Cold start system and method for hydrogen energy fuel cell automobile

Abstract

The invention discloses a cold start system and method for a hydrogen energy fuel cell automobile. The cold start system comprises a battery management system and a hydrogen fuel cell system. The battery management system detects the battery temperature, formulates a two-stage purging strategy and a two-stage heating strategy, and controls the battery system to execute the strategies; the hydrogen fuel cell system comprises an air subsystem, a cooling subsystem, a hydrogen subsystem and a hydrogen fuel cell; the air subsystem provides oxygen for the chemical reaction of the hydrogen fuel cell, purges the hydrogen fuel cell through blocking gas, and discharges liquid water in the cell; the hydrogen subsystem provides hydrogen for the chemical reaction of the hydrogen fuel cell, and liquid water in a hydrogen pipeline is purged through blocking gas; the cooling subsystem is used for heating the hydrogen fuel cell and cooling liquid before the automobile is started, and detecting the temperature of the hydrogen fuel cell for cooling treatment; according to the invention, liquid water generated in the hydrogen fuel cell and the hydrogen pipeline can be purged through a two-stage purging strategy, so that the liquid water in the pipeline is prevented from being quickly frozen at-40 DEG C, is not easy to unfreeze, blocks the pipeline and hinders starting of an automobile; when the automobile is restarted from the low-temperature environment, the success rate of cold start of the automobile in the environment of minus 40 DEG C is increased through the strategy of shutdown purging, internal heating and external auxiliary heating, and the shutdown time of the automobile is shortened.

Description

Technical Field

[0001] The present invention relates to the technical field of operation and starting of hydrogen fuel cell heavy-duty vehicles, and in particular to a cold starting system and method for hydrogen energy fuel cell vehicles. Background Art

[0002] How to achieve commercial application of hydrogen energy in automobiles and how to achieve wider application scenarios of hydrogen fuel cell vehicles have begun to become topics of discussion among technicians in the automotive industry.

[0003] Hydrogen fuel cells can convert the chemical energy of hydrogen into electrical energy. During the entire chemical reaction process, hydrogen with a certain humidity needs to react with oxygen to produce water and electrical energy. Compared with traditional internal combustion engines, the significant advantage of hydrogen fuel cells is that their reaction process does not produce pollution. Hydrogen fuel cells have a high thermoelectric conversion efficiency, with a theoretical thermoelectric conversion efficiency of 85%-90% and an actual conversion efficiency of 40%-60%.

[0004] However, when hydrogen fuel cell vehicles are in an application scenario below 0℃, after the shutdown operation, the liquid water generated during the operation of the vehicle will freeze, causing varying degrees of blockage in the air and hydrogen pipelines, affecting the reaction performance of the battery. If the diffusion layer and proton exchange layer inside the hydrogen fuel cell freeze, the flow channel structure inside the battery will expand. If the freezing problem is frequent, it will cause structural damage to the battery. If the catalytic layer freezes, it will seriously affect the battery catalytic performance after the car is started. And low temperature will seriously affect the output performance of hydrogen fuel cells and prolong their loading time. In particular, for hydrogen fuel cell heavy-duty vehicles with an output power of more than 270kW, the difficulty of cold starting the vehicle increases in an environment of -40℃. When the first cold start loading fails, the output power of the battery will drop, the voltage will drop below the normal value, and the hydrogen fuel cell system will stop working. If the cold start fails many times, the number of starts reaches the fault setting number, and the system will shut down urgently. Summary of the invention

[0005] The present invention provides a cold start system and method for a hydrogen fuel cell vehicle, so as to overcome the technical problem that the existing hydrogen fuel cell vehicles have more frequent icing problems in a low temperature environment of -40°C, the battery heating time is longer, the difficulty of cold start is increased, and the number of cold start failures is increased, which leads to emergency shutdown of the system.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A cold start system for a hydrogen fuel cell vehicle, comprising a battery management system and a hydrogen fuel cell system;

[0008] The battery management system is used to detect the temperature of the hydrogen fuel cell in the hydrogen fuel cell system after the car is shut down, formulate a two-stage purge strategy and a two-stage heating strategy with different shutdown purge times, and control the hydrogen fuel cell system to execute the two-stage purge strategy; when the car is started again, control the hydrogen fuel cell system to execute the two-stage heating strategy;

[0009] The hydrogen fuel cell system comprises an air subsystem, a cooling subsystem, a hydrogen subsystem and a hydrogen fuel cell;

[0010] The air subsystem includes an air compressor, an air proportional valve, an air filter, an intercooler, a blocking gas valve, a three-way ball valve and a humidifier which are sequentially connected in the air inlet direction of the hydrogen fuel cell, and also includes a first blocking gas bottle connected to the blocking gas valve; a back pressure valve connected to the outside is provided in the air outlet direction; the air subsystem is used to provide oxygen for the chemical reaction of the hydrogen fuel cell and purge the inlet and outlet of the hydrogen fuel cell and the air through the blocking gas in the first blocking gas bottle to discharge the residual liquid water in the hydrogen fuel cell;

[0011] The hydrogen subsystem includes a hydrogen storage tank, a stop valve, a flow meter, a hydrogen proportional valve, a flow guide, and a first circulation pump connected in sequence in the direction of the hydrogen inlet of the hydrogen fuel cell, and also includes a second blocking gas bottle connected to the hydrogen proportional valve; a second circulation pump and a drain valve and an exhaust valve connected to the second circulation pump are provided in the direction of the hydrogen outlet; the hydrogen subsystem is used to provide hydrogen for the chemical reaction of the hydrogen fuel cell, control the flow and pressure of the hydrogen, and purge the liquid water generated in the hydrogen inlet and outlet pipelines through the blocking gas in the second blocking gas bottle;

[0012] The cooling subsystem is used to heat the coolant and hydrogen fuel cell of the hydrogen fuel cell before the car is started, and at the same time detect whether the temperature of the hydrogen fuel cell exceeds the set value and control the radiator to cool down, thereby achieving temperature control of the hydrogen fuel cell.

