Filter circuit

Abstract

To provide a filter circuit that can reduce resonance.SOLUTION: An LC filter 20 is connected to an inverter 12 and is configured by combining an inductor unit 21, which is composed of a first inductor 23 and a second inductor 24, with a capacitor unit 22. When a current of a first current value Ia or more flows, a first core 23a of the first inductor 23 is configured not to be magnetically saturated, while a second core 24a of the second inductor 24 is configured to be magnetically saturated. As a result, when a current of the first current value Ia flows through the inductor unit 21, the inductance decreases from a first value La to a second value Lb. The first current value Ia is a value equal to or greater than the maximum value Imax of the DC current that flows when the inverter 12 is operated, and is smaller than the resonance suppression current Ir that is allowed as a resonance current.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a filter circuit. [Background technology]

[0002] Conventionally, LC filters, which combine inductors and capacitors to cut signals in a specific frequency band, are known as filter circuits. These LC filters are used to reduce noise superimposed on power lines (power supply lines) in inverters and converters of electric vehicles, etc.

[0003] However, such an LC filter has a trade-off problem: when the noise frequency approaches the resonant frequency of the LC filter, resonance occurs in the LC filter, increasing the current flowing through the LC filter. Therefore, it has been considered to use a diode to suppress the increase in harmonic current caused by resonance. Such a technique is described, for example, in Patent Document 1. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-50294 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when an attempt is made to reduce the increase in harmonic current by blocking the current in one direction using a diode, it was discovered that a surge voltage occurs between the anode and cathode of the diode, which becomes a new source of noise. While it is conceivable to provide a snubber circuit to suppress this noise, this would complicate the circuit configuration and create new problems such as an increase in the size of the circuit.

[0006] The present invention has been made in view of the above circumstances, and has as its main object to provide a filter circuit capable of reducing resonance. [Means for solving the problem]

[0007] A filter circuit for solving the above problem is a filter circuit that is connected to an electrical load and is configured by combining an inductor section consisting of one or more inductors and a capacitor section consisting of one or more capacitors, wherein the inductor section has an inductance that decreases from a first value to a second value when a current equal to or greater than a first current value flows, and the first current value is equal to or greater than the maximum value of the direct current that flows when the electrical load is operated, and is smaller than a resonance suppression current that is allowed as a resonance current.

[0008] When a first current value, which is equal to or greater than the maximum value of the DC current that flows when the electrical load is operated but is smaller than the resonance suppression current allowed as the resonance current, flows through the inductor section, the inductance of the inductor section decreases to a second value. This shifts the resonance frequency and allows the resonance to converge. This reduces the peak value of the current and reduces the voltage applied to the capacitor section before it exceeds the current value allowed as the resonance current, i.e., the resonance suppression current. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic configuration diagram of a power conversion system. [Figure 2] FIG. 4 is a diagram showing the relationship between the inductance of an inductor section and a current value. [Figure 3] FIG. 10 is a diagram showing the attenuation of an LC filter. [Figure 4] FIG. 4 is a diagram for explaining a transition of a current during resonance. [Figure 5] FIG. 10 is a schematic configuration diagram of a power conversion system according to a second embodiment. [Figure 6] FIG. 10 is a diagram schematically illustrating an inductor section according to a second embodiment. [Figure 7]FIG. 10 is a diagram schematically illustrating an inductor section according to a third embodiment. [Figure 8] FIG. 10 is a diagram schematically illustrating an inductor section according to a fourth embodiment. [Figure 9] FIG. 10 is a schematic configuration diagram of a power conversion system according to a fifth embodiment. [Figure 10] FIG. 11 is a diagram schematically illustrating an inductor section according to a fifth embodiment. [Figure 11] FIG. 13 is a diagram schematically illustrating an inductor section according to a sixth embodiment. [Figure 12] FIG. 10 is a diagram schematically illustrating an inductor section according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Several embodiments embodying filter circuits according to the present disclosure will be described with reference to the drawings. In several embodiments, functionally and / or structurally corresponding and / or associated parts may be assigned the same reference numerals or reference numerals that differ in the hundredth or higher digit. For corresponding and / or associated parts, reference may be made to the descriptions of other embodiments.

[0011] (First embodiment) A first embodiment will be described below with reference to the drawings. A power conversion system 10 of this embodiment is mounted on a vehicle such as an electric vehicle or a hybrid vehicle. As shown in Fig. 1, the power conversion system 10 of this embodiment includes a motor 11, an inverter 12 as a power converter, a battery 13 as a power source, a control device 14, and the like.

[0012] The motor 11 is, for example, a permanent magnet field type synchronous machine. The motor 11 is connected to an inverter 12 and functions as a main engine of the vehicle. The inverter 12 is, for example, a three-phase inverter and is connected to a battery 13 via an LC filter 20. The inverter 12 is a power converter that converts DC power supplied from the battery 13 into three-phase AC power and supplies it to the motor 11. The inverter 12 and the motor 11 are also electrical loads.

