CN116566211A - True bipolar isolation type modularized multi-level direct current transformer and control method - Google Patents

True bipolar isolation type modularized multi-level direct current transformer and control method Download PDF

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Publication number
CN116566211A
CN116566211A CN202310480479.2A CN202310480479A CN116566211A CN 116566211 A CN116566211 A CN 116566211A CN 202310480479 A CN202310480479 A CN 202310480479A CN 116566211 A CN116566211 A CN 116566211A
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China
Prior art keywords
voltage
voltage side
low
bridge
direct current
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Pending
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CN202310480479.2A
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Chinese (zh)
Inventor
董亮辉
牛昶
赖锦木
王要强
李宝伟
尹项根
陈卫
侯星宇
刘阳
尹越
陈俊宏
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Zhengzhou University
XJ Electric Co Ltd
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Zhengzhou University
XJ Electric Co Ltd
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Priority to CN202310480479.2A priority Critical patent/CN116566211A/en
Publication of CN116566211A publication Critical patent/CN116566211A/en
Pending legal-status Critical Current

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Classifications

    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • 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
    • H02M5/02—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 without intermediate conversion into dc
    • H02M5/04—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 without intermediate conversion into dc by static converters
    • H02M5/10—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 without intermediate conversion into dc by static converters using transformers
    • 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
    • H02M7/23—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 arranged for operation in parallel
    • 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]

Abstract

The invention discloses a true bipolar isolation type modularized multi-level direct current transformer and a control method, wherein the true bipolar isolation type modularized multi-level direct current transformer comprises a primary side topology formed by two single-phase modularized multi-level converters, a secondary side topology formed by four H-bridge structures and four two-winding intermediate frequency transformers; the positive single-phase modularized multi-level converter or the negative single-phase modularized multi-level converter of the primary side topology is connected with the secondary side topology in a parallel manner through two intermediate frequency transformers; the secondary winding of each two-winding intermediate frequency transformer is connected to the ac side of each H-bridge structure by a transmission inductance. The capacitor is connected in series with two anti-parallel IGBT switching tubes which are respectively connected in parallel with the positive electrode port and the negative electrode port of the low voltage side. The high-voltage side and the low-voltage side of the invention are both positive and negative bipolar ports, the positive and negative bipolar ports are independently controlled by a closed loop, the power transmission of the other pole is not affected by the single-pole structure fault, the fault tolerance during the fault is improved, and the range of direct current voltage and the range of connected load are expanded.

Description

True bipolar isolation type modularized multi-level direct current transformer and control method
Technical Field
The invention belongs to the field of power systems, and particularly relates to a true bipolar isolation type modularized multi-level direct current transformer and a control method.
Background
In the field of medium-high voltage direct current distribution networks, direct current transformers are required to realize the functions of grade conversion, electrical isolation and bidirectional electric energy control of direct current voltage, and in order to enable energy to flow bidirectionally, direct current transformers with a double-active-bridge (DAB) structure are widely applied to the field. However, the voltage-withstand capability of the switching tube is limited, and in order to alleviate the voltage stress of the switching tube, an input-series-output-parallel structure (ISOP) is further proposed, and the input ends and the output ends of the tributary transformers of a plurality of DAB structures are connected in series to improve the voltage-withstand level of the high voltage side and the power output level of the low voltage side, but the structure is composed of a plurality of DAB converters, so that the electric energy distribution and insulation design are complex and the device has a large volume.
Thus, an isolated modular multilevel DC/DC converter (isolated modular multilevel DC converter, IMMDC) has developed. The topology combines the advantages of a modularized multi-level converter and a DAB structure, the primary side adopts an MMC structure, the secondary side is still an H-bridge structure, the centralized capacitor at the direct current side is eliminated, and the power converter has the advantages of bidirectional power transmission, modularized design, easiness in voltage expansion, simplicity in redundancy design and the like.
However, most of IMMDCs applied at present are pseudo bipolar topologies, and a pseudo bipolar structure can provide low-voltage direct current buses with positive and negative polarities, but cannot realize asymmetric load operation of the positive and negative poles; and the high-frequency transformer required by the IMMDC applied at present has high manufacturing cost, complex control structure and asymmetric bridge arm parameters, and seriously affects the normal operation of the IMMDC.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a true bipolar isolation type modularized multi-level direct current transformer and a control method.
