Simplified non-isolated cascaded power electronic transformer with no load and system

Abstract

The invention discloses a simplified non-isolated cascade type power electronic transformer and system with no load, and belongs to the field of transformers, the power electronic transformer comprises a cascade structure formed by a plurality of rectification and inversion modules, the front stage of the cascade structure is a cascade rectification structure, and the rear stage of the cascade structure is a cascade inversion structure; the cascade structure comprises at least one no-load module, and the no-load module is arranged at the head end or the tail end of the cascade structure; when the number of the rectification inversion modules is 3, the other two rectification inversion modules are three-bridge-arm modules; and when the number of the rectification and inversion modules is greater than 3, the rectification and inversion module between the two three-bridge-arm modules is a two-bridge-arm module. According to the invention, a part of switching tubes in the non-isolated power electronic transformer with the no-load module are canceled, so that the cost of the converter can be reduced and the working efficiency can be improved on the premise of ensuring the original working range.

Description

Technical Field

[0001] This invention relates to the field of transformer technology, and in particular to a simplified non-isolated cascaded power electronic transformer and system with no-load operation. Background Technology

[0002] In-phase power supply devices can eliminate the need for phase separation within the traction power supply system and improve the power quality of three-phase power grids. Among these, in-phase power supply systems based on multi-tap transformers offer advantages such as input / output isolation and simple control modulation, and have been widely used in practical engineering. However, in-phase power supply systems based on multi-tap transformers also suffer from problems such as large size, low power density, and high cost.

[0003] The industry currently offers three main solutions to this problem: 1. Adopt Figure 1 The isolated power electronic transformer shown uses a high-frequency isolated DC-DC module to replace the bulky, low-power-density power frequency multi-tap transformer, thus achieving input-output isolation.

[0004] 2. Adopt Figure 2 The non-isolated power electronic transformer shown has a back-to-back single-module DC capacitor shared by the H-bridge converter with cascaded input and output. This topology completely eliminates the power frequency or high frequency isolation unit, resulting in the lowest cost.

[0005] 3. Using the non-isolated power electronic transformer with no-load module shown in Figure 3, this topology increases the range of input and output port level difference of the non-isolated converter through the no-load module, thereby improving the phase-shifting operating range of the converter.

[0006] The above-mentioned transformer has the following problems: 1. Fully isolated power electronic transformers do not have short-circuit paths, but the introduction of isolated DC-DC modules increases the number of power transmission stages, reduces system efficiency, and greatly increases the cost of in-phase power supply systems.

[0007] 2. Non-isolated power electronic transformers lack isolation modules, but due to short-circuit path limitations, many switching states are unavailable, restricting their operating range. In high-voltage scenarios requiring a large number of modules and high modulation depths, they cannot meet the phase-shifting requirements of traction transformers.

[0008] 3. The addition of the no-load module can expand the operating range of the power electronic transformer without significantly increasing the cost of the non-isolated power electronic transformer. However, when avoiding short-circuit paths, some switching transistors have overlapping switching states with other switching transistors, resulting in some switching transistors being practically useless during vector synthesis. Summary of the Invention

[0009] The purpose of this invention is to overcome the problems existing in the prior art and to provide a simplified non-isolated cascaded power electronic transformer and system with no-load operation.

[0010] The objective of this invention is achieved through the following technical solution: In one aspect, a simplified non-isolated cascaded power electronic transformer with no-load is provided, comprising a cascaded structure formed by multiple rectifier and inverter modules, wherein the front stage of the cascaded structure is a cascaded rectifier structure and the rear stage of the cascaded structure is a cascaded inverter structure. The cascaded structure includes at least one unloaded module, which is located at the first or last end of the cascaded structure. When the number of rectifier-inverter modules is 3, the other two rectifier-inverter modules are three-arm modules; when the number of rectifier-inverter modules is greater than 3, the rectifier-inverter module between the two three-arm modules is a two-arm module.

[0011] In some embodiments, when the number of unloaded modules is greater than 1, the unloaded modules are located on the same side of the first or last end of the cascaded structure.

[0012] Secondly, a traction network in-phase power supply system is provided, comprising a simplified non-isolated cascaded power electronic transformer with no-load as described in the first aspect, wherein the first end of the cascaded rectifier structure is connected to the positive terminal of the input single-phase power, the first end of the cascaded inverter structure is connected to the positive terminal of the output single-phase power, the last end of the cascaded rectifier structure is connected to the negative terminal of the input single-phase power, and the last end of the cascaded inverter structure is connected to the negative terminal of the output single-phase power.

[0013] 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.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. Compared to fully isolated power electronic transformers, the proposed topology does not require DC-DC isolation, reducing system size and cost; compared to non-isolated power electronic transformers, the proposed topology expands the usable vector boundary by utilizing unloaded modules.

[0015] 2. Compared with non-isolated power electronic transformers based on no-load operation, the proposed topology eliminates some switches, reduces system cost, and further reduces system switching losses.

[0016] 3. The proposed topology reduces the number of switches that have no practical switching significance, eliminates switching paths that may lead to short circuits, and avoids possible capacitor series-parallel short circuits, which can simplify the implementation of the modulation strategy. Attached Figure Description

[0017] Figure 1 This is a non-phase power supply system based on an isolated power electronic transformer; Figure 2 shows a non-isolated power electronic transformer-based in-phase power supply system; Figure 3 shows a non-isolated power electronic transformer with an unloaded module; Figure 4 is a topology diagram of the present invention when there is one unloaded module at the beginning of the three modules; Figure 5 is a topology diagram of the present invention when there is one unloaded module at the beginning of the four modules; Figure 6 is a topology diagram of the present invention when there is one unloaded module at the beginning of the five modules; Figure 7 shows the application of the proposed topology in the traction network when there is one unloaded module at the tail end. Detailed Implementation

[0018] 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.

