WO2014147755A1

WO2014147755A1 - Power converter

Info

Publication number: WO2014147755A1
Application number: PCT/JP2013/057871
Authority: WO
Inventors: 静里田村; 中武　浩; 加藤　昌則
Original assignee: 三菱電機株式会社
Priority date: 2013-03-19
Filing date: 2013-03-19
Publication date: 2014-09-25

Abstract

A power converter in which a fuses (13a, 13b) are respectively provided to DC lines (10a, 10b) between an electrolytic capacitor (11) and power modules (14) (14a-14c) constituting an inverter circuit (12), wherein first snubber capacitors (18) (18a-18c) are connected to terminal parts of the power modules (14), and a second snubber capacitor (19) is connected between the terminal part (9a) on the inverter circuit (12) side of the fuses (13a, 13b), and a terminal part (9b).

Description

Power converter

The present invention relates to a power converter.

As a power converter having a fuse, for example, there is one known in Patent Document 1 below. In Patent Document 1, a high-voltage film capacitor that is connected in parallel to a switching element group that is connected in a predetermined manner and absorbs a high-frequency current ripple due to switching, and a switching element group that is connected in parallel via a fuse. The structure which comprises the electrolytic capacitor group which suppresses the pulsation resulting from a frequency is disclosed.

Japanese Patent Laid-Open No. 2000-60108

As a recent technical trend, a switching element based on silicon carbide (SiC), which has a high withstand voltage and low loss, and can operate at high current, high temperature and high frequency (hereinafter referred to as “SiC-”). Attention has been paid to “SW element”.

On the other hand, when a power converter is configured using this SiC-SW element, since the SiC-SW element has a high switching speed, when the SiC-SW element causes a short-circuit fault, a surge generated by wiring inductance is generated. The voltage (short circuit surge voltage) becomes very large.

Furthermore, in the case of a power converter equipped with a fuse, the opposite of the PN bus bar with the positive side (P) bus bar and the negative side (N) bus bar in the fuse portion collapses, and the inductance of the fuse itself is also added, The short-circuit surge voltage becomes very large, and this short-circuit surge voltage may exceed the maximum rating of the SiC power module (hereinafter simply referred to as “power module”) on which the SiC-SW element is mounted. For this reason, when a SiC-SW element is applied to a power converter having a fuse, some countermeasure against a short-circuit surge voltage is required. In Patent Document 1, no consideration is given to the short-circuit surge voltage.

The present invention has been made in view of the above, and protects a power module by suppressing the influence of a short-circuit surge voltage even when a SiC-SW element is applied to a power converter having a fuse. An object of the present invention is to provide a power converter that can be used.

In order to solve the above-described problems and achieve the object, the present invention provides overcurrent protection for each of the high potential side DC line and the low potential side DC line between the smoothing capacitor and the SiC power module constituting the inverter circuit. In a power converter provided with an element, a first snubber capacitor connected to a terminal portion of the SiC power module, the high potential side DC line and the low potential between the overcurrent protection element and the inverter circuit A second snubber capacitor connected to the side DC line, wherein the second snubber capacitor is more than a wiring inductance component between the connection position and the connection position of the first snubber capacitor. The wiring inductance component from the connection position to the overcurrent protection element and the inductance component of the overcurrent protection element. Wherein the direction of the sum is connected so as to increase the.

According to the present invention, even when a SiC-SW element is applied to a power converter having a fuse, there is an effect that the power module can be protected by suppressing the influence of the short-circuit surge voltage.

1 is a diagram illustrating a configuration of a power converter according to Embodiment 1. FIG. FIG. 2 is a top view showing a structural arrangement example of the power converter according to the first embodiment. FIG. 3 is a diagram illustrating an equivalent circuit of a main part of the power converter according to the first embodiment. FIG. 4 is a diagram showing an example of a surge voltage waveform generated in the SiC-MOSFET. FIG. 5 is a diagram illustrating an equivalent circuit of a main part of the power converter according to the second embodiment. FIG. 6 is a diagram illustrating an equivalent circuit of a main part of the power converter according to the third embodiment. FIG. 7 is a diagram illustrating a configuration of the power converter according to the first embodiment.

Hereinafter, a power converter according to an embodiment of the present invention will be described with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

Embodiment 1 FIG.
1 is a circuit diagram showing a configuration of a power converter according to Embodiment 1. FIG. As shown in FIG. 1, the power converter according to the first embodiment includes a smoothing capacitor connected between a high potential (P potential) side DC line 10a and a low potential (N potential) side DC line 10b. As an electrolytic capacitor 11, an inverter circuit 12 having a power module 14 (14 a, 14 b, 14 c) and converting DC power into AC power, and a DC DC so as to be interposed between the electrolytic capacitor 11 and the inverter circuit 12. A fuse 13 (13a, 13b) as an overcurrent protection element inserted between the

lines

10a, 10b and a first connected in parallel to each

terminal portion

8a, 8b in the power module 14 (14a, 14b, 14c) Of the terminals provided in the snubber capacitor 18 (18a, 18b, 18c) and the

fuses

13a, 13b, the high potential side in the inverter circuit 12 Electrical connection between the terminal portion 9a (terminal portion of the fuse 13a inserted in the high potential side direct current (DC) line 10a) and the low potential side direct current portion in the inverter circuit 12 used for electrical connection with the direct current portion And a second snubber capacitor 19 connected between the terminal portion 9b used for connection (the terminal portion of the fuse 13b inserted in the DC line 10b on the low potential side).

The power modules 14 (14a, 14b, 14c) provided in the inverter circuit 12 are connected in parallel to form a three-phase inverter circuit. The power module 14a includes, for example, an SW element (that is, a SiC Schottky-Barrier Diode (SiC-SBD) 16) connected to the SiC-MOSFET 15 and the SiC-MOSFET 15 in antiparallel. SiC-SW element), and a circuit in which two sets of the SiC-SW elements are connected in series is configured. Here, a circuit in which two sets of SiC-SW elements are connected in series is referred to as an “arm”. The

other power modules

14b and 14c are similarly configured. That is, the illustrated inverter circuit 12 is a three-phase inverter circuit in which three arms are connected in parallel, and a motor 50 connected to a cable 60 drawn from a series connection point of SiC-SW elements in each power module. Is a three-phase motor (for example, a synchronous motor, an induction motor, etc.). Although FIG. 1 illustrates a three-phase inverter circuit, a number of arms corresponding to the required number of phases may be provided. Further, FIG. 1 illustrates a configuration in which two sets of SW elements connected in series are accommodated in a module, but an inverter circuit 12 is configured by accommodating six sets of SiC-SW elements in one module. Alternatively, the inverter circuit 12 may be configured by six modules in which one set of SiC-SW elements is accommodated in one module.

FIG. 2 is a diagram illustrating a structural arrangement example of the power converter according to the first embodiment, and is a top view of the inside of the power converter as viewed from above. 2, the electrolytic capacitor 11 itself shown in FIG. 1 is not shown, and a pair of positive and negative electrolytic capacitor connection terminals 21 is shown. The electrolytic capacitor 11 includes an electrolytic capacitor P terminal 24a electrically connected to the P potential copper bus bar 22a visible on the upper surface, and an electrolytic capacitor N terminal 24b electrically connected to the N potential copper bus bar 22b on the back surface side. Connected between.

The power module 14 (14a, 14b, 14c) includes a P terminal 25a electrically connected to the P potential copper bus bar 23a visible on the upper surface and an N terminal electrically connected to the N potential copper bus bar 23b on the back surface side. 25b. The output terminal 29 is a terminal provided at a series connection point between SiC-SW elements. The output terminal 29 is electrically connected to the cable 60 (see FIG. 1).

In addition, the area | region shown with the hatching of the broken line shows the hollow part in P electric potential

copper bus bar

22a, 23a.

The P potential

copper bus bars

22a and 23a and the N potential

copper bus bars

22b and 23b are arranged in close proximity to each other with an insulator interposed between the copper bus bars, and the inductance component of the PN line by each copper bus bar is made as small as possible. The surge voltage when the SW element is short-circuited (hereinafter referred to as “short-circuit surge voltage”) is reduced.

