CONSTANT VOLTAGE CONTROL METHOD AND SYSTEM OF A FUEL CELL VEHICLE

Abstract

Constant voltage control method for a fuel cell vehicle, comprising: Determine, via a control unit, whether vehicle status information meets a cold start condition when the fuel cell vehicle is started; Starting, by the control unit, of a constant voltage regulator on a fuel cell, when the vehicle status information meets the cold start condition; Compare, by the control unit, the rotational speed of an air blower for supplying air to the fuel cell with a predefined control stop condition; and The constant voltage control unit of the fuel cell terminates when the speed of the air blower meets the specified control stop condition.

Description

BACKGROUND 1. Technical field

[0001] The present invention relates to a constant voltage control method and system of a fuel cell vehicle which can prevent an overflow that can occur under constant voltage control when the temperature of a fuel cell stack is increased at the time of a cold start. 2. Description of the state of the art

[0002] A fuel cell vehicle equipped with a fuel cell system generates electricity by supplying hydrogen, which serves as fuel for a fuel cell stack, and is powered by an electric motor driven by the electricity generated by the fuel cell stack. The fuel cell system is a type of power generation system that converts the chemical energy of the fuel directly into electrical energy, rather than heat, through an electrochemical process within the fuel cell stack.

[0003] In the fuel cell system, highly purified hydrogen is supplied to an anode of a fuel cell from a hydrogen tank during operation, and atmospheric air is supplied directly to a cathode of the fuel cell by an air supply device such as an air blower.

[0004] The hydrogen supplied to the fuel cell stack is decomposed into hydrogen ions and electrons by a catalyst at the anode, and the hydrogen ions flow through a polymer electrolyte membrane to the cathode, while the oxygen supplied to the cathode combines with the electrons that reach the cathode through an external conducting wire, thereby producing water and generating electricity.

[0005] Meanwhile, unreacted hydrogen and condensate produced by water flowing from the cathode are released at the anode of the fuel cell, where the unreacted hydrogen is fed to the fuel cell stack and the condensate is held in a water separator and released to the outside.

[0006] However, it is impossible to completely remove the condensation, so generating voltage when starting a fuel cell vehicle that has been parked at sub-zero temperatures can be more difficult than when starting the vehicle at room temperature due to the cooling of the condensation remaining in the fuel cell. Specifically, if the fuel cell is cooled, the remaining condensation is also cooled, and consequently, fuel gases become blocked by ice and cannot reach the reaction zone.

[0007] Accordingly, many technologies have been developed to prevent such overflows. For example, a fuel cell system that includes an auxiliary purge valve capable of quickly thawing a purge valve and a hydrogen return valve can prevent energy consumption by a low-voltage battery for heating valves and a deterioration in cold-start reliability, and can start an internal combustion engine faster and more efficiently.

[0008] The description provided above as the prior art of the present invention is intended only to promote an understanding of the background of the present invention and should not be interpreted as being included in the prior art known to a person skilled in the art. SUMMARY

[0009] An object of the present invention is to provide a constant voltage control method and system for a fuel cell vehicle that can prevent overflow in a fuel cell due to a reduction in the throughput of air supplied to an air blower when constant voltage control is performed to maintain a fuel cell temperature at the time of a cold start.

[0010] To solve the problem of the present invention, a constant voltage control method for a fuel cell vehicle according to one embodiment of the present invention comprises: determining, by a control unit, whether vehicle state information (or vehicle state information) meets a cold start condition when the fuel cell vehicle is started; starting, by the control unit, a constant voltage control of a fuel cell when the vehicle state information meets the cold start condition; comparing, by the control unit, a rotational speed (revolutions per minute - RPM) of an air blower for supplying air to the fuel cell with a predetermined control stop condition; and terminating, by the control unit, the constant voltage control of the fuel cell when the rotational speed of the air blower meets the predetermined control stop condition.

[0011] The cold start condition can occur if an internal fuel cell stack temperature, which is included in the vehicle state information, is a specified temperature or lower.

[0012] The procedure may further include: after starting the constant voltage control, estimating / estimating, by the control unit, a minimum required calorific value based on the vehicle state information; and continuing the constant voltage control, by the control unit, until a calorific value of the fuel cell, accumulated from the start of the vehicle, exceeds the minimum required calorific value.

