Title of Invention

"INVERTER PHASE LEG USING PARALLEL CONNECTED IGBTs FOR HIGH POWER SNUBBERLESS INVERTER"

Abstract

This invention relates to an inverter phase leg module using parallel connected IGBTs for high power snubberless three phase inverter, said inverter phase leg module comprising an assembly of a heat sink (1) having a blower (2) mounted on top of said heat sink, plurality of IGBTs (3) are mounted on said heat sink and said IGBT, having positive busbar (4) connected to the collector terminals of IGBTs, and negative busbar (5) connected to emitter terminals of the bottom IGBTs and the AC output phase busbar (6) is formed by connecting the emitter terminals of the top IGBTs, a plurality of capacitors (7) mounted between a pair f of fiberglass sheets one at the bottom (8) and the other at the top (9) of the capacitor bank having DC input, positive busbar (10) and a negative busbar (11) and discharge resistors (12) connected between positive and negative busbars of paralled capacitors and the IGBT (3) assembly and the capacitor (7) assembly is connected by positive connecting busbar (13) and negative busbar (14), said positive connecting busbar (13) i* provided with a current sensor (15) connected to a fault detection and protection circuit (16).

Full Text

This invention relates to an inverter phase leg module using parallel connected IGBTs for high power snubberless inverters. An inverter is used to convert direct current (DC) power source to alternating current (AC) power source. Normally inverters use self-commutating devices, such as, gate-turn-off thyristors (GIOs), insulated gate-bipolar transistors (IGBTs), integrated gate—commutated thyristors (IGCTs) etc. The IGBT has become the most commonly used power semiconductor device for medium to high power inverters because of its voltage driven characteristics and the consequent simple gate drive circuit. Patent No. US 5/98916 discloses the assembly of high power inverter employing series connected devices with reduced stray loop inductance. The voltage rating of an inverter can be increased by connecting switching devices in series. Patent No. US 5422440 discloses low inductance bus arrangement for high power inverter. Low inductance is achieved by using electrically conducting bars having rounded edges and inserting dielectric materials between parallel conductors. Generally, snubber circuits, consisting of resistors, capacitors and diodes are connected across the 1BBT to protect it during turn-on and turn-off. There are several disadvantages associated with the use of snubber circuit across the IBBT. One of the main disadvantages of the snubber circuit is that it occupies spaces resulting in bulkier inverter. Another disadvantage with the snubber circuit is that the energy in the stray wiring inductance of the inverter circuit is dissipated as heat in the resistor of the snubber circuit. The heat loss in the snubber circuit decreases the inverter efficiency. Yet another disadvantage with voltage source type of I6BT based inverter is that a high value of capacitor bank has to be connected across DC link to maintain the DC link voltage ripple-free . A phase leg of inverter comprises of two switches in series across the DC link. If the two switches in a phase leg conduct simultaneously because of control circuit failure, the capacitors bank discharges through the IBBTs in the phase module, resulting in destruction of IBBTs due to shoot-through fault. Further disadvantages is that IGBTs of very high voltage and current ratings are not available. To realise high power IGBT inverter, IGBTs have to be connected in parallel. IGBTs of suitable characteristics have to be connected in parallel for equal current sharing. As mentioned earlier, the stray inductance in inverter circuit wiring causes additional loss, which has to be dissipated in the snubber circuit. As high power IGBTs are not available, it becomes necessary to connect a large number of IGBTs in parallel to form a phase leg for high power inverter. It is desirable to eliminate the snubber, so as to give compact and efficient inverter. But, at the same time, it requires careful consideration in the inverter assembly, so that the device can be protected during turn—on and turn-off without the use of snubber. Further, as the voltage source inverter is prone to failure due to shoot-through fault, it is desirable to incorporate protection device in each phase leg to protect the devices against shoot through fault. Therefore, the main objective of the present invention is to provide a simple and effective means to protect the high power inverter during turn—on and turn-off of the device and eliminate the snubber circuit. Another objective of the present invention is to provide the means for connecting iCJBIs in parallel in a phase leg such that the stray inductance in wiring is reduced to bare minimum. Yet another objective of the present invention is to provide a device for the phase module of I6BT inverter, with which the heat generated by the IGBTs is effectively dissipated to keep the junction temperature of IBBTs within permissible limit. A further objective of the present is to provide the means for the high power I6BT inverter for mounting the filter capacitors? and discharge resistors in such a way so as to reduce the stray inductance and consequent elimination of snubber circuit for realizing compact inverter. Still another objective of the present invention is to provide an ultra-fast acting current sensing and protection circuit to protect the 16Bfs in a phase module against over-current due to shoot-through fault or over-load. Still a further objective of the present invention is to connect three such 1SBT phase leg modules in a three-phase bridge configuration for conversion of power from DC to AC ,Q.r AXX to DC According to the present invention there is provided an inverter phase leg module using parallel connected IGBT* for high power snubberless three phase inverter, said inverter phase leg module comprising an assembly of a heat sink having a blower mounted on top of said heat sink, plurality of IGBTs are mounted on said heat sink and said IGBTs having positive busbars connected to the collector terminals of top IGBT, and negative busbar connected to emitter terminals of the bottom IGBTs and the AC output phase busbar is formed by connecting the emitter terminals of the top IGBTs, a plurality of capacitors mounted between a pair of fiberglass sheets one at the bottom and the other at the top of the capacitor bank having DC input positive busbar and a negative busbar and discharge resistors connected between positive and negative busbars of paralled capacitors and the IGBT assembly and the capacitor assembly is connected by positive connecting busbar and negative busbar, said positive connecting busbar is provided with a current sensor connected to a fault detection and protection circuit. The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to the nonlimiting exemplary embodiments of the invention represented in the accompanying drawings Figure 1 shows the assembly of the inverter phase leg module using parallel connected IGBTs of our invention. Figure 2 shows the assembly of the three-phase IGBT inverter connecting 3 numbers of the inverter phase leg module assembly of Figure 1. According to this invention, there is provided a device to manufacture 1BBT based high power three-phase inverter as shown in Figure 2 by connecting three numbers of phase modules and to assemble a phase module and as shown in Figure 2 by connecting requisite members of IBBTs (3) in parallel, mounting the capacitors (7) in series parallel and discharge resistors (12) of capacitors (7) to form the capacitor bank assembly (7,8,9), mounting the above mentioned capacitor bank to the power device assembly, mounting the device (3) on aluminum heat sink (1), mounting of the cooling blower (2) on one side of the heat sink (1), using of busbars (10,11) to form the positive (10) and negative (11) terminals of the capacitor bank (7) and their connection to the positive (4) and negative (5) DC terminals of the device assembly by busbars (13) and (14) respectively for equal current sharing, mounting of fast-acting current sensor (15) on the positive busbar (13) and sensing of the DC link current for shoot-through fault protection (16), snubberless and shoot-through fault protected operation of three-phase high power I6BT inverter. Figure 1 depicits the complete assembly of the I6BT phase module showing the fixing of IGBTs (3) and blower the blower (2)» it throws air over the heat sink (1) fins from the blower (2) end to the other end. A copper busbar (4) is connected to the collector terminals of top IBfaTs (3) to form the positive busbar (4) of the phase assembly module, a copper busbar (5) of appropriate cross section is connected to the emitter terminals of the bottom IGBTs to form the negative bus (5) of the phase assembly module. The AC terminal (6) of the phase module is formed by connecting the emitter terminals of the top IBBfs. The capacitors (7) are first assembled (by means of suitable clamps and fixisng screws) on the fiberglas sheet (8) at the bottom and a fiberglass sheet with openings at the top. The x voltage* and current ratings of the capacitors (7) and th» nuffl&SF* of capacitors (7) to be connected in series parallel combinations are selected to suit the voltage and current ratings of the IBBT inverter. The assembly shows three capacitors (7) in series and seven such series combination in parallel. The positive terminals of one extreme row of capacitors (7) are connected through a busbar (1Q> of appropriate thickness to form the positive input terminal. The negative terminals of this row of capacitors (?) are onnected to the positive terminals of the middle row of capacitors. The negative terminals of the capacitors of middle row are connected to the positive terminals of the third row by a busbar (11). The negative terminals of the third row of capacitors are connected by a bus-bar to form the input negative terminal of the phase assembly module. More numbers of the capacitors can be connected in series and parallel to cater to the inverter voltage and current ratings. The capacitors (7) should be close to each other and the busbar (10, 11) should be of rectangular cross-section . The area of cross-section is to be selected