CN104779609B - A kind of trend cooperative control method for interconnected network - Google Patents

Abstract

The invention discloses a kind of trend cooperative control method for interconnected network, comprise the steps: S1, the electrical network border of target area is carried out Static Equivalent process, make other grid parts being connected with target area, carry out equivalence stripping with target area；S2, according to the network information in target area, carries out global optimization to the interconnected network in target area, and the interconnection section delivering power making the interconnection of interconnected network constitute is maximum；S3, with maximum transmission power for determining power, under constant dc power control pattern, is determined the control parameter equation of THE UPFC；S4, obtains the control parameter value of each THE UPFC in target area according to controlling parameter equation, by controlling the setting of parameter value in THE UPFC, THE UPFC being carried out Collaborative Control.The present invention considers global information, by controlling the setting of parameter value, it is ensured that harmonious between flow controller in regional power grid.

Description

Power flow cooperative control method for interconnected power grid

Technical Field

The invention relates to a power flow cooperative control method, in particular to a power flow cooperative control method for an interconnected power grid, and belongs to the technical field of power system scheduling.

Background

Modern power systems, while developing rapidly, also expose the vulnerable side of the power transmission network. A new set of contradictions and problems are becoming increasingly prominent. In an interconnected power grid, the operation mode is complex, the actual power distribution and the ideal power distribution can be far away, the power flow distribution is often unreasonable, and large free flow can exist in the power distribution of the power transmission network, so that the utilization efficiency of the power transmission network is reduced, and the power loss is increased; due to the interference of various factors, the power flow quantity on the lines between the interconnected network areas is uncertain, and even a tidal current oscillation phenomenon exists. In the power market environment, in order to make the system operate in a specific power flow mode, the power flow transmission capacity of some lines is limited, so that the power flow is transmitted according to a determined path and capacity, and the like.

In order to meet the requirements of safe and reliable operation of power systems in new forms and commercial operation of power markets, the controllability and adjustability of power flow of power transmission networks are urgently needed to be improved. People are always exploring more advanced and effective power flow control means.

The power flow distribution of the power network is determined by the injection mode of the system and the network structure parameters. For a long time, under a determined network topology, the power flow regulation of an electric power network relies mainly on changing the injection pattern. However, changes in injection patterns will affect the optimal configuration of resources, especially in the context of the electricity market, and will also involve economic benefits for multiple parties, and are more difficult to deal with. Devices have also been made for the power flow control of systems, such as fixed capacitance compensation devices, by changing the topology of the network and the parameters of the network to regulate the power flow of the line. However, most of the devices are based on mechanical switches, have slow response speed, are difficult to realize continuous, quick and accurate adjustment of the system power flow, and cannot meet the requirements of modern power system power flow adjustment and other aspects of control.

With the development of modern power electronics and other related technologies, the development of Flexible Alternating Current Transmission (FACTS) technology provides a new control means for modern power systems, which FACTS is a new technology for controlling alternating current transmission that is formed by integrating power electronics technology, microprocessor and microelectronics technology, communication technology and control technology. In FACTS, a unified power flow controller (UPQC) replaces a mechanical high-voltage switch of a traditional component with a high-power electronic device, so that system parameters such as voltage, line impedance, power angle and the like are changed flexibly, quickly and accurately, and the transmission capacity, the power flow and voltage control capacity and the dynamic performance of a system of a power grid are greatly improved under the condition that a network structure is not changed.

During system operation, control of the UPFC adds new control parameters and constraints to the power system. What control strategy is adopted and how to effectively control the UPFC device is the key to achieving the UPFC function. Due to the limitation of the power flow calculation, the constraint which can be considered by the power flow calculation is only local, and the capability of processing the constraint is limited. Meanwhile, the result of load flow calculation only provides a feasible system operation state, the optimal control mode of the UPFC cannot be obtained, and the coordination control among a plurality of UPFCs cannot be considered. With the development of power system optimization power flow and different requirements of power flow control under new situation, the development direction of adopting an optimization method to seek a power flow control strategy of the UPFC is the development direction of the problem.

Disclosure of Invention

The invention aims to provide a power flow cooperative control method for an interconnected power grid.

