A nitrogen oxide sensor that can accurately and quickly detect the content of nitrogen oxides in exhaust gas plays a key role in the treatment of automotive exhaust gas. Due to the characteristics of gas diffusion and chamber structure, nitrogen oxide sensors are difficult to achieve high-precision and fast measurement due to strong coupling. In order to solve this problem, this paper proposes a decoupling control strategy for nitrogen oxide sensors. On the one hand, the strategy uses fuzzy feedforward compensation, and on the other hand, it uses PID control based on particle swarm optimization to achieve control. This not only eliminates the coupling between loops, but also improves the control accuracy. The analysis shows that the design of the decoupling control strategy for nitrogen oxide sensors proposed in this paper is feasible, which allows the nitrogen oxide sensors to work in a stable and reliable state.

There is inconsistency in the stack of multi-stack Solid Oxide Fuel Cell (SOFC) system, which can affect the efficiency and lifespan of the system. To improve the overall performance of the system when the stacks are inconsistent, the paper analyzes the impact of stack inconsistency and designs a power allocation strategy based on improved generalized predictive control (GPC). The types of stack inconsistency have been identified and online detection methods have been proposed at first. Then, through stack inconsistency analysis, it can be found that stack inconsistency can seriously affect the efficiency and lifespan of the system and the system lifespan can be maximized by adjusting the current. Furthermore, the following research also indicates that the point where the system has the highest lifespan is also the point where the overall performance of the system is optimal. Finally, to achieve the best performance of the system during actual operation, the paper designs a power allocation strategy based on improved generalized predictive control. The simulation results also show that the power allocation strategy designed in this paper can adjust the power of the stack in real-time online, ensuring maximum system lifespan and optimal overall performance.

Multi-stack fuel cell system(MFCS) are an important basis for large-scale application of solid oxide fuel cell(SOFC) technology, MFCS can provide higher system power and longer service life. As the number of stacks increases, different topologies can be formed between stacks, including parallel structures and series structures, and the physical characteristics of MFCS will also change. In this study, the degradation of the stacks is first considered, and the system model of series structure and parallel structure including the degradation of the stacks is built. The parallel structure proposed in this paper is the key to ensure the high efficiency and long lifetime of MFCS. Through the simulation of systems with different topologies, it is found that the power generation efficiency of the systems caused by the topologies varies greatly in different output power stages. The efficiency of the parallel structure in the low power stage is significantly better than that of the series structure, and the parallel structure is more conducive to the high efficiency of the system in the whole stage. Different topological structures also have a greater impact on the degradation of stacks. The degradation rates of stacks in parallel structures are close to each other, and the state of stacks is more consistent. The overall life of the system in parallel structures is also better than that in series structures.

To improve the control performance of the nitrogen oxides (NOx) sensor, a fuzzy decoupling compensator with direction control is developed for the decoupling control of NOx sensor. Considering the problems of feedforward compensation decoupling in the test of actual control effect, a fuzzy decoupling (FD) compensator is designed based on the idea of feedforward compensation decoupling and fuzzy control principle. Based on Speedgoat, the actual control effect of decoupling control method can be quickly verified and the actual test results show that the FD compensator can effectively reduce the overshoot and accelerate the system stability. Furthermore, as the FD compensation sometimes has a negative impact on the original control loop, a fuzzy decoupling compensator with directional control is designed on the basis of FD compensator. This method can determine the direction of decoupling compensation based on the change trend of the actual output value. The actual test results also show that the control performance of the FD compensator with directional control is further improved.

Monitoring and fault diagnosis playa major role in improving the performance and reliability of Solid Oxide Fuel Cell (SOFC) systems. However, current SOFC-related studies do not take into account the variation of gas concentration, leaving space for SOFC performance enhancement. In this paper, a model-based fault diagnosis method for gas leakage of SOFC stack is proposed based on gas sensing data. Compared to previous models, the fault model based on gas concentration is simpler, which facilitates for real-time online operation. The state values of the stack are defined in fault model to reflect the state of the stack and the adaptive thresholds are designed to eliminate the effects of data noise. Then, the gas leakage of SOFC stack can be diagnosed based on the relationship between the stack state values and the adaptive thresholds. The simulation results show that the method can diagnose the gas leakage fault of SOFC stack very well and the design of adaptive threshold can improve the robustness of the system and reduce the occurrence of misclassification.

