Patent Application
20160079620
This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2014-0122526 filed on Sep. 16, 2014, the entire contents of which are incorporated herein by reference.
(a) Technical Field
The present disclosure relates to a hydrogen purging device and method for a fuel cell system. More particularly, it relates to a hydrogen purging device and method which increase the hydrogen utilization factor of a fuel cell and the efficiency of a fuel cell system.
(b) Background Art
A fuel cell system applied to a hydrogen fuel cell vehicle, a type of environmentally friendly vehicle, includes a fuel cell stack configured to generate electrical energy from an electrochemical reaction of reactant gases (e.g., hydrogen as a fuel and oxygen as an oxidizer), a hydrogen supply device configured to supply hydrogen as a fuel to the fuel cell stack, an air supply device configured to supply air including oxygen to the fuel cell stack, a heat and water management system configured to adjust the operating temperature of the fuel cell stack and perform a water management function, and a fuel cell system controller configured to operate the fuel cell system.
High-pressure hydrogen supplied from the hydrogen tank 21 of the hydrogen supply device sequentially passes through the high pressure/low pressure regulators (not shown) and is then supplied at lower pressure to a fuel cell stack 10. In the hydrogen recirculation device, an ejector 25 and/or a recirculation blower is installed in a recirculation line 24 to recirculate non-reaction hydrogen remaining after being used in a hydrogen electrode (anode) of the fuel cell stack 10 to the anode, to thus promote reuse of the hydrogen. The air supply device is configured to humidify air supplied by the air blower 31 through the humidifier 32 and then supply the humidified air to the fuel cell stack 10.
Meanwhile, in the fuel cell system, nitrogen in the air supplied to an air electrode (cathode) and water (water and stem) generated in the cathode are crossed over through an electrolytic membrane inside the stack to move to the anode based on the operation of the fuel cell stack 10. In particular, the nitrogen deteriorates the performance of the stack by reducing the partial pressure of the hydrogen, and the generated water obstructs movement of the hydrogen by blocking the flow path of a separating plate channel. Therefore, the nitrogen in the air and liquid droplets in the channel, which are crossed over, should be removed through periodic purging of the anode, to maintain stable performance of the stack.
In a fuel cell system, as the quantity of foreign matters such as nitrogen, water and steam, which are crossed over to the anode through the electrolytic membrane inside the stack, increases, the amount of hydrogen in the anode decreases, and therefore, the reaction efficiency decreases. Accordingly, a hydrogen purge valve 40 is opened based on a predetermined period to perform a purge. In other words, oxygen of the anode is periodically exhausted by installing the hydrogen purge valve 40 configured to purge hydrogen in an exit (e.g., exhaust) side line of the anode of the fuel cell stack 10, to exhaust and remove foreign matters such as moisture and nitrogen of the separating plate in the fuel cell stack 10 and to increase hydrogen utilization factor.
As the foreign matters in the fuel cell stack are exhausted as described above, hydrogen concentration may be increased to increase hydrogen utilization factor, and to improve gas diffusivity and reactivity. The hydrogen purge valve 40 is an electronic control valve periodically opened/closed based on a command of a fuel cell system controller (not shown) to manage hydrogen concentration. When the hydrogen purge value 40 is opened, the foreign matters such as moisture and nitrogen in the fuel cell stack 10 are exhausted to the air through a vehicle exhaust pipe 34. When the hydrogen purge valve 40 is opened while a vehicle is being driven, hydrogen can be exhausted to the air through the rear end of the cathode, an air exhaust line 33 and the exhaust pipe 34 due to a difference in pressure between the anode (relatively high pressure) and the cathode of the fuel cell stack 10. In particular, foreign matters are exhausted together with the hydrogen, and thus the output of the fuel cell stack can be maintained.
In the hydrogen purge, as shown in
As a result, the hydrogen recirculation performance decreases due to an increase in the amount of nitrogen recirculated, and the Stoichiometry ratio (hereinafter, referred to as “SR”) of hydrogen decreases. In particular, the SR of hydrogen may be calculated by measuring an anode entrance hydrogen concentration and an anode exit hydrogen concentration of the stack and using the following expressions.
wherein, X represents a supply amount of hydrogen, Y represents a recirculation amount of nitrogen, and C represents a theoretical use amount of hydrogen (non-consideration of crossover).
When the purge reference is an operating temperature (e.g., static current condition of the stack) as shown in
When the purge reference is the operating temperature as shown in
Accordingly, stack current, stack operating temperature, stack operating pressure, and the like should be considered simultaneously when the purge period is determined. In the fuel cell system, the difference in pressure between the anode and cathode of the stack increases when the stack current increases. Particularly, the amount of heat generated in the stack increases, and therefore, the stack operating temperature increases. In particular, when the cooling performance of the fuel cell system is deficient, the stack operating temperature further increases, and therefore, the stack performance decreases. When the stack current increases to obtain a greater output, the difference in pressure between the anode and cathode of the stack additionally increases.