In order to achieve the purpose, the invention adopts the following technical scheme:

a power flow cooperative control method for interconnected power grids comprises the following steps:

s1, performing static equivalence processing on the power grid boundary of the target area to enable other power grid parts connected with the target area to be equivalently stripped from the target area;

s2, performing global optimization on the interconnected power grid in the target area according to the network information in the target area, and enabling the transmission power of an interconnected section formed by the connecting lines of the interconnected power grid to be maximum;

s3, determining a control parameter formula of the unified power flow controller in a constant power control mode by taking the maximum transmission power of an interconnection section formed by interconnection lines of an interconnection network as constant power;

and S4, obtaining the control parameter values of all unified power flow controllers in the target area according to the control parameter formula, and performing cooperative control on the unified power flow controllers by setting the control parameter values in the unified power flow controllers.

Preferably, in step S2, the globally optimizing the interconnected network in the target area to maximize the transmission power of the interconnection cross section formed by the interconnections of the interconnected network includes:

s21, reading system information of each node in the target area;

s22, setting upper and lower line constraints of each element according to system requirements, and obtaining the value range of each element which enables the maximum transmission power of an interconnection section formed by interconnection lines of an interconnection network;

and S23, establishing an optimization model solution according to the value range of each element to obtain the maximum transmission power of an interconnection section formed by interconnection lines of the interconnected power grid.

Preferably, among the inequality constraint conditions, the constraint conditions set for the tie lines of the interconnected power grid in the target area are: the transmission power of an interconnection section formed by interconnection lines of an interconnection power grid takes the maximum active power as the upper limit on the premise of meeting the thermal stability limit of an N-1 single circuit line, wherein N is a positive integer.

Preferably, in step S22, when performing the global optimization calculation, the constraint condition of the constant power global optimization and the inequality constraint condition need to be satisfied at the same time.

Preferably, in step S3, the control parameter formula is;

$V_B=\frac{\sqrt{(P_e^2+Q_e^2)(r_{\mathrm{lm}}^2+x_{\mathrm{lm}}^2)}}{V_m};$

wherein, P_eAnd Q_eRespectively the active power and the reactive power of the line between the nodes l and m; r is_lmIs the resistance of the line between nodes l and m; x is the number of_lmIs the inductive reactance of the line between nodes l and m; v_mIs the voltage of node m; theta_mIs the voltage phase of node m.

Preferably, in step S4, there are one or more unified power flow controllers.

According to the cooperative control method for the power flow of the interconnected power grid, the independent network is obtained by carrying out static equivalence analysis on the network, and on the basis, global optimization is comprehensively considered, so that the transmission power of an interconnected section formed by connecting lines of the interconnected power grid is maximized, and the requirement of a power system on the control capacity of the power flow is met; in addition, the amplitude and the phase angle of the output voltage of the series converter of the UPFC are adjusted according to the maximum transmission power of an interconnection section formed by interconnection lines of an interconnected power grid, the control parameter values of the UPFCs are obtained, the system obtains the optimal running state through setting of the control parameter values, the coordination among the tidal current controllers and among the multi-tidal current controllers in the regional power grid is guaranteed, and the cooperative control of the system is facilitated.

Drawings

Fig. 1 is a flowchart of a power flow cooperative control method for interconnected power grids according to the present invention;

FIG. 2 is a schematic diagram of a network partition structure relationship among external network nodes, internal network nodes and boundary connection nodes in the present invention;

fig. 3 is a working schematic diagram of the unified power flow controller;

FIG. 4 is a schematic diagram of a UPFC steady state equivalent circuit;

FIG. 5 is a phasor diagram for stable operation of a UPFC;

fig. 6 is an equivalent circuit diagram of a transmission line with a UPFC according to the present invention.

Detailed Description

The technical contents of the present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.

As shown in fig. 1, the power flow cooperative control method for the interconnected power grid provided by the present invention specifically includes the following steps: and performing static equivalence analysis on the network to determine a set of an external power grid, boundary points and a target power grid. And modifying the boundary admittance array and the network equation to obtain the partitioned independent network. On the basis, the whole network is globally optimized, network information such as node types, voltages, phase angles, admittance arrays, active power output, reactive power output and the like is read, global optimization is carried out according to upper and lower limits of voltage, active power output, reactive power output and reactive power compensation constraints required to be met by the system, distribution proportion of transmission power of the junctor and an optimized objective function are given, and a required transmission power value (maximum transmission power of an interconnection section formed by the junctors of the interconnected power grid) of the junctor is obtained. And adjusting the output voltage amplitude and the phase angle of a series current converter in a Unified Power Flow Controller (UPFC) according to the transmission power value of the connecting line to obtain the control parameter value of the UPFC. This process is described in detail below.

