Noise filter

Abstract

The present application relates to a noise filter. A noise filter (40) is provided between a DC / AC inverter (20) that performs switching operation at a first frequency and a DC / DC converter (50) that performs switching operation at a second frequency higher than the first frequency. The noise filter (40) includes a capacitor (82) and a common-mode choke coil (70). The common-mode choke coil (70) includes a core and a first winding (72) and a second winding (73) wound around the core. The common-mode choke coil (70) has an inductance that is larger than the first frequency and smaller than the second frequency, even in a case where the core is magnetically saturated.

Description

Technical Field

[0001] This invention relates to noise filters. Background Technology

[0002] As a noise filter, for example, it is described in Patent Document 1. The noise filter described in Patent Document 1 is connected between a first power conversion device and a second power conversion device. The noise filter includes a capacitor and a common-mode choke coil. The common-mode choke coil includes a core, a first winding, and a second winding. Furthermore, the common-mode choke coil has a leakage inductance. The noise filter reduces conducted noise. Conducted noise includes both normal-mode noise and common-mode noise. The common-mode choke coil is primarily used for reducing common-mode noise, but because it also has a normal-mode inductance as a leakage inductance, it is effective in reducing normal-mode noise as well.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2017-188681

[0004] However, the core can sometimes become magnetically saturated. In a saturated state, the core's permeability decreases. This, in turn, reduces the constant-mode inductance of the common-mode choke coil. This decrease in constant-mode inductance causes the resonant frequency of the noise filter to rise. If the constant-mode noise transmitted to the noise filter coincides with its resonant frequency, resonance occurs within the noise filter. In this case, the resonance that generates noise can be transmitted to devices connected to the noise filter. To prevent resonance in the noise filter, a separate constant-mode coil is sometimes used. However, this additional constant-mode coil increases the size of the noise filter. Summary of the Invention

[0005] The purpose of this invention is to provide a noise filter that can be miniaturized.

[0006] The noise filter that solves the above-mentioned problem is a noise filter provided between a first power conversion device that switches at a first frequency and a second power conversion device that switches at a second frequency higher than the first frequency, and includes a capacitor; and a common-mode choke coil, wherein the common-mode choke coil includes: a core; and a first winding and a second winding wound on the core, and the common-mode choke coil has an inductance at which the resonant frequency of the noise filter when the core is magnetically saturated is greater than the first frequency and less than the second frequency.

[0007] Amended in accordance with Article 28 / 41 of the PCT Treaty

[0008] IP22136595P

[0009] Therefore, even when the common-mode choke coil is magnetically saturated, the resonant frequency of the noise filter is greater than the first frequency and less than the second frequency. Thus, without needing to add a constant-mode coil to the noise filter, it is possible to suppress situations where the resonant frequency of the noise filter coincides with both the first and second frequencies. This allows for the miniaturization of the noise filter.

[0010] Regarding the noise filter mentioned above, it is preferable that the first winding and the second winding are flat windings.

[0011] Regarding the aforementioned noise filter, it is preferred that the first power conversion device is a DC / AC inverter and the second power conversion device is a DC / DC converter, and the noise filter is disposed between the input terminal of the DC / DC converter and the charging terminal connected to an external power source.

[0012] According to the present invention, the miniaturization of noise filters can be achieved. Attached Figure Description

[0013] Figure 1 This is a simplified circuit diagram of the system using the noise filter described in the implementation method.

[0014] Figure 2 This is a circuit diagram of the noise filter implementation method.

[0015] Figure 3 This is the front view of the common-mode choke coil.

[0016] Figure 4 This is a side view of a common-mode choke coil.

[0017] Figure 5 This is a diagram showing the overlap current characteristics of a common-mode choke coil. Detailed Implementation

[0018] The following is based on Figures 1-5 This section describes one embodiment of a noise filter. The noise filter of this embodiment is used, for example, in vehicles such as electric vehicles and hybrid vehicles.

[0019] like Figure 1 As shown, the vehicle Ve includes a start switch S, a power cord 10, a battery B, a DC / AC inverter 20 as a first power conversion device, a driving motor M, a charging terminal 30, a charging switch 31, a noise filter 40, a DC / DC converter 50 as a second power conversion device, and a load 60. The vehicle Ve is, for example, an electric vehicle or a hybrid vehicle that is driven by the driving motor M.

