Patent Application
20230308039
[0000.1] This application claims foreign priority benefits under 35 U.S.C. ยง 119 from German Patent Application No. 102022106988.5, filed Mar. 24, 2022, the content of which is hereby incorporated by reference in its entirety.
The present invention is directed at a AC drive for driving an electric motor or in e.g. grid converters and/or power converters. The AC drive comprises a 3-phase diode bridge, an inverter and a snubber board with multilayer printed circuit board elements, wherein the power lane in every layer of every element is connected to only one potential DC- or DC+, each element comprises two capacitors of inverted polarity, wherein each element comprises two C-shaped bus bars and wherein the C-shaped bus bars of two neighbouring elements are placed in close proximity to each other.
AC drives are prone to snubber voltages occurring at their IGBTs. During such situations, voltages within the drive may rise considerably when IGBTs are switched off. The voltage rise is induced by the inductance between the IGBTs and DC-link capacitors and/or the bus bar of the drive. The voltage rise may lead to problematic behaviour of the drive and/or damage of its components. As drive sizes and their manufacturing costs are reduced, custom snubber capacitor solutions, which could help alleviate the problem, are excluded for cost reasons.
If, alternatively, low cost capacitors are used to overcome this problem, then matching custom made bus bars are required, which in return increase the overall costs of the drive. Additionally, capacitor dimensions of standard capacitors are fixed and usually too large for the presently described AC drives. Therefore, multiple smaller parallel capacitors would have to be used, which decreases the performance of the AC drive through increased inductances of the custom made bus bar solution.
The aim of the present invention is to provide an improved AC drive, which overcomes these problems. This aim is achieved by a AC drive according to claim 1. Preferable embodiments of the invention are subject of the dependent claims.
According to the invention, a AC drive for driving an electric motor is provided. The drive comprises a 3-phase diode bridge, an inverter and a snubber board with multilayer printed circuit board elements, wherein the power lane in every layer of every element is connected to only one potential DC- or DC+ and each element comprises two capacitors of inverted polarity. Each element comprises two C-shaped bus bars wherein the C-shaped bus bars of two neighbouring elements are placed in close proximity to each other. The C-shaped bus bars may not be limited to being C-shaped but may be any shape e.g. I, L- shape.
The multilayer printed circuit board elements may be understood to comprise the bus bars. Alternatively, it is possible to regard the bus bars as components, which are separate from the multilayer printed circuit board elements. The close proximity of the bus bars may be understood as the bus bars being separated only by one component, such as an insulator, while being in close contact with said component.
The present invention uses a multilayer PCB with snubber capacitors, providing a low inductance path to the IGBTs or other active components of the drive. The pathway from the PCBA to the IGBTs is implemented with a low inductance design, wherein the DC+ and DC-bus bars are mechanically connected as close as possible to each other. Additionally, they have a large and flat area between them. This is facilitated by the large and flat middle section of the C-shaped bus bars.
The presently described drive provides a solution, which yields a very low inductance circuit for the snubber capacitors and therefore reduced IGBT snubber voltages. The presently described drive offers a cheaper solution compared to the above-mentioned known alternative solutions. Its manufacturing quality is enhanced at it can be easily assembled in automated assembly processes.
In a preferred embodiment of the invention, an insulator is provided between the C-shaped bus bars of two neighbouring elements and the C-shaped bus bars are spaced apart from each other by the thickness of the insulator. The insulator may be aligned in parallel to the middle section of the C-shaped bus bars. It may be glued or otherwise connected to the C-shaped bus bars. The distance between the two bus bars may therefore be slightly larger than the thickness of the insulator.
In another preferred embodiment of the invention, middle sections of adjacent C-shaped bus bars are in close contact with the insulators. The middle sections may be glued or otherwise connected to the insulator.
In another preferred embodiment of the invention, five multilayer printed circuit board elements are provided. The number of multilayer printed circuit board elements may be freely selected to provide the required characteristics to the drive. The multilayer printed circuit board elements may be identical to each other.
In another preferred embodiment of the invention, the multilayer printed circuit board elements comprise layers that are alternatingly connected to DC+ and DC-, wherein the layers are separated from each other by air gaps and/or PCB core material and/or prepregs.
In another preferred embodiment of the invention, the multilayer printed circuit board elements comprise a top layer connected to DC-, a second layer connected to DC+, a third layer connected to DC- and a bottom layer connected to DC+. Accordingly, there may be two groups of layers, one connected to DC+, the other one connected to DC-. The layers of one group may not overlap across their entire layers surface. The non-overlapping areas of the layers may be used for connecting the layers to either DC+ or DC-. The layers may be separated from each other by air gaps and/or PCB core material and/or prepregs.
In another preferred embodiment of the invention, the C-shaped bus bars are connected to the elements via screws and/or spacers, preferably SMD spacers and/or nuts, and/or through holes. The nuts may be hexagonal nuts.
In another preferred embodiment of the invention, the snubber board is installed directly to IGBT DC+ and DC- terminals of the drive.
In another preferred embodiment of the invention, the C-shaped bus bars are provided on one side of the snubber board and the capacitors are provided on the opposite side of the snubber board.
