Title of Invention	"A SNUBBERLESS INVERTER"
Abstract	The invention relates to A snubberless inverter comprising a plurality of IGBTs (3) mounted on a heat sink (1), the ac terminals of the IGBTs being connected to busbars (4) projecting onwards through slots in a fibre-glass sheet (5), the positive terminals of the IGBTs being connected to positive busbar (8a), the negative terminals of the IGBTs being connected to negative busbar (7a), a plurality of capacitors (6) being fixed to the fibre-glass sheet (5), their positive terminals being connected to the positive busbar (8b), their negative terminals being connected to the negative busbar (7b), a discharge resistance (9) is connected between busbars 7b and 8b to effectively discharge the capacitors (6) wherever the dc power to the capacitors are switched off.

Title of Invention

"A SNUBBERLESS INVERTER"

Abstract

The invention relates to A snubberless inverter comprising a plurality of IGBTs (3) mounted on a heat sink (1), the ac terminals of the IGBTs being connected to busbars (4) projecting onwards through slots in a fibre-glass sheet (5), the positive terminals of the IGBTs being connected to positive busbar (8a), the negative terminals of the IGBTs being connected to negative busbar (7a), a plurality of capacitors (6) being fixed to the fibre-glass sheet (5), their positive terminals being connected to the positive busbar (8b), their negative terminals being connected to the negative busbar (7b), a discharge resistance (9) is connected between busbars 7b and 8b to effectively discharge the capacitors (6) wherever the dc power to the capacitors are switched off.

Full Text	This invention relates to a snubberless inverter. An inverter is used for conversion of direct current (dc) supply to alternating current (ac) supply. The inverter normally uses self-turn-off devices, such as, gate-turn-off thyristors, insulated-gate-bipolar-transistors (IGBTs) etc. Presently, the IGBT has become the most common used device. An inverter commonly uses snubber circuit devices (consisting of resistors, capacitors and diodes) for protection of IGBTs during turn-on and turn-off. There are disadvantages associated with the use of snubber circuit device in an inverter. One of the main disadvantages is that the snubber circuit device occupy substantial space resulting in bulkier inverter. Another disadvantage of the present invention is that the snubber circuit consumes power and decrease the efficiency of inverter. Therefore the main object of the present invention is to provide a simple and effective device to protect the inverter during turn on and turn off of the inverter and replace the snubber circuit device. Another object of the present invention is to provide a device for the IGBT-based inverter which would result in a compact inverter. Still another object of the present invention is to provide a device for the IGBT-based inverter where the heat generated by the IGBTs is effectively dissipated to keep the temperature rise of IGBTs with in permissible limits. A further object of the present invention is to provide a device for the IGBT-based inverter where the discharge resistors for d.c. link capacitors are so assembled so as to result in a compact inverter assembly. According to this invention there is provided a snubberless inverter characterized in that a plurality of IGBTs mounted on a heat sink, the ac terminals of the IGBTs being connected to busbars projecting on wards through slots in a fibre-glass sheet, the positive terminals of the IGBTs being connected to positive busbar, the negative terminals of the IGBTs being connected to negative busbar, a plurality of capacitors being fixed to the fibre-glass sheet, their positive terminals being connected to the positive busbar, their negative terminals being connected to the negative busbar, a discharge resistance is connected between busbars to effectively discharge the capacitors when the input dc supply to the inventer is disconnected. The nature of the invention, its objective and further residing in the same will be apparent from the ensuing description made with reference to non-limiting exemplary embodiments of the invention represented in the accompanying drawing as given below: Fig. 1 Part-assembly, showing the fixing (on the heat sink ) of IGBTs, blower, and outgoing ac busbars; Fig. 2 Part-assembly, for showing mainly the assembly of dc link capacitors and the busbar connections of the negative terminals of the IGBTs with the negative terminals of the capacitors; Fig. 3 Part-assembly, for showing mainly the busbar connections of the positive terminals of the IGBTs with the positive terminals of the capa¬ citors and Fig. 4 Complete assembly of the IGBT-based inverter. Fig. 1 depicts the part-assembly, showing the fixing (on the heat sink) of IGBTs, blower, and outgoing ac busbars. First/ a proper heat sink (1) is selected for the assembly of inverter. The specification of heat sink (1) and blower (2) are selected such that the heat sink can dissipate the heat generated by the IGBTs during full-load operation.The length of heat sink is decided so that it can also accommodate the total number of IGBTs (3) required to obtair the inverter configuration. For example/ the assembly taken for explaining the present invention is for the case of a three-phase bridge inverter using three number of IGBT modules, each having two IGBTs with two built-in freewheeling diodes in it. Each IGBT is suitably fixed on the heat sink/ with adequate spacing inbetween any two IGBTs. The blower is fixed atone end of the heat sink/ such that its exhaust just fits over the complete face of the heat sink. When the supply is given to the blower/ it throws air over the heat sink fins from the blower-end to the other end, A copper busbar (4) connected to the ac terminal of each IGBT is taken out though a slot provided in the fibre - glass sheet (5) fixed at one side of the heat sink and forms one ac terminal of the IGBT inverter. Fig. 2 shows the part-assembly, explaining mainly the fixing arrangement of the capacitors and connections between the positive terminals of the IGBTs and the positive terminals of the dc link capacitors. The capacitors (6) are first assembled ( by means of suitably clamps and fixing screws) on the fibre-glass sheet (5). The fibre -glass sheet (5) is fixed on one face of the heat sink (1) in such a way that the negative terminals of the capacitors (6) are just above the negative terminals of the IGBTs (3). The voltage and current ratings of the capacitors and the number of capacitors are selected to suit the voltage and current ratings of the IGBT inverter. The assembly in Fig. 2 shows only three capacitors in parallel. But, in case there is a requirement of two capacitors in series, then one more row can be fixed on the fibre-glass (5) taken of an increased height above the first row, and the positive terminals of the first row capacitors are connected by copper links to the negative terminals of the second row capacitors to give series connection. A broad copper busbar is taken and bent at right angle. One horizontal face (7a) of this copper busbar is made to connect all the negative terminals of the IGBTs/ while the other vertical face (7b) of the copper busbar connects all the negative terminals of the capacitors. Thus/ one single copper busbar piece connects all the negative terminals of the IGBTs and capacitors. Fig. 3 is the part-assembly, explaining mainly the inter-connections of the positive terminals of IGBTs and capacitors. A copper busbar (8a) interconnects all the positive terminals of IGBTs (3). Another copper busbar (8a) interconnects all the positive terminals of capacitors (6). A third busbar (8c) connects the positive busbar(8b)of capacitors with the positive busbar (8a)of IGBTs Fig. 4 shows the complete assembly of all the components of IGBT- based inverter. Item 9 is a discharge resistor/ connected between the positive busbar (8b) and negative busbars (7b) of capacitors (6) for discharging the capacitors when the input dc supply to the inverter is disconnected. The discharge resist or is designed for dissi- pating the maximum capacitor voltage in a short period but the resistance should be high enough so that the continuous power loss in the discharge resistor ia kept as small as possible. From the above mentioned description of Figures 1 to 4/ the assembly of capacitors and the busbar connections of capacitors to the positive and negative terminals of IGBTs in the present invention is so made that the loop inductance between the capacitors and the IGBTs is made negligibly small . This has made it possible to operate the IGBT- based inverter assembled as per the present invention without the use of snubber components resulting in a compact and highly efficient inverter. The invention described hereinabove is in relation to a non-limiting embodiment and as defined by the accompanying claims. WE CLAIM; 1. A snubberless inverter characterized in that a plurality of IGBTs (3) mounted on a heat sink (1), the ac terminals of the IGBTs being connected to busbars (4) projecting on wards through slots in a fibre- glass sheet (5), the positive terminals of the IGBTs being connected to positive busbar (8a), the negative terminals of the IGBTs being connected to negative busbar (7a), a plurality of capacitors (6) being fixed to the fibre-glass sheet (5), their positive terminals being connected to the positive busbar (8b), their negative terminals being connected to the negative busbar (7b), a discharge resistance (9) is connected between busbars 7b and 8b to effectively discharge the capacitors (6) when the input dc supply to the inventer is disconnected. 2. A snabberless inverter as claimed in claim 1 wherein a blower (2) is fixed to the heat sink (1) in such a way that exhaust of the blower is directed on to the fins of the heat sink. 3. A snubberless inverter substantially as herein above described and illustrated with reference to drawings.

Full Text

This invention relates to a snubberless inverter.
An inverter is used for conversion of direct current (dc) supply to alternating current (ac) supply. The inverter normally uses self-turn-off devices, such as, gate-turn-off thyristors, insulated-gate-bipolar-transistors (IGBTs) etc. Presently, the IGBT has become the most common used device.
An inverter commonly uses snubber circuit devices (consisting of resistors, capacitors and diodes) for protection of IGBTs during turn-on and turn-off. There are disadvantages associated with the use of snubber circuit device in an inverter.
One of the main disadvantages is that the snubber circuit device occupy substantial space resulting in bulkier inverter.
Another disadvantage of the present invention is that the snubber circuit consumes power and decrease the efficiency of inverter.
Therefore the main object of the present invention is to provide a simple and effective device to protect the inverter during turn on and turn off of the inverter and replace the snubber circuit device.
Another object of the present invention is to provide a device for the IGBT-based inverter which would result in a compact inverter.
Still another object of the present invention is to provide a device for the IGBT-based inverter where the heat generated by the IGBTs is effectively dissipated to keep the temperature rise of IGBTs with in permissible limits.
A further object of the present invention is to provide a device for the IGBT-based inverter where the discharge resistors for d.c. link capacitors are so assembled so as to result in a compact inverter assembly.
According to this invention there is provided a snubberless inverter characterized in that a plurality of IGBTs mounted on a heat sink, the ac terminals of the IGBTs being connected to busbars projecting on wards through slots in a fibre-glass sheet, the positive terminals of the IGBTs being connected to positive busbar, the negative terminals of the IGBTs being connected to negative busbar, a plurality of capacitors being fixed to the fibre-glass sheet, their positive terminals being connected to the positive busbar, their negative terminals being connected to the negative busbar, a discharge resistance is connected between busbars to effectively discharge the capacitors when the input dc supply to the inventer is disconnected.
The nature of the invention, its objective and further residing in the same will be apparent from the ensuing description made with reference to non-limiting exemplary embodiments of the invention represented in the accompanying drawing as given below:
Fig. 1 Part-assembly, showing the fixing (on the heat
sink ) of IGBTs, blower, and outgoing ac
busbars;
Fig. 2 Part-assembly, for showing mainly the assembly
of dc link capacitors and the busbar connections
of the negative terminals of the IGBTs with
the negative terminals of the capacitors;
Fig. 3 Part-assembly, for showing mainly the busbar
connections of the positive terminals of the
IGBTs with the positive terminals of the capa¬
citors and
Fig. 4 Complete assembly of the IGBT-based inverter.
Fig. 1 depicts the part-assembly, showing the fixing (on the heat sink) of IGBTs, blower, and outgoing ac busbars. First/ a proper heat sink (1) is selected for the assembly of inverter. The specification of heat sink (1) and blower (2) are selected such that the heat sink can dissipate the heat generated by the IGBTs during full-load operation.The length of heat sink is decided so that it can also accommodate the total number of IGBTs (3) required to obtair the inverter configuration. For example/ the assembly
taken for explaining the present invention is for the case of a three-phase bridge inverter using three number of IGBT modules, each having two IGBTs with two built-in freewheeling diodes in it. Each IGBT is suitably fixed on the heat sink/ with adequate spacing inbetween any two IGBTs. The blower is fixed atone end of the heat sink/ such that its exhaust just fits over the complete face of the heat sink. When the supply is given to the blower/ it throws air over the heat sink fins from the blower-end to the other end, A copper busbar (4) connected to the ac terminal of each IGBT is taken out though a slot provided in the fibre - glass sheet (5) fixed at one side of the heat sink and forms one ac terminal of the IGBT inverter.
Fig. 2 shows the part-assembly, explaining mainly the fixing arrangement of the capacitors and connections between the positive terminals of the IGBTs and the positive terminals of the dc link capacitors. The capacitors (6) are first assembled ( by means of suitably clamps and fixing screws) on the fibre-glass sheet (5). The fibre -glass sheet (5) is fixed on one face of the heat sink (1) in such a way that the negative terminals of the capacitors (6) are just above the negative terminals of the IGBTs (3). The voltage and current ratings of the capacitors and the number of capacitors are selected to suit the voltage and current ratings of the IGBT inverter. The assembly in Fig. 2 shows only three
capacitors in parallel. But, in case there is a requirement of two capacitors in series, then one more row can be fixed
on the fibre-glass (5) taken of an increased height above the first row, and the positive terminals of the first row capacitors are connected by copper links to the negative terminals of the second row capacitors to give series connection. A broad copper busbar is taken and bent at right angle. One horizontal face (7a) of this copper busbar is made to connect all the negative terminals of the IGBTs/ while the other vertical face (7b) of the copper busbar connects all the negative terminals of the capacitors. Thus/ one single copper busbar piece connects all the negative terminals of the IGBTs and capacitors.
Fig. 3 is the part-assembly, explaining mainly the inter-connections of the positive terminals of IGBTs and capacitors. A copper busbar (8a) interconnects all the positive terminals of IGBTs (3). Another copper busbar (8a)
interconnects all the positive terminals of capacitors
(6). A third busbar (8c) connects the positive busbar(8b)of
capacitors with the positive busbar (8a)of IGBTs
Fig. 4 shows the complete assembly of all the components of IGBT- based inverter. Item 9 is a discharge resistor/ connected between the positive busbar (8b) and negative busbars (7b) of capacitors (6) for discharging the capacitors when the input dc supply to the inverter is disconnected. The discharge resist or is designed for dissi-
pating the maximum capacitor voltage in a short period but the resistance should be high enough so that the continuous power loss in the discharge resistor ia kept as small as possible.
From the above mentioned description of Figures 1 to 4/ the assembly of capacitors and the busbar connections of capacitors to the positive and negative terminals of IGBTs in the present invention is so made that the loop inductance between the capacitors and the IGBTs is made negligibly small . This has made it possible to operate the IGBT- based inverter assembled as per the present invention without the use of snubber components resulting in a compact and highly efficient inverter.
The invention described hereinabove is in relation to a non-limiting embodiment and as defined by the accompanying claims.

WE CLAIM;
1. A snubberless inverter characterized in that a plurality of IGBTs (3)
mounted on a heat sink (1), the ac terminals of the IGBTs being
connected to busbars (4) projecting on wards through slots in a fibre-
glass sheet (5), the positive terminals of the IGBTs being connected to
positive busbar (8a), the negative terminals of the IGBTs being
connected to negative busbar (7a), a plurality of capacitors (6) being
fixed to the fibre-glass sheet (5), their positive terminals being
connected to the positive busbar (8b), their negative terminals being
connected to the negative busbar (7b), a discharge resistance (9) is
connected between busbars 7b and 8b to effectively discharge the
capacitors (6) when the input dc supply to the inventer is
disconnected.
2. A snabberless inverter as claimed in claim 1 wherein a blower (2) is
fixed to the heat sink (1) in such a way that exhaust of the blower is
directed on to the fins of the heat sink.
3. A snubberless inverter substantially as herein above described and
illustrated with reference to drawings.

Documents:

2556-del-1997-abstract.pdf

2556-del-1997-claims.pdf

2556-del-1997-correspondence-others.pdf

2556-del-1997-correspondence-po.pdf

2556-del-1997-description (complete).pdf

2556-del-1997-drawings.pdf

2556-del-1997-form-1.pdf

2556-DEL-1997-Form-19.pdf

2556-del-1997-form-2.pdf

2556-del-1997-gpa.pdf

2556-del-1997-petition-others.pdf

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Patent Number

214711

Indian Patent Application Number

2556/DEL/1997

PG Journal Number

09/2008

Publication Date

29-Feb-2008

Grant Date

14-Feb-2008

Date of Filing

10-Sep-1997

Name of Patentee

BHARAT HEAVY ELECTRICALS LIMITED,

Applicant Address

BHEL HOUSE, SINI FORT NEW DELHI 110049, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	TATA VENKATA VITTAL RAO	BHARAT HEAVY ELECTRICALS LIMITED, CORPORATE RESEARCH & DEVELOPMENT DIVISION, VIKASANAGAR, HYDERABAD 500093, A.P. INDIA
2	SARIPALLI DEVA VARA PRASAD	BHARAT HEAVY ELECTRICALS LIMITED, CORPORATE RESEARCH & DEVELOPMENT DIVISION, VIKASANAGAR, HYDERABAD 500093, A.P. INDIA

PCT International Classification Number

H02M 7/42

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA