Abstract

The forefront of EV battery charger research accentuates the imperative of refining power density attributes while concurrently elevating the efficiency standards of power conversion processes. The conventional EV battery chargers are developed with two cascaded power conversion stages. The first stage converts the AC voltage to a DC voltage by employing power factor correction (PFC). The second stage is an isolated DC-DC converter stage. These two-stages are interconnected by DC-link capacitors. This two-stage battery charger suffers from low overall efficiency due to two different power conversion stages. At the same time, the power density is limited due to the inevitable presence of intermediate DC-link capacitors. Generally, high-value electrolytic capacitors are selected for the DC-link. More importantly, the battery charger is placed close to the internal combustion engine under the hood in the case of a plug-in hybrid EV (PHEV), where the ambient temperature is more than 150 °C. The electrolytic capacitors are most susceptible to failure at high ambient temperature, thus the reliability of the conventional two-stage EV battery charger is low in a high-temperature environment. Moreover, the existing research on battery chargers is mainly based on voltage-fed power converter topologies, where the feasibility of current-fed power converter topologies has received very limited attention.
This thesis work proposes and studies a family of novel snubber-less current-fed isolated single-stage bidirectional power converters (AC-DC and DC-DC) for multifunctional EV battery charging (G2V, V2G, and V2V) applications to address the shortcomings of the conventional two-stage battery chargers. The proposed modulation strategy and control technique are demonstrated for promising soft-switching operation of all semiconductor devices with bidirectional power flow capability. These converters enable zero current commutated (ZCC) without any active clamp circuit or passive snubbers, which significantly reduced switching losses, footprints, and cost. The converters steady-state operation and design equations are reported in detail. The simulation results from PSIM 11.04 software and the experimental results from 1.5 kW proof-of-concept laboratory hardware prototypes are provided in order to validate the report analysis, design, and performance.