阅读说明：本技术 一种模块化多电平换流器旁路机构及工作方法 (Modular multilevel converter bypass mechanism and working method ) 是由 谢文刚 肖风良 李伟 宋中建 张志成 罗光荣 武可 刘凯 于 2019-09-16 设计创作，主要内容包括：本发明提供一种模块化多电平换流器旁路机构及工作方法,包括：交流断路器QF和六个换流器组件；提高了每个子模块下部二极管耐受冲击电流的能力,有利于整个换流器将传统方案中每个子模块并联晶闸管的方式更改为每个桥臂所有子模块两端并联晶闸管,可优先选用大功率、高电压的晶闸管,减少了晶闸管的用量,经济性更高,控制也更为简单,同时也有利于整体结构的设计；在逆变模式下可大大减小通过各个子模块下部二极管的冲击电流,可靠性更高。(The invention provides a modular multilevel converter bypass mechanism and a working method thereof, wherein the modular multilevel converter bypass mechanism comprises the following steps: an alternating current breaker QF and six inverter assemblies; the capability of the diode at the lower part of each submodule to bear the impact current is improved, the whole converter is favorable for changing the mode that each submodule is connected with the thyristor in parallel in the traditional scheme into the mode that the thyristors are connected with both ends of all submodules in each bridge arm in parallel, the high-power and high-voltage thyristors can be preferentially selected, the using amount of the thyristors is reduced, the economy is higher, the control is simpler, and the design of the whole structure is also favorable; and the impact current passing through the lower diodes of each submodule can be greatly reduced in an inversion mode, and the reliability is higher.)

1. A modular multilevel converter bypass mechanism, comprising: an alternating current breaker QF and six inverter assemblies (6); the six converter assemblies (6) are divided into three groups, and each group is provided with two converter assemblies (6);

the first phase electric output end of the alternating current breaker QF is respectively connected with the two current converter assemblies (6) to form a loop;

the second phase electric output end of the alternating current breaker QF is respectively connected with the two current converter assemblies (6) to form a loop;

and the third-phase power output end of the alternating current breaker QF is respectively connected with the two current converter assemblies (6) to form a loop.

2. The modular multilevel converter bypass mechanism of claim 1,

the converter assembly (6) comprises: the bridge-arm current conversion device comprises a bypass unit (1), a current conversion submodule (2), a bridge arm resistor (4) and a bridge arm inductor (5);

the bypass unit (1) is connected with the converter submodule (2) in parallel, and a parallel circuit of the bypass unit (1) and the converter submodule (2) is connected with the bridge arm resistor (4) and the bridge arm inductor (5) in series.

3. The modular multilevel converter bypass mechanism of claim 2,

the converter submodule (2) is provided with a plurality of converter units (3), and the converter units (3) are connected in series.

4. The modular multilevel converter bypass mechanism of claim 2,

one end of a parallel circuit of the bypass unit (1) and the converter submodule (2) is connected with a loop;

the other end of the parallel circuit of the bypass unit (1) and the converter submodule (2) is connected with the first end of the bridge arm resistor (4);

the second end of the bridge arm resistor (4) is connected with the first end of the bridge arm inductor (5);

and the second end of the bridge arm inductor (5) is connected with the phase electricity output end of the alternating current breaker QF.

5. The modular multilevel converter bypass mechanism of claim 2,

the bypass unit (1) is provided with a first bypass thyristor (1-1) and a second bypass thyristor (1-2);

the first bypass thyristor (1-1) and the second bypass thyristor (1-2) are connected in parallel, and the conduction directions of the first bypass thyristor (1-1) and the second bypass thyristor (1-2) are opposite.

6. A working method of a modular multilevel converter bypass mechanism is characterized by comprising the following steps:

when the mechanism normally operates, the bypass unit does not act;

when a short-circuit fault occurs on the direct current side, the commutation unit of the commutation submodule is locked, and meanwhile, one bypass thyristor in the bypass unit is conducted.

