JP2006286409A - Humidification device for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a humidification control technique capable of appropriately controlling the humidification amount of supply gas. <P>SOLUTION: An always constant humidifying molar ratio is achieved regardless of the load variation of a fuel cell 140, by estimating excess responsiveness of the humidification amount and adjusting a bypass valve 160. An ECU 150 detects the load variations in the fuel cell 140, based on a current value detected by a current sensor 20 and finds the target humidifying amount, by referring to a map (not illustrated) comparing the current value to the humidifying amount of oxidizing gas. The ECU 150 conducts estimated control of the bypass valve 160, by estimating the excess responsiveness of the humidification so as to obtain the target humidifying amount. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control technology for a humidifier mounted on a fuel cell system.

  A fuel cell system is equipped with a solid polymer type fuel cell having a solid polymer membrane having proton conductivity in an electrolyte layer. Since the solid polymer membrane of this fuel cell exhibits high proton conductivity when in a wet state, it is important to keep the solid polymer membrane in a wet state in order to efficiently generate power. In order to keep the solid polymer membrane in a wet state, water that exchanges water between the oxidizing off-gas discharged from the cathode side of the fuel cell through the water vapor permeable membrane and the oxidizing gas supplied to the cathode side of the fuel cell. Exchangeable humidifiers (hereinafter simply referred to as “humidifiers”) are used.

  The oxidizing off gas discharged from the fuel cell is a gas with high humidity including generated water generated by an electrochemical reaction. Since the oxidizing off gas is heated inside the fuel cell and has a temperature substantially equal to the internal temperature of the fuel cell, the oxidizing gas taken from outside can be humidified without providing a special heat source or the like.

  As a method for controlling the humidification amount of the oxidizing gas, a method for controlling the humidification amount of the oxidizing gas based on the measurement result of the temperature of the oxidizing off gas passing through the humidifier and the temperature of the oxidizing gas passing through the humidifier is proposed. (For example, refer to Patent Document 1).

JP 2004-31073 A

  By the way, although the moisture content of the oxidation off-gas varies due to the change in the amount of generated water accompanying the load variation of the fuel cell, the humidification response of the humidifier is slow. There is a problem that can not be.

FIG. 5 is a diagram illustrating a conventional humidification control mode.
As shown in FIG. 5A, an operation is performed in which the load current A0 of the fuel cell rises to A1 (> A0) at time T1, while the load current A1 falls to A2 (<A1) at time T2. Hereinafter, in the case of performing “transient operation” generically), the moisture content of the oxidation off-gas from the fuel cell toward the humidifier during the transient operation changes gradually (see FIG. 5B). As described above, the humidification response during transient operation (hereinafter referred to as “transient response”) is slow, but conventionally the humidification of the oxidizing gas is controlled without considering the transient response. It was not possible to always control the humidification of the water (details will be described later).

  The present invention has been made in view of the circumstances described above, and an object thereof is to provide a humidification control technique capable of appropriately controlling the humidification amount of a supply gas.

  In order to solve the above-described problem, a fuel cell humidifier according to the present invention includes a humidifier that humidifies a supply gas supplied to a fuel cell using moisture contained in an off-gas discharged from the fuel cell, and the fuel. It is characterized by comprising detection means for detecting the load state of the battery, and control means for predictively controlling the amount of water introduced from the fuel cell to the humidifier based on the detected load state.

  According to this configuration, the amount of moisture introduced into the humidifier is controlled based on the load state of the fuel cell. As is well known, in a humidifier of the type that humidifies the supply gas using moisture contained in the off-gas discharged from the fuel cell, the responsiveness of the humidification (transient response) during transient operation in which the load of the fuel cell fluctuates ) Is slow. By predicting and controlling the amount of moisture introduced into the humidifier in anticipation of such transient response of humidification, it becomes possible to always achieve a constant humidification molar ratio regardless of the load fluctuation of the fuel cell (FIG. 3). reference).

  Here, in the above configuration, the control means determines that a ratio between the amount of the supplied gas that changes depending on the detected load state and the amount of the moisture introduced into the humidifier is substantially constant regardless of the load state. Thus, a mode in which the moisture amount is prospectively controlled is preferable.

