An Improved Triggering Method for a High Power Cycloconverter-Induction Motor Drive

A triggering method is discussed which is specifically designed for a traction drive consisting of a high-frequency alternator, a phase-controlled cycloconverter, and an induction motor. Because the motor operates with controlled slip the power-factor characteristics are known, and this is utilized to obtain cycloconverter simplification and to optimize machine sizes. Specific advantages over a conventional phase-controlled cycloconverter are 1) significantly higher alternator power factor, and 2) elimination of interphase reactors and current polarity sensing circuitry. Test results are described for a single cycloconverter-induction motor drive operating from a 420-Hz alternator in both motoring and electrical braking and for two drives operating in parallel from the same alternator. Motor efficiencies are within 1.5 percent of the sine-wave efficiencies and the alternator power factor varies from 0.78 to 0.84 over the motor speed range at full power. Electrical braking was achieved into grid resistors connected to the motor without requiring ``real'' power from the alternator. Operation of the two parallel drives from one alternator was successful despite severe alternator voltage distortion.