An Insight into the Dynamics of a Dual Active Bridge

TL;DR

This paper analyzes the zero dynamics of the Dual Active Bridge converter, revealing their impact on system stability and controller design, with a focus on stability under various load conditions.

Contribution

It provides a detailed state space and harmonic approximation analysis of the DAB system, highlighting the stability characteristics of zero dynamic states and their influence on control strategies.

Findings

System is stable for constant voltage operation across all power levels.

System becomes unstable under constant power load near maximum power.

Transformer winding currents are stable regardless of operating conditions.

Abstract

This paper aims at analyzing the effect of the zero dynamics of the Dual Active Bridge Isolated Bidirectional dc-dc converter (DAB) on the dynamics of the complete DAB system. It also explains its influence on controller design for the DAB system. In carrying out these analyses, the state space model of the DAB, as well as the first harmonic approximation (FHA) of the model are derived. The ZVS and the stability analysis of the system are undertaken based on the FHA model of the system. The system is shown to be stable for a constant output voltage operation for the entire power range while it is unstable for the constant power load (CPL) operation for load demands close to the system maximum power. It is also shown that the transformer winding currents are part of the zero dynamic states and are always stable regardless of the operating conditions of the system.