CN115473445A - Mixed type AC-AC converter - Google Patents

Mixed type AC-AC converter Download PDF

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Publication number
CN115473445A
CN115473445A CN202211193234.3A CN202211193234A CN115473445A CN 115473445 A CN115473445 A CN 115473445A CN 202211193234 A CN202211193234 A CN 202211193234A CN 115473445 A CN115473445 A CN 115473445A
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China
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mmc
voltage
current
control
rectifier
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CN202211193234.3A
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Chinese (zh)
Inventor
陈建福
唐捷
陈勇
裴星宇
吴宏远
李建标
杨锐雄
程旭
邹国惠
肖小清
曹彦朝
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Guangdong Power Grid Co Ltd
Zhuhai Power Supply Bureau of Guangdong Power Grid Co Ltd
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Guangdong Power Grid Co Ltd
Zhuhai Power Supply Bureau of Guangdong Power Grid Co Ltd
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Priority to CN202211193234.3A priority Critical patent/CN115473445A/en
Publication of CN115473445A publication Critical patent/CN115473445A/en
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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
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
    • H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
    • H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
    • H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • 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
    • 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
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without 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
    • H02M7/217—Conversion of ac power input into dc power output without 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
    • H02M7/219—Conversion of ac power input into dc power output without 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 in a bridge configuration
    • 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
    • H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Rectifiers (AREA)

Abstract

The application discloses mixed type AC-AC converter includes: the rectifier comprises a rectifier side alternating current bus, a converter transformer, a rectifier, an inverter side alternating current bus, an alternating current filter and a direct current filter; the rectifier consists of a high-voltage valve set LCC and a low-voltage valve set MMC, the high-voltage valve set and the low-voltage valve set of the inverter both adopt half-bridge sub-module type MMC, and a direct-current outlet of the high-voltage valve set MMC is connected with a high-power diode valve D in series; the LCC on the rectifying side adopts constant current control based on the direct current voltage of the MMC on the rectifying side, the MMC on the rectifying side adopts voltage amplitude-frequency control, and the MMC on the inverting side adopts constant direct current voltage control and constant reactive power control. The invention can realize the low-frequency sending of the pure new energy power generation base, well adapts to the power fluctuation of the new energy power generation base, fully utilizes the technical maturity of LCC and MMC, and can reduce the construction cost and the power loss compared with the conventional AC-AC converter based on back-to-back MMC.

Description

Mixed type AC-AC converter
Technical Field
The application relates to the technical field of converters, in particular to a hybrid AC-AC converter.
Background
The low-frequency alternating-current transmission technology can realize the transmission of a pure new energy power generation base, and the advantages of the low-frequency alternating-current transmission technology are mainly shown in two aspects: (1) Compared with power frequency alternating current transmission, the power transmission frequency is reduced, and the distance of electric energy transmission can be enlarged; (2) Compared with direct-current power transmission, alternating-current power transmission does not have the problem of lack of a circuit breaker, and an alternating-current power grid can be conveniently formed between new energy power generation bases. Therefore, for the pure new energy power generation base, the low-frequency alternating current transmission technology is a competitive scheme.
The core device of the low-frequency alternating current transmission technology is an alternating current-alternating current converter. The existing documents mostly adopt a phase-control type AC/AC converter based on a thyristor, the device has simple structure and convenient control, but a large amount of reactive power needs to be consumed in the normal operation process, and low-order harmonic and inter-harmonic with considerable numerical values can be generated, thereby causing a series of electric energy quality problems. The harmonic characteristics of the device can be improved by adopting a fully-controlled device to replace a thyristor, but the effect is not obvious. In recent years, research has proposed an improved topology structure using a matrix converter as an ac converter, but the feasibility of the matrix converter in the field of high-voltage large-capacity power transmission is still to be verified. The other technical route is an alternating current converter based on a back-to-back Voltage Source Converter (VSC), the VSC is high in technical maturity, flexible in control mode and good in harmonic characteristics, but the defects of high device manufacturing cost and large power loss exist.
In addition, in order to realize large-scale pure new energy delivery, the problem of voltage support of a delivery-end alternating current system must be solved. The conventional method is to bundle and send out new energy, hydroelectric power, thermal power and the like, the proportion of the new energy is limited to a certain extent, and the large-scale construction of matched thermal power deviates from the original intention of developing new energy. Theoretically, the new energy base can operate in a network-forming type control mode, but related engineering experience is less at present. Therefore, the existing and future new energy base of China still mainly adopts a network following type control mode in a short term, and the voltage support of a sending end alternating current system is provided by an alternating current-to-alternating current converter.
To date, few documents have been made on an ac converter suitable for low-frequency transmission in a renewable energy power generation base, and it is necessary to study the topology and control strategy of an ac converter suitable for low-frequency transmission in a renewable energy power generation base in order to further improve the economy and reliability of the ac converter.
Disclosure of Invention
The application provides a hybrid AC-AC converter which is used for solving the technical problems that an existing converter cannot well adapt to power fluctuation of a new energy power generation base, engineering cost is high, and power loss is large.
In view of the above, a first aspect of the present application provides a hybrid ac/dc converter, including: a rectifier module composed of a positive rectifier and a negative rectifier, and an inverter module composed of a positive inverter and a negative inverter;
the high-voltage end of the positive pole rectifier is connected with the high-voltage end of the positive pole inverter, the high-voltage end of the negative pole rectifier is connected with the high-voltage end of the negative pole inverter, the low-voltage end of the positive pole rectifier and the low-voltage end of the negative pole rectifier are connected with each other and serve as a direct-current side neutral point of the rectifier module, the low-voltage end of the positive pole inverter and the low-voltage end of the negative pole inverter are connected with each other and serve as a direct-current side neutral point of the inverter module, and the direct-current side neutral points of the rectifier module and the inverter module are both connected to the ground electrode, so that a true bipolar structure is formed;
the alternating current side of the rectifier module is connected with one side of an alternating current bus of the rectification side through a converter transformer, the direct current side of the rectifier module is connected with the direct current side of the inverter module, the alternating current side of the inverter module is connected with one side of an alternating current bus of the inversion side through a converter transformer, an alternating current filter is connected to the alternating current bus of the rectification side in parallel, the high-voltage ends of the positive pole rectifier and the negative pole rectifier are connected with the direct current filter in parallel, the other side of the alternating current bus of the rectification side is connected to a pure new energy power generation base, and the other side of the alternating current bus of the inversion side is connected to a receiving-end power grid.
Optionally, the positive rectifier and the negative rectifier each comprise: the first high-pressure valve bank and the first low-pressure valve bank are connected in series at a direct current side and connected in parallel at an alternating current side;
the first high-voltage valve bank is a power grid commutation converter LCC, and the first low-voltage valve bank is a modular multilevel converter MMC of a half-bridge submodule.
Optionally, the LCC comprises: two three-phase six-pulsation rectifier bridges, wherein the two three-phase six-pulsation rectifier bridges respectively adopt Y 0 Y and Y 0 A converter transformer in a delta connection mode is connected, and the phase difference between the valve sides of the two converter transformers is 30 degrees;
the MMC is a three-phase six-bridge-arm structure, each bridge arm is formed by cascading N half-bridge submodules and then connecting the N half-bridge submodules in series with a bridge arm reactance, and the MMC and the Y are adopted 0 The converter transformers are connected in a/[ delta ] connection mode.
Optionally, the positive inverter and the negative inverter each comprise: the second high-pressure valve bank and the second low-pressure valve bank are connected in series at a direct current side and in parallel at an alternating current side;
the second high-voltage valve bank and the second low-voltage valve bank are modular multilevel converter MMC of half-bridge submodule, a direct current outlet of the second high-voltage valve bank is connected with a high-power diode valve D in series, and the MMC and the Y-shaped converter MMC are adopted 0 A/[ delta ] connection mode converter transformer connection.
