Speed Control of a Brushless Static Kramer System

A new brushless speed control system is proposed which consists of a self-cascade induction motor and a brushless commutatorless motor. The slip power extracted from the stator terminals of the induction motor is converted to mechanical power by the commutatorless motor, which is coupled mechanically to the induction motor shaft. The field control method, the advance angle control method, and the dc chopper control method for speed variation are discussed. The experiments using a prototype self-cascade motor which has single-winding schemes both on the stator and rotor show that smooth peed variation can be achieved by dc chopper control. The proposed system offers the advantages of highly reliable, maintenance-free operation, and has less reactive power and smaller harmonic contents in supply lines than conventional systems.