[0019] 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.

[0020] This invention proposes a novel simplified non-isolated power electronic transformer topology with an unloaded module. This topology simplifies some of the switching transistors in a traditional non-isolated power electronic transformer with an unloaded module.

[0021] In one exemplary embodiment, such as Figure 4 As shown, when the number of cascaded rectifier-inverter modules is 3, the unloaded module is at the first end, and the other two rectifier-inverter modules are three-arm modules, relative to... Figure 3 The topology reduces the number of bridge arms of the cascaded converter by two.

[0022] In an exemplary embodiment, when the unloaded module is at the first end and the number of unloaded modules is 1, and the number of cascaded rectifier-inverter modules is 4, the proposed topology is as follows: Figure 5 As shown, the rectifier-inverter module between the two three-arm modules is a two-arm module, relative to... Figure 3 The topology reduces the number of four bridge arms in the cascaded converter.

[0023] In an exemplary embodiment, when the unloaded module is at the first end and the number of unloaded modules is 1, and the number of cascaded rectifier-inverter modules is 5, the proposed topology is as follows: Figure 6 As shown, the rectifier-inverter module between the two three-arm modules is a two-arm module, and the number of two-arm modules is two. Relative to... Figure 3 The topology reduces the number of bridge arms of the cascaded converter by 6.

[0024] Furthermore, when it is necessary to add unloaded modules, they only need to be added on the same side at both ends. "Same side" means that all newly added unloaded modules must be centrally located in the first or last area; they are not allowed to be scattered among non-isolated modules or dispersed at the first and last ends. For example, if two unloaded modules are required, both modules should be simultaneously placed on the input or output side of the cascaded structure, and the unloaded modules should be directly connected in series.

[0025] In an exemplary embodiment, when the unloaded module is 1 and at the tail end, the connection of the proposed topology in the traction network is as follows: Figure 7 As shown, the front stage is a cascaded rectifier structure, and the rear stage is a cascaded inverter structure. The first module to the (n-1)th module are cascaded non-isolated modules. The positive terminal of the input α phase is connected to the positive input A1P of the cascaded rectifier structure through a bridge arm and reactor L1. The negative terminal A1N of the first module is connected to the positive terminal A2P of the second module in the front stage. The negative terminal A2N of the second module in the front stage is connected to the positive terminal A3P of the third module in the front stage. This connection continues to the (n-1)th module of the cascaded rectifier (the last non-isolated module). Finally, the negative terminal An-1N of the (n-1)th module is connected to the positive terminal AnP of the unloaded module in the front stage. The negative terminal AnN of the unloaded module in the front stage is connected to the negative terminal of the α phase. Similarly, in the cascaded inverter structure, the positive terminal B1P of the first module is connected to the positive terminal of the β phase via reactor L2; the bridge arm output Bn-1P of the (n-1)th non-isolated module is connected to the positive terminal BnP of the subsequent unloaded module; and the negative terminal BnN of the subsequent unloaded module is connected to the negative terminal of the β phase. Wherein, C 1~ C n-1 It is connected in parallel between the positive and negative terminals of the DC bus of each module, absorbing / releasing energy during rectification to maintain the stability of the DC bus voltage. It provides continuous energy to the load during the inverter process.

[0026] As can be seen from the above embodiments, the proposed topology eliminates some switches, reducing system cost and further reducing system switching losses. Simultaneously, by reducing the number of switches with no practical switching function in the unloaded non-isolated hybrid power electronic transformer, potential short-circuit paths are eliminated, avoiding possible capacitor series-parallel short circuits and simplifying the implementation of the modulation strategy. Specifically, by eliminating the bidirectional switch between the unloaded module and the non-isolated module and replacing it with a direct DC bus connection, capacitor parallel short circuits are avoided; by removing the bridging arm and retaining only a single path between adjacent modules, capacitor series short circuits are avoided.

[0027] 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 simplified non-isolated cascaded power electronic transformer with no-load capability, characterized in that, The system includes a cascaded structure formed by multiple rectifier and inverter modules, wherein the front stage of the cascaded structure is a cascaded rectifier structure and the rear stage of the cascaded structure is a cascaded inverter structure. The cascaded structure includes at least one unloaded module, which is located at the first or last end of the cascaded structure. When the number of rectifier-inverter modules is 3, the other two rectifier-inverter modules are three-arm modules; when the number of rectifier-inverter modules is greater than 3, the rectifier-inverter module between the two three-arm modules is a two-arm module.

2. A simplified non-isolated cascaded power electronic transformer with no-load capability according to claim 1, characterized in that, When the number of unloaded modules is greater than 1, the unloaded modules are located on the same side of the first or last end of the cascaded structure.

3. A traction network in-phase power supply system, characterized in that, The present invention comprises a simplified non-isolated cascaded power electronic transformer with no-load as described in any one of claims 1-2, wherein the first end of the cascaded rectifier structure is connected to the positive terminal of the input single-phase power, the first end of the cascaded inverter structure is connected to the positive terminal of the output single-phase power, the last end of the cascaded rectifier structure is connected to the negative terminal of the input single-phase power, and the last end of the cascaded inverter structure is connected to the negative terminal of the output single-phase power.

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