CN217656426U

CN217656426U - MMC submodule and MMC system with bipolar conversion and fault clearing functions

Info

Publication number: CN217656426U
Application number: CN202220707861.3U
Authority: CN
Inventors: 李孝清
Original assignee: Hunan Huizhuo Electric Power Technology Co ltd
Current assignee: Hunan Huizhuo Electric Power Technology Co ltd
Priority date: 2022-03-29
Filing date: 2022-03-29
Publication date: 2022-10-25
Anticipated expiration: 2032-03-29

Abstract

The utility model discloses a MMC sub-module and MMC system with double-pole conversion and fault clearing function, the sub-module comprises a first IGBT branch, a second IGBT branch and a third IGBT branch which are connected in parallel; the first IGBT branch circuit comprises a first IGBT, a second IGBT and a freewheeling diode D1 which are connected with each other; the second IGBT branch comprises a first IGBT group, a capacitor and a second IGBT group which are sequentially connected, the first IGBT group comprises a third IGBT and a fourth IGBT which are mutually connected, and the second IGBT group comprises a fifth IGBT and a sixth IGBT which are mutually connected; and the third IGBT branch comprises a seventh IGBT. The utility model has the advantages of simple and compact structure, low cost, high safety and stability, bipolar conversion and fault clearing function, etc.

Description

MMC submodule and MMC system with bipolar conversion and fault clearing functions

Technical Field

The utility model relates to a flexible direct current transmission technical field especially relates to a MMC (Modular Multilevel Converter) submodule piece, MMC system that possesses bipolar conversion and trouble clearance function.

Background

The proportion of new energy in an electric power system is increasing day by day, and with the continuous access of new energy, a power transmission mode also faces huge challenges. The traditional long-distance large-capacity alternating current transmission mode is gradually replaced by a direct current transmission mode due to the defects of extremely large loss and the like. The flexible direct current transmission is a novel high-voltage direct current transmission technology, and is different from the traditional high-voltage direct current transmission, the flexible direct current transmission adopts an Insulated Gate Bipolar Transistor (IGBT) and a voltage source converter, and has good controllability and compatibility. The MMC system is a voltage type current converter adopting a modular multilevel direct current transmission mode, and can meet the current high requirements on electric energy and voltage grade.

A core component of the MMC system is a Sub-module (Sub-module) connected in series in an IGBT branch, and the MMC Sub-module generally adopts a half-bridge structure as shown in fig. 1 (a) or a full-bridge structure as shown in fig. 1 (b). The fault protection strategy is a key for ensuring the normal operation of the MMC system, and in the fault of the MMC system, the influence of the direct-current side short-circuit fault on the system is more important than other faults. Traditional half-bridge structure MMC submodule piece does not possess the fault clearing function, can have the potential safety hazard in the operation process. And although partial full-bridge structure MMC submodule piece possesses the trouble and clears away the function among the prior art, adopt usually when the direct current side trouble takes place through with submodule piece shutting and utilize the mode that the electric capacity discharges, reach the trouble and clear away the purpose, can have following problem:

1. in order to provide the full-bridge structure with the fault clearing function, the topology of the whole sub-module becomes more complex and is not easy to implement.

2. The problem of faults cannot be completely solved by using sub-module locking operation, faults can be isolated temporarily or the influence of the faults can be reduced, finally, a direct-current circuit breaker is still used for disconnecting a direct-current circuit, and the fault circuit cannot normally run after being cut off.

SUMMERY OF THE UTILITY MODEL

The to-be-solved technical problem of the utility model lies in: to the technical problem that prior art exists, the utility model provides a simple structure is compact, with low costs, the high bipolar conversion of possessing of safety and stability nature and trouble clearance function MMC submodule piece, MMC system.

In order to solve the technical problem, the utility model provides a technical scheme does:

an MMC sub-module with double-pole conversion and fault clearing functions comprises a first IGBT branch, a second IGBT branch and a third IGBT branch which are connected in parallel;

the first IGBT branch comprises a first IGBT, a second IGBT and a freewheeling diode D1 which are connected with each other, an emitter of the first IGBT is connected with a collector of the second IGBT, a first voltage output end A is connected between the emitter of the first IGBT and the collector of the second IGBT, a second voltage output end B is connected with an emitter of the second IGBT, and the freewheeling diode D1 is reversely connected with two ends of the first IGBT in parallel;

the second IGBT branch circuit comprises a first IGBT group, a capacitor and a second IGBT group which are sequentially connected, the first IGBT group comprises a third IGBT and a fourth IGBT which are mutually connected, the second IGBT group comprises a fifth IGBT and a sixth IGBT which are mutually connected, a collector electrode of the third IGBT is respectively connected with a collector electrode of the first IGBT and an emitter electrode of the sixth IGBT, an emitter electrode of the third IGBT and an emitter electrode of the fourth IGBT are respectively connected with one end of the capacitor, a collector electrode of the fifth IGBT and a collector electrode of the sixth IGBT are respectively connected with the other end of the capacitor, and a collector electrode of the fourth IGBT is connected with an emitter electrode of the fifth IGBT;

and the third IGBT branch comprises a seventh IGBT, and the emitter of the seventh IGBT is connected with the voltage output second end B.

Further, the switching states of the first IGBT, the second IGBT, the third IGBT, the fourth IGBT, the fifth IGBT, the sixth IGBT and the seventh IGBT are controlled to enter a voltage mode, a working state and the state of the capacitor, when a positive voltage U is arranged between the first voltage output end A and the second voltage output end B, the positive voltage mode is entered, when a negative voltage-U is arranged between the first voltage output end A and the second voltage output end B, the negative voltage mode is carried out, and the working state comprises any one of locking, putting in and cutting off.

Further, when the capacitor is charged in a negative voltage mode and enters a working state, the current is released through the capacitor to clear the fault.

Further, in the positive voltage mode, when the switch states are respectively open, close, open, and open, a current flows from the first voltage output terminal a to the second voltage output terminal B, and enters a blocking operating state, so that the capacitor is charged;

when the switch states are respectively closed, opened, closed, opened and opened, current flows from the first voltage output end A to the second voltage output end B, the capacitor enters a working state, and the capacitor is charged;

when the switch states are respectively open, closed, open and open, the current flows from the first voltage output end A to the second voltage output end B and enters a cut-off working state, and the capacitor bypasses.

Further, in the positive voltage mode, when the switch states are respectively open, close, and close, a current flows from the voltage output second end B to the voltage output first end a, and enters a locked working state, and the capacitor bypasses;

when the states of the switches are respectively closed, opened, closed, opened and opened, current flows from the voltage output second end B to the voltage output first end A, the voltage output first end A enters a working state, and the capacitor discharges;

when the states of the switches are closed, opened, closed, opened and closed respectively, the current flows from the second voltage output end B to the first voltage output end A, and enters a cut-off working state, and the capacitor bypasses.

Further, in the negative voltage mode, when the switch states are respectively open, close, and open, a current flows from the first voltage output terminal a to the second voltage output terminal B, and enters a blocking working state, and the capacitor discharges;

when the states of the switches are respectively closed, opened, closed and opened, current flows from the first voltage output end A to the second voltage output end B, the capacitor enters an operating state, and the capacitor discharges;

when the switch states are respectively open, closed, open, closed and open, the current flows from the first voltage output end A to the second voltage output end B and enters a cut-off working state, and the capacitor bypasses.

Further, in the negative voltage mode, when the switch states are respectively open, close, and close, a current flows from the second voltage output terminal B to the first voltage output terminal a, and enters a locked working state, and the capacitor bypasses;

when the switch states are respectively closed, opened, closed and opened, the current flows from the voltage output second end B to the voltage output first end A, the capacitor enters a working state, and the capacitor is charged;

when the states of the switches are closed, opened, closed and closed respectively, the current flows from the second voltage output end B to the first voltage output end A and enters a cut-off working state, and the capacitor bypasses.

Further, a collector of the seventh IGBT is connected to the collector of the first IGBT and the collector of the third IGBT, respectively, and an emitter of the third IGBT and an emitter of the fifth IGBT are connected to the second voltage output terminal, respectively.

Further, the positive electrode of the capacitor is connected to the emitter of the third IGBT and the emitter of the fourth IGBT, respectively, and the negative electrode of the capacitor is connected to the collector of the fifth IGBT and the collector of the sixth IGBT, respectively.

The MMC system comprises three-phase bridge arms, wherein each phase of the bridge arms comprises a plurality of MMC sub-modules connected in series, and the MMC sub-modules adopt the MMC sub-modules as above.

Compared with the prior art, the utility model has the advantages of: the utility model discloses use half-bridge submodule structure as the basis, through constituting the MMC submodule piece by 7 IGBT and an electric capacity, at normal during operation output positive voltage, can also export the negative voltage, when monopole trouble takes place, reverse the electric capacity two-stage, utilize electric capacity release current to reduce short-circuit current, reach the trouble and clear away the purpose from, when the fault line excision, utilize the reversal polarity can provide normal operating's reverse voltage, satisfy the unilateral demand of running, thereby realize carrying out unilateral operation with bipolar reversal, can reduce the influence of trouble to the both ends system.