The fuse 13 (13a, 13b) is provided when the capacity of the power converter is large. When the capacity of the power converter is large, a large amount of energy is also stored in the electrolytic capacitor 11. Therefore, in order to avoid the accidental expansion due to the large energy of the electrolytic capacitor 11 when a short circuit accident of the power module 14 occurs, the fuse 13 Is required. In the case of a power converter not provided with fuse 13 (13a, 13b), P potential copper bus bar 22a, P potential copper bus bar 23b, N potential copper bus bar 22b, and N potential copper bus bar 23b are integrated with each other. It is usually done.

A first snubber capacitor 18 (18a, 18b, 18c) is connected between a P potential terminal and an N potential terminal (not shown) of the power module 14 (14a, 14b, 14c). 2 shows an arrangement example in which two first snubber capacitors 18 are arranged in parallel for each power module 14, and 5 fuses 13 are provided for each P potential and N potential in order to improve the reliability of the power converter. Although an arrangement example in parallel (note: N potential side is not shown) is shown, all are examples and are not limited to this arrangement example.

In the configuration as described above, as described in the background section, the SiC-MOSFET 15 has a high switching speed, and a surge voltage generated due to the wiring inductance at the time of a short circuit failure becomes very large. In addition to this, when the SiC-MOSFET 15 is used and the fuse 13 is used for the above-described reason, the opposing portion of the PN copper bus bar is broken at the fuse 13 portion, and the inductance component of the fuse 13 itself is also added. And the inductance component between the power module 14 increases. For this reason, due to these two factors, the surge voltage generated in the power module 14 becomes large and may exceed the maximum rating, and some countermeasure is required.

FIG. 3 is a diagram showing an equivalent circuit of a main part of the power converter according to the first embodiment. In FIG. 3, Ls is a wiring inductance component inside the power module, Lpn1 is a wiring inductance component due to the PN copper bus bar (23a, 23b), Lpn2 is a wiring inductance component due to the PN copper bus bar (22a, 22b), and a fuse 13 and the inductance component. The first and second snubber capacitors (18, 19) are shown with a parasitic inductance component and a parasitic resistance component added to the original capacitance component. Regarding the SiC-SW element, the SiC-MOSFET 15 is indicated by a switch symbol, and the SiC-SBD 16 is indicated by a capacitance component and a resistance component. Other elements are denoted by the same reference numerals as those in FIG. 1 or FIG.

FIG. 4 is an example of a surge voltage waveform generated in the SiC-MOSFET 15. FIG. 4 shows a waveform when the second snubber capacitor 19 is not provided in the configuration of the first embodiment. In FIG. 4, the horizontal axis represents time, the vertical axis represents voltage, the waveform K1 represents the gate-source voltage (Vgs) generated in the SiC-MOSFET 15, and the waveform K2 represents the drain-source voltage generated in the SiC-MOSFET 15. (Vds).

As shown in the figure, the surge voltage generated in the SiC-SW element has a first wave (a component rising in the vertical axis direction) and a second wave (portion surrounded by an ellipse) that comes after the first wave. The first wave is generated mainly by the relationship between Ls and the first snubber capacitor 18, and the second wave is generated mainly by the relationship between Lpn (the sum of Lpn1 and Lpn2) and the first snubber capacitor 18. . Therefore, as a countermeasure against the first wave, it is preferable that the parasitic inductance and resistance of the first snubber capacitor 18 are small. In general, the smaller the capacitance of the capacitor, the smaller the parasitic inductance component and the parasitic resistance component.

On the other hand, as a countermeasure against the second wave, the capacity of the first snubber capacitor 18 must be large. This is because not only Ls but also Lpn is added to the inductance component caused by the second wave. In addition, if Lpn can be reduced, a special measure in consideration of the second wave is unnecessary. However, it is difficult to reduce Lpn. The reason is the following two points. The first reason is that the power converter assumed in the first embodiment is a power converter that requires the fuse 13, and it is difficult to reduce the inductance component of the fuse itself. The second reason is that even if a laminated bus bar having a very small inductance component is used as the PN bus bar, the laminated bus bar is divided at the fuse 13 and the opposing property of the laminated bus bar is broken by the fuse 13. This is because there is a limit to minimizing the inductance component.

