Power Conversion Device

Abstract

To provide a power conversion device which can miniaturize a transformer generating multiphase voltage.SOLUTION: A transformer 1 comprises: a primary side first coil 11 which is connected to a three-phase power supply 3; and a second coil 12 and a third coil 13 which constitute a secondary side to generate mutually-different three-phase power. The first coil 11 and the second coil 12 are star-connected. Three coils of the third coil 13 are formed by being branched from a position of 73% from a neutral point Q of the second coil 12. The third coil 13 after branching is wound around an iron core 4 in a different phase from the second coil 12 of the branching base by the winding number of 73% of the second coil 12 to generate the three phases. The voltage of the six phases is output from the secondary side in synchronization with the output of each phase of the second coil 12, and becomes the positive electrode waveform of the twelve phases after rectification by a full wave rectification circuit 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power conversion device that converts three-phase AC power into polyphase power using a transformer, and then converts it into DC power. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there has been a power conversion device that converts three-phase AC power into DC power using a transformer and a rectifier in order to obtain high-voltage DC power. For example, in Patent Document 1, a transformer having a star-connected primary winding, a star-connected secondary winding, and a delta-connected tertiary winding is used, a three-phase AC power supply is connected to the primary winding, and a total of 12 phases of voltage are generated by the secondary winding and tertiary winding, which are then rectified to generate DC power. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-295155 Summary of the Invention [Problem to be solved by the invention]

[0004] The transformer of the power conversion device disclosed in Patent Document 1 generates a 12-phase voltage by providing two windings, one star-connected and one delta-connected, on the secondary side as described above, making it possible to obtain a voltage with smaller ripples than when three-phase AC is directly rectified, and simplifying the equipment required for smoothing. However, since the two windings, the delta-connected winding on the secondary side of the transformer and the star-connected winding on the tertiary side, both have the same number of turns and are large, the core could not be made smaller and the transformer was large.

[0005] In view of the above problems, the present invention has an object to provide a power conversion device that can reduce the size of a transformer that generates polyphase voltages. [Means for solving the problem]

[0006] In order to solve the above problem, the invention of claim 1 is a power conversion device that uses a transformer to convert three-phase power into polyphase power, and rectifies the converted polyphase power with rectifying means for direct current conversion, characterized in that the transformer has a first winding on the primary side to which a three-phase power source is connected, and second and third windings that constitute the secondary side and generate different three-phase power, wound around a common iron core having different legs for each phase, the first winding is connected in either a delta connection or a star connection, while the second winding is star connected, and the three windings of the third winding are each formed by branching off from positions 73% from the neutral point of each winding of the second winding, and the branched third windings are wound on iron cores of phases different from the second winding of the branch base with 73% of the number of turns of the second winding to generate three phases, and a current of six phases, combined with the output of each phase of the second winding, is output from the secondary side. [Effects of the Invention]

[0007] According to the present invention, the third winding is formed by branching off from the middle of the second winding, so that the second winding can take over part of the winding, reducing the number of turns, and thus reducing the number of turns of the entire transformer, making it possible to make it smaller. In addition, the third winding is branched off at a position 73% from the neutral point of the second winding, and is wound around an iron core of a different phase from the second winding at the branch base with 73% of the number of turns of the second winding.This makes it possible for the second and third windings to make the waveform after full-wave rectification into a waveform with a total of 12 phases that is 30 degrees out of phase, making it possible to obtain direct current with little ripple. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a circuit diagram showing an example of a power conversion device according to the present invention. [Figure 2] 2 is a vector explanatory diagram of the voltages of each phase of the transformer in FIG. 1, where (a) shows the phase voltage of the primary winding, and (b) shows the phase voltage of the second and third windings, which are secondary windings. [Figure 3] 1A and 1B are diagrams illustrating the line voltage on the secondary side, where (a) is a vector diagram and (b) is a waveform diagram. [Figure 4] FIG. 10 is an explanatory diagram of transformer connections showing another embodiment of the power conversion device. [Figure 5] 5 shows a vector diagram of the voltages of each phase on the secondary side of the transformer in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009]

