Modeling and efficiency-based control of interleaved LLC converters for PV DC microgrid

In this paper, the interleaved LLC resonant converter with zero-voltage switching (ZVS) is investigated to form the PV module with series-connected PV panels in the dc microgrid system. The interleaved LLC resonant converter is analyzed as a whole and a small signal model of it is proposed based on Extended Describing Function (EDF). According to the proposed model, the analytical form of open-loop control-to-output transfer function and corresponding frequency response are obtained. Furthermore, based on the system efficiency model, a novel two-stage efficiency-based control scheme is proposed to achieve the stability and optimize the efficiency. The first stage is the phase-shedding control for the single PV module efficiency optimization and the second stage is the central controller for the multi-module system efficiency improvement. Two 2kW rated interleaved LLC converters connected into 270V DC power system verifies the feasibility of the proposed model and control strategy.