JP6769170B2 - Active noise suppressor - Google Patents

Description

The present invention relates to an active noise suppression device that suppresses the outflow of electromagnetic noise generated by an electric device to the outside.

With the widespread use of power electronics equipment, noise hazards generated by power electronics equipment are increasing. The laws and regulations of electromagnetic noise that started in Europe are spreading internationally, and power electronics equipment is required to reduce electromagnetic noise more than ever.

The most widely applied noise reduction technique in various devices today is the addition of EMI filters. For example, Patent Document 1 describes the problems of a conventional EMI filter. The filter configuration described in Patent Document 1 is configured by combining passive elements (reactor and capacitor). At this time, Patent Document 1 proposes an improvement method for a common mode choke coil for an EMI filter, which exhibits excellent noise characteristics even at 100 kHz or higher.

Here, in the EMI filter, the amount of noise reduction is generally significantly reduced when the frequency is several hundred kHz or more. This is mainly due to the following two points.

(1) The EMI filter is configured as an LC circuit consisting of a passive element consisting of a reactor and a capacitor, but an ideal passive element cannot be made.

(2) Unnecessary electromagnetic coupling / electrostatic coupling occurs depending on the arrangement and pattern of the parts constituting the EMI filter. That is, the effects of proximity between filter input / output and pattern intersection cannot be ignored.

For these reasons, most EMI filters, including Patent Document 1, are used to reduce noise in the subject of conduction noise regulation (150 kHz to 30 MHz). Therefore, there is almost no option other than adding an FM band countermeasure core (for example, Ni—Zn ferrite core) as a countermeasure against radiation noise in which high frequencies (30 MHz or more) are regulated.

However, although the number is small, an EMI filter specialized for radiation noise countermeasures as described in Patent Document 2 has been proposed. In this Patent Document 2, the core for FM band countermeasures and the shield wire are combined, and the low-pass filter is formed by the inductance of the core and the stray capacitance formed between the shield wire and the internal wiring to prevent radiation noise. EMI filter for. Both the core and stray capacitance are realized by configuring elements that maintain near-ideal characteristics in the frequency band (30 MHz or higher) regulated by radiation noise, but they have not yet been applied to products.

On the other hand, a noise reduction method (active noise suppression device) using an active element instead of a combination of passive elements (LC) has also been proposed (see Patent Documents 3 to 5). Although various methods have been proposed for these ActiNoise suppression devices, they are technically roughly divided into the following three types of functional blocks.
(A) Detection unit: Detects noise to be reduced (voltage detection by capacitor voltage division, current detection by CT, etc.)
(B) Control unit: Compensation voltage / current according to the control amount for noise reduction is output by the active element (transistors, operational amplifiers, etc. are applied to the active element).
(C) Coupling unit: The compensation voltage / current output by the control unit is coupled to the main circuit unit (transformer coupling, capacitor coupling).
Patent Document 3 discloses a current detection unit by CT, a control unit by an operational amplifier, and a coupling unit by a capacitor, and Patent Document 4 discloses a voltage detection unit by voltage division of a capacitor and a control unit composed of a transistor. And the trans-coupling portion are disclosed.

As described in Patent Documents 3 and 4, various configurations have been proposed in which the components of the detection unit, the control unit, and the coupling unit are combined in various ways.

Further, the connection location of the active noise suppression device is also distributed (detection) as described in Patent Document 4, in addition to the system side, the main circuit DC intermediate portion, and the output side as described in Patent Document 3. There are various configurations such as a configuration in which the part is the main circuit DC intermediate part and the coupling part is on the system side).

However, the actual situation is that the product application of the active noise suppression device has not progressed due to the following problems, except for some cases.
(1) Difficult to miniaturize The active noise suppression device is mainly operated so as to cancel the common mode noise voltage or the common mode noise current. At this time, there are many configurations in which a transformer is used for the detection unit and the coupling unit. In general, the lower the frequency of noise, the larger the countermeasure components tend to be. Therefore, the circuit constant should be designed based on the lowest frequency to be reduced. At this time, if an attempt is made to obtain a reduction effect sufficient to satisfy the standard at a frequency of several kHz to several tens of kHz or more, or a standard lower limit value of 150 kHz or more, there is no large difference between the volume of the transformer and the volume of the common mode choke coil. Significant miniaturization is difficult.
(2) It is difficult to obtain a large reduction effect in a high frequency band of several MHz or more. Like the above-mentioned EMI filter, an ideal element (capacitor, transformer) cannot be manufactured in an actual device. In addition, since a time delay (detection delay, drive delay of the canceling switching element) occurs, noise cannot be sufficiently canceled, and it is difficult to obtain a significant reduction effect, particularly in a region of several MHz or higher. Not only that, the active noise suppressor may even generate a frequency that becomes a noise source and increases the noise that flows out to the outside.

From these problems, an active noise suppression device that obtains a large noise reduction effect in a high frequency band of several MHz or more has been proposed (see Patent Document 5). In the active noise suppression device described in Patent Document 5, there is a point in the coupling portion, and an impedance element is added as the end of the conventional transformer coupling to perform impedance matching. Specifically, the impedance element is set so as to be matched with the common mode impedance of the electric motor according to the turns ratio of the coupling transistor. As a result, large noise reduction can be realized in a wide frequency band of low frequency to several MHz or more.

JP-A-7-22886 Japanese Unexamined Patent Publication No. 2014-161154 International Publication No. 2012/026186 Japanese Unexamined Patent Publication No. 2000-201044 Japanese Unexamined Patent Publication No. 2011-45191

However, there is a drawback that the load (for example, motor capacity, cable length, etc.) is limited in order to perform impedance matching as in the invention described in Patent Document 5. In other words, when using motors with different capacities or cable lengths, the impedance element for impedance matching must be adjusted each time. In the case of a general-purpose inverter applied to various uses, the above conditions are arbitrary, so it is practically difficult to adjust each time. That is, in the case of the invention described in Patent Document 5, it is difficult to develop it for applications other than the device in which the inverter and the load are uniquely limited.

