Exhaust energy recovery control system and method for fuel cell

Abstract

The invention discloses an exhaust energy recovery control system and method for a fuel cell. The system comprises an air compressor, a variable-section expansion machine, an intercooler, a stop valve and an exhaust sealing valve. The variable-section expansion machine and a compressor of the air compressor are coaxially arranged, the output end of the air compressor is connected with the input end of the intercooler, the output end of the intercooler is communicated with one end of the stop valve, the other end of the stop valve is communicated with an air inlet of the electric pile, and an exhaust port of the electric pile is connected with one end of the exhaust sealing valve. And the other end of the exhaust sealing valve is connected with the input end of the variable-section expansion machine. The variable-section expansion machine adjusts the opening degree of the variable section according to the power of the electric pile so as to adjust the exhaust back pressure of the fuel cell system, and the electric pile exhaust smoothly pushes the impeller of the variable-section expansion machine to rotate, so that power is provided for the rotation of the impeller of the compressor, and the power consumption of the motor of the air compressor is reduced. The energy recovery efficiency of electric push exhaust can be improved, and the power of the fuel cell system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen fuel cell control, and more specifically, to an exhaust energy recovery control system and method for a fuel cell. Background Art

[0002] A hydrogen fuel cell system is a device that generates electricity by electrochemically reacting hydrogen with oxygen to generate water and electricity. In order to improve the reaction efficiency, the air entering the stack needs to be pressurized by an air compressor. The air compressor is driven by a motor and consumes power, reducing the net output power of the entire fuel cell system. After the fuel cell system generates electricity, the remaining air will be discharged from the stack through the air outlet on the stack. This part of the exhaust also carries a certain amount of kinetic energy and heat. Therefore, how to efficiently recover the energy in this part of the exhaust to increase the power of the fuel cell system is of great significance. Summary of the invention

[0003] The present invention provides an exhaust energy recovery control system and method for a fuel cell, which solves the problem of energy waste in the exhaust of the fuel cell stack of the existing hydrogen fuel cell system, can improve the energy recovery efficiency of the electric propulsion exhaust, and improve the power of the fuel cell system.

[0004] To achieve the above objectives, the present invention provides the following technical solutions:

[0005] An exhaust energy recovery control system for a fuel cell, comprising: an air compressor, a variable cross-section expander, an intercooler, a stop valve and an exhaust sealing valve;

[0006] The variable cross-section expander is coaxially arranged with the compressor of the air compressor, the output end of the air compressor is connected to the input end of the intercooler, the output end of the intercooler is respectively connected to one end of the stop valve, the other end of the stop valve is connected to the air inlet of the fuel cell stack, the exhaust port of the fuel cell stack is connected to one end of the exhaust sealing valve, and the other end of the exhaust sealing valve is connected to the input end of the variable cross-section expander;

[0007] The variable cross-section expander adjusts the variable cross-section opening according to the power of the fuel cell stack to adjust the exhaust back pressure of the fuel cell system, and allows the exhaust of the fuel cell stack to smoothly drive the impeller of the variable cross-section expander to rotate, thereby providing power for the rotation of the compressor impeller and reducing the power consumption of the air compressor motor.

[0008] Preferably, it also includes: a water separator;

[0009] The water separator is arranged between the exhaust sealing valve and the variable cross-section expander, the input end of the water separator is connected to the output end of the exhaust sealing valve, the output end of the water separator is connected to the input end of the variable cross-section expander, and the drainage end of the water separator is connected to the output end of the variable cross-section expander;

[0010] The water separator is used to remove water from the exhaust gas of the fuel cell stack to reduce the moisture content of the exhaust gas of the fuel cell stack entering the variable cross-section expander.

[0011] Preferably, it also includes: a bypass valve;

[0012] One end of the bypass valve is connected to the output end of the exhaust sealing valve, and the other end of the bypass valve is connected to the output end of the intercooler.

[0013] Preferably, it also includes: a pressure sensor;

[0014] The pressure sensors are provided at the air inlet and the exhaust port of the fuel cell stack to detect the air inlet pressure and the exhaust pressure of the fuel cell stack;

[0015] The variable cross-section expander adjusts the variable cross-section opening according to the intake pressure and the exhaust pressure, thereby achieving the adjustment of the exhaust back pressure.

