Design Recommendations Considering Charging Pads’ Self-Inductance Variation With LCC–S and LCC–LCC Compensation Based IPT Chargers in Low Clearance EVs

Abstract

Inductive Power Transfer (IPT) based Electric Vehicle (EV) charging systems practically experience self-inductance variation in charging pads with air-gap, especially for low ground-clearances. Conventional design model ignores these variations, resulting in poor sizing and performance. This paper presents a comprehensive theoretical modelling and evaluation of system’s performance considering self-inductance variation for LCC-Series (LCC-S) and LCC-LCC type compensation. The work begins by examining various types of charging-pads with similar design-specifications, and finds circular-pad to exhibit least self-inductance variation. Subsequently, through extensive theoretical analysis, several contour-plots are derived, depicting variation of output voltage/current, output power, input Volt-Ampere (VA), input power-factor, and VA of compensation elements with various load and coupling-coefficient, for both the conventional and proposed models systematically. It is shown that proposed model provides accurate design recommendations over conventional model on various critical parameters, including optimal load, charging-time, dc-link voltage, maximum gain of secondary-side dc-dc converter, and VA ratings of the input and compensation elements. For example, proposed model predicts that a 7% increase in self-inductance with LCC-S type compensation (designed for 5kW) leads to 36.4% reduction in maximum output power, requiring compensatory increases in dc-bus voltage by 25.3% and input VA rating by 34.47%. The proposed model is validated experimentally.