A method to measure the DC bias in high frequency isolation transformer of the dual active bridge DC to DC converter and its removal using current injection and PWM switching

The Dual Active Bridge (DAB) bidirectional dc to dc converter has gained a significant popularity in high voltage, high power due to its several topological advantages. Due to non-ideal switching characteristics and delays in gating, DC bias may be generated in the high frequency transformer leading to increased loses and eventually saturation and failure of the transformer and the switches. This paper proposes a simple way to measure the dc bias in the transformer flux using the primary and secondary winding current. A simple duty cycle modulation of the primary bridge is proposed to eliminate the DC bias in lower power topologies. This method has been verified through experimental results. For high power applications a current injection method through a separate tertiary winding is proposed, and verified such that the magnetizing current is supplied separately by the tertiary winding eliminating the possibility of transformer saturation.