Evaluation of advantageous modulation methods fora dual active bridge converter with a wide outputvoltage range

Abstract

In this thesis two new modulation methods are proposed for a wide output voltage range dualactive bridge (DAB) converter for bidirectional EV charging application. The objective of theproposed modulation method is to maximize the number of ZVS events over the operating range,while maintaining low current stress. The first modulation method achieves this with fixed aswitching frequency, while the second achieves full ZVS operation using a variable switchingfrequency combined with alternative charging profiles. The design of the modulation method isdone through an analysis of the operating modes and the ZVS behaviour of the DAB converter.To verify the improvements to the ZVS behaviour of the proposed modulation method, the modulation method is implemented in a simulation and on an 11 kW prototype with an input voltagerange of 640 to 840 V, and an output voltage range from 250 to 1000 V, to ensure compatibilitywith various types of EV’s. A control system and a transient mitigation method are designedto facilitate the experimental verification. The proposed modulation method is compared to apeak current optimization for the DAB converter found in the literature. Measurements doneon the 11 kW prototype confirm that the improvements in ZVS are achieved. These improvements in ZVS of the proposed modulation method also result in increased efficiency comparedto the peak current optimization, especially in the low-power operating regions. The full powerefficiency over the entire voltage range of the peak current optimization, the proposed fixedfrequency, and the proposed variable frequency modulation are 97.895%, 97.879% and 97.964% respectively.