The concept of vehicle-to-grid has received considerable attentions over the past decade. Electric vehicle (EV), a common load of DC microgrids, can serve as distributed energy storage system to improve the reliability and stability of the DC microgrid, support integration of renewable energy source, and improve overall system efficiency. In order to achieve bidirectional power transmission between the DC microgrid and EV, this paper proposes a novel three-level CLLC resonant converter for off-board EV charger. By adding resonant CLLC components and by combining the working modes of the two three-level full bridges, the proposed converter adapts to the wide voltage range of EV, from 200 V to 700 V. An equivalent circuit model with first harmonic approximation approach is established to analyze the frequency characteristics of the resonant converter. Moreover, an algorithm of working mode selection is proposed on the principle of minimum transformer RMS current. Finally, a 3.5 kW hardware prototype was built to verify the feasibility and the advantage of the three-level CLLC resonant converter. The efficiency of the proposed converter changes little over a wide output voltage range, and the flying capacitor voltages of the proposed converter are balanced well.

Magnetically coupled resonance wireless power transfer systems (MCR WPT) have been developed in recent years. There are several key benefits of such systems, including dispensing with power cords, being able to charge multiple devices simultaneously, and having a wide power range. Hence, WPT systems have been used to supply the power for many applications, such as electric vehicles (EVs), implantable medical devices (IMDs), consumer electronics, etc. The literature has reported numerous topologies, many structures with misalignment effects, and various standards related to WPT systems; they are usually confusing and difficult to follow. To provide a clearer picture, this paper aims to provide comprehensive classifications for the recent contributions to the current state of MCR WPT. This paper sets a benchmark in order to provide a deep comparison between different WPT systems according to different criteria: (1) compensation topologies; (2) resonator structures with misalignment effects; and, (3) electromagnetic field (EMF) diagnostics and electromagnetic field interference (EMI), including the WPT-related standards and EMI and EMF reduction methods. Finally, WPT systems are arranged according to the application type. In addition, a WPT case study is proposed, an algorithm design is given, and experiments are conducted to validate the results obtained by simulations.

One promising topology for solid state transformer (SST) is modular multilevel cascaded converter, in which sub-module is composed of dual active bridge (DAB) and H-bridge. For SST application in PV system, the efficiency could be severely affected especially for DAB due to the wide voltage and power range of PV panels. Thus, the motivation of this paper is to deal with the control strategy to improve DAB efficiency inside SST for PV application. Instead of utilizing time-domain based analysis method, which requires complex modeling process, this paper models DAB under frequency domain by fully considering the effect of both fundamental and harmonic frequency component. To achieve high efficiency operation, multi-order reactive-current suppression (MRS) strategy is proposed for DAB by controlling phase shift angle as well as the duty cycles of primary and secondary side H-bridges. In terms of DAB controller design inside SST, the small signal model under MRS is established and notch filter is implemented to suppress the second order line frequency fluctuation in the control loop. Finally, 10kV/1MW SST prototype is introduced along with the system control structure and implementation method. The experiment of sub-module and SST confirms the effectiveness of proposed method.

DD planar coil with ferrite core is one popular coupling structure in wireless power transfer (WPT), especially for electric vehicle applications. The coil design is critical for improving the performance of WPT system. However, the coupler design purely relying on finite element analysis (FEA) software is time-consuming. Literature on the modeling of DD coil is lacking. Therefore, the model of DD coil with a ferrite core for calculating self-inductance, mutual inductance, and ac resistance is proposed in this article. The condition when primary and secondary coils have different sizes is also considered. The case that there is misalignment is also analyzed. Meanwhile, a genetic algorithm based on the proposed coil mathematical model is proposed to optimize the coil structure. For verifying the accuracy of the proposed model, the simulation model based on the FEA and a 1.2-kW laboratory prototype are built simultaneously. The calculation values based on the proposed model is highly consistent with the simulation results and experimental values. Error for calculating self-inductance and mutual inductance is within 5% when coils on the primary side and secondary side are in alignment. The error for calculating the ac resistance of the coil is within 10% when the frequency range is 0–200 kHz.

This paper proposes a new topology of the switched-capacitor multilevel inverter (SCMLI) for photovoltaics system, which can eliminate the leakage current. In the proposed topology, the capacitors are employed as a virtual DC power supply to boost the input voltage. Here, all capacitors are charging equal to DC source, thus, just one DC source is needed to achieve the staircase waveform. In this structure in order to make the negative levels, the capacitors are connected to the output in reverse polarity. Thus, the H-bridge circuit which is used in traditional SCMLI to build zero and negative voltage levels and leads a variable common mode voltage is removed. Due to the direct connection of the neutral terminal of the grid to the negative polarity of the PV; then this topology can eliminate the leakage current. In addition, the topology has an excellent ability to path the reverse current as well as an acceptable output waveform spectrum. The operating states of all components and loss calculations are analyzed and formulated accurately as well as simulated by using MATLAB-SIMULINK software. To confirm the performance of the proposed topology; a 500 W prototype is built and experimental results are presented.

Wireless power transfer (WPT) is a promising way of charging electric vehicles (EVs) for its convenience, safety, physical and electric isolation. For satisfying the high-power application or rapid charging, WPT systems based on multiple coils are usually used. Nowadays, LCC compensation is a commonly used topology. However, the conflict between the installation space limitation and the large volume induced by compensated inductors and multiple coils brings the critical challenge for EVs charging electric vehicles' charging. In this article, a method of integrating multiple decoupled coils is put forward. All the main coils and compensated inductors are integrated together for compacting the WPT system. Characteristics of the coupler are analyzed when it exists a misalignment both in x - direction and y -direction. Besides, an antimisalignment strategy based on optimizing the phase difference of current in main coils is proposed. Finally, a 3kW laboratory prototype is built to verify the proposed compact coupler and antimisalignment control strategy. The system output power only drops 3.2% and 9.2% respectively with a −200 mm and +200 mm misalignment in the x -direction compared with full alignment by adopting the proposed antimisalignment method. When it is fully aligned, the system can achieve 94%peak efficiency.