An I/Q Phase Detection-Based Harmonic- Insensitive Phase Synchronization Method for Bidirectional Wireless Power Transfer System

In bidirectional wireless power transfer (BWPT) systems, the secondary-side converter must be synchronized with the primary-side converter for stable power transmission, which is often done by detecting the phase of the secondary-side resonant current and adjusting the secondary-side excitation voltage to be in synchronization with the current. However, the resonant current often contains nonnegligible harmonics, which may cause large error in the detected phase. To solve the problem, this article proposes an in-phase/quadrature (I/Q)-based phase synchronization method for BWPT system, which is insensitive to the harmonics and does not require complicated signal processing circuit or digital signal processing technique. The basic characteristics of the BWPT system are introduced with the harmonic characteristics analyzed. The phase synchronization method is proposed, in which the resonant current signal is equivalently multiplied with a pair of virtual quadrature five-level staircase signals for phase detection. Certain orders of harmonics in the five-level staircase signals are eliminated to reduce the influence of current harmonics. The influence of harmonics on phase detection error of the proposed method is analyzed. The experimental results show that the phase-lock error with the proposed method is small under various conditions, and the proposed method has a fast transient response.