CN105119269A - Random power flow calculation method taking regard of multiterminal unified power flow controller - Google Patents

Abstract

The invention relates to a random power flow calculation method taking regard of a multiterminal unified power flow controller (UPFC). Firstly a power flow calculation model is established for a power grid including a multiterminal unified power flow controller. An equivalent multiterminal injection power model is established according to a real installation condition of the UPFC. A Newton-Raphson method is employed to carry out the power flow calculation, and stable state operation points of the power grid are determined. Linearization calculation is carried out on a power grid power flow equation including the UPFC equivalent multiterminal injection power model at stable state operation points, and a Jacobian matrix is obtained. Secondly a random probability density function is established for various random factors in the power grid. After each order of a semi-invariant of each random variable is calculated and obtained, the semi-invariants corresponding to node voltages and line powers of the power grid are calculated based on a Jcobian matrix by using a semi-invariant method. Finally a probability density function of the node voltages and the line powers is obtained. The random power flow calculation of the power grid including the multiterminal UPFC is realized. The random power flow calculation method creates conditions for analyzing the influence of randomness of the power grid to the operation of the power grid.

Description

A kind of probabilistic loadflow computational methods considering Multi-terminal Unified Power Flow Controller

Technical field

The present invention relates to a kind of power system computation method, particularly one comprises the probabilistic loadflow computational methods of Multi-terminal Unified Power Flow Controller (UPFC), belongs to power system dispatching and runs field.

Background technology

Along with the fast development of device for high-power power electronic and control technology thereof, flexible AC transmission technology (FACTS) has played more and more important effect at electrical network.As the fast dynamic element of spy, different from traditional electric-controlled mechanical device, FACTS device can be in real time, fast, the state of regulating system smoothly, meet the needs of flexible control system trend, can when not changing the operation plan of topology of networks and generating set, the controllability of system load flow and voltage is increased substantially, transmission line can be made to run under the thermally-stabilised limit close to it, increase the security domain of existing power system operation, and reduce transmission losses, greatly reduce the reserve capacity of interconnected systems, give play to the economy of networking operation better.

THE UPFC (UPFC) is third generation FACTS element, also be the strongest, the most comprehensive thyristor control device, it to be combined the novel tidal current controller formed by the STATCOM (STATCOM) of shunt compensation and the Static Series Synchronous Compensator (SSSC) of series compensation, its function all can the series connection of continually varying alternating voltage be added in power transmission line phase voltage by an amplitude produced by converter and phase angle, can to distinguish or simultaneously to the active power of electric power system, reactive power, voltage carries out controlling and regulating, by controlling in real time and dynamic compensation AC transmission system, realize the accurate adjustment to Line Flow, improve the conveying capacity of circuit.

In view of UPFC has stronger Line Flow control ability, considerable influence will be brought to operation states of electric power system after input, therefore reply carries out modeling analysis in detail containing the electric power system of UPFC, to understand its influence degree to electric power system, this just proposes challenge to traditional power flow algorithm.Traditional power flow algorithm is not owing to counting the impact of UPFC, because of but a kind of analytical method based on node boundary condition, and the power flow algorithm containing UPFC is except having node boundary condition, also has control constraints condition, therefore will the feature being different from traditional power flow algorithm be presented when embody rule.And consider that electrical network Uncertain Stochastic calculation of tidal current directly depends on the result of calculation of certainty trend, therefore the probabilistic loadflow containing UPFC is calculated, should select from component models, how to take into account the aspect such as the impact of UPFC and concrete power flow algorithm enforcement to discuss in earnest, calculate effect to obtain best probabilistic loadflow.UPFC is as the strongest FACTS device, and not only controlling functions is abundant for it, and model structure is comparatively typical, discussing fully it, has certain universal significance by the probabilistic loadflow algorithm of analysis package containing various FACTS device.

Summary of the invention

The object of the invention is to propose a kind of probabilistic loadflow computational methods considering Multi-terminal Unified Power Flow Controller, set up equivalent multiterminal injecting power model according to the actual installation situation of UPFC, Load flow calculation is carried out to electrical network and obtains steady operation point; Secondly, random chance density function is set up to enchancement factor various in electrical network (as node load, wind energy turbine set, photovoltaic generation), utilize the probability density function of Cumulants method computing node voltage and line power, the final probabilistic loadflow realized containing multiterminal UPFC calculates.

