Three-phase n-point cascaded simplified isolation-non-isolation hybrid power electronic transformer

Abstract

The application discloses a three-phase common N-point cascade type simplified isolation non-isolation hybrid power electronic transformer, and belongs to the technical field of transformers. Each phase input is connected to a neutral point through a cascade converter structure. The cascade converter structure comprises a plurality of rectification inversion modules, the front stage of the rectification inversion modules is a cascade rectification structure, and the rear stage of the rectification inversion modules is a cascade inversion structure. The cascade converter structure comprises at least one isolation module, and the isolation module is arranged at the first end of the cascade converter structure. When the number of the rectification inversion modules is 3, the second rectification inversion module is a three-bridge-arm structure, and the third rectification inversion module is a two-bridge-arm structure. When the number of the rectification inversion modules is greater than 3, the rectification inversion modules after the second rectification inversion module are all two-bridge-arm structures. The application reduces part of switch tubes of a non-isolation module of a topology, reduces switch loss and tube loss, and avoids the influence of redundant switch states on three-phase common N points.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of transformers, and in particular to a three-phase common N-point cascaded simplified isolation-non-isolation hybrid power electronic transformer. BACKGROUND

[0002] Three-phase-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, the power frequency transformer has problems such as high cost, large size, and low power density.

[0003] To solve this problem, the main solution in the industry at present is:

[0004] 1. Use a full-isolation power electronic transformer as shown in Figure 1 The typical architecture is composed of an AC-DC rectifier stage, a high-frequency isolation 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.

[0005] 2. Use an isolation-non-isolation hybrid power electronic transformer (HPET) as shown in Figure 2 It reduces the number of intermediate isolation DC-DC stages, further reduces the number of power transmission stages, and reduces system cost and power loss.

[0006] However, the existing solutions have the following problems:

[0007] 1. The full-isolation power electronic transformer needs to use isolation DC-DC to achieve electrical isolation between the input and output. The circuit structure is complex, and there are many switching devices, resulting in high cost.

[0008] 2. In the HPET, the potential difference between the input and output N points is determined by the switching state. If the input three-phase N points are directly connected to the three converters, the negative terminals of the output three-phase will have repeated switching states with other switching tubes. This part of the switching state cannot be used. On the one hand, the redundant switches have power loss, and on the other hand, under the influence of this part of the switching state, a potential difference may be generated between the input and output, causing the input three-phase and output three-phase of the HPET to not share the N point. In this case, driving the three-phase motor will generate common-mode voltage, causing bearing current damage to the motor. SUMMARY

[0009] The present application aims to overcome the problems in the prior art and provide a three-phase common N-point cascaded simplified isolation-non-isolation hybrid power electronic transformer.

[0010] The purpose of the present application is achieved by the following technical solutions:

[0011] Provided is a three-phase common N-point cascade type isolation non-isolation hybrid power electronic transformer, each phase input being connected to a neutral point through a cascade converter structure; the cascade converter structure comprises a plurality of rectification inversion modules, a front stage of which is a cascade rectification structure and a rear stage of which is a cascade inversion structure; wherein a positive terminal of the cascade rectification structure in a first rectification inversion module is connected to an AC power of a certain phase, and a positive terminal of the cascade inversion structure in the first rectification inversion module is connected to an AC power of a certain phase of a three-phase motor;

[0012] The cascade converter structure comprises at least one isolation module, and the isolation module is arranged at a first end of the cascade converter structure.

[0013] When the number of rectification inversion modules is 3, the second rectification inversion module is a three-bridge arm structure, and the third rectification inversion module is a two-bridge arm structure; when the number of rectification inversion modules is greater than 3, the rectification inversion modules after the second rectification inversion module are all two-bridge arm structures.

[0014] In some embodiments, the isolation module is an isolation type DC-DC module.

[0015] In some embodiments, when the number of isolation modules is greater than 1, the isolation modules are all arranged on the same side of the first end of the cascade converter structure.

