WO2020259211A1 - 混合型mmc控制方法及系统 - Google Patents

混合型mmc控制方法及系统 Download PDF

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Publication number
WO2020259211A1
WO2020259211A1 PCT/CN2020/093469 CN2020093469W WO2020259211A1 WO 2020259211 A1 WO2020259211 A1 WO 2020259211A1 CN 2020093469 W CN2020093469 W CN 2020093469W WO 2020259211 A1 WO2020259211 A1 WO 2020259211A1
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Prior art keywords
voltage
value
circulating current
reference value
current
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PCT/CN2020/093469
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English (en)
French (fr)
Inventor
栾洪洲
查鲲鹏
张帆
高瑞雪
黄金魁
白雪
朱晓超
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中电普瑞电力工程有限公司
南瑞集团有限公司
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Publication of WO2020259211A1 publication Critical patent/WO2020259211A1/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
    • 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
    • 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

  • This application relates to the technical field of flexible direct current transmission, in particular to a hybrid MMC control method and system.
  • VSC Grid commutation converter
  • the flexible DC converter has the advantages of independent active and reactive power regulation, weak grid access, no risk of commutation failure, and no need for synchronous networking. It is friendly to build a multi-terminal DC network, realize long-distance power transmission, and renewable energy grid connection Technical means.
  • DC transmission is developing towards higher voltage, larger transmission capacity and longer distance transmission.
  • VSC-LCC hybrid multi-terminal DC transmission is the future development trend.
  • the Udongde project under construction uses two VSC cascades and then parallels with LCC. Form a parallel multi-terminal power grid.
  • the half-bridge topology DC converter valve does not have the ability to clear DC faults. In order to isolate the fault current, a DC circuit breaker needs to be added, which increases equipment costs and increases control complexity.
  • the half-bridge/full-bridge sub-module hybrid modular multilevel converter (MMC) topology uses the full-bridge feature to block the DC side fault current, but the full-bridge sub-module accounts for at least 50%. The smaller the proportion of full-bridge sub-modules, the fewer insulated gate bipolar transistor (IGBT) power components and the lower the equipment cost.
  • IGBT insulated gate bipolar transistor
  • the hybrid MMC has step-down/half-voltage operation, single valve group online switching, and DC fault ride-through functions, if 50% of the full-bridge sub-module is used, the half-bridge sub-module capacitor voltage will no longer be current in the bridge arm When there is a zero-crossing point, it continues to charge and separates from the full-bridge sub-module capacitor voltage, causing the system to collapse. Therefore, the hybrid MMC is used in converter station step-down/half-voltage operation, single valve group online switching and DC fault ride-through conditions , Lack of effective control method system.
  • the embodiment of the application is to provide a hybrid MMC control method and system, which can at least solve the problem of the hybrid MMC in the prior art in the step-down/half-pressure operation of the converter station, the online switching of a single valve group, and the DC failure The problem of lack of an effective control method system under crossing conditions.
  • the embodiment of the present application provides a hybrid MMC control method, including:
  • the input of the hybrid MMC is controlled.
  • the converter voltage reference value determined by the capacitor voltage of the sub-module of the MMC converter valve is implemented through the following steps:
  • the q component of the current reference value is adjusted by the inner loop PI to obtain the q component of the converter voltage reference value.
  • i dref is the d component of the current reference value
  • U c-ref is the average measured value of the capacitor voltage of the MMC converter valve sub-module
  • U c-avr is the set value of the capacitor voltage of the MMC converter valve sub-module
  • k pd1 Is the proportional control coefficient adjusted by the d component inner loop PI
  • k id1 is the integral control coefficient of the d component inner loop PI control
  • i qref is the q component of the current reference value
  • Q ref is the measured value of reactive power
  • Q s is no
  • k pq1 is the proportional control coefficient of the q-component inner loop PI regulation
  • k iq1 is the integral control coefficient of the q-component inner loop PI control.
  • e sd is the d component of the converter voltage reference value
  • u sd is the d component of the MMC converter valve side voltage
  • ⁇ is the angular frequency
  • L Lt+0.5Larm, where Lt is the transformer leakage reactance value
  • Larm is Bridge arm reactor
  • i dref is the d component of the current reference value
  • i d is the d component of the current on the MMC converter valve side
  • k pd2 is the d component outer loop PI control proportional control coefficient
  • k id2 is the d component outer loop
  • e sq is the q component of the converter voltage reference value
  • u sq is the q component of the MMC converter valve side voltage
  • i qref is the q component of the current reference value
  • i q is the MMC conversion
  • k pq2 is the proportional control coefficient of the q component
  • the circulating current injection voltage value determined by the MMC converter valve bridge arm circulating current is realized through the following steps:
  • the expected value of circulation injection with d-axis and q-axis components is formulated through trigonometric function transformation
  • the circulating current injection amplitude is a preset multiple of the DC component of the bridge arm current.
  • the reference value of the three-phase circulating current voltage is calculated according to the bridge arm circulating current, the phase angle value, and the expected value of circulating current injection, as the circulating current injection voltage value, including:
  • the bridge arm circulating current is transformed by dq (Parker) to obtain the dq bridge arm circulating current and voltage feedforward quantity;
  • the initial circulating current injection voltage value is differentiated from the voltage feedforward amount, and park (Parker) inverse transformation is performed to obtain the circulating current injection voltage value.
  • the DC voltage set value established by the DC current set value is realized through the following steps:
  • the measured value of the direct current and the given value are differentiated and adjusted by PI to obtain the given value of the direct current voltage.
  • control pulse signal is formulated according to the converter voltage reference value determined by the reactive power and the active power, the preset circulating current suppression voltage and the DC voltage set value, and the control pulse signal is based on the control pulse signal ,
  • Control the investment of the hybrid MMC including:
  • the current reference value is obtained through the inner loop PI adjustment, and the current reference value is adjusted through the outer loop PI to obtain the converter voltage reference value;
  • a control pulse signal is formulated, and the input of the hybrid MMC is controlled according to the control pulse signal.
  • An embodiment of the application provides a hybrid MMC control system, the system includes: an inverter, a circulating current suppression controller, a mode selection controller, and a control pulse generator; wherein,
  • the inverter is configured to formulate a reference value of the inverter voltage
  • the circulating current suppression controller is configured to formulate the circulating current suppression voltage value under the converter station step-down/half-pressure operation, single valve group online switching and DC fault ride-through conditions;
  • the mode selection controller is configured to set the DC voltage given value under the converter station step-down/half-pressure operation, single valve group online switching and DC fault ride-through conditions;
  • the pulse control generator is configured to formulate control pulse signals for converter station step-down/half-pressure operation, single valve group online switching and DC fault ride-through conditions, and control the input of hybrid MMC according to the control pulse signal.
