An Optimal Variable Frequency Phase Shift Control Strategy for ZVS Operation Within Wide Power Range in IPT Systems

In inductive power transfer (IPT) systems, zero-voltage-switching (ZVS) operation within wide power range is an urgent requirement to improve system efficiency and reduce electromagnetic interference. The combination of phase shift (PS) control and variable frequency control is usually adopted to realize ZVS operation. However, in inductor-capacitor-capacitor-series (LCC-S) systems, the abovementioned hybrid strategy cannot be used directly due to nonnegligible harmonics, which result in detection difficulties or imprecise calculation of turn-off current. To solve this problem, this article proposes an optimal variable frequency phase shift (VFPS) control strategy for LCC-S systems to realize ZVS operation within wide power range. The universal harmonic-considered time-domain model of LCC-S system is deduced, and thus, the switching-moment current of power switches can be calculated accurately. Based on this value, an optimal working trajectory for ZVS operation with minimum frequency variation is presented. Finally, a 2.2-kW IPT prototype is built up to verify the universality of the deduced model and the validity of the proposed optimal VFPS control. Compared with PS control and the VFPS control based on fundamental-harmonic-approximation method, the systems realizes ZVS operation under wide power range with efficiency increase of 2.6%-6.9% and 0.8%-8.8%, respectively, and a peak efficiency of 96.4% is achieved.