nonNonlinear Output Characteristic of DAB Converter caused by ZVS Transition

Inhalt:
In order to incorporate renewable energies modern power converters with high efficiency and power density are essential. Resonant power converter topologies are implemented due to the reduction of switching losses, yielding higher switching frequencies which ultimately reduce the size of the magnetic components. Resonant topologies are known for several decades and main goal remains to optimize them in terms of efficiency and dynamics. It is essential to implement dynamic and robust control schemes over a wide operating range. In order to guarantee robust control the transfer function of the plant has to be known. In this paper the plant of a Dual Active Bridge Converter (DAB) was measured using a Bode 100 from Omicron LAB. A nonlinear phenomenon in the output characteristic can be observed, when a transition from soft switching (ZVS) to hard switching occurs. In this region, the gain of the transfer function of the plant drops significantly, which leads to a high drop in bandwidth and thereby decreasing the dynamics of the converter. Furthermore a technique is described by which the nonlinear region can be cancelled.