Further, since the main focus is on measures for the noise terminal voltage (150 kHz) or higher, the problem that the active noise suppression device becomes large cannot be solved. By limiting the frequency, especially the regulation target (30 MHz) of radiation noise, which is difficult to deal with, there is a possibility that the frequency can be increased and the size can be reduced. However, no reported example has been known that has realized an active noise suppression device capable of reducing radiation noise of several tens of MHz or more, and the degree of difficulty is extremely high.

Therefore, the present invention has been made by paying attention to the problems of the conventional examples described in the above patent documents, and is a case where the load, the cable, etc. are changed without adding the impedance matching part or the like. Also, an object of the present invention is to provide an active noise suppression device capable of obtaining a good noise reduction amount. Further, it is an object of the present invention to provide a compact active noise suppression device after limiting the frequency to be reduced to radiation noise of 10 MHz or more.

In order to achieve the above object, one aspect of the active noise suppression device according to the present invention is a noise detection unit that detects an electromagnetic noise source generated by an electric device and a noise that cancels the electromagnetic noise detected by the noise detection unit. A control unit that forms an offset signal and a signal coupling unit that supplies a noise canceling signal formed by this control unit to an electric device are provided, and at least one of a noise detection unit and a signal coupling unit is provided inside the electric device. It is composed of a wiring or a wiring electrically connected to an electric device and a floating capacitance formed between this wiring and a shield conductor that shields the wiring .

According to one aspect of the present invention, an active noise suppression device that reduces radiation noise of 10 MHz or higher can be realized. In particular, it can be made smaller than the conventional active noise suppression device that reduces noise of several tens of kHz or 150 kHz or more, and can exhibit a high-performance radiation noise reduction effect as compared with the target core of radiation noise.

It is a block diagram which shows 1st Embodiment of the active noise suppression apparatus which concerns on this invention, (a) is a plan view, (b) is a sectional view, (c) is a sectional view which shows the stray capacitance generated. It is a circuit diagram which shows the equivalent circuit of FIG. It is a characteristic diagram which shows the open loop gain characteristic of an operational amplifier. It is sectional drawing in the direction orthogonal to the longitudinal direction which shows the modification of the 1st Embodiment. It is a figure which shows the measurement result of the noise voltage fluctuation in the presence / absence of a ground wire and the presence / absence of a shield wire. It is sectional drawing which shows the cable structure which shows the 2nd Embodiment of the active noise suppression apparatus which concerns on this invention, (a) shows the three-phase cable which has a shield conductor in the outer layer, (b) is two steps in the outer layer. A three-phase cable having a shield conductor is shown, and (c) shows a three-phase cable having a built-in ground wire. It is a side view of a three-phase cable. It is an enlarged view which shows the measurement result of the noise voltage fluctuation in the case of having a shield wire in FIG. It is a block diagram which shows the 3rd Embodiment of the active noise suppression apparatus which concerns on this invention. It is a block diagram which shows the 4th Embodiment of the active noise suppression apparatus which concerns on this invention. It is a block diagram which shows the active noise suppression apparatus which verified the effect of 4th Embodiment. It is a waveform diagram of the electric field strength with respect to the frequency which shows the measurement result of radiation noise. It is a circuit diagram which shows the modification of the active noise suppression apparatus which concerns on this invention.

Next, an embodiment of the present invention will be described with reference to the drawings. In the description of the drawings below, the same or similar parts are designated by the same or similar reference numerals.
In addition, the embodiments shown below exemplify devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention describes the material, shape, structure, and the like of the components. The arrangement etc. is not specified as the following. The technical idea of the present invention may be modified in various ways within the technical scope specified by the claims stated in the claims.
Hereinafter, an embodiment of the active noise suppression device according to the present invention will be described with reference to the drawings.

As shown in FIG. 1, the active noise suppression device 10 is connected in the immediate vicinity of an electric device (not shown) such as an inverter that is a noise suppression target. As the electrical equipment, when the active noise suppression device 10 is not applied, it is assumed that a large radiation noise is emitted from the wiring targeted for radiation noise reduction. Here, the wiring targeted for radiation noise reduction is assumed to be a power wiring (input cable or load cable), a signal cable, or the like of a power conversion device that forms an unintended monopole antenna (dipole antenna). However, even if the wiring is not exposed to the outside of the power device, the wiring connected via the semiconductor element (for example, the DC positive electrode (P) wiring and the negative electrode (N) wiring of the power conversion device) is subject to radiation noise reduction. It becomes wiring.

The case where the active noise suppression device 10 includes a printed circuit board 11 which is a four-layer board as an insulating plate part formed of a rectangular insulating material connected to a single-phase input part on an input side of an electric device will be described. To do.

Inside the printed circuit board 11, for example, copper radiation noise reduction target wirings 12a and 12b extending in the longitudinal direction at a position closer to the center in the thickness direction between the front surface and the back surface of the printed circuit board 11 maintain a predetermined interval in the thickness direction. It is buried in parallel. For example, the left end of the radiation noise reduction target wirings 12a and 12b is connected to the single-phase input side of the electric device, and the right end is connected to the power supply system side.

A noise detection unit 13 is formed on the power supply system side at positions facing the radiation noise reduction target wirings 12a and 12b of the printed circuit board 11 at predetermined intervals in the longitudinal direction, and a signal is coupled to the single-phase input side of the electric device. The portion 14 is formed.

