CN115622110A - A flexible DC grid-connected system for offshore wind power and its control method - Google Patents

A flexible DC grid-connected system for offshore wind power and its control method Download PDF

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CN115622110A
CN115622110A CN202211242537.XA CN202211242537A CN115622110A CN 115622110 A CN115622110 A CN 115622110A CN 202211242537 A CN202211242537 A CN 202211242537A CN 115622110 A CN115622110 A CN 115622110A
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virtual
converter station
wind power
mmc converter
offshore
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范彩云
俎立峰
周晓风
韩坤
董朝阳
赵洋洋
刘路路
马俊杰
魏卓
樊宏伟
马太虎
慕小乐
周辉
柴卫强
冯敏
刘静一
李文雅
滕林阳
张壮
任如晨
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Xuji Group Co Ltd
XJ Electric Co Ltd
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XJ Electric Co Ltd
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    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00Circuit arrangements for AC mains or AC distribution networks
    • H02J3/36Arrangements for transfer of electric power between AC networks via a high-tension DC link
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381Dispersed generators
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20The dispersed energy generation being of renewable origin
    • H02J2300/28The renewable source being wind energy
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/70Wind energy
    • Y02E10/76Power conversion electric or electronic aspects

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  • Control Of Eletrric Generators (AREA)

Abstract

The invention belongs to the technical field of offshore wind power, and particularly relates to an offshore wind power flexible direct current grid-connected system and a control method thereof. In the operation process of the offshore wind power flexible direct current grid-connected system, firstly, a virtual rotor rotation angle is generated according to a virtual rotor dynamics link, and a virtual internal potential amplitude is generated according to a virtual excitation adjusting link; and then under the condition that the AC side of the marine MMC converter station is judged not to have AC system fault and the medium-high frequency harmonic content is larger than a set harmonic content threshold value, adopting an open-loop control mode for the marine MMC converter station, or else adopting a closed-loop control mode to directly obtain a modulation wave of the marine MMC converter station according to the generated virtual rotor rotation angle and the virtual inner potential amplitude. The invention inhibits the medium-high frequency harmonic oscillation which possibly occurs under the working condition of low-power operation, improves the wind power consumption capability of the offshore wind power plant, and further improves the safety and stability of the AC-DC hybrid large power grid system.

Description

一种海上风电柔性直流并网系统及其控制方法A flexible DC grid-connected system for offshore wind power and its control method

技术领域technical field

本发明属于海上风电技术领域,具体涉及一种海上风电柔性直流并网系统及其控制方法。The invention belongs to the technical field of offshore wind power, and in particular relates to an offshore wind power flexible DC grid-connected system and a control method thereof.

背景技术Background technique

随着世界各国对能源安全、生态环境、气候变化等问题日益重视,加快发展风电已成为国际社会推动能源转型发展、应对全球气候变化的普遍共识和一致行动。海上风电具有风能稳定、发电利用小时数高、基本不受地形地貌影响和适宜大规模开发等优点,且靠近电力负荷中心,便于电网就地消纳,避免了风电的长距离运输。因此,海上风电的开发与利用得到越来越多的关注与重视,已经成为全球可再生能源开发新的增长点与主要方向之一。根据全球风能协会GWEC最新数据,截至2021年底,全球海上风电累计装机容量达3310万千瓦,其中中国海上风电累计装机容量555.5万千瓦。与陆上风电场相比,海上风电场的优点主要是不占用土地资源,基本不受地形地貌影响,风速更高,风电机组单机容量更大,年利用小时数更高。As countries around the world pay more and more attention to issues such as energy security, ecological environment, and climate change, accelerating the development of wind power has become the general consensus and concerted action of the international community to promote energy transformation and development and respond to global climate change. Offshore wind power has the advantages of stable wind energy, high utilization hours of power generation, basically unaffected by terrain and landform, and suitable for large-scale development. It is also close to the power load center, which is convenient for local consumption by the grid and avoids long-distance transportation of wind power. Therefore, the development and utilization of offshore wind power has received more and more attention and attention, and has become one of the new growth points and main directions of global renewable energy development. According to the latest data from the Global Wind Energy Association GWEC, by the end of 2021, the cumulative installed capacity of offshore wind power in the world will reach 33.1 million kilowatts, of which the cumulative installed capacity of offshore wind power in China is 5.555 million kilowatts. Compared with onshore wind farms, the advantages of offshore wind farms are mainly that they do not occupy land resources, are basically not affected by topography, have higher wind speeds, larger single-machine capacity of wind turbines, and higher annual utilization hours.

MMC(Modular Multilevel Converter)换流器显著特点使MMC-HVDC输电技术成为国外大型远距离海上风电场并网的唯一选择。随着开发规模的扩大,输电容量和输电距离的增加,机组大型化、受端电网短路水平、电网安全稳定等因素,使得海上风电输电直流化方向的发展趋势愈加明显。The remarkable features of the MMC (Modular Multilevel Converter) converter make the MMC-HVDC power transmission technology the only choice for foreign large-scale long-distance offshore wind farms to be connected to the grid. With the expansion of development scale, the increase of transmission capacity and transmission distance, the large-scale unit, the short-circuit level of the receiving end power grid, the safety and stability of the power grid and other factors, the development trend of the direct current direction of offshore wind power transmission is becoming more and more obvious.

基于有功/无功控制的经典柔性直流输电系统在国内外已经得到了充分应用,国内外已经建立了多个柔性直流工程。传统柔性直流系统采用有功/无功控制模式,依赖所连接交流电网并通过锁相环技术得到交流电网同步相位,进而构建d/q空间的双闭环比例积分控制功能。但是,当柔性直流输电技术应用与海上风电送出场景时,所连接交流电网短路容量很小(短路比很小),该特点对传统柔性直流输电系统的安全稳定运行已经造成很大影响,甚至不能维持系统的正常运行。The classic flexible DC transmission system based on active/reactive power control has been fully applied at home and abroad, and many flexible DC projects have been established at home and abroad. The traditional flexible DC system adopts the active/reactive power control mode, relies on the connected AC grid and obtains the synchronous phase of the AC grid through the phase-locked loop technology, and then constructs the double closed-loop proportional-integral control function of d/q space. However, when the flexible DC transmission technology is applied to offshore wind power transmission scenarios, the short-circuit capacity of the connected AC grid is very small (the short-circuit ratio is very small), which has had a great impact on the safe and stable operation of the traditional flexible DC transmission system, and even cannot Maintain the normal operation of the system.