For this reason, the present invention adopts following technical scheme:

Consider probabilistic loadflow computational methods for Multi-terminal Unified Power Flow Controller, comprise the following steps:

(1) according to the actual installation position of multiterminal UPFC, the steady-state model of multiterminal UPFC is set up;

(2) according to electric network data and the multiterminal UPFC steady-state model set up, set up electric network swim calculated data model, and adopt Newton-Raphson approach to carry out Load flow calculation, determine the steady operation point of electrical network;

(3) according to the steady operation point of electrical network, the electric network swim equation calculated containing multiterminal UPFC carries out linearization calculation, and obtains Jacobian matrix;

(4) set up the probability density function of load in electrical network, wind power and photovoltaic plant active power stochastic variable, and calculate each rank cumulant of stochastic variable;

(5) according to Cumulants method, utilize existing each rank cumulant of stochastic variable and each rank cumulant of Jacobian matrix computing node voltage and circuit active power and probability density function thereof, the final calculating realized containing multiterminal UPFC electrical network probabilistic loadflow.

Multiterminal UPFC has two or more series transformers to be arranged on different circuits simultaneously, and shares a shunt transformer.

Multiterminal UPFC steady-state model, takes equivalent injected power method to carry out modeling.

When multiterminal UPFC comprise two be arranged on series transformer on different circuit and a shunt transformer time, according to equivalent power injection method, the control action of UPFC to trend is transferred on the node of circuit both sides, place, be equivalent to: the series side of UPFC is arranged on circuit i-j and i-k respectively, uses controllable voltage source respectively with represent, side in parallel is arranged on bus i side, uses controllable current source represent

with be respectively the equivalence of UPFC in bus i, j and k side and inject apparent power, its specific formula for calculation is as follows:

$S_i^F={\stackrel{\·}{U}}_i{\stackrel{\·}{I}}_{sh}^{*}-{\stackrel{\·}{U}}_i{\[{\stackrel{\·}{U}}_{se1}(g_{ij}+{\mathrm{jb}}_{ij}+\frac{{\mathrm{jB}}_{c1}}{2})\]}^{*}-{\stackrel{\·}{U}}_i{\[{\stackrel{\·}{U}}_{se2}(g_{ik}+{\mathrm{jb}}_{ik}+\frac{{\mathrm{jB}}_{c2}}{2})\]}^{*}---\left(1\right)$

$S_j^F={\stackrel{\·}{U}}_j{\[{\stackrel{\·}{U}}_{se1}(g_{ij}+{\mathrm{jb}}_{ij})\]}^{*}---\left(2\right)$

$S_k^F={\stackrel{\·}{U}}_j{\[{\stackrel{\·}{U}}_{se2}(g_{ik}+{\mathrm{jb}}_{ik})\]}^{*}---\left(3\right)$

In formula, be respectively the voltage of node i, j; g _ij+ jb _ij, g _ik+ jb _ikbe respectively node i and the admittance between j, i and k; B _c1, B _c2be respectively the admittance over the ground of node i and j, i and k; * represent and get conjugate.

During Load flow calculation containing multiterminal UPFC, for the node not comprising UPFC in outlet, its power balance equation is such as formula shown in (8) and (9):

ΔP _m＝P _G,m-P _L,m-∑ _n∈mU _mU _n(G _mncosθ _mn+B _mnsinθ _mn)(8)

ΔQ _m＝Q _G,m-Q _L,m-∑ _n∈mU _mU _n(G _mnsinθ _mn-B _mncosθ _mn)(9)

In formula, Δ P _m, Δ Q _mbe respectively the meritorious of node m and reactive power deviation; P _g,m, Q _g,mbe respectively generated power and the reactive power of node m; P _l,m, Q _l,mbe respectively the meritorious of node m and load or burden without work; G _mn, B _mnthe real part of the corresponding admittance matrix of difference node m and n and imaginary part; U _m, U _nbe respectively the voltage magnitude of node m and n; θ _mnfor the phase angle difference of node m and n.