[0020] The ignition switch S is used to switch the vehicle Ve between its start and stop states. The ignition switch S is operated, for example, by a passenger in the vehicle Ve. The start state allows the vehicle Ve to be driven. The stop state prevents the vehicle Ve from being driven. The ignition switch S is sometimes also called the ignition switch, system start switch, etc. The start state is sometimes also referred to as ignition on, stop.

[0021] The off state is sometimes referred to as ignition off.

[0022] Power line 10 is a component that supplies power to the electrical system of vehicle Ve. Power line 10 includes a high-voltage line 11 and a low-voltage line 12.

[0023] Battery B is, for example, a battery with a nominal voltage of 200V. Battery B serves as a power source supplying power to onboard electrical equipment such as the driving motor M and the load 60. Battery B can be, for example, a battery that connects to multiple charge-discharge storage devices such as lithium-ion batteries.

[0024] The positive terminal of battery B is connected to high-voltage line 11.

[0025] The negative terminal of battery B is connected to the low-voltage line 12.

[0026] The DC / AC inverter 20 is connected to the power line 10. The DC / AC inverter 20 receives the DC voltage from the battery B via the power line 10. The DC / AC inverter 20 includes a switching element 21. When the vehicle Ve is in the active state, the DC / AC inverter 20 performs a switching operation via the switching element 21 to convert the DC power supplied from the battery B into AC power and output it. The DC / AC inverter 20 performs power conversion, for example, using pulse width modulation (PWM). Pulse width modulation may employ a triangular wave comparison method, for example, using a triangular wave as the carrier wave. The switching element 21 of the DC / AC inverter 20 performs a switching operation at a first frequency f1. In this embodiment, the first frequency f1 is the switching frequency of the switching element 21 of the DC / AC inverter 20. The first frequency f1 is, for example, 10 kHz. The DC / AC inverter 20 generates conducted noise with the first frequency f1 as its main component through the switching operation of the switching element 21. The conducted noise generated by the DC / AC inverter 20 propagates to the power line 10.

[0027] The driving motor M is the power source that drives the wheels of the vehicle Ve. The driving motor M is driven by the power output from the DC / AC inverter 20. For example, a three-phase AC motor can be used for the driving motor M.

[0028] The charging terminal 30 is used to supply power from the external power source 100 to the vehicle Ve. The charging terminal 30 is connected to the external power source 100. The external power source 100 can be any power source that outputs DC voltage, for example, it includes a commercial power supply 101 and a charging AC / DC converter 102. The commercial power supply 101 is a system power source that supplies AC power to multiple user equipments via a distribution panel. In this embodiment, the AC power from the commercial power supply 101 is supplied to the charging AC / DC converter 102. That is, the charging AC / DC converter 102 can also be considered one of the user equipments.

[0029] The charging AC / DC converter 102 converts the input AC voltage into DC voltage and outputs it. The DC voltage output by the charging AC / DC converter 102 is supplied to the battery B via the charging terminal 30. That is, the external power supply 100 functions as a charging device for charging the battery B. When the vehicle Ve is connected to the external power supply 100, the vehicle Ve is in a stopped state. Hereinafter,

[0030] The state in which the external power source 100 charges the battery B is called the charging state.

[0031] The charging switch 31 is a switch that toggles the connection state between the charging terminal 30 and the power line 10. The charging switch 31 is connected to the power line 10. Furthermore, the charging switch 31 is positioned between the charging terminal 30 and the power line 10. When the charging switch 31 is on, the charging terminal 30 and the power line 10 are conductive. When the charging switch 31 is off, the charging terminal 30 and the power line 10 are insulated. The charging switch 31 is activated when the external power source 100 supplies power to the vehicle Ve. For example, a relay switch can be used in the charging switch 31, but any switch such as a MOSFET or IGBT can also be used.

[0032] Noise filter 40 is a filter circuit used to reduce conducted noise passing through it. Noise filter 40 is connected to power supply line 10. Details of noise filter 40 will be described later.

[0033] The DC / DC converter 50 includes a switching element 51, an input terminal 52, and an output terminal 53. The switching element 51 of the DC / DC converter 50 switches at a second frequency f2. That is, the second frequency f2 in this embodiment is the switching frequency of the switching element 51. The second frequency f2 is greater than the first frequency f1, for example, 170kHz.

