WO2023134225A1 - 一种低频输电系统及其控制方式 - Google Patents

一种低频输电系统及其控制方式 Download PDF

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WO2023134225A1
WO2023134225A1 PCT/CN2022/121941 CN2022121941W WO2023134225A1 WO 2023134225 A1 WO2023134225 A1 WO 2023134225A1 CN 2022121941 W CN2022121941 W CN 2022121941W WO 2023134225 A1 WO2023134225 A1 WO 2023134225A1
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frequency
low
power
power transmission
transmission system
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English (en)
French (fr)
Inventor
许烽
金玉琪
裘鹏
倪晓军
林进钿
黄晓明
陆承宇
陆翌
陈晓刚
徐华
毛航银
宣佳卓
陈骞
丁超
郑眉
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Electric Power Research Institute of State Grid Zhejiang Electric Power Co Ltd
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Electric Power Research Institute of State Grid Zhejiang Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; 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
    • H02J3/34—Arrangements for transfer of electric power between networks of substantially different frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; 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 networks by storage of energy
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; 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 feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of AC power input into AC power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/02—Conversion of AC power input into AC power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into DC
    • H02M5/04—Conversion of AC power input into AC power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into DC by static converters
    • H02M5/22—Conversion of AC power input into AC power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into DC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M5/275—Conversion of AC power input into AC power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into DC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M5/293—Conversion of AC power input into AC power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into DC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2101/00—Supply or distribution of decentralised, dispersed or local electric power generation
    • H02J2101/20—Dispersed power generation using renewable energy sources
    • H02J2101/28—Wind energy

Definitions

  • the invention belongs to the field of power system transmission, in particular to a low-frequency power transmission system and its control method.
  • Wind energy is a resource-rich, renewable green energy source. It has been favored by the world for its good ecological benefits and huge development potential, and is expected to become the world's leading energy source. Due to its huge development potential and commercial value, wind power has been valued by countries all over the world, and has been developed and utilized on a large scale. In my country, due to the remote location of most wind farms, the power system does not absorb enough wind power, thus inhibiting the development of wind power. Therefore, it is extremely important to solve the problems of wind power grid connection and long-distance large-capacity transmission.
  • Low-frequency power transmission is a useful supplement to power frequency AC transmission and DC power transmission by reducing transmission frequency, reducing line impedance, reducing cable charging reactive power, and improving power grid transmission capacity and regulation capabilities.
  • Scenarios such as partition interconnection and island interconnection power supply.
  • Offshore wind power low-frequency transmission system can use wind turbines to directly output low-frequency electric energy, transmit low-frequency electric energy to offshore platforms through the converging system, boost the voltage through low-frequency transformers and send it out through submarine cable lines, and finally convert low-frequency electric energy into industrial frequency, into the power frequency grid.
  • the power and low frequency of the AC/AC inverter are independent of each other, and the power transmission capacity is not affected by the power frequency voltage and power factor.
  • Low-frequency power transmission has obvious technical and economic advantages in the COSCO sea wind power transmission scenario. However, because low-frequency power transmission technology is still in its infancy and has no relevant engineering applications, research on its topological structure is almost blank.
  • the present invention proposes a low-frequency power transmission system, which can realize long-distance power transmission of energy sources such as wind power and pumped storage power stations, and take into account transmission efficiency and construction cost while ensuring effective power transmission.
  • a low-frequency power transmission system which includes a first frequency conversion sub-system, a second frequency conversion sub-system, a third frequency conversion sub-system, and a first low-frequency power supply sub-system and a second Low frequency power subsystem;
  • the frequency conversion transmission subsystem includes: an AC frequency conversion station connected to the power frequency AC power grid through a power frequency AC busbar and a power frequency AC transformer, which is used to convert power frequency AC power into low frequency AC power; AC switch;
  • the low-frequency power supply subsystem includes: a low-frequency wind farm or pumped storage power station/hydropower station; a low-frequency AC transformer connected to the low-frequency wind farm or pumped-storage power station/hydropower station, which is used for voltage conversion of the low-frequency alternating current of the low-frequency power supply subsystem; and A second low-frequency AC switch connected to the low-frequency AC transformer;
  • Both the first low-frequency AC switch and the second low-frequency AC switch are connected to the low-frequency power transmission network.
