WO2024113639A1 - 一种100％新能源送端电网的后备电压频率支撑方法 - Google Patents
一种100％新能源送端电网的后备电压频率支撑方法 Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 26
- 238000011217 control strategy Methods 0.000 claims abstract description 6
- 238000004146 energy storage Methods 0.000 claims description 32
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- 238000010248 power generation Methods 0.000 abstract description 4
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- 230000005540 biological transmission Effects 0.000 description 8
- 238000004088 simulation Methods 0.000 description 8
- 230000001052 transient effect Effects 0.000 description 8
- 238000010276 construction Methods 0.000 description 3
- 101100012902 Saccharomyces cerevisiae (strain ATCC 204508 / S288c) FIG2 gene Proteins 0.000 description 2
- 101100233916 Saccharomyces cerevisiae (strain ATCC 204508 / S288c) KAR5 gene Proteins 0.000 description 2
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Classifications
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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
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
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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
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
-
- 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
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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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
-
- 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
Definitions
- the present invention belongs to the technical field of power transmission and distribution of electric power systems, and in particular relates to a backup voltage and frequency support method for a 100% new energy sending-end power grid.
- the sending-end grid will present a form of 100% renewable energy base + UHV flexible DC system transmission.
- renewable energy power sources can operate in a conventional grid-following control mode; and the sending-end flexible DC converter station will adopt V/f control to provide a stable voltage and frequency reference for the 100% renewable energy sending-end grid.
- the 100% renewable energy sending-end power grid is fundamentally different from the conventional AC power grid.
- the voltage and frequency of the entire power grid are jointly supported by the synchronous power supplies distributed in the power grid, and the voltage and frequency support of conventional AC power grids is constructed from the bottom up by the synchronous machine; after a single synchronous machine is out of operation, the system still has the ability to operate stably.
- the 100% renewable energy sending-end power grid if only the sending-end flexible DC converter station adopts grid-type control, the voltage and frequency support of the entire power grid is only provided centrally by the sending-end converter station.
- the voltage and frequency support of the power grid is constructed from top to bottom by the sending-end flexible DC converter station; when a DC system failure causes the bipolar locking of the sending-end flexible DC converter station, the 100% new energy sending-end power grid will lose the voltage and frequency support power supply, and the sending-end power grid will not have the conditions for stable operation.
- transient energy can be balanced through various rotating devices.
- the 100% new energy sending-end power grid does not contain synchronous machine power supply.
- transient energy can only be balanced through the sending-end flexible DC converter station; when the sending-end flexible DC converter station has a bipolar lock, the transient energy will cause a sharp increase in the power of the sending-end power grid, seriously affecting the safety of electrical equipment in the sending-end power grid.
- the probability of bipolar blocking in UHV DC system is about once a year, among which the probability of temporary fault is the highest.
- the 100% renewable energy transmission end power grid needs to have a backup voltage and frequency support function; when bipolar blocking occurs in the DC transmission system due to a temporary fault, the backup voltage and frequency support function can be used to avoid the complete shutdown of the 100% renewable energy transmission end power grid.
- the present invention provides a backup voltage and frequency support method for a 100% renewable energy sending-end power grid.
- the method is simple to implement and has strong versatility. It can improve the operational reliability of the 100% renewable energy sending-end power grid and has great use value in actual projects.
- a backup voltage and frequency support method for a 100% new energy sending-end power grid comprises the following steps:
- the 100% new energy sending-end power grid includes multiple new energy stations, which may be photovoltaic power stations, onshore wind farms or offshore wind farms. After the new energy stations are connected to the AC system, they are boosted multiple times and then collected at the sending-end rectifier station.
- step (1) for all nodes in the power grid (i.e., AC busbars), there are multiple groups of voltage levels of these nodes (such as 35kV, 110kV, 220kV or 500kV, etc.), and all nodes except node O are selected from the nodes with the highest voltage level as supporting nodes, and node O is a node directly connected to the sending-end rectifier station.
- groups of voltage levels of these nodes such as 35kV, 110kV, 220kV or 500kV, etc.
- the backup voltage and frequency support device adopts an energy storage type MMC (modular multilevel converter), in which the energy storage elements adopt batteries or supercapacitors.
- the energy storage elements are connected in series and parallel to form an energy storage device.
- the energy storage device can be centrally arranged on the DC side of the MMC through an interface circuit, or it can be dispersed in the sub-modules of the MMC through the interface circuit.