The noise detection unit 13 covers, for example, solid patterns 21a and 21b for a copper shield conductor that cover the radiation noise reduction target wirings 12a and 12b formed at positions facing the radiation noise reduction target wirings 12a and 12b on both the front and back surfaces of the printed circuit board 11. Is equipped with.

The solid patterns 21a and 21b for both shield conductors are located at positions separated from both ends in the width direction of the radiation noise reduction target wirings 12a and 12b in the longitudinal direction along the side edges of the radiation noise reduction target wirings 12a and 12b, respectively. It is electrically connected by a conductive plating layer formed in a plurality of formed through vias 22.

Then, as shown in FIG. 1C, stray capacitance Cfd is formed between the radiation noise reduction target wirings 12a and 12b and the shield conductor solid patterns 21a and 21b facing them, respectively.

Further, the signal coupling unit 14 has the same configuration as that of the noise detection unit 13, and the solid patterns 31a and 31b for shield conductors formed on the front and back surfaces of the printed circuit board 11 and the solid patterns 31a for these shield conductors. And 31b are electrically connected by a conductive plating layer formed in a plurality of through vias 32.

In the signal coupling unit 14, as in the noise detection unit 13, as shown in FIG. 1C, between the radiation noise reduction target wirings 12a and 12b and the shield conductor solid patterns 31a and 31b facing them. A stray capacitance Cfc is formed.

Further, as shown in FIG. 1C, a control unit 15 is connected between the noise detection unit 13 and the signal coupling unit 14. The control unit 15 is composed of only an inverting amplifier 41. The inverting amplifier 41 is an electric device connected to an operational amplifier 42, a resistor R1 connected between the inverting input terminal of the operational amplifier 42 and a solid pattern 21b for a shield conductor of a noise detection unit 13, and a non-inverting input terminal. It is composed of a stable potential point 43 of the power converter and a feedback resistor R2 connected between an output terminal and an inverting input terminal, and the output terminal is connected to a solid pattern 31b for a shield conductor of a signal coupling portion 14. ..

Here, the stable potential point 43 of the power conversion device is assumed to be a housing, cooling fins, or the like that serves as a frame ground potential, and can generally be said to be a conductive portion having a large volume or area in the device.
Further, the connection between the stable potential point and the non-inverting input terminal of the operational amplifier 42 must be made with as low impedance as possible. If the impedance at the time of this connection is connected with a cable, the frequency at which noise can be reduced by the active noise suppression device becomes low. According to the experimental results of FIG. 12 described later, it was confirmed that the low noise effect could not be obtained at 70 MHz or higher when the cable was wired with 2.5 cm. It has also been confirmed that when the cable length is 10 cm (about 100 nH), the noise reduction effect of 30 MHz or more is reduced.

Therefore, the connection between the non-inverting input terminal and the stable potential point should be such that the wiring on the printed circuit board is the shortest that satisfies the restrictions such as withstand voltage and layout, and the wiring on the printed circuit board and the cooling fins that serve as the stable potential point are connected. For connection, it is preferable to use low impedance such as screwing with a stud bolt or the like, or providing a protruding connection portion on a cooling fin or the like and contacting the wiring on the printed circuit board with the connection portion.
Further, when the power conversion device is composed of a plurality of printed circuit boards and arranged so as to be stacked from stable potential points such as cooling fins, the printed circuit board on which the active noise suppression device is mounted is as low as possible, that is, cooled. By arranging it at a position close to the fins and ideally at the bottom layer (the shortest distance of the stable potential point serving as the cooling fin), it is possible to connect with low impedance and it becomes easy to obtain a good noise reduction effect.

A storage battery can be used as the power source for the operational amplifier 42, and an AC current flowing through the radiation noise reduction target wirings 12a and 12b can be rectified and supplied to a switching power source (not shown) to obtain a DC power source. By using a dedicated isolated power source for the power source of the operational amplifier 42, the noise reduction effect can be further enhanced.

Next, the operation of the first embodiment will be described with reference to the equivalent circuit of FIG.
When represented by an equivalent circuit, the noise detection unit 13 includes the wiring inductance Lc of the noise reduction target wirings 12a and 12b, the noise reduction target wirings 12a and 12b, and the solid patterns 21a and 21b for the shield conductor, as shown in FIG. It becomes a distributed constant line with the stray capacitance Cfd between them. Therefore, due to the influence of the wiring inductance, an LC resonance circuit is formed, and the characteristic of multiple resonance that repeats resonance and semi-resonance occurs.
In this distributed constant circuit, the stray capacitance Cfd operates as an ideal capacitor by setting the primary resonance frequency higher than the maximum frequency to be reduced.

A structure in which the primary resonance frequency of this LC resonance circuit is 100 MHz or more, which is a guideline for the maximum frequency at which noise is desired to be reduced by the active noise suppression device of the present invention (noise reduction target wirings 12a and 12b, solid pattern 21a for shield conductor, and the like. (Area and length facing 21b). However, strictly speaking, since the impedance changes due to the influence of resonance from a frequency lower than the resonance frequency, if the primary resonance frequency is set high to about 300 MHz, the stray capacitance functions as an ideal capacitor with good frequency characteristics. ..

Similarly, the signal coupling unit 14 having the same configuration as the noise detection unit 13 also forms an LC resonance circuit with the wiring inductance Lc and the stray capacitance Cfc, and the stray capacitance functions as an ideal capacitor having good frequency characteristics.

Then, the control unit 15 is connected between the noise detection unit 13 and the signal coupling unit 14. The control unit 15 is composed of an operational amplifier 42 and an inverting amplifier 41. Therefore, the noise voltage Vnoise detected by the noise detection unit 13 is inverted and amplified by the inverting amplifier 41 to be converted into an output voltage Vcompen that becomes a noise canceling signal, and the output voltage Vcompen is applied to the shield conductor solid pattern 31b of the signal coupling unit 14. To do. The signal coupling unit 14 can cancel the noise voltage Vnoise with the output voltage Vcompen to suppress the generation of radiation noise.