发明内容Contents of the invention

本发明的目的在于提供一种海上风电柔性直流并网系统及其控制方法,用以解决使用现有技术中的控制策略不能维持系统稳定正常运行的问题。The purpose of the present invention is to provide an offshore wind power flexible direct current grid-connected system and its control method to solve the problem that the control strategy in the prior art cannot maintain the stable and normal operation of the system.

为解决上述技术问题,本发明提供了一种海上风电柔性直流并网系统控制方法,包括如下步骤:In order to solve the above technical problems, the present invention provides a control method for an offshore wind power flexible DC grid-connected system, including the following steps:

1)在海上风电柔性直流并网系统运行过程中,根据虚拟转子动力学环节生成虚拟转子旋转角度θ,并根据虚拟励磁调节环节生成虚拟内电势幅值E;其中,所述虚拟转子动力学环节用于模拟同步发电机的转子运动方程,所述虚拟励磁调节环节用于模拟同步发电机的励磁控制;1) During the operation of the offshore wind power flexible DC grid-connected system, the virtual rotor rotation angle θ is generated according to the virtual rotor dynamics link, and the virtual internal potential amplitude E is generated according to the virtual excitation adjustment link; wherein, the virtual rotor dynamics link It is used to simulate the rotor motion equation of the synchronous generator, and the virtual excitation adjustment link is used to simulate the excitation control of the synchronous generator;

2)判断海上MMC换流站交流侧是否发生交流系统故障以及中高频谐波含量是否大于设定阈值:若未发生交流系统故障且中高频谐波含量大于设定谐波含量阈值,则对海上MMC换流站采用开环控制模式,以根据生成的虚拟转子旋转角度θ和虚拟内电势幅值E直接得到海上MMC换流站的调制波;并根据海上MMC换流站的调制波对海上MMC换流站进行控制。2) Judging whether there is an AC system failure on the AC side of the offshore MMC converter station and whether the medium and high frequency harmonic content is greater than the set threshold: if there is no AC system failure and the medium and high frequency harmonic content is greater than the set harmonic content threshold, then the offshore The MMC converter station adopts the open-loop control mode to directly obtain the modulation wave of the offshore MMC converter station according to the generated virtual rotor rotation angle θ and the virtual internal potential amplitude E; The converter station is controlled.

其有益效果为:本发明针对海上MMC换流站采用一种新的控制策略,首先通过模拟同步发电机的机电方程和励磁电压方程,不再依赖所连接交流电网获取锁相环相位,而是根据虚拟转子动力学环节得到虚拟转子旋转角度,并根据虚拟励磁调节环节生成虚拟内电势幅值,然后根据海上MMC换流站未发生交流系统故障以及中高频谐波含量较高的情况下,采用开关控制模式,禁止电流内环投入使用,以根据虚拟转子旋转角度和虚拟内电势幅值直接得到海上MMC换流站的调制波,抑制了小功率运行工况下可能发生的中高频谐波振荡,增加海上MMC换流站的固有惯量及阻尼特性,增强风电并网系统的频率及惯量支撑能力,提高了海上风电场风电消纳能力,并进一步提高了交直流混联大电网系统的安全稳定性,保证了以新能源发电为主体的交直流混联大电网的安全可靠稳定运行。Its beneficial effects are: the present invention adopts a new control strategy for the offshore MMC converter station, firstly by simulating the electromechanical equation and the excitation voltage equation of the synchronous generator, no longer relying on the connected AC grid to obtain the phase-locked loop phase, but The virtual rotor rotation angle is obtained according to the virtual rotor dynamics link, and the virtual internal potential amplitude is generated according to the virtual excitation adjustment link, and then according to the fact that there is no AC system failure in the offshore MMC converter station and the high-frequency harmonic content is high, adopt The switch control mode prohibits the current inner loop from being put into use, so as to directly obtain the modulation wave of the offshore MMC converter station according to the virtual rotor rotation angle and the virtual inner potential amplitude, which suppresses the mid-high frequency harmonic oscillation that may occur under low-power operating conditions , increase the inherent inertia and damping characteristics of the offshore MMC converter station, enhance the frequency and inertia support capacity of the wind power grid-connected system, improve the wind power consumption capacity of the offshore wind farm, and further improve the safety and stability of the AC-DC hybrid large power grid system It ensures the safe, reliable and stable operation of the AC-DC hybrid power grid with new energy power generation as the main body.

进一步地,若发生交流系统故障或者中高频谐波含量小于等于设定谐波含量阈值,则对海上MMC换流站采用闭环控制模式,以根据生成的虚拟转子旋转角度θ和虚拟内电势幅值E通过dq变换得到电流内环参考值,进而经过电流内环以及dq反变换,得到海上MMC换流站的调制波。Further, if an AC system fault occurs or the medium and high frequency harmonic content is less than or equal to the set harmonic content threshold, the closed-loop control mode is adopted for the offshore MMC converter station to generate virtual rotor rotation angle θ and virtual internal potential amplitude E obtains the reference value of the current inner loop through dq transformation, and then obtains the modulation wave of the offshore MMC converter station through the current inner loop and dq inverse transformation.

其有益效果为:在发生交流系统故障或者是中高频谐波含量较低的情况下,采用闭环控制模式,电流内环投入使用,以达到抑制故障电流的作用。The beneficial effect is: in the case of an AC system fault or a low-frequency harmonic content, the closed-loop control mode is adopted, and the current inner loop is put into use, so as to suppress the fault current.

进一步地,虚拟转子动力学环节的传递函数为:Furthermore, the transfer function of the virtual rotor dynamics link is:

Figure BDA0003885245000000021
Figure BDA0003885245000000021

Figure BDA0003885245000000022
Figure BDA0003885245000000022

式中,Tj为惯性时间常数;ω为虚拟角频率;Pe为虚拟电磁功率;D为阻尼因子;Pref为虚拟有功功率参考值,且Pref=Kf(FN-F),Kf为频差控制增益,FN为额定频率标幺值,F为电网频率实际值。In the formula, T j is the inertial time constant; ω is the virtual angular frequency; P e is the virtual electromagnetic power; D is the damping factor; P ref is the reference value of virtual active power, and P ref =K f (F N -F), K f is the frequency difference control gain, F N is the per unit value of the rated frequency, and F is the actual value of the grid frequency.

