CN105761161A - AC and DC power distribution network power supply mode evaluation method - Google Patents

Abstract

The invention relates to an AC and DC power distribution network power supply mode and an evaluation method. According to features of the AC and DC power distribution network, a typical AC and DC power distribution network topology structure is built, evaluation indexes are built respectively from five aspects of technical benefits, economic benefits, social benefits, environmental benefits and the practicality, an entropy weight fuzzy comprehensive evaluation method is then adopted, and a relative superiority and inferiority rank for the typical AC and DC power distribution network power supply mode is obtained according to the evaluation indexes. The method comprises the following steps: (1) a network topology in the typical power distribution network power supply mode is built; (2) an AC and DC hybrid power distribution network evaluation index system is built; and (3) a fuzzy entropy weight evaluation method is adopted to evaluate the typical power supply mode. Compared with the prior art, the method of the invention has the following advantages that an AC and DC power distribution network design and evaluation method for the system is provided, and effective guidance is provided for transformation of the existing distribution network and planning and design of a future AC and DC power distribution network.

Description

Method for evaluating power supply mode of alternating current-direct current power distribution network

Technical Field

The invention relates to a power supply mode and an evaluation method of an alternating current-direct current power distribution network. According to the characteristics of the AC/DC power distribution network, a typical AC/DC power distribution network topological structure is established, evaluation indexes are respectively established from five aspects of technical benefits, economic benefits, social benefits, environmental protection benefits and practicability, and then a fuzzy comprehensive evaluation method based on entropy weight is adopted to obtain the relative quality sequence of a typical AC/DC power distribution network power supply mode according to the evaluation indexes.

Background

With the continuous development of power electronic technology, compared with a pure alternating-current power distribution network, direct-current power supply has certain advantages in many aspects, for example, the direct-current power distribution network has the advantages of high electric energy quality, large transmission capacity, high reliability, simple system structure, economy, low electric energy loss and the like. Correspondingly, the power supply mode of the distribution network is characterized by comprising three modes, namely a direct-current distribution network, an alternating-current and direct-current hybrid distribution network and the like which are concerned and valued in the day in succession besides the traditional alternating-current power supply. How to select the power distribution network power supply structure mode with the best comprehensive economic and technical benefits according to the properties and the structural characteristics of the load has important significance for the construction and the operation of the power distribution network.

Compared with a relatively mature alternating current power supply system, the direct current power supply system and the alternating current-direct current hybrid power supply system are still in a starting stage all over the world, but are gradually valued by engineering circles and researchers. At present, relative superiority and inferiority of an alternating current power distribution network, a direct current power distribution network and an alternating current-direct current hybrid power distribution network are compared and analyzed by scholars from an economic perspective, and feasibility of ring-shaped and two-end topological structures of the direct current power distribution network is discussed from reliability of key equipment. Comprehensive analysis and evaluation on an alternating current power distribution network, a direct current power distribution network and an alternating current and direct current hybrid power distribution network which contain distributed power sources and energy storage devices from different angles are not researched.

Disclosure of Invention

Aiming at the defects of the prior art, the invention respectively establishes evaluation indexes from the five aspects of technical property, economical efficiency, social property, environmental protection and practicability to evaluate the power supply mode of the typical power distribution network and determine the optimal power supply mode of the power distribution network.

The technical scheme of the invention is as follows:

a method for evaluating a power supply mode of an AC/DC power distribution network is characterized by comprising the following steps:

(1) establishing a network topology under a typical power supply mode of a power distribution network;

(2) establishing an AC-DC hybrid power distribution network evaluation index system;

(3) and evaluating the typical power supply mode by adopting a fuzzy entropy weight evaluation method.

Further, in the step (1), the network topology types established in the typical power supply mode of the power distribution network include an alternating current/direct current power distribution network radial network topology structure, a direct current power distribution network radial network topology structure, an alternating current/direct current hybrid power distribution network double-end power supply network topology structure and an alternating current/direct current hybrid power distribution network ring network topology structure.

Further, the establishment of the evaluation index system of the alternating current-direct current hybrid power distribution network in the step (2) is as follows:

the method comprises the following steps: establishing a technical evaluation index system, which specifically comprises the following contents:

(1) network harmonic current content ratio α:

for an ac network, the network harmonic current content ratio is defined as the average of the total harmonic current content ratios of the different nodes, i.e.:

${\mathrm{\α}}_{AC}=\frac{\underset{i=1}{\overset{N_{AC}}{\Σ}}{I}_{h,i}^{AC}/I_{0,i}^{AC}}{N_{AC}}---\left(1\right)$

in the formula,is the effective value of the fundamental wave current of the ith node of the alternating current network,for total harmonic power of i-th node of AC networkEffective value of the flow, N_ACThe number of the nodes of the communication network is,the effective value of the kth (k is more than or equal to 0) harmonic current of the ith node of the alternating current network;

for a dc network, the ratio of the harmonic current content of the network is defined:

${\mathrm{\α}}_{DC}=\frac{\underset{i=1}{\overset{N_{DC}}{\Σ}}{I}_{h,i}^{DC}/I_{0,i}^{DC}}{N_{DC}}---\left(2\right)$

in the formula,the effective value of the fundamental current of the ith node of the direct current network,is the effective value of the total harmonic current of the ith node of the direct current network, N_DCThe number of the nodes of the direct current network,the effective value of the kth (k is more than or equal to 0) harmonic current of the ith node of the direct current network;

(2) network average voltage distortion rate ξ_avg: the average voltage distortion rate of the power distribution network is expressed by the average value of the voltage distortion rates of different voltage nodes, namely:

${\mathrm{\ξ}}_{avg}=\frac{\underset{i=1}{\overset{N_V}{\Σ}}{\mathrm{\ξ}}_i}{N_V}---\left(3\right)$

in the formula, N_VNumber of nodes of DC network being AC network, ξ_iThe voltage distortion rate of the node i can be expressed by the percentage of the ratio of the root mean square value of each harmonic voltage of the node to the effective value of the fundamental voltage, namely:

${\mathrm{\ξ}}_i=\sqrt{\frac{U_{i,2}^2+U_{i,3}^2+U_{i,4}^2+\mathrm{...}+U_{i,n}^2}{U_{i,1}^2}}\×100\%---\left(4\right)$

in the formula of U_i,2,U_i,3,…,U_i,nRepresenting the respective harmonic voltages of node i; for AC networks, U_i,1Representing the fundamental component of node i, while for a DC network, U_i,1Represents the DC component of node i;

(3) average sag amplitude Δ U of network voltage:

defining the average value of the voltage sag amplitudes of all the nodes as the average voltage sag amplitude of the network;

for an alternating current network, the voltage sag amplitude of any node is represented by the root mean square value of the sag voltage and the rated voltage root mean square value, namely:

${\mathrm{\ΔU}}_{AC}=\frac{\underset{i=1}{\overset{N_{AC}}{\Σ}}{U}_{i-rms1}/U_{i-rms2}}{N_{AC}}---\left(5\right)$

in the formula of U_i-rms1For node i to temporarily drop the effective value of the voltage, U_i-rms2The node i is a rated voltage effective value;

for a dc network, the definition of any node is the ratio of the sag bus voltage to the nominal bus voltage, i.e.:

${\mathrm{\ΔU}}_{DC}=\frac{\underset{i=1}{\overset{N_{DC}}{\Σ}}{U}_{i-dc}/U_{i-dc}}{N_{DC}}---\left(6\right)$

in the formula of U_i-dcFor temporarily dropping the bus voltage, U, of node i_i-dcThe nominal bus voltage at node i;

(4) average deviation of network voltage d:

for an alternating current network, the average deviation of the network voltage is defined as the average value of the voltage deviation of each node;

for an alternating current network:

$d_{AC}=\frac{\underset{i=1}{\overset{N_{AC}}{\Σ}}{d}_{AC,i}}{N_{AC}}---\left(7\right)$

in the formula (d)_AC,iVoltage deviation for ac network nodes:

$d_{AC,i}=\frac{(U_{rated-ac,i}-U_{load-ac,i})}{U_{rated-ac,i}}\×100\%---\left(8\right)$

in the formula of U_rated-acFor the rated voltage, U, of the AC network node i_load-acThe actual voltage when the load is accessed to the alternating current network node i;

for a dc network:

$d_{DC}=\frac{\underset{i=1}{\overset{N_{DC}}{\Σ}}{d}_{DC,i}}{N_{DC}}---\left(9\right)$

in the formula (d)_DC,iVoltage deviation for dc network node i:

$d_{DC,i}=\frac{(U_{rated-dc,i}-U_{load-dc,i})}{U_{rated-dc,i}}\×100\%---\left(10\right)$

in the formula of U_rated-dc,iFor the rated voltage, U, of the DC network node i_load-dcThe actual voltage when the load is accessed to the direct current network node i;