[0013] Furthermore, the cooling subsystem includes a first three-way valve, a deionizer, a coolant tank, a heating water pump, a second three-way valve, a fourth circulation pump and an auxiliary heating device connected to the second three-way valve, which are connected in sequence, and also includes a radiator connected to the first three-way valve; the auxiliary heating device includes a heater, a warm air core, a two-way valve and a third circulation pump which are connected in sequence.

[0014] Furthermore, an air inlet pressure sensor and a No. 1 temperature sensor are provided between the humidifier and the air inlet; an air outlet pressure sensor is provided between the air outlet and the back pressure valve; a No. 3 temperature sensor is provided between the hydrogen inlet and the drain, a No. 4 temperature sensor is provided between the hydrogen outlet and the second circulation pump, and a humidity sensor is provided on the drain.

[0015] A cold start method for a hydrogen fuel cell vehicle, comprising:

[0016] S1: After the car stops, the current temperature of the hydrogen fuel cell is obtained through the temperature sensor;

[0017] S2: setting an impedance threshold, a purge temperature threshold and a first-level purge strategy, and when the temperature of the current hydrogen fuel cell is less than the purge temperature threshold and the impedance value of the hydrogen fuel cell is less than the impedance threshold, the battery management system controls the air subsystem and the hydrogen subsystem to purge the hydrogen fuel cell according to the first-level purge strategy to discharge the residual liquid water inside the battery and the hydrogen pipeline;

[0018] S3: setting a humidity threshold and a secondary purge strategy in the hydrogen pipeline, and when the impedance value of the hydrogen fuel cell is greater than the impedance threshold and the humidity in the hydrogen pipeline is greater than the humidity threshold, stopping the primary purge strategy and executing the secondary purge strategy;

[0019] S4: before the hydrogen fuel cell is started, self-heating of the hydrogen fuel cell is performed;

[0020] S5: Set the heating temperature threshold, the first-level heating strategy and the second-level heating strategy to determine whether the current ambient temperature is greater than the heating temperature threshold. If so, execute the first-level heating strategy. If not, execute the first-level heating strategy and the second-level heating strategy at the same time to heat the coolant in the coolant tank. When the temperature of the coolant reaches the preset value, stop heating and complete the cold start.

[0021] Furthermore, the primary purge strategy includes:

[0022] The primary purge strategy includes:

[0023] S21, determining the purge time of the first-level purge strategy according to the impedance of the hydrogen fuel cell;

[0024] S22, switching the three-way ball valve of the air subsystem from the state leading to the humidifier when the hydrogen fuel cell is working normally to the state leading directly to the air inlet of the battery, increasing the speed of the air compressor and the opening of the proportional valve in the air subsystem to a preset threshold value through the battery management system, opening the blocking gas valve connected to the first blocking gas bottle, and passing the input air through the air compressor, the air proportional valve, the air filter and the intercooler, and entering the hydrogen fuel cell from the air inlet together with the blocking gas, purging the liquid water in the hydrogen fuel cell according to the set purging time, and then entering the pipeline from the air outlet of the hydrogen fuel cell, and being discharged to the outside through the back pressure valve;

[0025] S23, the first circulation pump in the hydrogen subsystem is turned off, the second circulation pump is turned on, the hydrogen proportional valve connected to the second blocking gas bottle is opened, the hydrogen in the hydrogen storage tank passes through the stop valve and flow meter, and together with the blocking gas, enters the hydrogen fuel cell from the hydrogen inlet through the hydrogen proportional valve and the flow guide, the fuel cell is purged according to the set purge time, and then enters the pipeline from the hydrogen outlet of the hydrogen fuel cell, the purged liquid water is discharged through the drain valve by the second circulation pump, and the gas is discharged to the outside through the exhaust valve;

[0026] S24. After the purge time is reached, the first-level purge strategy is stopped.

[0027] Furthermore, the secondary purge strategy includes:

[0028] The secondary purge strategy includes:

[0029] S31, determining the purge time of the secondary purge strategy according to the humidity;

[0030] S32, using the current humidity of hydrogen collected by the hydrogen humidity sensor as a judgment basis, when the impedance value of the hydrogen fuel cell is greater than the impedance threshold and the humidity in the hydrogen pipeline is greater than the humidity threshold, turning on the first circulation pump and the second circulation pump of the hydrogen subsystem, inputting the hydrogen and the blocking gas in the hydrogen storage tank, directly entering the first circulation pump through the guide device, and discharging the liquid water in the hydrogen through the drain valve;

[0031] S33. After the purge time is reached, the secondary purge strategy is stopped.

[0032] Furthermore, the purge time set in the first-level purge strategy is as shown in formula (1),

[0033]

[0034] Where t1 represents the purge time in the first-stage purge strategy, L1 is the length of the hydrogen inlet pipeline, L2 is the length of the hydrogen outlet pipeline, A is the pipeline cross-sectional area of ​​the hydrogen subsystem, and V an is the volume of the battery anode channel, Z m is the impedance value of the hydrogen fuel cell, M2 is the actual flow rate of the hydrogen inlet, as shown in formula (2),

[0035]

[0036] In the formula, Z1 and Z2 represent the hydrogen compression factors at the hydrogen inlet and standard atmospheric pressure respectively; p0 and p1 are the hydrogen pressures at the standard atmospheric pressure and hydrogen inlet respectively; T0 and T1 represent the standard temperature and the temperature of the hydrogen inlet respectively; and M1 is the hydrogen flow rate of the hydrogen storage tank.

