WO2018068435A1 - 多端高压直流输电系统换流器在线投入方法 - Google Patents

多端高压直流输电系统换流器在线投入方法 Download PDF

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Publication number
WO2018068435A1
WO2018068435A1 PCT/CN2017/070992 CN2017070992W WO2018068435A1 WO 2018068435 A1 WO2018068435 A1 WO 2018068435A1 CN 2017070992 W CN2017070992 W CN 2017070992W WO 2018068435 A1 WO2018068435 A1 WO 2018068435A1
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Prior art keywords
current
inverter
converter
transmission system
control section
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PCT/CN2017/070992
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English (en)
French (fr)
Inventor
康建爽
曹森
孙巍峰
冯广涛
王亚涛
刘威鹏
李楠
王柏恒
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Xuji Group Co Ltd
XJ Electric Co Ltd
State Grid Corp of China SGCC
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Xuji Group Co Ltd
XJ Electric Co Ltd
State Grid Corp of China SGCC
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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
    • H02J3/36—Arrangements for transfer of electric power between AC networks via high-voltage DC [HVDC] links; Arrangements for transfer of electric power between generators and networks via HVDC links
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Definitions

  • the invention relates to the technical field of direct current transmission, and relates to a method for online input of an inverter of a multi-terminal high voltage direct current transmission system.
  • the inverter with parallel topology has the characteristics of increasing power transmission capacity, enhancing DC transmission reliability and DC transmission flexibility, and the whole system has convenient insulation and high economical operation.
  • the DC transmission capacity can be increased by parallel converters instead of raising the DC voltage level; or for the failure of a certain inverter, It is convenient to exit the faulty converter without interrupting the transmission of DC power; or for the current limit of a converter, the current of the other converter on the parallel side can be increased to maintain the entire DC transmission capacity. constant.
  • the rectification side during normal operation, usually adopts a constant current control mode to ensure a constant DC transmission power; the inverter side adopts a constant arc-extinguishing angle control mode or a constant DC voltage control mode to ensure The rectifier side DC bus voltage is stabilized in a preset interval or a predetermined value.
  • the rectifier-side converter is required to adopt a constant current control mode, and at least one of the inverters on the inverter side is input in a constant voltage control mode.
  • the input When input, if multiple inverters are in constant voltage control mode The input will cause interference to other inverters in operation, resulting in problems such as commutation failure, large fluctuation of the firing angle, and DC voltage fluctuation.
  • the embodiment of the present invention is to provide a method for online input of a multi-terminal high-voltage direct current transmission system converter, which is used to solve the problem that the plurality of inverters are put into operation in the constant voltage control mode on the inverter side in the prior art.
  • the inverter causes interference problems.
  • an embodiment of the present invention provides a method for online input of an inverter for a multi-terminal high voltage direct current transmission system, comprising the following steps:
  • the converter on the control rectifier side operates in a constant current control mode to detect the operating state of the DC transmission system; when the DC transmission system is in the power transmission operation state, the converters on the inverter side to be controlled are controlled in a constant current control mode.
  • the inverter when the direct current transmission system is in a hot standby state, and when only one inverter is input to the inverter side, the inverter is controlled to be put into a constant voltage control mode; when the direct current transmission system is in a hot standby state, and When multiple inverters are input to the inverter side, one of them is controlled to input in a constant voltage control mode, and the other converters are input in a constant current control mode.
  • the multi-terminal HVDC transmission system includes two or more station-level DC transmission systems, and each station-level DC transmission system can operate in a rectification mode or in an inverter mode.
  • each station-level DC transmission system is composed of one converter of the rectifier station and one inverter of each inverter station.
  • the station-level direct current transmission system refers to a single-ended direct current transmission system.
  • the converter operating characteristic curve for the rectifier mode operation in the station-level direct current transmission system is divided into a minimum firing angle control section, a constant DC current control section, and a low-voltage current limiting control section; wherein, the minimum The trigger angle control section is used to solve the problem that when the AC system voltage drops abnormally and the rectifier side loses the constant current control right, the rectifier side is maintained at the minimum firing angle operating state; the constant DC current control section is the normal working section of the rectifier side converter, and is stable. Feeder converter outlet DC Busbar outlet current; low-voltage current-limiting control section is used to automatically limit the DC current reference value to achieve fast recovery of DC transmission system stability.
  • the converter operating characteristic curve of the inverter mode operation in the station-level direct current transmission system is divided into a constant DC voltage control section, a constant arc-extinguishing angle control section, and a constant DC current control.
