System and method for controlling a temperature of a fuel cell stack

Abstract

A method for controlling a temperature of a fuel cell stack (10), comprising: Performing a pump-off mode that turns off the cooling water pump (70) or operates the cooling water pump (70) while reducing the rotational speed of the cooling water pump (70) to be less than the reference rotational speed when a cooling water outlet temperature is equal to or less than a preset first temperature, while performing a pump-normal mode that sets a rotational speed of a cooling water pump (70) to be equal to or greater than a preset reference rotational speed and changes the rotational speed (revolutions per minute - rpm) based on the cooling water outlet temperature; and Performing the pump normal mode when a cooling water outlet temperature estimate of the fuel cell stack (10) exceeds a preset second temperature while the pump OFF mode is being performed, wherein the pump OFF mode is performed when the cooling water outlet temperature is equal to or lower than the preset first temperature and an air outlet temperature of the fuel cell stack (10) is lower than a first air outlet temperature, and the pump normal mode is performed when the cooling water outlet temperature estimate exceeds the preset second temperature or the air outlet temperature of the fuel cell stack (10) exceeds a preset second air outlet temperature.

Description

BACKGROUNDField of the invention

[0001] The present invention relates to a system and method for controlling a temperature of a fuel cell stack, and more particularly to a method for controlling a temperature of a fuel cell stack by adjusting a voltage of a coolant pump and a power converter. Description of the state of the art

[0002] A fuel cell vehicle includes a fuel cell stack in which a plurality of fuel cells used as a power source are stacked, a fuel supply system that supplies hydrogen or the like, which is a fuel, to the fuel cell stack, an air supply system that supplies oxygen, which is an oxidizer required for an electrochemical reaction, a water and heat management system that adjusts a temperature of the fuel cell stack, and the like. The fuel supply system reduces a pressure of compressed hydrogen in a hydrogen tank and supplies the compressed hydrogen to an anode of the fuel cell stack, and the air supply system supplies outside air, which is sucked by operating an air blower, to a cathode of the fuel cell stack.

[0003] When hydrogen is supplied to the anode of the fuel cell stack and oxygen is supplied to the cathode of the fuel cell stack, hydrogen ions are separated by a catalytic reaction in the anode. The separated hydrogen ions are transferred to an oxidation electrode, which is the cathode, through an electrolyte membrane. The hydrogen ions separated in the anode generate an electrochemical reaction together with electrons and the oxygen in the oxidation electrode, so that electrical energy can be obtained. Specifically, electrochemical oxidation of hydrogen is generated in the anode, and electrochemical reduction of oxygen is generated in the cathode. Furthermore, electricity and heat are generated due to the movement of electrons generated by the above-mentioned process, and water vapor or water is generated by the chemical bonding of hydrogen with oxygen.

[0004] Additionally, an exhaust device is provided to exhaust hydrogen, oxygen, and the like that do not react to form byproducts such as water vapor, water, and heat generated in the electrical power generation process of the fuel cell stack, and gases such as water vapor, hydrogen, and oxygen are exhausted to the atmosphere through an exhaust path. Components such as an air blower, a hydrogen recirculation blower, and a water pump for operating the fuel cell are connected to a main bus terminal to enable fuel cell startup. The main bus terminal can be connected to various types of relays that enable power interruption and power connection, and a diode that prevents reverse current from flowing into the fuel cell.

[0005] A fuel cell system used in a hydrogen fuel cell vehicle, which is one of the environmentally friendly vehicles, is configured to include a fuel cell stack that generates electrical energy from an electrochemical reaction of reaction gas, a hydrogen supply device that supplies hydrogen, which is a fuel, to the fuel cell stack, an air supply device that supplies air including oxygen, which is an oxidizer required for an electrochemical reaction, to the fuel cell stack, a water and heat management system that optimally adjusts an operating temperature of the fuel cell stack by dissipating heat, which is a byproduct of the electrochemical reaction of the fuel cell stack, to the outside and performs a water management function, and a fuel cell controller that operates the fuel cell system.to include.,

[0006] With this configuration, the fuel cell stack generates electrical energy from the electrochemical reaction of hydrogen and oxygen, which are reaction gases, and dissipates heat and water, which are byproducts. Accordingly, the fuel cell system essentially includes a device for cooling a fuel cell stack to prevent the temperature of the fuel cell stack from rising. In particular, a polymer electrolyte membrane fuel cell (PEMFC) has the advantages of a fast start-up time and a fast power conversion response time due to a low operating temperature and high power density. However, the PEMFC requires water and must therefore operate at a temperature of approximately 100°C or less.

[0007] Generally, in a cooling system for maintaining the fuel cell stack at an optimum temperature in the fuel cell system for a vehicle, a type of water cooling is widely used, which cools the fuel cell stack by circulating water through a cooling water channel in the fuel cell stack.