(5) network line loss Δ P:

the network line loss is defined as the sum of the line losses:

$\mathrm{\Δ}P=\underset{l=1}{\overset{N_L}{\Σ}}(P_{from,l}-P_{to,l})---\left(11\right)$

in the formula, P_from,P_toThe first direct current or alternating current line active power of the first power distribution network is respectively the head end and the tail end of the first direct current or alternating current line; n is a radical of_LThe total number of direct current lines and alternating current lines of the power distribution network;

(6) network average line drop Δ U^L：

The average line voltage drop of the network is defined as the average value of all line voltage drops in the network;

for an ac distribution network:

${\mathrm{\ΔU}}_{AC}^L=\frac{\underset{l=1}{\overset{N_{ACL}}{\Σ}}{\mathrm{\ΔU}}_{AC,l}}{N_{ACL}}---\left(12\right)$

${\mathrm{\ΔU}}_{AC,l}\≈\frac{P_{AC}{R}_{AC}+Q_{AC}{X}_{AC}}{U_{AC}}---\left(13\right)$

in the formula, P_AC、Q_ACRespectively the active power and the reactive power at the tail end of the line; r_AC、X_ACRespectively a line equivalent resistance and an equivalent reactance; u shape_ACThe effective value of the voltage of the node at the tail end of the line is obtained; n is a radical of_ACLIs the total number of AC lines;

for a dc distribution network, the network average line drop is defined as:

${\mathrm{\ΔU}}_{DC}^L=\frac{\underset{l=1}{\overset{N_{DCL}}{\Σ}}{\mathrm{\ΔU}}_{DC,l}}{N_{DCL}}---\left(14\right)$

${\mathrm{\ΔU}}_{DC,l}\≈\frac{P_{DC}{R}_{DC}}{U_{DC}}---\left(15\right)$

in the formula, P_DCActive power at the tail end of the direct current line; r_DCIs the equivalent resistance of the direct current cable; u shape_DCIs the voltage of the end node of the direct current line; n is a radical of_DCLIs the total number of the direct current lines;

(7) network voltage sag frequency N_F: the voltage sag frequency is the frequency of voltage sag occurrence in a certain time, the higher the numerical value of the frequency is, the higher the frequency degree of influence on sensitive loads is, and the voltage sag frequency estimation method based on user satisfaction is as follows:

$N_F=\underset{l=1}{\overset{N_L}{\Σ}}{\mathrm{\δ}}_l{L}_l---\left(16\right)$

in the formula,_l、L_lrespectively the fault rate of the first line and the length of the line in the unsatisfactory area;

(8) stability K of network bus voltage_V: the index represents the average stability of all nodes in the network, the maximum load capacity is used as the voltage stability margin of the system, and the power margin index K is used_VTo reflect the strength of the node [11 ]]：

$K_V=\frac{\underset{i=1}{\overset{N_V}{\Σ}}{K}_{V,i}}{N_V}---\left(17\right)$

$K_{V,i}=\frac{P_{cr,i}-P_{o,i}}{P_{o,i}}---\left(18\right)$

In the formula, P_cr,iIs the ultimate power of node i; p_o,iIs the operating power of node i; since the DC network has no problem of bus voltage stability, K can be considered_V＝1；

(9) "N-1" transferability:

the 'N-1' transfer rate refers to the proportion of transfer load to total load when the distribution network loses 1 element:

${\mathrm{\α}}_{N-1}=\frac{\underset{i=1}{\overset{N_V}{\Σ}}{P}_{rec1,i}}{\underset{i=1}{\overset{N_V}{\Σ}}{P}_{load,i}}\×100\%---\left(19\right)$

in the formula, P_rec1,iThe load power of the node i after the fault of the N-1 occurs; p_load,iThe load power of a node i before the fault occurs;

(10) "N-2" convertibility:

the 'N-2' transfer rate refers to the proportion of the transfer load to the total load when the power distribution network loses 2 elements:

${\mathrm{\α}}_{N-2}=\frac{\underset{i=1}{\overset{N_V}{\Σ}}{P}_{rec2,i}}{\underset{i=1}{\overset{N_V}{\Σ}}{P}_{load,i}}\×100\%---\left(20\right)$

in the formula, P_rec2,iThe load power of the node i after the N-2 fault occurs;

(11) line utilization factor gamma_E：

When the power grid is in the maximum load operation state, the ratio of the equipment load to the rated capacity of the equipment is mainly used for quantifying the load condition of the equipment in the power grid:

${\mathrm{\γ}}_E=\underset{1\≤l\≤N_L}{min}{\mathrm{\γ}}_{L,l}---\left(21\right)$

${\mathrm{\γ}}_{L,l}=\frac{P_{from,l}}{P_{L,l}^{\max }}---\left(22\right)$

in the formula, gamma_L,lThe load rate of the first line, namely the utilization rate of the first line;is the maximum transmission capacity of the line;

(12) user proportion of self-contained power supplies such as distributed generation and energy storage: the index represents the proportion of the power generation amount of the distributed power supply and the energy storage equipment in the power consumption amount of the user load, and is defined as follows:

$D_d=\frac{W_{dis-sto}}{W_{load}}\×100\%---\left(23\right)$

in the formula, W_dis-stoSupplying the electric quantity (kW & h) of user load to the distributed power supply and the energy storage equipment; w_loadFor the userLoad power consumption (kW · h);

step two: establishing a power supply reliability evaluation system, which specifically comprises the following contents:

(8) average failure outage number SAIFI: total number of blackouts per year divided by total number of users (times/user year);

$SAIFI=\frac{\underset{j=1}{\overset{N_C}{\Σ}}{N}_j^{US}}{N_C}---\left(24\right)$

in the formula, N_CThe total number of the users;the power failure frequency of the user j within one year;

(9) average outage duration SAIDI of user: average power off time per user over a year;

$SAIDI=\frac{\underset{j=1}{\overset{N_C}{\Σ}}{T}_j}{N_C}---\left(25\right)$

in the formula, T_jThe power failure duration time is the total power failure duration time of the user j within one year;

(10) power supply reliability ASAI: dividing the number of uninterrupted power supply hours of the user in one year by the total required number of power supply hours of the user;

$ASAI=\frac{T_h\×N_C-\underset{j=1}{\overset{N_C}{\Σ}}{T}_j}{T_h\×N_C}---\left(26\right)$

in the formula, T_hIndicating the number of hours of electricity required within a given time, e.g. in units of one year, typically T_h＝8760；

(11) The total electric quantity shortage index ENS of the system is that the system causes the total electric quantity loss of users due to power failure in one year;

$ENS=\underset{i=1}{\overset{N_C}{\Σ}}{E}_{loss,i}---\left(27\right)$

in the formula, E_loss,iThe power loss of the user caused by the ith power failure;

(12) average power off time CAIDI: average outage duration for each fault outage;

$CAIDI=\frac{\underset{j=1}{\overset{N_C}{\Σ}}{T}_j}{\underset{j=1}{\overset{N_C}{\Σ}}{N}_j^{US}}---\left(28\right)$

the power supply reliability indexes can be calculated by adopting a Monte Carlo simulation method according to the fault rates of different devices of the power distribution network;

(13) continuous power supply time CT of unit investment

The index reflects the contribution of investment of newly added or maintained lines/distributed power supplies/energy storage devices to the reliability, and newly added or maintained equipment can reduce the fault rate of corresponding equipment, so that the larger the value of the index is, the larger the contribution degree of the index to the improvement of the power supply reliability of the power distribution network is; the index has obvious influence on providing a radial distribution network with high power supply reliability and low contribution degree to a distribution network with high reliability;

$C_T=\underset{1\≤i\≤N_{EC}}{min}\frac{T_h\×A_{SAI,i}}{C_{R,i}}---\left(29\right)$

in the formula, N_ECThe total number of device types in the network; a. the_SAI,iRepresenting the power supply reliability of the power distribution network after the ith type of equipment is newly added or maintained; c_R,iRepresents the cost of adding or repairing the i-th equipment:

C_R,i＝N_AM,i·(a_EC,i+w_EC,i)(30)

in the formula, N_AM,iThe total number of types of newly added or maintained equipment; a is_EC,iThe unit price of the i-th equipment; w is a_EC,iFor the unit maintenance cost of the ith type equipment, when the equipment is updated, let w_EC,iWhen the equipment is maintained, let a be 0_EC,i＝0；

(14) Power supply capacity index GP for unit investment

The index represents the contribution degree of investment of a newly added transformer/line/distributed power supply/energy storage device to the power supply capacity of the power distribution network, and the larger the value of the index is, the more remarkable the improvement of unit investment on the power supply capacity of the power distribution network is;

$G_P=\underset{1\≤i\≤N_{EC}}{min}\frac{C_{P,i}}{C_{I,i}}---\left(31\right)$

in the formula, C_P,iMinimum value representing sum of rated capacities of each type of equipment after adding i types of equipment:

$C_{P,i}=\underset{1\≤i\≤N_{EC}}{min}\underset{k=1}{\overset{N_{EC,i}}{\Σ}}{P}_{i,k}^{\max }---\left(32\right)$

in the formula, N_EC,iIs the total number of the ith type of equipment;rated capacity of the kth device in the ith device;

C_I,irepresents the investment cost of newly added i-th equipment:

C_I,i＝N_add,ia_EC,i(33)

in the formula, N_add,iIndicating added devices of class iThe number of the particles;

the method comprises the following steps: establishing an economic evaluation index system, which specifically comprises the following contents

(5) Equipment investment cost index S_AC/DC

The equipment investment of the planning and construction of the power distribution network mainly comprises: investment in DC and AC cables, investment in inverters and rectifiers at the customer side, and investment in AC and DC transformers^,Alternating current and direct current circuit breaker investment, medium voltage converter station (VSC) investment and the like;

for an alternating current network, the equipment investment does not include a medium-voltage converter station, the user side does not include an inverter device, and the equipment investment calculation method comprises the following steps:

$S_{AC/DC}=\underset{i=1}{\overset{N_{Eac}}{\Σ}}{N}_{ac,i}{a}_{ac,i}.---\left(34\right)$

in the formula, N_Eac,iNumber of i-th AC devices, a_Eac,iFor the unit price, N, of the ith equipment in an alternating current network_EacThe total number of types of the communication equipment required by the construction of the communication network;

for a direct current network, an alternating current transformer is not arranged in the network, rectifying equipment is not arranged at a user side, and the equipment investment calculation method comprises the following steps:

$S_{AC/DC}=\underset{i=1}{\overset{N_{Edc}}{\Σ}}{N}_{dc,i}{a}_{dc,i}---\left(35\right)$

in the formula, N_Edc,iThe number of the i-th DC devices, a_Edc,iUnit price, N, for the ith equipment in a DC network_EdcThe total number of types of the AC equipment required for building the DC network;

for the alternating current-direct current hybrid power distribution network, the calculation method is the same as the above, and only all key equipment is included;

(6) depreciation cost D of equipment_C：

$D_C=\underset{i=1}{\overset{N_{EC}}{\Σ}}{D}_{C_i}---\left(36\right)$

In the formula,annual depreciation costs for class i devices:

$D_{C_i}=S_{B,i}\·r_{C,i}---\left(37\right)$

in the formula, S_B,iFor initial investment in class i equipment, r_C,iIs the age of the i-th equipment, r_C,i＝(1-λ_i)/N_Y，λ_iIs the net residual value rate, N, of the class i device_YThe depreciation age of the i-th equipment;

(7) effective power supply rate of unit investment E_R

The index reflects the contribution degree of investment of newly added transformer/line/distributed power supply/energy storage device/reactive power compensation device to the reduction of the line loss of the power distribution network, E_RThe larger the value is, the more obvious the effect of investment on reducing the line loss is;

$E_R=\underset{1\≤i\≤N_{EC}}{min}\frac{{\mathrm{\ΔA}}_i\%}{C_{I,i}}---\left(38\right)$

${\mathrm{\ΔA}}_i\%=\frac{{\mathrm{\ΔW}}_i}{W_S}\×100\%---\left(39\right)$

in the formula,. DELTA.A_i% is the line loss rate after the new ith equipment is added; Δ W_iThe line loss variation (kW & h) is expressed when the equipment is not added after the equipment is added; w_SRepresenting the total power supply (kW.h) of all power sources (including energy storage devices) before new equipment is added; for a direct current network, the number of the reactive compensation equipment is 0;

(8) maximum expected electricity sales per investment E_P

The index reflects the maximum electric quantity which can be provided for users in one year of the power distribution network under unit investment, and the indexThe greater the value, the unit investment pair E_PThe higher the contribution of (c);

$E_P=\frac{E_{max}}{C_E}---\left(40\right)$

in the formula, C_EWhich is the total investment of the power grid, $C_E=S_{AC/DC}+D_C++\underset{k=1}{\overset{N_{add,i}}{\Σ}}(C_{R,i}+C_{I,i}+C_{L,i}),$ reflects power supply capacity, power supply reliability, line loss and the likeInvestment, namely cost, corresponding to the influence factors; e_maxFor the maximum expected electricity sales of the power grid:

$E_{max}=T_h\×N_C\×A_{SAI}\×\underset{j=1}{\overset{N_C}{\Σ}}{P}_{load,j}---\left(41\right)$

in the formula, P_load,jAverage active power for user j;

the method comprises the following steps: establishing a social evaluation index system, which specifically comprises the following contents

The social benefits of the power distribution network are reflected by comprehensive scores of the satisfaction degree of the user to the power grid, and the scores of each power supply mode are given in the angle of the satisfaction degree of the user in the process of obtaining the indexes by adopting an expert score giving mode; evaluating 5 aspects of power supply quality, standard service, consultation service, electric charge payment and service management, wherein the full score of each aspect is 100, the minimum score is 0, the simulation user scores the 5 aspects and then takes an average value, the average value is fuzzified as the satisfaction degree of the user through a membership function, and then the comprehensive score of the satisfaction degree of the user is calculated according to the weight of each user:

$G_C=\underset{j=1}{\overset{N_C}{\Σ}}{\mathrm{\ω}}_{C,j}{f}_{C,j}---\left(42\right)$

in the formula, ω_C,jFor user j satisfaction weight, f_C,jIs a fuzzy membership value;

step five of the invention: establishing an environmental protection evaluation index system, which specifically comprises the following contents

(3) Carbon emission reduction: the emission of carbon dioxide discharged by the thermal power generation corresponding to the green energy generated energy is generally calculated by adopting the following formula:

$E_{c{o}_2}=0.4\mathrm{kg}/\mathrm{kwh}*2.493*W_g---\left(43\right)$

in the formula, W_gThe unit is the green energy power generation amount (kW.h);

(4) permeability P of clean energy_E: the index is used for reflecting the ratio of the generated energy of renewable energy sources such as water energy, wind energy, solar energy and the like in the power distribution network to the total generated energy, and the calculation formula is as follows:

$P_E=\frac{W_E}{W_{sum}}\×100\%---\left(44\right)$

in the formula, W_ERepresenting clean energy power generation (kW.h); w_sumThe total power generation (kW.h).

Further, the specific method for evaluating the typical power supply mode by adopting the fuzzy entropy weight evaluation method in the step (3) is as follows:

step 1, determining an evaluation index system and a comment set

On the basis of establishing an index system, setting a comment set as V ═ V₁,v₂,v₃,v₄,v₅Excellent, good, medium, qualified, poor. Each value in the comment set represents the degree of membership of a certain power mode scheme index to the comment.

Step 2 evaluation matrix normalization

Obtaining m evaluation matrixes of the schemes to be evaluated according to the evaluation index set:

$C^{\′}=\left[\begin{array}{c}{U}_1\\ U_2\\ .\\ .\\ .\\ U_m\end{array}\right]=\left[\begin{array}{cccc}{c}_{11}^{\′}& c_{12}^{\′}& ...& c_{1n}^{\′}\\ c_{21}^{\′}& c_{22}^{\′}& ...& c_{2n}^{\′}\\ & ...& ...& \\ c_{m1}^{\′}& c_{m2}^{\′}& ...& c_{mn}^{\′}\end{array}\right]$

in formula (II), c'_ij＝u_ij(i＝1，2，…m；j＝1，2，…n)。

Step 3, determining the entropy weight of the index and the comprehensive weight set thereof

From a normalized matrix C ═ C_ij]_m×nThe entropy and entropy weight of the evaluation index are calculated according to the following formula:

$H_j=-k\underset{i=1}{\overset{m}{\Σ}}{f}_{ij}{\mathrm{lnf}}_{ij},(j=1,2,...n)$

wherein k is 1/lnm,0≤H_j1 or less, and provided that when f_ijWhen equal to 0 f_ijlnf_ij0. Accordingly, the entropy weight of the jth index is defined as:

${\mathrm{\ω}}_j=\frac{1-H_j}{n-\underset{j=1}{\overset{n}{\Σ}}{H}_j}$

in the formula, 0 is not more than omega_jLess than or equal to 1 andfrom this, an entropy weight set of n evaluation indexes is obtained as ω ═ ω { ω ═ ω }₁,ω₂,…,ω_n}. Assume that the expert subjective weight of n evaluation indexes is λ ═ { λ ═ λ₁,λ₂,…λ_nThe combined weight of the entropy weights and the obtained comprehensive weight is:

$a_j=({\mathrm{\ω}}_j+{\mathrm{\μ\λ}}_j)/\underset{j=1}{\overset{n}{\Σ}}({\mathrm{\ω}}_j+{\mathrm{\μ\λ}}_j)$

in the formula, a_jThe comprehensive weight of the jth evaluation index is, mu is the relative effectiveness coefficient of the subjective weight to the objective entropy weight, and the value range of mu is set to be more than 0.3 and less than 3; if μ is 1, it means that the subjective and objective weights are included in the integrated weight with the same weight. And after calculation, obtaining a comprehensive index weight vector after the entropy weight of the evaluation index is integrated with the subjective weight of the expert. From this, the integrated weight set a ═ { a ═ can be derived₁,a₂,…,a_nTherein of

Step 4, constructing a fuzzy evaluation matrix of the scheme

For m schemes to be evaluated, the evaluation index set after the ith scheme is standardized is C_i＝{c_i1,c_i2,…c_inThe fuzzy subset of the j index on the evaluation set V can be calculated by its membership function to V, which is an isosceles triangle membership function:

$r_{ij}\left(v_k\right)=\left\{\begin{array}{cc}\frac{c_{ij}-p_k}{q_k-p_k}& p_k\≤c_{ij}\≤q_k\\ \frac{s_k-c_{ij}}{s_k-q_k}& q_k\≤c_{ij}\≤d_k\\ 0& \end{array}\right.$

wherein r is_ij(v_k) Is the jth index of the ith scheme relative to the comment v_kDegree of membership, p_k,q_k,s_kTo correspond to v_kSince the evaluation index is standardized, the corresponding value is taken according to 5 comments, and q is taken at present₁＝0,q₂＝0.25,q₃＝0.5,q₄＝0.75,q₅1 is ═ 1; to ensure each index

At least the membership degrees of the four comments can be obtained, and the bottom edge of an isosceles triangle is taken as 1.6;

from this, the fuzzy evaluation matrix of the ith scheme can be obtained as follows:

$R_i=\left[\begin{array}{cccc}{r}_{i1}\left(v_1\right)& r_{i1}\left(v_2\right)& \mathrm{...}& r_{i1}\left(v_5\right)\\ r_{i2}\left(v_1\right)& r_{i2}\left(v_2\right)& \mathrm{...}& r_{i2}\left(v_5\right)\\ & \mathrm{...}& \mathrm{...}& \\ r_{in}\left(v_1\right)& r_{in}\left(v_2\right)& \mathrm{...}& r_{in}\left(v_5\right)\end{array}\right],(i=1,2,\mathrm{...}m)$

step 5, solving a comprehensive evaluation fuzzy subset

Comprehensive evaluation set B of ith scheme_iFor fuzzy subsets on V, calculated by:

B_i＝AοR＝{b_i1,b_i2,b_i3,b_i4,b_i5}

wherein A is the comprehensive weight set, R_iFor the fuzzy evaluation matrix of the ith scheme, if the operator o employs an M (, +) model, then:

$b_{ik}=\underset{j=1}{\overset{n}{\Σ}}{a}_j\·r_{ij}\left(v_k\right),(k=1,2,3,4,5)$

to B_iAnd (3) carrying out normalization treatment:

${\hat{b}}_{ik}=b_{ik}/\underset{k=1}{\overset{5}{\Σ}}{b}_{ik},(k=1,2,3,4,5)$

the fuzzy comprehensive evaluation result of the ith scheme can be obtained as follows:

${\hat{B}}_i=\{{\hat{b}}_{i1},{\hat{b}}_{i2},{\hat{b}}_{i3},{\hat{b}}_{i4},{\hat{b}}_{i5}\}$

wherein,the degree of membership of the ith solution to the comment k indicates how much the solution i can be described by the comment k.

Step 6, sorting the schemes by utilizing the fuzzy comprehensive evaluation result

The fuzzy comprehensive evaluation result provides a lot of useful information for further selection of the network topology, and the information can be used for classifying or sequencing the m schemes to be evaluated. The evaluation result is quantified by assigning a score to each comment, and the evaluation set can be obtainedThen the composite score for scenario iMay then follow Z_iThe sizes are sorted.

The invention has the beneficial effects that: compared with the prior art, the invention has the following advantages: the design and evaluation method for the alternating current and direct current distribution network of the system can provide effective guidance for the transformation of the existing distribution network and the planning and design of the future alternating current and direct current distribution network.

Drawings

FIG. 1 is a general flow diagram of the present invention.

Fig. 2 a radial network topology of an ac distribution network.

Fig. 3 is a radial network topology structure of a direct current distribution network.

Fig. 4 shows a radial network topology structure of an ac/dc hybrid power distribution network.

Fig. 5 shows a double-end power supply network topology structure of an alternating current and direct current hybrid power distribution network.

Fig. 6 shows a ring network topology structure of an ac/dc hybrid power distribution network.

Figure 7 rating system.

Fig. 8 technical evaluation index.

Fig. 9 power supply reliability evaluation index.

FIG. 10 economic assessment indicators.

Fig. 11 social evaluation index.

FIG. 12 is an evaluation index of environmental protection.

Detailed Description

The invention will be further elucidated with reference to the drawing.

The invention relates to a method for planning an urban low-voltage alternating current and direct current distribution network, which mainly comprises the following steps:

step one, establishing a network topology under a typical power supply mode of a power distribution network;

step two, establishing an AC/DC hybrid power distribution network evaluation index system;

and thirdly, evaluating the typical power supply mode by adopting a fuzzy entropy weight evaluation method.

The contents of the steps are described in detail as follows:

the method comprises the following steps:

the network topology types under the typical power supply mode of the power distribution network are established to comprise an alternating current-direct current power distribution network radial network topology structure (figure 1), a direct current power distribution network radial network topology structure (figure 2), an alternating current-direct current hybrid power distribution network radial network topology structure (figure 3), an alternating current-direct current hybrid power distribution network double-end power supply network topology structure (figure 4) and an alternating current-direct current hybrid power distribution network ring network topology structure (figure 5):

the radial alternating-current power distribution network shown in fig. 1 is a common power supply mode, direct-current loads need to be rectified by rectifying equipment and then supplied with power, direct-current power supplies such as photovoltaic power generation and energy storage devices are connected to the grid through an inverter, the problem of conversion efficiency exists, and alternating-current power supplies such as wind power generation are directly connected to the grid, so that the utilization rate of wind power can be improved to the maximum extent; buses with different voltage levels are connected through a transformer, the network structure is simple, the construction cost is low, and the power supply reliability is relatively low.

In the radial direct-current power distribution network shown in fig. 2, direct-current power supply is performed on all direct-current loads, direct-current power supplies such as photovoltaic power generation and energy storage devices are directly connected to the grid, so that a large number of current conversion links can be saved, and alternating-current power supplies such as wind power generation need to be connected to the grid through a rectifier; buses with different voltage levels can be connected through a direct current transformer, and for an alternating current load, the alternating current load needs to be supplied with power through an inverter device, so that the network transmission capacity is large, and the network loss is small.

Fig. 3 shows a radial ac/dc hybrid power distribution network, in which dc power sources such as photovoltaic power generation and energy storage devices are directly connected to a dc network; alternating current loads are supplied with power by adopting an alternating current network, and alternating current power supplies such as wind power generation and the like are directly connected into the alternating current network, so that energy conversion loss generated by rectification and inversion can be effectively avoided; for the direct current load, a direct current network is adopted for power supply, the structure of the hybrid power distribution network is simple, and the construction cost is relatively increased.

The two-end power supply AC/DC hybrid power distribution network shown in FIG. 4 is powered by dual power sources, DC power sources such as photovoltaic power generation and energy storage devices are directly connected to a DC line, and AC power sources such as wind power generation are directly connected to an AC line; the two-end power supply mode provides two power supply lines for the load, one is a main line, the other is a standby line, when the line fails to cause the tripping of a line switch and power failure occurs, all or part of the load carried by the line can continue to supply power for the load through the standby line through the interconnection switch after fault isolation, and compared with a radial alternating current-direct current network, the radial alternating current-direct current network power supply system has higher power supply reliability and higher construction cost.

In the annular ac/dc hybrid power distribution network shown in fig. 5, the ac/dc load and the distributed power supply are connected in the same manner as the two-terminal power supply, and the network power supply reliability is further improved compared with the radial and two-terminal power supply network, where the dc network portion is in an annular structure and operates in an annular manner, and the ac portion is in an annular structure and operates in an open loop manner, and accordingly, the construction cost is also high.

The second step of the invention:

five macro evaluation systems of the power distribution network evaluation indexes are established as shown in figure 6:

the five macro-index systems include a plurality of micro-index systems, as shown in the following fig. 7 to 11:

the method comprises the following steps: a fuzzy entropy weight evaluation method is adopted to evaluate a typical power supply mode, and the method comprises the following steps:

step 1, determining an evaluation index system and a comment set

On the basis of establishing an index system, setting a comment set as V ═ V₁,v₂,v₃,v₄,v₅Excellent, good, medium, qualified, poor. Each value in the comment set represents the degree of membership of a certain power mode scheme index to the comment.

Step 2 evaluation matrix normalization

Obtaining m evaluation matrixes of the schemes to be evaluated according to the evaluation index set:

$C^{\′}=\left[\begin{array}{c}{U}_1\\ U_2\\ .\\ .\\ .\\ U_m\end{array}\right]=\left[\begin{array}{cccc}{c}_{11}^{\′}& c_{12}^{\′}& ...& c_{1n}^{\′}\\ c_{21}^{\′}& c_{22}^{\′}& ...& c_{2n}^{\′}\\ & ...& ...& \\ c_{m1}^{\′}& c_{m2}^{\′}& ...& c_{mn}^{\′}\end{array}\right]$

in formula (II), c'_ij＝u_ij(i＝1,2,…m；j＝1,2,…n)。

Step 3, determining the entropy weight of the index and the comprehensive weight set thereof

From a normalized matrix C ═ C_ij]_m×nThe entropy and entropy weight of the evaluation index are calculated according to the following formula:

$H_j=-k\underset{i=1}{\overset{m}{\Σ}}{f}_{ij}{\mathrm{lnf}}_j,(j=1,2,...n)$

wherein k is 1/lnm,0≤H_j1 or less, and provided that when f_ijWhen equal to 0 f_ijlnf_ij0. Accordingly, the entropy weight of the jth index is defined as:

${\mathrm{\ω}}_j=\frac{1-H_j}{n-\underset{j=1}{\overset{n}{\Σ}}{H}_j}$

in the formula, 0 is not more than omega_jLess than or equal to 1 andfrom this, an entropy weight set of n evaluation indexes is obtained as ω ═ ω { ω ═ ω }₁,ω₂,…,ω_n}. Assume that the expert subjective weight of n evaluation indexes is λ ═ { λ ═ λ₁,λ₂,…λ_nThe combined weight of the entropy weights and the obtained comprehensive weight is:

$a_j=({\mathrm{\ω}}_j+{\mathrm{\μ\λ}}_j)/\underset{j=1}{\overset{n}{\Σ}}({\mathrm{\ω}}_j+{\mathrm{\μ\λ}}_j)$

in the formula, a_jThe comprehensive weight of the jth evaluation index is, mu is the relative effectiveness coefficient of the subjective weight to the objective entropy weight, and the value range of mu is set to be more than 0.3 and less than 3; if μ is 1, it means that the subjective and objective weights are included in the integrated weight with the same weight. And after calculation, obtaining a comprehensive index weight vector after the entropy weight of the evaluation index is integrated with the subjective weight of the expert. From this, the integrated weight set a ═ { a ═ can be derived₁,a₂,…,a_nTherein of

Step 4, constructing a fuzzy evaluation matrix of the scheme

For m schemes to be evaluated, the evaluation index set after the ith scheme is standardized is C_i＝{c_i1,c_i2,…c_inThe fuzzy subset of the j index on the evaluation set V can be calculated by its membership function to V, which is an isosceles triangle membership function:

$r_{ij}\left(v_k\right)=\left\{\begin{array}{cc}\frac{c_{ij}-p_k}{q_k-p_k}& p_k\≤c_{ij}\≤q_k\\ \frac{s_k-c_{ij}}{s_k-q_k}& q_k\≤c_{ij}\≤d_k\\ 0& \end{array}\right.$

wherein r is_ij(v_k) Is the jth index of the ith scheme relative to the comment v_kDegree of membership, p_k,q_k,s_kTo correspond to v_kSince the evaluation index is standardized, the corresponding value is taken according to 5 comments, and q is taken at present₁＝0,q₂＝0.25,q₃＝0.5,q₄＝0.75,q₅1 is ═ 1; in order to ensure that each index can obtain at least the membership degrees of four comments, the bottom edge of an isosceles triangle is taken as 1.6;

from this, the fuzzy evaluation matrix of the ith scheme can be obtained as follows:

$R_i=\left[\begin{array}{cccc}{r}_{i1}\left(v_1\right)& r_{i1}\left(v_2\right)& \mathrm{...}& r_{i1}\left(v_5\right)\\ r_{i2}\left(v_1\right)& r_{i2}\left(v_2\right)& \mathrm{...}& r_{i2}\left(v_5\right)\\ & \mathrm{...}& \mathrm{...}& \\ r_{in}\left(v_1\right)& r_{in}\left(v_2\right)& \mathrm{...}& r_{in}\left(v_5\right)\end{array}\right],(i=1,2,\mathrm{...}m)$

step 5, solving a comprehensive evaluation fuzzy subset

Comprehensive evaluation set B of ith scheme_iFor fuzzy subsets on V, calculated by:

B_i＝AοR＝{b_i1,b_i2,b_i3,b_i4,b_i5}

wherein A is the comprehensive weight set, R_iFor the fuzzy evaluation matrix of the ith scheme, if the operator o employs an M (, +) model, then:

$b_{ik}=\underset{j=1}{\overset{n}{\Σ}}{a}_j\·r_{ij}\left(v_k\right),(k=1,2,3,4,5)$

to B_iAnd (3) carrying out normalization treatment:

${\hat{b}}_{ik}=b_{ik}/\underset{k=1}{\overset{5}{\Σ}}{b}_{ik},(k=1,2,3,4,5)$

the fuzzy comprehensive evaluation result of the ith scheme can be obtained as follows:

${\hat{B}}_i=\{{\hat{b}}_{i1},{\hat{b}}_{i2},{\hat{b}}_{i3},{\hat{b}}_{i4},{\hat{b}}_{i5}\}$

wherein,the degree of membership of the ith solution to the comment k indicates how much the solution i can be described by the comment k.

Step 6, sorting the schemes by utilizing the fuzzy comprehensive evaluation result

The fuzzy comprehensive evaluation result provides a lot of useful information for further selection of the network topology, and the information can be used for classifying or sequencing the m schemes to be evaluated. The evaluation result is quantified by assigning a score to each comment, and the evaluation set can be obtainedSynthesis of scheme i

Score ofMay then follow Z_iThe sizes are sorted.

Example (b):

the typical power distribution network power supply mode (shown in figures 1-5) established by the invention is an evaluation object. The load values of the power distribution network adopt the load types of the alternating current, direct current and alternating current and direct current hybrid power distribution network in the table 1.

TABLE 1 AC, DC and AC/DC hybrid distribution network load types

The numerical values of the indexes in the index system obtained through PSCAD simulation are shown in table 2, the subjective weight of each index is given by an expert, the objective weight adopts an entropy weight, the comprehensive weight is obtained by weighting the subjective weight and the objective weight which respectively account for 0.5, and the result is shown in table 3. TABLE 2 AC/DC MIXED SIMULATION INDEX VALUES

TABLE 3 subjective weighting of AC/DC hybrid simulation indicators

And substituting the comprehensive weight into a triangular membership function to obtain the final evaluation of each alternating current and direct current hybrid evaluation scheme which is 70.2, 67.8, 69.1, 69.6 and 70.1, namely, the evaluation result of the alternating current and direct current network is respectively the optimal full direct current, the alternating current and direct current hybrid annular power supply, the alternating current and direct current hybrid bidirectional power supply and the alternating current and direct current hybrid bidirectional power supply, and the alternating current and direct current hybrid single-ended power supply is respectively from the optimal state to the inferior state and the worst full alternating current state. The result shows that although the cost of key equipment in the direct-current distribution network is high, the direct-current distribution network has great advantages in the aspects of line loss, power supply reliability, electric energy quality, environmental protection benefit and the like under the condition of a large direct-current load proportion. Although the alternating current and direct current hybrid power distribution network has the advantages of the alternating current and direct current power distribution networks, due to the complexity of the topological structure, the investment cost is relatively high, and the comprehensive benefit is better than that of the alternating current power distribution network.

Claims (4)

1. A method for evaluating a power supply mode of an AC/DC power distribution network is characterized by comprising the following steps:

(1) establishing a network topology under a typical power supply mode of a power distribution network;

(2) establishing an AC-DC hybrid power distribution network evaluation index system;

(3) and evaluating the typical power supply mode by adopting a fuzzy entropy weight evaluation method.

2. The method for evaluating the power supply mode of the alternating current-direct current power distribution network according to claim 1, characterized by comprising the following steps of:

in the step (1), the network topology types under the typical power supply mode of the power distribution network are established to comprise an alternating current-direct current power distribution network radial network topology structure, a direct current power distribution network radial network topology structure, an alternating current-direct current hybrid power distribution network double-end power supply network topology structure and an alternating current-direct current hybrid power distribution network ring network topology structure.

3. The method for evaluating the power supply mode of the alternating current-direct current power distribution network according to claim 1, wherein the step (2) comprises the following specific steps of establishing an evaluation index system of the alternating current-direct current hybrid power distribution network:

the method comprises the following steps: establishing a technical evaluation index system, which specifically comprises the following contents:

(1) network harmonic current content ratio α:

for an ac network, the network harmonic current content ratio is defined as the average of the total harmonic current content ratios of the different nodes, i.e.:

${\mathrm{\α}}_{AC}=\frac{\underset{i=1}{\overset{N_{AC}}{\Σ}}{I}_{h,i}^{AC}/I_{0,i}^{AC}}{N_{AC}}---\left(1\right)$

in the formula,is the effective value of the fundamental wave current of the ith node of the alternating current network,effective value of total harmonic current of ith node of alternating current network, N_ACThe number of the nodes of the communication network is, the effective value of the kth (k is more than or equal to 0) harmonic current of the ith node of the alternating current network;

for a dc network, the ratio of the harmonic current content of the network is defined:

${\mathrm{\α}}_{DC}=\frac{\underset{i=1}{\overset{N_{DC}}{\Σ}}{I}_{h,i}^{DC}/I_{0,i}^{DC}}{N_{DC}}---\left(2\right)$

in the formula,the effective value of the fundamental current of the ith node of the direct current network,is the effective value of the total harmonic current of the ith node of the direct current network, N_DCThe number of the nodes of the direct current network, the effective value of the kth (k is more than or equal to 0) harmonic current of the ith node of the direct current network;

(2) network average voltage distortion rate ξ_avg: the average voltage distortion rate of the power distribution network is expressed by the average value of the voltage distortion rates of different voltage nodes, namely:

${\mathrm{\ξ}}_{avg}=\frac{\underset{i=1}{\overset{N_V}{\Σ}}{\mathrm{\ξ}}_i}{N_V}\left(3\right)$

in the formula, N_VNumber of nodes of DC network being AC network, ξ_iThe voltage distortion rate of the node i can be expressed by the percentage of the ratio of the root mean square value of each harmonic voltage of the node to the effective value of the fundamental voltage, namely:

${\mathrm{\ξ}}_i=\sqrt{\frac{U_{i,2}^2+U_{i,3}^2+U_{i,4}^2+\mathrm{...}+U_{i,n}^2}{U_{i,1}^2}}\×100\%---\left(4\right)$

in the formula of U_i,2,U_i,3,…,U_i,nRepresenting the respective harmonic voltages of node i; for AC networks, U_i,1Representing the fundamental component of node i, while for a DC network, U_i,1Represents the DC component of node i;

(3) average sag amplitude Δ U of network voltage:

defining the average value of the voltage sag amplitudes of all the nodes as the average voltage sag amplitude of the network;

for an alternating current network, the voltage sag amplitude of any node is represented by the root mean square value of the sag voltage and the rated voltage root mean square value, namely:

${\mathrm{\ΔU}}_{AC}=\frac{\underset{i=1}{\overset{N_{AC}}{\Σ}}{U}_{i-rms1}/U_{i-rms2}}{N_{AC}}---\left(5\right)$

in the formula of U_i-rms1For node i to temporarily drop the effective value of the voltage, U_i-rms2The node i is a rated voltage effective value;

for a dc network, the definition of any node is the ratio of the sag bus voltage to the nominal bus voltage, i.e.:

${\mathrm{\ΔU}}_{DC}=\frac{\underset{i=1}{\overset{N_{DC}}{\Σ}}{U}_{i-dc}/U_{i-dc}}{N_{DC}}---\left(6\right)$

in the formula of U_i-dcFor temporarily dropping the bus voltage, U, of node i_i-dcThe nominal bus voltage at node i;

(4) average deviation of network voltage d:

for an alternating current network, the average deviation of the network voltage is defined as the average value of the voltage deviation of each node;

for an alternating current network:

$d_{AC}=\frac{\underset{i=1}{\overset{N_{AC}}{\Σ}}{d}_{AC,i}}{N_{AC}}---\left(7\right)$

in the formula (d)_AC,iVoltage deviation for ac network nodes:

$d_{AC,i}=\frac{(U_{rated-ac,i}-U_{load-ac,i})}{U_{rated-ac,i}}\×100\%---\left(8\right)$

in the formula of U_rated-acFor the rated voltage, U, of the AC network node i_load-acThe actual voltage when the load is accessed to the alternating current network node i;

for a dc network:

$d_{DC}=\frac{\underset{i=1}{\overset{N_{DC}}{\Σ}}{d}_{DC,i}}{N_{DC}}---\left(9\right)$

in the formula (d)_DC,iVoltage deviation for dc network node i:

$d_{DC,i}=\frac{(U_{rated-dc,i}-U_{load-dc,i})}{U_{rated-dc,i}}\×100\%---\left(10\right)$

in the formula of U_rated-dc,iFor the rated voltage, U, of the DC network node i_load-dcThe actual voltage when the load is accessed to the direct current network node i;

(5) network line loss Δ P:

the network line loss is defined as the sum of the line losses:

$\mathrm{\Δ}P=\underset{l=1}{\overset{N_L}{\Σ}}(P_{from,l}-P_{to,l})---\left(11\right)$

in the formula, P_from,P_toThe first direct current or alternating current line active power of the first power distribution network is respectively the head end and the tail end of the first direct current or alternating current line; n is a radical of_LThe total number of direct current lines and alternating current lines of the power distribution network;

(6) network average line drop Δ U^L：

The average line voltage drop of the network is defined as the average value of all line voltage drops in the network;

for an ac distribution network:

${\mathrm{\ΔU}}_{AC}^L=\frac{\underset{l=1}{\overset{N_{ACL}}{\Σ}}{\mathrm{\ΔU}}_{AC,l}}{N_{ACL}}---\left(12\right)$

${\mathrm{\ΔU}}_{AC,l}\≈\frac{P_{AC}{R}_{AC}+Q_{AC}{X}_{AC}}{U_{AC}}---\left(13\right)$

in the formula, P_AC、Q_ACRespectively the active power and the reactive power at the tail end of the line; r_AC、X_ACRespectively a line equivalent resistance and an equivalent reactance; u shape_ACThe effective value of the voltage of the node at the tail end of the line is obtained; n is a radical of_ACLIs the total number of AC lines;

for a dc distribution network, the network average line drop is defined as:

${\mathrm{\ΔU}}_{DC}^L=\frac{\underset{l=1}{\overset{N_{DCL}}{\Σ}}{\mathrm{\ΔU}}_{DC,l}}{N_{DCL}}---\left(14\right)$

${\mathrm{\ΔU}}_{DC,l}\≈\frac{P_{DC}{R}_{DC}}{U_{DC}}---\left(15\right)$

in the formula, P_DCActive power at the tail end of the direct current line; r_DCIs the equivalent resistance of the direct current cable; u shape_DCIs the voltage of the end node of the direct current line; n is a radical of_DCLIs the total number of the direct current lines;

(7) network voltage sag frequency N_F: the voltage sag frequency is the frequency of voltage sag occurrence in a certain time, the higher the numerical value of the frequency is, the higher the frequency degree of influence on sensitive loads is, and the voltage sag frequency estimation method based on user satisfaction is as follows:

$N_F=\underset{l=1}{\overset{N_L}{\Σ}}{\mathrm{\δ}}_l{L}_l---\left(16\right)$

in the formula,_l、L_lrespectively the fault rate of the first line and the length of the line in the unsatisfactory area;

(8) stability K of network bus voltage_V: the index represents the average stability of all nodes in the network, the maximum load capacity is used as the voltage stability margin of the system, and the power margin index K is used_VTo reflect the strength of the node [11 ]]：

$K_V=\frac{\underset{i=1}{\overset{N_V}{\Σ}}{K}_{V,i}}{N_V}---\left(17\right)$

$K_{V,i}=\frac{P_{cr,i}-P_{o,i}}{P_{o,i}}---\left(18\right)$

In the formula, P_cr,iIs the ultimate power of node i; p_o,iIs the operating power of node i; since the DC network has no problem of bus voltage stability, K can be considered_V＝1；

(9) "N-1" transferability:

the 'N-1' transfer rate refers to the proportion of transfer load to total load when the distribution network loses 1 element:

${\mathrm{\α}}_{N-1}=\frac{\underset{i=1}{\overset{N_V}{\Σ}}{P}_{rec1,i}}{\underset{i=1}{\overset{N_V}{\Σ}}{P}_{load,i}}\×100\%---\left(19\right)$

in the formula, P_rec1,iThe load power of the node i after the fault of the N-1 occurs; p_load,iThe load power of a node i before the fault occurs;

(10) "N-2" convertibility:

the 'N-2' transfer rate refers to the proportion of the transfer load to the total load when the power distribution network loses 2 elements:

${\mathrm{\α}}_{N-2}=\frac{\underset{i=1}{\overset{N_V}{\Σ}}{P}_{rec2,i}}{\underset{i=1}{\overset{N_V}{\Σ}}{P}_{load,i}}\×100\%---\left(20\right)$

in the formula, P_rec2,iThe load power of the node i after the N-2 fault occurs;

(11) line utilization factor gamma_E：

When the power grid is in the maximum load operation state, the ratio of the equipment load to the rated capacity of the equipment is mainly used for quantifying the load condition of the equipment in the power grid:

${\mathrm{\γ}}_E=\underset{1\≤l\≤N_L}{min}{\mathrm{\γ}}_{L,l}---\left(21\right)$

${\mathrm{\γ}}_{L,l}=\frac{P_{from,l}}{P_{L,l}^{\max }}---\left(22\right)$

in the formula, gamma_L,lThe load rate of the first line, namely the utilization rate of the first line;is the maximum transmission capacity of the line;

(12) user proportion of self-contained power supplies such as distributed generation and energy storage: the index represents the proportion of the power generation amount of the distributed power supply and the energy storage equipment in the power consumption amount of the user load, and is defined as follows:

$D_d=\frac{W_{dis-sto}}{W_{load}}\×100\%---\left(23\right)$

in the formula, W_dis-stoSupplying the electric quantity (kW & h) of user load to the distributed power supply and the energy storage equipment; w_loadThe power consumption (kW.h) is loaded for the user;

step two: establishing a power supply reliability evaluation system, which specifically comprises the following contents:

(1) average failure outage number SAIFI: total number of blackouts per year divided by total number of users (times/user year);

$SAIFI=\frac{\underset{j=1}{\overset{N_C}{\Σ}}{N}_j^{US}}{N_C}---\left(24\right)$

in the formula, N_CThe total number of the users;the power failure frequency of the user j within one year;

(2) average outage duration SAIDI of user: average power off time per user over a year;

$SAIDI=\frac{\underset{j=1}{\overset{N_C}{\Σ}}{T}_j}{N_C}---\left(25\right)$

in the formula, T_jThe power failure duration time is the total power failure duration time of the user j within one year;

(3) power supply reliability ASAI: dividing the number of uninterrupted power supply hours of the user in one year by the total required number of power supply hours of the user;

$ASAI=\frac{T_h\×N_C-\underset{j=1}{\overset{N_C}{\Σ}}{T}_j}{T_h\×N_C}---\left(26\right)$

in the formula, T_hIndicating the number of hours of electricity required within a given time, e.g. in units of one year, typically T_h＝8760；

(4) The total electric quantity shortage index ENS of the system is that the system causes the total electric quantity loss of users due to power failure in one year;

$ENS=\underset{i=1}{\overset{N_C}{\Σ}}{E}_{loss,i}---\left(27\right)$

in the formula, E_loss,iThe power loss of the user caused by the ith power failure;

(5) average power off time CAIDI: average outage duration for each fault outage;

$CAIDI=\frac{\underset{j=1}{\overset{N_C}{\Σ}}{T}_j}{\underset{j=1}{\overset{N_C}{\Σ}}{N}_j^{US}}---\left(28\right)$

the power supply reliability indexes can be calculated by adopting a Monte Carlo simulation method according to the fault rates of different devices of the power distribution network;

(6) continuous power supply time CT of unit investment

The index reflects the contribution of investment of newly added or maintained lines/distributed power supplies/energy storage devices to the reliability, and newly added or maintained equipment can reduce the fault rate of corresponding equipment, so that the larger the value of the index is, the larger the contribution degree of the index to the improvement of the power supply reliability of the power distribution network is; the index has obvious influence on providing a radial distribution network with high power supply reliability and low contribution degree to a distribution network with high reliability;

$C_T=\underset{1\≤i\≤N_{EC}}{min}\frac{T_h\×A_{SAI,i}}{C_{R,i}}---\left(29\right)$

in the formula, N_ECThe total number of device types in the network; a. the_SAI,iRepresenting the power supply reliability of the power distribution network after the ith type of equipment is newly added or maintained; c_R,iRepresents the cost of adding or repairing the i-th equipment:

C_R,i＝N_AM,i·(a_EC,i+w_EC,i)(30)

in the formula, N_AM,iThe total number of types of newly added or maintained equipment; a is_EC,iThe unit price of the i-th equipment; w is a_EC,iFor the unit maintenance cost of the ith type equipment, when the equipment is updated, let w_EC,iWhen the equipment is maintained, let a be 0_EC,i＝0；

(7) Power supply capacity index GP for unit investment

The index represents the contribution degree of investment of a newly added transformer/line/distributed power supply/energy storage device to the power supply capacity of the power distribution network, and the larger the value of the index is, the more remarkable the improvement of unit investment on the power supply capacity of the power distribution network is;

$G_P=\underset{1\≤i\≤N_{EC}}{min}\frac{C_{P,i}}{C_{I,i}}---\left(31\right)$

in the formula, C_P,iMinimum value representing sum of rated capacities of each type of equipment after adding i types of equipment:

$C_{P,i}=\underset{1\≤i\≤N_{EC}}{min}\underset{k=1}{\overset{N_{EC,i}}{\Σ}}{P}_{i,k}^{\max }---\left(32\right)$

in the formula, N_EC,iIs the total number of the ith type of equipment;rated capacity of the kth device in the ith device;

C_I,irepresents the investment cost of newly added i-th equipment:

C_I,i＝N_add,ia_EC,i(33)

in the formula, N_add,iIndicating the number of the added i-th type devices;

the method comprises the following steps: establishing an economic evaluation index system, which specifically comprises the following contents

(1) Equipment investment cost index S_AC/DC

The equipment investment of the planning and construction of the power distribution network mainly comprises: investment in DC and AC cables, investment in inverters and rectifiers at the customer side, and investment in AC and DC transformers^,Alternating current and direct current circuit breaker investment, medium voltage converter station (VSC) investment and the like;

for an alternating current network, the equipment investment does not include a medium-voltage converter station, the user side does not include an inverter device, and the equipment investment calculation method comprises the following steps:

$S_{AC/DC}=\underset{i=1}{\overset{N_{Eac}}{\Σ}}{N}_{ac,i}{a}_{ac,i}.---\left(34\right)$

in the formula, N_Eac,iNumber of i-th AC devices, a_Eac,iFor the unit price, N, of the ith equipment in an alternating current network_EacThe total number of types of the communication equipment required by the construction of the communication network;

for a direct current network, an alternating current transformer is not arranged in the network, rectifying equipment is not arranged at a user side, and the equipment investment calculation method comprises the following steps:

$S_{AC/DC}=\underset{i=1}{\overset{N_{Edc}}{\Σ}}{N}_{dc,i}{a}_{dc,i}---\left(35\right)$

in the formula, N_Edc,iThe number of the i-th DC devices, a_Edc,iUnit price, N, for the ith equipment in a DC network_EdcThe total number of types of the AC equipment required for building the DC network;

for the alternating current-direct current hybrid power distribution network, the calculation method is the same as the above, and only all key equipment is included;

(2) depreciation cost D of equipment_C：

$D_C=\underset{i=1}{\overset{N_{EC}}{\Σ}}{D}_{C_i}---\left(36\right)$

In the formula,annual depreciation costs for class i devices:

$D_{C_i}=S_{B,i}\·r_{C,i}---\left(37\right)$

in the formula, S_B,iFor initial investment in class i equipment, r_C,iIs the age of the i-th equipment, r_C,i＝(1-λ_i)/N_Y，λ_iIs the net residual value rate, N, of the class i device_YThe depreciation age of the i-th equipment;

(3) effective power supply rate of unit investment E_R

The index reflects the contribution degree of investment of newly added transformer/line/distributed power supply/energy storage device/reactive power compensation device to the reduction of the line loss of the power distribution network, E_RThe larger the value is, the more obvious the effect of investment on reducing the line loss is;

$E_R=\underset{1\≤i\≤N_{EC}}{min}\frac{{\mathrm{\ΔA}}_i\%}{C_{I,i}}---\left(38\right)$

${\mathrm{\ΔA}}_i\%=\frac{{\mathrm{\ΔW}}_i}{W_S}\×100\%---\left(39\right)$

in the formula,. DELTA.A_i% is the line loss rate after the new ith equipment is added; Δ W_iThe line loss variation (kW & h) is expressed when the equipment is not added after the equipment is added; w_SRepresenting the total power supply (kW.h) of all power sources (including energy storage devices) before new equipment is added; for a direct current network, the number of the reactive compensation equipment is 0;

(4) maximum expected electricity sales per investment E_P

The index reflects the maximum electric quantity which can be provided for users in one year of the power distribution network under the unit investment, and the larger the value of the index is, the unit investment is opposite to the E_PThe higher the contribution of (c);

$E_P=\frac{E_{\max }}{C_E}---\left(40\right)$

in the formula, C_EWhich is the total investment of the power grid, $C_E=S_{AC/DC}+D_C++\underset{k=1}{\overset{N_{add,i}}{\Σ}}(C_{R,i}+C_{I,i}+C_{L,i}),$ reflects the influences of power supply capacity, power supply reliability, line loss and the likeInvestment, namely cost, corresponding to the factors; e_maxFor the maximum expected electricity sales of the power grid:

$E_{max}=T_h\×N_C\×A_{SAI}\×\underset{j=1}{\overset{N_C}{\Σ}}{P}_{load,j}---\left(41\right)$

in the formula, P_load,jAverage active power for user j;

the method comprises the following steps: establishing a social evaluation index system, which specifically comprises the following contents

The social benefits of the power distribution network are reflected by comprehensive scores of the satisfaction degree of the user to the power grid, and the scores of each power supply mode are given in the angle of the satisfaction degree of the user in the process of obtaining the indexes by adopting an expert score giving mode; evaluating 5 aspects of power supply quality, standard service, consultation service, electric charge payment and service management, wherein the full score of each aspect is 100, the minimum score is 0, the simulation user scores the 5 aspects and then takes an average value, the average value is fuzzified as the satisfaction degree of the user through a membership function, and then the comprehensive score of the satisfaction degree of the user is calculated according to the weight of each user:

$G_C=\underset{j=1}{\overset{N_C}{\Σ}}{\mathrm{\ω}}_{C,j}{f}_{C,j}---\left(42\right)$

in the formula, ω_C,jFor user j satisfaction weight, f_C,jIs a fuzzy membership value;

step five of the invention: establishing an environmental protection evaluation index system, which specifically comprises the following contents

(1) Carbon emission reduction: the emission of carbon dioxide discharged by the thermal power generation corresponding to the green energy generated energy is generally calculated by adopting the following formula:

$E_{{\mathrm{co}}_2}=0.4kg/kwh*2.493*W_g---\left(43\right)$

in the formula, W_gThe unit is the green energy power generation amount (kW.h);

(2) permeability P of clean energy_E: the index is used for reflecting the ratio of the generated energy of renewable energy sources such as water energy, wind energy, solar energy and the like in the power distribution network to the total generated energy, and the calculation formula is as follows:

$P_E=\frac{W_E}{W_{sum}}\×100\%---\left(44\right)$

in the formula, W_ERepresenting clean energy power generation (kW.h); w_sumThe total power generation (kW.h).

4. The method for evaluating the power supply mode of the alternating current-direct current power distribution network according to claim 1, wherein the specific method for evaluating the typical power supply mode by adopting the fuzzy entropy weight evaluation method in the step (3) is as follows:

step 1, determining an evaluation index system and a comment set

On the basis of establishing an index system, setting a comment set as V ═ V₁,v₂,v₃,v₄,v₅-excellent, good, medium, qualified, poor }; each value in the comment set represents the membership degree of a certain power supply mode scheme index to the comment;

step 2 evaluation matrix normalization

Obtaining m evaluation matrixes of the schemes to be evaluated according to the evaluation index set:

$C^{\′}=\left[\begin{array}{c}{U}_1\\ U_2\\ \·\\ \·\\ \·\\ U_m\end{array}\right]=\left[\begin{array}{cccc}{c}_{\mathrm{11}}^{\′}& c_{\mathrm{12}}^{\′}& ...& c_{\mathrm{1n}}^{\′}\\ c_{\mathrm{21}}^{\′}& c_{22}^{\′}& ...& c_{2n}^{\′}\\ & ...& ...& \\ c_{\mathrm{m1}}^{\′}& c_{\mathrm{m2}}^{\′}& ...& c_{mn}^{\′}\end{array}\right]$

in formula (II), c'_ij＝u_ij(i＝1,2,…m；j＝1,2,…n)；

Step 3, determining the entropy weight of the index and the comprehensive weight set thereof

From a normalized matrix C ═ C_ij]_m×nThe entropy and entropy weight of the evaluation index are calculated according to the following formula:

$H_j=-k\underset{i=1}{\overset{m}{\Σ}}{f}_{ij}{\inf }_{ij},(j=1,2,...n)$

wherein k is 1/lnm,0≤H_j1 or less, and provided that when f_ijWhen equal to 0f_ijlnf_ij0; accordingly, the entropy weight of the jth index is defined as:

${\mathrm{\ω}}_j=\frac{1-H_j}{n-\underset{j=1}{\overset{n}{\Σ}}{H}_j}$

in the formula, 0 is not more than omega_jLess than or equal to 1 andfrom this, an entropy weight set of n evaluation indexes is obtained as ω ═ ω { ω ═ ω }₁,ω₂,…,ω_n}; assume that the expert subjective weight of n evaluation indexes is λ ═ { λ ═ λ₁,λ₂,…λ_nThe combined weight of the entropy weights and the obtained comprehensive weight is:

$a_j=({\mathrm{\ω}}_j+{\mathrm{\μ\λ}}_j)/\underset{j=1}{\overset{n}{\Σ}}({\mathrm{\ω}}_j+{\mathrm{\μ\λ}}_j)$

in the formula, a_jThe comprehensive weight of the jth evaluation index is, mu is the relative effectiveness coefficient of the subjective weight to the objective entropy weight, and the value range of mu is set to be more than 0.3 and less than 3; if mu is 1, the subjective weight and the objective weight are participated in the comprehensive weight by the same weight; after calculation, obtaining a comprehensive index weight vector after the entropy weight of the evaluation index is integrated with the subjective weight of the expert; from this, the integrated weight set a ═ { a ═ can be derived₁,a₂,…,a_nTherein of

Step 4, constructing a fuzzy evaluation matrix of the scheme

For m schemes to be evaluated, the evaluation index set after the ith scheme is standardized is C_i＝{c_i1,c_i2,…c_inThe fuzzy subset of the j index on the evaluation set V can be calculated by its membership function to V, which is an isosceles triangle membership function:

$r_{ij}\left(v_k\right)=\left\{\begin{array}{cc}\frac{c_{ij}-p_k}{q_k-p_k}& p_k\≤c_{ij}\≤q_k\\ \frac{s_k-c_{ij}}{s_k-q_k}& q_k\≤c_{ij}\≤d_k\\ 0& \end{array}\right.$

wherein r is_ij(v_k) Is the jth index of the ith scheme relative to the comment v_kDegree of membership, p_k,q_k,s_kTo correspond to v_kSince the evaluation index is standardized, the corresponding value is taken according to 5 comments, and q is taken at present₁＝0,q₂＝0.25,q₃＝0.5,q₄＝0.75,q₅1 is ═ 1; in order to ensure that each index can obtain at least the membership degrees of four comments, the bottom edge of an isosceles triangle is taken as 1.6;

from this, the fuzzy evaluation matrix of the ith scheme can be obtained as follows:

$R_i=\left[\begin{array}{cccc}{r}_{i1}\left(v_1\right)& r_{i1}\left(v_2\right)& ...& r_{i1}\left(v_5\right)\\ r_{i2}\left(v_1\right)& r_{i2}\left(v_2\right)& ...& r_{i2}\left(v_5\right)\\ & ...& ...& \\ r_{in}\left(v_1\right)& r_{in}\left(v_2\right)& ...& r_{in}\left(v_5\right)\end{array}\right],(i=1,2,...m)$

step 5, solving a comprehensive evaluation fuzzy subset

Comprehensive evaluation set B of ith scheme_iFor fuzzy subsets on V, calculated by:

B_i＝AоR＝{b_i1,b_i2,b_i3,b_i4,b_i5}

wherein A is the comprehensive weight set, R_iFor the fuzzy evaluation matrix, an operator o is adopted for the ith schemeM (, +) model, then:

$b_{ik}=\underset{j=1}{\overset{n}{\Σ}}{a}_j\·r_{ij}\left(v_k\right),(k=1,2,3,4,5)$

to B_iAnd (3) carrying out normalization treatment:

${\hat{b}}_{ik}=b_{ik}/\underset{k=1}{\overset{5}{\Σ}}{b}_{ik},(k=1,2,3,4,5)$

the fuzzy comprehensive evaluation result of the ith scheme can be obtained as follows:

${\hat{B}}_i=\{{\hat{b}}_{i1},{\hat{b}}_{i2},{\hat{b}}_{i3},{\hat{b}}_{i4},{\hat{b}}_{i5}\}$

wherein,the membership degree of the ith scheme relative to the comment k represents how much the scheme i can be described by the comment k;

step 6, sorting the schemes by utilizing the fuzzy comprehensive evaluation result

The fuzzy comprehensive evaluation result provides a lot of useful information for further selection of network topology, and the information can be used for classifying or sequencing m schemes to be evaluated; the evaluation result is quantified by assigning a score to each comment, and the evaluation set can be obtainedThen the composite score for scenario iMay then follow Z_iThe sizes are sorted.