其有益效果为:采用虚拟转子环节生成虚拟转子旋转角度,不再依赖所连接交流电网获取锁相环相位,实现了海上MMC换流站具有传统同步发电机的惯量和阻尼特性。The beneficial effects are: the virtual rotor link is used to generate the virtual rotor rotation angle, the phase-locked loop phase is no longer dependent on the connected AC grid, and the offshore MMC converter station has the inertia and damping characteristics of the traditional synchronous generator.

进一步地,虚拟励磁调节环节的传递函数为:Furthermore, the transfer function of the virtual excitation regulation link is:

Figure BDA0003885245000000031
Figure BDA0003885245000000031

式中,Qref为无功功率参考值;Qe为无功功率实际值;Uac_ref为交流电压参考值;Uac为交流电压实际值;kq为无功功率偏差增益系数;kac为交流电压偏差增益系数;kp为虚拟励磁控制器比例增益;Ti为虚拟励磁控制器积分时间常数;E0为虚拟内电势参考值。In the formula, Q ref is the reference value of reactive power; Q e is the actual value of reactive power; U ac_ref is the reference value of AC voltage; U ac is the actual value of AC voltage; k q is the deviation gain coefficient of reactive power; k ac is AC voltage deviation gain coefficient; k p is the proportional gain of the virtual excitation controller; T i is the integral time constant of the virtual excitation controller; E 0 is the reference value of the virtual internal potential.

其有益效果为:采用虚拟励磁调节环节生成虚拟内电势幅值,实现了海上MMC换流站具有传统同步发电机的惯量和阻尼特性。The beneficial effect is: the virtual excitation adjustment link is used to generate the virtual internal potential amplitude, and the offshore MMC converter station has the inertia and damping characteristics of the traditional synchronous generator.

进一步地,未发生交流系统故障且中高频谐波含量大于设定谐波含量阈值时,海上MMC换流站的调制波为:Further, when there is no AC system failure and the medium and high frequency harmonic content is greater than the set harmonic content threshold, the modulation wave of the offshore MMC converter station is:

Figure BDA0003885245000000032
Figure BDA0003885245000000032

式中,ma、mb和mc分别为A、B、C三相调制波。In the formula, ma, m b and m c are A, B and C three-phase modulation waves respectively.

进一步地,发生交流系统故障或者中高频谐波含量小于等于设定谐波含量阈值时,电流内环参考值为:Further, when an AC system fault occurs or the medium and high frequency harmonic content is less than or equal to the set harmonic content threshold, the reference value of the current inner loop is:

Figure BDA0003885245000000033
Figure BDA0003885245000000033

Figure BDA0003885245000000034
Figure BDA0003885245000000034

式中,vd和vq分别为电流内环d轴、q轴电流内环参考值;va、vb和vc分别为由虚拟转子动力学环节与虚拟励磁调节环节生成的参考调制波;In the formula, v d and v q are the d-axis and q-axis reference values of the current inner loop respectively; v a , v b and v c are the reference modulation waves generated by the virtual rotor dynamics link and the virtual excitation adjustment link respectively ;

且海上MMC换流站的调制波为:And the modulation wave of the offshore MMC converter station is:

Figure BDA0003885245000000041
Figure BDA0003885245000000041

式中,vd_PI、vq_PI分别为d轴、q轴电流内环比例积分控制器输出,ma、mb和mc分别为A、B、C三相调制波。In the formula, v d_PI and v q_PI are the outputs of d-axis and q-axis current inner-loop proportional-integral controllers respectively, and ma, m b and m c are three-phase modulation waves of A, B and C , respectively.

进一步地,海上MMC换流站交流侧电压中高频谐波含量为:Uh=Uh1*(1-KLP50),海上MMC换流站交流侧电流中高频谐波含量为:Ih=Ih1*(1-KLP50),Uh为电压中高频谐波含量,Uh1为海上MMC换流站交流侧电压原始值,Ih为电流中高频谐波含量,Ih1为海上MMC换流站交流侧电流原始值,KLP50为低通滤波函数。Furthermore, the high-frequency harmonic content in the AC side voltage of the offshore MMC converter station is: U h =U h1 *(1-K LP50 ), and the high-frequency harmonic content in the AC side current of the offshore MMC converter station is: I h =I h1 *(1-K LP50 ), U h is the high-frequency harmonic content of the voltage, U h1 is the original voltage value of the AC side of the offshore MMC converter station, I h is the high-frequency harmonic content of the current, and I h1 is the offshore MMC converter The original value of the AC side current of the station, and K LP50 is a low-pass filter function.

其有益效果为:采用上述方式可快速得到海上MMC换流站交流侧电压/电流中高频谐波含量。The beneficial effect is that the high-frequency harmonic content in the AC side voltage/current of the offshore MMC converter station can be quickly obtained by adopting the above-mentioned method.

进一步地,采用双闭环控制策略生成陆上MMC换流站的调制波,并根据陆上MMC换流站的调制波对陆上MMC换流站进行控制;其中,双闭环控制策略中d轴外环选择定直流系统海上站端口电压控制,q轴外环选择定陆上站无功功率控制,d轴和q轴内环均选择定阀侧交流电流控制。Further, the modulation wave of the onshore MMC converter station is generated by using the double closed-loop control strategy, and the onshore MMC converter station is controlled according to the modulation wave of the onshore MMC converter station; wherein, in the double closed-loop control strategy, the d-axis The ring selects the port voltage control of the offshore station of the DC system, the outer ring of the q-axis selects the reactive power control of the land station, and the inner ring of the d-axis and the q-axis selects the AC current control of the fixed valve side.

其有益效果为:陆上MMC换流站采用经典的双闭环控制策略,可保证柔性直流输电工程的可靠、稳定运行。The beneficial effect is that the onshore MMC converter station adopts a classic double closed-loop control strategy, which can ensure the reliable and stable operation of the flexible direct current transmission project.

进一步地,采用零序判据和三相幅值判据来判断是否发生交流系统故障;其中,零序判据用于判断是否发生单相交流接地,三相幅值判据用于判断是否发生三相接地或两相接地故障。Further, the zero-sequence criterion and the three-phase amplitude criterion are used to judge whether an AC system fault occurs; among them, the zero-sequence criterion is used to judge whether a single-phase AC grounding occurs, and the three-phase amplitude criterion is used to judge whether a fault occurs Three-phase-to-ground or two-phase-to-ground fault.

