Three-phase common-N-point cascade type simplified isolation and non-isolation hybrid power electronic transformer

Abstract

The invention discloses a three-phase common-N-point cascade type simplified isolation and non-isolation hybrid power electronic transformer, and belongs to the technical field of transformers. Each phase of input is connected to a neutral point through a cascade type converter structure; the cascaded converter structure comprises a plurality of rectification and inversion modules, the preceding stage of each rectification and inversion module is a cascaded rectification structure, and the later stage of each rectification and inversion module is a cascaded inversion structure. The cascaded converter structure comprises at least one isolation module, and the isolation module is arranged at the head end of the cascaded converter structure; when the number of the rectification inversion modules is three, the second rectification inversion module is of a three-bridge-arm structure, and the third rectification inversion module is of a two-bridge-arm structure. And when the number of the rectification and inversion modules is greater than 3, the second and later rectification and inversion modules are of a two-bridge-arm structure. According to the invention, a part of switching tubes of the topology non-isolation module are reduced, the loss of a switching loss tube is reduced, and meanwhile, the influence of a redundant switching state on a three-phase common N point is avoided.

Description

Technical Field

[0001] This invention relates to the field of transformer technology, and in particular to a three-phase N-point cascaded simplified isolation and non-isolation hybrid power electronic transformer. Background Technology

[0002] Three-phase high-voltage frequency converters are widely used in the control and speed regulation of high-voltage motors. Traditional high-voltage frequency converters often use multi-tap transformers to step down the input voltage and isolate the input and output. However, power frequency transformers have problems such as high cost, large size, and low power density.

[0003] The main solutions currently available in the industry to address this issue are: 1. Adopting such Figure 1 The fully isolated power electronic transformer shown typically consists of an AC-DC rectifier stage, a high-frequency isolated DC-DC stage, and a DC-AC inverter stage. Replacing the power frequency transformer with a high-frequency transformer can significantly reduce the size and achieve electrical isolation between the input and output sides.

[0004] 2. Adopting, for example Figure 2 The hybrid isolated and non-isolated power electronic transformer (HPET) shown reduces some intermediate isolation DC-DC stages, further reducing the number of power transmission stages and lowering system cost and power loss.

[0005] However, the existing solution has the following problems: 1. Fully isolated power electronic transformers require isolated DC-DC converters to achieve electrical isolation between input and output. The circuit structure is relatively complex and there are many switching devices, resulting in higher costs.

[0006] 2. In HPET, the potential difference between the input and output N points is determined by the switching states. If the input three-phase N points are directly connected to the three converters, the switching states of the negative terminals of the output three phases may overlap with those of the other switches. These switching states are unusable. Firstly, redundant switching results in power loss; secondly, the influence of these switching states may create a potential difference between the input and output, preventing the HPET's input and output three phases from sharing the same N point. In this situation, a common-mode voltage will be generated when driving a three-phase motor, causing bearing current and damaging the motor. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems existing in the prior art and to provide a simplified isolation and non-isolation hybrid power electronic transformer with three-phase N-point cascade.

[0008] The objective of this invention is achieved through the following technical solution: A three-phase N-point cascaded isolated / non-isolated hybrid power electronic transformer is provided, wherein each phase input is connected to the neutral point through a cascaded converter structure; the cascaded converter structure includes multiple rectifier-inverter modules, with a cascaded rectifier structure at the front end and a cascaded inverter structure at the rear end; wherein the positive terminal of the cascaded rectifier structure in the first-end rectifier-inverter module is connected to a certain phase of AC power, and the positive terminal of the cascaded inverter structure in the first-end rectifier-inverter module is connected to a certain phase of AC power from a three-phase motor; The cascaded converter structure includes at least one isolation module, which is disposed at the first end of the cascaded converter structure; When the number of rectifier inverter modules is 3, the second rectifier inverter module has a three-bridge arm structure and the third rectifier inverter module has a two-bridge arm structure; when the number of rectifier inverter modules is greater than 3, the second and subsequent rectifier inverter modules all have a two-bridge arm structure.

