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Li Y.,Hubei Engineering University | Wang B.,Yuxi Power Supply Bureau of Yunnan Power Grid Co. | Zhu H.,Wuhan Guoce Science and Technology Co.
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2014

By introducing the energy balance equation in a benchmark dynamic model, a feasible operating space (FOS) for solid oxide fuel cell (SOFC) steady-state operating safety was proposed in this paper. The maximum electrical efficiency for a given active power (P) was proven to be on one of the boundaries of the FOS whencewhere the fuel utilization factor (u) and stack operating temperature (T) are the maximum and minimum allowable values respectively. The positions of the poles of the dynamic model indicate a hierarchical control scheme, which contains a fast and a slow control system, can be used for the SOFC power plant to achieve the maximum efficiency load-tracking inunder the grid-connected condition. Based on the relative gain array analysis, P and u as the two outputs of the fast active power control system are strongly dependent on the natural gas flow rate of the fuel processor and the phase shift angle (δ) of the power conditioning unit respectively. The system can therefore be decentralized to two single-input and two-single-output systems. The multiplicate model factor described the loop interactions were included in the design of corresponding proportional-integral-differential (PID) controll-erscontrollers. The oxygen flow rate was used to regulate T in the slow temperature control system. As δ has a significant effect on T, a feed-forward controller was used to reject the disturbance. The efficacy of the overall control scheme was verified by the simulation results. © 2014 Chin. Soc. for Elec. Eng.


Li Y.,Hubei Engineering University | Zhu H.,Wuhan Guoce Science and Technology Co.
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2011

Solid oxide fuel cell (SOFC) distributed generator (DG) is a promising DG technology. Starting from the fundamental thermodynamic analysis, a mathematical model governing the steady-state operating state of the hydrogen-fed SOFC was provided by including the mass balance, enthalpy balance and entropy balance equations. An analytical expression relating the SOFC performance variables such as fuel utilization factor, cell stack temperature and excess oxygen ratio were then derived. As the SOFC must be subject to some operating constraints, the concept feasible operating space (FOS) proposed in this paper can be used as a guideline for the SOFC operation and control. ©2011 Chin. Soc. for Elec. Eng.


Li Y.,Wuhan University | Wu Q.,Technical University of Denmark | Zhu H.,Wuhan Guoce Science and Technology Co.
Energies | Year: 2015

Based on the benchmark solid oxide fuel cell (SOFC) dynamic model for power system studies and the analysis of the SOFC operating conditions, the nonlinear programming (NLP) optimization method was used to determine the maximum electrical efficiency of the grid-connected SOFC subject to the constraints of fuel utilization factor, stack temperature and output active power. The optimal operating conditions of the grid-connected SOFC were obtained by solving the NLP problem considering the power consumed by the air compressor. With the optimal operating conditions of the SOFC for the maximum efficiency operation obtained at different active power output levels, a hierarchical load tracking control scheme for the grid-connected SOFC was proposed to realize the maximum electrical efficiency operation with the stack temperature bounded. The hierarchical control scheme consists of a fast active power control and a slower stack temperature control. The active power control was developed by using a decentralized control method. The efficiency of the proposed hierarchical control scheme was demonstrated by case studies using the benchmark SOFC dynamic model. © 2015 by the authors.


Li Y.,Hubei Engineering University | Ran B.,Hubei Engineering University | Zhu H.,Wuhan Guoce Science and Technology Co.
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2012

The maximum efficiency control scheme for a solid oxide fuel cell (SOFC) distributed generator (DG) in the grid-connected condition was proposed. By introducing the steady-state equations which govern the complex electrochemistry, thermodynamic and electrical processes of the SOFC DG, the relationship between the AC and DC sides of the SOFC DG was established. Analyses indicate that the control variables of the power conditioning unit are dependant of the control variables of the cell stack if the constant unity power factor operating scheme for the SOFC DG is chosen. However, the operating states of the SOFC DG under this control scheme must be subjected to the operating constraints denoted as feasible operating space (FOS). The non-linear programming method was then used to determine the maximum efficiency and the optimal control variables. Simulation results show that the SOFC DG under the maximum efficiency should maintain three DC-side operating variables constant simultaneously, namely, fuel utilization factor, excess oxygen ratio and stack operating temperature. © 2012 Chinese Society for Electrical Engineering.


Guo L.,Huazhong University of Science and Technology | Yin X.,Huazhong University of Science and Technology | Yan X.,China Huadian Corporation | Zhao X.,Wuhan Guoce Science and Technology Co.
Dianli Zidonghua Shebei/Electric Power Automation Equipment | Year: 2010

As there is high potential difference among the phases of the high voltage energy meter, optical fiber or wireless communication is needed to quickly transfer the energy information, which makes the hardware cost high. The realization of energy pulse based on separated phase metering and low speed communication is proposed, which separately acquires the energy information of phase A and C, integrates and cumulates them in phase B, calculates the energy increment of current period and equably generates the corresponding energy pulses during next period. Theory and practice show that the hardware cost is greatly lowered while the measurement accuracy ensured.

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