Research On Life Cycle Safety Efficiency Cost Evaluation Method For Power Network Planning

The development of national economy can not be separated from the support of the electric power industry.A scientific power network planning can not only improve the economic and social benefits of the power network itself,but also have an important impact on the development of other industries.The life cycle comprehensive evaluation of power network safety,efficiency and cost,namely,life cycle safety efficiency cost(SEC)evaluation for power networks,is of great significance for the optimization of power network planning,which plays an important roles at the improvements of the management level and operational efficiency of power networks.However,most existing SEC evaluation methods are limited to the assessments of power equipments and existing power networks,and the research on the life cycle SEC evaluation method for power network planning is rare.How to define and calculate the life cycle SEC indexes for the evaluation of power network planning,and how to construct the evaluation model for the life cycle SEC of the overall power network,are still worthy of further study and reflection.In this paper,the theory of life cycle SEC evaluation is introduced into the analysis and optimization of power network planning.A life cycle SEC evaluation index system and the corresponding evaluation models are established in this paper.In particular,the analysis and calculation methods for the life cycle SEC evaluation of power network planning are proposed.Main research works of this paper are as follows:1.With the consideration of the distinction between the SEC evaluation method for power network planning and the existing SEC evaluation methods,a life cycle SEC evaluation index system for power network planning is established.By sorting out the main links and the associated methods for calculating the established evaluation indexes,a technical roadmap for the life cycle SEC evaluation of power network planning is proposed.2.With the consideration of sequential characteristics(such as frequency and duration characteristics),random variables associated with the SEC evaluation of power networks are modeled based on Markov chains and probability-frequency distribution functions(PFDFs).An optimal decision-making model for determining the clustering number of random states is proposed to improve the accuracy of stochastic process modelling of Markov-chain-based random variables.Based on Markov chains,an improved PFDF method is proposed,which simplifies the analysis for random variables with sequential characteristics considered.A random model for wind farms is developed and represented as PFDF in which both wind speed uncertainties and wind turbine failures(or deratings)are considered.With the proposed method,the implementation of the randomness modelling of large wind farms becomes simple.Based on Markov chains of random vectors,the spatial correlation among random variables is addressed and incorporated into the PFDF method.3.One limitation of conventional probabilistic load flow(PLF)and probabilistic optimal power flow(POPF)is that only the probability information of random variables is obtained as a reference for related analyses.Based on Markov chains and PFDFs,a frequency and duration method for PLF and POPF is proposed for the SEC evaluation.With the proposed method,not only probability information but also sequential(such as frequency and duration)information of random outputs(such as node voltages and branch flows)of PLF and POPF are efficiently computed through the operations of PFDFs of associated random inputs(such as nodal power injections).4.A method for power network reliability evaluation is proposed based on the delivery point capability model to improve the efficiency of the SEC evaluation by using the decoupling characteristics between power network transfer capabilities and the corresponding loads(system-load decoupling).There are still some technical defects in the existing reliability evaluation methods based on system-load decoupling,such as the defects in the existing calculation models of transfer capabilities and the calculation methods of frequency and duration reliability indexes.In this paper,an optimal decision-making model is presented for calculating the transfer capabilities of delivery points in power networks,which is suitable for the reliability evaluation.In addition,a solution method for the presented decision-making model is proposed to enhance the computational efficiency.With the calculation of the transfer capabilities,the PFDFs of delivery point transfer capabilities,namely,delivery point capability models,are built based on Markov chains.Not only the probability but also the frequency and duration reliability indexes of delivery points and power networks can be efficiently obtained through the operations of delivery point capability models.5.With the consideration of the probabilistic equilibrium between the risk and profit of total transfer capability(TTC),a probabilistic optimal decision-making method for TTC is proposed for the SEC evaluation.A probabilistic optimal decision-making model for TTC is proposed with the objective of minimizing the expected operating cost.For the optimal decision-making of TTC,the load uncertainty and the mutually constrained relationship among transfer capabilities of different areas are considered and the relationship among the decision-making for various states of power networks are taken into account.The probabilistic optimal decision-making model is transformed into a bi-level linear programming model to be solved,to ensure the efficiency of the calculation.6.The life cycle SEC of power networks is evaluated based on the above research.A new evaluation model for the life cycle SEC of power network planning is proposed by regarding the power network as a whole.The evaluation model of each life cycle SEC index is established and calculated for the optimization of power network planning.A new method to determine the span of life cycle evaluation is proposed,and its application in the life cycle SEC evaluation of power networks is presented.RBTS-6,IEEE-RTS79,IEEE-300 testing systems and a real power network planning in central China are applied as examples to verify the validity of the models and analysis methods proposed in the paper.