| MS Seminar

Name of the Speaker: Mr. Satyam Kumar (EE22S051)
Guide: Dr. Kamalesh Hatua
Online meeting link: http://meet.google.com/teb-xhty-fes
Date/Time: 20th June 2025 (Friday), 11:00 AM
Title: A Dual-Loop Frequency Control Design for Dual Active Bridge Based CLLC Resonant Converter.

Abstract :

Resonant converters have become a preferred solution in various power electronics applications, including battery charging, uninterrupted power supplies, and microgrids, due to their higher efficiency, power density, and reliable soft switching performance. The dual active bridge (DAB) and DAB-CLLC resonant converters are promising topologies for bidirectional power flow applications. DAB has limited soft switching and is inefficient under light load conditions. DAB-CLLC resonant converter adds a resonant inductor and capacitor to the LLC topology, allowing bidirectional power flow while retaining the characteristics of the LLC converter.

The small-signal model of DC-DC converters is developed using the averaging concept, which is commonly applied to pulse width modulated (PWM) converters. However, this approach is not suitable for resonant converters because many of their state variables include AC components at the switching frequency, resulting in an inability to capture the system dynamics accurately.

This work proposes a unified small-signal model of a DAB-CLLC resonant converter, considering the internal phase shift in the primary bridge, the external phase shift between the two bridges, and the switching frequency as the model parameters. The extended describing function (EDF) concept and fundamental harmonic approximation (FHA) based equivalent circuit simplifications are utilized to arrive at a third-order model of the converter, which provides all necessary control transfer functions. The control architecture features a dual-loop setup that comprises an internal current and an external voltage loop. The external loop regulates the output voltage by generating a reference for the current loop, which adjusts the switching frequency accordingly. This strategy ensures stable operation across a wide range of line and load regulations with narrow variations in switching frequency, offering tight current and voltage regulation, along with improved transient response.

The proposed modeling and control strategy of DAB-CLLC is validated in a 400 V/200 V, 2 kW hardware prototype.