Yichao Liu gave a talk on the seminar of CiPES.

        On October 22, 2021, the master student of CiPES, Mr Yichao Liu made a presentation and the topic is "Steady-state and Peak Gain Analysis of LLC Resonant Converter with Extended Impedance Method".

       LLC resonant converters are widely used in modern power system since they can realize zero to full load ZVS capability. The steady state and peak gain analysis is of vital importance for circuit designers because peak gain points are actually the boundary between ZVS and ZCS region. The previous method are mainly divided in two parts: time domain and frequency domain method. Although time domain methods have the highest accuracy, multiple operation and working modes will bring trouble to the later optimization and control. Frequency domain methods are simple but their accuracy is low under light load condition.

       This talk adopts a frequency domain method called Extended Impedance Method (EIM) which models the circuit from the component level. In this way, the multiple operation and working modes can be avoided. This method converts the nonlinear components to be LTV by state-to-time mapping. Combined with other LTI components, the voltages and currents in the next iteration are calculated by the extended impedance matrices. This methods apply fixed-point iteration method on iterating the steady-state solution of LLC converters. The simulation time is reduced comparing with PSpice and relative error is around 1%.