METHOD FOR DYNAMIC STATE ESTIMATION OF NATURAL GAS NETWORK CONSIDERING DYNAMIC CHARACTERISTICS OF NATURAL GAS PIPELINES

Abstract

Provided is a method for a dynamic state estimation of a natural gas network considering dynamic characteristics of natural gas pipelines. The method can obtain a result of the dynamic state estimation of the natural gas network by establishing an objective function of the dynamic state estimation of the natural gas network, a state quantity constraint of a compressor, a state quantity constraint of the natural gas pipeline and a topological constraint of the natural gas network, and using a Lagrange method or an interior point method to solve a state estimation model of the natural gas network. The method takes the topological constraint of the natural gas network into consideration, and employs a pipeline pressure constraint in a frequency domain to implement linearization of the pipeline pressure constraint, thereby obtain a real-time, reliable, consistent and complete dynamic operating state of the natural gas network.

Description

TECHNICAL FIELD

The present disclosure relates to a method for a dynamic state estimation of a natural gas network considering dynamic characteristics of natural gas pipelines, belonging to the technical field of operation and control of an integrated energy system.

BACKGROUND

An integrated energy system has great advantages in terms of many aspects such as improving energy utilization efficiency, promoting new energy consumption, and reducing energy costs. It is a development trend of future energy systems. An Integrated Energy Management System (IEMS), which can regulate energy flows using information flows, is an intelligent decision-making “brain” that ensures a safe, economical, green, and highly efficient integrated energy system. The technology for estimating a state, as a basic module of the IEMS, is responsible for providing real-time, reliable, consistent, and complete operating state information, and thus it can provide the subsequent security analysis and optimization control with reliable operating data.

At present, researches on state estimations of a natural gas network are still in their infancy, not to mention state estimation technology that considers dynamic natural gas. Only some of the published literatures have proposed the dynamic state estimation methods based on Kalman filtering for a single natural gas pipeline. However, these methods fail to consider constraints of the natural gas network, and they require an initial state inside the pipeline to be known (generally assumed to be a steady state). In addition, a step of bad data identification is hard to be added to a format of an iterative solution of the Kalman filtering, which greatly limits its application. Thus, it is urgent to propose a method for a dynamic state estimation of a complex natural gas pipeline network, so as to provide sufficient data support for the operation and control of the integrated energy system.

SUMMARY

The present disclosure provides a method for a dynamic state estimation of a natural gas network considering dynamic characteristics of natural gas pipelines to obtain a real-time, reliable, consistent and complete operating state of the natural gas network, thereby overcoming the defects in the known state estimations of the natural gas network.

The method for the dynamic state estimation of the natural gas network considering the dynamic characteristic of the natural gas pipeline provided by the present disclosure includes:

step 1 of establishing a time-domain window and a frequency-domain window for the dynamic state estimation of the natural gas network, the step 1 including:

sub-step 1-1 of defining a time-domain window width as I^t, where I^t is a positive integer, and a value of I^t is determined by a dispatcher of the natural gas network; defining a u-th sampling time point in the time-domain window as τ_u=τ−uΔt, u=0, 1, . . . , I^t−1, where τ represents a current time point of the natural gas network, and Δt represents a sampling interval of the natural gas network; defining a current time-domain window width as I^t,e, where I^t,e is a positive integer, and a value of I^t,e is determined by the dispatcher of the natural gas network; and defining a historical time-domain window width as I^t,h, where I^t,h is a positive integer, and a value of I^t,h is determined by the dispatcher of the natural gas network, wherein I^t, I^t,e and I^t,h satisfy the following relational expression:

I ^t =I ^t,e +I ^t,h; and

sub-step 1-2 of defining a frequency-domain window width as I^f, where a value of I^f is determined by the dispatcher of the natural gas network; and defining a d-th frequency component in the frequency-domain window as ω_d, d=0, 1, . . . , I^f−1, where ω_d is calculated by the following formula:

${\omega }_d=\frac{d}{I^t·\Delta t}$

step 2 of constructing a measurement vector for the dynamic state estimation of the natural gas network, the step 2 including:

sub-step 2-1 of acquiring, from a data acquisition and monitoring control system of the natural gas network, all operation data of the natural gas network at a sampling time point τ_u in the time-domain window where the current time point τ of the natural gas network belongs, wherein the all operation data of the natural gas network comprises: a measurement value z_G+,u^ip of a natural gas flow at a head end of each pipeline in the natural gas network, and a measurement value z_G−,u^ip of a natural gas flow at a tail end of each pipeline in the natural gas network, where i_p represents a serial number of a pipeline in the natural gas network; a measurement value z_G+,u^ic of a natural gas flow at a head end of each compressor, and a measurement value z_G−,u^ic of a natural gas flow at a tail end of each compressor, where i_c represents a serial number of a compressor; a pressure measurement value z_pr,uⁱⁿ of each node of the natural gas network, where i_n represents a serial number of a node of the natural gas network; a measurement value z_gs,u^is of a natural gas flow of each natural gas source, where i_s represents a serial number of a natural gas source; and a measurement value z_gl,u^il of a natural gas flow of each natural gas load, where i_l represents a serial number of a natural gas load; and

sub-step 2-2 of constructing a measurement vector z_u for the dynamic state estimation of the natural gas network at the sampling time point τ_u:

