WO2020038275A1 - 一种双极双向直流变换器及其控制方法和控制装置 - Google Patents

一种双极双向直流变换器及其控制方法和控制装置 Download PDF

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Publication number
WO2020038275A1
WO2020038275A1 PCT/CN2019/100792 CN2019100792W WO2020038275A1 WO 2020038275 A1 WO2020038275 A1 WO 2020038275A1 CN 2019100792 W CN2019100792 W CN 2019100792W WO 2020038275 A1 WO2020038275 A1 WO 2020038275A1
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Prior art keywords
voltage
port
low
type
valve
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PCT/CN2019/100792
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English (en)
French (fr)
Inventor
杨晨
张中锋
田杰
谢晔源
李海英
王宇
葛健
Original Assignee
南京南瑞继保电气有限公司
南京南瑞继保工程技术有限公司
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Application filed by 南京南瑞继保电气有限公司, 南京南瑞继保工程技术有限公司 filed Critical 南京南瑞继保电气有限公司
Priority to JP2021509868A priority Critical patent/JP2021534714A/ja
Priority to EP19852160.1A priority patent/EP3823147A4/en
Priority to KR1020217004789A priority patent/KR20210032484A/ko
Priority to BR112021002644-4A priority patent/BR112021002644A2/pt
Priority to RU2021105725A priority patent/RU2754426C1/ru
Priority to US17/268,536 priority patent/US11223291B2/en
Publication of WO2020038275A1 publication Critical patent/WO2020038275A1/zh

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    • 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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33584—Bidirectional converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • 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
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/0077—Plural converter units whose outputs are connected in series
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • 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
    • 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
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
    • 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
    • H02M7/79—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 triode or transistor type requiring continuous application of a control signal
    • H02M7/797—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 triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—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
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/487—Neutral point clamped inverters
    • 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 present application relates to the field of power electronics applications, and relates to a DC power grid and a bidirectional DC converter, and in particular, to a bipolar bidirectional DC converter, a control method and a control device thereof.
  • Bidirectional DC converters as an important component of voltage conversion in DC grids, have attracted more and more attention from scholars in the field of DC grids.
  • the bidirectional DC converters of this type of application mostly use ISOP, ISOS structure or MMC back-to-back power conversion devices.
  • the power conversion device based on the MMC back-to-back structure is more suitable for power conversion between high to high / medium voltage DC power supply systems.
  • the DC bus of the system is generally used with a bipolar connection type, that is, the insulation voltage between the positive and negative poles of the DC bus is half the voltage between the positive and negative poles.
  • bipolar wiring types There are two types of bipolar wiring types: pseudo-bipolar and true bipolar.
  • pseudo-bipolar wiring type when one pole of the DC system bus is shut down, the other pole must also be shut down; while in the true bipolar wiring type, when the DC system has one pole shut down, it does not Will affect the operation of the other pole.
  • the MMC back-to-back structure is an isolated two-way DC converter. By combining it, it is easier to realize two-way power transmission between DC buses under different bus wiring types such as true / false bipolar.
  • the MMC back-to-back structure includes two MMC converter valve groups and a high-power industrial frequency or intermediate frequency AC transformer, and the construction cost is relatively high.
  • Some literatures have studied a two-way DC converter with AUTO-DC structure derived from the evolution of MMC back-to-back structure. The principle of this converter is similar to an AC autotransformer, and it is a non-isolated two-way DC converter. Compared with the MMC back-to-back structure, it can reduce the capacity of the AC transformer and the converter valve group, which is suitable for applications where the isolation requirements are not high.
  • the AUTO-DC structure is a non-isolated circuit. The AUTO-DC structure obtained by directly referring to the AC autotransformer cannot be directly applied in a bipolar system.
  • the negative or positive electrode of the low-voltage port will be the same as the negative or positive of the high-voltage port, so it is insulated from the ground.
  • the voltage will become half of the voltage between the positive and negative poles on the high voltage side, thereby increasing the insulation stress to ground on the low voltage side of the device.
  • the patent CN105048813A has optimized the AUTO-DC structure.
  • the optimized AUTO-DC structure can realize the power conversion between the DC power supply system where the high-voltage DC bus is a pseudo-bipolar and the low-voltage DC bus is also a pseudo-bipolar.
  • the solution of the patent CN105048813A can only be used to connect both ends of the low-voltage port to the low-voltage DC bus.
  • the positive and negative poles of the system when the low-voltage side has a pole bus out of service, this solution does not provide another pole to the neutral point circuit, so only the entire system can be out of service.
  • an embodiment of the present application provides a bipolar bidirectional DC converter, including: at least two valve group strings, which are distinguished according to a connection relationship between the valve group string and a low-voltage port of the bidirectional DC converter; Two valve cluster strings and at least six magnetic components are divided into I-type valve clusters and II-type valve clusters according to the connection relationship between the valve cluster strings and the low-voltage port of the bidirectional DC converter; low-voltage DC ports of I-type valve clusters
  • the positive pole of the bipolar bidirectional DC converter constitutes the positive pole of the low-side port of the bipolar bidirectional DC converter; the positive pole of the low-voltage DC port of the type II valve string is connected to the negative pole of the low-voltage DC port of the I-type valve string, forming the low-side port of the bipolar bidirectional DC converter.
  • the negative pole of the low-voltage DC port of the type II valve string constitutes the negative pole of the low-side port of the bipolar bidirectional DC converter; each valve string includes a high-voltage DC port, a low-voltage DC port, and at least three AC ports.
  • the positive poles of the high-voltage DC ports are connected as the positive poles of the high-voltage side ports of the bipolar bidirectional DC converter; the negative poles of all the high-voltage DC ports are connected,
  • the negative electrode for the bipolar high-pressure side port bidirectional converter DC; each AC port is connected to a magnetic element; the other end of the magnetic member all communicate with a valve port serial connection.
  • the bipolar bidirectional DC converter further includes a first isolation switch, a second isolation switch, a third isolation switch, a fourth isolation switch, a fifth isolation switch, and a sixth isolation switch.
  • the first isolation switch The switch is connected between the positive terminal of the high-voltage DC port of the valve group string and the positive terminal of the high-voltage DC bus; the second isolation switch is connected between the negative electrode of the high-voltage DC port of the valve group string and the negative terminal of the high-voltage DC bus.
  • the third disconnect switch is connected between the positive pole of the low voltage DC port of the type I valve string and the positive end of the low voltage DC bus; the fourth disconnect switch is connected to the low voltage DC of the type I valve string.
  • the fifth isolation switch is connected between the anode of the low-voltage DC port of the type II valve string and the neutral point of the low-voltage DC bus; the sixth The disconnector is connected between the negative pole of the low-voltage DC port of the type II valve string and the negative pole of the low-voltage DC bus.
  • the magnetic element is a reactor.
  • the magnetic element is an AC transformer.
  • the valve group strings each include a voltage source type converter
  • the voltage source type converter has the same number of AC ports as the valve group string
  • the voltage source type converter includes AC- A DC conversion circuit.
  • the AC-DC conversion circuit includes at least one AC port and one DC port.
  • the DC ports of all the voltage source converters in the valve group string are connected in series in sequence, and the positive terminal of the DC port of the first voltage source converter is the high voltage DC of the valve group string.
  • the positive terminal of the port, the negative terminal of the DC port of the last voltage source converter is the positive electrode of the high voltage DC port of the valve string; all the AC ports are the AC ports of the valve string.
  • the positive poles of two voltage source converter DC ports are selected from the valve group string and used as the low voltage DC port of the valve group string; wherein the positive electrode with a high voltage is used as the positive end of the low voltage DC port.
  • the negative terminal of the low voltage is used as the negative terminal of the low-voltage DC port.
  • the negative terminal selected is equal to the neutral point potential of the high-voltage DC bus.
  • the positive terminal selected is high-voltage DC The neutral potentials of the busbars are equal.
  • the negative poles of the two voltage source-type converter DC ports are selected from the valve group string to be used as the low-voltage DC port of the valve group string; wherein the negative electrode with the high voltage is used as the positive end of the low-voltage DC port, The negative electrode with low voltage is used as the negative terminal of the low-voltage DC port.
  • the negative terminal selected is equal to the neutral point potential of the high-voltage DC bus.
  • the positive terminal and the high voltage side are selected The neutral point potentials of the DC buses are equal.
  • the voltage source converter includes: at least two groups of four valve arms connected in series; wherein each valve arm includes a valve arm reactance and a power module connected in series; each group is connected in series up and down The two ends of the valve arm are connected in parallel to serve as a DC port of the voltage source converter; each group of valve arms in series connected up and down leads out as an AC port of the voltage source converter.
  • the power module includes: a half-bridge plus capacitor structure.
  • the power module includes a full-bridge plus capacitor structure.
  • the power module includes a full-bridge plus capacitor and a half-bridge plus capacitor structure.
  • the embodiment of the present application further provides a control method of the bipolar bidirectional DC converter as described above, including: closing all valve strings in a high voltage DC port and a disconnect switch connected to a positive electrode and a negative electrode of the low voltage DC port during normal operation.
  • the method further comprises: detecting a first potential difference between the positive electrode of the low-voltage DC port and the negative electrode of the low-voltage DC port of the type I valve string; and when the first potential difference deviates from a first target value, adjusting the The power transmitted by the voltage source converter of the type I valve string through the magnetic element until the first potential difference is equal to the first target value, wherein the voltage source type converter is located in the type I valve string Between the positive pole of the low voltage DC port and the negative pole of the low voltage DC port or between the positive pole of the low voltage DC port of the type I valve string and the positive pole of the high voltage DC port; detecting the negative pole of the low voltage DC port and the negative pole of the high voltage DC port of the type I valve string When the second potential difference deviates from the second target value, adjust the power transmitted by the voltage source converter of the I-type valve string through the magnetic element until the second potential difference is equal to The second target value, wherein the voltage source converter is located between the positive pole of the low-voltage DC
  • the first target value is a half of a positive and negative terminal voltage reference value of the low-voltage DC port of the bipolar bidirectional DC converter; the second target value is a high voltage of the bipolar bidirectional DC converter Half of the voltage reference of the positive and negative terminals of the DC port.
