Experimental study for the globally-stable Nyquist-stable 2-channel feedback system

In order to check the theoretical results of a previous study (Lurie 1980 a) a 16-order 2-ehannel non-linear feedback system was designed and tested. The average slope of the feedback cut-off was — 20 dB/octave. The system was unconditionally (globally) stable. In the prescribed frequency band the attained feedback was 30 dB greater than the theoretical limit for a single-loop system. A good agreement with the theory of the previous study was achieved It was found that (1) in order for the advantage over ordinary single-loop systems to be appreciable, the high-order linear part must be used ; (2) the large discrepancies in the characteristics of the non-linear links are admissible ; (3) the high-frequency noise components are damped significantly ; (4) output response to a step input is good for both small- and high-level signals to the input. No unexpected troubles were encountered during the experiments and the system was easy to handle.