The output power of a wireless power transfer (WPT) system depends highly on the load and the coupling conditions, which are variable in practical applications generally. In order to attain stable output power with high transfer efficiency under various coupling condition and load, this paper proposes a seriesseries compensated WPT system based on parity-time (PT) symmetry with front-end DC-DC converter and a novel primary-side-only control strategy. The strategy comprises the negative resistance control of PT-symmetric circuit, the online load identification approach by PT-symmetry, and the power closed-loop control method. The advantages are that the mutual inductance information is not needed, and dual-side wireless communication as well as the secondary-side control circuit is avoided, which compresses the volume of the secondary side, simplifies the control algorithm, and improves the robustness of the system. With the proposed primary-side-only control strategy, the output power is coupling-independent and can automatically stabilize at specified values over reasonable variations both in coupling coefficient and load. The experimental results obtained from a prototype are included. They confirm the proposed control strategy and indicate that system can stably output 200 W and 400 W with the maximum error 4.10% and 3.40% respectively when the coupling coefficient and loads vary, and achieves high overall efficiency at 91.9%. INDEX TERMS Wireless power transfer (WPT), load identification, coupling-independent, stable output power, high efficiency, parity-time (PT) symmetry.

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