Evaluation index and analysis method for voltage quality of power distribution network containing energy storage system

Abstract

The invention discloses an evaluation index and analysis method for voltage quality of a power distribution network containing an energy storage system. The method comprises the following steps: constructing an evaluation index system; acquiring historical original data of a plurality of monitoring nodes arranged at a multi-stage bus of the power distribution network containing the energy storage system; weight distribution of multi-stage bus data monitoring nodes: bus weights are distributed by taking bus voltage grades and load conditions connected to bus sending-out lines as indexes; establishing an evaluation system; by establishing the voltage quality evaluation index system of the power distribution network containing the energy storage system, the influence of energy storage access on the voltage of the power distribution network is studied, the utilization rate of system electric energy is improved, the network loss is reduced, and the electric energy quality is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of voltage quality analysis of a distribution network including an energy storage system, and in particular relates to an evaluation index and an analysis method for the voltage quality of a distribution network including an energy storage system. Background Art

[0002] With the widespread application of photovoltaic power generation and other distributed power sources in distribution networks, higher requirements are placed on the stable operation of the system. The randomness and intermittency of distributed power sources will lead to voltage and frequency fluctuations. The harmonic pollution caused by power electronic devices will also affect the stable operation of the power grid to varying degrees, bringing negative impacts on equipment safety and the economic operation of the power grid.

[0003] Among them, the energy storage system has a fast energy response speed and has the advantages of "low storage and high generation". It can alleviate the power supply shortage during peak hours of electricity consumption, and can also solve the problem of being unable to fill the active power shortage when using reactive power compensation devices, while taking into account the purpose of improving the power supply capacity of the distribution network and improving the low voltage condition; at the same time, the energy storage system can also improve the voltage fluctuations caused by the grid connection of distributed power sources and different types of loads on the system, and has the effect of smoothing the power load and stabilizing the operation of the system. It has a significant impact on the voltage regulation of the distribution network and can be used for the power regulation of the power grid system.

[0004] In order to enable the energy storage system to charge and discharge flexibly according to the grid status and load demand to maintain voltage stability, it is necessary to determine which energy storage system to deploy at which location and the energy storage capacity required at each location, analyze and evaluate the load characteristics and voltage quality issues of the distribution network, and evaluate them through corresponding voltage quality evaluation indicators.

[0005] Therefore, in order to solve the above problems, it is necessary to develop an evaluation index and analysis method for the voltage quality of the distribution network containing energy storage systems. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide an evaluation index and analysis method for the voltage quality of a distribution network containing an energy storage system, to establish an evaluation index system for the voltage quality of a distribution network containing an energy storage system, to study the impact of energy storage access on the voltage of the distribution network, to facilitate improving the system's power utilization rate, reducing network losses, and improving power quality.

[0007] The object of the present invention is achieved by: an evaluation index and analysis method for voltage quality of a distribution network including an energy storage system, comprising the following steps:

[0008] S1. Construct an evaluation index system, including establishing evaluation indicators and using voltage stability indicators to quantitatively evaluate the voltage quality of the distribution network containing the energy storage system;

[0009] S2. Collecting historical raw data of multiple monitoring nodes located at multi-level buses of a distribution network including an energy storage system;

[0010] S3. Weight allocation of multi-level bus data monitoring nodes; bus weight allocation based on bus voltage level and load conditions of bus outgoing lines, specifically including the following steps: S31. Establishing the calculation standard of load index and voltage level index; S32. Allocating the collective weight P of each level of bus in the distribution network according to the number of buses of each voltage level; i ; S33, according to the load conditions of each busbar transmission line, assign the weight Q of each busbar in the same voltage level busbar j ; S34, calculate the weight k of each bus in the distribution network ij , where k ij =P i Q j ;

[0011] S4. Establish an evaluation system; specifically, the following steps are included: S41. Establish a scoring formula; S42. Define the scoring level and set conditions for the total score level; S43. Calculate the score x at each monitoring node according to the scoring formula i ; S44, calculate the expected value E of each monitoring node score i and variance σ; S45, obtain the final evaluation result based on its expected value and variance as well as the limiting conditions, and calculate the score x of each single point i Draw a two-dimensional scatter plot and mark each point by area.

[0012] Furthermore, the voltage stability index in step S1 includes voltage fluctuation and voltage fluctuation frequency, wherein in the voltage fluctuation frequency index, the interval between two adjacent voltage changes less than 30ms is regarded as one voltage fluctuation;

[0013] In the voltage fluctuation index, the voltage fluctuation value is the two extreme values ​​of the voltage effective value U max and U min The difference between the rated voltage U N The percentage represents its relative percentage value, and its calculation formula is expressed as:

[0014] ,

[0015] Where U max and U min They are two adjacent extreme voltages of the power frequency voltage amplitude modulation wave; specifically, a voltage change rate greater than 0.2% per second is regarded as voltage fluctuation.

[0016] Furthermore, the method for calculating the collective weight of each level of bus in step S32 includes considering the difference in the influence degree of buses of different voltage levels, defining the weight ratio of the lower level bus to the adjacent upper level bus as 1:5 without considering other factors, assuming that the first level is the lowest voltage level and the mth level is the highest voltage level. If the number of voltage buses of each level is n1, n2…n m , the collective weight of the busbar at level i is:

[0017] .

[0019] Furthermore, in the busbars of the same voltage level in step S33, the weight distribution of each busbar is determined according to the proportion of load indicators in the transmission lines of each busbar, and the weight of each load indicator is determined by the hierarchical analysis method.

[0020] Furthermore, the load index includes primary load, secondary load, sensitive load and number of users, and the weight calculation formula of each bus in the same voltage level bus is:

[0021] Q j =W1a j +W2b j +W3c j +W4d j ;

[0022] where a j 、b j 、c j ,d j They are the load indicators connected to bus j in the bus with the same voltage level, namely the proportion of primary load, secondary load, sensitive load and number of users. W1, W2, W3 and W4 are the weights of each load indicator determined by the hierarchical analysis method.

[0023] Furthermore, the scoring formula in step S41 includes setting the upper limit of the voltage fluctuation at the monitoring node after grid connection to 0 points, and setting no voltage fluctuation to 100 points. Then, the scoring calculation formula within the unit sampling time of T hours is:

[0024] y T =100-(25r1+2.5r2+0.25r3+0.025r4) / T;

[0025] Among them, r1, r2, r3, and r4 respectively represent the frequencies corresponding to the four voltage fluctuation levels, and the values ​​of r1, r2, r3, and r4 meet the limited number of times, that is, r1≤T, r2≤10T, r3≤100T, r4≤1000T.

[0026] Furthermore, the definition of the scoring level in step S42 specifically includes: dividing 0-100 into four levels, [90, 100] is excellent, [70, 90) is good, [50, 70) is qualified, [30, 50) is poor, and [0, 30) is extremely poor; the limiting conditions of the total score level include:

[0027] The proportion of "very poor" scores is ≥ 3%, and the total score level shall not exceed the level of "poor";

[0028] The proportion of “poor” scores shall be ≥ 8%, and the total score level shall not exceed the level of “pass”.

[0029] Furthermore, the expected value E in step S44 i The calculation formula of the sum variance σ is as follows:

[0030]

[0031] ;

[0032] Among them, k i represents the weight of the i-th busbar.

[0033] Due to the adoption of the above technical scheme, the beneficial effects of the present invention are as follows: by establishing a voltage quality evaluation index system for a distribution network including an energy storage system, taking voltage fluctuation and voltage fluctuation frequency as evaluation indicators, and considering the bus level at which different monitoring nodes are located and the load conditions connected to the bus, weights are allocated to the buses at which different monitoring nodes are located, the weight of each bus in the bus of each voltage level is established, the expectation and variance of the monitoring node are obtained, and the dynamic performance differences of the overall distribution network and the distributed power source access are evaluated and determined, which facilitates the subsequent optimization control and adjustment of the distributed power source, line or device. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of the present invention.

[0035] Figure 2 It is a flowchart of step S3 in the present invention.

[0036] Figure 3 It is a flowchart of step S4 in the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0038] like Figure 1 , Figure 2 , Figure 3 As shown, an evaluation index and analysis method for the voltage quality of a distribution network including an energy storage system includes the following steps:

[0039] S1. Construct an evaluation index system; including establishing evaluation indicators, using voltage stability indicators to quantitatively evaluate the voltage quality of the distribution network containing the energy storage system; specifically, voltage stability indicators include voltage fluctuation and voltage fluctuation frequency, where the interval between two adjacent voltage changes less than 30ms in the voltage fluctuation frequency indicator is considered a voltage fluctuation; in the voltage fluctuation indicator, the voltage fluctuation value is the two extreme values ​​of the voltage effective value U max and U min The difference between the rated voltage U N The percentage represents its relative percentage value, and its calculation formula is expressed as:

[0040] ,

[0041] Where U max and U min They are two adjacent extreme voltages of the power frequency voltage amplitude modulation wave; specifically, a voltage change rate greater than 0.2% per second is regarded as voltage fluctuation.

[0042] S2. Collecting historical raw data from multiple monitoring nodes located at multi-level buses of a distribution network including an energy storage system.

[0043] S3. Weight allocation of multi-level bus data monitoring nodes: The bus weight is allocated based on the bus voltage level and the load situation of the bus transmission line as indicators, which specifically includes the following steps:

[0044] S31. Establish the calculation standards for load indicators and voltage level indicators.

[0045] S32. According to the number of buses at each voltage level, the collective weight P of buses at each level in the distribution network is allocated. i Specifically, the collective weight calculation method of each level of busbars includes considering the difference in the degree of influence of buses of different voltage levels. Without considering other factors, the weight ratio of the lower busbar to the adjacent upper busbar is defined as 1:5. The first level is the lowest voltage level, and the mth level is the highest voltage level. If the number of voltage buses at each level is n1, n2…n m , the collective weight of the busbar at level i is:

[0046] .

[0048] S33, according to the load conditions of each busbar transmission line, allocate the weight Q of each busbar in the same voltage level busbar j Specifically, among buses of the same voltage level, the weight distribution of each bus is determined according to the proportion of load indicators in the outgoing lines of each bus, and the weight of each load indicator is determined by the hierarchical analysis method.

[0049] The load indicators include primary load, secondary load, sensitive load and number of users. The weight calculation formula of each bus in the same voltage level bus is:

[0050] Q j =W1a j +W2b j +W3c j +W4d j ;

[0051] where a j 、b j 、c j ,d j They are the load indicators connected to bus j in the bus with the same voltage level, namely the proportion of primary load, secondary load, sensitive load and number of users. W1, W2, W3 and W4 are the weights of each load indicator determined by the hierarchical analysis method.

[0052] S34. Calculate the weight k of each bus in the distribution network ij , where k ij =P i Q j .

[0053] S4. Establish an evaluation system, which includes the following steps:

[0054] S41. Establishing a scoring formula; specifically, the scoring formula establishment includes setting the upper limit of the voltage fluctuation at the monitoring node after grid connection to 0 points, and setting no voltage fluctuation to 100 points, and the scoring calculation formula within the unit sampling time of T hours is:

[0055] y T =100-(25r1+2.5r2+0.25r3+0.025r4) / T;

[0056] Among them, r1, r2, r3, and r4 respectively represent the frequencies corresponding to the four voltage fluctuation levels, and the values ​​of r1, r2, r3, and r4 meet the limited number of times, that is, r1≤T, r2≤10T, r3≤100T, r4≤1000T.

[0057] S42, define the scoring level and conditionally limit the total score level; specifically, the scoring level is defined as follows: 0-100 is divided into four levels, [90, 100] is excellent, [70, 90) is good, [50, 70) is qualified, [30, 50) is poor, and [0, 30) is extremely poor; the limiting conditions of the total score level include:

[0058] The proportion of "very poor" scores is ≥ 3%, and the total score level shall not exceed the level of "poor";

[0059] The proportion of “poor” scores shall be ≥ 8%, and the total score level shall not exceed the level of “pass”.

[0060] S43, calculate the score x at each monitoring node according to the scoring formula i .

[0061] S44, calculate the expected value E of each monitoring node score i and variance σ; specifically, the expected value E i The calculation formula of the sum variance σ is as follows:

[0062]

[0063] ;

[0064] Among them, k i represents the weight of the i-th busbar.

[0065] S45. Obtain the final evaluation result based on its expected value, variance and limiting conditions, and calculate the score x of each single point. i Draw a two-dimensional scatter plot and mark each point by area.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the specific implementation modes of the present invention can still be modified or replaced by equivalents, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. An evaluation index and analysis method for voltage quality of a distribution network including an energy storage system, characterized in that: The following steps are involved: S1. Construct an evaluation index system, including establishing evaluation indicators and using voltage stability indicators to quantitatively evaluate the voltage quality of the distribution network containing the energy storage system; S2. Collecting historical raw data of multiple monitoring nodes located at multi-level buses of a distribution network including an energy storage system; S3. Weight allocation of multi-level bus data monitoring nodes; bus weight allocation based on bus voltage level and load conditions of bus outgoing lines, specifically including the following steps: S31. Establishing the calculation standard of load index and voltage level index; S32. Allocating the collective weight P of each level of bus in the distribution network according to the number of buses of each voltage level; i ; S33, according to the load conditions of each busbar transmission line, assign the weight Q of each busbar in the same voltage level busbar j ; S34, calculate the weight k of each bus in the distribution network ij , where k ij =P i Q j ; S4. Establish an evaluation system; specifically, the following steps are included: S41. Establish a scoring formula; S42. Define the scoring level and set conditions for the total score level; S43. Calculate the score x at each monitoring node according to the scoring formula i ; S44, calculate the expected value E of each monitoring node score i and variance σ; S45, obtain the final evaluation result based on its expected value and variance as well as the limiting conditions, and calculate the score x of each single point i Draw a two-dimensional scatter plot and mark each point by area.

2. The evaluation index and analysis method for voltage quality of a distribution network including an energy storage system according to claim 1, characterized in that: The voltage stability index in step S1 includes voltage fluctuation and voltage fluctuation frequency, wherein in the voltage fluctuation frequency index, the interval between two adjacent voltage changes less than 30ms is regarded as one voltage fluctuation; In the voltage fluctuation index, the voltage fluctuation value is the two extreme values ​​of the voltage effective value U max and U min The difference between the rated voltage U N The percentage represents its relative percentage value, and its calculation formula is expressed as: ， Where U max and U min They are two adjacent extreme voltages of the power frequency voltage amplitude modulation wave; specifically, a voltage change rate greater than 0.2% per second is regarded as voltage fluctuation.

3. The evaluation index and analysis method for voltage quality of a distribution network including an energy storage system according to claim 1, characterized in that: The method for calculating the collective weight of each level of bus in step S32 includes considering the difference in the influence degree of buses of different voltage levels, defining the weight ratio of the lower level bus to the adjacent upper level bus as 1:5 without considering other factors, assuming that the first level is the lowest voltage level and the mth level is the highest voltage level, if the number of voltage buses of each level is n1, n2...n m , the collective weight of the busbar at level i is:

4. The evaluation index and analysis method for voltage quality of a distribution network including an energy storage system according to claim 1, characterized in that: In the step S33, among the buses of the same voltage level, the weight allocation of each bus is determined according to the proportion of load indicators in the transmission lines of each bus, and the weight of each load indicator is determined by using the hierarchical analysis method.

5. The evaluation index and analysis method for voltage quality of a distribution network including an energy storage system according to claim 4, characterized in that: The load indicators include primary load, secondary load, sensitive load and number of users. The weight calculation formula of each bus in the same voltage level bus is: Q j =W1a j +W2b j +W3c j +W4d j ; where a j 、b j 、c j d j They are the load indicators connected to bus j in the bus with the same voltage level, namely the proportion of primary load, secondary load, sensitive load and number of users. W1, W2, W3 and W4 are the weights of each load indicator determined by the hierarchical analysis method.

6. The evaluation index and analysis method for voltage quality of a distribution network including an energy storage system according to claim 1, characterized in that: The scoring formula in step S41 includes setting the upper limit of voltage fluctuation at the monitoring node after grid connection to 0 points and no voltage fluctuation to 100 points. The scoring calculation formula within the unit sampling time of T hours is: y T =100-(25r1+2.5r2+0.25r3+0.025r4) / T; Among them, r1, r2, r3, and r4 respectively represent the frequencies corresponding to the four voltage fluctuation levels, and the values ​​of r1, r2, r3, and r4 meet the limited number of times, that is, r1≤T, r2≤10T, r3≤100T, r4≤1000T.

7. The evaluation index and analysis method for voltage quality of a distribution network including an energy storage system according to claim 1, characterized in that: The definition of the scoring level in step S42 specifically includes: dividing 0-100 into four levels, [90, 100] is excellent, [70, 90) is good, [50, 70) is qualified, [30, 50) is poor, and [0, 30) is extremely poor; the limiting conditions of the total score level include: The proportion of "very poor" scores is ≥ 3%, and the total score level shall not exceed the level of "poor"; The proportion of "poor" scores should be ≥ 8%, and the total score level should not exceed the "pass" level.

8. The evaluation index and analysis method for voltage quality of a distribution network including an energy storage system according to claim 1, characterized in that: The expected value E in step S44 i The calculation formula of the sum variance σ is as follows: ； Among them, k i represents the weight of the i-th busbar.

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