$Z_u=\left[\begin{array}{c}{Z}_{G^{+},u}\\ Z_{G^{-},u}\\ Z_{\mathrm{pr},u}\\ Z_{\mathrm{gs},u}\\ Z_{gl,u}\end{array}\right]$

where z_G+,u represents a column vector consisting of all the measurement values z_G+,u^ip of natural gas flows at head ends of respective pipelines in the natural gas network and all the measurement values z_G+,u^ic of natural gas flows at head ends of respective compressors at the sampling time point τ_u; z_G−,u represents a column vector consisting of all the measurement values z_G−,u^ip of natural gas flows at tail ends of respective pipelines in the natural gas network and all the measurement values z_G−,u^ic of natural gas flows at tail ends of respective compressors at the sampling time point: τ_u; z_pr,u represents a column vector consisting of all the pressure measurement values z_pr,uⁱⁿ of respective nodes of the natural gas network at the sampling time point τ_u; z_gs,u represents a column vector consisting of all the measurement values z_gs,u^is of natural gas flows of respective natural gas sources in the natural gas network at the sampling time point τ_u; and z_gl,u represents a column vector consisting of all the measurement values z_gl,u^il of natural gas flows of respective natural gas loads in the natural gas network at the sampling time point τ_u;

step 3 of constructing a state vector x_u for the dynamic state estimation of the natural gas network at the sampling time point τ_u:

$x_u=\left[\begin{array}{c}{x}_{G^{+},u}\\ x_{G^{-},u}\\ x_{\mathrm{pr},u}\\ x_{\mathrm{gs},u}\\ x_{gl,u}\end{array}\right]$

where x_G−,u represents a column vector consisting of all natural gas flows G_ip,u⁺ at the head ends of the respective pipelines in the natural gas network and all natural gas flows G_ic,u⁺ at the head ends of the respective compressors at the sampling time point τ_u; x_G−,u represents a column vector consisting of all natural gas flows G_ip,u⁺ at the tail ends of the respective pipelines in the natural gas network and all natural gas flows G_ic,u⁻ at the tail ends of the respective compressors at the sampling time point τ_u; x_pr,u represents a column vector consisting of all pressures h_in of the respective nodes of the natural gas network at the sampling time point τ_u; x_gs,u represents a column vector consisting of all natural gas flows G_is,u^gs of the respective natural gas sources in the natural gas network at the sampling time point τ_u; and x_gl,u represents a column vector consisting of all natural gas flows G_il,u^gl of the respective natural gas loads in the natural gas network at the sampling time point τ_u;

step 4 of establishing, based on the measurement vector constructed in the step 2 and the state vector constructed in the step 3, an objective function of the dynamic state estimation of the natural gas network as follows:

min J=Σ_u=0^It,e−1{[z_u−x_u]W⁻¹[z_u−x_u]^T}+Σ_u=It,e^It−1{[z_u−x_u]W⁻¹δ^u−It,e[z_u−x_u]^T}

where J represents an expression of the objective function; W represents a covariance matrix of a measurement error and is determined by the dispatcher of the natural gas network; a superscript T represents a matrix transpose; and δ represents a decay factor of a historical time window and is determined by the dispatcher of the natural gas network;

step 5 of establishing constraint conditions for the dynamic state estimation of the natural gas network, the step 5 including:

sub-step 5-1 of establishing constraints related to a flow and a pressure of the compressor in the natural gas network, the sub-step 5-1 including:

establishing a flow constraint of the head end and the tail end of a compressor:

G _{i c ,u} ⁺ =G _{i c ,u} ⁻ ,∀i _cϵΩ_c,∀u=0,1, . . . ,I^t−1

where Ω_c represents a set of serial numbers of all the compressors in the natural gas network; and

establishing a pressure constraint at the head end and the tail end of the compressor, wherein, for the compressor with a constant tail end pressure, the pressure constraint of the head end and the tail end of the compressor is as follows:

h _{i c ,u} ⁻ =h _{i c ,con} ⁻ ,∀i _cϵΩ_c,1,∀u=0,1, . . . ,I^t−1

where h_ic,u⁻ represents a tail end pressure of a compressor i_c at the sampling time point τ_u; h_ic,con⁻ represents a set value of a tail end pressure of the compressor i_c and is a constant determined by the dispatcher of the natural gas network; and Ω_c,1 represents a set of serial numbers of all the compressors with the constant tail end pressure in the natural gas network;

wherein, for a compressor with a constant compression ratio, the pressure constraint of the head end and the tail end of the compressor is as follows:

