A Power Grid Investment Portfolio Optimization Method Based on Transmission and Distribution Price Reform

Abstract

A power grid investment portfolio optimization method based on the reform of transmission and distribution prices includes collecting power grid power and financial data; calculating the power grid investment demand of different voltage levels and different project types; determining the total investment amount of power grid projects according to the average unit investment amount and the investment quantity demand of power grid projects; calculating the power grid investment capacity under the reform of transmission and distribution prices; determining the benefits of investment projects; constructing a power grid optimal investment portfolio model based on the maximum investment return; determining power grid investment constraints in different regions, different voltage levels, and different project types; solving the constructed power grid optimal investment portfolio model based on the determined power grid investment constraints to obtain the provincial power grid optimal investment portfolio with the maximum return. The present invention can reasonably arrange power grid enterprises to make investment portfolios to improve the overall asset return rate, and can also provide effective information for the power transmission and distribution supervision and audit department to evaluate the overall investment effect of power grid enterprises.

Description

Technical Field

[0001] The present invention relates to the field of electric power technology, and in particular to a power grid investment portfolio optimization method based on transmission and distribution price reform. Background Art

[0002] After the reform of transmission and distribution prices, the permitted income of power grid enterprises is composed of permitted income, permitted costs and taxes included in the price. Power grid enterprises should not only take power demand, power supply capacity and power grid reliability as the basis for investment, but also reasonably control costs, grasp the investment capacity of the enterprise itself, realize scientific investment decisions of power grid enterprises, and improve investment returns. The investment of power grid enterprises is different from general investment activities and has its own particularity. The scale of power grid investment is huge and the returns are slow. It is a typical capital-intensive and technology-intensive enterprise. At the same time, as a large state-owned enterprise, power grid enterprises should shoulder social responsibilities to meet the growth of power demand and the demand for power in social and economic development. Therefore, power grid enterprises need to invest limited funds in construction projects that can best improve the economy and reliability of power grids. Under the reform of transmission and distribution prices, power grid enterprises have changed from the traditional extensive income model of "purchase and sales price difference multiplied by sales volume" to the refined income model of "permitted cost plus reasonable income" regulated by the government. Under the new income model, the permitted costs and permitted income of power grid enterprises are directly linked to assets, and the level of transmission and distribution prices will be significantly affected by the scale of effective assets. Therefore, understanding the impact of different voltage levels and project types on the permitted income of the power grid is of great significance for rationally arranging the investment portfolio of power grid enterprises and improving the overall asset return rate. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a power grid investment portfolio optimization method based on the reform of transmission and distribution prices, which can reasonably arrange power grid enterprises to make investment portfolios to improve the overall asset return rate.

[0004] In order to solve the above technical problems, the present invention adopts the following technical method: a power grid investment portfolio optimization method based on the reform of transmission and distribution prices, comprising:

[0005] Step S1: Collecting power and financial data of the power grid, including the load characteristic curve of users in each year, line loss rate of lines of different voltage levels, investment quantity and investment amount of various types of projects in various regions and years, and financial statements and financial parameters of the power grid in each year;

[0006] Step S2: Calculate the grid investment demand of different voltage levels and different project types, wherein the grid investment demand includes the grid project investment quantity demand;

[0007] Step S3: Determine the total investment amount of the power grid project according to the average unit investment amount and the power grid project investment quantity requirement obtained in step S2;

[0008] Step S4: Calculate the power grid investment capacity under the transmission and distribution price reform;

[0009] Step S5: Determine the benefits of the investment project;

[0010] Step S6: constructing an optimal investment portfolio model for a power grid based on maximum investment returns;

[0011] Step S7: Determine grid investment constraints for different regions, different voltage levels, and different project types;

[0012] Step S8: Based on the grid investment constraints determined in step S7, the grid optimal investment portfolio model constructed in step S6 is solved to obtain the provincial grid optimal investment portfolio with the greatest return.

[0013] Furthermore, in step S2, calculating the grid investment demand of different voltage levels and different project types includes:

[0014] Step S21, calculating the peak load demand: first predict the power consumption of different types of users at different voltage levels according to the load characteristics of each user, and then calculate the maximum power load on the maximum load day according to the load rate, that is, the peak load demand;

[0015] The calculation formula for the power consumption is:

[0016] (1)

[0017] In the formula, is the power consumption of type p users in region i and voltage level j in year t, is the base annual electricity consumption of type p users in region i under voltage level j, r p is the annual growth rate of electricity consumption of type p users;

[0018] The calculation formula for the peak load demand is:

[0019] (2)

[0020] In the formula, is the peak load demand of type p users at voltage level j in region i in year t, is the power consumption of type p users in region i at voltage level j in year t, is the load rate of type p users in region i at voltage level j, is the simultaneous rate of type p users at voltage level j in region i;

[0021] Step S22, calculating the transmission and distribution loss: first, according to the power balance relationship under different voltage levels, calculate the transmission and distribution loss ratio between different voltage levels, including the line loss rate and transformer loss rate of different voltage levels at peak load; then construct a power balance model considering the transmission and distribution loss of different voltage levels, and iteratively calculate the line loss ratio and transformer loss ratio according to the power supply and consumption balance relationship of different voltage levels in each region;

[0022] The calculation formulas for the line loss ratio and the transformation loss ratio are:

[0023] (3)

[0024] (4)

[0025] In the formula, is the line loss ratio between voltage level j and voltage level j+1, is the line loss rate under voltage level j, is the line loss rate at voltage level j+1, is the loss ratio between voltage level j and voltage level j+1, is the loss rate of voltage level j, is the loss rate of voltage level j+1;

[0026] The power balance model is:

[0027] (5)

[0028] In the formula, is the grid load of voltage level j, is the power supply load obtained by voltage level j from voltage level j+1, is the line loss rate of voltage level j, is the user load of voltage level j, is the power supply load from voltage level j to voltage level j-1, is the line loss load of voltage level j, is the loss rate of power supply from voltage level j to voltage level j-1, is the power supply load obtained by voltage level j-1 from voltage level j, Transformer loss load for supplying power from voltage level j to voltage level j-1;

[0029] Step S23, predicting the maximum load increment demand: first, according to the power balance relationship of different voltage levels, calculate the annual maximum load total demand of each voltage level from low voltage level to high voltage level, and then calculate the maximum load increment demand;

[0030] The calculation formula for the maximum total load demand is:

[0031] (6)

[0032] In the formula, is the total maximum load demand of voltage level j in year t (including the load demand of this level and the load demand of power supply to the lower level), is the user load of voltage level j in year t, is the power supply load (including transformer loss) from voltage level j to voltage level j-1 in year t, is the line loss load of voltage level j in year t, is the line loss rate of voltage level j, It is the power supply load (minus transformer losses) obtained from voltage level j+1 for voltage level j in year t. The loss rate of power supply from voltage level j to voltage level j-1;

[0033] The calculation formula for the maximum load increment requirement is:

[0034] (7)

[0035] In the formula, is the maximum load increment demand of voltage level j in year t, is the total maximum load demand of voltage level j in year t+1, The maximum total load demand of voltage level j in year t;

[0036] Step S24, calculating the additional capacity demand: firstly, calculating the additional capacity demand of the power grid according to the maximum load incremental demand predicted in step S23, and then calculating the cumulative maximum load incremental demand of different voltage levels in various regions within a period of time according to the continuity of the maximum load incremental demand of the power grid, that is, the investment quantity demand of the power grid project;

[0037] The calculation formula for the additional capacity requirement is:

[0038] (8)

[0039] In the formula, is the additional capacity demand of voltage level j in year t, is the total maximum load demand of voltage level j in year t+1, is the total maximum load demand of voltage level j in year t, is the capacity ratio of voltage level j, is the maximum load increment demand of voltage level j in year t;

[0040] The calculation formula for the investment quantity requirement of the power grid project is:

[0041] (9)

[0042] In the formula, is the investment quantity demand of power grid projects of voltage level j in year t, is the additional capacity demand of voltage level j in year t, is the unit substation capacity of voltage level j.

[0043] Furthermore, in step S3, the calculation formula of the average unit investment is:

[0044] (10)

[0045] In the formula, is the average unit investment of a power grid project of voltage level j and project type k, is the average unit investment of substation of voltage level j and project type k, is the ratio length of the substation of voltage level j and project type k, The average investment per unit length of line of project type k at voltage level j.

