CN116566222A - Modular multilevel converter and its control method - Google Patents

Abstract

The invention provides a modularized multi-level converter and a control method thereof, wherein the modularized multi-level converter is of a three-phase rectifier bridge structure and comprises the following components: the controller and the first bridge arm and the second bridge arm with the same phase structures are connected with the positive electrode of the direct current side bus after the first ends of the three-phase first bridge arm are in short circuit, the second ends of the three-phase first bridge arm are connected with the corresponding phases of the alternating current side after the first ends of the three-phase first bridge arm and the second bridge arm are in short circuit, the second ends of the three-phase second bridge arm are connected with the negative electrode of the direct current side bus after the second ends of the three-phase second bridge arm are in short circuit, the first bridge arm and the second bridge arm comprise a working bridge arm, a bypass bridge arm and a bridge arm inductor, the working bridge arm and the bypass bridge arm are connected in parallel, the working bridge arm and the bridge arm inductor are connected in series, the controller is used for obtaining direct current side, judging whether the direct current side has short circuit fault or not according to the direct current side, and controlling the working bridge arm and the bypass arm when the short circuit fault is confirmed to be generated on the direct current side, so that fault current is cleared is realized, and overcurrent protection of the modular multilevel converter is realized.

Description

Modular multilevel converter and its control method

technical field

The invention relates to the technical field of multilevel power electronic converters, in particular to a modular multilevel converter and a control method thereof.

Background technique

Modular Multilevel Converter MMC (Modular Multilevel Converter) has the advantages of easy expansion of voltage levels, good output harmonic characteristics, and low electrical stress requirements for switching devices due to the cascaded structure of sub-modules, and is very suitable for renewable energy grid connection. , Large-scale power transmission and other fields have become one of the main realization forms of DC transmission technology.

In the related art, when a current short-circuit fault occurs on the DC side of the modular multilevel converter MMC, all the switch tubes will be turned off. Control the rectifier bridge, so that the AC side will continue to feed energy to the fault point of the DC side, eventually causing the overcurrent damage of the modular multilevel converter MMC.

Therefore, how to realize the overcurrent protection for the modular multilevel converter MMC is an urgent problem to be solved at present.

Contents of the invention

The present invention aims to solve the technical problems in the related art to a certain extent.

For this reason, first object of the present invention is to propose a kind of modular multilevel converter, the first bridge arm and the second bridge arm of each phase in the modular multilevel converter are all formed by working bridge arm, bypass bridge arm and bridge arm inductance, the working bridge arm and the bypass bridge arm are connected in parallel, and the working bridge arm and the bridge arm inductance are connected in series. overcurrent protection for multilevel converters.

The second object of the present invention is to provide a control method for a modular multilevel converter.

In order to achieve the above purpose, the embodiment of the first aspect of the present invention proposes a modular multilevel converter, the modular multilevel converter is a three-phase rectifier bridge structure, including: the controller and the structure of each phase are the same The first bridge arm and the second bridge arm of the three-phase, the first end of the first bridge arm of the three phases is short-circuited and connected to the positive pole of the DC side bus bar, and the second end of the first bridge arm of each phase is connected to the positive pole of the DC side bus bar. The first end of the second bridge arm is short-circuited and then connected to the corresponding phase on the AC side, and the second end of the second bridge arm of the three phases is short-circuited and then connected to the negative pole of the DC side bus bar; wherein, each phase Both the first bridge arm and the second bridge arm include a working bridge arm, a bypass bridge arm and a bridge arm inductance; wherein, the working bridge arm and the bypass bridge arm are connected in parallel, and the working bridge arm and the bypass bridge arm are connected in parallel. The bridge arm inductance is connected in series; the controller is respectively connected to the working bridge arm and the bypass bridge arm, the controller is used to obtain the DC side current, and judge whether a short circuit fault occurs on the DC side according to the DC side current, When it is determined that a short-circuit fault occurs on the DC side, the working bridge arm and the bypass bridge arm are controlled to clear the fault current.

