Apparatus and method for controlling humidification amount of membrane humidifier for fuel cell

1. An apparatus for controlling a humidification amount of a membrane humidifier for a fuel cell, comprising:

an air compressor configured to compress air and supply the air to the membrane humidifier;

a membrane humidifier configured to humidify the air supplied from the air compressor and supply the air to a stack;

a pressure control valve mounted at an outlet of the membrane humidifier to adjust pressure of humid air that flows from the stack to an exterior of a hollow fiber membrane of the membrane humidifier;

a first air shut-off valve mounted at an inlet of the stack to adjust pressure of air that flows from the air compressor to the inside of the hollow fiber membrane of the membrane humidifier;

a humidity sensor configured to measure humidity of the stack; and

a controller configured to:

increase pressure in the hollow fiber membrane of the membrane humidifier by reducing or blocking an amount of humid air supplied from the stack to the membrane humidifier when the measured humidity is equal to or greater than a reference value; and

increase pressure inside and outside the hollow fiber membrane of the membrane humidifier by blocking the outlet of the membrane humidifier through which humid air is supplied from the stack to the membrane humidifier and humid air is discharged when the measured humidity is equal to or less than the reference value.

2. The apparatus of claim 1 , wherein a second air shut-off valve is further mounted in a humid air discharge line connected from an outlet of the stack to an inlet of the membrane humidifier.

3. The apparatus of claim 1 , wherein the humidity sensor is configured to measure humidity of the stack to determine opening degrees of the pressure control valve and the air shut-off valves.

4. A method of controlling a humidification amount of a membrane humidifier for a fuel cell, comprising:

measuring, by a humidity sensor, humidity of a stack;

increasing, by a controller, pressure in a hollow fiber membrane of the membrane humidifier configured to humidify air supplied from an air compressor and supply the air to a stack, by reducing or blocking an amount of humid air supplied from the stack to the membrane humidifier when the measured humidity is equal to or greater than a reference value, wherein the membrane humidifier receives air compressed and supplied from the air compressor; and

increasing, by the controller, pressure inside and outside the hollow fiber membrane of the membrane humidifier by blocking an outlet of the membrane humidifier through which humid air is supplied from the stack to the membrane humidifier and humid air is discharged when the measured humidity is equal to or less than the reference value,

wherein a pressure control valve is mounted at the outlet of the membrane humidifier to adjust the pressure of the humid air that flows from the stack to an exterior of the hollow fiber membrane and a first air shut-off valve is mounted at an inlet of the stack to adjust the pressure of the air that flows from the air compressor to the inside of the hollow fiber membrane.

5. The method of claim 4 , further comprising:

decreasing, by the controller, an opening degree of a first air shut-off valve mounted at an inlet of the stack or closing the first air shut-off valve, or decreasing, by the controller, an opening degree of a second air shut-off valve mounted in a humid air discharge line that connects an outlet of the stack and an inlet of the membrane humidifier or closing the second air shut-off valve.

6. The method of claim 4 , wherein when pressure inside the hollow fiber membrane of the membrane humidifier is increased, a difference in partial pressure of moisture between the inside and an exterior of the hollow fiber membrane is decreased, causing a humidification amount of dry air flowing inside the hollow fiber membrane to decrease.

7. The method of claim 4 , further comprising:

decreasing, by the controller, an opening degree of a pressure control valve mounted at an outlet of the membrane humidifier or closing the pressure control valve when humid air is supplied from the stack to the membrane humidifier.

8. The method of claim 4 , wherein when pressure inside and outside the hollow fiber membrane of the membrane humidifier is increased, a difference in partial pressure of moisture between the inside and an exterior of the hollow fiber membrane is increased, causing a humidification amount of dry air flowing inside the hollow fiber membrane to increase.