PWM Plus Phase-Shift Control For Dual Active Full-Bridge DC-DC Converter

Renewable energy havs the feature of intermittence and randomness, energy storage devices arealways integrated with the renewable energy generation units to provide stable and continuous power.In general, a bidirectional dc-dc converter is required to control bidirectional power transfer of theenergy storage devices. The dual active full-bridge bidirectional (DAB) dc-dc converter is ideallysuited for high power applications because of low voltage and current stresses for power devices,symmetric structure and realization of zero-voltage-switching (ZVS). This thesis is dedicated toproposing the control strategy of the DAB converter to improve the overall efficiency over the wideinput or wide output voltage range.The operating principle and characteristics of the DAB converter with phase-shifted control isfirst analyzed in this thesis, and the ZVS lost at light load is explained. Based on this, the operatingprinciple and characteristics of the DAB converte with single-side PWM plus phase-shifted control isanalyzed, and an optimal single-side PWM plus phase-shifted control is proposed to realize ZVS overthe whole load range while greatly reduce the root-mean-square (RMS) current. To further reduce thecirculation loss at light load, the characteristics of the DAB converter in dual-side PWM plus phase-shifted control is analyzed and a hybrid PWM plus phase-shifted control is proposed, in which, theRMS current is minimum and the DAB converter achieves critical ZVS at light load.A3kW prototype with360V input and216V~360V output voltage is built and tested in the labto verify the feasibility of the proposed optimal single-side PWM plus phase-shifted control andhybrid PWM plus phase-shifted control. The experimental results show that the overall efficiency isimproved with the two proposed control and the RMS current at light load with hybrid PWM plusphase-shifted control strategy is reduced compared to that with optimal single-side PWM plus phase-shifted control strategy. However, the efficiency with hybrid PWM plus phase-shifted control is lowerthan that with single-side PWM plus phase-shifted control due to the critical ZVS at light load.