GB601633A - Improvements in and relating to reversible direct current motor systems - Google Patents

Abstract

601,633. Converting; automatic current control systems. GENERAL ELECTRIC CO., Ltd., and DALE, S. H. Oct. 10, 1945, Nos. 26477/45 and 21826/46. [Classes 38 (ii) and 38 (iv)] [Also in Group XXXVII] In a system whereby a reversible D.C. motor is supplied from an A.C. source through a grid controlled rectifier and inverter in parallel, the current circulating between the converters automatically controls the ignition timing of one converter. In the examples described the circulating current is kept constant. The currents through the cross connected pairs of converters 4, 5 and 6, 7 which connect the single phase A.C. supply to the D.C. motor 14, pass through the D.C. windings of saturable reactors 12, 13 and their sum, the armature current, through the D.C. windings of saturable reactors 15, 16. The difference between the A.C. currents from source 19 through the series connected windings on reactors 12, 13 and on reactors 15, 16 which pass after rectification at 20, 21 through resistances 22, 23 is thus dependent on twice the value of the circulating current. The parts are so dimensioned that the difference in P.D. across resistances 22, 23 is proportional to the circulating current. This P.D. is applied to the grid of a valve 34 to vary the current in the biassing winding of a saturable reactor 38 in a phase changing network 36, 37, 38 through which the grids of converters 4, 5 are energized from supply 1. The grids of converters 6, 7 are energized through a similar phase changing network 47, 48, 49, the saturable reactor 47 of which is varied by current derived from the anode circuit of valve 51, the grid of which is fed from potentiometer 52 at a voltage determined by the manual setting of the potentiometer added to that generated by tachometer generator 54 coupled to the motor 14. In operation, manual setting of the potentiometer controls the speed and direction of motor 14, by varying the timing of the grids of the converters 6, 7, 'the timing of the grids of converters 4, 5 being therefore determined, since they are automatically adjusted to keep the circulating current constant. In the modification described with reference to the drawing filed with the second Provisional Specification (not shown) for controlling the motor a signal is fed to a circuit which through valves varies the biassing current of saturable reactors 38, 47 of the phase shifting networks to retard the ignition of one converter pair and advance that of the other. The difference in P.D. across the resistances 22, 23 is applied to this valve circuit to vary both advance and retard in the same sense until the circulating current is equal. To protect against excessive current flow, the voltage developed across a resistance in the armature circuit is used to produce a voltage in the controlling circuit to which the signal is fed. It is stated that similar arrangements may be used with polyphase supplies.