METHODS OF RESEARCH OF RESONANT CONVERTERS

Analytical study of DC-DC resonant converters for the purpose of their analysis and correct design is a topical task. Currently, the fundamental harmonic method and the time domain analysis method are used to solve this problem. The use of the fundamental harmonic method for analyzing the steady-state characteristics of an LCC converter is simple only when using an LC smoothing filter at its output. For the widely used LCC converter with a capacitive filter at the output, the fundamental harmonic method yields a significant error. Therefore, the characteristics of an LCC converter are currently studied mainly by time analysis and simulation methods. The purpose of the study is to substantiate external characteristics of the LCC type converter using fundamental harmonic and time domain analysis methods and to compare the obtained results with the results of simulation modeling. Materials and methods. Mathematical modeling of the converter was carried out using methods of circuit theory and automatic control. Studying the converter with the help of time domain analysis, vector-matrix methods for solving differential equations, methods of separating motion and fitting were used. Simulation modeling of the converter was carried out in the MATLAB/Simulink dynamic modeling environment. Research results. External (load) characteristics of converters along with dependences of voltage gain on switching frequency allow to justify the choice of converter type and recommendations for their design. The derivation of external characteristics of the converter and dependences of short-circuit current and no-load voltage on switching frequency is given by the fundamental harmonic method. The time domain analysis is carried out for the most complex three-interval on a half-cycle switching mode of converter. The vector-matrix method is used to solve differential equations describing processes on three intervals of converter linearity. Analytical relationships are obtained that allow to calculate transient processes by the fitting method and to determine the characteristics of the steady-state mode. The latter is significantly complicated with an increase in the number of converter linearity intervals on a half-cycle of switching. This is explained by the fact that before calculating the characteristics of the steady-state mode, it is necessary to solve the nonlinear equation of this mode, which is greatly complicated already at three intervals of linearity on a half-cycle. Conclusions. The fundamental harmonic method for the LCC converter has limited application, since it gives approximate results, which are refined by more accurate methods. The time domain analysis method is the most suitable and accurate method of study. But its application becomes more complicated with the increase in the number of converter linearity intervals when analyzing its steady-state operating mode.