Furthermore, when the stack voltage decreases due to an increase in stack current, current limit control for decreasing the stack current and output is performed to protect the stack, and therefore, the difference in pressure between the anode and cathode of the stack and the stack operating temperature decrease. Accordingly, fuel cell operating states such as stack current, stack operating temperature and stack operating pressure are related to one another and changed in real time. Thus, when the optimal purge charge amount is derived in each operating state and then applied to hydrogen purge control, it may be possible to improve hydrogen recirculation performance and system efficiency.
The present invention provides a hydrogen purging device and method for a fuel cell system, in which the opening/closing of a hydrogen purge valve may be variably controlled based on a purge charge amount depending on an operating state of a fuel cell in the fuel cell system, to improve the hydrogen utilization factor of the fuel cell, system efficiency, hydrogen circulation performance, and the like.
In one aspect, the present invention provides a hydrogen purging device for a fuel cell system that may include: an operating state detector configured to detect an operating state of a fuel cell stack; a controller configured to determine an opening time of a hydrogen purge valve based on information regarding the stack operating state detected by the operating state detector, and output a control signal to open the hydrogen purge valve; and the hydrogen purge valve opened to hydrogen purge of the fuel cell stack in response to the control signal output from the controller. The controller may be configured to obtain every predetermined accumulation period, a variable purge charge amount that corresponds to a current stack operating state from a map, calculate a charge amount for a time period the accumulation period using a predetermined reference purge charge amount, perform accumulation by accumulating the calculated charge amount every accumulation period, and then determine the opening time of the hydrogen purge valve by comparing the accumulated charge amount with the reference purge charge amount.
In another aspect, the present invention provides a hydrogen purging method for a fuel cell system that may include: receiving and monitoring an operating state detected in real time from an operating state detector of a fuel cell stack; obtaining, every predetermined accumulation period, a variable purge charge amount that corresponds to a current stack operating state from a map; calculating a charge amount for a time period the accumulation period using a predetermined reference purge charge amount, and performing accumulation by accumulating the calculated charge amount every accumulation period; and determining an opening time of a hydrogen purge valve by comparing the accumulated charge amount with the reference purge charge amount, and opening the hydrogen purge value at the opening time.
Accordingly, in the hydrogen purging device and method for the fuel cell system according to the present invention, the opening/closing of the hydrogen purge valve may be variably controlled based on a purge charge amount depending on an operating state of the fuel cell in the fuel cell system, to improve the hydrogen utilization factor of the fuel cell, system efficiency, hydrogen circulation performance, and the like.
The above and other features of the present invention will now be described in detail with reference to exemplary embodiments thereof illustrated the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present invention, and wherein:
It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.
It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.
Although exemplary embodiment is described as using a plurality of units to perform the exemplary process, it is understood that the exemplary processes may also be performed by one or plurality of modules. Additionally, it is understood that the term controller/control unit refers to a hardware device that includes a memory and a processor. The memory is configured to store the modules and the processor is specifically configured to execute said modules to perform one or more processes which are described further below.
Furthermore, control logic of the present invention may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, controller/control unit or the like. Examples of the computer readable mediums include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards and optical data storage devices. The computer readable recording medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion, e.g., by a telematics server or a Controller Area Network (CAN).
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”
Hereinafter reference will now be made in detail to various exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.
The present invention provides a hydrogen purging device and method for a fuel cell system, in which the opening/closing of a hydrogen purge valve may be variably controlled based on a purge charge amount depending on an operating state of a fuel cell in the fuel cell system to improve the hydrogen utilization factor of the fuel cell, system efficiency, hydrogen circulation performance, and the like.
First, as shown in
Therefore, the operating state detectors (e.g., sensors) may be an operating temperature detector 1 and a stack current detector 2. Alternatively, the operating state detectors may be an operating pressure detector and the stack current detector. The operating temperature detector 1 may be a sensor configured to detect a stack temperature. More specifically, the operating temperature detector 1 may be a temperature sensor configured to detect a cooling water temperature of a stack entrance or stack exit (e.g., exhaust). The operating pressure detector may be a pressure sensor configured to detect an operating pressure of the stack, and the stack current detector 2 may be a current sensor.
As known in the art, the controller 3 configured to operate the fuel cell system, i.e., the fuel cell system controller may be configured to obtain, in real time, a current operating state of the fuel cell stack, e.g., information regarding stack current, stack operating temperature, stack operating pressure, or the like through sensors, and operate devices in various types of systems, using information regarding the obtained operating state as an input variable.
