The characteristics of oxy-coal combustion for a swirl burner with a specially designed preheating chamber are studied numerically. In order to increase the accuracy in the prediction of flame temperature and igni- ti...The characteristics of oxy-coal combustion for a swirl burner with a specially designed preheating chamber are studied numerically. In order to increase the accuracy in the prediction of flame temperature and igni- tion position, eddy dissipation concept （EDC） model with a skeletal chemical reaction mechanism was adopted to describe the combustion of volatile matter. Simulation was conducted under six oxidant stream conditions with dif- ferent OjN2/CO2 molar ratios： 21/79/0, 30/70/0, 50/50/0, 21/0/79, 30/0/70 and 50/0/50. Results showed that 02 en- richment in the primary oxidant stream is in favor of combustion stabilization, acceleration of ignition and increase of maximum flame temperature, while the full substitution of N2 by CO2 in the oxidant stream delays ignition and decreases the maximum flame temperature. However, the overall flow field and flame shapes in these cases are very similar at the same flow rate of the primary oxidant stream. Combustion characteristics of the air-coal is similar to that of the oxy-coal with 30% 02 and 70% CO2 in the oxidant stream, indicating that the rear condition is suitable for retrofitting an air-coal fired boiler to an oxy-coal one. The swirl burner with a specially designed preheating chamber can increase flame temperature, accelerate ignition and enhance burning intensity of pulverized coal under oxy-coal combustion. Also, qualitative experimental validation indicated the burner can reduce the overall NOx emission under certain 02 enrichment and oxy-coal combustion conditions against the air-coal combustion.展开更多
A predictive current control algorithm for the Buck-Boost DC-DC converter is presented in this paper. The continuous time model of the system is properly introduced, then, by imposing a proper PWM modulation pattern, ...A predictive current control algorithm for the Buck-Boost DC-DC converter is presented in this paper. The continuous time model of the system is properly introduced, then, by imposing a proper PWM modulation pattern, its discrete time model is achieved. This last one is successfully employed in determining the steady state locus of the Buck-Boost converter, both in CCM （continuous conduction mode） and DCM （discontinuous conduction mode）. A novel continuous time equivalent circuit of the converter is introduced too, with the aim of determining a ripple free representation of the state variables of the system, over both transient and steady state operation. Then, a predictive current control algorithm, suitable in both CCM and DCM, is developed and properly checked by means of computer simulations. The corresponding results have highlighted the effectiveness of the proposed modelling and of the predictive control algorithm, both in CCM and DCM.展开更多
Conductor corona performance is significant in the evaluation of electromagnetic environment for high voltage power transmission lines. The influence of artificial contaminated conductors on corona discharge was studi...Conductor corona performance is significant in the evaluation of electromagnetic environment for high voltage power transmission lines. The influence of artificial contaminated conductors on corona discharge was studied and turned out to be complicated. The ionized field strength on the corona cage was measured by field mill. Meanwhile, photos of corona plumes were photographed and grayed to quantitate the corona discharge intensity. Subsequently, a calculation model for equivalent electric field strength coefficient was established to evaluate the discharge intensity of conductors in coaxial cylindrical electrode. It could be found the computational results achieved an agreement with the observed experimental phenomena. By means of simulation results, a reasonable explanation was given to the finding that the closer the distance between the two protrusions was, the lower the corona discharge intensity and higher corona inception voltage of the conductors would be. In summary, the distributions of corona sources played an important role in the corona discharge and this work would provide an important reference for the evaluation of corona effects on the surface of contaminated conductors.展开更多
基金Supported by the Chinese Ministry of Science and Technology Project(2011DFA60390)The National High Technology Research and Development Program of China(2007AA05Z303)
文摘The characteristics of oxy-coal combustion for a swirl burner with a specially designed preheating chamber are studied numerically. In order to increase the accuracy in the prediction of flame temperature and igni- tion position, eddy dissipation concept （EDC） model with a skeletal chemical reaction mechanism was adopted to describe the combustion of volatile matter. Simulation was conducted under six oxidant stream conditions with dif- ferent OjN2/CO2 molar ratios： 21/79/0, 30/70/0, 50/50/0, 21/0/79, 30/0/70 and 50/0/50. Results showed that 02 en- richment in the primary oxidant stream is in favor of combustion stabilization, acceleration of ignition and increase of maximum flame temperature, while the full substitution of N2 by CO2 in the oxidant stream delays ignition and decreases the maximum flame temperature. However, the overall flow field and flame shapes in these cases are very similar at the same flow rate of the primary oxidant stream. Combustion characteristics of the air-coal is similar to that of the oxy-coal with 30% 02 and 70% CO2 in the oxidant stream, indicating that the rear condition is suitable for retrofitting an air-coal fired boiler to an oxy-coal one. The swirl burner with a specially designed preheating chamber can increase flame temperature, accelerate ignition and enhance burning intensity of pulverized coal under oxy-coal combustion. Also, qualitative experimental validation indicated the burner can reduce the overall NOx emission under certain 02 enrichment and oxy-coal combustion conditions against the air-coal combustion.
文摘A predictive current control algorithm for the Buck-Boost DC-DC converter is presented in this paper. The continuous time model of the system is properly introduced, then, by imposing a proper PWM modulation pattern, its discrete time model is achieved. This last one is successfully employed in determining the steady state locus of the Buck-Boost converter, both in CCM （continuous conduction mode） and DCM （discontinuous conduction mode）. A novel continuous time equivalent circuit of the converter is introduced too, with the aim of determining a ripple free representation of the state variables of the system, over both transient and steady state operation. Then, a predictive current control algorithm, suitable in both CCM and DCM, is developed and properly checked by means of computer simulations. The corresponding results have highlighted the effectiveness of the proposed modelling and of the predictive control algorithm, both in CCM and DCM.
基金supported by the National Natural Science Foundation of China(Grant No.51377096)Fok Ying-Tong Education Foundation(Grant No.151058)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.2016YQ01)Young Elite Scientists Sponsorship Program by China Association for Science and Technology(CAST)
文摘Conductor corona performance is significant in the evaluation of electromagnetic environment for high voltage power transmission lines. The influence of artificial contaminated conductors on corona discharge was studied and turned out to be complicated. The ionized field strength on the corona cage was measured by field mill. Meanwhile, photos of corona plumes were photographed and grayed to quantitate the corona discharge intensity. Subsequently, a calculation model for equivalent electric field strength coefficient was established to evaluate the discharge intensity of conductors in coaxial cylindrical electrode. It could be found the computational results achieved an agreement with the observed experimental phenomena. By means of simulation results, a reasonable explanation was given to the finding that the closer the distance between the two protrusions was, the lower the corona discharge intensity and higher corona inception voltage of the conductors would be. In summary, the distributions of corona sources played an important role in the corona discharge and this work would provide an important reference for the evaluation of corona effects on the surface of contaminated conductors.