[0046] Furthermore, in step S3, when determining the total investment amount of the power grid project, calculation is performed at different voltage levels, as follows:

[0047] The calculation formula for the investment amount of a certain type of project with a voltage level of 500kv is:

[0048] (11)

[0049] In the formula, is the investment amount of the power grid project of type k with voltage level 500kv in year t, is the number of power grid project investments of type k and voltage level 500 kV in region i in year t, is the average unit investment of a 500kv project type k power grid project, is the number of power grid project investments of type k with voltage level 500 kV in region i in year t-1, The investment amount of power grid projects of type k with voltage level 500 kV in region i in year t-2;

[0050] The calculation formula for the investment amount of a certain type of project with a voltage level of 220kv is:

[0051] (12)

[0052] In the formula, is the investment amount of the power grid project of type k with voltage level 220kv in year t, is the number of power grid project investments of type k with voltage level 220 kV in region i in year t, is the average unit investment of power grid project k with voltage level 220kv project type, The investment amount of power grid projects of type k with voltage level 220 kV in region i in year t-1;

[0053] The calculation formula for the investment amount of certain types of projects with voltage levels of 110kv and below is:

[0054] (13)

[0055] In the formula, is the investment amount of the power grid project of voltage level j and project type k in year t, is the number of power grid projects invested in region i, voltage level j, project type k in year t, is the average unit investment of power grid projects of voltage level j and project type k.

[0056] Furthermore, in step S4, the calculation formula for the grid investment capacity under the transmission and distribution price reform is:

[0057] (14)

[0058] Where Y t is the investment capacity in year t under the transmission and distribution price reform, L t is the retained profit in the tth year under the transmission and distribution price reform, Z t is the depreciation amount in the tth year under the transmission and distribution price reform, R t is the additional financing amount in year t under the transmission and distribution price reform, J t is the new current assets in year t under the transmission and distribution price reform;

[0059] The calculation formula of retained earnings is:

[0060] (15)

[0061] Where, L t is the retained profit in the tth year under the transmission and distribution price reform, P A,t is the permitted income in year t;

[0062] The calculation formula for the depreciation amount is:

[0063] (16)

[0064] In the formula, is the depreciation amount in the tth year under the transmission and distribution price reform, is the net value of fixed assets of category p formed before January 1, 2015, is the median depreciation period of the p-th type of fixed assets, The original value of fixed assets of category p formed in 2016 and later, is the depreciation period of the pth type of fixed assets, β is the residual value rate of fixed assets;

[0065] The calculation formula for the newly added current assets is:

[0066] (17)

[0067] In the formula, is the new current assets in year t, is the total operating cost in year t, is the total operating cost in year t-1, γ is the provision ratio for retained current assets;

[0068] The calculation formula for the additional financing amount is:

[0069] (18)

[0070] In the formula, is the newly added financing amount in year t, and the growth amount of liabilities in that year is the newly added financing amount in that year. is the total assets in year t-1, is the total profit in year t, is the total liabilities in year t-1, is the debt-to-asset ratio in year t.

[0071] Furthermore, in step S5, when determining the benefits of the investment project, under the reform of transmission and distribution prices, the power grid project investment will be included in the permitted costs and permitted income of the power grid enterprise through effective assets, wherein the relationship between the power grid project investment and effective assets is:

[0072] (19)

[0073] In the formula, is the change in effective assets caused by the additional investment in year t, is the investment amount of the power grid project in year t, The ratio is included in the effective assets.

[0074] Furthermore, in step S5, when determining the benefits of investment projects, for three different types of investment projects, namely, new projects, expansion projects and technological transformation projects, the benefits are reflected in the three aspects of meeting growth needs, reducing power supply losses and reducing power outage losses, as follows:

[0075] In terms of meeting the growth in load demand, the calculation formula is:

[0076] (20)

[0077] In the formula, is the direct economic benefit of the project in year t due to the improvement of the transmission capacity of the power grid, is the increase in power grid transmission capacity in year t, is the transmission and distribution price in year t;

[0078] In terms of reducing power supply loss, the calculation formula is:

[0079] (twenty one)

[0080] In the formula, is the direct economic benefit of the project in year t due to the reduction of power supply energy consumption, The reduction of grid loss in year t, is the transmission and distribution price in year t;

[0081] In terms of reducing power outage losses, the calculation formula is:

[0082] (twenty two)

[0083] In the formula, is the direct economic benefit of the project in year t due to the reduction of power outage losses, is the reduction in power loss due to direct power outage in year t, is the transmission and distribution price in year t;

[0084] Therefore, the calculation formula for the annual comprehensive economic benefits of different types of projects is:

[0085] (twenty three)

[0086] In the formula, is the comprehensive direct economic benefit of the project in year t, is the direct economic benefit of the project in year t due to the improvement of the transmission capacity of the power grid, is the direct economic benefit brought by reducing power supply energy consumption in year t, It is the direct economic benefit brought by the project in year t due to the reduction of power outage losses.

[0087] Furthermore, in step S6, the optimal investment portfolio model of the power grid based on the maximum investment return is constructed as follows:

[0088] (25)

[0089] In the formula, is the permitted income of the power grid enterprise in year t.

[0090] Furthermore, for power grid enterprises, the permitted income is composed of permitted costs, permitted revenues and taxes included in the price, and the calculation formula for the permitted income is:

[0091] (26)

[0092] In the formula, is the permitted income of the power grid enterprise in year t, is the permitted cost of the power grid company in year t, is the permitted revenue of the power grid enterprise in year t, is the price-inclusive tax of the power grid enterprise in year t;

[0093] The calculation formula of the allowable cost is:

[0094] (27)

[0095] In the formula, is the permitted cost of the power grid company in year t, is the base period allowable cost of the power grid enterprise, is the permissible cost change of the power grid company in year t, is the additional permitted cost of the power grid enterprise in year t, is the reduced permitted cost of the power grid company in year t, is the additional depreciation of the power grid enterprise in year t, is the new operation and maintenance cost of the power grid enterprise in year t. Here, it is worth mentioning that the depreciation and operation and maintenance costs in the allowable cost can be increased by the increase of effective assets. is the investment amount of project type k in region i, voltage level j, in year t-1, is the effective asset inclusion coefficient for the newly added investment of project type k at voltage level j, is the effective asset depreciation rate of the newly invested project type k of voltage level j;

[0096] The calculation formula of the permitted income is:

[0097] (28)

[0098] In the formula, is the permitted revenue of the power grid enterprise in year t, is the total effective assets of the power grid enterprise in year t, is the weighted average return on capital of the power grid enterprises in year t, is the total effective assets of the power grid enterprise in year t-1, is the change in effective assets of the power grid enterprise in year t-1, is the newly added effective assets of the power grid enterprise in year t-1, is the reduced effective assets of the power grid enterprise in year t-1, is the investment amount of the power grid project of region i, voltage level j, project type k in year t, is the effective asset inclusion coefficient for the newly added investment of project type k at voltage level j, is the weighted average return on capital of the power grid enterprises in year t, is the return on equity capital of the power grid enterprise in year t, is the debt-to-asset ratio of the power grid enterprise in year t, is the debt-to-capital return rate of the power grid enterprise in year t;

[0099] The calculation formula for the tax included in the price is:

[0100] (29)

[0101] In the formula, is the price-inclusive tax of the power grid enterprise in year t, is the income tax of the power grid enterprise in year t, is the urban maintenance and construction tax of the power grid enterprise in year t, is the education surcharge of the power grid enterprise in year t, is the total effective assets of the power grid enterprise in year t, is the debt-to-asset ratio of the power grid enterprise in year t, is the return on equity capital of the power grid enterprise in year t, is the income tax rate, is the permissible income of the power grid enterprise excluding value-added tax in year t, is the VAT rate, is the allowable input tax deduction for the cost of the power grid enterprise in year t, To build and maintain rates for cities, The additional rate for education fees.

[0102] Preferably, in step S7, the determined grid investment constraints include investment demand constraints, investment capacity constraints, transmission and distribution price constraints, balancing account profit and loss constraints, and non-negative and integer constraints;

[0103] The investment demand constraints include:

[0104] (1) Investment demand constraints in different regions:

[0105] For different regions, the investment in power grid projects should meet the basic local incremental load demand. Since the investment in 500kv power grids is often not differentiated by region and is uniformly planned by provincial power grid companies, the investment in power grid projects in different regions involves voltage levels below 500kv.

[0106] For a certain region, the investment in power grid projects should meet the following requirements:

[0107] (30)

[0108] In the formula, is the investment quantity demand of power grid projects with new loads of voltage level j in region i in year t, is the number of new grid project investments in region i and voltage level j in year t, is the investment amount of the expansion power grid project in region i and voltage level j in year t, is the investment amount of technical transformation power grid projects in region i and voltage level j in year t, is the total number of existing power grid projects in region i and voltage level j in year t, is the proportion of existing power grid projects that must undergo technical transformation in year t, is the proportion of existing power grid projects that have technical transformation conditions in year t. For different regions, the constraint expressions are the same, but the parameters are different;

[0109] (2) Investment demand constraints at different voltage levels:

[0110] Since 500kv power grid investment is often not differentiated by region and is uniformly planned by provincial power grid companies, the investment in power grid projects with a voltage level of 500kv should be considered uniformly, and the investment in power grid projects with a voltage level below 500kv needs to consider the investment needs of different voltage levels in different regions;

[0111] For voltage level 500kv, the power grid project investment should meet the following requirements:

[0112] (31)

[0113] (32)

[0114] In the formula, The investment quantity demand for the power grid project with a voltage level of 500kV for the new load in year t is: is the number of new grid projects with a voltage level of 500kV in year t, is the investment amount of the expansion power grid project with voltage level of 500kV in year t, is the investment amount of technical transformation power grid projects with voltage level of 500kV in year t, is the total number of existing power grid projects with voltage level of 500kV in year t, is the proportion of existing power grid projects that must undergo technical transformation in year t, is the proportion of existing power grid projects that have conditions for technical transformation in year t;

[0115] For voltage levels below 500kv, the investment in power grid projects should meet the following requirements:

[0116] (33)

[0117] In the formula, is the investment quantity demand of power grid projects with new loads of voltage level j in region i in year t, is the number of new grid project investments in region i and voltage level j in year t, is the investment amount of the expansion power grid project in region i and voltage level j in year t, is the investment amount of technical transformation power grid projects in region i and voltage level j in year t, is the total number of existing power grid projects in region i and voltage level j in year t, is the proportion of existing power grid projects that must undergo technical transformation in year t, is the proportion of projects with technical transformation conditions among existing power grid projects in year t. For different voltage levels, the constraint expressions are the same, but the parameters are different;

[0118] (3) Investment demand constraints for different project types:

[0119] Since new construction projects, expansion projects and technological transformation projects have different types and characteristics, the investment requirements and related constraints of different types of projects are different;

[0120] For power grid expansion projects, the investment should meet the following requirements:

[0121] (34)

[0122] In the formula, is the investment amount of the expansion power grid project with voltage level of 500kV in year t, is the total number of existing power grid projects with voltage level of 500kV in year t, is the proportion of existing power grid projects that have expansion conditions in year t, is the investment amount of the expansion power grid project in region i and voltage level j in year t, is the total number of existing power grid projects in region i and voltage level j in year t;

[0123] For technical transformation power grid projects, the investment should meet the following requirements:

[0124] (35)

[0125] In the formula, is the investment amount of technical transformation power grid projects with voltage level of 500kV in year t, is the total number of existing power grid projects with voltage level of 500kV in year t, is the proportion of existing power grid projects that must undergo technical transformation in year t, is the proportion of existing power grid projects that have technical transformation conditions in year t, is the investment amount of technical transformation power grid projects in region i and voltage level j in year t, is the total number of existing power grid projects in region i and voltage level j in year t;

[0126] For new construction and expansion projects, the sum of the investment in these two types of projects should meet the corresponding incremental load requirements:

[0127] (36)

[0128] In the formula, The investment quantity demand for the power grid project with a voltage level of 500kV for the new load in year t is: is the number of new grid projects with a voltage level of 500kV in year t, is the investment amount of the expansion power grid project with voltage level of 500kV in year t, is the investment quantity demand of power grid projects with new loads of voltage level j in region i in year t, is the number of new grid project investments in region i and voltage level j in year t, is the investment amount of the expansion power grid project in region i and voltage level j in year t;

[0129] The investment capacity constraint is:

[0130] The sum of the investment amounts of power grid projects in different regions, voltage levels and types shall not exceed the maximum investment capacity of provincial power grid enterprises, as shown in the following formula:

[0131] (37)

[0132] In the formula, is the number of power grid projects invested in region i, voltage level j, project type k in year t, is the average unit investment of a power grid project of voltage level j and project type k, is the internal capital of the enterprise in year t, is the external capital of the enterprise in year t;

[0133] The transmission and distribution price constraint is:

[0134] Under the reform of transmission and distribution prices, the government will not allow transmission and distribution prices to increase significantly between different regulatory cycles. The method for calculating transmission and distribution prices at different voltage levels is as follows:

[0135] (38)

[0136] In the formula, is the transmission and distribution price of voltage level j, is the total cost of transmission and distribution services at voltage level j, is the total power supply of voltage level j;

[0137] The total cost of transmission and distribution services at different voltage levels is calculated as follows:

[0138] (39)

[0139] In the formula, is the permitted income for voltage level j in year t, is the permitted income of the power grid enterprise in year t, is the effective asset proportion of voltage level j in year t, is the effective asset of the substation with voltage level j in year t, is the effective asset proportion of substations with voltage level j in year t, is the effective assets of the voltage level j line in year t, is the effective asset proportion of the line with voltage level j in year t, is the total cost of transmission and distribution services at voltage level j, is the effective asset of the line at voltage level j, is the effective asset of the substation at voltage level j+1, is the transformation ratio from voltage level j+1 to voltage level j, is the total cost of transmission and distribution services at voltage level j+1, is the ratio of power supply from voltage level j+1 to voltage level j;

[0140] The fluctuation range of transmission and distribution prices of different voltage levels in different regulatory cycles should be within a reasonable range, as shown in the following formula:

[0141] (40)

[0142] In the formula, is the transmission and distribution price of voltage level j in the previous regulatory cycle, is the lower limit of the fluctuation of the transmission and distribution price of voltage level j, is the transmission and distribution price of voltage level j, is the upper limit of fluctuation of transmission and distribution price of voltage level j;

[0143] The balance account profit and loss constraint is that the balance account loss is less than the allowed profit, as shown in the following formula:

[0144] (41)

[0145] In the formula, is the actual income of the power grid enterprise in year t, is the permitted income of the power grid enterprise in year t, is the permitted revenue of the power grid enterprise in year t, is the actual transmission and distribution capacity of the power grid enterprise at voltage level i in year t, is the approved value of transmission and distribution price for voltage level i in year t;

[0146] In a transmission and distribution price regulation cycle, the deviation between actual income and permitted income in each year is different, but in the accounting cycle, the total balance account amount should be greater than or equal to zero, as shown in the following formula:

[0147] (42)

[0148] In the formula, is the actual income of the power grid enterprise in year t, is the permitted income of the power grid enterprise in year t;

[0149] Among them, the non-negative and integer constraints are that the power grid investment project is a non-negative integer, as shown in the following formula:

[0150] (43)

[0151] In the formula, is the investment amount of power grid projects of type k with voltage level 500kv in year t, is the number of power grid projects invested in region i, voltage level j, project type k in year t, Is a positive integer.

[0152] The power grid investment portfolio optimization method based on the power transmission and distribution price reform provided by the present invention collects relevant information such as the investment demand, investment capacity and balance account of power grid enterprises, and on this basis, according to the maximum profit of power grid enterprises within a regulatory cycle, comprehensively constructs the optimal investment portfolio model of power grid enterprises by integrating the investment demand of different voltage levels and different types of power grid projects, so as to realize the optimization of different investment portfolios of power grid enterprises under the power transmission and distribution price reform, so as to maximize the benefits of power grid enterprises. The present invention can not only provide support for power grid enterprises to reasonably arrange investment, but also provide effective information for power transmission and distribution supervision departments to evaluate the overall investment effect of power grid enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0153] Figure 1 The present invention is a flowchart of a power grid investment portfolio optimization method based on transmission and distribution price reform. DETAILED DESCRIPTION

[0154] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments and drawings. The contents mentioned in the implementation modes are not intended to limit the present invention.

[0155] like Figure 1 As shown in the figure, a power grid investment portfolio optimization method based on the reform of transmission and distribution prices includes eight steps. The following takes the situation of the power grid in region A from 2019 to 2021 as an example to illustrate this method in detail.

[0156] Step S1: Collect the power and financial data of the power grid in region A from 2018 to 2021. These power and financial data include the load characteristic curves of users in each year, line loss rates of lines of different voltage levels, investment quantity and investment amount of various types of projects in each region and year, and financial statements and financial parameters of the power grid in each year.

[0157] Step S2: Calculate the grid investment demand for different voltage levels and different project types. The grid investment demand includes peak load demand, maximum load increment demand, new capacity demand and grid project investment quantity demand. The calculation of these grid investment demands consists of the following steps S21-24, which are as follows.