For the node installing UPFC in outlet, at least comprise node i, j, k, its power balance equation is such as formula shown in (10)-(15):

${\mathrm{\ΔP}}_i=P_{G,i}-P_{L,i}-{\mathrm{\Σ}}_{n\∈i}{U}_i{U}_n(G_{in}{\mathrm{cos\θ}}_{in}+B_{in}{\mathrm{sin\θ}}_{in})+\mathrm{Re}\left(S_i^F\right)---\left(10\right)$

${\mathrm{\ΔQ}}_i=Q_{G,i}-Q_{L,i}-{\mathrm{\Σ}}_{n\∈i}{U}_i{U}_n(G_{in}{\mathrm{sin\θ}}_{in}-B_{in}{\mathrm{cos\θ}}_{in})-\mathrm{Im}\left(S_i^F\right)---\left(11\right)$

${\mathrm{\ΔP}}_j=P_{G,j}-P_{L,j}-{\mathrm{\Σ}}_{n\∈j}{U}_j{U}_n(G_{jn}{\mathrm{cos\θ}}_{jn}+B_{jn}{\mathrm{sin\θ}}_{jn})+\mathrm{Re}\left(S_j^F\right)---\left(12\right)$

${\mathrm{\ΔQ}}_j=Q_{G,j}-Q_{L,j}-{\mathrm{\Σ}}_{n\∈j}{U}_j{U}_n(G_{jn}{\mathrm{sin\θ}}_{jn}-B_{jn}{\mathrm{cos\θ}}_{jn})-\mathrm{Im}\left(S_j^F\right)---\left(13\right)$

${\mathrm{\ΔP}}_k=P_{G,k}-P_{L,k}-{\mathrm{\Σ}}_{n\∈k}{U}_k{U}_n(G_{kn}{\mathrm{cos\θ}}_{kn}+B_{kn}{\mathrm{sin\θ}}_{kn})+\mathrm{Re}\left(S_k^F\right)---\left(14\right)$

${\mathrm{\ΔQ}}_k=Q_{G,k}-Q_{L,k}-{\mathrm{\Σ}}_{n\∈k}{U}_k{U}_n(G_{kn}{\mathrm{sin\θ}}_{kn}-B_{kn}{\mathrm{cos\θ}}_{kn})-Im\left(S_k^F\right)---\left(15\right)$

In formula, Re represents and gets real part, and Im represents and gets imaginary part, Δ P _i, Δ Q _i, Δ P _j, Δ Q _j, Δ P _k, Δ Q _kbe respectively the meritorious and reactive power deviation of node i, j, k; P _g,i, Q _g,i, P _g,j, Q _g,j, P _g,k, Q _g,kbe respectively node i, the generated power of j, k and reactive power; P _l,i, Q _l,i, P _l,j, Q _l,j, P _l,k, Q _l,kbe respectively the meritorious and load or burden without work of node i, j, k; G _in, B _in, G _jn, B _jn, G _kn, B _knthe respectively real part of node i and n, j and n, the corresponding admittance matrix of k and n and imaginary part; U _i, U _j, U _kbe respectively the voltage magnitude of node i, j, k; θ _in, θ _jn, θ _knfor the phase angle difference of node i and n, j and n, k and n.

The Multi-terminal Unified Power Flow Controller probabilistic loadflow computational methods that the present invention proposes, when achieving consideration load, generator and circuit randomness, probabilistic loadflow calculating is carried out to electrical network, effectively can analyze the control effects of Multi-terminal Unified Power Flow Controller for electric network swim, to the planning of actual electric network.Construction, operation have important practical significance.

The probabilistic loadflow computational methods of Multi-terminal Unified Power Flow Controller of the present invention (UPFC), for carrying out probabilistic loadflow calculating on the consideration various uncertain factor basis of electrical network, the probabilistic loadflow achieved containing multiterminal UPFC electrical network calculates, and creates condition for analyzing the impact of electrical network randomness on operation of power networks.

