SE333018B - - Google Patents

Abstract

1,114,429. Inverting. SIEMENS-SCHUCKERTWERKE A.G. 30 Sept., 1965 [30 Sept., 1964], No. 41646/65. Heading H2F. An inverter comprises an analogue/digital converter ADW for converting a variable amplitude D.C. input signal into a pulse frequency modulated signal which controls the operation of stepping circuits. Outputs are taken from the stepping circuits to control digital/ analogue converter DAW which produce output sine waves having a frequency dependent on the amplitude of the applied D.C. input. The amplitude of the output is controlled by a unit AS. The units DAW, one per phase, comprise four converters, each converter being formed by a number of parallel connected resistors which may be selectively switched into circuit by associated static switches, Figs. 1, 2 (not shown). The sinusoidal output signal, Fig. 4, may be considered as consisting of four basic wave shapes and each converter is arranged to simulate one of these, the stepping circuit determining which is selected. For example, during time period I, phase R is a positive voltage with a positive slope A, phase T is the same voltage with a negative slope A, and phase S is the sum of A and A with a negative sign. Thus, each unit DAW is arranged to produce the four waveforms ŒA, Œ #A. During each time period I-VI stepping circuit I selects either A or A in each unit DAW and a reversible counter VG determines whether the waveform selected is positive or negative going. The counter VG is stepped forward or backwards by a further stepping circuit II under the control of a circuit DV in dependence on the required direction of rotation of the phases. In a modification, Fig. 8 (not shown), the units DAW synthesize the waveform from the portions a, - a, b, - b shown in Fig. 4, and the waveform is divided into twelve periods.