Stabilisation of doubly-fed, slip-ring machines using the datum-shift method

Doubly-fed slip-ring machines have two notable properties; a very high peak-power capability and a range of synchronous speeds not found in more conventional synchronous machines. However, in general, these machines suffer from dynamic instability caused by negative damping torques and attention has been focused on devising means by which their effect can be eliminated, to produce a satisfactory machine. A new technique is described, in which stable operation is attained by combining the unstable operation of the machine at two load angles. Two methods of applying the technique to a machine are described, in which stable operation is obtained without any measurable adverse effect on steady-state performance.