Accompanying drawing explanation

Fig. 1 is the electrical network probabilistic loadflow computational methods flow chart containing multiterminal UPFC of the present invention;

Fig. 2 is the power source model of UPFC;

Fig. 3 is the power injection model of UPFC.

Embodiment

The technological means realized for making the present invention, creation characteristic, reaching object and effect is easy to understand, below in conjunction with embodiment, setting forth the present invention further.

The present invention is a kind of probabilistic loadflow computational methods for Multi-terminal Unified Power Flow Controller (UPFC), for carrying out probabilistic loadflow calculating on the consideration various uncertain factor basis of electrical network.As shown in Figure 1, comprise the following steps:

(1) according to the actual installation position of multiterminal UPFC, the steady-state model of multiterminal UPFC is set up;

(2) according to electric network data and the multiterminal UPFC steady-state model set up, set up electric network swim calculated data model, and adopt Newton-Raphson approach to carry out Load flow calculation, determine the steady operation point of electrical network;

(3) according to the steady operation point of electrical network, linearization calculation is carried out to the electric network swim equation containing multiterminal UPFC, and obtains Jacobian matrix;

(4) set up the probability density function of load in electrical network, wind power and photovoltaic plant active power stochastic variable, and calculate each rank cumulant of stochastic variable;

(5) according to Cumulants method, utilize existing each rank cumulant of stochastic variable and each rank cumulant of Jacobian matrix computing node voltage and circuit active power and probability density function thereof, the final calculating realized containing multiterminal UPFC electrical network probabilistic loadflow.

In step (1), multiterminal UPFC steady-state model, takes equivalent injected power method to carry out modeling, and for two series transformers and a shunt transformer, equivalent-circuit model as shown in Figure 2.

Wherein, the series side of UPFC is arranged on circuit i-j and i-k respectively, uses controllable voltage source respectively with represent, side in parallel is arranged on bus i side, uses controllable current source represent.UPFC regulates realization to the regulating action of transmission line trend mainly through series electrical potential source, and the amplitude phase place of this series electrical potential source is all adjustable, controls the active power passed through on transmission line and reactive power thus; Parallel-current source ensures that the total meritorious exchange capacity of UPFC equipment and system is zero.

According to equivalent power injection method, the control action of UPFC to trend can be transferred on the node of circuit both sides, place, be equivalent to a kind of network transformation, equivalent model as shown in Figure 3.

In figure, with be respectively the equivalence of UPFC in bus i, j and k side and inject apparent power, its specific formula for calculation is as follows:

$S_i^F={\stackrel{\·}{U}}_i{\stackrel{\·}{I}}_{sh}^{*}-{\stackrel{\·}{U}}_i{\[{\stackrel{\·}{U}}_{se1}(g_{ij}+{\mathrm{jb}}_{ij}+\frac{{\mathrm{jB}}_{c1}}{2})\]}^{*}-{\stackrel{\·}{U}}_i{\[{\stackrel{\·}{U}}_{se2}(g_{ik}+{\mathrm{jb}}_{ik}+\frac{{\mathrm{jB}}_{c2}}{2})\]}^{*}---\left(16\right)$

$S_j^F={\stackrel{\·}{U}}_j{\[{\stackrel{\·}{U}}_{se1}(g_{ij}+{\mathrm{jb}}_{ij})\]}^{*}---\left(17\right)$

$S_k^F={\stackrel{\·}{U}}_j{\[{\stackrel{\·}{U}}_{se2}(g_{ik}+{\mathrm{jb}}_{ik})\]}^{*}---\left(18\right)$

The active power of UPFC device itself should meet: series electrical potential source equals the active power of parallel-current source from Systemic absorption to the active power that system is injected, and its equation is expressed as:

$\mathrm{Re}(-{\stackrel{\·}{U}}_i{\stackrel{\·}{I}}_{sh}^{*})=\mathrm{Re}\left({\stackrel{\·}{U}}_{se1}{\stackrel{\·}{I}}_{ij}^{*}\right)+\mathrm{Re}\left({\stackrel{\·}{U}}_{se2}{\stackrel{\·}{I}}_{ik}^{*}\right)---\left(19\right)$

Wherein, be respectively the voltage of node i, j; g _ij+ jb _ij, g _ik+ jb _iknode i and the admittance between j, i and k respectively; B _c1, B _c2be respectively the admittance over the ground of node i and j, i and k; for the conjugate of UPFC side in parallel equivalent current; for the conjugate of electric current between circuit i and j; for the conjugate of electric current between circuit i and k.

