CN102780220A - Power flow calculation method for electric distribution network comprising PV constant distributed generation - Google Patents

Abstract

The invention relates to a power flow calculation method for an electric distribution network comprising a PV constant distributed generation. The method comprises the following steps of: 1, acquiring an impedance matrix of all PV nodes in a network; 2, setting a system parameter initial value; 3, acquiring an admittance matrix Y according to the position of the accessed PV constant distributed generation; 4, updating node current, and calculating each node voltage through a forward-backward sweep method; 5, judging whether the iterative node voltage meets convergence conditions or not, if so, turning to step 7, if not, turning to step 6; 6, calculating a current change amount Delta I of the PV nodes according to a formula: Delta I=Y Delta U, and turning to step 5; and 7, outputting a power flow calculation result. Compared with the prior art, the method has the advantages of exact calculation, being suitable for small load conditions and the like.

Description

The distribution power system load flow calculation method that contains the constant type distributed power source of PV

Technical field

The present invention relates to a kind of distribution network tidal current computing method, especially relate to the distribution power system load flow calculation method of the constant type distributed power source of a kind of PV of containing.

Background technology

Increasing distributed power source (Distributed Generations; Be called for short DG) the access power distribution network; To have circuit R/X numerical value bigger because power distribution network is compared power transmission network; Characteristics such as voltage is lower, and the three-phase imbalance situation is more serious, this makes the distribution trend calculate node type, computational methods has been proposed new requirement.

Before having, the distribution power system load flow calculation common method pushes back for method, modified Newton method, loop analysis and implicit expression Zbus Gaussian processes etc.Before push back Dai Fa because its computational efficiency is higher, and convergence is good, programming is simple, so in the distribution trend is calculated, be widely used at present.But because present increasing preceding pushing back for the injecting reactive current penalty method amount of calculation of method for PV node (node that is connected with PV type distributed power source), and do not consider the load influence, if it is less to insert duty ratio, its result of calculation is obviously inaccurate.Therefore need improve preceding pushing back for the method for method processing PV node.

Summary of the invention

The object of the invention is exactly for the defective that overcomes above-mentioned prior art existence the distribution power system load flow calculation method that contains the constant type distributed power source of PV that a kind of trend calculated convergence rate is fast, be fit to little load condition to be provided.

The object of the invention can be realized through following technical scheme:

A kind of distribution power system load flow calculation method that contains the constant type distributed power source of PV may further comprise the steps:

1) impedance matrix of all PV nodes in the acquisition network;

2) the system parameters initial value is set: the voltage perunit value of root node and all PV nodes is made as 1, and all node voltage perunit values are made as 1 during first iteration;

3) according to the position of the constant type distributed power source of PV that inserts, obtain admittance matrix Y;

4) upgrade node current, push back before the utilization for method and calculate each node voltage;

Whether each node voltage of 5) judging this iteration satisfies the condition of convergence, if, then change step 7), if not, then change step 6);

6) according to the electric current change amount Δ I of Δ I=Y Δ U calculating PV node, change step 5);

7) output calculation of tidal current.

Push back for method before in the described step 4) and be specially:

If the k time iteration obtains the i node voltage and flow into the i node current for

hence one can see that for

, the electric current that is provided by distributed power source is:

$I_{\mathrm{DG}}^{(k+1)}=\frac{S_{\mathrm{DGi}}^{\left(k\right)}}{U_i^{\left(k\right)}}$

Wherein, The k time iterative value of the power that

provides for i node place distributed power source, promptly

$S_{\mathrm{DGi}}^{\left(k\right)}=P_{\mathrm{DGi}}^{\left(k\right)}+{\mathrm{jQ}}_{\mathrm{DGi}}^{\left(k\right)}$

Electric current

is:

$I_{i-1}^{(k+1)}=-I_{\mathrm{DG}}^{(k+1)}+I_L^{(k+1)}+I_i^{(k+1)}$

Wherein,

is the k+1 time iterative value of load current;

K+1 voltage iterative value of i node does

$U_i^{(k+1)}=U_{i-1}^{(k+1)}-I_{i-1}^{(k+1)}{Z}_{i-1}$

Wherein, Z _I-1Impedance for the i-1 node.

Be meant with the condition of convergence in the described step: the absolute value of the difference of all these iteration voltage magnitudes of non-PV node and previous iteration voltage magnitude is less than set-point ε, and the absolute value of the difference of this iteration voltage magnitude of PV node and given voltage magnitude is also less than set-point ε.

Compared with prior art, application node admittance matrix of the present invention directly seeks out the required electric current change amount of next iteration, and upgrades electric current, need not come that more new node is idle through asking idle change amount.Because when node inserts under the less situation of duty ratio; System's admittance matrix had considerable influence when the equivalent admittance of load was calculated trend; Therefore the inventive method has been considered the equivalent influence of load simultaneously; Obtain new node admittance matrix, enable more accurately under the little load condition of processing node the distributed power source calculating of being incorporated into the power networks.

Description of drawings

Fig. 1 is the schematic flow sheet of the inventive method;

Fig. 2 is the network structure of the embodiment of the invention 2;

Fig. 3 is the scheme comparison diagram as a result in the embodiment of the invention 2.

Embodiment

Below in conjunction with accompanying drawing and specific embodiment the present invention is elaborated.

Embodiment 1

As shown in Figure 1, a kind of distribution power system load flow calculation method that contains the constant type distributed power source of PV may further comprise the steps:

1) impedance matrix of all PV nodes in the acquisition network;

2) the system parameters initial value is set: the voltage perunit value of root node and all PV nodes is made as 1, and all node voltage perunit values are made as 1 during first iteration;

3) according to the position of the constant type distributed power source of PV that inserts, obtain admittance matrix Y;

4) upgrade node current, push back before the utilization for method and calculate each node voltage:

If the k time iteration obtains the i node voltage and flow into the i node current for

hence one can see that for

, the electric current

that is provided by distributed power source is:

$I_{\mathrm{DG}}^{(k+1)}=\frac{S_{\mathrm{DGi}}^{\left(k\right)}}{U_i^{\left(k\right)}}$

Wherein, The k time iterative value of the power that

provides for i node place distributed power source, promptly

$S_{\mathrm{DGi}}^{\left(k\right)}=P_{\mathrm{DGi}}^{\left(k\right)}+{\mathrm{jQ}}_{\mathrm{DGi}}^{\left(k\right)}$

Electric current

is:

$I_{i-1}^{(k+1)}=-I_{\mathrm{DG}}^{(k+1)}+I_L^{(k+1)}+I_i^{(k+1)}$

Wherein,

is the k+1 time iterative value of load current;

K+1 voltage iterative value of i node does

$U_i^{(k+1)}=U_{i-1}^{(k+1)}-I_{i-1}^{(k+1)}{Z}_{i-1}$

Wherein, Z _I-1Impedance for the i-1 node;

Whether each node voltage of 5) judging this iteration satisfies the condition of convergence, if, then change step 7), if not, then change step 6);

Be meant with the condition of convergence in the described step: the absolute value of the difference of all these iteration voltage magnitudes of non-PV node and previous iteration voltage magnitude is less than set-point ε, and the absolute value of the difference of this iteration voltage magnitude of PV node and given voltage magnitude is also less than set-point ε;

6) according to the electric current change amount Δ I of Δ I=Y Δ U calculating PV node, change step 5);

7) output calculation of tidal current.

Embodiment 2

Adopt 33 nodes to join a net and analyze network structure such as Fig. 2.If the electrical network reference voltage is 12.66kV, reference power is 10MVA, and computational accuracy ε is 10 ^-4

For research inserts DG to the influence of system and the feasibility of algorithm, draft 8 schemes, as shown in table 1.Wherein, little load condition is that load with 7,8,24,25,30 5 nodes in former 33 node systems becomes original 1/10th.

Table 1 scheme is described

Get the part of nodes in the system, the voltage perunit value that calculates decreases result and iterations such as table 2 with net.Scheme 1-5 contrast is as shown in Figure 3.

Table 2 different schemes lower part node calculation of tidal current

Can find out that from table 2 behind the access distributed power source, each point voltage and distribution-free formula power supply are significantly improved, the DG access point improves at most.Therefore for concrete system, can DG be linked into the poorest point of system voltage situation, can well improve the stability of a system.

Scheme 2 is compared and can be known with scheme 3, and the distributed power source access point is terminal the closer to system, and then its effect of raising voltage is good more, and net decreases also more little.Under the little load condition, owing to total gaining merit all significantly reduces with idle, so voltage and net damage situation are better than the situation of normal duty.

Scheme 2 is compared with scheme 6,7, and the result can prove this algorithm validity with this much at one.From 16,18,32 node datas can find out that this algorithm embodies its relative superiority under the more situation of branch node number, and this has obvious embodiment in more large-scale power distribution network.

From table 2, it can also be seen that, obviously do not increase iterations behind the constant type distributed power source of access PV, guaranteed computational speed.Under little load condition, iterations is identical during with no DG, and scheme 4 is compared with scheme 8, and the result has obvious difference, and the criterion of proof algorithm is not accurate enough when handling little load condition, so this algorithm is feasible in the method for handling under the little load condition.

To sum up; According to pushing back before the power distribution network for power flow algorithm; Proposed the method for new processing PV node in conjunction with existing to inserting behind the DG preceding pushing back the research for method, the application node admittance matrix directly seeks out the required electric current change amount of next iteration; And the renewal electric current, need not come that more new node is idle through asking idle change amount.Because under the less situation of node access duty ratio, system's admittance matrix had considerable influence when the equivalent admittance of load was calculated trend, therefore considered the influence of load equivalence, obtain new node admittance matrix.Through emulation, prove that the method can be quick, accomplish the trend calculating that the constant type DG of PV is incorporated into the power networks effectively.

Claims (3)

1. a distribution power system load flow calculation method that contains the constant type distributed power source of PV is characterized in that, may further comprise the steps:

1) impedance matrix of all PV nodes in the acquisition network;

2) the system parameters initial value is set: the voltage perunit value of root node and all PV nodes is made as 1, and all node voltage perunit values are made as 1 during first iteration;

3) according to the position of the constant type distributed power source of PV that inserts, obtain admittance matrix Y;

4) upgrade node current, push back before the utilization for method and calculate each node voltage;

Whether each node voltage of 5) judging this iteration satisfies the condition of convergence, if, then change step 7), if not, then change step 6);

6) according to the electric current change amount Δ I of Δ I=Y Δ U calculating PV node, change step 5);

7) output calculation of tidal current.

2. a kind of distribution power system load flow calculation method that contains the constant type distributed power source of PV according to claim 1 is characterized in that, pushes back for method before in the described step 4) to be specially:

If the k time iteration obtains the i node voltage and flow into the i node current for

hence one can see that for

, the electric current

that is provided by distributed power source is:

$I_{\mathrm{DG}}^{(k+1)}=\frac{S_{\mathrm{DGi}}^{\left(k\right)}}{U_i^{\left(k\right)}}$

Wherein, The k time iterative value of the power that provides for i node place distributed power source, promptly

$S_{\mathrm{DGi}}^{\left(k\right)}=P_{\mathrm{DGi}}^{\left(k\right)}+{\mathrm{jQ}}_{\mathrm{DGi}}^{\left(k\right)}$

Electric current

is:

$I_{i-1}^{(k+1)}=-I_{\mathrm{DG}}^{(k+1)}+I_L^{(k+1)}+I_i^{(k+1)}$

Wherein,

is the k+1 time iterative value of load current;

K+1 voltage iterative value of i node does

$U_i^{(k+1)}=U_{i-1}^{(k+1)}-I_{i-1}^{(k+1)}{Z}_{i-1}$

Wherein, z _I-1Impedance for the i-1 node.

3. a kind of distribution power system load flow calculation method that contains the constant type distributed power source of PV according to claim 1; It is characterized in that; Be meant with the condition of convergence in the described step: the absolute value of the difference of all these iteration voltage magnitudes of non-PV node and previous iteration voltage magnitude is less than set-point ε, and the absolute value of the difference of this iteration voltage magnitude of PV node and given voltage magnitude is also less than set-point ε.

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