  • the working principles of the low-frequency AC transformer and the low-frequency AC switch are the same as those of the power-frequency AC transformer and the power-frequency AC switch respectively. Since the frequency becomes lower and the zero-crossing period becomes longer, the volume of the low-frequency AC transformer will be larger than that of the power-frequency AC transformer with the same voltage level and capacity. frequency AC transformer; the difficulty of arc extinguishing of low frequency AC switch is greater than that of power frequency AC switch.
  • the AC/AC frequency conversion substation of the second frequency conversion transmission subsystem adopts a thyristor-based cycloconverter, and each phase of the cycloconverter is composed of two groups of rectifier bridges in anti-parallel connection, changing the switching of the two groups of rectifier bridges
  • the frequency can change the output frequency
  • changing the gate trigger delay angle of the power semiconductor tube in the rectifier bridge can change the amplitude and working mode of the output voltage of the phase-controlled cycloconverter, so that the cycloconverter can conveniently work in the rectification and inverter states , to achieve four-quadrant operation.
  • thyristors are directly connected in series.
  • the alternating frequency substation of the third frequency conversion transmission sub-system adopts a frequency doubler transformer
  • the frequency doubler transformer is a triple frequency transformer formed by utilizing the ferromagnetic saturation characteristic.
  • the frequency tripler transformer can realize the AC interconnection between the fundamental frequency and one-third of the fundamental frequency, and energy intercommunication.
  • the low-frequency power supply in the first low-frequency power supply subsystem is a medium-to-long distance (70km-200km) offshore or land-based low-frequency wind farm, and its fan adopts a permanent magnet direct drive form, and its transformer, frequency converter and ring main unit Transformation is carried out to realize the transition from industrial frequency fan to low frequency fan, so that the fan can directly output low frequency electric energy.
  • the power source in the second low-frequency power supply subsystem is a medium-to-long-distance pumped storage power station or a hydropower station, which directly outputs low-frequency electric energy through low-frequency transformation and transmits power to the connected low-frequency power transmission network.
  • the low-frequency power transmission network adopts a radial or ring structure to connect various subsystems. Its fault protection principles can be used for reference to traditional power frequency power transmission networks, such as overcurrent protection and distance protection.
  • the AC/AC frequency conversion substation of the first frequency conversion transmission subsystem adopts a modular multi-level matrix converter, and has a three-phase nine-leg structure, and each bridge arm contains multiple full-bridge sub-modules and each A bridge arm is connected in series with an inductor;
  • the full bridge sub-module includes: a first IGBT with a reverse diode, a second IGBT with a reverse diode, a third IGBT with a reverse diode, a fourth IGBT with a reverse diode and a first capacitor, the The collector of the first IGBT with a reverse diode is connected to the collector of the second IGBT with a reverse diode and one end of the first capacitor, and the emitter of the first IGBT with a reverse diode is connected to the first capacitor.
  • the collectors of the three IGBTs with reverse diodes are connected as the high voltage end of the full bridge sub-module, the emitter of the third IGBT with reverse diodes is connected to the emitter of the fourth IGBT with reverse diodes and The other end of the first capacitor is connected, and the emitter of the second IGBT with reverse diode is connected with the collector of the fourth IGBT with reverse diode as the low voltage terminal of the full bridge sub-module.
  • the full-bridge sub-module also contains an energy storage module, so that the modular multilevel matrix converter has an energy storage function, and provides power/energy flexibility adjustment for the low-frequency power transmission system.
