Common mode filter circuit

Abstract

This common mode filter circuit comprises common mode transformers and capacitors. One end of a primary winding of each common mode transformer is connected to an output terminal of an inverter. Each capacitor has one end connected to an input terminal of the inverter, and another end of the primary winding is connected to another end of the capacitor. Secondary windings of the common mode transformers are mutually connected in series. One end of each secondary winding is connected to the output terminal of the inverter, and another end of the secondary winding is connected to a three-phase AC electric motor. The ratio of the number of turns between the primary winding and the secondary winding is 3:1.

Description

[Technical Field]

[0001] This disclosure relates to a common-mode filter circuit. [Background technology]

[0002] Technologies have been proposed to reduce noise in AC motors supplied with AC power from an inverter. A widely used noise reduction method on the output side of an inverter is to install a zero-phase reactor between the inverter and the AC motor. Installing a zero-phase reactor has some effect in reducing common-mode current. Installing a zero-phase reactor is a simple method that does not require a large reactor and is therefore widely used. Furthermore, for example, Patent Document 1 discloses a circuit in which three-phase wires connecting an inverter and an AC motor are passed inside a ring-shaped magnetic material, and a capacitor is connected to another wire wound around the inside and outside of the ring-shaped magnetic material. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-115223 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Incidentally, while the above-mentioned technologies have some effect in reducing common-mode current, they are insufficient in reducing common-mode voltage, which is a cause of bearing failure in AC motors. Therefore, the effectiveness of the above-mentioned technologies in noise suppression is limited.

[0005] Therefore, this disclosure describes a common mode filter circuit that can reduce common mode voltage. [Means for solving the problem]

[0006] One aspect of this disclosure is a common-mode filter circuit connected between an inverter having a pair of input terminals connected to a power supply and three output terminals outputting three-phase AC, and a three-phase AC motor supplied with three-phase AC from the output terminals of the inverter, comprising three common-mode transformers for canceling out the common-mode voltage of the three-phase AC, and three pairs of capacitors, each connected to the common-mode transformers and the input terminals of the inverter, wherein one end of the primary winding of each of the three common-mode transformers is connected to each of the three output terminals of the inverter, and the other end of the primary winding of each of the three common-mode transformers is connected to one of the three pairs of capacitors, each having one end connected to one of the pair of input terminals of the inverter. This is a common mode filter circuit in which one end of each pair of capacitors is connected to the other end of the other pair of capacitors in a set of three capacitors, each of which has one end connected to the other end of the pair of input terminals of the inverter; each of the three phase secondary windings of the three common mode transformers is connected in series with each other; one end of each of the three phase secondary windings of the three common mode transformers connected in series is connected to each of the three output terminals of the inverter; and the other end of each of the three phase secondary windings of the three common mode transformers connected in series is connected to a three-phase AC motor; and the ratio of the number of turns of the primary winding to the number of turns of the secondary winding of each of the three common mode transformers is 3:1. [Effects of the Invention]

[0007] According to one aspect of the common-mode filter circuit of this disclosure, the common-mode voltage can be reduced. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows a common mode filter circuit according to an embodiment. [Figure 2] Figure 1 is a perspective view showing a common mode transformer. [Figure 3](A) is a graph showing the AC voltage of one phase supplied from the inverter when there is no common mode filter circuit, (B) is a graph showing the AC voltage of one phase supplied from the inverter when a common mode choke coil is installed, (C) is a graph showing the common mode voltage when a common mode filter circuit according to the embodiment is installed, and (D) is a graph showing the common mode voltage when the voltage axis of (C) is magnified. [Modes for carrying out the invention]

