CN106356860B - A kind of voltage initial value setting method of distribution system three-phase power flow - Google Patents

Abstract

The invention discloses a voltage initial value setting method for three-phase power flow calculation of a power distribution system, comprising the following steps: forming an array Br of branch node connection relations; sorting the array Br; searching the array Br, and setting the voltage of each node The initial value of the phase angle; adjust the initial value of the phase angle of the three-phase voltage of each node; set the amplitude of the three-phase voltage of all nodes. The invention fully considers the voltage phase displacement of the transformer, determines the connection relationship between the nodes by searching the branches in the power distribution system, and sets the initial value of the phase angle of the three-phase node voltage of the connected nodes according to the digital labels of the branch connection groups . Setting the initial voltage value of each node according to the present invention can make the set initial voltage value of each node closer to the solution of the power flow calculation, improve the convergence of the three-phase power flow calculation of the power distribution system, and make the original flat start non-convergent The case can be converged, and the number of iterations in the original case of flat start convergence is less.

Description

A method for setting the initial value of voltage for three-phase power flow calculation of power distribution system

technical field

The invention relates to a method for calculating a three-phase power flow in a power distribution system, in particular to a method for setting an initial voltage value for the calculation of a three-phase power flow in a power distribution system.

Background technique

The power system is a very large and complex entity composed of equipment (components) that produce, transform, transmit, distribute and use electric energy, and is divided into two parts: the transmission system and the power distribution system. The power transmission system mainly plays the role of transforming and transmitting electric energy, and the voltage level is very high; the power distribution system mainly plays the role of transforming and distributing electric energy, and the voltage level is low.

Power system power flow calculation is a basic calculation for studying the steady-state operation of the power system. It determines the operating state of the entire network according to the given operating conditions and network structure. The power flow calculation is also the basis of other analysis of the power system, such as safety analysis, transient stability analysis, etc., all use power flow calculation.

The power distribution system is a network system that directly distributes electric energy to end users, which is composed of distribution lines, distribution transformers, distribution switches, distribution capacitors and distribution loads. To conduct power system analysis, it is first necessary to establish a suitable model for each component in the power system. Different from the three-phase symmetrical operation mode of the high-voltage transmission system, the load and network of the power distribution system may be asymmetrical. When performing power flow calculations for power distribution systems, the characteristics of three-phase asymmetry should be considered to perform three-phase power flow calculations. Therefore, the premise of the three-phase power flow calculation of the distribution system is to establish the three-phase model of each component of the distribution system.

The three-phase transformer model for single-phase power flow calculation adopts the transformer single-phase model, and people generally only care about the transformation ratio and equivalent impedance of the transformer. However, in the three-phase power flow calculation of power distribution system, the transformer model is much more complicated. Not only the transformation ratio and equivalent impedance of the transformer must be considered, but also the connection mode and connection group of the transformer winding and whether the neutral point is grounded or not. The primary side and the secondary side of the three-phase transformer each have three windings. Connect the head end and the end of the three-phase winding, and lead out the three-phase head end symmetrically. There are two connection methods: one is to connect the three-phase transformer three One end of the phase windings is connected together and the other end is led out, which is called a three-phase transformer star connection or Y connection; the other is to connect the first end of one phase winding and the end of the other phase winding in turn to form a triangle, which is called three-phase Transformer delta connection or D connection.

The primary and secondary windings of a three-phase transformer may be connected in star or delta. The national standard stipulates that when the three-phase transformer windings are connected in a star shape, the labels are Y (primary winding) and y (secondary winding). When the neutral point is drawn out, the labels are YN or yn; (primary winding) and d (secondary winding).

Since the primary and secondary windings of the three-phase transformer may be connected in a star or delta, the different connection methods of the primary and secondary windings of the three-phase transformer can be combined in various combinations, and the delta connection can be divided into left-hand wiring And the right row of wiring, the neutral point of the star connection is divided into grounded and ungrounded. After combining these connection methods, 16 combinations can be obtained.

The polarities of the primary and secondary windings of a three-phase transformer may be the same or opposite, so each combination has two polarities.

The phases of the primary and secondary windings of a three-phase transformer may correspond one-to-one, that is, phases A, B, and C of the primary winding correspond to phases a, b, and c of the secondary winding, respectively, and the corresponding windings are on the same iron core; The phases of the primary and secondary windings of a three-phase transformer may not correspond, that is, A of the primary winding corresponds to phase B or phase C of the secondary winding, but the three-phase voltages of the secondary winding must satisfy the relationship of positive phase sequence , so each polarity corresponds to 3 phase relationships.

Therefore, there are 6 phase relationships in each connection combination of the three-phase transformer, and there are 96 connection groups in 16 combinations.

The digital label of the three-phase transformer connection group is represented by the clock sequence number of the phase difference. The new national standard uses the phase difference judgment of the phase voltage phasor corresponding to the primary side and the secondary side, and uses the phase voltage phasor of the primary side as a reference to point to clock 0 o’clock. The clock point pointed to by the phase voltage phasor corresponding to the secondary side is the digital label of the three-phase transformer connection group, and the virtual neutral point of the triangle is the center of the triangle. Both sides of the three-phase transformer adopt the same connection method, that is, when Yy and Dd, the even-numbered points of points 0, 2, 4, 6, 8, and 10 are connected; one side of the three-phase transformer adopts star connection and the other side adopts delta connection , that is, when Yd and Dy, connect the odd-numbered points of 1, 3, 5, 7, 9, and 11 points.

In the power transmission system, since the three-phase load and the network are symmetrical, the voltage (or current) of the power transmission system is also symmetrical, that is, the magnitude of the three-phase voltage (or current) is equal, and the difference between the two-phase voltage (or current) The phase difference between them is 120°, phase B lags phase A by 120°, and phase C lags phase B by 120°. When analyzing and calculating, a single-phase value circuit can be used to calculate the voltage (or current) of a certain phase (such as phase A), and the voltage (or current) of the other two phases can be directly written according to the symmetrical relationship. The three-phase transformer model in the single-phase equivalent circuit only has the transformer transformation ratio and equivalent impedance.

In the power distribution system, due to the asymmetry of the three-phase load and the network, the voltage (or current) of the power distribution system is not symmetrical. When analyzing and calculating, the three-phase circuit model must be used to calculate together. In the three-phase value circuit, the three-phase transformer model should not only consider the transformation ratio and equivalent impedance of the transformer, but also consider the connection group of the primary winding and the secondary winding of the transformer.

According to the characteristics of the power system nodes, the power flow calculation divides the power system nodes into three categories: nodes whose active power and reactive power are known, nodes whose voltage amplitude and voltage phase angle are unknown are called PQ nodes; nodes whose active power and voltage amplitude are unknown Nodes with known node reactive power and unknown voltage phase angle are called PV nodes; nodes with known node voltage amplitude and voltage phase angle but unknown node active power and reactive power are called balanced nodes.

The power equation or current equation of power flow calculation is a nonlinear equation and must be solved iteratively. When the iterative method solves the power flow calculation problem, it is necessary to set the initial value of the voltage of each node. Generally, flat start is used for voltage initialization, and flat start is used for single-phase power flow calculation. The phase angle is taken as 0.0. When the three-phase power flow calculation adopts the initial value of the flat start voltage, the voltage amplitudes of the three-phase nodes of the PV node and the balance node take the given value, and the voltage amplitude of the three-phase nodes of the PQ node takes 1.0; the A-phase voltage of all nodes The phase angles are all taken as 0°, the phase angles of the B-phase voltage are all taken as -120°, and the phase angles of the C-phase voltage are all taken as 120°. The unit here is the per unit value except the phase angle.

As shown in Figure 1, the method for setting the initial voltage value of the three-phase power flow calculation of the existing power distribution system mainly includes the following steps:

A. Set the node count variable i=1;

B. Determine whether node i is a PQ node, if not, go to step C; otherwise, set the node voltage amplitude as follows:

U _iA =U _iB =U _iC =1.0 (1)

In the formula, U _iA , U _iB , U _iC are the three-phase node voltage amplitudes of node i respectively;

Go to step D;

C. PV node and balance node set the node voltage amplitude according to the following formula:

In the formula, U _iAS , U _iBS , U _iCS are the given values of three-phase node voltage amplitudes of node i respectively.

D. All nodes set the node voltage phase angle according to the following formula:

E, counting variable i=i+1;

F. Determine whether i is greater than the number of nodes n, if i is greater than n, end; otherwise, go to step B to set the initial value of the voltage of the next node.

Since the single-phase power flow calculation does not consider the voltage phase shift of the transformer, the phase angle difference of each node voltage is not too large, and the initial value of the voltage phase angle is set to 0° by flat start, which will not bring convergence problems to the power flow calculation. The three-phase power flow calculation needs to consider the voltage phase displacement of the transformer. If the flat start is used directly, the initial value of the phase angle of the A-phase voltage of each node is 0°, the initial value of the phase angle of the B-phase voltage is -120°, and the initial value of the phase angle of the C-phase voltage is 0°. If the initial value of the phase angle is 120°, the voltage of some nodes will deviate too far from the solution of the power flow calculation, causing the power flow calculation to diverge.

Contents of the invention

In order to solve the above-mentioned problems existing in the prior art, the present invention proposes a method for setting the initial voltage value of the three-phase power flow calculation of the power distribution system, which can fully consider the voltage phase shift of the transformer, and set it according to the digital labels of different transformer connection groups The initial value of the phase angle of each node voltage makes the set initial value of each node voltage close to the solution of the power flow calculation, thereby improving the convergence of the three-phase power flow calculation of the distribution system.

In order to achieve the above object, the technical solution of the present invention is as follows: a method for setting an initial voltage value for three-phase power flow calculation of a power distribution system, comprising the following steps:

A. Form an array Br of branch node connection relations;

The branch node connection relationship array Br is generated from the transmission line branch data and the transformer branch data. In the array Br, each branch contains three items: the first node number i of the branch, the last node number j and the digital label m of the connection group , where the number label of the transmission line branch connection group is 0. Forming the branch node connection relationship array Br includes the following steps:

A1. Take the first node i of the transmission line branch and the transformer branch, the last node number j and the digital label m of the connection group to form an array Br1, and the digital label m of the connection group of the transmission line branch is 0, and set the branch The number is nBr0;

A2, form array Br2 with array Br1, and exchange the first and last node numbers of each branch of array Br2, the number label of connection group becomes 12-m, and the number label of connection group is unchanged when it is 0;

A3, merge array Br1 and array Br2 to form array Br, the total number of data is nBr=2×nBr0;

B. Sort the array Br;

Sort the array Br according to the number of the first node from small to large, and use the array BrIS to record the starting position of each node as the first node of the branch in the array Br. Where: array element BrIS ₁ =1, array element BrIS _n+1 =nBr+1, then array element BrIS _i+1 -1 is the end position of node i as the head node of the branch in array Br. Here n is the number of nodes in the power distribution system.

C, search the array Br, and set the initial value of the phase angle of each node voltage;

Setting the initial value of the phase angle of each node voltage includes the following steps:

C1, make the n-dimensional access identification array Check set to 0, and make the counting variable k=1;

C2. Set the balance node number as s, set the initial value of the phase angle θ _sA of phase A of the balance node = 0°, set the check _s of the balance node to 1, and set the array element Gr _k = s. The array Gr stores the visited nodes and the nodes connected to these visited nodes;

C3, let i=Gr _k , p=BrIS _i ;

C4, the branch end node of setting array element Br _p is j, and the digital label of the connection group is m;

C5, judging whether node j has been visited, if node j has been visited, then turn to step C8;

C6, calculate the phase angle initial value of the node voltage of node j by following formula;

C7, put Check _j =1, node number j is added in the Gr array;

C8, let p=p+1;

C9. Judging whether p is greater than BrIS _i+1 -1, if p is not greater than BrIS _i+1 -1, go to step C4.

C10. Let k=k+1.

C11. Determine whether k is greater than the number of nodes n, if k is not greater than the number of nodes n, go to step C3; otherwise, end.

D. Adjust the initial value of the phase angle of the three-phase voltage of each node so that it is within the range of the main value (-180°, 180°];

By adding or subtracting an integer multiple of 360° to the initial value of the phase angle of the three-phase voltage of each node, adjust the initial value of the phase angle of the three-phase voltage of each node so that it is within the range of the main value (-180°, 180°] ;(-180°,180°] indicates the interval greater than -180° but less than or equal to 180°.

E. Set the amplitude of the three-phase voltage of all nodes; set the amplitude of the three-phase voltage of each node according to the principle of flat start, that is, set the amplitude of the three-phase voltage of all PV nodes and balance nodes to a given value, and set all PQ nodes The magnitude of the three-phase voltage is 1.0; end.

Compared with the prior art, the present invention has the following beneficial effects:

The invention fully considers the voltage phase displacement of the transformer, determines the connection relationship between the nodes by searching the branches in the power distribution system, and sets the initial value of the phase angle of the three-phase node voltage of the connected nodes according to the digital labels of the branch connection groups . The initial value of the phase angle of the phase A node voltage at the end node of the branch is set to the initial value of the phase angle of the phase A node voltage of the first node of the branch minus 30 times the number of the number label of the branch connection group. The initial value of the phase angle of the voltage of the phase B node at the end node of the branch is set to the initial value of the phase angle of the voltage of the phase A node at the end node of the lagging branch 120°, and the initial value of the phase angle of the voltage of the phase C node of the end node of the branch is set as the leading branch The initial value of the phase angle of the node voltage of phase A of the last node is 120°; the initial value of the amplitude of the node voltage of each node is still set according to the principle of flat start. Setting the initial voltage value of each node according to the present invention can make the set initial voltage value of each node closer to the solution of the power flow calculation, improve the convergence of the three-phase power flow calculation of the power distribution system, and make the original flat start non-convergent The case can be converged, and the number of iterations in the original case of flat start convergence is less.

Description of drawings

The present invention has 3 accompanying drawings. in:

Fig. 1 is a flow chart of a method for setting an initial value of voltage for three-phase power flow calculation in an existing power distribution system.

Fig. 2 is a flow chart of the method for setting the initial value of the voltage for three-phase power flow calculation of the power distribution system according to the present invention.

Figure 3 is a wiring diagram of a 33-node calculation example of the power distribution system.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings, and the 33-node calculation example shown in FIG. 3 is calculated according to the flow chart of the voltage initial value setting method shown in FIG. 2 .

The 33-node calculation example has 33 nodes, among which node 1 is a balance node, node 11 is a PV node, and other nodes are PQ nodes; there are 32 branches, including 1 transformer branch, which is located between nodes 10 and 11 .

The existing voltage initial value setting method and the voltage initial value setting method proposed by the present invention are used to calculate the 33-node calculation example, and the convergence accuracy is 0.000001 during calculation. In order to reflect the influence of the transformer connection group on the convergence of the power flow calculation, the transformer connection group is respectively set as Yy0, Yd1, Yy2, Yd3, Yy4, Yd5, Yy6, Yd7, Yy8, Yd9, Yy10, Yd11 in 12 cases. Calculated. Table 1 shows the iterative results of the power flow calculation using the two voltage initial value setting methods.

Table 1 Comparison of power flow calculation iteration times between two voltage initial value setting methods

It can be seen from Table 1 that, using the method for setting the initial voltage value of the present invention to perform power flow calculation on the 33-node calculation example, all 12 transformer connection groups can converge, and the number of iterations is 4 times; For example, in the power flow calculation, 8 of the 12 transformer connection groups do not converge, and only 4 converge, but the number of iterations is more than the method of the present invention. The calculation results of the example show that the method for setting the initial voltage value of the present invention can greatly improve the convergence of the three-phase power flow calculation of the power distribution system.

Taking the transformer connection group as Yd3 as an example, compare the initial value of the A-phase voltage phase angle of some nodes and the power flow solution in the power flow calculation of the voltage initial value setting method of the present invention. The comparison results are shown in Table 2.

Table 2 The initial value and power flow solution of some node A phase voltage phase angles of the present invention

node number Initial value (°) Tidal current solution (°) 1 0.00 0.00 2 0.00 0.05 3 0.00 0.32 4 0.00 0.53 5 0.00 0.76 6 0.00 1.00 7 0.00 0.83 8 0.00 1.18 9 0.00 1.56 10 0.00 1.96 11 -90.00 -87.94 12 -90.00 -87.93 13 -90.00 -88.03 14 -90.00 -88.11 15 -90.00 -88.15 16 -90.00 -88.18 17 -90.00 -88.26 18 -90.00 -88.27

It can be seen from Table 2 that when the transformer connection group is Yd3, due to the phase shifting effect of the transformer, the power flow calculation value of the node voltage phase angle of nodes 11 to 18 lags behind that of nodes 1 to 10 by nearly 90°. Adopt the voltage initial value setting method of the present invention to set the initial value of the node A phase voltage phase angle of nodes 11 to 18 to -90°, which is not much different from the solution of the power flow calculation, and the power flow calculation is easy to converge; if the node 11 is set according to the flat start The initial value of the phase angle of the node A phase voltage at node 18 is set to 0°, which is very different from the solution of the power flow calculation, and the power flow calculation is not easy to converge, or even diverges.

The present invention can be realized by using any programming language and programming environment, such as C language, C++, FORTRAN, Delphi, etc. The development environment can use Visual C++, Borland C++Builder, Visual FORTRAN, etc.

The present invention is not limited to this embodiment, and any equivalent ideas or changes within the technical scope disclosed in the present invention are listed in the protection scope of the present invention.

Claims (1)

1. a kind of voltage initial value setting method of distribution system three-phase power flow, it is characterised in that：Include the following steps：

A, branch node connection relation array Br is formed；

Branch node connection relation array Br is generated by power transmission line branch data and transformer branch data, each in array Br Branch includes branch first node i, minor details period j and the other number designation m of connection group tri-, wherein power transmission line branch connection group Other number designation is 0；Branch node connection relation array Br is formed to include the following steps：

A1, the first node i for taking power transmission line branch and transformer branch, minor details period j and the other number designation m of connection group are formed The other number designation m of connection group of array Br1, power transmission line branch are 0, if branch number is nBr0；

A2, array Br2 is formed with array Br1, and exchanges each branch first and last node numbers of array Br2, the other number designation of connection group Become 12-m, connection group other number designation is constant when being 0；

A3, merge array Br1 and array Br2 formation array Br, total data number is nBr=2 × nBr0；

B, array Br is ranked up；

The ascending sequence of first node number is pressed to array Br, array BrIS is used in combination to record each node as the first node of branch in number Initial position in group Br；Wherein：Array element BrIS₁=1, array element BrIS_n+1=nBr+1, then array element BrIS_i+1- 1 end position of the first node in array Br for node i as branch；Here n is the number of nodes of distribution system；

C, array Br is scanned for, the phase angle initial value of each node voltage is set；

The phase angle initial value of each node voltage is set, is included the following steps：

C1, it enables n dimensions access identities array Check set to 0, and enables counting variable k=1；

C2, balance nodes number are set as s, enables the phase angle initial value θ of balance nodes A phases_sA=0 °, balance nodes access identities Check_sIt sets 1, and enable array element Gr_k=s；Array Gr storage accessed node and with these nodes that accessed node is connected；

C3, i=Gr is enabled_k, p=BrIS_i；

C4, array element Br is set_pBranch end-node be j, the other number designation of connection group be m；

Whether C5, decision node j had accessed, and C8 was gone to step if node j has been accessed；

C6, by following formula calculate node j node voltage phase angle initial value；

C7, Check is set_j=1, node number j is appended in Gr arrays；

C8, p=p+1 is enabled；

C9, judge whether p is more than BrIS_i+1- 1, if p is not more than BrIS_i+1- 1, then go to step C4；

C10, k=k+1 is enabled；

C11, judge whether k is more than number of nodes n, C3 is gone to step if k is not more than number of nodes n；Otherwise terminate；

D, the phase angle initial value for adjusting each node three-phase voltage, make its main value (- 180 °, 180 °] in range；

By the phase angle initial value plus or minus 360 ° of integral multiple to each node three-phase voltage, each node three-phase voltage is adjusted Phase angle initial value, make its main value (- 180 °, 180 °] in range；(- 180 °, 180 °] it indicates more than -180 ° but is less than or equal to 180 ° Section；

E, the amplitude of the three-phase voltage of all nodes is set；The amplitude of each node three-phase voltage is set by flat startup principle, that is, is set The amplitude for setting all PV nodes and balance nodes three-phase voltage is given value, and the amplitude that all PQ nodes three-phase voltages are arranged is 1.0；Terminate.