CN111490693B

CN111490693B - MMC submodule new topological structure

Info

Publication number: CN111490693B
Application number: CN201910135940.4A
Authority: CN
Inventors: 张志文; 候维杨; 贺锐智; 黄守道
Original assignee: Hunan University
Current assignee: Hunan University
Priority date: 2019-02-25
Filing date: 2019-02-25
Publication date: 2021-10-26
Anticipated expiration: 2039-02-25
Also published as: CN111490693A

Abstract

The invention discloses a new topological structure of an MMC sub-module. The sub-moldThe block topology includes 2 diodes, 6 IGBTs and 2 capacitors; 2 diodes are respectively connected with 2 IGBTs in an anti-parallel mode to form a control switch, the on-off of a charge-discharge loop of the 2 capacitors is controlled, and the sub-module of the MMC outputs 0, V_cV and 2_cThree levels; the remaining 4 IGBTs are connected in anti-parallel two by two to form a fault current blocking circuit, thereby blocking the fault current. Compared with the traditional MMC, the invention adopts a brand-new sub-module topological structure, can output more levels under the condition of the same number of sub-modules, and can quickly cut off a fault current path when the MMC has direct current or alternating current faults, thereby realizing the blocking of the fault current of the MMC.

Description

MMC submodule new topological structure

Technical Field

The invention relates to the field of power electronics, in particular to a new topological structure of an MMC sub-module.

Background

Modular Multilevel Converter (MMC) based on fully-controlled power electronic devices has the advantages of high modularization, easy expansion, small conduction loss, high voltage waveform quality, capability of independently controlling active power and power, no commutation failure and the like, and has attracted great attention in the industry and academia since the advent. At present, the MMC is widely applied to the fields of flexible direct current transmission, distributed power generation, electric rail traction, static reactive compensation, motor driving, electric energy quality control and the like.

When the MMC is applied to the flexible direct current transmission field, in order to obtain good voltage waveform quality, the more the level number of output voltage is, the better is in principle, and the traditional half-bridge submodule can only output two levels of 0 and Uc, so that the submodule which can only be connected in series as much as possible can be connected in series, the submodules which are connected in series on a bridge arm of the MMC are increased, the number of required power switching devices and the number of capacitors are correspondingly increased, the total volume of the converter can be increased due to the excessive submodules, and the control of the MMC can be complicated. The MMC adopted in the current engineering mostly adopts level approximation modulation, the voltage value of a submodule needs to be acquired in each control period, too many submodules can cause great burden to a converter signal acquisition system and a communication system, and the requirement on the speed of a processor is high. The traditional MMC submodule adopts a half-bridge structure, is simple, but can only output two different levels. Therefore, the MMC submodule structure is designed, so that the MMC submodule structure can output a plurality of levels, and the MMC submodule structure is significant in application to high-voltage and high-power occasions.

Due to the limited voltage withstand level of power electronic devices, short circuit failure is a major problem facing MMC in practical applications at present. At present, most projects still adopt half-bridge sub-modules, when a direct current side and an alternating current side have faults, because anti-parallel diodes still can provide a path for fault current, a system is approximately in three-phase short circuit, the fault current cannot be cut off by locking a converter, and the safety of a power device and the safety of the converter system are seriously damaged. Meanwhile, because the direct current does not have a zero crossing point, arc quenching is difficult, the development progress of the high-voltage high-capacity direct current circuit breaker is slow, and if the direct current circuit breaker depends on an alternating current circuit breaker, the action is slow, and the recovery time is long. The sub-module with fault current blocking capability is an effective method for cutting off fault current. The existing MMC sub-module with fault current blocking capability comprises a single-phase full-bridge sub-module, a clamping dual sub-module and a self-resistance sub-module. However, the number of power switch devices added by the single-phase full-bridge submodule is 2 times that of the half-bridge submodule, so that the loss and the cost of the converter are increased, only two levels can be output, the number of the IGBTs and the number of the diodes required by the clamping double-submodule are large, and the structure is complex. The newly developed self-resistance type submodule is a fault current blocking circuit formed by two anti-parallel IGBTs and has the advantages of light structure, high reaction speed and simplicity and convenience in control, the self-resistance type submodule is of a half-bridge structure and can only output two different levels of 0 and Uc, when the number of the submodule is small, the number of the voltage waveform levels output by adopting the nearest level approach modulation is small, and the quality of the voltage waveform is seriously influenced.