  • the present invention also provides the control method of the above-mentioned low-frequency power transmission system, the content of which is as follows: the low-frequency power transmission system operates in five-terminal, four-terminal, three-terminal, two-terminal or one-terminal operating states, wherein the five-terminal operating state is a fully operating state, that is, three Both the variable frequency transmission subsystem and the two low frequency power supply subsystems are in the operating state; in all operating states, at least one variable frequency transmission subsystem is in the operating state, otherwise, the low frequency power transmission system cannot operate stably, and the variable frequency transmission subsystem and the low frequency power supply subsystem
  • the system has the ability to switch on and off online, and the normal operation of the low-frequency transmission system will not be affected during the on-line switch on and off;
  • the frequency of the low frequency transmission system is limited to 1/3 of the power frequency value due to the frequency multiplier transformer, and the frequencies of other subsystems must follow this frequency value; when the third variable frequency transmission When the electronic system is out of operation, the frequency of the low-frequency power transmission system can be adjusted through frequency control, but the frequency range needs to be within the operable range of the low-frequency AC transformer and low-frequency AC switch.
  • the present invention can not only realize the long-distance power transmission of wind power, pumped storage power stations and other energy sources, but also ensure the effective transmission of electric power; at the same time, the present invention provides a variety of options for AC and AC frequency conversion stations, which can match technical rationality and Topology structure of system construction cost.
  • Fig. 1 is the schematic diagram of low-frequency power transmission system of the present invention
  • M3C modular multilevel matrix converter
  • FIG. 3 is a schematic diagram of the full bridge sub-module in FIG. 2 .
  • a low frequency power transmission system as shown in Fig. 1 includes a first variable frequency power transmission subsystem, a second variable frequency power transmission subsystem and a third frequency variable power transmission subsystem, and a first low frequency power supply subsystem and a second low frequency power supply subsystem.
  • the frequency conversion transmission subsystem includes: an AC frequency conversion substation connected to the power frequency AC power grid through a power frequency AC busbar and a power frequency AC transformer, which is used to convert power frequency AC power into low frequency AC power; and a first low frequency AC power station connected to the AC frequency conversion station switch.
  • the low-frequency power supply subsystem includes: a low-frequency wind farm or a pumped storage power station/hydropower station; a low-frequency AC transformer connected to the low-frequency wind farm or a pumped-storage power station/hydropower station, which is used for voltage conversion of the low-frequency alternating current of the low-frequency power supply subsystem; and A second low frequency AC switch connected to the low frequency AC transformer. Both the first and second low-frequency AC switches are connected to the low-frequency power transmission network.
  • the low-frequency transmission network can adopt a radial or ring structure, and its fault protection principle can refer to the traditional power frequency transmission network, such as overcurrent protection, distance protection, etc.
  • the working principle of the low-frequency AC transformer and the low-frequency AC switch is the same as that of the power frequency AC transformer and the power frequency AC switch. As the frequency becomes lower and the zero-crossing period becomes longer, the volume of the low-frequency AC transformer will be larger than that of the power frequency AC transformer with the same voltage level and capacity. ; The arc extinguishing difficulty of low-frequency AC circuit breakers is greater than that of power frequency AC circuit breakers.
  • the AC-AC frequency conversion station of the first frequency conversion transmission subsystem adopts a modular multilevel matrix converter (M3C). It is formed by cascading two full-bridge sub-modules.
  • the three-phase AC systems on both sides of the M3C are respectively connected by 9 bridge arms, and each phase of the three-phase system on the input side is connected to each phase on the output side through a unique bridge arm. Since each bridge arm of M3C has the same structure, symmetrical parameters, and is independent of each other, it can be divided into three sub-converters a, b, and c from the input side three-phase system; from the output side three-phase system can be divided into u , v, w three sub-converters.
  • M3C modular multilevel matrix converter
  • each sub-converter is the same as the chained static var generator (STATCOM, referred to as SM in Figure 2), so it can also be considered that M3C is composed of three STATCOMs connected in parallel.
  • the inductance in each bridge arm of M3C can suppress the circulating current generated when the power of each phase bridge arm or the instantaneous value of the capacitor voltage of the sub-module is not completely consistent, and can suppress the inrush current when the low-frequency power transmission system fails, and enhance the stability of the low-frequency power transmission system. sex.
