AU727159B2 - Power converter - Google Patents

Description

U

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): KABUSHIKI KAISHA TOSHIBA Invention Title: POWER CONVERTER *o *e o o o ft ooooo oo oo The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 POWER CONVERTER The present application is a divisional application of Australian Application No. 58436/98, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION The present invention relates to a power converter using an insulated gate semiconductor device of a MOS gate structure, for example MOS-FET, IGBT (Insulated Gate Bipolar Transistor), IEGT (Injection Enhanced Gate Transistor) as a voltage drive switching element.

There is available a voltage drive switching 15 element as a switching element used in a power converter, for example an inverter which drives an induction motor converting a direct current power to an alternating current power other than a current drive switching element such as a thyristor, a gate turn-off thyristor (GTO) or transistor. As typical examples of a voltage drive switching element, there are named: an insulated gate semiconductor device of a MOS gate structure, for example MOS-FET, IGBT (Insulated Gate Bipolar Transistor), IEGT (Injection Enhanced Gate Transistor).

25 In general, an insulated-gate semiconductor element represented by an IGBT (Insulated Gate Bipolar Transistor) or an IEGT (Injection Enhanced Gate Transistor) is mounted on an insulated substrate. As such an insulated-gate semiconductor element, there are provided a bonding type insulated-gate semiconductor element wherein the emitter portion is connected to the terminal portion made of a copper plate by leads, and a pressure-welded insulated-gate semiconductor element wherein the emitter portion is pressure-welded to the terminal portion formed of a copper plate.

In the bonding type insulated-gate semiconductor element, dv/dt at the current cut-off time can be G:\MCooper\Keep\peci\58436.98-DIV.2.doc 12/11/99 3 sufficiently restricted by the inductance due to the leads. On the other hand, unlike the bonding type insulated-gate semiconductor element, the pressure-welded insulated-gate semiconductor element does not have leads connecting the emitter portion of the element and emitter terminal electrodes, and has a few inductance elements or none at all. Therefore, the pressure-welded insulated-gate semiconductor element is easily broken since the abovementioned dv/dt is high, as compared with the bonding type insulated-gate semiconductor element. Furthermore, in the pressure-welded insulated-gate semiconductor element, it can be considered to increase the thicknesses of the electrodes pressure-welded to the element in order to form inductance elements. In this case, the size of the pressure-welded insulated-gate semiconductor element is inevitably increased. Accordingly, withrespect to the size, the advantage of the pressure-welded insulated-gate semiconductor element is lost.

It is an object of embodiments of the invention to provide a power converter, which relizes an operation with high reliability.

BRIEF SUMMARY OF THE INVENTION The invention provides a power converter including: at least one insulated gate type voltage drive switching device; detecting means for detecting at least one of a set of device parameters and a set of electric parameters of the insulated gate type voltage drive switching device; and control means for controlling a gate of the insulated gate type voltage drive switching device based on a result of the detecting means, wherein said insulated gate type voltage drive switching device includes: G:\MCooper\Keep\Speci\58436.98-DIV.2.doc 12/11/99 4 an electrode pressure-welded to the insulated gate type voltage drive switching device; and an inductance element having a shape with features of a cylinder and a spiral, which is provided between an end of the insulated gate type voltage drive switching device and the electrode.

Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 9 The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate 20 presently preferred embodiments of the invention, and oo* o together with the general description given above and the detailed description of the preferred embodiments given :below, serve to explain the principles of the invention.

FIG. 1 is a view partially in section of a package of a flat type IEGT of an embodiment of the present invention; FIG. 2 is a sectional view taken on line II II of FIG. 1; FIG. 3 is a perspective view of a coil in the shape of a cylinder shown in FIG. 1; FIG. 4 is a perspective view of a coil in the shape of a quadrangular prism shown in FIG. 1; FIG. 5 is a sectional view along a central line of the coils shown in FIGS. 3 and 4; FIG. 6 is a perspective view of the coil in the shape of a cylinder shown in FIG. 1, which is applied with an insulating coating; and G:\MCooper\Keep\Speci\58436.98-DIV.2.doc 12/11/99 5 FIG. 7 is a sectional view along a central line of the coil shown in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION An embodiment which is preferably used for a voltage drive switching element will be described. The embodiment discloses a flat type IEGT and will be described in reference to FIGS. 1 to 3.

FIG. 1 shows a view partially in section of a package of a flat type IEGT and a porcelain insulator 310 in the shape of a ring mounted with covers made of a metal plate 311 joined at the upper and lower ends and copper posts 312, 313 are further joined, which are used as g 15 collector and emitter electrodes, which are conductive C members, and which can be subject to plastic deformation.

