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.