And S1, performing necessary static equivalence processing on the power grid boundary of the target area, and equivalently stripping other power grid parts connected with the target area from the target area to obtain the partitioned independent network.

In an actual power grid, the power grid inside the target area is not isolated, but is connected with an external power grid to form a whole. In actual calculation, only the part needing to be studied carefully is concerned, and the rest parts are subjected to network simplification to obtain the voltage-current relationship of the part to be studied carefully.

In one embodiment of the invention, the Chongqing cross section is taken as an example for analysis, so that the Hubei power grid connected with the Chongqing power grid belongs to an external node, static equivalence needs to be carried out for facilitating sensitivity calculation, and the node set is represented by E. In the Chongqing power grid, nodes directly connected with the Hubei power grid form a boundary node set and are represented by B. And all other Chongqing and Sichuan power grid nodes which are not directly connected with the Hubei power grid form an internal node set which is represented by I. The network partitioning structure relationship is shown in fig. 2.

Dividing the network equations expressed by the node admittance matrixes of the Chongqing, Sichuan and Hubei power grids according to I, B, E sets, and writing the network equations expressed in the form of block matrixes as follows:

$\left[\begin{array}{ccc}{Y}_{\mathrm{EE}}& Y_{\mathrm{EB}}& 0\\ Y_{\mathrm{BE}}& Y_{\mathrm{BB}}& Y_{\mathrm{BI}}\\ 0& Y_{\mathrm{IB}}& Y_{\mathrm{II}}\end{array}\right]\·\left[\begin{array}{c}{\stackrel{\·}{V}}_E\\ {\stackrel{\·}{V}}_B\\ {\stackrel{\·}{V}}_I\end{array}\right]=\left[\begin{array}{c}{\stackrel{\·}{I}}_E\\ {\stackrel{\·}{I}}_B\\ {\stackrel{\·}{I}}_I\end{array}\right]---\left(1\right)$

wherein Y represents a node admittance matrix, Y_EEAnd representing a node admittance matrix in the node set E, wherein the node admittance matrix reflects the electrical connection relation between the nodes, and if the two nodes are not directly connected, the mutual admittance is 0.

Cancelling (1) voltage variations at external nodesThe following network equation is obtained:

$\left[\begin{array}{cc}{\tilde{Y}}_{\mathrm{BB}}& Y_{\mathrm{BI}}\\ Y_{\mathrm{IB}}& Y_{\mathrm{II}}\end{array}\right]\·\left[\begin{array}{c}{\stackrel{\·}{V}}_B\\ {\stackrel{\·}{V}}_I\end{array}\right]=\left[\begin{array}{c}{\stackrel{\stackrel{\·}{~}}{I}}_B\\ {\stackrel{\·}{I}}_I\end{array}\right]$

wherein, ${\tilde{Y}}_{\mathrm{BB}}=Y_{\mathrm{BB}}-Y_{\mathrm{BE}}{Y}_{\mathrm{EE}}^{-1}{Y}_{\mathrm{EB}};$ ${\stackrel{\stackrel{\·}{~}}{I}}_{\mathrm{BB}}={\stackrel{\·}{I}}_B-Y_{\mathrm{BE}}{Y}_{\mathrm{EE}}^{-1}{\stackrel{\·}{I}}_E.$ is a static equivalence processed boundary admittance matrix, which includes contributions of equivalence branches generated after simplification of an external network.

And S2, performing global optimization on the interconnected power grid in the target area according to the network information in the target area, and enabling the transmission power of an interconnected section formed by the connecting lines of the interconnected power grid to be maximum.

And after equivalently stripping the target area and other power grid parts connected with the target area, carrying out global optimization on the interconnected power grid in the target area to ensure that the transmission power of an interconnected section formed by the connecting lines of the interconnected power grid is maximum. The optimization variables comprise power of the generator, control power of the unified power flow controller, switchable power transmission lines and the like. In an embodiment of the present invention, the objective function is the maximum transmission power of the interconnection section formed by the chongqing interconnection line, and the formula is as follows:

f＝P_hw+P_hb

wherein, P_hwIs the transmission power, P, of the A-connection between Chongqing_hbIs the transmission power of B-connection lines between Chongqing.