[0158] Step S21, calculate the peak load demand: first predict the power consumption of different types of users at different voltage levels according to the load characteristics of each user, and then calculate the maximum power load on the maximum load day according to the load rate, that is, the peak load demand.

[0159] The calculation formula for power consumption is:

[0160] (1)

[0161] In the formula, is the power consumption of type p users in region i at voltage level j in year t, is the base annual electricity consumption of type p users in region i under voltage level j, r p is the annual growth rate of electricity consumption of type p users;

[0162] The calculation formula for peak load demand is:

[0163] (2)

[0164] In the formula, is the peak load demand of type p users at voltage level j in region i in year t, is the power consumption of type p users in region i at voltage level j in year t, is the load rate of type p users in region i at voltage level j, is the simultaneous rate of type p users in region i at voltage level j.

[0165] Step S22, calculate the transmission and distribution loss: first, according to the power balance relationship under different voltage levels, calculate the transmission and distribution loss ratio between different voltage levels, including the line loss rate and transformer loss rate of different voltage levels at peak load; then construct a power balance model considering the transmission and distribution loss of different voltage levels, and iteratively calculate the line loss ratio and transformer loss ratio according to the power supply and consumption balance relationship of different voltage levels in each region.

[0166] Among them, the calculation formulas of line loss ratio and transformation loss ratio are:

[0167] (3)

[0168] (4)

[0169] In the formula, is the line loss ratio between voltage level j and voltage level j+1, is the line loss rate under voltage level j, is the line loss rate at voltage level j+1, is the loss ratio between voltage level j and voltage level j+1, is the loss rate of voltage level j, is the loss rate of voltage level j+1.

[0170] Among them, the power balance model is:

[0171] (5)

[0172] In the formula, is the grid load of voltage level j, is the power supply load obtained by voltage level j from voltage level j+1, is the line loss rate of voltage level j, is the user load of voltage level j, is the power supply load from voltage level j to voltage level j-1, is the line loss load of voltage level j, is the loss rate of power supply from voltage level j to voltage level j-1, is the power supply load obtained by voltage level j-1 from voltage level j, The transformer loss load that supplies power from voltage level j to voltage level j-1.

[0173] Step S23, predicting the maximum load increment demand: first, according to the power balance relationship of different voltage levels, calculate the annual maximum load total demand of each voltage level from low voltage level to high voltage level, and then calculate the maximum load increment demand.

[0174] The calculation formula for the maximum total load demand is:

[0175] (6)

[0176] In the formula, is the total maximum load demand of voltage level j in year t (including the load demand of this level and the load demand of power supply to the lower level), is the user load of voltage level j in year t, is the power supply load (including transformer loss) from voltage level j to voltage level j-1 in year t, is the line loss load of voltage level j in year t, is the line loss rate of voltage level j, It is the power supply load (minus transformer losses) obtained from voltage level j+1 for voltage level j in year t. It is the loss rate of power supply from voltage level j to voltage level j-1.

[0177] The calculation formula for the maximum load increment requirement is:

[0178] (7)

[0179] In the formula, is the maximum load increment demand of voltage level j in year t, is the total maximum load demand of voltage level j in year t+1, The maximum total load demand of voltage level j in year t.

[0180] Using the data in step S1 to perform the calculations in steps S21-23, the maximum load increment requirements for different voltage levels in region A from 2019 to 2021 are obtained as follows:

[0181] Table 1 Maximum load increment demand at different voltage levels in Region A from 2019 to 2021 (unit: MW)

[0182]

[0183] Step S24, calculate the additional capacity demand: first calculate the additional capacity demand of the power grid based on the maximum load incremental demand predicted in step S23, and then calculate the cumulative maximum load incremental demand of different voltage levels in various regions over a period of time based on the continuity of the maximum load incremental demand of the power grid, that is, the investment quantity demand of the power grid project.

[0184] The calculation formula for the additional capacity requirement is:

[0185] (8)

[0186] In the formula, is the additional capacity demand of voltage level j in year t, is the total maximum load demand of voltage level j in year t+1, is the total maximum load demand of voltage level j in year t, is the capacity ratio of voltage level j, is the maximum load increment demand of voltage level j in year t.

[0187] The calculation formula for the investment quantity requirement of power grid projects is:

[0188] (9)

[0189] In the formula, is the investment quantity demand of power grid projects of voltage level j in year t, is the additional capacity demand of voltage level j in year t, is the unit substation capacity of voltage level j.

[0190] According to formula (9), the investment quantity demand for various types of projects at various voltage levels in region A from 2019 to 2021 is as follows:

[0191] Table 2 Investment quantity demand for various projects of various voltage levels in Region A from 2019 to 2021 (unit: unit)

[0192]

[0193] Step S3: Determine the total investment amount of the power grid project according to the average unit investment amount and the power grid project investment quantity requirement obtained in step S2.

[0194] In step S3, the calculation formula of the average unit investment is:

[0195] (10)

[0196] In the formula, is the average unit investment of a power grid project of voltage level j and project type k, is the average unit investment of substation of voltage level j and project type k, is the ratio length of the substation of voltage level j and project type k, The average investment per unit length of line of project type k at voltage level j.

[0197] When determining the total investment amount of a power grid project, the calculation is performed at different voltage levels, as follows:

[0198] The calculation formula for the investment amount of a certain type of project with a voltage level of 500kv is:

[0199] (11)

[0200] In the formula, is the investment amount of the power grid project of type k with voltage level 500kv in year t, is the number of power grid project investments of type k and voltage level 500 kV in region i in year t, is the average unit investment of a 500kv project type k power grid project, is the number of power grid project investments of type k with voltage level 500 kV in region i in year t-1, It is the number of investments in power grid projects of type k with voltage level 500 kV in region i in year t-2.

[0201] The calculation formula for the investment amount of a certain type of project with a voltage level of 220kv is:

[0202] (12)

[0203] In the formula, is the investment amount of the power grid project of type k with voltage level 220kv in year t, is the number of power grid project investments of type k with voltage level 220 kV in region i in year t, is the average unit investment of power grid project k with voltage level 220kv project type, It is the number of investments in power grid projects of type k with voltage level 220 kV in region i in year t-1.

[0204] The calculation formula for the investment amount of certain types of projects with voltage levels of 110kv and below is:

[0205] (13)

[0206] In the formula, is the investment amount of the power grid project of voltage level j and project type k in year t, is the number of power grid projects invested in region i, voltage level j, project type k in year t, is the average unit investment of power grid projects of voltage level j and project type k.

[0207] Step S4: Calculate the grid investment capacity under the transmission and distribution price reform.

[0208] Under the reform of transmission and distribution prices, the calculation formula for grid investment capacity is:

[0209] (14)

[0210] Where Y t is the investment capacity in year t under the transmission and distribution price reform, L t is the retained profit in the tth year under the transmission and distribution price reform, Zt is the depreciation amount in the tth year under the transmission and distribution price reform, R t is the additional financing amount in year t under the transmission and distribution price reform, J t It is the newly added current assets in the tth year under the transmission and distribution price reform.

[0211] The calculation formula of retained earnings is:

[0212] (15)

[0213] Where, L t is the retained profit in the tth year under the transmission and distribution price reform, P A,t is the allowed return in year t.

[0214] The calculation formula for the depreciation amount is:

[0215] (16)

[0216] In the formula, is the depreciation amount in the tth year under the transmission and distribution price reform, is the net value of fixed assets of category p formed before January 1, 2015, is the median depreciation period of the p-th type of fixed assets, The original value of fixed assets of category p formed in 2016 and later, is the depreciation period of the pth type of fixed assets, and β is the residual value rate of fixed assets.

[0217] The calculation formula for the newly added current assets is:

[0218] (17)

[0219] In the formula, is the new current assets in year t, is the total operating cost in year t, is the total operating cost in year t-1, and γ is the provision ratio for retained current assets.

[0220] The calculation formula for the additional financing amount is:

[0221] (18)

[0222] In the formula, is the newly added financing amount in year t, and the growth amount of liabilities in that year is the newly added financing amount in that year. is the total assets in year t-1, is the total profit in year t, is the total liabilities in year t-1, is the debt-to-asset ratio in year t.

[0223] According to formulas (14)-(18), the grid investment capacity under the transmission and distribution price reform in region A from 2019 to 2021 is as follows:

[0224] Table 3 Grid investment capacity under the transmission and distribution price reform in Region A from 2019 to 2021

[0225]

[0226] Step S5: Determine the benefits of the investment project.

