Patent GB-801122-A (GB)
Title: Improvements in or relating to electric power translating semiconductor apparatus
IPC: H02M5/27
Filed: 1955-04-07
Abstract: 801,122. Converting; control systems for consumption apparatus. SIEMENS-SCHUCKERTWERKE A.G. April 7, 1955 [April 7, 1954], No. 10368/55. Classes 38 (2) and 38 (4). [Also in Groups XL (b) and XL (c)] A circuit for converting between voltages of different kinds, values and forms, with low losses and low wattless power, comprises semiconductor elements, by which a supply voltage is chopped at a control frequency into sections whose value or form can be controlled, from which sections the desired output voltage can be derived. The semi-conductors may be of the kind whose resistance increases in a magnetic field as described in Specifications 719,873, 759,047 and 797,506, [all in Group XXXVI] or of the kind exhibiting a magnetic barrier-layer effect as described in Specifications 750,134, 770,066, [both in Group XXXVI], and 801,096. Junctiontype transistors may also be used. To supply a load RL with a direct voltage value U2 from a direct voltage supply of value U1 (Fig. la) the supply voltage is chopped, so as to vary between values U4 and U3, by the periodic variation of current supplied through full-wave rectifier 100 from A.C. source A5 to winding W5 on magnetic core M5, Fig. 2a. The flux from this winding opposes that from winding WB which is fed from the D.C. source, to vary periodically the flux through semi-conductor S, trigger action to give sudden alteration of the value of semiconductor resistance between high and low being secured by feedback winding WF which carries load current as described in Specification 801,121. The load current is smoothed to value U2 by filter circuit R1, C1 and its value is controlled by varying resistors R5, RB to alter the ratio of the pulse to space times Te, Ta. The output voltage may alternatively be varied by altering the space times Ta only. The space time is that during which capacitor C10 charges through a variable resistor R<SP>1</SP>S, and the constant pulse time, that during which the capacitor C10 discharges through tube Gl and winding Ws (Fig. 2b). If the input voltage is alternating the output with be A.C. at a different voltage (Fig. 6a). By reversing alternate half waves at the input frequency variable directvoltage output is obtained. If the pulse widths are suitably varied the direct voltage will not vary at the input frequency (Fig. 27, not shown). A.C. may be derived from D.C. by reversing the supply at a fixed frequency and chopping it into pulses of widths varied at the output frequency which is determined by a resonant LC circuit (Fig. 3) (Fig. 4, not shown) (see Group XL (c)). If the pulses are derived from an input A.C. and are of equal width and reversed alternately, the output is an alternating voltage of the chopping frequency, modulated at the input frequency (Fig. 7). By making the pulse widths vary suitably the output may be at constant voltage (Fig. 26, not shown). In a supply system the higher modulated frequency may be used in the transmission transformers for increased efficiency, the original supply frequency being derived at the receiving end for supply to the load (Fig. 9, not shown) (see Group XL (c)). Fig. 10 shows a circuit for supplying a two-phase induction motor M from a three-phase supply R, S, T. Each two-phase winding I, II is connected through two pairs of switching devices S1-S8 to D.C. lines supplied through conventional rectifiers 7 from the three-phase supply. The control windings Wsl- Ws4 and Ws5-Ws8 of the switching devices in the respective phases are supplied from phase windings 90 degrees apart on a frequencyconverter 17 driven by motor M1 at a speed which determines that of motor M. In series with the outputs of frequency converter 17 are generators 16, 18 having triangular voltage curves so that the voltages supplied to windings Ws1-Ws8 have the form 22 (Fig. 12a). As each voltage curve intersects the ignition characteristics Z1, Z2, Z3, Z4 and extinction characteristics L1, L2, L3, L4 so the devices S1-S8 are switched on at points el-e7 and off at points a1-a6 to give the pulses shown in Fig. 12b which are smoothed to sine wave 24. A three-phase motor may be supplied by an analogous circuit. By subdividing the windings of motor M only two switching devices per phase are needed (Fig. 13, not shown). The switching devices may be blocked each alternate half-cycle or rectifiers 8-15 connected in series. Alternatively the width of the chopping sections may be kept constant and the chopping frequency varied or both varied together (Figs. 14, 15, not shown). For other systems by which the motor speed may be controlled, see Group XL (b). A two-phase motor may be supplied from the three-phase mains without rectification, through three transformers each having a primary winding connected between a different pair of supply phases, and each having two secondary windings, one connected to each phase winding of the motor (Fig. 18a, not shown). Switching devices in series with the primary windings chop pulses of controllable width from each half-cycle of the three-phase voltages, and switching devices in the secondary windings select such of these pulses as when smoothed give a two-phase sinusoidal output (Fig. 19). The voltages in the two phases I, II need not be equal. Alternatively an arrangement of switching devices needing no transformers is described (Fig. 20, not shown). Several pulses may be chopped out each halfcycle of the supply voltage, and by reversing alternate pulses and selecting appropriate pulses, voltages of lower frequency may be derived (Figs. 21a, 21b). With a poly-phase supply conversion to a lower frequency by the envelope-curve arrangement may be obtained. Alternatively such frequency conversion may be obtained by varying the instants of forced commutation between phases, the instants being progressively delayed by the action of and LC circuit resonant at the lower output frequency (Figs. 23, 24, not shown). When the instants of commutation occur at the same point in each cycle the output is a direct voltage whose value is determined by the instant of commutation. If the periods of conduction in each successive phase are all variable together, the output voltage at the lower frequency is variable (Fig. 25, not shown). For increasing the frequency, pulses may be chopped only from the phase voltages near their peaks, when the mean output voltage is higher than if only a single-phase source is available (Fig. 28). Two higher-frequency voltages so obtained may be superimposed, the output be modulated by varying the phase displacement between the two voltages. From this a voltage of regulable value of low frequency can be derived. Similarly the two superimposed voltages may have different frequencies. Such frequency converting arrangements may be used for equalizing load peaks in distribution systems with the aid of a flywheel generator. Arrangements for obtaining efficient operation of the semi-conductor devices with loads having various characteristics, such as are described in Specification 801,121, are referred to (Figs. 31, 32, 33, not shown). Specification 721,782, [Group X], also is referred to.