[0008] A temperature control system of the fuel cell system is in Fig. 1. As shown in Fig. 1, the fuel cell system includes a cooler 60 and a fan 21 that dissipate heat from the cooling water to the outside, a cooling water pipe 31 that is arranged between a fuel cell stack 10 and the cooler 60 to circulate the cooling water, a bypass pipe 32 and a 3-way valve 33 for bypassing the cooling water to prevent cooling water from flowing through the cooler 60, and a cooling water pump 70 for pumping the cooling water and supplying the pumped cooling water through the cooling water pipe 31. Specifically, the bypass pipe 32 is a cooling water pipe that does not pass through the cooler 60 by branching off from the cooling water pipe at upstream and downstream sides of the cooler to bypass cooling water, and the 3-way valve 33 serves to selectively control a cooling water flow between a main pipe and the Bypass line 32, which does not flow through the cooler.

[0009] Meanwhile, the fuel cell stack exhibits both an overflow phenomenon, where water overflows, and a dryout phenomenon, where water is supplied in insufficient amounts. To improve these phenomena, the temperature of the fuel cell stack must be maintained within a normal range (e.g., where water does not overflow or dry out). In other words, there is a need for a method for preventing the overflow phenomenon and the dryout phenomenon by adjusting the temperature of the fuel cell stack, while simultaneously minimizing power consumption by improving the operation of the cooling water pump and the (radiator) fan.

[0010] Incidentally, US 2012 / 0 122 004 A1 discloses a method for controlling a temperature of a fuel cell stack, comprising: performing a pump-off mode that turns off the cooling water pump or operates the cooling water pump while reducing the rotational speed of the cooling water pump to be less than the reference rotational speed when a cooling water outlet temperature is equal to or less than a preset first temperature, while performing a pump-normal mode that sets a rotational speed of a cooling water pump to be equal to or greater than a preset reference rotational speed and changes the rotational speed (revolutions per minute - rpm) based on the cooling water outlet temperature; and performing the pump-normal mode when a cooling water outlet temperature estimate of the fuel cell stack exceeds a preset second temperature while the pump-off mode is performed.

[0011] US 2014 / 0 138 044 A1 discloses a cooling system for cooling a heat source comprising a cooling unit configured to cool the heat source by a coolant flowing through the cooling unit, a heat exchanger configured to perform heat exchange between the coolant and the outside air, a liquid storage device configured to store the coolant in a liquid state, a first passage for the coolant connecting the heat exchanger to the liquid storage device, a second passage for the coolant connecting the liquid storage device to the cooling unit and comprising a main passage connecting the liquid storage device to the cooling unit and a sub-passage at least partially separated from the main passage, a pump provided at the sub-passage.

[0012] Furthermore, WO 2013 / 150797 A1 also shows a fuel cell for generating energy used to power a vehicle. An inlet valve for the reserve tank is designed such that the cooling water pressure regulated by the inlet valve for the reserve tank is slightly closer to the inlet side of a cooling water pump than the position of a cooling water circuit, which assumes a mean value between the outlet pressure of the cooling water pump while driving and the inlet pressure of the cooling water pump. Even if the fuel cell no longer generates energy, the cooling water pump continues to operate as long as the cooling water temperature exceeds a predetermined temperature, even while the vehicle is driving. The rotation of the cooling water pump is stopped after the cooling water temperature has dropped to at least the predetermined temperature.In a vehicle that uses the energy of the fuel cell as a driving power generation device, this prevents cavitation that may occur in the cooling water pump when the fuel cell is restarted immediately after stopping. OVERVIEW

[0013] An embodiment of the present invention is directed to a system and method for adjusting a temperature of a fuel cell stack, and an object of the present invention is to provide a method for adjusting a temperature of a fuel cell stack by adjusting a voltage of a coolant pump and a power converter. This object is achieved by a method for controlling a temperature of a fuel cell stack having the features of claims 1, 6, 12, 13, 15, or 16 and a system for controlling a temperature of a fuel cell stack having the features of claim 14. Further objects and advantages of the present invention can be gathered from the following description and will become apparent with reference to the embodiments of the present invention.In addition, it will be apparent to one of ordinary skill in the art to which the invention pertains that the objects and advantages of the present invention may be realized by the claimed means and combinations thereof.

[0014] According to an embodiment of the present invention, a method for adjusting a temperature of a fuel cell stack may include: performing a pump-off mode that turns off the cooling water pump or operates the cooling water pump while reducing the rotational speed of the cooling water pump to be less than the reference rotational speed when a cooling water outlet temperature is equal to or less than a preset first temperature, while performing a pump-normal mode that sets a rotational speed of a cooling water pump to be equal to or greater than a preset reference rotational speed and changes the rotational speed (revolutions per minute - rpm) based on the cooling water outlet temperature; and performing the pump-normal mode when a cooling water outlet temperature estimate of the fuel cell stack exceeds a preset second temperature while performing the pump-off mode.The pump OFF mode is performed when the cooling water outlet temperature is equal to or lower than the preset first temperature and an air outlet temperature of the fuel cell stack is lower than a first air outlet temperature, and the pump normal mode is performed when the cooling water outlet temperature estimate exceeds the preset second temperature or the air outlet temperature of the fuel cell stack exceeds a preset second air outlet temperature.

