Hybrid control of inductive power transfer charger for electric vehicles using LCCL-S resonant network in limited operating frequency range

In this paper, a hybrid control of IPT system is proposed in limited operating frequency range according to coupling coefficients. The coupling coefficient k and self-inductance of pad vary according to misalignment and vertical distance condition in inductive power transfer (IPT) system. Those variation cause change of output voltage and zero phase angle (ZPA) frequency. Proposed method enables the system to operate in zero voltage switching (ZVS) region close to ZPA frequency for low VA rating. Moreover, the excessive output voltage caused by k variation is also controlled by phase-shift control considering the voltage rating of power semiconductor. However the operable frequency of IPT system is restricted in standard of society of automotive engineers. Thus, phase-shift angle β should be calculated for ZVS operation under limited frequency condition because the frequency range of ZVS operation is reduced depending on the increase of β. The frequency range to operate system in ZVS region nearby ZPA frequency is deduced from β according to the coupling coefficient. Considering the limited frequency condition, the coupling coefficient range to apply the hybrid control is derived. The informative simulation and experimental results with a 3.3 kW IPT prototype are provided to verify the numerical analysis.