Abstract: A method for providing a current density set-point for a fuel cell stack in response to a power request from the stack where the set-point is determined based on system parameters that identify the life and degradation of the stack. The method includes dividing a current density range of the fuel cell stack into a predetermined number of sample regions, and selecting the sample regions in order from low to high during the current set-point analysis. The method calculates an average cell voltage for the current density of the selected sample region, and stack power from the average cell voltage. The method then determines whether a power request signal is less than the stack power for the selected sample region and greater than the calculated power for the previous sample region, and if so, calculates the current density set-point at the requested power based on these values.

Abstract: A fuel cell system can be initiated in shorter time while minimizing the deterioration of a fuel cell. The fuel cell system includes a fuel cell stack having a fuel electrode, an oxidizer electrode and an electrolyte membrane disposed there between, the fuel cell producing electricity by an electrochemical reaction of a fuel gas and an oxidizer gas, which are supplied to the fuel electrode and the oxidizer electrode, respectively; a fuel gas supplying device for supplying the fuel gas to the fuel cell stack; an oxidizer gas supplying device for supplying the oxidizer gas to the fuel cell stack; a current controlling device for extracting a current from the fuel cell stack; and a voltage sensor disposed in at least two of the fuel cell stacks.

Abstract: A method is generally described which includes operating an electrical energy storage device or an electrochemical energy generation device includes providing at least one thermal control structure formed of a high thermal conductive material. The high thermal conductive material having a high k-value, the high k-value being greater than approximately 410 W/(m*K). The thermal control structures are disposed adjacent at least a portion of the electrical energy storage device or the electrochemical energy generation device. The thermal control structures are configured to provide heat transfer away from the portion of the electrical energy storage device or the electrochemical energy generation device. The method also includes configuring a controller with a control algorithm to control the actions of a controllable fluid flow device as a function of a mobile device states. The mobile device using electricity from the electrical energy storage device or the electrochemical energy generation device.

Abstract: A method for determining membrane humidification by determining the membrane protonic resistance of a fuel cell stack at humidified conditions, and normalizing the base resistance of the fuel cell stack against the base resistance of a reference fuel cell stack.

Abstract: Systems and methods to control the delivery of coolant to a coolant loop within a vehicular fuel cell system. During periods of low power output from one or more fuel cell stacks, operation of a pump used to circulate coolant through the loop is intermittent, thereby reducing pump usage during such times. The frequency of pump operation, as measured by a pump on/off (i.e., pulsed) cycle, may be adjusted to keep a local temperature rise within the one or more stacks to no more than a small amount over the bulk stack temperature.

Abstract: To provide a fuel cell system capable of performing a purge operation necessary for realizing a stable output and being miniaturized without using a controller or a sensor, there is provided a fuel cell system having a main power generation part and a sub-power generation part positioned on a downstream side of a fuel flow path of the main power generation part, including: a purge valve provided on a downstream side of the fuel flow path of the sub-power generation part; and an actuator for opening/closing the purge valve with an electromotive force of the sub-power generation part.

Abstract: A method includes an in-stop-mode power generating process of, if an instruction to stop an operation of a fuel cell is detected, stopping supply of a fuel gas, and supplying an oxide gas to the fuel cell to generate power from an oxide-gas supply apparatus, and then stopping power generation of the fuel cell, and a gas replacing process of, after the power generation of the fuel cell is stopped, activating the gas replacement apparatus at a predetermined timing to supply a replacement gas to the anode side of the fuel cell to replace the fuel gas on the anode side with the replacement gas.

Abstract: A method of controlling a fuel cell system includes applying alternating current (AC) signals to an individual fuel cell. The AC signals have a plurality of different frequencies. A voltage across the individual fuel cell is determined at each of the plurality of different frequencies. An impedance characteristic of the individual fuel cell is determined based at least in part on the voltage across the individual fuel cell at each of the plurality of different frequencies. The individual fuel cell is controlled based at least in part on the impedance characteristic.

Abstract: A fuel cell system for a vehicle includes a fuel cell arrangement that is coupleable to a vehicle drive as a primary load, and to a plurality of secondary loads. A control apparatus which controls the primary load and the secondary loads includes a monitoring circuit that is operable in a special operating mode of the fuel cell system, with the secondary loads being switched on and/or off as a manipulated variable in order to maintain the output voltage, as a reference variable, at a low voltage value that is formed by a cell voltage of the fuel cells of less than 0.45 V on average.

Abstract: A method of operating a capacitive deionization cell using a regeneration cycle to increase pure flow rate and efficiency of the cell.

Abstract: A method of operating a high temperature fuel cell system containing a plurality of fuel cell stacks includes operating one or more of the plurality of fuel cell stacks at a first output power while operating another one or more of the plurality of the fuel cell stacks at a second output power different from the first output power.

Abstract: A fuel cell fleet has a plurality of fuel cell systems each connected to a data server. The data server may be configured to obtain operational data from of the plurality of fuel cell systems. An efficiency controller operably connected to the data server and is configured to predict an efficiency and a power output of the fleet from the operational data and optimize the efficiency of the fleet to minimize the fleet fuel consumption while maintaining a desired fleet output power. The efficiency may be determined by a ratio of the fleet output current or output power to the fleet fuel consumption.

Abstract: The present invention aims to provide a hydrogen generating method for generating hydrogen-containing gas little contaminated with nitrogen, CO, etc., by decomposing fuel containing an organic compound at low temperature while requiring the supply of no or little electric energy from an external source, and a hydrogen generating system based on the method. A hydrogen generating system based on the method can work under multiple conditions: (a) it works under a condition where electric energy is withdrawn from the hydrogen generating cell with the fuel electrode (12) serving as a negative electrode and the oxidizing electrode (14) as a positive electrode; and (b) it works under another condition where external electric energy is provided to the hydrogen generating cell with the fuel electrode (12) serving as cathode and the oxidizing electrode (14) as anode.

Abstract: A fuel cell system has a fuel cell generating power using a fuel gas and an oxidizing agent gas serving as materials of the system and a material supply section supplying the materials to the fuel cell. The power generated by the fuel cell is extracted to a load. A device for controlling the fuel cell system has: a material flow calculation section calculating a material flow supplied to the fuel cell so as to cause the fuel cell to generate the power of a required power generation amount; a material reduction limit detection section calculating a limit for reducing the material flow, based on a power generation state of the fuel cell; and a material flow change section controlling the material supply section so as to change the material flow calculated by the material flow calculation section to the limit calculated by the material reduction limit detection section.

Abstract: Provided is a fuel cell system including a fuel cell which is a DC power source and boosting unit which boosts the output voltage of the fuel cell for supply to a load. The boosting unit has: a main boosting unit which has a switch and a coil and boosts the output voltage of the fuel cell by a back electromotive force of the coil generated by a switching operation of the switch with respect to the coil; and a sub boosting unit having a snubber capacitor which adjusts a potential difference between the both electrodes of the switch by an accumulation amount and reduces the switching loss of the switch by adjusting the accumulation amount of the snubber capacitor upon a switching operation. The electricity of the snubber capacitor discharged when reducing the accumulation amount of the snubber capacitor is made to flow into processing unit other than the fuel cell by the sub boosting unit.

Abstract: A system and method for preventing anode reactant starvation. The system includes a hydrogen source, an anode bleed valve, and a cell voltage monitor. The system also includes an anode sub-system pressure sensor and a controller configured to control the anode sub-system. The controller determines the average cell voltage and estimates the hydrogen molar fraction and/or nitrogen molar fraction in the anode sub-system. The controller also receives measurement data from the cell voltage monitor and the pressure sensor, and determines whether there is a decrease in the minimum cell voltage in response to changes in the anode pressure. If the controller detects a decrease in the minimum cell voltage in response to changes in the anode pressure, the controller corrects for the decrease by increasing anode pressure and/or by decreasing the molar fraction of nitrogen in the anode sub-system.

Abstract: A method of operating a fuel cell electrochemical system includes receiving at least one of a cost of electricity and a cost of fuel and adjusting at least one of an operating efficiency and throughput of the fuel cell based on the at least one of the received cost of electricity and the received cost of fuel.

Abstract: An FC voltage increasing converter includes a plurality of converter parts having reactors. Regarding the first of the plurality of converter parts provided with a thermistor, the output starts to be limited when the temperature detected by the thermistor reaches a limitation starting temperature, which is obtained based on a reference heat-resistant temperature, which is obtained by subtracting an error of the thermistor from a specification heat-resistant temperature of each of the reactors. Meanwhile, regarding the second, third and fourth of the plurality of converter parts not provided with thermistors, the outputs start to be limited when the temperature detected by the thermistor reaches a limitation starting temperature obtained based on an allowable temperature, which is obtained by subtracting a characteristic-variation temperature of the reactor from the reference heat-resistant temperature of the reactor.