As described above, in the present embodiment, by configuring the control unit 15 only with the inverting amplifier 41, a simple configuration can be obtained as compared with the conventional example. Moreover, by configuring the inverting amplifier 41 with resistors R1 and R2 and the operational amplifier 42, the output voltage Vcompen, which is a noise canceling signal, is adjusted so that the noise voltage Vnoise becomes 0V as a result, and a very simple voltage feedback is performed. Realizes control. The ratios of the noise voltage Vnoise and the output voltage Vcompen are approximately determined by the ratio of the stray capacitances of the noise detection unit 13 and the signal coupling unit 14.

In the conventional example, a complicated configuration in which a buffer amplifier and a filter are combined is often adopted, but in the present embodiment, since the control unit 15 can be realized with a very simple configuration of one operational amplifier 421, the time delay can be minimized. it can.

By the way, in the simulation results, there is a prior document that uses only one inverting amplifier, but in reality, in the case of an active noise suppression device for reducing conduction noise of several to several hundred kHz, which is the conventional reduction target, an operational amplifier is used. Sufficient output characteristics cannot be obtained by using only. For this reason, there is no case in which the control unit is realized by one inverting amplifier in the prior literature showing the experimental results. In "An Optimized Feedback Common Mode Active Filter for Induction Motor Drives" described on pages 3153 to 3162 of "IEEE TRANSACTION ON POWER ELECTRONICS, VOL., 26 NO.11, NOVEMBER 2011", which is a non-patent document, In order to realize an active noise suppression device for conduction noise, operational amplifiers are used for each of the low-pass filter, linear amplifier, and power amplifier, and the configuration is complicated by using a total of three operational amplifiers.

In the present embodiment, the reason why the control unit 15 can be configured by one inverting amplifier 41 is that the energy compensated by the active noise suppression device is small in the radiation noise having a frequency of 10 MHz or higher, which is the noise reduction target, and one operational amplifier is used. This is because it can be sufficiently controlled.

Further, in the present embodiment, the inverting input terminal of the operational amplifier 42 constituting the inverting amplifier 41 of the control unit 15 is connected to the solid pattern 21b for the shield conductor of the noise detecting unit 13 via the resistor R1. A high-pass filter (a high-pass filter having a cutoff frequency of fz = 1 / (2πR1Cfd)) can be formed by the resistor R1 and the stray capacitance Cfd of the noise detection unit 13. As described above, the stray capacitance Cfd can exhibit excellent frequency characteristics, and the resistors R1 and R2 constituting the inverting amplifier 41 can exhibit excellent high frequency characteristics by using chip resistors. From this, it is possible to construct a good filter up to a high frequency band exceeding several tens of MHz to 100 MHz.

Here, the noise reduction effect is greatly different by appropriately setting the cutoff frequency of the high-pass filter composed of the resistor R1 and the stray capacitance Cfd of the noise detection unit 13. In order to reduce the radiation noise of 30 MHz or more, which is subject to the radiation noise regulation, the cutoff frequency must be lower than the regulation lower limit frequency of 30 MHz. In order to detect more accurately, it is preferable to set the cutoff frequency to 12.5 MHz or less so that the attenuation amount is 3 dB or less.

However, if the cutoff frequency is set too low, the voltage input to the operational amplifier 42 becomes large, which causes saturation of the operational amplifier 42. When the operational amplifier 42 is saturated, an appropriate compensation voltage cannot be output, so that the noise reduction effect is significantly deteriorated. Therefore, the cutoff frequency is preferably 3.5 MHz or more, which is a reduction amount of 30 MHz of 1 dB.

From the above, by setting the cutoff frequency of the high-pass filter composed of the resistor R1 and the stray capacitance Cfd of the noise detection unit 13 between 3.5 MHz and 12.5 MHz, a large amount of noise reduction can be obtained with a small operational amplifier 42. Active noise suppression device can be configured.

Ideally, the larger the gain of the inverting amplifier 41 described above, the greater the noise reduction effect, but the more likely it is to oscillate and become unstable. However, the operational amplifier 42 must select a product that can be used up to a high frequency band, but if the target is 30 MHz or higher, which is the target of radiation noise regulation, the open loop gain of the operational amplifier 42 alone will decrease.
That is, FIG. 3 shows an example of the frequency characteristics of the open loop gain of the low noise operational amplifier that can be used up to a high frequency (1 GHz). As shown in FIG. 3, an open loop gain of 60 dB can be obtained at 400 kHz or less, whereas the open loop gain decreases to about 23 dB at 30 MHz. Therefore, if the gain of the inverting amplifier 41 is set according to the gain of several MHz of the operational amplifier 42, it causes oscillation due to a few MHz component that is not subject to regulation.

Therefore, the resistance values of the resistors R1 and R2 are determined so as to be equal to or less than the open loop gain at 30 MHz of the operational amplifier 42. By doing so, it is possible to obtain a noise reduction amount that maximizes the performance of the operational amplifier 42 at the regulated frequency of 30 MHz or higher.
Therefore, the inverting amplifier 41 combined with the high-pass filter is obtained by determining the high-pass filter composed of the stray capacitance Cfd and the resistor R1 and then determining the resistance value of the resistor R2 suitable for the open loop gain of the operational amplifier 42. Can be designed properly.

As a result, all of the noise detection unit 13, the signal coupling unit 14, and the control unit 15 can realize a configuration suitable for the regulated frequency (30 MHz or more) of the radiation noise, and thus have better frequency characteristics than when individually applied. Is obtained.
Here, it is desirable that the noise detection unit 13 and the signal coupling unit 14 are arranged as close as possible. Also, the control unit 15 should be placed close to each other. This is because the voltage feedback control by the inverting amplifier 41 makes it easier for the operational amplifier 42 to oscillate when a propagation delay occurs between the noise detection unit 13 and the signal coupling unit 14.

Further, by arranging the noise detection unit 13 on the downstream side (load side or system side) of the signal coupling unit 14, the noise voltage Vnoise that cannot be canceled by the signal coupling unit 14 can be detected, and the radiation noise is surely reduced. can do.

In the first embodiment, the case where the printed circuit board 11 is formed in a rectangular plate shape when viewed from a plane has been described, but the present invention is not limited to this, and the printed circuit board 11 is formed in an L shape or a circle. It can be formed in an arc shape or in any shape.
Further, in the first embodiment described above, the case where the present invention is applied to the single-phase input side has been described, but the present invention is not limited to this, and the single-phase three-wire system, three-phase three-wire system, and three-phase four are not limited thereto. It can also be applied to linear systems and the like. For example, in order to configure a three-phase four-wire system, it can be configured as shown in FIG. 4A or FIG. 4B.

That is, in FIG. 4A, a four-layer printed substrate 11 is used, and the noise detection unit 13 (or signal coupling unit 14) formed on the printed substrate 11 is provided with the R-phase wiring 12r and the S-phase wiring 12s. The T-phase wiring 12t and the ground wiring 12e are arranged parallel to the same layer, the R-phase wiring 12r and the S-phase wiring 12s are opposed to the solid pattern 21a (or 31a) for the shield conductor. A floating capacitance is formed between the two, and the T-phase wiring 12t and the ground wiring 12e are opposed to the shield conductor peta pattern 21b (or 31b) to form a floating capacitance between the two.

In FIG. 4B, an 8-layer printed circuit board 11 is used, and the noise detection unit 13 (or signal coupling unit 14) formed on the printed circuit board 11 is provided with R-phase wiring 12r, S-phase wiring 12s, and T-phase. The wiring 12t and the ground wiring 12e are arranged parallel to each other in the thickness direction. Then, the solid patterns 21a (or 31a) and 21b (31b) for the shield conductor are arranged on the front and back surfaces of the printed circuit board 11, and the shield conductor peta pattern 21c (or 31c) is placed between the S-phase wiring 12s and the T-phase wiring 12t. Should be arranged individually. In this case, the widths of the R-phase wiring 12r, the S-phase wiring 12s, the T-phase wiring 12t, and the ground wiring 12e can be widened, so that a larger stray capacitance can be formed.

As described above, in the case of a single-phase three-wire system or a three-phase device including a ground wire, if the ground wire is included in the noise target reduction wiring, the radiation noise reduction effect can be further enhanced. The voltage fluctuation of the power line is suppressed by the proximity of the ground wire, and as a result, in the case of radiation noise, the potential fluctuation of the ground wire (corresponding to Vnoise) cannot be ignored. By including the ground wire in the noise reduction target wiring, the voltage fluctuation of the ground wire can be suppressed, so that the radiation noise reduction effect can be enhanced.

FIG. 5 shows the result of measuring the noise voltage Vnoise when applied to the power conversion device. It can be seen that the noise voltage Vnoise that causes the potential fluctuation in a substantially square wave shape due to the switching frequency of 50 kHz is observed. Compared to the condition without the ground wire shown by the thin solid wire in FIG. 5, the condition with the ground wire shown by the dark solid wire, that is, the noise voltage Vnoise detected in close proximity to the power wire and the ground wire is smaller, and the noise voltage itself It can be confirmed from the experimental results that is suppressed.
Therefore, the radiation noise suppression effect is enhanced by detecting the noise voltage Vnoise and attenuating it with the active noise suppression device in a state where the cables including the ground wire are bundled together.

Next, a second embodiment of the active noise suppression device according to the present invention will be described with reference to FIGS. 6 and 7.
In this second embodiment, instead of configuring the active noise suppression device 10 with the printed substrate 11, cables such as power wiring (input cable and load cable) and signal cable of, for example, a power conversion device constituting an electric device. The noise detection unit 13 and the signal coupling unit 14 are arranged in the above.
That is, in the second embodiment, as an example, the noise detection unit 13 and the signal coupling unit 14 are formed on a three-phase cable 51 such as a load cable or an input cable.

As shown in FIG. 6A, an example of the three-phase cable 51 is a columnar insulator in which the R-phase wiring 52r, the S-phase wiring 52s, the T-phase wiring 52t, and the ground wiring 52e are each insulated and coated. It has a 4-core cable configuration which is embedded in 53, a shield conductor 54 is arranged on the outer peripheral surface of the insulator 53, and an insulating coating 55 is arranged on the outer periphery of the shield conductor 54.

Even in this case, the stray capacitance Cf shown in the equivalent circuit of FIG. 2 can be formed between the shield conductor 54 and the R-phase wiring 52r, the S-phase wiring 52s, and the T-phase wiring 52t, respectively. Therefore, as shown in FIG. 7, the insulating coating 55 is removed in a circumferential shape so as to expose the shield conductor 54 at a position separated from the tip on the side connected to the electric device by a predetermined distance, and then the shield conductor 54 is removed. A separation portion 58 is formed by removing both ends in the axial direction in a circumferential shape and separating in the longitudinal direction. The front end side is used as a signal coupling part 14, and the rear end side is used as a noise detection unit 13.

Then, the inverting input terminal of the operational amplifier 42 constituting the inverting amplifier 41 of the control unit 15 is connected to the exposed shield conductor 54 of the noise detection unit 13 via the resistor R1, and the output terminal of the operational amplifier 42 is connected to the signal coupling unit 14. It is connected to the exposed shield conductor 54.