Drawings

FIG. 1 is a schematic diagram of a MMC sub-module in the prior art.

Fig. 2 is a schematic structural diagram of an MMC submodule having bipolar switching and fault clearing functions according to the present embodiment.

Fig. 3 is a schematic diagram illustrating the principle of the MMC submodule implementing fault clearing when a ground fault occurs in the present embodiment.

Fig. 4 is a schematic structural diagram of the MMC system employed in the present embodiment.

Illustration of the drawings: 1. a first IGBT branch circuit; 2. a second IGBT branch circuit; 21. a first IGBT group; 22. a second IGBT group; 3. and a third IGBT branch circuit.

Detailed Description

The invention will be further described with reference to the drawings and specific preferred embodiments without limiting the scope of the invention.

As shown in fig. 2, the MMC sub-module having the bipolar switching and fault clearing function in this embodiment includes a first IGBT leg 1, a second IGBT leg 2, and a third IGBT leg 3 connected in parallel;

the first IGBT branch circuit 1 comprises a first IGBT (IGBT 1), a second IGBT (IGBT 2) and a freewheeling diode D1 which are connected with each other, an emitter electrode of the first IGBT (IGBT 1) is connected with a collector electrode of the second IGBT (IGBT 2), a first voltage output end A is connected between the emitter electrode of the first IGBT (IGBT 1) and the collector electrode of the second IGBT (IGBT 2), a second voltage output end B is connected with an emitter electrode of the second IGBT, and the freewheeling diode D1 is reversely connected with two ends of the first IGBT (IGBT 1) in parallel;

the second IGBT branch 2 comprises a first IGBT group 21, a capacitor C and a second IGBT group 22 which are sequentially connected, the first IGBT group 21 comprises a third IGBT (IGBT 3) and a fourth IGBT (IGBT 4) which are mutually connected, the second IGBT (IGBT 2) group 22 comprises a fifth IGBT (IGBT 5) and a sixth IGBT (IGBT 6) which are mutually connected, a collector electrode of the third IGBT (IGBT 3) is respectively connected with a collector electrode of the first IGBT (IGBT 1) and an emitter electrode of the sixth IGBT (IGBT 6), an emitter electrode of the third IGBT (IGBT 3) and an emitter electrode of the fourth IGBT (IGBT 4) are respectively connected with one end of the capacitor C, a collector electrode of the fifth IGBT (IGBT 5) and a collector electrode of the sixth IGBT (IGBT 6) are respectively connected with the other end of the capacitor C, and a collector electrode of the fourth IGBT is connected with an emitter electrode of the fifth IGBT;

and the third IGBT branch 3 comprises a third IGBT, and an emitter of the third IGBT is connected with the voltage output second end B.

This embodiment is based on half-bridge submodule structure, constitute the MMC submodule piece through by 7 IGBT (IGBT 1 ~ IGBT 7) and a electric capacity (C), submodule piece output positive voltage when normal work, can also export the negative voltage, when unipolar fault takes place, with electric capacity C two-stage reversal, utilize electric capacity release current to reduce short-circuit current, reach the trouble self-clearing purpose, and when the fault line excision, utilize the antipole polarity can provide normal operating's reverse voltage, satisfy unilateral operation demand, thereby realize carrying out unilateral operation with bipolar reversal, unipolar operation mode based on behind the MMC unipolar fault can reduce the influence of trouble to both ends system, not only have the trouble clearance function promptly, still possess bipolar convertible function.

In this embodiment, the collector of the seventh IGBT is connected to the collector of the first IGBT and the collector of the third IGBT, respectively, and the emitter of the third IGBT and the emitter of the fifth IGBT are connected to the voltage output second terminal, respectively.

In this embodiment, the positive electrode of the capacitor is connected to the emitter of the third IGBT and the emitter of the fourth IGBT, respectively, and the negative electrode of the capacitor is connected to the collector of the fifth IGBT and the collector of the sixth IGBT, respectively.

