CN112224093A - Low-temperature starting control method for fuel cell automobile - Google Patents

Low-temperature starting control method for fuel cell automobile Download PDF

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CN112224093A
CN112224093A CN202010959163.8A CN202010959163A CN112224093A CN 112224093 A CN112224093 A CN 112224093A CN 202010959163 A CN202010959163 A CN 202010959163A CN 112224093 A CN112224093 A CN 112224093A
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fuel cell
soc
battery pack
low
power
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CN112224093B (en
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杨天
张宏超
王林波
董铭君
于佩良
岳东东
韩刚
黄东越
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Caac Yangzhou Automotive Engineering Research Institute Co Ltd
China Automotive Technology and Research Center Co Ltd
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Caac Yangzhou Automotive Engineering Research Institute Co Ltd
China Automotive Technology and Research Center Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L58/00—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles
    • B60L58/30—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling fuel cells
    • B60L58/31—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling fuel cells for starting of fuel cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02T90/40—Application of hydrogen technology to transportation, e.g. using fuel cells

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Abstract

The invention relates to a low-temperature starting control method for a fuel cell automobile, which comprises the following steps: s1, predicting the required power in the low-temperature starting stage; s2, setting the SOC target value of the battery pack during the last parking according to the required power; s3, performing shutdown purging operation of the fuel cell according to the SOC target value; and S4, setting the SOC target value as a starting initial state, and controlling the low-temperature starting of the fuel cell vehicle by the controller. The method optimizes the starting process and the last shutdown process of the fuel cell automobile by predicting the power requirements of the fuel cell at the starting stage and the driving initial stage, so that the driving experience of a user is guaranteed and the service life requirements of the fuel cell and a battery pack are also guaranteed in a low-temperature scene.

Description

Low-temperature starting control method for fuel cell automobile
Technical Field
The invention relates to the field of fuel cell automobiles, in particular to a low-temperature starting control method for a fuel cell automobile.
Background
The fuel cell operates in a low-temperature environment, if the preheating is insufficient, the freezing of the water inside the fuel cell can block the diffusion of reaction gas and prevent the reaction from proceeding, and in addition, the volume expansion causes structural damage to the porous medium. Therefore, during the low-temperature start of the fuel cell, a certain time is required for warm-up operation, and the internal temperature of the fuel cell is increased, so that the degradation of the performance and the service life of the fuel cell caused by the temperature is reduced. At present international advanced production motorcycle type generally adopts the self-heating mode to carry out the warm-up operation to fuel cell inside, realizes that fuel cell temperature rises to suitable temperature rapidly, finishes the warm-up operation, and fuel cell gets into normal operating mode, begins external output power. The self-heating mode is a mode of generating concentration voltage difference by reducing the stoichiometric ratio of air, so that the fuel cell works in a low-efficiency area, more energy is dissipated in a heat mode, and the warming effect is achieved.
However, there is a technical problem that if the warm-up operation time of the fuel cell is too short, the internal warm-up of the fuel cell is insufficient, resulting in deterioration of the performance and life of the fuel cell. If the warm-up time of the fuel cell is too long, the waiting time for the fuel cell to supply power to the driving motor is long, and the driving experience of a customer is influenced.
In view of the above, the present invention is particularly proposed.
Disclosure of Invention
The invention aims to provide a low-temperature starting control method for a fuel cell automobile, which optimizes the starting process and the last shutdown process of the fuel cell automobile by predicting the power requirements of a fuel cell at the starting stage and the driving initial stage, and realizes the purpose of ensuring the driving experience of a user and the service life requirements of the fuel cell and a cell pack in a low-temperature scene.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a low-temperature starting control method for a fuel cell automobile, which comprises the following steps:
s1, predicting the required power in the low-temperature starting stage;
s2, setting the SOC target value of the battery pack during the last parking according to the required power;
s3, performing shutdown purging operation of the fuel cell according to the SOC target value;
and S4, setting the SOC target value as a starting initial state, and controlling the low-temperature starting of the fuel cell vehicle by the controller.
As a further preferable technical solution, in step S1, the required power includes a driving required power, an air conditioning required power, and an accessory required power.
As a further preferable technical solution, the required driving power is predicted by a markov chain prediction method;
preferably, the prediction formula of the driving demand power is: preg-drive＝δvma；
Wherein v is the vehicle speed, m is the vehicle mass, a is the acceleration, δ is the mass conversion coefficient, δ is 1.03;
v and a use the state transition matrix [ T ]l(k)]ijV and a corresponding to the maximum value of (1);
preferably, the vehicle is driven from x for a history duration kiState transition to xjThe probability of a state is
Figure BDA0002682873460000021
Wherein, the matrix
Figure BDA0002682873460000022
And [ fi l(1)，fi l(2)，...，fi l(k)]Are given corresponding exponential weightings, wherein the weightings
Figure BDA0002682873460000024
Figure BDA0002682873460000025
Figure BDA0002682873460000026
0.9 is taken.
As a further preferable technical scheme, the required power of the air conditioner is 3 kW;
preferably, the accessory requires power of 2 kW.
As a further preferable technical solution, the SOC target value of the battery pack in step S2 is:
Figure BDA0002682873460000031
Wreq＝∫Preqdt；
therein, SOCminMinimum SOC, W, allowed for battery pack operationregFor the energy consumption during the start-up phase of a fuel cell vehicle, PreqFor said required power, Preq-purgeAccessory energy consumption in the shutdown purging process of the fuel cell is achieved, and Q is rated electric quantity of the cell pack;
preferably, SOCminThe content was 30%.
As a further preferable technical solution, the fuel cell shutdown purge operation in step S3 includes the steps of: firstly, judging whether the SOC target value is higher than an SOC threshold value, and if so, performing a first purging mode; if not, performing a second purging mode; ending purging until the purging stop condition is met;
preferably, the first purging mode includes: the fuel cell stops outputting power to the outside, enters an idling mode, and the battery pack provides all power consumption in the purging process;
preferably, the second purging mode includes: the fuel cell charges the battery pack until the SOC of the battery pack is higher than the SOC threshold value; then the fuel cell stops outputting power to the outside, enters an idling mode, and the battery pack provides all power consumption in the purging process;
preferably, the SOC threshold is 50%.
As a more preferable mode, the step S4 of controlling the low temperature start of the fuel cell vehicle by the controller includes the steps of: firstly, a driver makes a starting request, then the fuel cell executes a pre-starting purging operation, after the pre-starting purging operation is finished, the fuel cell enters a warming-up mode, and after the warming-up is finished, the fuel cell enters a normal power generation mode.
As a further preferable technical solution, the conditions for completing the purging operation before the start-up are: the cell voltage of the fuel cell is higher than 0.6V.
As a more preferable aspect, the warm-up mode includes: the air stoichiometric ratio is reduced, and a concentration difference and a voltage difference are generated, so that the fuel cell works in a low-efficiency area, and the warming-up is realized.
As a more preferable embodiment, the warm-up termination condition is: the fuel cell coolant temperature is greater than 55 ℃.
Compared with the prior art, the invention has the beneficial effects that:
(1) the method comprises the steps of synchronously considering the service life of a fuel cell, the service life of a battery pack and user experience, and dividing the whole starting process into three stages, wherein the battery pack at one stage is used as an independent energy source; the two-stage battery pack is used as a main energy source, and the fuel cell is used as an auxiliary energy source; the three-stage fuel cell serves as a primary energy source and the battery pack serves as an auxiliary energy source. The main optimization measure for the service life of the fuel cell is to delay the output time of the fuel cell to the external high power as far as possible, and the internal temperature of the fuel cell is enabled to reach the appropriate temperature as soon as possible through a warming-up mode. The main optimization measure for the service life of the battery pack is to set an SOC target value before last shutdown, so that the battery pack is always kept above the minimum limit while meeting the subsequent power output requirement. The main optimization measure for the user experience is that the battery pack can provide enough energy for vehicle running, air conditioning and accessories in the initial stage, and the use of the battery pack by the user is not influenced.
(2) A Markov chain prediction method is provided, the driving power requirement of a fuel cell automobile in a starting stage under a low-temperature environment is predicted, acceleration-vehicle speed is set as a state variable, and the energy consumption condition of the low-temperature starting process is predicted through historical data. In addition, the method has the advantages that the state probability transition matrix is updated and learned according to factors such as user habits, geographic positions and traffic conditions when the user uses the vehicle, so that the Markov chain mode prediction accuracy is improved in a personalized mode.
(3) The SOC management method for the battery pack can design an SOC target value before the shutdown of the fuel cell automobile through the predicted energy consumption condition and the lowest SOC requirement of the battery pack, and enables the SOC of the battery pack to meet the requirement by adopting different shutdown purging modes.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a flow chart of a low-temperature start control method for a fuel cell vehicle according to the present invention;
FIG. 2 is a flow chart of battery pack target SOC determination and implementation;
FIG. 3 is a flow chart of a fuel cell vehicle cold start control;
FIG. 4 is a schematic diagram of a fuel cell vehicle configuration;
fig. 5 is a diagram showing key signal changes before and after a low-temperature start of a fuel cell vehicle.
Icon: 1-a fuel cell stack; 2-a first DCDC; 3-a motor controller; 4-driving the motor; 5-power battery pack; 6-a second DCDC; 7-an accessory; 8-a main reducer; 9-differential and half-shaft.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that: the power battery pack is referred to as a battery pack.
Example 1
In order to secure the life of the fuel cell, the time point at which the fuel cell enters the normal power generation mode during the low-temperature start-up should be shifted back as much as possible so that the inside of the fuel cell is sufficiently warmed up. In order to guarantee the driving experience of the user, the time point when the vehicle enters the travelable state should be moved forward as far as possible. Therefore, during the starting stage of the fuel cell, the battery pack is required to be used as a main energy source to meet the power requirements of driving the vehicle and heating the air conditioner.
During the start-up phase of the fuel cell, the battery pack is continuously powered with a large power, and the operating range of the SOC is too low, which may result in the life of the battery pack being reduced. Therefore, the SOC of the battery pack needs to predict and set a target value in advance to meet the external output requirement in the starting stage and the life requirement of the battery pack itself.
In view of the above design considerations, as shown in fig. 1, the present embodiment provides a fuel cell vehicle low-temperature start control method, including the steps of:
s1, predicting the required power in the low-temperature starting stage;
s2, setting the SOC target value of the battery pack during the last parking according to the required power;
s3, performing shutdown purging operation of the fuel cell according to the SOC target value;
and S4, setting the SOC target value as a starting initial state, and controlling the low-temperature starting of the fuel cell vehicle by the controller.
The invention has the following advantages:
(1) the method comprises the steps of synchronously considering the service life of a fuel cell, the service life of a battery pack and user experience, and dividing the whole starting process into three stages, wherein the battery pack at one stage is used as an independent energy source; the two-stage battery pack is used as a main energy source, and the fuel cell is used as an auxiliary energy source; the three-stage fuel cell serves as a primary energy source and the battery pack serves as an auxiliary energy source. The main optimization measure for the service life of the fuel cell is to delay the output time of the fuel cell to the external high power as far as possible, and the internal temperature of the fuel cell is enabled to reach the appropriate temperature as soon as possible through a warming-up mode. The main optimization measure for the service life of the battery pack is to set an SOC target value before last shutdown, so that the battery pack is always kept above the minimum limit while meeting the subsequent power output requirement. The main optimization measure for the user experience is that the battery pack can provide enough energy for vehicle running, air conditioning and accessories in the initial stage, and the use of the battery pack by the user is not influenced.
(2) A Markov chain prediction method is provided, the driving power requirement of a fuel cell automobile in a starting stage under a low-temperature environment is predicted, acceleration-vehicle speed is set as a state variable, and the energy consumption condition of the low-temperature starting process is predicted through historical data. In addition, the method has the advantages that the state probability transition matrix is updated and learned according to factors such as user habits, geographic positions and traffic conditions when the user uses the vehicle, so that the Markov chain mode prediction accuracy is improved in a personalized mode.
(3) The SOC management method for the battery pack can design an SOC target value before the shutdown of the fuel cell automobile through the predicted energy consumption condition and the lowest SOC requirement of the battery pack, and enables the SOC of the battery pack to meet the requirement by adopting different shutdown purging modes.
In a preferred embodiment, in step S1, the required power includes a driving required power, an air conditioning required power, and an accessory required power. And in the low-temperature starting stage, the total required power consists of the required driving power, the required air conditioner power and the required accessory power. The required power of the accessories mainly comprises the work of related accessories such as an air compressor, a hydrogen pump, a cooling water pump and the like in the starting process of the fuel cell, and the required power value is small and has small fluctuation. The required power of the air conditioner is mainly related to the ambient temperature, and the required power value of the air conditioner can be obtained through a calibration test and stored in the controller according to the test result. The two parts are composed of required power, the power value is small, and the fluctuation range is small, so that the required power can be estimated through experience. The vehicle running power part has the largest energy consumption ratio and is influenced by a plurality of factors such as user habits, geographic environments, traffic jam conditions and the like, so that the vehicle running power part becomes the most critical part in the control method of the fuel cell vehicle starting stage and has the largest prediction difficulty.
In a preferred embodiment, the power demand for driving is predicted by a markov chain prediction method.
Preferably, the prediction formula of the driving demand power is: preg-drive＝δvma；
Wherein v is the vehicle speed, m is the vehicle mass, a is the acceleration, δ is the mass conversion coefficient, δ is 1.03;
v and a use the state transition matrix [ T ]l(k)]ijV and a corresponding to the maximum value of (1).
Preferably, the vehicle is driven from x for a history duration kiState transition to xjThe probability of a state is
Figure BDA0002682873460000081
Wherein, the matrix
Figure BDA0002682873460000082
And [ fi l(1)，fi l(2)，...，fi l(k)]Are given corresponding exponential weightings, wherein the weightings
Figure BDA0002682873460000084
Figure BDA0002682873460000085
Figure BDA0002682873460000086
0.9 is taken.
The invention adopts a machine learning algorithm to predict the change condition of the vehicle running demand power in the starting stage of the fuel cell. Considering that longitudinal dynamic variables such as vehicle speed, acceleration, torque, power and the like can be regarded as time series in the vehicle running process, a Markov chain prediction method can be adopted to establish a prediction model for time series samples, find out system characteristics and predict current values and future trends according to historical values of the time series. A markov chain refers to a discrete-time stochastic process in mathematics that has the markov property. In each step, the system can be transferred from one state to another state according to the probability distribution, and the most probable state of the system at the next moment can be predicted by using the current state and the probability distribution of the state transition.
In order to predict the power, the invention adopts a vehicle speed-acceleration two-dimensional vector to describe the state at each moment, namely the element characteristic description of a state probability transition matrix. Defining X as a Markov chain state space, X ═ X1，x2，...xs}；
Since vehicle speed-acceleration is used to describe the state, when t is k, the markov chain state can be expressed as: x is the number ofk＝(v(k)，a(k))；
The probability distribution of t ═ k + l is determined by the state transition probability matrix of step l, the invention recommends that l is taken to be 3, then the state x corresponding to time kiTransition to state x corresponding to time k + ljConditional probability of [ T ]l]ijCan be represented by the following formula:
Figure BDA0002682873460000087
Figure BDA0002682873460000088
i，j∈{1，2，...，s}；
wherein, Tl∈Rs×s，l＝1，2，...，NTIs the time scale of the markov chain.
Figure BDA0002682873460000091
For the observed passage of l time steps, from xiTransfer to xjThe frequency of transfer of (a); n is a radical ofi lFor the observed passage of l time steps, from xiFrequency of transitions to other states.
The method comprises the following steps of carrying out personalized prediction according to factors such as user habits, geographic environments and traffic jam conditions, and updating a state transition probability matrix according to historical data of a current vehicle, wherein the method comprises the following steps: from x within a history duration kiTransfer to xjThe probability of (c) can be represented by the following formula:
Figure BDA0002682873460000093
Figure BDA0002682873460000094
Figure BDA0002682873460000095
wherein the content of the first and second substances,
Figure BDA0002682873460000096
is x occurs at a history duration of kiTransfer to x via l step sizejThe frequency of (d);
Figure BDA0002682873460000097
for the history duration k, the state is defined by xiFrequency of transitions to other states.
Figure BDA0002682873460000098
Is an event xiTransfer to x via l step sizejAn indicator of occurrence, if the event occurs
Figure BDA0002682873460000099
Is 1, otherwise is 0. f. ofi lIs an event xiPassing step l to indicator of other state occurrence, if the event occurs, fi lIs 1, otherwise is 0.
The above formula can be further written as:
Figure BDA00026828734600000912
Figure BDA00026828734600000913
considering better personalized prediction, the influence of the historical observation value on the future system output is weakened along with the time, so different weights are given to the historical observation value according to the influence degree, and a forgetting factor is used
Figure BDA0002682873460000101
To replace
Figure BDA0002682873460000102
The final expression is:
Figure BDA0002682873460000103
wherein the matrix
Figure BDA0002682873460000104
And [ fi l(1)，fi l(2)，...，fi l(k)]Are given corresponding exponential weightings, wherein the weightings
Figure BDA0002682873460000106
Figure BDA0002682873460000107
Advising
Figure BDA0002682873460000108
0.9 is taken.
From [ T ] according to the derivation procedure described abovel(k)]ijAnd selecting the state corresponding to the maximum value as a prediction result. After the predicted values of the acceleration and the vehicle speed are obtained, the required power can be predicted through the following formula: preg-drive＝δvma；
Where v is the vehicle speed, m is the vehicle mass, a is the acceleration, and δ is the mass conversion factor, the recommendation is 1.03.
In the early stage of vehicle use, due to the lack of training data, enough historical data cannot be provided to predict the vehicle speed and acceleration more accurately. Training standard cycle working conditions in an off-line mode, such as a NEDC working condition, a CLTC working condition, a WLTC working condition, a UDDS working condition and the like, obtaining a state probability transition matrix of the standard cycle working conditions, using the state probability transition matrix as an initial transition matrix in a control part, and solving the problem that the vehicle lacks historical data in the initial use stage as far as possible. And updating and learning the state probability transition matrix according to factors such as user habits, geographic positions and traffic conditions when the user uses the vehicle, so as to improve the prediction accuracy of the Markov chain model in a personalized manner.
Using a Markov chain model prediction method, performing on-line self-learning by a fuel cell automobile controller, and calculating the initial driving stage P according to historical datareqValue, thereby energy consumption W for initial stage of drivingregAnd calculating and finally performing reverse estimation to obtain the target value of the SOC of the battery pack before the shutdown.
Preferably, the required power of the air conditioner is 3 kW.
Preferably, the accessory requires power of 2 kW.
In a preferred embodiment, the SOC target value of the battery pack in step S2 is:
Figure BDA0002682873460000111
Wreq＝∫Preqdt；
therein, SOCminMinimum SOC, W, allowed for battery pack operationregFor the energy consumption during the start-up phase of a fuel cell vehicle, PreqFor said required power, Preq-purgePurge fuel cell shutdownAnd (4) the accessory consumes energy, and Q is the rated electric quantity of the battery pack.
Preferably, SOCminThe content was 30%.
Step S1 predicts the required power P of the fuel cell vehicle in the starting stage by the Markov chain model prediction methodreqThen the energy consumption value W of the stagereqCan be expressed as: wreq＝∫Preqdt；
Since the battery pack becomes the main energy source during the start-up phase of the fuel cell, the power requirements for driving the vehicle and heating the air conditioner need to be met. The battery pack continuously supplies power with high power, the service life of the battery pack is reduced due to the fact that the working range of the SOC is too low, and therefore the SOC target value before the vehicle is shut down needs to be preset and is determined by the SOC target valueintIt means that the following conditions should be satisfied: SOCint≥ΔSOC+SOCmin；
Wherein the SOCminThe SOC is the lowest SOC of the battery pack allowed to work and is used as a threshold value of a battery pack service life protection strategy and is obtained by testing and calibrating in advance, and in the invention, the reference value is 30%. Δ SOC represents the amount of change in the SOC of the battery pack during the start-up, which may be approximated by the energy consumption during the start-up phase: wregΔ SOC × Q; wherein Q represents the rated charge of the battery pack.
The SOC target value can be derived from the above two equations:
Figure BDA0002682873460000112
Figure BDA0002682873460000113
wherein, Preq-purgeThe accessory energy consumption for the fuel cell shutdown purging process can be obtained in advance through calibration tests of different environmental temperatures and different water contents in the fuel cell, and is stored in the controller.
In a preferred embodiment, the fuel cell shutdown purge operation in step S3 includes the steps of: firstly, judging whether the SOC target value is higher than an SOC threshold value, and if so, performing a first purging mode; if not, performing a second purging mode; and ending the purging until the purging stopping condition is met.
Preferably, the first purging mode includes: the fuel cell stops outputting power to the outside, enters an idling mode, and the battery pack provides all power consumption in the purging process.
Preferably, the second purging mode includes: the fuel cell charges the battery pack until the SOC of the battery pack is higher than the SOC threshold value; and then the fuel cell stops outputting power to the outside, enters an idling mode, and the battery pack provides all power consumption in the purging process.
Preferably, the SOC threshold is 50%.
The flow of determining and implementing the target SOC of the battery pack is shown in fig. 2 below. After the driver makes a vehicle parking request, the controller queries the ambient temperature and the state of the fuel cell and calculates the power required by accessories in the parking purge process. Based on the Markov chain prediction model, the driving required power of the fuel cell in the starting stage can be obtained, the air conditioner required power can be obtained according to the month information, and the SOC target value is calculated by the method in the previous step. In order to reach the SOC setting target value, it is necessary to charge the battery pack by the power generation of the fuel cell before the last fuel cell shutdown. In consideration of a shutdown purge operation performed before the fuel cell is shut down in a low temperature environment, the internal liquid water is drained to prevent the internal freezing. According to the SOC state of different battery packs before shutdown purging, two purging modes are adopted.
When the SOC is higher than a given threshold value and the reference value is 50%, the battery pack can provide sufficient power, the requirements of stopping and purging accessory energy consumption, the driving energy consumption of the next fuel cell automobile starting stage, air conditioner energy consumption and accessory energy consumption are met, and the SOC is not lower than the lowest threshold value SOCminAnd seriously affects the life of the battery pack. In this case, the purge mode one is entered in view of reducing the hydrogen consumption amount of the fuel cell. In this mode, the fuel cell stops outputting power to the outside, enters an idle mode, and the battery pack provides all power consumption in the purging process. The purge is ended when a purge shutdown condition is met, such as the water content inside the fuel cell being below a certain threshold.
When SOC is below a given threshold, parameterConsidering that the battery pack can not provide sufficient power and can not meet the requirements of stopping and blowing accessory energy consumption, driving energy consumption of the next fuel cell automobile starting stage, air conditioner energy consumption and accessory energy consumption, and the SOC can not be lower than the lowest threshold SOC (system on chip)minThis can seriously affect the life of the battery pack. In this case, the purge mode two is entered in consideration of the battery pack SOC operating range. In the mode, the cell stack charges the battery pack before purging until the SOC is higher than a given threshold value and the reference value is 50%, then the cell stack stops outputting power to the outside, the idle mode is started, and the battery pack provides all power consumption in the purging process. The purge is ended when a purge shutdown condition is met, such as the water content inside the fuel cell being below a certain threshold.
In a preferred embodiment, the step S4, the controller performing the fuel cell vehicle low temperature start control includes the steps of: firstly, a driver makes a starting request, then the fuel cell executes a pre-starting purging operation, after the pre-starting purging operation is finished, the fuel cell enters a warming-up mode, and after the warming-up is finished, the fuel cell enters a normal power generation mode.
Preferably, the conditions for completion of the pre-start purge operation are: the cell voltage of the fuel cell is higher than 0.6V.
The low-temperature start control flow is shown in fig. 3 below. The driver makes a start request, and the fuel cell system accessories such as an air compressor and a hydrogen pump perform a warm-up operation and perform a purge operation to discharge the hydrogen-oxygen mixture inside the fuel cell to prevent the carbon carrier from oxidizing to reduce the life of the fuel cell. At this stage, the fuel cell does not output power externally, and the battery pack serves as a separate energy source. When the fuel cell satisfies the purge end condition, the fuel cell enters a warm-up mode. And setting a purging ending condition, namely, the condition that all hydrogen and oxygen mixed interfaces are discharged is required to be met.
Preferably, the warm-up mode includes: the air stoichiometric ratio is reduced, and a concentration difference and a voltage difference are generated, so that the fuel cell works in a low-efficiency area, and the warming-up is realized. The fuel cell enters a warm-up mode, the fuel cell works in a low-efficiency area by reducing the stoichiometric ratio of air and generating a concentration voltage difference mode, and more energy is dissipated in a heat mode to achieve the warm-up effect. The fuel cell is in a low-efficiency working area at the stage, only small power can be output, and the battery pack is used as a main energy source. As the SOC of the battery pack is reserved in the last step, the battery pack has enough output capacity, so that the driving experience of a user is not influenced.
The "air stoichiometric ratio" refers to a ratio of an oxygen consumption amount in air to a reference oxygen consumption amount, wherein the reference oxygen consumption amount is calculated by current, and the theoretical oxygen consumption amount is a complete reaction and can be converted into a ratio of an actual air consumption amount to the reference air consumption amount by an oxygen content in air.
The "concentration difference" refers to the difference in oxygen concentration generated at the cathode of the fuel cell.
The voltage difference refers to the difference between the voltage corresponding to the polarization characteristic curve of the galvanic pile and the current working voltage of the galvanic pile under the same current density.
The above-mentioned "low efficiency region" refers to a region deviating from the polarization characteristic curve.
Preferably, the warm-up end condition is: the fuel cell coolant temperature is greater than 55 ℃. The warm-up end condition is set to meet the requirement that the internal temperature of the fuel cell reaches a proper temperature, such as 55 ℃, and when the warm-up end condition is reached, the fuel cell enters a normal power generation mode.
The fuel cell enters a normal power generation mode, works in a high-efficiency area and becomes a main energy source, the battery pack serves as an auxiliary energy source, the effect of 'peak clipping and valley filling' on output power is achieved, the power change rate of the fuel cell is reduced, and the service life of the fuel cell is prolonged.
The present invention is particularly applicable to a fuel cell vehicle configuration shown in fig. 4, which includes a fuel cell stack 1, a first DCDC2, a motor controller 3(DCAC), a drive motor 4, a power cell pack 5, a second DCDC6, an accessory 7, a final drive 8, a differential, a half shaft 9, and the like, wherein the first DCDC refers to a fuel cell rear-end supercharger, and the second DCDC refers to a battery pack rear-end bidirectional DCDC. Air is introduced into the cathode of the fuel cell stack, hydrogen is introduced into the anode, and the reaction is carried out on the membrane electrode to generate electricity. The fuel cell supercharger can boost the output voltage of the fuel cell, and meet the requirement of an electric drive system, thereby reducing the number of single fuel cells. The bidirectional DCDC is connected to the rear end of the battery pack, the voltage of the battery pack can be boosted to the load voltage in the driving process, the output power is coordinated with the fuel cell, the dynamic load of the fuel cell is effectively reduced, and the energy recovered by the motor can be reduced through voltage reduction in the energy recovery process to charge the battery pack. The accessories comprise high-pressure accessories such as an air compressor, a hydrogen pump, a cooling water pump, an air conditioner and the like, and also comprise low-pressure accessories such as various valve bodies, sensors, actuators and the like.
The change of the key signals before and after the optimization by adopting the control method is shown in fig. 5, wherein the change of the key signals is the SOC of the battery pack and the total required power P from top to bottom in sequencereqAnd fuel cell output power PFCThe situation changes with time. The SOC curve schematically represents the change rule by a straight line, the actual change condition is nonlinear, a solid line represents before optimization, and a dotted line represents after optimization.
Wherein t1 is the time when the fuel cell finishes the shutdown purging, t1-t2 is that the vehicle is in the shutdown state, the temperature of the fuel cell is gradually reduced under the influence of the environmental temperature in the stage, and when the vehicle is started next time and the internal temperature of the fuel cell is lower than 0 ℃, the low-temperature startup control function of the fuel cell vehicle is activated.
The fuel cell low-temperature starting process before optimization is t2-t4 stages in the figure. The fuel cell system comprises a fuel cell, an air compressor, a hydrogen pump, a battery pack, a fuel cell, a battery pack, a low-temperature start process at-20 ℃, a fuel cell power supply and a power supply, wherein t2-t3 are stages of preparing and purging the fuel cell, the air compressor and the hydrogen pump are used for preheating operation, and hydrogen and oxygen mixed gas in the fuel cell is discharged in a purging mode, the fuel cell cannot output power outwards at the stage, all energy is provided by the battery pack, the time is set according to different ambient temperatures, and t2-t3 corresponding. Because the battery pack can provide energy, the driving of the vehicle and the starting of the air conditioner are not influenced.
t3-t4 is the warm-up stage of the fuel cell, which is operated in the low-efficiency region and only outputs a small power, in the present inventionThe reference value is 5kW, and most of the energy is provided by the battery pack. The time is set according to the internal temperature of the fuel cell, and t3-t4 corresponding to the low-temperature starting process at-20 ℃ is 200 s. The required power is high in the stage, the SOC of the battery pack is reduced rapidly, and when t4 is reached, the SOC is larger than the SOCmin. Wherein the SOCminRepresenting the lowest value that the proposed SOC allows to reach in view of the battery pack life, in the present invention, the reference value is 30%.
At time t4, the fuel cell enters the normal operation mode from the warm-up mode, and the fuel cell becomes the main power source.
The optimized low-temperature starting process of the fuel cell is t2-t5 stages in the figure. Wherein t2-t3 are fuel cell preparation and purging stages, and are unchanged from before optimization.
t3-t5 is a warm-up stage of the fuel cell which operates in a low efficiency region and outputs only a small amount of power, and in the present invention, the reference value is 5kW, and most of the energy is supplied from the battery pack. The time is set according to the internal temperature of the fuel cell, and t3-t5 corresponding to the low-temperature starting process at-20 ℃ is 300 s. The required power is high in the stage, the SOC of the battery pack is reduced rapidly, and when t5 is reached, the SOC is larger than the SOCmin. Wherein the SOCminRepresenting the lowest value that the proposed SOC allows to reach in view of the battery pack life, in the present invention, the reference value is 30%. Therefore, the optimized control method prolongs the warming-up time of the fuel cell on the premise of meeting the requirement of the SOC change range, so that the internal temperature of the fuel cell is closer to the appropriate temperature, and the optimization of the performance and the service life of the fuel cell is facilitated.
At time t5, the fuel cell enters the normal operation mode from the warm-up mode, and the fuel cell becomes the main power source.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention.

Claims (10)

1. A low-temperature starting control method of a fuel cell automobile is characterized by comprising the following steps:
s1, predicting the required power in the low-temperature starting stage;
s2, setting the SOC target value of the battery pack during the last parking according to the required power;
s3, performing shutdown purging operation of the fuel cell according to the SOC target value;
and S4, setting the SOC target value as a starting initial state, and controlling the low-temperature starting of the fuel cell vehicle by the controller.
2. The fuel cell vehicle low-temperature start-up control method according to claim 1, wherein the required power includes a driving required power, an air-conditioning required power, and an accessory required power in step S1.
3. The fuel cell vehicle low-temperature start control method according to claim 2, wherein the travel required power is predicted using a markov chain prediction method;
preferably, the prediction formula of the driving demand power is: preq-drive＝δvma；
Wherein v is the vehicle speed, m is the vehicle mass, a is the acceleration, δ is the mass conversion coefficient, δ is 1.03;
v and a use the state transition matrix [ T ]l(k)]ijV and a corresponding to the maximum value of (1);
preferably, the vehicle is driven from x for a history duration kiState transition to xjThe probability of a state is
Figure FDA0002682873450000011
Wherein, the matrix
Figure FDA0002682873450000012
And
Figure FDA0002682873450000013
are given corresponding exponential weightings, wherein the weightings
Figure FDA0002682873450000014
Figure FDA0002682873450000015
Figure FDA0002682873450000016
0.9 is taken.
4. The fuel cell vehicle low-temperature start control method according to claim 2, wherein the air conditioner demand power is 3 kW;
preferably, the accessory requires power of 2 kW.
5. The fuel cell vehicle low-temperature start-up control method according to claim 1, wherein the cell pack SOC target value in step S2 is:
Figure FDA0002682873450000021
Wreq＝∫Preqdt；
therein, SOCminMinimum SOC, W, allowed for battery pack operationreqFor the energy consumption during the start-up phase of a fuel cell vehicle, PreqFor said required power, Preq-purgeAccessory energy consumption in the shutdown purging process of the fuel cell is achieved, and Q is rated electric quantity of the cell pack;
preferably, SOCminThe content was 30%.
6. The fuel cell vehicle low-temperature start-up control method according to claim 1, wherein the fuel cell shutdown purge operation in step S3 includes the steps of: firstly, judging whether the SOC target value is higher than an SOC threshold value, and if so, performing a first purging mode; if not, performing a second purging mode; ending purging until the purging stop condition is met;
preferably, the first purging mode includes: the fuel cell stops outputting power to the outside, enters an idling mode, and the battery pack provides all power consumption in the purging process;
preferably, the second purging mode includes: the fuel cell charges the battery pack until the SOC of the battery pack is higher than the SOC threshold value; then the fuel cell stops outputting power to the outside, enters an idling mode, and the battery pack provides all power consumption in the purging process;
preferably, the SOC threshold is 50%.
7. The fuel cell vehicle low-temperature start control method according to any one of claims 1 to 6, wherein the controller performing the fuel cell vehicle low-temperature start control in step S4 includes the steps of: firstly, a driver makes a starting request, then the fuel cell executes a pre-starting purging operation, after the pre-starting purging operation is finished, the fuel cell enters a warming-up mode, and after the warming-up is finished, the fuel cell enters a normal power generation mode.
8. The fuel cell vehicle low-temperature start control method according to claim 7, characterized in that the conditions under which the pre-start purge operation is completed are: the cell voltage of the fuel cell is higher than 0.6V.
9. The fuel cell vehicle low-temperature start control method according to claim 7, wherein the warm-up mode includes: the air stoichiometric ratio is reduced, and a concentration difference and a voltage difference are generated, so that the fuel cell works in a low-efficiency area, and the warming-up is realized.
10. The fuel cell vehicle low-temperature start control method according to claim 7, wherein the warm-up end condition is: the fuel cell coolant temperature is greater than 55 ℃.
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