A thermal buffer plates 314 made of molybdenum are inserted between the copper posts 312, 313 at both ends of a chip 302 constructed of a gate section and a collector and emitter section in order to suppress a thermal strain of the device caused by a current pass and plural chips in the shape of a quadrangular prism shown in FIG. 2 are inserted to produce a flat type IEGT. A copper coil 315a as an inductance element is inserted between the copper 25 post 313 which is to be an emitter electrode and the thermal buffer plate 314. A gate pin 316 is formed at an end of a predetermined chip 302.

As shown in FIG.3, the coil 315a is prepared by mechanical processing of a copper rod to the shape of a hollow cylinder and a groove in the shape of a spiral is cut in the side portion of the hollow cylinder and an insulating sheet 317 such as normex is embedded as insulation between coils.

In such a manner, since the coil 315a in the shape of a cylinder as an inductance element is used and a voltage E imparted between both ends of the coil 315a occurring in cut-off is less that 50V, a voltage applied G:\MCooper\Keep\Speci\58436.98-DIV.2doc 12/11/99 I 6 to the insulating sheet 317 is a voltage which is a magnitude obtained by having the voltage E divided by the turn number of the coil 315a and thus no problem occurs in terms of dielectric strength. A value of the coil 315a can be suppressed less than 50 nH. The reason why is that the limit of withstand voltage of the gate of the device is on the order of 50V and dielectric breakdown happens if a voltage larger than this value is applied. In this structure, since a breaking current di/dt in a device under a high voltage is on the order of 1 kA/(L sec, L E/(di/dt) 50V/ 1KA 50 nH. For example, outer dimensions of the coil 315a at 25 nH with a safety factor of 2 is on the order of a diameter of 10 mm, the number of turns of 5 and a length of 6 mm.

15 Therefore, according to the embodiment, since a material of the coil 315a is copper, a pressure is applied to the copper posts 312, 313 and thereby the coil 315a is subject to plastic deformation, a dimensional error can be absorbed so as to secure uniform pressure given to chips.

20 In an aspect of characteristics, as is in the case of a device of a bonding type, when a current is cut off, a voltage L-di/dt occurs, and a gate voltage Vge Sactually applied to the device is not Eoff but reduced to Eoff L-di/dt, and a turn-off voltage is alleviated. For 25 this reason, a breaking phenomenon does not occur, thereby dv/di in turn-off is milder and a device breakdown can be prevented.

Moreover, when a large current is cut off, dv/dt is further milder and a device breakdown is prevented with more ease since di/dt is further larger and in company with this a gate voltage for off is automatically is decreased.

According to the embodiment, since as in the case of a device of a bonding type, as a withstand voltage of a device is higher and thereby a voltage E is higher, di/dt which is a increasing rate of a current di/dv E/L (where L indicates an inductance of an interconnection and the G:\MCooper\Keep\sreci\58436.98-DIV.2.doc 12/11/99 7 like) is in a reverse manner is smaller, it can be prevented that a current is concentrated in some devices and the devices are broken down if devices are connected in parallel.

A modified example of the inductance element shown in the embodiment will be described in reference to FIGS. 4 to 7.

The inductance element shown in FIG. 3 is a coil 315b in the shape of a quadrangular prism while the coil 315a is in the shape of a cylinder shown in FIG. 3. A current capacity can be increased since a sectional area for a current pass can be larger, as compared with the coil in the shape of a cylinder shown in FIG.3.

9 In the case of the coil 315b in the shape of a 15 quadrangular prism, as in the case of the coil in the 99o9 shape of a cylinder, since it is required that a voltage is generally limited to be lower than a withstand voltage between the gate and emitter, a voltage E between both ends of the coil 315b occurring when a current is cut off 20 is lower than 50V. Therefore a voltage applied to an insulating sheet 316 is a value which is obtained by having the voltage E divided by the turn number of the coil 315b and the voltage applied to the insulating sheet is a value having no problem in terms of a withstand voltage.

FIG. 5 is a sectional view along a central line of the coil 315a in the shape of a cylinder shown in FIG.

3 and a sectional view along a central line of the coil 315b in the shape of a cylinder shown in FIG. 4. As shown in the figures, gate electrodes Eg of the coil 315a of FIG. 3 in the shape of a cylinder and the coil 315b of FIG. 4 in the shape of a quadrangular prism are formed each by inserting a gate pin 321 having a spring nature connected by a wire to a cut-off portion 320 formed at a lower portion or the coil 315b.