  • the circulating current suppression controller is configured to set a circulating current suppression voltage value under normal operating conditions
  • the mode selection controller is configured to set a given value of DC voltage under normal operating conditions
  • the pulse control generator is configured to formulate control pulses under normal operating conditions and control the input of the hybrid MMC.
  • the inverter includes:
  • the outer loop power controller is configured to, under normal operating conditions, set the current reference value under normal operating conditions according to the reactive power and active power at the common connection point of the MMC converter valve through the outer loop PI adjustment ; Under the converter station step-down/half-pressure operation, single valve group online switching and DC fault ride-through conditions, according to the MMC converter valve neutron module capacitor voltage and reactive power reference value, through the outer loop PI adjustment, formulate Current reference value under special working conditions;
  • the inner loop power controller is configured to adjust the inverter voltage reference value under normal operating conditions through the inner loop PI adjustment according to the current reference value under normal operating conditions; according to the current reference value under special operating conditions, pass Inner loop PI adjustment, formulating the inverter voltage reference value under special working conditions.
  • the circulating current suppression controller sets the circulating current suppression voltage of the MMC converter valve to 0 under normal operating conditions
  • the circulating current suppression controller formulates the circulating current injection voltage value according to the grid current under the converter station step-down/half-voltage operation, single valve group online switching and DC fault ride-through conditions.
  • the circulation suppression controller includes:
  • Phase angle control module Phase angle control module, circulating current injection given module and circulating current injection control module
  • the phase angle control module performs park transformation and angle transformation according to the grid current to obtain the phase angle value injected by the circulating current;
  • the circulation injection given module according to the phase angle value and the circulation injection amplitude, through trigonometric function transformation, formulates the expected circulation injection value with d-axis and q-axis components;
  • the circulating current injection control module calculates the circulating current injection voltage value according to the bridge arm circulating current, the phase angle value and the expected value of circulating current injection;
  • the circulating current injection amplitude is a preset multiple of the DC component of the bridge arm current.
  • the mode selection controller sets a fixed-amplitude DC voltage given value under normal operating conditions
  • the mode selection controller is configured to make the difference between the DC current measurement value and the given value under the converter station step-down/half-pressure operation, single valve group online switching and DC fault ride-through conditions, and pass PI is adjusted to obtain a given value of DC voltage.
  • the technical solutions provided by the embodiments of this application include: when in converter station step-down/half-pressure operation, single valve group on-line commissioning and retreating, and DC fault ride-through conditions, it is determined based on the capacitor voltage of the neutron module of the MMC converter valve
  • the inverter voltage reference value, the circulating current injection voltage value determined by the MMC converter valve bridge arm circulating current and the DC voltage setting value determined by the DC current setting value, the control pulse signal is formulated, and the hybrid MMC is controlled according to the control pulse signal Investment.
  • the technical solutions provided in the embodiments of this application can be used in the converter station step-down/half-pressure operation, single valve group online switching and DC fault ride-through conditions, according to the commutation determined by the capacitor voltage of the sub-module of the MMC converter valve
  • the voltage reference value of the converter ensures the zero-crossing point of the MMC bridge arm current and realizes the balance of the capacitor voltage, avoiding the system caused by the capacitor voltage continuing to charge when the bridge arm current no longer has the zero-crossing point, and the voltage separation from the full bridge sub-module capacitor voltage.
  • the problem of crash In this scheme, the circulating current injection voltage value determined by the circulating current of the MMC converter valve arm, through the circulating current injection link, makes the bridge arm current always have a zero-crossing point, ensuring the safe operation of the MMC arm.
  • Figure 1 is a control block diagram of a hybrid MMC of this application
  • Figure 2 is a block diagram of the overall control of a traditional MMC in an embodiment of the application
  • FIG. 3 is a block diagram of the circulation injection control of this application.
  • FIG. 4 is a block diagram of the fundamental frequency separation phase lock angle control block diagram of this application.
  • Figure 5 is a block diagram of the given value of circulating current injection in this application.
  • This embodiment provides a hybrid MMC control method, including:
  • the input of the hybrid MMC is controlled.
  • the plan is to formulate the control pulse.
  • the specific formulation process is as described in the relevant plan.
  • the investment of the hybrid MMC according to the formulated control pulse signal can effectively control the investment of the MMC.
  • P ref and Q ref are the command values of active and reactive power input to the outer loop power controller
  • i d_ref and i q_ref are the dq axis current reference values output by the outer loop power controller.
  • the control system After adding the circulating current suppression additional control signal u cirj_ref , the control system finally outputs the upper and lower bridge arm voltage reference signals u pj_ref and unj_ref , which are the converter voltage reference values, and then generate the corresponding values through the multi-level carrier phase shift modulation algorithm Trigger pulse to control the turn-on and turn-off of each sub-module.
  • the hybrid MMC control block diagram is shown in Figure 1, where U c_avr is the average of the sub-module capacitor voltage The difference between the value and the preset value, and then through the PI adjustment of the outer loop, the d component of the current reference value is obtained; the q component of the current reference value is obtained in the same way as the traditional way, and the MMC converter valve is connected to the common point The measured value of reactive power at the position is different from the preset value. After the outer loop PI is adjusted, the q component of the current reference value is obtained. The dq component of the current reference value is adjusted by the inner loop PI to obtain Converter voltage reference value.
  • i dref is the d component of the current reference value
  • U c-ref is the average measured value of the capacitor voltage of the MMC converter valve sub-module
  • U c-avr is the set value of the capacitor voltage of the MMC converter valve sub-module
  • k pd1 Is the proportional control coefficient adjusted by the d component inner loop PI
  • k id1 is the integral control coefficient of the d component inner loop PI control
  • i qref is the q component of the current reference value
  • Q ref is the measured value of reactive power
  • Q s is no
  • k pq1 is the proportional control coefficient of the q-component inner loop PI regulation
  • k iq1 is the integral control coefficient of the q-component inner loop PI control.
  • e sd is the d component of the converter voltage reference value
  • u sd is the d component of the MMC converter valve side voltage
  • ⁇ is the angular frequency
  • L Lt+0.5Larm, where Lt is the transformer leakage reactance value
  • Larm is Bridge arm reactor
  • i dref is the d component of the current reference value
  • i d is the d component of the current on the MMC converter valve side
  • k pd2 is the d component outer loop PI control proportional control coefficient
  • k id2 is the d component outer loop
  • e sq is the q component of the converter voltage reference value
  • u sq is the q component of the MMC converter valve side voltage
  • i qref is the q component of the current reference value
  • i q is the MMC
  • k pq2 is the proportional control coefficient of the q component outer loop PI control
  • k pq2
  • the control system is divided into outer loop control and inner loop control.
