Stress compensated systems and methods of compensating for electrical and mechanical stress are discussed. One example system can include a first circuit and a global stress compensation component. The first circuit can be configured to generate a first signal and can comprise at least one local stress compensation component (e.g., employing dynamic element matching, chopping, etc.). The global stress compensation component can comprise one or more stress sensors configured to sense one or more stress components associated with the system. The global stress compensation component can be configured to receive the first signal and to compensate for stress effects on the first signal.

A fuel cell vehicle capable of generating electric power in an optimum wet state is provided. A fuel cell vehicle including a fuel cell, a radiator configured to cool a coolant which has been warmed by cooling the fuel cell and send it back to the fuel cell, a grille shutter configured to adjust a flow rate of air taken into the radiator from an air intake, a sensor configured to measure an impedance of the fuel battery, and a control unit configured to control the grille shutter to open and close. The control unit controls the grille shutter to open when a measured value of the impedance becomes greater than or equal to a predetermined threshold.

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.

A method of diagnosing level sensor failure in a fuel cell water trap, the method may include: determining whether a water level of a level sensor is changed in a fuel cell water trap, adding an amount of charge according to an operating time and comparing the added amount of charge with a preset threshold amount of charge, according to the result of the, forcibly opening a drain valve according to determining whether a channel voltage of a specific channel is abnormal as the result of the comparison, and diagnosing a failure of the level sensor according to determining whether the channel voltage of the specific cell is recovered as a normal state when the drain valve is opened.

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 fuel cell (FC) system is provided, having a FC stack supplied with a reaction gas and performing power generation by electrochemical reaction of the reaction gas. The FC system includes a supply passage, supplying the reaction gas to the FC stack; a discharge passage, distributing an off-gas discharged from a discharge outlet of the fuel cell stack; a bypass passage, communicate between the supply passage and the discharge passage; a cooling passage, provided in the discharge passage and having a heat sink to condense water in the off-gas; a circulation pump, provided in the bypass passage and circulating the off-gas discharged from the discharge passage to the supply passage when the FC system stops. When the FC system stops, as the temperature information of the FC stack from temperature information acquisition unit is equal to or larger than a predetermined first threshold temperature, the controller activates the circulation pump.

A fuel cell reversal event is diagnosed by integrating current density via a controller in response to determine an accumulated charge density. The controller executes a control action when the accumulated charge density exceeds a threshold, including recording a diagnostic code indicative of event severity. The control action may include continuing stack operation at reduced power capability when the accumulated charge density exceeds a first threshold and shutting off the stack when the accumulated charge density exceeds a higher second threshold. The event may be detected by calculating a voltage difference between an average and a minimum cell voltage, and then determining if the difference exceeds a voltage difference threshold. The charge density thresholds may be adjusted based on age, state of health, and/or temperature of the fuel cell or stack. A fuel cell system includes the stack and controller.

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 are disclosed for starting up a fuel cell system from starting temperatures below 0 C. The methods apply to systems comprising a solid polymer electrolyte fuel cell stack whose cathodes comprise an oxygen reduction reaction (ORR) catalyst and whose anodes comprise both a hydrogen oxidation reaction (HOR) catalyst and an oxidation evolution reaction (OER) catalyst. In the methods, from the beginning of starting up until the fuel cell temperature reaches 0 C., the fuel cell stack current is kept sufficiently low such that the current density drawn does not exceed the stack's capability for the oxidation evolution and the oxygen reduction reactions to occur at the anode and cathode respectively (i.e. current density drawn is less than the stack's maximum OER/ORR current density).