[0009] One aspect of this disclosure is a common-mode filter circuit connected between an inverter having a pair of input terminals connected to a power supply and three output terminals outputting three-phase AC, and a three-phase AC motor supplied with three-phase AC from the output terminals of the inverter, comprising three common-mode transformers for canceling out the common-mode voltage of the three-phase AC, and three pairs of capacitors, each connected to the common-mode transformers and the input terminals of the inverter, wherein one end of the primary winding of each of the three common-mode transformers is connected to each of the three output terminals of the inverter, and the other end of the primary winding of each of the three common-mode transformers is connected to one of the three pairs of capacitors, each having one end connected to one of the pair of input terminals of the inverter. This is a common mode filter circuit in which one end of each pair of capacitors is connected to the other end of the other pair of capacitors in a set of three capacitors, each of which has one end connected to the other end of the pair of input terminals of the inverter; each of the three phase secondary windings of the three common mode transformers is connected in series with each other; one end of each of the three phase secondary windings of the three common mode transformers connected in series is connected to each of the three output terminals of the inverter; and the other end of each of the three phase secondary windings of the three common mode transformers connected in series is connected to a three-phase AC motor; and the ratio of the number of turns of the primary winding to the number of turns of the secondary winding of each of the three common mode transformers is 3:1.

[0010] According to this configuration, a common mode filter circuit is provided between an inverter having a pair of input terminals connected to a power supply and three output terminals for outputting three-phase alternating current, and a three-phase alternating current motor supplied with three-phase alternating current from the output terminals of the inverter. The common mode filter circuit includes three common mode transformers for canceling the common mode voltage of the three-phase alternating current, and three pairs of capacitors respectively connected to the common mode transformers and the input terminals of the inverter.

[0011] One end of each primary winding of the three common mode transformers is connected to each of the three output terminals of the inverter. The other end of each primary winding of the three common mode transformers is connected to one end of one pair of capacitors out of the three pairs of capacitors whose one end is connected to one of the pair of input terminals of the inverter, and the other end of the other pair of capacitors out of the three pairs of capacitors whose one end is connected to the other of the pair of input terminals of the inverter. Thereby, a common mode voltage is detected in the primary windings of the three common mode transformers.

[0012] Each of the three-phase secondary windings of the three common mode transformers is connected in series with each other. One end of each of the three-phase secondary windings of the three common mode transformers connected in series with each other is connected to each of the three output terminals of the inverter. The other end of each of the three-phase secondary windings of the three common mode transformers connected in series with each other is connected to the three-phase alternating current motor. In each of the three common mode transformers, the primary winding is for each phase, the secondary winding has three phases together, and the ratio of the number of turns of the primary winding to the number of turns of the secondary winding is 3:1, so that the common mode voltage is appropriately canceled from the voltage of each phase. Thereby, the common mode voltage can be reduced.

[0013] In this case, the number of turns of each primary winding of the three common mode transformers may be 3, and the number of turns of each secondary winding of the three common mode transformers may be 1.

[0014] According to this configuration, since the number of turns of each primary winding of the three common-mode transformers is 3 and the number of turns of each secondary winding of the three common-mode transformers is 1, the number of turns of the thick secondary winding can be minimized. Since the current flowing through the primary winding is small, the primary winding can be made thin, and since the number of turns is 3, it occupies only a small space. Therefore, the common-mode transformer can be significantly miniaturized.

[0015] In this case, each primary winding of the three common-mode transformers may be wound 3 times by passing through the inside and outside of the annular iron core of the common-mode transformer, and each secondary winding of the three common-mode transformers may be wound 1 time by passing through the inside of the annular iron core of each of the three common-mode transformers only once.

[0016] According to this configuration, since the current flowing through the primary winding is small, the primary winding can be made thin, and since the primary winding is wound 3 times by passing through the inside and outside of the annular iron core of the common-mode transformer, it occupies only a small space. Also, since each secondary winding of the three common-mode transformers is wound 1 time by passing through the inside of the annular iron core of each of the three common-mode transformers only once, it is easy to increase the occupancy rate of the secondary winding and it is easy to miniaturize. Therefore, the common-mode transformer can be significantly miniaturized.

[0017] Hereinafter, embodiments will be described with reference to the drawings. As shown in FIG. 1, the common-mode filter circuit 10 of this embodiment is connected between an inverter 30 having a pair of input terminals 30a and 30b connected to a power supply 20 and three output terminals 30u, 30v, and 30w for outputting three-phase alternating current, and a three-phase alternating current motor 40 supplied with three-phase alternating current via a motor cable 50 from the output terminals 30u, 30v, and 30w of the inverter 30.

[0018] The power supply 20 is a DC power supply such as a battery and a converter. The inverter 30 is, for example, a voltage-type PWM inverter. The inverter 30 converts the DC voltage supplied from the power supply 20 via input terminals 30a and 30b into a three-phase AC voltage by the switching operation of power semiconductor elements (IGBT, SiC, etc.), and outputs the three-phase AC voltage from output terminals 30u, 30v, and 30w. The AC voltage converted by the inverter 30 is supplied to the three-phase AC motor 40 via the common-mode filter circuit 10 and the motor cable 50. The frame of the three-phase AC motor 40 is connected to the ground voltage via a ground wire.

[0019] The common mode filter circuit 10 comprises three common mode transformers 61, 62, and 63 that cancel out the common mode voltage of the three-phase AC, and three pairs of capacitors 71, 72, 73, 74, 75, and 76 connected to the common mode transformers 61, 62, and 63 and to the input terminals 30a and 30b of the inverter 30, respectively.

[0020] Common mode transformer 61 has a single-phase primary winding 61t and three-phase secondary windings 61u, 61v, 61w. Common mode transformer 62 has a single-phase primary winding 62t and three-phase secondary windings 62u, 62v, 62w. Common mode transformer 63 has a single-phase primary winding 63t and three-phase secondary windings 63u, 63v, 63w.

[0021] One end 61a, 62a, and 63a of the primary windings 61t, 62t, and 63t of the three common mode transformers 61, 62, and 63, respectively, are connected to the three output terminals 30u, 30v, and 30w of the inverter 30. Specifically, one end 61a of the primary winding 61t of common mode transformer 61 is connected to the three-phase U-phase output terminal 30u of inverter 30. One end 62a of the primary winding 62t of common mode transformer 62 is connected to the three-phase V-phase output terminal 30v of inverter 30. One end 63a of the primary winding 63t of common mode transformer 63 is connected to the three-phase W-phase output terminal 30w of inverter 30.

[0022] The other ends 61b, 62b, and 63b of the primary windings 61t, 62t, and 63t of the three common-mode transformers 61, 62, and 63, respectively, are connected to the other ends 71b, 73b, and 75b of the capacitors 71, 73, and 75, respectively. Capacitors 71, 73, and 75 are one of each pair of capacitors 71, 72, 73, 74, 75, and 76, respectively, of the three pairs of capacitors 71, 72, 73, 74, 75, and 76. One end 71a, 73a, and 75a of capacitors 71, 73, and 75 is connected to input terminal 30b, which is one of the pair of input terminals 30a and 30b of the inverter 30.

[0023] The other ends 61b, 62b, and 63b of the primary windings 61t, 62t, and 63t of the three common-mode transformers 61, 62, and 63, respectively, are connected to the other ends 72b, 74b, and 76b of the capacitors 72, 74, and 76, respectively. Capacitors 72, 74, and 76 are the other ends of the pairs of capacitors 71, 72, 73, 74, and 75, 76, respectively, of the three pairs of capacitors 71, 72, 73, 74, 75, and 76. One end 72a, 74a, and 76a of capacitors 72, 74, and 76 is connected to input terminal 30a, which is the other of the pair of input terminals 30a and 30b of the inverter 30.

[0024] In other words, the other end 61b of the primary winding 61t of the common mode transformer 61 connected to the U phase of the inverter 30 is connected to the other end 71b of capacitor 71, one end 71a of which is connected to one input terminal 30a of the inverter 30, and to the other end 72b of capacitor 72, one end 72a of which is connected to the other input terminal 30b of the inverter 30.

[0025] The other end 62b of the primary winding 62t of the common mode transformer 62 connected to the V phase of the inverter 30 is connected to the other end 73b of a capacitor 73, one end 73a of which is connected to one input terminal 30a of the inverter 30, and to the other end 74b of a capacitor 74, one end 74a of which is connected to the other input terminal 30b of the inverter 30.

[0026] The other end 63b of the primary winding 63t of the common mode transformer 63 connected to the W phase of the inverter 30 is connected to the other end 75b of capacitor 75, one end 75a of which is connected to one input terminal 30a of the inverter 30, and to the other end 76b of capacitor 76, one end 76a of which is connected to the other input terminal 30b of the inverter 30. The primary windings 61t, 62t, 63t and capacitors 71, 72, 73, 74, 75, 76 constitute a filter for detecting the common mode voltages of the U phase, V phase, and W phase.

[0027] The three phase secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w of the three common mode transformers 61, 62, and 63 are each connected in series with each other. One end 64ua, 64va, and 64wa of the three phase secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w of the three common mode transformers 61, 62, and 63, which are connected in series with each other, are each connected to the three output terminals 30u, 30v, and 30w of the inverter.

[0028] The other ends 64ub, 64vb, and 64wb of the three phase secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w of the three common mode transformers 61, 62, and 63, which are connected in series with each other, are connected to the respective phases of the three-phase AC motor 40 via motor cables 50.

[0029] In other words, one end 64ua of the secondary windings 61u, 62u, and 63u of the U-phase of the common mode transformers 61, 62, and 63, which are connected in series with each other, is connected to the U-phase output terminal 30u of the inverter 30, and the other end 64ub is connected to the U-phase of the three-phase AC motor 40.

[0030] The V-phase output terminal 30V of the inverter 30 is connected to one end 64VA of the V-phase secondary windings 61V, 62V, and 63V of common mode transformers 61, 62, and 63, which are connected in series with each other, and the other end 64Vb is connected to the V-phase of the three-phase AC motor 40.

[0031] The W-phase output terminal 30w of the inverter 30 is connected to one end 64wa of the W-phase secondary windings 61w, 62w, and 63w of common mode transformers 61, 62, and 63, which are connected in series with each other, and the other end 64wb is connected to the W-phase of the three-phase AC motor 40.

[0032] The ratio of the number of turns of the primary windings 61t, 62t, and 63t of the three common mode transformers 61, 62, and 63 to the number of turns of the secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w is 3:1. In this embodiment, the number of turns of the primary windings 61t, 62t, and 63t of the three common mode transformers 61, 62, and 63 is 3, and the number of turns of the secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w of the three common mode transformers 61, 62, and 63 is 1 (passing only inside the iron core 65 described later).

[0033] As shown in Figure 2, the three common mode transformers 61, 62, and 63 each have an annular iron core 65. Figure 2 shows common mode transformer 61 as a representative of the three common mode transformers 61, 62, and 63, but the same applies to the other common mode transformers 62 and 63 in the following description.

[0034] The primary windings 61t, 62t, and 63t of the three common-mode transformers 61, 62, and 63 are wound three times, passing through the inner 65i and outer 65o of the annular iron core of the common-mode transformer. Since only about 1-2A of current flows through the primary windings 61t, 62t, and 63t on the capacitor side 71, 72, 73, 74, 75, and 76, the conductor cross-sectional area of ​​the primary windings 61t, 62t, and 63t is very small. For example, copper tape with a thickness of 30-40 μm and a width of 2-4 mm can be used for the primary windings 61t, 62t, and 63t.

[0035] The secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w of the three common mode transformers 61, 62, and 63 are wound once by passing only once through the inner 65i of the annular iron core 65 of each of the three common mode transformers 61, 62, and 63. In other words, the U-phase secondary windings 61u, 62u, and 63u, which are connected in series and integrated with each other, the V-phase secondary windings 61v, 62v, and 63v, which are connected in series and integrated with each other, and the W-phase secondary windings 61w, 62w, and 63w, which are connected in series and integrated with each other, all pass through the inner 65i of the iron core 65 of each of the three common mode transformers 61, 62, and 63.

[0036] The operation and effects of the common-mode filter circuit 10 of this embodiment will be described below. Conventionally, in circuits equipped with a power supply, an inverter, and a motor, electromagnetic noise countermeasures have been proposed in which a noise filter is installed between the power supply and the inverter. In this configuration, the common-mode current is bypassed by the noise filter on the power supply side. In this configuration, by confining the common-mode current between the inverter and the motor, the outflow of the common-mode current to the power supply side is prevented. This configuration can be realized with a small common-mode inductor and a ground capacitor (Y capacitor).

[0037] However, in this configuration, the common-mode voltage cannot be attenuated, and the common-mode current on the motor side increases. Such a noise filter on the power supply side cannot reduce the radiated noise caused by the common-mode current on the motor side, nor the shaft voltage that causes electrolytic corrosion of the motor bearings. Furthermore, such a noise filter on the power supply side cannot reduce the intrusion of electromagnetic noise into the current sensor, angle sensor, and inverter control circuit.

[0038] On the other hand, as described in Patent Document 1 above, electromagnetic noise countermeasures have been proposed that involve installing a noise filter between the inverter and the motor. Furthermore, a configuration has been proposed for such a motor-side noise filter that suppresses the common-mode voltage itself, which is the cause of electromagnetic noise. In such a configuration, the common-mode current on both the power supply side and the motor side is attenuated. Therefore, in such a configuration, it is possible to reduce the radiated noise caused by the common-mode current on the motor side, which is a problem with the above-mentioned power supply-side noise filter, and the shaft voltage that causes electrolytic corrosion of the motor bearings.

[0039] However, in such motor-side noise filters, the common-mode inductor or common-mode transformer that constitutes the noise filter requires at least several turns. Therefore, in high-current inverters, the noise filter becomes larger.

[0040] For example, a configuration has been proposed in which a differential mode inductor and a common mode inductor are installed between the inverter and the motor. In this configuration, a differential mode capacitor is connected to each phase connection to the motor, and the other end of a filter capacitor, one end of which is connected to the input terminal of the inverter, is connected to each differential mode capacitor. In this configuration, the differential mode inductor and differential mode capacitor constitute a sinusoidal filter. In this configuration, the common mode inductor, differential mode capacitor, and filter capacitor constitute a common mode filter. However, differential mode inductors are very large. Common mode inductors also become large because they require several turns.

[0041] Another proposed configuration involves connecting small non-zero-sequence chokes to the outputs of each phase of the inverter, instead of using large differential-mode inductors. In this configuration, the non-zero-sequence chokes are connected to the primary winding of a common-mode transformer, and the outputs of each phase of the inverter are connected to the secondary winding of the common-mode transformer. In this configuration, the common-mode voltage is detected by the non-zero-sequence chokes, and the common-mode voltage is attenuated by the common-mode transformer. However, common-mode transformers require several turns to ensure sufficient excitation inductance, resulting in a larger overall size.

[0042] Therefore, conventional common-mode inductors and common-mode transformers require at least several turns. Consequently, conventional noise filters are unsuitable, especially for high-current inverters where the conductor cross-sectional area is large.

[0043] On the other hand, in this embodiment, a common mode filter circuit 10 is provided, which is connected between an inverter 30 having a pair of input terminals 30a, 30b connected to a power supply 20 and three output terminals 30u, 30v, 30w that output three-phase AC, and a three-phase AC motor 40 that is supplied with three-phase AC from the output terminals 30u, 30v, 30w of the inverter 30. The common mode filter circuit 10 comprises three common mode transformers 61, 62, 63 that cancel out the common mode voltage of the three-phase AC, and three pairs of capacitors 71, 72, 73, 74, 75, 76 connected to the common mode transformers 61, 62, 63 and the input terminals 30a, 30b of the inverter 30, respectively.

[0044] One end 61a, 62a, and 63a of the primary windings 61t, 62t, and 63t of the three common-mode transformers 61, 62, and 63, respectively, are connected to the three output terminals 30u, 30v, and 30w of the inverter 30.

[0045] The other ends 61b, 62b, and 63b of the primary windings 61t, 62t, and 63t of the three common-mode transformers 61, 62, and 63, respectively, are connected to the other ends 71b, 73b, and 75b of one of the three pairs of capacitors 71, 72, 73, 74, 75, and 76, which are each connected to one of the input terminals 30a, 30b of the inverter 30, with one end 71a, 73a, and 75a connected to the other end 71b, 73b, and 75b of capacitors 71, 72, 73, 74, and 75, and capacitors 75, 76, respectively.

[0046] Furthermore, the other ends 61b, 62b, and 63b of the primary windings 61t, 62t, and 63t of the three common-mode transformers 61, 62, and 63 are connected to the other ends 72b, 74b, and 76b of the other capacitors 72, 74, and 76 of three pairs of capacitors 71, 72, 73, 74, 75, and 76, respectively, of which one end 72a, 74a, and 76a are connected to the other input terminal 30b of the pair of input terminals 30a, 30b of the inverter 30. With this configuration, a common-mode voltage is detected on the primary windings 61t, 62t, and 63t of the three common-mode transformers 61, 62, and 63.

[0047] The three phase secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w of the three common mode transformers 61, 62, and 63 are each connected in series with each other. One end 64ua, 64va, and 64wa of the three phase secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w of the three common mode transformers 61, 62, and 63, which are connected in series with each other, are each connected to the three output terminals 30u, 30v, and 30w of the inverter 30. The other ends 64ub, 64vb, and 64wb of the three phase secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w of the three common mode transformers 61, 62, and 63, which are connected in series with each other, are connected to a three-phase AC motor 40.

[0048] In each of the three common-mode transformers 61, 62, and 63, the primary windings 61t, 62t, and 63t are for each phase, and the secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w are for three phases together. Since the ratio of the number of turns of the primary windings 61t, 62t, and 63t to the number of turns of the secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w is 3:1, the common-mode voltage is appropriately canceled from the voltage of each phase. As a result, the common-mode voltage can be reduced.

[0049] [[IDID=4]]Let the common-mode voltage of each phase at the output terminals 30u, 30v, and 30w of the inverter 30 be v cm ,

[0050] , v , w , , u , v , u , u , , w , , u , w , v , u , v v , v w And let the common-mode voltage of each phase filtered by the common-mode filter circuit 10 be v u ´, v v ´, v w ´. For example, in the secondary windings 61u, 62u, and 63u of the U phase, as shown in the following formula (1), in each of the three common-mode transformers 61, 62, and 63, the common-mode voltage v u , v v , v w is subtracted by 1 / 3 each. v u ´ = v u - (1 / 3)·v u - (1 / 3)·v v - (1 / 3)·v w (1)

[0050] The sum of 1 / 3 of the common-mode voltage v u , v v , v w of each phase is equal to the common-mode voltage v cm of each phase. Therefore, as shown in the following formula (2), in the U phase, the common-mode voltage can be canceled. The same applies to the V phase and the W phase. v u ´ = v u - (1 / 3)·v u - (1 / 3)·v v - (1 / 3)·v w = v u - vcm (2)

[0051] For example, as shown in Figure 3(A), a significant common-mode voltage is generated when there is no filter. As shown in Figure 3(B), even when a common-mode choke is installed, the high-frequency components are only slightly attenuated. On the other hand, as shown in Figure 3(C), in the common-mode filter circuit 10 of this embodiment, the common-mode voltage is attenuated to the point where it appears almost zero on the same voltage axis scale as in the case without a filter in Figure 3(A). As shown in Figure 3(D), in the common-mode filter circuit 10 of this embodiment, the common-mode voltage can be confirmed by increasing the voltage axis scale to 20 times that of the case without a filter in Figure 3(A).

[0052] Furthermore, in this embodiment, the ratio of the number of turns on the primary side to the number of turns on the secondary side is 3:1, so the number of turns of the thicker secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, 63w can be reduced. Since the current flowing through the primary windings 61t, 62t, 63t is small, the primary windings 61t, 62t, 63t can be made thin, and even with a large number of turns, they do not occupy a large space. Therefore, the common mode transformers 61, 62, 63 can be significantly miniaturized. In other words, in this embodiment, the excitation inductance of the common mode transformers 61, 62, 63 can be secured while supporting the high-current inverter 30.

