阅读说明：本技术 模块化并联四电平变换器系统及方法 (Modular parallel four-level converter system and method ) 是由 陈华 边惠惠 王灿运 孙宪良 杨建峰 于 2020-06-29 设计创作，主要内容包括：本公开提供了一种模块化四电平变换器系统,包括：第一子模块,和至少一个与第一子模块并联的第N子模块；每个子模块均包括变换器和控制器,第一子模块的变换器与第N子模块的变换器的直流侧并联,交流侧连接滤波器后通过电网并联；控制器根据零序环流信息对各个变换器间的环流进行控制；实现装备的大容量化需求的技术效果；不同调制度下改变矢量作用时间,降低了变换器间的环流；对于变换器电流、电路参数不相等工况依然适用。(The present disclosure provides a modular four-level converter system comprising: the system comprises a first sub-module and at least one Nth sub-module connected with the first sub-module in parallel; each submodule comprises a converter and a controller, the converter of the first submodule is connected with the direct current side of the converter of the Nth submodule in parallel, and the alternating current side of the first submodule is connected with a filter and then connected with the filter in parallel through a power grid; the controller controls the circulation among all the converters according to the zero sequence circulation information; the technical effect of realizing the requirement of large capacity of the equipment is achieved; the vector action time is changed under different modulation degrees, so that the circulating current between the converters is reduced; the method is still suitable for the working condition that the current and the circuit parameters of the converter are not equal.)

1. A modular four-level converter system, comprising: the system comprises a first sub-module and at least one Nth sub-module connected with the first sub-module in parallel; each submodule comprises a converter and a controller, the converter of the first submodule is connected with the direct current side of the converter of the Nth submodule in parallel, and the alternating current side of the first submodule is connected with a filter and then connected with the filter in parallel through a power grid; and the controller controls the circulation among the converters according to the zero sequence circulation information.

2. The modular four-level converter system according to claim 1, wherein the converter comprises three legs connected in parallel, each leg comprising a capacitor, a diode and six switching tubes connected in series in sequence, the switching tubes being clamped by the diode and the capacitor.

3. The modular four-level converter system according to claim 2, further comprising a control circuit, wherein the control circuit is a conditioning circuit, a sampling circuit, a controller and a driving circuit which are connected in sequence, and the driving circuit outputs a PWM signal to drive the switching tubes in the bridge arms to be turned on and off.

4. The modular four-level converter system according to claim 3, wherein the controller comprises a current controller and a zero sequence circulating current controller, the current controller adjusting the current values of the converter for d-axis and q-axis currents of each sub-module.

5. The modular four-level converter system according to claim 4, wherein the zero sequence circulating current controller is based on two converter circulating current information i of the first module_z1And i_z2Acquiring zero-sequence circulating current information by the inductances and the zero-sequence duty ratios of the Nth converter and the first converter; and controlling the circulation between the converters according to the zero sequence circulation information.

6. The modular four-level converter system according to claim 4, wherein said zero sequence circulating current controller implements circulating current suppression using a changed zero vector at low modulation and implements circulating current suppression using a changed small vector at high modulation.

7. The modular four-level converter system according to claim 5, wherein the obtaining of the zero-sequence circulating current information is specifically: and calculating the acquired data as zero-sequence circulating current information by subtracting the product of the inductance of the first filter and the zero-sequence circulating current of the first converter from the product of the inductance of the nth filter and the zero-sequence circulating current of the nth converter, then adding the product of the input voltage and the time to obtain a ratio, adding the difference value between the duty ratio of the nth converter which is one sixth of the product of the inductance of the first filter and the zero-sequence circulating current of the first converter and the duty ratio of the first converter, and further adding the difference value between the nth converter and the first converter which select different values according to the sector.

8. A method of using a modular four-level converter system according to any of claims 1-7, the steps comprising:

firstly, modeling a modular four-level converter system;

designing a current controller aiming at d-axis and q-axis currents of each submodule;

designing a zero-sequence circulation controller according to circulation information i of two converters_z1And i_z2And obtaining zero-sequence circulating current information by the inductances of the Nth converter and the first converter and the zero-sequence duty ratio.

9. The use of the method as claimed in claim 8, characterized in that the control of the converter-to-converter circulating currents is based on zero sequence circulating current information, circulating current suppression is achieved with changing zero vectors at low modulation and circulating current suppression is achieved with changing small vectors at high modulation.