According to this second embodiment, the equivalent circuit has the same configuration as that of the first embodiment described above, and the noise voltage Vnoise detected by the noise detection unit 13 is inverted and amplified by the inverting amplifier 41 to cancel the noise signal. By applying the output voltage Vcompen as a signal to the shield conductor 54 of the signal coupling portion 14, the noise voltage of the R-phase wiring 52r, the S-phase wiring 52s, and the T-phase wiring 52t can be canceled by the signal coupling portion 14. It is possible to obtain the same effect as that of the first embodiment described above. As a result, the noise voltage Vnoise can be set to approximately 0V as shown by the broken line in FIG. 5 described above.

Moreover, in the second embodiment, since the common shield conductor 54 is provided for each wiring of the three-phase cable, as compared with the case where the printed circuit board 11 is provided as in the first embodiment described above, The overall configuration can be made smaller

In the second embodiment, the case where the shield conductor 54 is arranged in a single layer has been described, but the present invention is not limited to this. That is, as shown in FIG. 6B, by arranging the second shield conductor 56 so as to surround the shield conductor 54 outside the shield conductor 54, a higher shielding effect can be exhibited and radiation noise can be reduced. It can be further reduced. In this case, the radiation noise reduction target wiring includes the shield conductor 54 in addition to the R-phase wiring 52r, the S-phase wiring 52s, the T-phase wiring 52t, and the ground wiring 52e. In the case of power converters and communication cables, shielded wires may be applied for the purpose of reducing noise outflow to the outside.

However, in reality, radiation noise is also emitted from the shield wire. This is because the potential of the shielded conductor 54 (corresponding to Vnoise) does not completely reach 0 V even when the shielded cable is applied, and is radiated to the outside due to a minute potential fluctuation. In such a case, by forming the second shield conductor 56 as shown in FIG. 6B, the potential fluctuation of the shield conductor 54 is formed between the shield conductor 54 and the second shield conductor 56. The stray capacitance can form a noise detection unit and a signal coupling unit, which makes it possible to further reduce radiation noise. Reference numeral 57 denotes an insulating coating that covers the second shield conductor 56.

Here, FIG. 5 described above shows the result of measuring the noise voltage Vnoise when applied to the power conversion device, but the noise voltage Vnoise including the shielded line is also shown as shown by the chain line. From FIG. 5, the noise voltage Vnoise of the shielded wire is smaller than that of other conditions, and the result suggesting that the shielded wire can reduce the radiated noise is obtained.
The result of enlarging the noise voltage characteristic line with the shield line shown in FIG. 5 is shown in FIG. As is clear from FIG. 8, a high-frequency peak voltage signal such as a large surge voltage of about ± 0.5V, which is significantly smaller than other conditions, can be confirmed at the moment of switching, and the noise voltage Vnoise is completely set. It cannot be set to 0V.

This noise voltage Vnoise changes greatly depending on the grounding method (connection method with the stable potential) of the shielded wire. For example, under the condition that the shield clamp can be connected with low impedance, the noise voltage Vnoise becomes significantly smaller as shown in FIG. 8, whereas in the case of so-called pigtail connection, there is a large change with the ground wire in FIG. May not be seen.
In any case, it is difficult to completely set the noise voltage Vnoise to 0V and it becomes a radiation noise source. Therefore, by configuring the noise detection unit 13 and the signal coupling unit 14 including the shield wire as described above, the radiation noise Can be further reduced.

Further, in the configuration of FIG. 6C, unlike a general 4-core cable, the ground wire 52e is divided and the distance between the R-phase wiring 52r, the S-phase wiring 52s and the T-phase wiring 52t and the ground wiring 52e is increased. Formed to be the same. The cable shown in FIG. 6C has a large stray capacitance between the R-phase wiring 52r, the S-phase wiring 52s, the T-phase wiring 52t, and the ground wiring 52e to the same extent as the shielded cable, and the noise detection unit 13 and The signal coupling unit 14 can be diverted.

As described in the above-mentioned paragraph number "0054", it is a technique peculiar to the noise suppression device for radiated noise to regard the ground wiring 52e and the shielded wire as the radiated noise reduction target wiring in this way. In the active noise suppression device for suppressing conduction noise, the ground wire and shield wire are not regarded as the wiring to be noise-reduced.

Although the 4-core wire has been described in the second embodiment, the same can be applied to a 3-core wire (three-phase three-wire, single-phase three-wire), a two-core wire (single-phase, direct current), and the like. Also, the signal line may have a larger number of cores.

In the first and second embodiments, the case where both the noise detection unit 13 and the signal coupling unit 14 are configured with stray capacitance has been described, but either the noise detection unit 13 or the signal coupling unit 14 is used. It may be configured by stray capacitance. As described above, in the variously proposed active noise suppression devices as in the prior art, an ideal capacitor cannot be realized, which causes noise to not be detected and coupled even at high frequencies. Therefore, by applying stray capacitance to the voltage detection unit and voltage coupling unit of the active noise suppression device proposed in the prior art, improvement in the amount of reduction in the high frequency band can be expected.

However, since the stray capacitance is very small compared to the capacitance detected by the conventional capacitor partial pressure, it is difficult to accurately capture the potential fluctuation in the frequency band for conduction noise. Further, the same problem arises in the conventional capacitor applied to the signal coupling unit 14. From this, it can be said that the noise detection unit 13 and the signal coupling unit 14 realized by the stray capacitance are more effective configurations for utilizing in reducing radiation noise.

Although it has been described that the stray capacitance functions as a capacitor having excellent frequency characteristics, strictly speaking, as shown in FIG. 2, it is a distribution constant circuit of wiring inductance and stray capacitance. Therefore, the characteristics of LC resonance and semi-resonance occur due to the influence of the wiring inductance. This is the same for both the printed circuit board shown in FIG. 1 and the cable shown in FIG. That is, by setting the primary resonance frequency higher than the frequency to be reduced in the distributed constant line as shown in FIG. 2, the capacitor operates as an ideal capacitor.

