CN113489070A - Flexible-direct parameter intelligent optimization method and system for new energy grid connection - Google Patents

Flexible-direct parameter intelligent optimization method and system for new energy grid connection Download PDF

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CN113489070A
CN113489070A CN202110626097.7A CN202110626097A CN113489070A CN 113489070 A CN113489070 A CN 113489070A CN 202110626097 A CN202110626097 A CN 202110626097A CN 113489070 A CN113489070 A CN 113489070A
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power
flexible
value
parameter
proportional
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CN113489070B (en
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杨立敏
朱艺颖
庞广恒
刘翀
李跃婷
雷霄
李新年
刘琳
吴娅妮
林少伯
王薇薇
胡涛
谢国平
王晶芳
刘世成
张晓丽
杨尚瑾
张晋华
刘浩芳
许锐文
付小蓓
贺郁文
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State Grid Corp of China SGCC
China Electric Power Research Institute Co Ltd CEPRI
State Grid Jiangsu Electric Power Co Ltd
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State Grid Corp of China SGCC
China Electric Power Research Institute Co Ltd CEPRI
State Grid Jiangsu Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/48—Controlling the sharing of the in-phase component
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/50—Controlling the sharing of the out-of-phase component
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The invention discloses a flexible direct parameter intelligent optimization method and system for new energy grid connection, and belongs to the technical field of system stability optimization. The method comprises the following steps: determining key parameters of a large-scale new energy island access flexible-straight system; acquiring instantaneous active power and reactive power at a grid-connected point of a large-scale new energy island access flexible-direct system in real time, and extracting characteristic components according to the instantaneous active power and the reactive power; setting key parameters of the intelligent optimization algorithm according to the system operation condition, and judging whether the system meets the input conditions of the intelligent optimization algorithm or not according to the characteristic components; if the difference meets the requirement, the proportion parameter of the outer ring proportion-integral controller of the flexible-direct island converter station is dynamically adjusted by adopting the intelligent optimization method according to the system operation condition until the characteristic component meets the exit condition of the intelligent optimization algorithm, so that the system stability is realized. The method can monitor the running state of the system in real time when 8-15 Hz oscillation occurs due to mismatching of control parameters when large-scale new energy is subjected to flexible direct grid connection.

Description

Flexible-direct parameter intelligent optimization method and system for new energy grid connection
Technical Field
The invention relates to the technical field of system stability optimization, in particular to a flexible-direct parameter intelligent optimization method and system for new energy grid connection.
Background
With the clean transformation of world energy electric power, new energy is rapidly developed, and the installed capacity is continuously increased. Power electronic equipment such as new energy power generation, direct current transmission technology, variable frequency load and the like are widely applied to source-grid-load, and the power electronization degree of a power system and the influence caused by the power electronization degree are continuously intensified.
The flexible direct-current transmission technology is a new generation transmission technology, has the advantages of flexibility, controllability, high reliability, capability of island power supply and the like compared with the traditional power grid commutation converter-based transmission technology, and is suitable for construction of large-scale new energy efficient admission, large-scale cities, islands and other regional transmission networks and efficient transmission and distribution networks. At present, flexible direct current transmission is an important implementation mode for large-scale new centralized external power transmission on land and on the sea.
In a scene of large-scale new energy transmission through flexible direct current, system oscillation is easily caused by interaction among a flexible direct current transmission system, an alternating current power grid and a new energy station. For example, subsynchronous oscillation of voltage and current occurs in the south-sink flexible direct-current transmission project, south-australian flexible direct-current transmission project and mansion flexible direct-current transmission project in the output change process of the wind farm; 250-350Hz medium frequency oscillation occurs in the BorWin1 project of the German offshore wind farm in the North sea, and core components are burnt out, so that the wind farm is shut down for a long time, and huge economic loss is caused; in the Luxi back-to-back gentle and straight project, 1270Hz high-frequency oscillation occurs when the multi-circuit alternating current transmission line is disconnected; in the debugging process of Zanbei flexible direct current power grid, after an isolated island of a converter station of health protection is unlocked and a grid-connected side switch is turned on, high-frequency oscillation occurs on the voltage of the grid side to cause system tripping, and locking failure occurs in delay single-pole operation, after an energy consumption resistor is withdrawn, surplus power of new energy causes short-time severe overvoltage of a sending end isolated island system, so that the equipment of a Zhongdu station and a new energy station are damaged in different degrees, and the new energy is completely disconnected from the grid.
In the digital-analog hybrid real-time simulation research of a large-scale new energy source through a Zhang Bei flexible direct current power grid delivery system, in the power boosting process of a photovoltaic station and a doubly-fed fan station which are connected to a Zhang Bei converter station in an isolated island mode, the alternating current voltage of a new energy source delivery grid frame generates an oscillation phenomenon of about 10 Hz.
With the development of onshore and offshore wind power in China, the oscillation risk of a new energy transmission system is gradually increased by the increase of the flexible and direct delivery capacity of new energy, and great threat is caused to the safety and stability of a power grid at a transmitting end and a receiving end.
At present, a time domain simulation analysis method or a frequency domain impedance analysis method and the like are adopted to select appropriate control parameters at the initial stage of system design of a flexible direct grid-connected system of large-scale new energy, and system resonance points are avoided. The off-line oscillation suppression method depends on an accurate new energy station equivalent model. However, the running state of a Static Var Generator (SVG) configured in the new energy station and the parameter error of a collection line both affect the resonance point of the system, thereby seriously affecting the suppression effect after parameter optimization.
Disclosure of Invention
Aiming at the problems, the invention provides an intelligent soft-direct parameter optimization method for new energy grid connection, which comprises the following steps:
determining key parameters of a large-scale new energy island access flexible-straight system;
acquiring instantaneous active power and reactive power at a grid-connected point of a large-scale new energy island access flexible-direct system in real time, and extracting characteristic components according to the instantaneous active power and the reactive power;
setting key parameters of the intelligent optimization algorithm according to the system operation condition, and judging whether the system meets the input conditions of the intelligent optimization algorithm or not according to the characteristic components;
if the difference meets the requirement, the proportion parameter of the outer ring proportion-integral controller of the flexible-direct island converter station is dynamically adjusted by adopting the intelligent optimization method according to the system operation condition until the characteristic component meets the exit condition of the intelligent optimization algorithm, so that the system stability is realized.
Optionally, the key parameters include an apparent power threshold, an oscillation component upper limit threshold, an oscillation component lower limit threshold, a control period, an initial value of a proportional parameter of an outer ring proportional-integral controller of the converter station with the flexible and straight island, an adjustment lower limit value of the proportional parameter of the outer ring proportional-integral controller of the converter station with the flexible and straight island, and an adjustment upper limit value of the proportional parameter of the outer ring proportional-integral controller of the converter station with the flexible and straight island.
Optionally, the feature component includes: the frequency and content of the oscillating component, the average apparent power;
the characteristic components are extracted according to instantaneous active power and reactive power, and the method specifically comprises the following steps:
and carrying out fast Fourier transform on the instantaneous active power and the instantaneous reactive power to obtain the frequency and the content of oscillation components, and obtaining the average apparent power of new energy outgoing of a preset number of fundamental wave periods by using a sliding window average value method on the instantaneous active power and the instantaneous reactive power.
Optionally, determining whether the feature component satisfies the input condition or the exit condition includes:
determining whether the per unit value of the average apparent power is larger than or equal to an apparent power threshold, if so, marking a position 1 by a system transmission power permission mark, determining whether the frequency of an oscillation component meets a preset range and whether the ratio of the content of the oscillation component to the average apparent power exceeds an upper limit threshold, if so, marking the position 1 by the oscillation component out-of-limit mark, and when the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are both 1, the characteristic component meets the input condition;
and determining whether the per unit value of the average apparent power is smaller than an apparent power threshold, if so, marking a position 0 of a system transmission power permission mark, determining whether the ratio of the content of the oscillation component to the average apparent power is smaller than an upper limit threshold, if so, marking the position 0 of the oscillation component out-of-limit mark, and if the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are both 0, judging that the characteristic component meets an exit condition.
Optionally, the optimization algorithm exit condition includes: and meeting exit conditions, wherein the value of the proportion parameter exceeds the upper adjustment limit value of the proportion parameter, or the value of the proportion parameter is lower than the lower adjustment limit value of the proportion parameter.
Optionally, adjusting a proportional parameter of an outer-loop proportional-integral controller of the converter station with the flexible-straight island until the characteristic component meets an input condition or an exit condition of the intelligent optimization algorithm, includes:
and increasing the value of the proportional parameter, determining whether the ratio of the content of the oscillation component to the average apparent power is reduced, if so, continuing to increase the value of the proportional parameter until the characteristic component meets the system stability condition, and if not, reducing the value of the proportional parameter until the characteristic component meets the input condition or the exit condition of the intelligent optimization algorithm.