In the present invention, the controller 3 may be configured to execute a hydrogen purge operation, i.e., an operation of the hydrogen purge valve 4, using information regarding an operating state obtained in real time during operation of the fuel cell system and the fuel cell stack. Referring to
In particular, the stack operating pressure may be applied as the stack operating state, in place of the stack operating temperature. The controller 3 may be configured to perform update by obtaining, every accumulation period (e.g., 100 msec), a variable purge charge amount based on the stack operating temperature and stack current obtained in real time from map data information, and reflect the obtained variable purge charge amount in current accumulation as follows. In other words, the controller 3 may be configured to calculate, every accumulation period, a charge amount (e.g., current amount) for a time that corresponds to the accumulation period, using the obtained variable purge charge amount, the stack current, and a predetermined reference purge charge amount using a predetermined calculation expression, and accumulate the calculated charge amount every accumulation period.
The controller 3 may further be configured to open the hydrogen purge valve 4 by turning on the hydrogen purge valve 4 when the charge amount accumulation value is greater than the reference purge charge amount by comparing the accumulation value with the reference purge charge amount, and then initialize the charge amount (Q). When the accumulation value is less than the reference purge charge amount, the charge amount calculation and accumulation may be continued, and the hydrogen purge value may be opened when the accumulation value is greater than the reference purge charge amount. In particular, the opening time of the hydrogen purge valve may be a previously set predetermined time, or may be a time determined based on stack current. The hydrogen purge and the control process thereof may be repeatedly performed during operation of the fuel cell stack.
Meanwhile, the reference purge charge amount may be a value obtained through a prior test repeatedly performed on the fuel cell system. The reference purge charge amount may be previously selected as a value that satisfies exit hydrogen concentration or hydrogen SR, determined by considering durability performance of the fuel cell stack, and enables the system to be operated. In the control process, the variable purge charge amount used in the charge amount calculation may be obtained from the stack operating temperature (or stack operating pressure) that is information regarding a real-time operating state of the fuel cell stack during driving of a vehicle, using map data information stored in the controller.
The map data will be described in detail. The map data may be formed by mapping the variable purge charge amount based on an operating condition of the fuel cell stack, i.e., the stack operating temperature (stack operating pressure) and the stack current. In particular, a variable purge charge amount for each operating condition may be obtained through a prior test repeatedly performed on the fuel cell system. Additionally, a hydrogen purge charge amount may be selected and used, which satisfies exit hydrogen concentration or hydrogen SR that represents the maximum durability performance of the stack for each operating condition (stack operating temperature or stack operating pressure and stack current) of the fuel cell stack.
As described above, a difference may occur in the exit hydrogen concentration and the hydrogen SR based on an operating state of the stack, i.e., stack current and stack operating temperature as shown in
As shown in
Accordingly, the purge charge amount may be related to the exit hydrogen concentration and the hydrogen SR in the operation of the fuel cell stack. Thus, the optimal purge charge amount for each operating condition (e.g., stack operating temperature or stack operating pressure and stack current) may be selected and mapped based on the exit hydrogen concentration or hydrogen SR that satisfies durability performance through the prior test in the formation of map data for determining the purge charge amount.
Referring to
For example, a hydrogen purge charge amount of about 4000 C, which is a condition satisfying a stack operating temperature of about 60° C., a stack current about 50 A and an exit hydrogen concentration of about 80% in a vehicle as a stack operating reference, may be set as a reference purge charge amount. As a result, according to the map data described above, update may be performed by obtaining, in real time, a variable purge charge amount that corresponds to an operating state of the fuel cell stack, monitored in real time, i.e., a current stack operating temperature (or stack operating pressure) and stack current, and the updated variable purge charge amount may be reflected in current accumulation.
The charge amount accumulation process in the control process of
Charge amount=current (A)×time (sec) of accumulation period×a(C)/b(C)
wherein, a represents a reference purge charge amount, b represents a variable purge charge amount, and a/b represents a variable purge factor.
For example, when the reference purge charge amount is about 4000 C when the accumulation period is set as about 100 msec as shown in
The accumulation may be performed by accumulating in real time charge amounts calculated every accumulation period as described above, and the accumulation value may then be compared with the reference purge charge amount. When the accumulation is greater than the reference purge charge amount, the hydrogen purge valve may be turned on, thereby performing hydrogen purge variable control. The accumulation of charge amounts is expressed as follows.
Accumulation value=Σ(current×accumulation time×a/b)
As described above, according to the hydrogen purging device and method of the present invention, the opening of the hydrogen purge valve may be determined using a purge charge amount varied based on an operating state of the fuel cell stack, to improve the hydrogen utilization factor of the fuel cell and the efficiency of the fuel cell system compared to the conventional art in which the purge charge amount is fixed.
The invention has been described in detail with reference to exemplary embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2014-0122526 | Sep 2014 | KR | national |