[0013] The battery 13 is, for example, a battery pack including a series connection of unit cells, and is a DC power supply in this embodiment. The unit cell is one battery cell or a series connection of multiple battery cells. The battery cell is, for example, a secondary battery such as a lithium-ion battery. The control device 14 is, for example, an ECU, and controls the motor 11 by controlling the inverter 12.

[0014] The positive terminal of the battery 13 is electrically connected to a positive bus 15 (positive power supply line), and the negative terminal of the battery 13 is electrically connected to a negative bus 16 (negative power supply line). The positive terminal of the inverter 12 is connected to the positive bus 15 via an LC filter 20, and the negative terminal of the inverter 12 is connected to the negative bus 16 via the LC filter 20. DC power is supplied to the inverter 12 from the battery 13 via the positive bus 15 and the negative bus 16.

[0015] A smoothing capacitor C10 is connected between the positive bus bar 15 and the negative bus bar 16. That is, the smoothing capacitor C10 is connected in parallel with the inverter 12 and the battery 13. The smoothing capacitor C10 may be provided inside or outside the inverter 12. In this embodiment, between the battery 13 and the LC filter 20, a first end of the smoothing capacitor C10 is connected to the positive bus bar 15 side, and a second end of the smoothing capacitor C10 is connected to the negative bus bar 16 side.

[0016] Next, the LC filter 20 will be described. The LC filter 20 is a filter circuit that attenuates signals in a specific frequency band, and in this embodiment, it is a low-pass filter for cutting noise. The LC filter 20 is provided between the positive bus 15 and negative bus 16 to which the inverter 12 is connected, and is configured by combining an inductor section 21 composed of one or more inductors and a capacitor section 22 composed of one or more capacitors. This will be described in detail below.

[0017] In this embodiment, inductor section 21 is composed of a series connection of first inductor 23 and second inductor 24. Capacitor section 22 is composed of one capacitor. Note that capacitor section 22 may be composed of multiple capacitors. Furthermore, inductor section 21 does not have to be composed of only an inductor, but may be composed of a combination of other elements, such as resistors. Similarly, capacitor section 22 does not have to be composed of only a capacitor, but may be composed of a combination of other elements, such as resistors.

[0018] The inductor unit 21 is connected in series to the positive bus 15. That is, it is connected between the positive terminal of the battery 13 and the positive terminal of the inverter 12. On the other hand, of both ends of the capacitor unit 22, a first end is connected to the positive bus 15 side, and a second end is connected to the negative bus 16 side. The first end of the capacitor unit 22 is connected between the inductor unit 21 and the positive terminal of the inverter 12.

[0019] The first inductor 23 is configured by winding a first coil 23b around a first core 23a, and the second inductor 24 is configured by winding a second coil 24b around a second core 24a. When a current of a predetermined first current value Ia flows through the inductor section 21, the first core 23a does not become magnetically saturated, but the second core 24a becomes magnetically saturated.

[0020] As a result, as shown in FIG. 2, when a current equal to or greater than the first current value Ia flows through the inductor unit 21, the inductance decreases from the first value La to the second value Lb. More specifically, when the current is less than the first current value Ia, the inductance of the inductor unit 21 is equal to the sum of the inductance L1 (shown by the dashed-dotted line) of the first inductor 23 and the inductance L2 (shown by the dashed-dotted line) of the second inductor 24. That is, the first value La≒L1+L2. When the current is at the first current value Ia, as shown by the dashed-dotted line in FIG. 2, the second core 24a is magnetically saturated and the inductance L2 of the second inductor 24 approaches zero, so the inductance of the inductor unit 21 becomes approximately equal to the inductance L1 of the first inductor 23. That is, the second value Lb≒L1. At the first current value Ia, the first core 23a is not magnetically saturated, so the inductance L1 of the first inductor 23 remains substantially the same.

[0021] Furthermore, when a current equal to or greater than a second current value Ib, which is greater than the first current value Ia, flows through the inductor section 21, the first core 23a becomes magnetically saturated, and as shown in Figure 2, the inductance L1 of the first inductor 23 also decreases, and as a result, the inductance of the inductor section 21 also decreases from the second value Lb.

[0022] The first current value Ia will be described. The first current value Ia is equal to or greater than the maximum value of the DC current (hereinafter referred to as the maximum operating current Imax) that is passed through the inverter 12 when the motor 11 is operated properly, and is smaller than the resonance suppression current Ir that is allowed as a resonance current. The maximum operating current Imax is determined based on the specifications of the connected electrical load, for example, the specifications of the motor 11 and the inverter 12.