Abstract: In a fuel cell system including a stack of polymer electrolyte fuel cells, the wet state of electrolyte membranes in the fuel cell stack is detected according to a variation in measurement value of an alternating current impedance (AC impedance) of the fuel cell stack. In an adequate level of water content of the electrolyte membranes, the measurement value of the AC impedance is substantially constant and has a very little variation. In an excess level of water content of the electrolyte membranes, the measurement value of the AC impedance has a significant variation. The AC impedance of the fuel cell stack is determinable by frequency analysis of high-frequency noise generated by an inverter included in the fuel cell system.

Abstract: A fluid regulating system is provided for controlling fluid to a fluid consuming battery having a fluid consuming cell. The fluid regulating system includes a valve and an actuator for opening and closing the valve. The actuator is controlled to open the valve when greater battery electrical output is required and to close the valve when lesser battery electrical output is required to operate a device. A controller controls operation of the actuator to open and close the valve based on a monitored rate of change in electrical output, such as voltage, compared to a rate of change threshold, wherein the valve is opened when the monitored rate of change exceeds the threshold.

Abstract: A system and method for determining a maximum average cell voltage set-point for fuel cells in a fuel cell stack that considers oxidation of the catalyst in the fuel cells. The method includes determining the average cell voltage, the stack current density (I) and an internal resistance (R) of membranes in the fuel cells to calculate an IR corrected average cell voltage. The IR corrected average cell voltage is then used to determine the oxidation state of the catalyst particles using, for example, an empirical model. The oxidation state of the particles is then used to calculate the maximum average cell voltage set-point of the fuel cells, which is used to set the minimum power requested from the fuel cell stack.

Abstract: A fuel cell system is provided that can establish, for a long time period, a stack to an idling stop state. The fuel cell system includes: an idling stop control means for setting the stack to an idling stop state by, decreasing both a supplied amount of air to the stack and generated electric current produced from the stack to less than during the idling power generation; and a discharge valve control means for determining whether there is a necessity to discharge nitrogen or generated water inside of the anode system, and for opening the purge valve or drain valve in a case of there being a necessity. The discharge valve control means shortens valve open times (PO2, DO2) of the purge valve and drain valve during idling stop to less than the valve open times (PO1, DO1) thereof during idling power generation.

Abstract: A power request controller that prevents a power request signal to a fuel cell stack controller from providing more compressor air and hydrogen gas than is necessary to meet the current power demands of the vehicle. The stack controller generates a signal of the available current from the fuel cell stack. This signal and the measured current actually being drawn from the stack are received by a proportional-integral (P-I) controller in the power request controller. If the available stack current is significantly greater than the stack current being used, the P-I controller will provide an output signal that reduces the power request signal to the stack controller so that the current produced by the stack and the current being drawn from the stack are substantially the same. A transient detector turns off the P-I controller so that it does not reduce the power request signal during an up-power transient.

Abstract: The present invention is directed to a solid oxide fuel cell system with a load following function. The system sets a command power value, based on the amount of load, and instructs an inverter to achieve a permitted power value corresponding to the command power value, which is a permitted amount of power to be extracted from the fuel cell system. The system also changes an amount of change per unit time in the next inverter permitted power value.

Abstract: A system and method for determining the maximum allowed stack current limit rate for a fuel cell stack that considers cell voltage. The method includes estimating a fuel cell stack voltage based on a fuel cell resistance value, stack variables and a current request signal. The fuel cell resistance value can be modeled based on stack temperature and stack relative humidity. The stack variables can include exchange current density and mass transfer coefficient. The method then uses the estimated fuel cell voltage and a look-up table based on estimated voltage to determine a current rate limit value for changing the current of the stack. The method then adds the current rate limit value and the current request signal to obtain the current set-point.

Abstract: This disclosure relates to module level redundancy for fuel cell systems. A monitoring component monitors a set of operational parameters for a fuel cell group. The fuel cell group includes a set of fuel cell units, each having a set of fuel cell stacks. The fuel cell stacks include a set of gas powered fuel cells that convert air and fuel into electricity using a chemical reaction. The monitoring component determines that the set of operational parameters do not satisfy a set of operational criteria, and, in response, a load balancing component adjusts the electrical output capacity of the set of fuel cell units included in the fuel cell group.