The invention also provides a flexible direct parameter intelligent optimization system for new energy grid connection, which comprises the following steps:
the key parameter determination module is used for determining key parameters of a large-scale new energy island access flexible-straight system;
the characteristic component extraction module is used for acquiring instantaneous active power and reactive power at a grid-connected point of a large-scale new energy island access flexible direct system in real time and extracting characteristic components according to the instantaneous active power and the reactive power;
the adjusting module is used for adjusting key parameters of the intelligent optimization algorithm according to the system operation condition and judging whether the input conditions of the intelligent optimization algorithm are met or not according to the characteristic components; and if so, adjusting the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station until the characteristic component meets the exit condition of the intelligent optimization algorithm.
Optionally, the key parameters include an apparent power threshold, an oscillation component upper limit threshold, an oscillation component lower limit threshold, a control period, an initial value of a proportional parameter of an outer ring proportional-integral controller of the converter station with the flexible and straight island, an adjustment lower limit value of the proportional parameter of the outer ring proportional-integral controller of the converter station with the flexible and straight island, and an adjustment upper limit value of the proportional parameter of the outer ring proportional-integral controller of the converter station with the flexible and straight island.
Optionally, the feature component includes: the frequency and content of the oscillating component, the average apparent power;
the characteristic components are extracted according to the instantaneous power and the reactive power, and the method specifically comprises the following steps:
and carrying out fast Fourier transform on the instantaneous active power and the instantaneous reactive power to obtain the frequency and the content of oscillation components, and obtaining the average apparent power of new energy outgoing of a preset number of fundamental wave periods by using a sliding window average value method on the instantaneous active power and the instantaneous reactive power.
Optionally, determining whether the feature component satisfies the input condition or the exit condition includes:
determining whether the per unit value of the average apparent power is larger than or equal to an apparent power threshold, if so, marking a position 1 by a system transmission power permission mark, determining whether the frequency of an oscillation component meets a preset range and whether the ratio of the content of the oscillation component to the average apparent power exceeds an upper limit threshold, if so, marking the position 1 by the oscillation component out-of-limit mark, and when the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are both 1, the characteristic component meets the input condition;
and determining whether the per unit value of the average apparent power is smaller than an apparent power threshold, if so, marking a position 0 of a system transmission power permission mark, determining whether the ratio of the content of the oscillation component to the average apparent power is smaller than an upper limit threshold, if so, marking the position 0 of the oscillation component out-of-limit mark, and if the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are both 0, judging that the characteristic component meets an exit condition.
Optionally, the optimization algorithm exit condition includes: and meeting exit conditions, wherein the value of the proportion parameter exceeds the upper adjustment limit value of the proportion parameter, or the value of the proportion parameter is lower than the lower adjustment limit value of the proportion parameter.
Optionally, adjusting a proportional parameter of an outer-loop proportional-integral controller of the converter station with the flexible-straight island until the characteristic component meets an input condition or an exit condition of the intelligent optimization algorithm, includes:
and increasing the value of the proportional parameter, determining whether the ratio of the content of the oscillation component to the average apparent power is reduced, if so, continuing to increase the value of the proportional parameter until the characteristic component meets the system stability condition, and if not, reducing the value of the proportional parameter until the characteristic component meets the input condition or the exit condition of the intelligent optimization algorithm.
The method can monitor the running state of the system in real time when 8-15 Hz oscillation occurs due to mismatching of control parameters when large-scale new energy is subjected to flexible direct-current grid connection, and find the optimal parameter matched with the actual running state of the system by intelligently optimizing the proportional parameter of the external ring proportional-integral controller of the direct-isolated island converter station, so that the effect of inhibiting oscillation is achieved.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a flow chart of an embodiment of the method of the present invention;
FIG. 3 is a schematic structural diagram of a simulation model in which large-scale new energy is sent out through a flexible direct grid connection in the embodiment of the method of the present invention;
fig. 4 is a waveform diagram of an active power per unit value, a reactive power per unit value and a voltage per unit value of a grid-connected point of the new energy station 1 in the embodiment of the method of the present invention;
fig. 5 is a waveform diagram of an active power per unit value, a reactive power per unit value and a voltage per unit value of a grid-connected point of the new energy station 2 in the embodiment of the method of the present invention;
FIG. 6 is a graph of the AC current and AC voltage waveforms for the post-soft-dc grid connection in an embodiment of the method of the present invention;
FIG. 7 is a waveform diagram of active power and reactive power at a post-soft-straight summing junction in an embodiment of a method of the present invention;
FIG. 8 is a waveform diagram of a back-soft-straight parameter Kp value, an optimization algorithm input excision identification bit and an oscillation component effective value change curve in the embodiment of the method;
fig. 9 is a block diagram of the system of the present invention.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, the same units/elements are denoted by the same reference numerals.
Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
The invention provides a flexible direct parameter intelligent optimization method for new energy grid connection, as shown in fig. 1, comprising the following steps:
determining key parameters of a large-scale new energy island access flexible-straight system;
acquiring instantaneous active power and reactive power at a grid-connected point of a large-scale new energy island access flexible-direct system in real time, and extracting characteristic components according to the instantaneous active power and the reactive power;
setting key parameters of the intelligent optimization algorithm according to the system operation condition, and judging whether the system meets the input conditions of the intelligent optimization algorithm or not according to the characteristic components;
if the difference meets the requirement, the proportion parameter of the outer ring proportion-integral controller of the flexible-direct island converter station is dynamically adjusted by adopting the intelligent optimization method according to the system operation condition until the characteristic component meets the exit condition of the intelligent optimization algorithm, so that the system stability is realized.
The key parameters comprise an apparent power threshold, an oscillation component upper limit threshold, an oscillation component lower limit threshold, a control period, an initial value of a proportional parameter of an outer ring proportional-integral controller of the flexible-direct island converter station, an adjustment lower limit value of the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station and an adjustment upper limit value of the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station.
Wherein the feature components include: the frequency and content of the oscillating component, the average apparent power;
the characteristic components are extracted according to the instantaneous power and the reactive power, and the method specifically comprises the following steps:
and carrying out fast Fourier transform on the instantaneous active power and the instantaneous reactive power to obtain the frequency and the content of oscillation components, and obtaining the average apparent power of new energy outgoing of a preset number of fundamental wave periods by using a sliding window average value method on the instantaneous active power and the instantaneous reactive power.
Wherein determining whether the feature component satisfies a drop-in condition or a drop-out condition includes:
determining whether the per unit value of the average apparent power is larger than or equal to an apparent power threshold, if so, marking a position 1 by a system transmission power permission mark, determining whether the frequency of an oscillation component meets a preset range and whether the ratio of the content of the oscillation component to the average apparent power exceeds an upper limit threshold, if so, marking the position 1 by the oscillation component out-of-limit mark, and when the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are both 1, the characteristic component meets the input condition;
and determining whether the per unit value of the average apparent power is smaller than an apparent power threshold, if so, marking a position 0 of a system transmission power permission mark, determining whether the ratio of the content of the oscillation component to the average apparent power is smaller than an upper limit threshold, if so, marking the position 0 of the oscillation component out-of-limit mark, and if the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are both 0, judging that the characteristic component meets an exit condition.
The method comprises the following steps of adjusting a proportional parameter of an outer ring proportional-integral controller of a converter station of a flexible-direct island until a characteristic component meets an input condition or an exit condition of an intelligent optimization algorithm, wherein the method comprises the following steps:
and increasing the value of the proportional parameter, determining whether the ratio of the content of the oscillation component to the average apparent power is reduced, if so, continuing to increase the value of the proportional parameter until the characteristic component meets the system stability condition, and if not, reducing the value of the proportional parameter until the characteristic component meets the input condition or the exit condition of the intelligent optimization algorithm.
The invention is further illustrated by the following examples:
the active power and reactive power of a large-scale new energy island access flexible-direct grid-connected point are used as controlled objects, oscillation characteristic quantities are extracted, when oscillation components exceed a limit value, a proportional parameter Kp of an outer ring proportional-integral controller of a flexible-direct island converter station is intelligently optimized on line, so that the oscillation components are restrained, and intelligent optimization is carried out, and the specific steps are shown in figure 2 and comprise:
step 1, extracting oscillation characteristic components and setting key parameters in an oscillation suppression algorithm;
instantaneous active power and instantaneous reactive power at a grid-connected point are collected in real time through a flexible direct control protection system, the collected instantaneous active power and instantaneous reactive power are subjected to fast Fourier transform, the frequency and the content of oscillation components are calculated, and the calculated average apparent power of new energy outgoing in 10 fundamental wave periods is calculated by adopting a sliding window average value method.
The key parameters in the invention mainly comprise: apparent power threshold SthUpper limit threshold value SSO of oscillation componentup_thLower limit threshold value SSO of oscillation componentdown_thControl period TcKp initial value KpinitAdjusting lower limit value DK of KppminAdjusting upper limit value DK of Kppmax。
Step 2, judging the input conditions of the stability of large-scale new energy through flexible direct grid connection;
and (2) judging whether the per unit value of the current average apparent power is larger than or equal to an apparent power threshold value or not in real time according to the apparent power calculated in the step (1), if the per unit value of the current average apparent power is larger than or equal to the apparent power threshold value, marking the position 1 of a system transmission power permission mark, judging whether the frequency is in the range of 8-15 Hz or not according to the frequency and the content of the oscillation component extracted in the step (1), calculating whether the ratio of the effective value of the current oscillation component to the average apparent power exceeds an upper limit threshold value or not, and if the ratio exceeds the upper limit, marking the position 1 of the oscillation component exceeding the upper limit. When the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are simultaneously 1, the method is put into use.
Step 3, judging the exit condition of the stability of the large-scale new energy through flexible direct grid connection;
and (3) judging whether the per unit value of the current average apparent power is smaller than an apparent power threshold value or not in real time according to the apparent power calculated in the step (1), and if the per unit value of the current average apparent power meets the condition, marking the position of a system transmission power permission mark as 0. And (3) calculating whether the ratio of the current oscillation component to the average apparent power is smaller than a lower limit threshold value or not according to the oscillation component amplitude extracted in the step (1), and if the ratio is out of limit, marking the position of an oscillation component out of limit mark to be 0. And exiting when the position of the system transmission power permission mark or the position of the oscillation component out-of-limit mark is 0 at the same time.
Step 4, optimizing the stability of the new energy conveying system;
on the basis of the initial value of the proportional parameter Kp of the outer ring proportional-integral controller of the flexible island converter station, which is set in the step 1, increasing DKp the proportional parameter Kp, observing whether the ratio of the oscillation component to the average apparent power is reduced, if so, continuing to increase the value Kp until the exit condition of the step 3 is met or the value Kp exceeds the upper adjusting limit value; if not, decreasing the Kp value until the exit condition of step 3 is satisfied or the Kp value is lower than the adjustment lower limit value.
In step 1, the apparent power threshold SthSetting according to 5% of rated apparent power, and setting the upper limit threshold value SSO of oscillation componentup_thAnd lower threshold SSOdown_thAll are set according to 0.133 percent, the control period Tc is set according to 500ms, and the initial value Kp of Kp is setinitAccording to conventional oscillation suppressionSetting the method, adjusting the lower limit value KpminAnd upper limit value KpmaxAccording to Kp initial value Kp respectivelyinit0.5 and 3 times of (Kp) and adjusting the step length DKpAccording to 0.067KpinitAnd (6) setting.
The method is applied to digital-analog hybrid simulation research of soft direct output of a large-scale new energy island in the north of China, a new generation digital-analog hybrid simulation platform based on a soft direct-end control device in the north of China engineering, and a hardware-in-the-loop real-time simulation model containing a new energy output grid structure shown in figure 3 is built, wherein the model comprises two wind power plants, the total installed capacity of the two wind power plants is 500MW, and the rated capacity of a soft direct current converter is Srate which is 1500 MW.
According to the above assumptions, the setting values of the key parameters are: apparent power threshold Sth5%, upper threshold value for oscillation component SSOup_th0.133%, lower threshold value SSOdown_thControl period T of 0.133%c500ms, initial KpinitAdjusting the lower limit value Kp to 0.3min＝0.15，Kpmax0.9, the step DK is adjusted by Kpp＝0.067Kpinit＝0.1。
The method comprises the following specific steps:
1. instantaneous active power and instantaneous reactive power at a grid-connected point are collected in real time through a flexible direct control protection system, the collected instantaneous active power and instantaneous reactive power are subjected to fast Fourier transform, and the frequency fSSO and the effective value AmSSO of an oscillation component are calculated to be max (P)AM,QAM)，PAMEffective value of the oscillating component of active power, QAMThe effective value of the reactive power oscillation component is obtained, wherein the calculated average apparent power Save sent by new energy in 10 fundamental wave periods is calculated by adopting a sliding window average value method.
2. Real-time judging current average apparent power per unit value Save_pu＝Save/SrateWhether or not it is greater than or equal to the apparent power threshold SthIf the condition is met, the system transmission power permission mark position 1 is marked, and whether the ratio of the current oscillation component AmSSO to the average apparent power Save exceeds the upper limit threshold or not is calculated according to the oscillation component effective value AmSSO extracted in the step 1Value SSOup_thIf the limit is out, the oscillation component is out of limit to flag position 1. When the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are simultaneously 1, the method is put into use.
3. When the suppression algorithm is put into use, the initial value Kp of the proportional parameter Kp of the outer ring proportional-integral controller of the flexible-direct island converter stationinitOn the basis of 0.3, the proportional parameter Kp is increased by DKp DKp＝0.067KpinitObserving whether the ratio of the oscillation component to the average apparent power is smaller than 0.1, and if so, continuing to increase the Kp value until the exit condition of the step 3 is met or the Kp value exceeds the adjusting upper limit value; if not, decreasing the Kp value until the exit condition of step 3 is satisfied or the Kp value is lower than the adjustment lower limit value.
4. Real-time judging current average apparent power per unit value Save_pu＝Save/SrateWhether or not less than apparent power threshold SthAnd 5%, if the condition is met, the system transmission power permission flag is set to 0. Calculating the current oscillation component AmSSO and the average apparent power SaveWhether the ratio of (A) is less than the lower threshold SSOdown_thIf the limit is out, the oscillation component is out of limit to flag position 0. And exiting when the position of the system transmission power permission mark or the position of the oscillation component out-of-limit mark is 0 at the same time.
The simulation analysis of the embodiment of the flexible-direct parameter intelligent optimization method suitable for improving the stability of the new energy transmission system is as follows:
without the intelligent optimization algorithm, Kp is KpinitWhen the new energy output is increased to 196MW, the system generates oscillation with the frequency of 10.2Hz, and the effective value P of the oscillation component of the active power of the new energy grid-connected pointAMAbout 8.3MW, the effective value Q of the oscillation component of the reactive powerAMThe power station has the advantages that the power station has the power of about 7.6MW, the active power, the reactive power and the alternating voltage of the wind power plant, the on-line alternating voltage, the alternating current, the active power and the reactive power of the flexible-direct island converter station all oscillate, and at the moment, the average apparent power per unit value Save_pu＝Save/Srate196 MW/1500-13.1% apparent work or moreRate threshold Sth5%, system transmission power permission flag position 1; effective value of oscillation component AmSSO ═ max (P)AM,QAM) 8.3MW, to average apparent power SaveIs 0.553%, exceeds the upper threshold SSOup_th0.133%, the oscillation component off-limits flag position 1. After the algorithm is put into use, when the proportional parameter Kp of the outer loop proportional-integral controller of the flexible-direct island converter station is adjusted to 0.6, the active power, the reactive power and the alternating voltage of the wind power plant, the oscillation of the online alternating voltage, the alternating current, the active power and the reactive power of the flexible-direct island converter station are quickly attenuated, and the system is recovered to be stable, as shown in FIGS. 4-8. When the ratio of the effective value of the oscillation component AmSSO to the average apparent power Save is less than the lower threshold SSOdown_thAnd (5) when the soft direct parameter intelligent optimization algorithm is equal to 0.133%, quitting, and finally, enabling the effective value AmSSO of the oscillation component to be close to 0 and enabling the oscillation to disappear.
According to the flexible-direct parameter intelligent optimization method for improving the stability of the new energy transmission system, the power of large-scale new energy accessed to a grid-connected point through a flexible-direct island is used as a detection object, and the oscillation state of the system is judged by extracting the oscillation characteristic component in the power. When the system oscillates, the proportional parameter Kp of the outer ring proportional-integral controller of the flexible-direct island converter station is intelligently adjusted, 8-15 Hz oscillation can be effectively inhibited, and the system is recovered to be stable, so that the safe operation of the flexible-direct converter and the new energy unit is ensured, secondary damage caused by system oscillation propagation is avoided, and the safety and reliability of the large-scale new energy through the flexible-direct island converter system are improved.
The invention further provides a flexible-direct parameter intelligent optimization system 200 for new energy grid connection, as shown in fig. 9, including:
the key parameter determining module 201 is used for determining key parameters of a large-scale new energy island access flexible-straight system;
the characteristic component extraction module 202 is used for collecting instantaneous active power and reactive power at a grid-connected point of a large-scale new energy island access flexible direct system in real time and extracting characteristic components according to the instantaneous active power and the reactive power;
the adjusting module 203 is used for adjusting key parameters of the intelligent optimization algorithm according to the system operation condition and determining whether the characteristic components meet the input conditions or exit conditions of the intelligent optimization algorithm; and if so, adjusting the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station until the characteristic component meets the input condition or the exit condition of the intelligent optimization algorithm.
The key parameters comprise an apparent power threshold, an oscillation component upper limit threshold, an oscillation component lower limit threshold, a control period, an initial value of a proportional parameter of an outer ring proportional-integral controller of the flexible-direct island converter station, an adjustment lower limit value of the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station and an adjustment upper limit value of the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station.
Wherein the feature components include: the frequency and content of the oscillating component, the average apparent power;
the characteristic components are extracted according to the instantaneous power and the reactive power, and the method specifically comprises the following steps:
and carrying out fast Fourier transform on the instantaneous active power and the instantaneous reactive power to obtain the frequency and the content of oscillation components, and obtaining the average apparent power of new energy outgoing of a preset number of fundamental wave periods by using a sliding window average value method on the instantaneous active power and the instantaneous reactive power.
Wherein determining whether the feature component satisfies a drop-in condition or a drop-out condition includes:
determining whether the per unit value of the average apparent power is larger than or equal to an apparent power threshold, if so, marking a position 1 by a system transmission power permission mark, determining whether the frequency of an oscillation component meets a preset range and whether the ratio of the content of the oscillation component to the average apparent power exceeds an upper limit threshold, if so, marking the position 1 by the oscillation component out-of-limit mark, and when the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are both 1, the characteristic component meets the input condition;
and determining whether the per unit value of the average apparent power is smaller than an apparent power threshold, if so, marking a position 0 of a system transmission power permission mark, determining whether the ratio of the content of the oscillation component to the average apparent power is smaller than an upper limit threshold, if so, marking the position 0 of the oscillation component out-of-limit mark, and if the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are both 0, judging that the characteristic component meets an exit condition.
Wherein the optimization algorithm exit condition comprises: and meeting exit conditions, wherein the value of the proportion parameter exceeds the upper adjustment limit value of the proportion parameter, or the value of the proportion parameter is lower than the lower adjustment limit value of the proportion parameter.
The method comprises the following steps of adjusting a proportional parameter of an outer ring proportional-integral controller of a converter station of a flexible-direct island until a characteristic component meets an input condition or an exit condition of an intelligent optimization algorithm, wherein the method comprises the following steps:
and increasing the value of the proportional parameter, determining whether the ratio of the content of the oscillation component to the average apparent power is reduced, if so, continuing to increase the value of the proportional parameter until the characteristic component meets the system stability condition, and if not, reducing the value of the proportional parameter until the characteristic component meets the input condition or the exit condition of the intelligent optimization algorithm.
The method can monitor the running state of the system in real time when 8-15 Hz oscillation occurs due to mismatching of control parameters when large-scale new energy is subjected to flexible direct-current grid connection, and find the optimal parameter matched with the actual running state of the system by intelligently optimizing the proportional parameter of the external ring proportional-integral controller of the direct-isolated island converter station, so that the effect of inhibiting oscillation is achieved.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein. The scheme in the embodiment of the invention can be realized by adopting various computer languages, such as object-oriented programming language Java and transliterated scripting language JavaScript.
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 flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams 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.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims (12)

1. A flexible-direct parameter intelligent optimization method for new energy grid connection comprises the following steps:
determining key parameters of a large-scale new energy island access flexible-straight system;
acquiring instantaneous active power and reactive power at a grid-connected point of a large-scale new energy island access flexible-direct system in real time, and extracting characteristic components according to the instantaneous active power and the reactive power;
setting key parameters of the intelligent optimization algorithm according to the system operation condition, and judging whether the system meets the input conditions of the intelligent optimization algorithm or not according to the characteristic components;
if the difference meets the requirement, the proportion parameter of the outer ring proportion-integral controller of the flexible-direct island converter station is dynamically adjusted by adopting the intelligent optimization method according to the system operation condition until the characteristic component meets the exit condition of the intelligent optimization algorithm, so that the system stability is realized.
2. The method according to claim 1, wherein the key parameters comprise an apparent power threshold, an oscillation component upper limit threshold, an oscillation component lower limit threshold, a control period, an initial value of a proportional parameter of an outer ring proportional-integral controller of the flexible-direct island converter station, an adjustment lower limit value of the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station and an adjustment upper limit value of the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station.
3. The method of claim 1, the feature components comprising: the frequency and content of the oscillating component, the average apparent power;
the characteristic components are extracted according to instantaneous active power and reactive power, and the method specifically comprises the following steps:
and carrying out fast Fourier transform on the instantaneous active power and the instantaneous reactive power to obtain the frequency and the content of oscillation components, and obtaining the average apparent power of new energy outgoing of a preset number of fundamental wave periods by using a sliding window average value method on the instantaneous active power and the instantaneous reactive power.
4. The method of claim 1, the determining whether a feature component satisfies a drop-in condition or a drop-out condition, comprising:
determining whether the per unit value of the average apparent power is larger than or equal to an apparent power threshold, if so, marking a position 1 by a system transmission power permission mark, determining whether the frequency of an oscillation component meets a preset range and whether the ratio of the content of the oscillation component to the average apparent power exceeds an upper limit threshold, if so, marking the position 1 by the oscillation component out-of-limit mark, and when the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are both 1, the characteristic component meets the input condition;
and determining whether the per unit value of the average apparent power is smaller than an apparent power threshold, if so, marking a position 0 of a system transmission power permission mark, determining whether the ratio of the content of the oscillation component to the average apparent power is smaller than an upper limit threshold, if so, marking the position 0 of the oscillation component out-of-limit mark, and if the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are both 0, judging that the characteristic component meets an exit condition.
5. The method of claim 1, the optimization algorithm exit condition, comprising: and meeting exit conditions, wherein the value of the proportion parameter exceeds the upper adjustment limit value of the proportion parameter, or the value of the proportion parameter is lower than the lower adjustment limit value of the proportion parameter.
6. The method according to claim 1, wherein the adjusting the proportional parameter of the outer loop proportional-integral controller of the flexible island converter station until the characteristic component meets the input condition or the exit condition of the intelligent optimization algorithm comprises:
and increasing the value of the proportional parameter, determining whether the ratio of the content of the oscillation component to the average apparent power is reduced, if so, continuing to increase the value of the proportional parameter until the characteristic component meets the system stability condition, and if not, reducing the value of the proportional parameter until the characteristic component meets the input condition or the exit condition of the intelligent optimization algorithm.
7. A flexible-direct parameter intelligent optimization system for new energy grid connection, the system comprising:
the key parameter determination module is used for determining key parameters of a large-scale new energy island access flexible-straight system;
the characteristic component extraction module is used for acquiring instantaneous active power and reactive power at a grid-connected point of a large-scale new energy island access flexible direct system in real time and extracting characteristic components according to the instantaneous active power and the reactive power;
the adjusting module is used for adjusting key parameters of the intelligent optimization algorithm according to the system operation condition and judging whether the input conditions of the intelligent optimization algorithm are met or not according to the characteristic components; and if so, adjusting the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station until the characteristic component meets the exit condition of the intelligent optimization algorithm.
8. The system according to claim 7, wherein the key parameters comprise an apparent power threshold, an oscillation component upper limit threshold, an oscillation component lower limit threshold, a control period, an initial value of a proportional parameter of an outer ring proportional-integral controller of the flexible-direct island converter station, an adjustment lower limit value of the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station and an adjustment upper limit value of the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station.
9. The system of claim 7, the feature components comprising: the frequency and content of the oscillating component, the average apparent power;
the characteristic components are extracted according to the instantaneous power and the reactive power, and the method specifically comprises the following steps:
and carrying out fast Fourier transform on the instantaneous active power and the instantaneous reactive power to obtain the frequency and the content of oscillation components, and obtaining the average apparent power of new energy outgoing of a preset number of fundamental wave periods by using a sliding window average value method on the instantaneous active power and the instantaneous reactive power.
10. The system of claim 7, the determining whether the feature component satisfies a drop-in condition or a drop-out condition, comprising:
determining whether the per unit value of the average apparent power is larger than or equal to an apparent power threshold, if so, marking a position 1 by a system transmission power permission mark, determining whether the frequency of an oscillation component meets a preset range and whether the ratio of the content of the oscillation component to the average apparent power exceeds an upper limit threshold, if so, marking the position 1 by the oscillation component out-of-limit mark, and when the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are both 1, the characteristic component meets the input condition;
and determining whether the per unit value of the average apparent power is smaller than an apparent power threshold, if so, marking a position 0 of a system transmission power permission mark, determining whether the ratio of the content of the oscillation component to the average apparent power is smaller than an upper limit threshold, if so, marking the position 0 of the oscillation component out-of-limit mark, and if the position of the system transmission power permission mark and the position of the oscillation component out-of-limit mark are both 0, judging that the characteristic component meets an exit condition.
11. The system of claim 7, the optimization algorithm exit condition, comprising: and meeting exit conditions, wherein the value of the proportion parameter exceeds the upper adjustment limit value of the proportion parameter, or the value of the proportion parameter is lower than the lower adjustment limit value of the proportion parameter.
12. The system according to claim 7, wherein the adjusting the proportional parameter of the outer loop proportional-integral controller of the flexible island converter station until the characteristic component meets the input condition or the exit condition of the intelligent optimization algorithm comprises:
and increasing the value of the proportional parameter, determining whether the ratio of the content of the oscillation component to the average apparent power is reduced, if so, continuing to increase the value of the proportional parameter until the characteristic component meets the system stability condition, and if not, reducing the value of the proportional parameter until the characteristic component meets the input condition or the exit condition of the intelligent optimization algorithm.
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