Optionally, the LCC employs a constant current control based on an MMC direct current voltage;
actual value U of MMC direct-current voltage on rectifying side MMCrec After a first-order inertia link, the command value U of the MMC direct-current voltage at the rectification side MMCrecref Subtracting, and outputting DC command value I under PI control dcref (ii) a The input of the constant current controller is I dcref And the actual value of the direct current I dc ，I dcref And I through a first-order inertia element dc After subtraction, a trigger over-front angle beta is output through PI control, a trigger lag angle alpha is obtained by subtracting PI radian from beta, and the minimum trigger lag angle alpha is set min =5 °, take α and α min The maximum value being the trigger lag angle alpha R And the trigger signal is used as a trigger signal of each switching device in the LCC at the rectification side.
Optionally, the MMC on the rectifying side adopts voltage amplitude-frequency control, and the control system comprises two control dimensions of a d axis and a q axis: the system comprises an outer ring controller, an inner ring controller and a triggering link;
phase voltage amplitude U of MMC alternating current outlet on rectifying side m Is a d-axis voltage command value u dref Let the q-axis voltage command value u qref =0, the input of the outer ring controller is the d-axis component u of the AC outlet voltage of the MMC at the rectification side d And q-axis component u q And u dref And u qref ，u dref And u qref Are respectively connected with u d And u q D-axis current reference value i is output through PI control after subtraction dref1 And q-axis current reference value i qref1 (ii) a Inner ring controlThe input of the controller is MMC alternating outlet current d-axis component i on the rectifying side d1 And q-axis component i q1 And i dref1 And i qref1 ，i dref1 And i qref1 Are respectively connected with i d1 And i q1 D-axis voltage modulation wave u is output through PI control after subtraction vdref1 And q-axis voltage modulation wave u vqref1 (ii) a The input of the trigger is u vdref1 And u vqref1 And the trigger signal of each switching device in the MMC at the rectifying side is output through dq/abc conversion and NLC modulation.
Optionally, the MMC on the contravariant side adopts constant direct current voltage control and constant reactive power control, and the control system includes: a direct current side control loop, and two control dimensions including d-axis and q-axis: the system comprises an outer ring controller, an inner ring controller and a triggering link;
d-axis instruction value U of outer ring controller MMCinvref The Q-axis command value Q of the outer loop controller is generated by the DC side control loop sref =0, the input to the outer loop controller is: actual value U of inversion side MMC direct current voltage MMCinv And the inversion side MMC alternating current outlet reactive power Qs and U MMCinvref And Q sref ，U MMCinv And Qs is respectively with U MMCinvref And Q sref D-axis current reference value i is output through PI control after subtraction dref2 And q-axis current reference value i qref2 (ii) a The input of the inner ring controller is an inversion side MMC alternating outlet current d-axis component i d2 And q-axis component i q2 And i dref2 And i qref2 ，i dref2 And i qref2 Are respectively connected with i d2 And i q2 D-axis voltage modulation wave u is output through PI control after subtraction vdref2 And q-axis voltage modulation wave u vqref2 (ii) a The input of the trigger is u vdref2 And u vqref2 And the trigger signals of each switching device in the inverter side MMC are output through dq/abc conversion and NLC modulation.
Optionally, the dc side control loop adopts a backup constant current control;
the input of the backup constant current control is the actual value I of the direct current at the inversion side dcinv And direct current finger generated by LCC at rectification sideLet value I dcref ，I dcref Multiply by 0.9 and I dcinv Subtracting, and outputting a DC voltage command value U through PI control dciref Get U out dciref And given instruction value U dcsteady The minimum value of the two is used as the d-axis command value U of the outer ring controller MMCinvref ；
When the system is operating normally, U MMCinvref By U dcsteady Determining; when the power generation base or receiving end power grid has an alternating current fault, U MMCinvref By U dciref And determining to realize that the MMC at the inversion side actively reduces the direct-current voltage.
Optionally, the dc line fault control strategy of the dc-side control loop includes:
s1, judging that a direct current line fault occurs when detecting that direct current reaches 1.5p.u;
s2, locking the MMC at the rectifying side and forcibly phase-shifting the LCC, wherein the step of forcibly phase-shifting is to firstly perform alpha R Set to 110 degrees, and after the direct current is reduced to below 1.0p.u., alpha is added R The slope rises to 135 °;
s3, after the direct current fault is cleared, keeping the control of the step S2 for 0.2S to finish the dissociation of the fault point;
s4, restarting the system, unlocking the fault pole MMC and alpha R The direct current voltage command value of the inverter side MMC is reduced to 0.75p.u. from 45 degrees in a linear mode, and after the direct current of the fault pole is recovered to 1.0p.u., the direct current is increased to a steady-state value in a linear mode.