  • the full bridge sub-module includes: a first IGBT with a reverse diode, a second IGBT with a reverse diode, a third IGBT with a reverse diode, a fourth IGBT with a reverse diode and The first capacitor, the collector of the first IGBT with a reverse diode is connected to the collector of the second IGBT with a reverse diode and one end of the first capacitor, and the first IGBT with a reverse diode
  • the emitter is connected to the collector of the third IGBT with a reverse diode as the high voltage end of the full bridge sub-module, and the emitter of the third IGBT with a reverse diode is connected to the fourth IGBT with a reverse diode
  • the emitter of the IGBT is connected to the other end of the first capacitor, the emitter of the second IGBT with reverse diode is connected to the collector of the fourth IGBT with reverse diode as the full bridge Low voltage side
  • the full-bridge sub-module may also contain an energy storage module, so that the modular multilevel matrix converter has a certain energy storage function, and provides flexible adjustment of power/energy for the low-frequency power transmission system.
  • the AC-AC frequency conversion station of the second frequency conversion transmission subsystem adopts a thyristor-based cycloconverter, and each phase of the cycloconverter is composed of two sets of rectifier bridges connected in antiparallel. Changing the switching frequency of the two sets of rectifier bridges can change the output frequency. Changing the gate trigger delay angle of the power semiconductor tube in the rectifier bridge can change the amplitude and working mode of the output voltage of the phase-controlled cycloconverter, so that the cycloconverter can conveniently work in the rectification and inversion states and realize four-quadrant operation.
  • the direct series connection technology of thyristors is generally used.
  • the AC-AC frequency conversion substation of the third frequency conversion transmission sub-system adopts a frequency doubler transformer, which is a triple frequency transformer formed by using the ferromagnetic saturation characteristic.
  • the frequency tripler transformer can realize the AC interconnection between the fundamental frequency and one-third of the fundamental frequency, and energy intercommunication.
  • the low-frequency power supply of the first low-frequency power supply subsystem is a medium-to-long-distance (70km-200km) offshore or land low-frequency wind farm.
  • the transition from fan to low-frequency fan enables the fan to have the ability to directly output low-frequency power.
  • the power source in the second low-frequency power supply subsystem is a medium-to-long-distance pumped storage power station or a hydropower station.
  • the power station can directly output low-frequency electric energy through low-frequency transformation to transmit power to the connected low-frequency power transmission system.
  • the control method of the above-mentioned low-frequency power transmission system is as follows: the low-frequency power transmission system operates in five-terminal, four-terminal, three-terminal, two-terminal or one-terminal operating states, among which the five-terminal operating state is a fully operating state, that is, three variable frequency transmission subs
  • the system and the two low-frequency power supply subsystems are in the running state; in all running states, at least one variable frequency transmission subsystem is in the running state, otherwise, the low-frequency power transmission system cannot operate stably, and the variable frequency transmission
  • the ability to switch on and off will not affect the normal operation of the low-frequency transmission system during the on-line switch on and off;
  • the frequency of the low frequency transmission system is limited to 1/3 of the power frequency value due to the frequency multiplier transformer, and the frequencies of other subsystems must follow this frequency value; when the third variable frequency transmission When the electronic system is out of operation, the frequency of the low-frequency power transmission system can be adjusted through frequency control, but the frequency range needs to be within the operable range of the low-frequency AC transformer and low-frequency AC switch.