The method for carrying out global optimization on the interconnected power grid in the target area to enable the transmission power of an interconnected section formed by connecting lines of the interconnected power grid to be maximum comprises the following steps:

and S21, reading system information such as node types, voltages, phase angles, active power output, reactive power output, admittance arrays and the like in the target area.

And S22, setting upper and lower line constraints such as voltage, active power output, reactive power output and active compensation according to system requirements, and obtaining the value range of each element which enables the maximum transmission power of the interconnection section formed by the interconnection lines of the interconnected power grid.

When performing global optimization calculation, the constraint condition and inequality constraint condition of constant power global optimization need to be satisfied at the same time. When the global optimization calculation is carried out according to the constraint conditions meeting the constant-power global optimization, a basic power flow equation needs to be met, and the power flow balance equation is the constraint conditions of the constant-power global optimization. Expressed as:

$\left\{\begin{array}{c}\mathrm{\Δ}{P}_i=P_{\mathrm{Gi}}-P_{\mathrm{Li}}-V_i\underset{j=1}{\overset{n}{\mathrm{\Σ}}}{V}_j(G_{\mathrm{ij}}\cos {\mathrm{\δ}}_{\mathrm{ij}}+B_{\mathrm{ij}}\sin {\mathrm{\δ}}_{\mathrm{ij}})=0\\ \mathrm{\Δ}{Q}_i=Q_{\mathrm{Gi}}+Q_{\mathrm{Ci}}-Q_{\mathrm{Li}}-V_i\underset{j=1}{\overset{n}{\mathrm{\Σ}}}{V}_j(G_{\mathrm{ij}}\sin {\mathrm{\δ}}_{\mathrm{ij}}-B_{\mathrm{ij}}\cos {\mathrm{\δ}}_{\mathrm{ij}})=0\end{array}\right.---(i=\mathrm{1,2},...,n)$

wherein, P_Gi、Q_GiActive output and reactive output of the generator are respectively; p_Li、Q_LiRespectively an active load and a reactive load of a node i; q_CiThe reactive power output of the reactive power compensation device which is the node i; v_i、V_jThe voltage amplitudes of the nodes i and j are obtained;_ijis the phase angle difference of the node voltages at the two ends of the branch ij; g_ij、B_ijThe real and imaginary parts of the admittance matrix elements of the node.

The inequality constraint conditions mainly comprise active output constraint, reactive output constraint and voltage amplitude constraint of the generator, and the expression is as follows:

wherein S is_AIs a collection of active power supply nodes; s is a set of all nodes; P _Gi the upper limit and the lower limit of the active power supply output are respectively; Q _Gi the upper limit and the lower limit of the reactive power output are respectively; V _i the upper limit and the lower limit of the node voltage amplitude are respectively;upper limit of active power for transmission line, P_hbIs a B link between Chongqing and Yu, P_hwIs an A connecting line between Chongqing and is restricted that the ratio of the transmission power of the B connecting line to the transmission power of the A connecting line is less than 3: the sum of the 1, B and a link transmit powers is less than the upper limit 39. P_{Zhang en line}And P_{Coiled thread}The active force of the Yu jaw connecting line is restricted to be less than the upper limit 26, and the ratio of the active force of the Yu jaw connecting line is less than 6 to 4 and more than 4 to 6.

In inequality constraint conditions, in order to meet the requirement of safety and stability of the interconnected power grid, constraint conditions are set for the tie lines of the interconnected power grid in the target area as follows: the transmission power of an interconnection section formed by interconnection lines of an interconnection power grid is limited to the maximum active power under the premise of meeting the thermal stability limit of an N-1 (N is a positive integer) single circuit line. When only a single loop in the interconnected power grid operates, the power equipment cannot be damaged due to overlarge power, and the safety and stability of the interconnected power grid are improved.

And S23, establishing an optimization model solution according to the value range of each element to obtain the maximum transmission power of an interconnection section formed by interconnection lines of the interconnected power grid.

