WO2016101787A1 - 一种孤岛转联网方法 - Google Patents

一种孤岛转联网方法 Download PDF

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Publication number
WO2016101787A1
WO2016101787A1 PCT/CN2015/096747 CN2015096747W WO2016101787A1 WO 2016101787 A1 WO2016101787 A1 WO 2016101787A1 CN 2015096747 W CN2015096747 W CN 2015096747W WO 2016101787 A1 WO2016101787 A1 WO 2016101787A1
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WIPO (PCT)
Prior art keywords
current
inverter
island
overcurrent
transmission system
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PCT/CN2015/096747
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English (en)
French (fr)
Inventor
董云龙
田杰
胡兆庆
李海英
曹冬明
刘海彬
卢宇
Original Assignee
南京南瑞继保电气有限公司
南京南瑞继保工程技术有限公司
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Application filed by 南京南瑞继保电气有限公司, 南京南瑞继保工程技术有限公司 filed Critical 南京南瑞继保电气有限公司
Priority to CA2970125A priority Critical patent/CA2970125C/en
Priority to DK15871856.9T priority patent/DK3211743T3/da
Priority to RU2017118086A priority patent/RU2674167C2/ru
Priority to US15/534,024 priority patent/US10418816B2/en
Priority to EP15871856.9A priority patent/EP3211743B1/en
Priority to KR1020177014862A priority patent/KR101972562B1/ko
Priority to ES15871856T priority patent/ES2761661T3/es
Publication of WO2016101787A1 publication Critical patent/WO2016101787A1/zh

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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
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
    • H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
    • H02H7/122—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for inverters, i.e. dc/ac converters
    • H02H7/1222—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for inverters, i.e. dc/ac converters responsive to abnormalities in the input circuit, e.g. transients in the DC input
    • 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
    • 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
    • H02J3/50—Controlling the sharing of the out-of-phase component
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • 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
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H02J1/04—Constant-current supply systems
    • 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
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/36—Means for starting or stopping converters
    • 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
    • H02M5/40—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 with intermediate conversion into dc
    • H02M5/42—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 with intermediate conversion into dc by static converters
    • H02M5/44—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 with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
    • H02M5/453—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 with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M5/458—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 with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M5/4585—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 with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only having a rectifier with controlled elements
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • 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 belongs to the field of power electronics, and in particular relates to a method for switching islands to flexible networking of a flexible direct current transmission system.
  • Flexible DC transmission uses a voltage source converter to control active power and reactive power independently and quickly, thereby improving system stability, suppressing system frequency and voltage fluctuations, and improving the steady-state performance of the grid-connected AC system.
  • Flexible DC transmission has great advantages in the fields of new energy grid-connected, distributed generation grid-connected, island power supply, and urban distribution network power supply. Therefore, research on flexible DC transmission related technologies is of great significance.
  • the near-end closing in the converter station is connected to the AC grid or the remote switch is closed, and the flexible DC converter station is connected in parallel to the active grid.
  • the flexible DC system needs to be controlled from the current island operation.
  • the mode is switched to the networked active operation control mode to keep the DC transmission system running.
  • the object of the present invention is to provide a method for detecting the change of the operating mode of the power grid into the networking state under the operation of the flexible direct current transmission system, and to ensure that the flexible direct current transmission system is accurately and smoothly changed from the islanding operation to the networked operation.
  • the control system determines whether the flexible DC transmission system enters the network state by detecting whether the current of the inverter bridge arm is overcurrent and the voltage changes on the grid side and the valve side, including the following steps:
  • step (1) In the case of island operation of the converter station of the flexible DC transmission system, check whether the three-phase AC current on the valve side of the converter or the current of the inverter arm is overcurrent, and the overcurrent setting is taken as the rated bridge arm current. n times. If an overcurrent occurs and lasts for a time t1, proceed to step (2), otherwise return to step (1);
  • step (3) blocking the converter, detecting whether the voltage on the AC side is lower than the threshold, if it is lower than the threshold, and lasting for t2, unlocking the inverter, returning to step (1), otherwise proceeding to step (3);
  • phase locking link of the control system is set to track the current AC side voltage phase, and the control mode is switched at the same time.