In this embodiment, the states of the first IGBT, the second IGBT, the third IGBT, the fourth IGBT, the fifth IGBT, the sixth IGBT, and the seventh IGBT are controlled to enter the voltage mode, the operating state, and the state of the capacitor C, when a positive voltage U is present between the first voltage output terminal a and the second voltage output terminal B, the positive voltage mode is entered, when a negative voltage-U is present between the first voltage output terminal a and the second voltage output terminal B, the negative voltage mode is performed, the operating state includes any one of locking, switching, and cutting, and when the operating state is switched in the negative voltage mode and the capacitor is charged, the current is released through the capacitor C to reduce and realize fault clearing. Namely, the MMC submodule in this embodiment is divided into two voltage modes: the positive voltage mode is a normal use mode, the negative voltage mode can be matched with the ground to form a single-side running system, namely when a ground fault occurs, two stages of the capacitor C are reversed, the capacitor C is used for releasing current to reduce short-circuit current, and when a fault line is cut off, reverse voltage in normal running is provided by using reverse polarity to meet the requirement of single-side running. Under the two voltage modes, the two voltage modes are specifically divided into locking, putting in and cutting off working states.

In the embodiment, in the positive voltage mode, when the switching states (IGBT 1 to IGBT 7) are sequentially opened, closed, opened and closed, respectively, the current flows from the first voltage output terminal a to the second voltage output terminal B, and enters the locking working state, and the capacitor C is charged;

when the switching states (IGBT 1-IGBT 7) are sequentially closed, opened, closed, opened and opened respectively, current flows from a first voltage output end A to a second voltage output end B, the power supply enters a working state, and a capacitor C is charged;

when the switching states (IGBT 1-IGBT 7) are respectively open, closed, open and open, the current flows from the first voltage output end A to the second voltage output end B and enters a cut-off working state, and the capacitor C bypasses.

In the positive voltage mode of the MMC sub-module in this embodiment, when the switching states (IGBT 1 to IGBT 7) are sequentially turned off, turned on, turned off, and turned on, respectively, current flows from the voltage output second terminal B to the voltage output first terminal a, and enters a locked working state, where the capacitor C bypasses;

when the switching states (IGBT 1-IGBT 7) are sequentially closed, opened, closed, opened and opened respectively, current flows from the second voltage output end B to the first voltage output end A, and enters a working state, and the capacitor C discharges;

when the switching states (IGBT 1-IGBT 7) are sequentially closed, opened, closed, opened and closed respectively, the current flows from the second voltage output end B to the first voltage output end A, and enters a cut-off working state, and the capacitor C bypasses.

In this embodiment, by controlling the on/off states of the switches (IGBT 1 to IGBT 7) according to the above-described manner, a positive voltage output mode, i.e., a normal operation mode, can be implemented, in which a state that current flows from the voltage output first terminal a to the current output second terminal B is locked, put into, and cut off, and the capacitor C is charged or bypassed, or a state that current flows from the voltage output second terminal B to the current output first terminal a is locked, put into, and cut off, and the capacitor C is discharged or bypassed.

In the negative voltage mode of the MMC sub-module in this embodiment, when the switching states (IGBT 1 to IGBT 7) are sequentially turned off, turned on, and turned off, respectively, a current flows from the voltage output first end a to the voltage output second end B, and enters a locking operating state, and the capacitor C discharges;

when the switching states (IGBT 1-IGBT 7) are sequentially closed, opened, closed and opened respectively, current flows from a first voltage output end A to a second voltage output end B, the voltage output end A enters a working state, and a capacitor C discharges;

when the switching states (IGBT 1-IGBT 7) are respectively open, closed, open, closed and open, the current flows from the first voltage output end A to the second voltage output end B and enters a cut-off working state, and the capacitor C bypasses.

In the negative voltage mode of the MMC sub-module in this embodiment, when the switching states (IGBT 1 to IGBT 7) are sequentially turned off, turned on, and turned on, respectively, a current flows from the voltage output second terminal B to the voltage output first terminal a, enters a locking operating state, and bypasses the capacitor C;

when the switching states (IGBT 1-IGBT 7) are sequentially closed, opened, closed and opened respectively, current flows from the voltage output second end B to the voltage output first end A, the voltage output first end A enters a working state, and the capacitor C is charged;

when the switch states (IGBT 1-IGBT 7) are closed, disconnected, closed and closed in sequence, the current flows from the voltage output second end B to the voltage output first end A, and enters a cut-off working state, and the capacitor C bypasses.

In this embodiment, by controlling the on/off states of the switches (IGBT 1 to IGBT 7) in the above manner, a negative voltage output mode can be implemented, in which a blocking, switching, and cutting state in which current flows from the voltage output first terminal a to the current second terminal B is implemented, and the capacitor C is discharged or bypassed, or a blocking, switching, and cutting state in which current flows from the voltage output second terminal B to the current first terminal a is implemented, and the capacitor C is charged or bypassed. Namely, the switching mode when the capacitor is charged in the negative voltage mode has a fault clearing function, and current is released through the capacitor to realize fault self-clearing.

