CN102879668B - Asymmetric fault analysis method for power distribution network including inverted distribution type power supply - Google Patents

Abstract

The invention discloses an asymmetric fault analysis method for a power distribution network including an inverted distribution type power supply. The asymmetric fault analysis method comprises the steps as follows: firstly, calculating a voltage amplitude value UPCC of a point of common coupling PCC when the power distribution network runs normally in combination with a fault through control strategy and an output characteristic of the distribution type power supply; and secondly, building an equation set of a positive sequence voltage amplitude value U+<PCC.f> of the PCC when the power distribution network has a fault to calculate a positive sequence voltage of the PCC when the power distribution network has the fault so as to finish fault analysis of the power distribution network including the inverted distribution type power supply. Compared with the prior art, the accuracy of fault analysis is improved.

Description

The asymmetric fault analytical approach of distribution network comprising inverse distributed power

Technical field

The present invention relates to power system fault analysis method, particularly the asymmetric fault analytical approach of distribution network comprising inverse distributed power.

Background technology

Symmetrical component method is that asymmetric fault is analyzed topmost method, for traditional synchronous motor, can adopt voltage source equivalence, and can adopt impedance equivalence in positive sequence network in negative sequence network.But inverse distributed power is completely different from traditional synchronous motor type of power, its output characteristics is determined by its control strategy completely under asymmetric fault condition, all can not adopt traditional synchronous motor Equivalent Model in positive and negative sequence network.Therefore, existing failure analysis methods will inevitably produce larger error.For realizing the asymmetric fault Accurate Analysis of distribution network comprising inverse distributed power, must be improved from the Equivalent Model of inverse type power supply and distribution network failure analytical model.

Summary of the invention

In order to overcome the above-mentioned shortcoming and deficiency of prior art, the present invention is directed to the inverse distributed power of positive-sequence component control, propose to take into account the power distribution network asymmetric fault analytical approach of fault traversing control strategy and output characteristics, realized the Accurate Analysis of the asymmetric fault of distribution network comprising inverse distributed power.

Object of the present invention is achieved through the following technical solutions: the asymmetric fault analytical approach of distribution network comprising inverse distributed power, comprises the following steps (the each variable in following step all represents perunit value):

The voltage magnitude U of the common connecting point (PCC) when S1 calculating power distribution network normally moves _pCC;

Compound sequence network when S2 sets up distribution network failure, distributed power source is only included in positive sequence network, the positive sequence voltage amplitude of the PCC while setting up distribution network failure solving equation group, specifically comprise the following steps:

The nodal voltage equation when compound sequence network of S21 during according to distribution network failure obtains fault:

$\left[Y^{\&prime;}\right]{\stackrel{\&CenterDot;}{U}}_f={\stackrel{\&CenterDot;}{I}}_f---\left(1\right)$

Wherein, $\left[Y^{\&prime;}\right]=\left[\begin{array}{cccc}{Y^{\&prime;}}_{11}& {Y^{\&prime;}}_{12}& \&CenterDot;\&CenterDot;\&CenterDot;& {Y^{\&prime;}}_{1m}\\ {Y^{\&prime;}}_{21}& {Y^{\&prime;}}_{22}& \&CenterDot;\&CenterDot;\&CenterDot;& {Y^{\&prime;}}_{2m}\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ {Y^{\&prime;}}_{m1}& {Y^{\&prime;}}_{m2}& \&CenterDot;\&CenterDot;\&CenterDot;& {Y^{\&prime;}}_{\mathrm{mm}}\end{array}\right]$ Bus admittance matrix while representing fault; Diagonal element Y _iiself-admittance during for node i fault, its value is connected to all branch road admittance sums of node i while equaling fault; Off-diagonal element Y ' _ijfor transadmittance when fault between node i, j, in the time there is branch road between node i, j, Y ' _ijequal to be directly connected in the negative value of the branch road admittance between node i, j; In the time there is not branch road between node i, j, Y ' _ij=0;

