Research on investment strategy of single power grid project based on combination weighting method

: Under the dual carbon target, it is a big problem for power grid enterprises to accurately invest and help the high-quality construction of new power systems. Under the situation of large-scale new energy grid connection, the grid investment strategy needs to be more reasonable and efficient. Therefore, this paper proposes a single project evaluation method of power grid based on combination weighting method, which provides a basis for the ranking of power grid projects, and also provides theoretical support for solving the investment decision-making problem of power grid single projects


Introduction
The power grid project has always played a very important role in China's electricity industry.It is not only closely related to people's daily activities, but also to the economic development of each place and the stability of society.In the past, due to the lack of understanding of the status and role of power grid projects, there has been no scientific planning and systematic management of investments in power grid projects, therefore, how to apply the limited funds to enhance the economic reliability of the power grid is an urgent issue to be considered.Research on the evaluation of power grids has focused on the pre-evaluation and post-evaluation of power grid projects.In the pre-evaluation, literature [1] evaluates transmission and substation projects based on three dimensions: financial, technical and cost.Literature [2][3] all evaluate the risks of grid projects and propose corresponding risk response measures.In the postevaluation, literature [4] combines whole life cycle costs and constructs an economic efficiency model to evaluate grid technology transformation projects.Literature [5][6] adopts fuzzy analysis method with fuzzy comprehensive evaluation to construct the secondary index evaluation of profitability, operation and debt servicing.The above studies evaluate grid projects before and after by improving the evaluation methods, but little has been done on the evaluation of grid operations.For the research on grid investment optimisation, literature [7] constructs a multi-objective multioperational decision optimisation model based on smart grid investment with the objective of optimal comprehensive benefits.In [8], an objective function is established based on the maximum utility of investment, taking into account economic rationality, social development and grid security, so as to construct an optimization model.The literature [9] considers the social and reliability of grid construction projects based on the economic efficiency of grid investment, and gives the optimal investment portfolio model.In order to consider the actual electricity demand in different regions, literature [10] carried out the investment optimisation analysis based on the optimal economic efficiency, and added regional factors in the analysis, so as to maximise the investment efficiency.The literature [11] constructs an investment optimisation model based on the annual expected maximum return, and the calculation example verifies that the model provides effective guidance for enterprises to rationalise project investment.In the literature [12], a multi-objective optimisation model is constructed by taking into account the economic, feasibility and developmental aspects of the grid investment, taking into account the financial and project constraints.To sum up, this paper adopts a combined weighting method that combines subjective weighting method with objective weighting method to evaluate the advantages and disadvantages of power grid engineering projects, which can effectively give play to the advantages of subjective weighting and objective weighting.The evaluation results support the decision-makers to screen the grid investment projects, which is conducive to laying the foundation for the subsequent investment behavior.

A comprehensive evaluation methodology for the initial screening of projects 2.1 Basic concepts of the Portfolio Empowerment Method
The combined weighting method is a weighted combination of subjective and objective weights.On the one hand, considering the complexity and uncertainty of the target and the decision maker's own preference for the target, it is very difficult to assess the target.On the other hand, considering that the merit of an assessment target is determined by the ranking of the comprehensive evaluation value, the greater the comprehensive value of the assessment target, the better the corresponding assessment target will be, so an increase in the comprehensive evaluation value will lead to an increase in the sum of the comprehensive evaluation values.

General steps of the Portfolio Empowerment
Method (1) Optimisation model for minimising the sum of squares of the subjective and objective weight deviations Let the vector of indicator weights derived from the subjective assignment method be W1j=(w11，w12，…， w1n)T，and the vector of indicator weights derived from the objective assignment method be W2j=(w21，w22， …，w2n)T，Then, considering the minimization of the sum of squares of deviations based on the subjective and objective weights, we can construct the following optimization model.
α β 1, (α 0, β 0) (2) Optimisation model to maximise integrated evaluation value Considering that the larger the combined assessment value of the assessment objectives, the better the corresponding assessment objectives, we can again construct the following optimization model.
(3)Optimisation modeling of the portfolio assignment method Generally speaking, multiple optimization objective functions cannot reach their optimal values at the same time, there will be more or less conflicts between them, so in order to synthetically solve the above two optimization models, we can construct the following optimization model based on minimization of the objective function and maximization of the objective function.
That is, α reflects the extent to which the decision maker favours subjective weights and β reflects the extent to which the decision maker favours objective weights.
(4)Calculate the weight of each indicator Calculate the coefficient according to α and β The weight of each index in the combination weighting method can be calculated by the following formula：

Establish hierarchical structure system
Taking the "investment benefit of power grid projects" as the target layer, a top-down hierarchical structure has been formed, with 3 module criteria layers and 12 attribute indicator layers.A hierarchical index system as shown in Figure 1 has been established：

Case study
The basic data collection includes the information collection of power grid investment projects and the collection of experts' scoring results of various indicators of different projects.There are 7 power grid engineering projects to be selected.First, calculate the proportion of weight distribution α and β The specific values are shown in Table 1: The size of the index weight reflects the importance of the index to the comprehensive evaluation.The summary table of subjective and objective weights and comprehensive weights of the index is as follows:

Conclusion
Considering the project investment portfolio involved in the power grid investment, this paper needs to comprehensively consider the relevant constraints and objective requirements when making investment decisions, not only to meet the investment demand, but also to arrange various investments within the allowable scope of investment capacity, and finally achieve the optimization of comprehensive benefits.Therefore, based on the comprehensive evaluation of the subjective and objective weighting method, the power grid engineering projects are sorted by single project, and the alternative investment projects are selected.Through the analysis of calculation examples, the following conclusions can be concluded: The investment decision of power grid project mainly takes into account the overall benefits of power grid investment, and analyzes from the dimensions of the economic rationality, technical feasibility, construction necessity.The Company's investment management and control ability and management level have been improved, which effectively supports the operation decisions of power grid enterprises and realizes the sustainable development of power grid enterprises.

Table 1
the weight coefficient of each index.Allocate proportion according to weight α and β The weight of each indicator in the combination weighting method can be calculated by the formula.The specific results are shown in Table2:

Table 3
Summary of Index Weights