[0009] In some embodiments, the isolation module is an isolated DC-DC module.

[0010] In some embodiments, when the number of isolation modules is greater than 1, all isolation modules are located on the same side of the first end of the cascaded converter structure.

[0011] In some embodiments, the negative terminal of the cascaded inverter structure of each rectifier-inverter module is directly connected to the neutral point.

[0012] It should be further noted that the technical features corresponding to the above embodiments can be combined or substituted with each other to form new technical solutions without conflict.

[0013] Compared with the prior art, the beneficial effects of the present invention are: 1. The simplified isolated / non-isolated hybrid power electronic transformer with three-phase N-point cascaded design of this invention connects each phase input to the neutral point via a cascaded converter structure. In this cascaded converter structure, the second rectifier-inverter module has a three-arm structure, while subsequent rectifier-inverter modules have two-arm structures, eliminating the bridge connection between subsequent modules. The negative terminal of the cascaded inverter structure of the second rectifier-inverter module is directly connected to the neutral point. This locks the output potential to the neutral point, discards redundant switches in some arms that are unusable in the switching state, avoids potential differences between the input and output caused by redundant switching states, ensures that the three-phase input and three-phase output share N points, and improves system reliability.

[0014] 2. This invention reduces some of the switching transistors in the non-isolated module of the topology, thereby reducing switching transistor losses, improving efficiency, significantly reducing hardware costs, simplifying control logic, reducing potential fault points in the topology, and enhancing reliability.

[0015] 3. This invention enables input and output to share a common ground, achieving input and output common ground on a non-isolated basis, reducing ground loops and simplifying circuit layout, thereby reducing design complexity and manufacturing costs. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a traditional isolated power electronic transformer topology. Figure 2 This is a schematic diagram of a traditional isolated / non-isolated hybrid power electronic transformer topology; Figure 3 This is a schematic diagram of a three-module cascaded transformer topology with an isolation module at the first end of the present invention; Figure 4 This is a schematic diagram of a four-module cascaded transformer topology with an isolation module at the first end of the present invention; Figure 5 This is a schematic diagram of the N-point topology of the three-module cascaded transformer of the present invention. Detailed Implementation

[0017] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] It should be noted that the defects in the solutions in the prior art are all the results of the inventors' practice and careful research. Therefore, the discovery process of the above problems and the solutions proposed by the embodiments of this application in the following text should be the inventors' contributions to this application in the process of invention and creation, and should not be understood as technical content known to those skilled in the art.

[0019] In one exemplary embodiment, a three-phase N-point cascaded simplified isolation / non-isolation hybrid power electronic transformer is provided, wherein each phase input is connected to the neutral point through a cascaded converter structure; the cascaded converter structure includes multiple rectifier-inverter modules, with a cascaded rectifier structure at the front end and a cascaded inverter structure at the rear end; wherein the positive terminal of the cascaded rectifier structure in the first-end rectifier-inverter module is connected to a certain phase of AC power, and the positive terminal of the cascaded inverter structure in the first-end rectifier-inverter module is connected to a certain phase of AC power from a three-phase motor; The cascaded converter structure includes at least one isolation module, which is disposed at the first end of the cascaded converter structure; When the number of rectifier inverter modules is 3, the second rectifier inverter module has a three-bridge arm structure and the third rectifier inverter module has a two-bridge arm structure; when the number of rectifier inverter modules is greater than 3, the second and subsequent rectifier inverter modules all have a two-bridge arm structure.

[0020] Each phase input is connected to the cascaded converter structure via a reactor. The isolation module is an isolated DC-DC module. When the number of isolation modules is greater than one, all isolation modules are located on the same side of the first end of the cascaded converter structure.

[0021] Furthermore, the negative terminal of the cascaded inverter structure of each rectifier-inverter module is directly connected to the neutral point. This locks the output potential to the neutral point, discarding redundant switches in some bridge arms that are unusable in the switching state, avoiding potential differences between the input and output caused by redundant switching states, ensuring that the three-phase input and three-phase output share N points, and improving system reliability.