FIG. 6 shows the coil 315a in the shape of a cylinder applied with insulating coating 330 such as of CG\MCooper\Keep\Speci\58436.98-DIV.2.doc 12/11/99

I

8 epoxy. In this case, while the coil 315a in the shape of a cylinder is an object, a similar effect can be obtained if the coil 315b of FIG.4 in the shape of quadrangular prism is applied with an insulating coating 330 such as of epoxy.

FIG. 7 is a sectional view along a central line of FIG. 6 and the insulating coating 330 is performed by a process in which the coil 315a which has mechanically been processed to form a spiral groove is first preheated, then subjected to a fluid dipping method and an electrostatic coating method, so that the groove in the shape of a spiral is insulated. The insulating coating 330 adhered at both ends of the coil 315a can mechanically removed to form an electrode. This insulating coating 330 has no problem as in the case of the insulating sheet 316 in oooterms of a withstand voltage.

:Though it is not shown, in the case where the plural number of the coils 315a shown in FIG. 1 or the coils 315b shown in FIG. 4 are connected in parallel and a larger current capacity is desired, copper spots 312, 313 which are to be the emitter electrodes and plural coils 315a in the shape of a cylinder or plural coils 315b in the shape of a quadrangular prism are arranged. As an arrangement of the plural coils, the coils 315a or 315b 25 are respectively connected to the copper posts 313 which are the emitter electrodes by using silver solder or the coils 315a or 315b are respectively subjected to press working or casting in one body with the copper posts 313.

Thereafter, a grooving processing in the shape of a spiral is conducted and then the insulating sheet 316 is inserted or the insulating coating 330 is embedded.

A switching element of the preferred embodiments of the present invention is characterized in: that in an insulated gate semiconductor element wherein the element and an electrode are pressure-welded, thermal buffer plates are provided at both end of the element and the element and the electrode, and the element G:\MCooper\Keep\Speci\58436.98-DIV.2.doc 12/11/99 r I I' 9 and the inductance element can respectively be connected to each other with the thermal buffer plate interposing therebetween; that spaces between turns of the inductance element can be subjected to an insulating treatment; that the insulating treatment can be performed by inserting an electrically insulating material between turns of the inductance element; that the insulating treatment can be performed by applying an electrically insulating coating between turns of the inductance element; and that plural inductance elements can in parallel be connected; and that the electrode and the plural inductance °oooo 15 elements can be formed in one body.

As mentioned above, according to embodiments of the present invention, since inductance elements can be pressure welded in a uniform manner in devices, there can be provided an insulated gate semiconductor element in 20 which dv/dt can be alleviated and imbalance of a current in turn-off in the case of parallel connection can be suppressed, while a scale merit as a pressure-welded, insulated-gate semiconductor element is utilized.

Additional advantages and modifications will 25 readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

G:\MCooper\Keep\Speci\58436.9O-DIV.2.doc 12/11/99

Claims (9)

1. A power converter including: at least one insulated gate type voltage drive switching device; detecting means for detecting at least one of a set of device parameters and a set of electric parameters of the insulated gate type voltage drive switching device; and control means for controlling a gate of the insulated gate type voltage drive switching device based on a result of the detecting means, wherein said insulated gate type voltage drive switching device includes: 15 an electrode pressure-welded to the insulated gate type voltage drive switching device; and S an inductance element having a shape with features of a cylinder and a spiral, which is provided between an end of the insulated gate type voltage drive 20 switching device and the electrode. e

2. A power converter as claimed in claim 1, wherein said inductance element has a shape with features of a quadrangular prism.

3. A power converter as claimed in claim 1, wherein said inductance element has a coil shape.

4. A power converter as claimed in any one of claims 1 to 3, further including a thermal buffer plate provided between terminals of the insulated gate type voltage drive switching device. A power converter as claimed in any one of claims 1 to 3, wherein said inductance element includes an insulating treatment subjecting space between turns of the inductance element.

G:\MCooper\Keep\Speci\58436.98-DIV.2.doc 12/11/99 4 S S 11

6. A power converter as claimed in claim 5, wherein said insulating treatment is performed by inserting an electrically insulating material between the turns of the inductance element.

7. A power converter as claimed in claim 5, wherein said insulating treatment is performed by applying an electrically insulating coating between the turns of the inductance element.

8. A power converter as claimed in claim 5, wherein said inductance element includes a plurality of inductance members to be connected in parallel. 15

9. A power converter as claimed in claim 5, wherein said electrode and the plurality of inductance members are formed in one body. i. A power converter as claimed in claim 1 and 20 substantially as herein described with reference to the accompanying drawings. Dated this 12th day of November 1999 KABUSHIKI KAISHA TOSHIBA 25 By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia G;\MCooper\Keep\Speci\58436.98-DIV.2.doc 12/11/99