The invention provides a true bipolar isolation type modularized multi-level direct current transformer, which comprises a primary side topology, four two-winding intermediate frequency transformers and a secondary side topology;
the primary side topology comprises two single-phase modularized multi-level converters, each single-phase modularized multi-level converter comprises two single-phase bridge arms which are connected in parallel, each phase of bridge arm comprises an upper bridge arm and a lower bridge arm, and the upper bridge arm and the lower bridge arm of each phase are connected in series through two bridge arm inductors or one coupling inductor; the two single-phase modularized multi-level converters are connected in series to form a positive-negative true bipolar structure, wherein the positive electrode of one single-phase modularized multi-level converter is used as the positive electrode of the primary side topology, the connection part of the two single-phase modularized multi-level converters is grounded, and the negative electrode of the other single-phase modularized multi-level converter is used as the negative electrode of the primary side topology;
the secondary side topology comprises four H-bridge structures which are connected in a staggered manner;
the first direct current output end of the first H bridge structure is connected with the first direct current output end of the third H bridge structure and then used as a first low-voltage direct current output end of the secondary side topology;
the second direct current output end of the first H bridge structure, the first direct current output end of the second H bridge structure, the second direct current output end of the third H bridge structure and the first direct current output end of the fourth H bridge structure are grounded after being connected and serve as second low-voltage direct current output ends of the secondary side topology;
the second direct current output end of the second H bridge structure is connected with the second direct current output end of the fourth H bridge structure;
and the two anti-parallel IGBT switching tubes connected in series by the capacitor are respectively connected in parallel with the positive electrode port and the negative electrode port of the low-voltage side.
The primary side homonymous end ports of every two-winding intermediate frequency transformers are connected in parallel and then connected to connection points of two bridge arm inductors or middle terminals of coupling inductors of one single-phase bridge arm of the single-phase modularized multi-level converter, and primary side heteronymous ends of every two-winding intermediate frequency transformers are connected in series and then connected to connection points of two bridge arm inductors or middle terminals of coupling inductors of the other single-phase bridge arm of the single-phase modularized multi-level converter;
the transformation ratio of the primary winding and the secondary winding of each two-winding intermediate frequency transformer is n:1, a step of; the secondary side homonymous port of each two-winding intermediate frequency transformer is connected with the alternating current outgoing line end of each H-bridge structure through a transmission inductor, and the sizes of the four transmission inductors are the sum of leakage inductance and external inductance of the four two-winding intermediate frequency transformers respectively.
The second aspect of the invention provides a control method of the true bipolar isolation type modularized multi-level direct current transformer, which comprises the following steps:
the system comprises a low-voltage side positive and negative bipolar voltage control loop, a bridge arm inner submodule capacitor voltage balance control loop, a high-voltage side power grid ground short circuit fault ride-through control loop and a low-voltage side power grid short circuit fault ride-through control loop;
the low-voltage side positive and negative bipolar voltage control ring is used for adjusting the magnitude of the low-voltage side positive and negative bipolar voltage, the bridge arm inner submodule capacitor voltage balance control ring is used for balancing and controlling the bridge arm inner submodule capacitor voltage, and the high-voltage side power grid ground short circuit fault ride-through control ring is used for maintaining the low-voltage side voltage constant when the high-voltage side single-pole ground short circuit fault occurs; the low-voltage side grid single-pole short-circuit fault ride-through control loop is used for maintaining constant low-voltage side non-fault pole voltage when the low-voltage side LVDC grid single-pole short-circuit fault occurs.
In one embodiment, the low-voltage side positive and negative bipolar voltage control loop collects voltages of the low-voltage side positive and negative ports in real time and compares the voltages with voltage reference values of the positive and negative ports; wherein, the voltage reference value of the positive electrode port at the low voltage side is differed from the voltage actual value of the positive electrode port, the positive electrode phase shift angle is obtained through the control of the first PI regulator, the positive pole phase shift angle shifts the square wave and then drives the power electronic switching devices of the first H bridge structure and the third H bridge structure; and the voltage reference value of the negative electrode port at the low voltage side is different from the voltage actual value of the negative electrode port, a negative electrode phase shift angle is obtained through control of the second PI regulator, and the power electronic switching devices of the second H bridge structure and the fourth H bridge structure are driven after the square wave phase shift is carried out by the negative electrode phase shift angle.
In one embodiment, the bridge arm inner submodule capacitor voltage balance control loop adopts a sequencing method to perform balance control on the bridge arm inner submodule capacitor voltage:
sequencing the capacitor voltage of each sub-module cascaded in each phase of bridge arm, and simultaneously calculating the trigger signals corresponding to different phase shift angles in a real-time working modeAccording to->Will->The larger trigger signal is distributed to the submodule with lower capacitance voltage; under quasi-square wave modulation, the calculation formula of charge conversion quantity in half period of capacitance access of the sub-module is +.>Wherein->For bridge arm current->For the alternating current component>Is a direct current component.
In one embodiment, the high-voltage side grid ground fault ride through control loop blocks driving pulses of the positive modularized multi-level converter and the first H bridge and the second H bridge of the low-voltage side after collecting that a single-pole ground fault occurs on the high-voltage side of the true bipolar isolation type modularized multi-level direct current transformer, such as that the positive pole has the ground fault, so as to terminate capacitor discharge of each sub-module in the positive modularized multi-level converter, shield influence of the fault high-voltage side on the non-fault low-voltage side, and clear fault current.
Similarly, when the high-voltage side negative electrode has a short circuit to ground fault, driving pulses of the modularized multi-level converter of the negative electrode and the third H bridge and the fourth H bridge of the low-voltage side are blocked, so that capacitor discharge of each sub-module in the modularized multi-level converter of the negative electrode is stopped, the influence of the fault high-voltage side on the non-fault low-voltage side is shielded, and fault current is cleared.
