Discrete Time Synchronization Modeling for Active Rectifiers in Wireless Power Transfer Systems

Active rectifiers in wireless power transfer systems exhibit many benefits compared to diode rectifiers, including increased efficiency, controllable impedance, and regulation capability. To achieve these benefits, the receivers must synchronize their switching frequency to the transmitter to avoid sub-fundamental beat frequency oscillations. Without additional communication, the receiver must synchronize to locally-sensed signals, such as voltages and currents induced in the power stage by the transmitter. However, the waveforms in the receiver are dependent on both the transmitter and receiver operation, resulting in an internal feedback between sensing and synchronization which prohibits the use of traditional phase-locked-loop design techniques. In this digest, a discrete time state space model is developed and used to derive a small signal model of these interactions for the purpose of designing stable closed-loop synchronization control. A prototype 150 kHz wireless power transfer converter is used to experimentally validate the modeling, showcasing stable synchronization.

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