Steady-State Time-Domain Analysis of LLCL Resonant Converter

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Anand, Tansha
Resonant Converter , LLCL , Time-Domain Analysis
This thesis presents a new LLCL resonant converter topology which is capable of providing zero voltage switching of MOSFET switches for a wider range of operating frequency as compared to conventional LLC resonant converter topology. The proposed topology (LLCL) is a modified form of conventional LLC resonant converter topology where an additional inductor is connected in parallel with the LLC resonant tank on the input side. For the analysis of a series resonant converter, frequency domain modelling (FDM) is usually sufficient due to the limited modes of operation. However, for a three or more element resonant tank, multiple modes of operation arises due to which FDM is restricted for analysis for operation below resonant frequency when the circuit enters in freewheeling mode otherwise known as Discontinuous Conduction Mode (DCM). Hence, a detailed time domain analysis is presented describing the steady state behavior of the circuit under continuous and discontinuous mode of operation. A comprehensive analysis of LLCL type converter is performed and compared with that of a conventional LLC resonant converter which demonstrates the benefits obtained by the proposed topology. Voltage gain and resonant tank component current stress is derived, as a function of various circuit parameters such as the ratio of inductors and normalized relative frequency, to assist in the design trade-offs. The time domain analysis is verified with simulation studies using PSIM 11.0.
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