WO2014176726A1 - A control method for blocking/deblocking converters of a series mtdc system and controller thereof - Google Patents

A control method for blocking/deblocking converters of a series mtdc system and controller thereof Download PDF

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Publication number
WO2014176726A1
WO2014176726A1 PCT/CN2013/074953 CN2013074953W WO2014176726A1 WO 2014176726 A1 WO2014176726 A1 WO 2014176726A1 CN 2013074953 W CN2013074953 W CN 2013074953W WO 2014176726 A1 WO2014176726 A1 WO 2014176726A1
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WO
WIPO (PCT)
Prior art keywords
converter
blocking
control method
pair
converters
Prior art date
Application number
PCT/CN2013/074953
Other languages
French (fr)
Inventor
Chunming YUAN
Xiaobo Yang
Dawei YAO
Chengyan YUE
Original Assignee
Abb Technology Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Abb Technology Ltd. filed Critical Abb Technology Ltd.
Priority to PCT/CN2013/074953 priority Critical patent/WO2014176726A1/en
Priority to CN201380042945.3A priority patent/CN104584359B/en
Publication of WO2014176726A1 publication Critical patent/WO2014176726A1/en

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Classifications

    • 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
    • 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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
    • H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/75—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
    • H02M7/757—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
    • H02M7/7575—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only for high voltage direct transmission link
    • 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
    • H02M1/325—Means for protecting converters other than automatic disconnection with means for allowing continuous operation despite a fault, i.e. fault tolerant converters
    • 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 series multi-terminal HVDC system (i.e. series MTDC system), and more particularly to a control method for blocking/deblocking converter(s) of a MTDC system and controller thereof.
  • the present invention is to propose a control method for blocking/deblocking converters) of a series MTDC system and controller thereof and achieve safe and reliable actions of blocking/deblocking converters.
  • the present invention provides control methods for blocking/deblocking converters) of a series MTDC system and controller thereof.
  • a control method for blocking a single converter of a series MTDC system comprises: selecting an assistant converter besides the target converter; making the powers of the two converters decreased to zero; triggering the bypass pair of the target converter, controlling switches of DC side orderly, and blocking the target converter; and adjusting the MTDC system into a new balance.
  • the method further comprises exiting the assistant converter after blocking the target converter.
  • the assistant converter is the one located at the same poie as the target converter with opposite position.
  • the assistant converter can be identified based on its position, power capacity, short circuit capacity, power grid security level and/or economic benefit.
  • the assistant converter is close to the grounding pole; the assistant converter has a matched power capacity with the target one; and/or the assistant converter is located in AC system with high short circuit capacity.
  • the matched power capacity of the assistant converter shall be same with or above that of the target one.
  • a control method for blocking at least two converters of a series MTDC system comprises: selecting the first pair from the target ones; making the powers of the selected converters decreased to zero; triggering the bypass pair of the inverter of the first pair, controlling switches of DC side orderly; and blocking the inverter; triggering the bypass pair of the rectifier of the first pair, controlling switches of DC side orderly; and blocking the rectifier; and blocking the next pair following the same procedure for the first pair if existing.
  • each pair of the target ones are in the same pole; the each pair includes a rectifier and an inverter; the power capacities of the rectifier and inverter in the each pair should be matched.
  • the pair with lower voltage level will be exited firstly.
  • the grounding electrodes need to be shifted to other converters after the converters with lowest voltage level being exited.
  • a control method for blocking at least two converters of a series MTDC system comprises: selecting the first pair from the target ones; making the powers of the selected converters decreased to zero; synchronously triggering the bypass pair of the inverter and rectifier, controlling switches of DC side orderly; and synchronously blocking the inverter and rectifier of the first pair; and blocking the next pair following the same procedure for the first pair if existing.
  • a control method for emergency blocking a target converter of a series MTDC system comprises: identifying the fault point, and triggering the bypass pair of the target converter; adjusting the power balance in the MTDC system, meanwhile controlling switches of DC side orderly; and blocking the target converter; and building a new operation balance in MTDC system.
  • DC voltages of at least one converter can be changed, or at least one converter can be exited.
  • a control method for deblocking a single converter of a series MTDC system comprises: controlling the switches of AC side and DC side; controlling the firing angle of the converter to decrease to a preset degree, and opening the bypass switch of the converter to be blocked; and building a new operation balance in the MTDC system.
  • a control method for deblocking a single converter of a series MTDC system comprises: controlling the switches of AC side and DC side; opening the bypass switch of the converter to be blocked, meanwhile triggering the firing angle at a preset degree; and building a new operation balance in the MTDC system.
  • a control method for deblocking at least two converters of a series MTDC system comprises: deblocking a rectifier into the MTDC system according to one of the above two control methods for deblocking a single converter of a series MTDC system; deblocking an inverter into the MTDC system according to one of the above two control methods for deblocking a single converter of a series MTDC system; and building a new operation balance in the MTDC system.
  • the rectifier and inverter can be deblocked synchronously.
  • a coordinated controller is provided.
  • the coordinated controller is configured to realize at least one of the above mentioned methods for blocking converter(s) of a series MTDC system and/or deblocking converter(s) of a series MTDC system.
  • the coordinated controller comprises a DC voltage synchronous control module - configured to keep the two DC voltages of the target converters followed each other.
  • the coordinated controller receives the blocking or deblocking feedback of the target converters, and transferred information into a master controller.
  • Embodiments of the present invention provide control methods for blocking/deblocking converters of a series MTDC and achieve reliable and smooth operations for blocking/deblocking converters.
