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 series-series 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 con-trol 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 pro-posed 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 experi-mental 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% respec-tively when the coupling coefficient and loads vary, and achieves high overall efficiency at 91.9%.

Wireless power transfer (WPT) is a promising technology for charging electric vehicles (EVs) due to its intelligence, convenience, and reliability. However, achieving high efficiency and high power with wide misalignment tolerance is still a major challenge in commercializing wireless charging technology in EVs. Here, a novel Parity-Time-Symmetric-based WPT (PT-based WPT) system with multiple decoupled receiving coils is developed to address the above issues. The circuit model of this PT-based WPT system is established. Our theoretical analysis shows that the output power and transfer efficiency of the proposed system also remain constant over a coupling coefficient variation. More importantly, compared to the conventional one-receiving-coil PT-based WPT system, the use of multiple receiving coils can effectively improve the transfer efficiency and reduce the current stress of system. In order to evaluate the proposed WPT system, a 1 kW laboratory prototype is built and tested. Experimental results show that a stable of power transfer is maintained with constant transfer efficiency of 96.1% within a range of 100-200 mm air gap. In particular, the same transfer efficiency is achieved at 100 mm air gap within a horizontal tolerance of 240 mm, while a horizontal tolerance of 100 mm at 200 mm air gap.

In this article, a robust wireless power transfer (WPT) system considering a wide variation in load resistance and coupling coefficient is proposed for electric vehicles charging. Here, a new implementation of the parity-time (PT)-symmetric circuit using a phase synchronization method is presented, in which a power-adjustable negative resistor is constructed only by a single-stage inverter. Moreover, based on the PT-symmetric circuit, a control strategy that does not require dual-side communication and extra dc–dc converters is developed for battery charging. Theoretical analysis shows that constant current (CC) and constant voltage (CV) outputs independent of load and position can be achieved, and the charging mode can be switched automatically. A scaled-down prototype with an 8-A charging current and a 120-V charging voltage is built to verify the feasibility of the proposed method. Experimental results demonstrate that within the transfer distance of 10–25 cm, the CC/CV outputs can be maintained during the charging process.

Cordless kitchen appliances powered by wireless power transfer (WPT) technology can operate without the clutter of cords, making them safer and easier to clean. In order to allow cordless kitchen appliances to be placed more freely, this article proposed a parity-time (PT) symmetric WPT system with stable output power in the whole coupling range. Here, a new implementation of a PT-symmetric circuit using a combination of self-oscillating methods and pulsewidth modulation (SO-PWM) is presented. The self-oscillating mode is activated in the strong coupling region, which guarantees a constant output power and constant transfer efficiency against the coupling coefficient variation. In the weak coupling region, the PWM mode with a fixed frequency and a variable duty cycle is adopted, and a control strategy based on primary-side-only parameters is presented to obtain stable power transmission. Besides, a corresponding coupling-region detection method based on the reflected resistance is proposed to ensure smooth switching between SO mode and PWM mode. The advantage is that the stable output power can be maintained in the whole coupling region without any extra dc–dc converter and dual-side communication requirements, while maintaining the same transfer efficiency as the standard PT-symmetric WPT system. A 500-W experimental prototype is built to verify the theoretical analysis. The results show that with a transfer efficiency of over 91.6%, the misalignment tolerance can be increased by 172%.

In recent years, the parity–time (PT) symmetry principle has been introduced into wireless power transfer (WPT) systems, which can improve the stability of WPT within a certain range. In this article, we analyze the generalized PT-symmetry conditions of four basic WPT topologies based on circuit theory (CT) and coupled mode theory (CMT). The results show that the series–parallel (SP) topology meets the PT-symmetry condition based on the CMT, although it does not meet the condition obtained by the CT. The symmetry between the energy of the two-resonance system is established in the SP topology. According to this unique characteristic, a constant-voltage WPT system for spinal cord stimulation is designed, which is independent of the transfer distance and load in a wide range.

This article proposed an autonomous wireless power transfer system with misalignment tolerance and improved control degree of freedom based on detuning control for battery charging, in which the outputs can be regulated continuously and smoothly without additional dc–dc converters while maintaining soft-switching or zero-phase-angle operation of the inverter. Theoretical analysis shows that constant current (CC) or constant voltage (CV) independent of coupling coefficient and load can be achieved without information exchange between transmitter and receiver, which eliminates wireless communication. Furthermore, when the detuning ratio is controlled to be constant, a transfer efficiency insensitive to the variation of the coupling coefficient can be obtained. A prototype with a 6-A charging current and a 36-V charging voltage is built to support the feasibility of the proposed method. Experimental results demonstrate that within the coupling coefficient range of 0.283–0.456, CC and CV with transfer efficiency greater than 91.5% can be achieved.