[0016] The present invention will be described in detail below with reference to the accompanying drawings, in which:

[0017] Fig. 1 is a circuit diagram showing an example of a power conversion device according to the present invention, which includes a transformer 1 that converts three-phase power supplied from a three-phase power source 3 into multi-phase power, and a full-wave rectifier circuit 2 that serves as rectifier means for rectifying the secondary side output of the transformer 1; The transformer 1 has three windings: a first winding 11 constituting the primary winding L1, a second winding 12 constituting the secondary winding L2, and a third winding 13. Each has three winding sections (11a-11c, 12a-12c, 13a-13c) to accommodate three-phase power, and all are star-connected. However, as will be described later, a portion of the third winding 13 is shared with the second winding 12. The three phases are referred to as R phase, S phase, and T phase, and in FIG. 1, they are described as R phase, S phase, and T phase from left to right.

[0010] Each phase of a three-phase power supply 3 is connected to three terminals (primary terminals) R1, S1, and T1 of the first winding 11. The second winding 12 has three output terminals (secondary terminals) R2, S2, and T2, and the third winding 13 has three output terminals (secondary terminals) R3, S3, and T3, each of which outputs three-phase power.

[0011] The iron core 4 around which each winding is wound has three legs 4a to 4c for generating three-phase power, and the winding portions (11a to 11c, 12a to 12c, 13a to 13c) of each winding 11, 12, 13 are wound around these three legs 4a to 4c for each phase. However, the third winding 13 is formed by branching off from the middle of the second winding 12. To be precise, it branches off at a position 73% from the neutral point Q and is wound around an iron core leg of a different phase from the second winding 12 at the branch base.

[0012] Specifically, the R-phase winding 13a of the third winding 13 branches off from the T-phase winding 12c of the second winding 12, and the S-phase winding 13b of the third winding 13 branches off from the R-phase winding 12a of the second winding 12. The T-phase winding 13c of the third winding 13 branches off from the S-phase winding 12b of the second winding 12. The third winding 13 has fewer turns than the second winding 12, and the ratio between the second winding 12 and the third winding 13 is 1:(√3-1) for reasons described below. In other words, the third winding 13 has approximately 73% of the number of turns of the second winding 12.

[0013] Figure 2 shows a vector diagram of the voltages generated in each phase of the transformer 1 configured as above, where (a) shows the voltages of each phase of the primary winding L1, and (b) shows the voltages of each phase of the secondary winding L2. The R-phase voltage V of the primary winding (first winding 11) R1 , S-phase voltage V S1 , T-phase voltage V T1 , and the R-phase voltage V of the second winding 12 on the secondary side R2 , S-phase voltage V S2 , T-phase voltage V T2 have a phase difference of 120 degrees from each other. On the other hand, the R-phase voltage V of the tertiary winding 13 R3 , S-phase voltage V S3 , T-phase voltage V T3 In this case, each winding of the third winding is branched off from the second winding, so that the neutral point Q is common to the second winding 12 as shown in FIG. 2, and the third winding 13 is star-connected as a whole.

[0014] Furthermore, as shown in FIG. 2(b), the three-phase voltage V output from the second winding 12 R2 , V S2 , V T2 , generates a voltage in phase with the primary winding L1, but the voltage V generated by the third winding 13 R3 , V S3 , V T3 In this case, a voltage that leads (or lags) by 120 degrees with respect to each phase of the secondary winding 12 is generated. The output voltage of the third winding 13 alone is 73% of that of the second winding 12 due to the winding ratio with the second winding 12.

