Harmonic performance of cycloconverter synchronous-motor marine propulsions systems

The development and use of a simulation package for cycloconverter synchronous motor drive systems are presented. The enhancements introduced to the software have permitted harmonic performance studies of several cycloconverter configurations with and without circulating currents. By considering a series of steady-state performance evaluations at different output frequencies it has been possible to approximate the operation of marine propulsion systems as in icebreakers and cruise vessels. Extensive simulation results on a 12 MW cycloconverter synchronous motor drive system with and without circulating currents are presented. The simulation studies indicate that the use of circulating current cycloconverter systems results in appreciable reduction in input current harmonics (around 58%) but at considerable increase in input power ratings (around 21%). The enhanced simulation technique described here demonstrates that this increased power rating can be reduced considerably by using discontinuous circulating current conducting for about 160° irrespective of the pulse number of the converter and power factor of the load