Therefore, measures other than reducing Lpn are required to satisfy both the first and second wave measures. Referring to FIG. 1, it is conceivable to increase the capacity of the first snubber capacitor 18 connected to the power module 14. However, as is apparent from the configuration around the power module 14 in FIG. 2, the actual situation is that there is almost no space for increasing the capacity of the first snubber capacitor 18. The shortage of the capacity of the first snubber capacitor 18 increases the rating of the SiC-MOSFET 15, slows the switching speed, and necessitates the addition of a protection circuit. Problems such as a decrease in reliability due to a decrease in the number of parts occur.

Therefore, in the power converter of the first embodiment, as shown in FIGS. 1 and 2, measures are taken to connect the second snubber capacitor 19 to the

terminals

9 a and 9 b provided in the fuse 13.

Note that FIG. 2 discloses an example in which six capacitors are arranged as the second snubber capacitor 19 using the empty space of the five fuses 13a provided on the upper surface side (P potential side). However, it goes without saying that the number is not limited to six.

The important point regarding the arrangement of the second snubber capacitor 19 is that the

terminals

9a and 9b of the fuse 13 to which the second snubber capacitor 19 is connected are terminals on the electrolytic capacitor 11 side (that is, electrical connection with the electrolytic capacitor 11). Terminal 9a, 9b on the inverter circuit 12 side (that is, a terminal for electrical connection with the inverter circuit 12). With such a connection, the second snubber capacitor 19 can effectively attenuate the large energy accumulated in the electrolytic capacitor 11 being transmitted to the power module 14 via the inductance component of the fuse 13. It becomes.

The capacitance value of the first snubber capacitor 18 is preferably smaller than the capacitance value of the second snubber capacitor 19. If a capacitor having a small capacitance value is selected as the first snubber capacitor 18, a capacitor having a small parasitic inductance component and parasitic resistance component is necessarily selected. As a result, the first snubber capacitor capacity optimum for the first wave countermeasure is set.

Note that, if the capacitance value of the first snubber capacitor 18 is reduced, the second wave countermeasure is negatively affected, but there is no problem because the second snubber capacitor 19 exists. In addition, if the capacitance value of the second snubber capacitor 19 is increased, the second snubber capacitor 19 effectively acts against the second wave. Furthermore, since the first snubber capacitor capacity and the added second snubber capacitor capacity are in a parallel connection relationship, the total value of the first and second snubber capacitor capacities effectively acts as a countermeasure against the second wave. To do.

With the above configuration, the first snubber capacitor capacity optimal for the first wave countermeasure and the second snubber capacitor capacity optimal for the second wave countermeasure are set.

As described above, according to the power converter of the first embodiment, the first snubber capacitor is connected to the terminal portion of the power module, and the second snubber is connected between the terminal portions on the inverter circuit side of the fuse. Since the capacitor is connected, the influence of the short-circuit surge voltage can be suppressed even when the SiC-SW element is used as the SW element of the inverter circuit. As a result, an increase in the rating of the SiC-SW device can be avoided, and measures such as slowing down the switching speed and measures such as the addition of a protective circuit are no longer necessary, and the reduction in efficiency due to increased power converter costs and loss is suppressed. In addition, problems such as a decrease in reliability due to an increase in the number of parts can be avoided.

In the case of using a low-inductance bus bar (for example, a laminated bus bar) in which an insulator is interposed between the terminal portion of the power module and the terminal portion of the fuse as in the present embodiment, the power module The inductance component between the terminal portion and the terminal portion of the electrolytic capacitor is dominated by the fuse. For this reason, the connection position of the second snubber capacitor may not be the terminal part of the fuse, but may be a position close to the inverter circuit side from the terminal part of the fuse. This is because Lpn2 is the sum of the wiring inductance component of the PN copper bus bar (22a, 22b) and the inductance component of the fuse 13, and between Lpn1, which is the wiring inductance component of the PN copper bus bar (23a, 23b), This is because the relationship of Lpn2> Lpn1 is always established, and the effect of suppressing the second surge voltage by the second snubber capacitor is obtained. However, the connection position of the second snubber capacitor is different from the connection position of the first snubber capacitor so that the roles of the first snubber capacitor and the second snubber capacitor are not affected (that is, Lpn1> 0). Need to be connected).

Embodiment 2. FIG.
In the first embodiment, the basic configuration of the power converter has been described. In the second embodiment, a configuration for reducing noise that increases when switching control of the SiC-SW element at high speed will be described.

FIG. 5 is a diagram illustrating an equivalent circuit of a main part of the power converter according to the second embodiment. In the second embodiment, as shown in FIG. 5, the inductance component (Lpn2) of the fuse 13 and the PN copper bus bar (22a, 22b) and the capacitance component C2 of the second snubber capacitor 19 are configured as an LC filter circuit 25. To do. If such an LC filter circuit 25 is configured, it is possible to reduce noise that increases when the SiC-SW element is switching-controlled at high speed.

In addition, what is necessary is just to select the value of Lpn2 and C2 according to the following (1) formula showing the impedance which looked at the power module 14 side from the electrolytic capacitor 11 as LC filter.

[1 / {jω * (C1 + C2)}] * [1 / {(jω) ^ 2 * Lpn1 * C1 * C2 / (C1 + C2) +1}] * {(jω) ^ 2 * Lpn1 * C1 + 1} + (jω * Lpn2) (1)
Lpn1: Inductance component of PN copper bus bar (23a, 23b) Lpn2: Inductance component of fuse 13 and PN copper bus bar (22a, 22b) C1: Capacitance component of first snubber capacitor 18 C2: Capacitance of second snubber capacitor 19 component

Embodiment 3 FIG.
In the first and second embodiments, the configuration of the power converter that effectively works in the phenomenon at the time of short-circuit interruption has been described. In the third embodiment, the configuration of the power converter that works effectively in a normal switching operation is explained. To do.

FIG. 6 is a diagram illustrating an equivalent circuit of a main part of the power converter according to the third embodiment. The SiC-SBD 16 has an advantage that there is no recovery operation. However, since the internal parasitic resistance is small, there is a possibility that the SiC-MOSFET 15 may vibrate due to the ON of the SiC-MOSFET 15 connected in parallel to cause a malfunction to the peripheral device. Concerned. Therefore, in the third embodiment, as shown in FIG. 6, an RC snubber circuit 26 in which a capacitor 31 and a resistor 32 are connected in series is added. The vibration at the time of the ON operation of the SiC-MOSFET 15 is caused by the impedance inside the power module, and thus becomes a high-frequency vibration. Therefore, it is preferable to select the capacitor 31 of the RC snubber circuit 26 having a low capacitance and a small parasitic inductance value.

The impedance of the RC snubber circuit 26 is expressed by the following equation (2). Therefore, the RC snubber circuit constant is close to the vibration frequency ωn expressed by the following equation (3), and the resistance value is selected so that the damping factor ζ expressed by the equation (4) satisfies ζ ≧ 0.8. It is preferable to do. In this case, it goes without saying that it is preferable to reduce the value of the parasitic inductance L.

{(Jω) ^ 2 * L * C + jω * R * C + 1} / (jω * C) (2)

Ωn = 1 / {2 * π * √ (L * C)) ≈vibration frequency (3)

Ζ = R / 2 * √ (C / L) (4)

In the third embodiment, as shown in FIG. 6, the RC snubber circuit 26 is shown to be provided at the terminal portion of the power module or outside, but may be provided inside the power module.

Embodiment 4 FIG.
FIG. 7 is a diagram illustrating the configuration of the power converter according to the fourth embodiment, which is different from the first embodiment in that the second snubber capacitor 19 is configured as an RDC snubber circuit 28. About others, it is the same as that of Embodiment 1, and while attaching | subjecting the same code | symbol about the same component, the overlapping description is abbreviate | omitted.