Abstract: A system and method for controlling the speed of a compressor in the event that an airflow meter that measures the airflow from the compressor to the cathode input of the stack fails. When a failure of the airflow meter is detected, an algorithm first deactivates the primary feedback control algorithms used to control cathode pressure and flow, and sets the cathode exhaust valve to a fully open position. The speed of the compressor is controlled by an open loop set-point and the airflow from the compressor is estimated by a model using compressor discharge pressure and the compressor speed. The cathode by-pass valve position is determined by calculating the difference between the requested cathode airflow and the modeled compressor output flow. The position of the by-pass valve is then adjusted using the valve characteristics and the compressor discharge pressure. The estimated airflow to the stack is used to control the maximum stack current.

Abstract: A system and method for determining a loss of cooling fluid from a thermal sub-system in a fuel cell system. The method includes monitoring current feedback from a high temperature pump that pumps the cooling fluid through a coolant loop. A measured current from the pump is compared to an expected current for the system operating conditions, and if that current is significantly less than what is expected, then it may be as a result of low cooling fluid. If the measured current is less than the expected current for a predetermined period of time, then the system can take mitigating action as a result of a low cooling fluid. Further, if the pump speed is too low to provide an accurate current measurement, then it can be increased if an overflow tank level sensor indicates a low cooling fluid level.

Abstract: A fuel cell system (1) which includes: a fuel cell (2) to be supplied with a gas for power generation, the gas unused for the power generation to be discharged out of the fuel cell (2); a circulation flow path (8) through which the discharged gas is resupplied to the fuel cell (2); a variable flow rate circulation pump (6) for circulating the gas through the circulation flow path (8); a valve (7) for discharging the gas in the circulation flow path (8) to the outside thereof; a voltage sensor (22) for measuring voltage of the fuel cell (2); and a controller (32) for controlling the circulation pump (6) and the valve (7). The circulation pump (6) and the valve (7) are controlled based on the voltage (CV) measured by the voltage sensor (22).

Abstract: A power supply apparatus has a combined power source with power cells configured electrically independently. A switch arbitrarily changes connection paths of the power cells by selectively connecting terminals of the power cells through switching elements. A detector detects differences in electrical potentials between power cell terminals. An output detector detects a power consumption in a load and/or an output power of the power source. ON-OFF states of the switching elements are controlled by a control signal generated based on voltage signals representing detected differences in electrical potentials, power consumption, and output power. A connection status of each power cell is controlled so as to halt outputting of the power cell having the lowest output voltage if it is detected that a detected power value is equal to or lower than an output power preset based on a power generating capacity of the power source.

Abstract: Provided is a fuel cell system that can suitably control a voltage converter in response to a judgment that an abnormal condition occurs in a power detection unit that detects a power passing through the voltage converter. The fuel cell system has: a first power detection unit that estimates an effective value of a converter input power by multiplying the converter input power, which is obtained from a battery voltage and a battery current, by a converter efficiency; a second power detection unit that estimates a converter output power from a fuel cell voltage, a fuel cell current and a driving motor load power; and a third power detection unit that estimates a converter flowing power from a current of a reactor measured by a current sensor (shown in a separate drawing). The fuel cell system also has similar detection units for current, and using one of the detection units or a combination of some of them, specifies a malfunctioning sensor and prohibits correction of parameters.

Abstract: There is provided a method for the activation of a fuel cell. An exemplary method comprises operating the fuel cell entirely or partially at least briefly in an electrolysis regimen during galvanic operation.

Abstract: A fuel cell system according to the present invention is characterized by comprising a measurement unit which measures an impedance of a fuel cell in a predetermined frequency region, and a regulation unit which regulates an amount of a gas to be supplied to the fuel cell based on a measured value of the impedance in the predetermined frequency region. According to such a constitution, the impedance of the fuel cell in the predetermined frequency region (e.g., a low frequency region) is measured, and the amount of the gas (e.g., an amount of an oxidizing gas) to be supplied to the fuel cell is regulated based on this measured value of the impedance. Here, since the impedance of the fuel cell in the predetermined frequency region largely differs with a fuel supply state (see FIG. 2), the amount of the gas to be supplied to the fuel cell can be regulated based on the measured value of the impedance to realize a highly efficient and stable operation.

