JP5532554B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device that reduces conduction noise and / or radiation noise. Specifically, the present invention relates to a power conversion device that reduces noise by providing resistance in a frequency region for reducing noise using a skin effect in a wiring and a substrate on a path through which a noise current flows.

  In recent years, as regulations regarding EMC (Electro-Magnetic Compatibility) become stricter, reduction of noise generated from various electric and electronic devices has become a technical issue. In particular, countermeasures are required for reducing noise generated by switching on and off of switching elements such as semiconductors which are components of these electric and electronic devices.

  In taking measures against noise, it is effective to add an impedance to a site serving as a path of noise current. For example, Patent Document 1 describes the insertion of a ferrite core. However, for example, when applied to a portion where a large current flows, care must be taken because the temperature easily rises due to self-heating due to loss of the core. In addition, depending on the material and target frequency, any ferrite core adds inductance, which can increase surge.

  Further, in Patent Document 2, although it is insulated in terms of direct current, it becomes a current path from the viewpoint of noise frequency, with respect to the fin connected to the power converter, the AC reactor, and the ground line of the motor that is a load. A method of adding a resistor as an external element is described. However, the wiring part to which the resistor is added acts as an inductance. This inductance is only about several nH to several tens of nH, but if applied to a portion where a large current flows, such as a main circuit of an inverter using a switching element, it causes a surge at the time of switching. Therefore, it is difficult to physically add a part to a portion where it is difficult to increase the inductance even if it is slight. Furthermore, the addition of parts leads to an increase in cost.

  The above measures require some external elements. On the other hand, a method for suppressing noise using the skin effect has also been proposed. For example, Patent Document 3 describes a method for suppressing noise at a skin wiring portion, which includes a main wiring with a low resistivity and a skin wiring with a high resistivity and magnetic permeability as a circuit pattern for a power inverter module.

  Further, in Patent Document 4, a skin portion is formed by plating a surface of an electrode including a copper wiring or bus bar constituting a power conversion circuit, or by coating a material mixed with a magnetic substance such as a resistive paint or ferrite. Describes a method of suppressing noise.

Japanese Patent No. 2851268 JP 2006-25467 A JP 2001-326300 A Japanese Patent Laid-Open No. 2005-20868

However, in the prior art, the target frequency for obtaining the skin effect was not clear. Furthermore, the skin thickness determined with this frequency was unknown.
Further, even if a high resistance coating is applied as in the prior art, the skin effect is not necessarily obtained. According to the skin effect, current flows through the skin or outer wall of the conductor, but when coated with a material with high resistance, no current flows through the coated part, forming a skin inside the coated part and forming a current. Flows. That is, even if a high-resistance coating is applied, no current flows through the coating portion, so that the resistance of the conductor cannot be provided. In addition, when, for example, a resin material having high resistance and low thermal conductivity is applied to a copper bar or the like, there is a problem that the heat dissipation characteristics of the bar are hindered.

  In order to solve the above problem, a power conversion device according to the present invention is a power conversion device including a semiconductor switching element, and a conductor used for wiring and / or a substrate inside the device is made of at least two kinds of materials. The first material of the materials is used for the central portion of the conductor, the second material of the materials is used for the skin of the conductor, the first material is copper, and the second material The material is bronze or chrome, and in the cross-sectional profile of the current density representing the relationship between the distance from the surface of the conductor and the current density, each of the surface of the first material and the surface of the second material has a peak value. It is characterized by appearing.

  ADVANTAGE OF THE INVENTION According to this invention, noise can be reduced by giving resistance using the skin effect with respect to the conductor part in the path | route through which the electric current in a power converter device flows. In the present invention, since there is no increase in inductance caused by the addition of parts, it can be applied to a part where surge countermeasures are difficult, and characteristics that are almost the same as the characteristics of the central conductor in terms of DC can be obtained. High frequency noise of 1 MHz to 100 MHz can be effectively suppressed.

  Next, the best form of the power converter according to the present invention will be described in detail with reference to the drawings.

In the power conversion device according to the present invention, the target frequency for causing the skin effect is 1 MHz to 100 MHz, which is a band of conduction noise and / or radiation noise generated via the semiconductor switching element. And in the power converter device which concerns on this invention, it is suitable to coat | cover with the skin thickness based on this frequency with respect to the conductor used for the wiring inside and / or a board | substrate. Here, when σ is conductivity (Ω ⁻¹ · m ⁻¹ ), μ is magnetic permeability (H / m), and ω is angular frequency (Hz), frequency f (Hz) and skin thickness D _S (m ) Is expressed by the following equation.

According to one embodiment of the present invention, copper is used as a material (also referred to as a first material) for the central portion of the conductor. The conductivity of copper is σ = 59.6 × 10 ⁶ [Ω ⁻¹ · m ⁻¹ ], and the magnetic permeability is μ≈μ ₀ = 4π × 10 ⁻⁷ [H / m]. the thickness _{D s} ≒ _65μm, in the case of 100MHz the skin depth _{D s} ≒ 6.5 [mu] m. Therefore, when copper is used as the first material, it is preferable to apply the coating in a thickness range of 6.5 μm to 65 μm.

  The present inventors have conducted intensive studies in order to find an optimum numerical range regarding the conductivity of the material used for coating.

First, FIG. 1 shows a bus bar used for analysis for such a purpose. This bus bar is U-shaped and has a thickness of 1 mm. The material of the center conductor is Cu. In this analysis, analysis software called Maxwell 3D from Ansoft was used.
In the analysis, the bus bar shape shown in FIG. 1 has symmetry with respect to the right and left as viewed in FIG. 1 and the thickness direction of the bus bar. As an analysis mode, an eddy current mode, which considers eddy currents, was used. Here, an example is shown in which the frequency is analyzed at 10 MHz as a frequency to be given resistance within the above range. In addition, the total resistance value and cross-sectional profile of the bus bar when the skin material was changed were obtained so that the change in resistance value due to the skin effect could be verified from the analysis results.

  As a result, it has been found that the material used for coating (also referred to as the second material) does not have to be high resistance. This was considered to be because even if a high-resistance material was applied, a skin would be formed inside the material and current would flow inside the conductor, so that resistance could not be provided.

Table 1 shows typical skin materials such as Cu (copper), gold (gold), bronze, chromium, stainless steel (Stainless Steel), neodymium iron (NdFe35), graphite and seawater. The respective conductivity, conductivity (Cu ratio) and resistance of (SeaWater) are shown. FIG. 2 is a graph of Table 1.

  As can be seen from Table 1 and FIG. 2, the resistance is highest when a conductive material, such as bronze or chromium, having a conductivity slightly lower than that of the central conductor (Cu) is used compared to the case where the material of the entire system is Cu. It rises and grows up to about 1.4 times. Furthermore, even if a material having a low conductivity is used, the resistance of the entire system is not increased.

  This can be attributed to the fact that no current flows through the epidermis. FIG. 3 shows a current profile of a cross section when the coating material (Cu, bronze, stainless steel, and graphite) is used as a parameter.

  When the entire system is made of Cu, the current increases toward the skin. On the other hand, when bronze with the highest resistance is used as described above, current flows through both the covering portion and the inner conductor, resulting in a two-stage profile. When a material having a lower conductivity is used, no current flows through the covering portion. Thus, it is understood that by covering with a conductive material having a slightly lower conductivity than the central conductor, a current flows through the covering portion, and the resistance value of the entire system can be increased.

  From the above, it was derived that the electrical conductivity when a peak occurs in the resistance value is about 2% or more and about 71% or less in terms of Cu ratio as shown in Table 1.

Next, an embodiment in which the power conversion device according to the present invention is applied to a specific device will be described.
FIG. 4 shows an embodiment in which the present invention is applied to an inverter device which is a kind of power converter as such an embodiment. FIG. 4 conceptually shows the circuit configuration of the inverter device 40 according to the present embodiment.
The inverter device 40 includes an IGBT (Insulated Gate Bipolar Transistor) module 1, a diode module 2, and a snubber capacitor 3 as main circuit elements. The IGBT module 1 functions as a switching element.
Moreover, the inverter apparatus 40 is provided with the copper bar wiring 4 inside, and has connected between circuit elements.
Further, the inverter device 40 is electrically connected to the load 7 and the AC voltage source 8 by the conductive wire 5 at both ends as shown in the figure.
And the inverter apparatus 40 is provided with the cooling fin 6 for cooling the whole.

As for the inverter device 40, specifically, if it is a conductor (a central portion made of the first material) existing in a path through which a noise current flows, such a conductor can be covered with the second material. The second material constitutes the skin part. The conductivity of the second material is 2% or more and 71% or less of the conductivity of the first material.
FIG. 5 shows an embodiment in which the input / output terminal 11 of the IGBT module 1 is applied as such a conductor. The input / output terminal 11 is covered with a covering 111.
In the form of FIG. 5, it is possible to cope with noise generated by resonance between the snubber capacitor 3 and the IGBT module 1.

FIG. 6 shows an embodiment in which the bonding wire 12 inside the IGBT module 1 is applied as the conductor. The bonding wire 12 is coated with a coating 121.
FIG. 7 shows an embodiment in which the snubber capacitor terminal 31 of the snubber capacitor 3 is applied as the conductor. The snubber capacitor terminal 31 is coated with a coating 311.
Furthermore, FIG. 8 shows an embodiment in which a copper bar 41 connected to an input / output terminal of the IGBT module 1 is applied as the conductor. The copper bar 41 is coated with a coating 411.
In addition, the conducting wire 51 can also be used instead of the copper bar 41 like the form of FIG. The conducting wire 51 is covered with a covering 511.
6 to 9 are places related to noise generated by resonance between the snubber capacitor 3 and the IGBT module 1. Therefore, by providing a skin portion at these application locations, a noise suppression effect can be expected in any form.

Of course, the conductor wiring can be applied to a conductor that exists in a path through which a noise current flows when viewed in an alternating current, even if it is insulated in a direct current.
FIG. 10 shows a configuration in which the cooling fins 61 are applied as an application target of such a conductor. The cooling fin 61 is coated with a coating 611. For the same purpose, FIG. 11 shows a configuration in which the copper base plate 13 of the IGBT module 1 is applied. The copper base plate 13 is coated with a coating 131.
These application locations are also affected by noise related to resonance between the snubber capacitor 3 and the IGBT module 1 in terms of alternating current. Therefore, by providing a skin portion at these application locations, a noise suppression effect can be expected in any form.
Note that each of the forms shown in FIGS. 5 to 11 can be implemented by any one, a combination of some, or all of them.

ここで、σは導電率（Ω^−１・ｍ^−１）であり、μは透磁率（Ｈ／ｍ）であり、ｆは周波数（Ｈｚ）であり、ｔは表皮へのめっき厚さ（ｍ）である。 The noise suppression effect by embodiment mentioned above is demonstrated. When Cu is used for the center conductor and the target frequency is set to 10 MHz, the resistance increases by 1.4 times as shown in the analysis result described above. Therefore, if the conductive path is formed of a material having high conductivity such as copper or aluminum in the form of FIGS. 5 to 11 and the impedance of the path is regulated by this, 3 dB (∵20 log (1.4 ) ≈3 dB) Noise current can be reduced. Further, (1) skin depth D _s when the frequency is increased as shown in equation becomes small. That is, since the current is more concentrated on the surface layer, the effect of the coating is enhanced. As represented by the following equation, the absorption loss A (unitless amount) is generally proportional to the 1/2 power of the frequency.

Here, σ is the conductivity (Ω ⁻¹ · m ⁻¹ ), μ is the magnetic permeability (H / m), f is the frequency (Hz), and t is the plating thickness (m ).

  When the target frequency is 30 MHz, 7.7 dB (∵20 log (1.4 × √ (30/10)) ≈7.7 dB), and when 100 MHz, 13 dB (∵20 log (1.4 × √ (100 / √) 10)) ≈13 dB).

It is a figure showing the copper bar model which analyzed the change of resistance to the conductivity of covering material. It is the graph which analyzed the change of the resistance with respect to the electrical conductivity of coating | covering material showing the principle of this invention. It is a cross-sectional profile of the current density in the analytical model of a copper bar. It is a circuit diagram of an inverter apparatus. It is a conceptual diagram which shows the noise countermeasure example by the covering to the input-output terminal of the IGBT module based on one Embodiment of this invention. It is a conceptual diagram which shows the noise countermeasure example by the coating | covering to the bonding wire inside IGBT module based on one Embodiment of this invention. It is a conceptual diagram which shows the noise countermeasure example by the covering to the snubber capacitor terminal based on one Embodiment of this invention. It is a conceptual diagram which shows the noise countermeasure example by the covering to the copper bar based on one Embodiment of this invention. It is a conceptual diagram which shows the noise countermeasure example by the covering to the conducting wire based on one Embodiment of this invention. It is a conceptual diagram which shows the noise countermeasure example by the coating | cover to the cooling fin based on one Embodiment of this invention. It is a conceptual diagram which shows the noise countermeasure example by the covering to the copper base of the IGBT module based on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 IGBT module 2 Diode module 3 Snubber capacitor 4 Copper bar wiring 5 Conductor wiring 6 Cooling fin 7 Load 8 AC voltage source 11 IGBT module input / output terminal 12 IGBT module bonding wire 13 Covered IGBT module copper base 31 Snubber Capacitor terminal 40 Inverter device 41 Copper bar 51 Conductor 61 Cooling fins 111, 121, 131, 311, 411, 511, 611 Cover

Claims (1)

A power conversion device including a semiconductor switching element,
The conductor used for the internal wiring and / or substrate of the device is composed of at least two kinds of materials,
The first material of the materials is used for the central part of the conductor,
Of the materials, the second material is used for the skin of the conductor,
The first material is copper, the second material is bronze or chrome, and in the current density cross-sectional profile representing the relationship between the distance from the surface of the conductor and the current density, the first material A peak value appears on each of the surface and the surface of the second material .

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