GB2433653A

GB2433653A - Multiplex rectifier circuit

Info

Publication number: GB2433653A
Application number: GB0525261A
Authority: GB
Inventors: Shigeo Takata; Shinsaku Kusube
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2004-07-29
Filing date: 2004-07-29
Publication date: 2007-06-27
Anticipated expiration: 2024-07-29
Also published as: CN1809954B; JPWO2006011206A1; WO2006011206A1; JP4440263B2; GB2433653B; CN1809954A; GB0525261D0

Abstract

A multiplex transformer capable of not only suppressing low order harmonic components sufficiently but also suppressing all harmonic components with good balance while suppressing an increase in size of a DC reactor passing a multiplexed DC current. Since the turn ratio of the multiplex transformer (10) is selected to be one that can not only suppress harmonics of a specified order but also suppress all harmonics with good balance and AC reactors (9, 7) are inserted in order to suppress harmonics furthermore, all harmonic components can be suppressed with good balance in addition to sufficient suppression of low order harmonic components while suppressing an increase in size of the DC reactor (3) passing a multiplexed DC current, and not only national regulations but also European regulations can be dealt with.

Description

-DESCRIPTION

MULTIPLEX RECTIFIER CIRCUIT

TECHNICAL FIELD

[0001] The present invention relates to a multiplex rectifier circuit that converts a three-phase alternating current (AC) power supply into a direct current (DC) power Supply having fewer harmonic components.

BACKGROUND ART

[0002] To convert a three-phase AC into a DC, the most common approach is to use a three-phase full-wave rectifier that includes six bridged rectifying elements. In this three-phase full-wave rectifier, the rectifying elements are applied with a current and they are sequentially switched over at 60 degrees intervals thereby outputting a rectified DC voltage. As a result, the rectified DC voltage has a cycle six times as long as that of a power supply frequency and includes a large voltage ripple. This turns into harmonics, which adversely influences an apparatus that uses the rectified DC voltage as a power supply.

[0003] To solve the disadvantage, Patent documents 1 and 2, for example, propose a multiplex rectifier circuit configured as follows. While a first rectifier circuit that converts ACs in three phases into DCs is provided, a multiplex transformer that transforms the ACs in three phases into six multiplex AC voltages in changed phases, and a second rectifier circuit that converts the six AC voltages output from this multiplex transformer into six DC voltages are provided. The DC voltages output from the first rectifier circuit are multiplexed with the DC voltages output from the second rectifier circuit, thereby obtaining a DC power supply having fewer harmonic components.

[0004] As the multiplex transformer, the Patent document 1 discloses a transformer that transforms AC voltages in three phases into AC voltages in a total of six phases located at points obtained by trisecting three circular arcs drawn by connecting each of three vertexes to two other vertexes of a equilateral triangle representing a relationship among voltages in an R phase, an S phase, and a T phase of the three-phase ACs in a transformer-vector diagram of the triangle.

[0005] As the multiplex transformer, the Patent document 2 discloses a transformer that inputs a three-phase AC and outputs two types of three-phase ACs in delayed phases by 20 degrees from a phase of the input three-phase AC in electric angle, respectively. Specifically, this transformer satisfies a transformer-vector diagram drawn relative to a transformer-vector diagram of a equilateral triangle that represents the relationship among voltages in three phases of the three-phase AC. Namely, the transformer-vector diagram of the hexagon is drawn by lines passing two respective points obtained by trisecting each of the circular arcs drawn by connecting each of the three vertexes of the equilateral triangle to two other vertexes, and lines passing the three respective vertexes of the equilateral triangle and parallel to sides facing the three respective vertexes. The transformer includes first coils and second coils respectively wound around cores corresponding to the three phases. One ends of the first coils, which are equal in polarity, are sequentially connected to one ends of the second coils in different phase, respectively. The other ends of the first coils, which are equal in polarity, are sequentially connected to the other ends of the second coils in different phases in a different combination from that for connection of the one ends. It is assumed that a, b, and c are equal to or greater than 2. A first tap is provided at an intermediate position of each first coil in the number of turns while the number of turns of each first coil is 2a. A second tap is provided at an inside position of each second coil by as much as the number of turns b from one end of the second coil while the number of turns of the second coil is (2b+c) A third tap is provided at an inside position of each second coil by as much as the number of turns b from the other end thereof. The first taps corresponding to the three respective phases serve as input terminals of the three-phase AC voltages, and the second taps corresponding to the three respective phases serve as first output terminals of the three-phase AC voltages. The third taps corresponding to the three respective phases serve as second output terminals of the three-phase AC voltages. A ratio of the numbers of turns a, b, and c (number-of-turns ratio a:b:c) is set as a:b:c=sin20 :sjn40(:sinl2Q( A cross-sectional area of a conductor in a portion corresponding to the number of turns c of the second coil is set smaller than those of the other portions.

[0006] In this way, the conventional multiplex rectifier circuit is intended to obtain DC power supply having fewer harmonic components by appropriately setting the number-of-turns ratio of the multiplex transformer that transforms the AC voltages in three phases from the three-phase AC power supply into six multiplex AC voltages in changed phases.

