A method and system for diagnosing a state of fuel cell are provided. The system includes a signal measurement unit that has a high pass filter with a predetermined cut-off frequency and a voltage measurement circuit, and that measures a first AC voltage to measure the fuel cell state diagnosis signal and a noise measurement unit including a band pass filter that has a predetermined pass band and a voltage measurement circuit, and that measures a second AC voltage to measure the fuel cell state diagnosis noise. A controller calculates a signal to noise ratio (SNR) of fuel cell state diagnosis data based on the first and second AC voltages, determines the corresponding fuel cell state diagnosis data to be reliable when the SNR value is greater than a predetermined reference value, and applies the fuel cell state diagnosis data to a control of a fuel cell vehicle.

A method of determining hydrogen deficiency of a fuel cell having a plurality of cell groups includes a reference value storage step of storing, as a reference value, a value of impedance in a state where hydrogen-off gas is discharged from the fuel cell and hydrogen gas and oxidant gas are supplied, a measured value calculation step of calculating a measured value of impedance based on a voltage of the cell groups and a current of the fuel cell, a corrected value calculation step of calculating a corrected value of impedance by correcting the measured value based on the reference value, and a determination step of determining that hydrogen deficiency occurs in a case where the corrected value exceeds a predetermined threshold.

An electrochemical fuel cell assembly comprises a fuel cell stack having a fuel delivery inlet and a fuel delivery outlet. The fuel cell stack further includes a number of fuel cells each having a membrane-electrode assembly and a fluid flow path coupled between the fuel delivery inlet and the fuel delivery outlet for delivery of fuel to the membrane-electrode assembly. A fuel delivery conduit is coupled to the fuel delivery inlet for delivery of fluid fuel to the stack. A bleed conduit is coupled to the fuel delivery outlet for venting fluid out of the stack. A variable orifice flow control device coupled to the bleed conduit configured to dynamically vary an amount of fluid from the fuel delivery outlet passing into the bleed conduit as a function of one or more of the control parameters: (i) measured fuel concentration; (ii) measured humidity; (iii) cell voltages of fuel cells in the stack; (iv) impedance of fuel cells in the stack; (v) resistance of fuel cells in the stack. The variable orifice flow control device may be coupled to a recirculation conduit and may be configured to dynamically vary a proportion of fluid from the fuel delivery outlet passing into the bleed conduit as a function of the control parameters.

The invention relates to a method for determining critical operating states in a fuel cell stack, consisting of single cells connected in series, wherein a low-frequency current or voltage signal is applied to the fuel cell stack, the resulting voltage or current signal is measured and the distortion factor thd is determined. According to the invention, the weighted sum of a term dependent on the membrane resistance RM and a term dependent on the distortion factor thd is used to determine an indicator THDA.sub.dryout correlating with the drying out of the fuel cell membranes of the fuel cell stack, the membrane resistance Rm being detected by impedance measurement.

The invention relates to a method for determining critical operating states in a fuel cell stack, consisting of single cells connected in series, wherein a low-frequency current or voltage signal is applied to the fuel cell stack, the resulting voltage or current signal is measured and the distortion factor thd is determined. According to the invention, the weighted sum of a term dependent on the membrane resistance RM and a term dependent on the distortion factor thd is used to determine an indicator THDA.sub.dryout correlating with the drying out of the fuel cell membranes of the fuel cell stack, the membrane resistance Rm being detected by impedance measurement.

A method for controlling a fuel cell system includes supplying an oxidant gas, via an oxidant gas supply channel, to a cathode electrode of a fuel cell. The oxidant gas is moistened to be supplied to the cathode electrode with a humidifier. An opening degree of a bypass channel valve is decreased via a feedforward control to a first opening degree when an impedance has reached a lower limit value. The opening degree of the bypass channel valve is increased via the feedforward control to a second opening degree when the impedance has reached an upper limit value. The first opening degree is smaller than the second opening degree.

A power supply system includes a power supply, a converter, and a processor. The converter converts voltage of the electric power supplied from the power supply. The processor is configured to generate a first control signal to control the converter to output a target voltage or a target current via a feedback control based on the first control signal. The processor is configured to generate a second control signal to detect a state of the power supply. The processor is configured to combine the first control signal and the second control signal to control the converter.

A fuel cell internal state detection system includes estimation object state quantity setting unit for setting a suitable estimation object state quantity as an index of an internal state, an impedance value acquisition unit configured to obtain an impedance value of a fuel cell, an impedance usability judging unit configured to judge whether or not the obtained impedance value is usable for the calculation of the estimation object state quantity, estimation object state quantity calculation unit for calculating the estimation object state quantity set by the estimation object state quantity setting unit on the basis of the obtained impedance value when the impedance value is judged to be usable for the calculation of the estimation object state quantity by the impedance usability judging unit, and an unusable-scene process execution unit configured to perform an unusable-scene process when the impedance value is judged not to be usable for the calculation of the estimation object state quantity by the impedance usability judging unit.

Disclosed are a redox flow battery and a method of measuring a state of charge (SOC) thereof. The method may include measuring an open circuit voltage (OCV) during a specific period of time when a charging or discharging operation of a redox flow battery is performed, analyzing a change in SOC of the redox flow battery based on the measured OCV, correcting Coulomb efficiency based on the change in SOC, and calculating a second SOC of the redox flow battery based on the corrected Coulomb efficiency. The Coulomb efficiency may be a parameter, in which information regarding actual operation factors of the redox flow battery is contained.

An AC component I addition unit of a diagnostic device superimposes an alternating current on an output current of a fuel cell. A Zn calculation unit calculates a cell impedance with respect to the alternating current with regard to any of a plurality of cells. A diagnosis unit diagnoses that any cell is subjected to hydrogen deficiency when an absolute value of the cell impedance exceeds (absolute value of a reference impedance+a predetermined value ). It is diagnosed that any cell is subjected to oxygen deficiency when the absolute value of the cell impedance is smaller than (absolute value of the reference impedancea predetermined value ).