阅读说明：本技术 一种提升柔直输送清洁能源稳定性的方法及系统 (Method and system for improving stability of soft and direct conveying of clean energy ) 是由 杨立敏 朱艺颖 刘翀 李跃婷 郭强 雷霄 李新年 刘琳 庞广恒 吴娅妮 林少伯 于 2021-06-04 设计创作，主要内容包括：本发明公开了一种提升柔直输送清洁能源稳定性的方法及系统,属于输电控制保护技术领域。本发明方法包括：获取大规模新能源孤岛接入柔直并网点处的有功功率及无功功率数据,确定有功功率及无功功率的振荡分量,并判断有功功率及无功功率的振荡分量是否满足持续偏高条件；若有功功率及无功功率的振荡分量满足持续偏高条件,则执行柔性直流输电系统输送清洁能源稳定策略；当执行执行柔性直流输电系统输送清洁能源稳定策略后,判断此时的有功功率无功功率是否恢复稳定；若恢复稳定,则维持柔直孤岛换流站外环比例-积分控制器的比例参数,使柔直输送清洁能源系统稳定运行。本发明提升柔性直流输电系统输送清洁能源稳定性。(The invention discloses a method and a system for improving stability of soft and direct transmission of clean energy, and belongs to the technical field of transmission control protection. The method comprises the following steps: acquiring active power and reactive power data of a large-scale new energy island access flexible direct-current grid-connected point, determining oscillation components of the active power and the reactive power, and judging whether the oscillation components of the active power and the reactive power meet a continuous high condition or not; if the oscillation components of the active power and the reactive power meet the continuous high condition, executing a clean energy source transmission stabilization strategy of the flexible direct current transmission system; after executing a strategy of carrying out the stabilization of the clean energy transmitted by the flexible direct current transmission system, judging whether the active power and the reactive power at the moment are recovered to be stable or not; and if the converter station is stable, maintaining the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station, so that the flexible-direct transmission clean energy system can stably operate. The invention improves the stability of the flexible direct current transmission system in conveying clean energy.)

1. A method of improving stability of a clean energy source for flexible direct transport, the method comprising:

acquiring active power and reactive power data of a large-scale new energy island access flexible direct-current grid-connected point, determining oscillation components of the active power and the reactive power, and judging whether the oscillation components of the active power and the reactive power meet a continuous high condition or not;

if the oscillation components of the active power and the reactive power meet the continuous high condition, executing a clean energy source transmission stabilization strategy of the flexible direct current transmission system;

after executing a strategy of carrying out the stabilization of the clean energy transmitted by the flexible direct current transmission system, judging whether the active power and the reactive power at the moment are recovered to be stable or not;

and if the converter station is stable, maintaining the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station, so that the flexible-direct transmission clean energy system can stably operate.

2. The method of claim 1, wherein the condition for determining that the oscillation component is continuously high is: the ratio of the maximum value of the active power oscillation component and the maximum value of the reactive power oscillation component to the apparent power average value Save exceeds an upper limit threshold value, and the duration time exceeds 500 ms.

3. The method of claim 1, the flexible direct current power transmission system delivering a clean energy stabilization strategy of: and adjusting the proportional parameter of an outer loop proportional-integral controller of the flexible-direct island converter station.

4. The method according to claim 1, wherein the determining condition for determining whether the active power and the reactive power are stable is:

the ratio of the oscillation component maximum value to the apparent power average value is less than the lower threshold value, and the duration exceeds 1 s.

5. A system for improving stability of a soft straight delivery of clean energy, the system comprising:

the power judgment unit is used for acquiring active power and reactive power data of a large-scale new energy island access flexible direct-current grid-connected point, determining oscillation components of the active power and the reactive power, and judging whether the oscillation components of the active power and the reactive power meet a continuous high condition or not;

the strategy execution unit is used for executing a clean energy transmission stability strategy of the flexible direct current power transmission system if the oscillation components of the active power and the reactive power meet the continuous high condition;

the system comprises a judging and stabilizing unit, a control unit and a control unit, wherein the judging and stabilizing unit judges whether the active power and the reactive power are stabilized or not after executing a clean energy source transmission stabilization strategy of a flexible direct current transmission system;

and if the system stably runs, the system stably runs by maintaining the proportional parameters of the outer ring proportional-integral controller of the flexible-direct island converter station so as to stably run the flexible-direct clean energy transmission system.

6. The system of claim 5, wherein the condition for determining that the oscillation component is continuously high is: the ratio of the maximum value of the active power oscillation component and the maximum value of the reactive power oscillation component to the apparent power average value Save exceeds an upper limit threshold value, and the duration time exceeds 500 ms.

7. The system of claim 5, the flexible direct current power transmission system delivering a clean energy stabilization strategy of: and adjusting the proportional parameter of an outer loop proportional-integral controller of the flexible-direct island converter station.

8. The system according to claim 5, wherein the determining condition for determining whether the active power and the reactive power are stable is:

the ratio of the oscillation component maximum value to the apparent power average value is less than the lower threshold value, and the duration exceeds 1 s.

Technical Field

The invention relates to the technical field of power transmission control protection, in particular to a method and a system for improving stability of clean energy in flexible and direct transmission.

Background

The flexible direct current transmission is used as a new generation of transmission technology, is also the transmission technology with highest controllability and best adaptability in the world at present, and can be used for large-scale efficient new energy acceptance and construction of regional transmission networks and efficient transmission and distribution networks of large-scale cities, islands and the like. The flexible direct current transmission can be used as an important implementation mode for externally transmitting electric energy by large-scale new energy due to the technical advantages of the flexible direct current transmission. When a large-scale new energy island is sent out through a flexible direct current transmission system, the flexible direct current island station adopts a double closed-loop controller to respectively control the amplitude and the frequency of alternating voltage of an island station access point. When the system is disturbed, if the flexible direct island controller and the new energy unit controller are not matched, the mutual action of the flexible direct island controller and the new energy unit controller is easy to generate oscillation phenomena with different frequencies, and great threat is caused to the safe and stable operation of the large-scale new energy through the flexible direct clean energy delivery system.

Many oscillation problems of new energy through a direct current sending system have occurred at home and abroad, and in 2014, a filter capacitor of a high-voltage direct current rectifier is burnt out due to harmonic oscillation about 290Hz generated by a north offshore wind farm through a flexible direct current transmission sending system based on a two-level voltage source type current converter, so that the whole wind farm is turned off for 10 months, and the direct economic loss exceeds 1 hundred million euros; in the debugging process of the grid-connected project of the south and Australia three-terminal flexible direct-current new energy station in 2014, a subsynchronous oscillation phenomenon with the frequency within the range of 20-30 Hz gradually occurs in the system, and the direct-current protection action of the flexible direct-current system is finally caused to stop running along with the further increase of the output power of the new energy station.

Disclosure of Invention

The invention aims to provide a method for improving the stability of soft and direct transmission of clean energy aiming at the oscillation of a large-scale new energy source which is disturbed by a soft and direct grid-connected external transmission system and aiming at inhibiting the oscillation and improving the stability of the soft and direct transmission system for transmitting the clean energy, which comprises the following steps:

acquiring active power and reactive power data of a large-scale new energy island access flexible direct-current grid-connected point, determining oscillation components of the active power and the reactive power, and judging whether the oscillation components of the active power and the reactive power meet a continuous high condition or not;

if the oscillation components of the active power and the reactive power meet the continuous high condition, executing a clean energy source transmission stabilization strategy of the flexible direct current transmission system;

after executing a strategy of carrying out the stabilization of the clean energy transmitted by the flexible direct current transmission system, judging whether the active power and the reactive power at the moment are recovered to be stable or not;

and if the converter station is stable, maintaining the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station, so that the flexible-direct transmission clean energy system can stably operate.

Optionally, the condition for determining that the oscillation component is continuously higher is as follows: the ratio of the maximum value of the active power oscillation component and the maximum value of the reactive power oscillation component to the apparent power average value Save exceeds an upper limit threshold value, and the duration time exceeds 500 ms.

Optionally, the strategy for stabilizing the clean energy delivered by the flexible direct current power transmission system is as follows: and adjusting the proportional parameter of an outer loop proportional-integral controller of the flexible-direct island converter station.

Optionally, the condition for determining whether the reactive power of the active power recovers to be stable is:

the ratio of the oscillation component maximum value to the apparent power average value is less than the lower threshold value, and the duration exceeds 1 s.

The invention also provides a system for improving the stability of the soft and direct conveying of clean energy, which comprises:

the power judgment unit is used for acquiring active power and reactive power data of a large-scale new energy island access flexible direct-current grid-connected point, determining oscillation components of the active power and the reactive power, and judging whether the oscillation components of the active power and the reactive power meet a continuous high condition or not;

the strategy execution unit is used for executing a clean energy transmission stability strategy of the flexible direct current power transmission system if the oscillation components of the active power and the reactive power meet the continuous high condition;

the system comprises a judging and stabilizing unit, a control unit and a control unit, wherein the judging and stabilizing unit judges whether the active power and the reactive power are stabilized or not after executing a clean energy source transmission stabilization strategy of a flexible direct current transmission system;

and if the system stably runs, the system stably runs by maintaining the proportional parameters of the outer ring proportional-integral controller of the flexible-direct island converter station so as to stably run the flexible-direct clean energy transmission system.

Optionally, the condition for determining that the oscillation component is continuously higher is as follows: the ratio of the maximum value of the active power oscillation component and the maximum value of the reactive power oscillation component to the apparent power average value Save exceeds an upper limit threshold value, and the duration time exceeds 500 ms.

Optionally, the strategy for stabilizing the clean energy delivered by the flexible direct current power transmission system is as follows: and adjusting the proportional parameter of an outer loop proportional-integral controller of the flexible-direct island converter station.

Optionally, the condition for determining whether the reactive power of the active power recovers to be stable is:

the ratio of the oscillation component maximum value to the apparent power average value is less than the lower threshold value, and the duration exceeds 1 s.

After the parameters of the flexible direct current transmission control system are optimized, the network active power, the reactive power, the converter direct current voltage, the grid-connected point alternating current voltage, the alternating current, the new energy station output, the reactive power at the SVG grid-connected node and the oscillation of the direct current capacitor voltage of the flexible direct current isolated island converter station disappear rapidly, and the system recovers stable operation.

Drawings

FIG. 1 is a flow chart of a method for improving stability of clean energy delivered in a flexible and straight manner according to the present invention;

FIG. 2 is a schematic structural diagram of a simulation model of large-scale new energy sent out through a flexible direct grid connection in an embodiment of the present invention;

FIG. 3 is a flow chart of a control strategy for stabilizing the delivery of clean energy by the flexible DC power transmission system according to the present invention;

FIG. 4 is a waveform diagram of bipolar active power and reactive power of a converter station of a flexible-direct island after a stability control strategy according to the present invention;

FIG. 5 is a waveform diagram of the positive DC voltage of the converter station of the flexible-direct island after the stability control strategy of the present invention;

FIG. 6 is a waveform diagram of AC voltage and AC current at a grid connection point of new energy after a stabilization control strategy according to the present invention;

FIG. 7 is a graph of the new energy farm station output waveform after the stabilization control strategy of the present invention;

FIG. 8 is a graph of reactive power at nodes of the SVG network and DC capacitor voltage waveforms after a stabilization control strategy according to the present invention;

fig. 9 is a structural diagram of a system for improving stability of soft and straight transportation of clean energy according to 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 method for improving stability of soft and straight conveying clean energy, which comprises the following steps as shown in figure 1:

acquiring active power and reactive power data of a large-scale new energy island access flexible direct-current grid-connected point, determining oscillation components of the active power and the reactive power, and judging whether the oscillation components of the active power and the reactive power meet a continuous high condition or not;

if the oscillation components of the active power and the reactive power meet the continuous high condition, executing a clean energy source transmission stabilization strategy of the flexible direct current transmission system;

after executing a strategy of carrying out the stabilization of the clean energy transmitted by the flexible direct current transmission system, judging whether the active power and the reactive power at the moment are recovered to be stable or not;

and if the converter station is stable, maintaining the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station, so that the flexible-direct transmission clean energy system can stably operate.

The condition for judging that the oscillation component is continuously higher is as follows: the ratio of the maximum value of the active power oscillation component and the maximum value of the reactive power oscillation component to the apparent power average value Save exceeds an upper limit threshold value, and the duration time exceeds 500 ms.

Wherein, the flexible direct current transmission system carries clean energy and stabilizes the strategy as: and adjusting the proportional parameter of an outer loop proportional-integral controller of the flexible-direct island converter station.

Wherein, the judgment condition for judging whether the active power and the reactive power are recovered stably is as follows:

the ratio of the oscillation component maximum value to the apparent power average value is less than the lower threshold value, and the duration exceeds 1 s.

The preferred embodiment for the specific application is as follows:

the invention is already applied to digital-analog hybrid real-time simulation research and engineering sites of Zhang Bei flexible direct engineering for conveying large-scale new energy, and the simulation research utilizes a new generation digital-analog hybrid simulation platform based on a Zhang Bei-Beijing end-to-end flexible direct control device of Zhang Bei engineering to build a hardware-in-the-loop real-time simulation model containing a new energy sending grid structure as shown in FIG. 2. The total installed capacity of the new energy is 4500MW, and the rated capacity of the soft direct current converter is 3000 MW.

The flow chart of the control strategy for stably conveying clean energy by the flexible direct current transmission system is shown in fig. 3, and the control strategy comprises the following specific steps:

(1) acquiring instantaneous active power and instantaneous reactive power at a grid-connected point in real time through a flexible direct control protection system, performing fast Fourier transform on the acquired instantaneous active power and instantaneous reactive power, and calculating the frequency focs and the amplitude AmSSO (amplitude modulation ) max (PAM, QAM) of an oscillation component;

wherein, PAM, QAM are the amplitude of active and reactive power respectively, and max (PAM, QAM) is the maximum value of the amplitude of active and reactive power.

(2) And calculating the calculated average apparent power Save sent by the new energy in 10 fundamental wave periods by adopting a sliding window average value method.

(3) Judging whether the frequency focs of the oscillation component is in the range of 5-15 Hz, judging whether the maximum value AmOCS of the oscillation component of the active power and the reactive power is max (PAM, QAM) and the ratio of the apparent power average value Save exceeds an upper limit threshold value THocs _ up is 1%, and judging whether the duration exceeds Delay _ up is 500 ms.

(4) And if the conditions are met, putting into a stable control strategy. Increasing DKp (0.46) from an initial value Kpoiit to 1.5 by a proportional parameter Kp of an outer ring proportional-integral controller of the converter station of the flexible-direct island converter station, and adjusting the value to Kpadjust1 (2.2);

if the condition is not satisfied, the stability control strategy is not engaged.

(5) And judging whether the ratio of the oscillation component maximum value AmOCS (maximum amplitude modulation) max (PAM, QAM) to the apparent power average value Save is less than the lower limit threshold value THocs _ down of 0.2% or not and the duration exceeds Delay _ down of 1s or not.

(6) If the conditions are met, maintaining the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station as an adjusted value;

and if the condition is not met, returning to the step (2), and continuing to adjust the proportional parameter of the outer loop proportional-integral controller of the flexible-direct island converter station until the value of the proportional parameter Kp is increased by the upper limit value Kpmax which is 2.38 Kpoiit.

The simulation analysis of the embodiment of the control strategy for stably conveying the clean energy by the flexible direct-current transmission system is as follows:

without the oscillation suppression method, Kp is 1.5, when the output of the new energy increases to 2380MW, the system oscillates at the frequency of 7.02Hz, the amplitude PAM of the active power of the new energy grid-connected point is about 250MW, the amplitude QAM of the reactive power is about 450MW, and the direct current voltage of the converter, the alternating current voltage of the grid-connected point, the output of the new energy field station and the SVG oscillate. The oscillation component amplitude AmSSO ═ max (PAM, QAM) ═ 450MW, the ratio to the average apparent power (Save ≈ 2400MW) is about 18.75%, the upper threshold value THocs _ up is exceeded 1%, and the duration exceeds Delay _ up 500 ms. And (4) meeting the conditions and inputting the proposed stability control strategy. As can be seen from fig. 2 to fig. 5, after the algorithm of the invention 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 2.2, the active power, the reactive power, the ac voltage, the output of the new energy station and the oscillation of the SVG of the new energy grid-connected point are rapidly attenuated, and the system is recovered to be stable, at this time, the amplitude AmSSO of the oscillation component is about max (PAM, QAM) 5MW, the ratio of the amplitude AmSSO to the average apparent power Save is 0.167%, the threshold value THocs _ down is smaller than the lower limit threshold value THocs _ down 0.2%, and the duration exceeds Delay _ down 1 s.

According to the method for stably controlling clean energy transmission of the flexible direct current transmission system based on parameter adjustment, power of large-scale new energy accessed to a grid-connected point through a flexible direct current island is used as a detection object, and the oscillation state of the system is judged by extracting oscillation characteristic components in the power. When the system oscillates, the oscillation can be effectively inhibited by adjusting the proportional parameter Kp of the outer ring proportional-integral controller of the flexible-straight island converter station, so that the system is recovered to be stable, the safe operation of the flexible-straight converter and the new energy unit is ensured, the secondary damage caused by the oscillation propagation of the system is avoided, and the safety and the reliability of the large-scale new energy through the flexible-straight grid system are improved.

The present invention further provides a system 200 for improving stability of clean energy delivered in a flexible and straight manner, as shown in fig. 9, comprising:

the power judgment unit 201 is used for acquiring active power and reactive power data of a large-scale new energy island access flexible direct-current grid-connected point, determining oscillation components of the active power and the reactive power, and judging whether the oscillation components of the active power and the reactive power meet a continuous high condition;

the strategy executing unit 202 is used for executing a clean energy stable transmission strategy of the flexible direct current transmission system if the oscillation components of the active power and the reactive power meet the continuous high condition;

a recovery stabilization judging unit 203, which judges whether the active power and the reactive power at the moment are recovered to be stable after executing a clean energy source transmission stabilization strategy of the flexible direct current transmission system;

and if the system stable operation unit 204 is stable, maintaining the proportional parameter of the outer ring proportional-integral controller of the flexible-direct island converter station, so that the flexible-direct transmission clean energy system can stably operate.

The condition for judging that the oscillation component is continuously higher is as follows: the ratio of the maximum value of the active power oscillation component and the maximum value of the reactive power oscillation component to the apparent power average value Save exceeds an upper limit threshold value, and the duration time exceeds 500 ms.

Wherein, the flexible direct current transmission system carries clean energy and stabilizes the strategy as: and adjusting the proportional parameter of an outer loop proportional-integral controller of the flexible-direct island converter station.

Wherein, the judgment condition for judging whether the active power and the reactive power are recovered stably is as follows:

the ratio of the oscillation component maximum value to the apparent power average value is less than the lower threshold value, and the duration exceeds 1 s.

After the parameters of the flexible direct current transmission control system are optimized, the network active power, the reactive power, the converter direct current voltage, the grid-connected point alternating current voltage, the alternating current, the new energy station output, the reactive power at the SVG grid-connected node and the oscillation of the direct current capacitor voltage of the flexible direct current isolated island converter station disappear rapidly, and the system recovers stable operation.

As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application 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 application can be implemented by adopting various computer languages, such as object-oriented programming language Java and transliterated scripting language JavaScript.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. 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 the preferred embodiments of the present application 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 alterations and modifications as fall within the scope of the application.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present application without departing from the spirit and scope of the application. Thus, if such modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include such modifications and variations as well.