[0015] The preset first temperature and the preset second temperature may be equal to or less than a target cooling water temperature at a cooling water inlet side. During the pump-off mode, a power limit value of the fuel cell stack may be set using the cooling water outlet temperature estimate. When the pump-off mode is performed, a power limit value of the fuel cell stack may be set based on non-circulation of cooling water. The cooling water outlet temperature estimate of the fuel cell stack may be initialized to the detected cooling water temperature before the pump-off mode is performed.

[0016] According to another embodiment of the present invention, a method for controlling a temperature of a fuel cell stack may include: performing a low-power avoidance mode that allows a power converter to reduce an upper limit voltage of a bus terminal when a cooling water outlet temperature calculation value is equal to or less than a preset third temperature while performing a power normal mode in which the upper limit voltage of the bus terminal between an output terminal of the fuel cell stack and the power converter has a predetermined value; and performing the power normal mode when the cooling water outlet temperature calculation value is equal to or greater than a preset fourth temperature while performing the low-power avoidance mode.The cooling water outlet temperature calculation value is a cooling water outlet temperature estimation value in a pump OFF mode, which can turn off a cooling water pump or operate the cooling water pump while reducing a rotational speed of the cooling water pump to be smaller than a preset reference rotational speed, and may be a sampling value of the cooling water outlet temperature in a pump normal mode, which can set the rotational speed of the cooling water pump to be equal to or larger than the preset reference rotational speed and change a rotational speed (rpm) based on the cooling water outlet temperature.

[0017] The preset third temperature and the preset fourth temperature may be equal to or lower than a target cooling water temperature at a cooling water inlet side. In the low-power avoidance mode, the charging current limit value of the power converter or a target state of charge of the high-voltage battery may be increased, and in the power normal mode, the increase in the charging current limit value of the power converter or the target state of charge of the high-voltage battery may be reduced. The reduction of the bus terminal voltage limit and the increase of the charging current limit value may be performed within a range of an allowable charging power or an allowable state of charge of the high-voltage battery. The low-power avoidance mode cannot be performed in the state where power generation of the fuel cell stack stops.Low power avoidance mode cannot be performed in a regenerative braking state.

[0018] According to yet another embodiment of the present invention, a method for controlling a temperature of a fuel cell stack may include: performing a pump-off mode that can turn off the cooling water pump or operate the cooling water pump while reducing the rotational speed of the cooling water pump to be lower than the reference rotational speed when a cooling water outlet temperature is equal to or lower than a preset first temperature, while performing a pump-normal mode that can set a rotational speed of a cooling water pump to be equal to or higher than a preset reference rotational speed and change a rotational speed (rpm) based on the cooling water temperature;and performing a low-power avoidance mode that allows a power converter to reduce a voltage limit of a bus terminal when a cooling water outlet temperature calculation value is equal to or less than a preset third temperature, while performing a power normal mode in which the voltage limit of the bus terminal between an output terminal of the fuel cell stack and the power converter has a predetermined value, wherein the first temperature may be equal to or greater than the third temperature;

[0019] According to yet another embodiment of the present invention, a method for controlling a temperature of a fuel cell stack may include: performing a pump-off mode that can turn off a cooling water pump or operate the cooling water pump while reducing a rotational speed of the cooling water pump to be less than a preset reference rotational speed when a heating value of the fuel cell stack is equal to or less than a preset first reference heating value, while performing a pump-normal mode that can set a rotational speed of the cooling water pump to be equal to or greater than a preset reference rotational speed and change a rotational speed (rpm) based on the cooling water temperature;and performing a low-power avoidance mode that allows a power converter to reduce a voltage limit of a bus terminal when a cooling water temperature at a cooling water outlet side detected by a temperature sensor is equal to or lower than a preset third temperature, while performing a power normal mode in which the voltage limit of the bus terminal between an output terminal of the fuel cell stack and the power converter has a predetermined value. If the heating value of the fuel cell stack exceeds a preset second reference heating value, the pump normal mode cannot be performed.

[0020] In another embodiment of the present invention, a system for controlling a temperature of a fuel cell stack comprises: a memory configured to store program instructions; and a processor configured to execute the program instructions, wherein the program instructions, when executed, are configured to: perform a pump-off mode that turns off the cooling water pump or operates the cooling water pump while reducing the rotational speed of the cooling water pump to be less than the reference rotational speed when a cooling water outlet temperature is equal to or less than a preset first temperature, while performing a pump-normal mode that sets a rotational speed of a cooling water pump to be equal to or greater than a preset reference rotational speed and changes a rotational speed (revolutions per minute - rpm) based on the cooling water outlet temperature;and perform the pump normal mode when a cooling water outlet temperature estimate of the fuel cell stack exceeds a preset second temperature while performing the pump OFF mode, wherein the pump OFF mode is performed when the cooling water outlet temperature is equal to or less than the preset first temperature and an air outlet temperature of the fuel cell stack is less than a first air outlet temperature, and the pump normal mode may be performed when the cooling water outlet temperature estimate exceeds the preset second temperature or the air outlet temperature of the fuel cell stack exceeds a preset second air outlet temperature.; BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and other features of the present invention will now be described in detail with reference to embodiments thereof illustrated by the accompanying drawings, which are given hereinafter for illustrative purposes only and are thus not limitative of the present invention. In the figures: Fig. 1 is an exemplary configuration diagram illustrating a temperature control system of a fuel cell system according to the prior art; Fig. 2 is an exemplary diagram illustrating an overall fuel cell system according to an embodiment of the present invention; Fig. 3 is an exemplary configuration diagram of a power grid of the fuel cell system according to the embodiment of the present invention; Fig. 4 is an exemplary diagram illustrating a standard operation of a coolant pump in a method for adjusting a temperature of a fuel cell stack according to an embodiment of the present invention; Fig. 5 is an exemplary graph illustrating a correlation between an ambient temperature and a target cooling water inlet temperature in the fuel cell stack according to an embodiment of the present invention; and Fig. 6 is an exemplary graph illustrating a relationship between an output current and a voltage or a power of the fuel cell stack for describing the method of adjusting a temperature of a fuel cell stack according to the embodiment of the present invention. DETAILED DESCRIPTION