In another preferred embodiment, the multilayer printed circuit board elements are mounted behind a high current bus bar with a sufficient clearance to avoid voltage arching.
In another preferred embodiment, the multi-layer printed circuit board elements are mounted behind a high current bus bar and comprise a low impedance path for electrical current to flow between the capacitors and the high current bus bar.
Further details and advantages of the invention will be described with reference to the figures. The figures show:
The power lane in every layer of every multilayer printed circuit board element 20, 21 is connected to only one potential DC- 1 or DC+ 2 and each element 20, 21 comprises two capacitors C1-C10 of inverted polarity.
In the embodiment of
Although only one multilayer printed circuit board element 21 is shown in
An electric connection between every other layer may be provided by means of through holes 17 and correspondingly placed conductors. In order to facilitate the electric connection of every other layer, the extension, in particular in a longitudinal direction of the snubber board 9, of adj acent layers such as the top layer 13 and the second layer 14 may be chosen such that they do not overlap over their entire lengths and/or surface areas.
In the embodiment of
In the embodiment of
If more than four layers are used in the multilayer printed circuit board elements 20, 21, then the additional layers may also be connected to alternating bus bars 18, 19. Accordingly, there may be two groups of layers, one connected to DC+ 2, the other one connected to DC- 1. The layers of one group may not overlap across their entire layer surface. The non-overlapping areas of the layers may be used for connecting the layers to either DC+ 2 or DC- 1.
The bottom layer 16, or more generally, the bottom-most layers of the multilayer printed circuit board elements 20, 21 may extend the least in a direction perpendicular to the bus bars 18, 19. Additionally or alternatively, the upper layers may extend further in said direction than the lower layers of the multilayer printed circuit board elements 20, 21. Going from the top layer 13 towards the bottom layer 16, each layer in a pair of adjacent layers may be of equal or similar length in the direction perpendicular to the bus bars 18, 19. The top pair of layers may be of greatest length and the bottom pair of layers may be of smallest length in the direction perpendicular to the bus bars 18, 19. Intermediate pairs of layers may be of intermediate length in the direction perpendicular to the bus bars 18, 19 and with respect to the top and bottom pair of layers.
The slightly deviating geometries of the layers of the multilayer printed circuit board elements 20, 21 make it possible to easily provide layers that are alternatingly connected to DC+ and DC- or rather the corresponding bus bars 18, 19. According to the embodiment of
The bus bar 19 and/or the multilayer printed circuit board element 21 may comprise a circular or partially circular hole or recess. Said holes and/or recesses may overlap at least partially for e.g. providing space for tools and/or components.
The insulator 22 may be of the same or similar length as the two bus bars 18, 19. The vertical direction of the insulator 22 may correspond to the direction of the screw 12. The insulator 22 may extend further in its vertical direction than the screw 12 and/or the two bus bars 18, 19.
Each of the multilayer printed circuit board elements 20, 21 may comprise two C-shaped bus bars 18, 19 or bus bars of any other suitable shape. Two bus bars 18, 19 of two neighbouring elements 20, 21 may be placed in close proximity to each other and may be preferably arranged in symmetry to one another.
Two neighbouring C-shaped bus bars 18, 19 are spaced apart from each other by the thickness of the insulator 22. The insulator 22 may be aligned in parallel to the middle sections of the C-shaped bus bars 18, 19. Both, the insulator 22 and the middle section of the C-shaped bus bars may be planar. The insulator 22 may be glued or otherwise connected to the C-shaped bus bars 18, 19.
In the embodiment of
The C-shaped bus bars 18, 19 are connected to the elements 20, 21 via screws 12. Additional or alternative spacers may be provided for connecting the elements 20, 21 to the bus bars 18, 19. For example, SMD spacers may be provided between the parallel end-portions of the C-shaped bus bars 18, 19. Additionally or alternatively, one or more nuts such as hexagonal nuts may be provided. The nuts may be screwed to the screw 12 such that the parallel end-portions of the bus bars 18, 19 are compressed by the screw head on the one side and the nut on the other side. Alternatively, only one of the end-portions of the C-shaped bus bars 18, 19 may be positioned between the screw head and the nut.
Through holes 17 may be provided in the layers of the multilayer printed circuit board elements 20, 21 for facilitating an electric connection between alternating layers of the multilayer printed circuit board elements 20, 21.
The embodiment of
The C-shaped bus bars 18, 19 are provided on one side of the snubber board 9 and the capacitors C1-C10 are provided on the opposite side of the snubber board 9. The snubber board 9 may be installed directly to IGBT DC+ and DC- terminals of the drive.
The low height or profile of the multilayer printed circuit board elements 20, 21 with components screws 12, capacitors C1 - C10, and C-shaped bus bars 18, 19 make it possible to locate them behind the high current bus bars 23.
By placing the multilayer printed circuit board elements 20, 21 behind the high current bus bar 23, less space is required inside the drive compared to a design having one area with high current bus bars 23 and another area with the multilayer printed circuit board elements 20, 21. The very short distance between the multilayer printed circuit board element 20, 21 and the high current bus bar 23 make the snubber capacitors C1-C10 very effective because of the low impedance path to conduct current.
While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102022106988.5 | Mar 2022 | DE | national |