其有益效果为:利用零序判据和三相幅值判据两个判据判断是否发生交流系统故障,可以准确且全面判断是否发生交流系统故障。The beneficial effect is that: using two criteria of the zero sequence criterion and the three-phase amplitude criterion to judge whether an AC system fault occurs, it is possible to accurately and comprehensively judge whether an AC system fault occurs.

为解决上述技术问题,本发明还提供了一种海上风电柔性直流并网系统,包括海上MMC换流站、直流海底电缆、陆上MMC换流站和控制装置;所述海上MMC换流站的交流侧用于连接海上风电场,直流侧连接直流海底电缆的一端;所述陆上MMC换流站的直流侧连接直流海底电缆的另一端,交流侧用于连接电网;所述控制装置包括处理器,所述处理器用于执行计算机程序指令以实现上述介绍的海上风电柔性直流并网系统控制方法,并能达到与该方法相同的有益效果。In order to solve the above technical problems, the present invention also provides an offshore wind power flexible DC grid-connected system, including an offshore MMC converter station, a DC submarine cable, an onshore MMC converter station and a control device; the offshore MMC converter station The AC side is used to connect to the offshore wind farm, and the DC side is connected to one end of the DC submarine cable; the DC side of the onshore MMC converter station is connected to the other end of the DC submarine cable, and the AC side is used to connect to the power grid; the control device includes processing The processor is used to execute computer program instructions to realize the control method of the offshore wind power flexible direct current grid-connected system described above, and can achieve the same beneficial effect as the method.

附图说明Description of drawings

图1是本发明的海上风电柔性直流并网系统示意图;Fig. 1 is a schematic diagram of the offshore wind power flexible DC grid-connected system of the present invention;

图2是本发明所使用的MMC换流阀拓扑结构及测点示意图;Fig. 2 is a schematic diagram of the topological structure and measuring points of the MMC converter valve used in the present invention;

图3是本发明的陆上MMC换流站控制功能框图;Fig. 3 is a control functional block diagram of the land MMC converter station of the present invention;

图4是本发明的电流内环控制及环流抑制控制框图;Fig. 4 is a block diagram of current inner loop control and circulation suppression control of the present invention;

图5是本发明的虚拟转子动力学与虚拟励磁环节控制框图;Fig. 5 is a control block diagram of virtual rotor dynamics and virtual excitation links of the present invention;

图6是本发明的海上MMC换流站控制流程示意图。Fig. 6 is a schematic diagram of the control flow of the offshore MMC converter station of the present invention.

具体实施方式detailed description

本发明基本思路在于,对海上MMC换流站和陆上MMC换流站采用不同的控制策略,特别是对于海上MMC换流站,其处于无源孤岛控制模式,所采用的控制策略包括多个环节,分别为用于生成虚拟转子旋转角度θ的虚拟转子动力学环节、用于生成虚拟内电势幅值E的虚拟励磁调节环节、电流内环控制环节、开环与闭环控制切换环节。在海上MMC换流站交流侧没有发生交流系统故障但中高频谐波含量较高的情况下,采用开环控制模式,禁止电流内环功能,根据拟转子旋转角度θ和虚拟内电势幅值E直接得到海上MMC换流站的调制波;在海上MMC换流站交流侧发生交流系统故障或者中高频谐波含量较低的情况下,采用闭环控制模式,电流内环需投入使用,根据拟转子旋转角度θ和虚拟内电势幅值E得到电流内环给定值,进而经过电流内环得到海上MMC换流站的调制波。The basic idea of the present invention is to adopt different control strategies for the offshore MMC converter station and the land MMC converter station, especially for the offshore MMC converter station, which is in the passive island control mode, and the adopted control strategy includes multiple The links are the virtual rotor dynamics link for generating the virtual rotor rotation angle θ, the virtual excitation adjustment link for generating the virtual internal potential amplitude E, the current inner loop control link, and the open-loop and closed-loop control switching links. In the case that there is no AC system fault on the AC side of the offshore MMC converter station but the high-frequency harmonic content is high, the open-loop control mode is adopted, and the current inner-loop function is prohibited. According to the pseudo-rotor rotation angle θ and the virtual internal potential amplitude E Directly obtain the modulated wave of the offshore MMC converter station; when the AC system failure occurs on the AC side of the offshore MMC converter station or the content of medium and high frequency harmonics is low, the closed-loop control mode is adopted, and the current inner loop needs to be put into use. The given value of the current inner loop is obtained by the rotation angle θ and the virtual inner potential amplitude E, and then the modulated wave of the offshore MMC converter station is obtained through the current inner loop.

为了使本发明的目的、技术方案及优点更加清楚明了,以下结合附图及实施例,对本发明进行进一步详细说明。应当理解,此处所描述的具体实施例仅用以解释本发明,并不用于限定本发明,即所描述的实施例仅仅是本发明一部分实施例,而不是全部的实施例。因此,以下对在附图中提供的本发明的实施例的详细描述并非旨在限制要求保护的本发明的范围,而是仅仅表示本发明的选定实施例。基于本发明的实施例,本领域技术人员在没有做出创造性劳动的前提下所获得的所有其他实施例,都属于本发明保护的范围。In order to make the object, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, and are not intended to limit the present invention, that is, the described embodiments are only some of the embodiments of the present invention, but not all of the embodiments. Accordingly, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts belong to the protection scope of the present invention.

海上风电柔性直流并网系统实施例:Embodiment of offshore wind power flexible DC grid-connected system:

