Patent Application
20230396116
This application claims priority to and the benefit of European Patent Application No. 22275074.7, filed Jun. 2, 2022, the entire content of which is herein incorporated by reference.
The present disclosure is concerned with providing electrical connection of the stator windings of an electric machine.
Electric machines i.e. electric motors or generators include a rotor assembly and a stator assembly. The rotor on which permanent magnets are mounted rotates relative to the stator, having windings, to generate electric power. Such operation and assemblies are well-known and will not be described in further detail here.
The stator assembly includes a plurality of windings made of conductive material (wire). An AC voltage is connected to the windings to generate a magnetic field. Different phases of the AC voltage supply are connected to different ones of the windings around the stator to interact with the magnets on the rotor to cause the rotor to rotate. High performance electric machines may have tens of such windings. In such high performance machines, minimising electrical losses is critical to maximise power density. Maximising power density is particularly important where, for example, space for the motor, or permissible size and/or weight of the motor are limited such as in aircraft or other vehicles.
Outer rotor machines (i.e. where the rotor is located radially outwards of the stator) can provide greater power density than conventional inner rotor machines. Also, losses can be reduced by using multi-strand conductors such as Litz wires for the windings. Litz wires are wires used in various electrical applications for carrying AC current. Litz wires comprise several thin wire strands which are then twisted or woven together to form a multi-strand conductor. Because of the way the strands of the Litz wire are twisted together, each strand is on the outside of the conductor for an equal proportion of the overall length and so the current is equally distributed between the strands which reduces resistance of the strands. Litz wires have reduced losses, due to proximity and skin effect characteristics, particularly at high frequencies. Litz wires with many strands and small diameter are easy to bend and form into motor windings.
The windings need to be electrically connected to the AC voltage supply, with different windings connected to different phases of the AC supply. Different configurations of winding connections are known that are able to create a rotating magnetic field from the stator due to the application of different AC phases to different windings. The rotating field causes rotation of the rotor. Various ways for making the electrical connection between the conductors of the windings and the supply terminals are known including crimping, soldering and welding. US 2020/0227969 discloses making the electrical connection via bus bars, whereby several windings to be connected to each phase can be attached to the same bus bar, via a stud around which the wires of the winding are wrapped and secured. The bus bars can then be arranged in a compact stacked manner around the end of the stator. The bus bar arrangement is particularly advantageous where the windings are formed from multi-strand conductors such as Litz wires. Challenges arise with other forms of connection when the conductors are multi-strand since it is difficult to retain all of the many small strands in a crimp or weld connection or the like. It is also difficult to retain such multi-strand conductors in stator slots, particularly in high vibrational environments or environments in which high temperature excursions are experienced. This last point is particularly an issue with outer rotor machines, since the stator slots are wider and the outer diameter of the stator is greater.
Whilst the use of bus bars to connect windings to the power supply is an improvement over individual winding connections, cooling and assembly of the stack of bus bars at the end of the stator is challenging, and becomes more so as machines become bigger and require more and more bus bars. In particular, a large amount of heat can be generated in the bus bar stack which is difficult to remove and which can cause damage to the machine.
There is, therefore, a need for improved connection of stator windings to power supply terminals.
According to the disclosure, there is provided a stator assembly comprising: an annular stator body around an axis (X), the stator body having a first side and a second side spaced axially from the first side and a stator body surface defined by the first and second sides and extending circumferentially around the axis; a plurality of conductive windings provided on the stator body surface, each conductive winding extending between the first side and the second side, the conductive windings arranged adjacent each other in the circumferential direction; and a first set of terminal connectors provided at the first side, and a second set of terminal connectors provided at the second side for conductively connecting the windings to a power supply, in use.
Examples of the connection arrangement and method according to the disclosure will now be described with reference to the drawings. It should be noted that variations are possible within the scope of the claims.
Referring first to
The example of
Apart from the location on the stator, the description of the windings 20 is essentially the same for the inner rotor and the outer rotor design.
Although shown as a simple block component in
Where bus bars are used, these are stacked on top of each other, as seen in
The stacking of the bus bars can be better seen in
Again as best seen in the example of
Whilst such assemblies and connection techniques are generally fit for purpose, the inventors have noted that keeping the assembly cool, especially for larger, higher power machines, is a challenge. The more connections e.g. bus bars, provided at the stator end for connecting the windings to the power supply, the greater the build-up and concentration of heat. Furthermore, if a faulty connection occurs in the system, particularly at one of the innermost connectors, it is necessary to disassembly the entire connector assembly e.g. all of the bus bars, which can be time and labour intensive.
The solution provided by the present inventors is to provide winding—AC voltage connections on both the front A and the back B sides of the stator. In this way, not all of the connections for all windings, are stacked together on one side of the stator. Various arrangements are possible, but the general concept is that the connections for the windings are shared between the two sides of the stator.
The concept of the disclosure can be applied to inner and outer rotor machines, and for any types of winding including, but not limited to multi-strand windings or Litz wire windings. Although described in relation to examples in which the windings are connected to the AC phase by means of bus bars, other types of connection are also feasible.
In another arrangement, as shown in
Other combinations of windings and winding ends being connected to the AC voltage supply on different sides of the stator are also feasible.
Having connections on both sides of the stator rather than just one, as is conventional, can provide significant advantages in assembly and maintenance of electrical machines by allowing access to both sides of the machine and allowing maintenance of only that side where failure has occurred.
By sharing the connection load between both sides of the stator, the amount of heat generated at the connectors e.g. in the bus bar stack, is considerably reduced and heat dissipation is improved.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22275074.7 | Jun 2022 | EP | regional |
