Zhou, Yong (2016-04). A New High Power Density Modular Multilevel DC-DC Converter with Localized Voltage Balancing Control for Arbitrary Number of Levels. Master's Thesis.
Thesis
A new modular multilevel DC-DC converter (MMC) with high power density and simplified localized voltage balancing control is proposed. Converter building block and controller module are built separately considering level propagation for each row. In the proposed configuration, the converter building blocks with the same power handling capability are connected in parallel in each row. This leads to a triangular structure from top to bottom. Converter building block consists of integrated H-bridge and mutually coupled inductors whose total current is nearly ripple free. These features are shown to reduce the voltage ripple of DC-link capacitors significantly, leading to a smaller capacitance and size. An optimized control algorithm with voltage feedback PI loop is proposed, resulting in the elimination of current sensors. Thus, the overall system complexity is reduced and the cost-effectiveness is increased. Significant ripple reduction of the inductor current and capacitor voltages is observed based on the simulation and prototype of a 5-level system. With a fully modular power stage module and localized control module, a system which has arbitrary number of level can be built by stacking the modules, thereby contributing to enhanced system redundancy.
