Patent GB-409734-A (GB)
Title: Improvements in and relating to electric converting apparatus
IPC: H02M7/00
Filed: 1932-10-03
Abstract: 409,734. Control of D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Willis, C. H.; 184, Prospect Avenue, Princeton, New Jersey, U.S.A.) Oct. 3, 1932, No. 27442. Convention date, Oct. 1, 1931. [Class 38 (iii).] Regenerative braking.-A D.C. motor 12 is supplied from an A.C. circuit 10 through a polyphase inductive winding and a group of electric valves, and a second group of valves, oppositely connected to the winding, is provided for transmitting energy in the reverse direction when the motor is regenerating. In the arrangement shown in Fig. 1, the A.C. circuit 10 is connected to the D.C. circuit 11 through a polyphase transformer having a winding 13 connected to the circuit 10 and a polyphase network 14 connected to the circuit 11 through oppositely-connected groups of valves 15-20 and 21-26. Adjacent valves of the two groups are interconnected through inductive windings 27, 28 across which are connected commutating condensers 29, 30. One side of the D.C. circuit is connected to the neutral of the network 14, while the other side is connected to the mid-points of the windings 27, 28 through opposite halves of a winding 31. The voltage ratio of the circuits and the power factor conditions on the A.C. side are controlled by varying the excitations of the grids of the valves from the secondaries 35 of a grid transformer, the primary 33 of which is excited from the circuit 10 through a phase shifter 34. When the apparatus acts as a rectifier, energy is transmitted through the valves 21-26 and winding 28, while under regenerative conditions energy passes back to the A.C. circuit through the valves 15-20 and winding 27. In a full-wave modification of the apparatus, Fig. 2, the two groups of valves and the commutating windings are duplicated, the rectifying circuit comprising the groups of valves 21-26 and 21<1>-26<1> associated with the windings 28, 281, and the regenerating circuit the valves 15-20 and 15<1>-20<1> and the windings 27, 271. The respective groups of valves are connected to spaced terminals 37, 38 on the network 14, from which circulating currents flow through the commutating windings. These circulating currents produce voltages across the commutating windings and their associated condensers which enable the current between adjacent valves to be commutated against the E.M.F. of the network, so that it is possible to operate the apparatus at very low power factors and under light loads. In a modification, Fig. 3 (not shown), the circulating currents are produced by means of independent inductive windings interconnecting the rectifying and regenerating valves. In another arrangement, Fig. 4, an automatic regulation of the voltage ratio of the A.C. and D.C. circuits in accordance with the load is obtained by adding to the excitation of the grid transformer an A.C. component obtained from an inductance bridge comprising reactors 45, 46 and 47, 48, the two latter being provided with saturating windings 49, 50 in series with the commutating windings 27, 28. One diagonal of the bridge is connected across the condenser 30, and the other to the primary winding of a transformer 51 provided with three secondary windings in series with the phase winding of the primary 33 of the grid transformer. With this arrangement any change in the load current affects the unbalance voltage of the bridge applied to the grid transformer, while the circulating current affects both reactors 47 and 48 equally, and is consequently without effect. Specifications 390,184 ; 409,682, and 409,713, [both in Group XXXV], are referred to.