[0016] Preferably, it also includes: a flow meter and a temperature sensor;

[0017] The flow meter is arranged at the air inlet of the air compressor and is used to detect the air intake flow rate;

[0018] The temperature sensor is arranged at the air inlet of the fuel cell stack and is used to detect the air inlet temperature;

[0019] The intercooler is connected to the flow meter and the temperature sensor signal, and is operated and controlled according to the intake air temperature and the intake air flow rate to reduce the intake air temperature to within a set temperature range.

[0020] The present invention also provides an exhaust energy recovery control method for a fuel cell, using the above control system, comprising:

[0021] Obtaining a required operating condition of the fuel cell system, and determining an operating exhaust flow requirement and an exhaust back pressure requirement according to the required operating condition;

[0022] The variable cross-section opening of the variable cross-section expander is adjusted according to the exhaust flow demand and the exhaust back pressure demand of the operating condition to adjust the exhaust back pressure of the fuel cell system, and the expander provides power to the compressor of the air compressor to reduce the power consumption of the air compressor motor.

[0023] Preferably, it also includes:

[0024] When the fuel cell system is working, the stack current is calculated based on the power demand of the fuel cell system and the polarization characteristic curve;

[0025] The air flow requirement and pressure setting value under the stack current are calculated by looking up the table according to the stack air operating conditions, and then the air compressor speed and the variable cross-section opening of the expander are controlled according to the air compressor Map and calibration results.

[0026] Preferably, it also includes:

[0027] When the fuel cell system is started, it first enters the self-check mode to check whether the opening of each valve and the variable cross-section opening of the expander is normal. If so, a cold start purge or a normal start purge is performed;

[0028] When entering the self-check mode, the stop valve, the exhaust sealing valve and the bypass valve are opened for 1 second and then closed to perform a self-check on whether the valve body is opened normally, and the variable cross-sectional opening of the variable cross-sectional expander is swung from the minimum to the maximum for 3 times to perform a self-check on whether the expander is opened normally;

[0029] During the cold start purge, the stop valve, the exhaust sealing valve and the bypass valve are opened to 100%, and the air compressor is operated at the first speed R1;

[0030] During normal startup purging, the shutoff valve, the exhaust sealing valve and the bypass valve are all opened to 100% and the air compressor is operated at a second speed R2, which is greater than the first speed R1.

[0031] Preferably, it also includes:

[0032] Determine whether the fuel cell system is successfully started. If not, the system is shut down by default, and the air compressor, stop valve, exhaust sealing valve and bypass valve are all closed. If yes, normal operation control is performed;

[0033] During normal operation, determine whether a shutdown command is received. If so, determine whether it is an emergency shutdown, low-temperature shutdown, or normal-temperature shutdown.

[0034] Preferably, it also includes:

[0035] When the fuel cell system is shut down, the cathode and anode of the stack are purged separately. When the cathode is purged, the air compressor speed is controlled to operate at the third speed R3. At this time, the stop valve is fully open, the bypass valve is closed, and the variable cross-section opening of the expander is set to the maximum, so that the air can purge the entire gas path of the stack;

[0036] After the cathode purge is completed, the cathode is sealed, the stop valve and the exhaust sealing valve are all closed, the cathode air path is sealed, the air compressor is still running at the third speed R3, the bypass valve is fully open, and the variable cross-section opening of the expander is the default opening, providing a certain flow of air to enter the tail exhaust through the bypass valve to dilute the hydrogen;

[0037] After the gas supply to the stack is stopped, the remaining air inside the fuel cell is gradually consumed by generating electricity with a small current. When the output voltage of the fuel cell is lower than 220V, the load is disconnected and the battery no longer outputs power to the outside.

[0038] When the anode purge is completed, the shutdown is completed. In the shutdown and power-off state, the stop valve and the exhaust sealing valve are both in the fully closed state.

[0039] The present invention provides an exhaust energy recovery control system and method for a fuel cell, which uses a variable cross-section expander and a compressor in an air compressor to be coaxially arranged, so that the stack exhaust provides rotational power to the compressor through the expander to reduce the power consumption of the air compressor motor, and adjusts the exhaust back pressure in the fuel cell system through the variable cross-section opening. The problem of energy waste in the stack exhaust of the existing hydrogen fuel cell system is solved, the energy recovery efficiency of the electric propulsion exhaust can be improved, and the power of the fuel cell system can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the specific embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below.

[0041] Figure 1 It is a schematic diagram of an exhaust energy recovery control system for a fuel cell provided by the present invention.

[0042] Figure 2 It is a schematic diagram of an exhaust energy recovery control method for a fuel cell provided by the present invention.

[0043] Figure 3 It is a schematic diagram of an exhaust energy recovery control process for a fuel cell provided by the present invention. DETAILED DESCRIPTION

[0044] In order to enable persons skilled in the art to better understand the solutions of the embodiments of the present invention, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and implementation modes.

[0045] In view of the problem of energy waste in the stack exhaust of the current hydrogen fuel cell system, the present invention provides an exhaust energy recovery control system and method for a fuel cell, which solves the problem of energy waste in the stack exhaust of the current hydrogen fuel cell system, can improve the energy recovery efficiency of the electric propulsion exhaust, and improve the power of the fuel cell system.

[0046] like Figure 1 As shown, an exhaust energy recovery control system for a fuel cell includes: an air compressor, a variable cross-section expander, an intercooler, a stop valve and an exhaust sealing valve. The variable cross-section expander is coaxially arranged with the compressor of the air compressor, the output end of the air compressor is connected to the input end of the intercooler, the output end of the intercooler is respectively connected to one end of the stop valve, the other end of the stop valve is connected to the air inlet of the stack, the exhaust port of the stack is connected to one end of the exhaust sealing valve, and the other end of the exhaust sealing valve is connected to the input end of the variable cross-section expander. The variable cross-section expander adjusts the variable cross-section opening according to the power of the stack to adjust the exhaust back pressure of the fuel cell system, and makes the exhaust of the stack smoothly drive the impeller of the variable cross-section expander to rotate, thereby providing power for the rotation of the compressor impeller and reducing the power consumption of the air compressor motor.

[0047] Specifically, the intercooler uses heat exchange to transfer part of the heat in the air and then cools the air to a suitable temperature for the stack to work. The expander is coaxial with the compressor of the air compressor. The exhaust gas of the stack passes through the expander, driving the expander impeller to rotate, thereby providing power for the rotation of the compressor impeller and reducing the power consumption of the air compressor motor. In order to improve the energy recovery efficiency within the entire operating range and solve the contradiction between different demands for the expander under large and small exhaust flow rates, a variable cross-section expander is used. At the high power point of the stack, the opening of the variable cross-section is increased, so that the exhaust gas with a larger flow rate can reach the impeller smoothly and drive the impeller to do work. At the low power point of the stack, the opening of the variable cross-section is reduced to form a tapered channel, increase the back pressure, and increase the kinetic energy of the exhaust gas with a smaller flow rate. By adjusting the opening of the variable cross-section of the expander, the energy recovery efficiency of each operating point can be improved.

[0048] In practical applications, when the variable cross-section of the expander is adjusted, it will affect the system back pressure. When VNT is adjusted to a large value, the exhaust is smooth and the back pressure is small. When VNT is adjusted to a small value, the flow channel cross-section becomes smaller and the back pressure is larger. Therefore, changes in VNT will affect the adjustment of the back pressure valve in the fuel cell system. In order to coordinate the control of the two, the calibration amount is large. Under different working conditions, the back pressure valve and the variable cross-section opening of the expander affect each other, and coordinated calibration is required, which is more complicated. Therefore, when using an expander with a variable cross-section, the back pressure valve can be cancelled, and only the variable cross-section opening of the expander can be adjusted to control the system back pressure.

[0049] An exhaust sealing valve is used at the exhaust outlet of the fuel cell stack to seal after shutdown to increase the life of the fuel cell stack. The valve has only two states: fully open and fully closed. It is fully open when the fuel cell stack is operating normally and fully closed when the fuel cell stack is shut down. No additional calibration is required.