[0053] Furthermore, in this embodiment, the number of turns for the primary windings 61t, 62t, and 63t of each of the three common mode transformers 61, 62, and 63 is 3, and the number of turns for the secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w of each of the three common mode transformers 61, 62, and 63 is 1. Therefore, the number of turns for the thicker secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w can be minimized. Since the current flowing through the primary windings 61t, 62t, and 63t is small, the primary windings 61t, 62t, and 63t can be made thinner. Also, since the number of turns for the primary windings 61t, 62t, and 63t is 3, they occupy only a small space. Therefore, the common mode transformers 61, 62, and 63 can be significantly miniaturized.

[0054] Furthermore, in this embodiment, since the current flowing through the primary windings 61t, 62t, and 63t is small, the primary windings 61t, 62t, and 63t can be made thin. The primary windings 61t, 62t, and 63t are wound three times by passing through the inner 65i and outer 65o of the annular iron core 65 of the common mode transformers 61, 62, and 63, and therefore occupy only a small space. Furthermore, since the secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w of each of the three common mode transformers 61, 62, and 63 are wound only once by passing through the inner 65i of the annular iron core 65 of each of the three common mode transformers 61, 62, and 63 only once, it is easy to increase the space factor of the secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, and 63w, and thus easy to miniaturize. Consequently, the common mode transformers 61, 62, and 63 can be significantly miniaturized.

[0055] Although embodiments have been described above, embodiments are not limited to those described above. For example, in this embodiment, an annular core 65 is disclosed that completely encloses the secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, 63w in a continuous manner. However, insofar as the magnetic circuit is formed by the core 65, an annular core 65 is also included that is divided at some point and encloses the secondary windings 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, 63w discontinuously. [Industrial applicability]

[0056] According to one aspect of the common-mode filter circuit of this disclosure, the common-mode voltage can be reduced. [Explanation of Symbols]

[0057] 10 Common-mode filter circuit 20 Power supply 30 Inverters 30a, 30b Input terminals 30u, 30v, 30w output terminal 40 Three-phase AC motor 50 Motor Cables 61, 62, 63 Common Mode Transformers 61t, 62t, 63t Primary winding 61u, 61v, 61w, 62u, 62v, 62w, 63u, 63v, 63w Secondary winding 61a,62a,63a One end 61b, 62b, 63b other end 64ua,64va,64wa one end 64ub, 64vb, 64wb other end 65 Iron Heart 65i Inside 65° Outer 71, 72, 73, 74, 75, 76 Capacitors 71a,72a,73a,74a,75a,76a One end 71b, 72b, 73b, 74b, 75b, 76b Other end

Claims

1. A common mode filter circuit is connected between an inverter having a pair of input terminals connected to a power source and three output terminals that output three-phase AC, and a three-phase AC motor that is supplied with the three-phase AC from the output terminals of the inverter, Three common-mode transformers that cancel out the common-mode voltage of the three-phase AC, Three pairs of capacitors connected to the common mode transformer and the input terminals of the inverter, Equipped with, One end of the primary winding of each of the three common-mode transformers is connected to each of the three output terminals of the inverter. The other end of the primary winding of each of the three common-mode transformers is connected to the other end of one of the three pairs of capacitors, each of which has one end connected to one of the pair of input terminals of the inverter, and to the other end of the other of the three pairs of capacitors, each of which has one end connected to the other of the pair of input terminals of the inverter. Each of the three phase secondary windings of the three common-mode transformers is connected in series with the others. One end of each of the three phase secondary windings of the three common-mode transformers connected in series with each other is connected to each of the three output terminals of the inverter. The other ends of the three phase secondary windings of the three common-mode transformers, which are connected in series with each other, are connected to the three-phase AC motor. The ratio of the number of turns in the primary winding to the number of turns in the secondary winding of each of the three common-mode transformers is 3:

1. Each of the three common mode transformers has 3 turns in its primary winding, and each of the three common mode transformers has 1 turn in its secondary winding. The primary winding of each of the three common mode transformers is wound three times, passing inside and outside the annular iron core of the common mode transformer. The secondary winding of each of the three common mode transformers is wound once by passing only once inside the annular core of each of the three common mode transformers. A common mode filter circuit in which the annular iron cores of each of the three common mode transformers are formed in a continuous manner so as to surround the secondary windings of each of the three common mode transformers connected in series with each other.

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