[0022] It is understood that the term "vehicle" or "vehicle-" or other synonymous 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 includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuel derived from sources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more power sources, such as both gasoline-powered and electric-powered vehicles.

[0023] Although the embodiment is described as using a plurality of units to perform the example process, it is understood that the example processes may also be performed by one or more modules. Furthermore, it is understood that the term controller refers to a hardware device including 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 described below.

[0024] Furthermore, the control logic of the present invention may be embodied as non-transitory computer-readable media on a computer-readable medium comprising executable program instructions executed by a processor, controller, or the like. Examples of computer-readable storage media 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 may also be decentralized in network-coupled computer systems such 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).

[0025] Unless expressly stated or evident from the context, the term "approximately" as used herein is understood to be within a range of standard tolerance in the art, for example, within 2 standard deviations of the mean values. "Approximately" can be understood to be 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 indicated by the context, all numerical values ​​provided herein are modified by the term "approximately."

[0026] Specific structural or functional descriptions in the embodiments of the present invention disclosed in this specification or application are presented only to illustrate the embodiments of the present disclosure. The descriptions may be embodied in various forms and should not be considered limited to the embodiments described in the specification or application.

[0027] Since embodiments of the present invention can be variously modified / changed and take various forms, specific embodiments are illustrated in the accompanying drawings and described in detail in this specification or application. However, it should be understood that the present invention is not limited to specific embodiments, but includes all modifications / changes, equivalents, and substitutions included within the spirit and scope of the present invention.

[0028] Terms such as "first" and / or "second" may be used to describe a variety of components, however, the components are not limited to the terms. The terms are used merely to distinguish one component from another. For example, the first component could be referred to as the second component, and similarly, the second component could be referred to as the first component, without departing from the scope of the present invention.

[0029] It is understood that when an element is referred to as being "coupled" or "connected" to another element, it may be directly connected or directly coupled to another element, or it may be connected or coupled to another element with another element interposed therebetween. On the other hand, it is understood that when an element is referred to as being "directly coupled" or "directly connected" to another element, it may be connected or coupled to another element without any other elements interposed therebetween. Other expressions explaining the relationship between elements, such as "between," "directly between," "adjacent / next," or "directly adjacent / contiguous," should be interpreted in the same manner.

[0030] The terminology used herein is for the purpose of describing particular embodiments 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 is further understood that the terms "comprise" and / or "comprising," when used in this specification, describe the presence of the specified features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more 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 elements.

[0031] Unless otherwise specified, all terms / expressions used herein, including technical and scientific terms / expressions, have the same meaning as those commonly understood by one of ordinary skill in the art. It is further understood that terms / expressions defined by the dictionary are consistent with the meaning in the context of the prior art and should not be interpreted in an idealized or overly formal sense unless the context clearly indicates otherwise.

[0032] Embodiments of the present invention will be described below with reference to the accompanying drawings. Like reference numerals used in each drawing indicate like components.

[0033] Fig. 2 is an exemplary diagram illustrating an overall fuel cell system according to an embodiment of the present invention. As in Fig. 2, the fuel cell system 100 may include a fuel cell stack 10, a warm-up of the fuel cell stack 10, a fuel cell load device 20 configured to prevent a voltage of the fuel cell stack 10 from increasing during startup and shutdown, an air blower 30, a humidifier 40, air shutoff valves 35 and 45 on an inlet side and an outlet side, a drain valve 42, a purge valve 44 configured to discharge and purge hydrogen from an anode to remove foreign matter such as droplets and nitrogen from a bipolar plate in the fuel cell stack 10 and to increase hydrogen utilization, a water separator 50, a hydrogen recirculation device 55 configured to recycle unreacted hydrogen remaining after the hydrogen in the anode of the fuel cell stack 10 is used,to the anode of the fuel cell stack 10 to promote the reuse of hydrogen, a hydrogen supply valve 57, a cooler 60 and a thermostat 65.

[0034] Although not in Fig. 1, a controller may be configured to operate / control opening and closing of various types and to measure a heating value of the fuel cell stack 10, and may be configured to receive detection values ​​of a temperature sensor, a voltage and current sensor, and the like to operate each component of the fuel cell system.

[0035] Fig. 3 shows an exemplary configuration diagram of a power grid of the fuel cell system according to the embodiment of the present invention. As in Fig. 3, a fuel cell-battery hybrid electric system for a vehicle may include the fuel cell 10, which is a main power source, and a high-voltage battery (main battery) 220, which is an auxiliary power source, which can be connected in parallel to each other via a main bus terminal 211, a bidirectional high-voltage direct current (DC / DC) converter 221 connected to the high-voltage battery 220 to adjust an output power of the high-voltage battery 220, an inverter 231 connected to the fuel cell 10 and the main bus terminal 211, which is an output side of the high-voltage battery 220, a drive motor 232 connected to the inverter 231, a high-voltage load 233, a low-voltage battery (auxiliary battery) 240, a low-voltage load 241 in a vehicle with the exception of the inverter 231 and the drive motor 232,a low-voltage DC / DC converter 242 connecting the low-voltage battery 240 and the main bus terminal 211 to convert a high voltage to a low voltage, and a fuel cell load device 20.

[0036] In this arrangement, the fuel cell stack 10 used as the main power source of the vehicle and the high-voltage battery 220 used as the auxiliary power source can be connected in parallel to any load in the system, such as the inverter 231 / drive motor 232, via the main bus terminal 211, and the bidirectional high-voltage DC / DC converter 221 connected to a high-voltage battery terminal can be connected to the main bus terminal 211, which is an output side of the fuel cell stack 10, to control an output of the fuel cell stack 10 and the output of the high-voltage battery 220 by adjusting the voltage (e.g., output voltage to the main bus terminal) from the bidirectional high-voltage DC / DC converter 221.

[0037] An output terminal of the fuel cell stack 10 may be connected to a diode 213 to prevent reverse current from flowing. A relay 214, which is provided to selectively connect the fuel cell stack 10 to the main bus terminal 211, may also be attached. The relay 214 may remain in a connected state while a vehicle in which the fuel cell stack 10 is operated is being driven / powered and when the fuel cell system is in an idle stop / restart state, and is in an interrupted state during a key-off (e.g., normal shutdown / shutdown based on the key-off) or an emergency shutdown. The relay 214 Fig. The fuel cell load device 20 shown in Figure 1 may include the high-voltage battery 220, the high-voltage load 233, the drive motor 232, and the like shown in Fig. 2 are shown.

[0038] Fig. 4 shows an exemplary diagram illustrating a standard operation of a coolant pump in a method for adjusting a temperature of a fuel cell stack according to an embodiment of the present invention, and Fig. 5 shows an exemplary graph illustrating a correlation between an ambient temperature and a target cooling water inlet temperature in the fuel cell stack according to an embodiment of the present invention.

[0039] Fig. 4 illustrates sections TH1 < TH2 < TH3 < TH4 < TH5 < TH6 for each step, which is previously set for a cooling water outlet temperature of the fuel cell stack 10. First, the method for adjusting a temperature of a fuel cell stack 10 may include turning off, by a controller, the cooling water pump 70 or operating (e.g., performing a pump-off mode) the cooling water pump 70 while reducing a rotation speed of the cooling water pump 70 to be lower than a preset reference rotation speed (e.g., preset base rotation speed) when the cooling water temperature on the cooling water outlet side is equal to or lower than a first temperature T1.

[0040] As in Fig. 4, the rotational speed (rpm) of the cooling water pump configured to supply cooling water to the fuel cell stack 10 may be set differently based on the preset temperature sections for each step based on which section the cooling water temperature at the cooling water outlet side of the fuel cell stack 10 belongs to.

[0041] Although not in Fig. 4, when the heating value of the fuel cell stack 10 is equal to or less than a first reference heating value, the controller may also be configured to turn off the cooling water pump 70 or operate the cooling water pump 70 (e.g., perform the pump OFF mode) while reducing the speed of the cooling water pump 70 to the preset reference speed, and when the air outlet temperature of the fuel cell stack is less than a preset first air outlet temperature, the controller may be configured to turn off the cooling water pump 70 or operate the cooling water pump while reducing the speed of the cooling water pump to the preset reference speed.

[0042] Further, when a torque value required in the motor connected to the fuel cell stack is less than a first required torque and is maintained for a first period of time, the controller may be configured to turn off the cooling water pump 70 or operate the cooling water pump 70 (e.g., perform the pump OFF mode) while reducing a rotational speed of the cooling water pump 70 to be less than the preset reference rotational speed.In response to determining that the larger of a cooling water temperature estimate at the cooling water outlet side of the fuel cell stack and the cooling water temperature at the cooling water outlet side detected by the temperature sensor exceeds a second temperature by turning off the cooling water pump 70 or operating the cooling water pump 70 while reducing the rotational speed of the cooling water pump 70 to be less than a lowest rotational speed, the controller may be configured to operate the cooling water pump 70 normally (e.g., perform a pump normal mode). The cooling water temperature estimate may be obtained by the method disclosed in Korean Patent Application Laid-Open KR 10 2011 0 138 443 A.

