Open AccessState variable derivation with numerical approach and efficiency optimisation method for phase‐shift LLC converters under wide voltage‐gain range
Author(s) -
Liu Shuo,
Zhang Fanghua
Publication year - 2019
Publication title -
iet power electronics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.637
H-Index - 77
eISSN - 1755-4543
pISSN - 1755-4535
DOI - 10.1049/iet-pel.2018.5213
Subject(s) - converters , range (aeronautics) , control theory (sociology) , variable (mathematics) , voltage , state variable , state (computer science) , electronic engineering , mathematics , computer science , engineering , physics , electrical engineering , algorithm , mathematical analysis , thermodynamics , control (management) , aerospace engineering , artificial intelligence
The phase‐shift modulation (PSM) brings wider voltage‐gain range compared with pulse‐frequency modulation (PFM) control to the LLC resonant converter in particular occasions such as battery charging converters. Current researches have less discussion about the converter current transfer gain especially at low voltage‐gain range. The switching frequency is much increased and high circulating current occurs under low voltage range, which brings large error in the fundamental harmonic approximation analysis. This work has proposed a numerical derivation method to derive the accurate transfer gain for LLC converters with PSM + PFM control. The accurate model and equations for resonant variables are built by the static state‐plane analysis. With the help of the iteration algorithm, numerical solutions are got for the resonant variables. The output current gain and the loss estimations are acquired and discussed at each operating point. The results also indicate that there are multiple solutions for the control variables, switching frequency and phase‐shift angle, at the same output point. The loss optimisation method is proposed and the losses on the switches are optimised by using lower switching frequency and greater phase angle. The simulation approach and the experiment prototype test have both proved the theoretical calculations and the optimisation results.