FPGA-Based Frequency Tracking Strategy with High-Accuracy for Wireless Power Transmission Systems

Aiming at the problem of the unavoidable phase-tracking error of the wireless power transfer (WPT) system caused by dead time, MOSFET drive and other factors, this paper proposes a frequency-tracking method with high accuracy based on a Field-Programmable Gate Array (FPGA) to track the current and voltage phase differences on the transmitting side. Compared with fixed-phase systems, the proposed method accurately controls the phase difference between voltage and current. It detects the phase difference in real time and adjusts the phase compensation angle dynamically to ensure that the system always operates under the optimal zero-voltage switching (ZVS) state, which reduces system loss. Experiments under operating conditions of varying transmission distances and load resistance values are carried out on a prototype. The experimental results show that the proposed method achieves a desired phase difference of 11.5° under the conditions of varying transmission distances and load resistance values, which meets the expectation of a phase difference between 10.5° and 13° to achieve ZVS. Within the range of over-coupling conditions, the output power and transmission efficiency of the WPT system are more significantly improved than those of the fixed-frequency system, which verifies the feasibility of the proposed method.