  • Fig.1 illustrates a single line diagram of a bipolar series MTDC with 4 terminals
  • Fig.2 illustrates a block diagram of a four-terminal MTDC system with a coordination controller proposed in the present invention
  • Fig.3 illustrates a control method for blocking a single converter of a series MTDC system according to an embodiment of the present invention
  • Fig.4 illustrates a control method for blocking at least two converters of a series MTDC system according to an embodiment of the present invention
  • Fig.5 illustrates a control method for blocking at least two converters of a series MTDC system according to an embodiment of the present invention
  • Fig.6 illustrates a control method for emergency blocking a target converter of a series MTDC system according to an embodiment of the present invention
  • Fig.7 illustrates a control method for deblocking a single converter of a series MTDC system according to an embodiment of the present invention
  • Fig.8 illustrates another control method for deblocking a single converter of a series MTDC system according to an embodiment of the present invention.
  • Fig.9 illustrates a control method for deblocking at least two converters of a series MTDC system according to an embodiment of the present invention.
  • the present invention is to be applied to for LCC based Series MTDC system, in which terminals are connected in series.
  • Fig.1 illustrates a single line diagram of a bipolar series MTDC with 4 terminals.
  • BPSxxx represents a bypass switch
  • Sxxx represents an isolated switch
  • Rxx represents a rectifier converter/terminal
  • Ixx represents an inverter converter/terminal.
  • each converter station usually includes four switches in DC side.
  • a bypass switch (BPS) is connected in parallel with the DC port of the converter. One point of BPS joints positive point of the DC port, and the other point of the BPS joints negative point of the DC port.
  • a switch (S1 ) is connected in parallel with the port of DC transmission lines. One point of S1 joints positive DC transmission line, and the other point of the S1 joints negative DC transmission line.
  • a switch (S2) is connected between the positive point of the DC port of the converter and the positive transmission line.
  • a switch (S3) is connected between the negative point of the DC port of the converter and the negative transmission line.
  • Fig.2 illustrates a block diagram of a four-terminai MTDC system with a coordination controller proposed in the present invention.
  • the R1+ is regarded as a current setting terminal (CST) while others are voltage setting terminals (VST).
  • the block for converters in a series MTDC system can be categorized as normal block and emergency block.
  • the normal block method is used for planning or non-emergency exiting, such as normal maintenance and exit during predictable failure, in the case of normal block, it can be divided into blocking a single converter and blocking multiple converters, for example at least two converters. While the emergency block method is used when fault occurs, a fast block of certain converters are needed.
  • Fig.3 illustrates a control method for blocking a single converter of a series MTDC system according to an embodiment of the present invention.
  • control method 300 for blocking a single converter of a series MTDC system comprises:
  • Step 302 selecting an assistant converter besides the target converter. That's, if only one converter need to be exited from the DC system, a corresponding converter is chosen as an assistant converter. For example, in the case that the inverter 12+ is the converter to be exited, R2+ is selected as the assistant converter. The firing angle of 12+ will be changed to about 90 degree finally, and be held;
  • Step 304 making the powers of the two converters decreased to zero.
  • the coordinated controller control the 12+ and R2+ power references with a preset decreasing ramp (for example 0.002 p.uJms).
  • the power reference of 12+ should be always lower than that of R2+ (This request can keep there is no overload in other terminals)
  • Step 306 triggering the bypass pair of the target converter, controlling switches of DC side orderly, and blocking the target converter. It's obvious for the person skilled in art how to orderly operate the switches for blocking a converter according to the teaching of the present invention especially based on the configuration of specific MTDC system. For example, trigger the bypass pair in the I2+; then close the bypass switch BPS 12+; when BPS 12+ is closed, block the bypass pair; close the switch S1 ⁇ 2+, and then open the bypass switch BPSI2+; then open switches S2I2+ and S3I2+; block the I2+, and then turn into isolate program and signal coordinated controller.
  • Step 308 adjusting the MTDC system into a new balance. It shall be noted that all solutions for adjusting the MTDC system in prior art can be used in the present invention, and it's obvious for the person to use such existing solution with some necessary modification.
  • the method further comprises exiting the assistant converter after blocking the target converter. That's, R2+ can operate at reduced power mode. System operators will decide whether R2+ should be exited or not finally.
  • the key of the blocking control method is the coordination between the target converter and the assistant converter.
  • DC voltages of the converter pair to be exited should be coordinated well to avoid disturbance on the CST.
  • a coordinated controller is introduced. Whether the assistant converter needs to exit or not, depends on careful consideration of reactive power absorption, AC voltage variation, power losses and the limit of operation voltage and so on.
  • the assistant converter is the one located at the same pole as the target converter with opposite position.
  • the performance of this Opposite position' is that if the target converter is a sending terminal, the assistant converter in opposite position should be a receiving terminal, and vice versa.
  • the assistant converter can be identified based on its position, power capacity, short circuit capacity, power grid security level and/or priority.
  • the assistant converter is close to the grounding pole; the assistant converter has a matched power capacity with the target one, for example, the matched power capacity of the assistant converter shall be same with or above that of the target one; and/or the assistant converter is located in AC system with high short circuit capacity. Other factors such as power grid security level, economic benefit, etc. are also considered during the determination of an assistant converter; especially the non-critical converter should be selected with high priority.
  • Fig.4 illustrates a control method for blocking at least two converters of a series TDC system according to an embodiment of the present invention.
  • control method 400 for blocking at least two converters of a series MTDC system comprises:
  • Step 402 selecting the first pair from the target ones. For example, R2+ and 12+ are selected as the exited converters.
  • Step 404 making the powers of the selected converters decreased to zero.