based on the DC link current to be handled by the capacitor assembly. Item 12 is a discharge resistor connected between the positive busbar and negative busbar of paralled capacitors (7) for discharging the capacitors (7) when the input DC supply to the inverter is disconnected. The discharge resistor (12) is designed for dissipating the maximum capacitor voltage in a short period* taut the resistance should be high enough so that the continuous power loss in the discharge resistor is kept as small as possible. The positive terminal and negative terminal of the capacitor assembly is connected to the positive and negative terminals of the IBBT assembly by the busbars (13) and (14) respectively. From the above mentioned description of the figure* the assembly and paralleling of the IBBTs (3) on heat sink (1)* the assembly of capacitors (7) and the connections of capacitor bank to the positive and negative terminals (13, 14) of the IBBT assembly in the present invention have been so made that the loop inductance between the capacitor assembly and the IBBT assembly 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 to a compact and high efficient inverter. Further, the busbar connections over the IBBT modules have been made such that equal currents flow through all the paralled IBBfs. J A fast acting, current sensor (15) connected in the positive busbar (13) connecting the capacitor assembly to the I6BT assembly. The output of the sensor is connected to a high speed shoot-through fault detection and protection circuit (16). Figure 2 depicts the complete assembly of the three-phase ISBT inverter. Three numbers of ISBT phase modules* as detailed in Figure 1* are connected to a common DC power and the AC outputs of individual phase modules form the AC output phase terminals (R, Y and B). (he invention described herein above is in relation to a non-limiting embodiment and as defined by the accompanying c1a i ms. WE CLAIMS 1. An inverter phase leg module using parallel connected I6BTS for high power snubberless three phase inverter» said inverter phase leg module comprising an assembly of a heat sink (1) having a blower (2) mounted on top of said heat sink? plurality of IGBTs (3) are mounted on said heat sink and said I6BT, having positive busbar (4) connected to the collector terminals of IGBTs, and negative busbar (5) connected to emitter terminals of the bottom IGBTs and the AC output phase busbar (6) is formed by connecting the emitter terminals of the top IGBTs, a plurality of capacitors (7) mounted between a pair of fiberglass sheets one at the bottom (8) and the other at the top (9) of the capacitor bank having DC input, positive busbar (1O) and a negative busbar (11) and discharge resistors (12) connected between positive and negative busbars of parallel capacitor* and the IGBT (3) assembly and the capacitor (7) assembly is connected by positive connecting busbar (13) and (negative busbar (14), said positive connecting busbar (13) is provided with a current sensor (15) connected to a fault detection and protection circuit (16). 2. The inverter phase leg module using parallel connected IGBTs as claimed in claim i wherein the three—phase IGBT inverter comprises of three such phase module and each phase module comprises of six numbers of two-in-one IGBT (3) modules in parallel with built in free wheeling diodes. 3. The inverter phase leg module using parallel connected IGBTs as claimed in claims 1 and 2 wherein each IGBT (3) is fixed on the heat sink having clear space in between. 4. The inverter phase leg module using parallel connected IGBTs as claimed in claim 1 wherein the busbars (4, 5; 1O» 11; 13» 14) are made of copper for inteconnecting all terminals for neglible loop inductance between DC link capacitors and the IGBTs. 5. The inverter phase leg module using parallel connected IGBTs as claimed in claims 1 and 4 wherein the capacitors (7) are mounted close to each other and the copper busbar (1O» 11) are of rectangular cross section. 6. The inverter phase leg module using parallel connected IBBTs as claimed in claim 1 wherein the discharge resistor (12) is connected between the positive busbar (10) and negative busbar (11) of the parallel capacitors (7) which discharges the capacitors (7) when the DC supply to the inverter is disconnected. 7. The inverter phase leg module using parallel connected IGBTs as claimed in claim 1 wherein said fast acting current sensor (15) mounted on the positive busbar (13) which connects the capacitor (7) assembling to the IGBT (3) assembly output of said sensor (15) is connected to high speed fault detection and protection circuit (16) for shoot through fault protection. 8. An inverter phase leg module using parallel connected IGBTs for high power snubberless three-phase inverter as herein described and illustrated with the accompanying drawings.

Documents:

1066-del-2001-abstract.pdf

1066-del-2001-claims.pdf

1066-del-2001-correspondence-others.pdf

1066-del-2001-correspondence-po.pdf

1066-del-2001-description (complete).pdf

1066-del-2001-drawings.pdf

1066-del-2001-form-1.pdf

1066-del-2001-form-19.pdf

1066-del-2001-form-2.pdf

1066-del-2001-form-3.pdf

1066-del-2001-gpa.pdf