JP2009225570A - Power conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress noise while securing turn-off tolerance. <P>SOLUTION: An impedance adding means 13 is inserted in series between a connection point between an IGBT 11 and a cathode side of a freewheeling diode 12 connected in reverse parallel with the IGBT 11, and the cathode side of the freewheeling diode 12. By providing the impedance adding means 13 with characteristics which work as a resistance component in a frequency range of 30 MHz or higher and have a small resistance value in a frequency range of less than 30 MHz, the impedance adding means 13 works as the resistance component only when the IGBT 11 is turned off, and works in the same manner as when no impedance exists when the IGBT 11 is turned off. Thereby, noise can be suppressed when the IGBT 11 is turned off, while preventing the addition of inductance when the IGBT 11 is turned on. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power conversion device in which a main circuit is formed from switching means including an insulated gate semiconductor element and a freewheeling diode connected in antiparallel with the insulated gate semiconductor element.

  In recent years, while EMC (electromagnetic compatibility or electromagnetic compatibility) regulations have become stricter, reduction of radiation noise has become a technical issue in various electric and electronic devices. In particular, a countermeasure is required for reducing noise generated by turning on and off the semiconductor element which is a main component in these devices. Noise in the semiconductor element is generated according to the switching timing. Therefore, various countermeasures are taken at each timing of turn-on and turn-off of the semiconductor element.

For example, as a general method, a measure is taken to insert a resistor (hereinafter also referred to as a gate resistor) between the gate of the semiconductor element and the gate drive circuit of the semiconductor element. This is to control the charging speed of the charge to the gate by inserting a resistor in the path for supplying the gate current, and as a result, to control the switching speed.
In general, turn-on and turn-off of a semiconductor element are performed by charge injection and extraction. Therefore, if the paths in each operation mode are separated, gate resistances are set separately at turn-on and turn-off. be able to. For this reason, by inserting a gate resistor, for example, individual measures such as changing the gate current gently at turn-on and changing the gate current quickly at turn-off can be easily taken.

In addition to this, as a countermeasure method in the gate drive circuit, for example, a method of inserting a capacitor C in parallel with the gate resistance as part of improving the trade-off between switching loss and switching noise has been proposed (for example, Patent Document 1 and Patent Document 2).
On the other hand, as a noise reduction measure at the time of turning on and turning off the semiconductor element, a measure is taken in the module, particularly the semiconductor element. For example, by providing a Middle Broad Buffer layer in a freewheeling diode connected in antiparallel to an IGBT (insulated gate bipolar transistor) as a semiconductor element, soft recovery characteristics and reverse recovery loss reduction at turn-on can be achieved. Have been proposed (for example, see Non-Patent Document 1).

Further, in addition to improving the characteristics of the semiconductor element itself for noise suppression, measures have been taken for its periphery and mounted circuits. For example, a method of reducing noise by adding an inductance by inserting an amorphous core marketed under the trade name of Spark Killer (manufactured by Toshiba Corporation) into the leg of a TO-3P type diode has also been proposed. (For example, refer to Patent Document 3).
There is also a method for reducing noise by adding inductance between a semiconductor element and a snubber circuit in a power conversion device in which semiconductor elements having freewheeling diodes connected in antiparallel are connected in series. It has been proposed (see, for example, Patent Document 4).

Japanese Patent No. 3666843 Japanese Patent No. 3767450 Japanese Patent No. 2851268 Japanese Patent No. 3577893 Technical Committee on Power Device / Power IC Technology Research, Power Device Development Has Changed Greatly, The Institute of Electrical Engineers of Japan, March 30, 2007, Technical Report No. 1082

  The above-described countermeasure using gate resistance is a widely used method. Further, as described in Patent Document 1 and Patent Document 2, a method in which measures are taken in the gate drive circuit is a method in which a drive circuit is mounted, such as an IPM (Intelligent Power Module). It can be considered as one of the effective means in the body module. However, all of these countermeasures depend on an external drive circuit, and it is necessary to improve the characteristics as a module. Therefore, as described in Non-Patent Document 1, improvement of characteristics related to the chip is achieved.

