Variable speed drive system

An a.c. variable speed drive system which can switch between a driving operation and regenerative operation of an inverter in accordance with the operation speed. This system includes a forced commutation type inverter for controlling a wound-rotor type induction motor at variable speed; an operation mode selection circuit for selectively outputting either a driving operation signal or a regenerative operation signal for the forced commutation type inverter by comparing an operation speed feedback signal from the would-rotor type induction motor with a predetermined judgement value; a forced commutation type inverter control circuit for causing the forced commutation type inverter to operate in a driving operation mode or a regenerative operation mode, in accordance with an output from the operation mode selection circuit; a connection circuit for supplying an output from a converter of the forced commutation type inverter to the wound-rotor type induction motor via a path suitable for the driving operation mode or the regenerative operation mode; and a switch circuit for switching a path of the connection circuit in accordance with an output of the operation mode selection circuit. The connection circuits include several switches.