An electrical machine (20) coupled to a compressor (12) having a rotatable shaft (16), comprising: a rotor forming part of the rotatable shaft and having at least two magnetic portions (22A, 22B) separated by an inclined non-magnetic portion (24) shaft, a stator comprising a laminated magnetic iron stack (28) surrounded by a winding (30) and disposed along a periphery of the rotor to define a first annular gap (32), a ring (34) of non-magnetic material disposed around the stator, a DC coil (38) disposed around the non-magnetic ring, and a casing (40) of magnetic material disposed around the DC coil and having radial walls (40A, 40B) that project inwardly towards the rotor by defining a second annular gap (42) therebetween.