[0037] Furthermore, the purge time set in the secondary purge strategy is as shown in formula (3),

[0038]

[0039] Where t2 is the purge time in the two-stage purge strategy, L3 is the length of the hydrogen pipeline, A is the pipeline cross-sectional area of ​​the hydrogen subsystem, M2 is the actual hydrogen inlet flow rate, and RH is the humidity in the hydrogen pipeline.

[0040] Furthermore, the primary heating strategy includes:

[0041] Close the radiator and the valve connected to the deionizer through the first three-way valve, start the heating water pump to heat the coolant in the coolant tank, and when the temperature of the coolant reaches a preset value, turn off the heating water pump to complete the cold start.

[0042] Furthermore, the secondary heating strategy includes:

[0043] Turn on the heater in the auxiliary heating device to heat the heater core;

[0044] Open the two-way valve and the second three-way valve connected to the valve of the third circulation pump in the auxiliary heating equipment, close the valve connected to the fourth circulation pump, so that the warm air formed by the warm air core forms a warm air loop in the pipeline, and the coolant is heated by the warm air loop and the heating water pump. When the coolant temperature of the cooling subsystem reaches the set value, close the two valves connected to the second three-way valve and the heating water pump and the third circulation pump, turn off the heating water pump, open the valve connected to the fourth circulation pump, and complete the cold start.

[0045] Beneficial effect: Under the technical conditions of the existing hydrogen fuel cell system, in order to solve the problem of high failure rate of automobile cold start, the present invention provides a cold start system for a hydrogen fuel cell automobile. After the automobile shutdown command is issued, the battery management system will detect the current temperature of the hydrogen fuel cell, formulate a two-stage purge strategy with different shutdown purge times, and purge the liquid water generated in the hydrogen fuel cell and the hydrogen pipeline to prevent the liquid water in the pipeline from freezing quickly and being difficult to thaw in a low temperature environment (-40°C), thereby blocking the pipeline and hindering the starting of the automobile. When the automobile is started again from a low temperature environment, the battery is first loaded and heated by itself, and an auxiliary heating device is installed in the cooling subsystem to realize external heating of the hydrogen fuel cell. Through this strategy of shutdown purge, internal heating and external auxiliary heating, the success rate of the automobile cold start in an environment of -40°C is improved, and the shutdown time of the automobile is shortened. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0047] Figure 1 A structural diagram of a hydrogen fuel cell system of a hydrogen fuel cell heavy-duty vehicle provided by the present invention;

[0048] Figure 2 This is the power system structure diagram of a hydrogen fuel cell heavy-duty vehicle;

[0049] Figure 3 A structural diagram of a hydrogen fuel cell for a hydrogen fuel cell heavy-duty vehicle;

[0050] Figure 4 A method flow chart of a cold start method for a hydrogen fuel cell vehicle provided by the present invention. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] This embodiment provides a cold start system for a hydrogen fuel cell vehicle. Figure 1 As shown, it includes a battery management system and a hydrogen fuel cell system;

[0053] The battery management system is used to detect the temperature of the hydrogen fuel cell in the hydrogen fuel cell system after the car is shut down, formulate a two-stage purge strategy and a two-stage heating strategy with different shutdown purge times, and control the hydrogen fuel cell system to execute the two-stage purge strategy; when the car is started again, control the hydrogen fuel cell system to execute the two-stage heating strategy;

[0054] The hydrogen fuel cell system comprises an air subsystem, a cooling subsystem, a hydrogen subsystem and a hydrogen fuel cell;

[0055] The air subsystem includes an air compressor, an air proportional valve, an air filter, an intercooler, a blocking gas valve, a three-way ball valve and a humidifier which are sequentially connected in the air inlet direction of the hydrogen fuel cell, and also includes a first blocking gas bottle connected to the blocking gas valve; a back pressure valve connected to the outside is provided in the air outlet direction; the air subsystem is used to provide oxygen for the chemical reaction of the hydrogen fuel cell and purge the inlet and outlet of the hydrogen fuel cell and the air through the blocking gas in the first blocking gas bottle to discharge the residual liquid water in the hydrogen fuel cell;

[0056] The hydrogen subsystem includes a hydrogen storage tank, a stop valve, a flow meter, a hydrogen proportional valve, a flow guide, and a first circulation pump (circulation pump 1) connected in sequence in the direction of the hydrogen inlet of the hydrogen fuel cell, and also includes a second blocking gas bottle connected to the hydrogen proportional valve; a second circulation pump (circulation pump 2) and a drain valve and an exhaust valve connected to the second circulation pump are provided in the direction of the hydrogen outlet; the hydrogen subsystem is used to provide hydrogen for the chemical reaction of the hydrogen fuel cell, control the flow and pressure of the hydrogen through valves at various levels, and purge the liquid water generated in the hydrogen inlet and outlet pipelines through the blocking gas in the second blocking gas bottle;

[0057] The cooling subsystem is used to heat the coolant and hydrogen fuel cell of the hydrogen fuel cell before the car is started, and at the same time detect whether the temperature of the hydrogen fuel cell exceeds the set value and control the radiator to cool down, thereby achieving temperature control of the hydrogen fuel cell.

