Magnetically geared machine for marine generation

Abstract

The present invention provides an electrical machine for use in marine generation comprising a marine turbine, a first rotor mechanically connected to the marine turbine, a second rotor and a stator. The first rotor is configured to transfer torque to the second rotor in a magnetically geared manner, and the second rotor is configured to induce an AC voltage in the stator.

1 . An electrical machine for use in marine generation comprising:
 a marine turbine;   a first rotor mechanically connected to the marine turbine;   a second rotor;   a stator;   wherein the first rotor is configured to transfer torque to the second rotor in a magnetically geared manner, and wherein the second rotor is configured to induce an AC voltage in the stator.   
     
     
         2 . The electrical machine of  claim 1 , further comprising an array of pole pieces;
 a first plurality of magnets; and   a second plurality of magnets.   
     
     
         3 . The electrical machine of  claim 2 , wherein the pole pieces are provided on the first rotor, the first plurality of magnets is provided on the second rotor and the second plurality of magnets is provided on the stator. 
     
     
         4 . The electrical machine of  claim 1 , wherein the first rotor, the second rotor and the stator are arranged concentrically around a shaft of the marine turbine. 
     
     
         5 . The electrical machine of  claim 1 , wherein the first rotor, the second rotor and the stator are arranged axially along a shaft of the marine turbine. 
     
     
         6 . The electrical machine of  claim 1 , wherein the pole number of the first plurality of magnets is different from the pole number of the second plurality of magnets and the gearing ratio between the first rotor and the second rotor is based on the ratio between the pole number of the first plurality of magnets and the pole number of the second plurality of magnets or the ratio between the number of pole pieces and the number of pole pairs of the first plurality of magnets. 
     
     
         7 . The electrical machine of  claim 3 , wherein the gearing ratio is equal to (P 2 /P 1 )+1 where P 1  is the number of pole pairs of the first plurality of magnets and P 2  is the number of pole pairs of the second plurality of magnets. 
     
     
         8 . The electrical machine of  claim 3 , wherein the gearing ratio is equal to Npp/P 1  where Npp is the number of pole pieces and P 1  is the number of pole pairs of the first plurality of magnets. 
     
     
         9 . The electrical machine of  claim 1 , further comprising a winding, wherein the winding is arranged to interact with the fundamental space harmonic of the magnetic field created by the first plurality of magnets, thereby inducing a voltage in the winding. 
     
     
         10 . The electrical machine of  claim 9 , wherein the winding is disposed on the stator. 
     
     
         11 . The electrical machine of  claim 1 , wherein torque is geared down between the first rotor and the second rotor, reducing the required active air gap area between the second rotor and the stator. 
     
     
         12 . The electrical machine of  claim 1 , wherein torque is geared down between the first rotor and the second rotor reducing the required stator mmf. 
     
     
         13 . The electrical machine of  claim 1 , wherein the second rotor is sealed within an enclosure formed by the first rotor. 
     
     
         14 . The electrical machine of  claim 1 , wherein a gap is provided between the stator and the first rotor which is open to the incursion of fluid. 
     
     
         15 . The electrical machine of  claim 1 , wherein the pole pieces and the first and second plurality of magnets are permanent magnets or electromagnets. 
     
     
         16 . The electrical machine of  claim 1 , wherein the first rotor comprises ferromagnetic pole pieces encapsulated within a non-magnetic portion of a frame. 
     
     
         17 . The electrical machine of  claim 16 , wherein the frame forms an enclosure around the second rotor. 
     
     
         18 . The electrical machine of  claim 17 , wherein the frame comprises end pieces connected to a shaft of the turbine which form an enclosure around the second rotor 
     
     
         19 . An arrangement comprising:
 one or more electrical machines according to  claim 1 ;   one or more passive or active rectifiers configured to convert the induced AC voltage to DC; and   one or more inverters to convert the DC voltage to AC voltage having a predetermined magnitude and frequency.   
     
     
         20 . An arrangement as claimed in  claim 19 , wherein the inverter is connected to a power grid, and the predetermined magnitude and frequency are the magnitude and frequency of the power grid. 
     
     
         21 . An arrangement as claimed in  claim 19 , wherein the number of rectifiers corresponds to the number of electrical machines, and each electrical machine is provided with a local rectifier. 
     
     
         22 . An arrangement as claimed in  claim 21 , wherein each rectifier is a passive rectifier. 
     
     
         23 . An arrangement as claimed in  claim 19 , wherein the one or more inverters comprises a single inverter. 
     
     
         24 . (canceled) 
     
     
         25 . (canceled)