  • the island control of the current flexible DC transmission system converter station is switched to the active control mode, and the inverter is unlocked.
  • the overcurrent setting value is taken as n times of the rated valve side current of the inverter or the current of the inverter bridge arm, n is in the range of 1 to 10, and the duration t1 is in the range of 0 to 1 s. , t2 ranges from 0 to 1 s;
  • the threshold value of the voltage on the AC side is in the range of 0 to 0.99 pu, and the duration t is in the range of 0 to 1 s;
  • the active power and the reactive power command can maintain the current active power and the reactive power running value, and can also be 0, and can gradually increase to the current running value by the slope.
  • the invention also includes an island-to-network control device, which comprises an inverter detection overcurrent unit, an AC-side voltage detection unit, and an island-to-network mode conversion unit.
  • the converter detects the overcurrent unit to detect whether the three-phase alternating current of the converter valve side or the current of the converter arm current is overcurrent, and the overcurrent setting is taken as The rated bridge arm current is n times; if an overcurrent occurs and lasts for t1, it enters the AC side voltage detection unit, otherwise it returns to the inverter to detect the overcurrent unit.
  • the AC side voltage detecting unit first locks the inverter, and then detects whether the AC side voltage is lower than a threshold. If it is lower than the threshold and lasts for t2, the inverter is unlocked, and the inverter is returned to detect the overcurrent unit to continue detecting. Otherwise, enter the island to network mode conversion unit.
  • the function of the island-to-network mode conversion unit is to perform a control mode conversion.
  • the active power and the reactive power command maintain the current active power and the reactive power running value, or after the conversion, the active power and the reactive power The power is converted to 0 and gradually rises to the pre-conversion run value.
  • the invention also includes an island-to-network control system, which comprises an inverter, an upper controller and a valve control device, wherein (1) in the case of an island operation of a converter station of a flexible direct current transmission system, the upper controller Detecting the three-phase AC current on the valve side of the converter or the overcurrent of the inverter arm current The flow setting is taken as n times the rated bridge arm current; if an overcurrent occurs and lasts for a time t1, the process proceeds to step (2), otherwise returns to step (1);
  • step (3) blocking the converter, detecting whether the voltage on the AC side is lower than the threshold, if it is lower than the threshold, and lasting for t2, unlocking the inverter, returning to step (1), otherwise proceeding to step (3);
  • the upper controller lock phase link sets the current AC side voltage phase and starts the control mode conversion.
  • the island control of the current flexible DC transmission system converter station is switched to the active control mode, and the inverter is unlocked.
  • the invention provides a method for detecting the change of the operating mode of the power grid into the networked state under the operation of the flexible direct current transmission system, and detecting the grid connection time accurately, and can smoothly switch to the network operation mode without causing impact on the power grid.
  • FIG. 1 is a schematic diagram of a dual station structure of a flexible direct current transmission system
  • FIG. 2 is a schematic diagram of a control mode of a grid-connected detection converter station
  • FIG. 3 is a schematic diagram of a control mode of a constant DC voltage control station
  • Figure 4 is a flow chart of flexible DC grid-connected detection in an island operation mode.
  • the flexible DC transmission converter stations 201-202 in the island operation As shown in FIG. 1 , the flexible DC transmission converter stations 201-202 in the island operation, the remote switch 102 is not closed, the flexible DC transmission system 201-202 is not connected to the AC grid 400, and the flexible DC transmission system 201-202 is at The island operation state, 202 is the fixed DC voltage control side, the control mode is shown in Figure 3, 201 is controlled by Figure 2, and Figure 3 is the constant DC voltage control mode, which remains unchanged before and after switching. The state is switched to the active control mode. If the switch 102 is closed, follow the steps below to check (see Figure 4) whether it is turned from island to network:
  • step (1) In the case of island operation of the converter station of the flexible DC transmission system, check whether the three-phase AC current on the valve side of the converter or the current of the inverter arm is overcurrent, and the overcurrent setting is taken as the rated bridge arm current. n times. If an overcurrent occurs and lasts for a time t1, proceed to step (2), otherwise return to step (1);
  • step (3) blocking the converter, detecting whether the voltage on the AC side is lower than the threshold, if it is lower than the threshold, and lasting for t2, unlocking the inverter, returning to step (1), otherwise proceeding to step (3);
  • Control system phase-locking link set to track the current AC side voltage phase, and start the control mode The conversion is switched from the island control of the current flexible DC transmission system to the active control mode, and the inverter is unlocked.