  • the coordinated controller controls power references of the 12+ and R2+ to decrease with a preset ramp (e.g. 0.002 p.u./ms), and l2+'s power reference is a little bit lower of R2+'s power reference.
  • the firing angle of 12+ and R2+ will be changed to 90 degree and be held.
  • Step 406 triggering the bypass pair of the inverter of the first pair, controlling switches of DC side orderly; and blocking the inverter. For example, trigger the bypass pair in the I2+; then close the BPSI2+, and block the bypass pair. Close the S112+, and open the BPSI2+, and then open S2I2+ and S3I2+. Block the I2+, and turn into isolate process, and signal the coordinated controller.
  • Step 408 triggering the bypass pair of the rectifier of the first pair, controlling switches of DC side orderly; and blocking the rectifier. For example, trigger the bypass pair in the R2+; and follow the similar process in step 406.
  • Step 410 blocking the next pair following the same procedure for the first pair if existing. If the power is not exactly match, the CST converter will keep DC current constant in the whole method, !n the end, the coordinated controller will make a new balance of power transmission.
  • each pair of the target ones are in the same pole; each pair includes a rectifier and an inverter; the power capacities of the rectifier and inverter in the each pair should be matched. If several pairs need to be exited, the pair with lower voltage level will be exited firstly. Especially, the grounding electrodes need to be shifted to other converters after the converters with lowest voltage level being exited.
  • Fig.5 illustrates a control method for blocking at least two converters of a series MTDC system according to an embodiment of the present invention.
  • the control method 500 for blocking at least two converters of a series MTDC system comprises: steps 502-508, in which, steps 502, 504 and 508 are same or similar to steps 402, 404 and 410 in Fig.4. In order to keep description concise, such steps won't be explained further.
  • Step 506 synchronously triggering the bypass pair of the inverter and rectifier, controlling switches of DC side orderly; and synchronously blocking the inverter and rectifier.
  • the method can improve the exit speed for both inverter and rectifier.
  • emergency block method plays an important role.
  • Fig.6 illustrates a control method for emergency blocking a target converter of a series MTDC system according to an embodiment of the present invention.
  • control method 600 for emergency blocking a target converter of a series MTDC system comprises:
  • Step 602 identifying the fault point, and triggering the bypass pair of the target converter. For example, when 12+ need to be exited under emergency operation, firstly confirm the fault can be insulated by bypass switch; trigger the bypass pair of I2+, but if the bypass pair is not available, the action can be canceled; The fault type will be detected and send to coordinated controller.
  • Step 604 adjusting the power balance in the MTDC system, meanwhile controlling switches of DC side orderly and blocking the target converter.
  • the CST automatically adjusts the active power balance in the DC system, in order to maintain the constant DC current. Close the BPSI2+, and then block the bypass pair (if the bypass pair is triggered); Close the S1 I2+, and open the BPSI2+, and then open S2I2+ and S312+; Block the I2+, and then turn into isolate program and signal coordinated controller;
  • Step 606 building a new operation balance in MTDC system.
  • the coordinated controller establishes a new operating balance of the MTDC system.
  • DC voltages of at least one converter can be changed, or at least one converter can be exited.
  • the control method for deblocking converters will play an important role.
  • the method is a planned operation. But there are different methods in single action or multiple. Two methods for deblocking a single converter are proposed.
  • Fig.7 illustrates a control method for deblocking a single converter of a series MTDC system according to an embodiment of the present invention.
  • control method 700 for deblocking a single converter of a series MTDC system comprises:
  • Step 702 controlling the switches of AC side and DC side. For example, 12+ is turned out of isolated status and energized; RPC (the reactive power controller) of 12+ is started up and put into calculated filters or reactive power compensation equipments and the tap changer operation is forbidden. Close switches S212+ and S3I2+; close the bypass switch BPS12+ and then open the switch S112+.
  • RPC the reactive power controller
  • Step 704 controlling the firing angle to decrease to a preset degree, and opening a bypass switch.
  • the firing angle drops with a preset ramp until the angle reaches a preset degree.
  • the degree is close to 90, and makes the current on BPSI2+ to slightly oscillate across zero. Then Open the BPSI2+.
  • Step 706 building a new operation balance in the MTDC system.
  • signal coordinated controller After BPSI2+ is opened, signal coordinated controller; get feedback from coordinated controller and increase DC voltage of I2+ with a calculated rise ramp.
  • the CST and coordinated controller adjust other DC voltages or DC current according to the principle of power conservation; finally, obtain a new balance in DC system, and open the tap changer operation.
  • another control method for deblocking a single converter of a series MTDC system is provided for opening BPS 12+ safely.
  • Fig.8 illustrates another control method for deblocking a single converter of a series MTDC system according to an embodiment of the present invention.
  • control method 800 for deblocking a single converter of a series MTDC system comprises:
  • Step 802 controlling the switches of AC side and DC side. For example, Opening the BPSI2+ at t 0 ; the firing angle is held at a small angle (The angle is a preset value), until t 0 +At (and At is a calculated time in advance).
  • Step 804 opening a bypass switch, meanwhile triggering the firing angle at a preset degree.
  • the current of BPS 12+ rapidly drops to zero through the lower firing angle; then the BPS 12+ is opened successfully.
  • Step 806 building a new operation balance in the MTDC system.
  • the advantage of the second method for deblocking a single converter shown in Fig.8 includes that the reactive power and reactive power changes are reduced due to the faster process.
  • converters shall be connected to the MTDC system at the same time.
  • One method is to enter one by one; the other is to enter pair by pair.
  • Fig.9 illustrates a control method for deblocking at least two converters of a series MTDC system according to an embodiment of the present invention.
  • control method 900 for deblocking at least two converters of a series MTDC system comprises:
  • Step 902 deblocking a rectifier according to the above mentioned method shown in Fig. 7 or 8 into the MTDC system.
  • the 12+ and R2+ will be linked into MTDC system.
  • R2+ is entered into DC system according to the method for deblocking single converter.
  • R2+ increases DC voltage with a calculated ramp until the voltage is reach to the reference value calculated by master control, and the CST maintains the DC current with adjusting its DC voltage;
  • Step 904 deblocking an inverter according to the above mentioned method shown in Fig. 7 or 8 into the MTDC system.
  • 12+ enters into MTDC system according to the method for deblocking single converter, then 12+ increases its DC voltage with a calculated ramp until rating voltage and the CST maintains the DC current.
  • Step 906 building a new operation balance in the MTDC system. Coordinated controller adjusts R2+ and 12+ to rise until rating, and then the DC system run in a new balance.
  • a coordinated controller is provided.
  • the coordinated controller is configured to direct the above mentioned method for blocking converter(s) of a series MTDC system and/or deblocking converter(s) of a series MTDC system.
  • the coordinated controller comprises a DC voltage synchronous control module configured to keep the two DC voltages of the target converters followed each other.
  • a master controller for a series MTDC system comprises: a choosing module, configured to choose one terminal as a current setting terminal (CST) and define other terminals as voltage setting terminals (VST); a configuration module, configured to configure a current reference of the series MTDC system as the input of the CST converter, generate current values for each VST converter based on said current reference and different margins thereof respectively and make the minimum value of current reference in the rectifier side larger than the maximum value of current reference in the inverter side.
  • a choosing module configured to choose one terminal as a current setting terminal (CST) and define other terminals as voltage setting terminals (VST)
  • VST voltage setting terminals
  • VST voltage setting terminals
  • configuration module configured to configure a current reference of the series MTDC system as the input of the CST converter, generate current values for each VST converter based on said current reference and different margins thereof respectively and make the minimum value of current reference in the rectifier side larger than the maximum value of current reference in the inverter side.

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  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

A control method for blocking/deblocking converters of a series multi-terminal direct current (MTDC) system and controller thereof are disclosed. For blocking a single converter, the method comprises: selecting an assistant converter besides the target converter (302); making the power of the two converters decreased to zero (304); triggering the bypass pair of the target converter, controlling switches of DC side orderly, and blocking said target converter (306); and adjusting the MTDC system into a new balance (308). A control method for blocking/deblocking multiple converters is also proposed. The control methods achieve safe and reliable operation of blocking/deblocking converters in a series MTDC system.

Description

A Control Method for Blocking/Deblocking Converters of a Series MTDC System and Controller Thereof
FIELD OF THE INVENTION
The invention relates to the series multi-terminal HVDC system (i.e. series MTDC system), and more particularly to a control method for blocking/deblocking converter(s) of a MTDC system and controller thereof.
BACKGROUND OF THE INVENTION By far, there is no engineering application of series MTDC. Only handful papers had studied the series MTDC in the past 50 years. Most of the papers only focused on topology principles and control methods. How to maintain the MTDC system under a normal operation when one or more converters enter/exit is a big issue to be solved. The present invention is to propose a control method for blocking/deblocking converters) of a series MTDC system and controller thereof and achieve safe and reliable actions of blocking/deblocking converters.
SUMMARY OF THE INVENTION The present invention provides control methods for blocking/deblocking converters) of a series MTDC system and controller thereof.
According to an aspect of the present invention, a control method for blocking a single converter of a series MTDC system is provided. The method comprises: selecting an assistant converter besides the target converter; making the powers of the two converters decreased to zero; triggering the bypass pair of the target converter, controlling switches of DC side orderly, and blocking the target converter; and adjusting the MTDC system into a new balance.
According to a preferred embodiment of the present invention, the method further comprises exiting the assistant converter after blocking the target converter.
According to a preferred embodiment of the present invention, the assistant converter is the one located at the same poie as the target converter with opposite position.
According to a preferred embodiment of the present invention, the assistant converter can be identified based on its position, power capacity, short circuit capacity, power grid security level and/or economic benefit.
According to a preferred embodiment of the present invention, the assistant converter is close to the grounding pole; the assistant converter has a matched power capacity with the target one; and/or the assistant converter is located in AC system with high short circuit capacity.
According to a preferred embodiment of the present invention, the matched power capacity of the assistant converter shall be same with or above that of the target one.
According to another aspect of the present invention, a control method for blocking at least two converters of a series MTDC system is provided. The method comprises: selecting the first pair from the target ones; making the powers of the selected converters decreased to zero; triggering the bypass pair of the inverter of the first pair, controlling switches of DC side orderly; and blocking the inverter; triggering the bypass pair of the rectifier of the first pair, controlling switches of DC side orderly; and blocking the rectifier; and blocking the next pair following the same procedure for the first pair if existing.
According to a preferred embodiment of the present invention, each pair of the target ones are in the same pole; the each pair includes a rectifier and an inverter; the power capacities of the rectifier and inverter in the each pair should be matched.
According to a preferred embodiment of the present invention, the pair with lower voltage level will be exited firstly.
According to a preferred embodiment of the present invention, the grounding electrodes need to be shifted to other converters after the converters with lowest voltage level being exited. According to another aspect of the present invention, a control method for blocking at least two converters of a series MTDC system is provided. The method comprises: selecting the first pair from the target ones; making the powers of the selected converters decreased to zero; synchronously triggering the bypass pair of the inverter and rectifier, controlling switches of DC side orderly; and synchronously blocking the inverter and rectifier of the first pair; and blocking the next pair following the same procedure for the first pair if existing.
According to another aspect of the present invention, a control method for emergency blocking a target converter of a series MTDC system is provided. The method comprises: identifying the fault point, and triggering the bypass pair of the target converter; adjusting the power balance in the MTDC system, meanwhile controlling switches of DC side orderly; and blocking the target converter; and building a new operation balance in MTDC system.
According to a preferred embodiment of the present invention, to build a new operation, DC voltages of at least one converter can be changed, or at least one converter can be exited.
According to another aspect of the present invention, a control method for deblocking a single converter of a series MTDC system is provided. The method comprises: controlling the switches of AC side and DC side; controlling the firing angle of the converter to decrease to a preset degree, and opening the bypass switch of the converter to be blocked; and building a new operation balance in the MTDC system.
According to another aspect of the present invention, a control method for deblocking a single converter of a series MTDC system is provided. The method comprises: controlling the switches of AC side and DC side; opening the bypass switch of the converter to be blocked, meanwhile triggering the firing angle at a preset degree; and building a new operation balance in the MTDC system.
According to another aspect of the present invention, a control method for deblocking at least two converters of a series MTDC system is provided. The method comprises: deblocking a rectifier into the MTDC system according to one of the above two control methods for deblocking a single converter of a series MTDC system; deblocking an inverter into the MTDC system according to one of the above two control methods for deblocking a single converter of a series MTDC system; and building a new operation balance in the MTDC system.
According to a preferred embodiment of the present invention, the rectifier and inverter can be deblocked synchronously.
According to another aspect of the present invention, a coordinated controller is provided. The coordinated controller is configured to realize at least one of the above mentioned methods for blocking converter(s) of a series MTDC system and/or deblocking converter(s) of a series MTDC system.
According to a preferred embodiment of the present invention, the coordinated controller comprises a DC voltage synchronous control module - configured to keep the two DC voltages of the target converters followed each other.
According to a preferred embodiment of the present invention, the coordinated controller receives the blocking or deblocking feedback of the target converters, and transferred information into a master controller.
Embodiments of the present invention provide control methods for blocking/deblocking converters of a series MTDC and achieve reliable and smooth operations for blocking/deblocking converters.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter of the invention will be explained in more details in the following description with reference to preferred exemplary embodiments which are illustrated in the drawings, in which:
Fig.1 illustrates a single line diagram of a bipolar series MTDC with 4 terminals;
Fig.2 illustrates a block diagram of a four-terminal MTDC system with a coordination controller proposed in the present invention;
Fig.3 illustrates a control method for blocking a single converter of a series MTDC system according to an embodiment of the present invention;
Fig.4 illustrates a control method for blocking at least two converters of a series MTDC system according to an embodiment of the present invention;
Fig.5 illustrates a control method for blocking at least two converters of a series MTDC system according to an embodiment of the present invention;
Fig.6 illustrates a control method for emergency blocking a target converter of a series MTDC system according to an embodiment of the present invention;
Fig.7 illustrates a control method for deblocking a single converter of a series MTDC system according to an embodiment of the present invention;
Fig.8 illustrates another control method for deblocking a single converter of a series MTDC system according to an embodiment of the present invention; and
Fig.9 illustrates a control method for deblocking at least two converters of a series MTDC system according to an embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Exemplary embodiments of the present invention are described in conjunction with the accompanying drawings hereinafter. For the sake of clarity and conciseness, not all the features of actual implementations are described in the specification.
The present invention is to be applied to for LCC based Series MTDC system, in which terminals are connected in series.
Fig.1 illustrates a single line diagram of a bipolar series MTDC with 4 terminals.
As shown in Fig.11 BPSxxx represents a bypass switch, Sxxx represents an isolated switch, Rxx represents a rectifier converter/terminal and Ixx represents an inverter converter/terminal. In practice, each converter station usually includes four switches in DC side. A bypass switch (BPS) is connected in parallel with the DC port of the converter. One point of BPS joints positive point of the DC port, and the other point of the BPS joints negative point of the DC port. A switch (S1 ) is connected in parallel with the port of DC transmission lines. One point of S1 joints positive DC transmission line, and the other point of the S1 joints negative DC transmission line. A switch (S2) is connected between the positive point of the DC port of the converter and the positive transmission line. A switch (S3) is connected between the negative point of the DC port of the converter and the negative transmission line.
Fig.2 illustrates a block diagram of a four-terminai MTDC system with a coordination controller proposed in the present invention.
As shown in Fig.2, the R1+ is regarded as a current setting terminal (CST) while others are voltage setting terminals (VST).
The block for converters in a series MTDC system can be categorized as normal block and emergency block. The normal block method is used for planning or non-emergency exiting, such as normal maintenance and exit during predictable failure, in the case of normal block, it can be divided into blocking a single converter and blocking multiple converters, for example at least two converters. While the emergency block method is used when fault occurs, a fast block of certain converters are needed.
Fig.3 illustrates a control method for blocking a single converter of a series MTDC system according to an embodiment of the present invention.