  • the circulation suppression in the inner loop control is basically the same as the half-bridge MMC.
  • the difference is: the d-axis current reference value I dref is directly obtained by the sub-module capacitor voltage controller instead of the DC voltage controller.
  • the setting of the DC voltage reference value U dcref is related to the control mode. When the station is in voltage control mode, U dcref is directly set to U dcref _ set ; in current mode, it is given by the DC current controller.
  • the mode selection logic realizes the switching between the DC current controller and the voltage controller.
  • the hybrid MMC active class outer loop control adopts constant DC voltage or constant active power control, and the reactive class outer loop control adopts constant AC voltage or reactive power control, and the circulating current is suppressed to 0; converter station step-down /Under half-voltage operation, single valve group online switching and DC fault ride-through conditions, the active power class outer loop controls the capacitor voltage of the stator module of the high valve group, the DC voltage set value adopts constant DC current control, and the low valve group has a fixed DC voltage or Constant active power and reactive power outer loop control adopt constant AC voltage or reactive power control.
  • the circulating current is switched to circulating current injection, and the system power voltage returns to normal, the control mode switches back to normal operating conditions and the circulating current injection mechanism is exited.
  • Circulating current injection control block diagram as shown in Figure 3.
  • PI proportional integral
  • the dq axis reference values u cird_ref and u cirq_ref are obtained through the inverse transformation of dq/abc coordinates, which is the circulating current injection voltage value.
  • i 2fd_ref and i 2fq_ref take the size of the circulating current expected to be injected, and the size of the circulating current injection is a fixed value, which is about 0.4 to 0.6 times the direct current.
  • the phase of the circulating current injection is in phase (I dc ⁇ 0) or opposite phase (I dc >0) with the reactive component of the real-time bridge arm.
  • the control block diagram of the grid voltage phase-locked angle as shown in Figure 4, the grid voltages E sa , E sb , E sc are phase-locked through PLL to obtain the grid voltage angle angle for coordinate transformation.
  • the grid currents i sa , i sb and i sc are transformed by abc/dq to obtain the AC currents i sd and i sq under the dq coordinate, and then through arctan (arctangent) transformation to obtain the angle theata1, add 90° or subtract 90° to theata1 to obtain the angle theata, used for coordinate system transformation in circulation injection and the phase of circulation injection.
  • Circulating current injection setpoint control block diagram using the angle theata obtained by separating the fundamental frequency to obtain i 2fd_ref and i 2fq_ref through cos (cosine) and sin (sine) operations.
  • amplifier is the amplitude of the circulation
  • the angle theata obtained by separating the fundamental frequency is obtained by cos and sin operations to obtain i 2fd_ref and i 2fq_ref respectively .
  • Ampl is also needed to be substituted, and Acos and Asin operations are performed.
  • A is the maximum amplitude of cos and sin.
  • the mode selects the preset DC voltage setting value; when the converter station is in step-down/half-pressure operation, single valve group online switching, and DC fault ride-through conditions, the The measured value of the DC current is different from the given value, and the given value of DC voltage is obtained through PI adjustment.
  • control pulse signal is formulated according to the converter voltage reference value established by reactive power and active power, the preset circulating current suppression voltage and the DC voltage set value, and the control pulse signal is controlled according to the control pulse signal.
  • the MMC When in the converter station step-down/half-pressure operation, single valve group on-line switching, and DC fault ride-through conditions, according to the converter voltage reference value established by the MMC converter valve neutron module capacitor voltage, the MMC exchanges
  • the circulating current injection voltage set by the circulating current of the flow valve bridge arm and the DC voltage set value set by the DC current set value are used to set the control pulse and control the input of the hybrid MMC.
  • the technical solution in the embodiment of this application can be based on the commutation determined by the capacitor voltage of the sub-module of the MMC converter valve in the converter station step-down/half-pressure operation, single valve group online switching and DC fault ride-through conditions
  • the voltage reference value of the converter ensures the zero-crossing point of the MMC bridge arm current, and realizes the balance of the capacitor voltage, and avoids the system crash caused by the capacitor voltage that continues to charge when the bridge arm current does not have the zero-crossing point, and is separated from the full-bridge sub-module capacitor voltage.
  • the circulating current injection voltage value determined by the circulating current of the MMC converter valve arm, through the circulating current injection link makes the bridge arm current always have a zero-crossing point, ensuring the safe operation of the MMC arm.
  • This embodiment provides a hybrid MMC control method system, including:
  • Inverter circulating current suppression controller, mode selection controller and control pulse generator
  • the inverter is configured to formulate a reference value of the inverter voltage
  • the circulating current suppression controller is configured to formulate the circulating current suppression voltage value under normal operating conditions and converter station step-down/half-pressure operation, single valve group online switching and DC fault ride-through conditions;
  • the mode selection controller is configured to set a given value of DC voltage under normal operating conditions and converter station step-down/half-pressure operation, single valve group online switching and DC fault ride-through conditions;
  • the pulse control generator is configured to formulate control pulse signals under normal operating conditions and converter station step-down/half-pressure operation, single valve group online switching and DC fault ride-through conditions, and control the control pulse signal according to the control pulse signal. Investment in hybrid MMC.
  • the inverter includes:
  • the outer loop power controller is configured to, under normal operating conditions, set the current reference value under normal operating conditions according to the reactive power and active power at the common connection point of the MMC converter valve through the outer loop PI adjustment ; Under the converter station step-down/half-pressure operation, single valve group online switching and DC fault ride-through conditions, according to the MMC converter valve neutron module capacitor voltage and reactive power reference value, through the outer loop PI adjustment, formulate Current reference value under special working conditions;
  • the inner loop power controller is configured to adjust the inverter voltage reference value under normal operating conditions through the inner loop PI adjustment according to the current reference value under normal operating conditions; according to the current reference value under special operating conditions, pass Inner loop PI adjustment, formulating the inverter voltage reference value under special working conditions.
  • the circulating current suppression controller sets the circulating current suppression voltage of the MMC converter valve to 0 under normal operating conditions
  • the circulating current suppression controller formulates the circulating current injection voltage value according to the grid current under the converter station step-down/half-voltage operation, single valve group online switching and DC fault ride-through conditions.