${\stackrel{\·}{I}}_{ij}=({\stackrel{\·}{U}}_i+{\stackrel{\·}{U}}_{se1})(g_{ij}+{\mathrm{jb}}_{ij}+{\mathrm{jB}}_{c1}/2)-{\stackrel{\·}{U}}_j(g_{ij}+{\mathrm{jb}}_{ij})---\left(20\right)$

${\stackrel{\·}{I}}_{ik}=({\stackrel{\·}{U}}_i+{\stackrel{\·}{U}}_{se2})(g_{ik}+{\mathrm{jb}}_{ik}+{\mathrm{jB}}_{c2}/2)-{\stackrel{\·}{U}}_j(g_{ik}+{\mathrm{jb}}_{ik})---\left(21\right)$

Formula (20), (21) are substituted into formula (19) respectively and arrange,

$\begin{array}{c}{U}_i{I}_{\mathrm{sh}}\cos ({\mathrm{\θ}}_i-{\mathrm{\θ}}_{\mathrm{sh}})+U_{\mathrm{se}1}^2{g}_{\mathrm{ij}}\\ +U_{\mathrm{se}1}{U}_i[\cos ({\mathrm{\θ}}_{\mathrm{se}1}-{\mathrm{\θ}}_i)g_{\mathrm{ij}}+\sin ({\mathrm{\θ}}_{\mathrm{se}1}-{\mathrm{\θ}}_i)(b_{\mathrm{ij}}+B_{c1}/2)]\\ -U_{\mathrm{se}1}{U}_j[\cos ({\mathrm{\θ}}_{\mathrm{se}1}-{\mathrm{\θ}}_j)g_{\mathrm{ij}}+\sin ({\mathrm{\θ}}_{\mathrm{se}1}-{\mathrm{\θ}}_j)b_{\mathrm{ij}}]\\ +U_{\mathrm{se}2}{U}_i[\cos ({\mathrm{\θ}}_{\mathrm{se}2}-{\mathrm{\θ}}_i)g_{\mathrm{ik}}+\sin ({\mathrm{\θ}}_{\mathrm{se}2}-{\mathrm{\θ}}_i)(b_{\mathrm{ik}}+B_{c2}/2)]\\ -U_{\mathrm{se}2}{U}_j[\cos ({\mathrm{\θ}}_{\mathrm{se}2}-{\mathrm{\θ}}_j)g_{\mathrm{ik}}+\sin ({\mathrm{\θ}}_{\mathrm{se}2}-{\mathrm{\θ}}_j)b_{\mathrm{ik}}]\\ =0\end{array}---\left(22\right)$

In formula: U _i, U _jfor the voltage magnitude of node i, j; θ _i, θ _jfor the voltage phase angle of node i, j; for the electric current between node i, j; for the electric current between node i, k; U _se1, U _se2for the voltage magnitude of series side equivalent source; θ _se1, θ _se2for the voltage phase angle of series side equivalent source; g _ij, b _ijfor real part and the imaginary part of admittance between node i and j; g _ik, b _ikfor real part and the imaginary part of admittance between node i and k; B _c1, B _c2be respectively the admittance over the ground of node i and j, i and k; I _sh, θ _shbe respectively side in parallel Injection Current amplitude and phase angle.

