Passive auxiliary circuit for series connection of a power...

Details Passive auxiliary circuit for series connection of a power... Passive auxiliary circuit for series connection of a power...

2000-11-27

2001-11-20

Riley, Shawn (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

C323S281000

Reexamination Certificate

active

06320362

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a passive auxiliary circuit for driving power switching elements connected in series for much higher rating of a power system.
2. Description of the Related Art
High voltage and current rating solid state switches are being used as devices for high voltage power system owing to development of solid state electronic device technology. Among solid state switches, an IGBT (Insulated Gate Bipolar Transistor) can operate at fast switching frequency and its driving circuit is so simple. In addition, the rating of an IGBT is higher than that of a MOSFET (Metal Oxided Semiconductor Field Effect Transistor). Therefore, an IGBT is replacing a thyristor and a GTO (Gate Turn Off) thyristor gradually in high-capacity power system as well as middle-capacity one.
However, an IGBT being used commonly at present has the rating of 3.3 kV/1200 A, so that, if the rating does not match the need for any several order kilovolt high voltage application such as a high-voltage pulse generator, a static var compensator, a high-voltage source inverter, and so on, several IGBTs should be connected in series for that need. Due to this reason, series connection methods of power semiconductor switches have been introduced in many papers recently.
When a plurality of power switches are to be connected in series for a high voltage application, it is very important to distribute the high voltage across all switches equally in order that an overvoltage exceeding a rating voltage of a single switch should not be applied across an arbitrary switch. Especially, since the characteristic difference is very large between each IGBT at the time when it is turned off, an IGBT may be destroyed if an overvoltage is applied due to the unbalance of voltage distribution.
To resolve such problems, various auxiliary circuits including passive elements only or active elements have been designed so far.
FIG. 1
shows a passive snubber circuit composed of a resistor Rs, a capacitor Cs, and a diode Ds, and
FIG. 2
shows a power circuit including an active gate driving circuitry. In the circuit of
FIG. 2
, each voltage across each switching element is detected and is compared with a predetermined reference, then, the gate driving circuitry is controlled based on the comparison result.
The voltage distributing method according to the snubber circuit of
FIG. 1
has such drawbacks that the size of a circuit is increased since the capacitance of the snubber capacitor Cs should be increased if a switching element is for high voltage, and a power loss is much large in proportion to switching frequency. Therefore, the method using a passive snubber circuit is not applicable to higher-capacity and higher-frequency power circuit because of much power loss.
The method using an active gate driving circuitry of FIG.
2
has advantages over the method of a passive snubber circuit in that the switching power loss is negligible and its operation is more reliable. However, a power circuit including the active gate driving circuitry becomes more complex if it has to comprise more switching elements to be connected in series since additional circuits for detection, comparison, and control are added to each switching element, which causes a reliability and insulation problem of an overall power circuit.
Besides the passive and the active circuits shown in
FIGS. 1 and 2
, various technologies for series connection between solid state power switches has been presented, however they still have disadvantages that the circuit structure is complicated and power loss is not negligible.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a passive auxiliary circuit for series connection of a solid state power switch, which has simple structure composed of small-capacity passive elements and is able to distribute a supplied high voltage equally across a plurality of semiconductor switches connected in series in a high-rating power supplying system.
A passive auxiliary circuit for series-connection of a semiconductor power switch according to the present invention, comprises two capacitors, which are connected in parallel across the power switch; two resistors dividing a voltage applied across the power switch, each resistor being connected in parallel with each of the capacitors; and a diode and a third resistor which are connected in series between a driving terminal of the power switch and a node connecting the two capacitors, wherein the diode is placed such that its cathode is directed to the driving terminal.
Another passive circuit for series-connection of a semiconductor power switch according to the present invention, comprises two capacitors, which are connected in series across the power switch; two resistors dividing a voltage applied across the power switch, each resistor being connected in parallel with each of the capacitors; a third resistor connected between a driving terminal of the power switch and a node connecting the two capacitors; and a diode inserted into a branch between a current inflow terminal of the power switch and one of the capacitors, wherein the diode is placed such that its anode is directed to the current inflow terminal.


REFERENCES:
patent: 4638240 (1987-01-01), Pauker et al.

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