Design and implementation of an inductive power transfer system for wireless charging of future electric transportation
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The motivation of this thesis was to formulate clear design guidelines for fabrication and control of an efficient series-series resonant inductive power transfer (SS-RIPT) system for electric vehicle battery charging application. In meeting this objective, several critical deficiencies about the field of RIPT based EV chargers specific to stationary charging have been solved. Firstly, to increase the tolerance to misalignments, use of an unsymmetrical coil pair for the charger has been proposed. An unsymmetrical coil pair, in which the outer diameter of the primary and the secondary coils are kept equal, whereas the inner diameter of the secondary is kept larger compared to the primary counterpart gives the best performance in misalignment conditions. By employing this unsymmetrical coil-pair, a charging pad which shows the horizontal tolerance to misalignment equal to 71% of the pad diameter has been presented. Secondly, a very simple yet novel analytical design procedure has been submitted, adopting which, eliminates the bifurcation issue for the entire range of load and coupling variation and therefore requires no sophisticated control. Finally, a simplified mathematical model of SS-RIPT system has been proposed for primary side control of output voltage and current. All the proposed theories and analysis have been verified by a 3.6 kW prototype of the SS-RIPT based charger fabricated in the lab. A DC-DC efficiency of 91% for rated load condition is achieved for the designed charger. For partial load conditions (less than 50% of the rated load), the efficiency is 87%.