CN112350320A - Method for improving dynamic reconfiguration of power distribution network - Google Patents

Abstract

A method for improving the dynamic reconfiguration of distribution network. On the premise of realizing the dynamic reconfiguration of the basic distribution network, according to the numerical analysis of the node voltage improvement before and after the reconfiguration, the number of optimal topologies is further integrated to realize the division of dynamic time periods. , the purpose of improving the power quality is achieved by changing the grid topology of the effective number of times; the method proposed by the invention is based on the active distribution network scene after the distributed power source is connected, and realizes the distribution network planning considering the dynamic behavior of the distributed power source. , and improved the algorithm on the basis of traditional dynamic network reconfiguration, which overcomes the problem of frequent grid topology changes in dynamic reconfiguration, and at the same time maintains that the node voltage can still be guaranteed under the condition of reducing grid topology changes. The optimization ability of the system enhances the practical engineering application significance of traditional distribution network reconstruction under the premise of improving power quality.

Description

Method for improving dynamic reconfiguration of power distribution network

Technical Field

The invention relates to the technical field of power distribution network planning of a power system, in particular to an active power distribution network technology after a high-permeability access distributed power supply, and discloses a method for improving dynamic reconfiguration of a power distribution network.

Background

With the rapid development of new energy power generation technology in China, a distributed power system with the largest scale and the highest permeability in the world is formed in China. The distributed generation output is influenced by weather factors, has strong randomness and large day and night change, and is influenced by factors such as random access lacking planning, three-phase unbalanced access and the like, so that the electric energy quality condition of the high-permeability distributed active power distribution network is worried, especially the voltage quality is often out of limit, a lot of difficulties are brought to the interaction mechanism analysis of the power distribution system, and the development of the active power distribution network containing the distributed power supply is hindered.

In order to reduce the influence of dynamic behavior of an active power distribution network containing a distributed power supply, the industry proposes a steady-state response mechanism for fundamentally solving an active power distribution system in a power distribution network planning period, namely, multi-period dynamic reconstruction of the power distribution network is realized by establishing a planning mathematical model, the reconstruction problem is essentially a nonlinear dynamic planning problem of multi-objective optimization, but the planning method has the problem of separation of dynamic period division from topology optimization, the condition that a switch cannot be closed during network reconstruction occurs, each action of a section switch and a contact switch has a safety risk and a power supply reliability risk, and the inherent defect of the method for reconstructing the power distribution network is insufficient. How to better solve the problem of dynamic planning of an active power distribution network containing distributed power supplies is still a technical problem which is not solved.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a method for improving the dynamic reconfiguration of a power distribution network, which solves the problem of frequent topology transformation of a grid frame in the dynamic reconfiguration, effectively improves the problem of separation of dynamic time division and topology optimization existing in the traditional planning method, and is an improvement on the traditional power distribution network reconfiguration method.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a method for improving dynamic reconfiguration of a power distribution network comprises the following steps:

(1) on the basis of calculating the power flow of the power distribution network by a Newton Raphson method, calculating the power flow condition of the power distribution network containing DGs by using a semi-invariant method, describing uncertainty of DG dynamic behavior to the power distribution network by Gram-Charlie series, simulating to obtain node voltage and branch power flow state of a certain topology, further realizing power distribution network reconstruction by adopting an NSGA-II algorithm to obtain an optimal topology structure at each time period of 24h a day, and taking the obtained 24 optimal topology structures as an initial reconstruction set;

(2) according to the 24 topological structures in the step (1), the topological structures are combined to reduce the action times of the network switch, the topological structures with similar structures are preliminarily combined, one topological structure is selected to replace other topological structures with similar shapes, and the output curve of the distributed power supply is a continuous function, so that the situation that the two topological structures are similar in the larger time period does not exist;

(3) for the integration of adjacent time topologies with dissimilar structures, the concepts of the optimal pressure rate rho and the optimal pressure parameter alpha are introduced:

maxα_t＝E_ρE_ΔZ (2)

in the formula, ρ_tVoltage optimization rate, α, before and after planning for each time period t of the day_tFor time t with voltage optimization desired, Z_opt.t’Planning a pre-voltage offset indicator for time period t, Z_opt.t”Planning the post-voltage offset, Δ Z, for a period of t_tFor voltage optimization purposes, E_ρAnd E_ΔZAre respectively rho_tAnd Δ Z_tAverage value of (d);

the optimal voltage rate rho and the optimal voltage parameter alpha are obtained by the formulas (1) and (2), then the voltage optimization degrees of all topologies are compared according to the optimal voltage parameter alpha, if the voltage optimization capacities of different topological structures are similar, the two topological structures are also similar in nature, and can be combined into one type;

(4) within 24 time periods within adjacent time periods_tCase of small phase difference | α_t-α_t-1|＜Δα_εBy default, t-period is combined with t-1 period, Δ α_εThe setting value is the maximum setting value; adjacent time segments alpha within 24 segments_tCase | α where difference is large_t-α_t-1|≥Δα_εThen, the alpha is compared according to the following principle_t，α_t+1，α_t-1If α is_t-α_t-1|≤|α_t-α_t+1If not, the t time period is combined with the t-1 time period;

(5) the condition of merging termination is the limit of the total number of actions of the section switch and the tie switch, so that the number of the integrated topological structures is less than the upper limit of the action times of the switches:

in the formula, S_∑Is the sum of the action times S of all branch switches and interconnection switches in the planning time period t_MaxFor limiting the number of physical actions of the branch switch and the tie switch, S_ζFor the number of Zeta actions of the switch within the programmed period t, S_ζ,MaxFor the limitation of the number of physical actions of the zeta-action switch, S_switchIs a collection of actionable switches;

if the limitation of the switch action requirement is not met, jumping to the step (4) to continue merging the topology, updating the time interval information after merging for one round, continuing the process circulation recombination until the circulation condition is met, and jumping out of the circulation if the limitation of the switch action requirement is met;

(6) and (3) if the cycle condition of the switch action constraint of the formula (3) is met, a cycle output dynamic reconfiguration execution mode is skipped to obtain a final typical topological structure.

The invention has the advantages that:

the difference of the dynamic behavior of the distributed power supply at different time intervals of 24h a day finally and essentially affects the reconstructed optimal topological structure, so that 24h a day can be divided into a plurality of time intervals, if the concept of limit is adopted, the time of day can be subdivided into n time intervals, the n optimal topological structures are also corresponding, in the practical engineering, the pressure is brought to the section switch and the contact switch by considering the frequent change of the dynamic topological structure, the unnecessary operation risk is caused, the action times of the remote control switch are required to be maintained at a lower level as much as possible, the requirement is provided for the action times of the movable switch, as the output curve of the distributed power supply changes less in the adjacent time intervals, the method for planning the 24h time intervals into less time intervals is feasible, the time intervals are planned based on the concept, the corresponding topological structures are reduced, the number of switching operations is reduced. But simultaneously, the requirement that the voltage improvement degree is not much different from the theoretical value in one day before and after the time period is reduced must be met, so that the method applies a semi-invariant random power flow algorithm to respectively simulate the random power flow of the topology in each time period, and the topology power quality conditions before and after the time period division are evaluated based on the obtained simulation data of the power distribution network.

Drawings

Fig. 1 is a detailed flowchart of the dynamic reconfiguration strategy of the present invention.

Fig. 2 is a diagram of an IEEE33 node power distribution system architecture.

Detailed Description

The present invention will be described in detail with reference to the accompanying drawings.

The theory presented is verified by taking an IEEE33 node power distribution network as an example. The head end reference voltage of the arithmetic example shown in FIG. 2 is 35kV, the three-phase power reference value is 15MVA, the total deterministic load of the network is 12MW + j6Mvar, and the balance node of the system is node No. 0. The system is provided with 33 nodes, wherein the nodes 0, 14 and 24 are connected to a distributed photovoltaic power supply, the node 7 is an EV charging station, the rest 29 nodes are deterministic load nodes, the nodes K1 to K32 are branch sectional switches, the nodes T1 to T5 are net rack connection switches, and the probability constraint condition confidence interval of the line capacity and the node voltage is 0.85.

Referring to fig. 1, a method for improving dynamic reconfiguration of a power distribution network includes the following steps:

step (1): on the basis of calculating the power flow of the power distribution network by a Newton Raphson method, a semi-invariant method is introduced to calculate the power flow condition of the power distribution network containing DGs, uncertainty of DG dynamic behavior on the power distribution network is described by Gram-Charlie series, the node voltage and branch power flow state of a certain topology are obtained through simulation, static reconstruction work of the IEEE-33 power distribution network in each unit time is further completed by adopting an NSGA-II algorithm, the optimal topology structure of each period of 24 hours a day is obtained, and the obtained 24 optimal topology structures are used as an initial reconstruction set.

Step (2): in the step (1), the topologies with similar structures are preliminarily combined, one of the topologies is selected to replace the topology with similar shape, and the output curve of the distributed power supply is a continuous function, so that the situation that the two topologies are similar in a larger time period does not exist; and then counting the voltage optimization conditions of the respective periods after the preliminary combination.

And (3): in the step (2), 24 topologies are preliminarily combined, and for the integration of the topologies with dissimilar structures at adjacent time, concepts of the optimal pressure rate ρ and the optimal pressure parameter α are introduced: and calculating according to the formula (1) and the formula (2) to obtain the optimal pressure rate rho and the optimal pressure parameter alpha of each time period after the initial combination

maxα_t＝E_ρE_ΔZ (2)

In the formula, ρ_tReflected is the pre-and post-planning voltage optimization rate, α, for each time period t of the day_tReflecting the desired degree of voltage optimization during the t period, Z_opt.t’Planning a pre-voltage offset indicator for time period t, Z_opt.t”Planning the post-voltage offset, Δ Z, for a period of t_tFor voltage optimization purposes, E_ρAnd E_ΔZAre respectively rho_tAnd Δ Z_tAverage value of (a).

And the optimal pressure rate rho and the optimal pressure parameter alpha are obtained by substituting the power flow calculation result into the formula (1) and the formula (2).

And step 1, obtaining the node voltage and branch power flow state of the topology. An optimal topological structure is formed after the static reconstruction of the power distribution network, and the node voltage value of the optimal topology can obtain the voltage deviation index Z after the optimization reconstruction_opt.t’The original voltage deviation condition Z can be obtained from the original topological node voltage which is not reconstructed optimally_opt.t”The required data can be obtained by substituting the equations (1) and (2).

Then comparing the voltage optimization degree of each topology according to the optimal voltage parameter alpha, if the voltage optimization capacities of different topology structures are similar, the two types of topology structures have similar essential action capacities, and can be combined into one type;

the results are shown in Table 1.

TABLE 1 time period after preliminary reconstitution

As shown in the results of table 1, 24 time periods are preliminarily combined into 10 time periods, the 10 time periods correspond to 10 typical topologies, the 10 time periods have similar topological structures from 2 o ' clock to 5 o ' clock in the morning, while the 6 o ' clock, 7 o ' clock and 8 o ' clock in the morning increase due to the increase of loads and the uncertainty of the distributed photovoltaic output, the optimal topological structures of the three time periods are greatly different, the loads in the daytime tend to be stable, the distributed photovoltaic power output tends to be stable, the topological structures thereof are similar, and the later time periods, particularly 19 o ' clock, 20 o ' clock and 21 o ' clock to 22 o ' clock, the topological structures thereof are different due to the influence of the charging power of the electric vehicle. And (4) after the initial combination, the number of actions of the tie switch and the section switch in the topology is still excessive, and the step is carried out for further combining the time periods.

And (4): comparing the voltage optimization degree (optimum voltage parameter) alpha of each time interval_t，α_t+1，α_t-1If α is_t-α_t-1|≤|α_t-α_t+1I thenthe time period t is combined with the time period t-1, otherwise, the time period t is combined with the time period t + 1; but provided that | α_t-α_t-1|＜Δα_εIn this embodiment, Δ α_εThe default prescribed t period is merged with the t-1 period, i.e., directly backwards, 0.0030/p.u.

And (5): the condition of merging termination is the limit of the action total number of the section switch and the tie switch, the action total number of the remote control switch in the embodiment is less than 15 times in one day, the IEEE33 node power distribution network has 5 remote control switches in total, namely the number of the typical topology networks needing to be output is less than 3, and the time periods of 24h in one day are merged into three large time periods. The iterative algorithm process of steps (4) and (5) is shown in table 2.

TABLE 2 iterative procedure for dynamic reconstruction periods

As shown in table 2, the entire merge requires 5 iterations to complete. The difference value between the optimal pressure parameter of the first iteration 2-5 point time period and the optimal pressure parameter of 6 points is smaller than the threshold value, and the time periods are directly merged backwards into 2-6 points; if the parameter difference value between the 7 point and the 8 point in the second iteration is larger than the threshold value, whether the optimal pressure parameter in the time interval is close to the 6 point or close to the 8 point needs to be considered, if the time interval is close to the 6 point, the optimal pressure parameter and the 6 point are combined forwards and integrated into a 2-7 point time interval; in the third iteration process, the parameter difference values between the sections from 8 points to 18 points are all smaller than the threshold value, so that the sections are directly combined into the 8-18-point time period; the remaining two iterations and so on.

And (6): and finally, outputting a dynamic reconstruction scheme to obtain a plurality of final typical topological structures. The dynamic reconstruction is divided into 3 reconstruction periods (23: 00-07: 00, 07: 00-19: 00, and 19: 00-23: 00) under the condition that the switch constraint condition is satisfied. On the premise of ensuring lower switching conversion times, the method enables the voltage value of the whole day of dynamic reconstruction and optimal reconstruction in each time period to be similar, but has relatively higher voltage optimization effect compared with a non-reconstruction and static reconstruction strategy.

Claims (1)

1. A method for improving dynamic reconfiguration of a power distribution network is characterized by comprising the following steps:

(1) on the basis of calculating the power flow of the power distribution network by a Newton Raphson method, calculating the power flow condition of the power distribution network containing DGs by using a semi-invariant method, describing uncertainty of DG dynamic behavior to the power distribution network by Gram-Charlie series, simulating to obtain node voltage and branch power flow state of a certain topology, further realizing power distribution network reconstruction by adopting an NSGA-II algorithm to obtain an optimal topology structure at each time period of 24h a day, and taking the obtained 24 optimal topology structures as an initial reconstruction set;

(2) according to the 24 topological structures in the step (1), the topological structures are combined to reduce the action times of the network switch, the topological structures with similar structures are preliminarily combined, one topological structure is selected to replace other topological structures with similar shapes, and the output curve of the distributed power supply is a continuous function, so that the situation that the two topological structures are similar in the larger time period does not exist;

(3) for the integration of adjacent time topologies with dissimilar structures, the concepts of the optimal pressure rate rho and the optimal pressure parameter alpha are introduced:

maxα_t＝E_ρE_ΔZ (2)

in the formula, ρ_tVoltage optimization rate, α, before and after planning for each time period t of the day_tFor time t with voltage optimization desired, Z_opt.t’Planning a pre-voltage offset indicator for time period t, Z_opt.t”Planning the post-voltage offset, Δ Z, for a period of t_tFor voltage optimization purposes, E_ρAnd E_ΔZAre respectively rho_tAnd Δ Z_tAverage value of (d);

the optimal voltage rate rho and the optimal voltage parameter alpha are obtained by the formulas (1) and (2), then the voltage optimization degrees of all topologies are compared according to the optimal voltage parameter alpha, if the voltage optimization capacities of different topological structures are similar, the two topological structures are also similar in nature, and can be combined into one type;

(4) within 24 time periods within adjacent time periods_tCase of small phase difference | α_t-α_t-1|＜Δα_εBy default, t-period is combined with t-1 period, Δ α_εThe setting value is the maximum setting value; adjacent time segments alpha within 24 segments_tCase | α where difference is large_t-α_t-1|≥Δα_εThen, the alpha is compared according to the following principle_t，α_t+1，α_t-1If α is_t-α_t-1|≤|α_t-α_t+1If not, the t time period is combined with the t-1 time period;

(5) the condition of merging termination is the limit of the total number of actions of the section switch and the tie switch, so that the number of the integrated topological structures is less than the upper limit of the action times of the switches:

in the formula, S_∑Is the sum of the action times S of all branch switches and interconnection switches in the planning time period t_MaxFor limiting the number of physical actions of the branch switch and the tie switch, S_ζFor the number of Zeta actions of the switch within the programmed period t, S_ζ,MaxFor the limitation of the number of physical actions of the zeta-action switch, S_switchIs a collection of actionable switches;

if the limitation of the switch action requirement is not met, jumping to the step (4) to continue merging the topology, updating the time interval information after merging for one round, continuing the process circulation recombination until the circulation condition is met, and jumping out of the circulation if the limitation of the switch action requirement is met;

(6) and (3) if the cycle condition of the switch action constraint of the formula (3) is met, a cycle output dynamic reconfiguration execution mode is skipped to obtain a final typical topological structure.

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