The countermeasure against the chip as shown in Non-Patent Document 1 is a useful means as a fundamental countermeasure, but since the characteristics of the chip differ from semiconductor manufacturer to semiconductor manufacturer, this should be used under the optimum drive conditions according to the application. Therefore, application technology and package technology are important.
On the other hand, the method of inserting an amorphous core into the legs of the diode (Patent Document 3) and the method of inserting inductance into each part of the main circuit of the power module (Patent Document 4) add an external impedance around the semiconductor element. This is a simple and useful means for suppressing noise generated during switching.

However, in the method of inserting an amorphous core, there is a possibility that noise cannot be suppressed depending on the frequency. In addition, the inductance is positively utilized in both the method of inserting the amorphous core and the method of inserting the inductance.
Here, in an element that switches with a large current, such as an IGBT, for example, the surge voltage Vs is determined by the current and the inductance as shown in the following equation (1).
Vs = L · dI / dt (1)

In equation (1), Vs is the surge voltage [V], L is the inductance [H] of the main circuit through which the switching current flows, and dI / dt is the current change rate [A / s].
For this reason, the addition of an inductance component is inconvenient in terms of ensuring surge resistance. That is, in order to suppress a surge in order to ensure a stable switching operation, it is often better to reduce the inductance as the breaking current is larger.

In addition, IGBTs are required to have a trade-off with turn-off resistance as the wafers become thinner. For this reason, it is preferable to avoid the addition of inductance during turn-off switching.
Accordingly, the present invention has been made paying attention to the above-mentioned conventional unsolved problems, and an object thereof is to provide a power conversion device capable of suppressing noise while ensuring turn-off resistance. .

  In order to achieve the above object, the invention according to claim 1 of the present invention mainly includes switching means comprising an insulated gate semiconductor element and a freewheeling diode connected in antiparallel with the insulated gate semiconductor element. In a power conversion device in which a circuit is formed, an impedance adding means is connected in series with the freewheeling diode between both ends of the insulated gate semiconductor element, and the impedance adding means is a lower limit of a frequency range subject to radiation noise reduction. A resistance value in a frequency region equal to or higher than a frequency near the value is larger than a resistance value in a frequency region lower than the frequency near the lower limit value.

The invention according to claim 2 is characterized in that a lower limit value of the radiation noise reduction target frequency region is about 30 MHz.
The invention according to claim 3 is characterized in that an Mn—Zn core is connected in series with the freewheeling diode as the impedance adding means.
The invention according to claim 4 is characterized in that a resistor element is connected in series with the freewheeling diode as the impedance adding means.
The invention according to claim 5 is characterized in that the resistance element is a shunt resistor or a metal clad resistor.

  According to the power conversion device of the present invention, there is no impedance adding means when the insulated gate semiconductor element is turned off, and the state is equivalent to the presence of the impedance adding means only when the insulated gate semiconductor element is turned on. The noise can be reduced while avoiding the above.

Embodiments of the present invention will be described below.
FIG. 1 is a conceptual diagram of an IGBT module to which the present invention is applied, and shows the configuration of a 6 in 1 module. That is, three phase arms in which two switching means SW are connected in series are connected in parallel.
The switching means SW includes an IGBT 11 as an insulated gate semiconductor element, a free wheeling diode 12 connected in antiparallel with the IGBT 11, a connection point between the cathode side of the free wheeling diode 12 and the collector side of the IGBT 11. Between the freewheeling diode 12 and the freewheeling diode 12, it is comprised with the impedance addition means 13 inserted in series with the freewheeling diode 12. FIG. The impedance adding means 13 has a resistance component in a frequency region of 30 MHz or higher, and a resistance value in a frequency region lower than 30 MHz is lower than a resistance value in a frequency region of 30 MHz or higher and does not act as a resistance component. have.

In addition, although FIG. 1 demonstrated the case where this invention was applied to 6 in 1 module, as shown in FIG. 2, it is also possible to apply to 2 in 1 module which connected two switching means SW in series, As shown in FIG. 3, it is also possible to apply to a 1 in 1 module comprising one switching means SW. In any case, as shown in FIGS. 2 and 3, each switching means SW has an impedance adding means 13 inserted in series with the freewheeling diode 12 as in the switching means SW of FIG.
Next, in the power conversion device using the module to which the present invention is applied, a path through which a current flows in each switching mode will be described. Since the operation of each switching means SW is the same, here, a case where a general chopper circuit is configured using one 2-in-1 module will be described.

FIG. 4 is a circuit diagram illustrating an example of a power conversion device including a chopper circuit.
In this power converter, a three-phase rectifier diode module 22 is connected to an AC power source 21. An electric field capacitor 23, a spike voltage preventing snubber capacitor 24, and an IGBT 2 in 1 module 25 shown in FIG. 2 are connected in parallel between the DC output terminals of the rectifier diode module 22. Further, a chopper inductance load 26 is connected in parallel to both ends of the switching means SWa of the switching means SWa and SWb connected in series constituting the 2-in-1 module 25.

  5 to 8 are circuit diagrams schematically showing the flow of current in each switching mode when the chopper operation is performed by turning on and off the switching means SWb in the power conversion device shown in FIG. FIG. 5 shows when the switching means SWb is turned on, FIG. 6 shows when the switching means SWb is turned off, FIG. 7 shows when the switching means SWb is turned off, and FIG. 8 shows that the switching means SWb is turned on. It represents the current flow at turn-on.

When the IGBT 11b of the switching means SWb is in the on state, current flows in the path of the rectifier diode module 22, the chopper inductance load 26, the IGBT 11b, and the rectifier diode module 22, as shown in FIG.
When the IGBT 11b is controlled to be turned off from this state, as shown in FIG. 6, a part of the current flowing through the path of the rectifier diode module 22, the chopper inductance load 26, the IGBT 11b, and the rectifier diode module 22 is When the IGBT 11b starts to flow through the free wheeling diode 12a and is turned off, the free wheeling diode 12a and the chopper inductance load 26 are recirculated as shown in FIG.

When the IGBT 11b is controlled to be in the ON state from this state, the IGBT 11b starts to flow along the path of the rectifier diode module 22, the chopper inductance load 26, the IGBT 11b, and the rectifier diode module 22, as shown in FIG. Along with this, the current flowing through the freewheeling diode 12a decreases, and after the freewheeling diode 12a enters reverse recovery, the freewheeling diode 12a enters the cut-off state and turns on in FIG.
Thus, the reverse recovery by the freewheeling diode 12a occurs only at the turn-on shown in FIG. For this reason, as a switching timing, impedance exists only in the current path at the time of turn-on.

  That is, since the impedance adding means 13a is connected in series only to the freewheeling diode 12a, as shown in FIG. 6, it is equivalent to the absence of impedance in the current path at the time of turn-off. Therefore, at the time of turn-off when the withstand capability becomes strict as the wafer is thinned, no inductance is added, and switching can be performed without changing the conventional circuit constant in which the impedance adding means 13 is not inserted.

  The impedance adding means 13 has a resistance component in a frequency region of 30 MHz or higher, which is a target frequency to suppress noise, which is a legally regulated value in EMC regulations, and a resistance value in a frequency region lower than 30 MHz is 30 MHz or higher. It can be applied if it is smaller than the resistance value in the frequency domain, that is, it does not affect the addition of inductance at turn-off. For example, if it is a magnetic body, a Mn-Zn core is preferable, and if not, a resistance element is preferable.

FIG. 9 shows the magnetic permeability characteristics of an example of the Mn—Zn-based core material, where μ ′ is the real part of the complex relative permeability and μ ″ is the imaginary part of the complex relative permeability.
As shown in FIG. 9, the core material acts as a resistance in a frequency region around about 10 MHz and acts as an inductance in a frequency region lower than 10 MHz. For this reason, when this Mn—Zn-based core material is applied as the impedance adding means 13, it is necessary to consider the surge resistance in the low frequency region, but the core size is optimized and suppressed to about 10 nH. You can apply in.

In addition, turn-on noise is mainly generated in a low current region. Therefore, by using a Mn-Zn core material, noise generated during switching at low current is removed, and when the current is large. What is necessary is just to use it saturated.
An example of arrangement when a core material is used as the impedance adding means 13 is shown in FIG.

  On the other hand, when a resistance element is used as the impedance adding means 13, depending on the applicable wattage, a chip resistance is used for a low current rating application, a shunt resistance, a metal cladding resistance, etc. for a high current rating. Is suitable. In any case, as shown in FIG. 11, it is desirable to directly attach to a substrate with good thermal conductivity such as a copper base substrate or an insulating ceramic substrate directly connected to the cooling body.

  10 and 11, 31 is a free wheeling diode chip, 32 is an IGBT chip, 33 is a Mn-Zn core, 34 is a metal clad resistor, 35 is a bonding wire to the free wheeling diode 31, and 36 is A bonding wire for an IGBT gate, 37 is a bonding wire between the freewheeling diode chip 31 and the IGBT chip 32, and 38 is a copper base substrate.

Next, a method for calculating a resistance value to be inserted when a core material or a resistance element is applied as the impedance adding means 13 as described above will be described.
FIG. 12 is a conceptual diagram of a noise path between the snubber and the module in the chopper circuit of FIG.
Wiring inductance is determined by wire bonding between chips and main circuit wiring, and capacitance is determined by stray capacitance between the collector and emitter of the IGBT 11.
When the wiring inductance and capacitance are determined, the impedance at a certain frequency is given by the following equation (2).
Z = (R ² + (ωL−1 / (ωC)) ² ) ^1/2 (2)
In equation (2), L is the total inductance [H] of the main circuit wiring, C is the stray capacitance [F] between the collector and emitter of the IGBT, and R is the insertion resistance [Ω] of the main circuit wiring.

Further, in this path, the impedance Zadd to be added to suppress noise is expressed by the following equation (3), and the resistance value Radd [Ω] necessary as a resistance value to be added is derived from the equation (4). be able to.
Zadd = Z (10 ^{dB / 20} ) −Z (3)
Radd = (Zadd ² − (ωL−1 / (ωC)) ² ) ^1/2 (4)
In equations (3) and (4), Zadd is an impedance [Ω] to be added, and dB is a noise reduction amount [dB] to be reduced.

Next, the effect of the present invention will be described.
FIG. 13 shows an example of measuring noise by separating switching noise at turn-on and switching noise at turn-off in the IGBT 11, where the horizontal axis is the IGBT cutoff current (rated current ratio), and the vertical axis is Electric field strength. For switching noise at turn-on and turn-off, a general chopper circuit was used, and the switching timing was temporally separated to measure each noise spectrum. Radiation noise is measured using an anechoic chamber by the 3 m method. As the chopper circuit, specifically, a circuit in which the impedance adding means 13 is not inserted in the general chopper circuit shown in FIG. 4 is used.

  In FIG. 13, the total noise is constituted by noise generated at turn-off and turn-on timings, and the absolute value of the total noise is determined in a portion where the absolute value is large. In particular, in the region where the current is small, the noise at the turn-on is dominant, and the noise at the turn-on tends to become the maximum in all the current regions. Therefore, this turn-on measure is important. This characteristic (current dependency) has a slightly different tendency depending on conditions such as the type of module, but the characteristic is that the noise at turn-on is dominant at a low current.

  Here, as described above, by inserting the impedance adding means 13 in series with the freewheeling diode 12, the impedance is inserted only at the time of turn-on, but it is equivalent to the case where no inductance is added at the time of turn-off. The state remains. Therefore, the turn-on noise that dominates the total noise can be reliably suppressed, and at the time of turn-off, although the impedance adding means 13 is added, the circuit can operate without any change from the conventional circuit characteristics.

  Therefore, it is possible to suppress only the turn-on noise generated by the power conversion device, and it is possible to suppress an increase in inductance at the time of turn-off switching where there is a concern about surge tolerance due to the thinning of the wafer. As described above, the turn-on noise dominates the total noise and has a large absolute value particularly in a low current region. For this reason, if the turn-on noise of the total noise can be suppressed, the absolute value of the total noise can be greatly suppressed.

In particular, the impedance adding means 13 is made to act as a resistance component in a frequency region of 30 MHz or higher, which is a legally regulated value of EMC regulations, and not to act as a resistance component in a frequency region lower than 30 MHz. This is preferable because it can reduce radiation noise.
In addition, although the impedance adding means 13 is inserted in series with the freewheeling diode 12 and an external countermeasure is taken for the power converter, the countermeasure can be taken within the module. There is no need for countermeasures for external circuits such as circuits, and noise countermeasures can be taken from the package side in addition to the characteristics of a single chip.

In the above embodiment, the case where the impedance adding means 13 is connected in series to the cathode side of the freewheeling diode 12 has been described, but it may be connected in series to the anode side of the freewheeling diode 12. Needless to say.
In the above embodiment, the case where a chopper circuit is formed as a power conversion device has been described. However, the present invention is not limited to this. For example, a single-phase or other-phase inverter circuit or the like is connected in reverse parallel to the IGBT 11. Any power conversion device in which a main circuit is formed from the freewheeling diode 12 to be applied can be applied.

Moreover, although the case where radiation noise in a frequency region of 30 MHz or higher is reduced has been described, the present invention is not limited to this, and radiation noise in an arbitrary frequency region can be reduced. In this case, the resistance value is reduced in the frequency region to be reduced. The impedance adding means 13 having a lower resistance value may be used in a frequency region lower than this frequency region.
Moreover, although the case where IGBT was applied as an insulated gate semiconductor element was demonstrated, it is not restricted to this, It can apply, even if it is power MOSFET etc.

It is a conceptual diagram of 6in1 module of IGBT to which the present invention is applied. It is a conceptual diagram of IGBT 2 in 1 module to which the present invention is applied. It is a conceptual diagram of 1 in 1 module of IGBT to which the present invention is applied. It is a circuit diagram which shows an example of the power converter device provided with the chopper circuit to which this invention is applied. It is explanatory drawing of the electric current path in the ON state in a chopper circuit. It is explanatory drawing of the current pathway in the turn-off state in a chopper circuit. It is explanatory drawing of the electric current path in the OFF state in a chopper circuit. It is explanatory drawing of the current pathway in the turn-on state in a chopper circuit. It is an example of the magnetic permeability characteristics μ ′ and μ ″ in the Mn—Zn core material. It is an example of a chip layout when a Mn—Zn core is inserted between a freewheeling diode chip and an IGBT chip. It is an example of a chip layout when a metal clad resistor is inserted between a freewheeling diode chip and an IGBT chip. It is a conceptual diagram of the noise path | route between a snubber circuit and IGBT module. It is a graph which shows the dependence of turn-on noise and turn-off noise with respect to IGBT interruption | blocking current.

Explanation of symbols

11 IGBT
DESCRIPTION OF SYMBOLS 12 Freewheeling diode 13 Impedance addition means 21 AC power supply 22 Rectifier diode module 23 Electric field capacitor 24 Snubber capacitor 25 IGBT2in1 module 26 Inductor load 31 for chopper Freewheeling diode chip 32 IGBT chip 33 Mn-Zn core 34 Metal clad resistance

Claims (5)

In a power conversion device in which a main circuit is formed by switching means including an insulated gate semiconductor element and a freewheeling diode connected in antiparallel with the insulated gate semiconductor element,
Impedance adding means is connected in series with the freewheeling diode between both ends of the insulated gate semiconductor element, and the impedance adding means has a resistance value in a frequency region that is equal to or higher than a frequency near a lower limit value of a frequency region targeted for radiation noise reduction. Is larger than a resistance value in a frequency region lower than the lower limit value vicinity frequency.   The power converter according to claim 1, wherein a lower limit value of the radiation noise reduction target frequency region is about 30 MHz.   The power converter according to claim 1 or 2, wherein an Mn-Zn based core is connected in series with the freewheeling diode as the impedance adding means.   The power conversion device according to claim 1 or 2, wherein a resistor element is connected in series with the freewheeling diode as the impedance adding means.   The power converter according to claim 4, wherein the resistance element is a shunt resistor or a metal clad resistor.

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