In one embodiment, after the short-circuit fault of the low-voltage side positive electrode of the true bipolar isolation type modularized multi-level direct current transformer is collected, the driving pulse of the first H bridge and the driving pulse of the third H bridge of the low-voltage side are blocked so as to shield the influence of the fault low-voltage side on the high-voltage side of the non-fault side and clear fault current;
similarly, when the low-voltage side power grid short-circuit fault ride-through control loop acquires a short-circuit fault of a low-voltage side negative electrode of the true bipolar isolation type modularized multi-level direct current transformer, driving pulses of a second H bridge and a fourth H bridge on the low-voltage side are blocked, so that the influence of the fault low-voltage side on a high-voltage side on a non-fault side is shielded, and fault current is cleared.
The invention also provides a control device of the true bipolar isolation type modularized multi-level direct current transformer, which comprises: the system comprises a memory, a processor and a control program stored in the memory and capable of running on the processor, wherein the control program realizes the steps of the control method when being executed by the processor.
Compared with the prior art, the invention has the following characteristics:
(1) Both the high voltage and low voltage dc ports have true bipolar structures. The high-voltage side of the true bipolar isolation type modularized multi-level direct current transformer is connected in series by adopting two modularized multi-level converters, so that a positive electrode and a negative electrode are constructed on the high-voltage side; the low-voltage side adopts four H-bridge structure staggered connection modes to construct a low-voltage direct current anode and a low-voltage direct current cathode, and the voltage range of the access of new energy power generation, direct current load and the like is expanded.
(2) The anti-jamming capability becomes strong. The high-voltage side and the low-voltage side of the invention are both positive and negative bipolar structures, each low-voltage output port of the low-voltage side is independently controlled by an independent control loop, even if one pole fails, the other pole is not influenced to work normally, uninterrupted power supply to a load can be ensured, and the reliability and fault tolerance of power transmission are greatly improved.
(3) The power decoupling method is characterized in that the arrangement positions and the power decoupling modes of the structural transmission inductors of the two-winding intermediate frequency transformers and the H-bridge are adopted in parallel connection on the low-voltage side of the unipolar modularized converter, the transmission inductors are arranged on the secondary sides of the two-winding intermediate frequency transformers, and the power of the four H-bridges on the low-voltage side is transmitted by the independent leakage inductance of the four two-winding intermediate frequency transformers, so that the power decoupling of the four H-bridges transmitted from the high-voltage side to the low-voltage side is realized.
(4) And the power device is saved. The invention integrates the upper bridge arm submodule and the lower bridge arm submodule which are in phase, saves part of power devices, and simultaneously, the upper bridge arm and the lower bridge arm are coupled to provide a circulation channel for the ripple power of the submodule, thereby being beneficial to reducing the capacitance voltage ripple of the submodule and reducing the capacitance requirement of the submodule.
(5) The voltage range of the connected load is extended. According to the invention, the capacity expansion and diffusion are carried out according to actual requirements, the voltage range of the load connected to the low-voltage side is widened, and the universal applicability is good.
Drawings
FIG. 1 is a schematic diagram of a true bipolar isolated modular multilevel DC transformer;
FIG. 2 is a schematic diagram of a half-bridge topology provided by the present invention;
FIG. 3 is a schematic diagram of a full bridge topology provided by the present invention;
FIG. 4 is a topological positive and negative bipolar voltage control block diagram of a true bipolar isolation type modular multilevel direct current transformer provided by the invention;
fig. 5 is a diagram of simulation results of transmission inductance current at the low-voltage side of a topology of a true bipolar isolation type modular multilevel direct current transformer;
FIG. 6 is a graph of simulation results of steady state moments of inductor current transmitted on the low-voltage side of a topology of a true bipolar isolated modular multilevel direct current transformer;
fig. 7 is a diagram of simulation results of dc current on the high-voltage side of a topology of a true bipolar isolated modular multilevel dc transformer provided by the present invention;
FIG. 8 is a diagram of the topological load current simulation result of a true bipolar isolated modular multilevel DC transformer provided by the invention;
FIG. 9 is a graph of steady-state current simulation results after abrupt change of topological load of a true bipolar isolated modular multilevel DC transformer;
fig. 10 is a diagram of simulation results of the voltage at the primary ac port of a topology intermediate-frequency transformer of a true bipolar isolated modular multilevel dc transformer;
FIG. 11 is a diagram of simulation results of secondary AC port voltages of a topological intermediate frequency transformer of a true bipolar isolated modular multilevel DC transformer;
fig. 12 is a topological load voltage waveform of a true bipolar isolated modular multilevel dc transformer provided by the present invention.
Fig. 13 is a schematic diagram of fault current and blocking condition of a true bipolar isolated modular multilevel dc transformer topology high voltage side positive electrode with a short circuit to ground fault.
Fig. 14 is a diagram of simulation results when a short circuit fault occurs in a positive pole of a topological high-voltage side of a true bipolar isolation type modularized multi-level direct current transformer.
Fig. 15 is an equivalent circuit schematic diagram of a true bipolar isolation type modular multilevel direct current transformer when a short circuit fault occurs at the positive pole of the topological low-voltage side.
Fig. 16 is a diagram of simulation results when a short circuit fault occurs in a positive pole of a topological low-voltage side of a true bipolar isolation type modularized multi-level direct current transformer.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific examples described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Example 1
As shown in fig. 1-3, the present embodiment provides a true bipolar isolated modular multilevel dc transformer, including a primary side topology, four two-winding intermediate frequency transformers, and a secondary side topology;
the primary side topology comprises two single-phase modularized multi-level converters, and the single-phase modularized multi-level converters comprise two single-phase bridge arms which are connected in parallel and are marked as an a-phase bridge arm and a b-phase bridge arm; each phase of bridge arm comprises an upper bridge arm and a lower bridge arm, wherein the upper bridge arm and the lower bridge arm of each phase are connected in series through two bridge arm inductors or one coupling inductor; the two single-phase modularized multi-level converters are connected in series to form a positive-negative true bipolar structure, wherein the positive electrode of one single-phase modularized multi-level converter is used as the positive electrode of the primary side topology, the connection part of the two single-phase modularized multi-level converters is grounded, and the negative electrode of the other single-phase modularized multi-level converter is used as the negative electrode of the primary side topology;
the secondary side topology comprises four H-bridge structures which are connected in a staggered manner;
the first direct current output end of the first H bridge structure is connected with the first direct current output end of the third H bridge structure and then used as a first low-voltage direct current output end of the secondary side topology;
the second direct current output end of the first H bridge structure, the first direct current output end of the second H bridge structure, the second direct current output end of the third H bridge structure and the first direct current output end of the fourth H bridge structure are grounded after being connected and serve as second low-voltage direct current output ends of the secondary side topology;
the second direct current output end of the second H bridge structure is connected with the second direct current output end of the fourth H bridge structure;
and the two anti-parallel IGBT switching tubes connected in series by the capacitor are respectively connected in parallel with the positive electrode port and the negative electrode port of the low-voltage side.
The primary side homonymous end ports of every two-winding intermediate frequency transformers are connected in parallel and then connected to connection points of two bridge arm inductors or middle terminals of coupling inductors of one single-phase bridge arm of the single-phase modularized multi-level converter, and primary side heteronymous ends of every two-winding intermediate frequency transformers are connected in series and then connected to connection points of two bridge arm inductors or middle terminals of coupling inductors of the other single-phase bridge arm of the single-phase modularized multi-level converter;
the secondary side homonymous port of each two-winding intermediate frequency transformer is connected with the alternating current outgoing line end of each H-bridge structure through a transmission inductor, and the sizes of the four transmission inductors are the sum of leakage inductance and external inductance of the four two-winding intermediate frequency transformers respectively.
In the embodiment, an upper bridge arm and a lower bridge arm of each single-phase bridge arm are formed by connecting N power modules in series; the power module adopts a half-bridge structure or a full-bridge structure; wherein, the liquid crystal display device comprises a liquid crystal display device,
the power module of the half-bridge structure comprises two power electronic switching devices with anti-parallel freewheeling diodes and a capacitor, wherein the two power electronic switching devices are connected in series, and the capacitor is connected in parallel at two ends of the two power electronic switching devices;
the power module of the full-bridge structure consists of four power electronic switching devices with anti-parallel freewheeling diodes and a capacitor; the upper and lower legs of each phase are connected in series with two inductors or one coupling inductor.
Each H-bridge structure comprises four power electronic switching devices with anti-parallel freewheeling diodes and a voltage stabilizing capacitor, and the two power electronic switching devices are connected in series and then connected in parallel with a series structure formed by the other two power electronic switching devices. In a specific implementation, the power electronic switching device comprises an IGBT switching tube.
Example 2
The embodiment provides a control method, which is applied to the true bipolar isolation type modularized multi-level direct current transformer in embodiment 1, wherein in the true bipolar isolation type modularized multi-level direct current transformer in embodiment 1, one end of each of four transmission inductors is connected to a homonymous port of a secondary side of each of four intermediate frequency transformers, the other end of each of the four transmission inductors is connected to an alternating current outlet end of each of four H-bridges, and the sizes of the four transmission inductors are the sum of leakage inductance and external inductance of each of the four intermediate frequency transformers; by placing the transmission inductance on the secondary side of the intermediate frequency transformer, the power of the four H bridges on the low voltage side is respectively transmitted by the independent leakage inductance of the four intermediate frequency transformers, so that the power decoupling of the four H bridges transmitted from the high voltage side to the low voltage side is realized.
