EP4178824A1

EP4178824A1 - Method for operating an electric drive system

Info

Publication number: EP4178824A1
Application number: EP21754699.3A
Authority: EP
Inventors: Ottmar Gehring; Christian Ballarin; Steffen Maus
Original assignee: Cellcentric GmbH and Co KG
Current assignee: Cellcentric GmbH and Co KG
Priority date: 2020-07-08
Filing date: 2021-07-05
Publication date: 2023-05-17
Also published as: JP2023532481A; JP7492612B2; KR20230028544A; DE102020004102A1; WO2022008413A1; US20240092186A1; CN115812048A

Abstract

The invention relates to a method for operating an electrical drive system of a motor vehicle (2) having a buffer battery (2.8) and a fuel cell (2.6) for providing electrical drive power. In the method, route data is determined and then consumption data is predicted on the basis of said route data. The invention is characterised in that, to optimise the operation of the fuel cell (2.6), a total energy requirement for the route is predicted on the basis of the predicted consumption data, after which an average fuel cell power is determined, which is needed, together with the energy stored in the buffer battery (2.8) at the start of the route, to define the total energy requirement over a constant power trajectory for the fuel cell (2.6). A check is then carried out as to whether limit values of the buffer battery (2.8) are violated while following the route with the power trajectory: If no limit value is violated, the fuel cell (2.6) is operated with the defined power trajectory; if a limit value is violated, the power of the fuel cell (2.6) is changed in the region of the violation of the limit value and then adjusted in order to achieve the average fuel cell power again over the total route, whereby a new power trajectory is defined. The check is then carried out again with the new power trajectory until a power trajectory without violation of limit values of the buffer battery (2.6) has been determined, according to which the fuel cell (2.6) is then operated.

Description

Method of operating an electric drive system

The invention relates to a method for operating an electric drive system of a motor vehicle, according to the type defined in more detail in the preamble of claim 1.

Electric drive systems for motor vehicles, in particular also for commercial vehicles, with a backup battery and at least one fuel cell are known from the general prior art. Furthermore, it is known that fuel cells react disadvantageously to very rapid and dynamic changes in the fuel cell power with regard to their performance and with regard to their service life. It is therefore also known for such electric drive systems to optimize them in such a way that these problems can be remedied.

In this context, the generic DE 102017213 088 A1 describes a method for operating an electric drive system of a motor vehicle with at least one fuel tank for a fuel cell and at least one traction battery. In this case, navigation data are read in and processed in order to use route information to predict consumption data and thereby define phases for the operation of the fuel cell and phases without operation of the fuel cell. The aim of the optimization can be, for example, an optimization of the overall range, an optimization of the performance, an optimization of the number of refueling stops or the like.

The object of the present invention is to further improve such a method.

According to the invention, this is achieved by a method having the features in the characterizing part of claim 1. Advantageous refinements and developments result from the dependent subclaims. Comparable to the method in the generic prior art, the method according to the invention provides that route data is determined, after which consumption data is predicted based on this route data and the operation of the fuel cell is optimized using this data. According to the invention, it is now provided that, in order to optimize the operation of the fuel cell, a total energy requirement for the planned route is determined, based on the forecast consumption data. An average fuel cell output is then determined, which is required to provide this total energy requirement together with the energy stored in the backup battery at the time of starting, so that the vehicle can cover the route.

An average fuel cell power or below also terms such as areas and phases, which can relate to the journey, mean mean values in each case with regard to time units or distance units. In essence, these units are dependent on each other, so that it does not play a significant role whether the considerations are made over the path or over the time required for this path.

The average fuel cell power, which is required to cover the entire route together with the energy that may still be stored in the buffer battery, is assumed to be the constant average fuel cell power over the entire route and is set in a corresponding constant power trajectory for the power required from the fuel cell . The fuel cell is then operated using this trajectory.

After this first constant power trajectory has been defined, a check is then carried out to determine whether limit values of the buffer battery are violated when covering the route with precisely this power trajectory. Such limit values can be, for example, temperatures that are too high, currents that are too high, a dynamic load on the backup battery that is too high, or the like. According to a particularly advantageous embodiment of the method according to the invention, its state of charge in particular is used as a limit value, possibly in addition to other of the variables mentioned, as a limit value for the backup battery. This is also used below for the exemplary description of the method, which, however, is not intended to be limited to just this state of charge. If the prognosis for the route with the fixed power trajectory for the fuel cell, which is constant at the first attempt, does not violate a limit value of the backup battery, then the process is already completed at this point so that operation can take place with this constant power trajectory corresponding to the average fuel cell power. If, on the other hand, a limit value is violated, then the power of the fuel cell is changed by a constant amount in the area, and here again either in the temporal or in the distance-related area, in which this violation of the limit value occurs. The power is thus increased or decreased, for example. If the limit value is, for example, the state of charge of the battery and this falls below a critical limit value, then the power of the fuel cell would be increased accordingly in order to have energy to recharge the buffer battery and thus prevent the state of charge from falling below the critical limit value.

Since the total power supplied by the fuel cell up to this point in time or location of the route has been increased by increasing the power in this exemplary scenario, the power of the fuel cell is now adjusted in the chronological sequence, reduced in the example just described by an average provide the average fuel cell power again over the entire route. This actually results in a new power trajectory for the power from the fuel cell, which in the example described above would look like this: it first starts constantly at the value of the average fuel cell power, then is temporarily increased in the area where the exemplary limit value of the state of charge is violated, to then continue to run constantly below the previously determined average fuel cell output.

This new power trajectory is now checked again in the manner described, with these steps being repeated until a power trajectory without violation of limit values of the buffer battery has been determined, which is then used to operate the fuel cell. This means that an average fuel cell output is determined easily and efficiently based on the average energy requirement per distance or unit of time or based on the total energy requirement required for the entire route and optimized with regard to violation of limit values of the backup battery. This is easy and efficient. It saves the backup battery since it can cushion critical states determined in advance via the prognosis and at the same time the power control of the fuel cell is phlegmatized by this trajectory, so that the fuel cell is operated at constant power as far as possible, which on the one hand benefits its efficiency and on the other hand the service life of the fuel cell.

According to an extraordinarily favorable development of the method according to the invention, the size of the phase during which the power of the fuel cell is adjusted is greater than the range in which the limit value is violated. The start of the phase is before the onset of the injury. This is possible because the optimization is based on a forecast and therefore does not have to wait until the limit value is actually violated. It can therefore already counteract such a violation of the limit value before it actually occurs in order to avoid it and thus in particular to protect the backup battery and to optimize its service life. Above all, however, a dynamic load on the fuel cell is dispensed with. This would be necessary if the violation of the limit value, for example falling below a critical state of charge, would only be "combatted" after it had been measured, in that the fuel cell would then be ramped up very strongly and dynamically with regard to its performance. But that would be bad for the fuel cell. By selecting the phase of compensation to be larger than the area of the injury, the amount of the jump in performance required can be reduced. This is also advantageous for the service life and the efficiency of the fuel cell.

Another very advantageous embodiment of the method according to the invention also provides that the power trajectory includes at least one phase with constant power in the respective phase. The power trajectory can therefore consist of a single phase, which is as long as the entire route or the time required for the route, for example in the event that no violation of a limit value of the backup battery is detected during the first check. It is then correspondingly constant at the average fuel cell power level, so that the fuel cell is continuously operated at steady-state power. If there are several phases, the output of the individual phases can deviate from one another, but it remains constant within the respective phase in order to allow the fuel cell to switch to having to expect the performance, which would be very disadvantageous in terms of the service life of the fuel cell.

Another very advantageous embodiment of this method also provides that, in the case of several phases, the transitions between the phases of constant power are specified in the form of ramps and/or curves. In this particularly favorable embodiment of the idea, there is no abrupt change in the power required from the fuel cell. Rather, ramps or possibly also curves can be specified, which are based in particular on a permitted rate of change in the power of the fuel cell, in order to further phlegmatize the operation of the fuel cell through "smooth" transitions between the individual phases of constant power and to correspondingly protect the fuel cell operate.