[0058] Specifically, the battery management system and hydrogen fuel cell system of the vehicle are applied to hydrogen fuel cell heavy-duty vehicles. The power system structure of hydrogen fuel cell heavy-duty vehicles is as follows: Figure 2 As shown, the dotted line represents the gas path, the thin solid line represents the circuit, and the thick solid line represents the mechanical structure. The electricity required for the operation of the car comes from the hydrogen fuel cell and the power battery respectively. The hydrogen output by the hydrogen storage tank is mixed with air and enters the hydrogen fuel cell for oxidation-reduction reaction to generate electricity. The electricity generated by the power battery and the hydrogen fuel cell is boosted and inverted by the DC / DC and DC / AC units to drive the car motor to run, and the motor drives the transmission mechanism to rotate the wheels. The hydrogen energy management system includes a hydrogen storage tank and a gas transmission pipeline. The battery and its management system include a hydrogen fuel cell, a power battery and a battery management system. The hydrogen fuel cell, the hydrogen energy management system, the battery management system, the power conversion system and the motor control system all communicate through the vehicle CAN bus. The data of each subsystem is transmitted to the vehicle controller (VCU, Vehicle Control Unit) in the form of a message for control;

[0059] The hydrogen fuel cell system is a system that uses the hydrogen fuel cell and power battery of the vehicle to generate electricity and control the system. The power battery uses a lithium iron phosphate battery. The hydrogen fuel cell system consists of a hydrogen fuel cell and an auxiliary system (air subsystem, hydrogen subsystem and cooling subsystem).

[0060] Figure 3 The structure diagram of the hydrogen fuel cell of the hydrogen fuel cell heavy-duty vehicle in the embodiment of the present invention is shown. The hydrogen fuel cell adopts a proton exchange membrane fuel cell to convert chemical energy into electrical energy. It is mainly composed of an end plate, a bipolar plate, a diffusion layer, a catalyst layer, and a proton exchange membrane. The diffusion layer supports the catalyst layer and collects current, and provides a channel for the exchange of multiple substances for the membrane electrode reaction. The catalyst layer provides a place for the electrochemical reaction. The proton exchange membrane only allows protons and water to pass through. The main structure includes an anode hydrogen supply system and a cathode air supply system. The cathode air supply system transports the humidified air generated by the air subsystem in the hydrogen fuel cell system to the battery cathode. The main function of the anode hydrogen supply system is to transfer the humidified hydrogen generated by the hydrogen subsystem in the hydrogen fuel cell system to the battery anode, and then reach the catalyst layer after passing through the diffusion layer. Under the action of the catalyst, the hydrogen undergoes an oxidation reaction and generates protons and electrons. The protons carry water molecules through the proton exchange membrane to the cathode side catalyst layer, and the electrons reach the cathode catalyst layer via the external circuit, the cathode plate, and the diffusion layer. Hydrogen ions, electrons and oxygen generate water and heat under the action of the cathode catalyst;

[0061] The hydrogen pressure in the hydrogen storage tank is about 35MPa, while the allowable pressure of the hydrogen inlet of the hydrogen fuel cell is 1-5MPa. Therefore, it takes a certain number of reactions before it can be discharged through the exhaust valve.

[0062] In this solution, nitrogen is used as the blocking gas in the first blocking gas bottle and the second blocking gas bottle to prevent the residual hydrogen in the anode chamber and the cathode air from continuing to undergo electrochemical reactions after the fuel cell is shut down. By adding blocking gas bottles with blocking gas to the air subsystem and hydrogen subsystem of the conventional hydrogen fuel cell system, adding a circulation valve to the hydrogen subsystem, and formulating two purge strategies, blocking gas and air are used together to purge and discharge residual water in the hydrogen fuel cells, components and pipelines before the car is shut down, so as to prevent the internal liquid water in the low temperature from freezing in the flow channel or gas diffusion layer inside the battery, thereby hindering the starting of the car, thereby increasing the success rate of cold start of the car.

[0063] In a specific embodiment, the cooling subsystem includes a first three-way valve (three-way valve 1), a deionizer, a coolant tank, a heating water pump, a second three-way valve (three-way valve 2), a fourth circulation pump (circulation pump 4) and an auxiliary heating device connected to the second three-way valve, and also includes a radiator connected to the first three-way valve; the auxiliary heating equipment includes a heater, a warm air core, a two-way valve and a third circulation pump (circulation pump 3) connected in sequence, and opening each valve can form a warm air circuit.

[0064] In this solution, an auxiliary heating device is set up to accelerate the temperature of the vehicle's hydrogen fuel cell and the coolant at a temperature of -40°C, thereby shortening the vehicle's start-up time.

[0065] In a specific embodiment, an air inlet pressure sensor and a No. 1 temperature sensor are provided between the humidifier and the air inlet; an air outlet pressure sensor is provided between the air outlet and the back pressure valve; a No. 3 temperature sensor is provided between the hydrogen inlet and the drain, a No. 4 temperature sensor is provided between the hydrogen outlet and the second circulation pump, and a humidity sensor is provided on the drain.

[0066] In this embodiment, a temperature sensor is set to facilitate checking the temperature of each port when the car is started, setting a heating strategy, and a humidity sensor is set to facilitate detecting the humidity in the hydrogen pipeline and formulating a purge strategy.

[0067] A cold start method for a hydrogen fuel cell vehicle, such as Figure 4 As shown, including:

[0068] S1: After the car stops, the current temperature of the hydrogen fuel cell is obtained through the temperature sensor;

[0069] S2: setting an impedance threshold, a purge temperature threshold and a first-level purge strategy, and when the temperature of the current hydrogen fuel cell is less than the purge temperature threshold and the impedance value of the hydrogen fuel cell is less than the impedance threshold, the battery management system controls the air subsystem and the hydrogen subsystem to purge the hydrogen fuel cell according to the first-level purge strategy to discharge the residual liquid water inside the battery and the hydrogen pipeline;

[0070] S3: setting a humidity threshold and a secondary purge strategy in the hydrogen pipeline, and when the impedance value of the hydrogen fuel cell is greater than the impedance threshold and the humidity in the hydrogen pipeline is greater than the humidity threshold, stopping the primary purge strategy and executing the secondary purge strategy;

[0071] S4: before the hydrogen fuel cell is started, self-heating of the hydrogen fuel cell is performed;

[0072] S5: Set the heating temperature threshold, the first-level heating strategy and the second-level heating strategy to determine whether the current ambient temperature is greater than the heating temperature threshold. If so, execute the first-level heating strategy. If not, execute the first-level heating strategy and the second-level heating strategy at the same time to heat the coolant in the coolant tank. When the temperature of the coolant reaches the preset value, stop heating and complete the cold start.

