In this article, a simple and accurate 3-D analytical model is presented to compute the magnetic-field distribution and the torque of eddy current coupling with Halbach magnets. By employing a group of H-formulations in the conductor region and Laplacian equations with magnetic scalar potential in other regions, the analytical magnetic distribution and electromagnetic torque of the coupling are predicted in the Cartesian coordinate system. The calculated results for a 300 kW coupling are compared with the numerical simulation results by using 3-D finite-element models and experimental results. The comparison verifies the low computational time and good accuracy of the proposed 3-D analytical analysis model.

This article proposes a novel variable frequency isolated bidirectional CLLC resonant converter with voltage-controlled variable capacitors (VCVCs) and auxiliary clamp circuits (ACCs). By employing the class II ceramic capacitors as VCVCs, the converter's modes in one switching cycle and the transient process to set up the dc voltage bias on VCVCs are analyzed in detail to explain the fundamental principles and lossless characteristics of ACCs in the steady state. Suitable ranges of capacitor voltage stress and current stress and gain characteristics of the converter are also given to design the resonant parameters. The converter's soft-switching characteristics, fast transient process, and high efficiency are well demonstrated by the experimental results obtained on a 500 W prototype. The high-efficiency range of the proposed converter with the VCVCs is 20%–100%, which is at least 10% wider than the others without VCVCs.

High-frequency link matrix converter (HFLMC) can directly realize dc/ac conversion without intermediate energy storage components, reduce the power conversion stage, and improve efficiency and power density. With the conventional space vector modulation strategy, the secondary-side voltage of the high-frequency transformer presents an asymmetric trapezoidal wave, which leads to the dc magnetic bias phenomenon and increases the current stress in secondary-side switches. This article proposes a novel space vector modulation strategy for HFLMC. It optimizes the space vector distribution, makes secondary-side voltage periodic and symmetric, and reduces the switching actions. The current stress is reduced, and the converter's efficiency is improved. Simulation and experiment results verify the advantages of the proposed modulation strategy.

High-frequency link matrix converters (HFLMCs) can transfer dc to ac with only one power conversion stage and without intermediate energy storage components. However, the space vector modulation (SVM) strategies and control methods in conventional HFLMCs produce excessive harmonics in the three-phase output currents and high current stress in the primary side of the isolated high-frequency transformers (HFTs). This article proposes a new optimal vector distribution SVM strategy, which maintains low switching action and reduces output current harmonic. The HFLMC's transmission power and the HFT's current stress with the proposed SVM strategy are analyzed, and a coordinated control method coupled with the modulation index and phase shift angle is determined. The proposed SVM strategy and the coordinated control can realize smaller total harmonic distortion (THD) of three-phase currents and lower HFT's current stress than the conventional SVM strategy. The simulation and experiment results confirm a low THD of 3.71% in the output current and a remarkable decrease of the current stress (2.5 to 3 A) in the HFT.

This paper proposes a novel rotor side brushless controller (RSBC) with bidirectional wireless power transmission (WPT) for a doubly-fed motor (DFM), which can realize the brushless DFM without changing the stator and rotor structures. The WPT-RSBC consists of a grid side converter, a series–series compensated resonant converter, and a rotor side converter. According to the operational characteristics of DFMs, the design requirements of the WPT-RSBC are given in this paper. The systematic selection method for four-quadrant operations of the DFM is introduced, and the variable bus voltage control strategy is proposed to improve its transmission efficiency. The mathematical model and small-signal model of each subsystem in the WPT-RSBC are given, and the stability of the primary and secondary DC bus is analyzed. An experimental platform is implemented to verify the feasibility of the WPT-RSBC. For the prototype, the air-gap length is 1 mm, and the RSBC's transmission efficiency can be up to 92%.