  • Section 4 design of the section and low-voltage current limiting control section; wherein, under normal circumstances, the converter operates in a constant DC current control section; and the constant DC voltage control section enters a constant DC voltage to prevent normal operation of the converter
  • the control section captures the DC voltage control right of other inverters on the inverter side, and raises its voltage margin setting value; the arc-extinguishing angle control section is used as a limiting section to prevent the arc-extinguishing angle of the inverter side from being too small.
  • the commutation failure occurs; the low-voltage current limiting control section is used to automatically limit the DC current reference value to achieve rapid recovery of the DC transmission system.
  • the converter operating characteristic curve input in the constant current control mode for the inverter mode operation in the station-level direct current transmission system is divided into a constant DC voltage control section, a fixed arc-extinguishing angle control section, and a fixed The four-stage design of the DC current control section and the low-voltage current-limiting control section; wherein, under normal circumstances, the converter operates in a constant DC voltage control section; the fixed arc-extinguishing angle control section is used as a restriction section to prevent the inverter side from operating If the arc extinction angle is too small, the commutation failure occurs; the constant DC current control section enters the constant DC current control section to prevent the normal operation of the converter, and sets a current margin, and the current reference value of the converter is The current reference value of the rectifier side converter is subtracted from the current reference value of the inverter on the inverter side, and the predetermined current margin value is subtracted; the low voltage current limiting control section is used to automatically limit the DC current reference value to achieve a fast
  • a multi-terminal high-voltage direct current transmission system converter online input method a high-voltage direct current transmission system in which two or more inverters are connected in parallel on the inverter side, in the power transmission operation process of the direct current transmission system
  • the inverter-side converter adopts the coordinated control of the constant current control mode to realize the stable online integration of the inverter, and does not interfere with the stable operation of other converters, avoiding the commutation failure, the large fluctuation of the trigger angle, and the DC voltage fluctuation. And so on.
  • the technical solution provided by the embodiment of the present invention can accurately control the power delivered by the inverter, and is convenient to adjust.
  • the degree and other departments flexibly control the transmission power of the inverter, and have practical guiding significance for the design of the actual control strategy of the parallel multi-terminal DC transmission system.
  • 1 is a typical three-terminal parallel direct current power transmission system according to an embodiment of the present invention
  • FIG. 3 is a control characteristic curve of a converter of a typical three-terminal parallel direct current power transmission system according to an embodiment of the present invention
  • FIG. 4 is a logic block diagram of an inverter input online to implement inner loop control according to an embodiment of the present invention
  • FIG. 5 is a waveform diagram of a simultaneous unlocking start recording of a typical three-terminal parallel multi-end system according to an embodiment of the present invention
  • FIG. 6 is a waveform diagram of recording of a typical three-terminal parallel multi-terminal system inverter-side converter after online input according to an embodiment of the present invention.
  • Figure 1 shows a typical three-terminal parallel DC transmission system.
  • the DC transmission system is designed for one-to-two mode, that is, it includes a rectifier station, an inverter station 1 and an inverter station 2, and three converter stations are connected in parallel.
  • the mode is connected to the same DC bus, the inverter station 1 is provided with a first converter and a second converter, and the inverter station 2 is provided with a third converter and a fourth converter.
  • the above three-terminal parallel DC transmission system is a bipolar operation mode, as shown in Fig. 1, which is equivalent to a two-pole operation mode DC transmission system composed of two groups of unipolar operation modes, wherein the first group is a rectifier station exchange Single-pole DC transmission system consisting of inverter Cv0-1, inverter station 1 converter Cv1-1 and inverter station 2 converter Cv2-1, the second group is rectifier station converter Cv0-2, inverter Station 1 converter Single-pole DC transmission system consisting of Cv1-2 and inverter station 2 inverter Cv2-2.
  • the converter rectifier Cv0-1 is operated in a constant current control mode to ensure that the power of the direct current transmission is constant, and then the working state of the direct current transmission system is detected.
  • the corresponding control strategy is selected and put into the inverter side converter.
  • the DC transmission system is in the power transmission operation state, that is, the inverter station Cv1-1 has been operated in the constant DC voltage mode, and then the inverter Cv2-1 is input, only the inverter Cv2-1 is controlled.
  • the constant current control mode is put into operation, the stable in-line integration of the inverter can be realized without disturbing the stable operation of other converters.