  • the method further comprises: detecting a third potential difference between the positive pole of the low-voltage DC port and the negative pole of the low-voltage DC port of the type II valve string; and adjusting the II when the third potential difference deviates from a third target value Power of the voltage source converter of the valve group through the magnetic element until the third potential difference is equal to the third target value, wherein the voltage source converter is located in the type II valve group string Between the low-voltage DC port positive electrode and the low-voltage DC port negative electrode or between the low-voltage DC port negative electrode and the high-voltage DC port negative electrode of the type II valve string; detecting the low-voltage DC port negative electrode and high-voltage DC port negative electrode of the type II valve string When the fourth potential difference deviates from the fourth target value, adjust the power transmitted by the voltage source converter of the type II valve string through the magnetic element until the fourth potential difference is equal to The fourth target value, wherein the voltage source converter is located between the positive pole of the low voltage DC port of the type II valve string to
  • the third target value is a half of a positive and negative terminal voltage reference value of the low-voltage DC port of the bipolar bidirectional DC converter; the fourth target value is a high voltage of the bipolar bidirectional DC converter Half of the voltage reference of the positive and negative terminals of the DC port.
  • the method further comprises: when a short-term fault occurs in the high-voltage DC bus, adjusting the switching states of the power modules composed of the full-bridge plus capacitor structure in all the valve string; Switch status of the group.
  • the method further comprises: adjusting the voltage source switching between the low-voltage DC ports in all type I valve strings when the positive end of the low-voltage DC bus is short-to-ground or at the neutral point.
  • the switching state of the power module composed of the full bridge plus capacitor structure of the current transformer; after the fault is recovered, the switching state of the above module is restored.
  • the method further comprises: adjusting the voltage source switching between the low-voltage DC ports of all type II valve strings when the negative end of the low-voltage DC bus is short-to-ground or at the neutral point.
  • the switching state of the power module composed of the full bridge plus capacitor structure of the current transformer; after the fault is recovered, the switching state of the above module is restored.
  • the method further comprises: when the positive end of the low-voltage side DC bus is to earth or a permanent fault occurs, the type I valve string is blocked, and the type I valve string high voltage DC port is disconnected at the same time.
  • Isolation switch or full-control switch connected to the positive and negative poles of the low-voltage DC port to isolate the above-mentioned faults; keep the working state of the type II valve string unchanged, and continue to complete the high-voltage DC bus to the negative and neutral points of the low-voltage DC bus Power conversion.
  • the method further comprises: when the negative end of the low-voltage DC bus to the ground or the neutral point has a permanent fault, the type II valve string is blocked, and the type II valve string high-voltage DC port is disconnected at the same time.
  • Isolation switch or full-control switch connected to the positive and negative poles of the low-voltage DC port to isolate the above-mentioned faults; keep the working status of the type I valve string unchanged, and continue to complete the high-voltage DC bus to the positive and neutral points of the low-voltage DC bus. Power conversion.
  • the embodiment of the present application further provides a control device for the bipolar bidirectional DC converter as described above, which includes a normal working unit, and the normal working unit controls to close all the valve strings when the bipolar bidirectional DC converter works normally.
  • Disconnectors connected to the positive and negative terminals of the DC port and the low-voltage DC port.
  • the control device further includes a first detection unit, a first adjustment unit, a second detection unit, and a second adjustment unit.
  • the first detection unit detects the positive and low voltages of the low-voltage DC port of the type I valve string.
  • the first potential difference of the negative terminal of the DC port when the first potential difference deviates from the first target value, the first regulating unit is enabled; the first regulating unit regulates the voltage source commutation of the type I valve string
  • the second detection unit detects a second potential difference between the negative electrode of the low-voltage DC port and the negative electrode of the high-voltage DC port of the type I valve string
  • a second regulating unit is enabled; the second regulating unit regulates the voltage source type converter of the type I valve string through the magnetic element.
  • the voltage source converter is located between the low-voltage DC port positive electrode of the type I valve string and the low-voltage DC port negative electrode or the I
  • the valve string is connected between the negative pole of the low voltage DC port and the negative pole of the high voltage DC port.
  • control device further includes a third detection unit, a third adjustment unit, a fourth detection unit, and a fourth adjustment unit, and the third detection unit detects the positive electrode of the low-voltage DC port of the type II valve string and the low-voltage DC.
  • the third potential difference of the negative terminal of the port when the third potential difference deviates from the third target value, the third adjustment unit is enabled; the third adjustment unit adjusts the voltage source converter of the type II valve group through The power transferred by the AC transformer until the third potential difference is equal to the third target value, wherein the voltage source converter is located between the low voltage DC port positive electrode of the type II valve string and the low voltage DC port negative electrode Or between the low-voltage DC port negative electrode of the type II valve string and the high-voltage DC port negative electrode; the fourth detection unit detects a fourth potential difference between the low-voltage DC port negative electrode and the high-voltage DC port negative electrode of the type II valve string When the fourth potential difference deviates from the fourth target value, a fourth adjustment unit is enabled; the fourth adjustment unit adjusts the voltage source converter of the type II valve string through the AC voltage conversion The transmitted power until the fourth potential difference is equal to the fourth target value, wherein the voltage source converter is located between the low voltage DC port positive electrode of the type II valve string or the low voltage DC port negative electrode or
  • the control device further includes a high-voltage DC bus short-term fault processing unit, a low-voltage side DC bus positive-side short-term fault processing unit, and a low-voltage side DC bus-negative short-term fault processing unit.
  • DC bus short-term fault processing unit When short-term faults occur in the high-voltage DC bus, adjust the switch states of the power modules composed of the full bridge plus capacitor structure in all valve cluster strings. After the fault is recovered, the switches of the above modules are restored. State; the low-voltage side DC bus positive short-term fault processing unit adjusts the low-voltage DC ports of all type I valve strings when the positive end of the low-voltage DC bus is short-to-ground or at a neutral point.
  • the switching state of the power module composed of the full-bridge plus capacitor structure of the voltage source converter is restored after the fault is restored; the switching state of the low-side DC bus negative terminal short-term fault processing unit is When the negative terminal of the low-voltage DC bus is short-to-ground or the neutral point, adjust the voltage source switching between the low-voltage DC ports of all type II valve strings.
  • the switching state of the power module of the full-bridge capacitor structure is added to the composition, until failure recovery, the module reconstructs the switching state.
  • control device further includes a positive-side permanent fault processing unit of the low-side DC bus, a negative-side permanent fault processing unit of the low-side DC bus, and the positive-side permanent fault processing unit of the low-voltage DC bus acts as a low voltage.
  • a positive-side permanent fault processing unit of the low-side DC bus a negative-side permanent fault processing unit of the low-side DC bus
  • the positive-side permanent fault processing unit of the low-voltage DC bus acts as a low voltage.
  • the technical solution provided in the embodiment of the present application compared with the circuit using the MMC back-to-back structure in the existing application, constructs the high-voltage side pseudo-bipolar and low-voltage side true bipolar structures in the same way.
  • the system Valve group and transformer capacity reduce system design costs.
  • the high-voltage side DC bus can adopt a pseudo-bipolar wiring method. At the same time, there is no positive and negative terminal-to-earth voltage on the low-voltage side and the same voltage on the high-voltage side to ground. , Leading to increased insulation stress.
  • FIG. 1 is a schematic structural diagram of a bipolar bidirectional DC converter proposed by the present application
  • FIG. 2 is a schematic diagram of each port definition of a single valve string
  • FIG. 3 is a schematic structural diagram of a bidirectional DC converter including only two valve trains and each valve train including only three VSCs;
  • FIG. 4 is a schematic structural diagram of a single voltage source converter
  • Figure 5 is a half-bridge plus capacitor power module
  • Figure 6 is a full-bridge plus capacitor power module
  • FIG. 7 is a schematic diagram of a control strategy for a type I valve train
  • FIG. 8 is a schematic diagram of a control strategy for a type II valve train
  • FIG. 9 is a schematic diagram of a control strategy of a type I valve group string provided by another embodiment.
  • FIG. 10 is a schematic diagram of a control strategy for a type II valve group string according to another embodiment.
  • a bipolar bidirectional DC converter is provided.
  • one pole of the low-voltage DC bus fails, it does not affect the normal operation of the other pole, and the power conversion from the high-voltage DC bus to the low-voltage DC bus can still be achieved.
  • a control method and a control device of a bipolar bidirectional DC converter are also provided.
  • FIG. 1 is a schematic structural diagram of a bipolar bidirectional DC converter proposed by the present application.
  • the bidirectional DC converter is composed of at least two valve strings and six magnetic elements.
  • Each valve string has a high-voltage DC port, a low-voltage DC port, and at least three AC ports.
  • the positive poles of the high-voltage DC ports of all valve strings are connected to form the positive pole of the high-voltage side port of the bidirectional DC converter; the negative poles of the high-voltage DC ports of all valve strings are connected to form the high-voltage side port of the two-way DC converter. negative electrode.
  • each AC port is connected to a magnetic element.
  • the other ends of the magnetic components connected to all the AC ports in a single valve string are connected in parallel.
  • the valve group string is divided into a type I valve group string and a type II valve group string.
  • the positive pole of the low-voltage DC port of the type I valve string constitutes the positive pole of the low-voltage side port of the bidirectional DC converter, and the negative end thereof forms the neutral point of the low-voltage side port of the bidirectional DC converter.
  • the positive pole of the low-voltage DC port of the type II valve string constitutes the neutral point of the low-voltage side port of the bidirectional DC converter, and the negative end forms the negative pole of the low-voltage side port of the bidirectional DC converter.
  • the neutral point of the low-side port of the two-way DC converter formed by the type I valve string and the type II valve string is the same point.
  • the module 101 is a type I valve group string
  • the module 102 is a type II valve group string
  • the module 103 is a magnetic element.
  • the components 104 to 111 are isolation switches.
  • components 104 to 107 are isolation switches connected to the high-pressure port of the valve string
  • components 108 to 111 are isolation switches connected to the low-pressure port of the valve string.
  • Isolation switches include full control switches, but not limited to them.
  • the first isolation switches 106 and 104 are respectively connected between the positive ends of the high-voltage DC ports of the type I valve cluster and the type II valve cluster and the positive end of the high-voltage DC bus.
  • the second isolation switches 107 and 105 are respectively connected between the negative terminal of the high-voltage DC port of the type I valve group string and the type-II valve group string and the negative terminal of the high-voltage DC bus.
  • the third isolation switch 110 is connected between the positive electrode of the low-voltage DC port of the type I valve string and the positive end of the low-voltage DC bus.
  • the fourth isolation switch 111 is connected between the negative pole of the low-voltage DC port of the type I valve string and the neutral point of the low-voltage DC bus.
  • the fifth isolation switch 108 is connected between the positive pole of the low-voltage DC port of the type II valve string and the neutral point of the low-voltage DC bus.
  • the sixth isolation switch 109 is connected between the negative electrode of the low-voltage DC port of the type II valve string and the negative electrode of the low-voltage DC bus.
  • Figure 2 is a schematic diagram of each port definition of a single valve string.
  • the assembly 201 illustrates the composition of a valve string, including a high-voltage DC port, a low-voltage DC port, and at least three AC ports.
  • the positive poles of the high-voltage DC ports of all the valve strings of the bi-directional DC converter are connected through the isolation switch respectively, and are connected to the positive end of the high-voltage DC bus.
  • the negative poles of the high-voltage DC ports of all the valve strings are connected through disconnectors and connected to the negative end of the high-voltage DC bus.
  • the positive and negative poles of the low-voltage DC port of the two-way DC converter type I valve string are respectively connected to the positive end and the neutral point of the low-voltage DC bus after being disconnected.
  • the positive and negative poles of the low-voltage DC port of the two-way DC converter type II valve string are respectively connected to the neutral point and the negative end of the low-voltage DC bus through isolating switches.
  • the component 202 is a reactor.
  • the magnetic element connected to a single valve string can be a reactor, and each outlet of the AC port is connected to a reactor.
  • the module 203 is an AC transformer.
  • the magnetic component connected to a single valve string can be an AC transformer, and an AC port is connected to an AC transformer.
  • Both type I and type II valve strings of bidirectional DC converters contain the same number of voltage source converters as the number of AC ports. All voltage source converters are implemented using AC-DC conversion circuits.
  • the AC-DC conversion circuit contains at least One AC port and one DC port.
  • the DC ports of all voltage source converters are connected in series one after the other.
  • the positive terminal of the DC port of the first voltage source converter and the last voltage source converter are connected in series.
  • the negative terminal of the DC port of the converter constitutes a high-voltage DC port of a valve string; all voltage source converters contain at least one AC port inside, and all AC ports are the AC ports of the valve string.
  • the voltage source converter is also called VSC. As shown in Figure 3, it shows a two-way DC converter with only two valve strings and each valve string with only three voltage source converters. .
  • components 301-306 represent voltage source converters of two valve train strings, namely VSC1-VSC6. Among them, VSC1, VSC2 and VSC3 are connected in series to form a type II valve group string, and VSC4, VSC5 and VSC6 are connected in series to form a type I valve group string.
  • the component 307 represents an AC transformer.
  • the voltage source type converters of the valve string two positive poles of the DC ports of the voltage source type converter are selected as the low voltage DC ports of the valve string.
  • the positive electrode with a high voltage serves as the positive terminal of the low-voltage DC port
  • the positive electrode with the low voltage serves as the negative terminal of the low-voltage DC port.
  • the potential of the negative terminal selected is equal to the neutral point of the high-voltage DC bus.
  • the potential of the positive end selected is equal to the neutral point of the high-voltage DC bus. As shown in Figure 3.
  • the voltage source type converters of the valve string two negative poles of the DC ports of the voltage source type converter are selected as the low voltage DC ports of the valve string.
  • the negative electrode with a high voltage serves as the positive terminal of the low-voltage DC port
  • the negative electrode with the low voltage serves as the negative terminal of the low-voltage DC port.
  • the potential of the negative terminal selected is equal to the neutral point of the high-voltage DC bus.
  • the potential of the positive end selected is equal to the neutral point of the high-voltage DC bus. As shown in Figure 3.
  • the voltage source converter of the valve group string includes at least two valve arms connected in series of four pairs.
  • Each valve arm consists of a valve arm reactance and a power module in series.
  • the upper and lower ends of each group of series-connected valve arms are connected in parallel to form a DC port of a voltage source converter.
  • Each group is connected in series with the middle point of the valve arms to form an AC port;
  • FIG. 4 is a detailed diagram of the structure of a voltage source converter in a valve train.
  • the component 401 represents the valve arm reactance
  • 402 represents the power module.
  • a valve arm reactance is connected in series with several power modules SM to form a valve arm.
  • six valve arms are used to form a voltage source converter, which is an MMC structure. All the connection points of the upper and lower valve arms are led out to output three-phase AC power. If any pair of valve arms are removed, the The voltage source converter can output single-phase AC power.
  • a voltage source converter of a valve string has a valve arm composed of a valve arm reactance and a power module in series. All power modules are composed of a half-bridge plus capacitor structure.
  • Figure 5 shows a power module with a half-bridge plus capacitor structure. As shown in Figure 5, Q1 and Q2 represent two fully-controlled switching devices of the half-bridge circuit.
  • all power modules are composed of a full-bridge plus capacitor structure.
  • Figure 6 shows a power module with a full-bridge plus capacitor structure.
  • Q1, Q2, Q3, and Q4 represent four fully-controlled switching devices in a full-bridge circuit.
  • all power modules are composed of a full bridge plus capacitor and a half bridge plus capacitor structure.
  • FIG. 7 is a schematic diagram of a control strategy for a type I valve string
  • FIG. 8 is a schematic diagram of a control strategy for a type II valve string.
  • a control method of a bipolar bidirectional DC converter is described.
  • a single I-type valve string uses the following control method.
  • Real-time detection of the potential difference between the positive pole of the low-voltage DC port and the negative pole of the low-voltage DC port of the type I valve string is compared with a first target value, and the first target value is half of a reference value of the positive and negative terminals of the low-voltage DC port of the bidirectional DC converter.
  • the detected value deviates from the first target value, adjust the voltage source converter between the positive pole of the low-voltage DC port and the negative pole of the low-voltage DC port of the type I valve string and the positive pole of the low-voltage DC port to the positive pole of the high-voltage DC port of the type I valve string
  • the voltage source type converter adjusts the detection value to a first target value through the power transmitted by the magnetic element.
  • Real-time detection of the potential difference between the negative pole of the low-voltage DC port and the negative pole of the high-voltage DC port of the type I valve string is compared with a second target value, which is a half of a reference value of the positive and negative terminals of the high-voltage DC port of the bidirectional DC converter.
  • a second target value which is a half of a reference value of the positive and negative terminals of the high-voltage DC port of the bidirectional DC converter.
  • a single type II valve group string adopts the following control method.
  • high-frequency switching is enabled by turning on Q1, Q4 to turn off Q2, Q3, and turning on Q2, Q3 to turn off Q1, Q4 to control the full bridge output current, that is, to control the magnitude of the fault current. After the fault recovers, return to the normal working state.
  • the type II valve string When the negative end of the low-voltage DC bus to the ground or the neutral point has a permanent fault, the type II valve string is blocked, and the type II valve string is disconnected from the high-voltage DC port and the low-voltage DC port. Switch to isolate the above fault. At the same time, the working status of the type I valve string remains unchanged, and the power conversion from the high-end DC bus to the positive end and neutral point of the low-voltage DC bus is continued.
  • the type I valve string can be isolated. Disconnect the switches shown in components 106, 107, 110, and 111 to isolate the type II valve string. As shown in Figure 1.
  • FIG. 7 is a schematic diagram of a control strategy of a type I valve string
  • FIG. 8 is a schematic diagram of a control strategy of a type II valve string.
  • the control device is also called a power splitter.
  • FIG. 9 is a schematic diagram of a control strategy for a type I valve train provided in another embodiment
  • FIG. 10 is a schematic diagram of a control strategy for a type II valve train provided in another embodiment.
  • the control device includes a normal working unit.
  • the normal working unit controls the isolation switch or full-control switch connected to the positive and negative poles of the high voltage DC port and the low voltage DC port of all valve strings when the bipolar bidirectional DC converter is working normally.
  • control device of the bipolar bidirectional DC converter further includes a first detection unit, a first adjustment unit, a second detection unit, and a second adjustment unit.
  • the first detection unit detects the first potential difference between the positive electrode of the low-voltage DC port and the negative electrode of the low-voltage DC port of the type I valve string in real time.
  • the first potential difference is compared with a first target value, and the first target value is half of a reference value of the positive and negative terminals of the low-voltage DC port of the bidirectional DC converter.
  • the first adjustment unit is enabled.
  • the first regulating unit regulates the voltage source converter between the positive pole of the low voltage DC port of the type I valve string and the negative pole of the low voltage DC port of the type I valve string and the voltage source type converter between the positive electrode of the low voltage DC port and the positive pole of the high voltage DC port of the type I valve string ,
  • the power transmitted through the magnetic element makes the first potential difference adjusted to a first target value.
  • the second detection unit detects the second potential difference between the negative electrode of the low-voltage DC port and the negative electrode of the high-voltage DC port of the type I valve string in real time.
  • the second potential difference is compared with a second target value, and the second target value is half of a reference value of the positive and negative terminals of the high-voltage DC port of the bidirectional DC converter.
  • the second adjustment unit is enabled.
  • the second regulating unit adjusts the voltage source converter between the positive pole of the low-voltage DC port and the negative pole of the low-voltage DC port of the type I valve string and the negative voltage source type commutation between the negative pole of the low-voltage DC port and the negative pole of the high-voltage DC port of the type I valve string
  • the power transmitted by the magnetic element adjusts the second potential difference to a second target value.
  • control device of the bipolar bidirectional DC converter further includes a third detection unit, a third adjustment unit, a fourth detection unit, and a fourth adjustment unit.
  • the third detection unit detects the third potential difference between the positive electrode of the low-voltage DC port and the negative electrode of the low-voltage DC port of the type II valve string in real time.
  • the third potential difference is compared with a third target value, and the third target value is half of a reference value of the positive and negative terminals of the low-voltage DC port of the bidirectional DC converter.
  • the third adjustment unit is enabled.
  • the third adjusting unit regulates the voltage source converter between the positive pole of the low voltage DC port and the negative pole of the low voltage DC port of the type II valve string and the negative voltage source type commutation between the negative pole of the low voltage DC port and the negative pole of the high voltage DC port of the type II valve string And the third potential difference is adjusted to a third target value by the power transmitted by the magnetic element.
  • the fourth detection unit detects the fourth potential difference between the negative electrode of the low-voltage DC port and the negative electrode of the high-voltage DC port of the type II valve string in real time.
  • the fourth potential difference is compared with a fourth target value, and the fourth target value is half of a reference value of the positive and negative terminals of the high-voltage DC port of the bidirectional DC converter.
  • the fourth adjustment unit is enabled.
  • the fourth regulating unit regulates the voltage source converter between the positive pole of the low voltage DC port and the negative pole of the low voltage DC port of the type II valve string and the voltage source converter between the positive pole of the low voltage DC port and the positive pole of the high voltage DC port of the type II valve string ,
  • the power transferred by the magnetic element makes the fourth potential difference adjusted to a fourth target value.
  • control device further includes a high-voltage DC bus short-term fault processing unit, a low-voltage side DC bus positive-side short-term fault processing unit, and a low-voltage side DC bus-negative short-term fault processing unit.
