457 Dynamic Modeling of the Dual-Active Bridge Topology for High-Power Applications Georgios D. Demetriades, Hans-Peter Nee * ABB AB Corporate Research 721 78 Västerås-SWEDEN email: georgios.demetriades@se.abb.com * Royal Institute of Technology-KTH Electrical Machines and Power Electronics Teknikringen 33- SE-100 44 Stockholm-SWEDEN email: hansi@kth.se Abstract—In the present paper the staedy-state and the dynamic behavior of the Dual-Active Bridge topology have been studied. The small-signal model of the converter has been derived and theoretical and experimental results are presented. The Dual-Active Bridge is an attractive solution for high- power applications where a bi-directional operation is needed. I. INTRODUCTION The Dual-Active Bridge (DAB) topology which was first presented by Kheraluwala et.al in [1], [2], and [3] consists of two switch-mode active bridges, one operating in the inversion mode and the other in the rectification mode. The ac-terminals of the bridges are interconnected by means of a high-frequency transformer, enabling power flow in both directions as shown in Figure 1. Each bridge can be controlled to generate a high-frequency square-wave voltage at its transformer terminals ( 0 , V V dc ± ± ). By incorporating a controlled amount of leakage inductance into the transformer the two square waves can be appropriately phase-shifted to control the power flow from one dc-source to the other. A bi- directional power transfer can be achieved. Power is delivered from the bridge generating the leading square wave. Maximum power transfer is achieved at a phase shift of 90 degrees. In a wide load range all the devices are operated at ZVS and therefore high efficiency is obtained. The DAB can operate with bi-directional power flow in both step-up and step-down operation II. STEADY-STATE OPERATION AND ANALYSIS The commutation sequence starts by assuming that the inductor current is flowing in the negative direction i.e. through the devices + A D , 3 s D and 2 s D as shown in Figure 1(a). While the current is flowing through diode + A D the voltage across the switch + A T is zero. The transistor + A T is switched on at zero voltage and eventually the current reverses and starts flowing through the transistor and through the diodes 1 s D and 4 s D as illustrated in Figure 1(b) and Figure 1(c). At a certain instant the transistor + A T is turned off and the energy stored in the inductance is transferred to the snubber capacitors by resonance. The snubber capacitor, which is placed across + A T , will take over the current, and the transistor turn-off occurs under ZVS conditions. Simultaneously, the snubber capacitor, which is connected across the transistor - A T , will be discharged and will eventually force the diode - A D to be forward-biased. Therefore, the inductor current starts flowing through the diode - A D and diodes 1 s D and 4 s D , as shown in Figure 1(d). Similarly, the transistor - A T is turned on at ZVS as shown in Figure 1(e) and Figure 1(f), and the commutation sequence will be repeated as above. dc V + dc V - + A T - A T + A D - A D s C s C σ L F T Ideal / 1 s T 2 s T 1 s D 2 s D 3 s T 4 s T 3 s D 4 s D C R (a) dc V + dc V - + A T - A T + A D - A D s C s C σ L F T Ideal / 1 s T 2 s T 1 s D 2 s D 3 s T 4 s T 3 s D 4 s D C R (b) dc V + dc V - + A T - A T + A D - A D s C s C σ L F T Ideal / 1 s T 2 s T 1 s D 2 s D 3 s T 4 s T 3 s D 4 s D C R (c) dc V + dc V - + A T - A T + A D - A D s C s C σ L F T Ideal / 1 s T 2 s T 1 s D 2 s D 3 s T 4 s T 3 s D 4 s D C R (d) dc V + dc V - + A T - A T + A D - A D s C s C σ L F T Ideal / 1 s T 2 s T 1 s D 2 s D 3 s T 4 s T 3 s D 4 s D C R (e) Figure 1:The equivalent circuits for each mode of operation 978-1-4244-1668-4/08/$25.00 ©2008 IEEE