[0007] Patent Document 1: Japanese Patent Application Laid-open No. 2002-10646 Patent Document 2: Japanese Patent Application Laid-open No. 2004-120878

DISCLOSURE OF INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

[0008] Meanwhile, in suppression of harmonics of the power supply, it is most desired to suppress fifth-order and seventh-order harmonics for the three phases. However, as a standard value, it is required to suppress harmonics in a well-balanced fashion as a whole without suppressing only specific-orders harmonics.

[0009] However, the conventional multiplex rectifier circuit has the following disadvantage. The conventional multiplex rectifier circuit is basically intended to eliminate specific-order harmonic components centering around low-order harmonics contained in the input current. The residual harmonic components since they are not suppressed are increased as compared with a case that multiplex voltages are not generated.

[0010] Furthermore, the conventional multiplex rectifier circuit has the following disadvantage. The number-of-turns ratio of the multiplex transformers selected to basically suppress the low-order harmonics is premised on the fact that a DC reactor to which the multiplex DCs are applied is very large and that the DC can be regarded as a DC without pulsating flows. Therefore, to realize the suppression effect, the DC reactor is inevitably made large in size, which, in turn, increases loss.

[0011] The present invention has been achieved in view of the conventional disadvantages. It is an object of the present invention to provide a multiplex rectifier circuit capable of sufficiently suppressing low-order harmonic components and then suppressing all harmonic components in a well-balanced fashion while suppressing an increase in size of a DC reactor to which multiplex DCs are applied.

MEANS FOR SOLVING PROBLEM

[0012] To achieve the above objects, the present invention includes a first rectifier circuit that converts a three-phase AC power supply into a DC power supply; a multiplex transformer that steps-down voltages of the three-phase AC power supply, and that transforms the voltages into AC voltages located at six spatial positions among circular arcs formed by connecting each of a first, a second, and a third vertexes of a equilateral triangle that depicts a relationship among the voltages in the respective phases of the three-phase AC power supply, respectively, in a transformer-vector diagram of the equilateral triangle from a first spatial position to a second spatial position between the circular arc formed by connecting the first vertex to the other second and third vertexes and a side connecting the second to the third vertexes, with the first spatial position distanced from the second vertex by 20 degrees or more, and the second spatial position distanced from the third vertex by 20 degrees or more; and a second rectifier circuit that rectifies the six AC voltages different in phase and output from the multiplex transformer, wherein the first rectifier circuit and the second rectifier circuit are connected in parallel so as to obtain multiplex DC outputs.

[0013] According to the present invention, it is possible to sufficiently suppress low-order harmonic components and, then, suppress all harmonic components in a well-balanced fashion while suppressing an increase in size of the DC reactor to which multiplex DCs are applied.

EFFECT OF THE INVENTION

[0014] According to the present invention, the multiplex rectifier circuit can be advantageously designed to satisfy not only Japanese standards but also European standards, since not only harmonic components in specific orders but also all harmonic components can be suppressed in a well-balanced fashion.

BRIEF DESCRIPTION OF DRAWINGS

[0015] Fig. 1 is a circuit diagram of an inverter circuit that includes a multiplex rectifier circuit according to a first embodiment of the present invention; Fig. 2 is an explanatory diagram of one example of a winding structure of a multiplex transformer shown in Fig. 1; Fig. 3 is a transformer-vector diagram for explaining an arrangement relationship among AC voltages transformed by the multiplex transformer shown in Fig. 1; Fig. 4 is a graph of a simulation result for a change in input current when the multiplex transformer is not employed in the rectifier circuit disclosed in the Patent documents 1 and 2; Fig. 5 is a graph of a frequency analysis result of the change in input current shown in Fig. 4; Fig. 6 is a graph of a simulation result for a change in input current when the multiplex transformer is employed in the rectifier circuit disclosed in the Patent documents 1 and 2; Fig. 7 is a graph of a frequency analysis result of the change in input current shown in Fig. 6; Fig. 8 is a graph of a simulation result for a change in input current when a DC reactor is added to the rectifier circuit using the multiplex transformer disclosed in the Patent documents 1 and 2; Fig. 9 is a graph of a frequency analysis result of the change in input current shown in Fig. 8; Fig. 10 is a graph of a simulation result for a change in input current when two AC reactors and a noise filter are eliminated from the configuration shown in Fig. 1; Fig. 11 is a graph of a frequency analysis result of the change in input current shown in Fig. 10; Fig. 12 is a graph of a simulation result for a change in input current when the noise filter is eliminated from the configuration shown in Fig. 1 (in which the two AC reactors are present) Fig. 13 is a graph of a frequency analysis result of the change in input current shown in Fig. 12; Fig. 14 is a circuit diagram of an inverter circuit that includes a multiplex rectifier circuit according to a second embodiment of the present invention; and Fig. 15 is a circuit diagram of an inverter circuit that includes a multiplex rectifier circuit according to a third embodiment of-the present invention.

