Noise filter and equipment unit

Abstract

A noise filter according to the present invention has one end electrically connected to a power supply line connecting a power supply and a device, and the other end grounded, and comprises a capacitor and an inductor connected in parallel. The parallel resonance frequency of the capacitor and the inductor is set within a first frequency band including the frequency at which the intensity of common mode noise generated in the device is greatest. The self-resonant frequency of the capacitor is set within a second frequency band including the frequency at which the intensity of normal mode noise generated in the device is greatest.

Description

Noise filters and equipment units

[0001] This application claims priority from Japanese Patent Application No. 2024-135333, filed on August 14, 2024, the contents of which are incorporated herein by reference.

[0002] There is known an on-board electric compressor that suppresses noise generation by grounding the primary and secondary sides of a switching transformer via a Y capacitor (see, for example, Patent Document 1).

[0003] International Publication No. 2020 / 012898

[0004] In an equipment unit including a power supply and an equipment having an inverter electrically connected to the power supply via a power line, the frequency band of common mode noise generated in the inverter may differ from the frequency band of normal mode noise. In this case, if an attempt is made to reduce the normal mode noise by grounding the power supply line via a Y capacitor, there is a risk that the common mode noise will propagate to the power supply via the Y capacitor and the ground.

[0005] An object of one aspect of the present invention is to provide a noise filter and an equipment unit that can suppress the propagation of both normal mode noise and common mode noise to a power supply.

[0006] One aspect of the noise filter of the present invention is a noise filter having one end electrically connected to a power line connecting a power source and an apparatus and the other end grounded, the noise filter including a capacitor and an inductor connected in parallel, a parallel resonant frequency of the capacitor and the inductor set in a first frequency band including a frequency at which the intensity of common-mode noise generated in the apparatus is maximized, and a self-resonant frequency of the capacitor set in a second frequency band including a frequency at which the intensity of normal-mode noise generated in the apparatus is maximized.

[0007] One aspect of the equipment unit of the present invention includes the noise filter described above and the equipment, wherein the equipment is a motor having a motor unit and an inverter electrically connected to the power supply, and the inverter generates a second current to be supplied to the motor unit from a first current supplied by the power supply.

[0008] According to one aspect of the present invention, the noise filter and the equipment unit can suppress the propagation of normal mode noise and common mode noise to the power supply.

[0009] Fig. 1 is a schematic diagram showing an equipment unit according to an embodiment. Fig. 2 is a diagram showing impedance characteristics of a noise filter according to an embodiment. Fig. 3 is a schematic diagram showing normal mode noise in the equipment unit according to an embodiment. Fig. 4 is a diagram showing measurement results of normal mode noise in the equipment unit according to an embodiment. Fig. 5 is a schematic diagram showing common mode noise in the equipment unit according to an embodiment. Fig. 6 is a diagram showing measurement results of common mode noise in the equipment unit according to an embodiment.

[0010] 1 is a schematic diagram showing a device unit 10 according to the present embodiment. The device unit 10 is a device unit that operates a device 20. In the present embodiment, the device 20 is a motor that is mounted on a vehicle such as a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHV), or an electric vehicle (EV) and drives the vehicle. The device unit 10 includes a noise filter 11, the device 20, a power line 31, a power supply 50, a connector 51, and a housing 40.

[0011] The housing 40 is box-shaped and houses the device 20 and the noise filter 11. In this embodiment, the housing 40 is made of metal. The housing 40 is conductive. The housing 40 is grounded via a ground plane 53.

[0012] The power supply 50 supplies a first current C1 to the device 20. The power supply 50 is, for example, a battery provided in the vehicle. In this embodiment, the first current C1 supplied by the power supply 50 to the device 20 is a direct current. Note that the first current C1 may also be an alternating current. The power supply 50 is disposed outside the housing 40. The power supply 50 is grounded via a ground line 50a and a ground plane 53.