In the embodiment provided by the invention, an optimization model is established according to the value ranges of the acquired voltage, active output, reactive output, active compensation and other elements, and an objective function f-P is obtained_hw+P_hbIs measured. Wherein, P_hwIs the transmission power, P, of the A-connection between Chongqing_hbIs the transmission power of B-connection lines between Chongqing. This maximum is the maximum transmission power of the interconnection section formed by the interconnections of the interconnected network.

And S3, determining a control parameter formula of the unified power flow controller in a constant power control mode by taking the maximum transmission power of an interconnection section formed by interconnection lines of the interconnected power grid as constant power so as to ensure that the control of each power flow controller meets the adjustment target of the target regional power grid.

The Unified Power Flow Controller (UPFC) is a functional combination of the STATCOM and the SSSC, and the two voltage type converters realized by the GTO share a direct current capacitor, so that the STATCOM and the SSSC are coupled.

The working principle diagram of the unified power flow controller is shown in fig. 3. The UPFC device can be regarded as a STATCOM device and an SSSC device, the dc sides of which are connected in parallel. Therefore, the UPFC has the advantages of both the STATCOM device and the SSSC device, namely, the UPFC has strong capacity of compensating line voltage and also has strong reactive power compensation capacity. Moreover, the UPFC also has functions that neither the STATCOM device nor the SSSC device has, for example, the series part can absorb and emit reactive power, and also can absorb and emit active power, and the parallel part can provide a channel for the active power of the series part, thereby realizing control of line power flow.

The UPFC dynamic model at a per unit value is:

$\left[\begin{array}{cc}{r}_E& -x_E\\ x_E& r_E\end{array}\right]\left[\begin{array}{c}{I}_{\mathrm{Ex}}\\ I_{\mathrm{Ey}}\end{array}\right]=\left[\begin{array}{c}{V}_{\mathrm{Etx}}\\ V_{\mathrm{Ety}}\end{array}\right]-\left[\begin{array}{cc}{k}_E{m}_E{V}_{\mathrm{dc}}& \cos {\mathrm{\δ}}_E\\ k_E{m}_E{V}_{\mathrm{dc}}& \sin {\mathrm{\δ}}_E\end{array}\right]---\left(2\right)$

$\left[\begin{array}{cc}{r}_B& -x_B\\ x_B& r_B\end{array}\right]\left[\begin{array}{c}{I}_{\mathrm{Bx}}\\ I_{\mathrm{By}}\end{array}\right]=\left[\begin{array}{cc}{k}_B{m}_B{v}_{\mathrm{dc}}& \cos {\mathrm{\δ}}_B\\ k_B{m}_B{v}_{\mathrm{dc}}& \sin {\mathrm{\δ}}_B\end{array}\right]-\left[\begin{array}{c}{V}_{\mathrm{Btx}}\\ V_{\mathrm{Bty}}\end{array}\right]---\left(3\right)$

$T_u=\frac{d{v}_{\mathrm{dc}}}{\mathrm{dt}}=k_E{m}_E(I_{\mathrm{Ex}}\cos {\mathrm{\δ}}_E+I_{\mathrm{Ey}}\sin {\mathrm{\δ}}_E)-k_B{m}_B(I_{\mathrm{Bx}}\cos {\mathrm{\δ}}_B+I_{\mathrm{By}}\sin {\mathrm{\δ}}_B)---\left(4\right)$

wherein, x is a real part, y is an imaginary part, and equations (2) to (4) jointly form a UPFC dynamic model under the standard model. Intermediate impedance Z_BAnd Z_ERespectively equalizing the impedance of the series and parallel transformers and the power loss of the corresponding converter; k is a radical of_EAnd k_BTwo parameters for UPFC; m is_EAnd m_BThe modulation ratios of the parallel and series converters are respectively; t is_uTime constant of UPFC;_Eand_Bis the phase of the sinusoidal control waveform; v. of_dcIs the instantaneous value of the dc capacitor voltage,andis converted to the terminal voltage of the UPFC on the converter side.

In steady state operation, a UPFC, as a passive component, must keep the capacitor voltage constant, i.e.:wherein,andthe output voltages of the parallel inverter and the series inverter respectively,andthe currents of the parallel inverter and the series inverter, respectively.