Optionally, the pure new energy power generation base specifically includes: and a wind power generation base and a photovoltaic power generation base which are controlled by a network following type are adopted.
According to the technical scheme, the method has the following advantages:
1. compared with the conventional AC-AC converter based on back-to-back VSC, the LCC-MMC and D-MMC hybrid AC-AC converter provided by the invention has the advantages that the construction cost and the power loss can be greatly reduced, and the LCC-MMC and D-MMC hybrid AC-AC converter has great application value in actual engineering.
2. The invention provides a control strategy of the LCC-MMC and D-MMC mixed AC-AC converter, can realize the sending of a 100% pure new energy power generation base, well adapts to the power fluctuation of the new energy power generation base, fully utilizes the technical maturity of the LCC and the MMC and plays a certain guiding role in future engineering design.
Drawings
Fig. 1 is a schematic structural diagram of a hybrid ac/ac converter provided in an embodiment of the present application;
fig. 2 is a schematic topology diagram of an MMC of a hybrid ac/ac converter provided in an embodiment of the present application;
fig. 3 is a schematic control structure diagram of a rectifying side LCC of a hybrid ac/dc converter provided in an embodiment of the present application;
fig. 4 is a schematic control structure diagram of a rectifying side LCC of a hybrid ac/dc converter provided in an embodiment of the present application;
fig. 5 is a schematic control structure diagram of a rectifying-side MMC of a hybrid ac/dc converter provided in an embodiment of the present application;
fig. 6 is a schematic control structure diagram of an inverter-side MMC of a hybrid ac/dc converter provided in an embodiment of the present application;
fig. 7a is a schematic diagram of an ac voltage simulation waveform of an ac bus on a rectifying side of a hybrid ac/dc converter provided in an embodiment of the present application;
fig. 7b is a schematic diagram of an ac current simulation waveform of an ac bus on a rectifying side of a hybrid ac/dc converter provided in an embodiment of the present application;
fig. 7c is a schematic diagram of an active power simulation waveform of an ac bus on a rectifying side of a hybrid ac/dc converter provided in the embodiment of the present application;
fig. 8a is a schematic diagram of simulated waveforms of dc voltages of an LCC on the positive rectification side and an MMC on the positive rectification side of a hybrid ac/ac converter provided in an embodiment of the present application;
fig. 8b is a schematic diagram of a simulated waveform of the positive dc current of the hybrid ac/ac converter according to the embodiment of the present application;
fig. 9a is a schematic diagram illustrating an ac voltage simulation waveform of an ac bus on an inverter side of a hybrid ac/dc converter provided in an embodiment of the present application;
fig. 9b is a schematic diagram of an ac current simulation waveform of an inverter-side ac bus of a hybrid ac/ac converter according to an embodiment of the present application;
fig. 9c is a schematic diagram of an active power simulation waveform of an inverter-side ac bus of a hybrid ac/ac converter provided in this embodiment.
Detailed Description
In order to make those skilled in the art better understand the technical solutions of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Referring to fig. 1, a hybrid ac/dc converter provided in an embodiment of the present application includes: a rectifier module composed of a positive rectifier and a negative rectifier, and an inverter module composed of a positive inverter and a negative inverter;
the high-voltage end of the positive pole rectifier is connected with the high-voltage end of the positive pole inverter, the high-voltage end of the negative pole rectifier is connected with the high-voltage end of the negative pole inverter, the low-voltage end of the positive pole rectifier and the low-voltage end of the negative pole rectifier are connected with each other and serve as a direct-current side neutral point of the rectifier module, the low-voltage end of the positive pole inverter and the low-voltage end of the negative pole inverter are connected with each other and serve as a direct-current side neutral point of the inverter module, and the direct-current side neutral points of the rectifier module and the inverter module are both connected with a ground electrode, so that a true bipolar structure is formed, as shown in fig. 1;
the alternating current side of the rectifier module is connected with one side of an alternating current bus of the rectification side through a converter transformer, the direct current side of the rectifier module is connected with the direct current side of the inverter module, the alternating current side of the inverter module is connected with one side of an alternating current bus of the inversion side through the converter transformer, an alternating current filter is connected to the alternating current bus of the rectification side in parallel, the high-voltage ends of the positive rectifier and the negative rectifier are connected with the direct current filter in parallel, the other side of the alternating current bus of the rectification side is connected to the pure new energy power generation, and the other side of the alternating current bus of the inversion side is connected to a receiving-end power grid.
