Measuring the Q-factor of IPT Magnetic Couplers

Accurately predicting the efficiency of an inductive power transfer based electric vehicle charger is essential for an optimal design. Typically, small-signal methods such as an LCR meter, impedance analyser or network analyser are used to determine the quality-factor (Q-factor) of the primary and secondary magnetic couplers. However, these methods fail to emulate the high VA stress and temperature a magnetic coupler is subjected to under normal operation. As such, this paper presents an alternate, frequency-domain based method to measure the large-signal Q-factor of a magnetic coupler. The proposed method eliminates the need for any phase information and merely requires static measurements. Experimental results verify the accuracy of the proposed method and also show a Q-factor variation of almost 17% between a small-signal and large-signal reading.