[0043] In addition, when the heating value of the fuel cell stack 10 exceeds a preset second reference heating value, when the air outlet temperature of the fuel cell stack 10 exceeds a second air outlet temperature, or when the torque value required in the motor connected to the fuel cell stack 10 exceeds a preset second required torque, the controller may be configured to operate the cooling water pump 70 normally (perform the pump normal mode). Even if the larger of the cooling water temperature estimate at the cooling water outlet side of the fuel cell stack 10 and the cooling water temperature at the cooling water outlet side detected by the temperature sensor is equal to or greater than the preset second temperature, the controller may be configured to operate the cooling water pump 70 normally.Specifically, the preset first temperature and the preset second temperature may be preset to be equal to or less than the target cooling water temperature on the cooling water inlet side. Furthermore, the preset second temperature may be preset to be greater than the preset first temperature, and the preset second reference calorific value may be preset to be greater than the first reference calorific value.

[0044] Furthermore, when the pump-off mode is performed, a power limit value of the fuel cell stack can be set based on the estimated cooling water temperature at the cooling water outlet side. When the pump-off mode is performed, the power limit value of the fuel cell stack can be set based on the non-circulation of the cooling water. For example, when the pump-off mode is performed, the power limit value of the fuel cell stack can be set to be approximately 30%. When the pump-off mode is performed, the cooling water cannot be circulated (e.g., it can be prevented or stopped from being circulated), and accordingly, it is not necessary to set the power limit value during the non-circulation of the cooling water.For reference, an initial value of the temperature estimation value can be set to be a temperature sensor value of the cooling water outlet before the pump OFF mode is executed. In other words, the initial value of the temperature estimation value can be initialized to the temperature sensor value each time before the pump OFF mode is executed.

[0045] When the cooling water pump 70 is turned off, a speed command value of the cooling water pump 70 may become 0, and when the cooling water pump 70 is operated while a speed of the cooling water pump 70 is reduced to be less than a minimum speed, the speed command value may be less than min_rpm (e.g., about 1500 rpm), which may be a lowest speed.

[0046] Fig. 6 shows an exemplary graph illustrating a relationship between an output current and a voltage or a power of the fuel cell stack for describing the method for adjusting a temperature of a fuel cell stack according to the embodiment of the present invention. In particular, Fig. 6 is an exemplary diagram illustrating a method of improving a fuel cell stack by charging the high-voltage battery 220 among the methods of adjusting a temperature of a fuel cell stack according to the embodiment of the present invention.

[0047] In other words, the method for improving a fuel cell stack by charging the high-voltage battery 220 can avoid low output power of the fuel cell stack. As a result, when the cooling water temperature estimation value at the cooling water outlet of the fuel cell stack or the cooling water temperature detected by the temperature sensor (e.g., cooling water temperature calculation value) is equal to or lower than a third temperature (hereinafter, Condition 1) while the power normal mode is being performed, the power converter 221 connecting the output terminal of the fuel cell stack to the high-voltage battery 220 can be configured to reduce a voltage limit of the bus terminal between the output terminal of the fuel cell stack and the power converter (e.g., perform a low-power avoidance mode).Furthermore, under condition 1, the power converter 221 may be configured to increase a charging current limit value of the power converter 221 and to increase a desired state of charge (SOC).

[0048] On the other hand, if the cooling water temperature estimate at the cooling water outlet of the fuel cell stack or the cooling water temperature detected by the temperature sensor (e.g., cooling water temperature calculation value) is equal to or greater than a fourth temperature (hereinafter, Condition 2), the power converter 221 may be configured to restore the reduced voltage upper limit to an original value (e.g., perform the power normal mode). Furthermore, upon satisfying Condition 2, the power converter may be configured to restore the previously increased charging current limit value and target state of charge to an original value (e.g., progressively reduce).In particular, the preset third temperature and the preset fourth temperature may be equal to or less than the target cooling water temperature at the cooling water inlet, and the preset fourth temperature may be greater than the preset third temperature. The preset fourth temperature may be less than the preset first temperature.

[0049] The charging current limit value and the target state of charge can be adjusted by decreasing and restoring the upper limit voltage. Furthermore, the upper limit voltage reduction of the power converter 221 cannot be performed when the charging power output from the fuel cell stack exceeds a permissible charging power of the high-voltage battery 220 or when the state of charge of the high-voltage battery 220 exceeds the permissible state of charge. The upper limit voltage reduction of the power converter 221 cannot be performed in a fuel cell stop (FC stop) state or a regenerative braking state.

[0050] When the cooling water temperature is equal to or lower than the first temperature even when the cooling water pump 70 is turned off or the cooling water pump 70 is operated while the rotational speed of the cooling water pump 70 is reduced to be lower than the preset reference rotational speed, when the cooling water temperature estimation value at the cooling water outlet of the fuel cell stack or the cooling water temperature detected by the temperature sensor (which differs when the pump OFF mode is performed and when the pump normal mode is performed) at the cooling water outlet is equal to or lower than the third temperature preset to be lower than the preset first temperature, the power converter may be configured to lower the voltage upper limit of the bus terminal to charge the power of the fuel cell stack to the high-voltage battery 220 and to increase the temperature of the fuel cell stack.In other words, since the temperature of the fuel cell stack is gradually reduced, the reduction of the temperature can be prevented by performing the pump OFF mode, and when the temperature is further reduced, the temperature of the fuel cell stack can be increased by charging the battery.

[0051] In addition, when the heating value of the fuel cell stack is equal to or less than the preset first reference heating value when the cooling water pump 70 is turned off or operated while the speed of the cooling water pump 70 is reduced to be less than the preset reference speed, and then when the heating value of the fuel cell stack exceeds the preset second reference heating value, the cooling water pump 70 can be operated normally (eg, operated in the pump normal mode).Specifically, during the power normal mode in which the upper limit voltage of the bus terminal between the output terminal of the fuel cell stack and the power converter has a predetermined value, when the cooling water temperature on the cooling water outlet side is detected by the temperature sensor, the power converter may be configured to perform the low-power avoidance mode that reduces the upper limit voltage of the bus terminal, and thus may not perform the pump normal mode if the heating value of the fuel cell stack exceeds the preset reference heating value. In other words, the upper limit voltage of the power converter 221 may be reduced to prevent the cooling water pump 70 from operating normally even when the power of the fuel cell stack is generated to increase the heating value.

[0052] According to the method for controlling a temperature of a fuel cell stack according to the embodiment of the present invention, it may be possible to maintain the temperature of the fuel cell stack within a normal range by turning the cooling water pump on and off based on the cooling water temperature at the cooling water outlet, thus preventing the phenomenon of overflow and dryness of the fuel cell stack. Furthermore, when it is necessary to increase the temperature of the fuel cell stack, it may be possible to increase the temperature of the fuel cell stack by charging the battery.