As shown in Fig.3, the control method 300 for blocking a single converter of a series MTDC system comprises:
Step 302, selecting an assistant converter besides the target converter. That's, if only one converter need to be exited from the DC system, a corresponding converter is chosen as an assistant converter. For example, in the case that the inverter 12+ is the converter to be exited, R2+ is selected as the assistant converter. The firing angle of 12+ will be changed to about 90 degree finally, and be held;
Step 304, making the powers of the two converters decreased to zero. For example, the coordinated controller control the 12+ and R2+ power references with a preset decreasing ramp (for example 0.002 p.uJms). During the blocking process, the power reference of 12+ should be always lower than that of R2+ (This request can keep there is no overload in other terminals)
Step 306, triggering the bypass pair of the target converter, controlling switches of DC side orderly, and blocking the target converter. It's obvious for the person skilled in art how to orderly operate the switches for blocking a converter according to the teaching of the present invention especially based on the configuration of specific MTDC system. For example, trigger the bypass pair in the I2+; then close the bypass switch BPS 12+; when BPS 12+ is closed, block the bypass pair; close the switch S1 \2+, and then open the bypass switch BPSI2+; then open switches S2I2+ and S3I2+; block the I2+, and then turn into isolate program and signal coordinated controller.
Step 308, adjusting the MTDC system into a new balance. It shall be noted that all solutions for adjusting the MTDC system in prior art can be used in the present invention, and it's obvious for the person to use such existing solution with some necessary modification.
According to a preferred embodiment of the present invention, the method further comprises exiting the assistant converter after blocking the target converter. That's, R2+ can operate at reduced power mode. System operators will decide whether R2+ should be exited or not finally.
The above embodiment exits an inverter if a rectifier needs to be exited, the person skilled in art knows that the corresponding method is similar according to above mentioned steps. But in this case, it should be noticed that if the CST will be exited from DC system, the current setting function of this CST must shift to other converter at first.
The key of the blocking control method is the coordination between the target converter and the assistant converter. DC voltages of the converter pair to be exited should be coordinated well to avoid disturbance on the CST. In this invention, a coordinated controller is introduced. Whether the assistant converter needs to exit or not, depends on careful consideration of reactive power absorption, AC voltage variation, power losses and the limit of operation voltage and so on.
In the present invention, the assistant converter is the one located at the same pole as the target converter with opposite position. The performance of this Opposite position' is that if the target converter is a sending terminal, the assistant converter in opposite position should be a receiving terminal, and vice versa. According to a preferred embodiment of the present invention, the assistant converter can be identified based on its position, power capacity, short circuit capacity, power grid security level and/or priority.
!n detail, the assistant converter is close to the grounding pole; the assistant converter has a matched power capacity with the target one, for example, the matched power capacity of the assistant converter shall be same with or above that of the target one; and/or the assistant converter is located in AC system with high short circuit capacity. Other factors such as power grid security level, economic benefit, etc. are also considered during the determination of an assistant converter; especially the non-critical converter should be selected with high priority.
in some cases, such as normal maintenance, several terminals/converters need to be exited. Some matched pairs with a rectifier and a suitable inverter should be predefined for exit operation.
Fig.4 illustrates a control method for blocking at least two converters of a series TDC system according to an embodiment of the present invention.
As shown in Fig.4, the control method 400 for blocking at least two converters of a series MTDC system comprises:
Step 402, selecting the first pair from the target ones. For example, R2+ and 12+ are selected as the exited converters.
Step 404, making the powers of the selected converters decreased to zero. For example, the coordinated controller controls power references of the 12+ and R2+ to decrease with a preset ramp (e.g. 0.002 p.u./ms), and l2+'s power reference is a little bit lower of R2+'s power reference. The firing angle of 12+ and R2+ will be changed to 90 degree and be held.
Step 406, triggering the bypass pair of the inverter of the first pair, controlling switches of DC side orderly; and blocking the inverter. For example, trigger the bypass pair in the I2+; then close the BPSI2+, and block the bypass pair. Close the S112+, and open the BPSI2+, and then open S2I2+ and S3I2+. Block the I2+, and turn into isolate process, and signal the coordinated controller.
Step 408, triggering the bypass pair of the rectifier of the first pair, controlling switches of DC side orderly; and blocking the rectifier. For example, trigger the bypass pair in the R2+; and follow the similar process in step 406.
Step 410, blocking the next pair following the same procedure for the first pair if existing. If the power is not exactly match, the CST converter will keep DC current constant in the whole method, !n the end, the coordinated controller will make a new balance of power transmission.
In the present invention, each pair of the target ones are in the same pole; each pair includes a rectifier and an inverter; the power capacities of the rectifier and inverter in the each pair should be matched. If several pairs need to be exited, the pair with lower voltage level will be exited firstly. Especially, the grounding electrodes need to be shifted to other converters after the converters with lowest voltage level being exited.
Fig.5 illustrates a control method for blocking at least two converters of a series MTDC system according to an embodiment of the present invention.
As shown in Fig.5, the control method 500 for blocking at least two converters of a series MTDC system comprises: steps 502-508, in which, steps 502, 504 and 508 are same or similar to steps 402, 404 and 410 in Fig.4. In order to keep description concise, such steps won't be explained further.
Step 506, synchronously triggering the bypass pair of the inverter and rectifier, controlling switches of DC side orderly; and synchronously blocking the inverter and rectifier.
Based on the synchronous process, the method can improve the exit speed for both inverter and rectifier.
When a terminal/converter needs to be blocked out of DC system due to failure or some other emergency operations, emergency block method plays an important role.
Fig.6 illustrates a control method for emergency blocking a target converter of a series MTDC system according to an embodiment of the present invention.
As shown in Fig.6, the control method 600 for emergency blocking a target converter of a series MTDC system comprises:
Step 602, identifying the fault point, and triggering the bypass pair of the target converter. For example, when 12+ need to be exited under emergency operation, firstly confirm the fault can be insulated by bypass switch; trigger the bypass pair of I2+, but if the bypass pair is not available, the action can be canceled; The fault type will be detected and send to coordinated controller.