- the backup voltage and frequency support device adopts a power synchronization control strategy, in which the active power control part makes a difference between the command value of the active power and the actual value and outputs the frequency compensation through a first-order inertia link, and the reactive power control part makes a difference between the command value of the AC voltage and the actual value and outputs the current command value through PI control, wherein the active power command value is set to 0 and the AC voltage command value is set to 1.0p.u.
- the transfer function of the first-order inertia link is Where D is the damping coefficient, H is the inertia time constant, s is the Laplace operator, and the gain coefficient 1/D is set to 0.005 ⁇ 0.02pu.
- step (3) the new energy station adjusts its active output according to the frequency, and the new active output command value is equal to the original active output command value multiplied by a proportional coefficient k.
- the proportional coefficient k is determined by the grid connection point frequency of the new energy station.
- the frequency threshold f th1 is set to 1.004 pu
- the frequency threshold f th2 is set to 1.01 pu.
- the present invention has the following beneficial technical effects:
- the present invention avoids unnecessary shutdown of 100% of the new energy sending-end power grid through the backup voltage and frequency support function, which can improve the system operation reliability and has great application value in practical engineering.
- FIG1 is a schematic diagram of the structure of a 100% new energy sending-end power grid through a flexible direct current transmission system in an embodiment.
- Figure 2(a) is a schematic diagram of the energy storage MMC structure in which the energy storage device is integrated into the submodule.
- Figure 2(b) is a schematic diagram of the energy storage type MMC structure in which the energy storage device is centrally installed on the DC side.
- FIG3( a ) is a schematic diagram of the structure of a power synchronization loop for power synchronization control.
- FIG3( b ) is a schematic diagram of the structure of a constant AC voltage loop for power synchronization control.
- FIG. 4 is a schematic diagram of a characteristic curve of the frequency adjustment proportional coefficient and the grid connection point frequency.
- FIG5 is a schematic diagram of simulation waveforms of active power of the sending-end converter station and each energy storage type MMC in the embodiment.
- FIG6 is a schematic diagram of a simulation waveform of frequency deviation of each energy storage type MMC in the embodiment.
- FIG7 is a schematic diagram of a simulation waveform of active power of a single new energy station in an embodiment.
- FIG8( a ) is a schematic diagram of a simulation waveform of the effective value of the 35 kV bus AC voltage in the embodiment.
- FIG8( b ) is a schematic diagram of a simulation waveform of the effective value of the 220 kV bus AC voltage in the embodiment.
- FIG8( c ) is a schematic diagram of a simulation waveform of the effective value of the 500 kV bus AC voltage in the embodiment.
- the 100% new energy sending-end power grid in this embodiment can be divided into 8 areas according to the geographical location.
- Each area is equivalent to an aggregated photovoltaic power station connected to a 35kV AC system.
- the rated power of the aggregated photovoltaic power station is equal to the sum of the rated powers of all photovoltaic power stations in the area, which is set to 500MW in this example.
- the 8 equivalent aggregated photovoltaic power stations are connected to 3 220kV AC busbars after voltage boosting, and then transmitted to 3 220kV substations through a double-circuit AC line of about 10km to boost the voltage to 500kV.
- Each 500kV busbar is respectively collected to a 500kV flexible direct current converter station through a double-circuit AC line of about 50km. All 220kV buses are equipped with dynamic reactive power compensation devices STATCOM (denoted as D1 ⁇ D6 ).
- STATCOM dynamic reactive power compensation devices
- All 500 kV busbars except those connected to the flexible DC converter station in the 100% renewable energy sending-end power grid are selected as backup voltage and frequency support nodes.
- An energy storage MMC is installed on the backup voltage and frequency support node as a backup voltage and frequency device.
- the energy storage MMC consists of 6 bridge arms, each of which contains N cascaded sub-modules and a bridge arm reactor L 0 . It was first proposed in the literature [Soong T, Lehn P W. Evaluation of Emerging Modular Multilevel Converters for BESS Applications [J]. IEEE Transactions on Power Delivery, 2014, 29(5): 2086-2094.];
- FIG2(a) shows an energy storage MMC in which an energy storage device is integrated into a sub-module. All sub-modules in the MMC are energy storage sub-modules, which consist of a half-bridge sub-module and an energy storage device.
- FIG2(b) shows an energy storage MMC in which an energy storage device is centrally installed on the DC side. All sub-modules in the MMC are ordinary half-bridge sub-modules, and the cascaded energy storage sub-modules are centrally arranged on the DC side.
- the active power controller adopts the power synchronization loop PSL shown in Figure 3(a).
- the active power command value Psref is subtracted from the measured value Ps and then passes through the first-order inertia link.
- Output frequency signal ⁇ where D is the damping coefficient, H is the inertia time constant, s is the Laplace operator, and P sref is set to 0.
- the reactive power controller is shown in Figure 3(b).
- u sd and u sq respectively represent the actual values of the d-axis and q-axis components of the AC bus voltage, and the difference between the two can be obtained through the PI controller to obtain the current command values of the d-axis and q-axis.
- Setting The command value of the AC bus voltage set up is 0. In this embodiment Set to 1.
- the active power command value of the photovoltaic power generation unit is dynamically adjusted by detecting the frequency deviation of the grid connection point. Equal to the active output command value of the photovoltaic power generation unit without considering the frequency regulation characteristics Multiply by the frequency adjustment proportional coefficient k fre . As shown in FIG4 , when the frequency is less than 1.004 pu, k fre is set to 1.0; when the frequency is greater than 1.01 pu, k fre is set to 0; when the frequency is greater than 1.004 pu and less than 1.01 pu, k fre decreases linearly from 1.0 to 0.
- the simulation model of the new energy grid shown in Figure 1 was built in the electromechanical transient simulation software PSS/E to test the effect of the backup constant voltage and constant frequency control strategy of the present invention.
- PSS/E electromechanical transient simulation software
- the energy storage MMC installed on the backup voltage and frequency support node can replace the flexible DC converter station to absorb the active power generated by the renewable energy station and maintain the power balance of the sending end system.
- the frequency output of each energy storage MMC The deviations are all within 0.0065pu, and after the sending-end converter station is put back into operation, the system frequency deviation will gradually disappear, and the system frequency will return to the steady-state equilibrium point.
- each new energy station can actively reduce its own active output as the frequency of the grid connection point increases, and assist in completing the fault crossing.
- the transient voltage of each AC busbar in the system can be controlled within 0.98pu to 1.1pu, and the system will not experience serious AC overvoltage.
- the backup constant voltage and constant frequency control strategy of the present invention can play a significant role in maintaining the voltage and frequency of the sending-end system, and the system will not experience large-scale frequency and voltage fluctuations. That is, the simulation proves the effectiveness of the present invention.
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Abstract
本发明公开了一种100％新能源送端电网的后备电压频率支撑方法，包括：(1)选择100％新能源送端电网中的后备电压频率支撑节点，包括后备电压频率支撑节点的电压等级和位置；(2)在后备电压频率支撑节点上安装后备电压频率装置，所有后备电压频率装置采用功率同步控制；(3)新能源发电单元根据并网点频率动态调节其有功出力。本发明方法填补了送端柔性直流换流站双极闭锁时100％新能源基地控制策略的空白，通过后备电压频率支撑功能避免100％新能源送端电网非必要停运，可以提升系统运行可靠性，在实际工程中有巨大的应用价值。
Description
本发明属于电力系统输配电技术领域，具体涉及一种100％新能源送端电网的后备电压频率支撑方法。
我国能源生产和需求呈逆向分布，即煤炭资源主要集中在中西部地区，可再生能源资源主要分布在“三北”地区和西南地区，而能源负荷主要集中在东部沿海地区。随着“3060双碳”目标的提出，未来我国将大力开发北部地区和西部地区的大型陆上新能源基地，可以预见这些新能源基地将普遍采用特高压直流输电技术外送。此外，我国将大力推进海上风电基地建设，加快推动海上风电集群化开发，重点建设山东半岛、长三角、闽南、粤东和北部湾五大千万千瓦级海上风电基地。
沙漠、戈壁、荒漠地区建设的大型陆上新能源发电基地联网代价大、本地常规电源建设难度大，大规模海上风电更是本身就不存在交流电网。因此，送端电网将呈现出100％新能源基地+特高压柔性直流系统外送的形态，在这种送端电网中，新能源电源可以运行在常规的跟网型控制模式；而送端柔性直流换流站将采用V/f控制，用于为100％新能源送端电网提供稳定的电压和频率基准。
在电压和频率支撑方面，100％新能源送端电网与常规交流电网存在本质不同。从电压频率支撑角度来看，对于常规交流电网而言，整个电网的电压和频率通过分布在电网当中的同步机电源共同支撑，常规交流电网的电压频率支撑由同步机至下而上构建；单台同步机退出运行之后，系统仍然具备稳定运行的能力。对于100％新能源送端电网而言，如果只有送端柔性直流换流站采用构网型控制，整个电网的电压和频率支撑只由送端换流站集中提供，100％新能源送
端电网电压频率支撑由送端柔性直流换流站从上至下构建；当直流系统故障导致送端柔性直流换流站双极闭锁后，100％新能源送端电网将失去电压频率支撑电源，此时送端电网将不具备稳定运行的条件。
从能量平衡角度来看，常规交流电网中存在大量旋转设备，暂态能量可以通过各种旋转设备平衡。100％新能源送端电网不含有同步机电源，正常情况下暂态能量只能通过送端柔性直流换流站平衡；当送端柔性直流换流站发生双极闭锁之后，暂态能量将导致送端电网出现电大幅度上升，严重影响送端电网中电气设备安全。
根据实际工程运行经验，特高压直流系统双极闭锁发生的概率约为每年1次，其中暂时性故障的概率最大。考虑到上述两点因素，100％新能源送端电网的需要具有后备电压频率支撑功能；在直流送出系统由于暂时性故障而发生双极闭锁时，可以通过后备电压频率支撑功能避免100％新能源送端电网全停。
到目前为止，已公开的绝大多数文献在并未考虑100％新能源送端电网的送端柔性直流换流站发生双极闭锁的情况；为了提升100％新能源送端电网的运行可靠性，很有必要对100％新能源送端电网的后备电压频率支撑方法进行研究。
发明内容
鉴于上述，本发明提供了一种100％新能源送端电网的后备电压频率支撑方法，该方法实施简单，通用性强，能够提升100％新能源送端电网的运行可靠性，在实际工程中有巨大的使用价值。
一种100％新能源送端电网的后备电压频率支撑方法，包括如下步骤：
(1)从100％新能源送端电网中选取支撑节点；
(2)在各支撑节点上安装后备电压频率支撑装置；
(3)新能源场站根据并网点频率动态调节自身的有功出力。
进一步地，所述100％新能源送端电网包含有多个新能源场站，所述新能源场站可以是光伏电站、陆上风电场或海上风电场，新能源场站接入交流系统后经过多次升压后汇集至送端整流站。
进一步地，所述步骤(1)对于电网中的所有节点(即交流母线)，这些节点的电压等级总共有多组(如35kV、110kV、220kV或500kV等)，从最高电压等级的节点中选取除节点O以外的其他所有节点即作为支撑节点，所述节点O为与送端整流站直接相连的节点。
进一步地，所述后备电压频率支撑装置采用储能型MMC(模块化多电平换流器)，其中的储能元件采用蓄电池或者超级电容，储能元件经过串并联后构成储能装置，储能装置可通过接口电路集中布置在MMC直流侧，也可通过接口电路分散在MMC的子模块内。
进一步地，所述后备电压频率支撑装置采用功率同步控制策略，有功功率控制部分将有功功率的指令值与实际值作差后经过一阶惯性环节输出频率补偿量，无功功率控制部分将交流电压的指令值与实际值作差后经过PI控制输出电流指令值，其中有功功率指令值设定为0，交流电压指令值设定为1.0p.u.。
进一步地，所述一阶惯性环节的传递函数为其中D为阻尼系数，H为惯性时间常数，s为拉普拉斯算子，增益系数1/D设置为0.005～0.02p.u.。
进一步地，所述步骤(3)中新能源场站根据频率调节其有功出力，新的有功出力指令值等于在原有功出力指令值基础上乘以一个比例系数k。
进一步地，所述比例系数k由新能源场站的并网点频率决定，当并网点频率小于等于预设的频率阈值fth1时，k＝1；当并网点频率大于等于预设的频率阈值fth2时，k＝0；当并网点频率在fth1～fth2之间，则比例系数k随并网点频率增加而减小且呈线性关系。
进一步地，所述频率阈值fth1设置为1.004p.u.，频率阈值fth2设置为1.01p.u.。
基于上述技术方案，本发明具有以下有益技术效果：
1.本发明后备电压频率支撑方法填补了送端柔性直流换流站双极闭锁时100％新能源基地控制策略的空白，能为未来工程设计提供一定的参考。
2.本发明通过后备电压频率支撑功能避免100％新能源送端电网非必要停运，可以提升系统运行可靠性，在实际工程中有巨大的应用价值。
图1为实施例中100％新能源送端电网经柔直送出系统的结构示意图。
图2(a)为储能装置集成在子模块中的储能型MMC结构示意图。
图2(b)为储能装置集中安装在直流侧的储能型MMC结构示意图。
图3(a)为功率同步控制的功率同步环结构示意图。
图3(b)为功率同步控制的定交流电压环结构示意图。
图4为频率调节比例系数与并网点频率的特性曲线示意图。
图5为实施例中送端换流站与各储能型MMC有功功率的仿真波形示意图。
图6为实施例中各储能型MMC频率偏差的仿真波形示意图。
图7为实施例中单个新能源场站有功功率的仿真波形示意图。
图8(a)为实施例中35kV母线交流电压有效值的仿真波形示意图。
图8(b)为实施例中220kV母线交流电压有效值的仿真波形示意图。
图8(c)为实施例中500kV母线交流电压有效值的仿真波形示意图。
为了更为具体地描述本发明，下面结合附图及具体实施方式对本发明的技术方案进行详细说明。
如图1所示，本实施例中的100％新能源送端电网根据地理位置的可以划分为8个区域，每个区域等效为一个聚合的光伏电站接入35kV交流系统，该聚合光伏电站的额定功率等于该区域所有光伏电站的额定功率之和，本实例中均设定为500MW。8个等效的聚合光伏电站经过升压分别接到3个220kV的交流母线上，再通过10km左右的双回交流线路输送至3个220kV的变电站升压至500kV，各500kV汇流母线分别通过50km左右的双回交流线路汇集到500kV的柔直换流站，所有220kV母线均安装有动态无功补偿装置STATCOM(记为D1～D6)。针对上述系统，本发明后备电压频率支撑方法具体实施过程如下：
(1)选取100％新能源送端电网中除连接柔直换流站以外的所有500kV汇流母线作为的后备电压频率支撑节点。
(2)在后备电压频率支撑节点上安装储能型MMC作为后备电压频率装置，储能型MMC由6个桥臂构成，每个桥臂中包含N个级联子模块和一个桥臂电抗器L0，其最早在文献[Soong T,Lehn P W.Evaluation of Emerging Modular Multilevel Converters for BESS Applications[J].IEEE Transactions on Power Delivery,2014,29(5):2086-2094.]有提出；图2(a)为储能装置集成在子模块中的储能型MMC，MMC中的所有子模块均为储能型子模块，其由一个半桥子模块与一个储能装置组成，储能装置通过一个双向DC/DC变换器与子模块电容并联；图2(b)为储能装置集中安装在直流侧的储能型MMC，MMC中的所有子模块为普通半桥子模块，级联式储能子模块集中布置在直流侧。