h _{i c ,u} ⁻ =r _{i c ,con} ·h _{i c ,u} ⁻ ,∀i _cϵΩ_c,2,∀u=0,1, . . . ,I^t−1

where h_ic,u⁺ represents a head end pressure of the compressor i_c at the sampling time point τ_u; r_ic,con represents a set value of a compression ratio of the compressor i_c and is a constant determined by the dispatcher of the natural gas network; and Ω_c,2 represents a set of serial numbers of all the compressors with the constant compression ratio in the natural gas network; and

wherein, for a compressor with a constant pressure difference, the pressure constraint of the head end and the tail end of the compressor id as follows:

h _{i c ,u} ⁻ −h _{i c ,u} ⁺ =Δh _{i c ,con} ,∀i _cϵΩ_c,3,∀u=0,1, . . . ,I^t−1

where Δh_ic,con represents a set value of a pressure difference between the tail end and the head end of the compressor i_c and is a constant determined by the dispatcher of the natural gas network; and Φ_c,3 represents a set of serial numbers of all the compressors with the constant pressure difference in the natural gas network;

sub-step 5-2 of establishing a flow constraint and a pressure constraint of the natural gas in the pipeline in the natural gas network, the sub-step 5-2 including:

establishing a two-port constraint of the pipeline in the natural gas network of each frequency component ω_d in the frequency-domain window:

$\left[\begin{array}{c}{h}_{i_p,d}^{-}\\ G_{i_p,d}^{-}\end{array}\right]=\left[\begin{array}{cc}{A}_{i_p,d}& B_{i_p,d}\\ C_{i_p,d}& D_{i_p,d}\end{array}\right]\left[\begin{array}{c}{h}_{i_p,d}^{+}\\ G_{i_p,d}^{+}\end{array}\right],\forall i_p\in {\Omega }_p,\forall d=0,1,\dots ,I^f-1$

where h_ip,d⁻ represents a value of a d-th component of a tail end pressure of a pipeline i_p in the natural gas network in a frequency-domain window I^f, and h_ip,d⁻ is a complex variable to be solved; h_ip,d⁺ represents a value of a d-th frequency component of a head end pressure of the pipeline i_p in the natural gas network, and h_ip,d⁺ is a complex variable to be solved; G_ip,d⁻ represents a value of a d-th component of a natural gas flow at the tail end of the pipeline i_p in the natural gas network in the frequency-domain window I^f, and G_ip,d⁻ is a complex variable to be solved; G_ip,d⁺ represents a value of a d-th component of a natural gas flow at the head end of the pipeline i_p in the natural gas network in the frequency-domain window, and G_ip,d⁺ is a complex variable to be solved; and A_ip,d, B_ip,d, C_ip,d and D_ip,d represent two-port parameters of a d-th component of the pipeline i_p in the natural gas network in the frequency-domain window, and values of A_ip,d, B_ip,d, C_ip,d and D_ip,d are respectively expressed as:

$A_{i_p,d}=\left[\cosh \left(l_{i_p}·a_{i_p,d}\right)-b_{i_p,d}·\sinh \left(l_{i_p}·a_{i_p,d}\right)\right]·e^{-\frac{k_{i_p}·l_{i_p}}{2}}$ $B_{i_p,d}=-\frac{z_{i_p,d}}{\sqrt{{\left(k_{i_p}\right)}^2+4·Z_{i_p,d}{Y}_{i_p,d}}}\sinh \left(l_{i_p}·a_{i_p,d}\right)·e^{-\frac{k_{i_p}·l_{i_p}}{2}}$ $C_{i_p,d}=-\frac{Y_{i_p,d}}{\sqrt{{\left(k_{i_p}\right)}^2+4·Z_{i_p,d}{Y}_{i_p,d}}}\sinh \left(l_{i_p}·a_{i_p,d}\right)·e^{-\frac{k_{i_p}·l_{i_p}}{2}}$ $D_{i_p,d}=\left[\cosh \left(l_{i_p}·a_{i_p,d}\right)+b_{i_p,d}·\sinh \left(l_{i_p}·a_{i_p,d}\right)\right]·e^{-\frac{k_{i_p}·l_{i_p}}{2}}$

where l_ip represents a length of the pipeline i_p in the natural gas network, k_ip, a_ip,d, b_ip,d, Z_ip,d and Y_ip,d represent values of the d-th frequency component of pipeline parameters of the natural gas network, and values of k_ip, a_ip,d, b_ip,d, Z_ip,d and Y_ip,d are respectively expressed as:

$k_{i_p}=-\frac{2g{D}_{i_p}\sin {\theta }_{i_p}-{{\lambda }_{i_p}\left(v_{\mathrm{base},i_p}\right)}^2}{2{\mathrm{RTD}}_{i_p}}$ $a_{i_p,d}=\frac{1}{2}\sqrt{{\left(k_{i_p,d}\right)}^2+4Z_{i_p,d}{Y}_{i_p,d}}$ $b_{i_p,d}=\frac{k_{i_p,d}}{\sqrt{{\left(k_{i_p,d}\right)}^2+4Z_{i_p,d}{Y}_{i_p,d}}}$ $Z_{i_p,d}=R_{i_p}+j{\omega }_d{L}_{i_p}$ $Y_{i_p,d}=j{\omega }_d{C}_{i_p}$

where g represents an acceleration of gravity; D_ip represents an inner diameter of the pipeline i_p in the natural gas network; θ_ip represents an angle of inclination of the pipeline i_p in the natural gas network; λ_ip represents a friction coefficient of the pipeline i_p in the natural gas network; v_base,ip represents a basic value of a flow velocity in the pipeline i_p in the natural gas network; R represents a gas constant of natural gas; T represents a temperature of the natural gas; j represents a complex number unit; and R_ip, L_ip and C_ip are parameters of the natural gas network, and values of R_ip, L_ip and C_ip are respectively expressed as:

R _{i p} =λ_ipv_base,ip/(A_ipD_ip)

L _{i p} =1/A_ip

C _{i p} =A _{i p} /(RT)

where A_ip represents a cross-sectional area of the pipeline i_p in the natural gas network;

establishing a time domain-frequency-domain mapping constraint of the natural gas flow at the head end of the pipeline of the natural gas network:

G _{i p ,u} ⁺=Σ_d=0^If−1[Re(G_ip,d⁺)·cos(θ_d−ω_d·uΔt)−Im(G_ip,d⁺)·sin(θ_d−ω_d·uΔt)]

where Re( ) represents valuing a real part of a complex number; Im( ) represents valuing an imaginary part of the complex number; and θ_d represents a parameter calculated with ω_d as follows:

θ_d=I^f·ω_d−ω_d

establishing a time domain-frequency-domain mapping constraint of the natural gas flow at the tail end of the pipeline of the natural gas network:

G _{i p ,u} ⁻=Σ_d=0^If−1[Re(G_ip,d⁻)·cos(θ_d−ω_d·uΔt)−Im(G_ip,d⁻)·sin(θ_d−ω_d·uΔt)], and

establishing a time domain-frequency-domain mapping constraint of the node of the natural gas network:

h _{i n ,u}=Σ_d=0^If−1[Re(h_in,d)·cos(θ_d−ω_d·uΔt)−Im(h_in,d)·sin(θ_d−ω_d·uΔt)]

where h_in,u represents a value of a d-th component of a pressure of a node i_n in the frequency-domain window; and h_in,u represents a complex variable to be solved; and

sub-step 5-3 of establishing a topological constraint of the natural gas network, the sub-step 5-3 including:

establishing a flow balance constraint of a node of the natural gas network:

${\sum }_{i_p\in {\Omega }_p^{+,i_n}}{G}_{i_p,u}^{+}-{\sum }_{i_p\in {\Omega }_p^{-,i_n}}{G}_{i_p,u}^{-}+{\sum }_{i_c\in {\Omega }_c^{+,i_n}}{G}_{i_c,u}^{+}-{\sum }_{i_c\in {\Omega }_c^{-,i_n}}{G}_{i_c,u}^{-}+{\sum }_{i_l\in {\Omega }_l^{-,i_n}}{G}_{i_l,u}^{gl}-{\sum }_{i_s\in {\Omega }_s^{+,i_n}}{G}_{i_s,u}^{gs}=0$

where Ω_p^+,in represents a set of serial numbers of pipelines connected to the node i_n at head ends; Ω_p^−,in represents a set of serial numbers of pipelines connected to the node i_n at tail ends; Ω_c^+,in represents a set of serial numbers of compressors connected to the node i_n at head ends; Ω_c^−,in represents a set of serial numbers of compressors connected to the node i_n at tail ends; Ω_s^+,in represents a set of serial numbers of natural gas sources connected to the node i_n; and Ω_l^−,in represents a set of serial numbers of natural gas loads connected to the node i_n;

establishing constraints of a pipeline-compressor-node time-domain pressure relationship in the natural gas network:

h _{i p ,u} ⁺ =h _{i n ,u} ,∀i _pϵΩ_p^+,in

h _{i p ,u} ⁻ =h _{i n ,u} ,∀i _pϵΩ_p^−,in

h _{i c ,u} ⁺ =h _{i n ,u} ,∀i _cϵΩ_c^−,in

h _{i c ,u} ⁻ =h _{i n ,u} ,∀i _cϵΩ_c^−,in, and

establishing constraints of a pipeline-node frequency-domain pressure relationship in the natural gas network:

h _{i p ,d} ⁺ =h _{i n ,d} ,∀i _pϵΩ_p^−,in

h _{i p ,d} ⁻ =h _{i n ,d} ,∀i _pϵΩ_p^−,in, and

step 6 of forming a dynamic state estimation model of the natural gas network by using the objective function of the dynamic state estimation of the natural gas network established in the step 4 and the constraint conditions for the dynamic state estimation of the natural gas network established in the step 5; solving, by using a Lagrange method or an interior point method, the dynamic state estimation model of the natural gas network, to obtain the state vector x_u, for the dynamic state estimation of the natural gas network at the sampling time point τ_u; and performing the dynamic state estimation of the natural gas network by considering the dynamic characteristics of the natural gas pipelines.

The method provided by the present disclosure has the following advantages.

According to the present disclosure, the method for the dynamic state estimation of the natural gas network considering the dynamic characteristic of the natural gas pipeline can obtain a result of the dynamic state estimation of the natural gas network by establishing the objective function of the dynamic state estimation of the natural gas network, the state quantity constraint of the compressor, the state quantity constraint of the natural gas pipeline and the topological constraint of the natural gas network are established, and by using the Lagrange method or the interior point method to solve a state estimation model of the natural gas network. The method according to the present disclosure takes the topological constraint of the natural gas network into consideration, and employs a pipeline pressure constraint in a frequency domain to implement linearization of the pipeline pressure constraint, thereby obtaining a real-time, reliable, consistent and complete dynamic operating state of the natural gas network.

DESCRIPTION OF EMBODIMENTS

A method for a dynamic state estimation of a natural gas network considering dynamic characteristics of natural gas pipelines provided by the present disclosure includes the following steps (1) to (5).

(1) A time-domain window and a frequency-domain window for the dynamic state estimation of the natural gas network are established. The step (1) includes the following steps (1-1) to (1-2).

(1-1) A time-domain window width is defined as I^t, where I^t is a positive integer, and a value of I^t is determined by a dispatcher of the natural gas network. A u-th sampling time point in the time-domain window is defined as τ_u=τ−uΔt, u=0, 1, . . . , I^t−1, where τ represents a current time point of the natural gas network, and Δt represents a sampling interval of the natural gas network. A current time-domain window width is defined as I^t,e, where I^t,e is a positive integer, and a value of I^t,e is determined by the dispatcher of the natural gas network. A historical time-domain window width is defined as I^t,h, where I^t,h is a positive integer. A value of I^t,h is determined by the dispatcher of the natural gas network. I^t, I^t,e and I^t,h satisfy the following relational expression:

I ^t =I ^t,e +I ^t,h.

(1-2) A frequency-domain window width is defined as I^f, where a value of I^f is determined by the dispatcher of the natural gas network. A d-th frequency component in the frequency-domain window is defined as ω_d, d=0, 1, . . . , I^f−1, where ω_d is calculated by the following formula:

${\omega }_d=\frac{d}{I^t·\Delta t}.$

(2) A measurement vector for the dynamic state estimation of the natural gas network is constructed. The step (2) includes the following steps (2-1) to (2-1).

(2-1) All operation data of the natural gas network at a sampling time point τ_u in the time-domain window where the current time point T of the natural gas network belongs is acquired from a data acquisition and monitoring and control system of the natural gas network. The all operation data of the natural gas network includes: a measurement value z_G+,u^ip of a natural gas flow at a head end of each pipeline in the natural gas network, and a measurement value z_G−,u^ip of a natural gas flow at a tail end of each pipeline in the natural gas network, where i_p represents a serial number of a pipeline in the natural gas network; a measurement value z_G+,u^ic of a natural gas flow at a head end of each compressor, and a measurement value z_G−,u^ic of a natural gas flow at a tail end of each compressor, where i_c represents a serial number of a compressor; a pressure measurement value z_pr,uⁱⁿ of each node of the natural gas network, where i_n represents a serial number of a node of the natural gas network; a measurement value z_gs,u^is of a natural gas flow of each natural gas source, where i_s represents a serial number of a natural gas source; and a measurement value z_gl,u^il of a natural gas flow of each natural gas load, where i_l represents a serial number of a natural gas load.

(2-2) A measurement vector z_u for the dynamic state estimation of the natural gas network at each sampling time point τ_u is constructed:

$z_u=\left[\begin{array}{c}{Z}_{G^{+},u}\\ Z_{G^{-},u}\\ Z_{\mathrm{pr},u}\\ Z_{\mathrm{gs},u}\\ Z_{\mathrm{gl},u}\end{array}\right],$

where z_G+,u represents a column vector consisting of all the measurement values z_G+,u^ip of natural gas flows at head ends of respective pipelines in the natural gas network and all the measurement values z_G+,u^ic of natural gas flows at head ends of respective compressors at the sampling time point τ_u; z_G−,u represents a column vector consisting of all the measurement values z_G−,u^ip of natural gas flows at tail ends of respective pipelines in the natural gas network and all the measurement values z_G−,u^ic of natural gas flows at tail ends of respective compressors at the sampling time point τ_u; z_pr,u represents a column vector consisting of all the pressure measurement values z_pr,uⁱⁿ of respective nodes of the natural gas network at the sampling time point τ_u; z_gs,u represents a column vector consisting of all the measurement values z_gs,u^is of natural gas flows of respective natural gas sources in the natural gas network at the sampling time point τ_u; and z_gl,u represents a column vector consisting of all the measurement values z_gl,u^il of natural gas flows of respective natural gas loads in the natural gas network at the sampling time point τ_u.

(3) A state vector x_u for the dynamic state estimation of the natural gas network at each sampling time point τ_u is constructed:

$x_u=\left[\begin{array}{c}{x}_{G^{+},u}\\ x_{G^{-},u}\\ x_{\mathrm{pr},u}\\ x_{\mathrm{gs},u}\\ x_{\mathrm{gl},u}\end{array}\right],$

where x_G−,u represents a column vector consisting of all natural gas flows G_ip,u⁺ at the head ends of the respective pipelines in the natural gas network and all natural gas flows G_ic,u⁺ at the head ends of the respective compressors at the sampling time point τ_u; x_G−,u represents a column vector consisting of all natural gas flows G_ip,u⁻ at the tail ends of the respective pipelines in the natural gas network and all natural gas flows G_ic,u⁻ at the tail ends of the respective compressors at the sampling time point τ_u, x_pr,u represents a column vector consisting of all pressures h_in of the respective nodes of the natural gas network at the sampling time point τ_u; x_gs,u represents a column vector consisting of all natural gas flows G_is,u^gs of the respective natural gas sources in the natural gas network at the sampling time point τ_u; and x_gl,u represents a column vector consisting of all natural gas flows G_il,u^gl of the respective natural gas loads in the natural gas network at the sampling time point τ_u.

(4) An objective function of the dynamic state estimation of the natural gas network is established based on the measurement vector constructed in step (2) and the state vector constructed in step (3):

min J=Σ_u=0^It,e−1{[z_u−x_u]W⁻¹[z_u−x_u]^T}+Σ_u=It,e^It−1{[z_u−x_u]W⁻¹δ^u−It,e[z_u−x_u]^T}

where J represents an expression of the objective function; W represents a covariance matrix of a measurement error and is determined by the dispatcher of the natural gas network; a superscript T represents a matrix transpose; and δ represents a decay factor of a historical time window and is determined by the dispatcher of the natural gas network.

(5) Constraint conditions for the dynamic state estimation of the natural gas network are established. The step (5) includes steps (5-1) to (5-3).

(5-1) Constraints related to a flow and a pressure of a compressor in the natural gas network are established. The step (5-1) includes steps (5-1-1) to (5-1-2).

(5-1-1) A flow constraint at a head end and a tail end of a compressor is established:

G _{i c ,u} ⁺ =G _{i c ,u} ⁻ ,∀i _cϵΩ_c,∀u=0,1, . . . ,I^t−1

where Ω_c represents a set of serial numbers of respective compressors in the natural gas network.

(5-1-2) A pressure constraint at a head end and a tail end of a compressor is established.

For a compressor with a constant tail end pressure, the pressure constraint at the head end and the tail end of the compressor being as follows:

h _{i c ,u} ⁻ =h _{i c ,con} ⁻ ,∀i _cϵΩ_c,1,∀u=0,1, . . . ,I^t−1

where h_ic,u⁻ represents a tail end pressure of a compressor i_c at the sampling time point τ_u, h_ic,con⁻ represents a set value of the tail end pressure of the compressor i_c, is a constant, and is determined by the dispatcher of the natural gas network, and Ω_c,1 represents a set of serial numbers of respective compressors with the constant tail end pressure in the natural gas network.

For a compressor with a constant compression ratio, the pressure constraint of the head end and the tail end of the compressor is as follows:

h _{i c ,u} ⁻ =r _{i c ,con} ·h _{i c ,u} ⁻ ,∀i _cϵΩ_c,2,∀u=0,1, . . . ,I^t−1

where h_ic,u⁺ represents a head end pressure of the compressor i_c at the sampling time point τ_u; r_ic,con represents a set value of a compression ratio of the compressor i_c and is a constant determined by the dispatcher of the natural gas network; and Ω_c,2 represents a set of serial numbers of all the compressors with the constant compression ratio in the natural gas network.

For a compressor with a constant pressure difference, the pressure constraint of the head end and the tail end of the compressor is as follows:

h _{i c ,u} ⁻ −h _{i c ,u} ⁺ =Δh _{i c ,con} ,∀i _cϵΩ_c,3,∀u=0,1, . . . ,I^t−1

where Δh_ic,con represents a set value of a pressure difference between the tail end and the head end of the compressor i_c and is a constant determined by the dispatcher of the natural gas network; and Φ_c,3 represents a set of serial numbers of all the compressors with the constant pressure difference in the natural gas network.

(5-2) A flow constraint and a pressure constraint of natural gas in a pipeline in the natural gas network are established. The step (5-2) includes steps (5-2-1) to (5-2-5).

