DE102022132851B3 - Method and device for thermal management of a fuel cell system of a vehicle - Google Patents

Abstract

The invention relates to a method for the thermal management of a fuel cell system of a vehicle, wherein a thermal output of an overall cooling system of the vehicle is estimated using a physical model, taking into account a current driving situation of the vehicle and existing environmental conditions, wherein a thermal output (Q̇ECO) in an ECO mode, which can be dissipated without switching on one or more auxiliary consumers, including at least one fan (4), and a heat output (Q̇POWER) of the overall cooling system in a power mode, which when one or more auxiliary consumers are switched on, including at least one fan (4) , can be dissipated, is determined, with a target power (Ps) currently available from the fuel cell system being determined in an energy management system (ENM) based on these heat outputs (Q̇ECO, Q̇POWER) and a decision being made as to whether the fuel cell system is operated in ECO mode or in power mode is used, using heuristic logic to determine how much energy the auxiliary consumers currently require for cooling, in order to determine a characteristic value (KW), which states how much electrical power currently has to be used to dissipate a certain heat output, with a value of more than 1 kW of electrical power per kW of heat output dissipated, the performance of the fuel cell system is not increased.

Description

The invention relates to a method for thermal management of a fuel cell system of a vehicle according to the preamble of claim 1 and a device for thermal management of a fuel cell system of a vehicle according to claim 10.

A fuel cell system generates waste heat during operation, which must be dissipated by a cooling system. On the other hand, when the outside temperatures are cold or when warming up, the fuel cell system must first be warmed up. A fuel cell system therefore requires a thermal management system in order to always be able to work in the correct temperature range.

The cooling ability of a thermal management system has limits. However, the thermal management system can dissipate different amounts of heat to the environment depending on the ambient conditions (outside temperature) and driving situation (driving speed, traffic). The fuel cell itself loses efficiency over its service life and therefore generates more and more waste heat while the electrical energy generated remains almost the same. If a thermal management system for a fuel cell system were to be designed in such a way that it can dissipate the maximum possible waste heat from the fuel cell system in all situations and in all states of aging of the fuel cell, it would be enormously large, heavy and expensive and therefore inefficient. With a moderate design of a thermal management system, the full fuel cell performance may not be available in all situations. This can lead to overheating of the fuel cell system and a loss of service life. In addition, in some situations there is the possibility that the waste heat could be dissipated, but the energy requirement for the auxiliary units used would be so high that it makes no sense from an energy perspective. The performance of the fuel cell system must therefore be reduced in such situations.

US 10,369,899 B2 describes systems and methods for determining battery heating conditions and preheat lead times of at least one minute or more, based on input parameters and sets of input parameters, to proactively and dynamically heat a secondary battery so that the battery has a specific power output and level of performance when used in an electric - or hybrid vehicle application.

The invention is based on the object of specifying a novel method and a novel device for thermal management of a fuel cell system of a vehicle.

The object is achieved according to the invention by a method for thermal management of a fuel cell system of a vehicle with the features of claim 1 and by a device for thermal management of a fuel cell system of a vehicle with the features of claim 10.

Advantageous embodiments of the invention are the subject of the subclaims.

In a method according to the invention for thermal management of a fuel cell system of a vehicle, a thermal output of an overall cooling system of the vehicle is estimated using a physical model, taking into account a current driving situation of the vehicle and existing environmental conditions. According to the invention, a heat output in an ECO mode, which can be dissipated without switching on one or more auxiliary consumers, including at least one fan and, for example, including at least one valve, and a heat output of the overall cooling system in a power mode, which can be dissipated when one or more auxiliary consumers are switched on several auxiliary consumers, including at least one fan and, for example, including at least one valve, can be dissipated, wherein in an energy management system, for example with the help of a current battery state of charge (SOC) and current driving resistances, which are the sum of air, roll - and slope resistance, a fuel cell target power independent of the thermal output is calculated, based on these heat outputs, a target power that is currently available from the fuel cell system and possibly limited by the thermal output is determined and a decision is made as to whether the fuel cell system is in ECO mode or in power mode is operated, using heuristic logic to determine how much energy the additional consumers required for cooling currently need in order to determine a characteristic value that says how much electrical power currently has to be used to dissipate a certain heat output, with a value of more than 1 kW of electrical power per kW of heat output dissipated, the performance of the fuel cell system is not increased.

In one embodiment it is provided that at a value of significantly less than 1 kW of electrical power per kW of heat output dissipated, in particular at a maximum of 0.2 kW of electrical power per kW of heat output, the energy management system increases the requested target power of the fuel cell.

In one embodiment, a driving speed and/or a temperature of a cooling medium is taken into account for the current driving situation.

In one embodiment, an ambient temperature is taken into account as an ambient condition.

In one embodiment, it is provided that the energy management system uses a map that takes into account the current aging of the fuel cell system to calculate the possible electrical power of the fuel cell and requests this from the fuel cell.

In one embodiment, an estimate of a mass flow of the cooling medium to be provided by one or more pumps is estimated from current waste heat from the fuel cell system, which is taken into account in addition to the current driving situation and the existing ambient conditions when estimating heat that can be dissipated by one or more coolers.

In one embodiment, if the waste heat from the fuel cell system is low, the required target temperature at the fuel cell system input can be set using one or more valves.

In one embodiment, when determining the waste heat required for the at least one fan, current waste heat from the fuel cell system and heat that can be dissipated by one or more coolers are also taken into account.

In one embodiment, a mass flow that is to be provided by the at least one fan is estimated from the waste heat required for the at least one fan in order to determine an energy-optimal distribution of the mass flows among the fans and a corresponding control of the fans.

In one embodiment, a prediction is made for a route ahead, with a course of the expected driving speed of the vehicle and a course of the expected ambient temperature being determined on the basis of a planned route in a web-based traffic service and/or by a prediction module, wherein by means of a thermal model of the cooling system, based on this data for the route ahead, it is determined how the feasible cooling performance of the cooling system as well as the corresponding characteristic value will develop in ECO mode and in power mode, and on this basis an optimal performance trajectory for the fuel cell system to be planned taking into account the route and external environmental influences.

• - Das Thermomanagement schätzt die aktuell mögliche Kühlleistung des Kühlsystems in zwei Leistungsstufen (ECO und Power)
• - mittels einer Schnittstelle zu einem Energiemanagement wird eine zentrale Regelungseinheit über die aktuell verfügbare Kühlleistung informiert,
• - ein Kennwert über den aktuell benötigten Leistungseinsatz pro abgeführtem Kilowatt Kühlleistung gibt Aufschluss darüber, ob das Investieren weiterer Energie auch eine verbesserte Kühlung des Systems mit sich bringt.

According to one aspect of the present invention, a device for thermal management of a fuel cell system of a vehicle is proposed, comprising an energy management system of the fuel cell system and a vehicle controller that is/are configured to carry out the method according to one of the preceding claims.

• - The thermal management estimates the currently possible cooling performance of the cooling system in two performance levels (ECO and Power)
• - by means of an interface to an energy management system, a central control unit is informed about the currently available cooling capacity,
• - a parameter showing the currently required power input per kilowatt of cooling power dissipated provides information about whether investing additional energy also results in improved cooling of the system.

The thermal management of a fuel cell commercial vehicle determines the currently available cooling capacity of the cooling system, taking into account the current driving conditions and ambient conditions. It can therefore provide information about the cooling potential without additional energy requirements (ECO mode) and with additional energy requirements (power mode), for example by fans. This information is made available to the energy management system via an interface, whereby the most energy-efficient operating points of the fuel cell system can be determined. A specific value of the power currently being used by auxiliary equipment per kW of excess heat dissipated is used to determine whether more cooling power is beneficial or not.

The service life of fuel cell systems depends to a large extent on good and constant temperature control in the optimal comfort range of the fuel cell. The more often overheating is avoided, the better the service life of the fuel cell will be. The interface according to the invention allows the fuel cell to be used more reliably in the optimal temperature range. The use of hydrogen as fuel must be made as efficient as possible. Operating conditions in which an unnecessarily large amount of hydrogen is consumed without generating an increase in driving performance or the on-board network should be avoided. Therefore the performance requirement must to the fuel cell can be regulated in such a way that the energy requirements of the auxiliary units are as optimal as possible. The present invention improves both points mentioned and can be designed optimally, since overheating and inefficient operating states of the fuel cell can be avoided by passing on the current or previous states of the thermal management system to the energy management system. Through the invention, the necessary design reserves of the thermal management system can be minimized and a maximally efficient thermal management can be designed; it is therefore always used almost optimally.

Exemplary embodiments of the invention are explained in more detail below with reference to drawings.

• 1 eine schematische Ansicht eines Verfahrens zur Schätzung einer abführbaren Wärmeleistung mit und ohne Zuschaltungen von Lüftern in einem Brennstoffzellenfahrzeug,
• 2 eine schematische Ansicht eines reaktiven Verfahrens zum Thermomanagement des Brennstoffzellenfahrzeugs, und
• 3 eine schematische Ansicht eines prädiktiven Verfahrens zum Thermomanagement des Brennstoffzellenfahrzeugs,
• 4 eine schematische Ansicht eines vereinfachten Modells zur Schätzung der abgeführten Kühlleistung durch einen Fahrzeug-Kühler,
• 5 eine schematische Ansicht eines Verfahrens zur Abschätzung von Luft-Massenströmen, und
• 6 einen schematischen Verlauf eines Fahrleistungshorizonts FLH bei vorausschauender Regelung.

Show:

• 1 a schematic view of a method for estimating a dissipable heat output with and without switching on fans in a fuel cell vehicle,
• 2 a schematic view of a reactive method for thermal management of the fuel cell vehicle, and
• 3 a schematic view of a predictive method for thermal management of the fuel cell vehicle,
• 4 a schematic view of a simplified model for estimating the cooling power dissipated by a vehicle radiator,
• 5 a schematic view of a method for estimating air mass flows, and
• 6 a schematic course of a mileage horizon FLH with predictive control.

Corresponding parts are provided with the same reference numbers in all figures.

1 is a schematic view of a method for estimating a dissipable heat output with and without switching on fans in a fuel cell vehicle.

2 is a schematic view of a reactive method for thermal management of the fuel cell vehicle.

The fuel cell vehicle has a vehicle controller 1, which is configured to carry out the regulation of the thermal management system. The vehicle control uses a physical model, taking into account the current driving situation, for example a driving speed v and a temperature T _KM of a cooling medium, and the existing environmental conditions, for example an ambient temperature Tu, to estimate the thermal output that can currently be dissipated by the overall cooling system, for example that by one or more coolers 5 dissipable heat Q̇ _K1 , Q̇ _K2 .

In a module 12 for the mileage-oriented and SOC-based energy distribution of a high-voltage battery, a current charge state SOC of the battery and current driving resistances AFW, which are composed of the sum of air, rolling and gradient resistance, are taken into account to determine a fuel cell target power without thermal limitation .

The mass flows of the cooling water can be determined based on the current pump speed, while the air mass flows are known from simulation calculations, measurements and empirical values. Any inaccuracies can be compensated for using a downstream correction factor or correction function.

For this estimation, the model uses, for example, maps relating to the thermal conductivity of the manufacturers of coolers at a constant predetermined air mass flow, which can be assumed to be different levels for ECO mode and power mode, through the cooler to the possible dissipable heat Q̇ _K1 , Q̇ _K2 . 4 shows a schematic view of a simplified model for estimating the cooling power dissipated by a cooler 5. To determine the correction value KoW, a difference between a cooling water inlet temperature T _W and an air inlet temperature T _L of the cooler 5 is formed and multiplied by the thermal conductivity value WLW determined by the characteristic map KF, which is calculated using a cooling water mass flow ṁ _W and a Air mass flow ṁ _L of the cooler is determined.

$$P=\frac{2\ast \pi \ast M\ast n}{60000}$$

P

Antriebsleistung (kW)

p

Betriebsdruck Pumpenausgang (bar)

Q

Volumenstrom (dm³/min)

ηges

Gesamtwirkungsgrad (-)

M

Drehmoment (Nm)

n

Pumpendrehzahl (1/min)

The following formulas can be used to estimate cooling water mass flows ṁ _W from the pump speed n: $$P=\frac{p\ast Q}{600\ast {\eta }_{Ges}}$$

$$P=\frac{2\ast \pi \ast M\ast n}{60000}$$

P

Drive power (kW)

p

Operating pressure pump outlet (bar)

Q

Volume flow (dm ³ /min)

ηtot

Overall efficiency (-)

M

Torque (Nm)

n

Pump speed (1/min)

The cooling water mass flow ṁ _W , for example, has a known relationship to the volume flow via the density of the cooling water.

The mass flow ṁ _W of a pump can be determined either from the drive power consumed and the operating pressure generated as in the formulas mentioned or by a linear relationship between pump speed and mass flow ṁ _W , which was previously determined by testing the present system.

The current mass flow ṁ _W relates to a maximum mass flow in the same way that the current pump speed relates to a maximum pump speed.

5 is a schematic view of a method for estimating air mass flows ṁ _L. The air mass flow ṁ _L through the cooler 6 can be derived from a combination of simulation results SE, in particular for determining an air mass flow ṁ _LL through a fan 4, and maps KF _EW with empirical values, in particular for determining an air mass flow ṁ _LFW from the airstream, as well as current ambient conditions how driving speed v and ambient temperature T _U are determined. A total air mass flow ṁ _tot can then be formed as the sum of the air mass flow ṁ _LL through the fan 4 and the air mass flow ṁ _LFW from the airstream.

On the one hand, a heat output Q̇̇ _ECO is determined, which can be dissipated without additional measures such as switching on one or more fans 4. The dissipable heat output Q̇ _ECO is determined, so to speak, which results exclusively from the airstream. This results in a heat output value that means the lowest energy consumption by the additional consumers (ECO mode). On the other hand, a heat output Q̇ _POWER can be determined, which can be dissipated including further measures such as switching on one or more fans 4. This results in a thermal output value that means increased energy consumption by the additional consumers, but enables more power from the fuel cell (power mode).

The vehicle control 1 for carrying out the thermal management has an interface 2 to an energy management system ENM of the fuel cell, which informs the energy management system ENM about these two currently possible thermal cooling capacities.

The energy management system ENM, in turn, can use this information to determine what electrical power can currently be used by the fuel cell. From a map that also takes into account the current aging of the fuel cell system, the energy management system ENM can calculate the possible electrical power of the fuel cell and request this from the fuel cell. Depending on the current situation, the ENM energy management system can then decide whether the fuel cell is operated at an operating point that means the least energy for the auxiliary units (thermal management in ECO mode) or whether the more energy-intensive power mode is required.

In addition, the vehicle control 1 uses heuristic logic to determine how much energy the additional consumers required for cooling, such as pumps 6 and fans 4, currently need. From this, a characteristic value KW can be determined as to how much electrical power currently needs to be used to dissipate a certain amount of heat.

In particular, an estimate for a mass flow ṁ _P of the cooling medium to be provided by one or more pumps 6 is estimated from a current waste heat Q̇ _BZ of the fuel cell system, which is in addition to that when estimating the heat Q̇ _K1 , Q̇ _K2 that can be dissipated by one or more coolers 5 current driving situation, for example the driving speed v and the temperature T _KM of the cooling medium, and the existing environmental conditions, for example the ambient temperature T _U , can be taken into account.

When determining additional waste heat Q̇ _L required for the at least one fan 4, a current waste heat Q̇ _BZ of the fuel cell system and heat Q̇ _K1 , Q̇ _K2 that can be dissipated by one or more coolers 5 can be taken into account.

From the waste heat Q̇̇ _L required for the at least one fan 4, a mass flow ṁ _L1 , ṁ _L2 can be estimated, which is to be provided by the at least one fan 4. From this, an energy-optimal distribution 9 of the mass flows ṁ _L1 , ṁ _L2 between the fans 4 and a corresponding control 3 of the fans 4 can be determined.

It is possible in certain situations that the cooling system could generate a large cooling output with heavy use of auxiliary units, for example fans 4, whereby the electrical energy consumption would be so great that the bottom line is that the additional fuel cell power gained thereby would be completely used up or even would still be exceeded.

In this case, hydrogen consumption would only increase, without having a positive effect on the high-voltage electrical system in the sense of a charging effect. The additional electrical power generated would be consumed directly by the auxiliary consumers. These conditions should be avoided. This is possible thanks to the thermal management parameter KW described above. If this characteristic value KW is, for example, at a value of over 1 kW of electrical power per kW of heat output dissipated, this indicates that operation is not making sense. In this case, the energy management system ENM will not further increase a target power P _s of the fuel cell system when taking into account the limitations of thermal management. If the value is significantly lower, for example 0.2 kW of electrical power per kW of heat output, the energy management system ENM can increase the requested target power P _s of the fuel cell.

3 is a schematic view of a predictive method for thermal management of the fuel cell vehicle.

In addition to the current situation, the vehicle control 1 can be configured to make a prediction for the route ahead. Based on the planned route, the course v(t) of the expected driving speed of the vehicle can be determined using a web-based traffic service and/or using another prediction module 7.

In addition, a slope and curvature profile of the route can be determined, for example from a digital map. From this information, it is possible to use a longitudinal dynamics model to determine a real, drivable speed curve as well as an associated drive and/or braking torque power requirement over a forecast horizon or driving performance horizon FLH (see 3 ). From the resulting energy requirements, a fuel cell power Ps(t) required in the forecast horizon can then be determined in the energy management ENM, in particular in a module 13 for determining the mileage-oriented and SOC-based energy distribution horizon of the high-voltage battery as part of the energy management ENM, and from the efficiency map Fuel cell waste heat can be determined. If you add the waste heat from the auxiliary consumers, the battery and a possible continuous brake, this results in the total cooling requirements, which can be plotted over the forecast horizon.

6 shows a schematic course of a driving performance horizon FLH with predictive control with trajectories for driving speed v (e.g. from speed prediction), road gradient FBS (e.g. from map) and ambient temperature T _U (e.g. from web service) over a route ahead s. Variables that can be calculated from this are an estimated drive power ATL, an estimated fuel cell performance BZL, a state of charge SOC of a battery, a waste heat Q̇ _BZ of the fuel cell system, an available cooling capacity Q̇ _K1 , Q̇ _K2 (e.g. due to wind) and a required fan connection BLZ.

Similarly, with a web-based weather service, a history of the expected ambient temperature T _U (t) as well as other weather data, such as rain, can be retrieved, for example from the cloud 8. Using a thermal model of the cooling system, this data can be used to calculate the route ahead How the feasible cooling performance of the cooling system and the corresponding energy consumption parameter KW will develop - both in ECO mode and in power mode. For this purpose, it is calculated whether the resulting expected fuel cell waste heat is based on the expected mileage for the route ahead s with the help of all actuators, for example one or more pumps 6, one or more coolers 5, one or more coolers 4 and one or more valves 11, can be discharged. If this is not the case, a limit violation LV is detected and the expected fuel cell target power is corrected in the energy management ENM.

Using this information, it is possible for the energy management system ENM to plan an optimal power trajectory P _s (t) for the fuel cell system, taking into account the route s and external environmental influences. For example, if the planning already knows that the fuel cell output BZL has to be reduced on an uphill stretch due to the thermal management (limit violations of the LV thermal system on the horizon), it can start up the fuel cell earlier - and in situations where the cooling situation is simpler - and in one High-voltage battery provides an appropriate energy buffer.

The device and the method can be used in a fuel cell vehicle, in particular in a commercial vehicle, for example a heavy commercial vehicle.

Reference symbol list

1

Vehicle control

2

interface

3

Control of the fans

4

Fan

5

cooler

6

pump

7

Prediction module

8th

Cloud

9

Distribution of mass flows

10

Consideration of the limitations of thermal management

11

Valve

12

module

13

module

AFW

current driving resistance

ATL

Drive power

Bank code

required fan activation

BZL

Fuel cell performance

ENM

Energy management

FBS

Road gradient

FLH

Mileage horizon

KF

Map

KFEW

Map with empirical values

KW

characteristic value

KoW

Correction value

LV

Limit violation

ṁges

Total air mass flow

ṁL

Air mass flow

ṁLFW

Air mass flow from the wind

ṁLL

Air mass flow through fans

ṁL1, ṁL2

Mass flow for fans

ṁP

Mass flow pump

ṁW

Cooling water mass flow

n

Pump speed

Ps

target performance

Ps(t)

expected course of target performance, performance trajectory

Q̇BZ

Waste heat from the fuel cell system

Q̇ECO

Heat output in ECO mode

Q̇K1, Q̇K2

Heat that can be dissipated by coolers

Q̇̇L

Waste heat for fans

Q̇POWER

Thermal output in power mode

s

Driving distance

SE

Simulation results

SOC

charging status

TKM

Temperature of a cooling medium

TL

Air inlet temperature

TU

Ambient temperature

Does)

Course of the expected ambient temperature

TW

Cooling water inlet temperature

v

Driving speed

v(t)

Course of the expected driving speed

WLW

Thermal conductivity

Claims (10)

Method for the thermal management of a fuel cell system of a vehicle, wherein a thermal output of an overall cooling system of the vehicle is estimated using a physical model, taking into account a current driving situation of the vehicle and existing environmental conditions, characterized in that a thermal output (Q̇ _ECO ) in an ECO mode, which can be dissipated without switching on one or more auxiliary consumers, including at least one fan (4), and a heat output (Q̇ _POWER ) of the overall cooling system in a power mode, which is when one or more auxiliary consumers are switched on, including at least one fan (4 ), can be dissipated, is determined, whereby a target power (P _s ) that can currently be called up by the fuel cell system is determined in an energy management system (ENM) on the basis of these heat outputs (Q̇ _ECO , Q̇ _POWER ) and a decision is made as to whether the fuel cell system is in ECO mode or in Power mode is operated, whereby heuristic logic is used to determine how much energy the additional consumers required for cooling currently need in order to determine a characteristic value (KW), which states how much electrical power currently has to be used to dissipate a certain heat output, whereby the performance of the fuel cell system is not increased at a value of more than 1 kW of electrical power per kW of heat output dissipated. Procedure according to Claim 1 , characterized in that at a value of clearly less than 1 kW of electrical power per kW of heat output dissipated, in particular at a maximum of 0.2 kW of electrical power per kW of heat output, the energy management system (ENM) increases the requested target power (Ps) of the fuel cell. Procedure according to one of the Claims 1 or 2 , characterized in that a driving speed (v) and/or a temperature (T _KM ) of a cooling medium is taken into account for the current driving situation. Method according to one of the preceding claims, characterized in that an ambient temperature (Tu) is taken into account as ambient conditions. Method according to one of the preceding claims, characterized in that the energy management system (ENM) calculates the possible electrical power of the fuel cell based on a map which takes into account the current aging of the fuel cell system and requests this from the fuel cell. Method according to one of the preceding claims, characterized in that an estimate for a mass flow (ṁ _P ) of the cooling medium to be provided by one or more pumps (6) is estimated from a current waste heat (Q̇ _BZ ) of the fuel cell system, which is used in the estimation by one or more coolers (5) of dissipable heat (Q̇ _K1 , Q̇ _K2 ) are taken into account in addition to the current driving situation and the existing ambient conditions. Method according to one of the preceding claims, characterized in that when determining additional waste heat (Q̇ _L ) required for the at least one fan (4), a current waste heat (Q̇ _BZ ) of the fuel cell system and heat that can be dissipated by one or more coolers (5). (Q̇ _K1 , Q̇ _K2 ) is taken into account. Procedure according to Claim 7 , characterized in that from the waste heat (Q̇ _L ) required for the at least one fan (4), a mass flow (ṁ _L1 , ṁ _L2 ) is estimated, which is to be provided by the at least one fan (4) in order to achieve an energy-optimal To determine the distribution (9) of the mass flows (ṁ _L1 , ṁ _L2 ) to the fans (4) and a corresponding control (3) of the fans (4). Method according to one of the preceding claims, characterized in that a prediction is made for a route ahead, a course (v(t)) of the route being determined based on a planned route in a web-based traffic service and/or by a prediction module (7). expected driving speed of the vehicle and a course of the expected ambient temperature (Tu(t)) are determined, using a thermal model of the cooling system based on this data for the route ahead to determine how the feasible cooling capacity of the cooling system and the corresponding characteristic value ( KW) in ECO mode and in power mode, and on this basis to plan an optimal power trajectory (P _s (t)) for the fuel cell system taking into account the driving distance and external environmental influences. Device for thermal management of a fuel cell system of a vehicle, comprising an energy management system (ENM) of the fuel cell system and a vehicle control (1) which is/are configured to carry out the method according to one of the preceding claims.

Images