A Study on CRM Switching for Low-Voltage ESSs to Improve Power Converter Efficiency

This study proposes and implements a DCHC-based CRM/CCM hybrid control with a switching-period limit condition to improve light-load efficiency in an AC-coupled ESS power converter. In grid-connected ESSs, the operating point continuously varies depending on load and grid conditions, and particularly in the light-load region, switching losses become relatively dominant, which can degrade overall system efficiency. Furthermore, in the medium-to-high-load regions, increased current ripple and peak current can lead to greater device stress and conduction losses, making it difficult to simultaneously ensure both efficiency and reliability across the entire load range with a single operating mode. To address this issue, this study proposes an approach that generates the current reference based on a PR controller and combines it with a DCHC-based current control structure to flexibly switch the control mode according to operating conditions. The proposed method is designed to balance the loss factors by reducing switching losses through CRM operation under light-load conditions, while concurrently employing CCM operation as the load increases to limit current ripple and device current stress. Consequently, this study demonstrates the potential for high-efficiency operation of the power converter system by improving the control strategy at the single-phase inverter stage in an AC-coupled ESS environment, and the validity of the proposed method is confirmed through simulation and experiments.