The stray capacitance and wiring inductance differ depending on the printed circuit board configuration and cable configuration, and the primary resonance frequency also differs greatly. However, as described later, the frequencies that have been experimentally confirmed to be effective in the present invention are from around 10 MHz to 100 MHz. Based on the above, the structure (length, area) must be such that the above-mentioned LC resonance and semi-resonance frequencies are 100 MHz or more. However, strictly speaking, since the impedance changes due to the influence of resonance from a frequency lower than the resonance frequency, if the primary resonance frequency is set to be increased to about 300 MHz, the stray capacitance functions as a capacitor having good frequency characteristics.

Next, a third embodiment of the active noise suppression device according to the present invention will be described with reference to FIG.
In this third embodiment, it is assumed that the active noise suppression device alone may not satisfy the legal regulations, and in order to deal with this, the FM band countermeasure is outside the noise detection unit 13 of the active noise suppression device. The core for noise is added.

In this third embodiment, as shown in FIG. 9, the FM band countermeasure core 61 as a noise reduction core is arranged on the system side / load side opposite to the signal coupling portion of the noise detection unit 13. It is configured in the same manner as the first or second embodiment described above except that the above-described first or second embodiment is used.

In this third embodiment, there is an effect of reducing the radiation noise due to the noise potential fluctuation Vnoise, which could not be sufficiently reduced by the active noise suppression device 10, by combining it with the addition of the countermeasure core of the prior art.

Next, a fourth embodiment of the active noise suppression device according to the present invention will be described with reference to FIG.
If the fluctuation of the noise voltage Vnoise is too large, the operational amplifier 42 is saturated and a sufficient noise reduction effect cannot be obtained. Therefore, the cutoff frequency of the high-pass filter composed of the resistor R1 and the stray capacitance Cfd of the noise detection unit 13 is appropriately set. The setting is described above. However, in order to reduce the radiation noise of 30 MHz, which is the lower limit frequency to be regulated, the setting range of the cutoff frequency is limited. Therefore, under the condition of large noise, that is, the condition of large fluctuation of the noise power supply Vnoise, the operational amplifier 42 It may not be possible to achieve both the prevention of saturation and the setting of an appropriate cutoff frequency.

Therefore, in the fourth embodiment, in order to solve the problem that the saturation prevention of the operational amplifier 42 and the setting of an appropriate cutoff frequency cannot be achieved at the same time, the power conversion device side, that is, noise detection from the signal coupling unit 14 of the active noise suppression device 10. An FM band countermeasure core 62 as a noise reduction core is arranged on the side opposite to the unit 13.

According to this fourth embodiment, it corresponds to a configuration in which the EMI filter configuration for reducing radiation noise described in Patent Document 2 and the active noise suppression device 10 are combined. The FM band countermeasure core 62 and the stray capacitance of the signal coupling portion 14 constitute an EMI filter for radiation noise countermeasures. Due to this filter effect, the peak of the noise voltage fluctuation Vnoise is reduced as compared with the coreless condition, so that the output of the operational amplifier 42 can be reduced. As a result, saturation of the operational amplifier 42 is avoided, and a good radiation noise reduction effect can be obtained.

Finally, an example in which the present invention has been experimentally verified will be described with reference to FIGS. 11 and 12.
In the experiment, as shown in FIG. 11A, a noise detection unit 13 and a signal coupling unit 14 are formed on the cable 51 shown in FIG. 6A of the second embodiment, and a signal coupling unit 14 is formed as needed. An FM band countermeasure core 62 is arranged on the side opposite to the noise detection unit 13 of 14, and a common mode is provided between the end of the cable 51 on the FM band countermeasure core 62 side and the housing simulated steel plate 63 as a stable potential. The noise source 64 is connected.

Here, as can be confirmed from FIGS. 11A and 11B, the shield of the noise detection unit 13 and the signal coupling unit 14 is configured to be wound around a part of the radiation noise reduction target wiring. Further, the control unit 15 is configured by mounting it on a small substrate at a portion surrounded by the square frame A shown in FIG. 11B.

And FIG. 12 is the result of actually measuring the radiation noise. Comparing before connecting the active noise suppression device and after connecting the active noise suppression device, it can be seen that the radiation noise reduction effect of about 10 dB or more is obtained in the regulated 30 MHz to 70 MHz by the present invention. However, at 70 MHz or higher, the radiation noise reduction effect of the active noise suppression device is not sufficiently obtained. This can be improved by shortening the wiring impedance (cable length 2.5 cm) connected to the non-inverting input terminal of the operational amplifier 42 and the stable potential point. In addition, it is presumed that the cause is that the radiation noise measurement is only in one direction and the entire circumference (360 °) cannot be measured. Further, in this result, the effect is verified by a simple prototype device as shown in FIG. 11B, but a larger reduction effect can be expected if it is verified by a product-level prototype.

In the first to fourth embodiments, the connection location of the active noise suppression device 10 has not been described in particular, but as in the prior art, any location on the system side, the main circuit DC intermediate portion, or the output side. The above effect can be exhibited even if it is connected to. However, in the case of a distributed arrangement (the signal coupling portion is on the system side in the DC intermediate portion of the detection unit main circuit), the operational amplifier 42 easily oscillates, which is difficult to apply.

Further, in the first to fourth embodiments, the case where the active noise suppression device is provided on the input side of the electric device has been described, but the active noise suppression device may be provided on the output side of the electric device.

Further, in the first to fourth embodiments, the case where one inverting amplifier is used as the control unit has been described, but when it is applied to the active common noise canceller (ACC) as shown in FIG. 13, it is controlled. The configuration of unit 15 is changed. The active common noise canceller converts the DC power of the DC power supply 71 into three-phase AC by the inverter 73, and arranges the noise detection unit 13 based on the floating capacitance described above on the three-phase AC lines U, V, and W which are the outputs of the inverter 73. At the same time, a signal coupling unit 14 composed of a common mode transformer CT is arranged, and a control unit 15 is connected between the noise detection unit 13 and the signal coupling unit 14.

Here, as the control unit 15, the first complementary buffer amplifier 74 in which the noise voltage Vnoise is input to the base, the high-pass filter 75 connected to the output side thereof, and the high-pass filter 75 connected to the output side of the high-pass filter 75 are connected. It is composed of two complementary buffer amplifiers 76, and the noise voltage from the noise detection unit 13 input to the first complementary buffer amplifier 74 is extracted by the high-pass filter 75 only for high-frequency components, and the extracted high-frequency components are second-complementary. It is applied to the winding W4 of the common mode transformer CT via the type buffer amplifier 76. The first and second complementary buffer amplifiers 74 and 76 are powered by an independent power source 77.

Further, it is connected to the connection point between the independent power supply 77, the other end of the primary coil of the common mode transformer CT, the other end of the resistor constituting the high-pass filter 75, the noise detection unit 13, and the base of the first complementary buffer amplifier 74. The other end of the capacitor Cn is connected to the connection point of the high withstand voltage capacitors CH1 and CH2 connected in parallel with the DC power supply 71, that is, the neutral point of the DC link voltage.

As described above, by configuring the control unit 15 as described above, the noise voltage generated in the AC electric circuit detected by the noise detection unit 13 is the second complementary type in which only the high frequency component is extracted by the high pass filter 75 of the control unit 15. A voltage between the high frequency component output via the buffer amplifier 76 and the neutral point of the independent power supply 77 (common with the neutral point of the DC link voltage) is applied to the common mode transformer CT. As a result, the noise voltage can be offset by superimposing a voltage having a magnitude opposite to that of the noise voltage.

10 ... Active noise suppression device, 11 ... Printed board, 12a, 12b ... Radiation noise reduction target wiring, 13 ... Noise detection unit, 14 ... Signal coupling unit, 15 ... Control unit, 21a, 21b ... Solid pattern for shield conductor, 22 ... Penetration via, 31a, 31b ... Solid pattern for shield conductor, 32 ... Penetration via, 41 ... Inversion amplifier, 42 ... Optics, 43 ... Stable potential point, 51 ... Three-phase cable, 52r ... R-phase wiring, 52s ... S-phase Wiring, 52t ... T-phase wiring, 52e ... Earth wiring, 54 ... Shield conductor, 56 ... Second shield conductor, 61, 62 ... FM band countermeasure core, 63 ... Housing simulated steel plate, 64 ... Common mode noise source, 71 ... DC power supply, 73 ... Inverter, 74 ... First complementary buffer amplifier, 75 ... High pass filter, 76 ... Second complementary buffer amplifier, 77 ... Independent power supply, CT ... Common mode transformer

Claims (7)

A noise detector that detects the source of electromagnetic noise generated by electrical equipment,
A control unit that forms a noise canceling signal that cancels the electromagnetic noise detected by the noise detection unit,
A signal coupling unit that supplies a noise canceling signal formed by the control unit to the electric device is provided.
At least one of the noise detection unit and the signal coupling unit is a wiring provided inside the electric device or a wiring electrically connected to the electric device, and the wiring and a shield conductor that shields the wiring . An active noise suppression device characterized by being composed of a floating capacitance formed between them. A noise detector that detects the source of electromagnetic noise generated by electrical equipment,
A control unit that forms a noise canceling signal that cancels the electromagnetic noise detected by the noise detection unit,
A signal coupling unit that supplies a noise canceling signal formed by the control unit to the electric device is provided.
At least one of the noise detection unit and the signal coupling unit is a wiring provided inside the electric device or a wiring electrically connected to the electric device, and the wiring and a shield conductor that shields the wiring . Consists of the floating capacity formed between
The control unit is an active noise suppression device including an operational amplifier that inverting and amplifies electromagnetic noise detected by the noise detection unit and supplies the electromagnetic noise to the signal coupling unit. At least one of the noise detection unit and the signal coupling unit has a wiring that is electrically connected to the electric device formed in the insulating plate portion and a shield conductor pattern that faces the wiring via the insulating portion. The active noise suppression device according to claim 1 or 2 , wherein the active noise suppression device is composed of the wiring and a floating capacitance formed between the shield conductor patterns. At least one of the noise detection unit and the signal coupling unit includes a plurality of insulation-coated wiring conductors connected to the electric device, a shield conductor that surrounds the plurality of insulation-coated wiring conductors with an insulating material, and the insulation. The active noise suppression device according to claim 1 or 2 , wherein the active noise suppression device is composed of a floating capacitance formed between a coated wiring conductor and the shield conductor. The active noise suppression apparatus according to any one of claims 1, characterized in that a noise reduction core on the opposite side 4 to the viewed from the noise detection unit and the signal combination unit. The active noise suppression device according to any one of claims 1 to 4 , wherein a noise reduction core is arranged on the side opposite to the noise detection unit when viewed from the signal coupling unit. The control unit includes a first complementary buffer amplifier to which the noise voltage of the noise detection unit is input, a high-pass filter connected to the output side of the first complementary buffer amplifier, and a high-frequency component extracted by the high-pass filter. The active noise suppression according to claim 1, further comprising a second complementary buffer amplifier into which is input, and applying the output of the second complementary buffer amplifier to a common mode transformer constituting a signal coupling unit. apparatus.