${\stackrel{\&CenterDot;}{U}}_f=\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_{1\&CenterDot;f}\\ {\stackrel{\&CenterDot;}{U}}_{2\&CenterDot;f}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{U}}_{\mathrm{PCC}\&CenterDot;f}^{+}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{U}}_{\mathrm{PCC}\&CenterDot;f}^{-}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{U}}_{m\&CenterDot;f}\end{array}\right]$ Node voltage while representing fault, wherein the positive and negative sequence voltage of PCC while being respectively fault;

${\stackrel{\&CenterDot;}{I}}_f=\left[\begin{array}{c}{\stackrel{\&CenterDot;}{I}}_{1\&CenterDot;f}\\ {\stackrel{\&CenterDot;}{I}}_{2\&CenterDot;f}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{I}}_{\mathrm{DG}\&CenterDot;f}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{I}}_{m\&CenterDot;f}\end{array}\right]$ The Injection Current of node while representing fault, wherein distributed power source during for fault (DG) injects the electric current of PCC;

be expressed as: ${\stackrel{\&CenterDot;}{I}}_{\mathrm{DG}\&CenterDot;f}=I_{d\&CenterDot;f}-{\mathrm{jI}}_{q\&CenterDot;f}---\left(2\right)$

Wherein, $\left\{\begin{array}{c}{I}_{d\&CenterDot;f}=P_{\left(0\right)}/U_{\mathrm{PCC}\&CenterDot;f}^{+}\\ I_{q\&CenterDot;f}=I_{q\left(0\right)}+k_q(U_{\mathrm{PCC}}-U_{\mathrm{PCC}\&CenterDot;f}^{+})\end{array}\right.$

In formula, I _df, I _qfdistributed power source output active current and reactive current while representing fault respectively; P ₍₀₎, I _{q (0)}represent respectively active power and the reactive current of normal motion time cloth formula power supply output, q ₍₀₎represent the reactive power of normal motion time cloth formula power supply output, k _qrepresent coefficient;

S22 carries out linear transformation to formula (1), obtains solving equation group;

S3 solves

S4 solves I _df, I _qf;

S5 defines I _ad=I _df+ I _qf, and judge I _adwhether exceed inverter rated current I _vSCnif, do not exceed and carry out step S6, otherwise, I made _df=I _vSCn-I _qf, by I _df, I _qfexpression formula substitution formula (1), and recalculate after carry out step S6;

S6 utilizes formula (1) to calculate in remove outer node voltage;

S7 is according to the branch current between following formula computing node j and node k:

${\stackrel{\&CenterDot;}{I}}_{\mathrm{jk}\&CenterDot;f}=\frac{{\stackrel{\&CenterDot;}{U}}_{i\&CenterDot;f}-{\stackrel{\&CenterDot;}{U}}_{k\&CenterDot;f}}{Z_{\mathrm{jk}}}$

Wherein, z _jkrepresent respectively branch current and branch impedance between node j and k, the voltage of node j, k while representing distribution network failure respectively.

The voltage magnitude U of PCC when calculating power distribution network described in step S1 and normally moving _pCC, specifically comprise the following steps:

Nodal voltage equation when power distribution network equal-value map is normally moved when the normal operation of S11 basis:

$\left[Y\right]\stackrel{\&CenterDot;}{U}=\stackrel{\&CenterDot;}{I}$

Wherein, $\left[Y\right]=\left[\begin{array}{cccc}{Y}_{11}& Y_{12}& \&CenterDot;\&CenterDot;\&CenterDot;& Y_{1n}\\ Y_{21}& Y_{22}& \&CenterDot;\&CenterDot;\&CenterDot;& Y_{2n}\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ Y_{n1}& Y_{n2}& \&CenterDot;\&CenterDot;\&CenterDot;& Y_{\mathrm{nn}}\end{array}\right]$ Bus admittance matrix while representing normal operation; Diagonal element Y _ijself-admittance while normally operation for node i, its value equals to be connected to while normally operation all branch road admittance sums of node i; Off-diagonal element Y _ijfor transadmittance when normal operation between node i, j, in the time there is branch road between node i, j, Y _ijequal to be directly connected in the negative value of the branch road admittance between node i, j; In the time there is not branch road between node i, j, Y _ij=0;