Abstract: A fuel cell system for use in transportation equipment, for example, can determine an abnormality in its fuel supply device without additional detectors being provided for abnormality detection. The fuel cell system is mounted on a motorbike, and includes a cell stack which includes a plurality of fuel cells, an aqueous solution pump arranged to supply aqueous methanol solution to the cell stack, a controller which includes a CPU, an inflow temperature sensor arranged to detect a temperature of aqueous methanol solution which is introduced to the cell stack, and an outflow temperature sensor arranged to detect a temperature of aqueous methanol solution discharged from the cell stack. The CPU obtains an inflow outflow temperature difference by calculating a difference between a detection result from the inflow temperature sensor and a detection result from the outflow temperature sensor.

Abstract: A power supply apparatus has a combined power source with power cells configured electrically independently. A switch arbitrarily changes connection paths of the power cells by selectively connecting power cell terminals through switching elements. A voltage detector detects differences in electrical potentials between the power cell terminals. A controller controls ON-OFF states of the switching elements by controlling the switch by a control signal generated based on voltage signals representing the differences in electrical potentials detected by the voltage detector so as to isolate one of the power cells to stop a supply of electric power therefrom when a voltage generated in the power cell has dropped to a specified voltage or lower. The controller restarts the supply of electric power from the power cell whose power supply has been stopped when the duration of a down time of the power cell has reached a predetermined time or longer.

Abstract: There is disclosed a fuel cell system capable of stably operating auxiliary devices driven at a high voltage and the like, even in a case where a poisoned electrode catalyst is recovered or a fuel cell is warmed up. On detecting that the electrode catalyst is poisoned, a controller derives a target operation point which is sufficient for recovering an activity of the poisoned electrode catalyst. Then, shift of the operation point from a usual operation point to a low-efficiency operation point is realized so that an output power is held to be constant.

Abstract: A fuel cell system that includes a control system for regulating the power produced by the fuel cell system. The fuel cell system includes a fuel cell stack adapted to produce electrical power from a feed. In some embodiments, the fuel cell system includes a fuel processing assembly adapted to produce the feed for the fuel cell stack from one or more feedstocks. The control system regulates the power produced by the fuel cell system to prevent damage to, and/or failure of, the system.

Abstract: A method and apparatus for operating an intermediate-temperature solid-oxide fuel cell stack (10) with a mixed ionic/electronic conducting electrolyte in order to increase its efficiency. The required power output of the solid-oxide fuel cell stack (10) is determined and one or more operating conditions of the solid fuel cell stack (10) are controlled dependent upon the determined required power output. The operating conditions that are controlled may be at least one or the temperature of the fuel cell stack and the dilution of fuel delivered to the fuel cell stack.

Abstract: Provided is a fuel cell system capable of accurately estimating I-V characteristics of a fuel cell. An impedance measurement section measures an impedance of the fuel cell and obtains a voltage drop caused by a direct-current resistance. An air stoichiometry judgment section detects the amount of oxidant gas supplied to the fuel cell and thereby judges whether or not the air stoichiometry ratio is 1 or higher at this time point. An estimated I-V characteristics line creation section determines that the remaining voltage component consists entirely of an activation voltage when the air stoichiometry ratio notified by the air stoichiometry judgment section is 1 or higher, while determining that the remaining voltage drop component includes the combination of the activation overvoltage and voltage drop corresponding to the change in the electromotive voltage when the notified air stoichiometry ratio is below 1.

Abstract: A system and method for detecting small hydrogen leaks in an anode of a fuel cell system. The method includes determining that a shut-down sequence has begun, and if so, deplete the cathode side of a fuel cell stack of oxygen. The method then increases the pressure of the anode side of the fuel cell stack to a predetermined set-point, and monitors the pressure decay of the anode side of the stack. The method compares the rate of pressure decay to an expected pressure decay rate, and if the measured pressure decay rate exceeds the expected pressure decay rate by a certain threshold, determines that a potential leak exists.

Abstract: A method for preventing a fuel cell voltage potential reversal including determining a relationship between the cell resistance and the current of a fuel cell stack at which a fuel cell voltage potential reversal will occur, operating the fuel cell stack according to a power demand requested, and determining the maximum cell resistance of the fuel cells in the stack. If the maximum cell resistance exceeds a threshold value for the current at which the fuel cell stack is being operated, the operation of the fuel cell stack is restricted to prevent the fuel cell voltage potential from reversing.

Abstract: A method of controlled fuel release from a fuel storage composition including applying an electric field to a section of the fuel storage composition, supplying a reagent to the section of the fuel storage composition, measuring a system parameter, and adjusting an electric field parameter based on the system parameter measurement.

Abstract: An output characteristic of a fuel cell is estimated by detecting an output current of the fuel cell and a voltage between terminals of the fuel cell, and then estimating the output characteristic of the fuel cell on the basis of the detected output current and the detected voltage between the terminals, and a basic output characteristic of the fuel cell.

Abstract: A fuel cell system includes a cell stack, a secondary battery, and a controller including a CPU, a main switch, and a stop button. After the main switch is turned OFF, if there is no power generation stopping command from the stop button, the CPU stops power generation in the cell stack after continuing power generation in the cell stack until a charge rate of the secondary battery becomes not lower than a first threshold value. If the charge rate is not lower than a second threshold value and is lower than the first threshold value, generation in the cell stack is stopped in response to the power generation stopping command from the stop button. If the charge rate is lower than the second threshold value, power generation in the cell stack is continued to charge the secondary battery until the charge rate becomes not lower than the second threshold value.

Abstract: It is possible to suppress over-discharge of an accumulator even when the accumulator is in charge-limited state in a fuel cell output control device. A vehicle drive control system including a fuel cell and an accumulator uses a control unit having: an FC output instruction value calculation module which calculates an output instruction value of a fuel cell according to a power required by a rotary machine; a regeneration limit judgment module which judges whether regeneration is limited for the rotary machine; a battery limit judgment module which judges whether charge of the accumulator is limited; and a required power correction module which corrects the required power of the fuel cell when the charge of the accumulator is limited and neither of the fuel cell or the rotary machine generates power, so as to limit discharge from the accumulator.

Abstract: Provided is a vehicular power source unit having an external electric power supply controlling element (94) configured to control the operation of a heater (16) and a recharger (22) operated by an electric power supplied from a commercial power source (70) via an external power source connector (25) according to a terminal voltage and temperature of a fuel cell (10) detected by a fuel cell state detecting element (91) and a state of a battery (20) detected by a battery state detecting element (92) when a fuel cell vehicle is halted, the supply of reactant gas to the fuel cell (10) by a fuel cell controlling element (93) is stopped and the external power source connector (25) is connected to the commercial power source (70).

Abstract: A method for controlling a vehicle including a fuel cell system and an energy storage unit includes, if the fuel cell system is charging the energy storage unit, determining an average ratio of (i) a change in energy stored in the energy storage unit and (ii) a mass of hydrogen consumed by the fuel cell system to generate the change in energy stored in the energy storage unit. The method also includes, if the fuel cell system is not charging the energy storage unit, selecting a target operating power for the fuel cell system based on vehicle power demand and the determined ratio that sufficiently minimizes drive cycle hydrogen consumption by the fuel cell system.

Abstract: Provides a solid oxide fuel cell with which product life can be extended while a practical output power is maintained. The present invention is a solid oxide fuel cell, having a fuel cell module (2), a fuel supply device (38), an oxidant gas supply device (45), and a controller (110) for controlling the fuel supply amount; whereby the controller is furnished with a degradation determining circuit (110a) for determining degradation in a fuel cell module, and with a fuel correction circuit (110b) for correcting operating conditions based on a degradation determination; the fuel correction circuit can execute an increasing correction mode for increasing the fuel supply amount supplied to the fuel cell module so that rated output power is maintained, or can execute a decreasing correction mode for reducing rated output voltage so that the fuel supply amount is reduced; there is also a mode selection device (110c) for selecting correction modes.

Abstract: A method for controlling a vehicle including a fuel cell system and an energy storage unit includes, if the fuel cell system is charging the energy storage unit, determining an average ratio of (i) a change in energy stored in the energy storage unit and (ii) a mass of hydrogen consumed by the fuel cell system to generate the change in energy stored in the energy storage unit. The method also includes, if the fuel cell system is not charging the energy storage unit, selecting a target operating power for the fuel cell system based on vehicle power demand and the determined ratio that sufficiently minimizes drive cycle hydrogen consumption by the fuel cell system.

Abstract: The present invention provides a method for controlling output of a fuel cell to improve fuel efficiency of a fuel cell hybrid vehicle, in which the fuel cell is operated at a constant power at a maximum efficiency point, wherein the fuel cell and a storage means are directly connected if the output and energy of the storage means is insufficient, and the power generation of the fuel cell is stopped when the level of energy of the storage means is increased during stopping or during low power operation such that the fuel cell is intensively operated at the maximum efficiency point, thus improving the fuel efficiency of the fuel cell and the efficiency of the fuel cell system.