  • High-voltage DC bus short-term fault processing unit When a high-voltage DC bus short-term fault occurs, adjust the switching state of the power module composed of the full bridge plus capacitor structure in all valve cluster strings. After the fault is recovered, the switch state of the above module is restored.
  • Low-voltage side DC bus positive short-term fault processing unit When the positive end of the low-voltage DC bus is short-to-ground or neutral, a voltage source type is adjusted between the low-voltage DC ports of all type I valve strings The switching state of the power module composed of the full-bridge plus capacitor structure of the inverter. After the fault is recovered, the switch state of the above module is restored.
  • Low-voltage side DC bus negative terminal short-term fault processing unit When the negative terminal of low-voltage side DC bus is short-to-ground or neutral point, adjust the voltage source type between the low-voltage DC ports of all type II valve strings The switching state of the power module composed of the full-bridge plus capacitor structure of the inverter. After the fault is recovered, the switch state of the above module is restored.
  • control device further includes a positive-side permanent failure processing unit of the low-side DC bus and a negative-side permanent failure processing unit of the low-side DC bus.
  • Positive end permanent fault processing unit of low-voltage side DC bus When the positive end of low-voltage side DC bus has a permanent fault to the ground or neutral point, the type I valve string is blocked and the type I valve string high voltage DC port The isolation switch or full-control switch connected to the positive and negative poles of the low-voltage DC port to isolate the above faults. At the same time, the working status of the type II valve string remains unchanged, and the power conversion from the high-voltage DC bus to the negative and neutral points of the low-voltage DC bus is continued.
  • Negative end permanent fault processing unit of low-voltage side DC bus When the negative end of low-voltage side DC bus has a permanent fault to the ground or neutral point, it locks the type II valve string and disconnects the type II valve string high-voltage DC port The isolation switch or full-control switch connected to the positive and negative poles of the low-voltage DC port to isolate the above faults. At the same time, the working status of the type I valve string remains unchanged, and the power conversion from the high-end DC bus to the positive end and neutral point of the low-voltage DC bus is continued.
  • the circuit shown in FIG. 3 is taken as an example to introduce a method for determining a quantitative parameter.
  • the high-voltage side voltage level is ⁇ E1 pseudo-bipolar, that is, the positive and negative terminal voltages of the high-voltage side port are 2E1.
  • the voltage level on the low side is ⁇ E2 true bipolar, that is, the voltage on the positive and negative terminals of the low-side port is 2E2, which satisfies E1> E2.
  • n E1 / E2
  • the rated power of the bidirectional DC converter is P, that is, the input and output power of the high-side port is P, and the output power of each pole of the low-side is P / 2.
  • the DC ports of VSC1 and VSC6 need to be designed to have the same rated voltage, E1; and the DC ports of VSC2 and VSC5 are designed to have the same rated voltage, E2, so the rated voltages of VSC3 and VSC4 are E2-E1.
  • the VSC body After knowing the rated power and DC port voltage of each VSC, the VSC body can be designed by referring to the existing design methods of voltage source converters based on the MMC structure.
  • the rated active power of the AC transformer connected to each VSC is the same as the rated power of its corresponding VSC.
  • the transformer voltage can be determined according to the VSC AC to DC transformer modulation ratio.
  • the technical solution provided in the embodiment of the present application compared with the circuit using the MMC back-to-back structure in the existing application, constructs the high-voltage side pseudo-bipolar and low-voltage side true bipolar structures in the same way.
  • the system Valve group and transformer capacity reduce system design costs.
  • the high-voltage side DC bus can adopt a pseudo-bipolar wiring method.

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Abstract

一种双极双向直流变换器及其控制方法和控制装置。双极双向直流变换器包括至少两个阀组串（101，102）和至少六个磁性元件（103），根据阀组串（101，102）和双向直流变换器低压侧端口的连接关系区分为I型阀组串（102）和II型阀组串（101）；I型阀组串（102）的低压直流端口的正极构成双极双向直流变换器低压侧端口的正极；Ⅱ型阀组串（101）的低压直流端口的正极连接I型阀组串（102）的低压直流端口的负极，构成双极双向直流变换器低压侧端口的中性点，Ⅱ型阀组串（101）的低压直流端口的负极构成双极双向直流变换器低压侧端口的负极；每个阀组串（101，102）包括高压直流端口、低压直流端口、至少三个交流端口，每个交流端口连接一磁性元件（103）；同一个阀组串（101，102）内的所有的交流端口连接的磁性元件（103）的另一端相连。

Description

一种双极双向直流变换器及其控制方法和控制装置 技术领域
本申请涉及电力电子应用领域，涉及直流电网和双向直流变换器，特别涉及一种双极双向直流变换器及其控制方法和控制装置。
背景技术
双向直流变换器作为直流电网中，实现电压变换的重要组成设备，获得了越来越多直流电网领域学者们的关注。在高压直流变换场合，受开关管器件应力和成本的影响，该类应用的双向直流变换器多采用ISOP、ISOS结构或基于MMC背靠背结构的电能变换装置。其中，基于MMC背靠背结构的电能变换装置更适合于高至高/中压直流供电系统间的电能变换。
为降低直流供电系统的对地绝缘应力，一般对系统的直流母线采用双极接线型式，即直流母线的正极和负极对地绝缘电压为正负极间电压的一半。双极接线型式一般有伪双极和真双极两种接线型式。在伪双极接线型式下，当直流系统的母线有一极停运时，将导致另一极也必须停运；而在真双极接线型式下，当直流系统的母线有一极停运时，不会影响另一极的运行。MMC背靠背结构是隔离型的双向直流变换器，通过组合可较容易地实现各种真/伪双极等不同母线接线型式下，直流母线之间的电能双向传递。
然而，MMC背靠背结构包含有两个MMC换流阀组和一个大功率工频或中频交流变压器，建设成本相对较高。有文献研究了一种由MMC背靠背结构演化得到的AUTO-DC结构的双向直流变换器，该变换器原理类似交流自耦变压器，是非隔离的双向直流变换器。相比MMC背靠背结构，能够减小交流变压器和换流阀组的容量，适合在一些对隔离要求不高的场合应用。但是，AUTO-DC结构是非隔离电路，直接参考交流自耦变压器得到的AUTO-DC结构，无法直接在双极系统中应用。例如，当高压侧端口的直流母线采用伪双极接线型式时，通过AUTO-DC结构变换后，低压侧端口的负极或正极将与高压侧端口负极或正极为同一点，因此，其对地绝缘电压将变为高压侧正负极间电压的一半，从而增加了设备低压侧的对地绝缘应力。
目前，有专利CN105048813A对AUTO-DC结构进行了优化，优化后的AUTO-DC结构可以实现高压侧直流母线为伪双极且低压侧直流母线同样为伪双极的直流供电系统之间的电能变换。但是，若实际直流系统中，当高压侧直流母线为伪双极而低压侧直流母线为真双极接线型式时，采用专利CN105048813A的方案，只能将低压侧端口的两端连接在低压直流母线的正负两极，当低压侧有一极母线停运后，该方案没有提供另一极对中性点回路，这样只能将整个系统停运。
发明内容
鉴于此，本申请实施例提供一种双极双向直流变换器，包括：至少两个阀组串，根据所述阀组串和所述双向直流变换器低压侧端口的连接关系来区分；包括至少两个阀组串和至少六个磁性元件，根据阀组串和双向直流变换器低压侧端口的连接关系区分为I型阀组串和II型阀组串；I型阀组串的低压直流端口的正极构成双极双向直流变换器低压侧端口的正极；Ⅱ型阀组串的低压直流端口的正极连接I型阀组串的低压直流端口的负极，构成双极双向直流变换器低压侧端口的中性点，Ⅱ型阀组串的低压直流端口的负极构成双极双向直流变换器低压侧端口的负极；每个阀组串包括高压直流端口、低压直流端口、至少三个交流端口，所有的所述高压直流端口的正极相连接，作为所述双极双向直流变换器高压侧端口的正极；所有的所述高压直流端口的负极相连接，作为所述双极双向直流变换器高压侧端口的负极；每个交流端口连接一磁性元件；同一个阀组串内的所有的交流端口连接的磁性元件的另一端相连接。
根据一些实施例，所述双极双向直流变换器还包括第一隔离开关、第二隔离开关、第三隔离开关、第四隔离开关、第五隔离开关、第六隔离开关，所述第一隔离开关连接在所述阀组串的高压直流端口的正极和高压直流母线正端之间；所述第二隔离开关连接在所述阀组串的高压直流端口的负极和高压直流母线负端之间；所述第三隔离开关连接在所述Ⅰ型阀组串的低压直流端口的正极与低压直流母线的正端之间；所述第四隔离开关连接在所述Ⅰ型阀组串的低压直流端口的负极与低压直流母线的中性点之间；所述第五隔离开关连接在所述Ⅱ型阀组串的低压直流端口的正极与低压直流母线的中性点之间；所述第六隔离开关连接在所述Ⅱ型阀组串的低压直流端口的负极与低压直流母线的负极之间。
根据一些实施例，所述磁性元件为电抗器。
根据一些实施例，所述磁性元件为交流变压器。
根据一些实施例，所述阀组串均包括电压源型换流器，所述电压源型换流器与所述阀组串的交流端口数目相同，所述电压源型换流器包括交流-直流变换电路，所述交流-直流变换电路至少包括一个交流端口和一个直流端口。
根据一些实施例，所述阀组串中的所有所述电压源型换流器的直流端口依次首尾串联，第一个电压源型换流器的直流端口正极为所述阀组串的高压直流端口的正极，最后一个电压源型换流器的直流端口负极为阀组串的高压直流端口的正极；所有所述交流端口为所述阀组串的交流端口。
根据一些实施例，在所述阀组串选取两个电压源型换流器直流端口的正极引出，作为所述阀组串的低压直流端口；其中，电压高的正极作为低压直流端口的正端，电压低的正极作为低压直流端口的负端；对于Ⅰ型阀组串，选取的负端与高压侧直流母线中性点电位相等；对于Ⅱ型阀组串，选取的正端与高压侧直流母线中性点电位相等。
可选地，在所述阀组串选取两个电压源型换流器直流端口的负极引出，作为所述阀组串的低压直流端口；其中，电压高的负极作为低压直流端口的正端，电压低的负极作为低压直流端口的负端；其中，对于Ⅰ型阀组串，选取的负端与高压侧直流母线中性点电位相等；对于Ⅱ型阀组串，选取的正端与高压侧直流母线中性点电位相等。
根据一些实施例，所述电压源型换流器包括：至少两组共四个两两串联的阀臂；其中，每个阀臂包括串联连接的阀臂电抗和功率模组；每组上下串联的阀臂两端并联，作为所述电压源型换流器的直流端口；每组上下串联的阀臂中点引出，作为所述电压源型换流器的交流端口。
根据一些实施例，所述功率模组包括：半桥加电容结构。
可选地，所述功率模组包括：全桥加电容结构。
可选地，所述功率模组包括：全桥加电容和半桥加电容结构。
本申请实施例还提供一种如上所述双极双向直流变换器的控制方法，包括：正常工作时，闭合所有阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关。
根据一些实施例，所述方法还包括：检测Ⅰ型阀组串的低压直流端口正极与低压直流端口负极的第一电位差；当所述第一电位差偏离第一目标值时，调节所述Ⅰ型阀组串的电压源型换流器经磁性元件传递的功率，直到所述第一电位差等于第一目标值，其中，所述电压源型换流器位于所述Ⅰ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅰ型阀组串的低压直流端口正极至高压直流端口正极之间；检测所述Ⅰ型阀组串的低压直流端口负极与高压直流端口负极的第二电位差；当所述第二电位差偏离第二目标值时，调节所述Ⅰ型阀组串的电压源型换流器经磁性元件传递的功率，直到所述第二电位差等于第二目标值，其中，所述电压源型换流器位于所述Ⅰ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅰ型阀组串低压直流端口负极至高压直流端口负极之间。
根据一些实施例，所述第一目标值为所述双极双向直流变换器的低压直流端口正负端电压基准值的一半；所述第二目标值为所述双极双向直流变换器的高压直流端口正负端电压基准值的一半。
根据一些实施例，所述方法还包括：检测Ⅱ型阀组串低压直流端口正极与低压直流端口负极的第三电位差；当所述第三电位差偏离第三目标值时，调节所述Ⅱ型阀组的电压源型换流器经磁性元件传递的功率，直到所述第三电位差等于所述第三目标值，其中，所述电压源型换流器位于所述Ⅱ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅱ型阀组串的低压直流端口负极至高压直流端口负极之间；检测所述Ⅱ型阀组串的低压直流端口负极与高压直流端口负极的第四电位差；当所述第四电位差偏离第四目标值时，调节所述Ⅱ型阀组串的电压源型换流器经磁性元件传递的功率，直到所述第四电位差等于所述第四目标值，其中，所述电压源型换流器位于所述Ⅱ型阀组串的低压直流端口正极至低压直流端口负极之间或所述 Ⅱ型阀组串的低压直流端口正极至高压直流端口正极之间。
根据一些实施例，所述第三目标值为所述双极双向直流变换器的低压直流端口正负端电压基准值的一半；所述第四目标值为所述双极双向直流变换器的高压直流端口正负端电压基准值的一半。
根据一些实施例，所述方法还包括：当高压直流母线发生短时性故障时，调整所有阀组串中全桥加电容结构组成的功率模组的开关状态；待故障恢复后，复原上述模组的开关状态。
根据一些实施例，所述方法还包括：当低压侧直流母线的正端对地或对中性点发生短时性故障时，调整所有Ⅰ型阀组串中低压直流端口之间电压源型换流器的全桥加电容结构组成的功率模组的开关状态；待故障恢复后，复原上述模组的开关状态。
根据一些实施例，所述方法还包括：当低压侧直流母线的负端对地或对中性点发生短时性故障时，调整所有Ⅱ型阀组串中低压直流端口之间电压源型换流器的全桥加电容结构组成的功率模组的开关状态；待故障恢复后，复原上述模组的开关状态。
根据一些实施例，所述方法还包括：当低压侧直流母线的正端对地或对中性点发生永久性故障时，闭锁Ⅰ型阀组串，同时断开Ⅰ型阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关或全控型开关，以隔离上述故障；保持Ⅱ型阀组串工作状态不变，继续完成高压直流母线对低压直流母线负端和中性点的电能变换。
根据一些实施例，所述方法还包括：当低压侧直流母线的负端对地或对中性点发生永久性故障时，闭锁Ⅱ型阀组串，同时断开Ⅱ型阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关或全控型开关，以隔离上述故障；保持Ⅰ型阀组串工作状态不变，继续完成高压直流母线对低压直流母线正端和中性点的电能变换。
本申请实施例还提供一种如上所述双极双向直流变换器的控制装置，包括正常工作单元，所述正常工作单元在所述双极双向直流变换器正常工作时控制闭合所有阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关。
根据一些实施例，所述控制装置还包括第一检测单元、第一调节单元、第二检测单元、第二调节单元，所述第一检测单元检测Ⅰ型阀组串的低压直流端口正极与低压直流端口负极的第一电位差，当所述第一电位差偏离第一目标值时，使能第一调节单元；所述第一调节单元调节所述Ⅰ型阀组串的电压源型换流器经磁性元件传递的功率，直到所述第一电位差等于第一目标值，其中，所述电压源型换流器位于所述Ⅰ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅰ型阀组串的低压直流端口正极至高压直流端口正极之间；所述第二检测单元检测所述Ⅰ型阀组串的低压直流端口负极与高压直流端口负极的第二电位差，当所述第二电位差偏离第二目标值时，使能第二调节单元；所述第二调节单元调节所述Ⅰ型阀组串的电压 源型换流器经磁性元件传递的功率，直到所述第二电位差等于第二目标值，其中，所述电压源型换流器位于所述Ⅰ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅰ型阀组串低压直流端口负极至高压直流端口负极之间。
根据一些实施例，所述控制装置还包括第三检测单元、第三调节单元、第四检测单元、第四调节单元，所述第三检测单元检测Ⅱ型阀组串低压直流端口正极与低压直流端口负极的第三电位差，当所述第三电位差偏离第三目标值时，使能第三调节单元；所述第三调节单元调节所述Ⅱ型阀组的电压源型换流器经交流变压器传递的功率，直到所述第三电位差等于所述第三目标值，其中，所述电压源型换流器位于所述Ⅱ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅱ型阀组串的低压直流端口负极至高压直流端口负极之间；所述第四检测单元检测所述Ⅱ型阀组串的低压直流端口负极与高压直流端口负极的第四电位差，当所述第四电位差偏离第四目标值时，使能第四调节单元；所述第四调节单元调节所述Ⅱ型阀组串的电压源型换流器经交流变压器传递的功率，直到所述第四电位差等于所述第四目标值，其中，所述电压源型换流器位于所述Ⅱ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅱ型阀组串的低压直流端口正极至高压直流端口正极之间。