[0073] Specifically, first, after the car stops, four temperature sensors are used to obtain the current temperature of the hydrogen fuel cell, providing data for the subsequent formulation of the purge strategy to achieve the purge effect; secondly, the impedance threshold, purge temperature threshold and first-level purge strategy are set to purge the hydrogen fuel cell. When the proton exchange membrane (PEM) is in a well-hydrated state, the water content inside the hydrogen fuel cell is inversely proportional to the impedance of the battery, that is, the lower the water content, the greater the impedance and the better the battery effect. When the water content is lower than a certain value, the impedance value will stop changing. Cold start requires reducing the water content in the hydrogen fuel cell, that is, the monitored impedance needs to be greater than a certain value. Therefore, the impedance threshold corresponding to the required water content is set to monitor the impedance of the hydrogen fuel cell in real time. Resistance, when the monitored impedance is less than the impedance threshold, it means that the water content is high and needs to be purged to reduce the water content; when the temperature of the hydrogen fuel cell is below zero, the liquid water will freeze, so it is necessary to set a purge temperature threshold. When the temperature of the hydrogen fuel cell is less than the purge temperature threshold, the battery is purged to discharge the residual liquid water inside the battery and the pipeline; again, the humidity threshold and the secondary purge strategy in the hydrogen pipeline are set to purge the hydrogen pipeline. The higher the humidity in the hydrogen pipeline, the higher the water content. At low temperatures, the liquid water in the pipeline freezes and easily blocks the pipeline, causing the vehicle to fail to start. Therefore, a humidity threshold that does not affect the start of the vehicle is set. When the humidity of the pipeline is detected to be greater than the threshold, the hydrogen pipeline is purged;

[0074] After the car is started again, the temperature of the car's hydrogen fuel cell needs to be increased. Therefore, first, the hydrogen fuel cell is self-heated before it is started; secondly, the heating temperature threshold, the first-level heating strategy and the second-level heating strategy are set. Above -40°C, only the first-level heating strategy is used to heat the battery coolant, thereby increasing the battery temperature and reducing cold start losses; below -40°C, the first-level and second-level heating strategies are executed simultaneously to perform internal and external heating of the coolant, thereby speeding up the coolant heating speed, improving the fuel cell efficiency, and increasing the success rate of cold start of the car in low temperature environments.

[0075] In a specific embodiment, after the car stops, the solution for obtaining the current temperature of the hydrogen fuel cell through the temperature sensor is:

[0076] When the driver is in the cab and powers off the vehicle on the vehicle's instrument cluster, the instrument cluster system sends a shutdown signal to the vehicle controller. The battery management system will receive the power-off signal sent by the vehicle controller. At the same time, the battery management system will detect the average temperature collected by the first, second, third, and fourth temperature sensors installed at the air and hydrogen inlet and outlet of the hydrogen fuel cell.

[0077] In a specific embodiment, an impedance threshold, a purge temperature threshold, and a first-level purge strategy are set. When the temperature of the current hydrogen fuel cell is less than the purge temperature threshold and the impedance value of the hydrogen fuel cell is less than the impedance threshold, the battery management system controls the air subsystem and the hydrogen subsystem to purge the hydrogen fuel cell according to the first-level purge strategy to discharge the residual liquid water in the battery and the hydrogen pipeline. The scheme is:

[0078] Set the purge temperature threshold to 0°C and the impedance threshold to 0.1MΩ;

[0079] The real-time impedance value of the hydrogen fuel cell is detected by the battery management system. The calculation process of the impedance value of the hydrogen fuel cell is as follows:

[0080] The battery management system transmits the detected hydrogen fuel cell voltage and current signals containing high-frequency components to the vehicle controller. After AD conversion, they are converted into voltage discrete signals and current discrete signals, as shown in formulas (4) and (5).

[0081]

[0082]

[0083] Where V RMS Represents a voltage discrete signal, V BAT represents the voltage signal of the hydrogen fuel cell, n represents the number of acquisitions, I RMS Represents the current discrete signal, I BAT Represents the hydrogen fuel cell current signal;

[0084] The impedance value is calculated by the amplitude of voltage and current. The effective value of the signal is the amplitude. The relationship between the effective value and the amplitude is shown in formulas (6) and (7).

[0085]

[0086]

[0087] Among them, V m is the voltage amplitude, I m is the amplitude of the current;

[0088] The battery impedance value is shown in formula (8),

[0089]

[0090] Among them, Z m is the impedance value of the hydrogen fuel cell;

[0091] The primary purge strategy includes:

[0092] S21, determining the purge time of the first-level purge strategy according to the impedance of the hydrogen fuel cell;

[0093] The purge time set in the first-level purge strategy is shown in formula (9),

[0094]

[0095] Where t1 represents the purge time in the first-stage purge strategy, L1 is the length of the hydrogen inlet pipeline (from the hydrogen storage tank to the hydrogen inlet), L2 is the length of the hydrogen outlet pipeline (from the hydrogen outlet to the exhaust valve outlet), A is the pipeline cross-sectional area of ​​the hydrogen subsystem, and V an is the volume of the battery anode channel, M2 is the actual flow rate of the hydrogen inlet, as shown in formula (10),

