CN103441518B - Three-phase Power Flow distribution determination method in single-phase load and alternate load mixing situation - Google Patents

Abstract

The present invention proposes the Three-phase Power Flow distribution determination method in a kind of single-phase load and alternate load mixing situation, first network topology, the low-pressure side payload of each node and load access way is obtained, then according to different access way, by low-pressure side load Equivalent Conversion, obtain the power output of each phase of medium voltage side, finally adopt the Three Phase Power Flow based on neutral point voltage skew, obtain Three-phase Power Flow distribution.The present invention is by the Load flow calculation problem in the inconsistent situation of load access way in equivalent transformation process power distribution network, propose the power distribution network Three-phase Power Flow distribution acquiring method in a kind of applicable single-phase load and alternate load mixing situation, make power distribution network operating analysis result more accurate.

Description

Three-phase Power Flow distribution determination method in single-phase load and alternate load mixing situation

Technical field

The invention belongs to power distribution network and run control technology field, be specifically related to the Three-phase Power Flow distribution determination method in a kind of single-phase load and alternate load mixing situation.

Background technology

Load flow calculation is the basis of distribution network planning, operating analysis, control and optimization, is the most basic, the most important calculating of power distribution network.Flourish, load various kinds along with Chinese national economy increase and distributed power source accesses the inconsistent of power distribution network mode, and the research of power distribution network three-phase power flow more and more receives publicity.

Power distribution network has many features being different from electric power transmission network, as outstanding in open loop operation (closed loop design, radial operation), three-phase imbalance situation, line resistance and reactance ratio is large, interstitial content is large, in addition, along with the difference of distributed power source network access mode, the extensive use of single-phase and three equal different powering modes, power distribution network Three-phase Power Flow should not adopt equivalence to become single-phase conventional process mode to calculate.In order to improve power distribution network automatic management level, ensure the safe and reliable operation of power distribution network, must to carry out in time power distribution network, three-phase power flow accurately, to be thus necessary to study the Three Phase Power Flow being suitable for power distribution network.According to the feature of power distribution network, many experts and scholars propose multiple Three Phase Power Flow, as improved Niu Lafa, circuit impedance method, forward-backward sweep method etc.For the pluses and minuses of these methods, patent " a kind of power distribution network Three Phase Power Flow based on neutral point excursion " proposes a kind of Three Phase Power Flow effectively accurately fast, and institute's extracting method well can process the known network of the load power output of each node.And actual power distribution network, the mode of low-pressure side load access medium voltage distribution network is not quite similar, a certain phase may be accessed, also may access certain two alternate, also may all access by three-phase, medium voltage distribution network had both comprised a certain single-phase load gone up mutually of access, also certain alternate or multiple alternate alternate load of access is comprised, thus be necessary that research is under the load condition of known low-pressure side, the Three Phase Power Flow that load access way differs, namely single-phase and alternate load mixes the tidal current computing method in situation.

Summary of the invention

For the deficiencies in the prior art, the present invention proposes the Three-phase Power Flow distribution determination method in a kind of single-phase load and alternate load mixing situation, by equivalent transformation, the equivalence of low-pressure side load is become the power stage of each phase of medium voltage side, can situation that effectively processing load access way is inconsistent, not only what be applicable to have access medium voltage side a certainly go up mutually, but also to have the power distribution network of single three-phase hybrid power supply pattern of certain alternate or multiple alternate load of access medium voltage side, be also applicable to single-phase, the alternate mixing of distributed power source access power distribution network situation under Load flow calculation.

Three-phase Power Flow distribution determination method in single-phase load provided by the invention and alternate load mixing situation, its improvements are, first network topology, the low-pressure side payload of each node and load access way is obtained, then according to different access way, by low-pressure side load Equivalent Conversion, obtain the power output of each phase of medium voltage side, finally adopt the Three Phase Power Flow based on neutral point voltage skew, calculate Three-phase Power Flow distribution.

Wherein, described load access way comprises star-star connection and delta connection two kinds of modes; Wherein,

When in distribution transformer, compression bonded line mode is star, by single-phase transformer access medium voltage side a certain go up mutually or be linked into each load gone up mutually of medium voltage side respectively by three-phase transformer be called single-phase load;

When compression bonded line mode is triangle in distribution transformer, be all called alternate load by the alternate of single-phase transformer access medium voltage side or by each alternate load of three-phase transformer access medium voltage side.

Wherein, described according to different access way, by low-pressure side load Equivalent Conversion, the step obtaining the power output of each phase of medium voltage side comprises:

When in distribution transformer, compression bonded line mode is star, if single-phase load is by any phase of single-phase transformer access medium voltage side, then the equivalent power that this phase exports is low-pressure side single-phase load size, and the power output of this other two-phase of node is 0;

When in distribution transformer, compression bonded line mode is star, three alternately all access single-phase load by three-phase transformer, then through Equivalent Conversion, the power that three-phase exports is each single-phase load size gone up mutually;

When in distribution transformer, compression bonded line mode is triangle, if by any one the alternate access alternate load of single-phase transformer at three-phase, then each phase power output is:

Alternate with B phase for access A phase: $\left\{\begin{array}{c}{S}_A=V_A{I_A}^{*}=V_A*S_a/(V_B-V_A)\\ S_B=V_B{I_B}^{*}=-V_B*S_a/(V_B-V_A)\\ S_C=0\end{array}\right.;$