The control method comprises a low-voltage side positive and negative bipolar voltage control loop, a bridge arm inner submodule capacitor voltage balance control loop, a high-voltage side power grid ground short circuit fault ride-through control loop and a low-voltage side power grid short circuit fault ride-through control loop;
the low-voltage side positive and negative bipolar voltage control ring is used for adjusting the magnitude of the low-voltage side positive and negative bipolar voltage, the bridge arm inner submodule capacitor voltage balance control ring is used for balancing and controlling the bridge arm inner submodule capacitor voltage, and the high-voltage side power grid ground short circuit fault ride-through control ring is used for maintaining the low-voltage side voltage constant when the high-voltage side single-pole ground short circuit fault occurs; the low-voltage side grid single-pole short-circuit fault ride-through control loop is used for maintaining constant low-voltage side non-fault pole voltage when the low-voltage side LVDC grid single-pole short-circuit fault occurs.
Specifically, the control steps of the low-voltage side positive and negative bipolar voltage control loop are as shown in fig. 4, and include: collecting voltages of a positive electrode port and a negative electrode port of the low-voltage side in real time and comparing the voltages with voltage reference values of the positive electrode port and the negative electrode port; wherein, the voltage reference value V of the low-voltage side positive electrode port outc,ref Actual value V of voltage with positive electrode port outc The difference is made, and the positive phase shift angle phi is obtained through the control of a first PI regulator 1 Positive electrodePhase shift angle phi 1 A power electronic switching device for driving the first H-bridge structure and the third H-bridge structure after shifting the square wave; voltage reference V of low-voltage side negative electrode port outd,ref Actual value V of voltage with negative electrode port outd The difference is made, and the negative phase shift angle phi is obtained through the control of a second PI regulator 2 Negative phase shift angle phi 2 And the square wave is phase-shifted to drive the power electronic switching devices of the second H-bridge structure and the fourth H-bridge structure.
Specifically, after the sub-module phase shifting is added, the phase shifting angle can lead to inconsistent charging time of each sub-module capacitor, so that the sub-module capacitor voltage is unbalanced, and the balance of the capacitor is a precondition for stable operation of the system, so that a bridge arm inner sub-module capacitor voltage balance control loop needs to be designed to control the balance of the bridge arm inner sub-module capacitor voltage.
Furthermore, the capacitor voltage balance control loop of the bridge arm inner submodule adopts a sequencing method to balance and control the capacitor voltage of the bridge arm inner submodule:
sequencing the capacitor voltage of each sub-module cascaded in each phase of bridge arm, and simultaneously calculating the trigger signals corresponding to different phase shift angles in a real-time working modeAccording to->Will->The larger trigger signal is distributed to the submodule with lower capacitance voltage; under quasi-square wave modulation, the calculation formula of the charge conversion quantity in half period of module capacitor access is +.>Wherein->For bridge arm current->For the alternating current component>Is a direct current component.
Specifically, after the high-voltage side power grid ground fault ride-through control loop acquires the positive line-to-ground fault of the high-voltage side outgoing line of the true bipolar isolation type modularized multi-level direct current transformer, driving pulses of the modularized multi-level converter of the positive electrode and the first H bridge and the second H bridge of the low-voltage side are blocked, capacitor discharge of each sub-module in the modularized multi-level converter of the positive electrode is terminated, influences of the fault side on the non-fault side are shielded, and fault current is cleared.
When the positive pole of the high-voltage side is in short circuit fault, blocking is achieved by blocking pulse signals of sub-modules on four bridge arms of the primary side topological positive pole modularized multi-level converter and pulse signals of IGBT on the secondary side topological first H bridge and the secondary side topological second H bridge, at the moment, the negative pole modularized multi-level converter works normally, power is transmitted to a positive pole port and a negative pole port of the low-voltage side through a third H bridge and a fourth H bridge, namely, the high-voltage side negative pole modularized multi-level converter works normally, and power transmission is carried out between the positive pole and the negative pole port of the low-voltage side.
In the same way, after the high-voltage side grid ground fault ride-through control loop acquires that the high-voltage side negative electrode of the true bipolar isolation type modularized multi-level direct current transformer has the ground fault, driving pulses of the modularized multi-level converter of the negative electrode, the third H bridge and the fourth H bridge of the low-voltage side are blocked so as to terminate capacitor discharge of each sub-module in the modularized multi-level converter of the negative electrode, shield the influence of the fault high-voltage side on the non-fault low-voltage side and clear fault current.
When the high-voltage side negative pole short circuit fault occurs, blocking is achieved through blocking pulse signals of sub-modules on four bridge arms of the primary side topological negative pole modularized multi-level converter and pulse signals of IGBT on the secondary side topological third H bridge and the fourth H bridge, at the moment, the positive pole modularized multi-level converter works normally, power is transmitted to a low-voltage side positive pole port and a low-voltage side negative pole port through the first H bridge and the second H bridge, namely, the high-voltage side positive pole modularized multi-level converter works normally, and power transmission is conducted between the low-voltage side positive pole and the low-voltage side negative pole port.
Specifically, after the positive short-circuit fault occurs on the low-voltage side of the true bipolar isolation type modularized multi-level direct current transformer, the low-voltage side power grid short-circuit fault ride-through control loop blocks driving pulses of a first H bridge and a third H bridge on the low-voltage side, shields influences of a fault side on a non-fault side, and clears fault current.
When the low-voltage side positive electrode port is in short circuit fault, pulse signals of IGBT (insulated gate bipolar transistor) on the first H bridge and the third H bridge are blocked to lock the first H bridge and the third H bridge, at the moment, the positive electrode and the negative electrode modularized multi-level converter work normally, power is transmitted to the low-voltage side negative electrode port through the second H bridge and the fourth H bridge, namely, the positive electrode and the negative electrode modularized multi-level converter work normally, and power transmission is carried out between the low-voltage side negative electrode port.
Similarly, after the short-circuit fault of the low-voltage side grid short-circuit fault ride-through control loop collects the short-circuit fault of the low-voltage side negative electrode of the true bipolar isolation type modularized multi-level direct current transformer, driving pulses of the second H bridge and the fourth H bridge on the low-voltage side are blocked, so that the influence of the fault low-voltage side on the high-voltage side on the non-fault side is shielded, and fault current is cleared.
Specifically, when the low-voltage side negative electrode port is in short circuit fault, pulse signals of IGBTs on the second H bridge and the fourth H bridge are blocked to lock the second H bridge and the fourth H bridge, at the moment, the positive electrode and the negative electrode modularized multi-level converter work normally, power is transmitted to the low-voltage side negative electrode port through the first H bridge and the third H bridge, namely, the positive electrode and the negative electrode modularized multi-level converter work normally, and power transmission is carried out between the low-voltage side negative electrode port.
Example 3
In this embodiment, simulation verification is performed on the transformer topology and the control method described in embodiment 1 and embodiment 2 in MATLAB software.
The simulation parameters are shown in table 1:
table 1 simulation parameters
Designing the rated voltage of the primary side to be 20kV (+ -10 kV) and the rated voltage of the secondary side to be 750V; considering withstand voltage class, each half bridge arm is formed by cascading 5 modules, rated capacitance voltage is 2kV, self inductance of bridge arm inductance is set to be 1.5mH, mutual inductance is set to be 1.495mH, transmission inductance is designed to be 10uH, and transformation ratio of an intermediate frequency transformer is set to be n:1, wherein n=10000/750, the PI parameter in the control circuit, the proportion link is set to 4, the integral link is set to 150, the load resistance is set to 2Ω, in addition, the resistance at 0.3S is suddenly changed in the simulation process, and the resistance is suddenly changed from original 2 to 6/7Ω. The simulation time was set to 0.8S.
Fig. 5 is a diagram of simulation results of the transmission inductor current at the low-voltage side of the topology of the true bipolar isolation modular multilevel dc transformer; FIG. 6 is a graph of simulation results of steady-state moments of the transmission inductor current at the low-voltage side of the topology of the true bipolar isolation type modular multilevel direct current transformer; fig. 7 is a diagram of simulation results of dc current on the high-voltage side of the topology of the true bipolar isolated modular multilevel dc transformer; FIG. 8 is a graph of the topological load current simulation results of the true bipolar isolated modular multilevel DC transformer; FIG. 9 is a graph of the steady-state current simulation results after abrupt change of the topological load of the true bipolar isolated modular multilevel DC transformer; FIG. 10 is a diagram of simulation results of the primary AC port voltage of the topology intermediate frequency transformer of the true bipolar isolated modular multilevel DC transformer; FIG. 11 is a graph of simulation results of the secondary AC port voltage of the topology intermediate frequency transformer of the true bipolar isolated modular multilevel DC transformer; fig. 12 is a topological load voltage waveform of the true bipolar isolated modular multilevel dc transformer.
(1) Simulation of true bipolar isolation type modularized multi-level direct current transformer when high-voltage side positive electrode port has ground short circuit fault
Fig. 13 shows a fault current schematic diagram and a blocking condition of the true bipolar isolated modular multilevel dc transformer when a single pole to ground short circuit fault occurs at the high voltage side positive pole port. Fig. 14 is a graph showing simulation results when a short-circuit to ground fault occurs in the high-voltage side positive electrode port. As can be seen from fig. 14, after the positive electrode of the 0.1s high-voltage dc power grid has a ground fault, the high-voltage dc positive electrode voltage drops to 0, and the modular multilevel converter of the high-voltage negative electrode still can normally operate by blocking the driving pulses of the modular multilevel converter of the positive electrode and the first H-bridge and the second H-bridge of the low voltage, and the port voltages of the low-voltage dc positive electrode and the negative electrode are controlled to be maintained at the rated voltages. The simulation result shows that the true bipolar isolation type modularized multi-level direct current transformer has the high-voltage side short circuit fault ride-through capability.
(2) Simulation of short-circuit fault of true bipolar isolation type modularized multi-level direct-current transformer at low-voltage side positive electrode port
Fig. 15 shows an equivalent circuit schematic of a true bipolar isolated modular multilevel dc transformer in the event of a single pole short circuit failure at the low side positive port. Fig. 16 shows simulation results of a true bipolar isolated modular multilevel dc transformer when a short circuit fault occurs at the low voltage side positive port.
As can be seen from fig. 16, after the positive electrode of the 0.3s low-voltage dc power grid has a short-circuit fault, the voltage of the positive electrode at the low-voltage side drops greatly, and at this time, the driving signals of the first H-bridge and the third H-bridge switching transistors are blocked, so that the influence of the fault side on the non-fault side is shielded, and the fault current is cleared. After the true bipolar isolation type modularized multi-level direct current transformer is adopted, the direct current of the high-voltage positive electrode and the direct current of the high-voltage negative electrode are always consistent. At this time, the voltage of the non-fault pole at the low-voltage side is still stable at 750V, and the simulation result shows that the true bipolar isolation type modularized multi-level direct current transformer has the short-circuit fault ride-through capability at the low-voltage side.
Example 4
The embodiment provides a control device of a true bipolar isolation type modularized multi-level direct current transformer, which is characterized by comprising: the control program is executed by the processor to implement the steps of the control method described in embodiment 2.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims (10)

1. The utility model provides a real bipolar isolation type modularization multi-level direct current transformer which characterized in that:
the device comprises a primary side topology, four two-winding intermediate frequency transformers and a secondary side topology;
the primary side topology comprises two single-phase modularized multi-level converters, each single-phase modularized multi-level converter comprises two single-phase bridge arms which are connected in parallel, each phase of bridge arm comprises an upper bridge arm and a lower bridge arm, and the upper bridge arm and the lower bridge arm of each phase are connected in series through two bridge arm inductors or one coupling inductor; the two single-phase modularized multi-level converters are connected in series to form a positive-negative true bipolar structure, wherein the positive electrode of one single-phase modularized multi-level converter is used as the positive electrode of the primary side topology, the connection part of the two single-phase modularized multi-level converters is grounded, and the negative electrode of the other single-phase modularized multi-level converter is used as the negative electrode of the primary side topology;
the secondary side topology comprises four H-bridge structures which are connected in a staggered manner;
the first direct current output end of the first H bridge structure is connected with the first direct current output end of the third H bridge structure and then used as a first low-voltage direct current output end of the secondary side topology;
the second direct current output end of the first H bridge structure, the first direct current output end of the second H bridge structure, the second direct current output end of the third H bridge structure and the first direct current output end of the fourth H bridge structure are grounded after being connected and serve as second low-voltage direct current output ends of the secondary side topology;
the second direct current output end of the second H bridge structure is connected with the second direct current output end of the fourth H bridge structure;
the bipolar modularized multi-level direct current transformer is characterized in that two anti-parallel IGBT switching tubes connected in series with a capacitor are respectively connected in parallel with a positive electrode port and a negative electrode port of a low-voltage side;
the primary side homonymous end ports of every two-winding intermediate frequency transformers are connected in parallel and then connected to connection points of two bridge arm inductors or middle terminals of coupling inductors of one single-phase bridge arm of the single-phase modularized multi-level converter, and primary side heteronymous ends of every two-winding intermediate frequency transformers are connected in series and then connected to connection points of two bridge arm inductors or middle terminals of coupling inductors of the other single-phase bridge arm of the single-phase modularized multi-level converter;
the transformation ratio of the primary winding and the secondary winding of each two-winding intermediate frequency transformer is n:1, a step of; the secondary side homonymous port of each two-winding intermediate frequency transformer is connected with the alternating current outgoing line end of each H-bridge structure through a transmission inductor, and the sizes of the four transmission inductors are the sum of leakage inductance and external inductance of the four two-winding intermediate frequency transformers respectively.
2. The true bipolar isolated modular multilevel dc transformer of claim 1, wherein the upper leg and the lower leg of each single phase leg are comprised of N cascaded power modules;
the power module adopts a half-bridge structure or a full-bridge structure;
the power module of the half-bridge structure comprises two power electronic switching devices with anti-parallel freewheeling diodes and a voltage stabilizing capacitor, wherein the two power electronic switching devices are connected in series, and the voltage stabilizing capacitor is connected in parallel at two ends of the two power electronic switching devices;
the power module of the full-bridge structure comprises four power electronic switching devices with anti-parallel freewheeling diodes and a voltage stabilizing capacitor, wherein the two power electronic switching devices are connected in series and then are connected in parallel with a series structure formed by the other two power electronic switching devices, and the voltage stabilizing capacitor is connected in parallel at two ends of any series structure.
3. The true bipolar isolated modular multilevel dc transformer of claim 1, wherein: each H-bridge structure comprises four power electronic switching devices with anti-parallel freewheeling diodes, and after the two power electronic switching devices are connected in series, the power electronic switching devices are connected in parallel with a series structure formed by the other two power electronic switching devices.
4. A true bipolar isolated modular multilevel dc transformer according to claim 2 or 3, characterized in that: the power electronic switching device includes an IGBT switching tube.
5. A control method of the true bipolar isolation type modularized multi-level direct current transformer according to any one of claims 1 to 4, which is characterized by comprising a low-voltage side positive and negative bipolar voltage control loop, a bridge arm inner submodule capacitor voltage balance control loop, a high-voltage side power grid single-pole to ground short-circuit fault ride-through control loop and a low-voltage side power grid single-pole short-circuit fault ride-through control loop;
the low-voltage side positive and negative bipolar voltage control ring is used for adjusting the magnitude of the low-voltage side positive and negative bipolar voltage, the bridge arm inner submodule capacitor voltage balance control ring is used for balancing and controlling the bridge arm inner submodule capacitor voltage, and the high-voltage side power grid ground short circuit fault ride-through control ring is used for maintaining the low-voltage side voltage constant when the high-voltage side single-pole ground short circuit fault occurs; the low-voltage side grid single-pole short-circuit fault ride-through control loop is used for maintaining constant low-voltage side non-fault pole voltage when the low-voltage side LVDC grid single-pole short-circuit fault occurs.
6. The control method according to claim 5, wherein the control step of the low-side positive-negative bipolar voltage control loop includes: collecting voltages of a positive electrode port and a negative electrode port of the low-voltage side in real time and comparing the voltages with voltage reference values of the positive electrode port and the negative electrode port; wherein, the voltage reference value of the positive electrode port at the low voltage side is differed from the voltage actual value of the positive electrode port, the positive electrode phase shift angle is obtained through the control of the first PI regulator, the positive pole phase shift angle shifts the square wave and then drives the power electronic switching devices of the first H bridge structure and the third H bridge structure; and the voltage reference value of the negative electrode port at the low voltage side is different from the voltage actual value of the negative electrode port, a negative electrode phase shift angle is obtained through control of the second PI regulator, and the power electronic switching devices of the second H bridge structure and the fourth H bridge structure are driven after the square wave phase shift is carried out by the negative electrode phase shift angle.
7. The control method according to claim 5, wherein the bridge arm inner submodule capacitor voltage balance control loop performs balance control on the bridge arm inner submodule capacitor voltage by adopting a sequencing method:
sequencing the capacitor voltage of each sub-module cascaded in each phase of bridge arm, and simultaneously calculating the trigger signals corresponding to different phase shift angles in a real-time working modeAccording to->Will->The larger trigger signal is distributed to the submodule with lower capacitance voltage; under quasi-square wave modulation, the calculation formula of charge conversion quantity in half period of capacitance access of the sub-module is +.>Wherein->For the bridge arm current,for the alternating current component>Is a direct current component.
8. The control method according to claim 5, characterized in that: after collecting that the positive pole of the high-voltage side of the true bipolar isolation type modularized multi-level direct current transformer has a ground short circuit fault, the high-voltage side grid ground short circuit fault ride-through control loop blocks driving pulses of the modularized multi-level converter of the positive pole and the first H bridge and the second H bridge of the low-voltage side so as to terminate capacitor discharge of each sub-module in the modularized multi-level converter of the positive pole, shield the influence of the fault high-voltage side on the non-fault low-voltage side and clear fault current;
after the high-voltage side grid ground fault ride-through control loop acquires that the high-voltage side negative electrode of the true bipolar isolation type modularized multi-level direct current transformer has the ground fault, driving pulses of the modularized multi-level converter of the negative electrode, a third H bridge and a fourth H bridge of the low-voltage side are blocked so as to terminate capacitor discharge of each sub-module in the modularized multi-level converter of the negative electrode, shield the influence of the fault high-voltage side on the non-fault low-voltage side and clear fault current.
9. The control method according to claim 5, characterized in that: after collecting that the positive electrode of the low-voltage side of the true bipolar isolation type modularized multi-level direct current transformer has a short circuit fault, the low-voltage side power grid short circuit fault ride-through control loop blocks driving pulses of a first H bridge and a third H bridge of the low-voltage side so as to shield the influence of the fault low-voltage side on the high-voltage side of the non-fault side and remove fault current;
after the short-circuit fault of the low-voltage side grid short-circuit fault ride-through control loop is collected, driving pulses of a second H bridge and a fourth H bridge on the low-voltage side are blocked after the short-circuit fault of the negative electrode of the low-voltage side of the true bipolar isolation type modularized multi-level direct current transformer is collected, so that the influence of the fault low-voltage side on the high-voltage side on the non-fault side is shielded, and fault current is cleared.
10. A control device for a true bipolar isolated modular multilevel dc transformer, comprising: memory, a processor and a control program stored on the memory and executable on the processor, which control program, when executed by the processor, implements the steps of the control method according to any one of claims 5-9.
CN202310480479.2A 2023-04-28 2023-04-28 True bipolar isolation type modularized multi-level direct current transformer and control method Pending CN116566211A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117394658A (en) * 2023-12-11 2024-01-12 国网湖北省电力有限公司 Bipolar electric energy router and control method thereof

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117394658A (en) * 2023-12-11 2024-01-12 国网湖北省电力有限公司 Bipolar electric energy router and control method thereof
CN117394658B (en) * 2023-12-11 2024-03-08 国网湖北省电力有限公司 Bipolar electric energy router and control method thereof

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