  • the normal unlocking mode is selected to be input to the converter, that is, the inverter Cv1 is controlled. -1 is put into operation in constant voltage control mode. If it is necessary to simultaneously input multiple inverters on the inverter side, one of the inverter-side converters is controlled to operate in the constant voltage control mode, and the other inverter-side converters are operated in the constant current control mode.
  • variable station 2 converter Cv2-1 operates in a constant voltage control mode.
  • Figure 3 shows the operation characteristic curve of the first group of single-pole direct current transmission systems of the above three-terminal bipolar direct current transmission system and the direct current transmission system is put into a plurality of inverters in a hot standby state, that is, the inverter side input Inverter station 1 converter Cv1-1 and inverter station 2 converter Cv2-1.
  • the characteristic curve of the rectifier station 1 corresponds to the rectifier-side converter operating characteristic curve shown in FIG.
  • the design curve of the rectifier side converter is divided into three sections, which correspond to the minimum firing angle control section, the fixed DC current control section and the low voltage current limiting control section.
  • the minimum firing angle control section is mainly used to solve the problem that when the AC system voltage drops abnormally and the rectifier side loses the constant current control right, the rectifier side is maintained at the minimum firing angle operating state, generally maintained at 5°; the constant DC current control section is the rectification side.
  • Normal working section of the converter stable DC converter outlet current of the converter inlet; low voltage current limiting
  • the control section is mainly applied to the DC voltage drop caused by the abnormality of the AC system, and automatically limits the DC current reference value to achieve rapid recovery of the DC transmission system.
  • the characteristic curve of the inverter Cv1-1 of the inverter station 1 is shown in Fig. 3.
  • the operating characteristic curve is divided into four sections, namely, the constant DC voltage control section, the fixed arc extinction angle control section, the constant DC current control section, and the low voltage limit. Flow control segment.
  • the inverter Cv1-1 operates in the constant DC current control section; in order to prevent the converter Cv1-1 from entering the constant DC voltage control section under normal operation, the DC voltage control of the inverter side inverter Cv2-1 is captured.
  • the arc-extinguishing angle control section is mainly used to prevent the arc-extinguishing angle of the inverter side from being too small, and the commutation failure occurs.
  • the control section belongs to the limiting section; the low-voltage current limiting control The segment is used to prevent the DC voltage from falling under abnormal conditions such as an AC voltage drop, and automatically limits the DC current reference value to achieve a fast recovery of the DC transmission system.
  • the characteristic curve of inverter 2 converter Cv2-1 is shown in the figure. Its operating characteristic curve is divided into four sections, namely constant DC voltage control section, fixed arc-extinguishing angle control section, constant DC current control section, low-voltage current limiting. Control segment. Under normal circumstances, the converter Cv2-1 runs in the fixed DC voltage control section; the fixed arc-extinguishing angle control section is used as the limiting section to prevent the arc-extinguishing angle of the inverter side from being too small, and the commutation failure occurs; The side converter Cv2-1 enters the constant DC current control section under normal operation, and the current margin is specially set, that is, the current reference value of the inverter side converter Cv2-1 in FIG.
  • the value Idref1 is subtracted from the inverter side converter Cv1-1 current reference value Idref2, and then the predetermined current margin value is subtracted (usually set to 10%); the low voltage current limiting control section is used to prevent abnormalities such as AC voltage drop. In this case, the DC voltage is dropped, and the DC current reference value is automatically limited to achieve a fast recovery of the DC transmission system.
  • Figure 4 shows the logic block diagram of the converter's online input to implement the inner loop control.
  • the specific inner loop control strategy can be understood by referring to the logic block diagram.
  • the arc extinction angle deviation, current deviation, and voltage deviation are selected by the comparator comparison.
  • the deviation calculation is performed for the deviation into the PI proportional-integral controller, and the calculation will be performed.
  • the result is converted into the corresponding firing angle by the inverse cosine change, and the inverter trigger control is performed to realize the predetermined control target.
  • FIG. 5 shows the waveform of the three-terminal parallel DC transmission system simultaneously unlocking and starting the recording.
  • MUDHA11 Sangtuda indicates the DC voltage of the rectifier station
  • A11IDact Sangtuda indicates the DC current of the rectifier station
  • A11firACT Sangtuda indicates the rectifier station.
  • B11IDact Peshawa indicates DC current of inverter station 1
  • B11firACT Peshawa
  • B12IDact Kabul
  • B12firACT indicates the firing angle of inverter station 2
  • B11UctlINV represents the constant voltage control of the inverter station 1
  • B12curCtl represents the constant current control of the inverter station 2.
