Rotor for permanent magnet generator

1. A rotary generator comprising:

at least one magnetic annulus pair comprising a first magnetic annulus and a second magnetic annulus with a gap therebetween;

a coil annulus in the gap;

the first and second magnetic annuli and the coil annulus having a common axis;

the first and second magnetic annuli of the at least one magnetic annulus pair each having:

a sequence of principle permanent magnets spaced around the common axis with alternating north and south poles facing the gap, corresponding principle permanent magnets of the first and second magnetic annuli of a magnetic annulus pair, with unlike poles facing the gap, facing each other across the gap such that lines of magnetic flux cross the gap between the corresponding principle permanent magnets, and

a sequence of intermediate permanent magnets, each of the intermediate permanent magnets being positioned between two of the principle permanent magnets, each intermediate permanent magnet having adjacent the gap a north pole facing a side of the principle permanent magnet of the two principle permanent magnets having a north pole facing the gap and each intermediate permanent magnet having adjacent the gap a south pole facing a side of the principle permanent magnet of the two principle permanent magnets with a south pole facing the gap,

the coil annulus having a sequence of coils arranged around the common axis such that the lines of magnetic flux cut the turns of the coils and thus induce electric currents in the coils as the magnetic annuli are caused to rotate relative to the coil annulus,

wherein the first and second magnetic annuli of the at least one magnetic annulus pair each further comprise a backing plate of ferromagnetic material, the principle permanent magnets being positioned between the backing plate and the gap and mounted to the backing plate such that adjacent principle permanent magnets are magnetically coupled to one another through the backing plate, and

a rotor of the generator comprising a plurality of the magnetic annulus pairs, adjacent magnetic annulus pairs sharing a common one of the backing plate such that, other than at axial end backing plates, each backing plate is populated on both sides with the sequences of principal and intermediate permanent magnets.

2. A rotary generator according to claim 1 wherein for a given size generator the ratio of the widths of the principle permanent and the intermediate permanent magnets together with the selection of the average width of the active portion of the layers of the stator coils used to generate emfs are each so determined such that the increase in the emfs generated in the coils is increased by at least 20% were there to be no interpoles present.

3. The rotary generator of claim 1 , wherein at least one side of the principle permanent magnets which extend in the radial direction are curved, preferably convex or concave.

4. The rotary generator of claim 1 , wherein at least one side of the intermediate permanent magnets which extend in the radial direction are curved, preferably convex or concave.

5. The rotary generator of claim 3 , wherein the curves of the sides of the principle permanent magnets and the intermediate permanent magnets are complementary such that the one can nestle into the other.

6. The rotary generator of claim 1 , further comprising ferromagnetic inserts of ferromagnetic material positioned between the intermediate permanent magnets and the principle permanent magnets.

7. The rotary generator of claim 1 , wherein the intermediate permanent magnets extend in length radially inwardly closer to the common axis than the principle permanent magnets and/or the intermediate permanent magnets extend radially outwardly further from the common axis than the principle permanent magnets.

8. The rotary generator of claim 1 , wherein the intermediate permanent magnets have a length in an axial direction of the rotary generator which is less than a length in the axial direction of the principle permanent magnets such that the corresponding principle permanent magnets are closer together than the distance between intermediate permanent magnets of the first magnetic annulus and intermediate permanent magnets of the facing second magnetic annulus.

9. The rotary generator of claim 1 in which the intermediate permanent magnet is constructed from a stack of laterally conjoined magnets each magnetized across their opposite sides and in attraction to its neighbour in such manner to provide a single interpole magnet of the desired overall width.

10. The rotary generator of claim 1 , wherein the backing plate has a thickness of 4 mm or greater.