[0050] The system further includes: a water separator; the water separator is arranged between the exhaust sealing valve and the variable cross-section expander, the input end of the water separator is connected to the output end of the exhaust sealing valve, the output end of the water separator is connected to the input end of the variable cross-section expander, and the drainage end of the water separator is connected to the output end of the variable cross-section expander. The water separator is used to remove water from the stack exhaust to reduce the moisture of the stack exhaust entering the variable cross-section expander.

[0051] In actual applications, in order to prevent the water in the exhaust from damaging the expander impeller, the exhaust gas of the fuel cell stack passes through the water separator to remove water before entering the expander of the air compressor to drive the expander impeller to rotate. Since the compressor and the expander impeller of the air compressor are coaxial, the expander drives the compressor impeller to work, reducing the power consumption of the compressor motor.

[0052] The system further comprises: a bypass valve; one end of the bypass valve is connected to the output end of the exhaust sealing valve, and the other end of the bypass valve is connected to the output end of the intercooler.

[0053] The system also includes: a pressure sensor; the pressure sensor is provided at the air inlet and the exhaust port of the fuel cell stack to detect the air inlet pressure and the exhaust pressure of the fuel cell stack; the variable cross-section expander adjusts the variable cross-section opening according to the air inlet pressure and the exhaust pressure, thereby realizing the adjustment of the exhaust back pressure.

[0054] The system also includes: a flow meter and a temperature sensor; the flow meter is arranged at the air inlet of the air compressor to detect the intake air flow rate; the temperature sensor is arranged at the air inlet of the fuel cell stack to detect the intake air temperature; the intercooler is connected to the flow meter and the temperature sensor signal, and operates and controls according to the intake air temperature and the intake air flow rate to cool the intake air temperature to within the set temperature range.

[0055] It can be seen that the present invention provides an exhaust energy recovery control system for fuel cells, which uses a variable cross-section expander coaxially arranged with the compressor in the air compressor, so that the stack exhaust provides rotational power to the compressor through the expander to reduce the power consumption of the air compressor motor, and adjusts the exhaust back pressure in the fuel cell system through the variable cross-section opening. The problem of energy waste in the stack exhaust of the existing hydrogen fuel cell system can be solved, the energy recovery efficiency of the electric propulsion exhaust can be improved, and the power of the fuel cell system can be improved.

[0056] Accordingly, if Figure 2 and Figure 3 As shown, the present invention also provides an exhaust energy recovery control method for a fuel cell, using the above control system, comprising:

[0057] S1: Obtaining a required operating condition of the fuel cell system, and determining an exhaust flow requirement and an exhaust back pressure requirement according to the required operating condition;

[0058] S2: adjusting the variable cross-section opening of the variable cross-section expander according to the exhaust flow demand and the exhaust back pressure demand of the working condition to adjust the exhaust back pressure of the fuel cell system, and enabling the expander to provide power to the compressor of the air compressor to reduce the power consumption of the air compressor motor.

[0059] The method further includes:

[0060] When the fuel cell system is working, the stack current is calculated based on the power demand of the fuel cell system and the polarization characteristic curve.

[0061] The air flow requirement and pressure setting value under the stack current are calculated by looking up the table according to the stack air operating conditions, and then the air compressor speed and the variable cross-section opening of the expander are controlled according to the air compressor Map and calibration results.

[0062] The method further includes:

[0063] When the fuel cell system is started, it first enters the self-check mode to check whether the opening of each valve and the variable cross-section opening of the expander is normal. If so, a cold start purge or a normal start purge is performed.

[0064] When entering the self-check mode, the stop valve, the exhaust sealing valve and the bypass valve are opened for 1 second and then closed to perform a self-check on whether the valve body opening is normal, and the variable section opening of the variable section expander is swung from minimum to maximum 3 times to perform a self-check on whether the expander opening is normal.

[0065] When performing cold start purging, the shut-off valve, the exhaust sealing valve and the bypass valve are all opened to 100% and the air compressor is operated at the first speed R1.

[0066] During normal startup purging, the shutoff valve, the exhaust sealing valve and the bypass valve are all opened to 100% and the air compressor is operated at a second speed R2, which is greater than the first speed R1.

[0067] The method further includes:

[0068] Determine whether the fuel cell system is successfully started. If not, it will be shut down by default, and the air compressor, stop valve, exhaust sealing valve and bypass valve will be closed. If it is, normal operation control will be carried out.