The modular multilevel converter of the embodiment of the present invention is a three-phase rectifier bridge structure, including: a controller and a first bridge arm and a second bridge arm with the same structure for each phase, and the first bridge arm of the three-phase first bridge arm The terminals are short-circuited and then connected to the positive pole of the DC side busbar. The second end of the first bridge arm of each phase is short-circuited to the first end of the second bridge arm and then connected to the corresponding phase of the AC side. The second bridge arm of the three-phase The second end of the second end is short-circuited and then connected to the negative pole of the DC side busbar; wherein, the first bridge arm and the second bridge arm of each phase include the working bridge arm, the bypass bridge arm and the bridge arm inductance; wherein, the working bridge arm and the bypass bridge arm The road and bridge arms are connected in parallel, and the inductors of the working bridge arm and the bridge arm are connected in series; the controller is respectively connected with the working bridge arm and the bypass bridge arm. In the case of a short-circuit fault on the side, the fault current is cleared by controlling the working bridge arm and the bypass bridge arm, thereby realizing the overcurrent protection of the modular multilevel converter.

In addition, the modular multilevel converter proposed in the embodiment of the first aspect of the present invention may also have the following additional technical features:

According to an embodiment of the present invention, the working bridge arm includes: at least one half-bridge sub-module and an auxiliary switch sub-module; wherein,

The half-bridge sub-module and the auxiliary switch sub-module are connected in series, and the controller is connected to the half-bridge sub-module and the auxiliary switch sub-module respectively.

According to an embodiment of the present invention, the half-bridge sub-module includes: a first switch tube, a second switch tube, and a capacitor; wherein,

The first end of the first switch tube is connected to the first end of the capacitor, and the second end of the first switch tube is connected to the first end of the second switch tube to serve as the half-bridge sub-module the positive pole;

The second end of the second switching tube is connected to the second end of the capacitor as the negative pole of the half-bridge sub-module;

The third terminal of the first switching transistor and the third terminal of the second switching transistor are respectively connected to the controller.

According to an embodiment of the present invention, the auxiliary switch submodule includes: a switch and a third switch tube; wherein,

The first end of the switch is used as the positive pole of the auxiliary switch sub-module;

The second end of the switch is connected to the second end of the third switch tube, and the first end of the third switch tube is used as the negative pole of the auxiliary switch sub-module;

A third end of the third switch tube is connected to the controller.

According to an embodiment of the present invention, the bypass bridge arm includes: m bidirectional thyristors; wherein,

Each of the bidirectional thyristors is connected in series, and the control terminal of the bidirectional thyristor is connected to the controller;

Wherein, the value of m is determined by the voltage borne by each bridge arm and the rated withstand voltage of the bidirectional thyristor.

According to an embodiment of the present invention, when the controller is used to judge whether a short-circuit fault occurs on the DC side according to the DC side current, it includes:

By detecting the magnitude or rate of change of the DC side current, it is judged whether a short circuit fault occurs on the DC side; wherein,

If the magnitude of the DC side current is greater than a set magnitude, then determine that a short circuit fault occurs on the DC side; or,

If the rate of change of the DC side current is greater than a set rate of change, it is determined that a short circuit fault occurs on the DC side.

According to an embodiment of the present invention, when the controller is used to control the working bridge arm and the bypass bridge arm so as to clear the fault current, it includes:

controlling the first switching tube in each half-bridge sub-module to be turned off and the second switching tube to be closed, and each bidirectional thyristor in each of the bypass bridge arms to be turned on, so that part of the fault current flows into the bypass bridge arm;

controlling the third switch tube in each auxiliary switch sub-module to be turned off, so that all the fault current flows into the bypass bridge arm;

controlling the switches in each of the auxiliary switch sub-modules to be turned off, so that the working bridge arm is cut off;

controlling the second switching tubes in each of the half-bridge sub-modules to be turned off, so that each of the working bridge arms enters a locked state;

sending a shutdown signal to all the bidirectional thyristors in each of the bypass bridge arms, until the fault current reaches a zero-crossing point, all the bidirectional thyristors in each of the bypass bridge arms are turned off, so as to realize the Clearance of fault current.

In order to achieve the above purpose, the embodiment of the second aspect of the present invention proposes a control method for a modular multilevel converter, including: obtaining a DC side current; judging whether a short circuit fault occurs on the DC side according to the DC side current; When it is determined that a short-circuit fault occurs on the DC side, the working bridge arm and the bypass bridge arm are controlled to clear the fault current.

According to the control method of the modular multilevel converter of the embodiment of the present invention, the DC side current is obtained first, and then it is judged whether a short-circuit fault occurs on the DC side according to the DC side current, and when it is determined that a short-circuit fault occurs on the DC side, the working The bridge arm and the bypass bridge arm are controlled to clear the fault current and realize the overcurrent protection of the modular multilevel converter.

In addition, the control method of the modular multilevel converter proposed in the embodiment of the second aspect of the present invention may also have the following additional technical features:

According to an embodiment of the present invention, the judging whether a short-circuit fault occurs on the DC side according to the DC side current includes:

By detecting the magnitude or rate of change of the DC side current, it is judged whether a short circuit fault occurs on the DC side; wherein,

If the magnitude of the DC side current is greater than a set magnitude, then determine that a short circuit fault occurs on the DC side; or,

If the rate of change of the DC side current is greater than a set rate of change, it is determined that a short circuit fault occurs on the DC side.

According to an embodiment of the present invention, the controlling the working bridge arm and the bypass bridge arm, so as to clear the fault current, includes:

controlling the first switching tube in each of the half-bridge sub-modules to be turned off and the second switching tube to be closed, and the bidirectional thyristors in each of the bypass bridge arms to be turned on, so that the fault current is absorbed by the bypass bridge arm shunt;

controlling the third switching tube in each of the auxiliary switch sub-modules to be turned off, so that the fault current is transferred to the bypass bridge arm;

controlling the switches in each of the auxiliary switch sub-modules to be turned off, so that the working bridge arm is cut off;

controlling the second switching tubes in each of the half-bridge sub-modules to be turned off, so that each of the working bridge arms enters a locked state;

sending a shutdown signal to all the bidirectional thyristors in each of the bypass bridge arms, until the fault current reaches a zero-crossing point, all the bidirectional thyristors in each of the bypass bridge arms are turned off, so as to realize the Clearance of fault current.

Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and easy to understand from the following description of the embodiments in conjunction with the accompanying drawings, wherein:

1 is a schematic diagram of a modular multilevel converter according to an embodiment of the present invention;

2 is a schematic diagram of a modular multilevel converter according to an embodiment of the present invention;

3 is a flowchart of a control method of a modular multilevel converter according to an embodiment of the present invention;

Fig. 4 is a flowchart of a control method of a modular multilevel converter according to an embodiment of the present invention.

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference numerals designate the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

The following describes the modular multilevel converter and its control method according to the embodiments of the present invention with reference to the accompanying drawings.

In the related art, the solution for realizing overcurrent protection of the modular multilevel converter MMC is to replace part or all of the half-bridge sub-modules in the modular multi-level converter MMC with full-bridge sub-modules, clamping New sub-modules such as double-type twin sub-modules and single-stage full-bridge sub-modules establish back EMF in the fault path through the new sub-modules, thereby blocking the AC feedback path. However, compared with the half-bridge sub-module, the application of the new sub-module structure will greatly increase the number of semiconductor devices and the operating loss of the system.

For this reason, the present invention proposes a kind of new modular multi-level converter, the first bridge arm and the second bridge arm of each phase in this modular multi-level converter are all formed by working bridge arm, bypass bridge arm and The bridge arm inductance is formed, the working bridge arm and the bypass bridge arm are connected in parallel, and the working bridge arm and the bridge arm inductance are connected in series. Through the control of the working bridge arm and the bypass bridge arm, the fault current can be cleared, thus realizing the modularization of multiple The overcurrent protection of the level converter does not need to greatly increase the number of semiconductor devices and the operating loss of the system.

FIG. 1 is a schematic diagram of a modular multilevel converter according to an embodiment of the present invention.

It should be noted that the modular multilevel converter in the embodiment of the present invention has a three-phase rectifier bridge structure.

As shown in FIG. 1 , the modular multilevel converter of the embodiment of the present invention includes: a controller (not shown in the figure) and a first bridge arm and a second bridge arm with the same structure of each phase.

Wherein, the first end of the three-phase first bridge arm is short-circuited and then connected to the positive pole P of the DC side bus bar, and the second end of the three-phase first bridge arm is short-circuited to the first end of the second bridge arm and then connected to the AC side. The corresponding phase (a phase or b phase or c phase) on the side is connected, and the second end of the second bridge arm of the three phases is short-circuited and connected to the negative pole N of the DC side bus bar. The first bridge arm and the second bridge arm of each phase all comprise working bridge arm 10, bypass bridge arm 20 and bridge arm inductance Larm; Larms are connected in series. The controller is respectively connected with the working bridge arm 10 and the bypass bridge arm 20. The controller is used to obtain the DC side current, and judge whether a short circuit fault occurs on the DC side according to the DC side current. Arm 10 and bypass bridge arm 20 are controlled to clear the faulty circuit.

