A Dual Active Bridge DC-DC Converter for Automotive Applications

Abstract

In the past years electric cars have been rapidly taking market share in the automotive industry. Stimulated by their sustainable image and due to large investments in the charging infrastructure, the electric automobile has gained popularity in the field of research. Many papers are written on a variety of power converters inside the cars to interface between batteries, chargers and motors. Usually, these converters are made as universal as possible, in order to suit the needs of many different vehicles. As a result, they are capable of operating at wide voltage and power ranges, often at the cost of weight or efficiency. The Dutch electric car startup Lightyear aims at a completely different strategy. Their car with integrated solar panels is designed with one goal: increasing efficiency. For that reason, all components have been reconsidered and, if sufficient gains in efficiency can be achieved, completely redesigned. One of these components is an isolated bidirectional DC-DC converter that ensures power transfer from the solar panels to the main battery. In this thesis that DC-DC converter is developed. Special focus is put on maximizing the efficiency to ensure as much energy from the solar panels can be used to power the car. First, all possible topologies that meet the requirements are investigated and the best option is selected. Then, a script is developed that configures the power stage of the converter using a provided list of components. The implementation with the highest average efficiency over the operating range is automatically selected. After that, alternative modulation strategies are investigated, aimed at reducing the conduction losses of the converter. Finally, a controller is created and validated for the designed converter. The result of the presented work is an isolated bidirectional DC-DC converter, achieving an average power stage efficiency of 98.1 % over a wide range of input voltages and output voltages at a constant power output.