This is also advantageous for the service life and efficiency of the fuel cell.

[0013] Another highly advantageous embodiment of the method according to the present invention further provides that the power trajectory includes at least one phase with a constant power within the respective phase. Thus, for example, if the buffer battery limit values ​​are not violated during the initial check, the power trajectory can consist of a single phase that lasts as long as the entire route or the required duration of the route. This power trajectory is then relatively constant at the average fuel cell power level, so that the fuel cell operates continuously at a fixed power level. In the case of multiple phases, the power levels of the individual phases may vary, but the power remains constant within the respective phases, necessitating a significant power change in the fuel cell, which is highly disadvantageous in terms of the fuel cell's service life.

[0014] Another highly advantageous embodiment of the method further provides that, in the case of multiple phases, the transition between the phases of constant power is predetermined in the form of a ramp and / or a curve. Thus, in this particularly advantageous embodiment of the concept, abrupt changes in the power required by the fuel cell are avoided. Instead, a ramp or, if necessary, a curve can be predetermined that specifically follows the permissible rate of change of the fuel cell's power. This allows the fuel cell's operation to be further stabilized by the "soft" transition between the individual phases of constant power, and accordingly to be operated in a protective manner.

[0015] A particularly advantageous refinement of the method according to the present invention can further provide that the check is performed from the starting point of each route until the first limit violation. This means that the check is repeated by starting from the starting point of the route until the first limit violation occurs. The fuel cell power is then adjusted so that the limit is no longer violated. Thus, during a renewed check, the check begins again at the starting point and then proceeds approximately from left to right in the route or time diagram until a new limit violation occurs, which represents a new "first" violation for the purpose of the check. The fuel cell power is then adjusted again, and the process is repeated, if necessary, until the limit is no longer violated along the entire route.

[0016] According to a particularly advantageous development of this concept, the method can predict consumption values ​​based on vehicle modeling by calculating the driving and braking torques along the route. Thus, in order to further improve operation according to the method according to the invention, this vehicle modeling allows for relatively good predictions of consumption values. The modeling can be "inputted" with appropriate parameters, such as the unladen weight, the vehicle's load, and other vehicle-specific boundary conditions that remain constant or also change over time.

[0017] In principle, as in the prior art described above, the route data can originate from the vehicle's navigation system. However, this method is particularly advantageous when route planning is carried out very prospectively, over a large route area or time period, and is generally adhered to relatively strictly. To this end, route planning can particularly utilize route data from a server external to the vehicle, which can, for example, be configured as part of a navigation system in the cloud or, according to the advantageous variant just described, as a transport management system for logistics planning. This type of logistics planning through a transport management system (which is predominant in the field of transporting goods by commercial vehicles, for example) provides very long-term and reliable route forecasts, including stops, refueling points, rest periods, and the like. Commonly used transport management systems also store information about the driver, the goods being transported, the weight of the goods, and other vehicle parameters, enabling extremely efficient and reliable forecasts. The relatively long time period used for pre-planning the route also allows the method according to the present invention to achieve further optimization with regard to operating the fuel cell as safely as possible.

[0018] As already mentioned, the state of charge of the buffer battery can be used as a limiting value. In this case, according to an advantageous refinement of using the state of charge as a limiting value, the starting value of the buffer battery's state of charge required to determine the total energy required can be measured accordingly, thereby using the buffer battery's actual state of charge. If the buffer battery can be recharged from a fixed power grid—i.e., if the vehicle is a so-called plug-in vehicle—a strategically optimal state of charge can be set before starting by recharging the buffer battery or by discharging and feeding current back into the power grid. A similar situation applies when recharging occurs on the road at the power grid, such as when unloading or loading a commercial vehicle. For example, if the road is downhill after such a charging stop, or after starting and the associated charging stop, it may be useful to feed electrical energy from the battery back into the power grid. Conversely, if the road is uphill, the buffer battery can be fully charged, depending on the circumstances.

[0019] According to a particularly advantageous development of this concept, the actual state of charge can be checked cyclically, wherein if it leaves a tolerance band around the predicted state of charge, the power trajectory for the remaining route is redefined. This has the advantage that if the power trajectory calculated based on pure modeling and predictions leads to more or less significant deviations during actual operation, corresponding recalculations or readjustments can be performed in order to optimize the planning again with regard to energy consumption and the service life of the fuel cell and / or buffer battery.

[0020] In the case of a state of charge exceeding or falling below a limit value, the modeled prediction reacts to this by integrating the area between the predicted curve and the respective limit value in order to obtain the energy content, which can then be compensated accordingly before a limit value violation occurs by increasing or decreasing the power of the fuel cell by a constant value over a corresponding time period, depending on the situation.

[0021] In addition to the pure driving route, route data within the meaning of the present invention may also include uphill climbs, downhill climbs, and other events that occur continuously along the route. Furthermore, route data may also include information, which may come from third parties, for example. This may include weather data, traffic data, data about current construction sites, traffic jams, and predicted traffic density distribution along the route. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Further advantageous embodiments of the method according to the invention are apparent from the exemplary embodiments described in detail below with reference to the accompanying drawings.

[0023] Figure 1 shows a schematic block diagram of a system with which the method according to the present invention can be performed; and

[0024] Figure 2 Shown are various diagrams of the cell state of charge and the power rating of a fuel cell, which diagrams are generated in an exemplary application of the method according to the invention. DETAILED DESCRIPTION

[0025] Next, according to Figure 1 The schematic block diagram in shows a possible more detailed sequence which also includes the method according to the invention in a preferred development.

[0026] The first step is logistics planning, indicated in the block 1, which is carried out by the fleet operator of a fleet of vehicles, particularly commercial vehicles. Logistics planning 1 typically takes place in a so-called transport management system (TMS). Transport orders are associated with individual vehicles 2 and their drivers. Furthermore, time and route planning is performed for the respective vehicles 2. The data packets generated in logistics planning 1 typically contain route data, i.e., the coordinates of the individual sections, a time schedule with departure times, loading and unloading times, rest periods, etc. Furthermore, the data packets contain information about the vehicles 2, such as various vehicle parameters, vehicle configuration, and vehicle identification numbers. Furthermore, the data packets contain data about the drivers and the vehicle's cargo, particularly its weight.

[0027] This data packet can be transmitted to driving strategy module 3 via the communication link 1a and received there by data interface 3.1. It is then further processed in driving prediction module 3.3. In accordance with the information about vehicle 2 in the data packet transmitted via communication link 1a, data about vehicle 2 is requested by another interface module 3.2 via communication link 2a / 2b, or read out using communication module 2.1 of vehicle 2. This data includes, for example, physical measurements of fuel tank 2.3, such as pressure, temperature, and fill level, detected by fuel tank control module 2.4, as well as the state of charge of buffer battery 2.8 and, for example, the thermal load of the buffer battery, which can be derived from battery management module 2.7. Driving prediction module 3.3 of driving strategy module 3 then calculates the energy requirement for the planned driving route with the planned vehicle, as well as other vehicle states, using the logistics planning data and vehicle data. The influence of traffic, possibly the driver, terrain, weather, and the traffic infrastructure is also taken into account. This information can be requested via the additional module 4, for example in the form of weather information 4.1 and / or traffic information 4.2 as data packets via the path 4b and / or retrieved via the path 4a.

[0028] Using the calculation results of the driving prediction module 3.3, the operating strategy module 3.4 can determine the optimal power requirement for the fuel cell 2.6.

[0029] The following process is used for this purpose. Based on the route data determined from logistics planning 1, the required driving and braking torques for the entire route are calculated using a vehicle model, into which the vehicle data for vehicle 2 is fed. The driving and braking torques are then converted into the power demand or recuperation power of the electric drive machine. This allows the average power demand to be calculated based on the individual route segments or time units along the entire route. This results in an average, constant power demand value for the entire route. The average power to be provided by fuel cell 2.8 is then calculated based on the energy in buffer battery 2.6 and this average power demand or total energy demand along the route. As a starting value for the state of charge of buffer battery 2.8, either a currently existing value detected by battery management module 2.7 can be used, or, if there is a possibility of connecting vehicle 2 or its buffer battery 2.8 to the grid, an optimal starting value for the state of charge (SOC) of buffer battery 2.8 can be set by charging buffer battery 2.8 or feeding energy from buffer battery 2.8 to the grid.

[0030] Now, assuming that the average fuel cell power remains constant over the entire route, it is checked based on the modeling already described above whether the limit value of the state of charge of the buffer battery 2.8 is exceeded with this power trajectory of the fuel cell 2.6. Figure 2In a), the rated power value of fuel cell 2.6 in kilowatts is indicated at the top, and the state of charge of buffer battery 2.8 is indicated as a percentage at the bottom. Two limit values, a lower state of charge that cannot be fallen below and an upper state of charge that cannot be exceeded, are shown as dashed lines. The power trajectory of fuel cell 2.6 is represented as a constant value corresponding to the average power required by fuel cell 2.6. In addition to the state of charge, other values, such as temperature, current intensity, current density, etc., may also be considered in addition to or as an alternative to the violation of the limit values ​​of buffer battery 2.8.

[0031] If, at a constant average power value of fuel cell 2.6 as a power trajectory, no limit violation of buffer battery 2.8 is detected, the strategic planning is already completed and fuel cell 2.6 is operated at this average value, ie, constant power trajectory.

[0032] As in Figure 2 As in the diagram of a), if the minimum state of charge is exceeded, a corresponding reaction must be taken. Figure 2 In the diagram, the check is always carried out from left to right and the check starts again at the start time or starting point of the route until the limit value is respectively undershot or exceeded. In this case, the minimum charge state of the buffer battery 2.8 is exceeded, which can be Figure 2 a) and Figure 2 b) is shown accordingly. To counteract this undershooting, the gray area, i.e. the energy sum, which is less than the lower limit value is identified, for example by integrating the area between the curve and the limit value. This value then corresponds to the energy sum that must be additionally provided by the fuel cell 2.6. Figure 2 In the diagram of b), this is achieved by increasing the power of fuel cell 2.6, specifically by an amount of energy that has previously been detected as being below the limit value of buffer battery 2.8. In order to keep the power fluctuations of the fuel cell as small as possible and to maintain a constant power for as long a period as possible during operation of fuel cell 2.6, the time or route section for which the power is increased is increased, for example doubled, compared to the time or route section for which the power is below the lower limit value. This can be achieved, for example, by Figure 2 In order to ultimately follow the average total power of the fuel cell 2.6 and thus the total energy generated by the fuel cell 2.6 over the route, the fuel cell power is then reduced accordingly over time or over the route, so that the average is achieved again. Figure 2 Same average power as in a).

[0033] Thus, a new power trajectory for the operation of the fuel cell 2.6 is now generated in this way. This new power trajectory is then also subjected to a new check, which is similar to the Figure 2 The diagram in a) is similar to Figure 2 c) shows this accordingly. Without violating the lower limit, the charge state of buffer battery 2.8 is now checked until the buffer battery has exceeded the upper limit of its charge. Here, the following reaction is now similarly implemented: the power provided by fuel cell 2.6 is reduced, at least for the period of time during which the upper limit is exceeded. This is done in Figure 2 d) is shown accordingly. Here again, a new power trajectory for the fuel cell 2.6 is generated, which has a correspondingly adapted power in the last section shown here, so that in total we obtain the average power for the route determined at the beginning and thus the total energy from the fuel cell 2.6. Now, during the re-examination, based on the Figure 2 The power trajectory shown in d) no longer violates the limit values ​​of the buffer battery 2 . 8 , so that an optimal operating strategy is found in which the limit values ​​of the buffer battery 2 . 8 are within the permissible limits.

[0034] As in Figure 2 As shown in the diagram of d), the power trajectory for the fuel cell 2.6 now consists of different phases with different powers of the fuel cell 2.6, wherein, however, the power remains constant within each phase. This enables a very safe operation of the fuel cell 2.6. The operation can be further improved by optionally using a ramp or, if necessary, also another curve instead of the sudden power changes (as shown here with a solid line), which follows the maximum rate of change possible for the fuel cell 2.6 without impairing the service life and the available power. Figure 2 In the diagram of d), the diagonal line is shown as a dashed line in the power trajectory.

[0035] Once the optimal operating strategy has been determined in operating strategy module 3.4, in the form of a power trajectory for fuel cell 2.6 and the associated course of the state of charge of buffer battery 2.8 that does not violate limit values ​​over the entire planned route, this data, after calculation (which, as shown here, can preferably be performed in the cloud), is presented to the fleet operator or dispatcher using the path indicated by 1b and simultaneously transmitted to vehicle 2 using the path indicated by 2b. Alternatively, instead of performing the calculation in driving strategy module 3 in the cloud, this calculation can also be performed completely in the vehicle, without further affecting the described method, but rather simply changing the communication path in a manner that is obvious to a person skilled in the art.

[0036] The calculated operating strategy in the form of a position- or time-dependent power setpoint value for fuel cell 2.6, i.e., the power trajectory of the fuel cell and the assumed pre-calculated course of the state of charge of buffer battery 2.8, is then transmitted via communication module 2.1 to central drive control module 2.2 of vehicle 2, which then implements the operating strategy accordingly in vehicle 2.

[0037] Drive control module 2.2 uses a precalculated power trajectory for fuel cell 2.6 to predetermine the setpoints in vehicle 2 via control module 2.5 of fuel cell 2.6. Simultaneously, drive control module 2.2 checks whether there are any deviations between the projected state of charge of buffer battery 2.8 and its actual course during driving. The actual course can be retrieved from battery management module 2.7. If there are deviations between the projected and actual state of charge of buffer battery 2.8, or if thermal load limits, current limits, current density limits, etc. are reached, drive control module 2.2 can modify the power demanded by fuel cell 2.6. This can also be ignored until certain predefined thresholds or tolerance bands relative to the calculated projected state of charge are reached. However, if this tolerance band is exceeded, it may be sensible not only to carry out further calculations in the vehicle 2 but also to reflect these calculations to the corresponding driving strategy module 3 in order to carry out the above-described planning process again for the remainder of the future route and thus optimize the planning even in the event of deviations on the road, such as those caused by unforeseen external events, such as sudden traffic jams caused by accidents, unplanned route deviations due to temporary diversions, etc.

[0038] If deviations from the route selected by the driver of the passing vehicle 2 are detected, corresponding re-planning can also be performed, whereupon re-planning is again performed in the manner and method described above, and the result of the re-planning can be distributed to the participating systems 1, 2. Within the scope of this result, the route data can also be updated with other information, such as updated traffic data, traffic flow data, weather information, etc.

Claims

1. A method for operating an electric drive system of a motor vehicle (2), the motor vehicle comprising at least one buffer battery (2.8) and at least one fuel cell (2.6) for providing electric drive power, wherein: determining route data and subsequently predicting consumption data based on the route data to optimize the operation of the fuel cell (2.6), It is characterized by: To optimize the operation of the fuel cell (2.6), a total energy requirement for the route is predicted based on the predicted consumption data, an average fuel cell power required to provide the total energy requirement together with the energy stored in the buffer battery (2.8) at the start of the route is subsequently determined, a constant power trajectory of the fuel cell (2.6) power required for this purpose is determined, and a check is then performed to determine whether the limit values ​​of the buffer battery (2.8) are violated when traveling the route using this power trajectory; If the limit values ​​are not violated, the fuel cell is operated using the determined power trajectory (2.6); If the limit value is violated, the power of the fuel cell (2.6) is changed to a constant value over time in the region of the limit violation, and then adapted so that the average fuel cell power is achieved again over the entire route, thereby determining a new power trajectory, and then The checking is repeated with the new power trajectory until a power trajectory is determined without violating the limit values ​​of the buffer battery (2.6), according to which the fuel cell (2.6) is then operated.

2. The method according to claim 1, characterized in that The length of the phase in which the power of the fuel cell (2.6) is adapted is defined as being greater than the region of the violation limit, wherein the starting point of the phase is before the onset of the violation.

3. The method according to claim 1 or 2, characterized in that The power trajectory includes at least one phase with a constant power throughout the phases.

4. The method according to claim 3, characterized in that In the case of a plurality of phases, the transitions between the phases of constant power are provided in the form of ramps and / or curves.

5. The method according to any one of claims 1 to 4, characterized in that The checks each start from the starting point of the route until the first violation of a limit value.

6. The method according to any one of claims 1 to 5, characterized in that Based on the modeling of the motor vehicle (2), a prediction of consumption values ​​is performed by calculating the driving and braking torques along the route.

7. The method according to any one of claims 1 to 6, characterized in that Route data is retrieved from a server outside the vehicle.

8. The method according to claim 7, characterized in that Route data is retrieved from the transportation management system of logistics planning (1).

9. The method according to any one of claims 1 to 8, characterized in that As a limit value, the state of charge of the buffer battery (2.8) is used.

10. The method according to claim 9, characterized in that As a starting value for the state of charge, the actual state of charge of the buffer battery (2.8) is used, or, if there is the possibility of recharging the buffer battery from a stationary grid, the strategically optimal state of charge is used, which is set before the start by charging / discharging on the grid.

11. The method according to claim 9 or 10, characterized in that The actual state of charge is checked cyclically, wherein if the actual state of charge leaves a tolerance band around the predicted state of charge, the power trajectory is redefined for the remaining route.

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