This paper presents the results of experimental work on flywheel energy storage systems for city buses. An efficient electronic hardware scheme is used to start the flywheel and traction machines. This scheme has been designed, fabricated and tested in our laboratory. A low frequency a.c. has been derived from an inverter fed from a three-phase uncontrolled rectifier to start the commutatorless d.c. motors. Commutation is achieved by using a capacitor and two auxiliary thyristors, whose ratings could be a fraction of full machine ratings, as they are needed during starting only. The frequency of the inverter output is controlled by a function generator. For successful commutation in all modes of operation, a capacitor voltage sensor circuit has been employed.