[0013] The minimum required heating value can be estimated based on the temperature, current and voltage of the fuel cell when the vehicle is started.

[0014] The procedure may further include: comparing the speed of the air blower with the predetermined control stop condition, by the control unit, comparing the speed of the air blower with a predetermined control hold condition; and maintaining, by the control unit, the constant voltage control at the fuel cell when the speed of the air blower meets the predetermined control hold condition.

[0015] The control stop condition can be that the rate of change of the air blower speed is a predetermined reference rate of change or higher, and the control hold condition can be that the rate of change of the air blower speed is less than the reference rate of change.

[0016] The control stop condition can be that the detected / sampled speed of the air blower is a predetermined reference speed or lower.

[0017] A constant voltage control system for a fuel cell vehicle according to a further embodiment of the present invention comprises: a fuel cell; an air blower that supplies air to the fuel cell; and a control unit that determines whether a vehicle state information (or vehicle state information) meets a cold start condition when the fuel cell vehicle is started, starts a constant voltage control at the fuel cell when the vehicle state information meets the cold start condition, and stops the constant voltage control at the fuel cell when the speed of the air blower meets a predetermined control stop condition as a result of comparing the speed of the air blower with the predetermined control stop condition.

[0018] The control unit can compare the speed of the air blower with a predefined control holding condition before comparing the speed of the air blower with a predefined control stop condition and can maintain constant voltage control at the fuel cell if the speed of the air blower meets the predefined control holding condition.

[0019] The control stop condition can be that the rate of change of the air blower speed is a predetermined reference rate of change or higher, and the control hold condition can be that the rate of change of the air blower speed is less than the reference rate of change.

[0020] A non-volatile, computer-readable medium containing program instructions / program directives that are executed by a processor includes: program instructions that determine whether a vehicle state information (or vehicle state information) meets a cold start condition when a fuel cell vehicle is started; program instructions that initiate constant voltage control at a fuel cell if the vehicle state information meets the cold start condition; program instructions that compare the rotational speed of an air blower used to supply air to the fuel cell with a predetermined control stop condition; and program instructions that terminate constant voltage control at the fuel cell if the rotational speed of the air blower meets the predetermined control stop condition.

[0021] In contrast to the prior art, where constant voltage regulation is carried out independently of the amount of air supplied by the air blower, the present invention terminates constant voltage regulation when there is a high probability of a fuel cell overflow. Because a small amount of air is supplied by an air blower, it is possible to prevent the fuel cell from overflowing, and consequently, it is possible to improve the durability and efficiency of the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other tasks, features, and advantages of the present disclosure will become clearer from the following detailed description in conjunction with the accompanying drawings. The figures show: Fig. 1 a voltage, current and air blower speed graph during the performance of a constant voltage control of a fuel cell stack according to an embodiment of the present invention; Fig. 2 a graph showing a change in the power output of a fuel cell stack according to an embodiment of the present invention; Fig. 3 a flowchart illustrating a constant voltage control method of a fuel cell vehicle according to an embodiment of the present invention; and Fig. 4 a view showing the configuration / arrangement of a constant voltage control system of a fuel cell vehicle according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] It is understood that the term "vehicle" or "vehicle-" or other equivalent terms as used herein include motor vehicles in general, such as passenger cars including sports utility vehicles (SUVs), buses, trucks, various utility vehicles, watercraft including a variety of boats and ships, aircraft and the like, and include hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other vehicles powered by alternative fuels (for example, fuel derived from sources other than petroleum). As referenced herein, a hybrid vehicle is a vehicle that has two or more sources of propulsion, such as both gasoline-powered and electric-powered vehicles.

[0024] The terminology used herein is intended for the purpose of describing certain embodiments and is not intended to limit the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It is further understood that the expressions "possess" and / or "possessing," when used in this description, describe the presence of the specified features, numbers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more features, numbers, steps, operations, elements, components, and / or groups thereof. As used herein, the expression "and / or" includes any and all combinations of one or more of the associated listed elements.Throughout this description, unless explicitly stated otherwise, the word "include / include" and variations such as "includes / includes" or "including / including" are understood to mean the inclusion of the specified elements, but not the exclusion of any other elements. Furthermore, the terms "-unit," "-device" ("-er," "-or"), and "-module" as used in this description refer to units for processing at least one function or operation and may be realized / implemented by hardware components or software components and combinations thereof.

[0025] Furthermore, the control logic of the present invention can be implemented as non-volatile, computer-readable media on a computer-readable medium comprising executable program instructions that are executed by a processor, a controller / control unit, or the like. Examples of computer-readable storage media include, without limitation, 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 decentralized in network-connected computer systems, so that the computer-readable medium is stored and executed in a distributed manner, e.g., by a telematics server or a controller area network (CAN).

[0026] Preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0027] When an internal combustion engine with a fuel cell stack 10 is started at a lower temperature, it is necessary to increase the temperature of the fuel cell stack 10 to deliver the power output desired by the user. Accordingly, when a vehicle equipped with a fuel cell 10 is started at a low temperature, the vehicle enters a normal driving mode but is started in a low-temperature start mode to increase the temperature of the fuel cell stack 10. There are many ways to increase the temperature of a stack, one of which is constant voltage regulation, where the output voltage of the fuel cell 10 is maintained at a predetermined level.

[0028] In general, the fuel cell 10 is operated at a predetermined voltage by regulating / controlling the air supply at a constant voltage, making it difficult to estimate the temperature increase of the fuel cell 10. Therefore, in the prior art, constant voltage control is terminated when it is determined that a reference level of a heating value, previously determined to be suitable through repeated experimentation, has been exceeded. However, constant voltage control can be terminated without a sufficient temperature increase, and in some cases, an overflow in the fuel cell 10 stack occurs due to a delayed termination of the constant voltage control.

[0029] Therefore, to solve these problems, the present invention proposes a method for determining the time at which the constant voltage control should be terminated by using the change in rotational speed (revolutions per minute - RPM) of the air blower 20 over the time (or over time) of the constant voltage control. The reason for selecting the rotational speed of the air blower as a reference for determining whether the constant voltage control should be terminated is shown in the graph in Fig. 1 is evident.

[0030] The graph in Fig. Figure 1 shows changes in the current and voltage of fuel cell 10 and the rotational speed of air blower 20 during constant voltage control. As can be seen from the graph, there is no large change in the current and voltage of fuel cell 10, but the rotational speed of air blower 20 decreases in the early phase (section 1) of constant voltage control, is maintained in the middle section (section 2), and increases in the last section (section 3). Therefore, it can be seen from the graph in Fig. 1 It is evident that it is possible to distinguish between sections ①, ② and ③ using the change in the speed of the air blower 20 during the constant voltage control.

[0031] The problem is the state of the stack power of fuel cell 10 in sections 1, 2, and 3, which can be seen from the graph of the change in stack power in Fig. 2 can be seen. As described above, an improvement in the performance of fuel cell 10 due to a temperature increase and a decrease in the performance of fuel cell 10 due to an overflow are factors that influence the fuel cell's stack power at the time of a cold start. Accordingly, it shows Fig. 2 shows both a graph of the change in stacking power as a function of the temperature increase and a graph of the change in stacking power due to an overflow, and further shows a graph of the change in stacking power as a function of both a temperature increase and an overflow.

[0032] The maximum stack power point is the point where the stack power is highest in the stack power change graph, taking into account both temperature increases and overflow, and where the efficiency of the constant voltage control of the fuel cell 10 stack is maximized. Therefore, the question arises as to which of sections ①, ②, and ③ maximizes the stack power. If a deterioration in stack power due to overflow is a concern, control / regulation to remove water from the stack is generally implemented by increasing the speed of the air blower in fuel cell 10. Thus, it is possible to estimate that the boundary point between section ② and section 3, where the speed of the air blower 20 begins to increase, is the point where the stack power is maximized.

[0033] The present invention provides a static voltage control method for a vehicle equipped with a fuel cell 10, which can optimize the stacking power of the fuel cell 10 based on the theory described above, comprising a cold start condition determination step (S10) in which a control unit 30 determines whether a vehicle state information (or vehicle state information) meets a cold start condition when the vehicle equipped with the fuel cell 10 is started, as described in Fig. Figure 3 shows. The constant voltage control according to the present invention corresponds to the case in which constant control is required under a cold start condition, so that the cold start condition determination step (S10) determines whether a vehicle state information fulfills a cold start condition before a constant voltage control is started.