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  • Power Engineering (AREA)
  • Ac-Ac Conversion (AREA)
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Abstract

本发明公开了一种低频输电系统及其控制方式。本发明包括变频输电子系统以及低频电源子系统；变频输电子系统包括：通过工频交流母线和工频交流变压器与工频交流电网连接的交交变频站、与所述交交变频站连接的第一低频交流开关；低频电源子系统包括：低频风电场或抽水蓄能电站/水电站、与低频风电场或抽水蓄能电站/水电站连接的低频交流变压器、与所述低频交流变压器连接的第二低频交流开关；所述第一低频交流开关和第二低频交流开关均与所述低频输电网络连接。本发明可实现风电、抽水蓄能电站等能源的远距离电力输送，在保障电力有效传输的同时，兼顾传输效率和建设成本。

Description

一种低频输电系统及其控制方式 技术领域
本发明属于电力系统输电领域，具体地说是一种低频输电系统及其控制方式。
背景技术
风能是一种资源丰富、可再生的绿色能源，以其良好的生态效益和巨大的发展潜力得到了全球的青睐，有望成为世界的主导能源。风电因巨大的开发潜能和商业化价值受到了世界各国的重视，并得到了大规模的开发和利用。在我国，由于风电场大多位置偏远，电力系统对风电的消纳不足，从而抑制了风电的发展，所以解决风电并网和远距离大容量输送的问题极其重要。
低频输电通过降低输电频率，减小线路阻抗、减少电缆充电无功、提升电网的输送能力和调控能力，是工频交流输电与直流输电方式的有益补充，适用于中远距离海上风电送出、城市电网分区互联、海岛互联供电等场景。海上风电低频输电系统可利用风机直接输出低频电能，通过汇集系统将低频电能传输至海上平台，并通过低频变压器升压后经海缆线路送出，最后通过陆上交交变频站将低频电能变换为工频，汇入工频电网。交交变频器的工、低频相互独立，输电能力不受工频电压、功率因数影响。
低频输电在中远海风电送出场景中有明显的技术经济优势，但由于低频输电技术尚处于发展起步阶段，并无相关工程应用，因此，针对其拓扑结构形式的研究几乎空白。
发明内容
针对上述现有技术存在的缺陷，本发明提出一种低频输电系统，其可实现风电、抽水蓄能电站等能源的远距离电力输送，在保障电力有效传输的同时，兼顾传输效率和建设成本。
为此，本发明采用如下的技术方案：一种低频输电系统，其包括第一变频输电子系统、第二变频输电子系统、第三变频输电子系统，以及第一低频 电源子系统和第二低频电源子系统；
变频输电子系统包括：通过工频交流母线和工频交流变压器与工频交流电网连接的交交变频站，其用于将工频交流电转换为低频交流电；与所述交交变频站连接的第一低频交流开关；
低频电源子系统包括：低频风电场或抽水蓄能电站/水电站；与低频风电场或抽水蓄能电站/水电站连接的低频交流变压器，其用于将低频电源子系统的低频交流电进行电压变换；与所述低频交流变压器连接的第二低频交流开关；
所述第一低频交流开关和第二低频交流开关均与所述低频输电网络连接。
所述的低频交流变压器和低频交流开关的工作原理分别与工频交流变压器和工频交流开关相同，由于频率变低、过零点周期变长，低频交流变压器体积将大于同电压等级同容量的工频交流变压器；低频交流开关的熄弧难度大于工频交流开关。
进一步地，所述第二变频输电子系统的交交变频站采用基于晶闸管的周波变换器，所述周波变换器的每一相都由反并联的两组整流桥组成，改变两组整流桥的切换频率就可改变输出频率，改变整流桥中电力半导体管的门极触发延迟角就可改变相控周波变换器输出电压的幅值和工作方式，使周波变换器方便地工作于整流和逆变状态，实现四象限运行。
更进一步地，整流桥内，为使得每个桥臂具备一定电压的承受能力，都采用晶闸管直接串联。