[0023] The resonance suppression current Ir will now be described. When a current (AC current) flows through the capacitor section 22, the capacitor section 22 generates heat. For this reason, the capacitor section 22 is designed to be heat-resistant so that it can withstand a certain amount of heat generation. However, if the heat generation exceeds the heat-resistance design limit, the reliability of the capacitor section 22 decreases. Therefore, even if a current (harmonic current) due to resonance flows through the capacitor section 22 and generates heat in the capacitor section 22, a resonant current that is permissible as being within the heat-resistance design limit of the capacitor section 22 is set as the resonance suppression current Ir. In other words, the resonance suppression current Ir is set based on the heat-resistance design of the capacitor section 22. The first current value Ia is set to be smaller than the resonance suppression current Ir, and the second current value Ib is set to be larger than the resonance suppression current Ir.

[0024] There are various methods for configuring the second core 24a to be magnetically saturated while preventing the first core 23a from being magnetically saturated when a current of the first current value Ia flows through the inductor portion 21. In this embodiment, for example, the material (magnetic body material) of the first core 23a is a metallic magnetic body (metal composite), and the material of the second core 24a is ferrite.

[0025] When the first core 23a is made of a magnetic metal and the second core 24a is made of ferrite, the saturation characteristics of the inductance with respect to the current are different, as shown in Fig. 2. That is, the inductance L2 of the second inductor 24 drops sharply at a certain current, while the inductance L1 of the first inductor 23 drops more gradually. As a result, the inductor section 21 has the inductance characteristics shown in Fig. 2, as described above.

[0026] Alternatively or additionally to the above method, a gap may be provided in the first core 23a, while no gap may be provided in the second core 24a. Even in this configuration, it is necessary to adjust the size of the gap so that the first core 23a is not magnetically saturated when a current of the first current value Ia flows.

[0027] Alternatively, gaps may be provided in both the first core 23 a and the second core 24 a, with the gap in the first core 23 a being larger than the gap in the second core 24 a. Even in this configuration, it is necessary to adjust the size of the gap so that when a current of the first current value Ia flows, the first core 23 a is not magnetically saturated, but the second core 24 a is magnetically saturated.

[0028] Alternatively, or in addition to the above method, the number of turns of the first coil 23b of the first inductor 23 may be made smaller than the number of turns of the second coil 24b of the second inductor 24. That is, because the number of turns and magnetic flux in an inductor are proportional to each other, the number of turns of the second coil 24b of the second inductor 24 may be increased to increase the magnetic flux passing through the second coil 24b and make it easier to achieve magnetic saturation. Even in this configuration, as in the above, it is necessary to adjust the number of turns so that the first core 23a is not magnetically saturated when a current of the first current value Ia flows, while the second core 24a is magnetically saturated.

[0029] The operation of the LC filter 20 configured as described above will be described. FIG. 3 shows the characteristics of the LC filter 20, with the horizontal axis representing frequency and the vertical axis representing attenuation (unit: dB), and FIG. 4 shows the characteristics of the inductor section 21, with the horizontal axis representing current and the vertical axis representing inductance. Referring to FIG. 3, the behavior of the LC filter 20 when noise having a frequency in a resonance band B2 near the resonance frequency fc1 passes through will be described. The resonance frequency fc1 of the LC filter 20 is shown in equation (1). "L1" is the inductance of the first inductor 23, "L2" is the inductance of the second inductor 24, and "C" is the capacitance of the capacitor section 22.

number

[0030] 3, when the frequency of a signal passing through the LC filter 20 is in the pass band B1 (such as a control signal), the signal passes through as is without being attenuated, just like a normal low-pass filter. On the other hand, when the frequency of a signal passing through the LC filter 20 is in the attenuation band B3 (such as harmonic noise), the signal is attenuated just like a normal low-pass filter.

[0031] On the other hand, when the frequency of the signal passing through the LC filter 20 falls within the resonance band B2, resonance occurs, and the peak value of the voltage increases, as does the peak value of the current. When the peak value of the current increases, it may momentarily exceed the first current value Ia, as indicated by arrow Y1 in Fig. 4. For ease of illustration and description, the width of the arrow Y1, i.e., the current value that momentarily exceeds the first current value Ia, is exaggerated and shown larger.

[0032] When the resonant current becomes equal to or greater than the first current value Ia, as indicated by the arrow Y2, the second core 24a of the second inductor 24 becomes magnetically saturated, and the inductance of the inductor unit 21 decreases from the first value La. However, as described above, even when the resonant current becomes equal to or greater than the first current value Ia, the first core 23a does not become magnetically saturated. Therefore, even when the inductance of the inductor unit 21 decreases from the first value La, the inductance of the inductor unit 21 remains at the second value Lb, which is approximately equal to the inductance L1 of the first inductor 23.