[0069] During normal operation, determine whether a shutdown command is received. If so, determine whether it is an emergency shutdown, low-temperature shutdown, or normal-temperature shutdown.

[0070] The method further includes:

[0071] When the fuel cell system is shut down, the cathode and anode of the stack are purged separately. When the cathode is purged, the air compressor speed is controlled to operate at the third speed R3. At this time, the stop valve is fully open, the bypass valve is closed, and the variable cross-sectional opening of the expander is set to the maximum, so that the air can purge the entire stack gas path.

[0072] After the cathode purge is completed, the cathode is sealed, the stop valve and the exhaust sealing valve are all closed, and the cathode air path is sealed. The air compressor still runs at the third speed R3, and the bypass valve is fully open. At this time, the variable cross-sectional opening of the expander is the default opening, providing a certain flow of air through the bypass valve to enter the tail exhaust dilution hydrogen.

[0073] After the gas supply to the fuel cell stack is stopped, the air remaining inside the fuel cell is gradually consumed through small current power generation. When the output voltage of the fuel cell is lower than 220V, that is, the average voltage of the single cell is lower than 0.59V, the load is disconnected and the battery no longer outputs power to the outside.

[0074] When the anode purge is completed, the shutdown is completed. In the shutdown and power-off state, the stop valve and the exhaust sealing valve are both fully closed. Prevent ambient air from entering the fuel cell stack during shutdown.

[0075] It can be seen that the present invention provides an exhaust energy recovery control method for a fuel cell, which adjusts the variable cross-section opening of a variable cross-section expander according to the exhaust flow demand and exhaust back pressure demand of the working condition to adjust the exhaust back pressure of the fuel cell system, and enables the expander to provide power to the compressor of the air compressor to reduce the power consumption of the air compressor motor. The problem of energy waste in the exhaust of the existing hydrogen fuel cell system can be solved, the energy recovery efficiency of the electric propulsion exhaust can be improved, and the power of the fuel cell system can be improved.

[0076] The above describes in detail the structure, features and effects of the present invention based on the embodiments shown in the drawings. The above is only a preferred embodiment of the present invention, but the present invention is not limited to the scope of implementation shown in the drawings. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which still do not exceed the spirit covered by the description and drawings, should be within the protection scope of the present invention.

Claims

1. An exhaust energy recovery control system for a fuel cell, characterized in that: include: Air compressor, variable area expander, intercooler, stop valve and exhaust sealing valve; The variable cross-section expander is coaxially arranged with the compressor of the air compressor, the output end of the air compressor is connected to the input end of the intercooler, the output end of the intercooler is respectively connected to one end of the stop valve, the other end of the stop valve is connected to the air inlet of the fuel cell stack, the exhaust port of the fuel cell stack is connected to one end of the exhaust sealing valve, and the other end of the exhaust sealing valve is connected to the input end of the variable cross-section expander; The variable cross-section expander adjusts the variable cross-section opening according to the power of the fuel cell stack to adjust the exhaust back pressure of the fuel cell system, and allows the exhaust of the fuel cell stack to smoothly drive the impeller of the variable cross-section expander to rotate, thereby providing power for the rotation of the compressor impeller and reducing the power consumption of the air compressor motor.

2. The exhaust energy recovery control system for a fuel cell according to claim 1, characterized in that: Also includes: Water distributor; The water separator is arranged between the exhaust sealing valve and the variable cross-section expander, the input end of the water separator is connected to the output end of the exhaust sealing valve, the output end of the water separator is connected to the input end of the variable cross-section expander, and the drainage end of the water separator is connected to the output end of the variable cross-section expander; The water separator is used to remove water from the exhaust gas of the fuel cell stack to reduce the moisture content of the exhaust gas of the fuel cell stack entering the variable cross-section expander.

3. The exhaust energy recovery control system for a fuel cell according to claim 2, characterized in that: Also includes: Bypass valve; One end of the bypass valve is connected to the output end of the exhaust sealing valve, and the other end of the bypass valve is connected to the output end of the intercooler.

