CONTACTLESS POWER TRANSFER FOR ELECTRIC VEHICLE CHARGING APPLICATION Master of Science Thesis

Contactless Power Transfer (CPT) is the process of transferring power between two or more physically unconnected electric circuits or devices by means of magnetic induction. The potential application of CPT can range from power transfer to low power home and office appliances to high power industrial systems. Medical, marine, transportation, battery charging applications where physical connections are either dangerous or impossible or inconvenient are all prospective candidates for use of this technology. This thesis mainly concentrates on development of fundamental theory of CPT and application of CPT technology in achieving driving range extension of Electric Vehicles (EV). The work in this thesis can be divided into three broad categories which are, analysis and development of design criteria of a CPT system, experimental and practical implementation, and range extension studies with on-road charging of EVs using CPT technology. The main components of a CPT system are specially constructed windings separated apart by a large air gap across which power transfer occurs. These windings form what we call as CPT transformer. In order to achieve efficient power transfer through this large air gap between the windings of the CPT transformer, principle of resonance is used. To increase power transfer capability and to reduce VA rating of the CPT system, capacitive compensation is used in both primary and secondary winding of the CPT transformer. In this regard, Series-Series (SS), Series-Parallel (SP), Parallel-Series (PS) and Parallel-Parallel (PP) topologies are analysed and design criteria for efficient and stable operation are presented. Constant current mode and constant voltage mode operation of SS compensated system are discussed and it is concluded that SS compensation topology is the most suitable topology for battery charging application. Power electronic requirements for efficient power transfer are investigated and it is concluded that use of active rectifiers in the output stage provide more controlling options and higher power transfer efficiency. To test the many analytically deduced design considerations and feasibility of a CPT system with respect to the efficiency of power transfer, an experimental setup is built. The efficiency of power transfer was measured to be close to 91%. But since DC power is required at the output to accomplish battery charging process, full bridge diode rectifier is employed in the output stage causing additional losses in the system which brings down the overall efficiency of system to 83.2%. To reduce losses in the rectifier stage, use of active rectifier is recommended. …