Claims

[1] A method for controlling a temperature of a fuel cell stack (10), comprising: Performing a pump-off mode that turns off the cooling water pump (70) or operates the cooling water pump (70) while reducing the rotational speed of the cooling water pump (70) to be less than the reference rotational speed when a cooling water outlet temperature is equal to or less than a preset first temperature, while performing a pump-normal mode that sets a rotational speed of a cooling water pump (70) to be equal to or greater than a preset reference rotational speed and changes the rotational speed (revolutions per minute - rpm) based on the cooling water outlet temperature; and Performing the pump normal mode when a cooling water outlet temperature estimate of the fuel cell stack (10) exceeds a preset second temperature while the pump OFF mode is being performed, wherein the pump OFF mode is performed when the cooling water outlet temperature is equal to or lower than the preset first temperature and an air outlet temperature of the fuel cell stack (10) is lower than a first air outlet temperature, and the pump normal mode is performed when the cooling water outlet temperature estimate exceeds the preset second temperature or the air outlet temperature of the fuel cell stack (10) exceeds a preset second air outlet temperature. [2] The method according to claim 1, wherein the preset first temperature and the preset second temperature are equal to or less than a target cooling water temperature at a cooling water inlet side. [3] The method of claim 1, wherein during the pump-OFF mode, a power limit value of the fuel cell stack (10) is set using the cooling water outlet temperature estimate. [4] The method according to claim 1, wherein, when the pump-OFF mode is performed, a power limit value of the fuel cell stack (10) is set based on non-circulation of cooling water. [5] The method of claim 1, wherein the cooling water outlet temperature estimate of the fuel cell stack (10) is initialized to the detected cooling water temperature before the pump-OFF mode is performed. [6] A method for controlling a temperature of a fuel cell stack (10), comprising: Performing a low-power avoidance mode to allow a power converter (221) to reduce a voltage upper limit of a bus terminal (211) when a cooling water outlet temperature calculation value is equal to or less than a preset third temperature, while performing a power normal mode in which the voltage upper limit of the bus terminal (211) between an output terminal of the fuel cell stack (10) and the power converter (221) has a predetermined value; and Performing the power normal mode when the cooling water outlet temperature calculation value is equal to or greater than a preset fourth temperature while performing the low power avoidance mode, wherein the cooling water outlet temperature calculation value is a cooling water outlet temperature estimation value in a pump-OFF mode that turns off a cooling water pump (70) or operates the cooling water pump (70) while reducing a rotational speed of the cooling water pump (70) to be less than a preset reference rotational speed, and a cooling water outlet temperature sampling value in a pump-normal mode that sets the rotational speed of the cooling water pump (70) to be equal to or greater than the preset reference rotational speed and changes a rotational speed (rpm) based on the cooling water outlet temperature. [7] The method according to claim 6, wherein the preset third temperature and the preset fourth temperature are equal to or less than a target cooling water temperature at a cooling water inlet side. [8] The method according to claim 6, wherein in the low power avoidance mode, a charging current limit value of the power converter (221) or a target charge level of the high-voltage battery (220) is increased, and in the power normal mode, the increase in the charging current limit value of the power converter (221) or the target charge level of the high-voltage battery (220) is reduced. [9] The method according to claim 8, wherein the reduction of the upper voltage limit of the bus terminal (211) and the increase of the charging current limit value are performed within a range of a permissible charging power or a permissible state of charge of the high-voltage battery (220). [10] The method according to claim 6, wherein the low power avoidance mode is not performed when power generation of the fuel cell stack (10) stops. [11] The method of claim 6, wherein the low power avoidance mode is not performed in a regenerative braking state. [12] A method for controlling a temperature of a fuel cell stack (10), comprising: Performing a pump-OFF mode that turns off the cooling water pump (70) or operates the cooling water pump (70) while reducing the rotational speed of the cooling water pump (70) to be less than the reference rotational speed when a cooling water outlet temperature is equal to or less than a preset first temperature, while performing a pump-normal mode that sets a rotational speed of a cooling water pump (70) to be equal to or greater than a preset reference rotational speed and changes a rotational speed (rpm) based on the cooling water temperature; and Performing a low-power avoidance mode that allows a power converter (221) to reduce a voltage upper limit of a bus terminal (211) when a cooling water outlet temperature calculation value is equal to or less than a preset third temperature, while performing a power normal mode in which the voltage upper limit of the bus terminal (211) between an output terminal of the fuel cell stack (10) and the power converter (221) has a predetermined value, wherein the cooling water outlet temperature calculation value is a cooling water outlet temperature estimate in the pump OFF mode and is a sample value of the cooling water outlet temperature in the pump normal mode, and where the first temperature is equal to or greater than the third temperature. [13] A method for controlling a temperature of a fuel cell stack (10), comprising: Performing a pump-off mode that turns off a cooling water pump (70) or operates the cooling water pump (70) while reducing a rotational speed of the cooling water pump (70) to be less than a preset reference rotational speed when a cooling water outlet temperature is equal to or less than a preset first temperature and a heating value of the fuel cell stack (10) is equal to or less than a preset first reference heating value, while performing a pump-normal mode that sets a rotational speed of the cooling water pump (70) to be equal to or greater than a preset reference rotational speed and changes a rotational speed (rpm) based on the cooling water temperature; and Performing a low-power avoidance mode that allows a power converter (221) to reduce a voltage upper limit of a bus terminal (211) when a cooling water outlet temperature calculation value is equal to or less than a preset third temperature, while performing a power normal mode in which the voltage upper limit of the bus terminal (211) between an output terminal of the fuel cell stack (10) and the power converter (221) has a predetermined value, wherein the first reference heating value is equal to or greater than a heating value of the fuel cell stack (10) in the low power avoidance mode, and the cooling water outlet temperature calculation value is a cooling water outlet temperature estimation value in the pump OFF mode and a sample value of the cooling water outlet temperature in the pump normal mode. [14] A system for controlling a temperature of a fuel cell stack (10), comprising: a memory configured to store program instructions; and a processor configured to execute the program instructions, wherein the program instructions, when executed, are configured to: performing a pump-OFF mode that turns off the cooling water pump (70) or operates the cooling water pump (70) while reducing the rotational speed of the cooling water pump (70) to be less than the reference rotational speed when a cooling water outlet temperature is equal to or less than a preset first temperature, while performing a pump-normal mode that sets a rotational speed of a cooling water pump (70) to be equal to or greater than a preset reference rotational speed and changes a rotational speed (revolutions per minute - rpm) based on the cooling water outlet temperature; and to perform the pump normal mode when a cooling water outlet temperature estimate of the fuel cell stack (10) exceeds a preset second temperature while the pump OFF mode is being performed, wherein the pump OFF mode is performed when the cooling water outlet temperature is equal to or lower than the preset first temperature and an air outlet temperature of the fuel cell stack (10) is lower than a first air outlet temperature, and the pump normal mode may be performed when the cooling water outlet temperature estimate exceeds the preset second temperature or the air outlet temperature of the fuel cell stack (10) exceeds a preset second air outlet temperature. [15] A method for controlling a temperature of a fuel cell stack (10), comprising: Performing a pump-off mode that turns off the cooling water pump (70) or operates the cooling water pump (70) while reducing the rotational speed of the cooling water pump (70) to be less than the reference rotational speed when a cooling water outlet temperature is equal to or less than a preset first temperature, while performing a pump-normal mode that sets a rotational speed of a cooling water pump (70) to be equal to or greater than a preset reference rotational speed and changes the rotational speed (revolutions per minute - rpm) based on the cooling water outlet temperature; and Performing the pump normal mode when a cooling water outlet temperature estimate of the fuel cell stack (10) exceeds a preset second temperature while the pump OFF mode is being performed, wherein during the pump-OFF mode, a power limit value of the fuel cell stack (10) is set using the cooling water outlet temperature estimate. [16] A method for controlling a temperature of a fuel cell stack (10), comprising: Performing a pump-off mode that turns off the cooling water pump (70) or operates the cooling water pump (70) while reducing the rotational speed of the cooling water pump (70) to be less than the reference rotational speed when a cooling water outlet temperature is equal to or less than a preset first temperature, while performing a pump-normal mode that sets a rotational speed of a cooling water pump (70) to be equal to or greater than a preset reference rotational speed and changes the rotational speed (revolutions per minute - rpm) based on the cooling water outlet temperature; and Performing the pump normal mode when a cooling water outlet temperature estimate of the fuel cell stack (10) exceeds a preset second temperature while the pump OFF mode is being performed, wherein, when the pump-OFF mode is performed, a power limit value of the fuel cell stack (10) is set based on non-circulation of cooling water.

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