[0096]

[0097] Wherein, Z1 and Z2 represent the hydrogen compression factor at the hydrogen inlet and standard atmospheric pressure, respectively; p0 and p1 represent the hydrogen pressure at the standard atmospheric pressure and hydrogen inlet, T0 and T1 represent the standard temperature and the temperature at the hydrogen inlet, respectively; M1 is the hydrogen flow rate of the hydrogen storage tank;

[0098] S22, switch the three-way ball valve of the air subsystem from the state leading to the humidifier when the hydrogen fuel cell is working normally to the state leading directly to the air inlet of the battery, increase the speed of the air compressor and the opening of the proportional valve in the air subsystem to the preset threshold value through the fuel cell management system, open the blocking gas valve connected to the first blocking gas bottle, and let the input air pass through the air compressor, air proportional valve, air filter and intercooler, and enter the hydrogen fuel cell from the air inlet together with the blocking gas, purge the liquid water in the hydrogen fuel cell according to the set purge time, and then enter the pipeline from the air outlet of the hydrogen fuel cell, and be discharged to the outside through the back pressure valve:

[0099] The primary purge strategy increases the air compressor speed and proportional valve opening of the air subsystem to a preset threshold value through the fuel cell management system, including:

[0100] The fuel cell management system transmits the CAN messages of "air compressor speed n" and "proportional valve opening k" to the vehicle controller, and the vehicle controller transmits the message instruction information of increasing the air compressor speed n and the proportional valve opening k to 2000 (r / min) and 100% respectively to the fuel cell management system, and controls the air compressor speed and the proportional valve opening k to reach the set values, that is, the air compressor speed is 2000 (r / min) and the proportional valve opening is 100%;

[0101] S23, the first circulation pump in the hydrogen subsystem is turned off, the second circulation pump is turned on, the hydrogen proportional valve connected to the second blocking gas bottle is opened, the hydrogen in the hydrogen storage tank passes through the stop valve and flow meter, and together with the blocking gas, enters the hydrogen fuel cell from the hydrogen inlet through the hydrogen proportional valve and the flow guide, the fuel cell is purged according to the set purge time, and then enters the pipeline from the hydrogen outlet of the hydrogen fuel cell, the purged liquid water is discharged through the drain valve by the second circulation pump, and the gas is discharged to the outside through the exhaust valve;

[0102] S24. After the purge time is reached, the first-level purge strategy is stopped.

[0103] When the water content inside the hydrogen fuel cell is higher than 0.75g / L, its impedance value is inversely proportional to the water content. However, when the water content is between 0-0.75 (g / L), the impedance value of the battery no longer changes. Therefore, the impedance value of the hydrogen fuel cell stack is detected by the battery management system, and the time of the first-level purge strategy is determined according to the impedance value to ensure that the water content in the hydrogen fuel cell stack is less than a certain content, so that the interior of the hydrogen fuel cell is dry and does not freeze at low temperatures.

[0104] In a specific embodiment, a humidity threshold and a secondary purge strategy are set in the hydrogen pipeline. When the impedance value of the hydrogen fuel cell is greater than the impedance threshold and the humidity in the hydrogen pipeline is greater than the humidity threshold, the primary purge strategy is stopped and the secondary purge strategy is executed as follows:

[0105] Set the humidity threshold in the hydrogen pipeline to 0.2g / L;

[0106] The secondary purge strategy includes:

[0107] S31, determining the purge time of the secondary purge strategy according to the humidity,

[0108] The purge time set in the secondary purge strategy is shown in formula (11),

[0109]

[0110] Where, t2 is the purge time in the two-stage purge strategy, L3 is the length of the hydrogen pipeline (from the hydrogen storage tank to the drain valve), A is the pipeline cross-sectional area of ​​the hydrogen subsystem, M2 is the actual hydrogen inlet flow rate, and RH is the humidity in the hydrogen pipeline;

[0111] S32. By using the current humidity of hydrogen collected by the hydrogen humidity sensor as a basis for judgment, when the impedance value of the hydrogen fuel cell is greater than the impedance threshold and the humidity in the hydrogen pipeline is greater than the humidity threshold, the first circulation pump and the second circulation pump of the hydrogen subsystem are turned on, and the hydrogen and blocking gas in the hydrogen storage tank are input directly into the first circulation pump through the guide valve, and the liquid water inside the hydrogen is discharged through the drain valve.

[0112] In this embodiment, the current humidity of hydrogen collected by the hydrogen humidity sensor is used as a basis for judgment. When the impedance value of the hydrogen fuel cell is greater than the impedance threshold and the humidity in the hydrogen pipeline is greater than the humidity threshold, the battery management system transmits the hydrogen humidity data to the vehicle controller, and the vehicle controller sends an instruction to control the execution of the secondary purge strategy, turning on the first circulation pump and the second circulation pump of the hydrogen subsystem. The hydrogen and blocking gas in the hydrogen storage tank directly enter the first circulation pump through the drain valve during input, and the liquid water inside the hydrogen is discharged through the drain valve. When the humidity sensor detects that the current humidity of the hydrogen pipeline is lower than the set value, the secondary purge strategy is stopped to ensure that the liquid water in the hydrogen pipeline will not block the pipeline due to freezing, thereby affecting the starting of the vehicle.

[0113] In a specific embodiment, before the hydrogen fuel cell is started, the scheme for self-heating the hydrogen fuel cell is:

[0114] The battery controls the content of hydrogen and oxygen entering to achieve electrochemical reaction to generate more heat energy. During the battery loading process, a constant voltage control method is adopted to control its loading power with the goal of stabilizing the battery voltage. Among them, the loading power of battery heating is formulated according to the rated power, peak power, load increase / reduction response rate, high-voltage output voltage and current of the fuel cell, and it is required to improve the self-heating ability of the battery.

