Noise cancellation device
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- DENSO CORP
- Filing Date
- 2026-01-08
- Publication Date
- 2026-07-30
Smart Images
Figure JP2026000397_30072026_PF_FP_ABST
Abstract
Description
Noise canceling device
[0006] ,
[0005] Cross-reference to related applications
[0001] This application is based on Japanese Application No. 2025-009021 filed on January 22, 2025, the contents of which are incorporated herein by reference.
[0002] This disclosure relates to a noise canceling device.
[0003] Conventionally, a noise canceling device for suppressing common mode noise in a motor drive device is known. Such a noise canceling device is described in, for example, Patent Document 1 and Patent Document 2.
[0004] Japanese Patent Application Laid-Open No. 2010-41908 Japanese Patent Application Laid-Open No. 2024-6698
[0005] Such a noise canceling device has, for example, a transformer circuit having an annular core and a conductor (primary coil) wound around the annular core as described in Patent Document 2. However, when winding a conductor around an annular core, a gap is formed between the conductors and the annular core is exposed from the gap. Since leakage magnetic flux is generated from this gap, there has been a problem that the coupling coefficient of the transformer circuit decreases and the noise reduction performance deteriorates.
[0006] This disclosure has been made to solve the above problems, and an object thereof is to provide a noise canceling device that can suppress leakage magnetic flux and suitably reduce noise.
[0007] A noise cancellation device for solving the above problems is a noise cancellation device for a motor drive device that drives a motor, comprising a noise cancellation circuit having an annular core through which a secondary conductor constituting a secondary coil connected to the motor drive device is inserted, and a primary coil attached to the annular core, wherein the annular core has a through hole on its inside through which the secondary conductor is inserted in a plan view, and a curved portion or corner portion on its outside, the primary conductor constituting the primary coil is arranged along the circumferential direction of the annular core in a plan view so as to alternately pass inside and outside the annular core, and the width dimension of the primary conductor in the circumferential direction is configured to be wider on the outside than on the inside of the annular core.
[0008] According to the above configuration, the area covering the surface of the annular core can be increased, and magnetic flux leakage from the annular core can be effectively suppressed. Therefore, a decrease in the coupling coefficient of the noise cancellation circuit can be suppressed, and as a result, a decrease in noise reduction performance can be suppressed.
[0009] The above-mentioned and other purposes, features and advantages of this disclosure will be further clarified by the following detailed description with reference to the attached drawings. The drawings are as follows: Figure 1 is a diagram of the drive system configuration; Figure 2 is a perspective view of the noise cancellation device; Figure 3 is a plan view of the annular core; Figure 4 is a cross-sectional view of the noise cancellation circuit; Figure 5 is a plan view of the noise cancellation circuit; Figure 6 is a bottom view of the noise cancellation circuit; Figure 7 is a plan view of the noise cancellation circuit; Figure 8 is a perspective view showing the stacked state of the noise cancellation circuit; Figure 9 is a perspective view of the secondary coil; Figure 10 is a partial cross-sectional view of the noise cancellation device; Figure 11 is a perspective view showing a part of the secondary coil; and Figure 12 is a view of the secondary coil. Figure 13 is a bottom view of the secondary coil, Figure 14 is a top view of the secondary coil, Figure 15 is a configuration diagram of a modified drive system, Figure 16 is a configuration diagram of a modified drive system, Figure 17 is a configuration diagram of a modified drive system, Figure 18 is a configuration diagram of a modified drive system, Figure 19 is a configuration diagram of a modified drive system, Figure 20 is a configuration diagram of a modified drive system, Figure 21 is a top view of a modified noise cancellation circuit, Figure 22 is a top view of a modified annular core, and Figure 23 is a bottom view of a modified noise cancellation circuit.
[0010] The following describes an embodiment in which a "noise cancellation device" is applied to a drive system 10 that drives a motor, with reference to the drawings. Note that functionally and / or structurally corresponding parts and / or related parts may be assigned the same reference numeral, or reference numerals with a difference of hundreds or more digits, between embodiments and modified examples. For corresponding parts and / or related parts, refer to the descriptions of other embodiments and modified examples.
[0011] As shown in Figure 1, the drive system 10 includes a motor 20 as a rotating electric machine, an inverter 30 as a motor drive device that supplies three-phase current to the motor 20, a DC power supply 40, a control device 50 that controls the inverter 30 and the like, and a noise cancellation device 60.
[0012] The motor 20 is, for example, the main motor of a vehicle (e.g., a hybrid vehicle or an electric vehicle) and is a permanent magnet synchronous motor having three phases (U phase, V phase, W phase) armature windings 21a to 21c. The inverter 30 is composed of a full bridge circuit having the same number of upper and lower arms as the number of phases of the armature windings 21a to 21c, and the current supplied to each armature winding 21a to 21c is adjusted by turning on and off switches (semiconductor switching elements) provided on each arm.
[0013] The control device 50 controls the power supply by switching each switch in the inverter 30 on and off based on various detection information and drive requests from the motor 20. As a result, the control device 50 supplies power to the motor 20 from the DC power supply 40 via the inverter 30, driving the motor 20. The positive terminal of the DC power supply 40 is connected to the positive terminal of the inverter 30 via the positive power supply path 11, and the negative terminal of the DC power supply 40 is connected to the negative terminal of the inverter 30 via the negative power supply path 12. The control device 50 also drives the motor 20 by outputting a pulse voltage from the inverter 30 through PWM control or the like. The inverter 30 and the motor 20 are connected via output lines 13 to 15 for each phase.
[0014] The noise cancellation device 60 is a device for suppressing common node noise. In this embodiment, the noise cancellation device 60 is provided on the paths of the positive-side power supply path 11 and the negative-side power supply path 12 between the DC power supply 40 and the inverter 30. The noise cancellation device 60 comprises a plurality of noise cancellation circuits 60a to 60c. The noise cancellation circuits 60a to 60c are provided in proportion to the number of phases of the motor 20, and in this embodiment, three are provided.
[0015] The configuration of the noise cancellation circuit 60a will now be explained. Note that the noise cancellation circuits 60a to 60c have the same configuration, differing only in their connections. Therefore, only the noise cancellation circuit 60a will be explained, and the explanations for noise cancellation circuits 60b and 60c will be omitted.
[0016] As shown in the perspective view of Figure 2, the noise cancellation circuit 60a has an annular core 61 through which a secondary conductor 76 forming a secondary coil 72 is inserted, and a primary coil 62 attached to the annular core 61. The secondary coil 72 attached to the annular core 61 is connected to power supply paths 11 and 12, as shown in Figure 1. The secondary coil 72 will be described later. Hereafter, the axial direction of the annular core 61 (Z direction in the figure) may be simply referred to as the axial direction, the circumferential direction of the annular core 61 (θ direction in the figure) may be simply referred to as the circumferential direction, and the radial direction of the annular core 61 (R direction in the figure) may be simply referred to as the radial direction.
[0017] The annular core 61 of this embodiment is an annular core (toroidal core) whose plan view is circular, as shown in the plan view of the annular core 61 in Figure 3. In other words, the annular core 61 has a through hole 63 that penetrates its center in its plan view, an inner circumferential surface 61a on the inside, and an outer circumferential surface 61b on the outside. The entire outer circumferential surface 61b of the annular core 61 of this embodiment corresponds to a curved surface. The through hole 63 is formed at the center of the annular core 61 along the axial direction of the annular core 61. In other words, the center of the through hole 63 and the center of the annular core 61 are formed to coincide.
[0018] Furthermore, as shown in the cross-sectional view of the noise cancellation circuit 60a in Figure 4, the annular core 61 is composed of a core body 64 made of magnetic material and an insulating tape 65 which serves as an insulator (insulating coating) covering the entire surface of the core body 64. Since the core body 64 is configured in an annular shape, it constitutes a closed magnetic circuit. The primary coil 62 is attached to the annular core 61 configured in this way by winding the primary conductor 66 around it.
[0019] As shown in the perspective view of Figure 2, the primary conductor 66 in this embodiment is made of a thin conductive metal foil and is attached so as to cover the surface of the annular core 61. Specifically, the primary conductor 66 is made of an elongated metal foil and is attached so as to alternately pass inside and outside the annular core 61, winding in a substantially helical manner along the circumferential direction of the annular core 61 in a plan view.
[0020] To explain in more detail, as shown in the cross-sectional view of Figure 4, the inner portions 66a constituting the primary conductor 66 are arranged at regular intervals in the circumferential direction on the inner circumferential surface 61a of the annular core 61. In this embodiment, 12 inner portions 66a are arranged at 30-degree intervals (i.e., at 12 locations).
[0021] For the sake of explanation, as shown in Figure 7, the first position (P1) will be used as the reference point, and the sections from the first position (P1) to the twelfth position (P12) will be described at 30-degree intervals counterclockwise. In this embodiment, each inner portion 66a will be described as being located one at each of the first position (P1) to the twelfth position (P12). Also, for the sake of illustration, the thickness dimension (radial dimension in the figure) of the primary conductor 66, which is a metal foil, is emphasized in Figures 4 and 7.
[0022] The inner portion 66a is attached to the annular core 61 so as to cover its inner circumferential surface 61a from the upper end to the lower end in the axial direction of the annular core 61 (the direction in which the through hole 63 extends). The width dimension L11 of the inner portion 66a in the circumferential direction is the same for each inner portion 66a, and the width dimension L21 of the gap between adjacent inner portions 66a in the circumferential direction is also the same.
[0023] Similarly, as shown in the cross-sectional view of Figure 4, the outer portions 66b constituting the primary conductor 66 are arranged at regular intervals in the circumferential direction on the outer circumferential surface 61b of the annular core 61. In this embodiment, 12 outer portions 66b are arranged at 30-degree intervals. Also, similar to the inner portions 66a, one outer portion 66b is arranged from the first position (P1) to the twelfth position (P12). The outer portions 66b are attached so as to cover the outer circumferential surface 61b from the upper end to the lower end in the axial direction of the annular core 61. The width dimension L12 of the outer portions 66b in the circumferential direction is the same for each outer portion 66b, and the width dimension L22 of the gap between adjacent outer portions 66b in the circumferential direction is the same for each outer portion 66b.
[0024] Furthermore, the width dimension L12 of the outer portion 66b in the circumferential direction is wider than the width dimension L11 of the inner portion 66a in the circumferential direction. On the other hand, the width dimension L22 of the gap between adjacent outer portions 66b in the circumferential direction is the same as the width dimension L21 of the gap between adjacent inner portions 66a in the circumferential direction. Note that the central angle θa of the sector formed by taking the outer portion 66b as a sector-shaped arc and centering the annular core 61 as the center of the sector is the same as the central angle θa of the sector formed by taking the inner portion 66a as a sector-shaped arc and centering the annular core 61 as the center of the sector. In other words, in this embodiment, the central angle θa is slightly less than 30 degrees.
[0025] As shown in the perspective view of Figure 2 and the plan view (top view) of the noise cancellation circuit 60a in Figure 5, the upper portions 66c constituting the primary conductor 66 are arranged at regular intervals in the circumferential direction so as to cover the upper end surface 61c of the annular core 61. These upper portions 66c are attached so as to cover the upper end surface 61c of the annular core 61 from the inner circumferential surface 61a to the outer circumferential surface 61b in the radial direction, connecting the inner portion 66a and the outer portion 66b. Furthermore, the width dimension L13 of the upper portions 66c in the circumferential direction is configured to gradually widen from the inside to the outside. In addition, the upper portions 66c are formed to expand diagonally with respect to the radial direction so as to connect the inner portion 66a to the outer portion 66b that is one position away in the circumferential direction (one position away in the clockwise direction when viewed from above). For example, as shown in Figure 7, the upper portion 66c is provided at an angle to the radial direction so as to connect the inner portion 66a at the first position (P1) and the outer portion 66b at the twelfth position (P12).
[0026] The width dimension L23 of the gap between adjacent upper portions 66c in the circumferential direction is the same for each. Also, the width dimension L23 of the gap between adjacent upper portions 66c in the circumferential direction is the same as the width dimensions L21 and L22 described above.
[0027] For the sake of explanation, the position of the upper portion 66c will be determined based on the inner position in the following description. For example, the upper portion 66c connecting the inner portion 66a of the first position (P1) and the outer portion 66b of the twelfth position (P12) will be referred to as the upper portion 66c of the first position (P1), and the upper portion 66c connecting the inner portion 66a of the second position (P2) and the outer portion 66b of the first position (P1) will be referred to as the upper portion 66c of the second position (P2). Hereafter, the position of the upper portion 66c will be determined similarly based on the inner position of the upper portion 66c.
[0028] As shown in the bottom view of the noise cancellation circuit 60a in Figure 6, the lower portion 66d of the primary conductor 66 is arranged at regular intervals in the circumferential direction so as to cover the lower end surface 61d of the annular core 61. This lower portion 66d is attached so as to cover the lower end surface 61d from the inner circumferential surface 61a to the outer circumferential surface 61b in the radial direction, so as to connect the inner portion 66a and the outer portion 66b. Furthermore, the width dimension L14 of the lower portion 66d in the circumferential direction is configured to gradually widen from the inside to the outside. In addition, the lower portion 66d is formed to expand straight in the radial direction so as to connect the inner portion 66a and the outer portion 66b at opposing positions in the circumferential direction. For example, as shown in Figure 7, the lower portion 66d (shown by a dashed line) is provided to expand straight in the radial direction so as to connect the inner portion 66a of the first position (P1) and the outer portion 66b of the first position (P1).
[0029] Furthermore, the width dimension L24 of the gap between adjacent lower portions 66d in the circumferential direction is the same for each. Also, the width dimension L24 of the gap between adjacent lower portions 66d in the circumferential direction is the same as the width dimensions L21 to L23 of the gaps described above.
[0030] For the sake of explanation, the position of the lower portion 66d will be determined based on the inner position. For example, as shown in Figure 7, the lower portion 66d that connects the inner portion 66a of the first position (P1) and the outer portion 66b of the first position (P1) will be referred to as the lower portion 66d of the first position (P1). The same applies to the other lower portions 66d.
[0031] As described above, by attaching the primary conductor 66 to the surface of the annular core 61, the inner portion 66a of the first position (P1) in the circumferential direction is connected to the lower portion 66d of the first position (P1) at the lower end surface 61d of the annular core 61, as shown in the plan view of Figure 7. In Figure 7, the inner portion 66a, the outer portion 66b, and the lower portion 66d are shown by dashed lines. This lower portion 66d of the first position (P1) is connected to the outer portion 66b of the first position (P1) at the lower end surface 61d of the annular core 61, as shown by the dashed arrow.
[0032] The outer portion 66b of this first position (P1) is connected to the upper portion 66c of the second position (P2) on the upper end surface 61c of the annular core 61, the inner side of which is positioned at the second position (P2). Then, as shown by the solid arrow, the upper portion 66c of the second position (P2) is connected to the inner portion 66a of the second position (P2) on the upper end surface 61c of the annular core 61.
[0033] Subsequently, the primary conductor 66 is wound multiple times (12 times in the figure) in a roughly spiral shape along the circumferential direction, from the second position (P2) to the third position (P3) to the twelfth position (P12). This winds the primary coil 62 onto the annular core 61. Note that there is a gap (see Figure 2) between the upper portion 66c and the outer portion 66b of the twelfth position (P12), and the coil is interrupted. In other words, these are the ends of the primary coil 62. One end of the primary coil 62 (the outer edge of the upper portion 66c of the twelfth position (P12)) is connected to one of the output lines 13 to 15 of the inverter 30. The other end (the upper end of the outer portion 66b of the twelfth position (P12)) is connected to the midpoint of a series connection of capacitors C11 and C12 (Y capacitor) which is connected between the positive side power supply path 11 and the negative side power supply path 12, as shown in Figure 1.
[0034] As shown in Figure 1, one end of the primary coil 62 of noise cancellation circuit 60a is connected to the output line 13, one end of the primary coil 62 of noise cancellation circuit 60b is connected to the output line 14, and one end of the primary coil 62 of noise cancellation circuit 60c is connected to the output line 13. The position of the end of the primary coil 62 may be arbitrarily changed; it may be located inside the annular core 61, or in the intermediate portion in the radial direction. It may also be located in the inner portion 66a or the outer portion 66b.
[0035] The noise cancellation device 60 comprises three noise cancellation circuits 60a to 60c configured as described above, a secondary coil 72 arranged to surround them, and an insulating structure 71 that fixes them in an insulated state. The secondary coil 72 and the insulating structure 71 will be described below.
[0036] As shown in Figure 8, the three noise cancellation circuits 60a to 60c are stacked such that the through-holes 63 (shown by dashed lines in Figure 8) of the annular core 61 are connected along the axial direction, that is, the positions of the through-holes 63 coincide in a plan view. In other words, they are stacked so that the centers of each annular core 61 coincide, and the axial, circumferential, and radial directions of each noise cancellation circuit 60a to 60c are the same. At this time, each noise cancellation circuit 60a to 60c is stacked at a predetermined distance from each other in the axial direction so that they do not come into contact with each other. Furthermore, in this stacked state of the noise cancellation circuits 60a to 60c, the inner circumferential surface 61a and the outer circumferential surface 61b of the annular core 61 coincide, as shown in the perspective view of Figure 8.
[0037] Furthermore, as shown in Figure 9, a secondary coil 72 is wound and positioned to surround the entirety of the three stacked noise cancellation circuits 60a to 60c. Then, to fix this state, almost the entirety of the three noise cancellation circuits 60a to 60c and the secondary coil 72 (excluding the upper end) is resin-molded to form a roughly cylindrical insulating structure 71.
[0038] In this case, as shown in the partial cross-sectional view of Figure 10, each noise cancellation circuit 60a to 60c is stacked with an insulating layer 71a interposed between them so as to be insulated from the other noise cancellation circuits 60a to 60c. Figure 10 is a partial cross-sectional view (longitudinal section) of the noise cancellation device 60, showing the insulating structure 71 and the secondary coil 72. Similarly, an insulating layer 71b is provided between each noise cancellation circuit 60a to 60c and the secondary coil 72 so as to be insulated from them. In other words, the insulating layer 71b is provided so as to cover the entirety of the three stacked noise cancellation circuits 60a to 60c.
[0039] As a result, as shown in the partial cross-sectional view of Figure 10, the insulating structure 71 fixes the arrangement of the three noise cancellation circuits 60a to 60c and the secondary coils 72, with them almost entirely housed inside. Although not shown in the figures, each primary coil 62 is provided with connection terminals connected to both ends of the primary coil 62, allowing connection to external wiring, and these connection terminals are exposed to the outside of the insulating structure 71.
[0040] Next, the configuration of the secondary coil 72 will be described. The secondary conductor 76 constituting the secondary coil 72 is arranged to be wound in a substantially helical shape along the circumferential direction, alternately passing inside and outside the stacked noise cancellation circuits 60a to 60c. As a result, the secondary coil 72 is wound around the entirety of the three noise cancellation circuits 60a to 60c. In this embodiment, as shown in Figure 1, two secondary coils 72a and 72b are wound around the noise cancellation circuits 60a to 60c. Note that the two secondary coils 72a and 72b may sometimes be referred to collectively as the secondary coil 72.
[0041] More specifically, as shown in the perspective views of FIGS. 9 and 11, the secondary conductor 76 of the secondary coil 72 in this embodiment is composed of a plurality of metal pieces. FIG. 11 is a perspective view of a part of the metal pieces constituting the secondary conductor 76. As shown in FIGS. 9 to 11, an inner metal column 76a constituting the secondary conductor 76 is disposed in the through hole 63 of the annular core 61 so as to face the inner peripheral surface 61a. Actually, the inner metal column 76a faces the inner peripheral surface 61a of the annular core 61 via the inner part 66a of the primary coil 62, the insulating layer 71b, and the like.
[0042] As shown in FIG. 11, this inner metal column 76a is a prismatic metal piece extending in the axial direction, and its cross section is substantially trapezoidal. This inner metal column 76a is disposed so as to cover the inner peripheral surface 61a from the upper end to the lower end of the stacked noise canceling circuits 60a to 60c along the axial direction (the direction in which the through hole 63 extends). The outer surface of the inner metal column 76a is a curved surface that conforms to the curvature of the opposing inner peripheral surface 61a.
[0043] As shown in FIG. 12 and the like, these inner metal columns 76a are arranged at regular intervals in the circumferential direction. In this embodiment, twelve inner metal columns 76a are arranged at 30-degree intervals (that is, at twelve locations). Hereinafter, for convenience of explanation, as shown in FIGS. 12 to 14, with the first position (P101) as a reference, the first position (P…
[0044] The width dimension L31 of the outer edge (the opposing surface of the inner peripheral surface 61a) of the inner metal column 76a in the circumferential direction is the same for each inner metal column 76a, and the width dimension of the gap between adjacent inner metal columns 76a in the circumferential direction is also the same.
[0045] As shown in FIGS. 9 to 11, an outer metal plate 76b constituting the secondary conductor 76 is disposed outside the annular core 61 so as to face the outer peripheral surface 61b. In actuality, the outer metal plate 76b faces the outer peripheral surface 61b of the annular core 61 through the outer portion 66b of the primary coil 62, the insulating layer 71b, and the like.
[0046] As shown in FIG. 11, the outer metal plate 76b is a substantially plate-shaped metal piece extending in the axial direction. This outer metal plate 76b is disposed so as to cover the outer peripheral surface 61b from the upper end to the lower end of the stacked noise canceling circuits 60a to 60c. The side surfaces (inner and outer surfaces) of the outer metal plate 76b are curved surfaces conforming to the curvature of the opposing outer peripheral surface 61b.
[0047] As shown in FIG. 12, these outer metal plates 76b are arranged at regular intervals in the circumferential direction. Similar to the inner metal posts 76a, each outer metal plate 76b is arranged one by one from the first position (P101) to the twelfth position (P112).
[0048] The width dimension L32 of the outer metal plate 76b in the circumferential direction is the same for each outer metal plate 76b, and the width dimension of the gap between adjacent outer metal plates 76b in the circumferential direction is also the same.
[0049] Also, the width dimension L32 of the outer metal plate 76b in the circumferential direction is wider than the width dimension L31 of the inner metal post 76a in the circumferential direction. On the other hand, the width dimension of the gap between adjacent outer metal plates 76b in the circumferential direction is the same as the width dimension of the gap between adjacent inner metal posts 76a in the circumferential direction. Note that the outer metal plate 76b is a sector-shaped arc, and the central angle of the sector with the center of the through hole 63 as the center of the sector is the same as the central angle of the sector with the outer peripheral surface of the inner metal post 76a as the sector-shaped arc and the center of the through hole 63 as the center of the sector.
[0050] As shown in the perspective view of Figure 9 and the plan view (top view) of Figure 12, the upper metal plates 76c constituting the secondary conductor 76 are arranged at regular intervals in the circumferential direction so as to cover the upper end surfaces 61c of the stacked noise cancellation circuits 60a to 60c. In reality, the upper metal plates 76c face the upper end surface 61c of the annular core 61 of the noise cancellation circuit 60a via the upper portion 66c of the primary coil 62 and the insulating layer 71b. These upper metal plates 76c are arranged so as to connect the inner metal column 76a and the outer metal plate 76b, covering the upper end surfaces 61c of the stacked noise cancellation circuits 60a to 60c from the inner circumferential surface 61a to the outer circumferential surface 61b in the radial direction.
[0051] The width dimension L33 of the upper metal plate 76c in the circumferential direction is configured to gradually widen from the inside to the outside. Furthermore, when viewed from above, the upper metal plate 76c is formed to widen diagonally with respect to the radial direction so as to connect the inner metal column 76a to the outer metal plate 76b that is one position away in the circumferential direction (one position away in the clockwise direction). For example, as shown in Figure 12, the upper metal plate 76c is formed to bend diagonally from the portion connected to the inner metal column 76a at the first position (P101) (shown by a dashed line) to the portion connected to the outer metal plate 76b at the twelfth position (P112) (shown by a dashed line).
[0052] Furthermore, the width of the gap between adjacent upper metal plates 76c in the circumferential direction is the same for each. Also, the width of the gap between adjacent upper metal plates 76c in the circumferential direction is approximately the same as the width between the outer metal plates 76b as described above.
[0053] For the sake of explanation, the position of the upper metal plate 76c will be determined based on its outer position in the following description. For example, the upper metal plate 76c connecting the inner metal column 76a at the first position (P101) and the outer metal plate 76b at the twelfth position (P112) will be referred to as the upper metal plate 76c at the twelfth position (P112), and the upper metal plate 76c connecting the inner metal column 76a at the second position (P102) and the outer metal plate 76b at the first position (P101) will be referred to as the upper metal plate 76c at the first position (P101). Hereafter, the position of the upper metal plate 76c will be determined similarly based on its outer position.
[0054] As shown in the perspective view of Figure 9 and Figure 11 and the bottom view of Figure 13, the lower metal plates 76d constituting the secondary conductor 76 are arranged at regular intervals in the circumferential direction so as to cover the lower end surfaces 61d of the stacked noise cancellation circuits 60a to 60c. In reality, the lower metal plates 76d face the lower end surface 61d of the annular core 61 of the noise cancellation circuit 60c via the lower portion 66d of the primary coil 62 and the insulating layer 71b. These lower metal plates 76d are arranged so as to connect the inner metal column 76a and the outer metal plate 76b, covering the lower end surfaces 61d of the stacked noise cancellation circuits 60a to 60c from the inner circumferential surface 61a to the outer circumferential surface 61b in the radial direction.
[0055] The width dimension L34 of the lower metal plate 76d in the circumferential direction is configured to gradually widen from the inside to the outside. Also, when viewed from below, the lower metal plate 76d is formed to widen diagonally with respect to the radial direction so as to connect the inner metal column 76a to the outer metal plate 76b that is one position away in the circumferential direction (one position away in the clockwise direction). For example, as shown in Figure 13, the lower metal plate 76d is formed to bend diagonally from the portion connected to the inner metal column 76a at the first position (P101) (shown by a dashed line) to the portion connected to the outer metal plate 76b at the second position (P102) (shown by a dashed line). Note that since Figure 13 is a bottom view of the secondary coil 72 viewed from below, the first position (P101) to the twelfth position (P112) will be reversed (clockwise).
[0056] Furthermore, the width of the gap between adjacent lower metal plates 76d in the circumferential direction is the same for each. Also, the width of the gap between adjacent lower metal plates 76d in the circumferential direction is approximately the same as the width between the outer metal plates 76b as described above.
[0057] In the following, the position of the lower metal plate 76d will be determined based on its outer position, similar to the upper metal plate 76c. For example, the lower metal plate 76d connecting the inner metal column 76a at the first position (P101) and the outer metal plate 76b at the second position (P102) will be referred to as the lower metal plate 76d at the second position (P102), and the lower metal plate 76d connecting the inner metal column 76a at the twelfth position (P112) and the outer metal plate 76b at the first position (P101) will be referred to as the lower metal plate 76d at the first position (P101). Thereafter, the position of the lower metal plate 76d will be determined similarly based on its outer position.
[0058] In this way, the inner metal column 76a, outer metal plate 76b, upper metal plate 76c, and lower metal plate 76d of the secondary conductor 76 are arranged to surround the stacked noise cancellation circuits 60a to 60c and connected to each other, thereby winding two secondary coils 72a and 72b. First, the connection configuration of the first secondary coil 72a will be described.
[0059] As shown in the plan view of Figure 14, the upper metal plate 76c at the first position (P101) in the circumferential direction is connected to the inner metal column 76a at the second position (P102), above the noise cancellation circuits 60a to 60c, as indicated by the solid arrow. In Figure 14, the inner metal column 76a, the outer metal plate 76b, and the lower metal plate 76d are shown by dashed lines. This inner metal column 76a at the second position (P102) is connected to the lower metal plate 76d at the third position (P103), below the noise cancellation circuits 60a to 60c.
[0060] The lower metal plate 76d of the third position (P103) is connected to the outer metal plate 76b of the third position (P103) below the noise cancellation circuits 60a to 60c, as indicated by the dashed arrow. The outer metal plate 76b of the third position (P103) is connected to the upper metal plate 76c of the third position (P103) above the noise cancellation circuits 60a to 60c. The upper metal plate 76c of the third position (P103) is connected to the inner metal column 76a of the fourth position (P104) above the noise cancellation circuits 60a to 60c, as indicated by the solid arrow. Thereafter, the secondary conductor 76 is wound multiple times (six times in the figure) in a substantially helical shape along the circumferential direction.
[0061] Thus, in the secondary coil 72a, the secondary conductors 76 are wound with one conductor skipped between them so that adjacent secondary conductors 76 in the circumferential direction are not connected. For example, looking only at the arrangement of the outer metal plates 76b, they are connected with one conductor skipped between them, from the 3rd position (P103) → 5th position (P105) → 7th position (P107) → 9th position (P109) → 11th position (P111) → 1st position (P101).
[0062] As shown in Figure 9, in this embodiment, the upper metal plate 76c at the first position (P101) and the outer metal plate 76b at the first position (P101) are not connected above the noise cancellation circuits 60a to 60c. In other words, the outer edge of the upper metal plate 76c at the first position (P101) and the upper end of the outer metal plate 76b at the first position (P101) form the ends of the secondary coil 72a and are connected to a connection terminal (not shown). Incidentally, for example, the outer edge of the upper metal plate 76c at the first position (P101) and the upper end of the outer metal plate 76b at the first position (P101) may be extended radially outward or axially upward to form a connection terminal. The secondary coil 72a is connected to the positive electrode power supply path 11 via this connection terminal.
[0063] Next, the second secondary coil 72b will be described. As shown in the plan view of Figure 14, the upper metal plate 76c at the 12th position (P112) in the circumferential direction is connected to the inner metal column 76a at the first position (P101) above the noise cancellation circuits 60a to 60c, as indicated by the solid arrows. This inner metal column 76a at the first position (P101) is connected to the lower metal plate 76d at the second position (P102) below the noise cancellation circuits 60a to 60c.
[0064] The lower metal plate 76d of the second position (P102) is connected to the outer metal plate 76b of the second position (P102) below the noise cancellation circuits 60a to 60c, as indicated by the dashed arrow. The outer metal plate 76b of the second position (P102) is connected to the upper metal plate 76c of the second position (P102) above the noise cancellation circuits 60a to 60c. The upper metal plate 76c of the second position (P102) is connected to the inner metal column 76a of the third position (P103) above the noise cancellation circuits 60a to 60c, as indicated by the solid arrow. Thereafter, the secondary conductor 76 is wound multiple times (six times in the figure) in a substantially helical shape along the circumferential direction.
[0065] Furthermore, in the secondary coil 72b, the secondary conductors 76 are wound with one conductor skipped so that adjacent secondary conductors 76 in the circumferential direction are not connected. For example, looking only at the arrangement of the outer metal plates 76b, they are connected with one conductor skipped at each position: 2nd position (P102) → 4th position (P104) → 6th position (P106) → 8th position (P108) → 10th position (P110) → 12th position (P112).
[0066] As shown in Figure 9, in this embodiment, the upper metal plate 76c at the 12th position (P112) and the outer metal plate 76b at the 12th position (P112) are not connected above the noise cancellation circuits 60a to 60c. In other words, the outer edge of the upper metal plate 76c at the 12th position (P112) and the upper end of the outer metal plate 76b at the 12th position (P112) form the ends of the secondary coil 72a and are connected to a connection terminal (not shown). Incidentally, for example, the outer edge of the upper metal plate 76c at the 12th position (P112) and the upper end of the outer metal plate 76b at the 12th position (P112) may be extended radially outward or axially upward to form a connection terminal. The secondary coil 72b is connected to the negative electrode power supply path 12 via this connection terminal.
[0067] As configured as described above, the primary coil 62 is positioned opposite the secondary coils 72a and 72b. The primary coil 62 and the secondary coils 72a and 72b constitute the CM transformers T1 to T3. The winding ratio of the primary coil 62 to the secondary coils 72a and 72b is 2:1. The principle by which common node noise is suppressed by these CM transformers T1 to T3 is well known, as described in, for example, Patent Document 1, so a detailed explanation will be omitted.
[0068] By configuring the noise cancellation device 60 as described above, the following effects are achieved.
[0069] The primary conductor 66 constituting the primary coil 62 is wound circumferentially so as to alternately pass inside and outside the annular core 61, and the circumferential width dimension of the primary conductor 66 is wider on the outside than on the inside of the annular core 61. More specifically, the circumferential width dimension L12 of the outer portion 66b constituting the primary conductor 66 is wider than the circumferential width dimension L11 of the inner portion 66a constituting the primary conductor 66. As a result, when the outer circumferential surface 61b of the annular core 61 is covered by the primary conductor 66, the gap between the primary conductors 66 can be reduced compared to when the circumferential width dimensions of the primary conductors 66 are the same. In other words, the area covering the outer circumferential surface 61b of the annular core 61 can be increased. This effectively suppresses magnetic flux leakage from the annular core 61. Therefore, a decrease in the coupling coefficient of the noise cancellation circuits 60a to 60c (transformer circuits) can be suppressed, and as a result, a decrease in noise reduction performance can be suppressed.
[0070] The sides of the annular core 61 (i.e., the inner circumferential surface 61a and the outer circumferential surface 61b) are covered by the primary conductors 66 such that the distance between the primary conductors 66 in the circumferential direction is the same both inside and outside. More specifically, the width dimensions L11 of the inner portion 66a and L12 of the outer portion 66b are determined so that the width dimension L21 between adjacent inner portions 66a and L22 between adjacent outer portions 66b are the same, thereby covering the inner circumferential surface 61a and the outer circumferential surface 61b, respectively. This increases the area of the annular core 61 covered by the primary conductors 66, thereby effectively suppressing magnetic flux leakage from the annular core 61. As a result, a decrease in the coupling coefficient of the noise cancellation circuits 60a to 60c is suppressed, and consequently, a decrease in noise reduction performance is suppressed.
[0071] The end faces (upper end face 61c and lower end face 61d) of the annular core 61 are covered by the primary side conductor 66. The upper portion 66c of the primary side conductor 66 covering the upper end face 61c is configured to gradually widen from the inside to the outside, and the lower portion 66d of the primary side conductor 66 covering the lower end face 61d is configured to gradually widen from the inside to the outside. This increases the area of the annular core 61 covered by the primary side conductor 66, thereby effectively suppressing magnetic flux leakage from the annular core 61. As a result, a decrease in the coupling coefficient of the noise cancellation circuits 60a to 60c is suppressed, and consequently, a decrease in noise reduction performance is suppressed.
[0072] The annular core 61 is composed of a core body 64 made of a magnetic material and an insulating tape 65 that covers the entire surface of the core body 64. The primary conductor 66 is constructed by attaching a conductive metal foil to the surface of the annular core 61 over the insulating tape 65. This makes it possible to reduce the gap between the core body 64 of the annular core 61 and the primary conductor 66 compared to when a wire is wrapped around it, and effectively suppresses magnetic flux leakage from the annular core 61. As a result, a decrease in the coupling coefficient of the noise cancellation circuits 60a to 60c is suppressed, and consequently, a decrease in noise reduction performance is suppressed. In addition, since the metal foil can be made thinner compared to the case of a wire, the noise cancellation circuits 60a to 60c can be miniaturized.
[0073] Furthermore, since the primary coil 62 is a coil in which one end is connected to the midpoint of the series connection of capacitors C11 and C12 and the other end is connected to the inverter 30, it is not intended to carry a large current. For this reason, it can be constructed from thin metal foil.
[0074] Multiple noise cancellation circuits 60a to 60c are stacked so that their through-holes 63 in the annular core 61 are connected. A secondary coil 72 is provided by winding a secondary conductor 76 along the circumferential direction so that it alternately passes inside and outside the stacked noise cancellation circuits 60a to 60c. This allows the secondary conductor 76 to cover the multiple noise cancellation circuits 60a to 60c, and magnetic flux leakage from the annular core 61 can be suitably suppressed compared to the case where the annular core 61 is covered only by the primary conductor 66. Furthermore, the number of turns in the secondary coil 72 can be increased compared to the case where the secondary coil 72 is constructed simply by inserting the secondary conductor 76 through the through-holes 63 of the annular core 61. As a result, a decrease in the coupling coefficient of the noise cancellation circuits 60a to 60c (transformer circuits) can be suppressed, and consequently, a decrease in noise reduction performance can be suppressed.
[0075] The circumferential width dimension of the secondary conductor 76 is wider on the outside than on the inside of the annular core 61. More specifically, the circumferential width dimension L32 of the outer metal plate 76b constituting the secondary conductor 76 is wider than the circumferential width dimension L31 of the inner metal column 76a constituting the secondary conductor 76. As a result, when the outer circumferential surface 61b of the annular core 61 is covered by the secondary conductor 76, the gap between the secondary conductors 76 can be reduced compared to when the circumferential width dimensions of the secondary conductors 76 are the same. In other words, the area covering the outer circumferential surface 61b of the annular core 61 can be increased. This effectively suppresses magnetic flux leakage from the annular core 61 and prevents a decrease in noise reduction performance.
[0076] The sides of the annular core 61 (i.e., the inner circumferential surface 61a and the outer circumferential surface 61b) are covered by the secondary conductors 76 such that the distance between the secondary conductors 76 in the circumferential direction is the same both inside and outside. More specifically, the width dimensions L31 of the inner metal columns 76a and L32 of the outer metal plates 76b are determined so that the width dimensions between adjacent inner metal columns 76a and outer metal plates 76b are the same, and the inner metal columns 76a and outer metal plates 76b are arranged to cover the inner circumferential surface 61a and outer circumferential surface 61b, respectively. This increases the area of the annular core 61 covered by the secondary conductors 76, thereby effectively suppressing magnetic flux leakage from the annular core 61 and preventing a decrease in noise reduction performance.
[0077] The end faces of the stacked noise cancellation circuits 60a to 60c are covered by the secondary conductor 76. More specifically, of the stacked noise cancellation circuits 60a to 60c, the upper end face 61c of the upper noise cancellation circuit 60a in the axial direction is covered by the upper metal plate 76c that constitutes the secondary conductor 76. Also, of the stacked noise cancellation circuits 60a to 60c, the lower end face 61d of the lower noise cancellation circuit 60c in the axial direction is covered by the lower metal plate 76d that constitutes the secondary conductor 76.
[0078] Furthermore, the upper metal plate 76c and the lower metal plate 76d are configured to gradually widen from the inside to the outside. This increases the area over which the annular core 61 is covered by the secondary conductor 76, thereby effectively suppressing magnetic flux leakage from the annular core 61. As a result, a decrease in noise reduction performance can be suppressed.
[0079] (Modifications) The configuration of the noise cancellation device 60 described in the above embodiment may be modified. Modifications are described below.
[0080] In the above embodiment, the secondary coil 72 is wound around the stacked noise cancellation circuits 60a to 60c, but the secondary coil 72 may be wound around each of the noise cancellation circuits 60a to 60c individually.
[0081] In the above embodiment, the distance between adjacent primary conductors 66 in the circumferential direction may be narrower on the outer side compared to the inner side. That is, the width dimension L22 between adjacent outer portions 66b may be narrower than the width dimension L21 between adjacent inner portions 66a. Similarly, the distance between adjacent secondary conductors 76 in the circumferential direction may be narrower on the outer side compared to the inner side.
[0082] In the above embodiment, the metal foil constituting the primary conductor 66 may be attached with an adhesive or the like, or a metal foil (metal coating) may be formed on the surface of the annular core 61 by plating. Alternatively, the metal foil constituting the primary conductor 66 may be formed by printing on the surface of the annular core 61, or by applying a conductive material to the surface of the annular core 61.
[0083] In the above embodiment, the secondary coil 72 may be formed by inserting a single secondary conductor 76 through a through hole 63 in the annular core 61.
[0084] In the above embodiment, the annular core 61 was covered with insulating tape 65 over the entire surface of the magnetic core body 64, but insulation may be provided by means other than insulating tape 65. For example, the core body 64 may be covered with an insulator by resin molding.
[0085] In the above embodiment, the circuit configuration of the drive system 10 may be changed as desired. For example, one end of the primary coil 62 may be grounded via the capacitor C1, as shown in Figure 15.
[0086] Furthermore, as shown in Figure 16, an AC power supply 141 may be used instead of the DC power supply 40, and the AC power supply 141 may be connected to the power supply paths 11 and 12 via a converter 142. Note that the other configurations are the same as in Figure 1 and are therefore omitted. Also, in Figure 16, as in Figure 15, one end of the primary coil 62 may be grounded via a capacitor C1.
[0087] Furthermore, as shown in Figure 17, multiple motor 20s and inverters 30s (two systems in Figure 17) may be provided. In this case, a noise cancellation device 60 should be provided for each system. Note that the configuration of the noise cancellation device 60 is the same as in Figure 1 and is therefore omitted.
[0088] Furthermore, as shown in Figure 18, it may also be used in a dual-winding motor 120 having two armature windings. Note that the configuration of the noise cancellation device 60 is basically the same as in Figure 1 and is therefore omitted.
[0089] In the above embodiment, as shown in Figure 19, the secondary coils 72 may be provided on each output line 13 to 15 between the inverter 30 and the motor 20. In this case, the noise cancellation device 60 will have three secondary coils 72 for each noise cancellation circuit 60a to 60c. One end of the primary coil 61 is connected to each output line 13 to 15, as in Figure 1, and the other end is connected to the midpoint of a series connection (Y capacitor) of two capacitors C11 and C12 connected between the positive side power supply path 11 and the negative side power supply path 12.
[0090] In this case, for example, as shown in Figure 20, one end of the primary coil 62 may be grounded via the capacitor C1.
[0091] In the above embodiment, the secondary coil 72 does not need to be made of metal pieces, but may be made of conductors. For example, the stacked noise cancellation circuits 60a to 60c may be covered with resin to form a cylindrical portion, and a conductor as the secondary conductor may be wound around the cylindrical portion to form the secondary coil.
[0092] - In the above embodiment, the shape of the annular core 61 was circular, but it may also be elliptical, oval, or polygonal. In the case of an oval or polygonal annular core, it is desirable that the width dimensions of the primary conductor 66 and the secondary conductor 76 are wider on the outside than on the inside of the annular core 61 at the curved or corner portions. For example, as shown in Figure 21, in the case of a quadrilateral annular core 161, the circumferential width dimension L112 of the outer portion 166b constituting the primary conductor 66 at its corners may be wider than the circumferential width dimension L111 of the inner portion 166a constituting the primary conductor 66. The same applies to the secondary conductor 76.
[0093] In the above embodiment, the annular core 61 does not need to be a single piece, and several may be combined to form a closed magnetic circuit core. For example, as shown in Figure 22, arc-shaped cores may be combined to form the annular core 261. In Figure 22, the annular core 261 is formed by combining semicircular arc-shaped cores 261a and 261b.
[0094] In the above embodiment, the upper portion 66c and lower portion 66d constituting the primary conductor 66 were configured to gradually widen from the inside to the outside, but as shown in Figure 23, they may be widened in stages. Similarly, the upper metal plate 76c and lower metal plate 76d constituting the secondary conductor 76 may also be widened in stages from the inside to the outside.
[0095] The following is an addition regarding the technical ideas derived from the above embodiments and modified examples. [Configuration 1] A noise cancellation device (60) for a motor drive device (30) that drives a motor (20), comprising a noise cancellation circuit (60a to 60c) having an annular core (61) through which a secondary conductor (76) constituting a secondary coil (72) connected to the motor drive device is inserted, and a primary coil (62) attached to the annular core, wherein the annular core has a through hole (63) on its inside for the secondary conductor to be inserted in a plan view, and a curved portion (61b) or corner portion on its outside, the primary conductor (66) constituting the primary coil is arranged along the circumferential direction (θ) of the annular core in a plan view so as to alternately pass inside and outside the annular core, and the width dimension (L11, L12) of the primary conductor in the circumferential direction is wider on the outside than on the inside of the annular core. [Configuration 2] The noise cancellation device according to Configuration 1, wherein the side surface of the annular core is covered with the primary conductor such that the distance between the primary conductors (L21, L22) in the circumferential direction at the curved surface or corner of the annular core is the same on both the inside and outside, or is narrower on the outside. [Configuration 3] The noise cancellation device according to Configuration 1 or 2, wherein the end faces (61c, 61d) of the annular core in the plan view are covered with the primary conductor, and the primary conductor covering the end faces at the curved surface or corner of the annular core is configured to gradually or stepwise widen from the inside to the outside. [Configuration 4] The noise cancellation device according to any one of Configurations 1 to 3, wherein the annular core is composed of a core body (64) which is a magnetic material and an insulator (65) which covers the entire surface of the core body, and the primary conductor is composed of a metal foil which is a conductor attached to the surface of the annular core. [Configuration 5] The noise cancellation device according to any one of Configurations 1 to 4, wherein one end of the primary coil is connected to the midpoint of a series connection of two capacitors (C11, C12) connected between the positive side power supply path (11) and the negative side power supply path (12), and the other end is connected to the motor drive device side.[Configuration 6] A noise cancellation device according to any one of Configurations 1 to 5, comprising a secondary coil composed of the secondary conductor, a plurality of noise cancellation circuits, the plurality of noise cancellation circuits stacked such that their through holes in the annular core are connected, and the secondary coil is provided by arranging the secondary conductor along the circumferential direction of the annular core in a plan view such that it alternately passes inside and outside the stacked plurality of noise cancellation circuits. [Configuration 7] A noise cancellation device according to Configuration 6, wherein at the curved surface or corner of the annular core, the circumferential width dimension (L31, L32) of the secondary conductor is wider on the outside than on the inside of the annular core. [Configuration 8] A noise cancellation device according to Configuration 6 or 7, wherein at the curved surface or corner of the annular core, the sides of the annular core of the stacked plurality of noise cancellation circuits are covered by the secondary conductor such that the distance between the secondary conductors in the circumferential direction is the same both inside and outside, or narrower on the outside. [Configuration 9] A noise cancellation device according to any one of Configurations 6 to 8, wherein, in a plan view, the end faces of a plurality of stacked noise cancellation circuits are covered by the secondary conductor, and the secondary conductor covering the end faces at the curved or corner portion of the annular core is configured to gradually or stepwise widen from the inside out. [Configuration 10] A noise cancellation device according to any one of Configurations 6 to 9, wherein the secondary coil is provided on the path of the power supply path (11, 12) between the power supply and the motor drive device, or on the path of the output line (13 to 15) between the motor drive device and the motor.
[0096] This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence. In addition, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of those elements, fall within the scope and concept of this disclosure.
Claims
1. A noise cancellation device (60) for a motor drive device (30) that drives a motor (20), comprising a noise cancellation circuit (60a to 60c) having an annular core (61) through which a secondary conductor (76) constituting a secondary coil (72) connected to the motor drive device is inserted, and a primary coil (62) attached to the annular core, wherein the annular core has a through hole (63) on its inside for the secondary conductor to be inserted in a plan view, and a curved portion (61b) or corner portion on its outside, the primary conductor (66) constituting the primary coil is arranged along the circumferential direction (θ) of the annular core in a plan view so as to alternately pass inside and outside the annular core, and the width dimension (L11, L12) of the primary conductor in the circumferential direction is wider on the outside than on the inside of the annular core.
2. The noise cancellation device according to claim 1, wherein the side surface of the annular core is covered with the primary conductors such that the distance between the primary conductors (L21, L22) in the circumferential direction is the same on both the inside and outside, or is narrower on the outside, at the curved surface or corner of the annular core.
3. The noise cancellation device according to claim 1, wherein the end faces (61c, 61d) of the annular core in the plan view are covered by the primary side conductor, and the primary side conductor covering the end faces at the curved portion or corner portion of the annular core is configured to gradually or stepwise widen from the inside outwards.
4. The noise cancellation device according to claim 1, wherein the annular core is composed of a core body (64) which is a magnetic material and an insulator (65) which covers the entire surface of the core body, and the primary conductor is formed by attaching a metal foil which is a conductor to the surface of the annular core.
5. The noise cancellation device according to claim 1, wherein one end of the primary coil is connected to the midpoint of a series connection of two capacitors (C11, C12) connected between the positive side power supply path (11) and the negative side power supply path (12), and the other end is connected to the motor drive device side.
6. A noise cancellation device according to any one of claims 1 to 5, comprising a secondary coil composed of the secondary conductor, wherein a plurality of noise cancellation circuits are provided, the plurality of noise cancellation circuits are stacked such that their through holes in the annular core are connected, and the secondary coil is provided such that the secondary conductor alternately passes inside and outside the stacked plurality of noise cancellation circuits, arranged along the circumferential direction of the annular core in a plan view.
7. The noise cancellation device according to claim 6, wherein, in the curved or corner portion of the annular core, the circumferential width dimension (L31, L32) of the secondary conductor is wider on the outside than on the inside of the annular core.
8. The noise cancellation device according to claim 6, wherein, at the curved surface or corner of the annular core, the sides of the annular core of a plurality of stacked noise cancellation circuits are covered by the secondary conductors such that the distance between the secondary conductors in the circumferential direction is the same both inside and outside, or narrower on the outside.
9. In the plan view, the end faces of the stacked plurality of noise cancellation circuits are covered by the secondary conductor, and the secondary conductor covering the end faces at the curved or corner portions of the annular core is configured to gradually or stepwise widen from the inside outwards, as described in claim 6.
10. The noise cancellation device according to claim 6, wherein the secondary coil is provided on the power supply path (11, 12) between the power supply and the motor drive device, or on the output line (13-15) between the motor drive device and the motor.