JP2024052240A - Common mode current detector and active noise canceller - Google Patents

Abstract

The present invention makes it possible to improve compensation performance by improving impedance characteristics and phase characteristics that are insufficient when one type of core is used.
[Solution] The noise detector 31 comprises a toroidal core 41 made of a first magnetic material, a toroidal core 42 made of a second magnetic material having frequency characteristics different from that of the first magnetic material, main circuit wiring 43 passing through the toroidal core 41 and the toroidal core 42, and a secondary winding 44 wound around the toroidal core 41 and the toroidal core 42 for detecting common mode current, and detects the common mode current flowing in the main circuit wiring 43 using a signal generated in the secondary winding 44.
[Selected figure] Figure 3

Description

This disclosure relates to a common mode current detector and an active noise canceller.

For example, Patent Document 1 describes a noise reduction device for a power conversion device in which an electric motor is connected as a load to an inverter device consisting of an AC power source, a rectifier circuit, a smoothing capacitor, and an inverter circuit, a leakage current detector is connected between the AC power source and the rectifier circuit, a first NPN-type transistor is connected between one end of the smoothing capacitor and the case of the motor, and a second PNP-type transistor is connected between the case of the motor and the other end of the smoothing capacitor, and the first and second transistors are driven by the output of the leakage current detector to inject a current to cancel out common-mode noise.

Japanese Patent No. 3044650

Here, a toroidal core (annular core) has frequency characteristics in terms of impedance and phase that are due to the magnetic material. For this reason, an active noise canceller equipped with a common mode current detector that uses one type of toroidal core as a detection core has a frequency band in which the compensation performance is insufficient.

The purpose of this disclosure is to improve compensation performance by improving the impedance and phase characteristics that are lacking when using a single type of core.

The common mode current detector of the present disclosure includes a first annular core made of a first magnetic material, a second annular core made of a second magnetic material having a frequency characteristic different from that of the first magnetic material, a main circuit wiring passing through the first annular core and the second annular core, and a detection wire wound around the first annular core and the second annular core for detecting a common mode current, and detects the common mode current flowing through the main circuit wiring by a signal generated in the detection wire. In this case, it is possible to improve compensation performance by improving impedance characteristics and phase characteristics that are insufficient when one type of core is used.
Here, the detection wire may be formed by winding the first annular core and the second annular core together. In this case, manufacturing costs are reduced compared to a case in which the first annular core and the second annular core are not wound together.
In addition, the detection wire may have a portion wound around only the first annular core and a portion wound around only the second annular core connected in series, which increases the degree of freedom in combination of the first and second annular cores compared to a case where the portion wound around only the first and second annular cores and the portion wound around only the second annular core are not connected in series.
Furthermore, the impedance frequency characteristics of the first annular core and the second annular core may cross over between 9 kHz and 30 MHz, which improves the impedance characteristics compared to a case where the impedance frequency characteristics do not cross over between 9 kHz and 30 MHz.
The frequency characteristics of the phases of the first and second annular cores may cross over between 9 kHz and 30 MHz, which improves the phase characteristics compared to a case where the frequency characteristics of the phases do not cross over between 9 kHz and 30 MHz.
Furthermore, the first magnetic material may be made of Mn-Zn ferrite, and the second magnetic material may be made of Ni-Zn ferrite, in which case the increase in manufacturing cost is suppressed compared to a case where the combination of Mn-Zn ferrite and Ni-Zn ferrite is not used.

From another viewpoint, the active noise canceller of the present disclosure includes a first annular core made of a first magnetic material, a second annular core made of a second magnetic material having a frequency characteristic different from that of the first magnetic material, a main circuit wiring passing through the first annular core and the second annular core, and a detection wire wound around the first annular core and the second annular core for detecting a common mode current, and includes a common mode current detector for detecting the common mode current flowing through the main circuit wiring by a signal generated in the detection wire. In this case, it is possible to improve the compensation performance by improving the impedance characteristics and phase characteristics that are insufficient when one type of core is used.
In such an active noise canceller, the detection wire may be formed by winding the first annular core and the second annular core together, a portion wound only around the first annular core and a portion wound only around the second annular core may be connected in series, the impedance frequency characteristics of the first annular core and the second annular core may intersect between 9 kHz and 30 MHz, the phase frequency characteristics of the first annular core and the second annular core may intersect between 9 kHz and 30 MHz, the first magnetic material may be made of Mn-Zn ferrite, and the second magnetic material may be made of Ni-Zn ferrite.

1 is a diagram showing a circuit configuration of a power conversion system according to an embodiment of the present invention; 1 is a graph showing impedance characteristics of toroidal cores made of different materials, where the vertical axis represents impedance (Ω) and the horizontal axis represents frequency (Hz). 1 is a diagram illustrating a configuration of an active noise canceller according to a first embodiment. FIG. 1 is a graph showing frequency characteristics for two different core materials alone and in combination, in which (a) shows impedance characteristics with the vertical axis being impedance (Ω), and (b) shows phase characteristics with the vertical axis being phase (deg). FIG. 1 is a circuit diagram showing a simplified circuit in which an active noise canceller detects a common mode current and outputs a cancellation signal. 6 is a graph showing the simulation results of AM1 and AM2 when a current flows through Ia in the circuit diagram of FIG. 5, where (a) shows the case of 100 kHz and (b) shows the case of 1 MHz. 11 is a graph showing frequency characteristics of impedance and phase of a detection core used in a simulation. 1 is a graph showing frequency characteristics of a toroidal core, in which the vertical axis of (a) is impedance (Ω), the vertical axis of (b) is phase (deg), and the horizontal axis of both is frequency (Hz). 1 is a graph showing frequency characteristics when Mn-Zn ferrite and Ni-Zn ferrite are used as a toroidal core, in which the vertical axis of (a) is impedance (Ω), the vertical axis of (b) is phase (deg), and the horizontal axis of both is frequency (Hz). FIG. 11 is a diagram illustrating a configuration of a noise detection unit according to a second embodiment.

Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings.
[Power conversion system 1]
1 is a diagram showing a circuit configuration of a power conversion system 1 according to the present embodiment. As shown in the figure, the power conversion system 1 includes an AC power supply 100, a motor 200, and a power conversion device 300.

The AC power source 100 is, for example, a three-phase, three-wire commercial AC power source, and supplies AC to the power conversion device 300. Here, the first to third phases are referred to as the R phase, S phase, and T phase. The power lines supplying the R phase, S phase, and T phase are referred to as the R phase, S phase, and T phase power lines. When no distinction is made between phases, they are referred to as power lines. Note that, although the following describes a case where a three-phase, three-wire AC power source is used, a similar concept can be used when a three-phase, four-wire AC power source or a single-phase AC power source is used.

The motor 200 is connected to the power conversion device 300 and is controlled as a load by three-phase AC. The motor 200 may be, for example, a DC brushless motor. Alternatively, the motor 200 may be another three-phase AC motor.

The power conversion device 300 includes a power terminal block 10, an inverter board 20, and a noise reduction circuit 30.

The power supply terminal block 10 is a part that connects wiring for inputting AC from the AC power supply 100. The power supply terminal block 10 has an R-phase input terminal, an S-phase input terminal, and a T-phase input terminal, which are not shown. The power supply terminal block 10 may also have an earth terminal E0 to which an external earth wire is connected, although this is shown in the figure at a position away from the power supply terminal block 10.

The inverter board 20 includes a rectifier unit 21, a smoothing capacitor 22, and an inverter unit 23. On the inverter board 20, the rectifier unit 21, the smoothing capacitor 22, and the inverter unit 23 are connected in this order from the AC power supply 100 side. The inverter unit 23 is then connected to the motor 200.

The rectifier 21 rectifies the AC supplied from the AC power source 100, and the smoothing capacitor 22 converts it to DC. The inverter 23 converts the DC output from the rectifier 21 into three-phase AC and supplies it to the motor 200. The DC voltage between both terminals of the smoothing capacitor 22 is the DC link voltage. The inverter 23 includes a switching element (not shown). For example, an insulated gate bipolar transistor (IGBT) may be used as the switching element.

The noise reduction circuit 30 includes a common mode noise reduction circuit having a noise detection unit 31 and a compensation circuit unit 35, and a noise filter 32. The common mode noise reduction circuit is an active type common mode noise reduction circuit that detects common mode noise and suppresses it through feedback, and constitutes an active noise canceller 50 (see FIG. 3).

The noise detection unit 31 detects a common mode noise current. An example of the noise detection unit 31 is a detection core. The detection core may be a toroidal core with a power line wound in a coil shape around it. The toroidal core is made of a magnetic material such as ferrite, for example, with a circular cross section (donut shape). The toroidal core is sometimes called an iron core. Note that the toroidal core does not have to be circular, and may be a polygonal frame shape such as a square or triangle. The cross-sectional shape may also be a square, triangle, etc.

Here, the coil-shaped portions of the power line wound around the trochoidal core are referred to as coils (windings) L1r, L1s, L1t, and L1a. These coils L1r, L1s, and L1t are conductors (wires) that form part of the power line.
Here, the coil refers to a conductor wound in a spiral (loop) shape to form an inductor. Note that the power supply line may simply be a conductor passing through a trochoidal core.
The noise detection unit 31 is an example of a common mode current detector.

The detection coil L1a is wound around the trochoidal core so as to be adjacent to the power line coils L1r, L1s, and L1t. That is, the power line coils L1r, L1s, and L1t and the coil L1a are arranged to be magnetically coupled (magnetically coupled).
The power supply lines L1r, L1s, and L1t are wound so as to have the polarity shown by "." In other words, when a current flows through the power supply lines L1r, L1s, and L1t, for example, in the right direction in the figure, the coil L1a is wound so that a current flows through the coils L1r, L1s, L1t, and L1a in the left direction in the figure. Therefore, the polarity shown by the above "." is the polarity according to the direction in which the current flows.

The common mode noise current is a high-frequency current that leaks to the ground through the floating capacitance of the motor 200, etc., due to the switching of the switching elements of the inverter unit 23. Therefore, the common mode noise current flows between the R-phase, S-phase, and T-phase power lines and the ground (earth).

When a common mode noise current flows through the power supply lines L1r, L1s, and L1t, a current proportional to the common mode noise current is induced in the coil L1a via the toroidal core. In this case, the power supply lines L1r, L1s, and L1t and the coil L1a function as a current transformer and form a detection transformer that detects the common mode noise current.

The noise detection unit 31 also includes a base resistor Rb. The base resistor Rb is a resistor for limiting the base current flowing through the compensation circuit unit 35. Here, the circuit connected between the connection part of the detection core and the base resistor Rb is the detection circuit.

The compensation circuit section 35 includes a first transistor Tr1, a second transistor Tr2, a first diode D1, a second diode D2, and an output capacitor Co.

The first transistor Tr1 is a PNP type, and the second transistor Tr2 is an NPN type, and the first and second transistors Tr1 and Tr2 have opposite polarities to each other. The first transistor Tr1 and the second transistor Tr2 are connected in series. That is, the emitter of the first transistor Tr1 and the emitter of the second transistor Tr2 are connected.
A DC link voltage V is applied between the collector of the first transistor Tr1 and the collector of the second transistor Tr2.

The first transistor Tr1 is connected between one end (negative side) of the DC link voltage V and the output capacitor Co. The second transistor Tr2 is connected between the other end (positive side) of the DC link voltage V and the output capacitor Co. The bases (control terminals) of the first and second transistors Tr1, Tr2 are connected to one output line of the coil L1a, and the interconnection point of the first and second transistors Tr1, Tr2 is connected to the other output line of the coil L1a. This causes the first and second transistors Tr1, Tr2 to operate inversely to each other.

The first and second diodes D1 and D2 are connected in anti-parallel to the first and second transistors Tr1 and Tr2 to protect them. The first and second diodes D1 and D2 do not have to be provided. Here, the power supply for the compensation circuit unit 35 is supplied from the DC link of the rectifier unit 21, but it is also possible to provide a power supply other than the rectifier unit 21.

One end of the output capacitor Co is connected to the connection point on the emitter side of the first and second transistors Tr1 and Tr2, and the other end is connected to the earth terminal E1 of the housing via the compensation path connection terminal.

The noise filter 32 is composed of coils connected in series to each of the power lines, and a capacitor Cy connected to each of the power lines and the earth terminal E2 of the housing. This forms a filter that removes high-frequency noise. Note that the power conversion device 300 does not necessarily have to include the noise filter 32.

In this embodiment, the compensation circuit unit 35 includes a transistor. However, the compensation circuit unit 35 is not limited to a transistor, and may include an operational amplifier.
Also, a configuration may be adopted in which the output capacitor Co is not present, or a configuration may be adopted in which, in addition to the output capacitor Co, a resistor is connected directly to the output capacitor Co. Alternatively, a configuration may be adopted in which the output capacitor Co is connected to a power line, and the DC power supply unit 33 is connected to earth directly or via a coupling capacitor.

Here, we will explain the operation of the power conversion system 1 in this embodiment.

A commercial AC power source 100 supplies AC voltage to the inverter board 20 via the power terminal block 10. In the inverter board 20, the rectifier 21 rectifies the AC current supplied from the AC power source 100 to DC. The inverter 23 supplies AC voltage to the motor 200 by controlling the on/off of the switching elements.

At that time, each time a pulsed voltage is applied from the inverter unit 23, a common mode noise current Ic flows from the motor 200 as shown in the figure. The noise detection unit 31 detects the common mode noise current in the power line input to the inverter board 20, and drives the first and second transistors Tr1, Tr2 of the compensation circuit unit 35. When the detected current by the noise detection unit 31 flows into the bases of the first and second transistors Tr1, Tr2, it is amplified by the first and second transistors Tr1, Tr2.

When the first transistor Tr1 is on (when a positive common-mode noise current Ic is generated), the compensation current Io is supplied from the DC link voltage V and flows through a current path (compensation path) that connects from the positive terminal to the negative terminal via the rectifier 21, the noise detector 31, the noise filter 32, the AC power supply 100, the output capacitor Co, and the first transistor Tr1. In this case, the common-mode noise current Ic, the compensation current Io, and the compensated common-mode noise current Ig flow in the direction of the arrows in the figure. The compensation current Io is subtracted from the common-mode noise current Ic from the motor 200 to reduce the common-mode noise current Ic. In other words, the compensation current Io compensates for the common-mode noise current Ic.

When the second transistor Tr2 is on (when a negative common mode noise current Ic is generated), the compensation current Io is supplied from the DC link voltage V and flows through a current path (compensation path) that connects from the positive terminal to the negative terminal via the second transistor Tr2, the output capacitor Co, the AC power supply 100, the noise filter 32, the noise detection unit 31, and the rectification unit 21. In this case, the common mode noise current Ic, the compensation current Io, and the compensated common mode noise current Ig flow in the direction opposite to the arrows in the figure. The negative compensation current Io is subtracted from the negative common mode noise current Ic from the motor 200, thereby reducing the common mode noise current Ic. In other words, the compensation current Io compensates for the common mode noise current Ic.

As described above, whether the first transistor Tr1 is on or the second transistor Tr2 is on, the compensated common-mode noise current Ig flows through the AC power supply 100.

Here, a toroidal core as a detection core is usually inserted to increase the impedance of the line and make it difficult for noise to flow. The impedance has frequency characteristics according to the material and shape.
FIG. 2 is a graph showing the impedance characteristics (one turn each) of toroidal cores made of different materials, with the vertical axis representing impedance (Ω) and the horizontal axis representing frequency (Hz).
2, the range of 0.1 to 1000 Ω is shown vertically and the range of 9 kHz to 100 MHz is shown horizontally for core materials 1 to 6. The impedance frequency characteristics vary among core materials 1 to 6, and one is selected from core materials 1 to 6 according to the band of noise to be reduced, for example.

[First embodiment]
FIG. 3 is a diagram illustrating the configuration of the active noise canceller 50 according to the first embodiment.
The active noise canceller 50 shown in the figure includes a noise detection section 31 and a compensation circuit section 35 (see FIG. 1).

The noise detection unit 31 is equipped with a combination of annular toroidal cores 41, 42 with different frequency characteristics. The main circuit wiring 43 including the above-mentioned power supply lines L1r, L1s, L1t (see FIG. 1) passes through the toroidal cores 41, 42. The secondary winding 44 including the above-mentioned coil L1a (see FIG. 1) is wound around the toroidal cores 41, 42, and the voltage is used as a detection signal. The secondary winding 44 is connected to the compensation circuit unit 35.

In the first embodiment shown in FIG. 3, the secondary winding 44 is wound around the toroidal cores 41 and 42 together, and the secondary winding 44 is wound around the toroidal cores 41 and 42 together. This makes the winding of the secondary winding 44 more efficient and reduces manufacturing costs.

In the first embodiment, a combination of two toroidal cores 41, 42 has been described, but this is not limiting, and a combination of three or more may be used. In addition, the combination of the toroidal cores 41, 42 may be such that the cores appear as one from the outside, for example by being mounted on a bobbin, or the toroidal cores 41, 42 may be configured to be bonded to each other.

The main circuit wiring 43 is an example of the main circuit wiring. As described above, the main circuit wiring 43 passes through the toroidal cores 41 and 42. The main circuit wiring 43 may be linear or may be wound around the toroidal cores 41 and 42 like the secondary winding 44.
The secondary winding 44 is an example of a detection wire. The toroidal core 41 is an example of a first annular core, and the toroidal core 42 is an example of a second annular core.

Here, a description will be given of frequency characteristics when the toroidal cores 41 and 42 are used in combination. As an example, a description will be given of a combination of core material 1 and core material 4 among core materials 1 to 6 shown in FIG.
Fig. 4 is a graph showing frequency characteristics of two different core materials 1 and 4, individually and in combination. In (a), the vertical axis is impedance (Ω) and shows the frequency characteristics of impedance, and in (b), the vertical axis is phase (deg) and shows the frequency characteristics of phase. The horizontal axis in both Figs. 4(a) and (b) is frequency (Hz). In the graph, the solid line is core material 1, the dotted line is core material 4, and the dashed line is a composite of core materials 1 and 4 combined. The frequency range shown in (a) and (b) is 9 kHz to 100 MHz.
A current detector using a toroidal core such as a ferrite core has frequency characteristics in terms of impedance and phase that are attributable to the magnetic material.

As a detector, it is advantageous to have a high impedance and a phase close to 0 degrees. However, there are some frequency bands in the range of 150 kHz to 30 MHz where the compensation performance is insufficient.
4A and 4B, in the case of core material 1 shown by the solid line, the impedance is low in the frequency band below 300 kHz, and the phase is far from 0 degrees. In the case of core material 4 shown by the dotted line, the impedance is low in the frequency band above 300 kHz, and the phase is far from 0 degrees around 8 MHz.
When the toroidal cores 41 and 42 are a combination of the core material 1 and the core material 4, the combined result is that a high impedance can be obtained over a wide frequency band, as shown by the dashed line in (a).

In addition, although core material 1 has a phase shift of 90° around 100 kHz, by using it in series with core material 4, the combined result has the phase characteristics shown by the dashed line in (b), making it possible to bring the phase in the low range closer to 0° while maintaining the phase in the high range near 0°.
In this way, when the core materials 1 and 4 are used in combination, as shown by the dashed lines in Figures 4(a) and 4(b), the detection gain increases over a wide band, the phase shift decreases, and the compensation performance of the active noise canceller is improved.

Here, the influence of the phase of the toroidal cores 41 and 42 on the performance of the canceller will be described.
Fig. 5 is a simplified circuit diagram showing an active noise canceller 50 detecting a common mode current and sending a cancellation signal. Fig. 6 is a graph showing the simulation results of AM1 and AM2 when a current flows through Ia in the circuit diagram of Fig. 5, where Fig. 6(a) shows the case of 100 kHz and Fig. 6(b) shows the case of 1 MHz. Fig. 7 is a graph showing the frequency characteristics of the impedance and phase of the detection core used in the simulation.

In the circuit shown in Figure 5, as shown in Figures 6(a) and (b), a phase shift occurs in the compensation current relative to the detected current depending on the phase of the detection core. As is clear from a comparison of Figures 6(a) and (b), the phase shift is smaller at 1 MHz than at 100 kHz. This depends on the characteristics of the core.

Also, as shown in Figure 7, at a frequency of 100 kHz, the phase difference is 80 degrees, while at a frequency of 1 MHz, the phase difference is -5 degrees, meaning there is almost no phase shift. As can be seen from the frequency characteristics of the impedance, the higher the frequency, the closer the phase approaches 0 degrees.

When simulating the waveforms of each part when the detection core is set to ideal L, there is a 90 degree phase shift between Ia and VBin shown in Figure 5. Therefore, it is better for the core not to be ideal L. If the phase characteristic of the core is 0 degrees, there will be no phase shift between Ia and VBin, and Io will be a current with the same phase as VBin, so the phases of Ia and Io will match.

8 is a graph showing the frequency characteristics of the toroidal cores 41 and 42, where (a) shows the impedance characteristics on the vertical axis, which is impedance (Ω), and (b) shows the phase characteristics on the vertical axis, which is phase (deg). The horizontal axes of both (a) and (b) show frequency (Hz). The toroidal core 41 shown by the solid line is the core material 4 (see FIG. 2), and the toroidal core 42 shown by the dotted line is the core material 2 (see FIG. 2).
As shown in Fig. 8(a), the impedance frequency characteristics of the toroidal core 41 and the toroidal core 42 intersect at a position 60a between 9 kHz and 30 MHz, and as shown in Fig. 8(b), the phase frequency characteristics also intersect at a position 60b between 9 kHz and 30 MHz. As a countermeasure against EMI, it is preferable that the positions 60a and 60b are between 9 kHz and 30 MHz.

By adopting a combination of magnetic materials that cross each other in this way, it is possible to improve the frequency characteristics of impedance and phase. Also, by adopting a combination of magnetic materials that cross only one of them, it is possible to improve the frequency characteristics of either impedance or phase.

9 is a graph showing frequency characteristics when Mn-Zn ferrite and Ni-Zn ferrite are used for the toroidal cores 41 and 42, where (a) shows impedance characteristics with the vertical axis being impedance (Ω), and (b) shows phase characteristics with the vertical axis being phase (deg). The horizontal axes of (a) and (b) are both frequency (Hz).
9A shows a combination of toroidal cores 41 and 42 made of a magnetic material made of Mn-Zn ferrite and a magnetic material made of Ni-Zn ferrite. When using such a combination of relatively inexpensive magnetic materials, it is possible to suppress an increase in manufacturing costs.

The toroidal cores 41 and 42 may both be made of Mn-Zn ferrite and made of magnetic materials with different frequency characteristics, or may both be made of Ni-Zn ferrite and made of magnetic materials with different frequency characteristics.

[Second embodiment]
FIG. 10 is a diagram for explaining the configuration of a noise detection unit 31 according to the second embodiment, which corresponds to the noise detection unit 31 (see FIG. 3) of the first embodiment.
10, as in the first embodiment, main circuit wiring 43 passes through the toroidal cores 41 and 42. In addition, the secondary winding 44 wound around the toroidal cores 41 and 42 is formed by connecting a secondary winding portion 44a wound only around the toroidal core 41 and a secondary winding portion 44b wound only around the toroidal core 42 in series.

Consider a case where toroidal core 41 with secondary winding portion 44a wound thereon and toroidal core 42 with secondary winding portion 44b wound thereon are commercially available. By purchasing wound toroidal cores 41 and 42 made of a combination of magnetic materials that improve frequency characteristics and connecting secondary winding portion 44a and secondary winding portion 44b to each other, noise detection unit 31 can be manufactured.
In this way, by adopting a configuration in which the toroidal cores 41 and 42 are wound with windings independently, the degree of freedom in combination can be improved.
Although the toroidal core 41 and the toroidal core 42 have been described separately here, they may have an integrated structure in appearance.

[Effects of the embodiment]
The noise detection unit 31 of this embodiment includes a toroidal core 41 made of a first magnetic material, a toroidal core 42 made of a second magnetic material having frequency characteristics different from that of the first magnetic material, a main circuit wiring 43 penetrating the toroidal core 41 and the toroidal core 42, and a secondary winding 44 wound around the toroidal core 41 and the toroidal core 42 for detecting a common mode current. The noise detection unit 31 detects the common mode current flowing in the main circuit wiring 43 by a signal generated in the secondary winding 44.
The noise detection unit 31 makes it possible to improve the compensation performance by improving the impedance characteristics and phase characteristics that are insufficient when one type of toroidal core is used.

In this embodiment, the secondary winding 44 may be formed by winding the toroidal core 41 and the toroidal core 42 together.
In this way, the manufacturing costs can be reduced compared to a case in which the toroidal core 41 and the toroidal core 42 are not wound together.

In this embodiment, the secondary winding 44 may be configured such that a secondary winding portion 44a wound only around the toroidal core 41 and a secondary winding portion 44b wound only around the toroidal core 42 are connected in series.
In this way, the degree of freedom in combining the toroidal cores 41 and 42 is improved compared to a case in which the secondary winding portion 44a, which is wound only around the toroidal core 41, and the secondary winding portion 44b, which is wound only around the toroidal core 41, are connected in series.

In this embodiment, the impedance frequency characteristics of the toroidal core 41 and the toroidal core 42 may intersect between 9 kHz and 30 MHz.
In this way, the impedance characteristics can be improved compared to a case where the impedance frequency characteristics do not cross over between 9 kHz and 30 MHz.

In this embodiment, the frequency characteristics of the phases of the toroidal core 41 and the toroidal core 42 may intersect between 9 kHz and 30 MHz.
In this way, the phase characteristic can be improved compared to a case where the phase frequency characteristic does not cross over between 9 kHz and 30 MHz.

In this embodiment, the first magnetic material may be comprised of Mn-Zn ferrite and the second magnetic material may be comprised of Ni-Zn ferrite.
In this way, the increase in manufacturing costs is suppressed compared to when the combination of Mn--Zn ferrite and Ni--Zn ferrite is not used.

The active noise canceller 50 of this embodiment includes a toroidal core 41 made of a first magnetic material, a toroidal core 42 made of a second magnetic material having frequency characteristics different from that of the first magnetic material, a noise detection unit 31 including a main circuit wiring 43 penetrating the toroidal core 41 and the toroidal core 42, and a secondary winding 44 wound around the toroidal core 41 and the toroidal core 42 for detecting a common mode current. The noise detection unit 31 detects the common mode current flowing through the main circuit wiring 43 by a signal generated in the secondary winding 44.
According to this active noise canceller 50, it is possible to improve compensation performance by improving impedance characteristics and phase characteristics that are insufficient when one type of toroidal core is used.

In the active noise canceller 50 of this embodiment, the secondary winding 44 may be formed by winding the toroidal core 41 and the toroidal core 42 together, and the secondary winding 44 may be formed by connecting in series a secondary winding portion 44a that winds only the toroidal core 41 and a secondary winding portion 44b that winds only the toroidal core 42.
In addition, in the active noise canceller 50, the impedance frequency characteristics of the toroidal core 41 and the toroidal core 42 may intersect between 9 kHz and 30 MHz, and the phase frequency characteristics of the toroidal core 41 and the toroidal core 42 may intersect between 9 kHz and 30 MHz.
Furthermore, in the active noise canceller 50, the first magnetic material may be made of Mn--Zn ferrite and the second magnetic material may be made of Ni--Zn ferrite.

Although the embodiment has been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims.

31...Noise detection unit, 41, 42...Toroidal core, 43...Main circuit wiring, 44...Secondary winding, 44a, 44b...Secondary winding portion, 50...Active noise canceller

Claims (7)

a first annular core made of a first magnetic material;
a second annular core made of a second magnetic material having a frequency characteristic different from that of the first magnetic material;
a main circuit wiring passing through the first annular core and the second annular core;
a detection wire wound around the first annular core and the second annular core for detecting a common mode current;
a common mode current flowing through the main circuit wiring is detected by a signal generated in the detection line.
Common mode current detector. The detection wire is wound around the first annular core and the second annular core.
2. The common mode current detector according to claim 1. The detection wire has a portion wound only around the first annular core and a portion wound only around the second annular core connected in series.
2. The common mode current detector according to claim 1. The frequency characteristics of the impedance of the first annular core and the impedance of the second annular core cross each other between 9 kHz and 30 MHz.
4. A common mode current detector according to claim 1. The frequency characteristics of the phases of the first annular core and the second annular core intersect between 9 kHz and 30 MHz.
4. A common mode current detector according to claim 1. the first magnetic material is made of Mn-Zn ferrite;
The second magnetic material is made of Ni-Zn ferrite.
4. A common mode current detector according to claim 1. An active noise canceller comprising a common mode current detector according to any one of claims 1 to 3.