a) A dual-converter supplies power to a 560 V, 50 A, separately excited D.C. motor with an armature resistance of 1.xy. The voltage drop on the bridge thyristors is 2VT = 4 V, at rated motor current. Power is supplied by an ideal three-phase source with a line voltage of 415 V.Find the necessary firing-angle and motor back e.m.f. for regeneration operation at rated load current with a terminal voltage of 500 V. b) Explain the technical factors should be taken into consideration when comparing the application of different types of a.c. drive to a particular motor and load. c) Draw an AC motor controller, explain the technology used and operational use. d) Discuss the protection problems associated with an a.c. drive, and outline the measures manufacturers have devised to guard their systems against electrical damage.