Patent GB-342336-A (GB)
IPC: H02M7/44
Filed: 1929-10-28
Abstract: 342,336. Power conversion apparatus. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London.- (Assignees of Sabbah, C. A. ; 1, Washington Avenue, Schenectady, New York, U.S.A.) Oct. 28, 1929, No. 32680. Convention date, Oct. 27, 1928. [Class 38 (ii).] Vapour and vacuum or low-pressure apparatus, arrangements of.-Power conversion apparatus for converting direct current to alternating current comprises a monocyclic square having one pair of opposite sides formed by condensers 19, 20, Fig. 1, and the other pair by inductances 17, 18 in series with resistances 15, 16 ; across one diagonal of the square is connected the D.C. supply in series with a winding 22 of a transformer 12 and a thermionic valve 13 ; across the other diagonal of the square is connected a valve 14 in series with a winding 23 of the transformer 12, the A.C. supply being taken from the secondary winding 21 of the transformer 12. The grid of valve 13 is connected to a tap on the resistance 15 and the grid of valve 14 to a tap on the resistance 16 so that the negative grid bias on the valves is proportional to the current flowing through the respective resistances. When the D.C. is switched on, its full value is imposed on the valve 13 which becomes conducting and current flows through the winding 22 of the transformer to charge the condensers 19, 20. As the condensers charge the current decreases, the negative grid bias on the valve 14 therefore decreases and the potential across the valve increases until a point is reached when the valve becomes conductive and current flows from the condensers 19, 20 through the winding 23 of the transformer 12 and through the valve 14. When the valve 14 becomes conducting the valve 13 is rendered non- conducting by an opposing e.m.f. induced in the winding 22. When the condensers 19, 20 are discharged the cycle again commences by the valve 13 becoming conductive. The frequency of the A.C. obtained is determined by the rate of charge and discharge of the condensers 19, 20, this depending on the characteristics of the valves and the values of their grid potentials. By varying the grid taps on the resistances 15, 16 the frequency can thus be varied. In a modification (Fig. 3, not shown), the windings 22, 23 are connected in series with the condensers 19, 20 respectively and each of the valves 13, 14 is connected in parallel with a high resistance the grid bias being supplied from a tap on the resistance. In another modification of the circuit of Fig. 1 resistances 15, 16 are removed and the grid bias of the valves supplied by additional windings on the transformer 12. The Specification as open to inspection under Sect. 91 (3) (a) comprises also a further modification of the circuit shown in Fig. 3, the condensers 19, 20 being replaced by the primary windings of two transformers, the secondaries of which are connected in series through a single condenser. In the circuit shown in Fig. 5 (Cancelled) the condenser 40 is charged from the D.C. supply through the valve 13 until its potential reaches a certain value determined by circuit conditions when the valve 14 becomes conductive and the condenser discharges, thus an alternating current flow is produced in the winding of the transformer 41. In a modification of this, shown in Fig. 7 (Cancelled), the varying grid-bias of the valves are supplied from additional windings 33, 35 on the transformer. This subject-matter does not appear in the Specification as accepted.