In step (2), during Load flow calculation containing multiterminal UPFC, for the node not comprising UPFC in outlet, its power balance equation is such as formula shown in (23) and (24):

ΔP _m＝P _G,m-P _L,m-∑ _n∈mU _mU _n(G _mncosθ _mn+B _mnsinθ _mn)(23)

ΔQ _m＝Q _G,m-Q _L,m-∑ _n∈mU _mU _n(G _mnsinθ _mn-B _mncosθ _mn)(24)

In formula, Δ P _m, Δ Q _mbe respectively the meritorious of node m and reactive power deviation; P _g,m, Q _g,mbe respectively generated power and the reactive power of node m; P _l,m, Q _l,mbe respectively the meritorious of node m and load or burden without work; G _mn, B _mnthe real part of the corresponding admittance matrix of difference node m and n and imaginary part; U _m, U _nbe respectively the voltage magnitude of node m and n; θ _mnfor the phase angle difference of node m and n;

For the node installing UPFC in outlet, with node i, j, k are example, and its power balance equation is such as formula shown in (25)-(30):

${\mathrm{\ΔP}}_i=P_{G,i}-P_{L,i}-{\mathrm{\Σ}}_{n\∈i}{U}_i{U}_n(G_{in}{\mathrm{cos\θ}}_{in}+B_{in}{\mathrm{sin\θ}}_{in})+\mathrm{Re}\left(S_i^F\right)---\left(25\right)$

${\mathrm{\ΔQ}}_i=Q_{G,i}-Q_{L,i}-{\mathrm{\Σ}}_{n\∈i}{U}_i{U}_n(G_{in}{\mathrm{sin\θ}}_{in}-B_{in}{\mathrm{cos\θ}}_{in})-\mathrm{Im}\left(S_i^F\right)---\left(26\right)$

${\mathrm{\ΔP}}_j=P_{G,j}-P_{L,j}-{\mathrm{\Σ}}_{n\∈j}{U}_j{U}_n(G_{jn}{\mathrm{cos\θ}}_{jn}+B_{jn}{\mathrm{sin\θ}}_{jn})+\mathrm{Re}\left(S_j^F\right)---\left(27\right)$

${\mathrm{\ΔQ}}_j=Q_{G,j}-Q_{L,j}-{\mathrm{\Σ}}_{n\∈j}{U}_j{U}_n(G_{jn}{\mathrm{sin\θ}}_{jn}-B_{jn}{\mathrm{cos\θ}}_{jn})-\mathrm{Im}\left(S_j^F\right)---\left(28\right)$

${\mathrm{\ΔP}}_k=P_{G,k}-P_{L,k}-{\mathrm{\Σ}}_{n\∈k}{U}_k{U}_n(G_{kn}{\mathrm{cos\θ}}_{kn}+B_{kn}{\mathrm{sin\θ}}_{kn})+\mathrm{Re}\left(S_k^F\right)---\left(29\right)$

${\mathrm{\ΔQ}}_k=Q_{G,k}-Q_{L,k}-{\mathrm{\Σ}}_{n\∈k}{U}_k{U}_n(G_{kn}{\mathrm{sin\θ}}_{kn}-B_{kn}{\mathrm{cos\θ}}_{kn})-Im\left(S_k^F\right)---\left(30\right)$

In formula, Re represents and gets real part, and Im represents and gets imaginary part, Δ P _i, Δ Q _i, Δ P _j, Δ Q _j, Δ P _k, Δ Q _kbe respectively the meritorious and reactive power deviation of node i, j, k; P _g,i, Q _g,i, P _g,j, Q _g,j, P _g,k, Q _g,kbe respectively node i, the generated power of j, k and reactive power; P _l,i, Q _l,i, P _l,j, Q _l,j, P _l,k, Q _l,kbe respectively the meritorious and load or burden without work of node i, j, k; G _in, B _in, G _jn, B _jn, G _kn, B _knthe respectively real part of node i and n, j and n, the corresponding admittance matrix of k and n and imaginary part; U _i, U _j, U _kbe respectively the voltage magnitude of node i, j, k; θ _in, θ _jn, θ _knfor the phase angle difference of node i and n, j and n, k and n.

Therefore, formula (16)-(19), (22)-(30) constitute the whole equations calculated containing multiterminal UPFC electric network swim.

In step (3), Newton-Raphson approach is adopted to carry out after Load flow calculation obtains system cloud gray model steady state point, carrying out to power flow equation the Jacobian matrix that linearisation obtains steady operation point to electrical network.After the cumulant of calculated load, wind power or photovoltaic stochastic variable, based on the cumulant of Cumulants method computing node voltage and circuit active power, and finally obtain probability density function, realize the calculating of probabilistic loadflow.