Alternate with C phase for access B phase: $\left\{\begin{array}{c}{S}_B=V_B{I_B}^{*}=V_B*S_b/(V_C-V_B)\\ S_C=V_C{I_C}^{*}=-V_C*S_b/(V_C-V_B)\\ S_A=0\end{array}\right.;$

Alternate with A phase for access C phase: $\left\{\begin{array}{c}{S}_C=V_C{I_C}^{*}=V_C*S_c/(V_A-V_C)\\ S_A=V_A{I_A}^{*}=-V_A*S_c/(V_A-V_C)\\ S_B=0\end{array}\right.;$

When in distribution transformer, compression bonded line mode is triangle, if by any two-phase alternate access alternate load of single-phase transformer at three-phase, then each phase power output is:

Alternate with B-C phase two for A-B phase: $\left\{\begin{array}{c}{S}_A=V_A{I_A}^{*}=V_A*\frac{S_a}{V_B-V_A}\\ S_B=V_B{I_B}^{*}=V_B(-\frac{S_a}{V_B-V_A}+\frac{S_b}{V_C-V_B})\\ S_C=V_C{I_C}^{*}=-V_C\frac{S_b}{V_C-V_B}\end{array}\right.;$

Alternate with C-A phase two for B-C phase: $\left\{\begin{array}{c}{S}_A=V_A{I_A}^{*}=-V_A*\frac{S_c}{V_A-V_C}\\ S_B=V_B{I_B}^{*}=V_B*\frac{S_b}{V_C-V_B}\\ S_C=V_C{I_C}^{*}=V_C(-\frac{S_b}{V_C-V_B}+\frac{S_c}{V_A-V_C})\end{array}\right.;$

Alternate with A-B phase two for C-A phase: $\left\{\begin{array}{c}{S}_A=V_A{I_A}^{*}=V_A*\frac{S_a-S_c}{V_B-V_A}+S_c\\ S_B=V_B{I_B}^{*}=V_B(-\frac{S_a-S_c}{V_B-V_A}+\frac{S_b-S_c}{V_C-V_B})+S_c\\ S_C=V_C{I_C}^{*}=-V_C\frac{S_b-S_c}{V_C-V_B}+S_c\end{array}\right.;$

When in distribution transformer, compression bonded line mode is triangle, if three-phase all accesses alternate load and three-phrase burden balance, then the power that three-phase exports is each single-phase load size gone up mutually;

When in distribution transformer, compression bonded line mode is triangle, if three-phase all accesses alternate load and three-phase load unbalance, then when three-phase all accesses alternate load but three-phase load unbalance time, each alternate payload is respectively S _a, S _b, S _c, the alternate load of Jiang Gexiang is divided into equal to unequal two parts, and each mutually alternate payload of equal part is S _c, unequal part is linked into the alternate load of A-B, B-C two-phase and is respectively S _a-S _c, S _b-S _c, unequal part accesses the processing method of alternate load by two-phase, and the equivalence that can obtain each phase of medium voltage side exports S _a, S _b, S _c,

$\left\{\begin{array}{c}{S}_A=V_A{I_A}^{*}=V_A*\frac{S_a-S_c}{V_B-V_A}+S_c\\ S_B=V_B{I_B}^{*}=V_B(-\frac{S_a-S_c}{V_B-V_A}+\frac{S_b-S_c}{V_C-V_B})+S_c\\ S_C=V_C{I_C}^{*}=-V_C\frac{S_b-S_c}{V_C-V_B}+S_c\end{array}\right.;$

Wherein, the Three Phase Power Flow that described employing offsets based on neutral point voltage, the step calculating Three-phase Power Flow distribution comprises:

(1) according to medium-voltage distribution network topology, each node on feeder line and each bar branch road are numbered;

(2) each node neutral point voltage side-play amount is introduced

(3) the neutral point excursion amount of node i is adopted the calculating phase voltage value of node i is revised:

(4) the three-phase electricity flow valuve of each branch road and the three-phase voltage value of each node is calculated;

(5) adopt Newton-Raphson approach to carry out iteration, revise neutral point voltage side-play amount;

(6) adopt superposition states to solve three-phase voltage, until meet stopping criterion for iteration, obtain Three-phase Power Flow distribution.

Wherein, step (3) adopts the neutral point excursion amount of node i revise the calculating phase voltage value of node i, its expression formula is:

$\left[\begin{array}{c}{\stackrel{\·}{U}}_{\mathrm{Ai}}\\ {\stackrel{\·}{U}}_{\mathrm{Bi}}\\ {\stackrel{\·}{U}}_{\mathrm{Ci}}\end{array}\right]=\left[\begin{array}{c}{\stackrel{\·}{V}}_{\mathrm{Ai}}-{\stackrel{\·}{V}}_{\mathrm{Ni}}\\ {\stackrel{\·}{V}}_{\mathrm{Bi}}-{\stackrel{\·}{V}}_{\mathrm{Ni}}\\ {\stackrel{\·}{V}}_{\mathrm{Ci}}-{\stackrel{\·}{V}}_{\mathrm{Ni}}\end{array}\right];$

In formula, be respectively the calculating phase voltage value of node i place A phase, B phase, C phase three-phase; be respectively node i place A phase, B phase, C phase three-phase electricity place value.

Wherein, the expression formula that step (4) calculates the three-phase electricity flow valuve of each branch road and the three-phase voltage value of each node comprises;

The equivalent output powers of the A phase of node i, B phase, C phase three-phase is respectively power output S _ai, power output S _bi, power output S _ci, adopt the equivalent output load current of revised calculating phase voltage value computing node i to be:

$\left[\begin{array}{c}{\stackrel{\·}{I}}_{\mathrm{ai}}\\ {\stackrel{\·}{I}}_{\mathrm{bi}}\\ {\stackrel{\·}{I}}_{\mathrm{ci}}\end{array}\right]=\left[\begin{array}{c}\frac{S_{\mathrm{Ai}}}{{\stackrel{\·}{U}}_{\mathrm{Ai}}}\\ \frac{S_{\mathrm{Bi}}}{{\stackrel{\·}{U}}_{\mathrm{Bi}}}\\ \frac{S_{\mathrm{Ci}}}{{\stackrel{\·}{U}}_{\mathrm{Ci}}}\end{array}\right];$

Wherein: be respectively the equivalent output load current of load at node i place A phase, B phase, C phase three-phase at node i place; Inference according to Kirchhoff's current law (KCL) has:

${\stackrel{\·}{I}}_{\mathrm{ai}}+{\stackrel{\·}{I}}_{\mathrm{bi}}+{\stackrel{\·}{I}}_{\mathrm{ci}}=0;$

Prospective method is adopted to calculate the three-phase branch current of each branch road for:

$\left[\begin{array}{c}{\stackrel{\·}{I}}_{\mathrm{Ai}}\\ {\stackrel{\·}{I}}_{\mathrm{Bi}}\\ {\stackrel{\·}{I}}_{\mathrm{Ci}}\end{array}\right]=\left[\begin{array}{c}{\stackrel{\·}{I}}_{\mathrm{ai}}+\underset{j\∈M}{\mathrm{\Σ}}{\stackrel{\·}{I}}_{\mathrm{Aj}}\\ {\stackrel{\·}{I}}_{\mathrm{bi}}+\underset{j\∈M}{\mathrm{\Σ}}{\stackrel{\·}{I}}_{\mathrm{Bj}}\\ {\stackrel{\·}{I}}_{\mathrm{ci}}+\underset{j\∈M}{\mathrm{\Σ}}{\stackrel{\·}{I}}_{\mathrm{Cj}}\end{array}\right];$

In formula, M is all lower floors branch road collection be directly connected with node i; For radial feeder line, levels is pressed current direction and is divided, and for node i and node j, if practical power flows to j from i, then i is the upper layer node of j; If practical power flows to i from j, then i is the lower level node of j; represent that node j is at A phase, B phase, C phase three-phase branch current respectively;

Adopt the three-phase voltage value of back substitution method computing node i, for:

$\left[\begin{array}{c}{\stackrel{\·}{U}}_{\mathrm{Ai}}\\ {\stackrel{\·}{U}}_{\mathrm{Bi}}\\ {\stackrel{\·}{U}}_{\mathrm{Ci}}\end{array}\right]=\left[\begin{array}{c}{\stackrel{\·}{U}}_{\mathrm{Ah}}-{\stackrel{\·}{I}}_{\mathrm{Ai}}*Z_{\mathrm{Ai}}\\ {\stackrel{\·}{U}}_{\mathrm{Bh}}-{\stackrel{\·}{I}}_{\mathrm{Bi}}*Z_{\mathrm{Bi}}\\ {\stackrel{\·}{U}}_{\mathrm{Ch}}-{\stackrel{\·}{I}}_{\mathrm{Ci}}*Z_{\mathrm{Ci}}\end{array}\right];$

In formula, node h is the upper layer node be directly connected with node; be respectively node h in A phase, B phase, C phase three-phase voltage value;

For the three-phase voltage value of headend node, represent with following formula:

$\left[\begin{array}{c}{\stackrel{\·}{U}}_{\mathrm{Ai}}\\ {\stackrel{\·}{U}}_{\mathrm{Bi}}\\ {\stackrel{\·}{U}}_{\mathrm{Ci}}\end{array}\right]=\left[\begin{array}{c}{\stackrel{\·}{U}}_{A0}-{\stackrel{\·}{I}}_{\mathrm{Ai}}*Z_{\mathrm{Ai}}\\ {\stackrel{\·}{U}}_{B0}-{\stackrel{\·}{I}}_{\mathrm{Bi}}*Z_{\mathrm{Bi}}\\ {\stackrel{\·}{U}}_{C0}-{\stackrel{\·}{I}}_{\mathrm{Ci}}*Z_{\mathrm{Ci}}\end{array}\right];$

In formula, be respectively headend node in A phase, B phase, C phase three-phase voltage value.

Wherein, step (5) adopts Newton-Raphson approach to carry out iteration, and the expression formula revising neutral point voltage side-play amount is;

Adopt Newton-Raphson approach, obtain the iterative formula of neutral point voltage side-play amount, represent with following formula:

$\begin{array}{c}{\stackrel{\·}{V}}_{\mathrm{Ni}}^{\left(k\right)}={\stackrel{\·}{V}}_{\mathrm{Ni}}^{(k-1)}-\frac{{({\stackrel{\·}{V}}_{\mathrm{Ai}}^{\left(k\right)}-{\stackrel{\·}{V}}_{\mathrm{Ni}}^{(k-1)})}^2}{S_{\mathrm{ai}}}\\ *(\frac{S_{\mathrm{ai}}}{{\stackrel{\·}{V}}_{\mathrm{Ai}}^{(k-1)}-{\stackrel{\·}{V}}_{\mathrm{Ni}}^{(k-1)}}+\frac{S_{\mathrm{bi}}}{{\stackrel{\·}{V}}_{\mathrm{Bi}}^{(k-1)}-{\stackrel{\·}{V}}_{\mathrm{Ni}}^{(k-1)}}+\frac{S_{\mathrm{ci}}}{{\stackrel{\·}{V}}_{\mathrm{Ci}}^{(k-1)}-{\stackrel{\·}{V}}_{\mathrm{Ni}}^{(k-1)}})\end{array};$

In formula, node i neutral point voltage side-play amount and A phase current potential when being respectively kth time iteration, be respectively the current potential of the neutral point voltage side-play amount at the node i place of gained during kth-1 iteration and A phase, B phase, C phase three-phase.

Compared with the prior art, beneficial effect of the present invention is:

1. the invention provides the Three-phase Power Flow distribution determination method in single-phase load and alternate load mixing situation, through strict theory deduction, with effectively solving the three-phase power flow problem under load known conditions;

2. the method equivalence of low-pressure side payload being become each phase output power value of medium voltage side provided by the invention, equivalent result can be used in each phase Three-phase Power Flow Calculation Method, can directly utilize low-pressure side load measurement or predict the outcome, and export without the need to the load measuring each node at medium voltage side, be applicable to practical application;

3. the present invention is when the alternate load of process three-phase, and have employed the method for load decomposition, alternate for three-phase load decomposition is become balance portion and uneven part, the equivalence that can calculate each phase fast exports, and avoids coupling problem;

4. the power distribution network Three Phase Power Flow based on neutral point excursion of the present invention's employing, adopt superposition states to solve, push back before combining for the optimization with Newton-Laphson method, principle is directly perceived, during calculating Three-phase Power Flow, Iterations of Multi is good, and computational speed is fast;

5. the Three-phase Power Flow distribution determination method in single-phase load provided by the invention and alternate load mixing situation, was both adapted to radial distribution networks, was also adapted to the Load flow calculation of weak ring power distribution network.

6. the present invention is by the Load flow calculation problem in the inconsistent situation of load access way in equivalent transformation process power distribution network, propose the power distribution network Three-phase Power Flow distribution acquiring method in a kind of applicable single-phase load and alternate load mixing situation, make power distribution network operating analysis result more accurate.

Accompanying drawing explanation

Fig. 1 is single-phase load provided by the invention mixes in situation three-phase power flow flow chart with alternate load.

Fig. 2 is medium voltage side star-star connection schematic diagram provided by the invention.

Fig. 3 is medium voltage side delta connection schematic diagram provided by the invention.

Fig. 4 is single-phase load provided by the invention access A phase schematic diagram.

Fig. 5 is that medium voltage side provided by the invention respectively all accesses single-phase load schematic diagram mutually.

Fig. 6 is that medium voltage side one provided by the invention accesses alternate load schematic diagram mutually.

Fig. 7 is that medium voltage side three-phase provided by the invention all accesses alternate load schematic diagram.

Fig. 8 is feed connection node provided by the invention, branch number schematic diagram.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described in further detail.

For the diversified situation of load access way in power distribution network, the present embodiment propose a kind of single-phase load and alternate load mixing situation under Three-phase Power Flow distribution determination method, be when known low-pressure side load measurement result or predict the outcome and the load access way of each node, adopt the method for equivalent transformation, obtain the equivalent output powers of each phase of medium voltage side, adopt the Three Phase Power Flow based on neutral point voltage skew again, obtain trend distribution.Its general thought as shown in Figure 1.

First network topology, the low-pressure side payload of each node and load access way is obtained, then according to different access way, by low-pressure side load Equivalent Conversion, obtain the power output of each phase of medium voltage side, finally adopt the Three Phase Power Flow based on neutral point voltage skew, calculate Three-phase Power Flow distribution.Concrete,

(1) load access way:

Medium voltage distribution network adopts three-phase three-wire system usually, and distribution transformer medium voltage side comprises star-star connection and delta connection two kinds of modes, as shown in accompanying drawing 2 and accompanying drawing 3.

Low-voltage network comprises single phase power supply and three phase supply pattern two kinds, and single phase power supply pattern adopts single-phase transformer, and three phase supply pattern adopts three-phase transformer.When in distribution transformer, compression bonded line mode is star, by single-phase transformer access medium voltage side a certain go up mutually or be linked into each load gone up mutually of medium voltage side respectively by three-phase transformer be referred to as single-phase load; When compression bonded line mode is triangle in distribution transformer, be all called alternate load by the alternate of single-phase transformer access medium voltage side or by each alternate load of three-phase transformer access medium voltage side.After obtaining the load data of low-pressure side by monitoring or load prediction, adopt following conversion method respectively single-phase and alternate load to be carried out Equivalent Conversion, obtain the power output size of each phase of medium voltage side.

(2) low-pressure side load is to the Equivalent Conversion of high-pressure side power output:

1, single-phase load;

For load access A phase, as shown in Figure 4, when in distribution transformer, compression bonded line mode is star, single-phase load S _aby the A phase of single-phase transformer access medium voltage side, the equivalent power that medium voltage side A phase exports is low-pressure side payload S _a, the power output of this other two-phase of node is 0, that is:

$\left\{\begin{array}{c}{S}_A{=S}_a\\ S_B=0\\ S_C=0\end{array}\right.---\left(1\right)$

Wherein, S _afor the size of low-pressure side single-phase load, S _a, S _b, S _cbe respectively S _athe power that after Equivalent Conversion, A, B, C respectively export mutually.It is similar that load accesses B phase and C phase time and A.

When in distribution transformer, compression bonded line mode is star, A, B, C tri-is alternate all accesses single-phase load S by three-phase transformer _a, S _b, S _c, as shown in Figure 5, through Equivalent Conversion, the power S that A, B, C respectively export mutually _a, S _b, S _cfor:

$\left\{\begin{array}{c}{S}_A{=S}_a\\ S_B=S_b\\ S_C=S_c\end{array}\right.---\left(2\right)$

2, alternate load;

1) one is mutually alternate;

Alternate for A, B, when in distribution transformer, compression bonded line mode is triangle, by single-phase transformer at the alternate load S of the alternate access of A, B _a, as shown in Figure 6.

Disregard transformer loss,

$\left\{\begin{array}{c}{S}_{\mathrm{AB}}{=S}_a\\ S_{\mathrm{BC}}=0\\ S_{\mathrm{CA}}=0\end{array}\right.---\left(3\right)$

Wherein, S _athe alternate payload of low-pressure side access, S _aB, S _bC, S _cAmedium voltage side A-B, B-C, C-A equivalent power output respectively.

Have according to Kirchhoff's current law (KCL):

$\left\{\begin{array}{c}{I}_A+I_{\mathrm{CA}}=I_{\mathrm{AB}}\\ I_B+I_{\mathrm{AB}}=I_{\mathrm{BC}}\\ I_C+I_{\mathrm{BC}}=I_{\mathrm{CA}}\\ I_A+I_B+I_C=0\end{array}\right.---\left(4\right)$

Wherein, I _a, I _b, I _cbe respectively the load current of each phase of medium voltage side, I _aB, I _bC, I _cAthe three-phase current of medium voltage side A-B, B-C, C-A phase respectively.

When disregarding transformer loss, in theory, I _bC=0, I _cA=0, can obtain thus:

$\left\{\begin{array}{c}{I}_A=I_{\mathrm{AB}}\\ I_B={-I}_{\mathrm{AB}}\\ I_C=I_{\mathrm{BC}}=0\end{array}\right.---\left(5\right)$

If the current potential of each phase of transformer medium voltage side is V _a, V _b, V _c, have:

S _AB＝S _a＝(V _B-V _A)I _AB ^*（6）

Convolution (3), (5) and (6) can obtain the power S that A, B, C respectively export mutually _a, S _b, S _cfor:

$\left\{\begin{array}{c}{S}_A=V_A{I_A}^{*}=V_A*S_a/(V_B-V_A)\\ S_B=V_B{I_B}^{*}=-V_B*S_a/(V_B-V_A)\\ S_C=0\end{array}\right.---\left(7\right)$

2) two-phase is alternate;

Alternate for A-B, B-C two, in like manner, when accessing alternate load when between A-B, B-C two-phase:

$\left\{\begin{array}{c}{S}_{\mathrm{AB}}{=S}_a\\ S_{\mathrm{BC}}=S_b\\ S_{\mathrm{CA}}=0\end{array}\right.---\left(8\right)$

S _bthe alternate payload that low-pressure side access B-C is alternate.

Have according to Kirchhoff's current law (KCL):

$\left\{\begin{array}{c}{I}_A=I_{\mathrm{AB}}\\ I_B={-I}_A-I_C\\ I_C={-I}_{\mathrm{BC}}\end{array}\right.---\left(9\right)$

Ignore the loss of power transformation device to have:

$\left\{\begin{array}{c}{S}_{\mathrm{AB}}=S_a=(V_B-V_A){I_{\mathrm{AB}}}^{*}\\ S_{\mathrm{BC}}=S_b=(V_C-V_B){I_{\mathrm{BC}}}^{*}\end{array}\right.---\left(10\right)$

Convolution (8), (9) and (10) can obtain the power S that A, B, C respectively export mutually _a, S _b, S _cfor:

$\left\{\begin{array}{c}{S}_A=V_A{I_A}^{*}=V_A*\frac{S_a}{V_B-V_A}\\ S_B=V_B{I_B}^{*}=V_B(-\frac{S_a}{V_B-V_A}+\frac{S_b}{V_C-V_B})\\ S_C=V_C{I_C}^{*}=-V_C\frac{S_b}{V_C-V_B}\end{array}\right.---\left(11\right)$

3, three-phase load

1) three-phase equilibrium

As shown in Figure 7, when three-phase all access alternate load and three-phrase burden balance time, each alternate payload is respectively S _a, S _b, S _c, the equivalence of each phase of medium voltage side exports S _a, S _b, S _cfor:

$\left\{\begin{array}{c}{S}_A{=S}_a\\ S_B=S_b\\ S_C=S_c\end{array}\right.---\left(12\right)$

2) three-phase imbalance

As shown in Figure 7, when three-phase all access alternate load but three-phase load unbalance time, each alternate payload is respectively S _a, S _b, S _c, the alternate load of Jiang Gexiang is divided into equal to unequal two parts, each mutually alternate payload of equal part is S _c, unequal part is linked into the alternate load of A-B, B-C two-phase and is respectively S _a-S _c, S _b-S _c, unequal part accesses the processing method of alternate load by two-phase, and the equivalence that can obtain each phase of medium voltage side exports S _a, S _b, S _c,

$\left\{\begin{array}{c}{S}_A=V_A{I_A}^{*}=V_A*\frac{S_a-S_c}{V_B-V_A}+S_c\\ S_B=V_B{I_B}^{*}=V_B(-\frac{S_a-S_c}{V_B-V_A}+\frac{S_b-S_c}{V_C-V_B})+S_c\\ S_C=V_C{I_C}^{*}=-V_C\frac{S_b-S_c}{V_C-V_B}+S_c\end{array}\right.---\left(13\right)$

(3) based on the three-phase power flow of neutral point voltage skew;

After adopting above-mentioned equivalent transformation to obtain the equivalent output powers of each phase of medium voltage side, adopt the Three Phase Power Flow based on neutral point voltage skew, calculate Three-phase Power Flow distribution, method is as follows:

(1) according to medium-voltage distribution network topology, as shown in Figure 8, each node on feeder line and each bar branch road are numbered;

(2) each node neutral point voltage side-play amount is introduced

(3) the neutral point excursion amount of node i is adopted the calculating phase voltage value of node i is revised;

$\left[\begin{array}{c}{\stackrel{\·}{U}}_{\mathrm{Ai}}\\ {\stackrel{\·}{U}}_{\mathrm{Bi}}\\ {\stackrel{\·}{U}}_{\mathrm{Ci}}\end{array}\right]=\left[\begin{array}{c}{\stackrel{\·}{V}}_{\mathrm{Ai}}-{\stackrel{\·}{V}}_{\mathrm{Ni}}\\ {\stackrel{\·}{V}}_{\mathrm{Bi}}-{\stackrel{\·}{V}}_{\mathrm{Ni}}\\ {\stackrel{\·}{V}}_{\mathrm{Ci}}-{\stackrel{\·}{V}}_{\mathrm{Ni}}\end{array}\right]---\left(14\right)$

Wherein: be respectively the calculating phase voltage value of node i place A, B, C three-phase; be respectively node i place A, B, C three-phase electricity place value.

(4) the three-phase electricity flow valuve of each branch road and the three-phase voltage value of each node is calculated;

The equivalent output powers of A, B, C three-phase of node i is respectively S _ai, S _bi, S _ci, adopt the equivalent output load current of revised calculating phase voltage value computing node i to be:

$\left[\begin{array}{c}{\stackrel{\·}{I}}_{\mathrm{ai}}\\ {\stackrel{\·}{I}}_{\mathrm{bi}}\\ {\stackrel{\·}{I}}_{\mathrm{ci}}\end{array}\right]=\left[\begin{array}{c}\frac{S_{\mathrm{Ai}}}{{\stackrel{\·}{U}}_{\mathrm{Ai}}}\\ \frac{S_{\mathrm{Bi}}}{{\stackrel{\·}{U}}_{\mathrm{Bi}}}\\ \frac{S_{\mathrm{Ci}}}{{\stackrel{\·}{U}}_{\mathrm{Ci}}}\end{array}\right]---\left(15\right)$

Wherein: be respectively the equivalent output load current of load at node i place A, B, C three-phase at node i place.Inference according to Kirchhoff's current law (KCL) has:

${\stackrel{\·}{I}}_{\mathrm{ai}}+{\stackrel{\·}{I}}_{\mathrm{bi}}+{\stackrel{\·}{I}}_{\mathrm{ci}}=0---\left(16\right)$

Prospective method is adopted to calculate the three-phase branch current of each branch road represent by following formula (17):

$\left[\begin{array}{c}{\stackrel{\·}{I}}_{\mathrm{Ai}}\\ {\stackrel{\·}{I}}_{\mathrm{Bi}}\\ {\stackrel{\·}{I}}_{\mathrm{Ci}}\end{array}\right]=\left[\begin{array}{c}{\stackrel{\·}{I}}_{\mathrm{ai}}+\underset{j\∈M}{\mathrm{\Σ}}{\stackrel{\·}{I}}_{\mathrm{Aj}}\\ {\stackrel{\·}{I}}_{\mathrm{bi}}+\underset{j\∈M}{\mathrm{\Σ}}{\stackrel{\·}{I}}_{\mathrm{Bj}}\\ {\stackrel{\·}{I}}_{\mathrm{ci}}+\underset{j\∈M}{\mathrm{\Σ}}{\stackrel{\·}{I}}_{\mathrm{Cj}}\end{array}\right]---\left(17\right)$

Wherein: M is all lower floors branch road collection be directly connected with node i; For radial feeder line, levels divides by current direction, and for node i and node j, if practical power flows to j from i, then i is the upper layer node of j; If practical power flows to i from j, then i is the lower level node of j; represent that node j is at A, B, C three-phase branch current respectively.

Adopt the three-phase voltage value of back substitution method computing node i, represent by following (18) formula:

$\left[\begin{array}{c}{\stackrel{\·}{U}}_{\mathrm{Ai}}\\ {\stackrel{\·}{U}}_{\mathrm{Bi}}\\ {\stackrel{\·}{U}}_{\mathrm{Ci}}\end{array}\right]=\left[\begin{array}{c}{\stackrel{\·}{U}}_{\mathrm{Ah}}-{\stackrel{\·}{I}}_{\mathrm{Ai}}*Z_{\mathrm{Ai}}\\ {\stackrel{\·}{U}}_{\mathrm{Bh}}-{\stackrel{\·}{I}}_{\mathrm{Bi}}*Z_{\mathrm{Bi}}\\ {\stackrel{\·}{U}}_{\mathrm{Ch}}-{\stackrel{\·}{I}}_{\mathrm{Ci}}*Z_{\mathrm{Ci}}\end{array}\right]---\left(18\right)$

Wherein: node h is the upper layer node be directly connected with node; be respectively node h in A, B, C three-phase voltage value;

For the three-phase voltage value of headend node, represent by following (19) formula:

$\left[\begin{array}{c}{\stackrel{\·}{U}}_{\mathrm{Ai}}\\ {\stackrel{\·}{U}}_{\mathrm{Bi}}\\ {\stackrel{\·}{U}}_{\mathrm{Ci}}\end{array}\right]=\left[\begin{array}{c}{\stackrel{\·}{U}}_{A0}-{\stackrel{\·}{I}}_{\mathrm{Ai}}*Z_{\mathrm{Ai}}\\ {\stackrel{\·}{U}}_{B0}-{\stackrel{\·}{I}}_{\mathrm{Bi}}*Z_{\mathrm{Bi}}\\ {\stackrel{\·}{U}}_{C0}-{\stackrel{\·}{I}}_{\mathrm{Ci}}*Z_{\mathrm{Ci}}\end{array}\right]---\left(19\right)$

Wherein: be respectively headend node in A, B, C three-phase voltage value.

(5) adopt Newton-Raphson approach to carry out iteration, revise neutral point voltage side-play amount;

Adopt Newton-Raphson approach, obtain the iterative formula of neutral point voltage side-play amount, represent by following (20) formula:

$\begin{array}{c}{\stackrel{\·}{V}}_{\mathrm{Ni}}^{\left(k\right)}={\stackrel{\·}{V}}_{\mathrm{Ni}}^{(k-1)}-\frac{{({\stackrel{\·}{V}}_{\mathrm{Ai}}^{\left(k\right)}-{\stackrel{\·}{V}}_{\mathrm{Ni}}^{(k-1)})}^2}{S_{\mathrm{ai}}}\\ *(\frac{S_{\mathrm{ai}}}{{\stackrel{\·}{V}}_{\mathrm{Ai}}^{(k-1)}-{\stackrel{\·}{V}}_{\mathrm{Ni}}^{(k-1)}}+\frac{S_{\mathrm{bi}}}{{\stackrel{\·}{V}}_{\mathrm{Bi}}^{(k-1)}-{\stackrel{\·}{V}}_{\mathrm{Ni}}^{(k-1)}}+\frac{S_{\mathrm{ci}}}{{\stackrel{\·}{V}}_{\mathrm{Ci}}^{(k-1)}-{\stackrel{\·}{V}}_{\mathrm{Ni}}^{(k-1)}})\end{array}---\left(20\right)$

Wherein: node i neutral point voltage side-play amount and A phase current potential when being respectively kth time iteration, be respectively the neutral point voltage side-play amount at the node i place of gained during kth-1 iteration and the current potential of A, B, C three-phase.

(6) adopt superposition states to solve three-phase voltage, until meet stopping criterion for iteration, obtain Three-phase Power Flow distribution

Finally should be noted that: above embodiment is only in order to illustrate that technical scheme of the present invention is not intended to limit, although with reference to above-described embodiment to invention has been detailed description, those of ordinary skill in the field are to be understood that: still can modify to the specific embodiment of the present invention or equivalent replacement, and not departing from any amendment of spirit and scope of the invention or equivalent replacement, it all should be encompassed in the middle of right of the present invention.

Claims (5)

1. the Three-phase Power Flow distribution determination method in single-phase load and alternate load mixing situation, it is characterized in that, first network topology, the low-pressure side payload of each node and load access way is obtained, then according to different access way, by low-pressure side load Equivalent Conversion, obtain the power output of each phase of medium voltage side, finally adopt the Three Phase Power Flow based on neutral point voltage skew, calculate Three-phase Power Flow distribution;

Described load access way comprises star-star connection and delta connection two kinds of modes; Wherein,

When in distribution transformer, compression bonded line mode is star, by single-phase transformer access medium voltage side a certain go up mutually or be linked into each load gone up mutually of medium voltage side respectively by three-phase transformer be called single-phase load;

When compression bonded line mode is triangle in distribution transformer, be all called alternate load by the alternate of single-phase transformer access medium voltage side or by each alternate load of three-phase transformer access medium voltage side;

Described according to different access way, by low-pressure side load Equivalent Conversion, the step obtaining the power output of each phase of medium voltage side comprises:

When in distribution transformer, compression bonded line mode is star, if single-phase load is by any phase of single-phase transformer access medium voltage side, then the equivalent power that this phase exports is low-pressure side single-phase load size, and the power output of this other two-phase of node is 0;

When in distribution transformer, compression bonded line mode is star, three alternately all access single-phase load by three-phase transformer, then through Equivalent Conversion, the power that three-phase exports is each single-phase load size gone up mutually;

When in distribution transformer, compression bonded line mode is triangle, if by any one the alternate access alternate load of single-phase transformer at three-phase, then each phase power output is:

Alternate with B phase for access A phase:

Alternate with C phase for access B phase:

Alternate with A phase for access C phase:

When in distribution transformer, compression bonded line mode is triangle, if by any two-phase alternate access alternate load of single-phase transformer at three-phase, then each phase power output is:

Alternate with B-C phase two for A-B phase:

Alternate with C-A phase two for B-C phase:

Alternate with A-B phase two for C-A phase:

When in distribution transformer, compression bonded line mode is triangle, if three-phase all accesses alternate load and three-phrase burden balance, then the power that three-phase exports is each single-phase load size gone up mutually;

When in distribution transformer, compression bonded line mode is triangle, if three-phase all accesses alternate load and three-phase load unbalance, then when three-phase all accesses alternate load but three-phase load unbalance time, each alternate payload is respectively S _a, S _b, S _c, the alternate load of Jiang Gexiang is divided into equal to unequal two parts, and each mutually alternate payload of equal part is S _c, unequal part is linked into the alternate load of A-B, B-C two-phase and is respectively S _a-S _c, S _b-S _c, unequal part accesses the processing method of alternate load by two-phase, and the equivalence that can obtain each phase of medium voltage side exports S _a, S _b, S _c,

2. Three-phase Power Flow distribution determination method as claimed in claim 1, is characterized in that, the Three Phase Power Flow that described employing offsets based on neutral point voltage, and the step calculating Three-phase Power Flow distribution comprises:

(1) according to medium-voltage distribution network topology, each node on feeder line and each bar branch road are numbered;

(2) each node neutral point voltage side-play amount is introduced

(3) the neutral point voltage skew of node i is adopted the calculating phase voltage value of node i is revised:

(4) the three-phase electricity flow valuve of each branch road and the three-phase voltage value of each node is calculated;

(5) adopt Newton-Raphson approach to carry out iteration, revise neutral point voltage side-play amount;

(6) adopt superposition states to solve three-phase voltage, until meet stopping criterion for iteration, obtain Three-phase Power Flow distribution.

3. Three-phase Power Flow distribution determination method as claimed in claim 2, is characterized in that, step (3) adopts the neutral point voltage skew of node i revise the calculating phase voltage value of node i, its expression formula is:

In formula, be respectively the calculating phase voltage value of node i place A phase, B phase, C phase three-phase; be respectively node i place A phase, B phase, C phase three-phase electricity place value.

4. Three-phase Power Flow distribution determination method as claimed in claim 2, it is characterized in that, the expression formula that step (4) calculates the three-phase electricity flow valuve of each branch road and the three-phase voltage value of each node comprises;

The equivalent output powers of the A phase of node i, B phase, C phase three-phase is respectively power output S _ai, power output S _bi, power output S _ci, adopt the equivalent output load current of revised calculating phase voltage value computing node i to be:

Wherein: be respectively the equivalent output load current of load at node i place A phase, B phase, C phase three-phase at node i place; be respectively the calculating phase voltage value of node i place A phase, B phase, C phase three-phase; Inference according to Kirchhoff's current law (KCL) has:

Prospective method is adopted to calculate the three-phase branch current of each branch road for:

In formula, M is all lower floors branch road collection be directly connected with node i; For radial feeder line, levels is pressed current direction and is divided, and for node i and node j, if practical power flows to j from i, then i is the upper layer node of j; If practical power flows to i from j, then i is the lower level node of j; represent that node j is at A phase, B phase, C phase three-phase branch current respectively;

Adopt the three-phase voltage value of back substitution method computing node i, for:

In formula, node h is the upper layer node be directly connected with node i; be respectively node h in A phase, B phase, C phase three-phase voltage value; Z _ai, Z _bi, Z _cibe respectively node i place A, B, C threephase load, for the three-phase voltage value of headend node, represent with following formula:

In formula, be respectively headend node in A phase, B phase, C phase three-phase voltage value.

5. Three-phase Power Flow distribution determination method as claimed in claim 2, is characterized in that, step (5) adopts Newton-Raphson approach to carry out iteration, and the expression formula revising neutral point voltage side-play amount is;

Adopt Newton-Raphson approach, obtain the iterative formula of neutral point voltage side-play amount, represent with following formula:

In formula, with node i neutral point voltage side-play amount and A phase current potential when being respectively kth time iteration, be respectively the current potential of the neutral point voltage side-play amount at the node i place of gained during kth-1 iteration and A phase, B phase, C phase three-phase.