Pressure controller design

　　When the fuel cell is shut down for a long time, the hydrogen concentration in the hydrogen system pipeline decreases due to the nitrogen penetration effect. However, since the stack does not need to output current at this time, the controller will not take any measures to maintain the hydrogen concentration at within the optimal range. If there is a sudden demand for the stack current output, it needs to be quickly restored to the optimal range of hydrogen concentration. The speed of supplying hydrogen from the hydrogen storage bottle to the hydrogen supply system pipeline is much faster than the speed of purging low-concentration hydrogen into the outlet manifold of the air supply system, where a pressure controller needs to be designed. The hydrogen supply is calculated based on the difference between the estimated hydrogen concentration and the optimal hydrogen concentration for the given operating conditions. After the hydrogen gas in the hydrogen supply system pipeline is pressurized through the pressure control operation, the purge control operation is started under continuous load conditions.

　　Purge controller design

　　Since most driving conditions consist of continuous load conditions, the purging operation frequency is much higher than the pressure control operation frequency. When the output value of the hydrogen concentration estimator is less than the optimal hydrogen concentration range, the controller only increases the hydrogen concentration (such as a semi-active actuator). When it is higher than the optimal hydrogen concentration range, the purge operation is not performed. In order to perform the above control, a minimum level of air flow velocity should be formed in the air supply system pipeline to prevent hydrogen from diffusing to the cathode electrode and reduce the impact on the current output. Due to the delayed response of the air compressor and the time required for fresh air delivery, it takes time for the air supply to form when the fuel cell is shut down, but under stable load conditions, there will be no delay in the blowing operation.

　　Performance evaluation

　　In order to verify the effectiveness of feedback control based on the hydrogen concentration estimator, Hyundai Motor Company conducted a large number of experiments in the NEXO fuel cell power system and SUV. Three main characteristics of the traditional Q-value method were evaluated: resistance to external interference, prevention of hydrogen starvation and efficiency improvement. For confidentiality reasons, Hyundai Motor Company only displays relative and expected values, not absolute and measured values.

　　Pressure control diagram

　　Resistant to external interference

　　Environmental stresses on Earth vary depending on factors such as climate, altitude and latitude. Since the pressure difference between the hydrogen supply system pipeline pressure and the ambient pressure will cause gas leakage, the purge controller is also closely related to the ambient pressure. It can be observed that on different daysThe changes in purge count under the same driving conditions during the period, and the estimation error is kept within a predetermined range. Under continuous operation under three driving conditions, the ambient pressure difference of 1.6kPa can cause 9 purge count differences. In the three working conditions, the working pressure of the hydrogen supply system is the same, but a 1.6kPa decrease in ambient pressure will increase the number of moles of purge gas, which will lead to an increase in hydrogen concentration during the purge and extend the purge time interval. Therefore, it was concluded that this technology has achieved optimal purge counts for ambient pressure changes such as formal operating conditions at different altitudes.

　　Prevent hydrogen outgassing to improve durability

　　In the study, the function of the pressure controller was also checked by suddenly applying a large load to the fuel cell system after a long shutdown. After the fuel cell system is shut down, the estimated hydrogen concentration is lower than the optimal concentration value due to the nitrogen permeation effect. However, before applying to large loads, it was observed that the hydrogen supply system pipeline pressure was increased to increase the hydrogen concentration to the optimal position according to the design requirements. The pressure rise of the hydrogen supply system pipeline is calculated based on the estimated hydrogen concentration value. The output value of the hydrogen concentration estimator does not experience overshoot, undershoot, and the error rises to the optimal range. It has been evaluated that this function is useful for preventing hydrogen starvation (extending fuel cell life).

　　Efficiency improvement

　　Hyundai Motor Company conducted an efficiency comparison between the conventional Q-value method and hydrogen concentration estimator-based feedback control technology in the NEXO fuel cell SUV. When using the Q-value method, the hydrogen concentration estimate spreads within the optimal hydrogen range, and the changes fluctuate greatly. However, the feedback control technology based on the estimated hydrogen concentration can maintain the estimated hydrogen concentration within the optimal range without crossing the upper and lower limits, and no deviation in the average value is observed in different driving conditions. In combined driving conditions, the efficiency is increased by 0.02MPGe because the hydrogen concentration value within the optimal range will improve hydrogen utilization.

　　in conclusion

　　Hyundai Motor Company has implemented and proven through its NEXO fuel cell SUV and fuel cell system experiments that a feedback controller based on a hydrogen concentration estimator is superior to the traditional Q value method. First, a simple cubic model with the same hydrogen supply system volume was established for embedded software development and found to have reliable performance and can be used as a hydrogen concentration estimator for hydrogen supply system pipelines. Secondly, the estimation error changes within a wide range of load conditions, such as UDDS, HWFET and US06 conditions, but the three calibration parameters can ensure that the error is controllable within a reasonable range. Furthermore, Hyundai Motor Company has developed feedback control technology based on a hydrogen concentration estimator, which exhibits good resistance to environmental pressure interference and improves durability and efficiency by preventing hydrogen shortage. Finally, compared with the traditional equivalent Q value method, Hyundai Motor Company's hydrogen concentration optimal operation control achieves improved efficiency under combined driving conditions. Dr. Fuel Cell

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