$\stackrel{\&CenterDot;}{U}=\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_1\\ {\stackrel{\&CenterDot;}{U}}_2\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{U}}_{\mathrm{PCC}}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{U}}_n\end{array}\right]$ Node voltage while representing normal operation, the voltage of PCC during for normal operation;

$\stackrel{\&CenterDot;}{I}=\left[\begin{array}{c}{\stackrel{\&CenterDot;}{I}}_1\\ {\stackrel{\&CenterDot;}{I}}_2\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{I}}_{\mathrm{DG}}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{I}}_n\end{array}\right]$ The Injection Current of node while representing normal operation, during for normal operation, DG injects the electric current of PCC node;

S12 tries to achieve according to nodal voltage equation then take absolute value and obtain U _pCC.

Compared with prior art, the present invention has the following advantages and beneficial effect: the present invention is by taking into account inverse distributed power control strategy and output characteristics, set up new distributed power source transient state Equivalent Model, can reflect more truly the fault current characteristics of distributed power source; Set up on this basis new distribution network failure analytical model, improved the accuracy of fault analysis.The lectotype selection that this method is distribution network comprising inverse distributed power and the protection aspect such as adjust provides the foundation of science, has very strong practicality in engineering practice.

Brief description of the drawings

Fig. 1 is the power distribution network line chart of embodiments of the invention.

Fig. 2 is the process flow diagram of the asymmetric fault analytical approach of the distribution network comprising inverse distributed power of embodiments of the invention.

Fig. 3 is the compound sequence network figure when distribution network failure shown in Fig. 1 in embodiments of the invention.

Embodiment

Below in conjunction with embodiment and accompanying drawing, the present invention is described in further detail, but embodiments of the present invention are not limited to this.

Embodiment

The present embodiment, taking the power distribution network shown in Fig. 1 as example, adopts the asymmetric fault analytical approach of distribution network comprising inverse distributed power of the present invention to carry out fault analysis, as shown in Figure 2, comprises the following steps:

The voltage magnitude U of PCC when S1 calculating power distribution network normally moves _pCC, specifically comprise the following steps:

Nodal voltage equation when power distribution network equal-value map is normally moved when the normal operation of S11 basis:

$\left[Y\right]\stackrel{\&CenterDot;}{U}=\stackrel{\&CenterDot;}{I}$

Nodal voltage equation while normally operation in the present embodiment is:

$\left[\begin{array}{cc}\frac{1}{Z_s}+\frac{1}{Z_{L1}}& -\frac{1}{L_1}\\ -\frac{1}{Z_{L1}}& \frac{1}{Z_{L1}}+\frac{1}{Z_{L2}}\end{array}\right]\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_M\\ {\stackrel{\&CenterDot;}{U}}_{\mathrm{PCC}}\end{array}\right]=\left[\begin{array}{c}\frac{{\stackrel{\&CenterDot;}{E}}_s}{Z_s}\\ {\stackrel{\&CenterDot;}{I}}_{\mathrm{DG}}\end{array}\right]$

Wherein the self-admittance of node M, PCC while being respectively normal operation, for the transadmittance between node M, PCC; Z _s, Z _l1, Z _l2represent respectively equivalent impedance, the L1 impedance of PCC lines upstream and the circuit L2 impedance of PCC downstream of system; represent system equivalent electromotive force, value is distributed power source rated current; the voltage of node M during for normal operation; the voltage of PCC during for normal operation; the electric current of ordering for injecting M.