[0022] In one example, such as Figure 3 As shown, the cascaded converter structure includes three cascaded rectifier-inverter modules. The first rectifier-inverter module is an isolated module, the second rectifier-inverter module has a three-arm structure, and the third rectifier-inverter module has a two-arm structure, eliminating some of the arm structures. Figure 2 The structure reduces the number of three bridge arms and corresponding switching transistors in the cascaded converter.

[0023] In one example, such as Figure 4 As shown, the cascaded converter structure includes four cascaded rectifier-inverter modules. The first rectifier-inverter module is an isolated module, the second rectifier-inverter module has a three-arm structure, and the third and fourth rectifier-inverter modules have a two-arm structure. Figure 2 The structure reduces the number of five bridge arms and corresponding switches in the cascaded converter. When an isolation module is needed, only one isolation module needs to be added at the beginning and connected in series on the same side. When there are more than three modules, only two bridge arm modules need to be added at the bottom.

[0024] In one example, such as Figure 5 As shown, the input ports of the cascaded converter structure are connected to one phase of the three-phase AC power supply and the neutral point N, respectively. The output ports are connected to one phase of the output three-phase AC motor and the upper N points, achieving a total of N input and output points. When the isolation module is 1 and the number of cascaded rectifier-inverter modules is 3, taking phase A as an example, the positive terminal of the input single-phase power supply is connected to the positive terminal A1P of the first module (isolation module) of the cascaded converter structure via reactor L1. The negative terminal A1N of the rectifier structure of the first module is connected to the positive terminal A2P of the rectifier structure of the second module. The negative terminal A2N of the rectifier structure of the second module is connected to the positive terminal A3P of the rectifier structure of the third module. The negative terminal A3N of the rectifier structure of the third module is connected to the neutral point N.

[0025] The positive terminal B1P of the inverter structure in module 1 is connected to a phase of the three-phase motor. The negative terminal B1N of the inverter structure of module 1 is connected to the positive terminal B2P of the inverter structure of module 2, and then directly connected to the neutral point N, so that the output potential is locked to the neutral point. The connection of the other two phases is similar to phase A, and will not be described in detail here. This invention reduces some of the switching transistors in the non-isolated topology module, reduces switching losses, and avoids the influence of redundant switching states on the three-phase N-point circuit.

[0026] The above detailed embodiments are a description of the present invention. It should not be considered that the specific embodiments of the present invention are limited to these descriptions. For those skilled in the art, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. A three-phase, N-point cascaded simplified isolation / non-isolation hybrid power electronic transformer, characterized in that, Each phase input is connected to the neutral point through a cascaded converter structure; the cascaded converter structure includes multiple rectifier-inverter modules, with a cascaded rectifier structure in the front stage and a cascaded inverter structure in the back stage; wherein, the positive terminal of the cascaded rectifier structure in the first-end rectifier-inverter module is connected to a certain phase of AC power, and the positive terminal of the cascaded inverter structure in the first-end rectifier-inverter module is connected to a certain phase of AC power of the three-phase motor; The cascaded converter structure includes at least one isolation module, which is located at the first end of the cascaded converter structure. When the number of rectifier inverter modules is 3, the second rectifier inverter module has a three-bridge arm structure and the third rectifier inverter module has a two-bridge arm structure; when the number of rectifier inverter modules is greater than 3, the second and subsequent rectifier inverter modules all have a two-bridge arm structure.

2. The three-phase common N-point cascaded simplified isolation and non-isolation hybrid power electronic transformer according to claim 1, characterized in that, The isolation module is an isolated DC-DC module.

3. The three-phase common N-point cascaded simplified isolation and non-isolation hybrid power electronic transformer according to claim 1, characterized in that, When the number of isolation modules is greater than 1, all isolation modules are located on the same side of the first end of the cascaded converter structure.

4. The three-phase common N-point cascaded simplified isolation and non-isolation hybrid power electronic transformer according to claim 1, characterized in that, The negative terminal of the cascaded inverter structure of each rectifier-inverter module is directly connected to the neutral point.

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