EXPLANATIONS OF LETTERS OR NUMERALS

[0016] 1 Three-phase AC power supply 2 First rectifier circuit 3 DC reactor (Second DC reactor) 4 Smoothing capacitor Reverse converter 6 Motor 7 AC reactor (First AC reactor) 8 Noise filter 9 AC reactor (Second AC reactor) Multiple transformer 11 First rectifier circuit 12 DC reactor (First DC reactor) 13 Rectifier circuit of inverter circuit 21 R-phase core 22 R-phase first coil 23 R-phase second coil 24 S-phase core 22 S-phase first coil 23 S-phase second coil 21 T-phase core 22 T-phase first coil 23 T-phase second coil 31 to 36 Spatial position where transformed AC voltages are arranged A, B, C Independent structure (power supply harmonic countermeasure apparatus) BEST MODE(S) FOR CARRYING OUT THE INVENTION [0017] Exemplary embodiments of a multiplex rectifier circuit according to the present invention will be explained below in detail with reference to the accompanying drawings.

[0018j

FIRST EMBODIMENT

Fig. 1 is a circuit diagram of an inverter circuit that includes a multiplex rectifier circuit according to a first embodiment of the present invention. The inverter circuit includes a first rectifier circuit 2, a DC reactor 3, a smoothing capacitor 4, and a reverse converter 5. The first rectifier circuit 2 is a three-phase full-wave rectifier provided relative to a three-phase AC power supply 1. The DC reactor 3 and the smoothing capacitor 4 constitute a smoothing circuit that smoothes DC voltages output from the first rectifier circuit 2. The reverse converter 5 switches over terminal voltages (DC voltages) of the smoothing capacitor 4 and generates AC voltages.

The inverter circuit is configured to drive and control a motor 6 by AC voltages output from the reverse converter 5.

[0019] The multiplex rectifier circuit according to the first embodiment is characterized as follows.

(1) The multiplex rectifier circuit basically includes a multiplex transformer 10 and a second rectifier circuit 11.

The multiplex transformer 10, which is provided relative to the first rectifier circuit 2 provided relative to the three-phase AC power supply 1, steps-down voltages of the three-phase AC power supply 1 and transforms the voltages into six AC voltages having different phases. The second rectifier circuit 11 rectifies the AC voltages output from the multiplex transformer 10 and multiplexes its rectified outputs with rectified outputs of the first rectifier circuit 2. An example of a configuration of the multiplex transformer 10 will-be explained later (with reference to Figs. 2 and 3) . Similarly to the first rectifier circuit 2, the second rectifier circuit 11 is configured to bridge diodes.

[0020] (2) An AC reactor 9 is provided, as substantially an essential constituent element, in an input stage of the multiplex transformer 10. The AC reactor 9 can be configured by a leakage inductance component of the multiplex transformer 10.

[0021] (3) An AC reactor 7 is directly connected to an output terminal of the three-phase AC power supply 1 so as to further suppress harmonic components of the power supply.

Through this AC reactor 7, AC voltages and AC currents are applied to respective elements of the multiplex rectifier circuit. (4) A noise filter 8 is provided among an output terminal of the AC reactor 7, the first rectifier circuit 2, and an input terminal of the AC reactor 9 so as to reduce power supply noise superimposed on the three-phase AC power supply 1.

[0022] As a result, the multiplex rectifier circuit according to the first embodiment can sufficiently suppress low-order harmonic components and then effectively suppress all harmonic components while suppressing an increase in size of the DC reactor 3 to which multiplex DC5 are applied, as compared with only the first rectifier circuit 2 that is, as compared with a case that the multiplex DCs are not generated. In Fig. 1, a circuit part from the AC reactor 7 to the DC reactor 3 surrounded by a broken line A serves as one block that includes a connection terminal connected to the three-phase AC power supply 1 and a connection terminal connected to the smoothing capacitor 4. This circuit part can be, therefore, regarded as one independent structure (power supply harmonic countermeasure apparatus) [0023] An example of the configuration of the multiplex transformer 10 will next be explained with reference to Figs. 2 and 3. Fig. 2 is an explanatory diagram of one example of a winding structure of the multiplex transformer 10. Fig. 3 is a transformer-vector diagram for explaining an arrangement relationship among the AC voltages transformed by the multiplex transformer 10.

[0024] With reference to Fig. 2, an R-phase first coil 22 and an R-phase second coil 23 are wound around an R-phase core 21. In the Rphase first coil 22, both ends are denoted by reference letters R7 and R6, respectively, and an intermediate tap R is provided at a position set by bisecting the number of turns at a ratio of a:a. In the R-phase second coil 23, both ends are denoted by reference letters S7 and T6, respectively, and intermediate taps S3 and T2 are provided at positions set by dividing the number of turns at a ratio of b:c:b, respectively. One end R7 of the R-phase first coil 22 is equal in polarity to one end S7 of the R-phase second coil 23.

[0025] A S-phase first coil 25 and a S-phase second coil 26 are wound around a S-phase core 24. In the S-phase first coil 25, both ends are denoted by reference letters S7 and S6, respectively, and an intermediate tap S is provided at a position set by bisecting the number of turns at a ratio of a:a. In the S-phase second coil 26, both ends are denoted by reference letters T7 and R6, respectively, and intermediate taps T3 and T2 are provided at positions set by dividing the number of turns at a ratio of b:c:b, respectively. One end S7 of the S-phase first coil 25 is equal in polarity to one end T7 of the S-phase second coil 26.

