Four Switch Buck/Boost Converter for DC Microgrid Applications

This paper describes a bidirectional, non-inverting, and non-isolated DC-DC converter, which connects different electronic devices up to a maximum operational voltage of 60 V. Special considerations about the transition between step-down and step-up are made and have been implemented in a fully functional prototype. The converter can operate in a stand-alone mode or can work in parallel with a DC microgrid. Therefore an algorithm was implemented to cooperate with a droop-controlled bus voltage. The paper issues an implementation of a novel modulation scheme and gives a comparison to existing schemes. A steady-state analysis shows the way of charging the bootstrap capacitor. Some effects on the length of the bootstrap interval are evaluated. Additionally the advantage of using a burst mode implementation is shown. Another important aspect in this paper is the control and design of the power electronic circuit of the converter itself. A prototype with 97.5% peak efficiency and 300 W nominal power was built. The theoretical analysis is verified by electrical measurements of the converter.