阅读说明：本技术 一种基于双向准z源的模块化多电平变换器子模块拓扑结构及其工作方法 (Modular multilevel converter submodule topological structure based on bidirectional quasi-Z source and working method thereof ) 是由 徐坤山 臧凤启 黄家才 曾元静 李本元 盛云龙 史建军 黄亚洲 赵贤林 于 2020-06-10 设计创作，主要内容包括：本发明公开了一种基于双向准Z源的模块化多电平变换器子模块拓扑结构及其工作方法,包括半桥电路,所述半桥电路和双向准Z源电路电连接。本发明降低了子模块电容电压值,减小了电容尺寸；子模块本身具有子模块电压控制能力,子模块电容电压波动可被控制的很小；加入了直通状态,降低了直通故障的概率,提高了结构可靠性。(The invention discloses a modular multilevel converter submodule topological structure based on a bidirectional quasi-Z source and a working method thereof. The invention reduces the voltage value of the sub-module capacitor and reduces the size of the capacitor; the sub-modules have sub-module voltage control capability, and the voltage fluctuation of the sub-module capacitor can be controlled very little; and a direct connection state is added, so that the probability of direct connection faults is reduced, and the structural reliability is improved.)

1. The modular multilevel converter submodule topological structure based on the bidirectional quasi-Z source is characterized by comprising a half-bridge circuit, wherein the half-bridge circuit is electrically connected with the bidirectional quasi-Z source circuit.

2. The modular multilevel converter sub-module topology structure based on bidirectional quasi-Z source of claim 1, wherein the bidirectional quasi-Z source circuit comprises a first inductor L₁A second inductor L₂A first capacitor C₀A second capacitor C₁And a third capacitance C₂And a switching tube Q₁The positive pole of first electric capacity with the one end of first inductance is connected, the other end of first inductance respectively with the projecting pole of switch tube and the negative pole of third electric capacity are connected, the collecting electrode of switch tube respectively with the positive pole of second electric capacity with the one end of second inductance is connected, the other end of second inductance respectively with the positive pole of third electric capacity with the collecting electrode of half-bridge circuit top tube is connected, the negative pole of first electric capacity respectively with the negative pole of second electric capacity with the projecting pole of half-bridge circuit low tube is connected.

3. The bi-directional quasi-Z source based modular multilevel converter sub-module topology of claim 2, wherein the half-bridge circuit comprises a first NPN power switch tube S₁And a second NPN power switch tube S₂。

4. The bi-directional quasi-Z source based modular multilevel converter sub-module topology of claim 2 or 3, wherein the switching tube Q₁Integrated with anti-parallel diode D₁(ii) a The first NPN power switch tube S₁And a second NPN power switch tube S₂Are respectively integrated with anti-parallel diodes.

5. An operating method of a modular multilevel converter sub-module topological structure based on a bidirectional quasi-Z source, which applies the modular multilevel converter sub-module topological structure based on the bidirectional quasi-Z source in any one of claims 1 to 4, and is characterized by comprising the following steps:

modular multilevel converter submoduleOutput sine modulation wave M₁And-through modulated wave M₂Respectively compared with the triangular carrier C to generate a switching signal CM₁And CM₂；

First NPN power switch tube S₁Is equal to CM₁XOR CM₂(ii) a Second NPN power switch tube S₂The switching signal is CM₁Taking the inverse; switch tube Q₁The switching signal is CM₂Taking the inverse;

when the first NPN power switch tube S₁And a switching tube Q₁Simultaneously conducted and the second NPN power switch tube S₂When the modular multilevel converter is turned off, the sub-modules of the modular multilevel converter are in an input state;

when the second NPN power switch tube S₂And a switching tube Q₁Simultaneously conducted first NPN power switch tube S₁When the modular multilevel converter is turned off, the submodule of the modular multilevel converter is in a cutting-off state;

when the first NPN power switch tube S₁And a second NPN power switch tube S₂Simultaneously conducting and switching tube Q₁When the modular multilevel converter is turned off, the sub-modules of the modular multilevel converter are in a through state.

6. The method of claim 5, wherein the through-going modulated wave M is a direct-to-Z-source-based modular multilevel converter sub-module topology₂The method is obtained by a proportional-integral control method, and comprises the following specific steps:

modular multilevel converter submodule voltage reference value and U_C1And U_C2Subtracting the sum to be used as the input of proportional integral and carrying out proportional integral operation to obtain a proportional integral value;

subtracting the proportional integral value from 1 to obtain a through modulated wave M₂。

Technical Field

The invention belongs to the technical field of topological structures of high-power converters, and particularly relates to a modular multilevel converter sub-module topological structure based on a bidirectional quasi-Z source and a working method thereof.