进一步地，所述第三变频输电子系统的交交变频站采用倍频变压器，所述的倍频变压器为利用铁磁饱和特性构成的三倍频变压器。三倍频变压器可实现基频和三分之一基频交流互联，能量互通。
进一步地，所述第一低频电源子系统中的低频电源为中远距离(70km-200km)海上或陆上低频风电场，其风机采用永磁直驱形式，对其变压器、变频器和环网柜进行改造，实现工频风机向低频风机的过渡，使得风机能直接输出低频电能。
进一步地，所述第二低频电源子系统中的电源为中远距离抽水蓄能电站 或水电站，通过低频改造，直接输出低频电能，向连接的低频输电网络送电。
进一步地，所述的低频输电网络采用放射状或环状结构，起到连接各子系统的作用，其故障保护原理可借鉴传统工频输电网络，如过流保护、距离保护等。
进一步地，所述第一变频输电子系统的交交变频站采用模块化多电平矩阵型换流器，且为三相九桥臂结构，每个桥臂均含有多个全桥子模块且每个桥臂串接电感；
所述全桥子模块包括：第一带反向二极管的IGBT、第二带反向二极管的IGBT、第三带反向二极管的IGBT、第四带反向二极管的IGBT和第一电容，所述第一带反向二极管的IGBT的集电极与第二带反向二极管的IGBT的集电极和所述第一电容的一端连接，所述第一带反向二极管的IGBT的发射极与所述第三带反向二极管的IGBT的集电极连接作为所述全桥子模块的高压端，所述第三带反向二极管的IGBT的发射极与所述第四带反向二极管的IGBT的发射极和所述第一电容的另一端连接，所述第二带反向二极管的IGBT的发射极与所述第四带反向二极管的IGBT的集电极连接作为所述全桥子模块的低压端。
更进一步地，所述全桥子模块内还含有储能模块，使得模块化多电平矩阵型换流器具备储能功能，为低频输电系统提供功率/能量灵活性调节。
本发明还提供上述低频输电系统的控制方式，其内容如下：低频输电系统运行在五端、四端、三端、两端或一端运行状态，其中，五端运行状态为完全运行状态，即三个变频输电子系统和两个低频电源子系统均处于运行状态；所有运行状态中，至少有一个变频输电子系统处于运行状态，否则，低频输电系统不能稳定运行，变频输电子系统和低频电源子系统均具备在线投退能力，在线投退期间都不会影响低频输电系统的正常运行；
当第三变频输电子系统投入运行时，低频输电系统的频率因倍频变压器的缘故，被限制于1/3工频频率值，其他子系统的频率必须跟随该频率值；当第三变频输电子系统退出运行时，低频输电系统的频率可通过频率控制进行调节，但频率范围需要在低频交流变压器和低频交流开关的可运行范围之内。
与现有技术相比，本发明具有的有益技术效果如下：
本发明不仅能够实现风电、抽水蓄能电站等能源的远距离电力输送，保障电力的有效传输；同时，本发明提供了多种交交变频站的选择，可为工程实际应用匹配兼顾技术合理性和系统建设成本的拓扑结构。
附图说明
图1为本发明低频输电系统示意图；
图2为本发明模块化多电平矩阵型换流器(M3C)示意图；
图3为图2中全桥子模块的示意图。
具体实施方式
为了更为具体地描述本发明，下面结合说明书附图及具体实施方式对本发明的技术方案及其相关原理进行详细说明。
如图1所示的一种低频输电系统，包括第一变频输电子系统、第二变频输电子系统和第三变频输电子系统，以及第一低频电源子系统和第二低频电源子系统。
变频输电子系统包括：通过工频交流母线和工频交流变压器与工频交流电网连接的交交变频站，其用于将工频交流电转换为低频交流电；以及与交交变频站连接的第一低频交流开关。低频电源子系统包括：低频风电场或抽水蓄能电站/水电站；与低频风电场或抽水蓄能电站/水电站连接的低频交流变压器，其用于将低频电源子系统的低频交流电进行电压变换；以及与低频交流变压器连接的第二低频交流开关。第一、第二低频交流开关均与低频输电网络连接。
低频输电网络可采用放射状或环状结构，其故障保护原理可借鉴传统工频输电网络，如过流保护、距离保护等。低频交流变压器和低频交流开关的工作原理分别与工频交流变压器和工频交流开关相同，由于频率变低、过零点周期变长，低频交流变压器体积将大于同电压等级同容量的工频交流变压器；低频交流断路器的熄弧难度大于工频交流断路器。