(5-2-1) A two-port constraint of the pipeline in the natural gas network of each frequency component ω_d in the frequency-domain window is established:

$\left[\begin{array}{c}{h}_{i_p,d}^{-}\\ G_{i_p,d}^{-}\end{array}\right]=\left[\begin{array}{cc}{A}_{i_p,d}& B_{i_p,d}\\ C_{i_p,d}& D_{i_p,d}\end{array}\right]\left[\begin{array}{c}{h}_{i_p,d}^{+}\\ G_{i_p,d}^{+}\end{array}\right],\text{∀}{i}_p\in {\Omega }_p,\text{∀}d=0,1,\dots ,I^f-1,$

where h_ip,d⁻ represents a value of a d-th component of a tail end pressure of a pipeline i_p in the natural gas network in a frequency-domain window I^f, and h_ip,d⁻ is a complex variable to be solved; h_ip,d⁺ represents a value of a d-th frequency component of a head end pressure of the pipeline i_p in the natural gas network, and h_ip,d⁺ is a complex variable to be solved; G_ip,d⁻ represents a value of a d-th component of a natural gas flow at the tail end of the pipeline i_p in the natural gas network in the frequency-domain window I^f, and G_ip,d⁻ is a complex variable to be solved; G_ip,d⁺ represents a value of a d-th component of a natural gas flow at the head end of the pipeline i_p in the natural gas network in the frequency-domain window, and G_ip,d⁻ is a complex variable to be solved; and A_ip,d, B_ip,d, C_ip,d and D_ip,d represent two-port parameters of a d-th component of the pipeline i_p in the natural gas network in the frequency-domain window, and values of A_ip,d, B_ip,d, C_ip,d and D_ip,d are respectively expressed as:

$A_{i_p,d}=\left[\cosh \left(l_{i_p}·a_{i_p,d}\right)-b_{i_p,d}·\sinh \left(l_{i_p}·a_{i_p,d}\right)\right]·e^{-\frac{k_{i_p}·l_{i_p}}{2}}$ $B_{i_p,d}=-\frac{Z_{i_p,d}}{\sqrt{{\left(k_{i_p}\right)}^2+4·Z_{i_p,d}{Y}_{i_p,d}}}\sinh \left(l_{i_p}·a_{i_p,d}\right)·e^{-\frac{k_{i_p}·l_{i_p}}{2}}$ $C_{i_p,d}=-\frac{Y_{i_p,d}}{\sqrt{{\left(k_{i_p}\right)}^2+4·Z_{i_p,d}{Y}_{i_p,d}}}\sinh \left(l_{i_p}·a_{i_p,d}\right)·e^{-\frac{k_{i_p}·l_{i_p}}{2}}$ $D_{i_p,d}=\left[\cosh \left(l_{i_p}·a_{i_p,d}\right)-b_{i_p,d}·\sinh \left(l_{i_p}·a_{i_p,d}\right)\right]·e^{-\frac{k_{i_p}·l_{i_p}}{2}},$

where l_ip represents a length of the pipeline i_p in the natural gas network, k_ip, a_ip,d, b_ip,d, Z_ip,d and Y_ip,d represent values of the d-th frequency component of pipeline parameters of the natural gas network, and values of k_ip, a_ip,d, b_ip,d, Z_ip,d and Y_ip,d are respectively expressed as:

$k_{i_p}=-\frac{2g{D}_{i_p}\sin {\theta }_{i_p}-{{\lambda }_{i_p}\left(v_{\mathrm{base},i_p}\right)}^2}{2{\mathrm{RTD}}_{i_p}}$ $a_{i_p,d}=\frac{1}{2}\sqrt{{\left(k_{i_p,d}\right)}^2+4Z_{i_p,d}{Y}_{i_p,d}}$ $b_{i_p,d}=\frac{k_{i_p,d}}{\sqrt{{\left(k_{i_p,d}\right)}^2+4Z_{i_p,d}{Y}_{i_p,d}}}$ $Z_{i_p,d}=R_{i_p}+j{\omega }_d{L}_{i_p}$ $Y_{i_p,d}=j{\omega }_d{C}_{i_p}$

where g represents an acceleration of gravity; D_ip represents an inner diameter of the pipeline i_p in the natural gas network; θ_ip represents an angle of inclination of the pipeline i_p in the natural gas network; λ_ip represents a friction coefficient of the pipeline i_p in the natural gas network; v_base,ip represents a basic value of a flow velocity in the pipeline i_p in the natural gas network; R represents a gas constant of natural gas; T represents a temperature of the natural gas; j represents a complex number unit; and R_ip, L_ip and C_ip are parameters of the natural gas network, and values of R_ip, L_ip and C_ip are respectively expressed as:

R _{i p} =λ_ipv_base,ip/(A_ipD_ip)

L _{i p} =1/A_ip

C _{i p} =A _{i p} /(RT)

where A_ip represents a cross-sectional area of the pipeline i_p in the natural gas network.

(5-2-3) A time domain-frequency-domain mapping constraint of the natural gas flow at the head end of the pipeline of the natural gas network is established:

G _{i p ,u} ⁺=Σ_d=0^If−1[Re(G_ip,d⁺)·cos(θ_d−ω_d·uΔt)−Im(G_ip,d⁺)·sin(θ_d−ω_d·uΔt)],

where Re( ) represents valuing a real part of a complex number; Im( ) represents valuing an imaginary part of the complex number; and θ_d represents a parameter calculated with ω_d as follows:

θ_d=I^f·ω_d−ω_d.