  • FIG. 6 is a waveform diagram of the recording after the inverter-side converter Cv1-1 is put into operation online, as shown in FIG. 6, after the inverter-side converter Cv1-1 is put into operation, its DC current control is performed.
  • the current is stabilized at 60A, the rectifier-side converter operates in a constant DC current control mode, maintaining its DC exit bus current unchanged, and the inverter-side converter Cv2-1 operates in a constant DC voltage control mode to maintain DC current. Balanced, the current flowing into its inverter is automatically reduced.
  • the above embodiment is a control situation in which the first group of single-pole direct current transmission systems of the three-terminal high-voltage direct current system is put into the inverter, and the method of inputting the second group of the single-pole direct current transmission system into the inverter is similar to the above embodiment, that is,
  • the unipolar system of the bipolar system can implement the above method independently, that is, the two inverters of each inverter station are independently controlled.
  • the bipolar operation of the above high-voltage DC system is actually equivalent to the bipolar operation mode composed of two unipolar operation modes.
  • the bipolar operation mode is split into two unipolar operation modes, according to the unipolar operation mode.
  • the converter input method is discussed. Therefore, the converter online input method of the present invention is also applicable to a unipolar operation HVDC transmission system, and the specific implementation method and the unipolar operation mode split in the above embodiment. the same.
  • the above embodiment is a case where the converter of the three-terminal high-voltage direct current transmission system is put on line.
  • the online input of the inverter of the multi-terminal high-voltage direct current transmission system of the present invention further includes two ends and three or more ends, as shown in FIG. 2 .
  • the specific method is similar to the above embodiment.
  • the technical solution described in the embodiment of the present invention is directed to the design of the on-line deployment of the inverter-side converter, which is one of the difficulties in the multi-terminal flexible direct current transmission system.
  • the inverter-side converter is put into operation online, and during the transient process and the steady-state operation, the stable operation of the already-operated converter station is not affected.
  • a high-voltage direct current transmission system in which two or more inverters are connected in parallel to the inverter side is used to apply a constant current to the inverter-side converter during the power transmission operation of the direct current transmission system.
  • Coordinated control of the control mode enables stable online integration of the inverter, and does not interfere with the stable operation of other converters, avoiding the occurrence of commutation failure, large fluctuation of the trigger angle, and DC voltage fluctuation.
  • the technical solution provided by the embodiment of the invention can realize precise control of the power delivered by the converter, facilitate the scheduling and other departments to flexibly control the transmission power of the converter, and have practical design of the actual control strategy of the parallel multi-terminal direct current transmission system. Guiding significance.
  • the technical solution of the present invention may be a software product in essence or in part contributing to the prior art.
  • a computer software product stored in a storage medium (such as ROM / RAM, disk, CD), including a number of instructions to make a terminal device (can be a mobile phone, computer, server, air conditioner, or Network devices, etc.) perform the methods described in various embodiments of the present invention.
  • the constant current control mode of the inverter on the inverter side is put into operation, and the constant current control mode of the inverter on the inverter side is put into operation, thereby realizing the stable online operation of the inverter. In and without disturbing the stable operation of other inverters.