所有储能型MMC均采用采用功率同步控制，有功功率控制器采用如图3(a)所示的功率同步环PSL，有功功率指令值Psref与测量值Ps作差后经过一阶惯性环节输出频率信号Δω，其中D为阻尼系数，H为惯性时间常数，s为拉普拉斯算子，设置Psref为0。无功功率控制器如图3(b)所示，分别表示交流母线电压d轴与q轴分量的指令值，usd、usq分别表示交流母线电压d轴与q轴分量的实际值，二者分别作差后经过PI控制器即可得到d轴和q轴的电流指令值。设置为交流母线电压的指令值设置为0，在本实施例中设置为1。
(3)光伏发电单元有功功率的指令值通过检测并网点的频率偏差进行动态调节，光伏发电单元的有功出力指令值等于光伏发电单元不考虑频率调节特性的有功出力指令值乘以频率调节比例系数kfre。如图4所示，当频率小于1.004p.u.时，kfre设置为1.0；当频率大于1.01p.u.时，kfre设置为0；当频率大于1.004p.u.小于1.01p.u.时，kfre从1.0到0线性下降。
本实施例中的系统参数如表1所示：
表1
在机电暂态仿真软件PSS/E中搭建图1所示的新能源电网的仿真模型，测试本发明后备定电压定频率控制策略的效果。在t＝2.0s之前，所有光伏电站均运行在光照强度为1000W/m2条件下的功率满发状态，三台储能型MMC输出有功功率均为0；假设t＝2.0s时，送端柔直换流站因故障退出运行，t＝3.5s时，送端柔直换流站重新投入运行。
从图5可以看出，在送端柔直换流站突然退出运行时，后备电压频率支撑节点上装设的储能型MMC能够代替柔直换流站吸收新能源场站发出的有功功率，维持送端系统的功率平衡。从图6可以看出，在送端柔直换流站突然退出运行、有功功率转移到储能型MMC的暂态过程中，各储能型MMC输出的频率
偏差均在0.0065p.u.以内，并且在送端换流站重新投入运行后，系统频率偏差将逐渐消失，系统频率将重新回到稳态平衡点。从图7可以看出，在送端柔直换流站突然退出运行、有功功率转移到储能型MMC的暂态过程中，各新能源场站能够随并网点频率升高主动降低自身的有功出力，协助完成的故障穿越。从图8(a)～图8(c)可以看出，整个暂态过程中，系统各交流母线的暂态电压均能控制在0.98p.u.到1.1p.u.以内，系统不会出现严重的交流过电压。
综上所述，在送端柔直换流站突然退出运行时，本发明后备定电压定频率控制策略在维持送端系统电压频率方面能够发挥明显的作用，系统不会出现大范围的频率波动与电压波动，即仿真证明了本发明的有效性。
上述对实施例的描述是为便于本技术领域的普通技术人员能理解和应用本发明。熟悉本领域技术的人员显然可以容易地对上述实施例做出各种修改，并把在此说明的一般原理应用到其他实施例中而不必经过创造性的劳动。因此，本发明不限于上述实施例，本领域技术人员根据本发明的揭示，对于本发明做出的改进和修改都应该在本发明的保护范围之内。
Claims (9)
- 一种100％新能源送端电网的后备电压频率支撑方法，包括如下步骤：(1)从100％新能源送端电网中选取支撑节点；(2)在各支撑节点上安装后备电压频率支撑装置；(3)新能源场站根据并网点频率动态调节自身的有功出力。
- 根据权利要求1所述的后备电压频率支撑方法，其特征在于：所述100％新能源送端电网包含有多个新能源场站，所述新能源场站可以是光伏电站、陆上风电场或海上风电场，新能源场站接入交流系统后经过多次升压后汇集至送端整流站。
- 根据权利要求1所述的后备电压频率支撑方法，其特征在于：所述步骤(1)对于电网中的所有节点，这些节点的电压等级总共有多组，从最高电压等级的节点中选取除节点O以外的其他所有节点即作为支撑节点，所述节点O为与送端整流站直接相连的节点。
- 根据权利要求1所述的后备电压频率支撑方法，其特征在于：所述后备电压频率支撑装置采用储能型MMC，其中的储能元件采用蓄电池或者超级电容，储能元件经过串并联后构成储能装置，储能装置可通过接口电路集中布置在MMC直流侧，也可通过接口电路分散在MMC的子模块内。
- 根据权利要求1所述的后备电压频率支撑方法，其特征在于：所述后备电压频率支撑装置采用功率同步控制策略，有功功率控制部分将有功功率的指令值与实际值作差后经过一阶惯性环节输出频率补偿量，无功功率控制部分将交流电压的指令值与实际值作差后经过PI控制输出电流指令值，其中有功功率指令值设定为0，交流电压指令值设定为1.0p.u.。
- 根据权利要求5所述的后备电压频率支撑方法，其特征在于：所述一 阶惯性环节的传递函数为其中D为阻尼系数，H为惯性时间常数，s为拉普拉斯算子，增益系数1/D设置为0.005～0.02p.u.。
- 根据权利要求1所述的后备电压频率支撑方法，其特征在于：所述步骤(3)中新能源场站根据频率调节其有功出力，新的有功出力指令值等于在原有功出力指令值基础上乘以一个比例系数k。
- 根据权利要求7所述的后备电压频率支撑方法，其特征在于：所述比例系数k由新能源场站的并网点频率决定，当并网点频率小于等于预设的频率阈值fth1时，k＝1；当并网点频率大于等于预设的频率阈值fth2时，k＝0；当并网点频率在fth1～fth2之间，则比例系数k随并网点频率增加而减小且呈线性关系。
- 根据权利要求8所述的后备电压频率支撑方法，其特征在于：所述频率阈值fth1设置为1.004p.u.，频率阈值fth2设置为1.01p.u.。
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