As the issues of security and stability of power systems are becoming increasingly significant,it is necessary to consider the constraints of the static voltage stability and transient stability,which are closely rela...As the issues of security and stability of power systems are becoming increasingly significant,it is necessary to consider the constraints of the static voltage stability and transient stability,which are closely related to the active power dispatch of power systems,in the daily power dispatch,i.e.the unit commitment.However,due to the complexity of these constraints and limitation of the existing analysis methods,there has been no unit commitment model reported so far that can deal with these security constraints.On the other hand,as lack of effective measures to evaluate the security margin of dispatch schemes,it is difficult for power system operators to integrate both the security and economy of power systems in unit commitment.To resolve the above-mentioned issues,a security region based security-constrained unit commitment model is presented in the paper,which gives consideration to both the security and economy of power systems.For the first time,the active power flow constraint,the static voltage stability constraint and the transient stability constraint are taken into account in unit commitment at the same time.The model presented in the paper takes the operating cost,the branch transmission capacity margin,the static voltage stability margin and the transient stability margin as sub-objectives.By adjusting the weighting factors of sub-objectives,it is convenient to adjust the preference on the security and economy of power systems and reach a balance.The IEEE RTS-24 test system is adopted to validate the correctness and the efficiency of the proposed model.展开更多
We develop a two-stage (four component) model for youths with serious drinking prob- lems and their treatment. The youths with alcohol problems are split into two classes, namely those who admit to having a problem ...We develop a two-stage (four component) model for youths with serious drinking prob- lems and their treatment. The youths with alcohol problems are split into two classes, namely those who admit to having a problem and those who do not. It is shown that the model possesses two steady states, one where people have no alcohol problems and one where there is an endemic state involving those with an alcohol problem. The stability of these states is analyzed and a threshold established such that each state will be stable depending on whether the incidence rate is above or below the threshold. The model is analyzed in the context of actual data.展开更多
In this paper, a multi-group SVIR epidemic model with age of vaccination is considered. The model allows the vaccinated individuals to become susceptible after the vaccine loses its protective properties, and the vacc...In this paper, a multi-group SVIR epidemic model with age of vaccination is considered. The model allows the vaccinated individuals to become susceptible after the vaccine loses its protective properties, and the vaccination classes satisfy first-order the partial differential equations structured by vaccination age. Combining the Lyapunov functional method with a graph-theoretic approach, we show that the global stability of endemic equilibrium for the strongly connected system is determined by the basic reproduction number. In addition, the dynamics for non-strongly connected model are also investi- gated, depending on the basic reproduction numbers corresponding to each strongly connected component. Numerical simulations are carried out to support the theoretical conclusions.展开更多
In this paper, a susceptible-exposed infective-recovered-susceptible (SEIRS) epidemic model with vaccination has been formulated. We studied the global stability of the corresponding single-group model, multi-group ...In this paper, a susceptible-exposed infective-recovered-susceptible (SEIRS) epidemic model with vaccination has been formulated. We studied the global stability of the corresponding single-group model, multi-group model with strongly connected network and multi-group model without strongly connected network by means of analyzing their basic reproduction numbers and the application of Lyapunov functionals. Finally, we provide some numerical simulations to illustrate our analysis results.展开更多
文摘As the issues of security and stability of power systems are becoming increasingly significant,it is necessary to consider the constraints of the static voltage stability and transient stability,which are closely related to the active power dispatch of power systems,in the daily power dispatch,i.e.the unit commitment.However,due to the complexity of these constraints and limitation of the existing analysis methods,there has been no unit commitment model reported so far that can deal with these security constraints.On the other hand,as lack of effective measures to evaluate the security margin of dispatch schemes,it is difficult for power system operators to integrate both the security and economy of power systems in unit commitment.To resolve the above-mentioned issues,a security region based security-constrained unit commitment model is presented in the paper,which gives consideration to both the security and economy of power systems.For the first time,the active power flow constraint,the static voltage stability constraint and the transient stability constraint are taken into account in unit commitment at the same time.The model presented in the paper takes the operating cost,the branch transmission capacity margin,the static voltage stability margin and the transient stability margin as sub-objectives.By adjusting the weighting factors of sub-objectives,it is convenient to adjust the preference on the security and economy of power systems and reach a balance.The IEEE RTS-24 test system is adopted to validate the correctness and the efficiency of the proposed model.
文摘We develop a two-stage (four component) model for youths with serious drinking prob- lems and their treatment. The youths with alcohol problems are split into two classes, namely those who admit to having a problem and those who do not. It is shown that the model possesses two steady states, one where people have no alcohol problems and one where there is an endemic state involving those with an alcohol problem. The stability of these states is analyzed and a threshold established such that each state will be stable depending on whether the incidence rate is above or below the threshold. The model is analyzed in the context of actual data.
基金This research was supported by grants from the Shandong Provincial Natural Science Foundation of China (No. ZR2015AM018), and Chinese NSF Grants (Nos. 11671110 and 11201097).
文摘In this paper, a multi-group SVIR epidemic model with age of vaccination is considered. The model allows the vaccinated individuals to become susceptible after the vaccine loses its protective properties, and the vaccination classes satisfy first-order the partial differential equations structured by vaccination age. Combining the Lyapunov functional method with a graph-theoretic approach, we show that the global stability of endemic equilibrium for the strongly connected system is determined by the basic reproduction number. In addition, the dynamics for non-strongly connected model are also investi- gated, depending on the basic reproduction numbers corresponding to each strongly connected component. Numerical simulations are carried out to support the theoretical conclusions.
基金This research is supported by National Natural Science Foundation of China (No. 11371111), Weihai Science and Technology Development Plan Project (No. 2013DXGJ06) and Shandong Provincial Natural Science Foundation of China (No. ZR2015AM018).
文摘In this paper, a susceptible-exposed infective-recovered-susceptible (SEIRS) epidemic model with vaccination has been formulated. We studied the global stability of the corresponding single-group model, multi-group model with strongly connected network and multi-group model without strongly connected network by means of analyzing their basic reproduction numbers and the application of Lyapunov functionals. Finally, we provide some numerical simulations to illustrate our analysis results.