Incremental Describing Function Analysis of Subharmonic Oscillations in Control Systems with Thyristor Converters

Often subharmonic oscillations of firing angle of thyristor converters with large magnitude in negative feedback control systems are a kind of jump phenomena. For their investigation rectifiers may be modeled by an asymmetrical saturation type nonlinearity in series with a linear block whose factors depend upon the number of pulses of the rectifier and the order of subharmonic in question. Application of the incremental describing function technique results in a set of curves, which is useful for the determination of the critical gain of the system and its design. Results of digital computer simulated systems are in good agreement with the predicted values