7. The method of operating a modular multilevel converter bypass mechanism of claim 6, further comprising:

when the mechanism works in a rectification mode, the converter submodule is locked and simultaneously triggers the second bypass thyristor to be conducted, and the second bypass thyristor of the bypass unit is conducted with the bridge arm resistor (4) and the bridge arm inductor (5).

8. The method of operating a modular multilevel converter bypass mechanism of claim 6, further comprising:

when the mechanism works in an inversion mode, the converter submodule is locked, meanwhile, a first bypass thyristor in the bypass unit is conducted, and a fault current and the converter submodule form a second loop through a bridge arm resistor, a bridge arm inductor and the converter submodule; a first loop is formed by the first bypass thyristor, and the first bypass thyristor and the converter submodule form shunting, so that the impact of short-circuit current on the diode is reduced;

after the first bypass thyristor forms a loop, the alternating current breaker QF trips, reclosing is carried out after the current on the direct current side attenuates, the converter submodule is unlocked after the reclosing is successful, and the mechanism is restarted.

Technical Field

The invention relates to the technical field of level converters, in particular to a modular multilevel converter bypass mechanism and a working method.

Background

With the continuous progress of the power semiconductor technology, the flexible direct current transmission (VSC-HVDC) technology based on the voltage source converter becomes a novel power transmission system developed recently, the flexible direct current transmission (VSC-HVDC) technology directly inverts the direct current voltage into the alternating current voltage with controllable amplitude and phase by adopting the Pulse Width Modulation (PWM) technology, the phase change is not required by the voltage of the receiving-end power grid, the system capacity of the receiving-end power grid is not limited, and the flexible direct current transmission system can be used for the connection between an isolated small system and a main grid. The modular multilevel converter MMC is widely applied to VSC-HVDC, and a basic unit of the modular multilevel converter MMC is a half-bridge or full-bridge converter unit; the structure of the converter is similar to that of a chain converter, and a plurality of groups of converter units are cascaded together to form a converter bridge arm; and 6 groups of cascade current converting bridge arms are combined together to form the three-phase current transformer.

When the converter has a direct-current short-circuit fault, if the converter works in a rectification mode, bypass thyristors which are connected with each submodule in parallel need to be conducted, so that a bypass of each bridge arm of the converter is realized, for a high-voltage converter valve, the number of submodules is large, the structure is complex, the cost is high, and the control difficulty is increased; if the converter works in an inversion mode, fault current can form a loop through a diode at the lower part of each submodule, and large impact current can cause damage to the diode, so that the stability of the system is not facilitated.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides a modular multilevel converter bypass mechanism which improves the capability of a diode at the lower part of each submodule of enduring impulse current and is beneficial to the structural optimization of the whole converter, and the modular multilevel converter bypass mechanism comprises: an alternating current breaker QF and six inverter assemblies; the six converter assemblies are divided into three groups, and each group is provided with two converter assemblies;

a first phase electric output end of the alternating current breaker QF is respectively connected with the two current converter assemblies to form a loop;

the second phase electric output end of the alternating current breaker QF is respectively connected with the two current converter assemblies to form a loop;

and the third-phase power output end of the alternating current breaker QF is respectively connected with the two current converter assemblies to form a loop.

It is further noted that the inverter assembly includes: the bridge arm comprises a bypass unit, a converter submodule, a bridge arm resistor and a bridge arm inductor;

the bypass unit is connected with the converter submodule in parallel, and a parallel circuit of the bypass unit and the converter submodule is connected with the bridge arm resistor and the bridge arm inductor in series.

It should be further noted that the converter submodule is provided with a plurality of converter units, and the plurality of converter units are connected in series.

It should be further noted that one end of the parallel circuit of the bypass unit and the converter submodule is connected with the loop;

the other end of the parallel circuit of the bypass unit and the converter submodule is connected with the first end of the bridge arm resistor;

the second end of the bridge arm resistor is connected with the first end of the bridge arm inductor;

and the second end of the bridge arm inductor is connected with the phase electricity output end of the alternating current breaker QF.