[0034] According to the present invention, the cold-start condition is that the internal stack temperature is at or below a predetermined reference temperature. However, directly estimating the internal stack temperature is difficult, so it may be possible to consider a method for indirectly estimating the internal stack temperature from the temperature of the stack's cooling water. The longer the vehicle is stopped, the greater the difference between the stack's cooling water temperature and the internal stack temperature, making it possible to estimate the internal stack temperature by taking into account the time the vehicle has been stopped. The temperature reference can vary depending on the vehicle's performance and the requirements of a designer.

[0035] When the vehicle state information meets the cold start condition, a constant voltage control start step (S20) is performed to increase the stack temperature of the fuel cell 10. When the constant voltage control is started as described above, the speed of the air blower 20 determines whether the constant voltage control should be maintained or stopped. In the present invention, it is assumed that the cumulative heating value attributable to the increase in the stack temperature of the fuel cell 10 exceeds a minimum value before the constant voltage control is stopped based on the speed of the air blower 20.

[0036] This is because the first action to be taken during a cold start of the fuel cell 10 stack is to increase the stack temperature for the fuel cell 10 in order to deliver power. Furthermore, even if overflow is accelerated by reducing the speed of the air blower 20 to raise the temperature, the overflow is also reduced by the increase in the temperature of the fuel cell 10, so it is important to first increase the stack temperature of the fuel cell 10 in the early phase of the cold start.

[0037] Accordingly, in the present invention, the minimum required calorific value is estimated from the vehicle state information(s) by the control unit 30, and the control unit 30 maintains constant voltage control until the calorific value of the fuel cell 10, accumulated from the time the vehicle is started, exceeds the minimum required calorific value. The minimum required calorific value can correspond to the minimum reference of the cumulative calorific value described above, and the cumulative calorific value of the stack can be obtained by integrating the product of the stack's output current and output voltage for a predetermined time. The minimum required calorific value can vary depending on the stack temperature of the fuel cell 10 and the vehicle's power output.

[0038] When the cumulative calorific value exceeds the minimum required calorific value, the temperature for minimum stacking power has been reached, and thereafter, constant voltage control is carried out based on the speed of the air blower 20, as described above. Specifically, according to the present invention, the control unit 30 determines whether the rate of change of the speed of the air blower 20 is a reference rate of change or higher (S30). This is because, as described above, by comparing Fig. 1 and Fig. 2, the most suitable time at which the constant voltage regulation should be terminated, the boundary point between section 2 and section 3 in Fig. Section 1 corresponds to the case where the speed of the air blower 20 increases at a predetermined rate. That is, the rate of change of the speed of the air blower 20 has a negative value in section 1, a value close to zero in section 2, and a positive value in section 3. Therefore, the case where the rate of change of the speed of the air blower 20 is a predetermined reference rate or higher is considered the reference for terminating the constant voltage control. This allows the system to determine, using the differences in values, the point at which section 2 transitions into section 3. Consequently, the reference rate of change can vary according to the implementation of the control procedure, but it must have a positive value. The small change in the speed of the air blower 20 in section 2 can be a value that can be compensated for by a difference / tolerance.

[0039] Therefore, if the rate of change of the rotational speed of the air blower 20 is the reference rate of change or higher, then section 3 in Fig. 1. During constant voltage control, it is determined that the point at which the stack power is maximized has been reached, and accordingly, a constant voltage control termination step (S60) is performed, at which the constant voltage control is terminated, as in Fig. 1 shown and carried out.

[0040] In contrast, if the rate of change of the rotational speed of the air blower 20 is less than the reference rate of change, then the rotational speed of the air blower 20 lies in section ① or section 2� in the Fig. 1 shown in the graph, so that in this case the constant voltage control can be continued and accordingly, as in Fig. As shown in Figure 1, a constant voltage control maintenance step (S40) is performed. However, even in this case, if the absolute value of the speed of the air blower 20, that is, the speed of the air blower 20, is excessively reduced so that it is equal to or less than a reference speed, it is possible to determine that this is the point in time at which the stack power is maximized. Consequently, even if the rate of change of the speed of the air blower 20 is less than the reference rate of change, as shown in Figure 1, the following applies: Fig. Figure 1 shows that the constant voltage control is completed by the constant voltage control termination step (S60).