Background

Modular Multilevel Converters (MMC) are widely used in the fields of flexible dc transmission systems, power quality management, energy storage, medium-high voltage power transmission, and the like, and are considered to be medium-high voltage high-power converters with the greatest development prospect. The half-bridge sub-module is the most widely applied sub-module topology structure in the MMC due to the simple structure and control and the lowest cost. However, the sub-module of the structure has high capacitance voltage and large fluctuation, the voltage fluctuation of the sub-module is equal to the voltage fluctuation of the capacitor, so that the circulating current alternating current component is large, a circulating current suppression strategy is required to suppress the circulating current alternating current component, and the control complexity is increased. In addition, if the two switching tubes of the half-bridge sub-module are not normally connected directly due to factors such as interference on driving, the short-circuit current of the capacitor can damage the switching tubes, the capacitor and other devices.

For the problem of large fluctuation of sub-module capacitor voltage, the existing research mostly adopts an improved control strategy to reduce the fluctuation of the capacitor voltage, but the suppression capability is limited. In order to solve the direct connection problem, documents propose an MMC direct connection sub-module topology based on a clamping circuit and an energy transfer circuit, but the topology has more elements and larger loss, and the voltage of a capacitor playing a role in energy storage is too high. In the prior art, a comprehensive solution is not provided from three aspects of overhigh voltage of a sub-module capacitor, reduction of voltage fluctuation of the sub-module and improvement of topology reliability.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides the modular multilevel converter submodule topological structure based on the bidirectional quasi-Z source and the working method thereof, so that the capacitance voltage value of the submodule is reduced, the voltage fluctuation of the submodule is reduced, and the structural reliability is improved.

In order to achieve the purpose, the invention adopts the following technical scheme:

a modular multilevel converter sub-module topological structure based on a bidirectional quasi-Z source comprises a half-bridge circuit, wherein the half-bridge circuit is electrically connected with the bidirectional quasi-Z source circuit.

A working method of a modular multilevel converter sub-module topological structure based on a bidirectional quasi-Z source comprises the following steps:

sinusoidal modulation wave M output by submodule of modular multilevel converter₁And-through modulated wave M₂Respectively compared with the triangular carrier C to generate a switching signal CM₁And CM₂；

First NPN power switch tube S₁Is equal to CM₁XOR CM₂(ii) a Second NPN power switch tube S₂The switching signal is CM₁Taking the inverse; switch tube Q₁The switching signal is CM₂Taking the inverse;

when the first NPN power switch tube S₁And a switching tube Q₁Simultaneously conducted and the second NPN power switch tube S₂When the modular multilevel converter is turned off, the sub-modules of the modular multilevel converter are in an input state;

when the second NPN power switch tube S₂And a switching tube Q₁Simultaneously conducted first NPN power switch tube S₁When the modular multilevel converter is turned off, the submodule of the modular multilevel converter is in a cutting-off state;

when the first NPN power switch tube S₁And a second NPN power switch tube S₂Simultaneously conducting and switching tube Q₁When the modular multilevel converter is turned off, the sub-modules of the modular multilevel converter are in a through state.

In order to optimize the technical scheme, the specific measures adopted further comprise:

further, the bidirectional quasi-Z source circuit comprises a first inductor L₁A second inductor L₂A first capacitor C₀A second capacitor C₁And a third capacitance C₂And a switching tube Q₁The positive pole of the first capacitor is connected with one end of the first inductor, soThe other end of the first inductor is connected with the emitting electrode of the switch tube and the negative electrode of the third capacitor respectively, the collector electrode of the switch tube is connected with the positive electrode of the second capacitor and one end of the second inductor respectively, the other end of the second inductor is connected with the positive electrode of the third capacitor and the collector electrode of the upper tube of the half-bridge circuit respectively, and the negative electrode of the first capacitor is connected with the negative electrode of the second capacitor and the emitting electrode of the lower tube of the half-bridge circuit respectively.

Further, the half-bridge circuit comprises a first NPN power switch tube S₁And a second NPN power switch tube S₂。

Further, the switch tube Q₁Integrated with anti-parallel diode D₁(ii) a The first NPN power switch tube S₁And a second NPN power switch tube S₂Are respectively integrated with anti-parallel diodes.

Further, the through modulated wave M₂The method is obtained by a proportional-integral control method, and comprises the following specific steps:

modular multilevel converter submodule voltage reference value and U_C1And U_C2Subtracting the sum to be used as the input of proportional integral and carrying out proportional integral operation to obtain a proportional integral value;

subtracting the proportional integral value from 1 to obtain a through modulated wave M₂。

The invention has the beneficial effects that:

the modular multilevel converter submodule topological structure based on the bidirectional quasi-Z source and the working method thereof reduce the capacitance voltage value of the submodule and reduce the size of the capacitor; the sub-modules have sub-module voltage control capability, and the voltage fluctuation of the sub-module capacitor can be controlled very little; and a direct connection state is added, so that the probability of direct connection faults is reduced, and the structural reliability is improved.

Drawings

Fig. 1 is a schematic view of the topology of the present invention.

Fig. 2 is a schematic diagram of a modular multilevel converter based on half-bridge sub-modules according to the present invention.

Fig. 3 is a schematic diagram of the working principle of the modulation mode of the present invention.

FIG. 4 is a control block diagram of a submodule of the present invention.

FIG. 5 is a waveform diagram of simulation of the present invention.

Detailed Description

The invention will now be described in further detail with reference to the accompanying figures 1-5.

It should be noted that the terms "upper", "lower", "left", "right", "front", "back", etc. used in the present invention are for clarity of description only, and are not intended to limit the scope of the present invention, and the relative relationship between the terms and the terms is not limited by the technical contents of the essential changes.

As shown in fig. 2, in one embodiment of the present invention, each phase of the modular multilevel converter is formed by connecting an upper bridge arm and a lower bridge arm through two bridge arm inductors, each bridge arm includes N sub-modules, and each sub-module topology includes a half-bridge circuit and a bidirectional quasi-Z source circuit.

In one embodiment of the invention, the sub-module topology of the invention comprises a half-bridge circuit and a bi-directional quasi-Z source circuit, as shown in fig. 1. The half-bridge circuit is composed of two NPN power switch tubes S containing antiparallel diodes₁And S₂Composition is carried out; the bidirectional quasi-Z source circuit consists of two inductors L₁And L₂Three capacitors C₀、C₁And C₂And an integrated anti-parallel diode D₁Switch tube Q₁And (4) forming. Capacitor C₀Positive electrode of (2) is connected with an inductor L₁，L₁The other end is connected with a switch tube Q₁Emitter and C₂Negative electrode of (2), Q₁Collector electrode connection C₁Positive electrode and inductor L₂，L₂The other end is connected with a capacitor C₂Anode and half-bridge circuit of₁Collector electrode of, capacitor C₀Negative pole of the capacitor C₁And half-bridge circuit lower tube S₂An emitter of (1).

In one embodiment of the present invention, as shown in fig. 3 and 4, the sub-module outputs a sine modulation wave M₁And straightTwo modulation waves M₁Respectively compared with the triangular carrier C to generate a switching signal CM₁And CM₂。S₁Switching signal equal to CM₁XOR CM₂，S₂The switching signal being CM₁Inverting and switching tube Q₁The signal being CM₂And (6) taking the inverse. When S is₁And Q₂Are simultaneously conducted and S₂When the submodule is switched off, the submodule is in an on state according to the direction of input current of the submodule. When S is₂And Q₂Are simultaneously conducted and S₁When the sub-module is switched off, the sub-module is in a cut-off state. When S is₁And S₂Are simultaneously on and Q₂When the sub-module is turned off, the sub-module is in a through state; the submodule through state control adopts a Proportional Integral (PI) control strategy: submodule voltage reference value and U_C1And U_C2The sum of (1) is subtracted as the input of PI, and then the value obtained after PI operation is subtracted from 1 to obtain M₂Then comparing with the carrier C to obtain a switching signal; the switching state of the sub-module is obtained by the obtained sine reference modulation wave M₁The comparison with the carrier C yields the switching signal.

As shown in FIG. 5, the rated voltage of the sub-module is 250V, and U is shown in the simulation waveform diagram_C0、U_C1And U_C2The voltages of the capacitor voltage are fluctuated up and down at 160V, 205V and 45V respectively, which shows that the capacitor voltage is stable and the value of the capacitor voltage is greatly reduced. U shape_C1+U_C2The value of (A) fluctuates above and below 250V, which shows that the voltage of the submodule is stable, and the fluctuation value is greatly smaller than the waveform value of the capacitor voltage.

The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention.