Cycloconverter Control of the Doubly Fed Induction Motor

A new variable speed commutatorless electric drive system has been developed which has a speed-torque characteristic similar to that of a dc series motor. Efficient use of active material was attained by series connecting rotor and stator windings of the rotating machine and by achieving control over the torque angle relationship between rotor and stator MMF waves. Stabilized operation results from sensing shaft position (at any speed) by use of magnetodiodes and, through semiconductor logic, gating the thyristors of a 400-Hz three-phase half-wave cycloconverter in such a fashion as to maintain an essentially constant MMF torque angle. Energy return to the power system during the generating portion of each half-cycle was attained using magnetodiode current sensing and semiconductor logic. Experimental results obtained with a 5-hp machine correlate with analytical predictions.