[0115] In this solution, the battery is first self-heated to ensure uniform temperature of the battery stack, avoid local overheating or overcooling, and improve starting efficiency.

[0116] In a specific embodiment, a heating temperature threshold, a primary heating strategy, and a secondary heating strategy are set to determine whether the current ambient temperature is greater than the heating temperature threshold. If so, the primary heating strategy is executed. If not, the primary heating strategy and the secondary heating strategy are executed at the same time to heat the coolant in the coolant tank. When the temperature of the coolant reaches a preset value, the heating is stopped. The solution for completing the cold start is:

[0117] The heating threshold is -40°C, the preset temperature of the coolant is 60°C, and the first-level heating strategy is:

[0118] Close the radiator and the radiator and the valve connected to the deionizer through the first three-way valve, start the heating water pump to heat the coolant in the coolant tank, and when the temperature of the coolant reaches a preset value, turn off the heating water pump, stop executing the first-level heating strategy, and complete the cold start;

[0119] The secondary heating strategy is:

[0120] Turn on the heater in the auxiliary heating device to heat the heater core;

[0121] Open the two-way valve and the second three-way valve connected to the valve of the third circulation pump in the auxiliary heating equipment, close the valve connected to the fourth circulation pump, so that the warm air formed by the warm air core forms a warm air loop in the pipeline, and the coolant is heated by the warm air loop and the heating water pump. When the coolant temperature of the cooling subsystem reaches 60°C, close the two valves connected to the second three-way valve and the heating water pump and the third circulation pump, turn off the heating water pump, open the valve connected to the fourth circulation pump, and complete the cold start.

[0122] The heating threshold is -40℃. If the current ambient temperature is greater than -40℃, the first-level heating strategy is executed to heat the coolant to assist the battery in heating up. If the current ambient temperature is below -40℃, the first-level heating strategy and the second-level heating strategy are executed at the same time to heat the coolant at the same time, thereby improving the heating efficiency, shortening the vehicle starting time, reducing the loss of cold start, and extending the battery life.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cold start system for a hydrogen fuel cell vehicle, characterized in that: Including battery management system and hydrogen fuel cell system; The battery management system is used to detect the temperature of the hydrogen fuel cell in the hydrogen fuel cell system after the car is shut down, formulate a two-stage purge strategy and a two-stage heating strategy with different shutdown purge times, and control the hydrogen fuel cell system to execute the two-stage purge strategy; when the car is started again, control the hydrogen fuel cell system to execute the two-stage heating strategy; The hydrogen fuel cell system comprises an air subsystem, a cooling subsystem, a hydrogen subsystem and a hydrogen fuel cell; The air subsystem includes an air compressor, an air proportional valve, an air filter, an intercooler, a blocking gas valve, a three-way ball valve and a humidifier which are sequentially connected in the air inlet direction of the hydrogen fuel cell, and also includes a first blocking gas bottle connected to the blocking gas valve; a back pressure valve connected to the outside is provided in the air outlet direction; the air subsystem is used to provide oxygen for the chemical reaction of the hydrogen fuel cell and purge the inlet and outlet of the hydrogen fuel cell and the air through the blocking gas in the first blocking gas bottle to discharge the residual liquid water in the hydrogen fuel cell; The hydrogen subsystem includes a hydrogen storage tank, a stop valve, a flow meter, a hydrogen proportional valve, a flow guide, and a first circulation pump connected in sequence in the direction of the hydrogen inlet of the hydrogen fuel cell, and also includes a second blocking gas bottle connected to the hydrogen proportional valve; a second circulation pump and a drain valve and an exhaust valve connected to the second circulation pump are provided in the direction of the hydrogen outlet; the hydrogen subsystem is used to provide hydrogen for the chemical reaction of the hydrogen fuel cell, control the flow and pressure of the hydrogen, and purge the liquid water generated in the hydrogen inlet and outlet pipelines through the blocking gas in the second blocking gas bottle; The cooling subsystem is used to heat the coolant and hydrogen fuel cell of the hydrogen fuel cell before the car is started, and at the same time detect whether the temperature of the hydrogen fuel cell exceeds the set value and control the radiator to cool down, thereby achieving temperature control of the hydrogen fuel cell.

2. A cold start system for a hydrogen fuel cell vehicle according to claim 1, characterized in that: The cooling subsystem includes a first three-way valve, a deionizer, a coolant tank, a heating water pump, a second three-way valve, a fourth circulation pump and an auxiliary heating device connected to the second three-way valve, and also includes a radiator connected to the first three-way valve; the auxiliary heating device includes a heater, a warm air core, a two-way valve and a third circulation pump connected in sequence.

3. A cold start system for a hydrogen fuel cell vehicle according to claim 1, characterized in that: An air inlet pressure sensor and a No. 1 temperature sensor are provided between the humidifier and the air inlet; an air outlet pressure sensor is provided between the air outlet and the back pressure valve; a No. 3 temperature sensor is provided between the hydrogen inlet and the flow guide, a No. 4 temperature sensor is provided between the hydrogen outlet and the second circulation pump, and a humidity sensor is provided on the flow guide.

