Digitally controlled rectifying system for driving a motor

Claim 1

A digitally controlled rectifying system used for driving a direct current (d.c.) motor through a forward and reverse converters connected in an anti-parallel fashion so as to block a circulation current, said system comprising: (a) a pulse generator coupled to the drive shaft of said motor; (b) a speed measuring means which counts pulses generated by said pulse generator and produces a digital value in correspondence to the rotational speed of said motor; (c) a speed controller which receives a speed command signal and the output of said speed measuring means; (d) a current controller which receives the output of said speed controller and the output of a current transformer coupled to an alternating current (a.c.) input power line to said converters; (e) logic means which receives the output of said current transformer and the output of a voltage sensor connected to detect the output voltage of said converters, said logic means operating on the firing phase angle of said converters to shift by 180° at a time of gate switching operation so that the load current is forced to become zero, said logic means operating on the firing phase angle of said converters to shift following the gate switching operation so that the load current is substantially zero; and switch means operated by said logic means to supply gate pulses to one of said forward and reverse converters.