Water removing system and method of fuel cell vehicle using impedance

Abstract

A water removing system and method of a fuel cell vehicle using impedance are provided. The system measures measure the low frequency impedance of a fuel cell stack when a fuel cell system is stopped in a low temperature condition, and adjusts the air supply amount and supply time for removing the water supercharged into the fuel cell stack using the measured low frequency impedance. Thus, air is prevented from being unnecessarily supercharged into the fuel cell stack and at the same time, the water remaining in the fuel cell stack is removed.

Claims

1. A water removing system of a fuel cell vehicle using impedance, comprising: a fuel cell stack; an air supply unit configured to supply air to the fuel cell stack; an outside air temperature sensor configured to measure an outside air temperature; a coolant temperature sensor configured to measure a coolant water temperature of the fuel cell vehicle; an impedance measuring unit configured to measure a low frequency impedance of the fuel cell stack; and a controller including a processor configured to: communicate with the outside air temperature sensor and the coolant temperature sensor; operate the air supply unit based on the low frequency impedance of the fuel cell stack measured in the impedance measuring unit; instruct the impedance measuring unit to measure the low frequency impedance of the fuel cell stack when the outside air temperature measured by the outside air temperature sensor or the coolant water temperature measured by the coolant temperature sensor is equal to or less than a respective reference value when a starting stop signal is received; operate the air supply unit once the impedance measuring unit starts to measure the low frequency impedance of the fuel cell stack, and reduce a driving speed of the air supply unit or stop driving the air supply unit when the low frequency impedance of the fuel cell stack reaches a minimum reference value.

2. The water removing system of the fuel cell vehicle using impedance of claim 1, wherein the minimum reference value is set to a point after a mass transfer resistance reduces as an amount of water of the fuel cell stack reduces and the low frequency impedance of the fuel cell stack measured at one low frequency decreases, and before the impedances in a low frequency band and a middle frequency band increase due to excessive water removal in the fuel cell stack.

3. The water removing system of the fuel cell vehicle using impedance of claim 1, wherein the controller is further configured to: instruct the impedance measuring unit to repeatedly measure a set of low frequency impedances of the fuel cell stack while the air supply unit operates; and reduce the driving speed of the air supply unit or stop driving the air supply unit when a difference between two subsequent low frequency impedances in the set of low frequency impedances of the fuel cell stack becomes less than the minimum reference value.

4. A water removing system of a fuel cell vehicle using impedance, comprising: a fuel cell stack; an air supply unit configured to supply air to the fuel cell stack; an impedance measuring unit configured to measure a low frequency impedance of the fuel cell stack; an outside air temperature sensor configured to measure an outside air temperature, a coolant temperature sensor configured to measure a coolant temperature of the fuel cell vehicle; and a controller including a processor configured to: operate the air supply unit based on the low frequency impedance of the fuel cell stack measured in the impedance measuring unit; operate the air supply unit when the impedance measuring unit measures the low frequency impedance of the fuel cell stack to reduce the driving speed of the air supply unit or stop the driving thereof when the low frequency impedance of the fuel cell stack reaches a minimum reference value; instruct the impedance measuring unit to repeatedly measure a set of low frequency impedances of the fuel cell stack while the air supply unit operates; reduce the driving speed of the air supply unit or stop driving the air supply unit when a difference between two subsequent low frequency impedances in the set of low frequency impedances of the fuel cell stack becomes less than the minimum reference value communicate with the outside air temperature sensor and the coolant temperature sensor; and instruct the impedance measuring unit to measure the low frequency impedance of the fuel cell stack when the outside air temperature or the coolant water temperature is equal to or less than the reference value when a starting stop signal is received.

5. The water removing system of the fuel cell vehicle using impedance of claim 4, wherein the minimum reference value is set to a point after a mass transfer resistance reduces as an amount of water of the fuel cell stack reduces and the low frequency impedance of the fuel cell stack measured at one low frequency decreases, and before the impedances in a low-frequency band and a middle-frequency band increase due to excessive water removal in the fuel cell stack.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other features of the present disclosure will now be described in detail with reference to exemplary embodiments thereof illustrated the accompanying drawings which are given herein below by way of illustration only, and thus are not limitative of the present disclosure, and wherein:

(2) FIG. 1 is a block diagram illustrating a water removing system of a fuel cell vehicle using impedance according to an exemplary embodiment of the present disclosure;

(3) FIG. 2 is a flowchart illustrating a water removing method of the fuel cell vehicle using the impedance according to an exemplary embodiment of the present disclosure; and

(4) FIGS. 3A and 3B are graphs illustrating that the low frequency impedance is changed according the amount of water remaining in a fuel cell stack in the water removing system and method of the fuel cell vehicle according to an exemplary embodiment of the present disclosure.

(5) 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 disclosure. The specific design features of the present disclosure as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in section by the particular intended application and use environment. In the drawings, reference numbers refer to the same or equivalent sections of the present disclosure throughout the several figures of the drawing.