  • the circulation suppression controller includes:
  • Phase angle control module Phase angle control module, circulating current injection given module and circulating current injection control module
  • the phase angle control module performs park transformation and angle transformation according to the grid current to obtain the phase angle value injected by the circulating current;
  • the circulation injection given module according to the phase angle value and the circulation injection amplitude, through trigonometric function transformation, formulates the expected circulation injection value with d-axis and q-axis components;
  • the circulating current injection control module calculates the circulating current injection voltage value according to the bridge arm circulating current, the phase angle value and the expected value of circulating current injection;
  • the circulating current injection amplitude is a preset multiple of the DC component of the bridge arm current.
  • the mode selection controller sets a fixed-amplitude DC voltage given value under normal working conditions
  • the mode selection controller makes the difference between the DC current measurement value and the given value under the converter station step-down/half-pressure operation, single valve group online switching and DC fault ride-through conditions, and adjusts it through PI, Get the given value of DC voltage.
  • the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, this application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.
  • a computer-usable storage media including but not limited to disk storage, CD-ROM, optical storage, etc.
  • These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing equipment to work in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including the instruction device.
  • the device implements the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.
  • These computer program instructions can also be loaded on a computer or other programmable data processing equipment, so that a series of operation steps are executed on the computer or other programmable equipment to produce computer-implemented processing, so as to execute on the computer or other programmable equipment.
  • the instructions provide steps for implementing functions specified in a flow or multiple flows in the flowchart and/or a block or multiple blocks in the block diagram.
  • the technical solutions in the embodiments of this application can obtain the converter voltage reference value under the converter station step-down/half-pressure operation, single valve group online switching and DC fault ride-through conditions;
  • the control pulse signal is formulated according to the voltage reference value, the circulating current injection voltage value and the DC voltage given value; according to the control The pulse signal controls the input of the hybrid MMC.
  • the converter voltage reference value determined by the capacitor voltage of the sub-module of the MMC converter valve ensures the zero-crossing point of the MMC bridge arm current, realizes the balance of the capacitor voltage, and avoids the zero-crossing point of the bridge arm current due to the capacitor voltage.

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Abstract

本申请实施例公开了一种混合型MMC控制方法及系统，其中所述方法包括：换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，根据由MMC换流阀中子模块电容电压制定的换流器电压参考值，由桥臂环流制定的环流注入电压值和由直流电流给定值制定的直流电压给定值，制定控制脉冲信号，依据控制脉冲信号，控制所述混合型MMC的投入。

Description