7, the resistor 34 and the second snubber capacitor 19 provided in the RDC snubber circuit 28 operate as a snubber circuit, and the diode 35 performs a clamping operation. Therefore, according to the power converter which concerns on Embodiment 4, it becomes possible to heighten a surge suppression effect rather than Embodiment 1 by snubber operation | movement and clamp operation | movement.

In the fourth embodiment, the second snubber capacitor 19 is configured as an RDC snubber circuit. However, the first snubber capacitor 18 may be configured as an RDC snubber circuit. That is, at least one of the first snubber capacitor 18 and the second snubber capacitor 19 may be configured as an RDC snubber circuit.

As described above, according to the power converter of the fourth embodiment, since at least one of the first and second snubber capacitors is configured as an RDC snubber circuit, the surge suppression effect can be further enhanced. An effect is obtained.

In the fourth embodiment, the second snubber capacitor is configured as an RDC snubber circuit as shown in FIG. 7, but the first snubber capacitor may be configured as an RDC snubber circuit. That is, in the power converter according to the fourth embodiment, it is sufficient that at least one of the first and second snubber capacitors is configured as an RDC snubber circuit, and the surge suppression effect can be enhanced.

The configurations shown in the above first to fourth embodiments are examples of the configuration of the present invention, and can be combined with other known techniques, and can be combined within the scope of the present invention. Needless to say, the configuration may be modified by omitting the unit.

As described above, the present invention is useful as a power converter that can protect the power module by suppressing the influence of the short-circuit surge voltage.

8a, 8b terminal part (power module), 9a, 9b terminal part (fuse), 10a DC line (high potential side), 10b DC line (low potential side), 11 electrolytic capacitor, 12 inverter circuit, 13, 13a, 13b Fuse, 14, 14a, 14b, 14c Power module (SiC power module), 18, 18a, 18b, 18c First snubber capacitor, 19 Second snubber capacitor, 21 Electrolytic capacitor connection terminal, 22a, 23a P potential

copper bus bar

22b, 23b N potential copper bus bar, 24a electrolytic capacitor P terminal, 24b electrolytic capacitor N terminal, 25a P terminal, 25b N terminal, 26 RC snubber circuit, 28 RDC snubber circuit, 29 output terminal, 31 capacitor, 32, 34 resistance , 35 die Over de, 50 motor, 60 cable.

Claims

In a power converter provided with an overcurrent protection element in each of a high potential side DC line and a low potential side DC line between a smoothing capacitor and an SiC power module constituting an inverter circuit,
A first snubber capacitor connected to a terminal portion of the SiC power module;
A second snubber capacitor connected between the high potential side DC line and the low potential side DC line between the overcurrent protection element and the inverter circuit;
With
The second snubber capacitor has a wiring inductance component from the connection position to the overcurrent protection element and the overcurrent protection rather than a wiring inductance component from the connection position to the connection position of the first snubber capacitor. A power converter characterized by being connected so that the sum of the inductance component of the elements is larger.
In the power converter in which an overcurrent protection element is provided in each of the high potential side DC line and the low potential side DC line between the smoothing capacitor and the SiC power module constituting the inverter circuit,
A first snubber capacitor is connected to a terminal portion of the SiC power module, and a second snubber capacitor is connected between each terminal portion on the inverter circuit side in the overcurrent protection element. converter.
The power converter according to claim 1 or 2, wherein a capacitance value of the second snubber capacitor is set to be larger than a capacitance value of the first snubber capacitor.
4. The capacitance value of the second snubber capacitor is selected so that an LC filter is configured by the overcurrent protection element and the second snubber capacitor. 5. The power converter as described in.
The power converter according to any one of claims 1 to 4, wherein an RC snubber circuit for high-frequency countermeasures is provided in a terminal portion or inside of the SiC power module.
The power converter according to any one of claims 1 to 3, wherein at least one of the first and second snubber capacitors is configured as an RDC snubber circuit.