[0026] A T-phase first coil 28 and a T-phase second coil 29 are wound around a T-phase core 27. In the T-phase first coil 28, both ends are denoted by reference letters T7 and T6, respectively, and an intermediate tap T is provided at a position set by bisecting the number of turns at a ratio of a:a. In the T-phase second coil 29, both ends are denoted by reference letters R7 and S6, respectively, and intermediate taps R3 and S2 are provided at positions set by dividing the number of turns at a ratio of b:c:b, respectively. One end T7 of the T-phase first coil 28 is equal in polarity to one end R7 of the T-phase second coil 29.

[0027] One end R7 of the R-phase first coil 22 is connected to one end R7 of the T-phase second coil, and the other end R6 of the R- phase first coil 22 is connected to the other end R6 of the S-phase second coil 26. One end S7 of the 5- phase first coil 25 is connected to one end S7 of the R-phase second coil 23, and the other end S6 of the S-phase first coil 25 is connected to the other end S6 of the T-phase second coil 29. One end T7 of the T-phase first coil 28 is connected to one end S7 of the S-phase second coil 26, and the other end T6 of the T-phase first coil 28 is connected to the other end T6 of the R-phase second coil 23.

The number-of-turns ratio a:b:c is, for example, 41:88:83.

[0028] The multiplex transformer 10 is configured to have the connection relationship explained above. The intermediate taps R, S, and T serve as input terminals, to which phase lines corresponding to the R, S, and T phases of the three-phase AC power supply 1 are connected, respectively. The intermediate taps S3, T2, T3, R2, R3, and S2 serve as output terminals, which are connected to corresponding input terminals of the second rectifier circuit 11, respectively.

j0029] An arrangement relationship among six potentials fetched from the intermediate taps S3, T2, T3, R2, P.3, and S2 on a transformer-vector diagram is shown in Fig. 3.

Namely, the multiplex transformer 10 adjusts the number-of-turns ratio of a:b:c shown in Fig. 2, and generates six AC voltages arranged at six spatial positions 31 to 36, respectively. As shown in Fig. 3, in a transformer-vector diagram of a equilateral triangle representing a phase relationship among voltages in the respective phases of the three-phase AC power supply 1, it is assumed that vertexes of the equilateral triangle are R, S, and T, respectively.

The AC voltages are located at the six spatial positions 31 to 36 between circular arcs formed by connecting each of the vertexes to the two other vertexes and respective sides of the equilateral triangle. The first spatial position 31 and the second spatial position 32 are located between the circular arc formed by connecting the vertex P. to the two other vertexes S and T and the side of the triangle connecting the vertexes T and S. In addition, the first spatial position 31 is distanced from the vertex S by 20 degrees or more, and the second spatial position 32 is distanced from the vertex T by 20 degrees or more.

[0030] As indicated by UXU in Fig. 3, the multiplex transformer disclosed in the Patent documents 1 and 2 generates AC voltages located at respective positions on the circular arcs formed by connecting each vertex of the equilateral triangle to the two other vertexes by trisecting the circular arcs. Namely, according to the present invention, the number-of-turns ratio differs from that disclosed in the Patent documents 1 and 2.

Accordingly, a winding method for the multiplex transformer for generating the desired potentials shown in Fig. 3 is not limited to the method shown in Fig. 2 as long as the number-of-turns ratio a:b:c specified in the present invention is satisfied. For example, any one of various methods disclosed in the Patent document 1 can be used.

[0031] In the multiplex rectifier circuit thus configured, peak secondary-side voltages of the multiplex transformer are lower than the respective voltages in the R, S, and T phases of the three-phase AC voltages shifted in phase by degrees, respectively. However, if the voltages are arranged so as to have a period in which a relatively highest voltage or a relatively lowest voltage is present, and the second rectifier circuit 11 is connected to the first rectifier circuit 2, then the second rectifier circuit 11 can be made conductive only in the period in which the highest or lowest voltage is present.

[0032] This follows that a conductive period of the first rectifier circuit 2 is shortened and a conductive period of the second rectifier circuit 11 via the multiplex transformer 10 occurs, as compared with the case that only the first rectifier circuit 2 is provided (that is, multiplex currents are not generated) . The currents via the multiplex transformer 10 are divided to the R, S, and T phases on the secondary side by connections of the transformer. Therefore, a current in each of the R, S. and T phases is closer to a sinusoidal wave in which harmonic components are suppressed as a whole.

[0033] It is noted that the suppression effect tends to be greater if the DC reactor 3 has a larger capacity and the smoothing capacitor 4 has a smaller capacity. In addition, by positively adding the AC reactor 7 to a power supply line as a constituent element, the harmonic components can be further suppressed as a whole. It should be noted, however, that this AC reactor 7 is high in current and large in size since all input currents of the multiplex rectifier circuit are applied to the AC reactor 7.

[0034] The harmonic suppression effect according to the present invention will be explained, while comparing this effect with the effect attained by the conventional technique (the Patent documents 1 and 2) . Figs. 4 to 9 are charts for explaining the harmonic suppression effect attained by the conventional technique (the Patent documents 1 and 2) . Figs. 10 to 13 are charts for explaining the harmonic suppression effect attained by the present invention. Each chart depicts an evaluation result of a simulation. The noise filter 8 is eliminated from the configuration.

[0035] The number-of-turns ratio of the multiplex transformer disclosed in the Patent documents 1 and 2 is set such that the AC voltages in six phases generated by the multiplex transformer are arranged at the positions on the circular arcs connecting each of the three vertexes to the two other vertexes by trisecting the circular arcs as already explained with reference to Fig. 3. The Patent documents 1 and 2 disclose the same thing as the number-of-turns ratio of the multiplex transformer in different expressions. It is assumed herein that the number-of-turns ratio of the multiplex transformer a:b:c is set as a:b:c=sin20o:sjn12O0:sine12Qo43:81:1O9 This is described in the Patent document 2. Furthermore, the AC reactors 7 and 9 shown in Fig. 1 are not shown in the Patent Documents 1 and 2, and it is not suggested at all that the AC reactors 7 and 9 are present.

[0036] The simulation is carried out in conditions that the AC reactors 7 and 9 shown in Fig. 1 are not present, a phase-to-phase voltage of the three-phase AC power supply 1 is 400 volts at 50 hertz, capacities of the DC reactor 3 and the smoothing capacitor 4 are 2.9 millihenries and 1650 microfarads, respectively (on an assumption that two capacitors of 3300 microfarads are connected in series) that are general for a load of about 8 kilowatts, and a load is 7900 watts.

[0037] Fig. 4 is a chart that depicts a simulation result for a change in input current when the multiplex transformer is not employed in the rectifier circuit disclosed in the Patent Documents 1 and 2. Fig. 5 is a chart that depicts a frequency analysis result of the change in input current shown in Fig. 4. In Fig. 1, this simulation corresponds to a state in which the three-phase AC power supply 1 is directly connected to the first rectifier circuit 2 and in which a route of the AC reactor 9, the multiplex transformer 10, and the second rectifier circuit 11 is not present. In Fig. 5, a power supply frequency (50 hertz) is shown on a left end, from which lower to higher harmonics are shown rightward.

[0038] -Fig. 6 is a chart that depicts a simulation result for a change in input current of the rectifier circuit using the multiplex transformer disclosed in the Patent Documents 1 and 2. Fig. 7 is a chart that depicts a frequency analysis result of the change in input current shown in Fig. 6. In Fig. 1, this simulation corresponds to a state in which the three-phase AC power supply 1 is directly connected to the first rectifier circuit 2, and in which the multiplex transformer 10 and the second rectifier circuit 11 are connected in parallel to the first rectifier circuit 2. As shown in Figs. 6 and 7, when the multiplex transformer is used, the harmonic suppression effect emerges. However, the low-order harmonics are not reduced so sufficiently as expected in the Patent Documents 1 and 2.

In this simulation, 17th_order and 19th_order harmonic components remain by 5.85% and 3.87% of a fundamental wave, respectively.

[0039] Fig. 8 is a chart that depicts a simulation result for a change in input current when the DC reactor is added to the rectifier circuit using the multiplex transformer disclosed in the Patent Documents 1 and 2. Fig. 9 is a chart that depicts a frequency analysis result of the change in input current shown in Fig. 8. If the DC reactor of 10 millihenries, which is not assumed in the Patent Documents 1 and 2, is added to the rectifier circuit, the simulation result is that shown in Figs. 8 and 9. In Figs. 8 and 9, low-order harmonic components such as a fifth-order harmonic component is substantially suppressed while 17th_order and 19th_order harmonic components remain by 5.25% and 4.27% of the fundamental wave, respectively.

[0040] The number-of-turns ratio of the multiplex transformer according to the present invention is adjusted so that the AC voltages in six phase generated by the transformer are located at the spatial positions between circular arcs formed by connecting each of the vertexes to the two other vertexes and respective sides of the equilateral triangle formed by connecting the three phase potentials corresponding to the R phase, the S phase, and the T phase ton one another by lines, with angles with respect to the sides of the equilateral triangle being greater than 20 degrees in notation as transformer vectors, as explained with reference to Fig. 3. By way of example, the number-of-turns ratio a:b:c=41:88:83 shown in Fig. 2 is adopted.

This number-of-turns ratio a:b:c=41:88:83 indicates that the AC voltages are generated at the spatial positions each at line voltage of 0.994 relative to a line voltage 1 of one side of the equilateral triangle, and at an angle with respect to the side of 22 degrees, respectively.

[0041] The simulation is carried out, similarly to the conventionaltechnique, in conditions that a phase-to-phase voltage of the three-phase AC power supply 1 is 400 volts at 50 hertz, capacities of the DC reactor 3 and the smoothing capacitor 4 are 2.9 millihenries and 1650 microfarads (on an assumption that two capacitors of 3300 microfarads are connected in series) that are general for a load of about 8 kilowatts, and a load is 7900 watts.

[0042] Fig. 10 is a chart that depicts a simulation result for a change in input current when the two AC reactors and the noise filter are eliminated from the configuration shown in Fig. 1. Fig. 11 is a chart that depicts a frequency analysis result of the change in input current shown in Fig. 10. As shown in Figs. 10 and 11, the low-order harmonic components are suppressed to be low as a whole and the 17th_order and 19th_order harmonic components remain by 4.74% and 3.62% of the fundamental wave, respectively.

[0043] In suppression of the harmonics of the power supply, it is most desired to suppress the fifth-order and the seventh-order harmonic components in three phases. However, as a standard value, it is also required to keep harmonic components in balance as a whole. For example, for specified consumers in Japan, target values of remaining harmonic components are as follows. Upper limit currents per kilowatt as whole voltage receiving equipment are 3.5 milliampers for the fifth-order, 2.5 milliampers for the seventh-order, 1.6 milliamperes for the eleventh order, 1.3 milliampers for the 13th_order, 1.0 milliamper for the 17th_ order, 0.9 milliamper for the 19th_order, 0.76 milliampere for the 23rd_order, and 0.7 milliamper for the 24th and the following orders.

[0044] According to the European Standards IEC-61000-3-2, limits for harmonic current emissions are equal to or smaller than 16 ampers per phase. Among them, upper limits of harmonic residual amounts at respective orders of individual equipment in absolute value are: 1.14 amperes for the fifth-order, 0.77 ampere for the seventh-order, 0.33 ampere for the eleventh-order, 0.21 ampere for the 13th_order, 0.15x(15/n) for the 15th to 39th_orders (odd orders) , where n is an order.

[0045] As can be seen, it is required on the standards to suppress harmonics not only at specific orders but also whole orders in a well-balanced fashion. This requirement can be realized by selecting the number-of-turns ratio of the multiplex transformer as explained in the present invention, as shown in Figs. 12 and 13. The harmonic suppression effect can be achieved particularly when the AC reactors 7 and 9 are simultaneously employed in the multiplex rectifier.

[0046] Fig. 12 is a chart that depicts a simulation result for a change in input current when the noise filter is eliminated from the configuration shown in Fig. 1 (in which the two AC reactors are present) . Fig. 13 is a chart that depicts a frequency analysis result of the change in input current shown in Fig. 12. Figs. 12 and 13 are the simulation result when the AC reactor 9 has a capacity of 3.7 millihenries and the AC reactor 7 has a capacity of 4.5 millihenries. This simulation result also satisfies the IEC-61000-3-2.

[0047] The simulation result derives from the following respects or effects. In the multiplex transformer 10, the harmonic components are suppressed wholly in a well-balanced fashion in advance and the 17th_order and 19th_ order harmonics are particularly suppressed to be low. The AC reactor 9 is provided to make it possible to positively suppress harmonic components (specifically and 19th components) caused by stepped currents from the multiplex transformer 10.

[0048] According to the present invention, the number-of-turns ratio of the multiplex transformer 10 is selected so as to generate the AC voltages each at a line voltage of 0.994 relative to a line voltage 1 of one side of the equilateral triangle and at an angle relative to each side of, for example, 22 degrees. By so selecting, even if manufacturing irregularity is present, harmonic residue irregularity is suppressed, all harmonic components are suppressed as compared with the case that multiplex currents are not generated, and it is possible to satisfy various standards. By inserting the AC reactor 7, it is possible to further suppress harmonic residual amounts.

[0049] Furthermore, by adopting the number-of-turns ratio according to the present invention, a conducting angle of the first rectifier circuit 2 is increased as compared with the conventional technique (Patent Documents 1 and 2). A current duty of the second rectifier circuit 11 is reduced and, therefore, that of the multiplex transformer 10 is reduced, and the effect of suppressing a current capacity to be low can be expected.

[0050] In these specific simulation examples, the power supply is 400 volts. Similar results are obtained for the power supply of 200 volts. In the examples, the capacity of the DC reactor 3 is not changed. However, by increasing the capacity thereof, the low-order harmonic components can be suppressed. By keeping a balance among the capacity of the DC reactor 3 and those of the AC reactors 7 and 9, the harmonics can be efficiently reduced. The AC reactor 7 is particularly preferably selected to have a capacity as small as possible so as to prevent an increase in loss since all main currents are applied to the AC reactor 7.

In these specific simulation examples, the capacities of the AC reactors 7 and 9 are selected to satisfy the IEC- 61000-3-2 for the limit of the input current to 16 amperes per phase. However, when the apparatus has a maximum capacity, the other-capacities of the AC reactors 7 and 9 can be selected.

[0051] Meanwhile, if it is necessary to sufficiently suppress harmonics in a standard state as a product, the multiplex rectifierx circuit is constantly connected since shipping.

Therefore, when the AC reactor 9, the multiplex transformer 10, the first rectifier circuit 2, the second rectifier circuit 11, and the DC reactor 3, which are heating members, as well as, if needed, the AC reactor 7 and the noise filter 8 are separately arranged as an independent structure A, it is possible to suppress heat stresses applied to the smoothing capacitor 4, the reverse converter 5, and electronic components such as a control circuit therefor. Needless to say, the components in the independent structure (power supply harmonic countermeasure apparatus) A do not always have to be those mentioned above, and they are selected appropriately according to structural demand for the product.

[0052] As explained so far, according to the first embodiment, the number-of-turns ratio of the multiplex transformer is selected so as to be able to suppress not only specific-order harmonics but also all harmonics in a well-balanced fashion as a whole. In addition, the AC reactor is inserted so as to further suppress the harmonics. It is, therefore, possible to sufficiently suppress low-order harmonic components and then all harmonic components while suppressing an increase in size of the DC reactor to which multiplex DCs are applied. Accordingly, the multiplex rectifier circuit according to this embodiment can be designed to satisfy not only Japanese standards but also European standards.

[0053]

SECOND EMBODIMENT

Fig. 14 is a circuit diagram of a configuration of an inverter circuit using a multiplex rectifier circuit according to a second embodiment of the present invention.

In Fig. 14, like or equivalent constituent elements to those shown in Fig. 1 (the first embodiment) are denoted by like reference letters and numerals. The constituent elements related to the second embodiment will be mainly explained herein.

[0054] According to the second embodiment, the rectifier circuit is configured as follows. As shown in Fig. 14, a DC reactor 12 is arranged between a parallel connection terminal on which the first rectifier circuit 2 and the second rectifier circuit 11 are connected in parallel and the other end of the DC reactor 3 having one end connected to the smoothing capacitor 4. Namely, according to the second embodiment, the DC reactor is divided into the DC reactors 3 and 12.

[0055] Although the DC reactor 12 is not always necessary, it is arranged because it is effective to increase an L value of the DC reactor so as to improve harmonic suppression level. With this configuration, a circuit part (the AC reactor 9, the multiplex transformer 10, the second rectifier circuit 11, and the DC reactor 12) surrounded by a broken line B is provided as an independent structure (a power supply harmonic countermeasure apparatus) so as to be able to additionally provided afterwards.

[0056] Namely, it normally suffices to provide the DC reactor 3 to suppress the power supply harmonics. If further measures are selectively introduced, or specifically, if it is necessary to satisfy specified consumer guideline for power supply harmonics, the independent structure (power supply harmonic countermeasure apparatus) B can be additionally provided in the multiplex rectifier circuit.

By doing so, it is possible to suppress an increase in size, weight, and cost of a product according to standard

specifications.

[0057] Specific examples of circuit constants are as follows.

It should be noted that capacities of the DC reactors and the capacitor are selected on an assumption that the load of about 8 kilowatts is applied similarly to the first embodiment. If the phase-to-phase voltage of the three-phase AC power supply 1 is 200 volts, it is assumed that an L value of a sum of the DC reactors 3 and 12 is 0.5 millihenry, the capacity of the smoothing capacitor 4 is 3300 microfarads, and an L value of the AC reactor 9 is 0.5 millihenry.

[0058] If the phase-to-phase voltage of the three-phase AC power supply 1 is 400 volts, it is assumed that the L value of a sum of the DC reactors 3 and 12 is 2.9 millihenries, the capacity of the smoothing capacitor 4 is 1650 microfarads, and the L value of the AC reactor 9 is 1.0 millihenry.

[0059] As can be seen, the second embodiment can exhibit the same advantages as those of the first embodiment. Besides, it is possible to suppress an increase in size, weight, and cost of the product according to standard specifications.

[0060]

THIRD EMBODIMENT

Fig. 15 is a circuit diagram of a configuration of an inverter circuit using a multiplex rectifier circuit according to a third embodiment of the present invention.

In Fig. 15, like or equivalent constituent elements to those shown in Fig. 14 (the second embodiment) are denoted by like reference letters and numerals. The constituent elements related to the third embodiment will be mainly explained herein.

[0061] In Fig. 15, a rectifier circuit 13, the DC reactor 3, the smoothing capacitor 4, and the reverse converter 5 constitute an ordinary inverter circuit. As shown in Fig. 15, according to the third embodiment, the AC reactor 7, the noise filer 8, the first rectifier circuit 2, the AC reactor 9, the multiplex transformer 10, the second rectifier circuit 11, and the DC reactor 11 on the three-phase AC power supply 1 side are prepared as an independent structure (a power supply harmonic countermeasure apparatus) C. An external connection terminal and a reference potential connection terminal of the DC reactor 11 can be connected to input units of the rectifier circuit 13 of the inverter circuit.

[0062] As for diodes that are constituent elements of the rectifier circuit 13, it is necessary to design capacities and radiations thereof in consideration of a possible temperature rise in advance. This is because conduction duty concentrates on two specific diodes when the power supply harmonic countermeasure apparatus C is inserted into the inverter circuit.

[0063] As for the DC reactors, since the DC reactor 12 is arranged in series to the DC reactor 3 according to the third embodiment, circuit constants are set similarly to those according to the second embodiment.

[0064] As can be seen, according to the third embodiment, the inverter circuit is simply configured so that the power supply harmonic countermeasure apparatus C is additionally inserted between the three-phase AC power supply 1 and the input units of the rectifier circuit 13. It is advantageously possible to easily add the apparatus C afterwards. In the third embodiment, an example of application of the present invention to the second embodiment has been explained. The structure A shown in the first embodiment (Fig. 1) can be additionally inserted between the three-phase AC power supply and the input unit of the rectifier circuit as the power supply harmonic countermeasure apparatus similarly to the apparatus C. [0065] In the first to the third embodiments, the cases that the present invention is utilized in the rectifier part of the inverter circuit have been explained. Needless to say, the present invention can be applied to other DC loads with the same configuration. While the load is not limited to a specific one, the rectifier circuit of a large-sized apparatus is normally a diode rectifier circuit that does not include a regenerative converter. Therefore, the power supply harmonic countermeasure apparatus C or the like can be easily added to the apparatus afterwards.