It should be further noted that the bypass unit is provided with a first bypass thyristor and a second bypass thyristor;

the first bypass thyristor and the second bypass thyristor are connected in parallel, and the conduction directions of the first bypass thyristor and the second bypass thyristor are opposite.

The invention also provides a working method of the modularized multi-level converter bypass mechanism, which comprises the following steps:

when the mechanism normally operates, the bypass unit does not act;

when a short-circuit fault occurs on the direct current side, the commutation unit of the commutation submodule is locked, and meanwhile, one bypass thyristor in the bypass unit is conducted.

When the mechanism works in a rectification mode, the converter submodule is locked and simultaneously triggers the second bypass thyristor to be conducted, and the second bypass thyristor of the bypass unit is conducted with the bridge arm resistor and the bridge arm inductor.

When the mechanism works in an inversion mode, the converter submodule is locked, meanwhile, a first bypass thyristor in the bypass unit is conducted, and a fault current and the converter submodule form a second loop through a bridge arm resistor, a bridge arm inductor and the converter submodule; a first loop is formed by the first bypass thyristor, and the first bypass thyristor and the converter submodule form shunting, so that the impact of short-circuit current on the diode is reduced;

after the first bypass thyristor forms a loop, the alternating current breaker QF trips, reclosing is carried out after the current on the direct current side attenuates, the converter submodule is unlocked after the reclosing is successful, and the mechanism is restarted.

According to the technical scheme, the invention has the following advantages:

the mode that each submodule is connected with the thyristor in parallel in the traditional scheme is changed into the mode that the thyristors are connected with two ends of all submodules in parallel in each bridge arm, the high-power and high-voltage thyristors can be preferentially selected, the using amount of the thyristors is reduced, the economy is higher, the control is simpler, and the design of the whole structure is facilitated; and the impact current passing through the lower diodes of each submodule can be greatly reduced in an inversion mode, and the reliability is higher.

Drawings

In order to more clearly illustrate the technical solution of the present invention, the drawings used in the description will be briefly introduced, 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 that other drawings can be obtained based on these drawings without creative efforts.

Fig. 1 is a schematic diagram of a modular multilevel converter with the bypass architecture;

fig. 2 is a schematic diagram of a discharge circuit when the inverter operates in the inverter mode.

The reference numerals in the figures have the meaning: the circuit comprises a bypass unit 1, a first bypass thyristor 1-1, a second bypass thyristor 1-2, a converter submodule 2, a converter unit 3, a bridge arm resistor 4, a bridge arm inductor 5, a converter assembly 6, a circuit I8, a circuit II 9 and an alternating current breaker QF, wherein the bypass unit 1, the bridge arm resistor 1-1, the bridge arm inductor 5, the converter assembly 6, the circuit I8, the circuit II 9 and the alternating current breaker QF are arranged in sequence.

Detailed Description

In order to make the objects, features and advantages of the present invention more obvious and understandable, the technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments and drawings. 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 scope of protection of this patent.

The invention provides a modular multilevel converter bypass mechanism, as shown in fig. 1 and 2, comprising: an ac circuit breaker QF and six inverter assemblies 6; the six converter assemblies 6 are divided into three groups, and each group is provided with two converter assemblies 6;

the first phase electric output end of the alternating current breaker QF is respectively connected with the two current converter assemblies 6 to form a loop; the second phase electric output end of the alternating current breaker QF is respectively connected with the two current converter assemblies 6 to form a loop; and the third-phase power output end of the alternating current breaker QF is respectively connected with the two current converter assemblies 6 to form a loop.

