An electrical machine, such as a switched reluctance motor, has a rotor and a controller arranged to energize at least one electrically energizable phase winding in dependence on the angular position of the rotor. The controller may employ a control law table derived by applying a predetermined DC link voltage to the windings. Differences between an applied DC link voltage and the predetermined DC link voltage may be compensated by applying a predetermined correction to the angular position of energization of the phase winding in dependence on the value applied DC link voltage. Such a compensation factor may be derived from a relationship held in memory.