根据一些实施例，所述控制装置还包括高压直流母线短时性故障处理单元、低压侧直流母线正端短时性故障处理单元、低压侧直流母线负端短时性故障处理单元，所述高压直流母线短时性故障处理单元当高压直流母线发生短时性故障时，调整所有阀组串中全桥加电容结构组成的功率模组的开关状态，待故障恢复后，复原上述模组的开关状态；所述低压侧直流母线正端短时性故障处理单元当低压侧直流母线的正端对地或对中性点发生短时性故障时，调整所有Ⅰ型阀组串中低压直流端口之间电压源型换流器的全桥加电容结构组成的功率模组的开关状态，待故障恢复后，复原上述模组的开关状态；所述低压侧直流母线负端短时性故障处理单元当低压侧直流母线的负端对地或对中性点发生短时性故障时，调整所有Ⅱ型阀组串中低压直流端口之间电压源型换流器的全桥加电容结构组成的功率模组的开关状态，待故障恢复后，复原上述模组的开关状态。
根据一些实施例，所述控制装置还包括低压侧直流母线的正端永久故障处理单元、低压侧直流母线的负端永久故障处理单元，所述低压侧直流母线的正端永久故障处理单元当低压侧直流母线的正端对地或对中性点发生永久性故障时，闭锁Ⅰ型阀组串，同时断开Ⅰ型阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关或全控型开关，以隔离上述故障；同时保持Ⅱ型阀组串工作状态不变，继续完成高压直流母线对低压直流母线负端和中性点的电能变换；所述低压侧直流母线的负端永久故障处理单元当低压侧直流母线的负端对地或对中性点发生永久性故障时，闭锁Ⅱ型阀组串，同时断开Ⅱ型阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关或全控型开关，以隔离上述故障；同时保持Ⅰ型阀组串工作状态不变，继续完成高压直流母线对低压直流母线正端和中性点的电能变换。
本申请实施例提供的技术方案，相比现有应用中采用MMC背靠背结构的电路，用同样方式构建高压侧伪双极、低压侧真双极结构，根据本专利提出的方案，可以减少系统的阀组和变压器容量，降低系统设计成本。相比现有文献提出的AUTO-DC 方案，根据本专利提出的方案，高压侧直流母线可以采用伪双极接线方式，同时，低压侧不存在正负端对地电压与高压侧对地电压相同，导致绝缘应力提高的问题。相比现有文献提出的优化AUTO-DC方案，根据本专利提出的方案，当低压侧直流母线有一极发生故障停运时，不影响另一极的正常运行，仍然可以实现高压直流母线至低压直流母线的电能变换，满足低压侧直流母线的真双极接线。
附图说明
为了更清楚地说明本申请实施例中的技术方案，下面将对实施例描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为本申请提出的一种双极双向直流变换器结构示意图；
图2为单个阀组串每个端口定义示意图；
图3为仅包含两个阀组串且每个阀组串仅包含三个VSC的双向直流变换器结构示意图；
图4为单个电压源型换流器结构示意图；
图5为半桥加电容功率模组；
图6为全桥加电容功率模组；
图7为Ⅰ型阀组串的控制策略示意图；
图8为Ⅱ型阀组串的控制策略示意图；
图9为另一实施例提供的Ⅰ型阀组串的控制策略示意图；
图10为另一实施例提供的Ⅱ型阀组串的控制策略示意图。
具体实施方式
为使本申请实施例的目的、技术方案和优点更加清楚，以下将结合附图和实施例，对本申请技术方案的具体实施方式进行更加详细、清楚的说明。然而，以下描述的具体实施方式和实施例仅是说明的目的，而不是对本申请的限制。其只是包含了本申请一部分实施例，而不是全部的实施例，本领域技术人员对于本申请的各种变化获得的其他实施例，都属于本申请保护的范围。
应当理解，本申请的权利要求、说明书及附图中的术语“第一”、“第二”、“第三”和“第四”等是用于区别不同对象，而不是用于描述特定顺序。本申请的说明书和权利要求书中使用的术语“包括”和“包含”指示所描述特征、整体、步骤、操作、元素和/或组件的存在，但并不排除一个或多个其它特征、整体、步骤、操作、元素、组件和/或其集合的存在或添加。
本申请为解决AUTO-DC变换器接入高压侧直流母线为伪双极而低压侧直流母线为真双极系统的问题，提供了一种双极双向直流变换器。当低压侧直流母线有一极发生故障停运时，不影响另一极的正常运行，仍然可以实现高压直流母线至低压直流母线的电能变换。同时提供了双极双向直流变换器的控制方法和控制装置。
图1为本申请提出的一种双极双向直流变换器结构示意图。
参见图1，双向直流变换器由至少两个阀组串和六个磁性元件构成。
每个阀组串均有一个高压直流端口，一个低压直流端口和至少三个交流端口。所有阀组串的高压直流端口的正极相连接，构成所述双向直流变换器高压侧端口的正极；所有阀组串的高压直流端口的负极相连接，构成所述双向直流变换器高压侧端口的负极。
所有阀组串中，每个交流端口与一个磁性元件连接。单个阀组串内的所有交流端口所连接磁性元件的另一端并联。
根据阀组串和双向直流变换器低压侧端口的连接关系将阀组串分为Ⅰ型阀组串和Ⅱ型阀组串。Ⅰ型阀组串的低压直流端口的正极构成所述双向直流变换器低压侧端口的正极，其负端构成所述双向直流变换器低压侧端口的中性点。Ⅱ型阀组串的低压直流端口的正极构成所述双向直流变换器低压侧端口的中性点，其负端构成所述双向直流变换器低压侧端口的负极。Ⅰ型阀组串和Ⅱ型阀组串构成的双向直流变换器低压侧端口的中性点为同一点。
如图1所示，组件101是Ⅰ型阀组串，组件102是Ⅱ型阀组串，组件103是磁性元件。
如图1所示，组件104～组件111是表示隔离开关。其中，组件104～组件107是阀组串高压侧端口连接的隔离开关，组件108～组件111是阀组串低压侧端口连接的隔离开关。隔离开关包括全控性开关，但并不以此为限。
第一隔离开关106、104分别连接在Ⅰ型阀组串和Ⅱ型阀组串的高压直流端口的正极和高压直流母线正端之间。第二隔离开关107、105分别连接在Ⅰ型阀组串和Ⅱ型阀组串的高压直流端口的负极和高压直流母线负端之间。第三隔离开关110连接在Ⅰ型阀组串的低压直流端口的正极与低压直流母线的正端之间。第四隔离开关111连接在Ⅰ型阀组串的低压直流端口的负极与低压直流母线的中性点之间。第五隔离开关108连接在Ⅱ型阀组串的低压直流端口的正极与低压直流母线的中性点之间。第六隔离开关109连接在所述Ⅱ型阀组串的低压直流端口的负极与低压直流母线的负极之间。
图2为单个阀组串每个端口定义示意图。
参见图2，组件201示意了一个阀组串的组成，包括高压直流端口，低压直流端口和至少三个交流端口。
双向直流变换器所有阀组串的高压直流端口的正极分别经隔离开关后连接，连接高压直流母线正端。所有阀组串的高压直流端口的负极分别经隔离开关后连接，连接高压直流母线负端。双向直流变换器Ⅰ型阀组串的低压直流端口的正极与负极分别经隔离开关后，连接低压直流母线的正端和中性点。双向直流变换器Ⅱ型阀组 串的低压直流端口的正极与负极分别经隔离开关后，连接低压直流母线的中性点和负端。
如图2所示，组件202是电抗器，单个阀组串所连接的磁性元件可以为电抗器，交流端口的每一个出线端连接一个电抗器。组件203是交流变压器。单个阀组串所连接的磁性元件可以为交流电变压器，一个交流端口连接一个交流变压器。
双向直流变换器的Ⅰ型和Ⅱ型阀组串均包含与交流端口数目相同的电压源型换流器，所有电压源型换流器采用交流-直流变换电路实现，交流-直流变换电路至少包含一个交流端口和一个直流端口。
双向直流变换器的Ⅰ型和Ⅱ型阀组串中，所有电压源型换流器的直流端口依次首尾串联连接，第一个电压源型换流器的直流端口正极和最后一个电压源型换流器的直流端口负极，构成一个阀组串的高压直流端口；所有电压源型换流器内部至少包含一个交流端口，所有交流端口即为所述阀组串的交流端口。
为简化表示，电压源型换流器亦称为VSC，如图3所示，示意了一个只有两个阀组串且每个阀组串只有三个电压源型换流器的双向直流变换器。图3中，组件301-306表示两个阀组串的电压源型换流器，即VSC1-VSC6。其中，VSC1、VSC2和VSC3串联构成Ⅱ型阀组串，VSC4、VSC5和VSC6串联构成Ⅰ型阀组串。组件307表示交流变压器。
在阀组串的所有电压源型换流器中，选取两个电压源型换流器直流端口的正极引出，作为所述阀组串的低压直流端口。其中，电压高的正极作为低压直流端口的正端，电压低的正极作为低压直流端口的负端。对于Ⅰ型阀组串，选取的负端与高压侧直流母线中性点电位相等。对于Ⅱ型阀组串，选取的正端与高压侧直流母线中性点电位相等。如图3所示。
在所述阀组串的所有电压源型换流器中，选取两个电压源型换流器直流端口的负极引出，作为所述阀组串的低压直流端口。其中，电压高的负极作为低压直流端口的正端，电压低的负极作为低压直流端口的负端。对于Ⅰ型阀组串，选取的负端与高压侧直流母线中性点电位相等。对于Ⅱ型阀组串，选取的正端与高压侧直流母线中性点电位相等。如图3所示。
阀组串的电压源型换流器，包含至少两组共四个两两串联的阀臂。每个阀臂由阀臂电抗和功率模组依次串联构成。每组上下串联的阀臂两端并联，构成电压源型换流器的直流端口。每组上下串联的阀臂中点引出，构成交流端口；
图4详细绘制了一个阀组串中电压源形换流器的结构示意图。
如图4所示，组件401表示阀臂电抗，402表示功率模组。一个阀臂电抗与数个功率模组SM串联，构成一个阀臂。图4中，采用六个阀臂构成一个电压源型换流器，即MMC结构，所有上下两个阀臂的连接点引出，可以输出三相交流电；若去掉任意一对阀臂，则所述电压源形换流器可以输出单相交流电。
阀组串的电压源型换流器，其阀臂由阀臂电抗和功率模组依次串联构成。所有功率模组全部采用半桥加电容结构组成。图5为半桥加电容结构的功率模组。如图5所示，Q1和Q2表示半桥电路两个全控型开关器件。
可选地，所有功率模组全部采用全桥加电容结构组成。图6为全桥加电容结构的功率模组。如图6所示，Q1、Q2、Q3和Q4表示全桥电路四个全控型开关器件。
可选地，所有功率模组混合采用全桥加电容以及半桥加电容结构组成。
图7为Ⅰ型阀组串的控制策略示意图，图8为Ⅱ型阀组串的控制策略示意图，结合图7、图8，说明一种双极双向直流变换器的控制方法。
如图7、图8所示，正常工作时，闭合所有阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关。结合图6所示，正常工作时，开通Q1、Q4关断Q2、Q3投入全桥功率模组，开通Q1、Q3关断Q2、Q4，或者开通Q2、Q4关断Q1、Q3退出全桥功率模组。
如图7所示，单个Ⅰ型阀组串采用如下控制方法。
实时检测Ⅰ型阀组串低压直流端口正极与低压直流端口负极的电位差。将该电位差与第一目标值比较，第一目标值为双向直流变换器低压直流端口正负端电压基准值的一半。当检测值偏离第一目标值时，调节Ⅰ型阀组串低压直流端口正极至低压直流端口负极之间电压源型换流器与Ⅰ型阀组串低压直流端口正极至高压直流端口正极之间电压源型换流器，经磁性元件传递的功率，使检测值调节至第一目标值。
实时检测Ⅰ型阀组串低压直流端口负极与高压直流端口负极的电位差。将该电位差与第二目标值比较，所述第二目标值为双向直流变换器高压直流端口正负端电压基准值的一半。当检测值偏离第二目标值时，调节Ⅰ型阀组串低压直流端口正极至低压直流端口负极之间电压源型换流器与Ⅰ型阀组串低压直流端口负极至高压直流端口负极之间电压源型换流器，经磁性元件传递的功率，使检测值调节至第二目标值。
如图8所示，单个Ⅱ型阀组串采用如下控制方法。
实时检测Ⅱ型阀组串低压直流端口正极与低压直流端口负极的电位差。将该电位差与第三目标值比较，所述第三目标值为双向直流变换器低压直流端口正负端电压基准值的一半。当检测值偏离第三目标值时，调节Ⅱ型阀组串低压直流端口正极至低压直流端口负极之间电压源型换流器与Ⅱ型阀组串低压直流端口负极至高压直流端口负极之间电压源型换流器，经磁性元件传递的功率，使检测值调节至第三目标值。
实时检测Ⅱ型阀组串低压直流端口负极与高压直流端口负极的电位差。将该电位差与第四目标值比较，所述第四目标值为双向直流变换器高压直流端口正负端电压基准值的一半。当检测值偏离第四目标值时，调节Ⅱ型阀组串低压直流端口正极至低压直流端口负极之间电压源型换流器与Ⅱ型阀组串低压直流端口正极至高压直流端口正极之间电压源型换流器，经磁性元件传递的功率，使检测值调节至第四目标值；