It should be noted that the rated frequencies of the pure new energy power generation base, the rectifier side converter transformer and the rectifier are selected to be 8-20 Hz.
Further, the rectifier of the embodiment is composed of a high-voltage valve bank LCC and a low-voltage valve bank MMC, which are connected in series at the direct current side and in parallel at the alternating current side; the LCC comprises two three-phase six-pulse rectifier bridges, the two rectifier bridges are respectively connected with the converter transformers adopting Y0/Y and Y0/delta connection modes, and the phase difference of the valve sides of the two converter transformers is 30 degrees; the MMC is connected with a converter transformer adopting a Y0/delta wiring mode; high-low voltage valve banks of the inverter all adopt half-bridge sub-module type MMC, the direct-current outlet of the high-voltage valve bank MMC is connected with a high-power diode valve D in series, and the MMC is connected with a converter transformer adopting a Y0/delta wiring mode; the structure of a three-phase six-pulse rectifier bridge in the LCC is shown in figure 2, and the structure of the MMC is shown in figure 3.
Further, the pure new energy power generation base of the embodiment comprises a wind power generation base and a photovoltaic power generation base which are controlled by a grid following type, and a low-frequency alternating current transmission line is connected to a rectification side alternating current bus of an LCC-MMC and D-MMC hybrid alternating current converter.
In one embodiment, the rectifying-side LCC adopts constant-current control based on the direct-current voltage of the rectifying-side MMC as shown in fig. 4, specifically:
actual value U of MMC direct-current voltage on rectifying side MMCrec After a first-order inertia link, the instruction value U of the MMC direct-current voltage at the rectification side MMCrecref Subtracting, and outputting DC current instruction value I under PI control dcref (ii) a The input of the constant current controller is I dcref And the actual value of the direct current I dc ，I dcref And I through a first-order inertia element dc After subtraction, a trigger over-rake angle beta is output through PI control, and a trigger lag angle alpha is obtained by subtracting PI radian from beta, so that the minimum trigger lag angle alpha is min =5 °, take α and α min The middle maximum value being the trigger lag angle alpha R As respective switches in the LCC on the rectifying sideA trigger signal of the element.
As shown in fig. 5, the rectification side MMC adopts voltage amplitude-frequency control, specifically:
the control system comprises two control dimensions of d axis and q axis: the system comprises an outer ring controller, an inner ring controller and a triggering link;
phase voltage amplitude U of alternating current outlet of MMC at rectification side m Is a d-axis voltage command value u dref Let the q-axis voltage command value u qref =0, the input of the outer ring controller is the d-axis component u of the AC outlet voltage of the MMC at the rectification side d And q-axis component u q And u dref And u qref ，u dref And u qref Are respectively connected with u d And u q D-axis current reference value i is output through PI control after subtraction dref1 And q-axis current reference value i qref1 (ii) a The input of the inner ring controller is an MMC alternating outlet current d-axis component i on the rectifying side d1 And q-axis component i q1 And i dref1 And i qref1 ，i dref1 And i qref1 Are respectively connected with i d1 And i q1 D-axis voltage modulation wave u is output through PI control after subtraction vdref1 And q-axis voltage modulated wave u vqref1 (ii) a The input of the trigger is u vdref1 And u vqref1 And the trigger signal of each switching device in the MMC at the rectifying side is output through dq/abc conversion and NLC modulation.