  A bypass passage for bypassing the humidifier for the off gas, an off gas passage from the fuel cell to the humidifier, and a bypass amount of the off gas provided in at least one of the bypass passage or the off gas passage. A flow control valve to adjust, and the control means controls the moisture amount by controlling at least one of an on / off time and a valve opening degree of the flow control valve based on the load state. Embodiments are also preferred.

  In the above configuration, a temperature adjustment mechanism that adjusts the temperature of the fuel cell is provided, and the control means adjusts the temperature of the fuel cell based on the load state, thereby controlling the moisture amount in anticipation. The aspect which performs is also preferable.

  As described above, according to the present invention, the humidification amount of the supply gas can be appropriately controlled.

  Embodiments according to the present invention will be described below with reference to the drawings.

A. FIG. 1 shows a schematic configuration of a fuel cell system 100 according to this embodiment. In the present embodiment described below, it is assumed that the fuel cell system 100 is used as an on-vehicle power generation system of a fuel cell vehicle (FCHV), but for various mobile objects (for example, ships and airplanes). It may be used as an onboard power generation system or a stationary power generation system.

  The fuel cell (cell stack) 140 is means for generating electric power from supplied fuel gas and oxidant gas, and has a stack structure in which a plurality of single cells including MEAs and the like are stacked in series. The fuel cell 140 includes a fuel gas passage 141 and an oxidizing gas passage 142. A fuel gas such as hydrogen gas is supplied to the fuel gas passage 141, while the oxidizing gas passage 142 is humidified through the humidifier 120. Oxidizing gas (supply gas) such as fresh air is supplied. The fuel cell 140 is provided with an ammeter (detection means) 20 that measures the load current J, and the ECU 150 is notified of the current value measured by the ammeter 20.

  The humidifier 120 exchanges water and heat between the oxidizing off-gas discharged from the oxidizing gas passage 142 of the fuel cell 140 via the water vapor exchange membrane 121 and the oxidizing gas supplied to the oxidizing gas passage 142 of the fuel cell 140. It is a means for exchanging.

  The oxidizing gas is taken in from the outside by the compressor 110 and supplied from the supply gas passage 10 to the oxidizing gas passage 142 of the fuel cell 140 via the humidifier 120. Here, a flow rate sensor or the like for measuring the flow rate of the oxidizing gas is provided in the supply gas flow path 10 on the upstream side of the humidifier 120.

  The oxidant gas supplied to the oxidant gas passage 142 of the fuel cell 140 is consumed by a predetermined amount by an electrochemical reaction, and then discharged to the off-gas passage 11 as an oxidant off-gas. Here, a bypass valve for controlling the flow of the oxidizing offgas between the offgas passage (offgas passage) 11 and the bypass passage (bypass passage) 12 is provided in the offgas passage 11 upstream of the humidifier 120. A (flow control valve) 160 is provided. Instead of providing the bypass valve 160 in the bypass flow path 12, a three-way valve (switching valve, flow distribution valve, etc .; flow control valve) may be provided at the branch point of the off-gas flow path 11 and the bypass flow path 12, or In addition, a valve (on / off valve or the like; a flow control valve) may be provided in the off gas passage 11 on the humidifier side of the branch point. Of course, these valves may be provided in appropriate combination.

  The bypass flow path 12 is a flow path for bypassing the humidifier 120 with respect to the oxidizing off gas. In this embodiment, the flow rate of the oxidizing off gas introduced into the humidifier 120 and the flow rate of the oxidizing off gas that bypasses the humidifier 120 are adjusted by controlling the opening degree of the bypass valve 160, the on / off time, and the like.

  Here, when a linear valve is adopted as the bypass valve 160, the flow rate of the oxidizing off gas introduced into the humidifier 120 is adjusted by controlling the opening degree. On the other hand, when an on / off valve is employed as the bypass valve 160, the flow rate of the oxidizing off gas introduced into the humidifier 120 is adjusted by controlling the on / off time. In the following description, a case where a linear valve is used as the bypass valve 160 is assumed.

