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Ya-Xiong Wang,Fei-Fei Qin,Kai Ou,Young-Bae Kim 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
DC/DC converters with hybrid proton exchange membrane (PEM) fuel cell and battery power sources are designed and implemented using sliding mode control (SMC). The converters are typically comprised by unidirectional boost converter and bidirectional converter which are used for regulating the bus voltage and managing power distribution. SMC is selected to control the converters since it can cope with the high non-linear characteristic of the coupled system as well as ensure the stability. The hybrid power control system is constructed in MATLAB/Simulink platform. A comparative approach based on conventional proportional-integral (PI) control is developed to compare the control performance with SMC. The experimental validation is carried out with National Instruments (NI) LabVIEW-based hybrid PEMFC/battery supplied DC/DC converters system prototype.
Real-Time Control for Air Excess Ratio of a PEM Fuel Cell System
Ya-Xiong Wang,Young-Bae Kim IEEE 2014 IEEE/ASME transactions on mechatronics Vol.19 No.3
<P>This paper studies the modeling and air flow control for a proton exchange membrane (PEM) fuel cells using model predictive control (MPC). The PEM fuel cell model was constructed using cell current-voltage relationships, including Nernst voltage, activation, ohmic, and concentration voltage loss. A thermal model was also included for PEM fuel cell model to represent the pressure characteristics. The validity of the model was evaluated by determining the model parameters, and its accuracy was verified against the experimental data. To prevent starvation that might occur in the fuel cell hybrid vehicle system, air flow control was utilized using MPC. MATLAB/Simulink model was first constructed to simulate the efficacy of MPC using the linearized model. The validity and performance superiority of the model were then confirmed by comparing them with the proportional-integral control result. To apply the MPC in real-time, a LabVIEW-based experimental rig was constructed, and its efficacy in preventing air starvation was verified.</P>
Temperature Control for a Polymer Electrolyte Membrane Fuel Cell by Using Fuzzy Rule
Ya-Xiong Wang,Fei-Fei Qin,Kai Ou,Young-Bae Kim IEEE 2016 IEEE transactions on energy conversion Vol.31 No.2
<P>Temperature control for a polymer electrolyte membrane fuel cell (PEMFC) is important in improving power efficiency and increasing fuel cell lifetime. If the temperature of the cell is too low, then the electrochemical reaction response becomes slow, thereby preventing evaporations of liquid water in the membrane. As a result, cell performance is decreased. However, too high temperature leads to waste in catalyst and heat because of excessive chemical reactions and to liquid water evaporation, which decreases proton conductivity. This study develops an electrochemical dynamical model and a thermal model of a PEMFC using MATLAB/Simulink for simulation. Fuzzy control rules are also built to regulate the temperature of a PEMFC. The fuzzy inputs include temperature error, its derivative, and external load current. The cooling fan speed is chosen as an output variable to regulate the temperature of a fuzzy control because the fuel cell utilizes the air cooling method. After confirming that the designed fuzzy rules are effective for controlling cell temperature, a real experimental device is built using an H-100 fuel cell and a cooling fan to verify the effectiveness of the proposed method.</P>
Robust Time-Delay Control for the DC–DC Boost Converter
Ya-Xiong Wang,Duck-Hyun Yu,Young-Bae Kim IEEE 2014 IEEE transactions on industrial electronics Vol.61 No.9
<P>This paper studies a robust control for regulating a boost converter capacitor output voltage. The boost converter is inherently a highly nonlinear system that displays interconnected state variables and system parameter variations due to load change with input disturbances. Therefore, a robust control scheme is required to cope with these characteristics. The main objective of controlling the capacitor output voltage is to keep the output voltage constant under input voltage variations with fast response, and little overshoot and ripples. To satisfy this objective, a robust control with time-delay concept is introduced. The control utilizes time-delayed switching input to the converter, as well as output current and voltage variables, to replace the unknown dynamics and disturbance. To prove the effectiveness of the algorithm, two operating point variations are considered: variations in source voltage, and changes in output load. Simulations are performed using MATLAB/Simulink to show the effectiveness of the algorithm by choosing the output voltage lift, drop, settling time, and ripples as the system performance criteria. Then, a comparison of the results is made of the proportional and integral control, and the sliding mode control. An experimental test is also performed to demonstrate the effectiveness of the system.</P>
Ya-Feng Song,Xiong-Xiong Kong,Wei-Bin Tang,Zhong-Qiang Suo,Huan Zhang,Chen-Yang Li,Qian Jia,Cai-Xia Xue,Yan-Wu Lu,Chao-Pu Yang 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.11
We investigate the polarization effect in intersubband transitions in polar and nonpolar GaN-based multiple-quantum well (MQW) structures for terahertz (THz) emissions by using systematic comparisons and design a nonpolar GaN/Al$_{0.2}$Ga$_{0.8}$N two-well-based MQW structure with an emitting photon of 7.27 THz (30.07 meV). Its lower energy separation (92.7 meV) matches the resonant phonon depopulation condition for better population inversion. It shows a lower threshold current density $J\rm_{th}$ at all temperatures (1.548 kA/cm$^2$ at 90 K) and a higher output power of up to 86.1 mW at 5.8 K and 33.6 mW at 100 K. Our results for the polar GaN MQW are very close to the experimental data in the literature. We find that the $J\rm_{th}$ of the nonpolar GaN MQW increases more slowly than that of the polar GaN MQW as temperature increases, indicating the nonpolar GaN MQW may be a worth-trying direction for improving the operation temperature. These results can provide meaningful references for the design and fabrication of nonpolar GaN-based THz MQW or quantum cascade structures.