Dual Active Bridge Series Resonant Converter with Pulse Modulation Z. Pavlović The main feature of the proposed modulation is the elimination of the switching losses of the active devices that allows operating the DAB SRC at high switching frequency (500 kHz, 1kW converter). Thus, the transformer design is more compact and the resonant inductor is entirely composed of the transformer leakage inductance; no external inductor is needed. Selected application for concept validation Project sponsored by load Electrical power architecture of the ¨More Electric Aircraft¨ The architecture and the bus voltage levels established by the military standard MIL-STD-704 240 V : 290 V range (270 V nominal) for higher voltage bus and the 22 V : 36 V range (28 V nominal) for lower voltage bus 1 kW 28 V – 270 V converter Bidirectional Paralleling capability Concept Goal: ZVS and ZCS operation of all the switches High switching frequency High efficiency M1=M4 M2=M3 Fixed ratio between input and output voltage t M5=M8=M6=M7 Bidirectional DC-DC transformer t LV side bridge Power transfer HV side bridge V1 V2 t nV1 M1 M3 vCR M5 M7 V1 Vb - + + + Va V1 iLR V2 - - Vtank t 2Vb -2Vb M2 M4 Power flow Vtank = V2-V1 M6 M8 case 1 case 2 ZVS and ZCS in both bridges! iLR t t0 t1 t4 t2 ZVS in the LV bridge Coss discharged to vCR/2 vCR much lower than Vb Reducing zero current interval to minimum Optimum point operation Load regulation by voltage difference Va - Vb Experimental results Experimental results with round wire transformer imag ETD49/25/16 core, N87 material Voltage waveform vDS2 affected by the TO220 case parasitic inductances ZVS, M2 @ 700 W output power High magnetizing current, imag! Higher conduction losses Lower transformer efficiency due to gap η = 85.9 % Far distant from the expected 93 %! Needed experimental validation with: DirectFET case style switching devices Improved layout (Q3D Extractor estimation loss: 11.6 W) Planar transformer ZVS, M6 CONCLUSIONS The proposed modulation is a good solution for applications in two stage, high power isolated converters. The main feature of this modulation is the elimination of the power transistor switching losses in both full-bridge sides of the converter, full ZVS and approximately ZCS are achieved in all the switches. This allows for higher switching frequencies to be adopted and, consequently, it allows reducing the size of the magnetic components. The proposed solution requires frequency variation to control the delivered power. Another control variable is the intermediate bus voltage, VC; by changing this voltage the control frequency band can be narrowed. Therefore, a non-isolated second stage is required to regulate the intermediate bus voltage while the proposed DAB SRC provides the electrical isolation and high voltage step.