如图7、图8所示，当高压直流母线发生短时性故障时，调整所有阀组串中全桥加电容结构组成的功率模组的开关状态。待故障恢复后，复原上述模组的开关状态。
当低压侧直流母线的正端对地或对中性点发生短时性故障时，调整所有Ⅰ型阀 组串中低压直流端口之间电压源型换流器的全桥加电容结构组成的功率模组的开关状态。待故障恢复后，复原上述模组的开关状态。
当低压侧直流母线的负端对地或对中性点发生短时性故障时，调整所有Ⅱ型阀组串中低压直流端口之间电压源型换流器的全桥加电容结构组成的功率模组的开关状态。待故障恢复后，复原上述模组的开关状态。
当发生短时性故障时，通过开通Q1、Q4关断Q2、Q3和开通Q2、Q3关断Q1、Q4的高频切换，控制全桥输出电流，即控制故障电流的大小。待故障恢复后，回到前述正常工作状态。
如图7、图8所示，当低压侧直流母线的正端对地或对中性点发生永久性故障时，闭锁Ⅰ型阀组串，同时断开Ⅰ型阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关，以隔离上述故障。同时Ⅱ型阀组串工作状态保持不变，继续完成高压直流母线对低压直流母线负端和中性点的电能变换。
当低压侧直流母线的负端对地或对中性点发生永久性故障时，闭锁Ⅱ型阀组串，同时断开Ⅱ型阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关，以隔离上述故障。同时Ⅰ型阀组串工作状态保持不变，继续完成高压直流母线对低压直流母线正端和中性点的电能变换。
断开组件104、105、108和109所示开关，可以隔离Ⅰ型阀组串。断开组件106、107、110和111所示开关，可以隔离Ⅱ型阀组串。如图1所示。
本申请实施例同时提出了双极双向直流变换器的控制装置。图7为Ⅰ型阀组串的控制策略示意图，图8为Ⅱ型阀组串的控制策略示意图。控制装置也叫做功率分配器。图9为另一实施例提供的Ⅰ型阀组串的控制策略示意图，图10为另一实施例提供的Ⅱ型阀组串的控制策略示意图。
控制装置包括正常工作单元。正常工作单元在双极双向直流变换器正常工作时控制闭合所有阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关或全控型开关。
可选地，双极双向直流变换器的控制装置还包括第一检测单元、第一调节单元、第二检测单元、第二调节单元。
第一检测单元实时检测Ⅰ型阀组串低压直流端口正极与低压直流端口负极的第一电位差。将第一电位差与第一目标值比较，第一目标值为双向直流变换器低压直流端口正负端电压基准值的一半。当第一电位差偏离第一目标值时，使能第一调节单元。第一调节单元调节Ⅰ型阀组串低压直流端口正极至低压直流端口负极之间电压源型换流器与Ⅰ型阀组串低压直流端口正极至高压直流端口正极之间电压源型换流器，经磁性元件传递的功率，使第一电位差调节至第一目标值。
第二检测单元实时检测Ⅰ型阀组串低压直流端口负极与高压直流端口负极的第二电位差。将该第二电位差与第二目标值比较，第二目标值为双向直流变换器高压直流端口正负端电压基准值的一半。当第二电位差偏离第二目标值时，使能第二调节单元。第二调节单元，调节Ⅰ型阀组串低压直流端口正极至低压直流端口负极之间电压源型换流器与Ⅰ型阀组串低压直流端口负极至高压直流端口负极之间电压源型换流器，经磁性元件传递的功率，使第二电位差调节至第二目标值。
可选地，双极双向直流变换器的控制装置还包括第三检测单元、第三调节单元、第四检测单元、第四调节单元。
第三检测单元实时检测Ⅱ型阀组串低压直流端口正极与低压直流端口负极的第三电位差。将该第三电位差与第三目标值比较，第三目标值为双向直流变换器低压直流端口正负端电压基准值的一半。当第三电位差偏离第三目标值时，使能第三调节单元。第三调节单元，调节Ⅱ型阀组串低压直流端口正极至低压直流端口负极之间电压源型换流器与Ⅱ型阀组串低压直流端口负极至高压直流端口负极之间电压源型换流器，经磁性元件传递的功率，使第三电位差调节至第三目标值。
第四检测单元实时检测Ⅱ型阀组串低压直流端口负极与高压直流端口负极的第四电位差。将该第四电位差与第四目标值比较，第四目标值为双向直流变换器高压直流端口正负端电压基准值的一半。当第四电位差偏离第四目标值时，使能第四调节单元。第四调节单元调节Ⅱ型阀组串低压直流端口正极至低压直流端口负极之间电压源型换流器与Ⅱ型阀组串低压直流端口正极至高压直流端口正极之间电压源型换流器，经磁性元件传递的功率，使第四电位差调节至第四目标值。
可选地，控制装置还包括高压直流母线短时性故障处理单元、低压侧直流母线正端短时性故障处理单元、低压侧直流母线负端短时性故障处理单元。
高压直流母线短时性故障处理单元当高压直流母线发生短时性故障时，调整所有阀组串中全桥加电容结构组成的功率模组的开关状态。待故障恢复后，复原上述模组的开关状态。低压侧直流母线正端短时性故障处理单元当低压侧直流母线的正端对地或对中性点发生短时性故障时，调整所有Ⅰ型阀组串中低压直流端口之间电压源型换流器的全桥加电容结构组成的功率模组的开关状态。待故障恢复后，复原上述模组的开关状态。低压侧直流母线负端短时性故障处理单元当低压侧直流母线的负端对地或对中性点发生短时性故障时，调整所有Ⅱ型阀组串中低压直流端口之间电压源型换流器的全桥加电容结构组成的功率模组的开关状态。待故障恢复后，复原上述模组的开关状态。
可选地，控制装置还包括低压侧直流母线的正端永久故障处理单元、低压侧直流母线的负端永久故障处理单元。
低压侧直流母线的正端永久故障处理单元当低压侧直流母线的正端对地或对中性点发生永久性故障时，闭锁Ⅰ型阀组串，同时断开Ⅰ型阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关或全控型开关，以隔离上述故障。同时Ⅱ型阀组串工作状态保持不变，继续完成高压直流母线对低压直流母线负端和中性点的电能变换。
低压侧直流母线的负端永久故障处理单元当低压侧直流母线的负端对地或对中性点发生永久性故障时，闭锁Ⅱ型阀组串，同时断开Ⅱ型阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关或全控型开关，以隔离上述故障。同时Ⅰ型阀组串工作状态保持不变，继续完成高压直流母线对低压直流母线正端和中性点的电能变换。
为定量说明本专利的调节原理，以图3所示电路为例，介绍定量参数确定方法。假设高压侧电压等级为±E1伪双极，即高压侧端口正负端电压为2E1。低压侧电压 等级为±E2真双极，即低压侧端口正负端电压为2E2，满足E1>E2，设n＝E1/E2，则n>1。假设该双向直流变换器的额定功率为P，即高压侧端口出入功率为P，而低压侧两极每极输出功率为P/2。
根据电压等级划分，需设计VSC1和VSC6的直流端口额定电压相等，均为E1；并设计VSC2和VSC5的直流端口额定电压相等均为E2，所以VSC3和VSC4的额定电压为E2-E1。
由基尔霍夫(KCL)定律可知，VSC1、VSC2和VSC3，以及VSC4、VSC5和VSC6分别串联，所以直流端口的电流相等，因此VSC1和VSC6的额定功率为P/4；根据n＝E1/E2，可以推导出VSC3和VSC4的额定设计功率为(n-1)/n*(P/4)，VSC1和VSC6以及VSC3和VSC4的交流端口功率将分别经过磁性元件传递至VSC2和VSC5，因此，VSC2和VSC5的额定功率为(2n-1)/n*(P/4)。
在已知各VSC的额定功率、直流端口电压后，可以参考现有基于MMC结构电压源型换流器的设计方法设计VSC本体。
各VSC连接的交流变压器额定有功与其对应VSC额定功率相同，变压器电压可根据VSC交流至直流的变压调制比来确定。
至此可根据本专利设计一个实际应用于高压侧为伪双极接线，低压侧为真双极接线的双向直流变换器。
本申请实施例提供的技术方案，相比现有应用中采用MMC背靠背结构的电路，用同样方式构建高压侧伪双极、低压侧真双极结构，根据本专利提出的方案，可以减少系统的阀组和变压器容量，降低系统设计成本。相比现有文献提出的AUTO-DC方案，根据本专利提出的方案，高压侧直流母线可以采用伪双极接线方式，同时，低压侧不存在正负端对地电压与高压侧对地电压相同，导致绝缘应力提高的问题。相比现有文献提出的优化AUTO-DC方案，根据本专利提出的方案，当低压侧直流母线有一极发生故障停运时，不影响另一极的正常运行，仍然可以实现高压直流母线至低压直流母线的电能变换，满足低压侧直流母线的真双极接线。
需要说明的是，以上参照附图所描述的每个实施例仅用以说明本申请而非限制本申请的范围，本领域的普通技术人员应当理解，在不脱离本申请的精神和范围的前提下对本申请进行的修改或者等同替换，均应涵盖在本申请的范围之内。此外，除上下文另有所指外，以单数形式出现的词包括复数形式，反之亦然。另外，除非特别说明，那么任何实施例的全部或一部分可结合任何其它实施例的全部或一部分来使用。

Claims (27)

  1. 一种双极双向直流变换器，包括：
    至少两个阀组串，根据所述阀组串和所述双向直流变换器低压侧端口的连接关系来区分；包括：
    I型阀组串，所述I型阀组串的低压直流端口的正极构成所述双极双向直流变换器低压侧端口的正极；
    II型阀组串，所述Ⅱ型阀组串的低压直流端口的正极连接所述I型阀组串的低压直流端口的负极，构成所述双极双向直流变换器低压侧端口的中性点，所述Ⅱ型阀组串的低压直流端口的负极构成所述双极双向直流变换器低压侧端口的负极；
    其中，每个所述阀组串包括：
    低压直流端口；
    高压直流端口，所有的所述高压直流端口的正极相连接，作为所述双极双向直流变换器高压侧端口的正极；所有的所述高压直流端口的负极相连接，作为所述双极双向直流变换器高压侧端口的负极；
    至少三个交流端口，每个所述交流端口连接一个磁性元件；
    至少六个所述磁性元件，每个所述磁性元件的一端连接所述交流端口，同一个所述阀组串内的所有的所述交流端口所连接的所述磁性元件的另一端相连接。
  2. 根据权利要求1所述的双极双向直流变换器，还包括：
    第一隔离开关，连接在所述阀组串的高压直流端口的正极和高压直流母线正端之间；
    第二隔离开关，连接在所述阀组串的高压直流端口的负极和高压直流母线负端之间；
    第三隔离开关，连接在所述Ⅰ型阀组串的低压直流端口的正极与低压直流母线的正端之间；
    第四隔离开关，连接在所述Ⅰ型阀组串的低压直流端口的负极与低压直流母线的中性点之间；
    第五隔离开关，连接在所述Ⅱ型阀组串的低压直流端口的正极与低压直流母线的中性点之间；
    第六隔离开关，连接在所述Ⅱ型阀组串的低压直流端口的负极与低压直流母线的负极之间。
  3. 根据权利要求1所述的双极双向直流变换器，其中，所述磁性元件为电抗器。
  4. 根据权利要求1所述的双极双向直流变换器，其中，所述磁性元件为交流变压器。
  5. 如权利要求1所述的双极双向直流变换器，其中，所述阀组串均包括：
    电压源型换流器，与所述阀组串的交流端口数目相同，所述电压源型换流器包括：
    交流-直流变换电路，至少包括一个交流端口和一个直流端口。
  6. 如权利要求5所述的双极双向直流变换器，其中，
    所述阀组串中的所有所述电压源型换流器的直流端口依次首尾串联，第一个电压源型换流器的直流端口正极为所述阀组串的高压直流端口的正极，最后一个电压源型换流器的直流端口负极为阀组串的高压直流端口的负极；
    所有所述交流端口为所述阀组串的交流端口。
  7. 如权利要求5所述的双极双向直流变换器，其中，
    在所述阀组串选取两个电压源型换流器直流端口的正极引出，作为所述阀组串的低压直流端口；其中，电压高的正极作为低压直流端口的正端，电压低的正极作为低压直流端口的负端；
    对于Ⅰ型阀组串，选取的负端与高压侧直流母线中性点电位相等；对于Ⅱ型阀组串，选取的正端与高压侧直流母线中性点电位相等。
  8. 如权利要求5所述的双极双向直流变换器，其中，
    在所述阀组串选取两个电压源型换流器直流端口的负极引出，作为所述阀组串的低压直流端口；其中，电压高的负极作为低压直流端口的正端，电压低的负极作为低压直流端口的负端；其中
    对于Ⅰ型阀组串，选取的负端与高压侧直流母线中性点电位相等；对于Ⅱ型阀组串，选取的正端与高压侧直流母线中性点电位相等。
  9. 如权利要求5所述的双极双向直流变换器，其中，所述电压源型换流器包括：
    至少两组共四个两两串联的阀臂；其中，每个阀臂包括串联连接的阀臂电抗和功率模组；每组上下串联的阀臂两端并联，作为所述电压源型换流器的直流端口；每组上下串联的阀臂中点引出，作为所述电压源型换流器的交流端口。
  10. 如权利要求9所述的双极双向直流变换器，其中，所述功率模组包括：半桥加电容结构。
  11. 如权利要求9所述的双极双向直流变换器，其中，所述功率模组包括：全桥加电容结构。
  12. 如权利要求9所述的双极双向直流变换器，其中，所述功率模组包括：全桥加电容和半桥加电容结构。
  13. 一种如权利要求1至12之任一项所述双极双向直流变换器的控制方法，包括：
    正常工作时，闭合所有阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关。
  14. 如权利要求13所述的方法，还包括：
    检测Ⅰ型阀组串的低压直流端口正极与低压直流端口负极的第一电位差；
    当所述第一电位差偏离第一目标值时，调节所述Ⅰ型阀组串的电压源型换流器经磁性元件传递的功率，直到所述第一电位差等于第一目标值，其中，所述电压源型换流器位于所述Ⅰ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅰ型阀组串的低压直流端口正极至高压直流端口正极之间；
    检测所述Ⅰ型阀组串的低压直流端口负极与高压直流端口负极的第二电位差；
    当所述第二电位差偏离第二目标值时，调节所述Ⅰ型阀组串的电压源型换流器经磁性元件传递的功率，直到所述第二电位差等于第二目标值，其中，所述电压源型换流器位于所述Ⅰ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅰ型阀组串低压直流端口负极至高压直流端口负极之间。
  15. 如权利要求14所述的方法，其中，
    所述第一目标值为所述双极双向直流变换器的低压直流端口正负端电压基准值的一半；
    所述第二目标值为所述双极双向直流变换器的高压直流端口正负端电压基准值的一半。
  16. 如权利要求13所述的方法，还包括：
    检测Ⅱ型阀组串低压直流端口正极与低压直流端口负极的第三电位差；
    当所述第三电位差偏离第三目标值时，调节所述Ⅱ型阀组的电压源型换流器经磁性元件传递的功率，直到所述第三电位差等于所述第三目标值，其中，所述电压源型换流器位于所述Ⅱ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅱ型阀组串的低压直流端口负极至高压直流端口负极之间；
    检测所述Ⅱ型阀组串的低压直流端口负极与高压直流端口负极的第四电位差；
    当所述第四电位差偏离第四目标值时，调节所述Ⅱ型阀组串的电压源型换流器经磁性元件传递的功率，直到所述第四电位差等于所述第四目标值，其中，所述电压源型换流器位于所述Ⅱ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅱ型阀组串的低压直流端口正极至高压直流端口正极之间。
  17. 如权利要求16所述的方法，其中，
    所述第三目标值为所述双极双向直流变换器的低压直流端口正负端电压基准值的一半；
    所述第四目标值为所述双极双向直流变换器的高压直流端口正负端电压基准值的一半。
  18. 如权利要求13所述的方法，还包括：
    当高压直流母线发生短时性故障时，调整所有阀组串中全桥加电容结构组成的功率模组的开关状态；
    待故障恢复后，复原上述模组的开关状态。
  19. 如权利要求13所述的方法，还包括：
    当低压侧直流母线的正端对地或对中性点发生短时性故障时，调整所有Ⅰ型阀组串中低压直流端口之间电压源型换流器的全桥加电容结构组成的功率模组的开关状态；
    待故障恢复后，复原上述模组的开关状态。
  20. 如权利要求13所述的方法，还包括：
    当低压侧直流母线的负端对地或对中性点发生短时性故障时，调整所有Ⅱ型阀组串中低压直流端口之间电压源型换流器的全桥加电容结构组成的功率模组的开关状态；
    待故障恢复后，复原上述模组的开关状态。
  21. 如权利要求13所述的方法，还包括：
    当低压侧直流母线的正端对地或对中性点发生永久性故障时，闭锁Ⅰ型阀组串，同时断开Ⅰ型阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关或全控型开关，以隔离上述故障；
    保持Ⅱ型阀组串工作状态不变，继续完成高压直流母线对低压直流母线负端和中性点的电能变换。
  22. 如权利要求13所述的方法，还包括：
    当低压侧直流母线的负端对地或对中性点发生永久性故障时，闭锁Ⅱ型阀组串，同时断开Ⅱ型阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关或全控型开关，以隔离上述故障；
    保持Ⅰ型阀组串工作状态不变，继续完成高压直流母线对低压直流母线正端和中性点的电能变换。
  23. 一种如权利要求1至12之任一项所述双极双向直流变换器的控制装置，包 括：
    正常工作单元，在所述双极双向直流变换器正常工作时控制闭合所有阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关。
  24. 如权利要求23所述的控制装置，还包括：
    第一检测单元，检测Ⅰ型阀组串的低压直流端口正极与低压直流端口负极的第一电位差，当所述第一电位差偏离第一目标值时，使能第一调节单元；
    第一调节单元，调节所述Ⅰ型阀组串的电压源型换流器经磁性元件传递的功率，直到所述第一电位差等于第一目标值，其中，所述电压源型换流器位于所述Ⅰ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅰ型阀组串的低压直流端口正极至高压直流端口正极之间；
    第二检测单元，检测所述Ⅰ型阀组串的低压直流端口负极与高压直流端口负极的第二电位差，当所述第二电位差偏离第二目标值时，使能第二调节单元；
    第二调节单元；调节所述Ⅰ型阀组串的电压源型换流器经磁性元件传递的功率，直到所述第二电位差等于第二目标值，其中，所述电压源型换流器位于所述Ⅰ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅰ型阀组串低压直流端口负极至高压直流端口负极之间。
  25. 如权利要求23所述的控制装置，还包括：
    第三检测单元，检测Ⅱ型阀组串低压直流端口正极与低压直流端口负极的第三电位差，当所述第三电位差偏离第三目标值时，使能第三调节单元；
    第三调节单元，调节所述Ⅱ型阀组的电压源型换流器经磁性元件传递的功率，直到所述第三电位差等于所述第三目标值，其中，所述电压源型换流器位于所述Ⅱ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅱ型阀组串的低压直流端口负极至高压直流端口负极之间；
    第四检测单元，检测所述Ⅱ型阀组串的低压直流端口负极与高压直流端口负极的第四电位差，当所述第四电位差偏离第四目标值时，使能第四调节单元；
    第四调节单元，调节所述Ⅱ型阀组串的电压源型换流器经磁性元件传递的功率，直到所述第四电位差等于所述第四目标值，其中，所述电压源型换流器位于所述Ⅱ型阀组串的低压直流端口正极至低压直流端口负极之间或所述Ⅱ型阀组串的低压直流端口正极至高压直流端口正极之间。
  26. 如权利要求23所述的控制装置，还包括：
    高压直流母线短时性故障处理单元，当高压直流母线发生短时性故障时，调整所有阀组串中全桥加电容结构组成的功率模组的开关状态，待故障恢复后，复原上述模组的开关状态；
    低压侧直流母线正端短时性故障处理单元，当低压侧直流母线的正端对地或对中性点发生短时性故障时，调整所有Ⅰ型阀组串中低压直流端口之间电压源型换流器的全桥加电容结构组成的功率模组的开关状态，待故障恢复后，复原上述模组的开关状态；
    低压侧直流母线负端短时性故障处理单元，当低压侧直流母线的负端对地或对中性点发生短时性故障时，调整所有Ⅱ型阀组串中低压直流端口之间电压源型换流器的全桥加电容结构组成的功率模组的开关状态，待故障恢复后，复原上述模组的开关状态。
  27. 如权利要求23所述的控制装置，还包括：
    低压侧直流母线的正端永久故障处理单元，当低压侧直流母线的正端对地或对中性点发生永久性故障时，闭锁Ⅰ型阀组串，同时断开Ⅰ型阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关或全控型开关，以隔离上述故障；同时保持Ⅱ型阀组串工作状态不变，继续完成高压直流母线对低压直流母线负端和中性点的电能变换；
    低压侧直流母线的负端永久故障处理单元，当低压侧直流母线的负端对地或对中性点发生永久性故障时，闭锁Ⅱ型阀组串，同时断开Ⅱ型阀组串高压直流端口和低压直流端口正极与负极所连接的隔离开关或全控型开关，以隔离上述故障；同时保持Ⅰ型阀组串工作状态不变，继续完成高压直流母线对低压直流母线正端和中性点的电能变换。
PCT/CN2019/100792 2018-08-21 2019-08-15 一种双极双向直流变换器及其控制方法和控制装置 WO2020038275A1 (zh)

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JP2021509868A JP2021534714A (ja) 2018-08-21 2019-08-15 バイポーラ双方向直流変換器およびその制御方法と制御装置
EP19852160.1A EP3823147A4 (en) 2018-08-21 2019-08-15 BIDIRECTIONAL BIPOLAR DIRECT CURRENT CONVERTER, AND ASSOCIATED CONTROL METHOD AND CONTROL DEVICE
KR1020217004789A KR20210032484A (ko) 2018-08-21 2019-08-15 양극성 양방향 직류 컨버터 및 그 제어 방법과 제어 장치
BR112021002644-4A BR112021002644A2 (pt) 2018-08-21 2019-08-15 transformador cc bidirecional bipolar, e método de controle e dispositivo para seu controle
RU2021105725A RU2754426C1 (ru) 2018-08-21 2019-08-15 Двухполюсный двунаправленный преобразователь постоянного тока, а также способ и устройство управления ним
US17/268,536 US11223291B2 (en) 2018-08-21 2019-08-15 Bipolar bidirectional DC converter, and control method and control device therefor

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