[0033] As a result, the LC filter 20 becomes substantially equivalent to an LC filter configured with the first inductor 23 and the capacitor section 22. As a result, as shown in FIG. 3, the resonant frequency of the LC filter 20 changes from fc1 to fc2, and the resonant band B2 shifts. Specifically, the resonant band B2 shifts to a resonant band B2' on the right side (the side where the frequency increases) in FIG. 3. The resonant band B2' is a band near the resonant frequency fc2 of the LC filter configured with the first inductor 23 and the capacitor section 22. Here, the resonant frequency fc2 of the LC filter 20 is expressed by equation (2).

number

[0034] As a result, the band that was previously the resonance band B2 becomes the pass band of the LC filter configured by the first inductor 23 and the capacitor unit 22, and the resonance converges. As a result, the peak value of the current decreases, as shown by the arrow Y3 in Fig. 4. Accordingly, the peak value of the voltage also decreases, as shown by the arrow Y4 in Fig. 3.

[0035] When the current continues to decrease and becomes less than the first current value Ia, the inductance of the inductor section 21 returns to the first value La, and the cycle of the arrows Y1 → Y2 → Y3 described above may be repeated again.

[0036] The effects of the first embodiment will be described below.

[0037] When a current having a first current value Ia, which is equal to or greater than the maximum operating current value Imax and smaller than the resonance suppression current Ir allowed as a resonance current, flows through the inductor section 21, the inductance of the inductor section 21 decreases from the first value La to the second value Lb. This shifts the resonance frequency from fc1 to fc2, and the previous resonance band B2 becomes a pass band, allowing the resonance to converge. The first current value Ia is equal to or greater than the maximum value (Imax) of the DC current flowing when the inverter 12 is operating and smaller than the resonance suppression current (Ir) allowed as a resonance current. This reduces the peak value of the current before it exceeds the current value allowed as a resonance current (resonance suppression current Ir), thereby reducing the peak value of the voltage applied to the capacitor section 22. This prevents excessive current from flowing through the capacitor section 22.

[0038] When a current equal to or greater than a second current value Ib, which is greater than the resonance suppression current Ir, flows through the inductor section 21, the inductance of which decreases again from the second value Lb. Therefore, the inductance of the inductor section 21 does not decrease from the second value Lb until a current equal to or greater than the second current value Ib flows. Therefore, until a current equal to or greater than the second current value Ib flows through the inductor section 21, the inductance does not become zero, and it is possible to suppress the flow of a large current.

[0039] At the first current value Ia, the inductor section 21 can be easily constructed by connecting in series a first inductor 23 having a first core 23a that does not become magnetically saturated and a second inductor 24 having a second core 24a that becomes magnetically saturated.

[0040] The second core 24a is made of a material that is more susceptible to magnetic saturation than the first core 23a. In this embodiment, the first core 23a is made of a metallic magnetic material, and the second core 24a is made of ferrite. Due to the characteristics of these materials, the inductance L2 of the second inductor 24 decreases more steeply than the inductance L1 of the first inductor 23. That is, the inductance L2 of the second inductor 24 decreases more steeply when a current equal to or greater than the first current value Ia flows, while the inductance L1 of the first inductor 23 decreases more gradually than the inductance L1 of the second inductor 24 when a current equal to or greater than the second current value Ib flows. Therefore, the inductance of the inductor unit 21 also decreases more steeply when the current exceeds the first current value Ia, significantly shifting the resonance band. This allows resonance to be immediately suppressed, thereby suppressing an increase in current.

[0041] The resonance suppression current Ir is determined based on the heat resistance design of the capacitor section 22. Therefore, even if resonance occurs temporarily, the reliability of the capacitor section 22 will not be reduced due to heat generation in the capacitor section 22.

[0042] (Modification of the first embodiment) In the first embodiment, the locations of the first inductor 23 and the second inductor 24 may be interchanged. Furthermore, depending on the location of the noise source, the locations of the capacitor section 22 and the inductor section 21 may be interchanged, and the inductor section 21 may be arranged on the inverter 12 side.

[0043] (Second embodiment) A second embodiment in which the configuration of the LC filter 20 of the first embodiment is partially modified will be described.

[0044] 5, the inductor section 121 of the LC filter 20 of the second embodiment includes a first inductor 123 which is a choke coil configured by winding two coils 123b and 123c around a single toroidal first core 123a, and a second inductor 124 which is a choke coil configured by winding two coils 124b and 124c around a single toroidal second core 124a. The inductor section 121 is a series connection of the first inductor 123 and the second inductor 124.

[0045] More specifically, as shown in FIG. 6, a series connection of a coil 123b of the first inductor 123 and a coil 124b of the second inductor 124 is connected in series to the positive bus 15. Similarly, a series connection of a coil 123c of the first inductor 123 and a coil 124c of the second inductor 124 is connected in series to the negative bus 16. Note that the coils 123b and 123c are wound in different directions, and the coils 124b and 124c are wound in different directions. Furthermore, the coils 123b and 124b are wound in the same direction, and the coils 123c and 124c are wound in the same direction. Specifically, the positions are the points (·) representing polarities shown on 123a, 123b, 124a, and 124b in FIG. 5. Furthermore, the number of turns of the coils 123b and 123c is the same, and the number of turns of the coils 124b and 124c is the same. The number of turns of the coils 123b and 123c and the number of turns of the coils 124b and 124c may be the same or different.

[0046] The first core 123a is made of a metallic magnetic material as in the first embodiment, and the second core 124a is made of ferrite as in the first embodiment. Note that the characteristics and functions of the LC filter 20 are the same as those of the first embodiment, and therefore a description thereof will be omitted.

[0047] According to the second embodiment, the same effects as those of the first embodiment can be obtained.

[0048] (Third embodiment) A third embodiment will be described, in which the configuration of the LC filter 20 of the second embodiment is partially modified.

[0049] 7, the inductor section 221 of the third embodiment is configured with a series connection of a first inductor 223 and a second inductor 224. However, the third embodiment differs from the second embodiment in the configuration of the first core 223a of the first inductor 223. The configuration of the second inductor 224 is similar to that of the second inductor 124 of the second embodiment, and so the same reference numerals are used and detailed description thereof is omitted.

[0050] As shown in Fig. 7, the first core 223a is configured by providing a gap (gap) in a part of a toroidal core. That is, the first core 223a is approximately C-shaped. The first core 223a is also made of ferrite, similar to the second core 124a. That is, the first inductor 223 differs from the second inductor 224 in that the first core 223a has a gap, while the second core 124a does not have a gap. Note that the coils of the first inductor 223 are the same as the coils 123b and 123c of the second embodiment, and therefore the same reference numerals are used and description thereof will be omitted.

[0051] The first core 223a has a gap, which makes it less susceptible to magnetic saturation than the second core 124a. The first core 223a of the third embodiment is provided with an adjusted gap size so that it does not become magnetically saturated even when a current of the first current value Ia flows through the inductor portion 221, but begins to become magnetically saturated when a current of the second current value Ib or more flows.

[0052] As a result, the first inductor 223 has characteristics similar to those of the first inductor 23 of the first embodiment and the first inductor 123 of the second embodiment. Therefore, the characteristics and operation of the LC filter 20 of the third embodiment are also substantially similar to those of the first and second embodiments, and therefore a description thereof will be omitted.

[0053] According to the third embodiment, it is possible to obtain the same effects as in the first embodiment. Furthermore, with the simple configuration of providing a gap, it is possible to prevent magnetic saturation even when a current of the first current value Ia flows through the inductor portion 221. Furthermore, since the current that causes magnetic saturation can be changed by changing the size of the gap, adjustment is easy.

[0054] (Modification of the third embodiment) In the third embodiment, gaps may be provided in both the first core 223a and the second core 124a. In this case, the gap in the first core 223a needs to be larger than the gap in the second core 124a. In this case, when a current of the first current value Ia flows, the size of the gap needs to be adjusted so that the first core 223a is not magnetically saturated, while the second core 124a is magnetically saturated.

[0055] Furthermore, the method used in the third embodiment of providing a gap in the first core 223a of the first inductor 223 or adjusting the size of the gap between the first core 223a of the first inductor 223 and the second core 124a of the second inductor 224 may also be adopted in the second embodiment.

[0056] (Fourth embodiment) A fourth embodiment in which the configuration of the LC filter 20 of the second embodiment is partially modified will be described with reference to FIG.

[0057] As in the second embodiment, the inductor section 321 of the fourth embodiment is configured with a series connection of a first inductor 323 and a second inductor 324. However, unlike the second embodiment, the fourth embodiment differs from the second embodiment in the configuration of the first core 323a and the configuration of the coils 323b and 323c of the first inductor 323. The configuration of the second inductor 324 is similar to that of the second inductor 124 of the second embodiment, and so the same reference numerals are used and detailed description thereof is omitted.

[0058] In the fourth embodiment, the first core 323a has the same configuration as the second core 124a, that is, the first core 323a is toroidal and made of ferrite.

[0059] On the other hand, in the fourth embodiment, the number of turns of the coils 323b and 323c of the first inductor 323 is smaller than the number of turns of the coils 124b and 124c of the second inductor 324. In other words, the number of turns of the coils 124b and 124c of the second inductor 324 is greater. Therefore, even if the same current flows through the first inductor 323 and the second inductor 324, the magnetic flux generated in the first inductor 323 is smaller than the magnetic flux generated in the second inductor 324, making it less likely to become magnetically saturated.

[0060] In the fourth embodiment, the number of turns of the coils 323b and 323c of the first inductor 323 is adjusted so that the first core 323a does not become magnetically saturated when a current of the first current value Ia flows through the inductor unit 321, but begins to become magnetically saturated when a current of the second current value Ib or more flows. On the other hand, as in the above embodiments, the number of turns of the coils 124b and 124c of the second inductor 324 is adjusted so that the second core 124a becomes magnetically saturated when a current of the first current value Ia flows through the inductor unit 321.