[0016] In some embodiments, a negative terminal of the cascade inversion structure of each rectification inversion module is directly connected to the neutral point.

[0017] It should be further pointed out that the technical features corresponding to the above-mentioned embodiments can be combined or replaced with each other to form new technical solutions without conflict.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] 1. The three-phase common N-point cascade type simplified isolation non-isolation hybrid power electronic transformer of the present application connects each phase input to a neutral point through a cascade converter structure, in the cascade converter structure, the second rectification inversion module is a three-bridge arm structure, and the rectification inversion modules after the second rectification inversion module are all two-bridge arm structures, the cross-bridge connection between the subsequent modules is cancelled, and the negative terminal of the cascade inversion structure of the second rectification inversion module is directly connected to the neutral point. The potential of the output side is locked to the neutral point, the redundant switching tubes of part of the bridge arms in the unusable switching state are discarded, the potential difference between the input and the output caused by the influence of the redundant switching state is avoided, the input three-phase and the output three-phase are common to N points, and the reliability of the system is improved.

[0020] 2. The present application reduces part of the switching tubes of the non-isolation module of the topology, reduces the switching tube loss, thereby improving the efficiency, significantly reducing the hardware cost, simplifying the control logic, reducing the potential fault points existing in the topology, and enhancing the reliability.

[0021] 3. The application makes input and output common, realizes input and output common on the basis of non-isolation, reduces the ground loop and simplifies the circuit layout, and reduces design complexity and manufacturing cost. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a schematic diagram of a traditional isolated power electronic transformer topology;

[0023] Figure 2 It is a schematic diagram of a traditional isolated non-isolated hybrid power electronic transformer topology;

[0024] Figure 3 It is a schematic diagram of a three-module cascaded transformer topology of a first-end isolated module of the application;

[0025] Figure 4 It is a schematic diagram of a four-module cascaded transformer topology of a first-end isolated module of the application;

[0026] Figure 5 It is a schematic diagram of a common N-point topology structure of a three-module cascaded transformer of the application. DETAILED DESCRIPTION

[0027] The technical solutions of the application will be described clearly and completely below in combination with the drawings. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. The components of the embodiments of the application described and shown in the drawings can be arranged and designed in various different configurations. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0028] It should be noted that the defects in the above prior art solutions are the results obtained by the inventors after practice and careful study. Therefore, the discovery process of the above problems and the solutions proposed by the embodiments of the application to the above problems should be the contributions made by the inventors to the application in the process of invention and creation, and should not be understood as technical content known to those skilled in the art.

[0029] In an exemplary embodiment, a three-phase common N-point cascaded simplified isolated non-isolated hybrid power electronic transformer is provided, and each phase input is connected to the neutral point through a cascaded converter structure; the cascaded converter structure includes a plurality of rectifier-inverter modules, the front stage of which is a cascaded rectifier structure, and the rear stage of which is a cascaded inverter structure; wherein the positive end of the cascaded rectifier structure in the first-end rectifier-inverter module is connected to the AC power of a certain phase, and the positive end of the cascaded inverter structure in the first-end rectifier-inverter module is connected to the AC power of a certain phase of a three-phase motor;

[0030] The cascade converter structure comprises at least one isolation module, and the isolation module is arranged at the head end of the cascade converter structure.

[0031] When the number of rectification inversion modules is 3, the second rectification inversion module is a three-bridge-arm structure, and the third rectification inversion module is a two-bridge-arm structure; when the number of rectification inversion modules is greater than 3, the rectification inversion modules after the second rectification inversion module are all two-bridge-arm structures.

[0032] The input of each phase is connected to the cascade converter structure through a reactor. The isolation module is an isolation type DC-DC module. When the number of isolation modules is greater than 1, the isolation modules are all arranged on the same side of the head end of the cascade converter structure.

[0033] Further, the negative end of the cascade inversion structure of each rectification inversion module is directly connected to the neutral point, so that the potential of the output side is locked to the neutral point, the redundant switch tubes of part of the bridge arms in the unusable switch state are discarded, the potential difference between the input and the output caused by the influence of the redundant switch state is avoided, the input three-phase and the output three-phase share the N point, and the reliability of the system is improved.

[0034] In an example, as shown in Figure 3 The cascade converter structure comprises three cascaded rectification inversion modules, the head end rectification inversion module is an isolation module, the second rectification inversion module is a three-bridge-arm structure, and the third rectification inversion module is a two-bridge-arm structure. Part of the bridge arm structure is cancelled, and compared with the structure of Figure 2 , 3 bridge arms and corresponding switch tubes of the cascade converter are reduced.

[0035] In an example, as shown in Figure 4 The cascade converter structure comprises four cascaded rectification inversion modules, the head end rectification inversion module is an isolation module, the second rectification inversion module is a three-bridge-arm structure, and the third and fourth rectification inversion modules are two-bridge-arm structures. Compared with the structure of Figure 2 , 5 bridge arms and corresponding switch tubes of the cascade converter are reduced. When it is necessary to increase the isolation module, the isolation module is only needed to be added at the head end and connected in series on the same side, and when the number of modules is greater than 3, the two-bridge-arm module is only needed to be added below.

[0036] In an example, as shown in Figure 5As shown, the input side ports of the cascade converter structure are connected to one phase of the three-phase AC and the neutral point N respectively, and the output side ports are connected to one phase of the output three-phase AC motor and the N point respectively, realizing the input and output common N point. When the isolation module is 1 and the number of cascade rectifier-inverter modules is 3, taking the A phase as an example, the positive terminal of the input single-phase power is connected to the positive terminal A1P of the first module (isolation module) of the cascade converter structure through the 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, and the negative terminal A3N of the rectifier structure of the third module is connected to the neutral point N.

[0037] The positive terminal B1P of the inverter structure of the first module is connected to a phase of the three-phase motor ), the negative terminal B1N of the inverter structure of the first module is connected to the positive terminal B2P of the inverter structure of the second module, and then directly connected to the neutral point N, so that the potential of the output side is locked to the neutral point. The connections of the other two phases are similar to the A phase, which will not be described here. The present application reduces the number of switches of the non-isolation module of the topology, reduces the switching loss and tube loss, and avoids the influence of redundant switch states on the three-phase common N point.

[0038] The above specific embodiments are detailed descriptions of the present application, which cannot be considered as limiting the specific embodiments of the present application to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, some simple deductions and substitutions can be made without departing from the concept of the present application, which should be considered as belonging to the protection scope of the present application.

Claims

1. A three-phase N-point cascaded simplified isolated non-isolated hybrid power electronic transformer, characterized in that, Each phase input is connected to a neutral point through a cascaded converter structure; the cascaded converter structure comprises a plurality of rectifier-inverter modules, the front stage of which is a cascaded rectifier structure and the rear stage of which is a cascaded inverter structure; wherein the positive end of the cascaded rectifier structure in the first rectifier-inverter module is connected to the AC power of a certain phase, and the positive end of the cascaded inverter structure in the first rectifier-inverter module is connected to the AC power of a certain phase of the three-phase motor; the negative end of the cascaded inverter structure of each rectifier-inverter module is directly connected to the neutral point; The cascaded converter structure comprises at least one isolation module, and the isolation module is arranged at the front end of the cascaded converter structure. When the number of rectifier-inverter modules is 3, the second rectifier-inverter module is a three-bridge arm structure, and the third rectifier-inverter module is a two-bridge arm structure; when the number of rectifier-inverter modules is greater than 3, the rectifier-inverter modules after the second are all two-bridge arm structures, and the cross-bridge connection between the subsequent rectifier-inverter modules is cancelled, so that the potential of the output side is locked to the neutral point.

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

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

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