The reversible solid oxide cell (rSOC) is an emerging solution for power-gas conversion in renewable energy networks owing to its high efficiency and bi-directional operation. However, there are still many unidentified safety issues endangering the stability and lifespan of rSOC that need to be addressed before its widespread commercialization. In this paper, a novel one-dimensional rSOC stack model incorporating peripheral auxiliary components is introduced to investigate the transient behavior of the co-flow rSOC stack during electrolysis-fuel cell transition and to develop a safety-oriented optimization strategy for the switching process. This is the first comprehensive study of thermal-material safety hazards for rSOC in the system environment and the first proposal of a dual-model predictive control strategy to avoid nonlinearities in global predictive control during cross-mode switching. It is found that localized extreme temperature gradients, fuel starvation and thermal oscillations are the main safety issues faced by rSOC in switching transients. The conclusion that the current stride and the rate of current change are key factors in guaranteeing the transient safety of rSOC is obtained by evaluating targeted dispatch currents. On this basis, the constraint of current-change rate of 7 A s-1 is incorporated into the controller design, further results indicated that the proposed cooperative control strategy effectively prevents the reactant crisis with smoother thermodynamic responses, which are all within the safety threshold.

The unequal heat gain in south and north orientation of a building causes higher energy consumption which should have been avoided. In this paper, an active pipe-embedded building envelope system is proposed to achieve heat redistribution between north and south rooms to reduce building heating load. The system is mainly composed of closed-loop pipes embedded in external walls which will absorb and transfer the solar heat gain from the south façade to the north. On cloudless days, the structure can effectively raise the surface temperature of the north wall, thus reducing the heat loss through the envelope. We present all the mathematical equations and a mathematical model validated against experimental data in the literature. To further check the feasibility of the system, the heat transfer of a pipe-embedded external wall and a conventional wall are compared, with the same configurations under typical weather conditions in five building climate zones of China. The results show that the heating load reduction during heating season for the room adopting this system relative to the one without it is 12.8% for hot summer and cold winter climate. For severe cold climate and cold climate, the heating loads in January are reduced by 4.6% and 8.7%, respectively. The system plays a minor role in reducing building energy consumption in the hot summer and warm winter zone. Besides, energy consumption of building in summer can also be reduced, although not as effectively as in winter. This study may guide a better design and control of low energy building in further research and practice.

To improve the performance of the NOx sensor, a combined model based on the electrochemical model and the diffusion model is developed for the main oxygen pumping cell of the NOx sensor. One important feature of this combined model is that the model eliminates the intermediate variable and only shows the relationship between the pumping voltage and the pumping current. To validate the model at different gas concentrations, the sensor is mounted on the designed test rig. Then, the simulation results are compared with experimental data from the test rig and good agreement is obtained. Comparing the cathode and anode overpotential, it is found that the anode concentration overpotential can be ignored. In addition, since the activation overpotentials of the cathode and anode are relatively small, they can all be regarded as linear changes with the pumping current. The subsequent characteristic analysis determines the changes of the internal characteristics of the sensor during operation, which will provide guidance for the design and control of the sensor.

The zirconia solid electrolyte SOFC (solid oxide fuel cell) has the characteristics of oxygen ion conduction function, high-temperature resistance, thermoelectric coupling effect, etc. A NOx sensor based on zirconia solid electrolyte has common characteristics and problems with the SOFC in principle and application. The research objective of this paper is to solve the application problems of smart NOx sensors in diesel vehicles or gasoline vehicles. Improvements in the application performance of the NOx sensor can help the NOx emissions of gasoline vehicles or diesel vehicles better meet the requirements of emission regulations. The smart NOx sensor is a regulatory sensor required by vehicles for China’s Phase VI Vehicle Exhaust Emission Regulations or Euro Phase VI Vehicle Exhaust Emission Regulations. The smart NOx sensor is a key sensor device for improving fuel efficiency and reducing pollution. Moreover, its measurement performance includes dynamic immunity to interference, response speed, and measurement accuracy, which are key factors affecting vehicle emissions. This paper focuses on the impact of the physical structure, electrode characteristics, and control strategies of the sensor on its performance during the application. An excellent sensor structure, electrode structure, and control strategy are given based on application analysis and experimental testing. The results show that the application performance of this smart NOx sensor meets the requirements of exhaust aftertreatment systems.