Simulation and Control of Dual Active Bridge Converter for Solid State Transformer Application

Abstract

Dual active bridge (DAB) converter is a symmetrical converter with identical primary and secondary bridges, capable of providing bidirectional power flow control. It has many advantages, such as electrical isolation, high reliability, ease of realizing soft-switching control and, moreover, having complete symmetry of configuration that allows seamless control for bidirectional power flow, - thus, supporting its candidature for use in the isolation DC-DC con-version stage of solid state transformer (SST). However, the main issue with the cascaded modular DAB converter is the power unbalance across the H-bridges. This occur due to the parameter mismatch, especially the leakage inductance of the transformer, the power may be unequal for each DC-DC converter, and therefore the current stress of them will not be the same. This paper presents a detail analysis, control strategy and simulation of cascaded three module DAB converter for use as DC-DC conversion stage of SST with a dedicated voltage and power balance controller meant to ensure smooth power transfer between the primary and secondary DAB converters, regulation of the low voltage DC (LVDC) link voltages to their reference values and to resolve any parameter variations in the high frequency transformer like leakage inductance. The entire system including the proposed control strategy was simulated in MATLAB® using Simulink® and other power system toolboxes. The effectiveness of the proposed control method was demonstrated on a three module DAB converter whose transformer leakage inductances were set to different values. The results show that the controller was able to balance both the LVDC link voltage and the power in each DAB.