S12 tries to achieve according to nodal voltage equation then take absolute value and obtain U _pCC;

Compound sequence network (as shown in Figure 3) when S2 sets up distribution network failure, distributed power source is only included in positive sequence network, the positive sequence voltage of the PCC while setting up electric network fault solving equation group, concrete steps are as follows:

The nodal voltage equation when compound sequence network of S21 during according to distribution network failure obtains fault:

$\left[Y^{\&prime;}\right]{\stackrel{\&CenterDot;}{U}}_f={\stackrel{\&CenterDot;}{I}}_f---\left(1\right)$

Wherein, $\left[Y^{\&prime;}\right]=\left[\begin{array}{cccc}{Y^{\&prime;}}_{11}& {Y^{\&prime;}}_{12}& \&CenterDot;\&CenterDot;\&CenterDot;& {Y^{\&prime;}}_{1m}\\ {Y^{\&prime;}}_{21}& {Y^{\&prime;}}_{22}& \&CenterDot;\&CenterDot;\&CenterDot;& {Y^{\&prime;}}_{2m}\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ {Y^{\&prime;}}_{m1}& {Y^{\&prime;}}_{m2}& \&CenterDot;\&CenterDot;\&CenterDot;& {Y^{\&prime;}}_{\mathrm{mm}}\end{array}\right]$ The admittance matrix of node while representing fault; Diagonal element Y _iiself-admittance during for node i fault, its value is connected to all branch road admittance sums of node i while equaling fault; Off-diagonal element Y ' _ijfor transadmittance when fault between node i, j, in the time there is branch road between node i, j, Y ' _ijequal to be directly connected in the negative value of the branch road admittance between node i, j, in the time there is not branch road between node i, j, Y ' _ij=0;

? $\left[\begin{array}{ccc}\frac{1}{Z_s}+\frac{1}{Z_{L1}}& -\frac{1}{Z_{L1}}& 0\\ -\frac{1}{Z_{L1}}& \frac{1}{Z_{L1}}+\frac{1}{2\mathrm{\&beta;}{Z}_{L2}}& -\frac{1}{2\mathrm{\&beta;}{Z}_{L2}}\\ 0& -\frac{1}{2\mathrm{\&beta;}{Z}_{L2}}& \frac{1}{2\mathrm{\&beta;}{Z}_{L2}}+\frac{1}{Z_s}+\frac{1}{Z_{L1}}\end{array}\right]\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_{M\&CenterDot;f}\\ {\stackrel{\&CenterDot;}{U}}_{\mathrm{PCC}\&CenterDot;f}^{+}\\ {\stackrel{\&CenterDot;}{U}}_{\mathrm{PCC}\&CenterDot;f}^{-}\end{array}\right]=\left[\begin{array}{c}\frac{{\stackrel{\&CenterDot;}{E}}_s}{Z_s}\\ {\stackrel{\&CenterDot;}{I}}_{\mathrm{DG}\&CenterDot;f}\\ 0\end{array}\right]$

Wherein the self-admittance of node M, PCC positive sequence voltage node, PCC negative sequence voltage node while being respectively fault; transadmittance during for fault between node M, PCC positive sequence voltage node; , represent the transadmittance between PCC positive sequence voltage node and PCC negative sequence voltage node, β is the abort situation being illustrated in circuit L2, and value is 0 ~ 100%; the positive and negative sequence voltage of PCC while being respectively fault; during for fault, DG injects the electric current of PCC; According to distributed power source control strategy, be expressed as:

${\stackrel{\&CenterDot;}{I}}_{\mathrm{DG}\&CenterDot;f}=I_{d\&CenterDot;f}-{\mathrm{jI}}_{q\&CenterDot;f}---\left(2\right)$

Wherein, $\left\{\begin{array}{c}{I}_{d\&CenterDot;f}=P_{\left(0\right)}/U_{\mathrm{PCC}\&CenterDot;f}^{+}\\ I_{q\&CenterDot;f}=I_{q\left(0\right)}+k_q(U_{\mathrm{PCC}}-U_{\mathrm{PCC}\&CenterDot;f}^{+})\end{array}\right.$

In formula, i _df, I _qffault current, active current and the reactive current of distributed power source output while representing fault respectively; P ₍₀₎, I _{q (0)}represent respectively active power and the reactive current of normal motion time cloth formula power supply output, q ₍₀₎represent the reactive power of normal motion time cloth formula power supply output, k _qrepresent coefficient;

