Bi-Directional AC-DC Converters for Electric Vehicles
Koushki Foroushani, Behnam
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Transportation industry typically rely on conventional fossil energy resources such as petroleum. This source of energy, however, is neither renewable nor emission-free. Nowadays transportation sectors are replacing their conventional internal combustion vehicles by Electric Vehicles (EVs). Much research efforts have been devoted to improve EVs and EV infrastructure. EV battery and thus the on-board EV battery charger are among the most important parts of an EV. There are specific requirements for EV chargers in terms of weight, safety, reliability, cost and efficiency. Meeting power quality standards imposed by grid and operation with wide range of DC voltage and current are among the other requirements. In addition, EV battery chargers can be used for ancillary services and also feed the power back to the grid in peak hours and operate like a distributed energy storage for grid. This requires bi-directional power flow through the charger. One problem associated with single-phase on-board EV battery chargers, is the low frequency power ripple that reflected in the DC-side. This double frequency ripple causes extra heat and reduces the life span of the battery. Another issue is the reliability reduction due to the use of unreliable electrolytic capacitors. This thesis proposes a family of on-board Single-stage bidirectional battery chargers to handle a wide range of active and reactive power control. Single-stage power conversion is chosen due to lower component count, better efficiency and higher power density. All power converter topologies proposed in this thesis are operated under zero voltage switching (ZVS). In proposed converter topologies electrolytic capacitors are removed, while the battery current maintained DC and free from low frequency ripple. The innovative resonant control schemes enable the proposed topologies to successfully perform complicated tasks of optimization, power transfer, cancellation of low frequency current ripple on the battery-side and maintaining ZVS for all the switching instants. The proposed dynamic controller uses a novel variable duty-cycle and variable phase-shift control to achieve the functionalities of the resonant circuit controller. A 1kW experimental setup with AC voltage of 230V and DC voltage of 200V-400V is developed to verify the viability of the proposed battery charging systems.