Optimum Metal Object Detection (MOD) Sensing pattern design for Self-inductance based MOD system using parallel-resonant circuit

Abstract

A optimum Metal Object Detection (MOD) sensing pattern for self-inductance based MOD system using parallel-resonant circuit is proposed. The proposed MOD sensing pattern is placed on transmitting (Tx) pad of an electric vehicles (EVs) inductive power transfer (IPT) system and it is composed of several loop coil sets. Each loop coil set is constituted of two spatially bilateral symmetric loop coils and two loop coils are connected in series with opposite polarity to cancel out a induced voltage on the loop coils which is induced by Tx coil current. In addition, every loop coils are with same size and same number of turns to achieve similar inductance for constant resonance condition. Through simulations and experiments, each loop coil sets’ induced voltage and inductance is measured and a induced voltage variation rate is calculated when position error between Tx pad and the MOD sensing pattern happens. A prototype of proposed MOD sensing pattern is fabricated and the induced voltage of each loop coil sets becomes within 0.31 Vrms when 85 kHz, 10 Arms Tx current flows. The maximum inductance difference rate of loop coil sets is +1.5 % and -0.9 %, compared to the median inductance and the induced voltage variation rate due to the position error is 8.32 % and 59.16 % for 1 mm and 10 mm position error, respectively, which is twice less than conventional MOD sensing pattern.