Thus, in steady state operating conditions, a UPFC can be represented by two branches of impedance in series with an ideal voltage source, with parallel branch currentsCan always be decomposed intoAndthe two components, the UPFC steady state equivalent circuit, are shown in FIG. 4.Andtwo components at the node voltageIn phase and vertical.The reactive component of the parallel branch is equivalent to STATCOM in function, and parallel reactive compensation is provided for the system;is the active component of the parallel branch current, and the function of the parallel branch current is to absorb or inject active power from or into the alternating current system so as to ensure direct current voltage v_dcIs constant, thereby realizing series voltage source360 degree adjustment of the phase. In this case, the electric field energy stored in the dc capacitor in the UPFC neither increases nor decreases, and thus the dc voltage is constant.

Due to the formula:the independent control variables are changed from 4 to 3, namely:

wherein,is the phase angle of the series voltage source; v_BmaxAnd I_qmaxIs a constant related to the rated capacity of the UPFC. The phasor diagram for stable operation of a UPFC is shown in fig. 5.

The UPFC main control functions in the control and parameter calculation of the unified power flow controller are voltage control, phase angle control and line reactance control. Wherein, voltage control mainly includes: if the reactive power of the parallel part of the UPFC is controlled independently, the UPFC is equivalent to a static synchronous compensator to provide reactive compensation at the moment, and the purpose of supporting the node voltage is achieved. The phase angle control mainly comprises: if the UPFC adopts a phase angle control mode, the active power required by the load is compensated by the injection voltage at the series side, and the transmission active power of the transmission line can be continuously regulated and controlled under the condition that the voltage phases at the two ends of the transmission line are not required to be regulated and controlled, so that the power flow direction and the power flow in the power system are economic and reasonable. The line reactance control mainly comprises: if the injected voltage vector of the series part is made perpendicular to the line current, then the UPFC now behaves as a series compensation device. The method can continuously regulate and control, can perform bidirectional compensation (increase and decrease voltage), does not cause LC oscillation under proper control, and is an advanced and effective advanced technology for regulating and controlling the node voltage of a power grid, compensating line inductance, enhancing the transmission power limit of a power system and improving the stability of the power system.

The combination of these functions can fully develop the powerful functions of the UPFC. Line reactance control and phase angle control are interrelated functions that can be integrated into a common controller to control line active and reactive power to desired levels. On the other hand, the parallel compensation part of the UPFC can execute an independent reactive compensation function to control the voltage, and can also be coordinated with a general controller to control the line power flow together. Several control functions of a UPFC can be switched from one function to another in real time. This functional flexibility makes UPFCs have great potential in addressing a variety of problems with power systems.

The equivalent circuit of the transmission line containing the Unified Power Flow Controller (UPFC) is shown in FIG. 6, under the condition of neglecting equivalent reactance of a series transformer of the UPFC, the capacity constraint problem of the UPFC is not considered, and the UPFC is decoupled from the power system by adopting a basic method of injecting power by an additional node. The algorithm can be conveniently combined with the traditional Newton method load flow calculation. In the calculation, because the UPFC can provide parallel compensation for the system independently of the series compensation, the voltage amplitude of a node connected with a UPFC parallel transformer can be controlled to be a fixed value, and the compensated reactive power can also be controlled to be a fixed value; series compensation of the UPFC can control two operating variables simultaneously, thus controlling the active and reactive power delivered by the line on which the UPFC is located to a constant value.

Let the UPFC control the line transmit power to: p_ml+jQ_ml＝P_c+jQ_c；

Wherein, P_cAnd Q_cWhen the maximum transmission power of the interconnection section formed by the interconnection lines of the interconnected network is the maximum, the active power and the reactive power between the node m and the node l are the maximum, and when the maximum transmission power of the interconnection section formed by the interconnection lines of the interconnected network is the constant power, the P is the maximum_cAnd Q_cIs a constant.

$P_{\mathrm{lm}}=(\frac{P_c^2+Q_c^2}{V_m^2}+b_{\mathrm{lm}0}^2{V}_m^2+2b_{\mathrm{lm}0}{Q}_c)r_{\mathrm{lm}}-P_c$

$\begin{array}{c}{Q}_{\mathrm{lm}}=-V_l{I}_q-V_l[(((1-b_{\mathrm{lm}0}{x}_{\mathrm{lm}})P_c+b_{\mathrm{lm}0}{r}_{\mathrm{lm}}{Q}_c)V_m^{-1}+b_{\mathrm{lm}0}^2{r}_{\mathrm{lm}}{V}_m)\sin {\mathrm{\θ}}_{\mathrm{lm}}-\\ \left(((b_{\mathrm{lm}0}{r}_{\mathrm{lm}}{P}_c-(1-b_{\mathrm{lm}0}{x}_{\mathrm{lm}})Q_c)V_m^{-1}-(2-b_{\mathrm{lm}0}{x}_{\mathrm{lm}})b_{\mathrm{lm}0}{V}_m)\right)\cos {\mathrm{\θ}}_{\mathrm{lm}}]\end{array}$

Wherein, middle P_lmAnd Q_lmRespectively the active power and the reactive power of the line between the nodes l and m; r is_lmAnd b_lm0Respectively, the resistance and susceptance of the line between nodes l and m; v_lAnd V_mThe voltages at nodes l and m, respectively; theta_lmIs the phase angle difference of the voltages across. The power drawn by the UPFC from node l may be expressed in terms of node voltage and branch power as a control parameter V for the UPFC_BAndindependently, the power drawn from node m via the line on which the UPFC is located is controlled by the UPFC to be constant P_cAnd Q_c. The power of the node m flowing out of the transmission line where the UPFC is located is as follows:

$P_{\mathrm{ml}}+j{Q}_{\mathrm{ml}}={\stackrel{\·}{V}}_m{(\frac{{\stackrel{\·}{V}}_m-{\stackrel{\·}{V}}_l}{r_{\mathrm{lm}}+j{x}_{\mathrm{lm}}}+j{b}_{\mathrm{lm}0})}^{*}-{\stackrel{\·}{V}}_m{\left(\frac{{\stackrel{\·}{V}}_B}{r_{\mathrm{lm}}+j{x}_{\mathrm{lm}}}\right)}^{*}=P_c+j{Q}_c$

order to

$P_f+j{Q}_f={\stackrel{\·}{V}}_m{(\frac{{\stackrel{\·}{V}}_m-{\stackrel{\·}{V}}_l}{r_{\mathrm{lm}}+j{x}_{\mathrm{lm}}}+j{b}_{\mathrm{lm}0})}^{*}$

Then:

$P_e+j{Q}_e=(P_c-P_f)+j(Q_c-Q_f)=-{\stackrel{\·}{V}}_m{\left(\frac{{\stackrel{\·}{V}}_B}{r_{\mathrm{lm}}+j{x}_{\mathrm{lm}}}\right)}^{*}$

the solution is:

$V_B=\frac{\sqrt{(P_e^2+Q_e^2)(r_{\mathrm{lm}}^2+x_{\mathrm{lm}}^2)}}{V_m}$

wherein, P_eAnd Q_eRespectively the active power and the reactive power of the line between the nodes l and m; r is_lmIs the line between nodes l and mThe resistance of the circuit; x is the number of_lmIs the inductive reactance of the line between nodes l and m; v_mIs the voltage of node m; theta_mIs the voltage phase of node m.

Therefore, a control parameter formula of the UPFC when the transmission power of the interconnection section formed by the interconnection lines of the interconnected power grid is maximum, namely the control parameter formula under the optimal control mode of the UPFC is obtained.

And S4, obtaining the control parameter values of all the unified power flow controllers in the target area according to the control parameter formula, and enabling the unified power flow controllers to operate in the optimal control mode through setting the control parameter values in the unified power flow controllers.

In the embodiment provided by the invention, the control parameter formula of the unified power flow controller is obtained when the transmission power of an interconnection section formed by interconnection lines of an interconnection power grid is maximum, the control parameter value under the optimal control mode of the UPFC can be obtained by obtaining all variables (active power, reactive power, voltage amplitude and voltage phase) of the unified power flow controller related in the control parameter formula, the system can obtain the optimal running state by setting the control parameter value, the coordination among the power flow controllers and among the multi-power flow controllers in the regional power grid is ensured, the cooperative control can be realized, and the unified scheduling and the economic running requirements of the system are facilitated. In one embodiment of the invention, one UPFC is respectively arranged on a connecting line A between Chongqings and a connecting line B between Chongqings, and the coordination control between the two UPFCs is comprehensively considered, so that the system obtains the optimal running state. According to the network information in the target area, the interconnected power grid in the target area is globally optimized, so that the transmission power of an interconnection section formed by interconnection lines of the interconnected power grid is maximum, and as shown in table 1-1, each physical quantity is represented by a per unit value.