Step 604, adjusting the power balance in the MTDC system, meanwhile controlling switches of DC side orderly and blocking the target converter. The CST automatically adjusts the active power balance in the DC system, in order to maintain the constant DC current. Close the BPSI2+, and then block the bypass pair (if the bypass pair is triggered); Close the S1 I2+, and open the BPSI2+, and then open S2I2+ and S312+; Block the I2+, and then turn into isolate program and signal coordinated controller;
Step 606, building a new operation balance in MTDC system. The coordinated controller establishes a new operating balance of the MTDC system. According to a preferred embodiment of the present invention, to build a new operation, DC voltages of at least one converter can be changed, or at least one converter can be exited.
If other converters need to be blocked, the method is the same. But if the exit converter is the CST, the current control task will be shifted to another terminal automatically. And the rest procedures are the same. In fact, the normal exit can use this method too, but with higher disturbance (overshoot of current and voltage) in the DC system.
When the exited terminals/converters need to be re-entered into the DC system, the control method for deblocking converters will play an important role. The method is a planned operation. But there are different methods in single action or multiple. Two methods for deblocking a single converter are proposed.
Fig.7 illustrates a control method for deblocking a single converter of a series MTDC system according to an embodiment of the present invention.
As shown in Fig.7, the control method 700 for deblocking a single converter of a series MTDC system comprises:
Step 702, controlling the switches of AC side and DC side. For example, 12+ is turned out of isolated status and energized; RPC (the reactive power controller) of 12+ is started up and put into calculated filters or reactive power compensation equipments and the tap changer operation is forbidden. Close switches S212+ and S3I2+; close the bypass switch BPS12+ and then open the switch S112+.
Step 704, controlling the firing angle to decrease to a preset degree, and opening a bypass switch. In detail, de-block the converter when the firing angle is deblocked at 90 degree. And then the firing angle drops with a preset ramp until the angle reaches a preset degree. The degree is close to 90, and makes the current on BPSI2+ to slightly oscillate across zero. Then Open the BPSI2+.
Step 706, building a new operation balance in the MTDC system. After BPSI2+ is opened, signal coordinated controller; get feedback from coordinated controller and increase DC voltage of I2+ with a calculated rise ramp. The CST and coordinated controller adjust other DC voltages or DC current according to the principle of power conservation; finally, obtain a new balance in DC system, and open the tap changer operation. According to the present invention, another control method for deblocking a single converter of a series MTDC system is provided for opening BPS 12+ safely.
Fig.8 illustrates another control method for deblocking a single converter of a series MTDC system according to an embodiment of the present invention.
As shown in Fig.8, the control method 800 for deblocking a single converter of a series MTDC system comprises:
Step 802, controlling the switches of AC side and DC side. For example, Opening the BPSI2+ at t0; the firing angle is held at a small angle (The angle is a preset value), until t0+At (and At is a calculated time in advance).
Step 804, opening a bypass switch, meanwhile triggering the firing angle at a preset degree. The current of BPS 12+ rapidly drops to zero through the lower firing angle; then the BPS 12+ is opened successfully.
Step 806, building a new operation balance in the MTDC system.
The advantage of the second method for deblocking a single converter shown in Fig.8 includes that the reactive power and reactive power changes are reduced due to the faster process.
In some cases, converters shall be connected to the MTDC system at the same time. One method is to enter one by one; the other is to enter pair by pair.
Fig.9 illustrates a control method for deblocking at least two converters of a series MTDC system according to an embodiment of the present invention.
As shown in Fig.9, the control method 900 for deblocking at least two converters of a series MTDC system comprises:
Step 902, deblocking a rectifier according to the above mentioned method shown in Fig. 7 or 8 into the MTDC system. For example, the 12+ and R2+ will be linked into MTDC system. At first, R2+ is entered into DC system according to the method for deblocking single converter. R2+ increases DC voltage with a calculated ramp until the voltage is reach to the reference value calculated by master control, and the CST maintains the DC current with adjusting its DC voltage;
Step 904, deblocking an inverter according to the above mentioned method shown in Fig. 7 or 8 into the MTDC system. 12+ enters into MTDC system according to the method for deblocking single converter, then 12+ increases its DC voltage with a calculated ramp until rating voltage and the CST maintains the DC current.
Step 906, building a new operation balance in the MTDC system. Coordinated controller adjusts R2+ and 12+ to rise until rating, and then the DC system run in a new balance.
Another method for deblocking at least two converters of a series MTDC system is proposed that the pair actions synchronously, i.e. the rectifier and inverter can be deblocked synchronously, and the R2+ and 12+ will step up their DC voltages adjusted by a controller.
According to another aspect of the present invention, a coordinated controller is provided. The coordinated controller is configured to direct the above mentioned method for blocking converter(s) of a series MTDC system and/or deblocking converter(s) of a series MTDC system. In detail, the coordinated controller comprises a DC voltage synchronous control module configured to keep the two DC voltages of the target converters followed each other.
According to a preferred embodiment of the present invention, the coordinated controller receives the blocking or deblocking feedback of the target converters, and modifies parameters in a master controller. For example, a master controller for a series MTDC system comprises: a choosing module, configured to choose one terminal as a current setting terminal (CST) and define other terminals as voltage setting terminals (VST); a configuration module, configured to configure a current reference of the series MTDC system as the input of the CST converter, generate current values for each VST converter based on said current reference and different margins thereof respectively and make the minimum value of current reference in the rectifier side larger than the maximum value of current reference in the inverter side. For any detail about master controller, the whole description of PCT/CN2012/073796 filed on April 11 , 2012 ("Master Control Method for a Series MTDC System and Element Thereof) can be cited in the present invention for reference.
Compared with the existing prior arts, the proposed solution of the present invention is much more practical and easier for implementation on the series MTDC system. Referring to the description of the exemplary embodiments, those skilled in the art appreciate the advantages of the present invention: 1 , According to a control method for blocking/deblocking converters) of a series MTDC system and controller thereof proposed in the present invention, a number of methods are proposed for converter entering/exiting in a series MTDC system.
2, According to a control method for blocking/deblocking converter(s) of a series MTDC system and controller thereof proposed in the present invention, the safe and reliable actions are provided, and a smooth of entering and exiting process can be achieved.
3, According to a control method for blocking/deblocking converter(s) of a series MTDC system and controller thereof proposed in the present invention, a new criterion for selecting an assistant converter is introduced; and the suitable and exact setting At can help designer stay away from potential traps.
4, According to a control method for blocking/deblocking converters) of a series MTDC system and controller thereof proposed in the present invention, reactive power control action in entering is introduced. A calculated reactive power setting is necessary in entering because the big firing angle with large constant DC current in starting leads huge reactive power absorbed by converter.
Though the present invention has been described on the basis of some preferred embodiments, those skilled in the art should appreciate that those embodiments should by no means limit the scope of the present invention. Without departing from the spirit and concept of the present invention, any variations and modifications to the embodiments should be within the apprehension of those with ordinary knowledge and skills in the art, and therefore fall in the scope of the present invention which is defined by the accompanied claims.

Claims

1. A control method for blocking a single converter of a series MTDC system, wherein said method comprises:
selecting an assistant converter besides the target converter;
making the powers of the two converters decreased to zero;
triggering the bypass pair of the target converter, controlling switches of DC side orderly, and blocking said target converter; and
adjusting the MTDC system into a new balance.
2. The control method according to claim 1 , wherein said method further comprises exiting said assistant converter after blocking said target converter.
3. The control method according to claim 1 or 2, wherein said assistant converter is the one located at the same pole as the target converter with opposite position.
4. The control method according to claim 3, wherein said assistant converter can be identified based on its position, power capacity, short circuit capacity, power grid security level and/or economic benefit.
5. The control method according to claim 4, wherein said assistant converter is close to the grounding pole; said assistant converter has a matched power capacity with said target one; and/or said assistant converter is located in AC system with high short circuit capacity.
6. The control method according to claim 5, wherein said matched power capacity of said assistant converter shall be same with or above that of said target one.
7. A control method for blocking at least two converters of a MTDC system, wherein said method comprises:
selecting the first pair from the target ones; making the powers of the selected converters decreased to zero;
triggering the bypass pair of the inverter of said first pair, controlling switches of DC side orderly; and blocking the inverter;
triggering the bypass pair of the rectifier of said first pair, controlling switches of DC side orderly; and blocking the rectifier; and
blocking the next pair following the same procedure for the first pair if existing.
8. The control method according to claim 7, wherein each pair of the target ones are in the same pole; said each pair includes a rectifier and an inverter; the power capacities of the rectifier and inverter in said each pair-should be matched.
9. The control method according to claim 7 or 8, wherein the pair with lower voltage level will be exited firstly.
10. The control method according to claim 9, wherein the grounding electrodes need to be shifted to other converters after the converters with lowest voltage level being exited.
11. A control method for blocking at least two converters of a series MTDC system, wherein said method comprises:
selecting the first pair from the target ones;
making the powers of the selected converters decreased to zero;
synchronously triggering the bypass pair of the inverter and rectifier, controlling switches of DC side orderly; and synchronously blocking the inverter and rectifier of the first pair; and
blocking the next pair following the same procedure for the first pair if existing.
12. A control method for emergency blocking a target converter of a series MTDC system, wherein said method comprises:
identifying the fault point, and triggering the bypass pair of said target converter; adjusting the power balance in the MTDC system, meanwhile controlling switches of DC side orderly; and blocking the target converter; and
building a new operation balance in MTDC system.
13. The control method according to claim 12, wherein, to build a new operation, DC voltages of at least one converter can be changed, or at least one converter can be exited.
14. A control method for deblocking a single converter of a series MTDC system, wherein said method comprises:
controlling the switches of AC side and DC side;
controlling the firing angle of the converter to decrease to a preset degree, and opening the bypass switch of the converter to be blocked; and building a new operation balance in the MTDC system.
15. A control method for deblocking a single converter of a series MTDC system, wherein said method comprises:
controlling the switches of AC side and DC side;
opening the bypass switch of the converter to be blocked, meanwhile triggering the firing angle at a preset degree; and
building a new operation balance in the MTDC system. 6. A control method for deblocking at least two converters of a series MTDC system, wherein said method comprises:
deblocking a rectifier into the MTDC system according to the method of claim 14 or 15;
deblocking an inverter into the MTDC system according to the method of claim 14 or 15; and
building a new operation balance in the MTDC system.
17. The control method according to claim 16, wherein said rectifier and inverter can be deblocked synchronously.
18. A coordinated controller, wherein said coordinated controller is configured to realize the method for blocking converter(s) of a series MTDC system according to any one of claims 1 -13 and/or deblocking converter(s) of a series MTDC system according to any one of claims 14-17.
19. The coordinated controller according to claim 18, wherein said coordinated controller comprises a DC voltage synchronous control module, configured to keep the two DC voltages of the target converters followed each other.
20. The coordinated controller according to claim 18 or 19, wherein said coordinated controller receives the blocking or deblocking feedback of the target converters, and transferred information into a master controller.
PCT/CN2013/074953 2013-04-28 2013-04-28 A control method for blocking/deblocking converters of a series mtdc system and controller thereof WO2014176726A1 (en)

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