【摘要】Optical Engineering + Application conference in 2016 had only few reports dedicated to high-accuracy position control systems for optical complexes. However, at SPIE Optics + Photonics Exhibition 2016 dozens of companies offered such projects. In that respect, this report may be of interest for academic community. The main method for assessment of performance of automatic control systems is assessment of stability of a system as it allows the evaluation of dynamics and accuracy as well as the method for additional adjustment and technological capacity of the whole complex comprising the system. As a rule, complex systems do not reduce to linear systems or other known variants, so their analysis is normally based on modeling or simplified calculation. In the suggested paper the known criterion of stability for non-linear systems by Popov involves not frequency locus of linear part, but logarithmic frequency characteristics of the system, including non-linear frequency characteristics. It allows the development of conditions of stability and methods of adjustment for such complex systems as servo drives with non-rigid mechanics and alternating-current systems which cannot be analyzed with the help of known methods, In the systems where the stated methods are used accuracy and speed performance are increased fivefold at an average. All theoretical calculations are confirmed by experiments and modeling.