Three-Phase Unfolding Based Soft DC-Link Converter Topologies for AC to DC Applications

Battery electric vehicles (BEVs) and plugin hybrid electric vehicles (PHEVs) are more efficient than internal combustion-based vehicles. Adaption of EVs will help reduce the carbon emissions produced by the transportation sector. The charging infrastructure has to grow at a rapid pace to encourage EV adaption. Installing higher capacity fast chargers will help alleviate the range anxiety of battery electric vehicle customers. More public charging stations are required for the full adaption of EVs. Utility power is distributed as ‘alternating current.’ A battery requires ‘direct current’ (DC) source to charge it. Hence a power converter that converts AC source to DC source is required to charge an electric vehicle battery. Public transportation is another sector that is adapting electric vehicles at a fast pace. These vehicles require more power to operate and hence have huge battery packs. These vehicles require ultra-high-power charger to keep the charging time reasonable. A 60 Hz stepdown transformer is required at the facility to use the power. The cost and time to install this heavy transformer will inhibit the setting up a charging station. Power converters than can connect to medium voltage directly will eliminate the need for the step-down transformer saving space and cost. Commercially available state-of-the-art fast charging converters are adapted from general purpose commercial and industrial application rectifiers. The efficiencies of these converters tend to be lower (around 94%) due to the two-stage power conversion architecture. All the power that flows from the AC utility grid to charge the battery will be processed and filtered through two power conversion stages. Due to the anticipated increase in demand, there is a renewed interest in developing power converter topologies specific to battery charging applications. The objective here is to develop cheaper and compact power converters for battery charging. This dissertation proposes an innovative quasi-single stage power converter topologies for battery charging applications and direct medium voltage connected converters. The proposed topology fundamentally can achieve higher efficiency and power density than the conventional two-stage based converters. Only one stage requires filtering and incurs power conversion losses. Control burden is usually higher for single stage topologies. Innovative control approaches are presented to simplify the control complexity.