  • duration t1 ranges from 0 to 1 s
  • t2 ranges from 0 to 1 s.
  • the inverter 201 switches from island control to active control mode according to the above steps.
  • the network side 400 is a passive system. After the switch 102 is closed, the bridge arm overcurrent phenomenon does not occur under normal conditions, so the control mode does not change; or the AC side voltage is detected after the inverter is blocked. Below the threshold, the networked detection condition is immediately blocked for a period of time, and the operation from the island operation to the network operation is prohibited, and the inverter trigger pulse is immediately released. At the end of the detection networking process, the inverter 201 still maintains the original island operation state. .
  • the invention also provides an island-to-network control device, comprising an inverter detection over-current unit, an AC-side voltage detection unit, and an island-to-network mode conversion unit; in the case of a flexible DC transmission system converter station island operation, The inverter detects the overcurrent unit to detect whether the three-phase alternating current of the converter valve side or the inverter arm current is overcurrent, and the overcurrent setting is taken as n times of the rated bridge arm current; if overcurrent occurs, The duration t1 enters the AC side voltage detecting unit, otherwise returns to the inverter to detect the overcurrent unit;
  • the AC side voltage detecting unit first locks the inverter, and then detects whether the AC side voltage is lower than a threshold. If it is lower than the threshold and lasts for t2, the inverter is unlocked, and the inverter is returned to detect the overcurrent unit to continue detecting. Otherwise, enter the island-to-network mode conversion unit;
  • the function of the island-to-network mode conversion unit is to perform a control mode conversion.
  • the active power and the reactive power command maintain the current active power and the reactive power running value, or after the conversion, the active power and the reactive power The power is converted to 0 and gradually rises to the pre-conversion run value.
  • the invention also provides an island-to-network control system, comprising an inverter, an upper controller and a valve control device, wherein (1) in the case of an island operation of a converter station of a flexible direct current transmission system, the upper controller detects the inverter Whether the valve-side three-phase AC current or the inverter arm current has an overcurrent condition, and the overcurrent setting is taken as n times the rated bridge arm current; if an overcurrent occurs and the duration is t1, the process proceeds to step (2). Otherwise return to step (1);
  • step (3) blocking the converter, detecting whether the voltage on the AC side is lower than the threshold, if it is lower than the threshold, and lasting for t2, unlocking the inverter, returning to step (1), otherwise proceeding to step (3);
  • the upper controller lock phase link sets the current AC side voltage phase and starts the control mode conversion.
  • the island control of the current flexible DC transmission system converter station is switched to the active control mode, and the inverter is unlocked.