Inverter side MMC adopts and decides direct current voltage control and decides reactive power control as shown in figure 6, and is specific:
the control system includes: a direct current side control loop, and two control dimensions including d-axis and q-axis: the system comprises an outer ring controller, an inner ring controller and a triggering link;
d-axis instruction value U of outer ring controller MMCinvref The Q-axis command value Q of the outer loop controller is generated by the DC side control loop sref =0, the input to the outer loop controller is: actual value U of inversion side MMC direct current voltage MMCinv And the inversion side MMC alternating current outlet reactive power Qs and U MMCinvref And Q sref ，U MMCinv And Qs is respectively with U MMCinvref And Q sref D-axis is output through PI control after subtractionCurrent reference value i dref2 And q-axis current reference value i qref2 (ii) a The input of the inner ring controller is an inversion side MMC alternating outlet current d-axis component i d2 And q-axis component i q2 And i dref2 And i qref2 ，i dref2 And i qref2 Are respectively connected with i d2 And i q2 D-axis voltage modulation wave u is output through PI control after subtraction vdref2 And q-axis voltage modulated wave u vqref2 (ii) a The input of the trigger element is u vdref2 And u vqref2 And the trigger signals of each switching device in the inverter side MMC are output through dq/abc conversion and NLC modulation.
The direct current side control loop adopts backup constant current control;
the input of the backup constant current control is the actual value I of the direct current at the inversion side dcinv And a DC current command value I generated by the LCC at the rectification side dcref ，I dcref Multiply by 0.9 and I dcinv Subtracting, and outputting a DC voltage command value U through PI control dciref Get U dciref And given instruction value U dcsteady The minimum value of the sum is used as the d-axis command value U of the outer ring controller MMCinvref ；
When the system is operating normally, U MMCinvref By U dcsteady Determining; when the power generation base or receiving end power grid has an alternating current fault, U MMCinvref By U dciref And determining to realize that the MMC at the inversion side actively reduces the direct-current voltage.
The direct current line fault control strategy of the direct current side control loop comprises the following steps:
s1, judging that a direct current line fault occurs when detecting that direct current reaches 1.5p.u;
s2, locking the MMC at the rectifying side and forcibly shifting the phase of the LCC, wherein the step of forcibly shifting the phase is to firstly perform alpha R Set to 110 degrees, and after the direct current is reduced to below 1.0p.u., alpha is added R The slope rises to 135 degrees;
s3, after the direct current fault is cleared, keeping the control of the step S2 for 0.2S to finish the dissociation of the fault point;
s4, restarting the system, unlocking the fault pole MMC, alpha R Linearly decreasing from 45 DEGWhen the voltage reaches 15 degrees, the direct current voltage command value of the inverter side MMC is reduced to 0.75p.u., and after the direct current of the fault pole is recovered to 1.0p.u, the direct current is linearly increased to a steady-state value.
The system parameters in this embodiment are shown in table 1:
TABLE 1
Figure BDA0003870280440000091
And a corresponding simulation platform is built in the electromagnetic transient simulation software PSCAD/EMTDC to simulate the power fluctuation of the new energy power generation base. In the simulation, the step reduction of the output active power of the 2s new energy power generation base from 5000MW to 3000MW is assumed, fig. 7a to 7c show the simulation result of the key electrical quantity of the alternating current bus at the rectification side, fig. 8a to 8b show the simulation result of the direct current voltage and the direct current, fig. 9a to 9c show the simulation result of the key electrical quantity of the alternating current bus at the inversion side, and the simulation result proves the effectiveness of the invention.
The terms "first," "second," "third," "fourth," and the like in the description of the present application and in the above-described drawings are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
It should be understood that in the present application, "at least one" means one or more, "a plurality" means two or more. "and/or" is used to describe the association relationship of the associated object, indicating that there may be three relationships, for example, "a and/or B" may indicate: only A, only B and both A and B are present, wherein A and B may be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single item(s) or plural items. For example, at least one (one) of a, b, or c, may represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", wherein a, b, c may be single or plural.
In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other manners. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one type of logical functional division, and other divisions may be realized in practice, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.
The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present application may be substantially implemented or contributed to by the prior art, or all or part of the technical solution may be embodied in a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: a usb disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk, or an optical disk.
The above embodiments are only used to illustrate the technical solutions of the present application, and not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions in the embodiments of the present application.

