Variable-speed inverter-fed synchronous motor employing natural commutation

A drive system is described which uses two conventional thyristor convertors to provide a d.c. link between a.c. mains and the varying-frequency voltages of a synchronous-machine stator, both convertors being naturally commutated by line voltages; the result is a variable-speed drive. The paper describes a detailed analysis of machine behaviour in the absence of saturation, but taking account of winding resistances. This analysis is used to investigate the effects of assumptions made in deriving a simple analysis, which takes account of magnetic saturation. The validity of the simple analysis is demonstrated by comparison with results obtained from tests on a practical drive system.