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.

An apparatus and method for determining the condition of an electricity-producing cell such as a fuel cell is disclosed. A signal is injected into an electricity-producing cell, a voltage and/or current response is measured, and the impedance response of the electricity-producing cell is calculated using the injected signal and the response. The injected signal is a broadband signal that includes a plurality of superimposed waveforms at different frequency set points across a frequency range. The distribution of the waveform frequency set points is linear at either or both of a lower portion and an upper portion of the frequency range, and is logarithmic at a mid-range of the frequency range. The response at each of the frequency set points are simultaneously obtained and the impedance response across the frequency range is calculated and used to determine a condition of the electricity-producing cell.

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 10 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 15 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.

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 for observing a state of an electrochemical system including a fuel cell including the following steps: measuring parameters that are representative of the fuel cell in operation; forming a control vector; forming a measurement vector; calculating a temporal variation, referred to as a non-corrected temporal variation; calculating a corrective term in sliding mode; calculating an estimate of the state of the electrochemical system; reiterating above steps while incrementing the measurement time.

A multichannel fuel cell test station for testing a performance of a fuel cell membrane electrode assembly (MEA) is provided. The multichannel fuel cell test station may include a cell mounting portion configured to receive a plurality of unit cells, a gas supply configured to supply fuel gas to the unit cells and including a pressure generator and a mass flow controller (MFC), a temperature controller configured to maintain a constant ambient temperature of the unit cells, a humidifying portion configured to maintain a constant humidification state around the unit cells, a measurer configured to measure performances and electrochemical impedances of the unit cells, and a controller configured to control the gas supply, the temperature controller, the humidifying portion and the measurer.

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.

Methods, systems, and techniques are provided for acquiring fuel cell polarization data, obtaining fuel cell polarization parameters from the fuel cell polarization data, and validating the reliability of the obtained data and parameters. In some aspects methods for acquiring and parameterizing proton exchange membrane fuel cell polarization data include measuring at least one current-voltage point for an operating fuel cell, and determining at least one polarization parameter of the fuel cell by evaluating a closed form solution using the at least one current-voltage point.

A system for measuring a moisture content of an ion-exchange membrane in a fuel-cell stack is provided. The fuel-cell stack includes N electrochemical cells separated by bipolar plates, with N being a natural integer. The system includes a current generator, a voltage measurement device, and an impedance measurement device. The current generator enables a current to be applied to the fuel-cell stack. The voltage measurement device measures voltages of the cells of the fuel-cell stack. The impedance measurement device determines an impedance of an ion-exchange membrane according to a voltage ripple measured by the voltage measurement device across terminals of a corresponding one of the cells of the fuel-cell stack when the current is applied by the current generator. The impedance measurement device is installed in the voltage measurement device.

A method for diagnosing a water-containing state of a fuel cell stack includes steps of: applying an alternating current (AC) signal having a predetermined frequency to the fuel cell stack to calculate each of an electrolyte membrane impedance, an anode impedance, and a cathode impedance from an output voltage and an output current of the fuel cell stack corresponding to the AC signal; and diagnosing the water-containing state of the fuel cell stack on the basis of the electrolyte membrane impedance, the anode impedance, and the cathode impedance.