第一变频输电子系统的交交变频站采用模块化多电平矩阵型换流器(M3C)，如图2所示，M3C为三相九桥臂结构，每个桥臂均由一个电感和N个全桥子模块级联而成。M3C两侧的三相交流系统分别由9个桥臂连接，且输入侧三相系统的每一相均经由唯一的桥臂同输出侧的各相连接。由于M3C 各个桥臂的结构相同、参数对称，且相互独立，故从输入侧三相系统来看，可分为a、b、c三个子转换器；从输出侧三相系统又可分为u、v、w三个子转换器。每个子转换器的结构与链式的静止无功发生器(STATCOM，图2中简称SM)相同，因此也可以认为M3C是由三个STATCOM并联构成。M3C各桥臂中的电感能够抑制在各相桥臂功率或子模块电容电压瞬时值不完全一致时产生的环流，且能够在低频输电系统发生故障时抑制冲击电流，增强低频输电系统运行的稳定性。
其中，如图3所示，全桥子模块包括：第一带反向二极管的IGBT、第二带反向二极管的IGBT、第三带反向二极管的IGBT、第四带反向二极管的IGBT和第一电容，所述第一带反向二极管的IGBT的集电极与第二带反向二极管的IGBT的集电极和所述第一电容的一端连接，所述第一带反向二极管的IGBT的发射极与所述第三带反向二极管的IGBT的集电极连接作为所述全桥子模块的高压端，所述第三带反向二极管的IGBT的发射极与所述第四带反向二极管的IGBT的发射极和所述第一电容的另一端连接，所述第二带反向二极管的IGBT的发射极与所述第四带反向二极管的IGBT的集电极连接作为所述全桥子模块的低压端。
所述的全桥子模块内还可含有储能模块，使得模块化多电平矩阵型换流器具备一定的储能功能，为低频输电系统提供功率/能量的灵活性调节。
第二变频输电子系统的交交变频站采用基于晶闸管的周波变换器，周波变换器的每一相都由反并联的两组整流桥组成。改变两组整流桥的切换频率就可以改变输出频率。改变整流桥中电力半导体管的门极触发延迟角就可以改变相控周波变换器输出电压的幅值和工作方式，使周波变换器方便地工作于整流和逆变状态，实现四象限运行。整流桥内，为使得每个桥臂具备一定电压的承受能力，一般都采用晶闸管直接串联技术。
第三变频输电子系统的交交变频站采用倍频变压器，倍频变压器为利用铁磁饱和特性构成的三倍频变压器。三倍频变压器可实现基频和三分之一基频交流互联，能量互通。
第一低频电源子系统的低频电源为中远距离(70km-200km)海上或陆上低频风电场，风机采用永磁直驱形式，对其变压器、变频器和环网柜进行改 造，可实现工频风机向低频风机的过渡，使得风机具备直接输出低频电能的能力。
第二低频电源子系统中的电源为中远距离抽水蓄能电站或水电站，电站通过低频改造，可直接输出低频电能，向连接的低频输电系统送电。
上述低频输电系统的控制方式，其内容如下：低频输电系统运行在五端、四端、三端、两端或一端运行状态，其中，五端运行状态为完全运行状态，即三个变频输电子系统和两个低频电源子系统均处于运行状态；所有运行状态中，至少有一个变频输电子系统处于运行状态，否则，低频输电系统不能稳定运行，变频输电子系统和低频电源子系统均具备在线投退能力，在线投退期间都不会影响低频输电系统的正常运行；
当第三变频输电子系统投入运行时，低频输电系统的频率因倍频变压器的缘故，被限制于1/3工频频率值，其他子系统的频率必须跟随该频率值；当第三变频输电子系统退出运行时，低频输电系统的频率可通过频率控制进行调节，但频率范围需要在低频交流变压器和低频交流开关的可运行范围之内。
本发明应用了具体个例对本发明的原理及实施方式进行了阐述，以上实施例的说明只是用于帮助理解本发明的核心思想。应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明原理的前提下，还可以对本发明进行若干改进和修饰，这些改进和修饰也落入本发明权利要求的保护范围内。

Claims (10)

  1. 一种低频输电系统，其特征在于，包括第一变频输电子系统、第二变频输电子系统、第三变频输电子系统，以及第一低频电源子系统和第二低频电源子系统；
