There are two different approaches, namely conductive and inductive charging, to charge plug-in electric vehicles (PEVs). Conductive chargers have hard-wired connection between the power supply and the PEI for charging, and usually consist of a power factor correction (PFC) AC/DC rectifier followed by a DC/DC converter. Inductive charging or contactless charging does not use wired connection between the supply and the PEI for charging.
Conductive PEV chargers can be classified on the basis of the power level. Currently supported power levels are AC level 1 (L1, 1.92kW max.), AC level 2 (L2, 19.2 kW max.), and DC level 3 (L3, greater than 19.2kW). Depending on the location of the charger, conductive PEV chargers can be classified as on-board or off-board. The on-board PEI charger resides inside the PEV, and usually consists of two power stages: ac/dc stage for rectification of the grid voltage and power factor correction (PFC) and dc/dc stage for galvanic isolation and battery current/voltage regulation. This type of charger is also known as two-stage on-board charger. Off-board chargers are typically fast, high power DC charging solutions (L3 and 20 kW or more), where the PEI for charging is installed on an external charging infrastructure.
Inductive charging techniques use primary (transmitter) and secondary (receiver) coils for transferring power using the principle of magnetic induction. During its early stages, inductive chargers or inductive power transfer (IPT) systems used contactless stationary transformers. Currently, IPT systems consist of a resonant converter in order to transfer power through a large air gap and a rectifier to charge the battery. Inductive chargers are classified mainly based on the number of locations at which power transfer happens, magnetic structure, and the arrangement of the passive elements (L and C) within the resonant circuit. If power transfer happens only at discrete locations, the charger is termed as lumped or concentrated. On the other hand, if power can be transferred at multiple locations between the primary and the secondary coils, the IPT system is called as distributed system. Depending on the shape of the primary and the secondary, there are different IPT systems utilizing E, U, W or I shaped cores. In order to improve the magnetic coupling between the primary and secondary and also improve the power transfer capabilities, different arrangements of the passive elements within the resonant converter are possible.
In our research group, we have been studying, and developing innovative methods to:
Enhance charger efficiency over the wide-range of load powers,
Integrate various power electronic interfaces on the vehicle to substantially augment the power density of the converters and chargers.