S22 carries out linear transformation to formula (1), obtains solving equation group, be specially:

With voltage-phase is benchmark, ${\stackrel{\&CenterDot;}{E}}_s=E_s(\cos \mathrm{\&alpha;}+j\sin \mathrm{\&alpha;}),$ Obtain solving equation group:

$\left\{\begin{array}{c}a{\left(U_{\mathrm{PCC}\&CenterDot;f}^{+}\right)}^2+e{U}_{\mathrm{PCC}\&CenterDot;f}^{+}-c=E_s{U}_{\mathrm{PCC}\&CenterDot;f}^{+}\cos \mathrm{\&alpha;}\\ b{\left(U_{\mathrm{PCC}\&CenterDot;f}^{+}\right)}^2+f{U}_{\mathrm{PCC}\&CenterDot;f}^{+}-d=E_s{U}_{\mathrm{PCC}\&CenterDot;f}^{+}\sin \mathrm{\&alpha;}\end{array}\right.$

In formula, a+jb=[1/ (2 β Z _l2+ Z _s+ Z _l1)+1/ (Z _s+ _l1)-jk _q/ U _n] (Z _s+ Z _l1), c+jd=U _pCCi _{d (0)}(Z _s+ Z _l1), e+jf=j (I _{q (0)}+ k _qu _pCC/ U _n) (Z _s+ Z _l1);

S3 solves

S4 solves I _df, I _qf;

S5 defines I _ad=I _df+ I _qf, and judge I _adwhether exceed inverter rated current I _vACnif, do not exceed and carry out step S6, otherwise, I made _df=I _vSCn-I _qf, by I _df, I _qfexpression formula substitution formula (1) and formula (2), and recalculate after carry out step S6;

Wherein, recalculate process as follows:

By I _df, I _qfexpression formula substitution formula (1) and formula (2), obtain solving equation group:

$\left\{\begin{array}{c}{U}_{\mathrm{PCC}\&CenterDot;f}^{+}(a-K_q/U_n)c{E}_s\cos \mathrm{\&alpha;}+d{E}_s\sin \mathrm{\&alpha;}=I_{\max }-(I_{q\left(0\right)}+K_q{U}_{\mathrm{PCC}\&CenterDot;f}^{+}/U_n)\\ U_{\mathrm{PCC}\&CenterDot;f}^{+}(b-K_q/U_n)-d{E}_s\cos \mathrm{\&alpha;}-c{E}_s\sin \mathrm{\&alpha;}=-(I_{q\left(0\right)}{K}_q{U}_{\mathrm{PCC}}/U_n)\end{array}\right.$

In formula, a+jb=1/ (2 β Z _l2+ Z _s+ Z _l1)+1/ (Z _s+ Z _l1), c+jd=1/ (Z _s+ Z _l1); S6 utilizes formula (1) to calculate in remove outer node voltage;

S7 is according to the branch current between following formula computing node j and k:

${\stackrel{\&CenterDot;}{I}}_{\mathrm{jk}\&CenterDot;f}=\frac{{\stackrel{\&CenterDot;}{U}}_{i\&CenterDot;f}-{\stackrel{\&CenterDot;}{U}}_{k\&CenterDot;f}}{Z_{\mathrm{jk}}}$

Wherein, z _jkrepresent respectively branch current and branch impedance between node j and k, the voltage of node j, k while representing distribution network failure respectively.

In Fig. 1 of the present embodiment, the equivalent impedance Z of distribution network system _sfor 1.3j (Ω), the equivalent impedance Z of circuit L1 _l1, L2 equivalent impedance Z _l2be respectively 1.18+3.56j (Ω), 0.59+1.78j (Ω), distributed power source rated capacity and inverter interface rated capacity are respectively 4MW, 8MVA, k _qbe 2.Can obtain I by above-mentioned condition _vSCn=0.46kA.The meritorious ratings that is output as of distributed power source before fault, is idlely output as zero.

Enumerating two kinds of different short circuit condition is below explained:

Situation 1:

Two-phase short-circuit fault occurs in L2 line end, i.e. β=100% carries out step S1 ~ S4, calculates value be 7.26kV, U _pCCfor 10.1kV.By U _pCC, can obtain I _df, I _qf, I _dGfbe respectively 0.32kA, 0.13kA, 0.35kA.Due to I _df+ I _qf<I _vSCn, by I _df, I _qfwhen substitution distribution network failure, nodal voltage equation can be tried to achieve for 4.10kV, be respectively 0.365kA, 0.48kA, be all 0.48kA.

Situation 2:

Two-phase short-circuit fault occurs in L2 circuit 70% place, i.e. β=70% carries out step S1 ~ S4, and obtains solving equation group, calculates value be 6.92kV, U _pCCfor 10.1kV.By U _pCC, can obtain I _df, I _qfbe respectively 0.33kA, 0.14kA.Due to I _df+ I _qf>I _vSCn, recalculate I _df, I _dGffor 0.32kA, 0.35kA.Finally try to achieve for 4.10kV, be respectively 0.39kA, 0.52kA, be all 0.52Ka.

Above-described embodiment is preferably embodiment of the present invention; but embodiments of the present invention are not limited by the examples; other any do not deviate from change, the modification done under Spirit Essence of the present invention and principle, substitutes, combination, simplify; all should be equivalent substitute mode, within being included in protection scope of the present invention.

Claims (1)

1. the asymmetric fault analytical approach of distribution network comprising inverse distributed power, is characterized in that, comprises the following steps:

The voltage magnitude U of common connecting point PCC when S1 calculating power distribution network normally moves _pCC, be specially:

Nodal voltage equation when power distribution network equal-value map is normally moved when the normal operation of S11 basis:

$\left[Y\right]\stackrel{.}{U}=\stackrel{.}{I}$

Wherein, $\left[Y\right]=\left[\begin{array}{cccc}{Y}_{11}& Y_{12}& ...& Y_{1n}\\ Y_{21}& Y_{22}& ...& Y_{2n}\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ Y_{n1}& Y_{n2}& ...& Y_{\mathrm{nn}}\end{array}\right],$ Bus admittance matrix while representing normal operation; Diagonal element Y _iiself-admittance while normally operation for node i, its value equals to be connected to while normally operation all branch road admittance sums of node i; Off-diagonal element Y _ijfor transadmittance when normal operation between node i, j, in the time there is branch road between node i, j, Y _ijequal to be directly connected in the negative value of the branch road admittance between node i, j; In the time there is not branch road between node i, j, Y _ij=0;

$\stackrel{\&CenterDot;}{U}=\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_1\\ {\stackrel{\&CenterDot;}{U}}_2\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{U}}_{\mathrm{PCC}}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{U}}_n\end{array}\right]$ Node voltage while representing normal operation, the voltage of common connecting point PCC during for normal operation;

$\stackrel{\&CenterDot;}{I}=\left[\begin{array}{c}{\stackrel{\&CenterDot;}{I}}_1\\ {\stackrel{\&CenterDot;}{I}}_2\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{I}}_{\mathrm{DG}}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{I}}_n\end{array}\right]$ The Injection Current of node while representing normal operation, for the electric current of normal motion time cloth formula power supply injection common connecting point PCC node;

S12 tries to achieve according to nodal voltage equation then take absolute value and obtain U _pCC;

Compound sequence network when S2 sets up distribution network failure, distributed power source is only included in positive sequence network, the positive sequence voltage amplitude of the common connecting point PCC while setting up distribution network failure solving equation group, specifically comprise the following steps:

The nodal voltage equation when compound sequence network of S21 during according to distribution network failure obtains fault:

$\left[Y^{\&prime;}\right]{\stackrel{\&CenterDot;}{U}}_f={\stackrel{\&CenterDot;}{I}}_f---\left(1\right)$