Abstract

本发明公开一种柔性直流输电系统孤岛转联网的切换方法,处于孤岛运行下柔性直流输电系统,通过检测换流器阀侧三相交流电流或换流器桥臂电流是否出现过流现象，以及检测交流侧电压变化情况判断柔性直流输电系统是否进入联网状态,控制系统从孤岛运行控制方式切换到联网控制方式，切换瞬间通过改变功率指令,以及相位跟踪当前电网电压方式,平稳切换到联网控制方式，保持系统持续运行。

Description

一种孤岛转联网方法 技术领域
本发明属于电力电子领域，特别涉及一种柔性直流输电系统孤岛转联网的切换方法。
背景技术
柔性直流输电采用电压源型换流器，可以独立、快速控制控制有功功率和无功功率，从而提高系统的稳定性，抑制系统频率和电压的波动，提高并网交流系统的稳态性能。柔性直流输电在新能源并网、分布式发电并网、孤岛供电、城市配网供电等领域具有较大的优势，因此柔性直流输电相关技术的研究具有重要的意义。
柔性直流输电系统的处于孤岛运行时，换流站内近端合闸接入交流电网或者远端开关合闸，将柔性直流换流站并联进有源电网运行，需要柔性直流系统从当前孤岛运行控制方式转换到联网有源运行控制方式，保持直流输电系统继续运行。
当柔性直流输电系统处于孤岛运行时，如果由于开关合闸操作，导致柔性直流输电系统进入联网状态，需要准确检测柔性直流输电系统进入联网时刻，及时从当前孤岛运行转换到有源运行，否则较长时间会导致电网失步，导致柔性直流输电系统停运，同时还需要平稳切换至联网方式运行，避免切换瞬间引起过流或者过压现象，导致柔性直流输电系统保护动作退出运行。目前柔性直流输电系统孤岛运行下检测电网运行方式变化进入联网的检测方式和平滑控制未见相关报道。
发明内容
本发明的目的，在于提供一种柔性直流输电系统孤岛运行下检测电网运行方式变化进入联网状态方法，保证柔性直流输电系统准确、平滑从孤岛运行转为联网运行。
为了达成上述目的，本发明采用的技术方案是：
控制系统通过检测换流器桥臂电流是否出现过流现象以及网侧和阀侧电压变化情况判断柔性直流输电系统是否进入联网状态，包括如下步骤：
(1)在柔性直流输电系统换流站孤岛运行情况下，检测换流器阀侧三相交流电流或换流器桥臂电流是否出现过流情况，过流定值取为额定桥臂电流的n倍。如果出现过流，并持续时间t1，则进入步骤(2)，否则返回步骤(1)；
(2)闭锁换流器，检测交流侧电压是否低于阈值，如果低于阈值，且持续时间t2，则解锁换流器，返回步骤(1)，否则进入步骤(3)；
(3)控制系统锁相环节设定跟踪当前交流侧电压相位，同时启动控制方式转换，由当前柔性直流输电系统换流站孤岛控制转换到有源控制方式，并解锁换流器。
以上步骤(1)中，过流定值取为换流器额定阀侧电流或者换流器桥臂电流的n倍，n取值范围为1～10，持续时间t1取值范围为0～1s,t2取值范围为0～1s；
以上步骤(2)中，交流侧电压的阈值取值范围为0～0.99pu，持续时间t取值范围为0～1s；
以上步骤(3)所述控制方式转换的瞬间，有功功率和无功功率指令可以维持当前有功功率和无功功率的运行值，也可以为0，可通过斜率逐渐升至当前运行值。
本发明还包括一种孤岛转联网控制装置，其特征在于包括换流器检测过流单元，交流侧电压检测单元，以及孤岛转联网模式转换单元。
在柔性直流输电系统换流站孤岛运行情况下，上述换流器检测过流单元检测换流器阀侧三相交流电流或换流器桥臂电流是否出现过流情况，过流定值取为额定桥臂电流的n倍；如果出现过流，并持续时间t1，则进入交流侧电压检测单元，否则返回换流器检测过流单元。
所述交流侧电压检测单元先闭锁换流器，然后检测交流侧电压是否低于阈值，如果低于阈值，且持续时间t2，则解锁换流器，返回换流器检测过流单元继续进行检测，否则进入孤岛转联网模式转换单元。
所述孤岛转联网模式转换单元作用是进行控制方式转换，在控制方式转换的瞬间，有功功率和无功功率指令维持当前有功功率和无功功率的运行值，或者转换后，有功功率和无功功率转换到0，逐渐升到转换前运行值。
本发明还包括一种孤岛转联网控制系统，其特征在于，包括换流器、上层控制器以及阀控装置，其中，(1)在柔性直流输电系统换流站孤岛运行情况下，上层控制器检测换流器阀侧三相交流电流或换流器桥臂电流是否出现过流情况，过 流定值取为额定桥臂电流的n倍；如果出现过流，并持续时间t1，则进入步骤(2)，否则返回步骤(1)；
(2)闭锁换流器，检测交流侧电压是否低于阈值，如果低于阈值，且持续时间t2，则解锁换流器，返回步骤(1)，否则进入步骤(3)；
(3)上层控制器锁相环节设定跟踪当前交流侧电压相位，同时启动控制方式转换，由当前柔性直流输电系统换流站孤岛控制转换到有源控制方式，并解锁换流器。
采用上述方案后，本发明的有益效果为：
本发明提供的一种柔性直流输电系统孤岛运行下检测电网运行方式变化进入联网状态方法，检测并网时刻准确，可以平滑切换到联网运行方式，不会给电网造成冲击。
附图说明
图1是柔性直流输电系统双站结构示意图；
图2是并网检测换流站控制方式示意图；
图3是定直流电压控制站的控制方式示意图；
图4是孤岛运行方式下的柔性直流并网检测流程图。
具体实施方式
以下将结合附图及具体实施例，对本发明的技术方案进行详细说明。
如图1所示，处于孤岛运行的柔性直流输电换流站201-202，远端开关102未合闸，柔性直流输电系统201-202没有接入交流电网400，柔性直流输电系统201-202处于孤岛运行状态,202为定直流电压控制侧,采用控制方式见图3,201采用图2控制方式,图3为定直流电压控制方式，在切换前后保持不变，图2中并网检测环节检测到联网状态就切换到有功控制方式。如果开关102合闸,按照如下步骤检测(见图4)是否由孤岛转为联网状态运行:
(1)在柔性直流输电系统换流站孤岛运行情况下，检测换流器阀侧三相交流电流或换流器桥臂电流是否出现过流情况，过流定值取为额定桥臂电流的n倍。如果出现过流，并持续时间t1，则进入步骤(2)，否则返回步骤(1)；
(2)闭锁换流器，检测交流侧电压是否低于阈值，如果低于阈值，且持续时间t2，则解锁换流器，返回步骤(1)，否则进入步骤(3)；
(3)控制系统锁相环节设定跟踪当前交流侧电压相位，同时启动控制方式 转换，由当前柔性直流输电系统换流站孤岛控制转换到有源控制方式，并解锁换流器。
以上持续时间t1取值范围为0～1s,t2取值范围为0～1s。
当开关102合上后，如果网侧400为有源状态，则换流器201按照以上步骤从孤岛控制转换到有源控制方式。特殊情况下，网侧400为无源系统，开关102合上后，正常情况下不会出现桥臂过流现象，因此控制方式不转换；或者会因闭锁换流器后，检测到交流侧电压低于阈值，立即封锁该联网检测条件一段时间，禁止从孤岛运行转为联网运行，并且同时立即放开换流器触发脉冲，本次检测联网过程结束，换流器201仍然维持原孤岛运行状态。
本发明还提供一种孤岛转联网控制装置，包括换流器检测过流单元，交流侧电压检测单元，以及孤岛转联网模式转换单元；在柔性直流输电系统换流站孤岛运行情况下，所述换流器检测过流单元检测换流器阀侧三相交流电流或换流器桥臂电流是否出现过流情况，过流定值取为额定桥臂电流的n倍；如果出现过流，并持续时间t1，则进入交流侧电压检测单元，否则返回换流器检测过流单元；
所述交流侧电压检测单元先闭锁换流器，然后检测交流侧电压是否低于阈值，如果低于阈值，且持续时间t2，则解锁换流器，返回换流器检测过流单元继续进行检测，否则进入孤岛转联网模式转换单元；
所述孤岛转联网模式转换单元作用是进行控制方式转换，在控制方式转换的瞬间，有功功率和无功功率指令维持当前有功功率和无功功率的运行值，或者转换后，有功功率和无功功率转换到0，逐渐升到转换前运行值。
本发明还提供一种孤岛转联网控制系统，包括换流器、上层控制器以及阀控装置，其中，(1)在柔性直流输电系统换流站孤岛运行情况下，上层控制器检测换流器阀侧三相交流电流或换流器桥臂电流是否出现过流情况，过流定值取为额定桥臂电流的n倍；如果出现过流，并持续时间t1，则进入步骤(2)，否则返回步骤(1)；
(2)闭锁换流器，检测交流侧电压是否低于阈值，如果低于阈值，且持续时间t2，则解锁换流器，返回步骤(1)，否则进入步骤(3)；
(3)上层控制器锁相环节设定跟踪当前交流侧电压相位，同时启动控制方式转换，由当前柔性直流输电系统换流站孤岛控制转换到有源控制方式，并解锁换流器。
以上实施例仅为说明本发明的技术思想，不能以此限定本发明的保护范围，凡是按照本发明提出的技术思想，在技术方案基础上所做的任何改动，均落入本发明保护范围之内。

Claims (6)

  1. 一种柔性直流输电系统孤岛转联网的切换方法,其特征在于，包括如下步骤：
    (1)在柔性直流输电系统换流站孤岛运行情况下，检测换流器阀侧三相交流电流或换流器桥臂电流是否出现过流情况，过流定值取为额定桥臂电流的n倍；如果出现过流，并持续时间t1，则进入步骤(2)，否则返回步骤(1)；
    (2)闭锁换流器，检测交流侧电压是否低于阈值，如果低于阈值，且持续时间t2，则解锁换流器，返回步骤(1)，否则进入步骤(3)；
    (3)控制系统锁相环节设定跟踪当前交流侧电压相位，同时启动控制方式转换，由当前柔性直流输电系统换流站孤岛控制转换到有源控制方式，并解锁换流器。
  2. 如权利要求1所述的一种柔性直流输电系统孤岛转联网的切换方法,其特征在于，所述步骤(1)中，过流定值取为换流器额定阀侧电流或者换流器桥臂电流的n倍，n取值范围为1～10，持续时间t1取值范围为0～1s,t2取值范围为0～1s。
  3. 如权利要求1所述柔性直流输电系统孤岛转联网的方法，所述步骤(2)中，交流侧电压的阀值取值范围为0～0.99pu，持续时间t取值范围为0～1s。
  4. 如权利要求1所述柔性直流输电系统孤岛转联网的方法，步骤(3)所述控制方式转换的瞬间，有功功率和无功功率指令维持当前有功功率和无功功率的运行值，或者转换后，有功功率和无功功率转换到0，逐渐升到转换前运行值。
  5. 一种孤岛转联网控制装置，其特征在于包括换流器检测过流单元，交流侧电压检测单元，以及孤岛转联网模式转换单元；在柔性直流输电系统换流站孤岛运行情况下，所述换流器检测过流单元检测换流器阀侧三相交流电流或换流器桥臂电流是否出现过流情况，过流定值取为额定桥臂电流的n倍；如果出现过流，并持续时间t1，则进入交流侧电压检测单元，否则返回换流器检测过流单元；
    所述交流侧电压检测单元先闭锁换流器，然后检测交流侧电压是否低于阈值，如果低于阈值，且持续时间t2，则解锁换流器，返回换流器检测过流单元继续进行检测，否则进入孤岛转联网模式转换单元；
    所述孤岛转联网模式转换单元作用是进行控制方式转换，在控制方式转换的瞬间，有功功率和无功功率指令维持当前有功功率和无功功率的运行值，或者转 换后，有功功率和无功功率转换到0，逐渐升到转换前运行值。
  6. 一种孤岛转联网控制系统，其特征在于，包括换流器、上层控制器以及阀控装置，其中，(1)在柔性直流输电系统换流站孤岛运行情况下，上层控制器检测换流器阀侧三相交流电流或换流器桥臂电流是否出现过流情况，过流定值取为额定桥臂电流的n倍；如果出现过流，并持续时间t1，则进入步骤(2)，否则返回步骤(1)；
    (2)闭锁换流器，检测交流侧电压是否低于阈值，如果低于阈值，且持续时间t2，则解锁换流器，返回步骤(1)，否则进入步骤(3)；
    (3)上层控制器锁相环节设定跟踪当前交流侧电压相位，同时启动控制方式转换，由当前柔性直流输电系统换流站孤岛控制转换到有源控制方式，并解锁换流器。
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