  The cooling mechanism (temperature adjustment mechanism) 130 is a device that cools the fuel cell 140, and in addition to the temperature sensor 21 that detects the temperature T1 of the coolant such as cooling water, a pump that pressurizes and circulates the cooling water, and cooling water A heat exchanger that radiates heat to the outside (all not shown) is provided.

  The ECU (control means) 150 centrally controls each part of the fuel cell system 100 by executing various control programs incorporated in a memory such as a ROM or a hard disk. Further, the ECU 150 performs humidification amount control described later based on sensor signals supplied from each sensor. Hereinafter, humidification control of the fuel cell system according to the present embodiment will be described in detail.

<Humidification control>
2 and 3 are diagrams showing a humidification control mode when the operation shown in FIG. 5 is performed. FIG. 2 shows a conventional example, and FIG. 3 shows an example according to the present invention. Here, FIGS. 2 (a) and 3 (a) show the oxidation introduced into the humidifier 120 when the oxidation off-gas amount discharged from the fuel cell 140 is A and the bypassed oxidation off-gas amount is B, respectively. It is a figure which shows the change of the amount of off gas (AB), and FIG.2 (b) and FIG.3 (b) are figures which show the humidification molar ratio (= water mole / air mole) of oxidizing gas. The humidification molar ratio of the oxidizing gas represents the ratio of the humidification amount (number of moles of water) by the humidifier 120 and the amount of oxidizing gas (number of moles of air) introduced from the compressor 110.

  In the conventional humidification control, the oxidation introduced into the humidifier 120 by adjusting the bypass valve 160 without considering the transient response of humidification according to the load fluctuation of the fuel cell 140 (see times T1 and T2). The off gas amount (AB) was controlled (see FIG. 2A). For this reason, the humidification molar ratio of the oxidizing gas changes according to the load fluctuation as shown in FIG. 2B, and there is a problem that appropriate humidification control cannot be performed.

  More specifically, when the load current increases from A0 to A1 at time T1 (see FIG. 5A), the amount of moisture contained in the oxidation off-gas discharged from the fuel cell 140 increases as the load current increases. . However, the increase in moisture contained in the oxidizing off gas does not immediately appear as the humidifying amount of the humidifier 120, but the oxidizing gas passage 142 from the fuel cell 140 to the humidifier 120 and the off gas passage 11 (hereinafter “humidified”). Loop ”) and a delay corresponding to the flow rate of the oxidizing off gas appear (see FIG. 5B). Without considering such transient response, the amount of oxidizing off gas (AB) introduced into the humidifier 120 in accordance with the load fluctuation of the fuel cell 140 is controlled. The humidification molar ratio of fluctuates greatly (see FIG. 2B). In general, the humidification molar ratio of the oxidizing gas needs to be kept constant (for example, 0.2) at all times. Therefore, it is necessary to prevent such fluctuation of the humidification molar ratio.

  Therefore, in the present invention, as shown in FIG. 3A, a constant humidification molar ratio is always realized regardless of the load fluctuation of the fuel cell 140 by adjusting the bypass valve 160 in advance by considering the transient response. (See FIG. 3B).

FIG. 4 is a flowchart showing a humidification control process during transient operation executed by the ECU 150.
When ECU 150 detects a load fluctuation (transient operation) of fuel cell 140 based on the current value detected by current sensor 20 (step S1), ECU 150 determines the current value and the target humidification amount of oxidizing gas (hereinafter, “target humidification amount”). ”) With reference to a map (not shown) and the like, the target humidification amount is obtained, and then the bypass valve 160 is controlled (expected control) in consideration of the transient response of humidification (step S2). Specifically, the control value of the bypass valve 160 (in the case of this embodiment) expecting the humidification response from the time constant determined by the volume of the humidification loop and the flow rate of the oxidizing off gas (hereinafter referred to as “time constant of the humidification loop”). And the bypass valve 160 is controlled according to the obtained control value. The control value of the bypass valve 160 may be obtained using a map (not shown) that associates the time constant of the humidification loop with the control value of the bypass valve 160. By performing such control, a constant humidification molar ratio can always be obtained regardless of the load fluctuation of the fuel cell 140 (see FIG. 3B).

  As described above, according to the present embodiment, by performing the bypass control in consideration of the transient response of humidification, it is possible to always obtain a constant humidification molar ratio of the oxidizing gas regardless of the load fluctuation of the fuel cell. It becomes possible.

B. In the present embodiment described above, the amount of moisture introduced into the humidifier 120 is controlled by adjusting the amount of oxidizing off gas (AB) introduced into the humidifier 120 by the bypass valve 160. Instead of changing the amount of oxidizing off gas (AB) introduced into the vessel 120, the amount of water contained in the oxidizing off gas introduced into the humidifier 120 may be controlled by adjusting the temperature of the fuel cell 140. Specifically, the temperature of the fuel cell 140 may be adjusted by the cooling mechanism 130 to adjust the amount of moisture contained in the oxidizing off gas discharged from the fuel cell 140. As is well known, when the temperature of the fuel cell 140 increases, the amount of water contained in the oxidation off gas increases, while when the temperature of the fuel cell 140 decreases, the amount of water contained in the oxidation off gas decreases. The amount of moisture introduced into the humidifier 120 may be controlled by utilizing such a phenomenon. Of course, the amount of moisture introduced into the humidifier 120 may be controlled by using the adjustment of the bypass valve 160 and the temperature adjustment of the fuel cell 140 together. Further, the flow rate per unit time of the oxidizing off gas is adjusted by adjusting various control valves (not shown) provided in the off gas flow path 11 and the like, thereby being included in the oxidizing off gas introduced into the humidifier 120. The amount of moisture generated may be controlled. In this embodiment, the load state of the fuel cell 140 is detected by detecting the load current of the fuel cell 140, but the load state of the fuel cell 140 is detected by detecting other parameters (such as the temperature of the fuel cell). Of course, it may be detected.

It is a figure which shows the structure of the fuel cell system which concerns on this embodiment. It is a figure which shows the control aspect of the conventional humidification. It is a figure which shows the control aspect of the humidification which concerns on this embodiment. It is a flowchart which shows the humidification control process which concerns on the same embodiment. It is a figure which shows the control aspect of the conventional humidification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Fuel cell system, 110 ... Compressor, 120 ... Humidifier, 121 ... Steam exchange membrane, 130 ... Cooling mechanism, 140 ... Fuel cell, 141 ... Fuel gas passage 142 ... oxidizing gas passage, 150 ... ECU, 160 ... bypass valve, 10 ... supply oxidizing gas passage, 11 ... oxidation off gas passage, 12 ... purge passage, 21 ... Temperature sensor, 20 ... Current sensor.

Claims (5)

A humidifier that humidifies a supply gas supplied to the fuel cell using moisture contained in the off-gas discharged from the fuel cell;
Detecting means for detecting a load state of the fuel cell;
And a control means for predictively controlling the amount of water introduced from the fuel cell to the humidifier based on the detected load state.   The control means predictively controls the water amount so that a ratio of the supply gas amount that changes depending on the detected load state and the water amount introduced into the humidifier is substantially constant regardless of the load state. The humidifying device for a fuel cell according to claim 1. A bypass passage for bypassing the humidifier for the off gas, an off gas passage from the fuel cell to the humidifier, and a bypass amount of the off gas provided in at least one of the bypass passage or the off gas passage is adjusted. A flow control valve,
The said control means carries out speculative control of the said moisture content by controlling at least any one of the on-off time of the said flow control valve based on the said load state, and a valve opening degree, It is characterized by the above-mentioned. The humidifier for fuel cells as described.   The control means obtains a control value of the flow rate control valve expecting humidification responsiveness from a time constant determined by the volume of the humidification loop from the fuel cell to the humidifier and the flow rate of the off gas, and obtains the calculated control value. 4. The fuel cell humidifier according to claim 3, wherein the flow control valve is controlled accordingly.   The humidifying device for a fuel cell according to any one of claims 1 to 4, wherein the detection means is a current sensor that detects a current value of the fuel cell.

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