Wherein, $\left[Y^{\&prime;}\right]=\left[\begin{array}{cccc}{Y^{\&prime;}}_{11}& {Y^{\&prime;}}_{12}& ...& {Y^{\&prime;}}_{1m}\\ {Y^{\&prime;}}_{21}& {Y^{\&prime;}}_{22}& ...& {Y^{\&prime;}}_{2m}\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ \&CenterDot;& \&CenterDot;& & \&CenterDot;\\ {Y^{\&prime;}}_{m1}& {Y^{\&prime;}}_{m2}& ...& {Y^{\&prime;}}_{\mathrm{mm}}\end{array}\right]$ Bus admittance matrix while representing fault; Diagonal element Y' _iiself-admittance during for node i fault, its value is connected to all branch road admittance sums of node i while equaling fault; Off-diagonal element Y' _ijfor transadmittance when fault between node i, j, in the time there is branch road between node i, j, Y' _ijequal to be directly connected in the negative value of the branch road admittance between node i, j, in the time there is not branch road between node i, j, Y' _ij=0;

${\stackrel{\&CenterDot;}{U}}_f=\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_{1\&CenterDot;f}\\ {\stackrel{\&CenterDot;}{U}}_{2\&CenterDot;f}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{U}}_{\mathrm{PCC}\&CenterDot;f}^{+}\\ .\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{U}}_{\mathrm{PCC}\&CenterDot;f}^{-}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{U}}_{m\&CenterDot;f}\end{array}\right]$ Node voltage while representing fault, wherein the positive and negative sequence voltage of common connecting point PCC while being respectively fault;

${\stackrel{\&CenterDot;}{I}}_f=\left[\begin{array}{c}{\stackrel{\&CenterDot;}{I}}_{1\&CenterDot;f}\\ {\stackrel{\&CenterDot;}{I}}_{2\&CenterDot;f}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{I}}_{\mathrm{DG}\&CenterDot;f}\\ \&CenterDot;\\ \&CenterDot;\\ \&CenterDot;\\ {\stackrel{\&CenterDot;}{I}}_{m\&CenterDot;f}\end{array}\right]$ The Injection Current of node while representing fault, wherein during for fault, distributed power source injects the electric current of common connecting point PCC;

be expressed as: ${\stackrel{.}{I}}_{\mathrm{DG}\&CenterDot;f}=I_{d\&CenterDot;f}-{\mathrm{jI}}_{q\&CenterDot;f}---\left(2\right)$

Wherein, $\left\{\begin{array}{c}{I}_{d\&CenterDot;f}=P_{\left(0\right)}/U_{\mathrm{PCC}\&CenterDot;f}^{+}\\ I_{q\&CenterDot;f}=I_{q\left(0\right)}+k_q(U_{\mathrm{PCC}}-U_{\mathrm{PCC}\&CenterDot;f}^{+})\end{array}\right.$

In formula, I _df, I _qfactive current and the reactive current of distributed power source output while representing fault respectively; P ₍₀₎, I _{q (0)}represent respectively active power and the reactive current of normal motion time cloth formula power supply output, q ₍₀₎represent the reactive power of normal motion time cloth formula power supply output, k _qrepresent coefficient;

S22 carries out linear transformation to formula (1), obtains solving equation group;

S3 solves

S4 solves I _df, I _qf;

S5 defines I _ad=I _df+ I _qf, and judge I _adwhether exceed inverter rated current I _vSCnif, do not exceed and carry out step S6, otherwise, I made _df=I _vSCn-I _qf, by I _df, I _qfexpression formula substitution formula (1) and formula (2), and recalculate after carry out step S6;

S6 utilizes formula (1) to calculate in remove outer node voltage;

S7 is according to the branch current between following formula computing node j and node k:

${\stackrel{\&CenterDot;}{I}}_{\mathrm{jk}\&CenterDot;f}=\frac{{\stackrel{\&CenterDot;}{U}}_{j\&CenterDot;f}-{\stackrel{\&CenterDot;}{U}}_{k\&CenterDot;f}}{Z_{\mathrm{jk}}}$

Wherein, represent respectively branch current and branch impedance between node j and k, the voltage of node j, k while representing distribution network failure respectively.