Calculation and Modeling of Transition Processes in DC Resonant Converters of LLC Type

Abstract

For a linear equivalent circuit of a dc–dc converter of LLC type, a generalized vector-matrix equation is obtained for individual intervals of circuit linearity. When solving the third-order vector-matrix differential equation for an LC circuit based on the method of dividing processes into fast (in the LC circuit) and slow (in the converter output circuit) ones, the output voltage of the converter is assumed to be constant over the circuit half-cycle operation. This voltage is calculated by averaging over the average value of the converter output current obtained in the previous half-cycle. The processes in the dc–dc converter are calculated using the fitting method, in which the value of the LC circuit state vector at the end of the circuit linearity interval is used as its initial value in the next linearity interval. This method includes a standard algorithm for calculating the process over a half-cycle. A half-cycle can consist of several intervals of linearity. The start and end moments of these intervals are determined, as well as the voltage values on the output diagonal of the inverter bridge and on the secondary winding of the output transformer. The integral of the converter output current is calculated. The comparison of the calculated results with the results of simulation in the MATLAB/Simulink environment at the start confirms the correctness of the proposed method for calculating transients.