Evaluation of advantageous modulation methods for a dual active bridge converter with a wide output voltage range

MSc thesis of Coen Straathof

In this thesis two new modulation methods are proposed for a wide output voltage range dual active bridge (DAB) converter for bidirectional EV charging application. The objective of the proposed 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 a fixed switching frequency, while the second achieves full ZVS operation using a variable switching frequency combined with alternative charging profiles. 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 voltage range of 640 to 840 V, and an output voltage range from 250 to 1000 V, to ensure compatibility with various types of EV’s.  Measurements done on the 11 kW prototype confirm that the improvements in ZVS are achieved compared to a peak current optimization found in literature. These improvements in ZVS of the proposed modulation method also result in increased efficiency compared to the peak current optimization, especially in the low-power operating regions.