混合型MMC控制方法及系统
相关申请的交叉引用
本申请基于申请号为201910563456.1、申请日为2019年06月26日的中国专利申请提出，并要求该中国专利申请的优先权，该中国专利申请的内容在此以引入方式并入本申请。
技术领域
本申请涉及柔性直流输电技术领域，具体涉及一种混合型MMC控制方法及系统。
背景技术
面对全球能源安全、环境污染和气候变化的严峻挑战，国家大力开发和利用可再生清洁能源，优化能源结构。电网换相换流器(LCC)成熟、可靠，是高效的远距离大容量输电方式，但存在弱交流系统下的高换相失败风险。柔性直流换流器(VSC)具有有功无功独立调节、弱电网接入、无换相失败风险、无需同步联网等优点，是构建多端直流网络、实现远距离输电、可再生能源并网的友好技术手段。直流输电向着更高电压、更大传输容量和更远距离输电的方向发展，VSC-LCC混合多端直流输电是未来的发展趋势，在建的乌东德工程采用两个VSC级联后同LCC并联形成并联多端电网。
半桥拓扑直流换流阀不具备直流故障清除能力，为了隔离故障电流需要增加直流断路器，增加了设备成本，增大了控制复杂度。半桥/全桥子模块混合型模块化多电平换流器(MMC)拓扑，利用全桥特性阻断直流侧故障电流，但全桥子模块占比至少50％。全桥子模块占比越小，绝缘栅双极型晶体管(IGBT)功率元件越少，设备成本越低。混合型MMC若具有降 压/半压运行、单阀组在线投退、以及直流故障穿越功能，如果采用50％的全桥子模块占比，半桥子模块电容电压会在桥臂电流不再有过零点时仍持续充电，与全桥子模块电容电压分离，导致系统崩溃，因此，混合型MMC在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，缺少有效的控制方法体系。
发明内容
本申请实施例在于提供一种混合型MMC控制方法及系统，至少能够解决现有技术中所存在的混合型MMC在换流站降压/半压运行、单阀组在线投退、以及直流故障穿越工况下，缺少有效的控制方法体系的问题。
本申请实施例提供的技术方案是：
本申请实施例提供一种混合型MMC控制方法，包括：
正常工况下，根据由无功功率和有功功率制定的换流器电压参考值、预设的环流抑制电压和直流电压给定值，制定控制脉冲信号，并控制所述混合型MMC的投入；
当在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，获得换流器电压参考值；
获得由MMC换流阀桥臂环流制定的环流注入电压值和由直流电流给定值制定的直流电压给定值；
根据所述电压参考值、环流注入电压值和所述直流电压给定值，制定控制脉冲信号；
依据控制脉冲信号，控制所述混合型MMC的投入。
前述方案中，当在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，根据由MMC换流阀中子模块电容电压制定的换流器电压参考值，由MMC换流阀桥臂环流制定的环流注入电压值和由直流电流给定值制定的直流电压给定值，制定控制脉冲信号，并控制所述混合型MMC 的投入。
前述方案中，所述由MMC换流阀中子模块电容电压制定的换流器电压参考值，通过下述步骤来实现：
将MMC换流阀中子模块电容电压的平均测量值与设定值作差，并通过外环PI(比例-积分混合变量)调节，得到电流参考值的d分量(d轴分量)；
将所述电流参考值的d分量通过内环PI调节，得到换流器电压参考值的d分量；
将MMC换流阀公共连接点处无功功率的测量值与设定值作差，并通过外环PI调节，得到电流参考值的q分量(q轴分量)；
将所述电流参考值的q分量通过内环PI调节，得到换流器电压参考值的q分量。
前述方案中，所述电流参考值的d分量和q分量的制定，分别如下式所示：
Figure PCTCN2020093469-appb-000001
Figure PCTCN2020093469-appb-000002
其中，i dref为电流参考值的d分量，U c-ref为MMC换流阀子模块电容电压的平均测量值，U c-avr为MMC换流阀子模块电容电压的设定值，k pd1为d分量内环PI调节的比例控制系数，k id1为d分量内环PI控制的积分控制系数，i qref为电流参考值的q分量，Q ref为无功功率的测量值，Q s为无功功率的设定值，k pq1为q分量内环PI调节的比例控制系数，k iq1为q分量内环PI控制的积分控制系数。
前述方案中，所述换流器电压参考值的d分量和q分量的计算，分别 如下式所示：
Figure PCTCN2020093469-appb-000003
Figure PCTCN2020093469-appb-000004
其中，e sd为换流器电压参考值的d分量，u sd为MMC换流阀侧电压的d分量，ω为角频率，L＝Lt+0.5Larm，其中Lt为变压器漏抗值，Larm为桥臂电抗器，i dref为所述电流参考值的d分量，i d为MMC换流阀侧电流的d分量，k pd2为d分量外环PI控制比例控制系数，k id2为d分量外环PI控制的积分控制系数，e sq为换流器电压参考值的q分量，u sq为MMC换流阀侧电压的q分量，i qref为所述电流参考值的q分量，i q为MMC换流阀侧电流的q分量，k pq2为q分量外环PI控制比例控制系数，k iq2为q分量外环PI控制的积分控制系数。
前述方案中，所述由MMC换流阀桥臂环流制定的环流注入电压值，通过下述步骤来实现：
将电网电流，进行park变换和角度变换，得到环流注入的相角值；
根据所述相角值和环流注入幅值，通过三角函数变换，制定具有d轴和q轴分量的环流注入期望值；
根据所述桥臂环流、相角值和环流注入期望值，计算得到环流注入电压值；
其中，所述环流注入幅值为桥臂电流直流分量的预设倍数。
前述方案中，根据所述桥臂环流、相角值和环流注入期望值，计算得到三相环流电压参考值，作为环流注入电压值，包括：
将所述桥臂环流，通过dq(派克)变换，得到dq桥臂环流和电压前馈 量；
将所述dq桥臂环流和环流注入期望值，进行PI调节，得到初始环流注入电压值；
将所述初始环流注入电压值与电压前馈量作差，并进行park(派克)反变换，得到环流注入电压值。
前述方案中，所述由直流电流给定值制定的直流电压给定值，通过下述步骤来实现：
将所述直流电流测量值与给定值作差，并通过PI调节，得到直流电压给定值。
前述方案中，所述正常工况下，根据由无功功率和有功功率制定的换流器电压参考值、预设的环流抑制电压和直流电压给定值，制定控制脉冲信号，依据控制脉冲信号，控制所述混合型MMC的投入，包括：
基于所述MMC换流阀公共连接点处的无功功率和有功功率，通过内环PI调节得到电流参考值，将所述电流参考值通过外环PI调节得到换流器电压参考值；
将MMC换流阀的环流抑制电压设置为0；
根据所述电压参考值、环流抑制电压和所述直流电压给定值，制定控制脉冲信号，依据控制脉冲信号，控制所述混合型MMC的投入。
本申请实施例提供一种混合型MMC控制系统，所述系统包括：换流器、环流抑制控制器、模式选择控制器和控制脉冲发生器；其中，
所述换流器，配置为制定换流器电压参考值；
所述环流抑制控制器，配置为制定换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下的环流抑制电压值；
所述模式选择控制器，配置为制定换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下的直流电压给定值；
所述脉冲控制发生器，配置为制定换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下的控制脉冲信号，依据控制脉冲信号，控制混合型MMC的投入。
前述方案中，
所述环流抑制控制器，配置为制定正常工况下的环流抑制电压值；
所述模式选择控制器，配置为制定正常工况下的直流电压给定值；
所述脉冲控制发生器，配置为制定正常工况下的控制脉冲，并控制所述混合型MMC的投入。
前述方案中，所述换流器，包括：
外环功率控制器和内环功率控制器；
所述外环功率控制器，配置为在正常工况下，根据所述MMC换流阀公共连接点处的无功功率和有功功率，通过外环PI调节，制定正常工况下的电流参考值；在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，根据MMC换流阀中子模块电容电压和无功功率参考值，通过外环PI调节，制定特殊工况下的电流参考值；