[0015] FIG. 3 is an explanatory diagram of the voltage (inter-terminal voltage) generated at the T2 and T3 terminals when the R2 terminal is used as the reference, where (a) is a vector diagram and (b) is a waveform diagram. The reasons for the branching position of the third winding 13 from the second winding 12 at 73% and the turns ratio of the third winding 13 to the second winding 12 at 1:0.73 will be explained with reference to FIG. In Figure 3, the voltage between R2 and T3, V R1-T3 The magnitude of the voltage V between R2 and T2 R2-T2 To generate such a voltage, the voltage e between the neutral point Q and T3 terminals of the third winding 13 is set as shown in FIG. T3 However, there must be a phase difference of 180 degrees with the R2 terminal, and the generated voltage must be √3-1 times the second winding 12, i.e., 73% of the magnitude. Therefore, the voltage vector e taken over by the second winding 12 is S2 and the voltage V generated in the third winding 13 S2-T3 The absolute values ​​of the phase voltages are set equal to each other and the magnitude is set to 73% of the phase voltage of the second winding 12.

[0016] As a result, the voltages at the T2 and T3 terminals, with the R2 terminal as the reference, have waveforms with the same absolute value but a phase difference of 30 degrees, as shown in Figure 3. Similarly, the voltages at the R2 and R3 terminals, with the S2 terminal as the reference, and the voltages at the S2 and S3 terminals, with the T2 terminal as the reference, have waveforms with the same absolute value but a phase difference of 30 degrees.

[0017] The terminal voltage generated in this way generates six waveforms, each shifted by 30 degrees within a 180-degree phase. Therefore, when these generated voltages are full-wave rectified, 12 positive-polarity waveforms can be generated, each shifted by 30 degrees within a 360-degree phase, making it possible to obtain DC with little ripple. Furthermore, because the third winding 13 is formed by branching off from the middle of the second winding 12, part of the winding can be taken over by the second winding 12, reducing the number of turns. As a result, the number of turns in the entire transformer 1 can be reduced, enabling miniaturization.

[0018] 4 shows another embodiment of a power conversion device, which differs from the above embodiment in the configuration of the transformer 1. The winding destination of the third winding 13 branched from the second winding 12 differs from the above embodiment, with the third winding 13 branched from the S-phase of the second winding 12 wound around the R-phase leg 4a, the third winding 13 branched from the T-phase of the second winding 12 wound around the S-phase leg 4b, and the third winding 13 branched from the R-phase of the second winding 12 wound around the T-phase leg 4c. The branching position of the third winding 13 from the second winding 12 and the number of turns of the third winding are the same as those of the above embodiment.

[0019] Fig. 5 is a vector diagram of the secondary winding L2 in the case of the connection in Fig. 4. As shown in Fig. 5, the above configuration differs from the above configuration in that the voltage V generated by the third winding 13 R3 , V S3 , V T3 The magnitudes are the same, but the phases are 120 degrees different. The voltage generated by the third winding 13 may have such a voltage phase, and the line voltage generated on the secondary side is similar to the above-described form. For example, the voltages at the T2 terminal and the T3 terminal with the R2 terminal as the reference have waveforms with the same absolute values ​​and a phase difference of 30 degrees. The waveform after rectification can be made into a 12-phase positive waveform, making it possible to obtain DC with small ripples.

[0020] In the above embodiment, the primary winding 11 is star-connected, but may be delta-connected. [Explanation of symbols]

[0021] 1·· Transformer, 2·· Full-wave rectifier circuit (rectification means), 3·· Three-phase power supply, 4·· Iron core, 11·· First winding, 12·· Second winding, 13·· Third winding, L1·· Primary winding, L2·· Secondary winding.

Claims

[Claim 1] A power conversion device that converts three-phase power into polyphase power using a transformer, and rectifies the converted polyphase power with a rectifier to convert it into direct current, The transformer has a first winding on a primary side to which a three-phase power supply is connected, and second and third windings constituting a secondary side and generating different three-phase power respectively, wound around a common iron core having different legs for each phase; the first winding is connected in either a delta connection or a star connection, the second winding is star connected, and three windings of the third winding are formed by branching off from positions 73% from the neutral point of each winding of the second winding, The third winding after branching is wound around an iron core of a different phase from the second winding of the branch base with 73% of the number of turns of the second winding, thereby generating three phases, and a six-phase current, combined with the outputs of each phase of the second winding, is output from the secondary side.

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