Claims (10)

1. A hybrid ac/dc converter, comprising: a rectifier module composed of a positive rectifier and a negative rectifier, and an inverter module composed of a positive inverter and a negative inverter;
the high-voltage end of the positive pole rectifier is connected with the high-voltage end of the positive pole inverter, the high-voltage end of the negative pole rectifier is connected with the high-voltage end of the negative pole inverter, the low-voltage end of the positive pole rectifier and the low-voltage end of the negative pole rectifier are connected with each other and serve as a direct-current side neutral point of the rectifier module, the low-voltage end of the positive pole inverter and the low-voltage end of the negative pole inverter are connected with each other and serve as a direct-current side neutral point of the inverter module, and the direct-current side neutral points of the rectifier module and the inverter module are both connected to the ground electrode, so that a true bipolar structure is formed;
the alternating current side of the rectifier module is connected with one side of an alternating current bus of the rectification side through a converter transformer, the direct current side of the rectifier module is connected with the direct current side of the inverter module, the alternating current side of the inverter module is connected with one side of an alternating current bus of the inversion side through a converter transformer, an alternating current filter is connected to the alternating current bus of the rectification side in parallel, the high-voltage ends of the positive pole rectifier and the negative pole rectifier are connected with the direct current filter in parallel, the other side of the alternating current bus of the rectification side is connected to a pure new energy power generation base, and the other side of the alternating current bus of the inversion side is connected to a receiving-end power grid.
2. The hybrid ac/ac converter of claim 1, wherein the positive rectifier and the negative rectifier each comprise: the high-pressure valve bank and the low-pressure valve bank are connected in series at a direct current side and in parallel at an alternating current side;
the first high-voltage valve bank is a power grid commutation converter LCC, and the first low-voltage valve bank is a modular multilevel converter MMC of a half-bridge submodule.
3. The hybrid AC-AC converter of claim 2, wherein the LCC comprises: two three-phase six-pulse rectifier bridges, wherein the two three-phase six-pulse rectifier bridges respectively adopt Y 0 Y and Y 0 The converter transformers in a delta connection mode are connected, and the phase difference of the valve sides of the two converter transformers is 30 degrees;
the MMC is a three-phase six-bridge-arm structure, each bridge arm is formed by cascading N half-bridge submodules and then connecting the N half-bridge submodules in series with a bridge arm reactance, and the MMC and the Y are adopted 0 The converter transformers are connected in a/[ delta ] connection mode.
4. The hybrid ac/ac converter of claim 3, wherein the positive inverter and the negative inverter each comprise: the second high-pressure valve bank and the second low-pressure valve bank are connected in series at a direct current side and in parallel at an alternating current side;
the second high-voltage valve group and the second low-voltage valve group are modular multilevel converter MMC with half-bridge sub-modules, a direct-current outlet of the second high-voltage valve group is connected with a high-power diode valve D in series, and the MMC and the Y-shaped module are adopted 0 A/[ delta ] connection mode converter transformer connection.
5. The hybrid AC-AC converter according to claim 4, wherein the LCC employs constant current control based on MMC DC voltage;
actual value U of MMC direct-current voltage on rectifying side MMCrec After a first-order inertia link, the instruction value U of the MMC direct-current voltage at the rectification side MMCrecref Subtracting, and outputting DC current instruction value I under PI control dcref (ii) a The input of the constant current controller is I dcref And the actual value of the direct current I dc ，I dcref And I through a first-order inertia element dc After subtraction, a trigger over-front angle beta is output through PI control, a trigger lag angle alpha is obtained by subtracting PI radian from beta, and the minimum trigger lag angle alpha is set min =5 °, take α and α min The maximum value being the trigger lag angle alpha R And the trigger signal is used as a trigger signal of each switching device in the LCC at the rectification side.
