A novel analog controller design scheme for LLC resonant converter used in battery charging application

Abstract

A new generation of batteries must be charged according to the charging curves recommended by battery manufacturers. For high reliability, low cost, high speed, and pulse by pulse protection ability, the controller of these chargers are commonly designed by analog circuits. Analog controllers can be implemented by internal circuits of analog controller ICs with additional passive elements. This paper proposes a controller design approach for battery charger applications with an LLC converter. The proposed approach stands on a novel method for applying the well-known least-squares (LS) identification method for designing the classic controller with changing the identification problem to the design problem. Compared with other methods, the proposed approach benefits from design a controller with desired structure and desired performance, simultaneously. Here, modelling of LLC converter has been carried out by the first harmonic approximation (FHA) method. For controller design, the linear model has been extracted by linearizing the non-linear FHA model. In addition, for providing the reduced switching losses and increased efficiency, the passive elements of the resonance tank and isolation transformer ratio have been designed to operate the converter in the zero-voltage switching (ZVS) region. To verify the controller and designed converter, some simulation and experimental results are provided.