    变频输电子系统包括：通过工频交流母线和工频交流变压器与工频交流电网连接的交交变频站，其用于将工频交流电转换为低频交流电；与所述交交变频站连接的第一低频交流开关；
    低频电源子系统包括：低频风电场或抽水蓄能电站/水电站；与低频风电场或抽水蓄能电站/水电站连接的低频交流变压器，其用于将低频电源子系统的低频交流电进行电压变换；与所述低频交流变压器连接的第二低频交流开关；
    所述第一低频交流开关和第二低频交流开关均与所述低频输电网络连接。
  2. 根据权利要求1所述的低频输电系统，其特征在于，所述第二变频输电子系统的交交变频站采用基于晶闸管的周波变换器，所述周波变换器的每一相都由反并联的两组整流桥组成，改变两组整流桥的切换频率就可改变输出频率，改变整流桥中电力半导体管的门极触发延迟角就可改变相控周波变换器输出电压的幅值和工作方式，使周波变换器方便地工作于整流和逆变状态，实现四象限运行。
  3. 根据权利要求2所述的低频输电系统，其特征在于，整流桥内，为使得每个桥臂具备一定电压的承受能力，都采用晶闸管直接串联。
  4. 根据权利要求1所述的低频输电系统，其特征在于，所述第三变频输电子系统的交交变频站采用倍频变压器，所述的倍频变压器为利用铁磁饱和特性构成的三倍频变压器。
  5. 根据权利要求1所述的低频输电系统，其特征在于，所述第一低频电源子系统中的低频电源为中远距离海上或陆上低频风电场，其风机采用永磁直驱形式，对其变压器、变频器和环网柜进行改造，实现工频风机向低频风机的过渡，使得风机能直接输出低频电能。
  6. 根据权利要求1所述的低频输电系统，其特征在于，所述第二低频电源子系 统中的电源为中远距离抽水蓄能电站或水电站，通过低频改造，直接输出低频电能，向连接的低频输电网络送电。
  7. 根据权利要求1所述的低频输电系统，其特征在于，所述的低频输电网络采用放射状或环状结构。
  8. 根据权利要求1-7任一项所述的低频输电系统，其特征在于，所述第一变频输电子系统的交交变频站采用模块化多电平矩阵型换流器，且为三相九桥臂结构，每个桥臂均含有多个全桥子模块且每个桥臂串接电感；
    所述全桥子模块包括：第一带反向二极管的IGBT、第二带反向二极管的IGBT、第三带反向二极管的IGBT、第四带反向二极管的IGBT和第一电容，所述第一带反向二极管的IGBT的集电极与第二带反向二极管的IGBT的集电极和所述第一电容的一端连接，所述第一带反向二极管的IGBT的发射极与所述第三带反向二极管的IGBT的集电极连接作为所述全桥子模块的高压端，所述第三带反向二极管的IGBT的发射极与所述第四带反向二极管的IGBT的发射极和所述第一电容的另一端连接，所述第二带反向二极管的IGBT的发射极与所述第四带反向二极管的IGBT的集电极连接作为所述全桥子模块的低压端。
  9. 根据权利要求8所述的低频输电系统，其特征在于，所述全桥子模块内还含有储能模块，使得模块化多电平矩阵型换流器具备储能功能，为低频输电系统提供功率/能量灵活性调节。
  10. 权利要求1-9任一项所述低频输电系统的控制方式，其特征在于，低频输电系统运行在五端、四端、三端、两端或一端运行状态，其中，五端运行状态为完全运行状态，即三个变频输电子系统和两个低频电源子系统均处于运行状态；所有运行状态中，至少有一个变频输电子系统处于运行状态，否则，低频输电系统不能稳定运行，变频输电子系统和低频电源子系统均具备在线投退能力，在线投退期间都不会影响低频输电系统的正常运行；
    当第三变频输电子系统投入运行时，低频输电系统的频率因倍频变压器的缘故，被限制于1/3工频频率值，其他子系统的频率必须跟随该频率值；当第三变频输电子系统退出运行时，低频输电系统的频率可通过频率控制进行调节，但频率范围需要在低频交流变压器和低频交流开关的可运行范围之内。
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