Multi-objective Dynamic Optimal Power Flow Under Fixed Transmission Price Mode

Due to the rapid economic development of our country,there are many problems existing such as large fossil energy consumption,inefficient energy utilization,increasing pollutant emission and gradual deterioration of the environment.Therefore,the national strategy of building an ecology-civilized,resource-conserving and environment-friendly society has been put forward.As for the power system industry,in order to achieve the goal of cleaning development,the clean energy represented by wind and photovoltaic power has developed rapidly.However,large amounts of wind and photovoltaic power are being discarded.The main reason is the shortage of system reserve and the severe peak regulation load on thermal power units.In addition,the new power system reformation came out in March 2015,and the State Grid would no longer make profits by the difference between the purchase and the sale price.Instead,it would begin to charge a “net fee”,which is the fee of power transmission and distribution approved by the government according to the principle of "permitted cost plus reasonable income".Because the “net fee” is directly related to the tidal current distribution,the impact of power flow optimization on the incomes of the State Grid has become a new topic worthy of discussion.Based on the above problems,this paper focues on the optimal power flow problem and has carried out three aspects of research work :First of all,according to the current changes in the operating environment of the system,this paper analyzes the improvement of t he traditional optimal power flow model.In view of the wind-photovoltaic power discarding phenomena and the concerning peak regulation problem of the thermal power,the improved mode l integrates the minimum power discard of renewable energy and the minimum cost of thermal power peak regulation to the objective functions.Considering the new interest demands of the State Grid,the maximum of “net fee” income under fixed transmission price mode is also introduced into the optimization category.On this basis,while integrating thermal power generation energy conservation and emissio n reduction requirements,a dynamic optimal power flow model with five targets is established,where the economic benefits of three parties of thermal power,renewable energy and the State Grid are taken into account.In addition,the model also considers the medium and long term power contract factors in the power market,and refines the active power generation plan of thermal power unit s into two components,one of which is constrained by the diurnal decomposition value of the power contracts,and the other is determined by the power flow optimization process combined with the constraints of the first component.Secondly,based on the multi-objective fuzzy optimization theory,corresponding membership functions are determined for each objective function according to the optimization needs.The membership satisfaction variable is introduced,and thus the multi-objective optimal power flow model is transformed into a single objective optimization model by the maximum satisfaction principle.The primal-dual interior point method is applied to solve the model.The key formulas during the solution process are derived,including the corresponding Jacobian and Hessian matrixes of each objective function,equality constraints and inequality constraints.Finally,taking IEEE 14-node system as an example,the multi-objective fuzzy optimization combined with the primal-dual interior point method is used to solve the multi-objective optimal power flow model on the MATLAB platform.The results show that there are conflicts or connections between the objective functions.The multi-objective fuzzy optimization can effectively obtain a compromise solution for each target,so that the overall economic benefit of the system can reach a satisfactory level: the wind-photovoltaic power discard can be reduced,the cost of peak regulation can be suppressed,the requirements of energy conservation and emission deduction for thermal power units can be insured,and the “net fee” income of the State Grid can be guaranteed.In addition,by changing the model constraints,the influence of related factors on the optimization result of the optimal power flow is analyzed,such as the influence of the thermal power regulation space on the renewable energy accommodation,the influence of the thermal power contract on the short-term generation plan of the units,and the influence of the line condition on the “net fee” income of the State Grid,which demonstrates the application value of the new model.