本发明的一种海上风电柔性直流并网系统实施例,应用于(深)远海上风电柔性直流输电系统,如图1所示,该海上风电柔性直流并网系统包括海上交流升压站、海上MMC换流站、直流海底电缆、陆上MMC换流站和控制装置。海上交流升压站的低压侧用于连接海上风电场,高压侧连接海上MMC换流站的交流侧,海上MMC的直流侧连接直流海底电缆的一端,直流海底电缆的另一端连接陆上MMC换流站的直流侧,陆上MMC换流站的交流侧用于连接陆上交流电网。海上MMC换流站和陆上MMC换流站的MMC换流阀拓扑结构及电压、电流测点如图2所示,换流阀子模块可采用典型的半桥子模块或全桥子模块结构,也可以采用一定比例半桥与一定比例全桥混合模块结构。控制装置包括海上控制装置和陆上控制装置,海上控制装置和陆上控制装置之间站间通信,这两个控制装置均为嵌入式工业控制平台或PC装置,海上控制装置用于对海上MMC换流站输出调制波,陆上控制装置用于对陆上MMC换流站输出调制波。这两个控制装置均包括处理器和存储器,处理器执行存储在存储器中的计算机指令可以实现相应的换流站控制策略。An embodiment of an offshore wind power flexible DC grid-connected system of the present invention is applied to a (deep) offshore wind power flexible DC transmission system. As shown in Figure 1, the offshore wind power flexible DC grid-connected system includes an offshore AC booster station, an offshore MMC converter stations, DC submarine cables, onshore MMC converter stations and control devices. The low-voltage side of the offshore AC booster station is used to connect to the offshore wind farm, the high-voltage side is connected to the AC side of the offshore MMC converter station, the DC side of the offshore MMC is connected to one end of the DC submarine cable, and the other end of the DC submarine cable is connected to the onshore MMC converter. The DC side of the converter station and the AC side of the onshore MMC converter station are used to connect to the onshore AC grid. The MMC converter valve topology and voltage and current measurement points of the offshore MMC converter station and onshore MMC converter station are shown in Figure 2. The converter valve sub-module can adopt a typical half-bridge sub-module or full-bridge sub-module structure , can also adopt a certain proportion of half bridge and certain proportion of full bridge hybrid module structure. The control device includes an offshore control device and an onshore control device, and the inter-station communication between the offshore control device and the onshore control device, both of which are embedded industrial control platforms or PC devices, and the offshore control device is used to control the offshore MMC The converter station outputs modulated waves, and the onshore control device is used to output modulated waves to the onshore MMC converter station. These two control devices both include a processor and a memory, and the processor executes computer instructions stored in the memory to implement a corresponding converter station control strategy.

对于陆上MMC换流站,采用经典的柔性直流输电系统双闭环控制策略,如图3所示,d轴外环选择定直流系统海上站端口电压控制,q轴外环选择定陆上站无功功率控制,d轴和q轴内环选均择定电流控制,为基于MMC环流阀侧交流电流的直接电流控制,如图4所示。For the onshore MMC converter station, the classic double closed-loop control strategy of the flexible HVDC transmission system is adopted, as shown in Figure 3, the d-axis outer loop is selected to control the port voltage of the DC system offshore station, and the q-axis outer loop is selected to set the onshore station without For power control, the d-axis and q-axis inner rings both select constant current control, which is a direct current control based on the alternating current at the side of the MMC circulation valve, as shown in Figure 4.

对于海上MMC换流站,所采用的控制策略包括虚拟转子动力学环节、虚拟励磁调节环节、电流内环控制环节、开环与闭环控制切换环节。如图5所示,虚拟转子动力学环节用于生成虚拟转子旋转角度θ,虚拟励磁调节环节用于生成虚拟内电势幅值E,开环与闭环控制切换环节用于实现开环控制模式和闭环控制模式的切换。控制策略具体如下:在海上MMC换流站的交流侧未发生交流系统故障且发生中/高频谐波振荡时,采用开环控制模式,即,禁止电流内环控制功能,根据虚拟内电势幅值E和虚拟转子旋转角度θ直接生成海上MMC换流站调制波;在海上MMC换流站的交流侧发生交流系统故障或者未发生中/高频谐波振荡时,采用闭环控制模式,即,由虚拟内电势幅值E和虚拟转子旋转角度θ经过dq变换后生成电流内环参考值,电流内环的输出经dq反变换后生成MMC换流站调制波。这么处理是因为,电流内环控制环节对抑制故障电流有重要作用,但是电流内环控制环节的投入会引入潜在的中高频谐波谐振风险。For offshore MMC converter stations, the control strategies adopted include virtual rotor dynamics link, virtual excitation regulation link, current inner loop control link, open-loop and closed-loop control switching link. As shown in Figure 5, the virtual rotor dynamics link is used to generate the virtual rotor rotation angle θ, the virtual excitation adjustment link is used to generate the virtual internal potential amplitude E, and the open-loop and closed-loop control switching link is used to realize the open-loop control mode and closed-loop control mode. Control mode switching. The specific control strategy is as follows: when there is no AC system failure and medium/high frequency harmonic oscillation occurs on the AC side of the offshore MMC converter station, the open-loop control mode is adopted, that is, the current inner-loop control function is prohibited, and according to the virtual internal potential amplitude The value E and the virtual rotor rotation angle θ directly generate the modulation wave of the offshore MMC converter station; when the AC system fault occurs on the AC side of the offshore MMC converter station or no medium/high frequency harmonic oscillation occurs, the closed-loop control mode is adopted, that is, The reference value of the current inner loop is generated by the dq transformation of the virtual inner potential amplitude E and the virtual rotor rotation angle θ, and the output of the current inner loop is generated by the dq inverse transformation to generate the modulation wave of the MMC converter station. The reason for this is that the current inner loop control link plays an important role in suppressing the fault current, but the input of the current inner loop control link will introduce potential medium and high frequency harmonic resonance risks.

虚拟转子动力学环节模拟同步发电机的转子运动方程(机电方程),从而生成虚拟转子旋转角度θ,其传递函数为:The virtual rotor dynamics link simulates the rotor motion equation (electromechanical equation) of the synchronous generator, thereby generating a virtual rotor rotation angle θ, and its transfer function is:

Figure BDA0003885245000000061
Figure BDA0003885245000000061

式中,Tj为惯性时间常数,常取5-10秒;ω为虚拟角频率(1标幺额定值为100π);Pref为虚拟有功功率参考值(标幺值);Pe为虚拟电磁功率(取MMC换流阀有功率实际值,标幺值),取MMC换流器阀侧有功功率实际值,可由瞬时功率理论计算得到;D为阻尼因子;θ为虚拟转子旋转角度。特别地,虚拟有功功率参考值由有功-频率下垂特性得到,即虚拟有功功率参考值模拟同步发电机的一次调频功能,其关系为:Pref=Kf(FN-F),Kf为频差控制增益,FN为额定频率标幺值(缺省值为1),F为电网频率实际值。In the formula, T j is the inertial time constant, which usually takes 5-10 seconds; ω is the virtual angular frequency (the rated value of 1 per unit is 100π); P ref is the virtual active power reference value (per unit value); P e is the virtual Electromagnetic power (take the actual value of the active power of the MMC converter valve, per unit value), take the actual value of the active power at the valve side of the MMC converter, which can be calculated from the instantaneous power theory; D is the damping factor; θ is the virtual rotor rotation angle. In particular, the virtual active power reference value is obtained from the active power-frequency droop characteristic, that is, the virtual active power reference value simulates the primary frequency modulation function of the synchronous generator, and its relationship is: P ref =K f (F N -F), K f is Frequency difference control gain, F N is the per-unit value of the rated frequency (the default value is 1), and F is the actual value of the grid frequency.

虚拟励磁调节环节模拟同步发电机的励磁控制,在系统电压波动时,通过偏差比例改变励磁电压,最终影响机组与系统的交换无功,从而生成虚拟内电势幅值E,其传递函数为:The virtual excitation adjustment link simulates the excitation control of the synchronous generator. When the system voltage fluctuates, the excitation voltage is changed through the deviation ratio, which finally affects the reactive power exchange between the unit and the system, thereby generating the virtual internal potential amplitude E. The transfer function is:

Figure BDA0003885245000000071
Figure BDA0003885245000000071

其中,Qref为无功功率参考值,以MMC注入系统感性无功为正;Qe为无功功率实际值;Uac_ref为交流电压参考值,缺省值为1;Uac为交流电压实际值;kq为无功功率偏差增益系数;kac为交流电压偏差增益系数;kp为虚拟励磁控制器比例增益;Ti为虚拟励磁控制器积分时间常数;E0为虚拟内电势参考值,缺省值为1。Among them, Q ref is the reference value of reactive power, and the inductive reactive power injected into the system by MMC is positive; Q e is the actual value of reactive power; U ac_ref is the reference value of AC voltage, the default value is 1; U ac is the actual value of AC voltage value; k q is the reactive power deviation gain coefficient; k ac is the AC voltage deviation gain coefficient; k p is the proportional gain of the virtual excitation controller; T i is the integral time constant of the virtual excitation controller; E 0 is the reference value of the virtual internal potential , the default value is 1.

在闭环控制模式下,电流内环控制环节由d轴和q轴比例积分控制环节组成,d轴和q轴电流参考值由式(3)、(4)得到,然后通过式(5)得到海上MMC换流站的调制波。In the closed-loop control mode, the current inner loop control link is composed of the d-axis and q-axis proportional-integral control links. The d-axis and q-axis current reference values are obtained by formulas (3) and (4), and then obtained by formula (5). Modulated wave of MMC converter station.

Figure BDA0003885245000000072
Figure BDA0003885245000000072

Figure BDA0003885245000000073
Figure BDA0003885245000000073

Figure BDA0003885245000000074
Figure BDA0003885245000000074

在开环控制模式下,由式(5)直接得到海上MMC换流站的调制波。In the open-loop control mode, the modulated wave of the offshore MMC converter station can be obtained directly from formula (5).

Figure BDA0003885245000000075
Figure BDA0003885245000000075

下面结合图6的海上MMC换流站的控制流程图,对整个海上风电柔性直流并网系统所采用的控制方法的整个流程进行介绍:The following is an introduction to the entire process of the control method adopted by the entire offshore wind power flexible DC grid-connected system in combination with the control flow chart of the offshore MMC converter station in Figure 6:

1)两个MMC换流站完成初始化运行条件设置,初始化成功则进入正常运行工况。陆上MMC换流站选择双闭环控制策略,双闭环控制策略中d轴外环选择定直流系统海上站端口电压控制,q轴外环选择定陆上站无功功率控制,d轴和q轴内环选均择电流环。由陆上MMC换流站完成对海上MMC换流站中MMC子模块直流侧的充电。1) The two MMC converter stations have completed the initialization operation condition setting, and if the initialization is successful, they will enter the normal operation condition. The onshore MMC converter station chooses a double closed-loop control strategy. In the double closed-loop control strategy, the outer ring of the d-axis chooses to control the port voltage of the offshore station of the DC system, and the outer ring of the q-axis chooses the reactive power control of the land station. The d-axis and q-axis The inner loop selects the current loop. The charging of the DC side of the MMC sub-module in the offshore MMC converter station is completed by the onshore MMC converter station.

2)海上MMC环路站通过直流侧充电完成后,根据虚拟转子动力学环节,利用公式(1)生成dq正反变换所需的虚拟转子旋转角度θ,根据虚拟励磁环节,利用公式(2)生成虚拟内电势幅值E。2) After the charging of the offshore MMC loop station is completed through the DC side, according to the virtual rotor dynamics link, use the formula (1) to generate the virtual rotor rotation angle θ required for dq positive and negative transformation, and according to the virtual excitation link, use the formula (2) A virtual internal potential magnitude E is generated.

3)海上MMC换流站实时采集交流电压和电流信号,通过快速傅里叶变换或低通滤波等通用方法获取中高频谐波幅值,Uh=Uh1*(1-KLP50),Ih=Ih1*(1-KLP50),Uh为电压中高频谐波含量,Uh1为海上MMC换流站交流侧电压原始值,Ih为电流中高频谐波含量,Ih1为海上MMC换流站交流侧电流原始值,KLP50为低通滤波函数;并采用零序判据和三相幅值判据判断是否发生交流侧故障,零序判据主要用于判断是否发生单相交流接地,三相幅值判据用于判断是否发生三相接地或两相接地故障:3) The offshore MMC converter station collects AC voltage and current signals in real time, and obtains the amplitude of medium and high frequency harmonics through general methods such as fast Fourier transform or low-pass filtering, U h = U h1 *(1-K LP50 ), I h =I h1 *(1-K LP50 ), U h is the high-frequency harmonic content of the voltage, U h1 is the original voltage value of the AC side of the offshore MMC converter station, I h is the high-frequency harmonic content of the current, and I h1 is the offshore The original value of the AC side current of the MMC converter station, K LP50 is a low-pass filter function; and the zero-sequence criterion and the three-phase amplitude criterion are used to judge whether the AC side fault occurs, and the zero-sequence criterion is mainly used to judge whether a single-phase AC grounding, the three-phase amplitude criterion is used to judge whether a three-phase grounding or two-phase grounding fault occurs:

如果此时无交流系统故障产生且中高频谐波含量大于设定谐波含量阈值Δsetting1(5%),则海上MMC换流站采用开环控制模式。MMC开环控制的原理是禁止闭环模式下的电流内环控制功能,直接根据公式(6),由虚拟转子相位角度和内电势幅值生成三相正序调制波;If no AC system fault occurs at this time and the medium and high frequency harmonic content is greater than the set harmonic content threshold Δsetting1 (5%), the offshore MMC converter station adopts the open-loop control mode. The principle of the MMC open-loop control is to prohibit the current inner-loop control function in the closed-loop mode, and directly according to the formula (6), the three-phase positive sequence modulation wave is generated by the virtual rotor phase angle and the internal potential amplitude;

如果此时交流系统发生故障或者中高频谐波含量小于等于设定谐波含量阈值Δsetting1,则海上MMC换流站采用闭环控制模式,此时需要投入电流内环控制功能。根据上述产生的虚拟转子旋转角度和虚拟内电势幅值,生成三相参考电压矢量,经dq正变换后生成内环电流d/q轴参考值,即公式(3)~(4),经内环电流的比例积分控制后输出d/q轴电压,再经dq反变换最终产生海上MMC换流站的触发调制波,即公式(5)。If the AC system fails at this time or the medium and high frequency harmonic content is less than or equal to the set harmonic content threshold Δsetting1, the offshore MMC converter station adopts the closed-loop control mode, and the current inner-loop control function needs to be put into use at this time. According to the above-mentioned generated virtual rotor rotation angle and virtual internal potential amplitude, a three-phase reference voltage vector is generated, and the d/q axis reference value of the inner ring current is generated after dq forward transformation, that is, formulas (3) to (4). After the proportional integral control of the ring current, the d/q axis voltage is output, and then the dq inverse transformation is performed to finally generate the trigger modulation wave of the offshore MMC converter station, that is, the formula (5).

综上,本发明的海上风电柔性直流并网系统控制方法,通过模拟传统同步发电机的机电方程和励磁回路方程,不再依赖所连接交流电网获取锁相环相位,而是根据虚拟转子动力学环节得到虚拟转子旋转角度,同时利用虚拟励磁调节环节生成虚拟内电势幅值,实现了海上MMC换流站具有传统同步发电机的惯量和阻尼特性,并通过判断谐波幅值切换开闭环控制避免中高频谐波振荡,增强了海上风电柔性直流并网系统的新能源消纳能力,保证了以新能源发电为主体的交直流混联大电网的安全可靠稳定运行。To sum up, the control method of the offshore wind power flexible DC grid-connected system of the present invention, by simulating the electromechanical equation and the excitation circuit equation of the traditional synchronous generator, no longer depends on the connected AC grid to obtain the phase-locked loop phase, but according to the virtual rotor dynamics link to obtain the virtual rotor rotation angle, and use the virtual excitation adjustment link to generate the virtual internal potential amplitude, which realizes the inertia and damping characteristics of the traditional synchronous generator in the offshore MMC converter station, and switches the open-closed loop control by judging the harmonic amplitude to avoid The medium and high frequency harmonic oscillation enhances the new energy absorption capacity of the offshore wind power flexible DC grid-connected system, and ensures the safe, reliable and stable operation of the AC-DC hybrid power grid with new energy power generation as the main body.

海上风电柔性直流并网系统控制方法实施例:Embodiment of control method for offshore wind power flexible DC grid-connected system:

本发明的一种海上风电柔性直流并网系统控制方法实施例,针对是如图1所示的海上风电柔性直流并网系统,该方法的整体思路在于,根据虚拟转子动力学环节得到虚拟转子旋转角度,并利用虚拟励磁调节环节生成虚拟内电势幅值,根据得到的虚拟转子旋转角度和虚拟内电势幅值,进而根据海上MMC换流站是否发生交流系统故障以及中高频谐波含量,采用不同的方式得到海上MMC换流站的调制波。该方法增强了MMC换流站惯量支撑和阻尼能力,实现了(深)远海上风电柔性直流输电系统对新能源的可靠友好接入,并最终保证了以新能源为主体的交直流混联大电网的灵活性及安全稳定性。关于该方法的具体实施过程同海上风电柔性直流并网系统实施例中介绍的海上风电柔性直流并网系统控制方法一致,流程如图6所示,本实施例不再赘述整个详细过程。An embodiment of a control method for an offshore wind power flexible DC grid-connected system of the present invention is aimed at the offshore wind power flexible DC grid-connected system shown in Figure 1. The overall idea of the method is to obtain the virtual rotor rotation according to the virtual rotor dynamics link angle, and use the virtual excitation adjustment link to generate the virtual internal potential amplitude, according to the obtained virtual rotor rotation angle and virtual internal potential amplitude, and then according to whether the offshore MMC converter station has an AC system fault and the content of medium and high frequency harmonics, different The modulation wave of the offshore MMC converter station is obtained by the method. This method enhances the inertial support and damping capacity of the MMC converter station, realizes the reliable and friendly access of new energy to the (deep) offshore wind power flexible direct current transmission system, and finally guarantees the new energy-based AC-DC hybrid large-scale The flexibility and safety and stability of the power grid. The specific implementation process of this method is consistent with the control method of the offshore wind power flexible DC grid-connected system introduced in the embodiment of the offshore wind power flexible DC grid-connected system.

以上给出了具体的实施方式,但本发明不局限于所描述的实施方式。本发明的基本思路在于上述基本方案,对本领域普通技术人员而言,根据本发明的教导,设计出各种变形的模型、公式、参数并不需要花费创造性劳动。在不脱离本发明的原理和精神的情况下对实施方式进行的变化、修改、替换和变型仍落入本发明的保护范围。Specific embodiments have been given above, but the present invention is not limited to the described embodiments. The basic idea of the present invention lies in the above-mentioned basic scheme. For those of ordinary skill in the art, according to the teaching of the present invention, it does not need to spend creative labor to design various deformation models, formulas, and parameters. Changes, modifications, substitutions and variations to the implementations without departing from the principle and spirit of the present invention still fall within the protection scope of the present invention.