[0061] As a result, the first inductor 323 has characteristics similar to those of the first inductor 123 of the first embodiment and the first inductor 223 of the second embodiment. Therefore, the characteristics and operation of the LC filter 20 of the fourth embodiment are also substantially similar to those of the first and second embodiments, and therefore a description thereof will be omitted.

[0062] In the fourth embodiment, in addition to the same effects as those of the second embodiment, the following effects can be obtained.

[0063] By adjusting the number of turns, it is possible to change whether magnetic saturation occurs or not, which simplifies the design.

[0064] The method of adjusting the number of turns in the fourth embodiment may be adopted in the second and third embodiments.

[0065] (Fifth embodiment) A fifth embodiment in which the configuration of the LC filter 20 of the second embodiment is partially modified will be described with reference to FIGS.

[0066] As in the second embodiment, the inductor section 421 of the fifth embodiment is configured with a series connection of a first inductor 423 and a second inductor 424. However, unlike the second embodiment, the fifth embodiment differs from the second embodiment in the configuration of the second inductor 424. Note that the first inductor 423 is the same as in the second embodiment, and therefore the same reference numeral is used and a description thereof is omitted.

[0067] 10, second core 424a has the same shape as first core 123a (i.e., a toroidal core) and is made of ferrite. As described above, first core 123a is made of a magnetic metal material that is not susceptible to magnetic saturation.

[0068] In the second inductor 424, two coils 424b and 424c are provided on the second core 424a. The coil 424b is connected to the positive bus 15, and the coil 424c is connected to the negative bus 16. The winding direction of the coil 424c is changed midway. Therefore, the coil 424c can be said to be composed of a series connection of the coils 424c1 and 424c2, which have different winding directions. The number of turns of the coil 424b is the same as the number of turns of the coil 424c (the sum of the number of turns of the coil 424c1 and the number of turns of the coil 424c2).

[0069] Coils 424b and 424c1 are wound in different directions, while coils 424b and 424c2 are wound in the same direction. In other words, coils 424c1 and 424c2 are wound in different directions. Specifically, this is the position of the dots (·) indicating polarity on coils 424b, 424c1, and 424c2 in FIG. 9.

[0070] Because of this configuration, second inductor 424 functions both as a normal coil that reduces normal mode noise and as a common choke coil that reduces common mode noise. In Fig. 10, the shaded area corresponds to the normal coil, and the remaining area corresponds to the common choke coil.

[0071] That is, when normal mode noise is present, the magnetic flux generated by part of coil 424b (the coil in the non-shaded area) and the magnetic flux generated by coil 424c2 cancel each other out. Therefore, when normal mode noise is present, the remaining coil 424b (the coil in the shaded area) and coil 424c1 function as normal coils, reducing the normal mode noise.

[0072] On the other hand, when common mode noise is present, the magnetic flux generated by part of coil 424b (the coil in the shaded area) and the magnetic flux generated by coil 424c1 cancel each other out. Therefore, when common mode noise is present, the remaining coil 424b (the coil other than the shaded area) and coil 424c2 function as a common choke coil, reducing the common mode noise.

[0073] The number of turns of each coil 424b, 424c1, 424c2 and the physical size (size, cross-sectional area, etc.) of the second core 424a are adjusted so that when a current of the first current value Ia flows, a magnetic flux that magnetically saturates the second core 424a is generated by the second inductor 424 (more specifically, by the part that functions as a normal coil).

[0074] As a result, the inductor section 421 has characteristics similar to those of the inductor sections 21 and 121 of the first and second embodiments. Therefore, the characteristics and actions of the LC filter 20 of the fifth embodiment are also substantially similar to those of the first and second embodiments. Therefore, a description thereof will be omitted.

[0075] According to the fifth embodiment, it is possible to obtain the same effects as in the first embodiment. Furthermore, since the second inductor 424 has the function of a common choke coil, there is no need to provide a separate common choke coil, which reduces the number of parts and makes it possible to make the device smaller.

[0076] (Modification of the fifth embodiment) In the fifth embodiment, the total number of turns of the coil 424c1 and the coil 424c2 may be different from the number of turns of the coil 424b.

[0077] In the fifth embodiment, the material of the first core 123a of the first inductor 423 and the material of the second core 424a of the second inductor 424 may be changed as desired. Furthermore, the material of the first core 123a of the first inductor 423 and the material of the second core 424a of the second inductor 424 may be the same. In this case, the number of turns of each of the coils 424b, 424c1, and 424c2 and the size of the second core 424a must be adjusted appropriately. In other words, adjustments must be made so that the second inductor 424 generates a magnetic flux that magnetically saturates the second core 424a when a current of the first current value Ia flows.

[0078] (Sixth embodiment) A sixth embodiment in which the configuration of the LC filter 20 of the first embodiment is partially modified will be described.

[0079] As shown in FIG. 11, the inductor section 521 of the LC filter 20 of the sixth embodiment is configured by winding a first coil 502 and a second coil 503 around one toroidal core member 501.

[0080] The core member 501 is configured by combining a first core 501a and a second core 501b having different magnetic permeabilities. Specifically, the first core 501a is made of a metallic magnetic material, and the second core 501b is made of ferrite. As shown in Fig. 11, the core member 501 is configured by combining the annular first core 501a and the annular second core 501b. The first core 501a is formed concentrically with the second core 501b, and the outer diameter of the first core 501a is arranged to match the inner diameter of the second core 501b.

[0081] The winding is then passed through the inside of the first core 501a, then the outside of the second core 501b, and then the inside of the first core 501a again, and this process is repeated to wind the winding around the core member 501, thereby forming the first coil 502. One end of the first coil 502 is connected to the battery 13 side of the positive bus 15, and the other end is connected to the inverter 12 side of the positive bus 15.

[0082] Similarly, a winding is wound around the core member 501 to form a second coil 503. One end of the second coil 503 is connected to the negative bus bar 16 on the side of the battery 13, and the other end is connected to the negative bus bar 16 on the side of the inverter 12.

[0083] The LC filter 20 configured in this manner is an equivalent circuit to the LC filter 20 in the second embodiment, and has the same characteristics as the LC filter 20 in the second embodiment. That is, when a current of a predetermined first current value Ia flows through the inductor portion 521, the first core 501a does not reach magnetic saturation, while the second core 501b reaches magnetic saturation.

[0084] As a result, similar to the second embodiment, when a current equal to or greater than the first current value Ia flows through the inductor section 521, the inductance decreases from the first value La to the second value Lb. Note that the characteristics and operation of the LC filter 20 in the sixth embodiment are the same as those in the second embodiment, and therefore a description thereof will be omitted.

[0085] In the sixth embodiment, the number of coils can be reduced compared to the second embodiment, and the number of parts can be reduced. Note that the sixth embodiment also has the same effects as the second embodiment.

[0086] (Modification of the sixth embodiment) In the sixth embodiment, the shapes of the first core 501a and the second core 501b may be changed. For example, the second core 501b may be made larger than the first core 501a. The materials of the first core 501a and the second core 501b may also be changed. For example, the first core 501a and the second core 501b may be made of the same material. In this case, it is necessary to provide a gap only in the first core 501a, or to provide a gap in both the first core 501a and the second core 501b, thereby increasing the gap in the first core 501a.

[0087] Although the core member 501 in the sixth embodiment is configured to have a toroidal shape, its shape may be changed as desired. For example, as shown in FIG. 12, a core member 601 that is an EI core may be used. In this case, the core member 601 may be divided symmetrically, and a coil 602 may be formed by winding a wire around both cores (first core 601a and second core 601b) in the same manner. The first core 601a and second core 601b constituting the core member 601 have different magnetic permeabilities. Specifically, the first core 601a is made of a metallic magnetic material, and the second core 601b is made of ferrite. The inductor section 621 configured in this manner is an equivalent circuit to the inductor section 21 in the first embodiment and has the same effects as the second embodiment.

[0088] The shape of the core is not limited to an EI core, but may be another shape such as an EE core or an EER core.

[0089] The technical ideas that can be derived from the above-described embodiment and its modifications will be described below.

[0090] [Configuration 1] A filter circuit (20) is connected to an electrical load (12) and is configured by combining an inductor section (21, 121, 221, 321, 421, 521, 621) configured with one or more inductors (23, 24, 123, 124, 223, 224, 323, 324, 423, 424) and a capacitor section (22) configured with one or more capacitors, When a current equal to or greater than a first current value (Ia) flows through the inductor section, the inductance decreases from a first value (La) to a second value (Lb), A filter circuit in which the first current value is equal to or greater than the maximum value (Imax) of the DC current that flows when the electrical load is operated, and is smaller than a resonance suppression current (Ir) that is allowed as a resonance current.

[0091] [Configuration 2] When a current equal to or greater than a second current value (Ib) that is greater than the first current value flows through the inductor unit, the inductance of the inductor unit decreases again from the second value, 2. The filter circuit according to claim 1, wherein the second current value is greater than the resonance suppression current.

[0092] [Configuration 3] The inductor section is configured by connecting a plurality of inductors in series, the plurality of inductors include at least first inductors (23, 123, 223, 323, 423) configured by winding coils (23b, 123b, 123c, 323b, 323c) around first cores (23a, 123a, 223a, 323a), and second inductors (24, 124, 224, 324, 424) configured by winding coils (24b, 124b, 124c, 424b, 424c) around second cores (24a, 124a, 424a), The filter circuit according to configuration 1 or 2, wherein when a current of the first current value flows in the inductor section, the first core does not reach magnetic saturation, but the second core reaches magnetic saturation.

