Implementation of the Constant Current and Constant Voltage Charge of Inductive Power Transfer Systems With the Double-Sided LCC Compensation Topology for Electric Vehicle Battery Charge Applications

Abstract

When compared to plugged-in chargers, inductive power transfer (IPT) methods for electric vehicle (EV) battery chargers have several benefits, such as greater convenience and higher safety. In an EV, the battery is an indispensable component, and lithium-ion batteries are identified as the most competitive candidate to be used in EVs due to their high power density, long cycle life, and better safety. In order to charge lithium-ion batteries, constant current/constant voltage (CC/CV) is often adopted for high-efficiency charging and sufficient protection. However, it is not easy to design an IPT battery charger that can charge the batteries with a CC/CV charge due to the wide range of load variations, because it requires a wide range of variation in its operating frequency, duty, or phase-shift. Furthermore, zero phase angle (ZPA) condition for the primary inverter cannot be achieved over the entire charge process without the help of additional switches and related driver circuits to transform the topology. This paper proposes a design method that makes it possible to implement the CC/CV mode charge with minimum frequency variation during the entire charge process by using the load-independent characteristics of an IPT system under the ZPA condition without any additional switches. A theoretical analysis is presented to provide the appropriate procedure to design the double-sided LCC compensation tank which can achieve both CC and CV mode charge under ZPA condition at two different resonant frequencies. As a consequence, the proposed method is advantageous in that the efficiency of compensation tank is very high due to achieving the perfect resonant operation during the entire charge process. A 6.6-kW prototype charger has been implemented to demonstrate the feasibility and validity of the proposed method. A maximum efficiency of 96.1% has been achieved with a 200-mm airgap at 6.6 kW during the CC mode charge.