In this embodiment, the first bridge arm is the upper bridge arm, the second bridge arm is the lower bridge arm, the first end of the upper bridge arm is the upper end of the upper bridge arm, and the second end of the upper bridge arm is the upper end of the upper bridge arm. The lower end, the first end of the lower bridge arm is the upper end of the lower bridge arm, and the second end of the lower bridge arm is the lower end of the lower bridge arm. The structures of the upper bridge arm and the lower bridge arm are symmetrical, and both include a working bridge arm 10 , a bypass bridge arm 20 , and a bridge arm inductance Lrm. The intersection of the lower end of the upper bridge arm of each phase and the lower end of the lower bridge arm is connected to the corresponding phase on the AC side, the upper end of the three-phase upper bridge arm is connected to the positive pole P of the bus bar on the DC side, and the lower end of the three-phase lower bridge arm is connected to the DC side. Negative N connection of side bus bar.

The controller needs to obtain the DC side current in real time, and judge whether a short-circuit fault occurs on the DC side by detecting the amplitude or rate of change of the DC side current; wherein, if the amplitude of the DC side current is greater than the set amplitude (the set amplitude can be 1.5 times of the rated current amplitude), then it is determined that a short circuit fault occurs on the DC side; or, if the rate of change of the DC side current is greater than the set rate of change (the set rate of change can be 1.5 times the rate of change of the rated current times), it is determined that a short-circuit fault has occurred on the DC side. When it is determined that a short-circuit fault occurs on the DC side, the fault circuit is cleared through the control of the working bridge arm 10 and the bypass bridge arm 20, thereby realizing the protection of the modular multilevel converter.

FIG. 2 is a schematic diagram of a modular multilevel converter according to one embodiment of the present invention.

As shown in Figure 2, the working bridge arm 10 of the embodiment of the present invention includes: at least one half-bridge sub-module HBSM (Half-Bridge Sub-Module) (such as HBSM ₁ ~ HBSM _n ) and auxiliary switch sub-module ASSM (Auxiliary Switch Sub-Module); wherein, the half-bridge sub-module HBSM and the auxiliary switch sub-module ASSM are connected in series, and the controller is connected to the half-bridge sub-module HBSM and the auxiliary switch sub-module ASSM respectively.

That is to say, the working bridge arm 10 includes at least one half-bridge sub-module HBSM connected in series in the forward direction and one auxiliary switch sub-module ASSM.

As shown in FIG. 2, the half-bridge sub-module HBSM of the embodiment of the present invention includes: a first switching tube S1, a second switching tube S2, and a capacitor C; wherein, the first terminal of the first switching tube S1 and the first terminal of the capacitor C Connected at one end, the second end of the first switching tube S1 is connected to the first end of the second switching tube S2 as the positive pole of the half-bridge sub-module HBSM; the second end of the second switching tube S2 is connected to the second end of the capacitor C After being connected, it is used as the negative pole of the half-bridge sub-module HBSM; the third terminal of the first switching tube S1 and the third terminal of the second switching tube S2 are respectively connected to the controller.

Wherein, the first end of the first switching tube S1 is the collector of the first switching tube S1, the second end of the first switching tube S1 is the emitter of the first switching tube S1, and the third end of the first switching tube S1 is The base of the first switching tube S1. The first end of the second switching tube S2 is the collector of the second switching tube S2, the second end of the second switching tube S2 is the emitter of the second switching tube S2, and the third end of the second switching tube S2 is the second The base of the switch tube S2. The first end of the capacitor C is the positive pole of the capacitor C, and the second end of the capacitor C is the negative pole of the capacitor C.

That is to say, the emitter of the first switching tube S1 is connected to the collector of the second switching tube S2, and leads out to the anode of the half-bridge sub-module HBSM; the emitter of the second switching tube S2 leads out to the half-bridge sub-module HBSM The collector of the first switching transistor S1 is connected to the positive electrode of the capacitor C, and the emitter of the second switching transistor S2 is connected to the negative electrode of the capacitor C.

As shown in Figure 2, the auxiliary switch submodule ASSM of the embodiment of the present invention includes: a switch S _FMS and a third switch tube S3; wherein, the first end of the switch S _FMS is used as the positive pole of the auxiliary switch submodule ASSM; the switch S _FMS The second end of the third switch tube S3 is connected to the second end, and the first end of the third switch tube S3 is used as the negative pole of the auxiliary switch sub-module ASSM; the third end of the third switch tube S3 is connected to the controller.

Wherein, the first end of the third switching tube S3 is the collector of the third switching tube S3, the second end of the third switching tube S3 is the emitter of the third switching tube S3, and the third end of the third switching tube S3 is The base of the third switch tube S3. The switch S _FMS can be a fast mechanical switch.

That is to say, the first end of the switch S _FMS leads to the anode of the auxiliary switch sub-module ASSM, the second end of the switch S _FMS is connected to the emitter of the third switching tube S3, and the collector of the third switching tube S3 leads to The negative pole of the auxiliary switch sub-module ASSM.

It should be noted that, in the embodiment of the present invention, both ends of the first switching tube S1 are connected in parallel with the first diode D1, both ends of the second switching tube S2 are connected in parallel with the second diode D2, and both ends of the third switching tube S3 are connected in parallel with the third diode D1. Diode D3.

As shown in Figure 2, the bypass bridge arm 20 of the embodiment of the present invention includes: m bidirectional thyristors T1-Tm, each bidirectional thyristor is connected in series, and the control terminal of the bidirectional thyristor is connected to the controller; wherein, the value of m is determined by each bridge The voltage that the arm bears and the rated withstand voltage of the bidirectional thyristor are determined. Specifically: the voltage on each bridge arm is half of the bus voltage V _dc on the DC side, that is, V _dc /2. If the rated withstand voltage of the three triacs is V _T , the number of m should be greater than or equal to V _dc /2V _T .

Fig. 3 is a flowchart of a control method of a modular multilevel converter according to an embodiment of the present invention.

As shown in FIG. 3, the control method of the multi-module multi-level converter in the embodiment of the present invention includes:

Step S301, when the controller determines that no short-circuit fault occurs on the DC side, the modular multilevel converter is in a normal working state. At this time, it is necessary to control the working bridge arm to be put into operation and flow current, specifically to control the half-bridge sub-module The first switching tube S1 and the second switching tube S2 in the HBSM work complementary; the switch S _FMS in the auxiliary switch sub-module ASSM is closed, and the third switching tube S3 is turned on; all bidirectional thyristors T1~Tm in the bypass bridge arm are controlled to be closed off, so that there is no current flowing in the bypass bridge arm 20.

Step S302, judging whether a short-circuit fault has been detected on the DC side. If yes, execute step S303; if no, return to execute step S301.

Step S303, controlling the first switching tube S1 in each half-bridge sub-module HBSM to turn off to prevent further discharge of the capacitor C, and controlling the second switching tube S2 to close to prepare for the operation of the auxiliary switching sub-module ASSM; controlling each bypass bridge The bidirectional thyristors T1 ˜ Tm in the arm 20 are turned on, so that the fault current is shunted by the bypass bridge arm 20 , and the magnitude of the fault current flowing through the second switching transistor S2 in the working bridge arm 10 is reduced. That is, the fault processing step S1: S1 is turned off in the HBSM, and S2 is turned on; T1˜Tm in the bypass bridge arm 20 are turned on.

Step S304 , controlling the third switch tube S3 in each auxiliary switch sub-module ASSM to be turned off, so that the fault current is transferred to the bypass bridge arm 20 . That is the fault handling step S2: S3 in the AASM is turned off.

Step S305, control the switch S _FMS in each auxiliary switch sub-module ASSM to disconnect, so that the working bridge arm 10 is cut off, and all the switching tubes in the system are protected. At this time, the AC short-circuit current passes through the three-phase standby bridge arm, Thyristors have strong current resistance and are not affected by short-circuit currents. That is, the fault handling step S3: the S _FMS in the AASM is disconnected.

Step S306, controlling the second switching tube S2 in each half-bridge sub-module HBSM to be turned off, so that each working bridge arm 10 enters a locked state, and sends a shutdown signal to all the triacs T1-Tm in each bypass bridge arm 20 . That is, the fault processing step S4: S2 in the HBSM is turned off; T ₁ -T _m in the bypass bridge arm 20 are turned off.

Step S307, waiting for the fault current elimination stage. Among them, according to the characteristics of the triacs, when all the triacs T1-Tm in each bypass bridge arm 20 receive the shutdown signal, the triacs T1-Tm will be turned off naturally when the fault current reaches the zero-crossing point. After all the bidirectional thyristors in the three-phase standby bridge arm are turned off, the fault current can be eliminated.

Step S308, judging whether the DC side short-circuit fault point is cleared. If yes, return to step S301; if not, return to step S307.

The modular multilevel converter of the embodiment of the present invention can realize reliable protection for the switching tube in the modular multilevel converter: the switching tube is the most vulnerable device to be damaged by overcurrent in the modular multilevel converter. The invention transfers all the fault current to the standby bridge arm by using the auxiliary switch sub-module ASSM after detecting the current short-circuit fault on the DC side, so that no fault current flows through the switching tubes in the modular multilevel converter during the fault clearing stage , realizing the reliable protection of the switch tube in the modular multilevel converter.

The modular multilevel converter of the embodiment of the present invention can clear the fault current faster, and can clear the fault current within 20 ms: the spare bridge arm in the modular multilevel converter of the present invention provides a three-phase AC short-circuit fault path , after the fault processing step S4 removes the signal of the bidirectional thyristor of the standby bridge arm, the fault current is cleared when the AC short-circuit current reaches the zero-crossing point, wherein the three-phase AC short-circuit current will reach the zero-crossing point within half a cycle (such as 10ms) , considering the action time from step S1 to step S4, the present invention can clear the short-circuit fault current within 20ms.

The additional loss of the modular multilevel converter of the embodiment of the present invention is very small under normal working conditions: Compared with the half-bridge modular multilevel converter in the related art, the modular multilevel converter of the embodiment of the present invention In the normal working state of the leveling converter, the current of each bridge arm only flows through one switch such as a fast mechanical switch and one switch tube, and the extra loss caused is very small.

The accessory cost of the modular multilevel converter of the embodiment of the present invention is relatively small: Compared with the solution of replacing the new sub-module, the modular multilevel converter of the embodiment of the present invention only adds 6 switch tubes and 6 switches For example, a fast mechanical switch and a certain number of triacs. Since the cost of the triacs is much lower than that of switches of the same voltage level, the modular multilevel converter of the embodiment of the present invention has a cost advantage. In the modular multilevel converter of the embodiment of the present invention, the switch tube in the auxiliary switch sub-module ASSM does not bear the voltage of the bridge arm, so only conventional models are needed, and the current of the switch such as a fast mechanical switch is controlled by the current of the working bridge arm. It operates only after it is completely transferred to the bypass bridge arm, and there is no problem of difficult arc suppression. Therefore, the present invention has lower requirements for switches such as fast mechanical switches, and the overall cost of the auxiliary switch sub-module ASSM is lower.

The modular multi-level converter of the embodiment of the present invention is conveniently applied to the transformation of the existing half-bridge modular multi-level converter: the present invention can retain all the devices of the existing half-bridge modular multi-level converter , it only needs to add an auxiliary switch sub-module ASSM and a bypass bridge arm for each bridge arm, which can maximize the use of the resources of the existing half-bridge MMC, and is convenient for modification and has good applicability.

It should be noted that the switches in the present invention, such as fast mechanical switches, can be replaced by other types of switches, as long as the function of physically cutting off the circuit can be realized; the bidirectional thyristor in the bypass bridge arm 20 in the present invention can be replaced Two unidirectional thyristors connected in antiparallel.

To sum up, the modular multilevel converter of the embodiment of the present invention is a three-phase rectifier bridge structure, including: the first bridge arm and the second bridge arm with the same structure of the controller and each phase, and the first bridge arm of the three phases The first end of the bridge arm is short-circuited and connected to the positive pole of the DC side busbar, and the second end of the first bridge arm of each phase is short-circuited to the first end of the second bridge arm and then connected to the corresponding phase of the AC side. Three-phase The second end of the second bridge arm of the second bridge arm is short-circuited and then connected to the negative pole of the DC side bus bar; wherein, the first bridge arm and the second bridge arm of each phase include a working bridge arm, a bypass bridge arm and a bridge arm inductance; where, The working bridge arm and the bypass bridge arm are connected in parallel, and the inductors of the working bridge arm and the bridge arm are connected in series; the controller is connected to the working bridge arm and the bypass bridge arm respectively, and the controller is used to obtain the DC side current and judge whether there is a short circuit on the DC side according to the DC side current Fault, when it is determined that a short-circuit fault occurs on the DC side, through the control of the working bridge arm and the bypass bridge arm, the fault current is cleared, thereby realizing the overcurrent protection of the modular multilevel converter.

Fig. 4 is a flowchart of a control method of a modular multilevel converter according to an embodiment of the present invention.

As shown in FIG. 4, the control method of the modular multilevel converter in the embodiment of the present invention includes the following steps:

S401. Obtain the DC side current.

S402. Determine whether a short-circuit fault occurs on the DC side according to the DC side current.

S403. When it is determined that a short-circuit fault occurs on the DC side, control the working bridge arm and the bypass bridge arm, so as to clear the fault current.

According to an embodiment of the present invention, judging whether a short-circuit fault occurs on the DC side according to the DC side current includes:

By detecting the amplitude or rate of change of the DC side current, it is judged whether a short circuit fault occurs on the DC side; among them,

If the amplitude of the DC side current is greater than the set amplitude, it is determined that a short circuit fault occurs on the DC side; or,

If the rate of change of the DC side current is greater than the set rate of change, it is determined that a short circuit fault occurs on the DC side.

According to an embodiment of the present invention, the working bridge arm and the bypass bridge arm are controlled to realize the removal of the fault current, including:

controlling the first switching tube in each half-bridge sub-module to be turned off and the second switching tube to be closed, and each bidirectional thyristor in each bypass bridge arm to be turned on, so that part of the fault current flows into the bypass bridge arm;

controlling the third switch tube in each auxiliary switch sub-module to be turned off, so that all the fault current flows into the bypass bridge arm;

Control the switches in each auxiliary switch sub-module to turn off, so that the working bridge arm is cut off;

controlling the second switching tubes in each half-bridge sub-module to be turned off, so that each working bridge arm enters a locked state;

A shutdown signal is sent to all bidirectional thyristors in each bypass bridge arm until the fault current reaches a zero-crossing point, and all bidirectional thyristors in each bypass bridge arm are turned off, so as to clear the fault current.

It should be noted that, for details not disclosed in the control method of the modular multilevel converter in the embodiment of the present invention, please refer to the details disclosed in the modular multilevel converter in the embodiment of the present invention, and the details are not repeated here. repeat.

According to the control method of the modular multilevel converter of the embodiment of the present invention, the DC side current is obtained first, and then it is judged whether a short-circuit fault occurs on the DC side according to the DC side current, and when it is determined that a short-circuit fault occurs on the DC side, the working The bridge arm and the bypass bridge arm are controlled to clear the fault current and realize the overcurrent protection of the modular multilevel converter.

In the description of this specification, descriptions referring to the terms "one embodiment", "some embodiments", "example", "specific examples", or "some examples" mean that specific features described in connection with the embodiment or example , structure, material or feature is included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the described specific features, structures, materials or characteristics may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples and features of different embodiments or examples described in this specification without conflicting with each other.

In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be interpreted as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

Any process or method descriptions in flowcharts or otherwise described herein may be understood to represent modules, segments or portions of code comprising one or more executable instructions for implementing custom logical functions or steps of a process , and the scope of preferred embodiments of the invention includes alternative implementations in which functions may be performed out of the order shown or discussed, including in substantially simultaneous fashion or in reverse order depending on the functions involved, which shall It is understood by those skilled in the art to which the embodiments of the present invention pertain.

Claims (10)

