A series compensation enabled ZVS range enhancement of a dual active bridge converter for wide range load conditions

A novel ZVS range control technique using an auxiliary series transformer for a Dual Active Bridge (DAB) DC-DC converter is proposed. The auxiliary transformer fed with an additional H-bridge at the secondary, adds a phase-controlled voltage in series with the main converter voltage either at the primary or secondary. This addition helps to control the reactive power flowing through the main converters of the DAB. Hence the power-factor of the main converters can be controlled in such a way that the DAB can maintain ZVS even at light loads. Also it operates at minimum reactive power at higher loads while it still operates in ZVS and thus results in higher efficiency on both extremes. The series transformer carries dominantly reactive power since the compensation angle is most often near quadrature. For medium/high power DAB, the cost and additional losses associated with the series circuit can be neglected due to significant efficiency improvement. The external inductor can be eliminated by using a series transformer designed with enough leakage inductance hence saving the additional magnetic cost. The proposed technique is validated with simulations followed by experiment on a hardware implementation. The technique is also simulated for a medium voltage DAB system with actual switching and magnetic data to bring out the efficiency improvements.