[0041] Therefore, according to the present invention, it is possible to improve the stack performance by terminating constant voltage control at the point in time when the stack performance is maximized based on the rotational speed of the air blower 20. Furthermore, the temperature of the stack cell of the fuel cell 10 is not uniform due to a lack of circulation of the stack cooling water during a cold start, but in this case, it is possible to prevent a deterioration in the durability of the fuel cell stack 10 by continuing constant voltage control.

[0042] Furthermore, the constant voltage control system for a vehicle equipped with the fuel cell 10 according to the present invention, as described in Fig.Figure 4 shows the following components: the fuel cell 10, the air blower 20, which supplies air to the fuel cell 10, and the control unit 30, which determines whether a vehicle state information meets a cold start condition when the vehicle equipped with the fuel cell 10 is started, starts a constant voltage control of the fuel cell 10 when the vehicle state information meets the cold start condition, and stops the constant voltage control at the fuel cell 10 when the speed of the air blower 20 meets a predetermined control stop condition as a result of comparing the speed of the air blower with the predetermined control stop condition.

[0043] Although the present invention has been described with reference to certain embodiments shown in the drawings, it is obvious to a person skilled in the art that the present invention can be changed and modified in various ways without deviating from the scope of the present invention as described in the following claims.

Claims

[1] Constant voltage control method for a fuel cell vehicle, comprising: Determine, via a control unit, whether vehicle status information meets a cold start condition when the fuel cell vehicle is started; Starting, by the control unit, of a constant voltage regulator on a fuel cell, when the vehicle status information meets the cold start condition; Compare, by the control unit, the rotational speed of an air blower for supplying air to the fuel cell with a predefined control stop condition; and The constant voltage control unit of the fuel cell terminates when the speed of the air blower meets the specified control stop condition. [2] Method according to claim 1, wherein the cold start condition occurs when an internal fuel cell stack temperature, which is included in the vehicle state information, is a predetermined temperature or lower. [3] Method according to claim 1, further comprising: after starting the constant voltage control, estimating, by the control unit, a minimum required heating value based on the vehicle state information; and continuing the constant voltage control, by the control unit, until a heating value of the fuel cell, accumulated from the start of the vehicle, exceeds the minimum required heating value. [4] Method according to claim 3, wherein the minimum required heating value is estimated from a temperature, a current and a voltage of the fuel cell when the vehicle is started. [5] Method according to claim 1, further comprising: before comparing the rotational speed of the air blower with the predetermined control stop condition, The control unit compares the speed of the air blower with a predetermined control holding condition; and Maintained by the control unit, the constant voltage regulation at the fuel cell, when the speed of the air blower meets the specified control holding condition. [6] Method according to claim 5, wherein the control stop condition is that a rate of change of the rotational speed of the air blower is a predetermined reference rate of change or higher, and the control hold condition is that the rate of change of the rotational speed of the air blower is less than the reference rate of change. [7] Method according to claim 1, wherein the control stop condition is that a detected rotational speed of the air blower is a predetermined reference rotational speed or lower. [8] Constant voltage control system for a fuel cell vehicle, comprising: a fuel cell; an air blower that supplies air to the fuel cell; and a control unit that determines whether vehicle state information meets a cold start condition when the fuel cell vehicle is started, starts a constant voltage control at the fuel cell if the vehicle state information meets the cold start condition, and stops the constant voltage control at the fuel cell if the speed of the air blower meets a predetermined control stop condition as a result of comparing the speed of the air blower with the predetermined control stop condition. [9] System according to claim 8, wherein the control unit compares the speed of the air blower with a predetermined control holding condition before comparing the speed of the air blower with a predetermined control stop condition and maintains a constant voltage control at the fuel cell when the speed of the air blower meets the predetermined control holding condition. [10] System according to claim 9, wherein the control stop condition is that a rate of change of the rotational speed of the air blower is a predetermined reference rate of change or higher, and the control hold condition is that the rate of change of the rotational speed of the air blower is less than the reference rate of change. [11] Non-volatile computer-readable medium containing program instructions that are executed by a processor, comprising the computer-readable medium: Program commands that determine whether a vehicle status information meets a cold start condition when a fuel cell vehicle is started; Program commands that initiate constant voltage regulation on a fuel cell when the vehicle status information meets the cold start condition; Program commands that compare the rotational speed of an air blower supplying air to the fuel cell with a predefined control stop condition; and Program commands that terminate the constant voltage control at the fuel cell when the speed of the air blower meets the specified control stop condition.

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