1. A modular multilevel converter, characterized in that, said modular multilevel converter is a three-phase rectifier bridge structure, comprising: a first bridge arm and a second bridge arm with the same structure of a controller and each phase Bridge arm, the first end of the first bridge arm of the three phases is short-circuited and connected to the positive pole of the DC side bus, the second end of the first bridge arm of each phase is connected to the first end of the second bridge arm After the ends are short-circuited, they are connected to the corresponding phases on the AC side, and the second ends of the second bridge arms of the three phases are short-circuited and then connected to the negative pole of the DC side bus bar; wherein, The first bridge arm and the second bridge arm of each phase include a working bridge arm, a bypass bridge arm and a bridge arm inductance; wherein, the working bridge arm and the bypass bridge arm are connected in parallel, and the working bridge arm connected in series with the bridge arm inductance; The controller is respectively connected with the working bridge arm and the bypass bridge arm, and the controller is used to obtain the DC side current, and judge whether a short circuit fault occurs on the DC side according to the DC side current, and determine whether the DC side has a short circuit fault. In the event of a short-circuit fault, the working bridge arm and the bypass bridge arm are controlled to clear the fault current. 2. The modular multilevel converter according to claim 1, wherein the working bridge arm comprises: at least one half-bridge sub-module and an auxiliary switch sub-module; wherein, The half-bridge sub-module and the auxiliary switch sub-module are connected in series, and the controller is connected to the half-bridge sub-module and the auxiliary switch sub-module respectively. 3. The modular multilevel converter according to claim 2, wherein the half-bridge sub-module comprises: a first switching tube, a second switching tube and a capacitor; wherein, The first end of the first switch tube is connected to the first end of the capacitor, and the second end of the first switch tube is connected to the first end of the second switch tube to serve as the half-bridge sub-module the positive pole; The second end of the second switching tube is connected to the second end of the capacitor as the negative pole of the half-bridge sub-module; The third terminal of the first switching transistor and the third terminal of the second switching transistor are respectively connected to the controller. 4. The modular multilevel converter according to claim 2, wherein the auxiliary switch sub-module comprises: a switch and a third switch tube; wherein, The first end of the switch is used as the positive pole of the auxiliary switch sub-module; The first end of the third switch tube is used as the negative pole of the auxiliary switch sub-module; The second end of the switch is connected to the second end of the third switch transistor, and the third end of the third switch transistor is connected to the controller. 5. The modular multilevel converter according to claim 1, wherein the bypass bridge arm comprises: m bidirectional thyristors; wherein, Each of the bidirectional thyristors is connected in series, and the control terminal of the bidirectional thyristor is connected to the controller; Wherein, the value of m is determined by the voltage borne by each bridge arm and the rated withstand voltage of the bidirectional thyristor. 6. The modular multilevel converter according to any one of claims 1-5, wherein when the controller is configured to determine whether a short-circuit fault occurs on the DC side according to the DC side current, it includes : By detecting the magnitude or rate of change of the DC side current, it is judged whether a short circuit fault occurs on the DC side; wherein, If the magnitude of the DC side current is greater than a set magnitude, then determine that a short circuit fault occurs on the DC side; or, If the rate of change of the DC side current is greater than a set rate of change, it is determined that a short circuit fault occurs on the DC side. 7. The modular multilevel converter according to any one of claims 1-5, wherein the controller is used to control the working bridge arm and the bypass bridge arm, so as to realize When clearing the fault current, include: controlling the first switching tube in each half-bridge sub-module to be turned off and the second switching tube to be closed, and each bidirectional thyristor in each of the bypass bridge arms to be turned on, so that part of the fault current flows into the bypass bridge arm; controlling the third switch tube in each auxiliary switch sub-module to be turned off, so that all the fault current flows into the bypass bridge arm; controlling the switches in each of the auxiliary switch sub-modules to be turned off, so that the working bridge arm is cut off; controlling the second switching tubes in each of the half-bridge sub-modules to be turned off, so that each of the working bridge arms enters a locked state; sending a shutdown signal to all the bidirectional thyristors in each of the bypass bridge arms, until the fault current reaches a zero-crossing point, all the bidirectional thyristors in each of the bypass bridge arms are turned off, so as to realize the Clearance of fault current. 8. A method for controlling a modular multilevel converter according to any one of claims 1-7, comprising: Obtain the DC side current; According to the current on the DC side, it is judged whether a short circuit fault occurs on the DC side; When it is determined that a short-circuit fault occurs on the DC side, the working bridge arm and the bypass bridge arm are controlled to clear the fault current. 9. The control method of the modularized multilevel converter according to claim 8, wherein said determining whether a short-circuit fault occurs on the DC side according to the DC side current comprises: By detecting the magnitude or rate of change of the DC side current, it is judged whether a short circuit fault occurs on the DC side; wherein, If the magnitude of the DC side current is greater than a set magnitude, then determine that a short circuit fault has occurred on the DC side; or, If the rate of change of the DC side current is greater than a set rate of change, it is determined that a short circuit fault occurs on the DC side. 10. The control method of the modular multilevel converter according to claim 8, wherein the controlling the working bridge arm and the bypass bridge arm to realize the removal of the fault current comprises : controlling the first switching tube in each of the half-bridge sub-modules to be turned off and the second switching tube to be closed, and the bidirectional thyristors in each of the bypass bridge arms to be turned on, so that part of the fault current flows into the bypass bridge arm; controlling the third switching tube in each of the auxiliary switch sub-modules to be turned off, so that all the fault current flows into the bypass bridge arm; controlling the switches in each of the auxiliary switch sub-modules to be turned off, so that the working bridge arm is cut off; controlling the second switching tubes in each of the half-bridge sub-modules to be turned off, so that each of the working bridge arms enters a locked state; sending a shutdown signal to all the bidirectional thyristors in each of the bypass bridge arms, until the fault current reaches a zero-crossing point, all the bidirectional thyristors in each of the bypass bridge arms are turned off, so as to realize the Clearance of fault current.