Numeric control for three=phase oscillator - is by comparison of numeric sinusoids and of sawtooth waveform

摘要

Numeric control of three phase oscillators esp. high powered thyristor circuits used in electric motor control. Control is based on the generation of three 120 deg. displaced sinusoids and a sawtooth waveform at three times the sinusoid frequency, both waveform types being represented numerically. A clock source working at a frequency (NsFs) which is a product of the number of waveform steps and their frequency, feeds a periodic counter (5) working between zero and number of steps - 1. This controls three passive programmed memories (6,7,8) providing a binary output representative of the sinusoid step amplitudes. The binary signals are multiplied (9,10,11) and compared (12,13,14) using a further clock source working at the product of the number of sawtooth steps and three times the sinusoid frequency. A second counter (NdFd) works between zero and three times the sinusoid frequency and supplies a further counter (15) and memory (16) the binary words feeding the comparator second inputs.