[0013] As described above, in this embodiment, the device 20 is a motor. The device 20 is housed inside the housing 40. In this embodiment, the device 20 is a three-phase AC motor. However, the device 20 may be another type of motor, such as a DC motor. The device 20 includes a motor unit 21 and an inverter 22.

[0014] The motor unit 21 has a rotor (not shown) and a stator (not shown). When the inverter 22 supplies a second current C2, which is a three-phase AC current, to the stator, the rotor is driven to rotate. Although not shown, the rotational torque of the rotor is transmitted to an axle of the vehicle. As a result, the device 20 rotates the axle and drives the vehicle.

[0015] The inverter 22 is electrically connected to the power supply 50 via a power supply line 31. The inverter 22 generates a second current C2 to be supplied to the motor unit 21 from a first current C1 supplied by the power supply 50. The inverter 22 supplies the second current C2 to a stator (not shown) included in the motor unit 21. In this embodiment, the inverter 22 generates the second current C2, which is an AC current, from the first current C1, which is a DC current. The inverter 22 includes a current generating unit 23 and a control unit 25.

[0016] The current generating unit 23 is electrically connected to the power supply 50 via the power supply line 31. The current generating unit 23 is electrically connected to the motor unit 21. The current generating unit 23 generates a second current C2 from the first current C1 and supplies the second current C2 to the motor unit 21. The current generating unit 23 has a switching element 24. That is, the inverter 22 has the switching element 24.

[0017] The switching elements 24 generate the second current C2 from the first current C1. In this embodiment, the switching elements 24 are power semiconductor elements such as insulated gate bipolar transistors (IGBTs) and metal-oxide-semiconductor field-effect transistors (MOSFETs). The inverter 22 includes a plurality of switching elements 24. This allows the inverter 22 to generate three-phase AC current. In this embodiment, the switching frequency Fs of each switching element 24 is equal to or greater than 0.01 MHz and equal to or less than 0.2 MHz.

[0018] When the switching element 24 generates the second current C2, common mode noise N1 is generated. The common mode noise N1 includes noise that is a sum of noises at frequencies that are integer multiples of the switching frequency Fs. In this embodiment, the frequency Fm1 at which the intensity of the common mode noise N1 is greatest is in the range of 0.3 MHz to 0.6 MHz. The common mode noise N1 propagates from the inverter 22 to the power supply line 31 and the ground plane 53. If the common mode noise N1 propagates to the power supply 50 via the power supply line 31 and the ground plane 53, malfunction of the power supply 50 may occur. In this case, the current value of the first current C1 becomes unstable, thereby impairing the stability of the operation of the device 20.

[0019] The control unit 25 is electrically connected to the current generating unit 23. The control unit 25 controls the operation of each switching element 24. This allows the frequency and amplitude of the second current C2 generated by the switching elements 24 to be set to desired frequencies and amplitudes. In this embodiment, the control unit 25 is a microcomputer. In this embodiment, the clock frequency Fc, which is the frequency at which the control unit 25 transmits control signals to the switching elements 24, is in the range of 10 MHz or higher and 500 MHz or lower. In this embodiment, the clock frequency Fc of the control unit 25 is higher than the switching frequency Fs of the switching elements 24.

[0020] When the control unit 25 operates, normal mode noise N2 is generated. The normal mode noise N2 includes noise having substantially the same frequency as the clock frequency Fc. In this embodiment, the frequency Fm2 at which the intensity of the normal mode noise N2 is greatest is in the range of 30 MHz to 100 MHz. The normal mode noise N2 propagates from the inverter 22 to the power supply line 31. If the normal mode noise N2 propagated to the power supply line 31 propagates to the power supply 50, there is a risk of malfunctioning of the power supply 50. In this case, the current value of the first current C1 becomes unstable, thereby impairing the stability of the operation of the device 20.

[0021] In this embodiment, the first frequency band F1 is a frequency band that includes a frequency Fm1 at which the intensity of the common-mode noise N1 generated in the device 20 is maximized. As shown in FIG. 2 , in this embodiment, the first frequency band F1 is in the range of 0.1 MHz to 1.0 MHz. As described above, the switching frequency Fs of the switching element 24 is in the range of 0.01 MHz to 0.2 MHz. Therefore, the first frequency band F1 includes the switching frequency Fs.

[0022] In this embodiment, the second frequency band F2 is a frequency band that includes a frequency Fm2 at which the intensity of normal mode noise N2 generated in the device 20 is maximized. In this embodiment, the second frequency band F2 is in the range of 10 MHz or higher and 100 MHz or lower. In this embodiment, the first frequency band F1 is lower in frequency than the second frequency band F2. As described above, the clock frequency Fc of the control unit 25 is in the range of 10 MHz or higher and 500 MHz or lower. Therefore, the second frequency band F2 includes the clock frequency Fc.

[0023] As shown in FIG. 1 , the power supply line 31 includes a first line 31a and a second line 31b. The first line 31a is disposed outside the housing 40. One end of the first line 31a is connected to the power supply 50. The other end of the first line 31a is connected to the connector 51. The second line 31b is disposed inside the housing 40. A second inductor 32 is provided on the second line 31b. One end of the second line 31b is connected to the connector 51. This allows the connector 51 to electrically connect the first line 31a and the second line 31b. In this embodiment, the connector 51 is attached to the housing 40. The other end of the second line 31b is connected to the device 20. More specifically, the other end of the second line 31b is connected to the current generating unit 23. This allows the power supply line 31 to electrically connect the power supply 50 and the device 20. The first current C1 is supplied to the current generating unit 23 of the device 20 via the power supply line 31.

[0024] The noise filter 11 is a noise filter that suppresses common mode noise N1 from flowing from the power supply line 31 to the ground plane 53 and allows normal mode noise N2 from flowing from the power supply line 31 to the ground plane 53. The noise filter 11 is disposed inside the housing 40. One end 11a of the noise filter 11 is electrically connected to the second line 31b. As a result, the one end 11a of the noise filter 11 is electrically connected to the power supply line 31. The other end 11c of the noise filter 11 is electrically connected to the housing 40. As described above, the housing 40 is grounded via the ground plane 53. Therefore, the other end 11c of the noise filter 11 is grounded via the housing 40 and the ground plane 53. The noise filter 11 includes a capacitor 12 and an inductor 14. In this embodiment, the capacitor 12 and the inductor 14 are connected in parallel.

[0025] In this embodiment, the capacitance of the capacitor 12 is 2500 pF. The parasitic inductance of the capacitor 12 is 4 nH. Therefore, the self-resonant frequency Fr of the capacitor 12 is 50 MHz. As a result, the impedance of the capacitor 12 is minimized at a frequency of 50 MHz. As described above, the second frequency band F2 is in the range of 10 MHz to 100 MHz. Therefore, the self-resonant frequency Fr of the capacitor 12 is set to the second frequency band F2.

[0026] In this embodiment, the inductor 14 has an inductance of 33 μH. Therefore, the parallel resonant frequency Fp of the capacitor 12 and the inductor 14 is 0.6 MHz. As a result, the impedance of the noise filter 11 reaches a maximum at a frequency of 0.6 MHz. As described above, the first frequency band F1 is in the range of 0.1 MHz to 1.0 MHz. Therefore, the parallel resonant frequency Fp of the capacitor 12 and the inductor 14 is set to the first frequency band F1.

[0027] FIG. 2 is a diagram showing the impedance characteristics of the noise filter 11 of this embodiment. The horizontal axis in FIG. 2 represents frequency F. The vertical axis in FIG. 2 represents the impedance Im of the noise filter 11. As shown in FIG. 2, the impedance Im increases as frequency F increases up to 0.6 MHz, and reaches a maximum at 0.6 MHz. This is because, as described above, the parallel resonance frequency Fp of the capacitor 12 and the inductor 14 is 0.6 MHz. As described above, the parallel resonance frequency Fp of the capacitor 12 and the inductor 14 is set to the first frequency band F1. As a result, the noise filter 11 of this embodiment can increase the impedance Im in the first frequency band F1.

[0028] When the frequency F is greater than 0.6 MHz, the impedance Im decreases as the frequency F increases, and reaches a minimum at a frequency F of 50 MHz. This is because the self-resonant frequency Fr of the capacitor 12 is 50 MHz, as described above. As described above, the self-resonant frequency Fr of the capacitor 12 is set to the second frequency band F2. As a result, the noise filter 11 of this embodiment can reduce the impedance Im in the second frequency band F2.

[0029] As described above, the second frequency band F2 is a frequency band that includes the frequency Fm2 at which the intensity of the normal mode noise N2 generated in the device 20 is maximized. Therefore, the second frequency band F2 is a frequency band in which the intensity of the normal mode noise N2 is high. Furthermore, as described above, the noise filter 11 of this embodiment can reduce the impedance Im in the second frequency band F2. Therefore, the normal mode noise N2 easily passes through the noise filter 11. Therefore, as shown in FIG. 3 , in this embodiment, the normal mode noise N2 generated in the device 20 flows through the power supply line 31 toward the power supply 50, then flows into the noise filter 11, and easily returns to the device 20 via the ground plane 53. That is, in this embodiment, the normal mode noise N2 easily returns to the device 20 via the noise filter 11 and the ground plane 53. The normal mode noise N2 that has returned to the device 20 is converted into thermal energy in various parts of the device 20, such as the inverter 22, and is then dissipated to the outside of the device unit 10. Therefore, in this embodiment, the normal mode noise N2 can be prevented from propagating to the power supply 50 via the power supply line 31.

[0030] Fig. 4 is a diagram showing measurement results of normal mode noise N2 in the equipment unit 10 of this embodiment. The horizontal axis of Fig. 4 is frequency F. The vertical axis of Fig. 4 is intensity A2 of the normal mode noise N2. The intensity A2 of the normal mode noise N2 in this embodiment is shown by a solid line, and the intensity A2 of the normal mode noise N2 when the equipment unit 10 does not include the noise filter 11 is shown by a dashed line. Note that in Fig. 4, the noise standard S specified in CISPR25 by the Comite international Spécial des Perturbations Radioélectriques (CISPR) of the International Electrotechnical Commission (IEC) is shown by a dashed line.

[0031] 4, when the equipment unit 10 does not include the noise filter 11, the intensity A2 of the normal mode noise N2 exceeds standard S in the second frequency band F2, which is a frequency band including the frequency Fm2 at which the intensity A2 of the normal mode noise N2 is greatest. In contrast, in the equipment unit 10 of the present embodiment, which includes the noise filter 11, the intensity A2 of the normal mode noise N2 can be reduced, and therefore the intensity A2 of the normal mode noise N2 can be made smaller than standard S. This is because, as described above, the normal mode noise N2 easily returns to the equipment 20 via the noise filter 11 and the ground plane 53.

[0032] As described above, the first frequency band F1 is a frequency band including the frequency Fm1 at which the intensity of the common-mode noise N1 generated in the device 20 is maximized. Therefore, the first frequency band F1 is a frequency band including the frequency Fm1 at which the intensity of the common-mode noise N1 is high. Furthermore, as described above, the noise filter 11 of this embodiment can increase the impedance Im in the first frequency band F1. Therefore, the common-mode noise N1 is less likely to pass through the noise filter 11. Therefore, as shown in FIG. 5 , this embodiment can prevent the common-mode noise N1 generated in the device 20 from traveling along the power supply line 31 toward the power supply 50 and then propagating to the ground plane 53 via the noise filter 11. In this embodiment, the common-mode noise N1 is converted into thermal energy in the capacitor 12 or the inductor 14 that constitutes the noise filter 11, and the heat is dissipated to the outside of the device 20. Therefore, this embodiment can prevent the common-mode noise N1 from propagating to the power supply 50 via the noise filter 11, the ground plane 53, and the ground line 50a.

[0033] Fig. 6 is a diagram showing measurement results of common mode noise N1 in the equipment unit 10 of this embodiment. The horizontal axis of Fig. 6 represents frequency F. The vertical axis of Fig. 6 represents intensity A1 of the common mode noise N1. The intensity A1 of the common mode noise N1 in this embodiment is shown by a solid line, and the intensity A1 of the common mode noise N1 when the equipment unit 10 does not include the noise filter 11 is shown by a dashed line. Note that Fig. 6 also shows the noise standard S specified in CISPR25 by the Comite international Spécial des Perturbations Radioélectriques (CISPR) of the International Electrotechnical Commission (IEC).

[0034] 6, when the equipment unit 10 does not include the noise filter 11, the intensity A1 of the common mode noise N1 exceeds standard S in the first frequency band F1, which is a frequency band including the frequency Fm1 at which the intensity of the common mode noise N1 is greatest. In contrast, in the equipment unit 10 of the present embodiment, which includes the noise filter 11, the intensity A1 of the common mode noise N1 can be reduced, and therefore the intensity A1 of the common mode noise N1 can be made smaller than standard S. This is because, as described above, the noise filter 11 can prevent the common mode noise N1 from propagating to the power supply 50 via the ground plane 53 or the like.

[0035] Next, an example of a procedure for determining the capacitance and parasitic inductance of capacitor 12 and the inductance of inductor 14 in noise filter 11 will be described. First, the intensity of noise generated in device 20 is measured to determine the frequency Fm2 at which the intensity of normal mode noise N2 is maximized. Next, the capacitance and parasitic inductance of capacitor 12 are determined so that the self-resonant frequency Fr of capacitor 12 is set to a second frequency band F2 that includes frequency Fm2. This reduces the impedance of capacitor 12 in the second frequency band F2, thereby reducing the intensity A2 of normal mode noise N2 as described above.

[0036] Next, a noise filter having only capacitor 12 is connected to power line 31 and housing 40, and the intensity of noise generated in device 20 is measured again to determine the frequency Fm1 at which the intensity of common-mode noise N1 is maximized. Next, the inductance of inductor 14 is determined so that the parallel resonant frequency Fp of capacitor 12 and inductor 14 is set to the first frequency band F1 that includes frequency Fm1. This increases the impedance of noise filter 11 in first frequency band F1, thereby reducing the intensity A1 of common-mode noise N1 as described above.

[0037] According to this embodiment, the noise filter 11 has one end 11a electrically connected to the power line 31 connecting the power supply 50 and the device 20 and the other end 11c grounded, and includes a capacitor 12 and an inductor 14 connected in parallel. The parallel resonant frequency Fp of the capacitor 12 and the inductor 14 is set to a first frequency band F1 including a frequency Fm1 at which the intensity of common-mode noise N1 generated in the device 20 is maximized, and the self-resonant frequency Fr of the capacitor 12 is set to a second frequency band F2 including a frequency Fm2 at which the intensity of normal-mode noise N2 generated in the device 20 is maximized. Therefore, as described above, the impedance of the noise filter 11 can be reduced in the second frequency band F2 where the intensity of the normal-mode noise N2 is high. As a result, as described above, the normal-mode noise N2 generated in the device 20 easily passes through the noise filter 11 and easily returns to the device 20 via the noise filter 11 and the ground plane 53. This prevents the normal-mode noise N2 from propagating to the power supply 50 via the power line 31. Furthermore, in this embodiment, as described above, the impedance of the noise filter 11 can be increased in the first frequency band F1, in which the intensity of the common-mode noise N1 is high. This makes it possible to suppress the common-mode noise N1 generated in the device 20 from propagating to the ground plane 53 via the noise filter 11. This therefore makes it possible to suppress the common-mode noise N1 from propagating to the power supply 50 via the noise filter 11, the ground plane 53, and the ground line 50a. This makes it possible to suppress the normal mode noise N2 and the common mode noise N1 from propagating to the power supply 50, thereby stabilizing the operation of the power supply 50. This therefore makes it possible to suppress the current value of the first current C1 from becoming unstable, thereby stabilizing the operation of the device 20.

[0038] According to this embodiment, the first frequency band F1 is lower in frequency than the second frequency band F2. Therefore, among noises generated in the device 20, common mode noise N1, which has a frequency lower than that of the normal mode noise N2, can be preferably suppressed from propagating to the power supply 50. Furthermore, among noises generated in the device 20, normal mode noise N2, which has a frequency higher than that of the common mode noise N1, can be preferably suppressed from propagating to the power supply 50. As a result, since the normal mode noise N2 and the common mode noise N1 can each be preferably suppressed from propagating to the power supply 50, the operation of the power supply 50 can be preferably stabilized. Therefore, the operation of the device 20 can be preferably stabilized.

[0039] According to this embodiment, the equipment unit 10 includes a noise filter 11 and an equipment 20. The equipment 20 is a motor having a motor section 21 and an inverter 22 electrically connected to a power supply 50. The inverter 22 generates a second current C2 to be supplied to the motor section 21 from a first current C1 supplied by the power supply 50. As described above, in this embodiment, the noise filter 11 can suppress the propagation of normal mode noise N2, which is generated when the inverter 22 generates the second current C2, to the power supply 50 via the power supply line 31. Also, as described above, the noise filter 11 can suppress the propagation of common mode noise N1, which is generated when the inverter 22 generates the second current C2, to the power supply 50 via the noise filter 11, the ground plane 53, and the ground line 50a. This can favorably stabilize the operation of the power supply 50. Therefore, the operation of the equipment 20, i.e., the motor, can be favorably stabilized.

[0040] According to this embodiment, the inverter 22 has a switching element 24 that generates the second current C2, and the first frequency band F1 includes the switching frequency Fs of the switching element 24. This makes it easy to reduce the difference between the parallel resonant frequency Fp of the noise filter 11 and the switching frequency Fs. This more effectively prevents common-mode noise N1 generated by the switching operation of the switching element 24 from passing through the noise filter 11 and propagating to the power supply 50. This makes it possible to effectively stabilize the operation of the power supply 50. This also makes it possible to effectively stabilize the operation of the device 20.

[0041] According to this embodiment, the inverter 22 includes a switching element 24 that generates the second current C2 and a control unit 25 that controls the operation of the switching element 24, and the second frequency band F2 includes the clock frequency Fc of the control unit 25. This makes it easy to reduce the difference between the self-resonant frequency Fr of the capacitor 12 and the clock frequency Fc. As a result, as described above, the normal mode noise N2, whose frequency is approximately the same as the clock frequency Fc, is more likely to pass through the noise filter 11 and return to the device 20 more effectively. This more effectively prevents the normal mode noise N2 from propagating to the power supply 50. This more effectively stabilizes the operation of the power supply 50. This more effectively stabilizes the operation of the device 20.

[0042] The present invention is not limited to the above-described embodiments, and other configurations and methods may be adopted within the scope of the technical concept of the present invention. For example, the first frequency band, the second frequency band, the parallel resonant frequency, and the self-resonant frequency are not limited to the ranges and values ​​of the above-described embodiments, and can be appropriately determined based on the frequency bands in which the intensity of common-mode noise generated in the device is high and the frequency bands in which the intensity of normal-mode noise is high. Furthermore, if the frequency at which the intensity of common-mode noise is maximized is higher than the frequency at which the intensity of normal-mode noise is maximized, it is preferable that the first frequency band be set higher than the second frequency band.

[0043] Furthermore, the capacitance and parasitic inductance of the capacitors and the inductance of the inductors of the noise filter are not limited to those in the above-described embodiment, and can be determined appropriately based on the frequency bands in which the intensity of common mode noise is high and the frequency bands in which the intensity of normal mode noise is high.

[0044] As long as at least one capacitor and at least one inductor are connected in parallel, the number of capacitors and the number of inductors included in the noise filter are not limited to those in this embodiment. In other words, the noise filter may include multiple capacitors and multiple inductors.

[0045] The equipment unit may include a plurality of noise filters, which may be connected in series or in parallel between the power supply line and the ground plane.

[0046] The noise filter may be electrically connected to each of the first line and the ground plane, and in this case as well, it is possible to suppress propagation of normal mode noise and common mode noise to the power supply.

[0047] The equipment included in the equipment unit is not limited to a motor, but may be, for example, an electrical appliance or other equipment.

[0048] Although the embodiments of the present invention have been described above, the configurations and combinations thereof in the embodiments are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible without departing from the spirit of the present invention. Furthermore, the present invention is not limited to the embodiments.

[0049] The present technology may be configured as follows: (1) A noise filter having one end electrically connected to a power line connecting a power source and an apparatus and the other end grounded, the noise filter including a capacitor and an inductor connected in parallel, wherein the parallel resonant frequency of the capacitor and the inductor is set to a first frequency band including a frequency at which the intensity of common mode noise generated in the apparatus is maximized, and the self-resonant frequency of the capacitor is set to a second frequency band including a frequency at which the intensity of normal mode noise generated in the apparatus is maximized. (2) The noise filter according to (1), wherein the first frequency band is a frequency lower than the second frequency band. (3) An apparatus unit including the noise filter according to (1) or (2) and the apparatus, wherein the apparatus is a motor having a motor unit and an inverter electrically connected to the power source, and the inverter generates a second current to be supplied to the motor unit from a first current supplied by the power source. (4) The apparatus unit according to (3), wherein the inverter has a switching element that generates the second current, and the first frequency band includes a switching frequency of the switching element. (5) The equipment unit according to (3) or (4), wherein the inverter includes a switching element that generates the second current and a control unit that controls an operation of the switching element, and the second frequency band includes a clock frequency of the control unit.

[0050] 10...equipment unit, 11...noise filter, 12...capacitor, 14...inductor, 20...equipment, 21...motor section, 22...inverter, 24...switching element, 25...control section, 31...power supply line, C1...first current, C2...second current, F1...first frequency band, F2...second frequency band, Fc...clock frequency, Fp...parallel resonant frequency, Fr...self-resonant frequency, Fs...switching frequency, N1...common mode noise

Claims

1. A noise filter having one end electrically connected to a power line connecting a power source and an apparatus and the other end grounded, the noise filter having a capacitor and an inductor connected in parallel, the parallel resonant frequency of the capacitor and the inductor set to a first frequency band including a frequency at which the intensity of common mode noise generated in the apparatus is at its maximum, and the self-resonant frequency of the capacitor set to a second frequency band including a frequency at which the intensity of normal mode noise generated in the apparatus is at its maximum.

2. The noise filter according to claim 1, wherein the first frequency band is lower in frequency than the second frequency band.

3. An equipment unit comprising the noise filter according to claim 1 or 2 and the equipment, wherein the equipment is a motor having a motor section and an inverter electrically connected to the power supply, and the inverter generates a second current to be supplied to the motor section from a first current supplied by the power supply.

4. The equipment unit of claim 3, wherein the inverter has a switching element that generates the second current, and the first frequency band includes a switching frequency of the switching element.

5. The equipment unit according to claim 3, wherein the inverter has a switching element that generates the second current and a control unit that controls the operation of the switching element, and the second frequency band includes a clock frequency of the control unit.

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