6. The hybrid AC-AC converter according to claim 4, wherein the MMC on the rectifying side employs voltage amplitude-frequency control, and the control system comprises two control dimensions of d-axis and q-axis: the system comprises an outer ring controller, an inner ring controller and a triggering link;
phase voltage amplitude U of MMC alternating current outlet on rectifying side m Is a d-axis voltage command value u dref Let the q-axis voltage command value u qref =0, the input of the outer ring controller is the d-axis component u of the AC outlet voltage of the MMC at the rectification side d And q-axis component u q And u dref And u qref ，u dref And u qref Are respectively connected with u d And u q D-axis current reference value i is output through PI control after subtraction dref1 And q-axis current reference value i qref1 (ii) a The input of the inner ring controller is an MMC alternating outlet current d-axis component i on the rectifying side d1 And q-axis component i q1 And i dref1 And i qref1 ，i dref1 And i qref1 Are respectively connected with i d1 And i q1 D-axis voltage modulation wave u is output through PI control after subtraction vdref1 And q-axis voltage modulation wave u vqref1 (ii) a The input of the trigger is u vdref1 And u vqref1 And the trigger signal of each switching device in the MMC at the rectifying side is output through dq/abc conversion and NLC modulation.
7. The hybrid AC-AC converter according to claim 4, wherein the MMC on the inverting side employs constant DC voltage control and constant reactive power control, and the control system comprises: a direct current side control loop, and two control dimensions including d-axis and q-axis: the system comprises an outer ring controller, an inner ring controller and a triggering link;
d-axis instruction value U of outer ring controller MMCinvref Generated by a direct current side control loop to make the Q-axis command value Q of the outer loop controller sref =0, the input to the outer loop controller is: actual value U of inversion side MMC direct-current voltage MMCinv And the inversion side MMC alternating current outlet reactive power Qs and U MMCinvref And Q sref ，U MMCinv And Qs is respectively with U MMCinvref And Q sref D-axis current reference value i is output through PI control after subtraction dref2 And q-axis current reference value i qref2 (ii) a The input of the inner ring controller is an inversion side MMC alternating outlet current d-axis component i d2 And q-axis component i q2 And i dref2 And i qref2 ，i dref2 And i qref2 Are respectively connected with i d2 And i q2 D-axis voltage modulation wave u is output through PI control after subtraction vdref2 And q-axis voltage modulated wave u vqref2 (ii) a The input of the trigger element is u vdref2 And u vqref2 And the trigger signals of each switching device in the inverter side MMC are output through dq/abc conversion and NLC modulation.
8. The hybrid ac/ac converter according to claim 7, wherein the dc-side control loop employs a backup constant current control;
the input of the backup constant current control is the actual value I of the direct current at the inversion side dcinv And a DC current command value I generated by the LCC at the rectification side dcref ，I dcref Multiply by 0.9 and I dcinv Subtracting, and outputting a DC voltage command value U through PI control dciref Get U dciref And given instruction value U dcsteady The minimum value of the two is used as the d-axis command value U of the outer ring controller MMCinvref ；
When the system is operating normally, U MMCinvref From U dcsteady Determining; when the power generation base or receiving end power grid has an alternating current fault, U MMCinvref By U dciref And determining to realize that the MMC at the inversion side actively reduces the direct-current voltage.
9. The hybrid ac/ac converter according to claim 8, wherein the dc line fault control strategy of the dc-side control loop comprises:
s1, judging that a direct current line fault occurs when detecting that direct current reaches 1.5p.u;
s2, locking the MMC at the rectifying side and forcibly phase-shifting the LCC, wherein the step of forcibly phase-shifting is to firstly perform alpha R Set at 110 degree, reduce the DC current to 1.0p.u, and then reduce alpha R The slope rises to 135 °;
s3, after the direct current fault is cleared, keeping the control of the step S2 for 0.2S to finish the dissociation of the fault point;
s4, restarting the system, unlocking the fault pole MMC and alpha R The direct current voltage command value of the inverter side MMC is reduced to 0.75p.u. from 45 degrees to 15 degrees in a linear mode, and the direct current of the fault pole is recovered to 1.0p.u. and then is increased to a steady-state value in a linear mode.
10. The hybrid ac/ac converter according to claim 1, wherein the renewable energy power generation base comprises: and a wind power generation base and a photovoltaic power generation base which are controlled by a network following type are adopted.
CN202211193234.3A 2022-09-28 2022-09-28 Mixed type AC-AC converter Pending CN115473445A (en)

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