10. The use method according to claim 8, wherein the obtaining of the zero sequence circulating current information specifically includes: and calculating the acquired data as zero-sequence circulating current information by subtracting the product of the inductance of the first filter and the zero-sequence circulating current of the first converter from the product of the inductance of the nth filter and the zero-sequence circulating current of the nth converter, then adding the product of the input voltage and the time to obtain a ratio, adding the difference value between the duty ratio of the nth converter which is one sixth of the product of the inductance of the first filter and the zero-sequence circulating current of the first converter and the duty ratio of the first converter, and further adding the difference value between the nth converter and the first converter which select different values according to the sector.

Technical Field

The present disclosure relates to a modular parallel four-level converter system and method.

Background

The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.

With the rapid development of new energy, the grid-connected power quality of the new energy is required to be higher by the power grid. The advent of four-level inverters just solved this problem. Compared with the traditional two-level inverter and the traditional three-level inverter, the four-level inverter has the advantages of good output waveform quality, small filter size and the like. Among the four-level topologies, the NNPC topology is gaining wide attention due to the small number of switches. In addition, due to the influence of current stress of the switching tube, the capacity of a single inverter is limited, and the application in a high-power occasion is difficult to meet. The parallel connection of the inverters becomes an ideal scheme in a high-power photovoltaic grid-connected power generation system and a wind power generation system.

However, for the mismatch of resistance and inductance between modules, and the difference of algorithms between different converters, the circulating current between the converters is increased. The circulating current affects the output current waveform quality of the inverter and burns out the IGBT itself when severe.

Disclosure of Invention

In order to solve the technical problem, the present disclosure provides a modular four-level converter system and a control method, which implement the circulating current suppression of multiple high-power conversion systems and improve the waveform quality of a grid-connected converter.

In a first aspect, the present disclosure provides a modular four-level converter system comprising: the system comprises a first sub-module and at least one Nth sub-module connected with the first sub-module in parallel; each submodule comprises a converter and a controller, the converter of the first submodule is connected with the direct current side of the converter of the Nth submodule in parallel, and the alternating current side of the first submodule is connected with a filter and then connected with the filter in parallel through a power grid; and the controller controls the circulation among the converters according to the zero sequence circulation information.

In a second aspect, the present disclosure also provides a method of using the modular four-level converter system according to the first aspect, the steps including:

modeling the modular four-level converter system;

designing a current controller aiming at d-axis and q-axis currents of each submodule;

designing a zero-sequence circulation controller according to circulation information i of two converters_z1And i_z2And obtaining zero-sequence circulating current information by the inductances of the Nth converter and the first converter and the zero-sequence duty ratio.

Furthermore, the circulation between each converter is controlled according to the zero sequence circulation information, circulation suppression is realized by changing a zero vector in a low modulation degree, and circulation suppression is realized by changing a small vector in a high modulation degree.

Compared with the prior art, this disclosure possesses following beneficial effect:

1. according to the converter, the first sub-module and the at least one Nth sub-module which is connected with the first sub-module in parallel are arranged through parallel connection of the converters, the converters of the first sub-module are connected with the direct current side of the converters of the Nth sub-module in parallel, the alternating current side of the converters of the Nth sub-module is connected with the filter in parallel through the power grid, the technical problem that due to the influence of current stress of a switch tube, the capacity of a single converter is limited, the application in a high-power occasion is difficult to meet is solved, and the technical effect of large-.

2. The method controls the circulation among all converters according to the zero sequence circulation information, realizes circulation suppression by changing a zero vector at a low modulation degree, realizes circulation suppression by changing a small vector at a high modulation degree, solves the technical problems that the mismatching of resistance and inductance among modules can cause the circulation between the converters to be intensified, the circulation can influence the waveform quality of the output current of the converters, and the IGBT can be burnt out when the circulation is serious because of different algorithms among different converters, realizes the change of the vector action time under different modulation degrees, and reduces the circulation among the converters.

3. The present disclosure designs an optimal controller for d-axis and q-axis currents; adding optimal circulation controller, designing zero-sequence circulation controller, zeroThe sequence circulation controller is based on circulation information i of two converters_z1And i_z2The inductance and the zero sequence duty ratio of the Nth converter and the first converter acquire zero sequence circulation information, the technical problems that circulation can affect the waveform quality of output current of the converters and the IGBT can be burnt out when serious are solved, and the method is still applicable to working conditions that current and circuit parameters of the converters are unequal.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.

Fig. 1 is a structural diagram of a parallel system of four-level converters in embodiment 1 of the present disclosure;

fig. 2 is a control circuit diagram of a parallel four-level converter in embodiment 1 of the present disclosure;

fig. 3 is a block diagram of a control system controller in embodiment 2 of the present disclosure.

The specific implementation mode is as follows:

the present disclosure is further described with reference to the following drawings and examples.

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.