Patent GB-835904-A (GB)
Title: Improvements in or relating to controllable electric converters employing semi-conductor elements
IPC: H02M7/00
Filed: 1956-11-12
Abstract: 835,904. Control of motors. SIEMENS-SCHUCKERTWERKE A.G. Nov. 12, 1956 [Nov. 12, 1955], No. 34590/56. Class 38 (3). [Also in Group XXXV] Transistors connected in bridge arrangement for operation as rectifiers and/or inverters to supply electric motors are so controlled that the ratio of their conducting to non- conducting time can be altered to control the output by impulses generated by a push-pull arrangement of transistors. Fig. 1 shows transistors 1-6 interconnecting three-phase A.C. circuit R, S, T and D.C. circuit 7. Figs. 2a, 2b, 2c, 2d show a bridge arrangement of transistors 101-104 connected between single-phase A.C. at 9 and D.C. at 7. Figs. 2a, 2b show by arrows the required state of conductivity of the transistors for operation as rectifiers for two consecutive halves of an A.C. cycle and Figs. 2c, 2d show the required states for reversal of D.C. polarity. To enable this the transistors are of symmetrical design and controlled from symmetrical circuits so that the collector and emitter functions of the outer electrodes may be exchanged. Fig. 3a shows suitable control circuits and the required polarities of the control voltages to enable the bridge to operate as shown in Fig. 2a. Windings 12, 13 connected between the base and two other electrodes respectively are energized from transformer winding 11, the voltages they apply leaving the transistors blocked. Voltages, as shown, induced from a control circuit including windings 16, 17 (Fig. 1), in secondary windings 14, 15 in series with windings 12, 13 make transistor 101 conductive with its lower electrode acting as emitter. By appropriate voltages induced in the control windings associated with the other transistors 102, 103, 104, the last of these is also conducting and the first two blocked, the emitter electrodes being indicated by arrow heads. Fig. 6 shows a suitable circuit for energizing windings 14, 15 to control all the transistors to produce the conditions of Fig. 2 (a), (b), (c), (d). Windings 14, 15 are energized respectively from batteries 115, 125 through transistors 110, 111, 120, 121 according to the polarity of D.C. supply 210 which controls the conductivity of transistors 112, 122 energized from batteries 114, 124, in the control circuits of the former transistors. The selected two of these are made conductive alternately to energize the two halves of windings 16, 17 from batteries 115 or 125 and consequently winding 14 or 15 by application of an alternating voltage to transformers 113, 123. These transistors are protected against over-voltage by rectifiers 116, 117, 126, 127. The voltage applied to transformers 113, 123 may have a triangular, sinusoidal or sawtooth form, of the supply or other frequency. It is shown with reference to Fig. 7 (a), (b), (c) (not shown) that the voltages induced in windings 14, 15 are rectangular of a length a with zero periods of length b determined by the value of voltage 210. This varies the voltage from batteries 114, 124 across transistors 112, 122 to give a phase-angle control of transistors 110, 111, 120, 121. The rectangular wave is preferably applied through a full-wave rectifier to transistors 101-104 so that they are made conductive for periods which are reduced as the emitter-collector voltages of transistors 112, 122 are higher. Curves are given showing respectively the the forms of output voltage of a three-phase rectifying circuit as shown in Fig. 1 when the frequency of the voltage applied to transformer 113 is greater than and equal to the supply frequency (Figs. 8a, 8b, not shown). In both cases the output voltage is the maximum possible reduced by the factor a/a + b as determined by voltage 210. As the output polarity is reversed the value of the factor may be reduced (Fig. 8a, not shown). If polarity reversal is not needed, only one transistor per phase need be controllable and the transistors need not be symmetrical (Figs. 9a-d, not shown). Instead of the control circuit of Fig. 6 an amplivibrator circuit of the kind described in Specification 789,412 may be used (Fig. 10, not shown). A control sequency for inverter operation is described (Figs. 5a-d, not shown).