More than show and describe basic step of the present invention and computational methods and advantage of the present invention.The technical staff of the industry should understand; the present invention is not restricted to the described embodiments; what describe in above-described embodiment and specification just illustrates principle of the present invention; without departing from the spirit and scope of the present invention; the present invention also has various changes and modifications, and these changes and improvements all fall in the claimed scope of the invention.Application claims protection range is defined by appending claims and equivalent thereof.

Claims (6)

1. consider probabilistic loadflow computational methods for Multi-terminal Unified Power Flow Controller, it is characterized in that, comprise the following steps:

(1) according to the actual installation position of multiterminal UPFC, the steady-state model of multiterminal UPFC is set up;

(2) according to electric network data and the multiterminal UPFC steady-state model set up, set up electric network swim calculated data model, and adopt Newton-Raphson approach to carry out Load flow calculation, determine the steady operation point of electrical network;

(3) according to the steady operation point of electrical network, linearization calculation is carried out to the electric network swim equation containing multiterminal UPFC, and obtains Jacobian matrix;

(4) set up the probability density function of load in electrical network, wind power and photovoltaic plant active power stochastic variable, and calculate each rank cumulant of stochastic variable;

(5) according to Cumulants method, utilize existing each rank cumulant of stochastic variable and each rank cumulant of Jacobian matrix computing node voltage and circuit active power and probability density function thereof, the final calculating realized containing multiterminal UPFC electrical network probabilistic loadflow.

2. the probabilistic loadflow computational methods of consideration Multi-terminal Unified Power Flow Controller according to claim 1, is characterized in that, multiterminal UPFC has two or more series transformers to be arranged on different circuits simultaneously, and share a shunt transformer.

3. the probabilistic loadflow computational methods of consideration Multi-terminal Unified Power Flow Controller according to claim 2, is characterized in that, multiterminal UPFC steady-state model, take equivalent injected power method to carry out modeling.

4. the probabilistic loadflow computational methods of the consideration Multi-terminal Unified Power Flow Controller according to Claims 2 or 3, it is characterized in that, when multiterminal UPFC comprise two be arranged on series transformer on different circuit and a shunt transformer time, according to equivalent power injection method, the control action of UPFC to trend is transferred on the node of circuit both sides, place, be equivalent to: the series side of UPFC is arranged on circuit i-j and i-k respectively, uses controllable voltage source respectively with represent, side in parallel is arranged on bus i side, uses controllable current source represent;

with be respectively the equivalence of UPFC in bus i, j and k side and inject apparent power, its specific formula for calculation is as follows:

$S_i^F={\stackrel{\·}{U}}_i{\stackrel{\·}{I}}_{sh}^{*}-{\stackrel{\·}{U}}_i{\[{\stackrel{\·}{U}}_{se1}(g_{ij}+{\mathrm{jb}}_{ij}+\frac{{\mathrm{jB}}_{c1}}{2})\]}^{*}-{\stackrel{\·}{U}}_i{\[{\stackrel{\·}{U}}_{se2}(g_{ik}+{\mathrm{jb}}_{ik}+\frac{{\mathrm{jB}}_{c2}}{2})\]}^{*}---\left(1\right)$

$S_j^F={\stackrel{\·}{U}}_j{\[{\stackrel{\·}{U}}_{se1}(g_{ij}+{\mathrm{jb}}_{ij})\]}^{*}---\left(2\right)$

$S_k^F={\stackrel{\·}{U}}_j{\[{\stackrel{\·}{U}}_{se2}(g_{ik}+{\mathrm{jb}}_{ik})\]}^{*}---\left(3\right)$

In formula, be respectively the voltage of node i, j; g _ij+ jb _ij, g _ik+ jb _ikbe respectively node i and the admittance between j, i and k; B _c1, B _c2be respectively the admittance over the ground of node i and j, i and k; * represent and get conjugate.

5. the probabilistic loadflow computational methods of consideration Multi-terminal Unified Power Flow Controller according to claim 4, it is characterized in that, during Load flow calculation containing multiterminal UPFC, for the node not comprising UPFC in outlet, its power balance equation is such as formula shown in (8) and (9):

ΔP _m＝P _G,m-P _L,m-∑ _n∈mU _mU _n(G _mncosθ _mn+B _mnsinθ _mn)(8)

ΔQ _m＝Q _G,m-Q _L,m-∑ _n∈mU _mU _n(G _mnsinθ _mn-B _mncosθ _mn)(9)

In formula, Δ P _m, Δ Q _mbe respectively the meritorious of node m and reactive power deviation; P _g,m, Q _g,mbe respectively generated power and the reactive power of node m; P _l,m, Q _l,mbe respectively the meritorious of node m and load or burden without work; G _mn, B _mnthe real part of the corresponding admittance matrix of difference node m and n and imaginary part; U _m, U _nbe respectively the voltage magnitude of node m and n; θ _mnfor the phase angle difference of node m and n.

6. the probabilistic loadflow computational methods of consideration Multi-terminal Unified Power Flow Controller according to claim 5, it is characterized in that, for the node installing UPFC in outlet, at least comprise node i, j, k, its power balance equation is such as formula shown in (10)-(15):

${\mathrm{\ΔP}}_i=P_{G,i}-P_{L,i}-{\mathrm{\Σ}}_{n\∈i}{U}_i{U}_n(G_{in}{\mathrm{cos\θ}}_{in}+B_{in}{\mathrm{sin\θ}}_{in})+\mathrm{Re}\left(S_i^F\right)---\left(10\right)$

${\mathrm{\ΔQ}}_i=Q_{G,i}-Q_{L,i}-{\mathrm{\Σ}}_{n\∈i}{U}_i{U}_n(G_{in}{\mathrm{sin\θ}}_{in}-B_{in}{\mathrm{cos\θ}}_{in})-Im\left(S_i^F\right)---\left(11\right)$

${\mathrm{\ΔP}}_j=P_{G,j}-P_{L,j}-{\mathrm{\Σ}}_{n\∈j}{U}_j{U}_n(G_{jn}{\mathrm{cos\θ}}_{jn}+B_{jn}{\mathrm{sin\θ}}_{jn})+\mathrm{Re}\left(S_j^F\right)---\left(12\right)$

${\mathrm{\ΔQ}}_j=Q_{G,j}-Q_{L,j}-{\mathrm{\Σ}}_{n\∈j}{U}_j{U}_n(G_{jn}{\mathrm{sin\θ}}_{jn}-B_{jn}{\mathrm{cos\θ}}_{jn})-Im\left(S_j^F\right)---\left(13\right)$

${\mathrm{\ΔP}}_k=P_{G,k}-P_{L,k}-{\mathrm{\Σ}}_{n\∈k}{U}_k{U}_n(G_{kn}{\mathrm{cos\θ}}_{kn}+B_{kn}{\mathrm{sin\θ}}_{kn})+\mathrm{Re}\left(S_k^F\right)---\left(14\right)$

${\mathrm{\ΔQ}}_k=Q_{G,k}-Q_{L,k}-{\mathrm{\Σ}}_{n\∈k}{U}_k{U}_n(G_{kn}{\mathrm{sin\θ}}_{kn}-B_{kn}{\mathrm{cos\θ}}_{kn})-Im\left(S_k^F\right)---\left(15\right)$

In formula, Re represents and gets real part, and Im represents and gets imaginary part, Δ P _i, Δ Q _i, Δ P _j, Δ Q _j, Δ P _k, Δ Q _kbe respectively the meritorious and reactive power deviation of node i, j, k; P _g,i, Q _g,i, P _g,j, Q _g,j, P _g,k, Q _g,kbe respectively node i, the generated power of j, k and reactive power; P _l,i, Q _l,i, P _l,j, Q _l,j, P _l,k, Q _l,kbe respectively the meritorious and load or burden without work of node i, j, k; G _in, B _in, G _jn, B _jn, G _kn, B _knthe respectively real part of node i and n, j and n, the corresponding admittance matrix of k and n and imaginary part; U _i, U _j, U _kbe respectively the voltage magnitude of node i, j, k; θ _in, θ _jn, θ _knfor the phase angle difference of node i and n, j and n, k and n.