(a) Field of the Invention
The present invention relates to a method and an apparatus to diagnose a fault of a fuel cell stack.
(b) Description of the Related Art
A fuel cell is a type of battery that directly converts chemical energy generated by oxidation of fuel to electrical energy which can be utilized by any number of devices. For the most part, a fuel cell is identical to a chemical cell in that it uses an oxidation and reduction reaction to produce energy. However, in a fuel cell, reactants are intermittently supplied from an outside source and thus, reaction products are consecutively removed from a fuel cell system. In a chemical cell, however, the battery reaction is performed within a closed system.
Currently, commercialization of the fuel cell has begun to take off because the reaction product of the fuel cell is pure water and thus is very environmentally friendly. Accordingly, research for using fuel cells as an energy source for vehicles is of great interest in the automotive industry.
A fuel cell is often made up of a stack assembly in which a plurality of unit cells are consecutively disposed one on top of/next to the other, which is referred to within the industry as a fuel cell stack. Electrical energy is produced by providing each unit cell of the fuel cell stack with hydrogen as a fuel and oxygen as an oxidizer. However, when performance deterioration or a failure occurs in any one cell among the unit cells that make up the fuel cell stack, the entire performance of the fuel cell stack is deteriorated and thus, a stable operation is not provided.
In the related art, performance of the fuel cell stack is diagnosed by measuring voltage output from each unit cell of the fuel cell stack. Such diagnosis method includes a total harmonic distortion analysis (THDA) method. The THDA method diagnoses cell voltage by calculating a distortion rate through frequency analysis of the stack voltage. Even though the THDA method may easily detect a drop in cell voltage, it is substantially difficult to quantitatively measure what has caused the drop in cell voltage.
Also, there is a method of measuring impedance of the fuel cell stack using an electrochemical impedance spectroscopy (EIS). This method supplies a current or voltage as a sinusoidal waveform to the fuel cell stack and then measures a current (I) and voltage (V) of the fuel cell stack and calculates impedance based on the measured current (I) and voltage (V) of the fuel cell stack.
However, this method diagnoses the humidification state by measuring the load on a stack, but does not diagnose the drop in cell voltage. Accordingly, a separate apparatus such as a space vector modulator (SVM) or a capacitive voltage multiplier (CVM) is required.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.