An extraordinarily favorable development of the method according to the invention can also provide for the check to take place from the start of the route to the first violation of a limit value. The test is therefore carried out iteratively, from the start of the route to the first violation of a limit value. The fuel cell performance is then adjusted to no longer violate this limit, which means that if the test is repeated, it starts again at the start and then tests from left to right in a distance or time diagram, so to speak, until a limit violation occurs again, if necessary, which then represents the new “first” violation for this review. The performance of the fuel cell is then also adjusted again and, if necessary, this is repeated until no more limit values are violated over the entire route.

According to a very advantageous development of the idea, the method can carry out the prognosis of the consumption values on the basis of a modeling of the vehicle with a calculation of drive and braking torques on the route. Such modeling of the vehicle, which can be "fed" with corresponding parameters such as the curb weight, the vehicle load and other vehicle-specific boundary conditions that remain the same or that change over time, allows a relatively good forecast of the consumption values in order to be able to use the to improve the method according to the invention even further. In principle, the route data can originate from a navigation device of the vehicle, as is the case in the generic prior art mentioned at the outset. However, the method has its particular advantages when the route planning is carried out in a very forward-looking manner and over a large route area or period of time and is typically also adhered to relatively strictly. For this purpose, it can in particular use route data from a vehicle-external server, which can be designed, for example, 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. Such a logistics planning using a transport management system, as it occurs above all in the field of transporting goods with commercial vehicles, provides a very long-term and reliable route forecast with stopping points, refueling points, rest periods and the like. The driver, the moving load, its weight and other vehicle parameters are also stored in the transport management systems typically used, so that the forecast can be made extremely efficiently and reliably. Due to the relatively large period of time over which the route is planned in advance, a further optimization with regard to the most economical operation of the fuel cell is also achieved by the method according to the invention.

As already mentioned, the state of charge of the buffer battery can be used as a limit value. In this case, according to an advantageous development of using the state of charge as a limit value, a starting value of the state of charge of the backup battery, which is required for considering the total energy required, can be measured accordingly, so that the actual state of charge of the backup battery is used. If it is possible to recharge the buffer battery from a stationary power grid, i.e. if the vehicle is a so-called plug-in vehicle, then a strategic charge can be made by recharging the buffer battery or by discharging and feeding electricity back into the power grid optimized state of charge before the start. The same applies if recharging takes place on the way from the power grid, for example when a commercial vehicle is being loaded or unloaded. If, for example, after such a charging stop or following the start and the associated charging stop, there is a downhill stretch, then it can make sense to feed electrical energy back from the battery into the power grid. If, on the other hand, you go uphill, the buffer battery can be fully charged if possible . According to a very advantageous development of this idea, the actual state of charge can be checked cyclically, with the power trajectory being redetermined for the remaining route if it leaves a tolerance band around the predicted state of charge. This has the advantage that in the event that the power trajectory created on the basis of pure modeling and prognosis leads to more or less significant deviations during real operation, a corresponding recalculation or readjustment is possible in order to plan again with regard to energy consumption and To optimize the life of the fuel cell and / or the backup battery.

In the case of the state of charge, if the limit value in the modeled forecast is exceeded or not reached, the reaction can be such that the area between the forecast curve and the respective limit value is integrated accordingly in order to obtain an energy content, which is then correspondingly represented by a Increasing or reducing the power of the fuel cell by a constant value for a corresponding period of time, if possible before the limit value is violated, can be compensated accordingly.

The route data within the meaning of the present invention can also include inclines, declines and other events that are permanently present on the route in addition to the pure route. In addition, the route data can also contain information that can come from third-party providers, for example. This can include, for example, weather data, traffic data, data about current construction sites, traffic jams, the forecast of traffic density distributions on the route and the like.

Further advantageous refinements of the method according to the invention also result from the exemplary embodiment which is described in more detail below with reference to the figures. show:

1 shows a schematic block diagram of a system with which the method according to the invention can be carried out; and FIG. 2 shows various diagrams of the battery state of charge and the nominal power value of the fuel cell, which result in an exemplary application of the method according to the invention.

A possible detailed sequence, which includes, among other things, the method according to the invention in a preferred development, is described below with reference to a schematic block diagram in FIG.

A first step is a logistics planning in the box labeled 1 here, which is carried out by a fleet operator of a fleet of vehicles, in particular commercial vehicles. In general, this logistics planning 1 is carried out in a so-called transport management system (TMS). Transport orders are linked to individual vehicles 2 and their drivers. Furthermore, a time and route planning for the respective vehicle 2 is carried out. The data package created in this way in logistics planning 1 typically contains the route data, ie the coordinates of the individual sections, a schedule with departure times, loading and unloading times, break times and the like. In addition, information about the vehicle 2, for example various vehicle parameters, its equipment, its vehicle identification number and the like, is stored in the data packet. The data packet also contains data on the driver and on the vehicle's load, and here in particular on its weight.

This data packet can be transmitted via the communication labeled 1a to a driving strategy module 3 and received there via a data interface 3.1. It is then further processed in a driving prediction module 3.3. Matching the information about vehicle 2 from the data packet transmitted via communication 1a, data about vehicle 2 is requested via communication 2a/2b via a further interface module 3.2 or read out using a communication module 2.1 of vehicle 2. These include, for example, physical measured values of the tank 2.3, such as pressure, temperature and filling quantity, which are recorded by a tank control module 2.4, and the state of charge of a backup battery 2.8 and, for example, their thermal load, which can come from a battery management module 2.7. Using the logistics planning data and the vehicle data, the driving prediction module 3.3 of the driving strategy module 3 then calculates the energy requirement and other vehicle states on the planned route with the planned vehicle. The influences of the traffic, if necessary the driver, the topography, the weather and the traffic infrastructure are also taken into account accordingly. This information can be requested via additional modules 4, for example in the form of weather information 4.1 and/or traffic information 4.2 as data packets via route 4b and/or retrieved via route 4a.

An operating strategy module 3.4 can use the calculated results of the driving prediction module 3.3 to determine an optimized power requirement for a fuel cell 2.6.

The process described below is used for this. On the basis of the route data already determined from logistics planning 1, the necessary drive and braking torques for the entire route are now calculated using a vehicle model, into which the vehicle data of vehicle 2 flow. These are then converted into a power requirement or into a recuperation power from the electric drive machine. From this, an average power requirement based on the respective route section or the respective time unit can be calculated for the entire route. There is therefore an average constant value of the power requirement over the entire route. An average power to be supplied by the fuel cell 2.8 can then be calculated on the basis of the energy in the backup battery 2.6 and this average power requirement or the total energy requirement on the route. As a starting value for the state of charge of the buffer battery 2.8, either the actual value that has been recorded via the battery management module 2.7 can be used or, if there is a possibility of connecting the vehicle 2 or its buffer battery 2.8 to a power grid, it can be done by charging the Buffer battery 2.8 or feeding back energy from the buffer battery 2.8 into the network, an optimal starting value for the state of charge (SOC) of the buffer battery 2.8 can be set.

Based on the modeling already described above, with an assumed average fuel cell power, which over the entire route remains constant, checked whether limit values of the state of charge of the backup battery 2.8 are exceeded with such a power trajectory of the fuel cell 2.6 or not. In Fig. 2a) the power setpoint of the fuel cell 2.6 is given in kilowatts at the top and the state of charge of the backup battery 2.8 as a percentage at the bottom. In this case, two limit values of a lower state of charge not to be undershot and an upper state of charge not to be exceeded are drawn in with a dashed line. The power trajectory of the fuel cell 2.6 is shown as a constant value corresponding to the average power required by the fuel cell 2.6. The check for a violation of a limit value of the backup battery 2.8 can supplement or alternatively take other values into account in addition to the state of charge, for example temperatures, current intensities, current densities or the like.

If the constant mean power value of the fuel cell 2.6 as a power trajectory does not indicate any violation of the limit values of the buffer battery 2.8, then the strategic planning is already complete and the fuel cell 2.6 is operated with this mean value, i.e. a constant power trajectory.

If, as in the illustration in FIG. 2a), the charge falls below the minimum state of charge, an appropriate response must be made. The test always takes place from left to right in the diagrams in FIG. 2 and begins again at the starting time or starting point of the route until a corresponding undershooting or overshooting of a limit value. In this case, the charge level of the buffer battery 2.8 falls below the minimum level, which can be seen accordingly in FIGS. 2a and 2b. In order to counteract this shortfall, the gray area below the lower limit value, i.e. an amount of energy, is identified, for example by integrating the area between the curve and the limit value. This value then corresponds to an amount of energy that must also be provided by the fuel cell 2.6. In the illustration of FIG. 2b), this is brought about by increasing the power of the fuel cell 2.6, namely by the amount of energy previously identified as lying below the limit of the backup battery 2.8. In order to keep the change in performance of the fuel cell as small as possible and to remain in operation of the fuel cell 2.6 with constant performance for as long a period as possible, the time or distance segment during which the performance is increased accordingly is compared to the time or distance segment during which below the lower limit, enlarged, e.g. doubled, as can be seen from the representation of FIG. 2b). In order to ultimately comply with 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 course of the fuel cell power is then reduced accordingly, again based on the time or the route, so that on average the same average power as in Fig. 2a is achieved.

In this way, a new power trajectory for the operation of the fuel cell 2.6 has now emerged. This is then also subjected to a renewed test, which is shown analogously to the illustration in FIG. 2a) in FIG. 2c). The test now runs without violating the lower limit value for the state of charge of the backup battery 2.8 until it exceeds the upper limit value of its charge accordingly. The reaction here is analogous, in that the power provided by the fuel cell 2.6 is lowered, specifically at least for the period during which the upper limit value was exceeded. This is shown accordingly in the representation of FIG. 2d). Here, too, a new power trajectory for the fuel cell 2.6 is created with a correspondingly adapted power in the last section shown here, so that the sum total of the average power and thus the total energy from the fuel cell 2.6 for the route, which was determined at the beginning, get. Based on the power trajectory, which is shown in FIG. 2d), a renewed check no longer results in violations of the limit values of the backup battery 2.8, so that the optimal operating strategy has been found in which the limit values of the backup battery 2.8 are within the permissible limits .

As shown in the representation of FIG. 2d), the power trajectory for the fuel cell 2.6 now consists of different phases with different power levels of the fuel cell 2.6, with the power remaining constant within each of the phases, however. This enables a very gentle operation of the fuel cell 2.6. This can be further improved by optionally using ramps or other curves instead of a sudden change in performance, as shown here with a solid line, which are based on the maximum rate of change that can be used for the fuel cell 2.6 without a loss service life and performance is possible. In the representation of FIG. 2d), these ramps are drawn in as dashed lines in the power trajectory. If an optimal operating strategy in the form of a power trajectory for the fuel cell 2.6 over the entire planned route and an associated course of the state of charge of the buffer battery 2.8, which does not violate any limit values, has now been determined in the operating strategy module 3.4, then this data is calculated after the calculation, which as here shown, preferably in a cloud, displayed to the fleet operator or dispatcher in the logistics planning 1 on the path designated 1b and at the same time transmitted to the vehicle 2 on the path designated 2b. Alternatively, instead of the calculation in the driving strategy module 3 in the cloud, this calculation could also be carried out completely in the vehicle, which does not further affect the method described, but only changes the communication paths in a manner that is self-evident to the person skilled in the art.

The calculated operating strategy is then forwarded in the form of a location- or time-dependent power target value for the fuel cell 2.6, i.e. its power trajectory and an assumed precalculated course of the state of charge of the buffer battery 2.8 via the communication module 2.1 to a central drive control module 2.2 of the vehicle 2, which then Operating strategy in the vehicle 2 implemented accordingly.

The drive control module 2.2 uses the precalculated power trajectory for the fuel cell 2.6 to specify desired values in the vehicle 2 via the control module 2.5 of the fuel cell 2.6. At the same time, the drive control module 2.2 checks whether there are any deviations between the planned course of the state of charge of the buffer battery 2.8 and the real course during the journey, which can be called up from the battery management module 2.7. If there are deviations between the planned and the actual course of the state of charge of the backup battery 2.8 or if thermal load limits are reached,

Current limits, current density limits or the like, then the drive control module 2.2 can make corrections in the power requirement of the fuel cell 2.6. Up to a certain predefined threshold or a tolerance range around the calculated planned state of charge, this can also remain unnoticed. However, if such a tolerance band is exceeded, it can make sense if the further calculation is not only carried out in the vehicle 2, but is also reflected back to the corresponding driving strategy module 3 in order to carry out the planning process described above again for the remainder of the route ahead and thus the Optimizing planning, even if deviations occurred on the way, for example due to unforeseeable external events such as a sudden traffic jam due to an accident, an unplanned deviation from the route due to a short-term detour or the like.

If a deviation from the route selection by the driver of the vehicle 2 is detected, a corresponding replanning can be initiated, which can then take place in the manner described above and the result of which can be distributed to the systems 1, 2 involved. As part of this, route data can also be updated, in particular with additional information, e.g. updated traffic data, traffic flow data, weather information or the like.

Claims

patent claims

1. A method for operating an electric drive system of a motor vehicle (2), which comprises at least one backup battery (2.8) and at least one fuel cell (2.6) for providing electric drive power, with route data being determined and then, based on this route data, consumption data being forecast, to optimize the operation of the fuel cell (2.6), characterized in that to optimize the operation of the fuel cell (2.6) based on the forecast consumption data, a total energy requirement for the route is forecast, after which an average fuel cell power is determined, which is required to to provide the total energy requirement with the energy stored in the buffer battery (2.8) at the start of the route, whereby a constant power trajectory for the power required for this from the fuel cell (2.6) is defined, after which a check is carried out as to whether de r route with the power trajectory limit values of the buffer battery (2.8) are violated: if no limit value is violated, the fuel cell (2.6) is operated with the specified power trajectory; if a limit value is violated, the power of the fuel cell (2.6) is changed in the area where the limit value is violated by an amount that remains constant over time, and then adjusted in order to achieve the average fuel cell power again over the entire distance, with a new power trajectory is defined, after which the test is run through again with the new power trajectory until a power trajectory has been determined without violating limit values of the backup battery (2.6), after which the fuel cell (2.6) is then operated.

2. The method according to claim 1, characterized in that the size of the phase, during which the power of the fuel cell (2.6) is adjusted, is specified to be greater than the range of violation of the limit value, with the start of the phase being before the start of the violation.

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

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

5. The method according to any one of claims 1 to 4, characterized in that the test is carried out from the start of the route to the first violation of a limit value.

6. The method according to any one of claims 1 to 5, characterized in that the prognosis of the consumption values based on a modeling of the motor vehicle (2) with a calculation of drive and braking torques on the route.

7. The method according to any one of claims 1 to 6, characterized in that the route data from a vehicle-external server, in particular from a transport management system of a logistics planning (1), are queried.

8. The method according to any one of claims 1 to 7, characterized in that the state of charge of the buffer battery (2.8) is used as the limit value.

9. The method according to claim 8, characterized in that the actual state of charge of the buffer battery (2.8) or, in the case of a possibility of recharging the buffer battery from a stationary power grid, a strategically optimized state of charge is used as the starting value of the state of charge, which is then used by charging/discharging is set on the mains before starting.

10. The method according to claim 8 or 9, characterized in that the actual state of charge is checked cyclically, with the power trajectory for the remaining route being redetermined in the event that this leaves a tolerance band around the predicted state of charge.