Auto-transformer for use with multiple pulse rectifiers
View Patent ↗Zig-zag connected, phase shifting, auto-transformers that provides the inherent ability to block the flow of zero sequence currents that are associated with multiple-pulse rectifiers. The transformer coils are wound in three separate, multi-wound windings on three single-phase cores. A vector oriented winding scheme is provided with three output windings and three internal zig-zag configured pairs of windings. The three internal zig-zag windings are connected at corresponding ends of a first winding to form an electrical neutral. The second windings of the three internal zig-zag windings respectively tap one of the output windings. The external power source connects to a point along each of the second windings of the pair of internal windings.
1. A transformer comprising:
at least three input terminals arranged for electrical connection to a three phase power source;
at least six output terminals arranged for electrical connection to an external multiple phase load; and
a first coil, a second coil and a third coil each containing at least a first winding, a second winding and a third winding, each winding being isolated relative to each other and having a first end and a second end, wherein:
each of said third windings is tapped at corresponding points;
the first ends of the first windings are electrically connected together to form an electrical neutral;
said second winding of said first coil is electrically connected to the tap of said third winding of said second coil;
said second winding of said second coil is electrically connected to the tap of said third winding of said third coil; and
said second winding of said third coil is electrically connected to the tap of said third winding of said first coil;
the second end of said first winding of said first coil is electrically connected to said second end of said second winding of said second coil;
the second end of said first winding of said second coil is electrically connected to said second end of said second winding of said third coil;
the second end of said first winding of said third coil is electrically connected to said second end of said second winding of said first coil;
each of the three first ends of said third windings is connected to a separate one of said at least six output terminals; and
each of the three second ends of said third windings is connected to a separate one of the remaining output terminals.
2. The transformer of claim 1 , wherein said transformer is constructed using single phase cores.
3. The transformer of claim 1 , wherein said transformer is constructed using a five legged three phase core.
4. The transformer of claim 1 , wherein:
said first end of said second winding of said first coil is electrically connected to the tap of said third winding of said second coil;
said first end of said second winding of said second coil is electrically connected to the tap of said third winding of said third coil; and
said first end of said second winding of said third coil is electrically connected to the tap of said third winding of said first coil.
5. The transformer of claim 1 , wherein the tap of each said third winding is electrically connected to a separate one of said at least three input terminals.
6. The transformer of claim 1 , wherein said second windings are tapped at corresponding points.
7. The transformer of claim 6 , wherein each tap of the second windings is connected to a separate one of said at least three input terminals and wherein:
said first end of said second winding of said first coil is electrically connected to the tap of said third winding of said second coil;
said first end of said second winding of said second coil is electrically connected to the tap of said third winding of said third coil; and
said first end of said second winding of said third coil is electrically connected to the tap of said third winding of said first coil.
8. The transformer of claim 6 , wherein:
said tap of said second winding of said first coil is electrically connected to said tap of said third winding of said second coil;
said tap of said second winding of said second coil is electrically connected to said tap of said third winding of said third coil; and
said tap of said second winding of said third coil is electrically connected to said tap of said third winding of said first coil.
9. The transformer of claim 8 , wherein each of said first ends of said second windings is electrically connected to a separate one of said at least three input terminals.
10. The transformer of claim 1 , wherein each of said first, second, and third coils contain a fourth isolated winding with a first end electrically connected to a separate one of said at least three input terminals and a second end electrically connected to the first end of corresponding ones of said second windings to form a zig-zag configuration.
11. An AC to DC converter system comprising:
an N-pulse rectifier providing a set of output terminals, where N is a multiple of 6 and at least 12, and corresponds to a number of inputs of said N-pulse rectifier;
a transformer having at least three input terminals arranged for electrical connection to an external three phase power source and at least six output terminals arranged for electrical connection to an external multiple phase load;
wherein said transformer further comprises:
a first coil, a second coil and a third coil each containing at least a first winding, a second winding and a third winding, each winding being isolated relative to each other and having a first end and a second end, wherein:
each of said third windings is tapped at corresponding points;
the first ends of the first windings are electrically connected together to form an electrical neutral;
said second winding of said first coil is electrically connected to the tap of said third winding of said second coil;
said second winding of said second coil is electrically connected to the tap of said third winding of said third coil; and
said second winding of said third coil is electrically connected to the tap of said third winding of said first coil;
the second end of said first winding of said first coil is electrically connected to said second end of said second winding of said second coil;
the second end of said first winding of said second coil is electrically connected to said second end of said second winding of said third coil;
the second end of said first winding of said third coil is electrically connected to said second end of said second winding of said first coil;
each of the three first ends of said third windings is connected to a separate one of said at least six output terminals; and
each of the three second ends of said third windings is connected to a separate one of remaining output terminals; and
wherein the N inputs of the N-pulse rectifier are indirectly connected via the transformer to receive power applied to said three input terminals.
12. The converter system of claim 11 , wherein said transformer is constructed using a five legged three phase core.
13. The converter system of claim 11 , wherein:
said first end of said second winding of said first coil is electrically connected to the tap of said third winding of said second coil;
said first end of said second winding of said second coil is electrically connected to the tap of said third winding of said third coil; and
said first end of said second winding of said third coil is electrically connected to the tap of said third winding of said first coil.
14. The converter system of claim 11 , wherein the tap of each said third winding is electrically connected to a separate one of said at least three input terminals.
15. The converter system of claim 11 , wherein said second windings are tapped at corresponding points.
16. The converter system of claim 15 , wherein each tap of the second windings is connected to a separate one of said at least three input terminals and wherein:
said first end of said second winding of said first coil is electrically connected to the tap of said third winding of said second coil;
said first end of said second winding of said second coil is electrically connected to the tap of said third winding of said third coil; and
said first end of said second winding of said third coil is electrically connected to the tap of said third winding of said first coil.
17. The converter system of claim 15 , wherein:
said tap of said second winding of said first coil is electrically connected to said tap of said third winding of said second coil;
said tap of said second winding of said second coil is electrically connected to said tap of said third winding of said third coil;
said tap of said second winding of said third coil is electrically connected to said tap of said third winding of said first coil; and
wherein each of said first ends of said second windings is electrically connected to a separate one of said at least three input terminals.
18. The converter system of claim 11 , wherein each of said first, second, and third coils contain a fourth isolated winding with a first end electrically connected to a separate one of said at least three input terminals and a second end electrically connected to the first end of corresponding ones of said second windings.
19. The converter system of claim 11 , wherein the output terminals to which the three first ends of the third windings are connected and the remaining output terminals to which the three second ends of the third windings are connected are respectively coupled to a first and second set of input terminals of the N-pulse rectifier.
20. The converter system of claim 11 , wherein said first, second, and third isolated windings together make up a first set of transformer windings, said converter system further comprising:
multiple levels of transformer windings with a first level including said first set of transformer windings and a second level including a second and a third set of transformer windings;
wherein the output terminals of the first level to which the three first ends of the third windings are connected and the remaining output terminals of the first level to which the three second ends of the third windings are connected are respectively coupled to input terminals of the second and third sets of transformer windings at the second level; and
wherein the first three and second three ends of the third windings of each of the second and third sets of transformer windings are coupled to separate input terminals of a 4N-pulse rectifier.