(5-2-4) A time domain-frequency-domain mapping constraint of the natural gas flow at the tail end of the pipeline of the natural gas network is established:

G _{i p ,u} ⁻=Σ_d=0^If−1[Re(G_ip,d⁻)·cos(θ_d−ω_d·uΔt)−Im(G_ip,d⁻)·sin(θ_d−ω_d·uΔt)].

(5-2-5) A time domain-frequency-domain mapping constraint of nodes of the natural gas network is established:

h _{i n ,u}=Σ_d=0^If−1[Re(h_in,d)·cos(θ_d−ω_d·uΔt)−Im(h_ib,d)·sin(θ_d−ω_d·uΔt)],

where h_in,u represents a value of a d-th component of a pressure of a node i_n in the frequency-domain window; and h_in,u represents a complex variable to be solved.

(5-3) A topological constraint of the natural gas network is established. The step (5-3) includes steps (5-3-1) to (5-3-3).

(5-3-1) A flow balance constraint of a node of the natural gas network is established:

${\sum }_{i_p\in {\Omega }_p^{+,i_n}}{G}_{i_p,u}^{+}-{\sum }_{i_p\in {\Omega }_p^{-,i_n}}{G}_{i_p,u}^{-}+{\sum }_{i_c\in {\Omega }_c^{+,i_n}}{G}_{i_c,u}^{+}-{\sum }_{i_c\in {\Omega }_c^{-,i_n}}{G}_{i_c,u}^{-}+{\sum }_{i_l\in {\Omega }_l^{-,i_n}}{G}_{i_l,u}^{gl}-{\sum }_{i_s\in {\Omega }_s^{+,i_n}}{G}_{i_s,u}^{gs}=0,$

where Ω_p^+,in represents a set of serial numbers of pipelines connected to the node i_n at head ends; Ω_p^−,in represents a set of serial numbers of pipelines connected to the node i_n at tail ends; Ω_c^+,in represents a set of serial numbers of compressors connected to the node i_n at head ends; Ω_c^−,in represents a set of serial numbers of compressors connected to the node i_n at tail ends; Ω_s^+,in represents a set of serial numbers of natural gas sources connected to the node i_n; and Ω_l^−,in represents a set of serial numbers of natural gas loads connected to the node i_n.

(5-3-2) Constraints of a pipeline-compressor-node time-domain pressure relationship in the natural gas network are established:

h _{i p ,u} ⁺ =h _{i n ,u} ,∀i _pϵΩ_p^+,in

h _{i p ,u} ⁻ =h _{i n ,u} ,∀i _pϵΩ_p^−,in

h _{i c ,u} ⁺ =h _{i n ,u} ,∀i _cϵΩ_c^−,in

h _{i c ,u} ⁻ =h _{i n ,u} ,∀i _cϵΩ_c^−,in.

(5-3-3) Constraints of a pipeline-node frequency-domain pressure relationship in the natural gas network are established:

h _{i p ,d} ⁺ =h _{i n ,d} ,∀i _pϵΩ_p^−,in

h _{i p ,d} ⁻ =h _{i n ,d} ,∀i _pϵΩ_p^−,in.

(6) A dynamic state estimation model of the natural gas network is formed by using the objective function of the dynamic state estimation of the natural gas network established in step (4) and the constraint conditions for the dynamic state estimation of the natural gas network established in step (5). The dynamic state estimation model of the natural gas network is solved by using a Lagrange method or an interior point method, to obtain the state vector x_u for the dynamic state estimation of the natural gas network at each sampling time point τ_u. Consequently, the dynamic state estimation of the natural gas network considering the dynamic characteristic of the natural gas pipeline is implemented.

In the embodiments of the present disclosure, commercial software Gurobi or Cplex is used to solve the dynamic state estimation model of the natural gas network.

Claims

1. A method for a dynamic state estimation of a natural gas network considering dynamic characteristics of natural gas pipelines, the method comprising: step 1 of establishing a time-domain window and a frequency-domain window for the dynamic state estimation of the natural gas network, the step 1 comprising: sub-step 1-1 of defining a time-domain window width as It, where It is a positive integer, and a value of It is determined by a dispatcher of the natural gas network; defining a u-th sampling time point in the time-domain window as τu=τ−uΔt, u=0, 1, . . . , It−1, where τ represents a current time point of the natural gas network, and Δt represents a sampling interval of the natural gas network; defining a current time-domain window width as It,e, where It,e is a positive integer, and a value of It,e is determined by the dispatcher of the natural gas network; and defining a historical time-domain window width as It,h, where It,h is a positive integer, and a value of It,h is determined by the dispatcher of the natural gas network, wherein It, It,e and It,h satisfy the following relational expression: It=It,e+It,h; andsub-step 1-2 of defining a frequency-domain window width as If, where a value of If is determined by the dispatcher of the natural gas network; and defining a d-th frequency component in the frequency-domain window as ωd, d=0, 1, . . . , If−1, where ωd is calculated by the following formula: