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This article introduces a single-stage grid-tied ac–dc conversion system designed for wireless charging applications. The proposed system employs a T-type converter to process soft dc-link voltages that are generated by a 3- $\phi $ Unfolder. To achieve multiple control-related tasks simultaneously, such as input power factor correction and output power regulation, a modulation scheme is presented for the high-frequency T-type converter. The T-type converter-based soft-dc to dc system is modeled using the phasor transformation technique, and closed-loop control analysis is performed to effectively regulate the battery current. In addition, in order to facilitate power level scalability, a modular architecture is proposed, and a board with dimensions of 26.2 in ( $L$ ) $\times13.2$ in ( $W$ ) $\times4.5$ in ( $H$ ), including the cold plate, is designed to house three T-type converters, each rated for 21 kW of output power. Hardware results of a 21-kW prototype are presented based on a single T-type module. The prototype demonstrates an ac–dc efficiency from the grid to the battery of $\sim 96\%$ and a grid current total harmonic distortion of 1.27%. To demonstrate the modular structure for multiple T-type converters operated in tandem, six T-type converter modules are tested in parallel, and corresponding hardware results are presented as well.

Utilizing the remaining capacity in retired lithium-ion (Li-ion) batteries from electric vehicles (EVs) for second-life applications has shown economic and environmental benefits. However, achieving homogeneity among the capacities of cells before their second life is critical to exploit the benefits. This article proposes a new active reconditioning approach with the potential to make short-term reconditioning of batteries before second life feasible. A control objective map (COM) determines each cell’s state-of-charge (SOC) operating window based on its capacity relative to other cells. The SOC reference translates into distinct differential currents through the cells, wherein the higher-capacity cells undergo more frequent and deep charge and discharge cycles than their lower-capacity counterparts. The proposed solution achieves capacity homogeneity within the battery pack with low reconditioning time and minimal fade in the overall pack capacity. The feasibility of the reconditioning approach under varying load and environmental conditions is assessed through simulations, encompassing factors such as the number of cycles per day, depth-of-discharge (DOD), battery pack temperature, and cell resting time at different SOCs. The simulation model employs a battery pack with 16 series-connected 75-Ah Kokam lithium nickel manganese cobalt oxide (NMC) cells with a 3.6% initial capacity imbalance. A reconditioning time of 1.3 months is achieved with a final capacity imbalance of 0.1% and an overall capacity fade of 0.005%, thereby confirming the viability of the reconditioning process. Moreover, experimental validation using eight retired battery cells from a Nissan Leaf demonstrates a substantial decrease in the capacity imbalance of cells from 9.4% to 2.15% within 78 days, effectively affirming the efficacy of the proposed reconditioning scheme.

As the penetration rate of renewable energy and electric vehicle keeps increasing, dc microgrids incorporating renewable energy, battery energy storage, and dc loads, such as electric vehicle chargers and electric buildings, are attracting more attention for their effectiveness of integrating zero-carbon-emission elements and reducing system costs. One key challenge in dc microgrids is the small-signal stability analysis and associated system design and operation. This article proposes a new online continuous small-signal stability monitoring method to address the challenge without adding hardware or interrupting the system operation. The proposed method evaluates stability continuously by measuring the crossover frequency and phase margin of the system impedance minor loop gain. Detailed system modeling and analysis and design of the stability monitoring method are presented in this article. Experimental results for a scaled-down system with three 2-kW power converters operating at 100 kHz are provided to validate the proposed method and demonstrate the effectiveness in monitoring the system stability margins under different conditions.