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Abstract

一种多端高压直流输电系统换流器在线投入方法，包括：通过对逆变侧的一端换流器采用定电压控制模式投入运行、对逆变侧的其它端换流器采用控制模式投入运行，实现换流器的稳定在线并入，并且不会干扰其它换流器的稳定运行。

Description

多端高压直流输电系统换流器在线投入方法 技术领域
本发明涉及直流输电技术领域，涉及一种多端高压直流输电系统换流器在线投入方法。
背景技术
特高压直流输电技术领域中，并联拓扑结构的换流器具有增加送电能力、增强直流输电可靠性和直流输电灵活性等特点，且整个系统绝缘配合方便，运行经济性高。具体地，针对我国西部高海拔地区，如西藏、青海等，受海拔因素影响，可以通过并联换流器代替升高直流电压等级的方式提升直流输送容量；或者针对某个换流器的故障，可以方便退出该故障换流器，且不会中断直流功率的传输；或者针对若某个换流器出现电流限制时，可以通过提高并联侧另一换流器通过的电流，保持整个直流传输容量不变。
现有技术中的双端直流输电系统，在正常运行过程中，整流侧通常采用定电流控制模式，确保直流输送功率恒定；逆变侧采用定熄弧角控制模式或定直流电压控制模式，确保整流侧直流母线电压稳定在预设区间或预定值。
对于多端直流输电系统，要求整流侧换流器采用定电流控制模式，逆变侧的换流器至少一个为定电压控制模式投入，在投入时，如果多个换流器都采用定电压控制模式投入，会对其他正在运行中的换流器造成干扰，导致换相失败、触发角大幅波动、直流电压波动等问题。
发明内容
为克服上述缺陷，本发明实施例期望提供一种多端高压直流输电系统换流器在线投入方法，用于解决现有技术中在逆变侧以定电压控制模式投入多个换流器对正在运行换流器造成干扰的问题。
为实现上述目的，本发明实施例的技术方案是这样实现的：
一方面，本发明实施例提出一种多端高压直流输电系统换流器在线投入方法，包括以下步骤：
控制整流侧的换流器运行于定电流控制模式，检测直流输电系统的工作状态；当直流输电系统处于送电运行状态时，控制需投入的逆变侧的换流器均以定电流控制模式投入。
作为一种实施方式，当直流输电系统处于热备用状态，且当逆变侧只投入一个换流器时，控制该换流器以定电压控制模式投入；当直流输电系统处于热备用状态，且当逆变侧投入多个换流器时，控制其中一个以定电压控制模式投入，其他换流器以定电流控制模式投入。
作为一种实施方式，所述的多端高压直流输电系统包括两个或两个以上的站级直流输电系统，每个站级直流输电系统可以运行于整流模式，亦可运行于逆变模式。
其中，每个站级直流输电系统由整流站的一个换流器、每个逆变站中的一个逆变器组成。
其中，所述站级直流输电系统是指单端直流输电系统。
作为一种实施方式，对于站级直流输电系统中整流模式运行的换流器运行特性曲线，分为最小触发角控制段、定直流电流控制段、低压限流控制段三段设计；其中，最小触发角控制段用于解决当交流系统电压异常下跌，整流侧失去定电流控制权后，将整流侧维持在最小触发角运行状态；定直流电流控制段为整流侧换流器正常工作段，稳定送端换流器出口直流 母线出口电流；低压限流控制段用于自动限制直流电流参考值，达到快速恢复直流输电系统稳定。
作为一种实施方式，对于站级直流输电系统中逆变模式运行以定电压控制模式投入的换流器运行特性曲线，分为定直流电压控制段、定熄弧角控制段、定直流电流控制段、低压限流控制段四段设计；其中，正常情况下，所述换流器运行在定直流电流控制段；定直流电压控制段为防止所述换流器正常运行情况下进入定直流电压控制段，夺取逆变侧其他换流器直流电压控制权，特将其电压裕度设定值抬高；定熄弧角控制段作为限制段，用于防止逆变侧运行熄弧角过小，发生换向失败；低压限流控制段用来自动限制直流电流参考值，达到快速恢复直流输电系统稳定。
作为一种实施方式，对于站级直流输电系统中逆变模式运行的以定电流控制模式投入的所述换流器运行特性曲线，分为定直流电压控制段、定熄弧角控制段、定直流电流控制段、低压限流控制段四段设计；其中，正常情况下，所述换流器运行在定直流电压控制段；定熄弧角控制段作为限制段，用于防止逆变侧运行熄弧角过小，发生换相失败；定直流电流控制段为防止所述换流器正常运行情况下进入定直流电流控制段，设定电流裕度，所述换流器的电流参考值为整流侧换流器电流参考值减去逆变侧其他换流器电流参考值，再减去预定电流裕度值；低压限流控制段用于自动限制直流电流参考值，达到快速恢复直流输电系统稳定。
本发明实施例提出的多端高压直流输电系统换流器在线投入方法，对逆变侧并联两个或两个以上换流器的高压直流输电系统，在直流输电系统送电运行过程中，通过对逆变侧换流器采用定电流控制模式的协调控制，实现换流器的稳定在线并入，并且不会干扰其它换流器的稳定运行，避免换向失败、触发角大幅波动、直流电压波动等情况的发生。同时，本发明实施例提供的技术方案，能够实现对换流器输送功率的精确控制，便于调 度等部门灵活控制换流器的输送功率，并且对并联多端直流输电系统实际控制策略的设计具有实际指导意义。
附图说明
图1是本发明实施例提供的典型三端并联直流输电系统；
图2是本发明实施例提供的典型多端并联直流输电系统；
图3是本发明实施例提供的典型三端并联直流输电系统换流器控制特性曲线；
图4是本发明实施例提供的换流器在线投入实现内环控制的逻辑框图；
图5是本发明实施例提供的典型三端并联多端系统同时解锁启动录波的波形图；
图6是本发明实施例提供的典型三端并联多端系统逆变侧换流器在线投入后的录波的波形图。
具体实施方式
应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。下面结合附图与具体实施方式对本发明做进一步详细描述。
下面结合附图对本发明的具体实施方式作进一步的说明。
图1所示为一典型的三端并联直流输电系统，该直流输电系统为一送二模式设计，即包含一个整流站、逆变站1和逆变站2，且三个换流站采用并联方式连接在同一直流母线上，逆变站1设有第一换流器和第二换流器，逆变站2设有第三换流器和第四换流器。
上述的三端并联直流输电系统为双极运行方式，如图1所示，它相当于两组单极运行方式组成的一个双极运行方式的直流输电系统，其中，第一组为整流站换流器Cv0-1、逆变站1换流器Cv1-1和逆变站2换流器Cv2-1组成的单极直流输电系统，第二组为整流站换流器Cv0-2、逆变站1换流器 Cv1-2和逆变站2换流器Cv2-2组成的单极直流输电系统。以第一组单极直流输电系统为例，首先，控制整流站换流器Cv0-1运行于定电流控制模式，保证直流输送的功率恒定，然后检测直流输电系统的工作状态。
在换流器投入前，根据直流输电系统的工作状态——热备用状态或送电运行状态，选择相应的控制策略投入逆变侧换流器。当直流输电系统处于送电运行状态时，即逆变站1换流器Cv1-1已经运行在定直流电压模式，再投入换流器Cv2-1时，只需控制换流器Cv2-1以定电流控制模式投入运行，即可实现换流器的稳定在线并入，并且不会干扰其它换流器的稳定运行。
当直流输电系统处于热备用状态时，若逆变侧只需投入一个换流器，比如逆变站1换流器Cv1-1，选择正常解锁方式投入该换流器，即控制换流器Cv1-1以定电压控制模式投入运行。若需要同时在逆变侧投入多个换流器，控制其中一个逆变侧换流器运行于定电压控制模式，其他逆变侧换流器运行于定电流控制模式。比如，投入逆变站1换流器Cv1-1和逆变站2换流器Cv2-1，控制其中一个换流器逆变站1换流器Cv1-1运行在定电流控制模式，控制逆变站2换流器Cv2-1运行在定电压控制模式。
图3所示的是以上述三端双极直流输电系统的第一组单极直流输电系统且直流输电系统处于热备用状态下投入多个换流器的运行特性曲线情况，即逆变侧投入逆变站1换流器Cv1-1和逆变站2换流器Cv2-1的情况。整流站1特性曲线对应图1所示的整流侧换流器运行特性曲线。整流侧换流器运行特性曲线设计，将其特性曲线分为三段设计，分别对应最小触发角控制段、定直流电流控制段、低压限流控制段。最小触发角控制段主要用于解决当交流系统电压异常下跌，整流侧失去定电流控制权后，将整流侧维持在最小触发角运行状态，一般维持在5°；定直流电流控制段为整流侧换流器正常工作段，稳定送端换流器出口直流母线出口电流；低压限流 控制段主要应用于受交流系统异常等原因的直流电压下跌，自动限制直流电流参考值，达到快速恢复直流输电系统稳定。
逆变站1换流器Cv1-1的特性曲线如图3所示，其运行特性曲线分四段设计，即定直流电压控制段、定熄弧角控制段、定直流电流控制段、低压限流控制段。正常情况下，换流器Cv1-1运行在定直流电流控制段；为防止换流器Cv1-1正常运行情况下进入定直流电压控制段，夺取逆变侧换流器Cv2-1直流电压控制权，特将其电压裕度设定值抬高；定熄弧角控制段主要用于防止逆变侧运行熄弧角过小，发生换向失败，该控制段属于限制段；低压限流控制段用来防止如交流电压下跌等异常工况下引起直流电压下跌，自动限制直流电流参考值，达到快速恢复直流输电系统稳定。