Control targets for tables 1-1 UPFC

According to the control parameter formula of the UPFC, the data in the table 1-1 are utilized to obtain the control parameter value of the UPFC under the section as shown in the table 1-2.

	VB	φB
			B connecting line	0.0083	114.5419
A connecting line	0.013	－63.0929

Tables 1-2UPFC control parameter values

The system obtains the optimal running state by setting the control parameter value.

In summary, the cooperative control method for the power flow of the interconnected power grid provided by the invention determines the set of the external power grid, the boundary point and the target power grid by performing static equivalence analysis on the network, and modifies the boundary admittance array and the network equation to obtain the partitioned independent network. On the basis, the whole network is subjected to global optimization, network information of each node is read, and global optimization is carried out according to upper and lower limits of voltage, active output, reactive output and reactive compensation which need to be met by the system, so that the transmission power of an interconnection section formed by interconnection lines of an interconnected power grid is maximized, the global optimization is comprehensively considered, and the control capacity requirement of the power system on the power flow is met; in addition, the output voltage amplitude and the phase angle of a series converter of the UPFC are adjusted according to the maximum transmission power of an interconnection section formed by interconnection lines of an interconnected power grid to obtain a control parameter formula of the UPFC, the control parameter value of each UPFC is obtained according to the control parameter formula of the UPFC and relevant information, the system obtains the optimal running state through setting of the control parameter value, the coordination and consistency among the tidal current controllers in the regional power grid are guaranteed, the cooperative control can be realized, and the unified scheduling and the economic running requirements of the system are facilitated.

The power flow cooperative control method for the interconnected power grid provided by the invention is explained in detail above. Any obvious modifications thereof, which would occur to one skilled in the art without departing from the true spirit of the invention, would constitute a violation of the patent rights of the present invention and would bear corresponding legal responsibility.

Claims (3)

1. A power flow cooperative control method for interconnected power grids is characterized by comprising the following steps:

s1, performing static equivalence processing on the power grid boundary of the target area to enable other power grid parts connected with the target area to be equivalently stripped from the target area;

s2, reading network information in a target area and system information of each node, setting upper and lower limit constraints of each element according to system requirements, and obtaining a value range of each element which enables an interconnection section formed by interconnection lines of an interconnection network to have maximum transmission power, wherein when global optimization calculation is carried out, constraint conditions and inequality constraint conditions of constant power global optimization are simultaneously met;

establishing an optimization model solution according to the value range of each element to obtain the maximum transmission power of an interconnection section formed by interconnection lines of an interconnection power grid;

s3, taking the maximum transmission power of an interconnection section formed by interconnection lines of an interconnection network as a constant power, and determining a control parameter formula of the unified power flow controller as follows in a constant power control mode;

$V_B=\frac{\sqrt{(P_e^2+Q_e^2)(r_{lm}^2+x_{lm}^2)}}{V_m};$

wherein, V_BIs the voltage of the series voltage source,is the phase angle of a series voltage source, P_eAnd Q_eActive power and none of the line between nodes l and m, respectivelyWork power; r is_lmIs the resistance of the line between nodes l and m; x is the number of_jmIs the inductive reactance of the line between nodes l and m; v_mIs the voltage of node m; theta_mIs the voltage phase of node m;

and S4, obtaining the control parameter values of all unified power flow controllers in the target area according to the control parameter formula, and performing cooperative control on the unified power flow controllers by setting the control parameter values in the unified power flow controllers.

2. The power flow cooperative control method according to claim 1, characterized in that:

among the inequality constraints, the constraint conditions set for the tie lines of the interconnected power grid in the target area are as follows: the transmission power of an interconnection section formed by interconnection lines of an interconnection power grid takes the maximum active power as the upper limit on the premise of meeting the thermal stability limit of an N-1 single circuit line, wherein N is a positive integer.

3. The power flow cooperative control method according to claim 1, characterized in that:

in step S4, there are one or more unified power flow controllers.