Claims (10)

1. A control method for an offshore wind power flexible direct current grid-connected system is characterized by comprising the following steps:
1) In the operation process of the offshore wind power flexible direct current grid-connected system, generating a virtual rotor rotation angle theta according to a virtual rotor dynamics link, and generating a virtual internal potential amplitude E according to a virtual excitation regulation link; the virtual rotor dynamics link is used for simulating a rotor motion equation of the synchronous generator, and the virtual excitation adjusting link is used for simulating excitation control of the synchronous generator;
2) Whether alternating current system faults occur on the alternating current side of the marine MMC convertor station or not and whether medium-high frequency harmonic content is larger than a set threshold value or not are judged: if the alternating current system fault does not occur and the medium-high frequency harmonic content is larger than the set harmonic content threshold value, adopting an open-loop control mode for the marine MMC convertor station to directly obtain a modulation wave of the marine MMC convertor station according to the generated virtual rotor rotation angle theta and the virtual internal potential amplitude E; and controlling the marine MMC converter station according to the modulation wave of the marine MMC converter station.
2. The offshore wind power flexible direct current grid-connected system control method according to claim 1, characterized in that if an alternating current system fault occurs or the medium-high frequency harmonic content is less than or equal to a set harmonic content threshold value, a closed-loop control mode is adopted for the offshore MMC converter station, a current inner-loop reference value is obtained through dq transformation according to the generated virtual rotor rotation angle theta and the virtual inner potential amplitude E, and then a modulation wave of the offshore MMC converter station is obtained through current inner-loop and dq inverse transformation.
3. The offshore wind power flexible direct current grid-connected system control method according to claim 1, characterized in that the transfer function of the virtual rotor dynamics link is:
Figure FDA0003885244990000011
Figure FDA0003885244990000012
in the formula, T j Is the inertia time constant; omega is a virtual angular frequency; p e Is a virtual electromagnetic power; d is a damping factor; p ref Is a virtual active power reference value, and P ref =K f (F N -F),K f Controlling gain for frequency difference, F N And F is the per unit value of the rated frequency and the actual value of the grid frequency.
4. The offshore wind power flexible direct current grid-connected system control method according to claim 1, characterized in that the transfer function of the virtual excitation adjusting link is:
Figure FDA0003885244990000013
in the formula, Q ref Is a reactive power reference value; q e The actual value of the reactive power is obtained; u shape ac_ref Is an AC voltage reference value; u shape ac Is the actual value of the alternating voltage; k is a radical of q Is a reactive power deviation gain coefficient; k is a radical of ac Is an AC voltage deviation gain coefficient; k is a radical of formula p Proportional gain of the virtual excitation controller; t is i Integrating a time constant for the virtual excitation controller; e 0 Is a virtual internal potential reference value.
5. The offshore wind power flexible direct current grid-connected system control method according to claim 1, characterized in that when an alternating current system fault does not occur and the medium-high frequency harmonic content is greater than a set harmonic content threshold value, the modulation wave of the offshore MMC converter station is:
Figure FDA0003885244990000021
in the formula, m a 、m b And m c Three-phase modulation waves A, B and C are respectively.
6. The offshore wind power flexible direct current grid-connected system control method according to claim 2, wherein when an alternating current system fault occurs or the medium-high frequency harmonic content is less than or equal to a set harmonic content threshold value, the current inner loop reference value is as follows:
Figure FDA0003885244990000022
Figure FDA0003885244990000023
in the formula, v d And v q Current inner ring reference values of a d axis and a q axis of the current inner ring are respectively; v. of a 、v b And v c Respectively generating reference modulation waves by a virtual rotor dynamics link and a virtual excitation regulation link;
and the modulation wave of the marine MMC convertor station is as follows:
Figure FDA0003885244990000024
in the formula, v d_PI 、v q_PI D-axis and q-axis currents respectivelyInner loop proportional integral controller output, m a 、m b And m c Three-phase modulation waves A, B and C are respectively.
7. The offshore wind power flexible direct current grid-connected system control method according to any one of claims 1 to 6, characterized in that the high frequency harmonic content in the alternating current side voltage of the offshore MMC converter station is: u shape h =U h1 *(1-K LP50 ) And the medium-high frequency harmonic content of the alternating current side current of the marine MMC converter station is as follows: I.C. A h =I h1 *(1-K LP50 ),U h Is the harmonic content of high and medium frequency in voltage, U h1 For original value, I, of alternating-current side voltage of marine MMC convertor station h Is the content of high-frequency harmonic in current, I h1 For original value, K, of alternating current side current of marine MMC converter station LP50 Is a low pass filter function.
8. The offshore wind power flexible direct current grid-connected system control method according to any one of claims 1 to 6, characterized in that a double closed-loop control strategy is adopted to generate a modulation wave of a onshore MMC converter station, and the onshore MMC converter station is controlled according to the modulation wave of the onshore MMC converter station; in the double closed-loop control strategy, the d-axis outer ring selects fixed direct-current system offshore station port voltage control, the q-axis outer ring selects fixed onshore station reactive power control, and the d-axis inner ring and the q-axis inner ring both select fixed valve side alternating current control.
9. The offshore wind power flexible direct current grid-connected system control method according to any one of claims 1 to 6, characterized by adopting a zero sequence criterion and a three-phase amplitude criterion to judge whether an alternating current system fault occurs; the zero-sequence criterion is used for judging whether single-phase alternating current grounding occurs, and the three-phase amplitude criterion is used for judging whether three-phase grounding or two-phase grounding faults occur.
10. A flexible direct current grid-connected system for offshore wind power comprises an offshore MMC converter station, a direct current submarine cable, a land MMC converter station and a control device; the alternating current side of the marine MMC converter station is used for being connected with an offshore wind power plant, and the direct current side of the marine MMC converter station is connected with one end of a direct current submarine cable; the direct current side of the onshore MMC converter station is connected with the other end of the direct current submarine cable, and the alternating current side of the onshore MMC converter station is used for connecting a power grid; the control device is characterized by comprising a processor, wherein the processor is used for executing computer program instructions to realize the control method of the offshore wind power flexible direct current grid-connected system according to any one of claims 1 to 9.
CN202211242537.XA 2022-10-11 2022-10-11 A flexible DC grid-connected system for offshore wind power and its control method Pending CN115622110A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117526397A (en) * 2024-01-04 2024-02-06 国网经济技术研究院有限公司 Flexible direct-current inner-loop-free network construction control method and system with current limiting function

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117526397A (en) * 2024-01-04 2024-02-06 国网经济技术研究院有限公司 Flexible direct-current inner-loop-free network construction control method and system with current limiting function
CN117526397B (en) * 2024-01-04 2024-04-26 国网经济技术研究院有限公司 Flexible DC non-inner-loop grid-type control method and system with current limiting function

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