A major challenge for practical wireless power transfer (WPT) applications is to attain stable power transfer with high and constant transfer efficiency under a dynamic change of coupling condition. In order to address the issue, this paper proposes a novel nonlinear parity-time-symmetric (PT) model, wherein the nonlinear saturable gain is provided by a self-oscillating controlled inverter. In this paper, the transfer performance and stability criterion of the nonlinear PT-based WPT system are analyzed based on the coupled-mode theory (CMT). The theoretical analysis shows that the proposed system automatically achieves constant output power with constant transfer efficiency against the variation of coupling coefficient. Moreover, based on the gain saturation mechanism, the control strategy for the inverter only need detect the current in the transmitter, which eliminates auxiliary circuits of wireless communication for feedback control from the receiver. As a case study of dynamic charging, a drone-in-flight wireless charging platform is improved by applying the nonlinear PT-symmetric model. Experimental results show that, when the flying drone hovers in a confined 3-D volume of space above the WPT platform, a stable output power is maintained with approximately constant transfer efficiency of 93.6%.

A single-switch quadratic buck-boost converter with continuous input port current and continuous output port current is proposed in this paper. Compared with the traditional buck-boost converter, the proposed converter can obtain a wider range of the voltage conversion ratio with the same duty cycle. Moreover, the proposed converter can operate with continuous input port current and continuous output port current compared to the existing counterparts with inherently discontinuous input port current and discontinuous output port current. The operating principle and steady-state performance of the proposed converter under continuous inductor current mode is analyzed in detail. Then, the comparison between the proposed converter and the existing quadratic buck-boost converters has been conducted to demonstrate the unique features of the proposed one. Finally, experimental results from a prototype built in the lab are recorded to verify the effectiveness and validity of the proposed quadratic buck-boost converter.

This paper proposes a family of switched-boost dc-dc converters for the high stepup voltage conversion applications, such as renewable energy power generation, uninterruptible power supply, and automobile high-intensity discharge headlamps. Compared with other dc-dc converters, the proposed switched-boost converter, which combines the traditional switched-boost network with the switched-capacitor/switched-inductor cells, has the following features: higher output voltage gain, a fewer passive components such as inductors and capacitors, and lower voltage stress across the output diode and power switches. Another advantage of the proposed topology is its expandability. If a higher voltage conversion ratio is required, additional cells can be easily cascaded by adding one inductor and three diodes. The structure, operating principle analysis, parameter design, and comparison with other dc-dc converters are also analyzed. Finally, both simulations and experimental results are presented to verify the effectiveness of the proposed converter.

Transformerless photovoltaic grid-connected inverters have become more and more popular in the field of distributed photovoltaic power generation systems due to the advantages on high efficiency, low cost and small size. However, common-mode currents in the transformerless photovoltaic inverters can result in serious electromagnetic interference problems and safety issues, which will reduce the reliability of the photovoltaic inverter systems. In this paper, an improved H5 topology, namely H5-D topology, is proposed, in which a clamping diode is added on the basis of H5 topology to eliminate the common-mode voltage fluctuation in H5 topology. Further, the simulation results of the H5-D topology and H5 topology are given and compared by using PSIM software, especially, on the performance of common-mode currents suppression. Finally, the experimental prototypes of the H5-D topology and H5 topology are built and tested, the experimental results validate the advantages of the H5-D topology. The proposed H5-D topology provides a new practical topology for distributed photovoltaic grid-connected power generation systems.

A high step-up DC-DC converter with active switched LC-network is proposed in this paper, which can be used in the photovoltaic (PV) system as the front-end stage to generate the required dc bus voltage. Based on the transformerless DC-DC converter with an active switched inductor (ASL) network, this proposed converter introduces an active switched capacitor (ASC) network, only one capacitor and one diode are added, while the voltage gain is efficiently increased by a compound of ASL and ASC network. The structure of the proposed converter is simple and voltage stresses on the additional diode and capacitor are low. In addition, unlike other voltage-boosting structures that utilized switched capacitor, the proposed converter avoids the extreme instantaneous currents of capacitor. The detailed analysis of the proposed converter and performance comparison with recently published ASL network-based converters are presented. Finally, a 100 W, 20/200 V prototype circuit is operated to verify its performance.

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%.