Three-level neutral point clamping type inverter circuit

Electric power conversion systems – Current conversion – Including automatic or integral protection means

Reexamination Certificate

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Details

C363S132000

Reexamination Certificate

active

06226192

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a neutral point clamping type inverter circuit forming a power conversion apparatus which performs a variable speed driving operation and an inter-system interlink operation or the like for a motor.
BACKGROUND ART
As a snubber circuit for a neutral point clamping type inverter circuit, an individual snubber circuit type has been employed in general in which a snubber circuit is provided at each of respective switching elements, as disclosed in Japanese Patent Unexamined Publication No. Hei 7-135781 and Japanese Patent Unexamined Publication No. Hei 8-294285.
Japanese Patent Unexamined Publication No. Hei 7-135781 discloses a control method wherein a snubber circuit formed by a resistor, a capacitor and a diode is provided at each of respective switching elements so that an inverter can be stopped without breaking the switching element due to the excessive voltage or the like applied thereto.
Japanese Patent Unexamined Publication No. Hei 8-294285 discloses a technique wherein a snubber circuit formed by a resistor, a capacitor and a diode is provided at each of respective switching elements and each of the snubber circuits is formed as a voltage clamping type snubber circuit to which a half of the power source voltage is applied thereby to reduce the loss of the snubber circuit.
However, in the case of providing a snubber circuit at a neutral point clamping type inverter circuit of a relatively middle or small capacity, if the individual snubber circuit type having a snubber circuit at each of the switching elements is employed, there arises a problem that the number of parts becomes large and the cost of the snubber circuits becomes expensive.
Therefore, an object of the present invention is to provide a three-level neutral point clamping type inverter circuit wherein the snubber circuits are formed by a smaller number of parts
DISCLOSURE OF THE INVENTION
A three-level neutral point clamping type inverter circuit according to the present invention includes a positive bus line, a negative bus line and a neutral line, wherein a plurality of switching elements are connected in series between the positive bus line and a phase voltage output terminal and a plurality of switching elements are connected in series between the negative bus line and the phase voltage output terminal, the three-level neutral point clamping type inverter circuit further includes:
a first snubber capacitor provided between the positive bus line and the neutral line;
a second snubber capacitor provided between the negative bus line and the neutral line;
a first snubber diode having a cathode coupled to the positive bus line and an anode coupled to the phase voltage output terminal; and
a second snubber diode having an anode coupled to the negative bus line and a cathode coupled to the phase voltage output terminal.
A three-level neutral point clamping type inverter circuit according to the present invention includes a positive bus line, a negative bus line and a neutral line, wherein a plurality of switching elements are connected in series between the positive bus line and a phase voltage output terminal and a plurality of switching elements are connected in series between the negative bus line and the phase voltage output terminal, the three-level neutral point clamping type inverter circuit further includes:
a first RCD snubber circuit having a first diode whose anode is coupled to the positive bus line, a first snubber capacitor coupled between a cathode of the first diode and the neutral line, and a first discharge resistor coupled in parallel to the first diode;
a second RCD snubber circuit having a second diode whose cathode is coupled to the negative bus line, a second snubber capacitor coupled between an anode of the second diode and the neutral line, and a second discharge resistor coupled in parallel to the second diode;
a first snubber diode having a cathode coupled to a connection point between the first diode of the first RCD snubber circuit and the first snubber capacitor and having an anode coupled to the phase voltage output terminal; and
a second snubber diode having an anode coupled to a connection point between the second diode of the second RCD snubber circuit and the second snubber capacitor and having a cathode coupled to the phase voltage output terminal.
According to the present invention, in a three-level neutral point clamping type inverter circuit which includes a positive bus line, a negative bus line and a neutral line, wherein a plurality of switching elements are connected in series between the positive bus line and a phase voltage output terminal and a plurality of switching elements are connected in series between the negative bus line and the phase voltage output terminal, the three-level neutral point clamping type inverter circuit is not arranged in a manner that a snubber circuit is provided at each of the respective switching elements but arranged in a manner that first and second snubber capacitors or first and second RCD snubber circuits are provided between the positive
egative bus line and the neutral line, and further first and second snubber diodes are provided between the positive
egative bus line and the phase voltage output terminal or between the first and second RCD snubber circuits and the phase voltage output terminal, whereby the snubber circuits can be formed by smaller number of parts. Accordingly, the snubber circuits can be provided within a three-level neutral point clamping type inverter circuit of a relatively middle or small capacity without increasing cost largely and further the quality of the inverter circuit can be improved. Further, the increase of the size of the inverter apparatus can be suppressed.


REFERENCES:
patent: 4881159 (1989-11-01), Holtz et al.
patent: 5953222 (1999-09-01), Mizutani
patent: 1-198280 (1989-08-01), None
patent: 7-135781 (1995-05-01), None
patent: 7-312878 (1995-11-01), None
patent: 8-294285 (1996-11-01), None

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