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The main challenge of medium-frequency transformers is the number of design parameters, constraints and objectives, and the difficulty of handling them on a particular design. This paper presents a novel computer-aided optimal design for MF transformers using a multiobjective genetic algorithm, in particular the nondominated sorting genetic algorithm II. The proposed methodology has the aim of reaching the best MF transformer for a given power converter topology, by optimizing transformer efficiency, weight, and also, transformer leakage and magnetizing inductances at the same time. The proposed methodology and the optimal solutions are validated with the design and the development of two 10-kVA/500-V transformers considering two different topologies. Finally, some experimental measurements are presented so as to demonstrate the proposed models and the performance of built transformers. [ABSTRACT FROM AUTHOR]

This paper presents new analytical equations, parametrized with respect to the number of converter phases, for multiphase isolated dc–dc topologies. This paper describes five multiphase isolated converter models, as well as their level of accuracy. Based on these new parametric models, a thorough comparative among various common high-power converter topologies is carried out, highlighting the best topology regarding efficiency, cost, and power density. The analytical results are firstly compared and verified using PLECS simulation software, and validated finally by experimental measurements with a 10-kW/20-kHz/500-V configurable laboratory prototype. Due to the low computation cost and accuracy, the developed analytical models provide important insights for optimization-based design methodologies. Furthermore, this paper highlights, depending on the targeted application and objectives, the benefits of each analyzed converter configuration. [ABSTRACT FROM AUTHOR]

A new feed-forward control technique for a dc–dc step-up converter based on the asymmetric multistage stacked boost architecture (MSBA) is proposed. The developed feed-forward controller directly handles the load current and the perturbations that may be caused by the dynamic operation of the converter. Thus, there is no time delay for estimating the error in a control process, and therefore, both robust steady-state operation and high dynamic performance can be achieved. The asymmetric MSBA dc–dc converter is a single-output high-voltage topology that embodies several in-series active voltage-balancing circuits. Thus, there is a need for an improved balancing control method. This can be accomplished by replacing the conventional proportional-integral controllers with feed-forward type and therefore improved balancing between the stages can be attained, because the steady-state errors are suppressed and the dynamic response can be enhanced. A thorough theoretical analysis is conducted for verifying the stability of the suggested feed-forward control technique in an asymmetric MSBA converter, and selective simulation and experimental results are demonstrated in order to validate the effectiveness and feasibility of the proposed control scheme. [ABSTRACT FROM PUBLISHER]

The grid-connected modular multilevel converter (MMC) is very likely to operate under asymmetric grid conditions. Such a converter features several unique characteristics, which make its analysis different from other types of power converters in similar cases. In this paper, the three well-established control techniques, i.e., balanced current and negative sequence current injection for active/reactive power oscillation elimination, are tailored for the MMC case taking into account grid current limitation under fault conditions. Since the focus is laid on the MMC design impact during grid asymmetries, the three methods are compared in terms of branch energy variation increase as well as maximum achievable active power transfer. Moreover, the effect of circulating current second-order harmonic injection for capacitive storage reduction as well as dc-link oscillation elimination is also studied. Finally, experimental results from a downscaled laboratory prototype verify the theoretical studies. [ABSTRACT FROM PUBLISHER]