[0093] [Configuration 4] The filter circuit of configuration 3, wherein a gap is provided in the first core, while no gap is provided in the second core, or the gap provided in the first core is larger than the gap provided in the second core.

[0094] [Configuration 5] 5. The filter circuit according to configuration 3 or 4, wherein the number of windings of the coil of the first inductor is smaller than the number of windings of the coil of the second inductor.

[0095] [Configuration 6] the second inductor is configured by two coils wound around the second core, 6. The filter circuit according to any one of configurations 3 to 5, wherein in the second inductor, one of the two coils has a winding direction that changes midway.

[0096] [Configuration 7] the inductor section is an inductor configured by winding a coil (502, 503, 602) around a core member (501, 601) that is a combination of a first core (501a, 601a) and a second core (501b, 601b) that have different magnetic permeabilities, 2. The filter circuit according to configuration 1, wherein when a current of the first current value flows in the inductor section, the first core is not magnetically saturated, but the second core is magnetically saturated.

[0097] [Configuration 8] 8. The filter circuit according to any one of configurations 3 to 7, wherein the second core is made of a material that is more susceptible to magnetic saturation than the first core.

[0098] [Configuration 9] the first core is made of a metallic magnetic material, and the second core is made of ferrite, 7. The filter circuit according to any one of configurations 3 to 6, wherein the inductance of the second inductor drops more steeply than the inductance of the first inductor.

[0099] [Configuration 10] A filter circuit according to any one of configurations 1 to 9, wherein the value of the resonant current that is allowed as being within the range of the heat resistance design of the capacitor section even when the resonant current flows through the capacitor section and causes the capacitor section to heat up is defined as the resonance suppression current. [Explanation of symbols]

[0100] 11...motor, 12...inverter, 13...battery, 14...control device, 15...positive busbar, 16...negative busbar, 20...LC filter, 21,121,221,321,421,521,621...inductor section, 22...capacitor section, 23,123,223,323,423...first inductor, 23a,123a,223a,323a...first core, 24,124,224,324,424...second inductor, 24a,124a,424a...second core.

Claims

1. A filter circuit (20) is connected to an electrical load (12) and is configured by combining an inductor section (21, 121, 221, 321, 421, 521, 621) configured with one or more inductors (23, 24, 123, 124, 223, 224, 323, 324, 423, 424) and a capacitor section (22) configured with one or more capacitors, When a current equal to or greater than a first current value (Ia) flows through the inductor section, the inductance decreases from a first value (La) to a second value (Lb), A filter circuit, wherein the first current value is equal to or greater than the maximum value (Imax) of the DC current that flows when the electrical load is operated, and is smaller than a resonance suppression current (Ir) that is allowed as a resonance current.

2. When a current equal to or greater than a second current value (Ib) that is greater than the first current value flows through the inductor unit, the inductance of the inductor unit decreases again from the second value, The filter circuit according to claim 1 , wherein the second current value is greater than the resonance suppression current value.

3. The inductor section is configured by connecting a plurality of inductors in series, The plurality of inductors include at least first inductors (23, 123, 223, 323, 423) configured by winding coils (23b, 123b, 123c, 323b, 323c) around a first core (23a, 123a, 223a, 323a), and second inductors (24, 124, 224, 324, 424) configured by winding coils (24b, 124b, 124c, 424b, 424c) around a second core (24a, 124a, 424a), The filter circuit according to claim 1 , wherein when the current of the first current value flows in the inductor section, the first core is not magnetically saturated, but the second core is magnetically saturated.

4. 4. The filter circuit according to claim 3, wherein a gap is provided in the first core, while no gap is provided in the second core, or the gap provided in the first core is larger than the gap provided in the second core.

5. 4. The filter circuit according to claim 3, wherein the number of windings of the coil of said first inductor is smaller than the number of windings of the coil of said second inductor.

6. the second inductor is configured by two coils wound around the second core, 4. The filter circuit according to claim 3, wherein the winding direction of one of the two coils in the second inductor is changed midway.

7. The inductor unit is an inductor configured by winding a coil (502, 503, 602) around a core member (501, 601) that is a combination of a first core (501a, 601a) and a second core (501b, 601b) that have different magnetic permeabilities, The filter circuit according to claim 1 , wherein when the current of the first current value flows in the inductor section, the first core is not magnetically saturated, but the second core is magnetically saturated.

8. 8. The filter circuit according to claim 3, wherein the second core is made of a material that is more susceptible to magnetic saturation than the first core.

9. the first core is made of a metallic magnetic material, and the second core is made of ferrite, 7. The filter circuit according to claim 3, wherein the inductance of the second inductor decreases more steeply than the inductance of the first inductor.

10. A filter circuit as described in any one of claims 1 to 7, wherein the value of the resonant current that is allowed as being within the range of the heat resistance design of the capacitor section even when the resonant current flows through the capacitor section and causes the capacitor section to heat up is defined as the resonance suppression current.

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