逆变站2换流器Cv2-1的特性曲线如图所示，其运行特性曲线分四段设计，即定直流电压控制段、定熄弧角控制段、定直流电流控制段、低压限流控制段。正常情况下，换流器Cv2-1运行在定直流电压控制段；定熄弧角控制段作为限制段，用于防止逆变侧运行熄弧角过小，发生换相失败；为防止逆变侧换流器Cv2-1正常运行情况下进入定直流电流控制段，特设定电流裕度，即图3中逆变侧换流器Cv2-1的电流参考值为整流侧换流器电流参考值Idref1减去逆变侧换流器Cv1-1电流参考值Idref2，再减去预定电流裕度值(通常设定为10％)；低压限流控制段用来防止如交流电压下跌等异常工况下引起直流电压下跌，自动限制直流电流参考值，达到快速恢复直流输电系统稳定。
图4所示为换流器在线投入实现内环控制的逻辑框图，具体内环控制策略可参考所述逻辑框图理解。如图4所示，熄弧角偏差、电流偏差、电压偏差通过比较器比较选择，依据运行工况(整流运行或逆变运行)选取对于偏差进入PI比例-积分控制器进行偏差计算，将计算后结果通过反余弦变化转换为对应触发角，进行换流器触发控制，实现预定控制目标。
图5所示为三端并联直流输电系统同时解锁启动录波的波形图，图中：MUDHA11(Sangtuda)表示整流站直流电压，A11IDact(Sangtuda)表示整流站直流电流，A11firACT(Sangtuda)表示整流站触发角，B11IDact(Peshawa)表示逆变站1直流电流，B11firACT(Peshawa)表示逆变站1触发角，B12IDact(Kabul)表示逆变站2直流电流，B12firACT(Kabul)表示逆变站2触发角，B11UctlINV表示逆变站1定电压控制，B12curCtl表示逆变站2定电流控制。
如图5所示，逆变站1换流器Cv1-1运行在定直流电流控制模式，直流电流稳定在60A，逆变站2换流器Cv2-1运行在定直流电压控制模式，整流站直流出口母线电压维持在495.5KV，整流站换流器运行在定直流电流控制模式，其直流母线出口电流维持在130A。附图6所示为逆变侧换流器Cv1-1在线投入运行后的录波的波形图，如图6所示，逆变侧换流器Cv1-1投入运行后，其定直流电流控制器将其电流稳定在60A，整流侧换流器运行在定直流电流控制模式，维持其直流出口母线电流不变，逆变侧换流器Cv2-1运行在定直流电压控制模式，维持直流电流平衡，流入其换流器的电流自动减小。
以上实施例是三端高压直流系统双极的第一组单极直流输电系统投入换流器的控制情况，其第二组单极直流输电系统投入换流器的方法与上述实施例类似，即双极系统的单极系统可以独立实施上述方法，也就是各逆变站的两个换流器实现独立控制。上述高压直流系统的双极运行实际上相当于两个单极运行模式组成的双极运行模式，本实施例中正是将双极运行模式拆分成两个单极运行模式，按照单极运行模式对换流器投入方法进行讨论的，因此，本发明所述的换流器在线投入方法同样适用于单极运行的高压直流输电系统，具体实现方法与上述实施例中拆分的单极运行模式相同。
以上实施例是三端高压直流输电系统换流器在线投入的情况，本发明所述的多端高压直流输电系统换流器的在线投入还包括两端及三端以上的情况，如图2所示，具体方法同上述实施例类似。
本发明实施例所述技术方案针对多端柔性直流输电系统中难点之一即逆变侧换流器在线投入展开设计研究。通过不同换流器间控制器的相互配合，实现逆变侧换流器在线投入运行，并且在投入暂态过程以及稳态运行过程中，不对已经运行换流站的稳定运行产生影响。
本发明实施例所述技术方案，对逆变侧并联两个或两个以上换流器的高压直流输电系统，在直流输电系统送电运行过程中，通过对逆变侧换流器采用定电流控制模式的协调控制，实现换流器的稳定在线并入，并且不会干扰其它换流器的稳定运行，避免换向失败、触发角大幅波动、直流电压波动等情况的发生。同时，本发明实施例提供的技术方案，能够实现对换流器输送功率的精确控制，便于调度等部门灵活控制换流器的输送功率，并且对并联多端直流输电系统实际控制策略的设计具有实际指导意义。