4. The exhaust energy recovery control system for a fuel cell according to claim 3, characterized in that: Also includes: Pressure sensor; The pressure sensors are provided at the air inlet and the exhaust port of the fuel cell stack to detect the air inlet pressure and the exhaust pressure of the fuel cell stack; The variable cross-section expander adjusts the variable cross-section opening according to the intake pressure and the exhaust pressure, thereby achieving the adjustment of the exhaust back pressure.

5. The exhaust energy recovery control system for a fuel cell according to claim 4, characterized in that: Also includes: Flow meters and temperature sensors; The flow meter is arranged at the air inlet of the air compressor and is used to detect the air intake flow rate; The temperature sensor is arranged at the air inlet of the fuel cell stack and is used to detect the air inlet temperature; The intercooler is connected to the flow meter and the temperature sensor signal, and is operated and controlled according to the intake air temperature and the intake air flow rate to reduce the intake air temperature to within a set temperature range.

6. An exhaust energy recovery control method for a fuel cell, using the control system according to claim 5, characterized in that: include: Obtaining a required operating condition of the fuel cell system, and determining an operating exhaust flow requirement and an exhaust back pressure requirement according to the required operating condition; The variable cross-section opening of the variable cross-section expander is adjusted according to the exhaust flow demand and the exhaust back pressure demand of the operating condition to adjust the exhaust back pressure of the fuel cell system, and the expander provides power to the compressor of the air compressor to reduce the power consumption of the air compressor motor.

7. The exhaust energy recovery control method for a fuel cell according to claim 6, characterized in that: Also includes: When the fuel cell system is working, the stack current is calculated based on the power demand of the fuel cell system and the polarization characteristic curve; The air flow requirement and pressure setting value under the stack current are calculated by looking up the table according to the stack air operating conditions, and then the air compressor speed and the variable cross-section opening of the expander are controlled according to the air compressor Map and calibration results.

8. The exhaust energy recovery control method for a fuel cell according to claim 7, characterized in that: Also includes: When the fuel cell system is started, it first enters the self-check mode to check whether the opening of each valve and the variable cross-section opening of the expander is normal. If so, a cold start purge or a normal start purge is performed; When entering the self-check mode, the stop valve, the exhaust sealing valve and the bypass valve are opened for 1 second and then closed to perform a self-check on whether the valve body is opened normally, and the variable cross-sectional opening of the variable cross-sectional expander is swung from the minimum to the maximum for 3 times to perform a self-check on whether the expander is opened normally; During the cold start purge, the stop valve, the exhaust sealing valve and the bypass valve are opened to 100%, and the air compressor is operated at the first speed R1; During normal startup purging, the shutoff valve, the exhaust sealing valve and the bypass valve are all opened to 100% and the air compressor is operated at a second speed R2, which is greater than the first speed R1.

9. The exhaust energy recovery control method for a fuel cell according to claim 7, characterized in that: Also includes: Determine whether the fuel cell system is successfully started. If not, the system is shut down by default, and the air compressor, stop valve, exhaust sealing valve and bypass valve are all closed. If yes, normal operation control is performed; During normal operation, determine whether a shutdown command is received. If so, determine whether it is an emergency shutdown, low-temperature shutdown, or normal-temperature shutdown.

10. The exhaust energy recovery control method for a fuel cell according to claim 9, characterized in that: Also includes: When the fuel cell system is shut down, the cathode and anode of the stack are purged separately. When the cathode is purged, the air compressor speed is controlled to operate at the third speed R3. At this time, the stop valve is fully open, the bypass valve is closed, and the variable cross-section opening of the expander is set to the maximum, so that the air can purge the entire gas path of the stack; After the cathode purge is completed, the cathode is sealed, the stop valve and the exhaust sealing valve are all closed, the cathode air path is sealed, the air compressor is still running at the third speed R3, the bypass valve is fully open, and the variable cross-section opening of the expander is the default opening, providing a certain flow of air to enter the tail exhaust through the bypass valve to dilute the hydrogen; After the gas supply to the stack is stopped, the remaining air inside the fuel cell is gradually consumed by generating electricity with a small current. When the output voltage of the fuel cell is lower than 220V, the load is disconnected and the battery no longer outputs power to the outside. When the anode purge is completed, the shutdown is completed. In the shutdown and power-off state, the stop valve and the exhaust sealing valve are both in the fully closed state.

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