The converter assembly 6 comprises: the bridge-arm current converter comprises a bypass unit 1, a converter submodule 2, a bridge arm resistor 4 and a bridge arm inductor 5; the bypass unit 1 is connected with the converter submodule 2 in parallel, and a parallel circuit of the bypass unit 1 and the converter submodule 2 is connected with the bridge arm resistor 4 and the bridge arm inductor 5 in series.

The converter submodule 2 according to the present invention is provided with a plurality of converter cells 3, and the plurality of converter cells 3 are connected in series.

One end of a parallel circuit of the bypass unit 1 and the converter submodule 2 is connected with a loop; the other end of the parallel circuit of the bypass unit 1 and the converter submodule 2 is connected with the first end of the bridge arm resistor 4; the second end of the bridge arm resistor 4 is connected with the first end of the bridge arm inductor 5; and the second end of the bridge arm inductor 5 is connected with the phase electricity output end of the alternating current breaker QF.

The bypass unit 1 is provided with a first bypass thyristor 1-1 and a second bypass thyristor 1-2; the first bypass thyristor 1-1 and the second bypass thyristor 1-2 are connected in parallel, and the conduction directions of the first bypass thyristor 1-1 and the second bypass thyristor 1-2 are opposite.

The technical scheme adopted by the invention is realized by connecting a bypass structure in parallel at two ends of all sub-modules of each bridge arm of the modular multilevel converter, namely the bypass structure is firstly connected in parallel with two ends of each bridge arm sub-module of the multilevel converter and then connected in series with a bridge arm inductor and a bridge arm inductor.

Moreover, the mode that each submodule is connected with the thyristor in parallel in the traditional scheme is changed into the mode that the thyristors are connected with two ends of all submodules in parallel in each bridge arm, the high-power and high-voltage thyristors can be preferentially selected, the using amount of the thyristors is reduced, the economy is higher, the control is simpler, and meanwhile, the design of the whole structure is facilitated.

The multi-level converter bypass structure provided by the invention can realize reliable bypass of the whole converter valve when a direct-current short-circuit fault occurs, has a simple structure and high economical efficiency, improves the capability of a diode at the lower part of each submodule of the sub-modules to bear impact current, and is beneficial to the structural optimization of the whole converter.

The invention also provides a working method of the modularized multi-level converter bypass mechanism, which comprises the following steps:

when the mechanism normally operates, the bypass unit does not act; when a short-circuit fault occurs on the direct current side, the commutation unit of the commutation submodule is locked, and meanwhile, one bypass thyristor in the bypass unit is conducted.

When the mechanism works in a rectification mode, the converter submodule is locked and simultaneously triggers the second bypass thyristor to be conducted, and the second bypass thyristor of the bypass unit is conducted with the bridge arm resistor 4 and the bridge arm inductor 5.

When the mechanism works in an inversion mode, the converter submodule is locked, meanwhile, a first bypass thyristor in the bypass unit is conducted, and a fault current and the converter submodule form a second loop 9 through a bridge arm resistor, a bridge arm inductor and the converter submodule; namely, the fault current forms a second loop 9 through the bridge arm resistor, the bridge arm inductor and the diode of the converter submodule.

And a first loop 8 is formed by the first bypass thyristor, the first bypass thyristor and the converter submodule form shunt, namely the first bypass thyristor and diodes at the lower part of each submodule form shunt, and the impact of short-circuit current on the diodes is reduced.

After the first bypass thyristor forms a loop, the alternating current breaker QF trips, reclosing is carried out after the current on the direct current side attenuates, the converter submodule is unlocked after the reclosing is successful, and the mechanism is restarted.

The mode that each converter submodule is connected with the thyristor in parallel in the traditional scheme is changed into the mode that the thyristors are connected with two ends of all converter submodules in parallel in each bridge arm, the high-power and high-voltage thyristors can be preferentially selected, the using amount of the thyristors is reduced, the economy is higher, the control is simpler, and the design of the whole structure is facilitated; and the impact current passing through the lower diodes of each submodule can be greatly reduced in an inversion mode, and the reliability is higher.