需要说明的是，在本文中，术语“包括”、“包含”或者其任何其他变体意在涵盖非排他性的包含，从而使得包括一系列要素的过程、方法、物品或者装置不仅包括那些要素，而且还包括没有明确列出的其他要素，或者是还包括为这种过程、方法、物品或者装置所固有的要素。在没有更多限制的情况下，由语句“包括一个……”限定的要素，并不排除在包括该要素的过程、方法、物品或者装置中还存在另外的相同要素。
上述本发明实施例序号仅仅为了描述，不代表实施例的优劣。
通过以上的实施方式的描述，本领域的技术人员可以清楚地了解到上述实施例方法可借助软件加必需的通用硬件平台的方式来实现，当然也可以通过硬件，但很多情况下前者是更佳的实施方式。基于这样的理解，本发明的技术方案本质上或者说对现有技术做出贡献的部分可以以软件产品 的形式体现出来，该计算机软件产品存储在一个存储介质(如ROM/RAM、磁碟、光盘)中，包括若干指令用以使得一台终端设备(可以是手机，计算机，服务器，空调器，或者网络设备等)执行本发明各个实施例所描述的方法。
以上仅为本发明的优选实施例，并非因此限制本发明的专利范围，凡是利用本发明说明书及附图内容所作的等效结构或等效流程变换，或直接或间接运用在其他相关的技术领域，均同理包括在本发明的专利保护范围内。
工业实用性
本发明实施例中，通过对逆变侧的一端换流器采用定电压控制模式投入运行、对逆变侧的其它端换流器采用定电流控制模式投入运行，实现换流器的稳定在线并入，并且不会干扰其它换流器的稳定运行。

Claims (6)

  1. 一种多端高压直流输电系统换流器在线投入方法，所述方法包括：
    控制整流侧的换流器运行于定电流控制模式，检测直流输电系统的工作状态；当直流输电系统处于送电运行状态时，控制需投入的逆变侧的换流器均以定电流控制模式投入。
  2. 根据权利要求1所述的多端高压直流输电系统换流器在线投入方法，其中，当直流输电系统处于热备用状态，且当逆变侧只投入一个换流器时，控制该换流器以定电压控制模式投入；当直流输电系统处于热备用状态，且当逆变侧投入多个换流器时，控制其中一个以定电压控制模式投入，其他换流器以定电流控制模式投入。
  3. 根据权利要求2所述的多端高压直流输电系统换流器在线投入方法，其中，所述的多端高压直流输电系统包括两个或两个以上的站级直流输电系统，每个站级直流输电系统由整流站的一个换流器、每个逆变站中的一个逆变器组成。
  4. 根据权利要求3所述的多端高压直流输电系统换流器在线投入方法，其中，对于站级直流输电系统中整流站的换流器运行特性曲线，分为最小触发角控制段、定直流电流控制段、低压限流控制段三段设计；其中，最小触发角控制段用于解决当交流系统电压异常下跌，整流侧失去定电流控制权后，将整流侧维持在最小触发角运行状态；定直流电流控制段为整流侧换流器正常工作段，稳定送端换流器出口直流母线出口电流；低压限流控制段用于自动限制直流电流参考值，达到快速恢复直流输电系统稳定。
  5. 根据权利要求3所述的多端高压直流输电系统换流器在线投入方法，其中，对于站级直流输电系统中逆变站以定电压控制模式投入的换流器运行特性曲线，分为定直流电压控制段、定熄弧角控制段、定直流电流控制段、低压限流控制段四段设计；其中，正常情况下，所述换流器运行在定 直流电流控制段；定直流电压控制段为防止所述换流器正常运行情况下进入定直流电压控制段，夺取逆变侧其他换流器直流电压控制权，特将其电压裕度设定值抬高；定熄弧角控制段作为限制段，用于防止逆变侧运行熄弧角过小，发生换向失败；低压限流控制段用来自动限制直流电流参考值，达到快速恢复直流输电系统稳定。
  6. 根据权利要求3所述的多端高压直流输电系统所述换流器在线投入方法，其中，对于站级直流输电系统中逆变站的以定电流控制模式投入的所述换流器运行特性曲线，分为定直流电压控制段、定熄弧角控制段、定直流电流控制段、低压限流控制段四段设计；其中，正常情况下，所述换流器运行在定直流电压控制段；定熄弧角控制段作为限制段，用于防止逆变侧运行熄弧角过小，发生换相失败；定直流电流控制段为防止所述换流器正常运行情况下进入定直流电流控制段，设定电流裕度，所述换流器的电流参考值为整流侧换流器电流参考值减去逆变侧其他换流器电流参考值，再减去预定电流裕度值；低压限流控制段用于自动限制直流电流参考值，达到快速恢复直流输电系统稳定。
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