The current flow direction when the fault is cleared is as shown in fig. 3, and the voltage output second end B sequentially passes through the fourth IGBT (IGBT 4), the capacitor C, the sixth IGBT (IGBT 6), the first IGBT (IGBT 1) and the voltage output first end a sequentially through the capacitor C, so that the ground current can be reduced, and the fault clearing is realized.

Assuming that the switching signal of each IGBTn (n =1, 2.. 7) is VTn (n =1, 2.. 7), it is closed when the signal is 1 and is open when the signal is 0. Let the voltage of the capacitor be U, the operation state, the current direction and the state of the capacitor C of the MMC submodule in each voltage mode in this embodiment are shown in table 1.

Table 1

The above-mentioned MMC submodule piece of this embodiment possesses two kinds of operating modes (positive voltage, negative voltage) totally 12 operating condition, not only possesses the trouble and clears away the function, and bipolar can also change moreover for can form unilateral operation system with ground connection cooperation when ground fault, reduce the fault influence, thereby ensure submodule piece safety and stability's operation, and the simple structure of whole submodule piece, easily realize.

The present embodiment further includes an MMC system, as shown in fig. 4, including three-phase bridge arms, each of which includes a plurality of MMC sub-modules (SM 1 to SM) connected in series _N ) Each MMC sub-module (or partially designated MMC sub-module) adopts the MMC sub-module as described above, namely SM 1-SM _N The structure shown in fig. 2 is adopted. Through adopting above-mentioned MMC submodule piece in MMC system, each submodule piece has trouble clearance function and bipolar conversion function, can reduce the trouble influence with the unilateral operation system of ground connection cooperation constitution when ground fault, and need not the whole overall arrangement of adjustment system and can realize, the whole cost of realizing of greatly reduced system.

The foregoing is illustrative of the preferred embodiment of the present invention and is not to be construed as limiting the invention in any way. Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments by the technical entity of the present invention should fall within the protection scope of the technical solution of the present invention.

Claims

1. An MMC submodule with bipolar conversion and fault clearing functions, comprising: the IGBT power supply comprises a first IGBT branch (1), a second IGBT branch (2) and a third IGBT branch (3) which are connected in parallel;

the first IGBT branch circuit (1) comprises a first IGBT, a second IGBT and a freewheeling diode D1 which are connected with each other, wherein an emitter of the first IGBT is connected with a collector of the second IGBT, a voltage output first end A is connected between the emitter of the first IGBT and the collector of the second IGBT, an emitter of the second IGBT is connected with a voltage output second end B, and the freewheeling diode D1 is reversely connected in parallel at two ends of the first IGBT;

the second IGBT branch circuit (2) comprises a first IGBT group (21), a capacitor and a second IGBT group (22) which are sequentially connected, the first IGBT group (21) comprises a third IGBT and a fourth IGBT which are mutually connected, the second IGBT group (22) comprises a fifth IGBT and a sixth IGBT which are mutually connected, a collector electrode of the third IGBT is respectively connected with a collector electrode of the first IGBT and an emitter electrode of the sixth IGBT, an emitter electrode of the third IGBT and an emitter electrode of the fourth IGBT are respectively connected with one end of the capacitor, a collector electrode of the fifth IGBT and a collector electrode of the sixth IGBT are respectively connected with the other end of the capacitor, and a collector electrode of the fourth IGBT is connected with an emitter electrode of the fifth IGBT;

and the third IGBT branch (3) comprises a seventh IGBT, and the emitter of the seventh IGBT is connected with the voltage output second end B.

2. The MMC sub-module with bipolar conversion and fault clearance of claim 1, wherein the collector of the seventh IGBT is connected to the collector of the first IGBT and the collector of the third IGBT respectively, and the emitter of the third IGBT and the emitter of the fifth IGBT are connected to the voltage output second terminal respectively.

3. The MMC sub-module with bipolar conversion and fault clearance function of claim 1, wherein the positive pole of the capacitor is connected with the emitter of the third IGBT and the emitter of the fourth IGBT respectively, and the negative pole of the capacitor is connected with the collector of the fifth IGBT and the collector of the sixth IGBT respectively.

4. An MMC system comprising three phase legs, each phase of said legs comprising a plurality of serially connected MMC sub-modules, wherein said MMC sub-modules comprise the MMC sub-modules of any of claims 1-3.