In wireless power transfer (WPT) systems, achieving accurate voltage regulation and efficient operation are critical. Current research achieves constant voltage output and zero voltage switch (ZVS) with additional DC-DC converters and variable resonant networks. However, these approaches increase system losses and costs. Therefore, this paper proposes a two-sided LCL phase-shifting control strategy. The internal phase shift angle of the inverter and active rectifier (AR) is used to achieve constant voltage output and maximum efficiency tracking, and the external phase shift angle between the two converters achieves ZVS of all switching tubes. By analyzing the power loss, the constraint condition between the internal phase shift angle is obtained. The minimum external phase shift angle δ_opt of ZVS is further determined, and the system’s high efficiency is realized. In addition, the power angle θ_power is introduced as the intermediate variable, and the frequency synchronization of the primary and secondary sides is realized using the voltage-controlled oscillator (VCO).

Firstly, utilizing the fundamental wave equivalent model, the constant voltage characteristics of the system and the constraint conditions of the inverter output voltage and AR input voltage pulse-width ratio D₁ and D₂ are analyzed. The results show that transmission efficiency peaks when the AC voltage ratio α =1. With load variations, achieving constant voltage output and maximum efficiency tracking is feasible by adjusting D₁ and D₂. Secondly, based on the time-domain harmonics model, the derivation and simplification of the time-domain expression of inductance current are conducted. The simplified model is then analyzed to determine the external phase shift angle δ. By comparing δ of the inverter and AR, the δ_opt is obtained. Thirdly, the overall control strategy is introduced. The constant voltage output is achieved by adjusting D₁ and D₂. The introduction of θ_power as an intermediate variable establishes the relationship between δ and θ_power, enabling indirect control of δ through the regulation of θ_power. Subsequently, the frequency synchronization of the primary and secondary sides is realized using a VCO, effectively solving the synchronization challenge associated with an active rectifier.

Finally, system simulations and experiments were conducted. The experimental results show that the system can achieve ZVS for all MOSFETs and maintain a constant voltage output regardless of load variations. Moreover, the proposed synchronous control strategy can effectively track the switching frequency of the inverter and precisely adjust the required δ_opt. As D₁ and D₂ consistently adhere to the maximum efficiency constraints during system adjustments, the system also achieves maximum efficiency tracking. When the coupling coefficient k is 0.31, the transmission efficiency of the system is the highest, and the maximum efficiency is 93.8%.