[0034] The input terminal 52 of the DC / DC converter 50 is connected to the power supply line 10 via a noise filter 40. A DC / AC inverter 20 is connected to the power supply line 10. Therefore, it can also be said that the noise filter 40 is located between the DC / AC inverter 20 and the DC / DC converter 50. Additionally, a charging terminal 30 is provided on the power supply line 10. Therefore, it can also be said that the noise filter 40 is located between the input terminal 52 of the DC / DC converter 50 and the charging terminal 30 provided by the external power supply 100.

[0035] The DC / DC converter 50 steps down the voltage input to its input terminal 52 and outputs it through the switching action of its switching element 51. The output voltage of the output terminal 53 of the DC / DC converter 50 is, for example, 12V. Due to the switching action of the switching element 51 of the DC / DC converter 50, conducted noise with a second frequency f2 as its main component is generated from the input terminal 52 of the DC / DC converter 50.

[0036] Load 60 is an electronic component installed in vehicle Ve. Examples of load 60 include lighting and audio equipment. Load 60 is driven by a DC voltage output from the output terminal 53 of DC / DC converter 50. The driving voltage of load 60 is, for example, 12V.

[0037] The following is a detailed description of the noise filter 40.

[0038] like Figure 2 As shown, the noise filter 40 includes a common-mode choke coil 70, a first bypass capacitor 80, a second bypass capacitor 81, and a capacitor 82.

[0039] like Figures 2-4 As shown, the common-mode choke coil 70 includes a core 71, a first winding 72, and a second winding 73.

[0040] The core 71 is formed of a strongly magnetic material, such as a ferrite core. In this embodiment, the core 71 is formed in a ring shape. As used in this description, the term "ring shape" sometimes refers to any construction forming the ring, or a continuous shape without ends, or a general ring shape with C-shaped gaps. The shape of "ring shape" includes circles, ellipses, and pointed or rounded polygons, but is not limited to these.

[0041] The first winding 72 is wound around the core 71. The first end of the first winding 72 is connected to the high-voltage line 11.

[0042] The second winding 73 is wound around the core 71. The first end of the second winding 73 is connected to the low-voltage line 12.

[0043] The first winding 72 and the second winding 73 are wound around the core 71 so that when current in the same direction, i.e. common mode current, flows to the first winding 72 and the second winding 73, they generate mutually reinforcing magnetic fluxes. On the other hand, when current in opposite directions, i.e. constant mode current, flows to the first winding 72 and the second winding 73, they generate mutually canceling magnetic fluxes.

[0044] When a constant-mode current flows through the first winding 72 and the second winding 73, the common-mode choke coil 70 generates leakage flux. Therefore, the common-mode choke coil 70 when the core 71 is not magnetically saturated can be considered as having an imaginary constant-mode coil L1, which has a constant-mode inductance La as a leakage inductance. The imaginary constant-mode coil L1 is composed of a first imaginary constant-mode coil L11 having a constant-mode inductance as the leakage inductance of the first winding 72, and a second imaginary constant-mode coil L12 having a constant-mode inductance as the leakage inductance of the second winding 73. The first imaginary constant-mode coil L11 is connected in series with the first end of the first winding 72. The second imaginary constant-mode coil L12 is connected in series with the first end of the second winding 73.

[0045] like Figure 2 As shown, the first bypass capacitor 80 and the second bypass capacitor 81 are connected in series. The first bypass capacitor 80 and the second bypass capacitor 81 are grounded. The first bypass capacitor 80 and the second bypass capacitor 81 form a series connection body C1. The first end of the series connection body C1 is connected to the second end of the first winding 72. The second end of the series connection body C1 is connected to the second end of the second winding 73.

[0046] The first end of capacitor 82 is connected to the second end of the first winding 72. The second end of capacitor 82 is connected to the second end of the second winding 73. That is, capacitor 82 is connected in parallel with the series connector C1.

[0047] The noise filter 40 of this embodiment has a common-mode choke coil 70, a series connector C1, and a capacitor 82 in sequence from the power line 10 toward the input terminal 52 of the DC / DC converter 50.

[0048] The noise filter 40 functions as a low-pass filter circuit for common-mode current through the common-mode choke coil 70 and the series connector C1. Additionally, the noise filter 40 also functions as a low-pass filter circuit for constant-mode current through the imaginary constant-mode coil L1 and capacitor 82. In other words, the noise filter 40 simultaneously reduces both common-mode and constant-mode noise.

[0049] However, during charging, the external power source 100 supplies power to the input terminal 52 of the DC / DC converter 50 via the charging terminal 30. The power supplied to the input terminal 52 of the DC / DC converter 50 is output from the output terminal 53 of the DC / DC converter 50 to the load 60. Therefore, during charging, conducted noise generated from the input terminal 52 of the DC / DC converter 50 propagates to the power line 10 via the noise filter 40. The conducted noise propagating to the power line 10 propagates to the external power source 100 via the charging terminal 30. The conducted noise propagating to the external power source 100 may propagate to other user equipment via the distribution panel. In such a case, the intensity of the conducted noise propagating from the vehicle Ve to the external power source 100 needs to be lower than the specified reference value determined by specified specifications, such as ECE regulation 10.

[0050] Here, the current flowing into the common-mode choke coil 70 has a DC current component supplied from the battery B or the external power supply 100, and an AC current component generated from the DC / DC converter 50. The AC current component includes conducted noise generated from the DC / DC converter 50. This DC current component energizes the core 71. Hereinafter, this DC current component will be referred to as the DC overlap current Idc.

[0051] Figure 5 X represents the DC overlap characteristic of the common-mode choke coil 70 in this embodiment. Furthermore, the DC overlap characteristic in this embodiment refers to the relationship between the DC overlap current Idc flowing through the common-mode choke coil and the constant-mode inductance of the common-mode choke coil.

[0052] like Figures 2-5 As shown, if a certain amount of DC overlapping current Idc flows into the common-mode choke coil 70, the core 71 becomes magnetically saturated. Consequently, the magnetic coupling between the first winding 72 and the second winding 73 via the core 71 is lost. Furthermore, the permeability of the core 71 decreases to the same level as that of an air-core coil. Hereinafter, the value of the DC overlapping current Idc at which the constant-mode inductance of the common-mode choke coil 70 begins to decrease is referred to as the magnetic saturation allowable current Isat1. Furthermore, the constant-mode inductance of the common-mode choke coil 70 when the DC overlapping current Idc is the magnetic saturation allowable current Isat1 is referred to as the critical inductance Lb.

[0053] If the DC overlap current Idc exceeds the magnetic saturation allowable current Isat1, the constant-mode inductance decreases from the critical inductance Lb, converging to a certain residual inductance Lc. Hereinafter, the inductance between the critical inductance Lb and the residual inductance Lc will be referred to as inductance Ld. If the constant-mode inductance decreases, the noise removal performance of the noise filter 40 decreases.

[0054] Load 60 is driven regardless of whether the vehicle Ve is in a driving or charging state. Therefore, regardless of whether the vehicle Ve is in a driving or charging state, the battery B or the external power source 100 needs to supply power to the DC / DC converter 50. The power required to drive load 60 in the driving state is greater than that in the charging state. Therefore, the maximum current Idc1 during charging is less than the maximum current Idc2 during driving. Furthermore, the maximum current Idc1 during charging is the maximum value of the DC superimposed current Idc during the charging state. Additionally, the maximum current Idc2 during driving is the maximum value of the DC superimposed current Idc during the driving state.

[0055] The noise filter 40 in this embodiment is a component used to suppress conducted noise propagating from the DC / DC converter 50 to the external power supply 100. In this embodiment, conducted noise may propagate to the external power supply 100 when the vehicle Ve is in a charging state. In other words, when the vehicle Ve is in a driving state, the noise reduction function of the noise filter 40 may be lower than that in the charging state.

[0056] Therefore, in this embodiment, the core 71 is designed such that the magnetic saturation allowable current Isat1 of the common mode choke coil 70 is greater than the maximum current Idc1 during charging and less than the maximum current Idc2 during driving.

[0057] On the other hand, if the core 71 is magnetically saturated, the constant mode inductance of the common mode choke coil 70 will decrease from the critical inductance Lb and converge to a certain residual inductance Lc.

[0058] If the resonant frequency f0, determined by the constant-mode inductance of the common-mode choke coil 70 and the capacitance of the capacitor 82, becomes close to the second frequency f2 due to the reduction of the constant-mode inductance, then the noise filter 40 may resonate due to the conducted noise of the DC / DC converter 50.

[0059] Therefore, the inductance Ld of the common-mode choke coil 70 is set to a value where the resonant frequency f0 is greater than the first frequency f1 and less than the second frequency f2. Specifically, the first winding 72 and the second winding 73 are flat windings, and the number of turns of the inductor in the first winding 72 and the number of turns of the inductor in the second winding 73 are set to a ratio where the resonant frequency f0 is greater than the first frequency f1 and less than the second frequency f2.

[0060] The function of this embodiment will be explained.

[0061] like Figure 5As shown in the DC overlap characteristic X of the common-mode choke coil 70 of this embodiment, the maximum charging current Idc1 of the common-mode choke coil 70 of this embodiment is smaller than the magnetic saturation allowable current Isat1. Therefore, the core 71 is not magnetically saturated during charging. Furthermore, the maximum driving current Idc2 of the common-mode choke coil 70 of this embodiment is larger than the magnetic saturation allowable current Isat1. Therefore, the core 71 often becomes magnetically saturated during driving. When the core 71 is magnetically saturated, the constant-mode inductance of the common-mode choke coil 70 decreases from the critical inductance Lb and converges to a certain residual inductance Lc. Therefore, the noise removal performance of the noise filter 40 decreases. However, even when the core 71 is magnetically saturated, the common-mode choke coil 70 of this embodiment is set such that the resonant frequency f0 of the noise filter 40 is greater than the first frequency f1 and less than the second frequency f2. That is, the resonant frequency f0 of the noise suppression filter 40 is the same as both the first frequency f1 and the second frequency f2. The conducted noise generated by the DC / DC converter 50 is noise with the second frequency f2 as the main component, so even if the core 71 is magnetically saturated, the resonance of the noise filter 40 caused by the conducted noise generated by the DC / DC converter 50 is suppressed.

[0062] On the other hand, such as Figure 5 As shown in the overlapping current characteristic Y of the common-mode choke coil of the comparative example, the magnetic saturation allowable current Isat2 of the common-mode choke coil of the comparative example is the same as the maximum current Idc2 during driving. Therefore, the core of the common-mode choke coil of the comparative example is designed to not generate magnetic saturation in the charging state and to be difficult to magnetically saturate in the driving state. However, in order to maintain the constant-mode inductance and increase the magnetic saturation allowable current, it is necessary to increase the size of the core.

[0063] The effects of this implementation method will be explained.

[0064] (1) The common-mode choke coil 70 has an inductance Ld such that when the core 71 is magnetically saturated, the resonant frequency f0 of the noise filter 40 is greater than the first frequency f1 and less than the second frequency f2. Therefore, without additional common-mode coils in the noise filter 40, it is possible to suppress the resonance of the noise filter 40 due to conducted noise generated from the DC / DC converter 50. Thus, miniaturization of the noise filter 40 is possible.

[0065] (2) The magnetic saturation allowable current Isat1 of the common-mode choke coil 70 is greater than the maximum current Idc1 during charging and less than the maximum current Idc2 during driving. Therefore, the noise removal performance of the noise filter 40 is maintained at least during charging. In addition, by making the magnetic saturation allowable current Isat1 smaller than the maximum current Idc2 during driving, the volume of the core 71 is reduced. As a result, the noise removal performance of the noise filter 40 can be maintained during charging and the noise filter 40 can be miniaturized.

[0066] (3) By using a flat winding for the first winding 72, the inductance per unit volume of the common-mode choke coil 70 is increased. As a result, the noise filter 40 can be made smaller.

[0067] (4) A noise filter 40 is disposed between the input terminal 52 of the DC / DC converter 50 and the charging terminal 30. Conducted noise generated from the input terminal 52 of the DC / DC converter 50 during the charging state is reduced by the noise filter 40. When the external power supply 100 and the vehicle Ve are connected, conducted noise generated by the vehicle Ve may propagate from the vehicle Ve to the external power supply 100 via the charging terminal 30. Therefore, a noise filter 40 is required to suppress the propagation of such conducted noise. The vehicle Ve is connected to the external power supply 100 when the external power supply 100 is charging the battery B, i.e., during the charging state. The noise filter 40 only needs to perform noise removal performance during the charging state. The maximum current Idc1 during charging is smaller than the maximum current Idc2 during driving. The common-mode choke coil 70 only needs to prevent the core 71 from becoming magnetically saturated due to the DC superimposed current Idc during the charging state, and it only needs to suppress the resonance of the noise filter 40 during the driving state. Therefore, by configuring the noise filter 40 between the input terminal 52 and the charging terminal 30 of the DC / DC converter 50 as described in the embodiment, the core 71 can be miniaturized and the propagation of conducted noise from the vehicle Ve to the external power supply 100 can be suppressed, compared to the case where magnetic saturation does not occur even when the core 71 is in motion. Thus, the noise filter 40 can be miniaturized.

[0068] Each implementation method can be modified as follows. Each implementation method and the following variations can be combined with each other as long as they are not technically contradictory.

[0069] The location of the noise filter 40 is not limited to between the input terminal 52 and the charging terminal 30 of the DC / DC converter 50. For example, it can also be connected between the output terminal 53 of the DC / DC converter 50 and the load 60. This allows for the suppression of conducted noise propagating from the DC / DC converter 50 to the load 60.

[0070] The first power conversion device is not limited to the DC / AC inverter 20, but can be any device that generates switching noise.

[0071] The second power conversion device is not limited to the DC / DC converter 50; it can be any device as long as it is a component that generates switching noise at a higher frequency than the first power conversion device.

[0072] The first winding 72 and the second winding 73 can be of any structure as long as they have an inductor Ld whose resonant frequency f0, which serves as the noise filter 40 when the core 71 is magnetically saturated, is greater than the first frequency f1 and less than the second frequency f2. For example, the first winding 72 and the second winding 73 can also be various windings such as round wires or rectangular wires, instead of flat windings.

[0073] As long as the second winding 73 has the same frequency and DC current characteristics as the first winding 72, the number of turns of the second winding 73 may not be the same as the number of turns of the first winding 72. Similarly, the type of winding of the second winding 73 may not be the same as the type of winding of the first winding 72.

[0074] The shape of the core 71 is not limited to a ring shape, as long as it can ensure the magnetic coupling between the first winding 72 and the second winding 73. For example, the shape of the core 71 can also be rod-shaped.

[0075] The core 71 does not need to be closed into a ring shape as long as it can ensure the magnetic coupling between the first winding 72 and the second winding 73. For example, the core 71 can also have a gap.

[0076] The charging switch 31 may not be located on the vehicle Ve. For example, it may be located on an external power source 100.

[0077] Alternatively, the charging terminal 30 can be omitted.

[0078] The order of the components constituting the noise filter 40 is not limited to any particular implementation method and is arbitrary.

[0079] Alternatively, the series connector C1 can be omitted.

[0080] Explanation of reference numerals in the attached figures

[0081] 20…DC / AC Inverter

[0082] 30…charging terminal

[0083] 40… Noise Filter

[0084] 50…DC / DC converter

[0085] 52…input terminal

[0086] 70… Common Mode Choke Coil

[0087] 71…core

[0088] 72…First winding

[0089] 73…Second winding

[0090] 82… capacitor

[0091] f0…resonant frequency

[0092] f1…first frequency

[0093] f2…second frequency

[0094] Ld…Inductor.

Claims

1. A noise filter disposed between a first power conversion device that switches at a first frequency and a second power conversion device that switches at a second frequency higher than the first frequency, comprising a capacitor and a common-mode choke coil. The aforementioned common-mode choke coil includes a core and a first winding and a second winding wound on the core. The common-mode choke coil has an inductance whose resonant frequency of the noise filter when the core is magnetically saturated is greater than the first frequency and less than the second frequency.

2. The noise filter according to claim 1, wherein, The first winding and the second winding mentioned above are flat windings.

3. The noise filter according to claim 1 or 2, wherein, The aforementioned first power conversion device is a DC / AC inverter. The aforementioned second power conversion device is a DC / DC converter. The noise filter is positioned between the input terminal of the aforementioned DC / DC converter and the charging terminal connected to an external power source.

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