Control and Optimization of Power in LLC Converter Using Phase Control

LLC resonant converters are popular among resonant topologies due to their high efficiency and ability to achieve ZVS and ZCS for wide input range. LLC resonant converters are controlled by frequency modulation (FM), which makes converter difficult to optimize the system in terms of achieving efficient power conversion. FM technique also generate wide range of harmonics which leads to a wide sweep in operating frequency, which can run into regulatory EMI test limits and cause electromagnetic compatibility issues. The performance of LLC topology extends to their poor efficiency at lighter loads, due to constant high magnetization current. In order to increase maximum power efficiency conversion, there is a necessity maintaining fixed frequency which indeed generates high EMI issues at heavy loads. These limitations can be dramatically improved by Phase Shift Modulation (PSM) technique which is investigated in this thesis. PSM controlled technique is expected to not only improve the power supply efficiency at lighter loads. In this thesis, characteristics of LLC converter using phase control is analyzed systematically and compared with conventional frequency modulation technique. Using SIMPLIS simulations, PSM and FM techniques are compared and efficiencies are recorded. At higher loads, both FM and PSM controlled techniques exhibit maximum efficiency of 94.86%. The maximum efficiency of PSM LLC converter is observed at 97.47%. At lighter load conditions, efficiency of PSM LLC converter is observed as 91.66% and FM LLC converter as 82.8%. From simulation results, PSM technique has more controlled resonant tank currents with controlled conduction losses than conventional FM driven converter