Disclosure of Invention

The invention aims to provide a new topological structure of an MMC sub-module, which can output three levels and has fault current blocking capability, and can solve the problems of complex control and heavy volume caused by excessive current transformer sub-modules, slow action and long recovery time of a system in a mode of realizing fault isolation by adopting a circuit breaker.

In order to achieve the purpose, the invention provides the following scheme:

an MMC sub-module new topology comprising: the charging and discharging circuit comprises two IGBTs, two diodes and two capacitors, wherein one IGBT and one diode are connected in an anti-parallel mode to charge and discharge one capacitor; the fault current blocking loop comprises four IGBTs, and every two IGBTs are connected in anti-parallel; the emitting electrodes of the IGBTs in the charging and discharging loop and the anodes of the diodes are connected with the collecting electrodes of every two IGBTs in the fault current blocking loop in an anti-parallel connection mode; the collector of the IGBT and the cathode of the diode in the charge-discharge loop are connected with the anode of the capacitor; the negative electrode of one capacitor is connected with the IGBTs connected in reverse parallel in the fault current blocking circuit in pairs, and the negative electrode of the other capacitor is respectively connected with the emitting electrode of the IGBT in the charging and discharging circuit, the positive electrode of the diode and the collecting electrode of the IGBT connected in reverse parallel in the fault current blocking circuit in pairs.

Optionally, the two capacitors are identical and are 595 uF.

Optionally, the charge-discharge loop is used for independently outputting 0, V_cV and 2_cThree levels.

Optionally, when a current flows from the voltage positive terminal, the diode is turned on, and the capacitor is charged.

Optionally, when a current flows from the voltage negative terminal, the IGBT in the charge-discharge loop is turned on, and the capacitor discharges.

Optionally, when a fault occurs, each IGBT latches.

Optionally, when a current flows from the voltage positive terminal, the diode is connected in series with the capacitor.

According to the specific embodiment provided by the invention, the invention discloses the following technical effects: 1) the blocking loop of the fault current is formed by the anti-parallel IGBTs, the structure is compact, the implementation is simple, the action is rapid, the use is convenient, the fault current can be cut off rapidly, the system can recover rapidly for the non-permanent fault, and the M is improvedThe power supply reliability of the MC; 2) the two capacitors are respectively controlled, and the sub-modules can independently output 0 and V through different combinations of the switch tubes_cV and 2_cThe output of three levels and multiple levels can improve the waveform quality of voltage and current, when the same level number is output, the number of sub-modules is reduced, the size of the MMC is correspondingly reduced, and the control complexity of the MMC is also correspondingly reduced.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

FIG. 1 is a diagram of a new topology structure of an MMC sub-module according to the present invention;

FIG. 2 is i_sm>When 0, the submodule outputs a 0-level working mode diagram;

FIG. 3 is i_sm<When 0, the submodule outputs a 0-level working mode diagram;

FIG. 4 shows i_sm>0 time sub-module output V of the invention_cA/2 level working mode diagram;

FIG. 5 shows i_sm<0 time sub-module output V of the invention_cA/2 level working mode diagram;

FIG. 6 shows i_sm>0 time sub-module output V of the invention_cA level working mode diagram;

FIG. 7 shows i_sm<0 time sub-module output V of the invention_cA level working mode diagram;

FIG. 8 shows i_sm>Circuit diagram after submodule fault locking of the invention at 0;

FIG. 9 shows i_sm>When 0 time, the submodule fault of the invention is locked, and then the MMC grid-connected equivalent circuit diagram of the submodule structure of the invention is adopted;

FIG. 10 shows i_sm<Circuit diagram after submodule fault locking of the invention at 0;

FIG. 11 shows i_sm<And 0, adopting the MMC grid-connected equivalent circuit diagram of the submodule structure after the submodule fault is locked.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of 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 invention.

FIG. 1 is a diagram of a new topology structure of an MMC sub-module of the present invention. As shown in fig. 1, a new topology of MMC submodule includes: the charging and discharging circuit comprises two IGBTs, two diodes and two capacitors, wherein one IGBT and one diode are connected in an anti-parallel mode to charge and discharge one capacitor; the fault current blocking loop comprises four IGBTs, and every two IGBTs are connected in anti-parallel; the emitting electrodes of the IGBTs in the charging and discharging loop and the anodes of the diodes are connected with the collecting electrodes of every two IGBTs in the fault current blocking loop in an anti-parallel connection mode; the collector of the IGBT and the cathode of the diode in the charge-discharge loop are connected with the anode of the capacitor; the negative electrode of one capacitor is connected with the IGBTs connected in reverse parallel in the fault current blocking circuit in pairs, and the negative electrode of the other capacitor is respectively connected with the emitting electrode of the IGBT in the charging and discharging circuit, the positive electrode of the diode and the collecting electrode of the IGBT connected in reverse parallel in the fault current blocking circuit in pairs.

In fig. 1, the charge/discharge circuit is composed of a control switch composed of IGBT tubes T1 and T2 and diodes D1 and D2 connected in anti-parallel, and capacitors C1 and C2, and the fault current blocking circuit is composed of a switch assembly composed of a pair of IGBT tubes T3 and T4, and T5 and T6 connected in anti-parallel.

Both of the capacitors are identical and 595 uF.

The conventional half-bridge submodule structure only comprises one capacitor, so that only 0 and U can be output_cTwo kinds of different levels, different with traditional half-bridge submodule piece, the MMC submodule piece has two condensers, and their control switch all comprises diode and IGBT anti-parallel, and the control switch of two condensers links to each other with the positive pole of controlled capacitance respectively, can control the charge-discharge process of two condensers respectively, makes the many level of modularization converter submodule piece can be through the different combinations of switch tube, independently exports 0, V_cV and 2_cThe modularized multi-level converter submodule can utilize fewer modules to increase effective level output, and therefore higher voltage and current waveform quality is obtained.

The control switch that diode and IGBT anti-parallel constitute provides the route of charging and discharging for the condenser, and when the electric current flowed into the many level converter submodule piece of modularization from voltage positive pole port, the diode switched on, and the electric capacity charges, and when the electric current flowed into the many level converter submodule piece of modularization from voltage negative pole port, the IGBT switched on, and the electric capacity discharges, and the electric capacity is through constantly charging and discharging, reaches voltage balance, guarantees that the MMC normally works.

When the fault current flows in from the negative port, the fault current can be quickly blocked by locking all the IGBTs, and if the fault current flows in from the positive port, the passing path is equivalent to that a plurality of diodes are connected in series with a capacitor, so that the diodes can be blocked by means of reverse voltage, and the fault current can be blocked.

FIG. 2 is i_sm>When 0, the submodule outputs a 0-level working mode diagram. FIG. 4 shows i_sm>0 time sub-module output V of the invention_cA/2 level operation mode diagram. FIG. 6 shows i_sm>0 time sub-module output V of the invention_cAnd (4) a level working mode diagram. As shown in fig. 2, 4 and 6, when i_sm>At 0, maintain T₃Opening, T₁、T₂And T6 off, output voltage V _o0, capacitance C₁And C₂Are all bypassed; if T₁、T₆Opening, T₂、T₃Turn-off, output voltage V_o＝V_cA capacitor C1 is inserted into the bridge arm to participate in work and is charged, and the voltage of the capacitor rises; if it is T₁、T₂Opening, T₃、T₆When it is turned off, the voltage V is output_o＝V_cCapacitor C₁And C₂Inserted bridge arm, C₁And C₂Is charged and the voltage rises.

FIG. 3 is i_sm<When 0, the submodule outputs a 0-level working mode diagram. FIG. 5 shows i_sm<0 time sub-module output V of the invention_cA/2 level operation mode diagram. FIG. 7 shows i_sm<0 time sub-module output V of the invention_cAnd (4) a level working mode diagram. As shown in fig. 3, 5 and 7, when i_sm<At 0, maintain T₄Opening, T₁、T₂And T₅Turn-off, output voltage V _o0, capacitance C₁And C₂Are all bypassed; if T₁、T₅Opening, T₂、T₄Turn-off, output voltage V_o＝V _c2, the capacitor C1 is inserted into the bridge arm to participate in work and is discharged, and the voltage of the capacitor is reduced; if it is T₁、T₂Opening, T₄、T₆When it is turned off, the voltage V is output_o＝V_cCapacitor C₁And C₂Inserted bridge arm, C₁And C₂Is charged and the voltage rises. In the working process of the sub-modules, the capacitors are continuously charged and discharged, and the balance of the capacitor voltage is achieved.

FIG. 8 shows i_sm>Circuit diagram after sub-module fault lockout of the invention at 0. As shown in fig. 8, the current flows from the positive terminal of the sub-module to control all IGBTs to latch, and the current flows in the sub-module in the forward direction to charge the capacitor, which is equivalent to the diode D when viewed from the sub-module level₁And D₂After being connected in series with the capacitor C₁And C₂In series, at this time, the capacitance C₁、C₂Voltage on diode D₁And D₂Reverse bias is performed to turn off, so that the fault current is rapidly attenuated, and the fault current is suppressed. FIG. 9 shows i_sm>And after 0 fault is locked, the MMC grid-connected equivalent circuit diagram with the sub-module structure is adopted. Taking B, C two phases as an example, a loop through which a fault current flows is equivalent to 8n diodes and 8n capacitors which are connected in series, the diodes are reversely biased to be cut off in the same way, the bridge arm current is rapidly attenuated, and the fault current is restrained.

FIG. 10 shows i_sm<Circuit diagram after sub-module fault lockout of the invention at 0. As shown in fig. 10, current flows from the negative terminal of the sub-module, all IGBTs are controlled to be locked, and at the moment, due to the locking of T4, T5 and T2, the unidirectional circulation of D1 and D2 is realized, and the fault current is not passed and is blocked forcibly. FIG. 11 shows i_sm<And after 0 fault is locked, the MMC grid-connected equivalent circuit diagram with the sub-module structure is adopted. Taking B, C two phases as an example, after latching occurs, the path of the fault current is directly blocked by the series-latched IGBT, and the fault current cannot flow into the MMC, so that the system blocks the fault current.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.

The principles and embodiments of the present invention have been described herein using specific examples, which are presented solely to aid in the understanding of the apparatus and its core concepts; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims

1. An MMC sub-module new topology, comprising: the charging and discharging circuit comprises two IGBTs, two diodes and two capacitors, wherein one IGBT and one diode are connected in an anti-parallel mode to charge and discharge one capacitor(ii) a The fault current blocking circuit comprises four IGBTs, and every two IGBTs of the fault current blocking circuit are connected in an anti-parallel mode; the emitting electrodes of the IGBTs in the charging and discharging loop and the anodes of the diodes are connected with the collecting electrodes of every two IGBTs in the fault current blocking loop in an anti-parallel connection mode; the collector of the IGBT and the cathode of the diode in the charge-discharge loop are connected with the anode of the capacitor; the negative electrode of one capacitor is connected with the IGBTs connected in reverse parallel in the fault current blocking circuit in pairs, and the negative electrode of the other capacitor is respectively connected with the emitting electrode of the IGBT in the charging and discharging circuit, the positive electrode of the diode and the collecting electrode of the IGBT connected in reverse parallel in the fault current blocking circuit in pairs; the charge-discharge loop is used for independently outputting 0, V_cV and 2_cThree levels.

2. The MMC sub-module new topology of claim 1, wherein both of the capacitors are identical, being 595 uF.

3. The MMC sub-module new topology of claim 2, wherein when current flows in from voltage positive port, the diode conducts and the capacitor charges.

4. The MMC sub-module new topology of claim 2, wherein when current flows in from voltage negative port, the IGBT in the charge-discharge loop is turned on and the capacitor is discharged.

5. The MMC sub-module new topology of claim 2, wherein each of the IGBTs latches when a fault occurs.

6. The MMC sub-module new topology of claim 2, wherein the diode is in series with the capacitor when current flows in from a voltage positive port.