The low coupling coefficient between the transmitter and receiver is the major constraint of a wireless power transfer (WPT) system. Although some approaches, such as increasing the quality factor and achieving precise impedance matching, can reduce the adverse impacts of the low coupling coefficient and improve the system performance, high leakage magnetic flux between the transmitter and receiver remains a problem. With the increase in transfer distance and the misalignment between the transmitter and receiver, the increasing leakage magnetic flux of nondirectional fields degrades the WPT system performance. This paper proposes an active field orientation method to shape the magnetic flux so as to minimize the leakage flux. The amplitude and phase angle of the magnetizing current are controlled, and a coil structure for minimizing the coupling among the transmitters and generating a three-dimensional magnetic field is proposed. This method realizes three-dimension full-range field orientation with adjustable magnitude and direction of B-field at an arbitrary point, and as a result the B-field is concentrated with reduced leakage magnetic flux. The proposed field orientation shaping technique is verified by theoretical analysis, simulation, and experimental results.

It is well known that a high voltage across the coupling plates of a Capacitive Power Transfer (CPT) system is beneficial to increase its power transfer capability, but a high voltage may lead to high insulation requirements and cause safety concerns. This paper proposes a compensation design method for achieving the maximum power of CPT systems under coupling voltage constraints. Basic on a simplified capacitive coupling model and thorough power transfer characteristics analysis, a family of compensation topologies are derived to maintain a 90 degrees phase shift between the input and output voltages across the CPT coupler against load variations, so that the coupling voltages (which practically need to be limited) are fully utilized for power transfer purposes. A full design process for determining the compensation parameters is presented, and an example 2kW CPT system is built and tested using LC compensation at the primary side to boost the input voltage to the coupler; and one of the proposed compensation topologies (CLC) at the secondary side for impedance transformation of a given load with a specified voltage and power requirements. Experimental results show a good agreement with theoretical analysis, which demonstrate the phase difference between the voltages before and after the coupler is kept nearly 90 degrees, and a maximum possible power transfer of 2.039kW is achieved under the given voltage limits and coupling conditions. A system end to end (DC-DC) efficiency of 90.29% is obtained when the air gap between the coupling plates is 150mm, and the coupling capacitance is only 13.84 pF.

In this paper, a novel finite control set model predictive control (FCS-MPC)-based solution is proposed to eliminate the common-mode voltage (CMV) in matrix converters. Different from the existing MPC-based CMV reduction methods, which usually utilize all the possible switching configurations, in the proposed method, only the six rotating vectors, which produce no CMV, are included in the FCS to synthesize the output voltage and the input current. Therefore, zero CMV can be achieved naturally and no CMV related term needs to be included in the cost function. In addition, compared with other zero CMV methods, e.g., the enhanced space-vector modulation using rotating vectors, the proposed MPC-based method can significantly reduce the computational complexity without detracting the CMV elimination performance. Moreover, a modified four-step commutation strategy is proposed to effectively mitigate the CMV spikes due to the dead time, which usually exists when using the conventional current-based four-step commutation strategy. Finally, the feasibility and effectiveness of the proposed method are validated by using experimental studies.

This paper proposes a three-dimensional (3D) wireless charging cylinder with improved compensation topology to generate a stable rotating magnetic field for charging multiple loads around it. The induced voltage of each receiver is kept constant against load variations when the distance between the transmitter and the receiver is fixed. The 3D charging cylinder has a simple configuration with two perpendicular LCL-compensated transmitter coils driven by separate power inverters sharing a common DC source. The system is fully analyzed with the maximum load limit determined, and a design guidance is provided. Both theoretical and experimental results demonstrate that the transmitter currents remain constant against load variations when the total load is within the maximum load limit, and the transfer efficiency is increased with the increase of the total reflected impedance. Compared to the conventional series-series (SS) compensated WPT system, the proposed 3D configuration can maintain the transmitter currents to be constant within the maximum load limit so that multiple loads can be added without affecting each other. It has found that the transmitter currents of the proposed configuration are kept constant at their initial values when four loads with the resistance of 0.5 each are randomly placed at 21cm from the center of the charging cylinder. By contrast, the transmitter currents of the SS compensated WPT system are obviously changed, together with the load voltages.

This letter proposes a dual-frequency tuning method for improved coupling tolerance of an inductively coupled wireless power transfer (WPT) system by exploiting the fundamental and 3rd order harmonic components of a square-wave voltage out of a full-bridge inverter. A dual-frequency hybrid compensation topology is designed to simultaneously utilize the characteristics of series-series (SS) and LCL-S networks under the two different frequencies. Consequently, the output power of the proposed system under a fixed load is maintained approximately constant against coupling variations. A practical hybrid WPT system with a 100 kHz square-wave excitation and a 10.5 $\Omega$ resistive load is built to verify the theoretical modelling and analysis. Experimental results show that the system achieves an approximately constant output voltage and power of around 39 V and 150 W against a coupling coefficient variation from 0.52 to 0.72, with maximum fluctuations less than 5% and 10%, respectively.

This paper proposes a single-phase power factor correction (PFC) rectifier to achieve high power factor, wide output voltage range, and ripple power decoupling without using electrolytic capacitors. It consists of two parts: PFC circuit and output voltage regulation circuit. The load side is involved in both parts, which is different from the regular two-stage conversion structure. The proposed rectifier can be directly applied to low voltage cases due to the wide output voltage range. And the decoupling capacitor voltage can be smaller than the peak grid voltage, which reduces the voltage stress. Besides, the low-frequency ripple power buffer is implemented without a dedicated power-buffering controller. This paper first introduces the circuit structure, operation principles, and control method. Then, the system design consideration is given. Finally, the effectiveness of the proposed topology is verified by the simulations and experimental results.