DETAILED DESCRIPTION

(6) 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.

(7) 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.

(8) The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. 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.

(9) 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.”

(10) Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

(11) FIG. 1 is a diagram illustrating a water removing system of a fuel cell vehicle using impedance according to the present disclosure, and reference numeral 10 denotes a fuel cell stack. When a fuel cell system is stopped according to the traveling termination of a fuel cell vehicle, water that is a byproduct of the electrochemical reaction remains in the fuel cell stack 10, and particularly, the water remains in a channel of a separator, etc. To remove the water remaining in the fuel cell stack 10, an air compressor 12 that is an air supply unit may be turned on by a controller 30, which is a controller for overall operation of the fuel cell system to thus supercharge air into the fuel cell stack.

(12) According to the present disclosure, an impedance measuring device 20, which is an impedance measuring unit configured to measure the low frequency impedance, may be connected to the fuel cell stack 10. The impedance measuring device 20 may be configured to begin measuring the low frequency impedance of the fuel cell stack based on the control instruction or signal from the controller 30 before the air compressor 12 is driven (OFF state). In addition, the impedance measuring device 20 may be configured to repeatedly measure, several times, the low frequency impedance of the fuel cell stack according to the control instruction of the controller while air is supercharged into the stack according to the ON driving of the air compressor 12, that is, even while the water in the stack is removed by the air supercharged according to the ON driving of the air compressor.

(13) In addition, a high voltage battery 22 and a high voltage power converter 24 may be connected to the fuel cell stack 10 via a switch 26, as a configuration for supplying a current for impedance measurement. The water removing system of the present disclosure may include the controller 30 for an impedance measuring procedure and an air compressor driving control. In particularly, the controller 30 may be configured to transmit the control instruction for measuring the low frequency impedance of the fuel cell stack to the impedance measuring device 20, when the outside air temperature or the coolant temperature is equal to or less than a reference value in a state where the fuel cell system has been stopped.

(14) In addition, when the impedance measuring device 20 starts measuring the low frequency impedance of the fuel cell stack, the controller 30 may be configured to turn on the air compressor 12 for supercharging air into the fuel cell stack, then perform a control for maintain the ON state or turn the air compressor 12 off based on the low frequency impedance of the fuel cell stack measured in the impedance measuring device 20, and turn off the air compressor when the low frequency impedance of the fuel cell stack reaches the minimum reference value.

(15) Herein, a water removing method using impedance of the present disclosure having the above configuration will be described as follows. FIG. 2 is a flowchart illustrating a water removing method of a fuel cell vehicle using impedance according to the present disclosure.

(16) Firstly, when the fuel cell system is stopped according to the traveling termination of the fuel cell vehicle S101, whether the fuel cell stack is in a low temperature state may be determined S102. In other words, when the fuel cell system is stopped, the controller 30 may be configured to confirm whether the outside air temperature or the coolant temperature is in a low temperature state of the reference value or less, based on a temperature signal from an outside air temperature sensor and a temperature signal from a coolant temperature sensor. Preferably, the low temperature ranges from 0° C. or more to 10° C. or less to discharge water remaining in the stack to the outside.

(17) As a confirmed result in the S102, in response to determining that the outside air temperature or the coolant temperature is equal to or less than the reference value, the low frequency impedance Z.sup.Re(1) of the fuel cell stack may be measured S103. For this purpose, the current from the high voltage battery 22 may be supplied to the fuel cell stack 10 through the high voltage power converter 24 while the switch 26 is turned on or off according to the control instruction (the current command) of the controller 30, and in addition, the impedance measuring device 20 may be configured to measure the low frequency impedance Z.sup.Re(1) of the fuel cell stack by the control signal of the controller 30 to transmit a measurement result to the controller 30.

(18) At this time, the frequency during measurement of the impedance of the fuel cell stack is one of the frequencies related to the mass transfer resistance of the stack (e.g., water remaining in the stack), and is preferably about 30 Hz or less experimentally, and since an impedance measurement time increases with low frequencies but the mass transfer resistance is generated, thereby improving the impedance measurement reliability. Subsequently, when the impedance measuring device starts measuring the low frequency impedance Z.sup.Re(1) of the fuel cell stack, air may be supercharged into the fuel cell stack to remove the water remaining in the fuel cell stack 10 S104.

(19) In other words, the air compressor 12 may be turned ON by an operation instruction signal of the controller 30, thereby supercharging air into the fuel cell stack. Therefore, the water remaining in the fuel cell stack may be discharged to the outside and removed through the purge portion of the fuel cell stack together with the flow of air by the flow force of the air supercharged into the fuel cell stack.

(20) Further, while the water is removed according to the operation of the air compressor 12, the low frequency impedances Z.sup.Re(n), n=2, 3, . . . of the fuel cell stack may be repeatedly measured several times in the same manner as the measurement method in the S103-S105. At this time, the supply time of the air supplied to the fuel cell stack 10 by the driving of the air compressor 12 that is the air supply unit may be variably adjusted by an impedance measuring period Z.sup.Re(n−1)−Z.sup.Re(n) obtained by subtracting the currently measured low frequency impedance Z.sup.Re(n) from the previously measured low frequency impedance Z.sup.Re(n−1) In other words, the greater the impedance measuring period Z.sup.Re(n−1)−Z.sup.Re(n), the longer the air supply time is set, and the smaller the impedance measuring period Z.sup.Re(n−1)−Z.sup.Re(n), the shorter the air supply time is set.

(21) Meanwhile, referring to the upper diagram of FIG. 3A, the low frequency impedance measured at one low frequency is high due to the mass transfer resistance (e.g., the water remaining in the stack) before the water remaining in the fuel cell stack is removed (e.g., before the S104). On the other hand, referring to the lower diagram of FIG. 3A, the mass transfer resistance (e.g., the water remaining in the stack) reduces and the low frequency impedance measured at one low frequency gradually decreases, when the water remaining in the fuel cell stack starts being removed (e.g., after the S104).

(22) When the water remaining in the fuel cell stack is excessively removed, for example, the moisture of an electrolyte membrane, etc. is excessively removed in addition to the water present in the channel of the separator, the impedances of the low frequency band and the middle frequency band increase, as illustrated in the lower diagram of FIG. 3B, due to an increase in the resistance of the electrolyte membrane and the hydrogen ion migration resistance, etc.

(23) Therefore, as illustrated in the lower diagram of FIG. 3A and the upper diagram of FIG. 3B, a point after the mass transfer resistance reduces and the low frequency impedance measured at one low frequency gradually decreases, and before the impedances of the low frequency band and the middle frequency band increase due to the excessive water removal in which the water present in the electrolyte membrane and the electrode of the fuel cell stack is removed may be set to a minimum reference value of the low frequency impedance.

(24) In other words, the minimum reference value may be set to a point at which the mass transfer resistance in the stack reduces as the amount of water in the fuel cell stack gradually reduces, such that the low frequency impedance of the fuel cell stack measured at one low frequency gradually decreases to no longer decrease, and at the same time, a point before the impedances of the low frequency band and the middle frequency band entirely increase due to the excessive water removal in which the water present in the electrolyte membrane and the electrode of the fuel cell stack is removed.

(25) Preferably, a method for determining whether the low frequency impedance of the fuel cell stack reaches the minimum reference value determines that the low frequency impedance reaches the minimum reference value when an absolute value obtained by subtracting the finally measured low frequency impedance from the previously measured low frequency impedance as in the following Equation 1, or the subtracted value as in the following Equation 2 is less than the minimum reference value.
|Z.sup.Re(n−1)−Z.sup.Re(n)|<minimum reference value  Equation 1
Z.sup.Re(n−1)−Z.sup.Re(n)<minimum reference value  Equation 2

(26) Therefore, when the low frequency impedance of the fuel cell stack converges to the minimum reference value while the air is supercharged into the fuel cell stack to remove water, the water remaining in the channel of the separator in the stack may be determined to have been maximally removed, thereby stopping the air from being supercharged into the stack to prevent water from being excessively removed.

(27) Accordingly, the controller 30 may be configured to determine whether the low frequency impedance Z.sup.Re(n), n=2, 3, . . . measured by the S105 has reached the minimum reference value S106, and turn OFF the operation of the air compressor 12 when the measured low frequency impedance reaches the minimum reference value S107.

(28) As described above, it may be possible to adjust the air supply amount and supply time for removing the water supercharged into the fuel cell stack using the low frequency impedance, and to adjust the amounts and time until before the water is excessively removed while maximally removing the water remaining in the channel of the separator, thereby preventing air from being unnecessarily supercharged and at the same time, efficiently removing the water remaining in the stack.

(29) In other words, there has been a problem in the conventional water removing method in that the moisture present in the electrolyte membrane in addition to the water present in the channel of the separator is removed, thereby rather causing the over-drying phenomenon to occur. However, in the water removing method using the low frequency impedance of the present disclosure, it may be possible to determine as a state where the water remaining in the channel of the separator has been removed when the low frequency impedance reduces to reach the minimum reference value, thereby sufficiency removing only the water remaining in the channel of the separator, and therefore, preventing the over-drying phenomenon from occurring.

(30) In addition, it is only necessary to supply the air for removing the water to the fuel cell stack until the low frequency impedance reduces to reach the minimum reference value even if the amount of water remaining in the fuel cell stack is changed according to the specifications and the operating method of the fuel cell system, such that it may be possible to obtain the constant water removing effect even if the specifications and the operating method of the fuel cell system are different from each other.

(31) As described above, although the exemplary embodiments of the present disclosure have been described in detail, the claims of the present disclosure is not limited to the above-described embodiments, and various modifications and improvements by those skilled in the art using the basic concept of the present disclosure defined in the appended claims may also be included the claims of the present disclosure.