所述内环功率控制器，配置为根据正常工况下的电流参考值，通过内环PI调节，制定正常工况下的换流器电压参考值；根据特殊工况下的电流参考值，通过内环PI调节，制定特殊工况下的换流器电压参考值。
前述方案中，所述环流抑制控制器，在正常工况下，将MMC换流阀的环流抑制电压设置为0；
所述环流抑制控制器，在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，根据电网电流，制定环流注入电压值。
前述方案中，所述环流抑制控制器，包括：
相角控制模块、环流注入给定模块和环流注入控制模块；
所述相角控制模块，根据电网电流，进行park变换和角度变换，得到 环流注入的相角值；
所述环流注入给定模块，根据所述相角值和环流注入幅值，通过三角函数变换，制定具有d轴和q轴分量的环流注入期望值；
所述环流注入控制模块，根据所述桥臂环流、相角值和环流注入期望值，计算得到环流注入电压值；
其中，所述环流注入幅值为桥臂电流直流分量的预设倍数。
前述方案中，所述模式选择控制器在正常工况下，设置固定幅值的直流电压给定值；
所述模式选择控制器，配置为在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，将所述直流电流测量值与给定值作差，并通过PI调节，得到直流电压给定值。
与现有技术相比，本申请实施例的有益效果为：
本申请实施例提供的技术方案，包括：当在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，根据由MMC换流阀中子模块电容电压制定的换流器电压参考值，由MMC换流阀桥臂环流制定的环流注入电压值和由直流电流给定值制定的直流电压给定值，制定控制脉冲信号，依据控制脉冲信号，控制混合型MMC的投入。
本申请实施例提供的技术方案，可在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，根据由MMC换流阀中子模块电容电压制定的换流器电压参考值，保证了MMC桥臂电流过零点，实现电容电压平衡，避免了由于电容电压在桥臂电流不再有过零点时仍继续充电、与全桥子模块电容电压分离而导致的系统崩溃的问题。本方案中由MMC换流阀桥臂环流制定的环流注入电压值，通过环流注入环节，使得桥臂电流始终存在过零点，保证了MMC桥臂的安全运行。
附图说明
图1为本申请的一种混合型MMC控制框图；
图2为本申请实施例中传统MMC整体控制框图；
图3为本申请的环流注入控制框图；
图4为本申请的基频分离锁相角控制框图；
图5为本申请的环流注入给定值框图。
具体实施方式
为了更好地理解本申请，下面结合说明书附图和实例对本申请的内容做进一步的说明。
实施例1：
本实施例提供了一种混合型MMC控制方法，包括：
正常工况下，根据由无功功率和有功功率制定的换流器电压参考值、预设的环流抑制电压和直流电压给定值，制定控制脉冲信号，并控制所述混合型MMC的投入；
当在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，获得换流器电压参考值；
获得由MMC换流阀桥臂环流制定的环流注入电压值和由直流电流给定值制定的直流电压给定值；
根据所述电压参考值、环流注入电压值和所述直流电压给定值，制定控制脉冲信号；
依据控制脉冲信号，控制所述混合型MMC的投入。
作为一个实现方案，当在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，根据由MMC换流阀中子模块电容电压制定的换流器电压参考值，由MMC换流阀桥臂环流制定的环流注入电压值和由直流电流给定值制定的直流电压给定值，制定控制脉冲信号，并控制所述混合 型MMC的投入。
可以理解，本申请实施例中，在正常工况下或非正常工况下(在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下)，采用不同的方案进行控制脉冲的制定，具体制定过程如相关方案所述，依据制定的控制脉冲信号进行混合型MMC的投入，可有效控制MMC的投入。
传统的MMC整体控制框图如图2所示。P ref、Q ref为输入外环功率控制器的有功、无功功率指令值，i d_ref、i q_ref为外环功率控制器输出的dq轴电流参考值。在加入环流抑制附加控制信号u cirj_ref后，控制系统最终输出上、下桥臂电压参考信号u pj_ref和u nj_ref，即为换流器电压参考值，然后通过多电平载波移相调制算法生成相应的触发脉冲，进而控制各个子模块的开通与关断。
当在换流站降压/半压运行、单阀组在线投退、以及直流故障穿越工况下时，混合型MMC控制框图，如图1所示，其中U c_avr为子模块电容电压的平均值与预先设定的给定值作差，然后经过外环的PI调节，得到电流参考值的d分量；电流参考值的q分量跟传统方式的获取方式相同，将MMC换流阀公共连接点处的无功功率的测量值与预先设定的设定值作差，通过外环PI调节后，得到电流参考值的q分量，将电流参考值的dq分量，通过内环的PI调节，得到换流器电压参考值。
所述电流参考值的d分量和q分量的制定，分别如下式所示：
Figure PCTCN2020093469-appb-000005
Figure PCTCN2020093469-appb-000006
其中，i dref为电流参考值的d分量，U c-ref为MMC换流阀子模块电容电压的平均测量值，U c-avr为MMC换流阀子模块电容电压的设定值，k pd1为 d分量内环PI调节的比例控制系数，k id1为d分量内环PI控制的积分控制系数，i qref为电流参考值的q分量，Q ref为无功功率的测量值，Q s为无功功率的设定值，k pq1为q分量内环PI调节的比例控制系数，k iq1为q分量内环PI控制的积分控制系数。
所述换流器电压参考值的d分量和q分量的制定，分别如下式所示：
Figure PCTCN2020093469-appb-000007
Figure PCTCN2020093469-appb-000008
其中，e sd为换流器电压参考值的d分量，u sd为MMC换流阀侧电压的d分量，ω为角频率，L＝Lt+0.5Larm，其中Lt为变压器漏抗值，Larm为桥臂电抗器，i dref为所述电流参考值的d分量，i d为MMC换流阀侧电流的d分量，k pd2为d分量外环PI控制比例控制系数，k id2为d分量外环PI控制的积分控制系数，e sq为换流器电压参考值的q分量，u sq为MMC换流阀侧电压的q分量，，i qref为所述电流参考值的q分量，i q为MMC换流阀侧电流的q分量，k pq2为q分量外环PI控制比例控制系数，k iq2为q分量外环PI控制的积分控制系数。
控制系统分为外环控制和内环控制。内环控制中环流抑制和半桥MMC基本相同。不同的是：d轴电流参考值I dref直接由子模块电容电压控制器得到，而不是由直流电压控制器得到。直流电压参考值U dcref的给定与控制模式相关。当该站处于电压控制模式时，U dcref直接设定为U dcref_ set；电流模式时，由直流电流控制器给出。模式选择逻辑实现直流电流控制器和电压控制器的切换。
正常工况下，混合型MMC有功类外环控制采用定直流电压或定有功功率控制，无功类外环控制采用定交流电压或无功功率控制，且环流抑制为0；换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，有功类外环控制高阀组定子模块电容电压，直流电压给定值采用定直流电流控制，低阀组定直流电压或定有功功率，无功类外环控制均采用定交流电压或无功功率控制，环流切换至环流注入，且系统功率电压恢复正常时，控制模式切换回正常工况，退出环流注入机制。
环流注入控制框图，如图3所示。桥臂环流i cirj(j＝a，b，c)经过abc/dq坐标变换后得到dq坐标下的桥臂电流i 2fd和i 2fq，将它们与环流dq轴分量的参考值i 2fd_ref和i 2fq_ref相减后，经过比例积分(PI)调节器，再引入电压前馈量2ω 0L 0i 2fq和2ω 0L 0i 2fd以消除其中的dq轴耦合部分，即可得到内部不平衡压降的dq轴参考值u cird_ref和u cirq_ref。最后经过dq/abc坐标逆变换得到三相环流电压参考值u cirj_ref，即为环流注入电压值。i 2fd_ref和i 2fq_ref取期望注入的环流大小，环流注入的大小为固定值，约为直流电流的0.4到0.6倍。环流注入的相位同实时桥臂无功分量同相(I dc<0)或反相(I dc>0)。
电网电压锁相角控制框图，如图4所示，电网电压E sa、E sb、E sc经过PLL锁相得到用于坐标变换的电网电压角度angle。电网电流i sa、i sb、i sc经过abc/dq变换得到dq坐标下的交流电流i sd、i sq，再经过arctan(反正切)变换得到角度theata1，theata1加90°或者减90°得到角度theata，用于环流注入中坐标系变换以及环流注入的相位。
环流注入给定值控制框图，如图5所示，利用分离基频得到的角度theata分别经过cos(余弦)、sin(正弦)运算得到i 2fd_ref和i 2fq_ref。其中，ampl为环流幅度，在分离基频得到的角度theata分别经过cos、sin运算得到i 2fd_ref和i 2fq_ref，还需要将ampl代入，经过Acos、Asin运算，A为cos和sin的最大幅值。
当在正常工况下时，模式选择预先设定的直流电压给定值；当在换流站降压/半压运行、单阀组在线投退、以及直流故障穿越工况下时，将所述直流电流测量值与给定值作差，并通过PI调节，得到直流电压给定值。
最后，正常工况下，根据由无功功率和有功功率制定的换流器电压参考值、预设的环流抑制电压和直流电压给定值，制定控制脉冲信号，依据控制脉冲信号，控制所述混合型MMC的投入；
当在换流站降压/半压运行、单阀组在线投退、以及直流故障穿越工况下，根据由MMC换流阀中子模块电容电压制定的换流器电压参考值，由MMC换流阀桥臂环流制定的环流注入电压值和由直流电流给定值制定的直流电压给定值，制定控制脉冲，并控制混合型MMC的投入。本申请实施例中的技术方案，可在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，根据由MMC换流阀中子模块电容电压制定的换流器电压参考值，保证了MMC桥臂电流过零点，实现电容电压平衡，避免了电容电压在桥臂电流不存在过零点时仍继续充电，与全桥子模块电容电压分离而导致的系统崩溃。本方案中由MMC换流阀桥臂环流制定的环流注入电压值，通过环流注入环节，使得桥臂电流始终存在过零点，保证了MMC桥臂的安全运行。
实施例2：
本实施例提供了一种混合型MMC控制方法系统，包括：
换流器、环流抑制控制器、模式选择控制器和控制脉冲发生器；
所述换流器，配置为制定换流器电压参考值；
所述环流抑制控制器，配置为制定正常工况和换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下的环流抑制电压值；
所述模式选择控制器，配置为制定正常工况和换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下的直流电压给定值；
所述脉冲控制发生器，配置为制定正常工况和换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下的控制脉冲信号，依据控制脉冲信号，控制所述混合型MMC的投入。
所述换流器，包括：
外环功率控制器和内环功率控制器；
所述外环功率控制器，配置为在正常工况下，根据所述MMC换流阀公共连接点处的无功功率和有功功率，通过外环PI调节，制定正常工况下的电流参考值；在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，根据MMC换流阀中子模块电容电压和无功功率参考值，通过外环PI调节，制定特殊工况下的电流参考值；
所述内环功率控制器，配置为根据正常工况下的电流参考值，通过内环PI调节，制定正常工况下的换流器电压参考值；根据特殊工况下的电流参考值，通过内环PI调节，制定特殊工况下的换流器电压参考值。
所述环流抑制控制器，在正常工况下，将MMC换流阀的环流抑制电压设置为0；
所述环流抑制控制器，在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，根据电网电流，制定环流注入电压值。
所述环流抑制控制器，包括：
相角控制模块、环流注入给定模块和环流注入控制模块；
所述相角控制模块，根据电网电流，进行park变换和角度变换，得到环流注入的相角值；
所述环流注入给定模块，根据所述相角值和环流注入幅值，通过三角函数变换，制定具有d轴和q轴分量的环流注入期望值；
所述环流注入控制模块，根据所述桥臂环流、相角值和环流注入期望值，计算得到环流注入电压值；
其中，所述环流注入幅值为桥臂电流直流分量的预设倍数。
所述模式选择控制器在正常工况下，设置固定幅值的直流电压给定值；
所述模式选择控制器在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，将所述直流电流测量值与给定值作差，并通过PI调节，得到直流电压给定值。
显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其它实施例，都属于本申请保护的范围。
本领域内的技术人员应明白，本申请的实施例可提供为方法、系统、或计算机程序产品。因此，本申请可采用完全硬件实施例、完全软件实施例、或结合软件和硬件方面的实施例的形式。而且，本申请可采用在一个或多个其中包含有计算机可用程序代码的计算机可用存储介质(包括但不限于磁盘存储器、CD-ROM、光学存储器等)上实施的计算机程序产品的形式。
本申请是参照根据本申请实施例的方法、设备(系统)、和计算机程序产品的流程图和/或方框图来描述的。应理解可由计算机程序指令实现流程图和/或方框图中的每一流程和/或方框、以及流程图和/或方框图中的流程和/或方框的结合。可提供这些计算机程序指令到通用计算机、专用计算机、嵌入式处理机或其他可编程数据处理设备的处理器以产生一个机器，使得通过计算机或其他可编程数据处理设备的处理器执行的指令产生用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的装置。
这些计算机程序指令也可存储在能引导计算机或其他可编程数据处理设备以特定方式工作的计算机可读存储器中，使得存储在该计算机可读存储器中的指令产生包括指令装置的制造品，该指令装置实现在流程图一个 流程或多个流程和/或方框图一个方框或多个方框中指定的功能。
这些计算机程序指令也可装载到计算机或其他可编程数据处理设备上，使得在计算机或其他可编程设备上执行一系列操作步骤以产生计算机实现的处理，从而在计算机或其他可编程设备上执行的指令提供用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的步骤。
以上仅为本申请的实施例而已，并不用于限制本申请，凡在本申请的精神和原则之内，所做的任何修改、等同替换、改进等，均包含在申请待批的本申请的权利要求范围之内。
工业实用性
本申请实施例中的技术方案，可在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，获得换流器电压参考值；获得由MMC换流阀桥臂环流制定的环流注入电压值和由直流电流给定值制定的直流电压给定值；根据所述电压参考值、环流注入电压值和所述直流电压给定值，制定控制脉冲信号；依据控制脉冲信号，控制所述混合型MMC的投入。其中，由MMC换流阀中子模块电容电压制定的换流器电压参考值，保证了MMC桥臂电流过零点，实现电容电压平衡，避免了由于电容电压在桥臂电流不再有过零点时仍继续充电、与全桥子模块电容电压分离而导致的系统崩溃的问题。本方案中由MMC换流阀桥臂环流制定的环流注入电压值，通过环流注入环节，使得桥臂电流始终存在过零点，保证了MMC桥臂的安全运行。

Claims (15)

  1. 一种混合型MMC控制方法，所述方法还包括：
    当在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，获得换流器电压参考值；
    获得由MMC换流阀桥臂环流制定的环流注入电压值和由直流电流给定值制定的直流电压给定值；
    根据所述电压参考值、环流注入电压值和所述直流电压给定值，制定控制脉冲信号；
    依据控制脉冲信号，控制所述混合型MMC的投入。
  2. 根据权利要求1所述的方法，其中，所述方法还包括：
    正常工况下，根据由无功功率和有功功率制定的换流器电压参考值、预设的环流抑制电压和直流电压给定值，制定控制脉冲信号，依据控制脉冲信号，控制所述混合型MMC的投入。
  3. 如权利要求1所述的方法，其中，所述获得换流器电压参考值，包括：
    获得由MMC换流阀中子模块电容电压制定的换流器电压参考值；
    所述获得由MMC换流阀中子模块电容电压制定的换流器电压参考值通过下述步骤来实现：
    将MMC换流阀中子模块电容电压的平均测量值与设定值作差，并通过外环比例-积分混合参量PI调节，得到电流参考值的d分量；
    将所述电流参考值的d分量通过内环PI调节，得到换流器电压参考值的d分量；
    将MMC换流阀公共连接点处无功功率的测量值与设定值作差，并通过外环PI调节，得到电流参考值的q分量；
    将所述电流参考值的q分量通过内环PI调节，得到换流器电压参考值 的q分量。
  4. 如权利要求3所述的方法，其中，所述电流参考值的d分量和q分量的制定，分别如下式所示：
    Figure PCTCN2020093469-appb-100001
    Figure PCTCN2020093469-appb-100002
    其中，i dref为电流参考值的d分量，U c-ref为MMC换流阀子模块电容电压的平均测量值，U c-avr为MMC换流阀子模块平均电容电压的设定值，k pd1为d分量内环PI调节的比例控制系数，k id1为d分量内环PI控制的积分控制系数，i qref为电流参考值的q分量，Q ref为无功功率的测量值，Q s为无功功率的设定值，k pq1为q分量内环PI调节的比例控制系数，k iq1为q分量内环PI控制的积分控制系数。
  5. 如权利要求3所述的方法，其中，所述换流器电压参考值的d分量和q分量的制定，分别如下式所示：
    Figure PCTCN2020093469-appb-100003
    Figure PCTCN2020093469-appb-100004
    其中，e sd为换流器电压参考值的d分量，u sd为MMC换流阀侧电压的d分量，ω为角频率，L＝Lt+0.5Larm，其中Lt为变压器漏抗值，Larm为桥臂电抗器值，i dref为所述电流参考值的d分量，i d为MMC换流阀侧电流的d分量，k pd2为d分量外环PI控制比例控制系数，k id2为d分量外环PI控制的积分控制系数，e sq为换流器电压参考值的q分量，u sq为MMC 换流阀侧电压的q分量，i qref为所述电流参考值的q分量，i q为MMC换流阀侧电流的q分量，k pq2为q分量外环PI控制比例控制系数，k iq2为q分量外环PI控制的积分控制系数。
  6. 如权利要求1所述的方法，其中，所述由MMC换流阀桥臂环流制定的环流注入电压值，通过下述步骤来实现：
    将电网电流，进行派克变换和角度变换，得到环流注入的相角值；
    根据所述相角值和环流注入幅值，通过三角函数变换，制定具有d轴和q轴分量的环流注入期望值；
    根据所述桥臂环流、相角值和环流注入期望值，计算得到环流注入电压值；
    其中，所述环流注入幅值为桥臂电流直流分量的预设倍数。
  7. 如权利要求6所述的方法，其中，所述根据所述桥臂环流、相角值和环流注入期望值，计算得到三相环流电压参考值，作为环流注入电压值，包括：
    将所述桥臂环流，通过派克dq变换，得到dq桥臂环流和电压前馈量；
    将所述dq桥臂环流和环流注入期望值，进行比例-积分混合变量PI调节，得到初始环流注入电压值；
    将所述初始环流注入电压值与电压前馈量作差，并进行派克反变换，得到环流注入电压值。
  8. 如权利要求1所述的方法，其中，所述由直流电流给定值制定的直流电压给定值，通过下述步骤来实现：
    将所述直流电流测量值与给定值作差，并通过PI调节，得到直流电压给定值。
  9. 如权利要求2所述的方法，其中，所述正常工况下，根据由无功功率和有功功率制定的换流器电压参考值、预设的环流抑制电压和直流电压 给定值，制定控制脉冲信号，依据控制脉冲信号，控制所述混合型MMC的投入，包括：
    基于所述MMC换流阀公共连接点处的无功功率和有功功率，通过内环PI调节得到电流参考值，将所述电流参考值通过外环PI调节得到换流器电压参考值；
    将MMC换流阀的环流抑制电压设置为0；
    根据所述电压参考值、环流抑制电压和所述直流电压给定值，制定控制脉冲信号，并控制所述混合型MMC的投入。
  10. 一种混合型MMC控制系统，所述系统包括：
    换流器、环流抑制控制器、模式选择控制器和控制脉冲发生器；
    所述换流器，配置为制定换流器电压参考值；
    所述环流抑制控制器，配置为制定换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下的环流抑制电压值；
    所述模式选择控制器，配置为制定换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下的直流电压给定值；
    所述脉冲控制发生器，配置为制定换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下的控制脉冲信号，依据控制脉冲信号，控制混合型MMC的投入。
  11. 如权利要求10所述的系统，其中，
    所述环流抑制控制器，配置为制定正常工况下的环流抑制电压值；
    所述模式选择控制器，配置为制定正常工况下的直流电压给定值；
    所述脉冲控制发生器，配置为制定正常工况下的控制脉冲，并控制所述混合型MMC的投入。
  12. 如权利要求10所述的系统，其中，所述换流器，包括：
    外环功率控制器和内环功率控制器；
    所述外环功率控制器，配置为在正常工况下，根据所述MMC换流阀公共连接点处的无功功率和有功功率，通过外环PI调节，制定正常工况下的电流参考值；在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，根据MMC换流阀中子模块电容电压和无功功率参考值，通过外环PI调节，制定特殊工况下的电流参考值；
    所述内环功率控制器，配置为根据正常工况下的电流参考值，通过内环PI调节，制定正常工况下的换流器电压参考值；根据特殊工况下的电流参考值，通过内环PI调节，制定特殊工况下的换流器电压参考值。
  13. 如权利要求10所述的系统，其中，所述环流抑制控制器，在正常工况下，将MMC换流阀的环流抑制电压设置为0；
    所述环流抑制控制器，配置为在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，根据电网电流，制定环流注入电压值。
  14. 如权利要求13所述的系统，其中，所述环流抑制控制器，包括：
    相角控制模块、环流注入给定模块和环流注入控制模块；
    所述相角控制模块，配置为根据电网电流，进行park变换和角度变换，得到环流注入的相角值；
    所述环流注入给定模块，配置为根据所述相角值和环流注入幅值，通过三角函数变换，制定具有d轴和q轴分量的环流注入期望值；
    所述环流注入控制模块，配置为根据所述桥臂环流、相角值和环流注入期望值，计算得到环流注入电压值；
    其中，所述环流注入幅值为桥臂电流直流分量的预设倍数。
  15. 如权利要求10所述的系统，其中，所述模式选择控制器在正常工况下，配置为设置固定幅值的直流电压给定值；
    所述模式选择控制器配置为在换流站降压/半压运行、单阀组在线投退以及直流故障穿越工况下，将所述直流电流测量值与给定值作差，并通过 PI调节，得到直流电压给定值。
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