Gate driver for MOS control semiconductor devices

Details Gate driver for MOS control semiconductor devices Gate driver for MOS control semiconductor devices

2003-05-13

2004-03-09

Wells, Kenneth B. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Signal converting, shaping, or generating

Current driver

C327S436000, C327S470000

Reexamination Certificate

active

06703874

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention generally relates to a semiconductor power converting apparatus with employment of semiconductor elements and the like. More specifically, the present invention is directed to a semiconductor power converting apparatus capable of suppressing an occurrence of an overvoltage while a switching operation is carried out.
As disclosed in IPEC2000 S-17-3 “Development of IGBT series and Parallel Connection Technology for High Power Converters”, each of arms of a power converter constituted by a series connection of MOS control semiconductors such as IGBTs, so that an MOS control semiconductor power converter for outputting a high AC voltage and a high DC voltage can be realized. Since the MOS control semiconductor elements which are series-connected to each other and constitute each of these arms are turned ON, or OFF at the same time in response to a pulse signal controlled by either the PWM control or the PAM control, the DC voltage may be converted into the AC voltage and/or the AC voltage may be converted into the DC voltage.
On the other hand, another technique is opened by which the MOS control semiconductors series-connected to each other, which constitute the respective arms, may be protected from overvoltages. The published abstract of the Japanese Electric Society Industrial Application Department Meeting in 1999, vol. 2, entitled “Switching Test of Flat-pack IGBTs connected in Series”, pp. 119-120 describes the following protection technique. That is, the avalanche element is connected between the gate and the collector of the IGBT, while the avalanche element is brought into the conductive state when this avalanche element exceeds a predetermined voltage and thus avalanches. The voltage of the avalanche element is also increased in connection with the increase of the collector voltage the IGBT. When this voltage of the avalanche element exceeds the avalanche voltage of the avalanche element, the current is supplied from the collector of the IGBT to the gate thereof via this avalanche element, so that the gate voltage of the IGBT is increased so as to lower the impedance of the IGBT. As a result, the collector voltage of the IGBT is suppressed in order that the IGBT can be protected from the element destruction (breakdown) by applying the overvoltage to this IGBT. Also, this publication entitled “Switching Test for Series-Connection of Planar IGBTs”, vol. 2 (1999) of the lecture on Japanese Electric Society Industrial Application Department discloses that the MOS control semiconductors can be protected in such a manner that the gate voltage is increased so as to increase the saturated current value.
SUMMARY OF THE INVENTION
However, in the above-described publication entitled “Switching Test for Series-Connection of Planar IGBTs” in the published abstract of Japanese Electric Society Industrial Application Department Meeting in 1999, vol. 2, in such a case that the overcurrent is supplied to such an arm under ON state among the arms which constitute the MOS control semiconductor converter, the MOS control semiconductor having the lowest saturated current selected from the MOS control semiconductors which constitute this MOS control semiconductor series-connection limits this overcurrent to the saturated current value of this IGBT. As a consequence, since the MOS control semiconductor having the lowest saturated current limits the current, the impedance thereof is increased and the voltage sharing of this MOS control semiconductor is increased. Thus, the semiconductor element may be destroyed due to the application of the overvoltage.
On the other hand, in the above-described publication entitled “Switching Test for Series-Connection of Planar IGBTs” in the published abstract of Japanese Electric Society Industrial Application Department Meeting in 1999, vol. 2, since such an expensive semiconductor element having a high-voltage withstanding avalanche voltage equivalent to that of such an IGBT to be protected is required.
The present invention has an object to provide a semiconductor power converting apparatus containing such a circuit capable of preventing an application of an overvoltage. That is, in order to protect MOS control semiconductor devices from the overvoltage, when an overcurrent flows through these MOS control semiconductor devices, this circuit can avoid such an operation that the overvoltage is applied to such an MOS control semiconductor having a minimum saturated current among the series-connected MOS control semiconductor devices, while such a semiconductor element having an avalanche voltage equal to the high withstand voltage is not employed.
According to one aspect of the present invention, a semiconductor power converting apparatus, according to an aspect of the present invention, is featured by that while a current is supplied to a gate of an IGBT from a gate driver of an MOS control semiconductor, a gate voltage of such an MOS control semiconductor which is reached to a saturated current is increased higher than a gate voltage obtained under steady ON state, and thus, the saturated current value of this MOS control semiconductor element is increased.
In general, such a relationship as shown in
FIG. 2
is established between a collector-to-emitter voltage (will be referred to as a “collector voltage” hereinafter) of an MOS control semiconductor such as an IGBT, and a collector current of this MOS control semiconductor. When the collector voltage is increased at an arbitrary gate-to-emitter voltage (will be referred to as a “gate voltage” hereinafter), the collector current is also increased in connection with this operation. When this increased collector current is reached to a certain current value, this collector current does not exceed this reached current value. This maximum current value is referred to as a “saturated current value.” The higher the gate voltage is increased, the larger the saturated current value is increased.
As indicated in
FIG. 3
, while MOS control semiconductors
11
to
14
such as IGBTs having different saturated current values from each other are series-connected to each other and then the series-connected MOS control semiconductors are connected to a voltage source
21
, it is so assumed that saturated current values of the respective IGBTs (namely, saturated current value at gate voltages under steady ON states) are defined by IGBT
11
<IGBT
12
<IGBT
13
<IGBT
14
. In the case that all of the IGBT series-connected to each other are brought into ON states, a current may flow through this IGBT series-connection at a current increased rate which is determined based upon both a leakage impedance
23
of a wiring line and the voltage source
21
. Generally speaking, since a gate voltage of an IGBT is controlled in such a manner that this gate voltage may become a certain gate voltage higher than a threshold value, the IGBT is transferred from an OFF state into an ON state. In this connection, “a certain gate voltage higher than a threshold value” will be referred to as a “steady ON gate voltage” hereinafter in this specification.
In the case that a current flowing through the IGBT series-connection indicated in
FIG. 3
reaches the saturated current value during the steady ON gate voltage of the IGBT
11
having the lowest saturated current, this IGBT
11
having the lowest saturated current limits this current. As a consequence, since the IGBT
11
limits the current, the impedance thereof is increased. Since a voltage applied to a certain element is equal to a product between an impedance of this element and a current flowing through this element, the collector voltage of the IGBT
11
is increased while the impedance is increased.
However, when the collector voltage of the IGBT under ON state exceeds a previously set value, if the gate circuit owns such a function that the higher the collector becomes, the higher the gate voltage of the IGBT is increased, then the gate voltage of the IGBT
11
becomes higher than the steady ON gate voltage in connection with

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