Design and Dynamic Performance Analysis of a Snubber-less LLC Converter Using Variable Frequency Control for Electric Vehicle Industry

Inductor-Inductor-Capacitor (LLC) resonant converters are widely used in on-board chargers (OBC) for electric vehicle (EV) application, due to their high power density and high efficiency. Main problem of low Q LLC resonant converter is poor output voltage regulation and low efficiency at light loads for wide input and output range application. Implementation of traditional fixed frequency control methods leads to high switching loss i.e., no zero voltage switching (ZVS) facility and significant circulating currents at light loads. To address these issues, a wide range of switching frequencies are essential. This increases the turn-off loss and magnetic core loss, leading to significant reduction in efficiency. This paper presents a variable frequency control (VFC) technique for improving the ZVS and light load efficiency of a half-bridge LLC resonant converter. The proposed VFC achieves ZVS operation of all primary side switches for wide input and output voltage range variation without any additional snubbers. The obtained measured efficiency of the converter was of 96% at full load and 87% at light load without loss of ZVS operation. Further, design, steady-state and dynamic performance (DP) analysis of a half-bridge LLC converter is presented. which validate the theoretical analysis.