[0066] A suitable example of applying the present invention includes a use of the present invention as a rectifier circuit in an air conditioner. Namely, the motor 6 shown in Figs. 1, 14, and 15 corresponds to a compressor motor in the air conditioner. The air conditioner has a high product inverter ratio and a high capacity occupation ratio in power supply equipment. Due to this, power supply harmonics are often regarded as undesirable factors. In the air conditioner, the compressor motor driven by an inverter is low in inertia and it is more difficult to generate regenerative energy. Thus, it is desirable to apply the present invention to the air conditioner. In addition, the air conditioner normally includes a heat exchange air blower around an inverter circuit and an air flow generated by the air blower can be made use of even to cool down the multiplex transformer of the present invention. Therefore, advantageously, it is unnecessary to provide additional components.

INDUSTRIAL APPLICABILITY

[0067] As explained so far, the multiplex rectifier circuit according to the present invention is useful as the rectifier circuit capable of being designed to satisfy not only the Japanese standards but also the European standards, and particularly suitable as the rectifier circuit that can flexibly meet requirement level.

Claims

-CLAIMS

1. A multiplex rectifier circuit comprising: a first rectifier circuit that converts a three-phase AC power supply into a DC power supply; a multiplex transformer that steps-down voltages of the three-phase AC power supply, and that transforms the voltages into AC voltages located at six spatial positions among circular arcs formed by connecting each of a first, a second, and a third vertexes of a equilateral triangle that depicts a relationship among the voltages in the respective phases of the three-phase AC power supply, respectively, in a transformer-vector diagram of the equilateral triangle from a first spatial position to a second spatial position between the circular arc formed by connecting the first vertex to the other second and third vertexes and a side connecting the second to the third vertexes, with the first spatial position distanced from the second vertex by 20 degrees or more, and the second spatial position distanced from the third vertex by 20 degrees or more; and a second rectifier circuit that rectifies the six AC voltages different in phase and output from the multiplex transformer, wherein the first rectifier circuit and the second rectifier circuit are connected in parallel so as to obtain multiplex DC outputs.

2. The multiplex rectifier circuit according to claim 1, further comprising an AC reactor arranged between the three-phase AC power supply and the multiplex transformer.

3. A multiplex rectifier circuit comprising: a first AC reactor to which a three-phase AC power supply is connected, and a second AC reactor to which an output terminal of the first AC reactor is connected; a first rectifier circuit that converts the three-phase AC power supply into a DC power supply; a multiplex transformer that steps-down voltages of the three-phase AC power supply, and that transforms the voltages into AC voltages located at six spatial positions among circular arcs formed by connecting each of a first, a second, and a third vertexes of a equilateral triangle that depicts a relationship among the voltages in the respective phases of the three-phase AC power supply, respectively, in a transformer-vector diagram of the equilateral triangle from a first spatial position to a second spatial position between the circular arc formed by connecting the first vertex to the other second and third vertexes and a side connecting the second to the third vertexes, with the first spatial position distanced from the second vertex by 20 degrees or more, and the second spatial position distanced from the third vertex by 20 degrees or more; and a second rectifier circuit that rectifies the six AC voltages different in phase and output from the multiplex transformer, wherein the first rectifier circuit and the second rectifier circuit are connected in parallel so as to obtain multiplex DC outputs.

4. The multiplex rectifier circuit according to claim 3, further comprising a noise filter arranged between the first AC reactor and both the first rectifier circuit and the second AC reactor.

5. The multiplex rectifier circuit according to claim 3, wherein a DC reactor that constitutes a smoothing circuit performing a smoothing processing for the multiplex DC is separated from a smoothing capacitor and connected to a parallel connection terminal on which the first rectifier circuit and the second rectifier circuit are connected in parallel, the respective elements from the first AC reactor to the DC reactor constitute an independent structure.

6. The multiplex rectifier circuit according to claim 3, wherein a DC reactor includes a first DC reactor with one end connected to a parallel connection terminal on which the first rectifier circuit and the second rectifier circuit are connected in parallel; and a second DC reactor connected between other end of the first reactor and a smoothing capacitor, wherein the second AC reactor, the multiplex transformer, the second rectifier circuit, and the first DC reactor constitute an independent structure.

7. The multiplex rectifier circuit according to claim 1, wherein other end and a reference potential end of a DC reactor with one end connected to a parallel connection terminal on which the first rectifier circuit and the second rectifier circuit are connected in parallel are connected to input units of the rectifier circuit of an inverter circuit.

8. The multiplex rectifier circuit according to claim 3, wherein the other end and a reference potential end of a DC reactor with one end connected to a parallel connection terminal on which the first rectifier circuit and the second rectifier circuit are connected in parallel are connected to input units of the rectifier circuit of an inverter circuit.