CN117829616A

CN117829616A - New energy station voltage supporting capability evaluation method and system under asymmetric fault

Info

Publication number: CN117829616A
Application number: CN202311609941.0A
Authority: CN
Inventors: 赵康; 汪挺; 蒋哲; 程定一; 朱元振; 邢法财; 房俏; 马琳琳; 周宁; 刘文学; 马欢; 武诚; �田�浩; 李新; 乔立同
Original assignee: State Grid Corp of China SGCC; Electric Power Research Institute of State Grid Shandong Electric Power Co Ltd; State Grid Shandong Electric Power Co Ltd
Current assignee: State Grid Corp of China SGCC; Electric Power Research Institute of State Grid Shandong Electric Power Co Ltd; State Grid Shandong Electric Power Co Ltd
Priority date: 2023-11-29
Filing date: 2023-11-29
Publication date: 2024-04-05

Abstract

The application provides a new energy station voltage supporting capability evaluation method and system under asymmetric faults, wherein the method comprises the following steps: and establishing a new energy station voltage supporting capability comprehensive evaluation system, and judging whether to start the new energy station voltage supporting capability comprehensive evaluation system or not based on a monitoring result of grid-connected point voltage. According to the method and the device, the comprehensive evaluation index of the voltage supporting capability of the new energy station is obtained through calculation based on the obtained reactive margin index, the power oscillation index and the voltage symmetry index, so that the comprehensive evaluation of the voltage supporting capability of the new energy grid-connected system is realized, and the single evaluation index that only the grid-connected voltage is considered in the evaluation of the voltage supporting capability is avoided.

Description

New energy station voltage supporting capability evaluation method and system under asymmetric fault

Technical Field

The invention relates to the field of power systems, in particular to a new energy station voltage supporting capability evaluation method and system under asymmetric faults.

Background

Along with the continuous increase of the capacity of the new energy unit, the new energy unit should have low voltage ride through capability, and provide a certain voltage support for the power grid in case of failure. The stable working range of the power system after the fault occurs is related to the voltage supporting capability of the new energy grid-connected system, and the voltage supporting capability is weak and easily causes the stability of the system control to be reduced, so that the voltage supporting capability assessment of the new energy grid-connected system during the fault is particularly important. Most of voltage drop in the power system is caused by asymmetric faults, so that the voltage support evaluation and control method of the new energy grid-connected system is significant for safe and reliable operation of the power system under the condition of researching the asymmetric faults.

The inventor finds that the following problems exist in the current voltage support evaluation and control method of the new energy station under the asymmetric fault:

(1) The voltage supporting capability of the new energy grid-connected system is a comprehensive concept, and most of the evaluation of the voltage supporting capability only considers the single evaluation index of grid-connected point voltage. In the asymmetric fault, the output power of the new energy grid-connected system has double frequency oscillation, and if the output oscillation amplitude of the new energy unit is larger, the unit loss, the light discarding and wind discarding and other phenomena can be caused due to the inertia and the scheduling failure of the rotary power generation device. Meanwhile, the control of the inverter under the asymmetric fault is easy to cause overcurrent and damage power electronic devices. Therefore, a comprehensive evaluation method for the voltage supporting capability of the new energy grid-connected system under the asymmetric faults comprising the over-current limit of the inverter, the oscillation limit of the output of the inverter and the voltage supporting effect of the grid-connected point should be proposed.

(2) In the current research on the voltage support control method of the new energy grid-connected system under the asymmetric fault, most of the research aims at improving the voltage amplitude of the grid-connected point, and ignores the influence of the voltage symmetry on the power grid, so that the power grid is in an unbalanced running state, overvoltage is easy to occur on the grid-connected point, and meanwhile, a large amount of negative sequence current exists in the power grid, so that the safe and stable running of the power grid is not facilitated. Therefore, the voltage support control method of the new energy grid-connected system should give consideration to the positive and negative sequence voltage support effect of grid-connected points.

Therefore, it is needed to provide a new energy station voltage supporting capability evaluation method and system under asymmetric faults, which give consideration to reactive capacity margin indexes, power oscillation indexes and grid-connected point voltage symmetry indexes.

The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.

Disclosure of Invention

In order to solve the problems, the application provides a new energy station voltage supporting capability evaluation method and system under asymmetric faults, and the new energy station voltage supporting capability comprehensive evaluation index is calculated based on the acquired reactive margin index, the power oscillation index and the voltage symmetry index, so that comprehensive evaluation of the new energy grid-connected system voltage supporting capability is realized.

According to a first aspect of an embodiment of the present invention, there is provided a new energy station voltage supporting capability evaluation method under an asymmetric fault, the method including:

establishing a new energy station voltage supporting capacity comprehensive evaluation system, wherein the new energy station voltage supporting capacity comprehensive evaluation system comprises a new energy station voltage supporting capacity comprehensive evaluation index obtained by calculation based on the acquired reactive margin index, power oscillation index and voltage symmetry index;

Based on the monitoring result of the grid-connected point voltage, judging whether to start the new energy station voltage supporting capability comprehensive evaluation system:

if the voltage of the grid connection point is not qualified, starting the comprehensive evaluation system for the voltage supporting capability of the new energy station to evaluate the voltage supporting capability of the new energy station under the asymmetric fault;

and if the voltage of the parallel power grid is qualified, not starting the comprehensive evaluation system for the voltage supporting capability of the new energy station.

In some embodiments, obtaining a monitoring result of the grid-tie point voltage includes:

setting a grid-connected point positive sequence voltage threshold value, and judging whether the grid-connected voltage is qualified or not based on the grid-connected point positive sequence voltage threshold value:

if the parallel grid voltage is low and the grid-connected point positive sequence voltage threshold value is low, judging that the parallel grid voltage is unqualified;

and otherwise, judging that the parallel grid voltage is qualified.

In some embodiments, starting the comprehensive evaluation system for the voltage supporting capability of the new energy station to evaluate the voltage supporting capability of the new energy station under the asymmetric fault comprises:

acquiring a final current instruction output by a later-stage inverter based on low-voltage ride through control, wherein the final current instruction meets reactive capacity margin indexes and power oscillation indexes;

acquiring a voltage symmetry index based on the final current instruction;

Acquiring a comprehensive evaluation index of the voltage supporting capability of the new energy station based on the reactive capacity margin index, the power oscillation index and the voltage symmetry index;

and judging the voltage supporting capacity of the new energy station under the asymmetric fault based on the comprehensive evaluation index of the voltage supporting capacity of the new energy station.

In some embodiments, the final current command includes at least one of a reactive current command output by the inverter, a first adjusted negative sequence reactive current command, and a second adjusted negative sequence reactive current command, the final current command output by the inverter is obtained based on low voltage ride through control, the final current command meeting a reactive capacity margin indicator and a power oscillation indicator, including:

acquiring a reactive current instruction output by the inverter according to the maximum and minimum voltage limit values output by the inverter during the low voltage ride through period;

calculating a reactive capacity margin index according to a reactive current instruction output by the inverter and combining an overcurrent limit value of the inverter, and calculating a first negative sequence reactive current instruction output by the inverter according to the reactive margin index, so that the inverter can provide maximum voltage support while meeting the reactive capacity margin index;

according to the reactive current instruction output by the inverter, calculating a power oscillation index by combining the power oscillation limit value of the inverter, and calculating a second negative sequence reactive current instruction output by the inverter according to the power oscillation index, so that the inverter can provide maximum voltage support while meeting the power oscillation index.

In some embodiments, calculating the reactive capacity margin indicator in combination with the inverter over-current limit according to the reactive current command output by the inverter includes:

and calculating an active current instruction according to the reactive current instruction output by the inverter, and taking the maximum outputtable positive sequence active current instruction as a reactive capacity margin index.

In some embodiments, the reactive capacity margin indexCan be expressed as:

s.t.

wherein I is _a 、I _b 、I _c A, b, c three-phase current amplitude values output by the inverter; wherein,positive and negative sequence active current instructions output by the inverter; />A positive and negative sequence reactive current instruction output by the inverter; />The positive sequence component amplitude of the network side voltage is obtained; r is R _g And X is _g The resistance and reactance value in the circuit; />And->The positive and negative sequence voltage reference values of the grid connection points are respectively expressed as follows:

wherein,V _max and V is equal to _min Respectively setting maximum and minimum voltage values of grid-connected points; gamma ray _max And gamma is equal to _min The maximum and minimum values of the cosine of the phase angle difference of the three-phase positive and negative voltage are expressed as:

wherein,is the phase included angle of the positive and negative sequence voltages. 7. The method of claim 5, wherein the step of determining the position of the probe is performed,

calculating a first negative sequence reactive current regulation instruction output by the inverter according to the reactive margin index, wherein the first negative sequence reactive current regulation instruction comprises:

Judging whether the reactive capacity margin index meets the requirement:

if the reactive capacity margin index meets the requirement, the inverter outputs a first positive-sequence active current instruction corresponding to the reactive capacity margin index;

if the reactive margin index does not meet the requirement, the first positive sequence active current instruction is adjusted to 0, the reactive margin index value is 0, the negative sequence reactive current instruction output by the inverter is adjusted to inhibit overcurrent, and the adjusted negative sequence reactive current instruction output by the inverter is used as the first adjusting negative sequence reactive current instruction.

In some embodiments, if the reactive margin indicator is greater than zero, then the requirement is met; otherwise, the requirements are not satisfied.

In some embodiments, calculating the power oscillation index in combination with the inverter power oscillation limit according to the reactive current command output by the inverter comprises:

according to the reactive current instruction output by the inverter, the oscillation amplitude of active power output by the inverter is obtained, the active power oscillation amplitude initial value output by the inverter when the positive sequence active current instruction is 0 is calculated, and the difference between the active power oscillation limit value and the active power oscillation amplitude initial value of the inverter is used as a power oscillation index.

In some embodiments, the oscillation amplitude of the active power output by the inverter may be expressed as:

Wherein,is the active power oscillation amplitude of the inverter, V ⁺ For positive sequence voltage amplitude of grid-connected point, V ^- The negative sequence voltage amplitude of the grid-connected point is set; />Positive and negative sequence active current instructions output by the inverter; />A positive and negative sequence reactive current instruction output by the inverter;

continuing active power oscillation based limitingLet->And (3) calculating:

wherein,when an active current instruction is output to an inverter as 0, an active power oscillation amplitude initial value is obtained; the power oscillation index is characterized by->

In some embodiments, calculating a second adjusted negative sequence reactive current command of the inverter output based on the power oscillation index comprises:

judging whether the active power oscillation evaluation index meets the requirements:

if the initial value of the power oscillation amplitude is smaller than the power oscillation limit valueThe active power oscillation evaluation index of the inverter meets the requirement, and an active current instruction output by the inverter is calculated according to the power oscillation index and is used as a second positive sequence active current instruction;

if the initial value of the power oscillation amplitude is larger than the power oscillation limit value, the active power oscillation evaluation index of the inverter is not in accordance with the requirement, the output reactive current exceeds the power oscillation limit, the second positive sequence active current instruction is adjusted to 0, the power oscillation index value is 0, the negative sequence reactive current instruction of the inverter is adjusted to inhibit the active power oscillation, and the negative sequence reactive current instruction of the inverter is adjusted to serve as the second negative sequence reactive current instruction.

In some embodiments, obtaining a voltage symmetry index based on the final current command includes:

the final current instruction comprises at least one of a reactive current instruction which is output by an inverter and meets reactive capacity margin indexes and power oscillation indexes, a first adjusting negative sequence reactive current instruction and a second adjusting negative sequence reactive current instruction, and a negative sequence voltage component at the position of the grid-connected point is calculated, wherein the first adjusting negative sequence reactive current instruction is acquired based on the reactive capacity margin indexes, the second adjusting negative sequence reactive current instruction is acquired based on the power oscillation indexes, and the formula for calculating the negative sequence voltage component at the position of the grid-connected point is as follows:

wherein,the calculation formula of (2) is as follows:

when the reactive margin index and the power oscillation index meet the requirements, calculating a negative sequence voltage component at a grid-connected point based on a reactive current instruction which is output by the inverter and meets the reactive capacity margin index and the power oscillation index, wherein the reactive current instruction is as follows:

when the reactive power margin index is not in accordance with the requirement and the power oscillation index is in accordance with the requirement, calculating a negative sequence voltage component at a grid-connected point based on a first adjusting negative sequence reactive current instruction acquired by the reactive power capacity margin index, wherein the first adjusting negative sequence reactive current instruction is as follows:

When the reactive margin index meets the requirement and the power oscillation index does not meet the requirement, calculating a negative sequence voltage component at the grid-connected point based on a second adjusting negative sequence reactive current instruction acquired by the power oscillation index, wherein the second adjusting negative sequence reactive current instruction is as follows:

when the reactive power margin index and the power oscillation index are not in accordance with the requirements, calculating a negative sequence voltage component at a parallel point according to the minimum value in a first adjustment negative sequence reactive current instruction obtained based on the reactive power margin index and a second adjustment negative sequence reactive current instruction obtained based on the power oscillation index, wherein the final current instruction is characterized as follows:

wherein, the grid-connected point negative sequence voltage V ^- And the evaluation index of the voltage symmetry of the new energy grid-connected system is obtained.

In some embodiments, obtaining the new energy station voltage support capability comprehensive assessment index based on the reactive capacity margin index, the power oscillation index, and the voltage symmetry index comprises:

weighting the three indexes, and calculating the comprehensive evaluation index of the voltage supporting capability of the new energy station;

the formula is as follows:

wherein, alpha, beta and gamma are the weights occupied by three evaluation indexes under the comprehensive evaluation system respectively, and alpha+beta+gamma=1.

According to a second aspect of the present application, there is provided a new energy station voltage support capability assessment system under asymmetric fault, the system comprising:

The system comprises an evaluation system establishment module, a new energy station voltage supporting capability comprehensive evaluation system and a control module, wherein the evaluation system establishment module is configured to establish a new energy station voltage supporting capability comprehensive evaluation system, and the new energy station voltage supporting capability comprehensive evaluation system comprises a new energy station voltage supporting capability comprehensive evaluation index acquired based on reactive margin indexes, power oscillation indexes and voltage symmetry indexes;

the starting judging module is configured to judge whether to start the new energy station voltage supporting capability comprehensive evaluation system based on the monitoring result of the grid-connected point voltage:

According to a third aspect of the present application, there is provided a computer readable storage medium having stored thereon a computer program which, when executed by a processor, implements the steps of the new energy station voltage support capability assessment method under asymmetric faults of any of the above embodiments.

According to a fourth aspect of the present application, there is provided an electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the steps of the new energy station voltage support capability assessment method under asymmetric faults as in any of the above embodiments when the program is executed.

The technical scheme provided by the embodiment of the invention can have the following beneficial effects:

according to the embodiment of the application, the over-current limit and the output power oscillation limit of the inverter in the low-pass period are considered, the reactive capacity margin index and the active power oscillation index under the asymmetric fault are provided, the voltage symmetry index is combined, a comprehensive evaluation system of the voltage supporting capability of the new energy station is established, the comprehensive evaluation system of the voltage supporting capability of the new energy station is started under the condition that the voltage of the grid-connected point is unqualified, the comprehensive evaluation index of the voltage supporting capability of the new energy station is obtained through calculation based on the obtained reactive capacity margin index, the power oscillation index and the voltage symmetry index, and the comprehensive evaluation of the voltage supporting capability of the new energy grid-connected system is realized, so that the evaluation of the voltage supporting capability is avoided, and only the single evaluation index of the grid-connected point voltage is considered; in the asymmetric fault, the phenomena of unit loss, light rejection, wind rejection and the like caused by inertia and scheduling incapability of timely responding of a rotary power generation device when the output oscillation amplitude of a new energy unit is large due to the double frequency oscillation of the output power of a new energy grid-connected system can be avoided; meanwhile, the phenomenon that the power electronic device is damaged due to overcurrent easily caused by the control of the inverter under the asymmetric fault is avoided.

The method aims at improving the grid-connected point voltage symmetry, combines the reactive capacity margin index and the power oscillation index, and provides a low-pass control method under the asymmetric fault of the new energy grid-connected system, so that the grid-connected point voltage can be more symmetrical by a current instruction output by the inverter on the premise of meeting the over-current limit and the power oscillation limit of the inverter, the negative sequence component of the grid side is reduced, and the supporting effect of the new energy grid-connected system on the grid side is improved.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.

FIG. 1 is a flow chart illustrating a method for evaluating voltage support capability of a new energy station under an asymmetric fault, according to an exemplary embodiment;

FIG. 2 is a diagram illustrating a topology of a new energy station, according to an exemplary embodiment;

FIG. 3 is a diagram illustrating a voltage phasor positive and negative sequence dq decomposition phasor for an asymmetric fault according to an example embodiment;

FIG. 4 is a schematic diagram of a framework of a new energy station voltage support capability assessment system under an asymmetric fault, according to an example embodiment.

Detailed Description

The following description and the drawings illustrate specific embodiments of the application sufficiently to enable those skilled in the art to practice them. Portions and features of some embodiments may be included in, or substituted for, those of others. The scope of the embodiments of the present application encompasses the full ambit of the claims, as well as all available equivalents of the claims.

In this application, the terms "first," "second," and the like are used merely to distinguish one element from another element and do not require or imply any actual relationship or order between the elements. Indeed the first element could also be termed a second element and vice versa. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a structure, apparatus, or device that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such structure, apparatus, or device. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a structure, apparatus or device comprising the element. In this application, each embodiment is described in a progressive manner, and each embodiment focuses on a difference from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.

The terms "longitudinal," "transverse," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like in this application refer to an orientation or positional relationship based on that shown in the drawings, merely for convenience of description and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be configured and operated in a particular orientation, and thus should not be construed as limiting the invention. In the description of the present application, unless otherwise specified and defined, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, mechanically or electrically connected, may be in communication with each other in two elements, may be directly connected, or may be indirectly connected through an intermediary, and may be interpreted as specifically meaning by those of ordinary skill in the art in view of the circumstances.

In this application, the term "plurality" means two or more, unless otherwise indicated.

In this application, the character "/" indicates that the front and rear objects are an or relationship. For example, A/B represents: a or B.

In this application, the term "and/or" is an association relationship describing an object, meaning that three relationships may exist. For example, a and/or B, represent: a or B, or, A and B.

In one embodiment of the present application, a method for evaluating voltage supporting capability of a new energy station under an asymmetric fault is provided, as shown in fig. 1, where the method includes:

step S1, a new energy station voltage supporting capability comprehensive evaluation system is established, wherein the new energy station voltage supporting capability comprehensive evaluation system comprises a new energy station voltage supporting capability comprehensive evaluation index obtained through calculation based on the acquired reactive margin index, the power oscillation index and the voltage symmetry index.

In some embodiments, reactive margin indicators and power oscillation indicators are proposed according to inverter overcurrent limits and power oscillation limits. Meanwhile, a voltage symmetry index is calculated according to a current instruction output by the inverter, and a new energy station voltage support strength comprehensive evaluation system is established. In some specific examples, fig. 2 shows a topological structure diagram of a new energy station, fig. 3 shows a voltage phasor positive-negative sequence dq decomposition phasor diagram under an asymmetric fault, and is described below with reference to fig. 2-3.

1. Reactive margin index: since the total capacity that the inverter can output is limited, it should be considered how the active and reactive currents output by the inverter are distributed. According to the reactive current instruction output by the inverter, and the magnitude of the negative sequence active current is set to 0, the magnitude of the positive sequence active current can be used for representing the reactive capacity margin of the inverter.

In the embodiment of the application, the decoupling double synchronous reference coordinate system (Decoupled Double Synchronous Reference Frame, DDSRF) is applied to conduct positive and negative sequence dq decomposition on the voltage of the grid-connected point, and then positive and negative sequence voltage amplitude values of the grid-connected point are obtained. The three-phase current output by the inverter can be expressed as positive and negative sequence current in a stationary reference frame:

wherein I is _a 、I _b 、I _c A, b, c three-phase current amplitude values output by the inverter;positive and negative sequence active current instructions output by the inverter; />A positive and negative sequence reactive current instruction output by the inverter; i ⁺ And I ^- Positive and negative sequence current amplitude values output by the inverter; /> Is the phase included angle of the positive and negative sequence voltages.

The three-phase current should satisfy:

max{I _a ,I _b ,I _c }≤I _max

wherein I is _max Is the maximum value of the inverter output phase current.

According to the reactive current instruction output by the inverter, the maximum outputtable positive sequence active instruction, namely the reactive margin index Can be expressed as:

s.t.

2. power oscillation index: in the asymmetric fault, the power output by the inverter has double frequency oscillation, and if the oscillation amplitude is too large, the voltage at the direct current side can be caused to oscillate at the same frequency, and the stability of the power grid voltage can be influenced. Therefore, the power oscillation evaluation of the inverter should be included in the index for evaluating the voltage supporting capability of the new energy grid-connected system.

In the stationary reference frame, the oscillation amplitude of the inverter output active power can be expressed as:

wherein,v is the active oscillation amplitude of the inverter ⁺ For positive sequence voltage amplitude of grid-connected point, V ^- The negative sequence voltage component amplitude of the grid-connected point can be used for representing the evaluation index of the voltage symmetry of the new energy grid-connected system; /> Positive and negative sequence active current instructions output by the inverter; />And the reactive current instruction is a positive and negative sequence reactive current instruction output by the inverter.

Given active power oscillation limitsLet I _p ⁺ =0, calculate:

wherein,when the output active current of the inverter is 0, the initial amplitude of power oscillation; />And the reactive current instruction is a positive and negative sequence reactive current instruction output by the inverter. Define the power oscillation index calculation formula as +.>

3. Voltage symmetry index: according to the active reactive current instruction output by the inverter, the amplitude V of the negative sequence voltage component at the grid-connected point ^- It can be calculated as:

wherein the method comprises the steps ofThe amplitude of the negative sequence component of the grid-side voltage can be used for representing the evaluation index of the voltage symmetry of the new energy grid-connected system; omega is the angular frequency under the power frequency of the power grid; l (L) _g And R is R _g The inductance and resistance values in the circuit; /> Positive and negative sequence active current instructions output by the inverter; />And the reactive current instruction is a positive and negative sequence reactive current instruction output by the inverter.

Grid-connected point negative sequence voltage V at this time ^- And the evaluation index of the voltage symmetry of the new energy grid-connected system is obtained. V (V) ^- The larger the voltage of the grid-connected point is, the less symmetry is provided; v (V) ^- The smaller the voltage at the point of connection, the more symmetrical.

4. Comprehensive evaluation indexes of voltage supporting capability of new energy stations: in summary, the three evaluation indexes can be defined as the comprehensive evaluation index of the voltage supporting capability of the new energy station:

wherein, alpha, beta and gamma are the weights occupied by three evaluation indexes under the comprehensive evaluation system respectively, and alpha+beta+gamma=1; v (V) ^- The method is an evaluation index of voltage symmetry of the new energy grid-connected system;is a reactive margin index; the power oscillation index is defined as +.>The larger the evaluation index value is, the stronger the positive and negative sequence voltage supporting capability of the new energy system is in asymmetric faults; in contrast, the smaller the evaluation index value is, the weaker positive and negative sequence voltage supporting capability of the new energy system is shown in the asymmetric fault.

Step S2, judging whether to start the new energy station voltage supporting capability comprehensive evaluation system based on the monitoring result of the grid-connected point voltage:

In some embodiments, if the parallel grid voltage is qualified, the inverter operates normally, and the new energy station voltage supporting capability comprehensive evaluation system is not started.

and otherwise, judging that the parallel grid voltage is qualified.

In some specific examples, the grid tie point positive sequence voltage threshold is 0.9p.u. Specifically, a decoupling double-synchronous reference frame phase-Locked Loop (Decoupled Double Synchronous Reference Frame Phase-Locked Loop, DDSRF-PLL) can be used for collecting positive and negative sequence voltages of grid-connected points, and whether the grid-connected points fall down or not is monitored in real time. And if the positive sequence voltage amplitude falling depth of the grid-connected point is below 0.9p.u., judging that the grid-connected voltage is unqualified, and at the moment, starting the comprehensive evaluation system for the voltage supporting capability of the new energy station to evaluate the voltage supporting capability of the new energy station under the asymmetric fault.

s21, acquiring a final current instruction output by the rear-stage inverter based on low-voltage ride through control, wherein the final current instruction meets reactive capacity margin indexes and power oscillation indexes.

In some embodiments, the final current command includes at least one of a reactive current command, a first regulated negative sequence reactive current command, and a second regulated negative sequence reactive current command output by the inverter. The first negative sequence reactive current regulation command and the second negative sequence reactive current regulation command are obtained based on the reactive current command output by the inverter. Specifically, after the new energy station voltage supporting capability comprehensive evaluation system is started to evaluate the new energy station voltage supporting capability under the asymmetric fault, the new energy grid-connected system enters a low voltage ride through control mode, and in the low voltage ride through control mode, a first adjusting negative sequence reactive current instruction and a second adjusting negative sequence reactive current instruction are obtained based on a reactive current instruction output by an inverter.

In some embodiments, obtaining a final current command of the inverter output based on the low voltage ride through control, the final current command meeting a reactive capacity margin indicator and a power oscillation indicator, includes:

S211, acquiring a reactive current instruction output by the inverter according to the maximum and minimum voltage limit values output by the inverter during the low voltage ride through period.

In some embodiments, based on positive-negative sequence decomposition, when an asymmetric fault occurs, the positive sequence relationship between the grid-side voltage and the grid-tie point voltage and the inverter output current can be written as:

wherein v is ⁺ Representing a positive sequence component of the grid-connected point voltage; i.e ⁺ Representing a positive sequence component of the inverter output current;is a positive sequence component of the network side voltage; t represents the moment; l (L) _g And R is R _g Is the inductance and resistance in the line.

Similarly, the negative sequence relationship can be written as:

wherein v is ^- A negative sequence component representing the grid-connected point voltage; i.e ^- A negative sequence component representing an inverter output current;is a negative sequence component of the network side voltage; l (L) _g And R is R _g Is the inductance and resistance in the line.

The above formula is modified to obtain:

wherein,the positive sequence component amplitude of the network side voltage is obtained; v (V) ⁺ The amplitude of the positive sequence component of the voltage at the grid-connected point is obtained.

Wherein,the positive sequence component amplitude of the network side voltage is obtained; v (V) ^- Is the amplitude of the negative sequence component of the grid-connected point voltage.

The three-phase voltage at the point of the grid connection can be written as:

wherein V is _a 、V _b 、V _c The amplitude of the three-phase voltages a, b and c at the grid-connected point;is the phase included angle of the positive and negative sequence voltages.

When an asymmetric fault occurs, the maximum and minimum values of the grid-connected point phase voltages are given. It should be noted that in order for the system to operate within safe limits, the grid-tie phase voltages should not exceed the maximum and minimum limits specified by the operating guidelines, while in order for the grid-tie voltages to be symmetrical, the maximum and minimum values of the phase voltages should be as close as possible. According to the relationship between the phase voltage and the positive and negative sequence voltage, the voltage of the maximum and minimum phases can be expressed as:

wherein V is _max And V is equal to _min Respectively setting maximum and minimum voltage values of grid-connected points; gamma ray _max And gamma is equal to _min The maximum and minimum value of the cosine of the phase angle difference of the three-phase positive and negative voltage can be expressed as:

in some specific examples, solving the above may be aimed at maximizing the positive and negative sequence voltage supporting effect, and the reactive current instruction output by the subsequent inverter is:

wherein,a positive and negative sequence reactive current instruction output by the inverter; />The positive sequence component amplitude of the network side voltage is obtained; r is R _g The resistance value in the circuit; />And->The positive and negative sequence voltage reference values of the grid connection points can be specifically expressed as follows:

/>

wherein,at this time, the reactive current instruction output by the inverter is generated, and then the reactive capacity margin index is calculated based on the reactive current instruction output by the inverter.

S212, calculating a reactive capacity margin index according to a reactive current instruction output by the inverter and combining an overcurrent limit value of the inverter, and calculating a first negative sequence reactive current instruction output by the inverter according to the reactive margin index, so that the inverter can provide maximum voltage support while meeting the reactive capacity margin index.

In some embodiments, the maximum outputtable positive-sequence active command, i.e. reactive margin index, is based on the reactive current command output by the inverterCan be expressed as:

s.t.

wherein I is _a 、I _b 、I _c A, b, c three-phase current amplitude values output by the inverter;positive and negative sequence active current instructions output by the inverter; />A positive and negative sequence reactive current instruction output by the inverter; />The positive sequence component amplitude of the network side voltage is obtained; r is R _g And X is _g The resistance and reactance value in the circuit; />And->The positive and negative sequence voltage reference values of the grid connection points are respectively expressed as follows:

/>

Wherein,V _max and V is equal to _min Respectively setting maximum and minimum voltage values of grid-connected points; gamma ray _max And gamma is equal to _min The maximum and minimum value of the initial phase difference cosine of the three-phase positive and negative sequence voltage is expressed as:

wherein,the initial phase difference is the positive and negative sequence voltage.

In some embodiments, calculating a first adjusted negative sequence reactive current command for the inverter output based on the reactive capacity margin indicator comprises:

judging whether the reactive capacity margin index meets the requirement:

if the reactive margin index does not meet the requirement, the first positive sequence active current instruction is adjusted to 0, the reactive margin index value is 0, the negative sequence reactive current instruction output by the inverter is adjusted to inhibit overcurrent, and the adjusted negative sequence reactive current instruction output by the inverter is used as the first adjusting negative sequence reactive current instruction. In some embodiments, if the reactive margin indicator is greater than zero, then the requirement is satisfied; otherwise, the requirements are not satisfied. In particular, ifThe new energy grid-connected system has reactive capacity margin, further voltage support can be carried out, and the specific reactive capacity margin can be expressed as +. >Namely, the first positive sequence active current instruction is +.>

If it isThe new energy grid-connected system does not have reactive capacity margin, the current voltage support strength exceeds the maximum support capability available by the inverter, and reactive power is adjustedThe flow instruction, the first adjusted negative sequence reactive current instruction, is obtained based on the following formula:

wherein,positive and negative sequence active current instructions output by the inverter; />A positive and negative sequence reactive current instruction output by the inverter; r is R _g And X is _g The resistance and reactance value in the circuit; />For the positive sequence voltage reference value of the grid-connected point, I _max The inverter overcurrent limit is expressed as follows:

/>

The inverter can provide maximum voltage support on the premise of meeting reactive capacity margin index limit. At this time, the first positive sequence active current command is 0, and the negative sequence reactive current command is used for calculating the voltage symmetry index subsequently. In some embodiments, when the reactive margin index does not meet the requirement, the adjusted reactive current instruction is further subjected to a trade-off with a reactive current instruction adjusted based on the active power oscillation index to calculate the voltage symmetry index, which can be seen in detail below.

S213, calculating a power oscillation index according to the reactive current instruction output by the inverter and combining the power oscillation limit value of the inverter, and calculating a second negative sequence reactive current instruction output by the inverter according to the power oscillation index, so that the inverter can provide maximum voltage support while meeting the power oscillation index.

In some embodiments, in the stationary reference frame, the oscillation amplitude of the active power output by the inverter may be expressed as:

wherein,is the active power oscillation amplitude of the inverter, V ⁺ For positive sequence voltage amplitude of grid-connected point, V ^- Negative sequence electricity for grid connection pointA magnitude of the pressing force; />Positive and negative sequence active current instructions output by the inverter; />A positive and negative sequence reactive current instruction output by the inverter;

Continuing active power oscillation based limitingLet->And (3) calculating:

wherein,

wherein,when an active current instruction is output to an inverter as 0, an active power oscillation amplitude initial value is obtained; the power oscillation index is characterized by->The meaning of the remaining parameters may be found above and will not be described here again. />

if the initial value of the power oscillation amplitude is larger than the power oscillation limit value, the active power oscillation evaluation index of the inverter is not in accordance with the requirement, the output reactive current exceeds the power oscillation limit, the second positive sequence active current instruction is adjusted to 0, the power oscillation index value is 0, the negative sequence reactive current instruction output by the inverter is adjusted to inhibit the active power oscillation, and the negative sequence reactive current instruction of the inverter is adjusted to serve as the second negative sequence reactive current instruction. According to the embodiment of the application, the new energy grid-connected system can ensure the maximum voltage supporting strength and simultaneously enable the power oscillation amplitude output by the inverter to meet the requirement.

In some specific examples, ifUnder the voltage supporting strength, the power oscillation evaluation index can be met, the inverter can still provide positive-sequence active current, and at the moment, the positive-sequence active current instruction output by the inverter is calculated according to the power oscillation index and used as a second positive-sequence active current instruction, wherein the second positive-sequence active current instruction is->The calculation may be based on the following formula:

s.t.

the power oscillation index can be expressed asThe meaning of the remaining parameters may be referred to above and will not be described here again.

If it isThe power oscillation amplitude of the new energy grid-connected system exceeds a set value, the voltage support strength of the power grid is insufficient to meet the requirement of stable operation of the power grid, and the second negative sequence reactive current regulation instruction can be obtained based on the following formula: />

The meaning of each parameter in the formula can be referred to above, and will not be described herein.

According to the embodiment of the application, the new energy grid-connected system ensures the maximum voltage supporting strength and simultaneously enables the power oscillation amplitude output by the inverter to meet the requirement. At this time, the negative sequence reactive current command is adjusted to obtain a second adjusted negative sequence reactive current command for subsequent calculation of the voltage symmetry index.

In some embodiments of the present application, if the final reactive capacity margin index and the active power oscillation index are both satisfied, a minimum value of two positive-sequence active current instructions corresponding to the two indexes is selected as a final positive-sequence active current instruction, and if one of the indexes is not satisfied, the final positive-sequence active current instruction is set to 0.

In some embodiments, the calculation of the voltage symmetry index is related to the negative sequence reactive current command only, and is unrelated to the negative sequence active current, so that the negative sequence active current is 0, and the negative sequence reactive current command is obtained by selecting and selecting reactive current commands respectively adjusted based on the reactive capacity margin index and the active power oscillation index, which can be seen in the following.

From this, it can be known that the voltage symmetry index can be obtained based on the negative-sequence reactive current instruction obtained from the two indexes of the active power oscillation index according to the reactive capacity margin index, and specifically, see step S22.

S22, acquiring a voltage symmetry index based on the final current instruction.

and calculating a negative sequence voltage component at the grid-connected point based on at least one of a reactive current instruction, a first negative sequence reactive current instruction and a second negative sequence reactive current instruction which are output by the inverter and meet the reactive capacity margin index and the power oscillation index. The first adjusted negative sequence reactive current command is obtained based on a reactive capacity margin indicator and the second adjusted negative sequence reactive current command is obtained based on a power oscillation indicator, and in some embodiments, the calculation formula of the negative sequence voltage component at the grid-connected point is generally as follows:

From the above, in the embodiment of the present application, the calculation of the voltage symmetry index is related to the negative-sequence reactive current command only, and is independent of the negative-sequence active current, so that the negative-sequence active currentFor 0, the calculation formula based on which the acquisition of the negative sequence voltage component at the point of connection can be simplified is as follows:

wherein,the calculation formula of (2) is as follows:

when the reactive power margin index is not in accordance with the requirement and the active power oscillation index is in accordance with the requirement, calculating a negative sequence voltage component at a grid-connected point based on a first adjusting negative sequence reactive current instruction acquired by the reactive power capacity margin index, wherein the first adjusting negative sequence reactive current instruction is as follows:

when the reactive margin index meets the requirement and the active power oscillation index does not meet the requirement, calculating a negative sequence voltage component at the grid-connected point based on a second adjusting negative sequence reactive current instruction acquired by the power oscillation index, wherein the second adjusting negative sequence reactive current instruction is as follows:

Wherein the grid-connected point negative sequence voltage V ^- And the evaluation index of the voltage symmetry of the new energy grid-connected system is obtained.

Wherein, andnegative sequence voltage V of net point ^- And the evaluation index of the voltage symmetry of the new energy grid-connected system is obtained. V (V) ^- The larger the voltage of the grid-connected point is, the less symmetry is provided; v (V) ^- The smaller the voltage at the point of connection, the more symmetrical.

The meaning of each parameter in the above formulae can be referred to above, and will not be described herein.

S23, acquiring a comprehensive evaluation index of the voltage supporting capability of the new energy station based on the reactive capacity margin index, the power oscillation index and the voltage symmetry index.

Acquiring a comprehensive evaluation index of the voltage supporting capability of the new energy station based on the reactive capacity margin index, the power oscillation index and the voltage symmetry index, wherein the comprehensive evaluation index comprises the following components:

the formula is as follows:

wherein, alpha, beta and gamma are the weights occupied by three evaluation indexes under the comprehensive evaluation system respectively, and alpha+beta+gamma=1; v (V) ^- The method is an evaluation index of voltage symmetry of the new energy grid-connected system;is a reactive margin index; the power oscillation index is defined as +.>

S24, judging the voltage supporting capacity of the new energy station under the asymmetric fault based on the comprehensive evaluation index of the voltage supporting capacity of the new energy station.

The larger the comprehensive evaluation index value of the voltage supporting capability of the new energy station is, the stronger the positive and negative sequence voltage supporting capability of the new energy system is represented in the asymmetric fault; in contrast, the smaller the comprehensive evaluation index value of the voltage supporting capability of the new energy station is, the weaker positive and negative sequence voltage supporting capability of the new energy system is represented in the asymmetric fault.

As can be seen from the above, in some embodiments of the present application, the reactive margin index and the power oscillation index are calculated first, the reactive current command is adjusted based on the two indexes, and the voltage symmetry index is calculated using the adjusted reactive current command.

Further, the reactive margin index and the power oscillation index are independent of each other, so that the active power instruction or the reactive power instruction obtained by final calculation based on the two indexes can only take the minimum value of the two indexes, and if the maximum value is taken, the other index is inevitably not met. If no active power instruction is generated based on the reactive margin index and the power oscillation index, the two indexes are not satisfied, the two indexes are set to zero, the reactive current instruction is readjusted, and the specific adjustment mode is shown in the formula.

The second positive-sequence active current instruction in the embodiment of the application is used for perfect control, and the minimum value in the first positive-sequence active current instruction and the second positive-sequence active current instruction determined according to the two indexes is used as the last active current instruction.

In the embodiment of the application, the evaluation of the new energy station is based on an active current instruction obtained based on a reactive margin index, a power instruction obtained based on a power oscillation index and a negative sequence voltage value of a voltage symmetry index, the obtained reactive power instruction is used for calculating the voltage symmetry index, the first positive sequence active current instruction is used for calculating the reactive margin index, the second positive sequence active current instruction is used for perfecting control, and the final inverter is required to achieve a voltage control effect and is required to complete the active power instruction and the reactive power instruction together. If the reactive current command is adjusted, the active current command also needs to be correspondingly adjusted, and the final active current command is determined by the reactive margin index and the power oscillation index.

In some embodiments, a new energy station voltage support capability assessment system under asymmetric faults is provided, as shown in fig. 4, the system comprising:

Further, the start-up discrimination module includes:

the grid-connected point voltage real-time monitoring module is used for monitoring the grid-connected point voltage in real time and judging whether the grid-connected point voltage is qualified or not;

the inverter low-voltage ride through module is used for generating reactive current instructions with the aim of improving the voltage symmetry of the grid-connected point when the voltage of the grid-connected point is unqualified, and combining active current instructions given by other modules, and controlling the voltage and the current of the inverter through the positive-negative sequence current inner loop and the phase-locked loop;

and the reactive capacity margin evaluation module is used for calculating positive-sequence active current according to the reactive current instruction given by the inverter low-voltage ride-through module and combining the inverter overcurrent limit value, and taking the positive-sequence active current as a reactive capacity margin index. According to the reactive capacity margin index, the current instruction output by the inverter is regulated and returned to the low voltage ride through module of the inverter;

And the power oscillation evaluation module is used for calculating a power oscillation index according to the reactive current instruction given by the inverter low voltage ride through module and combining the inverter power oscillation limit value. According to the power oscillation index, calculating and adjusting a current instruction output by the inverter, and returning the current instruction to the low voltage ride through module of the inverter;

and the comprehensive evaluation system establishment module is used for calculating the negative sequence voltage of the grid-connected point according to the active and reactive current instructions given by other modules and taking the negative sequence voltage as a voltage symmetry index. And combining the reactive capacity margin index and the power oscillation index to establish a comprehensive evaluation system of the voltage support strength, thereby completing the comprehensive evaluation of the voltage support capacity of the new energy grid-connected system under the asymmetric fault.

It should be noted here that, in this embodiment, each module corresponds to each step in the embodiment of the method for evaluating the voltage supporting capability of the new energy station under the asymmetric fault, and the specific implementation process is the same, and will not be described here again.

The working principle of the system for evaluating the voltage supporting capability of the new energy station under the asymmetric fault of the present embodiment is the same as that of the method for evaluating the voltage supporting capability of the new energy station under the asymmetric fault of the above embodiments, and will not be described herein.

In some embodiments, a computer readable storage medium is provided, on which a computer program is stored, which when being executed by a processor, implements the steps of the method for evaluating the voltage supporting capability of a new energy station under an asymmetric fault as described in the above embodiments.

In some embodiments, an electronic device is provided that includes a memory, a processor, and a computer program stored on the memory and executable on the processor, the processor implementing the steps of the method for evaluating voltage support capability of a new energy station under an asymmetric fault as described in the above embodiments when the program is executed by the processor.

The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The method for evaluating the voltage supporting capability of the new energy station under the asymmetric fault is characterized by comprising the following steps:

2. The method of claim 1, wherein the step of determining the position of the substrate comprises,

the method for acquiring the monitoring result of the grid-connected point voltage comprises the following steps:

and otherwise, judging that the parallel grid voltage is qualified.

3. The method of claim 1, wherein the step of determining the position of the substrate comprises,

starting the new energy station voltage supporting capability comprehensive evaluation system to evaluate the new energy station voltage supporting capability under the asymmetric fault, comprising the following steps:

acquiring a voltage symmetry index based on the final current instruction;

4. The method of claim 3, wherein the step of,

The final current instruction comprises at least one of a reactive current instruction output by an inverter, a first adjusting negative sequence reactive current instruction and a second adjusting negative sequence reactive current instruction, the final current instruction output by the inverter is obtained based on low voltage ride through control, the final current instruction meets reactive capacity margin indexes and power oscillation indexes, and the final current instruction comprises:

5. The method of claim 4, wherein the step of determining the position of the first electrode is performed,

According to the reactive current instruction output by the inverter, calculating a reactive capacity margin index by combining an overcurrent limit value of the inverter, comprising:

6. The method of claim 5, wherein the step of determining the position of the probe is performed,

the reactive capacity margin indexCan be expressed as:

s.t.

wherein,is the phase included angle of the positive and negative sequence voltages.

7. The method of claim 5, wherein the step of determining the position of the probe is performed,

Judging whether the reactive capacity margin index meets the requirement:

8. The method of claim 7, wherein the step of determining the position of the probe is performed,

if the reactive margin index is greater than zero, the requirement is met; otherwise, the requirements are not satisfied.

9. The method of claim 4, wherein the step of determining the position of the first electrode is performed,

according to the reactive current instruction output by the inverter, calculating a power oscillation index by combining the power oscillation limit value of the inverter, comprising:

10. The method of claim 9, wherein the step of determining the position of the substrate comprises,

the oscillation amplitude of the active power output by the inverter can be expressed as:

continuing active power oscillation based limitingLet->And (3) calculating:

11. The method of claim 9, wherein the step of determining the position of the substrate comprises,

calculating a second negative sequence reactive current command output by the inverter according to the power oscillation index, including:

if the initial value of the power oscillation amplitude is smaller than the power oscillation limit valueThe active power oscillation evaluation index of the inverter meets the requirement, and the inverse is calculated according to the power oscillation indexThe active current instruction output by the transformer is used as a second positive sequence active current instruction;

12. The method of claim 3, wherein the step of,

acquiring a voltage symmetry index based on the final current command includes:

wherein,the calculation formula of (2) is as follows:

13. The method of claim 3, wherein the step of,

the formula is as follows:

wherein, alpha, beta Sgamma are the weights occupied by three evaluation indexes under the comprehensive evaluation system respectively, and alpha+beta+gamma=1.

14. A system for evaluating voltage supporting capability of a new energy station under an asymmetric fault, the system comprising:

15. A computer-readable storage medium having stored thereon a computer program which, when executed by a processor, implements the steps of the new energy station voltage support capability assessment method under asymmetric faults of any of claims 1 to 13.

16. An electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the steps of the new energy station voltage support capability assessment method under asymmetric faults of any of claims 1-13 when the program is executed.