4. A cold start method for a hydrogen fuel cell vehicle, applied to a cold start system for a hydrogen fuel cell vehicle as claimed in any one of claims 1 to 3, characterized in that: include: S1: After the car stops, the current temperature of the hydrogen fuel cell is obtained through the temperature sensor; S2: setting an impedance threshold, a purge temperature threshold and a first-level purge strategy, and when the temperature of the current hydrogen fuel cell is less than the purge temperature threshold and the impedance value of the hydrogen fuel cell is less than the impedance threshold, the battery management system controls the air subsystem and the hydrogen subsystem to purge the hydrogen fuel cell according to the first-level purge strategy to discharge the residual liquid water inside the battery and the hydrogen pipeline; S3: setting a humidity threshold and a secondary purge strategy in the hydrogen pipeline, and when the impedance value of the hydrogen fuel cell is greater than the impedance threshold and the humidity in the hydrogen pipeline is greater than the humidity threshold, stopping the primary purge strategy and executing the secondary purge strategy; S4: before the hydrogen fuel cell is started, self-heating of the hydrogen fuel cell is performed; S5: Set the heating temperature threshold, the first-level heating strategy and the second-level heating strategy to determine whether the current ambient temperature is greater than the heating temperature threshold. If so, execute the first-level heating strategy. If not, execute the first-level heating strategy and the second-level heating strategy at the same time to heat the coolant in the coolant tank. When the temperature of the coolant reaches the preset value, stop heating and complete the cold start.

5. A cold start method for a hydrogen fuel cell vehicle according to claim 4, characterized in that: The primary purge strategy includes: S21, determining the purge time of the first-level purge strategy according to the impedance of the hydrogen fuel cell; S22, switching the three-way ball valve of the air subsystem from the state leading to the humidifier when the hydrogen fuel cell is working normally to the state leading directly to the air inlet of the battery, increasing the speed of the air compressor and the opening of the proportional valve in the air subsystem to a preset threshold value through the battery management system, opening the blocking gas valve connected to the first blocking gas bottle, and passing the input air through the air compressor, the air proportional valve, the air filter and the intercooler, and entering the hydrogen fuel cell from the air inlet together with the blocking gas, purging the liquid water in the hydrogen fuel cell according to the set purging time, and then entering the pipeline from the air outlet of the hydrogen fuel cell, and being discharged to the outside through the back pressure valve; S23, the first circulation pump in the hydrogen subsystem is turned off, the second circulation pump is turned on, the hydrogen proportional valve connected to the second blocking gas bottle is opened, the hydrogen in the hydrogen storage tank passes through the stop valve and flow meter, and together with the blocking gas, enters the hydrogen fuel cell from the hydrogen inlet through the hydrogen proportional valve and the flow guide, the fuel cell is purged according to the set purge time, and then enters the pipeline from the hydrogen outlet of the hydrogen fuel cell, the purged liquid water is discharged through the drain valve by the second circulation pump, and the gas is discharged to the outside through the exhaust valve; S24. After the purge time is reached, the first-level purge strategy is stopped.

6. A cold start method for a hydrogen fuel cell vehicle according to claim 4, characterized in that: The secondary purge strategy includes: S31, determining the purge time of the secondary purge strategy according to the humidity; S32, using the current humidity of hydrogen collected by the hydrogen humidity sensor as a judgment basis, when the impedance value of the hydrogen fuel cell is greater than the impedance threshold and the humidity in the hydrogen pipeline is greater than the humidity threshold, turning on the first circulation pump and the second circulation pump of the hydrogen subsystem, inputting the hydrogen and the blocking gas in the hydrogen storage tank, directly entering the first circulation pump through the guide device, and discharging the liquid water in the hydrogen through the drain valve; S33. After the purge time is reached, the secondary purge strategy is stopped.

7. A cold start method for a hydrogen fuel cell vehicle according to claim 5, characterized in that: The purge time set in the first-level purge strategy is shown in formula (1): Where t1 represents the purge time in the first-stage purge strategy, L1 is the length of the hydrogen inlet pipeline, L2 is the length of the hydrogen outlet pipeline, A is the pipeline cross-sectional area of ​​the hydrogen subsystem, and V an is the volume of the battery anode channel, Z m is the impedance value of the hydrogen fuel cell, M2 is the actual flow rate of the hydrogen inlet, as shown in formula (2), Where Z1 and Z2 represent the hydrogen compression factors at the hydrogen inlet and standard atmospheric pressure, respectively; p0, p1 are the standard atmospheric pressure and the hydrogen pressure at the hydrogen inlet, T0, T1 represent the standard temperature and the temperature of the hydrogen inlet respectively, and M1 is the hydrogen flow rate of the hydrogen storage tank.

8. A cold start method for a hydrogen fuel cell vehicle according to claim 5, characterized in that: The purge time set in the secondary purge strategy is shown in formula (3), Where t2 is the purge time in the two-stage purge strategy, L3 is the length of the hydrogen pipeline, A is the pipeline cross-sectional area of ​​the hydrogen subsystem, M2 is the actual hydrogen inlet flow rate, and RH is the humidity in the hydrogen pipeline.

9. A cold start method for a hydrogen fuel cell vehicle according to claim 4, characterized in that: The primary heating strategy includes: Close the radiator and the valve connected to the radiator and the deionizer through the first three-way valve, start the heating water pump to heat the coolant in the coolant tank, and when the temperature of the coolant reaches a preset value, turn off the heating water pump to complete the cold start.

10. A cold start method for a hydrogen fuel cell vehicle according to claim 4, characterized in that: The secondary heating strategy includes: Turn on the heater in the auxiliary heating device to heat the heater core; Open the two-way valve and the second three-way valve connected to the valve of the third circulation pump in the auxiliary heating equipment, close the valve connected to the fourth circulation pump, so that the warm air formed by the warm air core forms a warm air loop in the pipeline, and the coolant is heated by the warm air loop and the heating water pump. When the coolant temperature of the cooling subsystem reaches the set value, close the two valves connected to the second three-way valve and the heating water pump and the third circulation pump, turn off the heating water pump, open the valve connected to the fourth circulation pump, and complete the cold start.

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