[0227] When determining the benefits of investment projects, under the reform of transmission and distribution prices, the investment in power grid projects will be included in the permitted costs and permitted income of power grid enterprises through effective assets. The relationship between power grid project investment and effective assets is:

[0228] (19)

[0229] In the formula, is the change in effective assets caused by the additional investment in year t, is the investment amount of the power grid project in year t, The ratio is included in the effective assets.

[0230] In addition, when determining the benefits of investment projects, for three different types of investment projects, namely new projects, expansion projects and technical transformation projects, their benefits are reflected in meeting growth needs, reducing power supply losses and reducing power outage losses, as follows:

[0231] In terms of meeting the growth in load demand, the calculation formula is:

[0232] (20)

[0233] In the formula, is the direct economic benefit of the project in year t due to the improvement of the transmission capacity of the power grid, is the increase in power grid transmission capacity in year t, is the transmission and distribution price in year t;

[0234] In terms of reducing power supply loss, the calculation formula is:

[0235] (twenty one)

[0236] In the formula, is the direct economic benefit of the project in year t due to the reduction of power supply energy consumption, The reduction of grid loss in year t, is the transmission and distribution price in year t;

[0237] In terms of reducing power outage losses, the calculation formula is:

[0238] (twenty two)

[0239] In the formula, is the direct economic benefit of the project in year t due to the reduction of power outage losses, is the reduction in power loss due to direct power outage in year t, is the transmission and distribution price in year t;

[0240] Therefore, the calculation formula for the annual comprehensive economic benefits of different types of projects is:

[0241] (twenty three)

[0242] In the formula, is the comprehensive direct economic benefit of the project in year t, is the direct economic benefit of the project in year t due to the improvement of the transmission capacity of the power grid, is the direct economic benefit brought by reducing power supply energy consumption in year t, It is the direct economic benefit brought by the project in year t due to the reduction of power outage losses.

[0243] Step S6: Construct an optimal power grid investment portfolio model based on maximizing investment returns.

[0244] In step S6, the optimal investment portfolio model of the power grid based on the maximum investment return is constructed as follows:

[0245] (25)

[0246] In the formula, is the permitted income of the power grid enterprise in year t.

[0247] For power grid enterprises, the permitted income consists of permitted costs, permitted revenues and taxes included in the price, and the calculation formula for permitted income is:

[0248] (26)

[0249] In the formula, is the permitted income of the power grid enterprise in year t, is the permitted cost of the power grid company in year t, is the permitted revenue of the power grid enterprise in year t, is the price-inclusive tax of the power grid enterprise in year t;

[0250] The calculation formula of the allowable cost is:

[0251] (27)

[0252] In the formula, is the permitted cost of the power grid company in year t, is the base period allowable cost of the power grid enterprise, is the permissible cost change of the power grid company in year t, is the additional permitted cost of the power grid enterprise in year t, is the reduced permitted cost of the power grid company in year t, is the additional depreciation of the power grid enterprise in year t, is the new operation and maintenance cost of the power grid enterprise in year t. Here, it is worth mentioning that the depreciation and operation and maintenance costs in the allowable cost can be increased by the increase of effective assets. is the investment amount of project type k in region i, voltage level j, in year t-1, is the effective asset inclusion coefficient for the newly added investment of project type k at voltage level j, is the effective asset depreciation rate of the newly invested project type k of voltage level j;

[0253] The calculation formula of the permitted income is:

[0254] (28)

[0255] In the formula, is the permitted revenue of the power grid enterprise in year t, is the total effective assets of the power grid enterprise in year t, is the weighted average return on capital of the power grid enterprises in year t, is the total effective assets of the power grid enterprise in year t-1, is the change in effective assets of the power grid enterprise in year t-1, is the newly added effective assets of the power grid enterprise in year t-1, is the reduced effective assets of the power grid enterprise in year t-1, is the investment amount of the power grid project of region i, voltage level j, project type k in year t, is the effective asset inclusion coefficient for the newly added investment of project type k at voltage level j, is the weighted average return on capital of the power grid enterprises in year t, is the return on equity capital of the power grid enterprise in year t, is the debt-to-asset ratio of the power grid enterprise in year t, is the debt-to-capital return rate of the power grid enterprise in year t;

[0256] The calculation formula for the tax included in the price is:

[0257] (29)

[0258] In the formula, is the price-inclusive tax of the power grid enterprise in year t, is the income tax of the power grid enterprise in year t, is the urban maintenance and construction tax of the power grid enterprise in year t, is the education surcharge of the power grid enterprise in year t, is the total effective assets of the power grid enterprise in year t, is the debt-to-asset ratio of the power grid enterprise in year t, is the return on equity capital of the power grid enterprise in year t, is the income tax rate, is the permissible income of the power grid enterprise excluding value-added tax in year t, is the VAT rate, is the allowable input tax deduction for the cost of the power grid enterprise in year t, To build and maintain rates for cities, The additional rate for education fees.

[0259] Step S7: Determine grid investment constraints for different regions, different voltage levels, and different project types.

[0260] The determined grid investment constraints include investment demand constraints, investment capacity constraints, transmission and distribution price constraints, balance account profit and loss constraints, and non-negative and integer constraints.

[0261] The investment demand constraints include:

[0262] (1) Investment demand constraints in different regions:

[0263] For different regions, the investment in power grid projects should meet the basic local incremental load demand. Since the investment in 500kv power grids is often not differentiated by region and is uniformly planned by provincial power grid companies, the investment in power grid projects in different regions involves voltage levels below 500kv.

[0264] For a certain region, the investment in power grid projects should meet the following requirements:

[0265] (30)

[0266] In the formula, is the investment quantity demand of power grid projects with new loads of voltage level j in region i in year t, is the number of new grid project investments in region i and voltage level j in year t, is the investment amount of the expansion power grid project in region i and voltage level j in year t, is the investment amount of technical transformation power grid projects in region i and voltage level j in year t, is the total number of existing power grid projects in region i and voltage level j in year t, is the proportion of existing power grid projects that must undergo technical transformation in year t, is the proportion of existing power grid projects that have technical transformation conditions in year t. For different regions, the constraint expressions are the same, but the parameters are different;

[0267] (2) Investment demand constraints at different voltage levels:

[0268] Since 500kv power grid investment is often not differentiated by region and is uniformly planned by provincial power grid companies, the investment in power grid projects with a voltage level of 500kv should be considered uniformly, and the investment in power grid projects with a voltage level below 500kv needs to consider the investment needs of different voltage levels in different regions;

[0269] For voltage level 500kv, the power grid project investment should meet the following requirements:

[0270] (31)

[0271] (32)

[0272] In the formula, The investment quantity demand for the power grid project with a voltage level of 500kV for the new load in year t is: is the number of new grid projects with a voltage level of 500kV in year t, is the investment amount of the expansion power grid project with voltage level of 500kV in year t, is the investment amount of technical transformation power grid projects with voltage level of 500kV in year t, is the total number of existing power grid projects with voltage level of 500kV in year t, is the proportion of existing power grid projects that must undergo technical transformation in year t, is the proportion of existing power grid projects that have conditions for technical transformation in year t;

[0273] For voltage levels below 500kv, the investment in power grid projects should meet the following requirements:

[0274] (33)

[0275] In the formula, is the investment quantity demand of power grid projects with new loads of voltage level j in region i in year t, is the number of new grid project investments in region i and voltage level j in year t, is the investment amount of the expansion power grid project in region i and voltage level j in year t, is the investment amount of technical transformation power grid projects in region i and voltage level j in year t, is the total number of existing power grid projects in region i and voltage level j in year t, is the proportion of existing power grid projects that must undergo technical transformation in year t, is the proportion of projects with technical transformation conditions among existing power grid projects in year t. For different voltage levels, the constraint expressions are the same, but the parameters are different;

[0276] (3) Investment demand constraints for different project types:

[0277] Since new construction projects, expansion projects and technological transformation projects have different types and characteristics, the investment requirements and related constraints of different types of projects are different;

[0278] For power grid expansion projects, the investment should meet the following requirements:

[0279] (34)

[0280] In the formula, is the investment amount of the expansion power grid project with voltage level of 500kV in year t, is the total number of existing power grid projects with voltage level of 500kV in year t, is the proportion of existing power grid projects that have expansion conditions in year t, is the investment amount of the expansion power grid project in region i and voltage level j in year t, is the total number of existing power grid projects in region i and voltage level j in year t;

[0281] For technical transformation power grid projects, the investment should meet the following requirements:

[0282] (35)

[0283] In the formula, is the investment amount of technical transformation power grid projects with voltage level of 500kV in year t, is the total number of existing power grid projects with voltage level of 500kV in year t, is the proportion of existing power grid projects that must undergo technical transformation in year t, is the proportion of existing power grid projects that have technical transformation conditions in year t, is the investment amount of technical transformation power grid projects in region i and voltage level j in year t, is the total number of existing power grid projects in region i and voltage level j in year t;

[0284] For new construction and expansion projects, the sum of the investment in these two types of projects should meet the corresponding incremental load requirements:

[0285] (36)

[0286] In the formula, The investment quantity demand for the power grid project with a voltage level of 500kV for the new load in year t is: is the number of new grid projects with a voltage level of 500kV in year t, is the investment amount of the expansion power grid project with voltage level of 500kV in year t, is the investment quantity demand of power grid projects with new loads of voltage level j in region i in year t, is the number of new grid project investments in region i and voltage level j in year t, is the investment amount of the expansion power grid project in region i and voltage level j in year t;

[0287] Among them, the investment capacity constraint is:

[0288] The sum of the investment amounts of power grid projects in different regions, voltage levels and types shall not exceed the maximum investment capacity of provincial power grid enterprises, as shown in the following formula:

[0289] (37)

[0290] In the formula, is the number of power grid projects invested in region i, voltage level j, project type k in year t, is the average unit investment of a power grid project of voltage level j and project type k, is the internal capital of the enterprise in year t, is the external capital of the enterprise in year t;

[0291] Among them, the transmission and distribution price constraint is:

[0292] Under the reform of transmission and distribution prices, the government will not allow transmission and distribution prices to increase significantly between different regulatory cycles. The method for calculating transmission and distribution prices at different voltage levels is as follows:

[0293] (38)

[0294] In the formula, is the transmission and distribution price of voltage level j, is the total cost of transmission and distribution services at voltage level j, is the total power supply of voltage level j;

[0295] The total cost of transmission and distribution services at different voltage levels is calculated as follows:

[0296] (39)

[0297] In the formula, is the permitted income for voltage level j in year t, is the permitted income of the power grid enterprise in year t, is the effective asset proportion of voltage level j in year t, is the effective asset of the substation with voltage level j in year t, is the effective asset proportion of substations with voltage level j in year t, is the effective assets of the voltage level j line in year t, is the effective asset proportion of the line with voltage level j in year t, is the total cost of transmission and distribution services at voltage level j, is the effective asset of the line at voltage level j, is the effective asset of the substation at voltage level j+1, is the transformation ratio from voltage level j+1 to voltage level j, is the total cost of transmission and distribution services at voltage level j+1, It is the ratio of power supply from voltage level j+1 to voltage level j.

[0298] The fluctuation range of transmission and distribution prices of different voltage levels in different regulatory cycles should be within a reasonable range, as shown in the following formula:

[0299] (40)

[0300] In the formula, is the transmission and distribution price of voltage level j in the previous regulatory cycle, is the lower limit of the fluctuation of the transmission and distribution price of voltage level j, is the transmission and distribution price of voltage level j, is the upper limit of fluctuation of transmission and distribution price of voltage level j;

[0301] Among them, the balance account profit and loss constraint is that the balance account loss is less than the allowed profit, as shown in the following formula:

[0302] (41)

[0303] In the formula, is the actual income of the power grid enterprise in year t, is the permitted income of the power grid enterprise in year t, is the permitted revenue of the power grid enterprise in year t, is the actual transmission and distribution capacity of the power grid enterprise at voltage level i in year t, is the approved value of transmission and distribution price for voltage level i in year t;

[0304] In a transmission and distribution price regulation cycle, the deviation between actual income and permitted income in each year is different, but in the accounting cycle, the total balance account amount should be greater than or equal to zero, as shown in the following formula:

[0305] (42)

[0306] In the formula, is the actual income of the power grid enterprise in year t, is the permitted income of the power grid enterprise in year t;

[0307] Among them, the non-negative and integer constraints are that the power grid investment project is a non-negative integer, as shown in the following formula:

[0308] (43)

[0309] In the formula, is the investment amount of power grid projects of type k with voltage level 500kv in year t, is the number of power grid projects invested in region i, voltage level j, project type k in year t, Is a positive integer.

[0310] Step S8: Based on the grid investment constraints determined in step S7, the grid optimal investment portfolio model constructed in step S6 is solved to obtain the provincial grid optimal investment portfolio with the greatest return, as shown in Table 4 below.

[0311] Table 4 Overall investment scale of power grid in Region A from 2019 to 2021

[0312]

[0313] Among them, the basic investment demand data is the estimated number of power grid planning and is a known parameter.

[0314] In the optimal investment portfolio of the provincial power grid, the investment amount of Area A from 2019 to 2021 is calculated according to different voltage levels and different project types according to formulas (9), (10), and (11) in this implementation method, and the data shown in Table 5 are obtained.

[0315] Table 5 Investment amount of power grid projects of different voltage levels and project types in Region A from 2019 to 2021

[0316]

[0317] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention may also be implemented in other ways. Any obvious replacement without departing from the concept of the present technical solution is within the protection scope of the present invention.

[0318] In order to make it easier for ordinary technicians in the field to understand the improvements of the present invention over the prior art, some drawings and descriptions of the present invention have been simplified, and for the sake of clarity, some other elements are omitted in this application document. Ordinary technicians in the field should realize that these omitted elements may also constitute the content of the present invention.

Claims

1. A power grid investment portfolio optimization method based on transmission and distribution price reform, characterized in that: include: Step S1: Collecting power and financial data of the power grid, including the load characteristic curve of users in each year, line loss rate of lines of different voltage levels, investment quantity and investment amount of various types of projects in various regions and years, and financial statements and financial parameters of the power grid in each year; Step S2: Calculate the grid investment demand of different voltage levels and different project types, wherein the grid investment demand includes the grid project investment quantity demand; Step S21, calculating the peak load demand: first predict the power consumption of different types of users at different voltage levels according to the load characteristics of each user, and then calculate the maximum power load on the maximum load day according to the load rate, that is, the peak load demand; Step S22, calculating the transmission and distribution loss: first, according to the power balance relationship under different voltage levels, calculate the transmission and distribution loss ratio between different voltage levels, including the line loss rate and transformer loss rate of different voltage levels at peak load; then construct a power balance model considering the transmission and distribution loss of different voltage levels, and iteratively calculate the line loss ratio and transformer loss ratio according to the power supply and consumption balance relationship of different voltage levels in each region; The power balance model is: （5） In the formula, is the grid load of voltage level j, is the power supply load obtained by voltage level j from voltage level j+1, is the line loss rate of voltage level j, is the user load of voltage level j, is the power supply load from voltage level j to voltage level j-1, is the line loss load of voltage level j, is the loss rate of power supply from voltage level j to voltage level j-1, is the power supply load obtained by voltage level j-1 from voltage level j, The transformer loss load for supplying power from voltage level j to voltage level j-1; Step S23, predicting the maximum load increment demand: first, according to the power balance relationship of different voltage levels, calculate the annual maximum load total demand of each voltage level from low voltage level to high voltage level, and then calculate the maximum load increment demand; Step S24, calculating the additional capacity demand: firstly, calculating the additional capacity demand of the power grid according to the maximum load incremental demand predicted in step S23, and then calculating the cumulative maximum load incremental demand of different voltage levels in various regions within a period of time according to the continuity of the maximum load incremental demand of the power grid, that is, the investment quantity demand of the power grid project; Step S3: Determine the total investment amount of the power grid project according to the average unit investment amount and the power grid project investment quantity requirement obtained in step S2; Step S4: Calculate the power grid investment capacity under the transmission and distribution price reform; Step S5: Determine the benefits of the investment project; Step S6: constructing an optimal investment portfolio model for a power grid based on maximum investment returns; Step S7: Determine grid investment constraints for different regions, different voltage levels, and different project types; Step S8: Based on the grid investment constraints determined in step S7, the grid optimal investment portfolio model constructed in step S6 is solved to obtain the provincial grid optimal investment portfolio with the greatest return.

2. The power grid investment portfolio optimization method based on transmission and distribution price reform according to claim 1 is characterized by: In step S2: The calculation formula for the power consumption is: （1） In the formula, is the power consumption of type p users in region i at voltage level j in year t, is the base annual electricity consumption of type p users in region i under voltage level j, r p is the annual growth rate of electricity consumption of type p users; The peak load demand calculation formula is: （2） In the formula, is the peak load demand of type p users at voltage level j in region i in year t, is the power consumption of type p users in region i at voltage level j in year t, is the load rate of type p users in region i at voltage level j, is the simultaneous rate of type p users at voltage level j in region i; The calculation formulas for the line loss ratio and the transformation loss ratio are: （3） （4） In the formula, is the line loss ratio between voltage level j and voltage level j+1, is the line loss rate under voltage level j, is the line loss rate at voltage level j+1, is the loss ratio between voltage level j and voltage level j+1, is the loss rate of voltage level j, is the loss rate of voltage level j+1; The calculation formula for the maximum total load demand is: （6） In the formula, is the total maximum load demand of voltage level j in year t, including the load demand of this level and the load demand of power supply to the lower level, is the user load of voltage level j in year t, is the power supply load from voltage level j to voltage level j-1 in year t, including transformer losses, is the line loss load of voltage level j in year t, is the line loss rate of voltage level j, is the power supply load obtained by voltage level j from voltage level j+1 in year t, minus transformer losses, The loss rate of power supply from voltage level j to voltage level j-1; The calculation formula for the maximum load increment requirement is: （7） In the formula, is the maximum load increment demand of voltage level j in year t, is the total maximum load demand of voltage level j in year t+1, The maximum total load demand of voltage level j in year t; The calculation formula for the additional capacity requirement is: （8） In the formula, is the additional capacity demand of voltage level j in year t, is the total maximum load demand of voltage level j in year t+1, is the total maximum load demand of voltage level j in year t, is the capacity ratio of voltage level j, is the maximum load increment demand of voltage level j in year t; The calculation formula for the investment quantity requirement of the power grid project is: （9） In the formula, is the investment quantity demand of power grid projects of voltage level j in year t, is the additional capacity demand of voltage level j in year t, is the unit substation capacity of voltage level j.

3. The power grid investment portfolio optimization method based on transmission and distribution price reform according to claim 2 is characterized by: In step S3, the calculation formula of the average unit investment is: （10） In the formula, is the average unit investment of power grid projects of voltage level j and project type k, is the average unit investment of substation of voltage level j and project type k, is the ratio length of the substation of voltage level j and project type k, The average investment per unit length of line of project type k at voltage level j.

4. The power grid investment portfolio optimization method based on transmission and distribution price reform according to claim 3 is characterized by: In step S3, when determining the total investment amount of the power grid project, calculations are performed at different voltage levels, as follows: The calculation formula for the investment amount of a certain type of project with a voltage level of 500kv is: （11） In the formula, is the investment amount of the power grid project of type k with voltage level 500kv in year t, is the number of power grid project investments of type k and voltage level 500 kV in region i in year t, is the average unit investment of a 500kv project type k power grid project, is the number of power grid project investments of type k with voltage level 500 kV in region i in year t-1, The investment amount of power grid projects of type k with voltage level 500 kV in region i in year t-2; The calculation formula for the investment amount of a certain type of project with a voltage level of 220kv is: （12） In the formula, is the investment amount of the power grid project of type k with voltage level 220kv in year t, is the number of power grid project investments of type k with voltage level 220 kV in region i in year t, is the average unit investment of power grid project k with voltage level 220kv project type, The investment amount of power grid projects of type k with voltage level 220 kV in region i in year t-1; The calculation formula for the investment amount of certain types of projects with voltage levels of 110kv and below is: （13） In the formula, is the investment amount of the power grid project of voltage level j and project type k in year t, is the number of power grid projects invested in region i, voltage level j, project type k in year t, is the average unit investment of power grid projects of voltage level j and project type k.

5. The power grid investment portfolio optimization method based on transmission and distribution price reform according to claim 4 is characterized by: In step S4, the calculation formula for the grid investment capacity under the transmission and distribution price reform is: （14） Where Y t is the investment capacity in year t under the transmission and distribution price reform, L t is the retained profit in the tth year under the transmission and distribution price reform, Z t is the depreciation amount in the tth year under the transmission and distribution price reform, R t is the additional financing amount in year t under the transmission and distribution price reform, J t is the new current assets in year t under the transmission and distribution price reform; The calculation formula of retained earnings is: （15） Where, L t is the retained profit in the tth year under the transmission and distribution price reform, P A,t is the permitted income in year t; The calculation formula for the depreciation amount is: （16） In the formula, is the depreciation amount in the tth year under the transmission and distribution price reform, is the net value of fixed assets of category p formed before January 1, 2015, is the median depreciation period of the p-th type of fixed assets, The original value of fixed assets of category p formed in 2016 and later, is the depreciation period of the pth type of fixed assets, β is the residual value rate of fixed assets; The calculation formula for the newly added current assets is: （17） In the formula, is the new current assets in year t, is the total operating cost in year t, is the total operating cost in year t-1, γ is the provision ratio for retained current assets; The calculation formula for the additional financing amount is: （18） In the formula, is the newly added financing amount in year t, and the growth amount of liabilities in that year is the newly added financing amount in that year. is the total assets in year t-1, is the total profit in year t, is the total liabilities in year t-1, is the debt-to-asset ratio in year t.

6. The power grid investment portfolio optimization method based on transmission and distribution price reform according to claim 5 is characterized by: In step S5, when determining the benefits of the investment project, under the reform of transmission and distribution prices, the power grid project investment will be included in the permitted costs and permitted income of the power grid enterprise through effective assets, wherein the relationship between the power grid project investment and effective assets is: （19） In the formula, is the change in effective assets caused by the additional investment in year t, is the investment amount of the power grid project in year t, The ratio is included in the effective assets.

7. The power grid investment portfolio optimization method based on transmission and distribution price reform according to claim 6 is characterized by: In step S5, when determining the benefits of investment projects, for three different types of investment projects, namely new projects, expansion projects and technical transformation projects, their benefits are reflected in the three aspects of meeting growth needs, reducing power supply losses and reducing power outage losses, as follows: In terms of meeting the growth in load demand, the calculation formula is: （20） In the formula, is the direct economic benefit of the project in year t due to the improvement of the transmission capacity of the power grid, is the increase in power grid transmission capacity in year t, is the transmission and distribution price in year t; In terms of reducing power supply loss, the calculation formula is: （21） In the formula, is the direct economic benefit of the project in year t due to the reduction of power supply energy consumption, The reduction of grid loss in year t, is the transmission and distribution price in year t; In terms of reducing power outage losses, the calculation formula is: （22） In the formula, is the direct economic benefit of the project in year t due to the reduction of power outage losses, is the reduction in power loss due to direct power outage in year t, is the transmission and distribution price in year t; Therefore, the calculation formula for the annual comprehensive economic benefits of different types of projects is: （23） In the formula, is the comprehensive direct economic benefit of the project in year t, is the direct economic benefit of the project in year t due to the improvement of the transmission capacity of the power grid, is the direct economic benefit brought by reducing power supply energy consumption in year t, It is the direct economic benefit brought by the project in year t due to the reduction of power outage losses.

8. The power grid investment portfolio optimization method based on transmission and distribution price reform according to claim 7 is characterized by: In step S6, the optimal investment portfolio model of the power grid based on the maximum investment return is constructed as follows: （25） In the formula, is the permitted income of the power grid enterprise in year t.

9. The power grid investment portfolio optimization method based on transmission and distribution price reform according to claim 8 is characterized by: For power grid enterprises, the permitted income is composed of permitted costs, permitted revenues and taxes included in the price. The calculation formula for the permitted income is: （26） In the formula, is the permitted income of the power grid enterprise in year t, is the permitted cost of the power grid enterprise in year t, is the permitted revenue of the power grid enterprise in year t, is the price-inclusive tax of the power grid enterprise in year t; The calculation formula of the allowable cost is: （27） In the formula, is the permitted cost of the power grid enterprise in year t, is the base period allowable cost of the power grid enterprise, is the permissible cost change of the power grid company in year t, is the additional permitted cost of the power grid enterprise in year t, is the reduced permitted cost of the power grid company in year t, is the additional depreciation of the power grid enterprise in year t, is the new operation and maintenance cost of the power grid enterprise in year t. Here, it is worth mentioning that the depreciation and operation and maintenance costs in the allowable cost can be increased by the increase of effective assets. is the investment amount of project type k in region i, voltage level j, in year t-1, is the effective asset inclusion coefficient for the newly added investment of project type k at voltage level j, is the effective asset depreciation rate of the newly invested project type k of voltage level j; The calculation formula of the permitted income is: （28） In the formula, is the permitted revenue of the power grid enterprise in year t, is the total effective assets of the power grid enterprise in year t, is the weighted average return on capital of the power grid enterprises in year t, is the total effective assets of the power grid enterprise in year t-1, is the change in effective assets of the power grid enterprise in year t-1, is the newly added effective assets of the power grid enterprise in year t-1, is the reduced effective assets of the power grid enterprise in year t-1, is the investment amount of the power grid project of region i, voltage level j, project type k in year t, is the effective asset inclusion coefficient for the newly added investment of project type k at voltage level j, is the weighted average return on capital of the power grid enterprises in year t, is the return on equity capital of the power grid enterprise in year t, is the debt-to-asset ratio of the power grid enterprise in year t, is the debt-to-capital return rate of the power grid enterprise in year t; The calculation formula for the tax included in the price is: （29） In the formula, is the price-inclusive tax of the power grid enterprise in year t, is the income tax of the power grid enterprise in year t, is the urban maintenance and construction tax of the power grid enterprise in year t, is the education surcharge of the power grid enterprise in year t, is the total effective assets of the power grid enterprise in year t, is the debt-to-asset ratio of the power grid enterprise in year t, is the return on equity capital of the power grid enterprise in year t, is the income tax rate, is the permissible income of the power grid enterprise excluding VAT in year t, is the VAT rate, is the allowable cost input tax deduction amount of the power grid enterprise in year t, To build and maintain rates for cities, The additional rate for education fees.

10. The power grid investment portfolio optimization method based on transmission and distribution price reform according to claim 9 is characterized in that: In step S7, the determined grid investment constraints include investment demand constraints, investment capacity constraints, transmission and distribution price constraints, balance account profit and loss constraints, and non-negative and integer constraints; The investment demand constraints include: (1) Investment demand constraints in different regions: For different regions, the investment in power grid projects should meet the basic local incremental load demand. Since the investment in 500kv power grids is often not differentiated by region and is uniformly planned by provincial power grid companies, the investment in power grid projects in different regions involves voltage levels below 500kv. For a certain region, the investment in power grid projects should meet the following requirements: （30） In the formula, is the investment quantity demand of power grid projects with new loads of voltage level j in region i in year t, is the number of new grid project investments in region i and voltage level j in year t, is the investment amount of the expansion power grid project in region i and voltage level j in year t, is the investment amount of technical transformation power grid projects in region i and voltage level j in year t, is the total number of existing power grid projects in region i and voltage level j in year t, is the proportion of existing power grid projects that must undergo technical transformation in year t, is the proportion of existing power grid projects that have technical transformation conditions in year t. For different regions, the constraint expressions are the same, but the parameters are different; (2) Investment demand constraints at different voltage levels: Since 500kv power grid investment is often not differentiated by region and is uniformly planned by provincial power grid companies, the investment in power grid projects with a voltage level of 500kv should be considered uniformly, and the investment in power grid projects with a voltage level below 500kv needs to consider the investment needs of different voltage levels in different regions; For voltage level 500kv, the power grid project investment should meet the following requirements: （31） （32） In the formula, The investment quantity demand for the power grid project with a voltage level of 500kV for the new load in year t is: is the number of new grid projects with a voltage level of 500kV in year t, is the investment amount of the expansion power grid project with voltage level of 500kV in year t, is the investment amount of technical transformation power grid projects with voltage level of 500kV in year t, is the total number of existing power grid projects with voltage level of 500kV in year t, is the proportion of existing power grid projects that must undergo technical transformation in year t, is the proportion of existing power grid projects that have conditions for technical transformation in year t; For voltage levels below 500kv, the investment in power grid projects should meet the following requirements: （33） In the formula, is the investment quantity demand of power grid projects with new loads of voltage level j in region i in year t, is the number of new grid project investments in region i and voltage level j in year t, is the investment amount of the expansion power grid project in region i and voltage level j in year t, is the investment amount of technical transformation power grid projects in region i and voltage level j in year t, is the total number of existing power grid projects in region i and voltage level j in year t, is the proportion of existing power grid projects that must undergo technical transformation in year t, is the proportion of projects with technical transformation conditions among existing power grid projects in year t. For different voltage levels, the constraint expressions are the same, but the parameters are different; (3) Investment demand constraints for different project types: Since new construction projects, expansion projects and technological transformation projects have different types and characteristics, the investment requirements and related constraints of different types of projects are different; For power grid expansion projects, the investment should meet the following requirements: （34） In the formula, is the investment amount of the expansion power grid project with voltage level of 500kV in year t, is the total number of existing power grid projects with voltage level of 500kV in year t, is the proportion of existing power grid projects that have expansion conditions in year t, is the investment amount of the expansion power grid project in region i and voltage level j in year t, is the total number of existing power grid projects in region i and voltage level j in year t; For technical transformation power grid projects, the investment should meet the following requirements: （35） In the formula, is the investment amount of technical transformation power grid projects with voltage level of 500kV in year t, is the total number of existing power grid projects with voltage level of 500kV in year t, is the proportion of existing power grid projects that must undergo technical transformation in year t, is the proportion of existing power grid projects that have technical transformation conditions in year t, is the investment amount of technical transformation power grid projects in region i and voltage level j in year t, is the total number of existing power grid projects in region i and voltage level j in year t; For new construction and expansion projects, the sum of the investment in these two types of projects should meet the corresponding incremental load requirements: （36） In the formula, The investment quantity demand for the power grid project with a voltage level of 500kV for the new load in year t is: is the number of new grid projects with a voltage level of 500kV in year t, is the investment amount of the expansion power grid project with voltage level of 500kV in year t, is the investment quantity demand of power grid projects with new loads of voltage level j in region i in year t, is the number of new grid project investments in region i and voltage level j in year t, is the investment amount of the expansion power grid project in region i and voltage level j in year t; The investment capacity constraint is: The sum of the investment amounts of power grid projects in different regions, voltage levels and types shall not exceed the maximum investment capacity of provincial power grid enterprises, as shown in the following formula: （37） In the formula, is the number of power grid projects invested in region i, voltage level j, project type k in year t, is the average unit investment of power grid projects of voltage level j and project type k, is the internal capital of the enterprise in year t, is the external capital of the enterprise in year t; The transmission and distribution price constraint is: Under the reform of transmission and distribution prices, the government will not allow transmission and distribution prices to increase significantly between different regulatory cycles. The method for calculating transmission and distribution prices at different voltage levels is as follows: （38） In the formula, is the transmission and distribution price of voltage level j, is the total cost of transmission and distribution services at voltage level j, is the total power supply of voltage level j; The total cost of transmission and distribution services at different voltage levels is calculated as follows: （39） In the formula, is the permitted income for voltage level j in year t, is the permitted income of the power grid enterprise in year t, is the effective asset proportion of voltage level j in year t, is the effective asset of the substation with voltage level j in year t, is the effective asset proportion of substations with voltage level j in year t, is the effective assets of the voltage level j line in year t, is the effective asset proportion of the line with voltage level j in year t, is the total cost of transmission and distribution services at voltage level j, is the effective asset of the line at voltage level j, is the effective asset of the substation at voltage level j+1, is the transformation ratio from voltage level j+1 to voltage level j, is the total cost of transmission and distribution services at voltage level j+1, is the ratio of power supply from voltage level j+1 to voltage level j; The fluctuation range of transmission and distribution prices of different voltage levels in different regulatory cycles should be within a reasonable range, as shown in the following formula: （40） In the formula, is the transmission and distribution price of voltage level j in the previous regulatory cycle, is the lower limit of the fluctuation of the transmission and distribution price of voltage level j, is the transmission and distribution price of voltage level j, is the upper limit of fluctuation of transmission and distribution price of voltage level j; The balance account profit and loss constraint is that the balance account loss is less than the allowed profit, as shown in the following formula: （41） In the formula, is the actual income of the power grid enterprise in year t, is the permitted income of the power grid enterprise in year t, is the permitted revenue of the power grid enterprise in year t, is the actual transmission and distribution capacity of the power grid enterprise at voltage level i in year t, is the approved value of the transmission and distribution price of voltage level i in year t; In a transmission and distribution price regulation cycle, the deviation between actual income and permitted income in each year is different, but in the accounting cycle, the total balance account amount should be greater than or equal to zero, as shown in the following formula: （42） In the formula, is the actual income of the power grid enterprise in year t, is the permitted income of the power grid enterprise in year t; Among them, the non-negative and integer constraints are that the power grid investment project is a non-negative integer, as shown in the following formula: （43） In the formula, is the investment amount of power grid projects of type k with voltage level 500kv in year t, is the number of power grid projects invested in region i, voltage level j, project type k in year t, Is a positive integer.

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