Power Balance Method using Coupled Shunt Inductor and Multiple-Input Transformer for ISOP LLC Converter

Abstract

High-capacity power-supply systems using a large input voltage typically improve efficiency and can be miniaturized by dividing the input voltage into multiple small voltages, thereby minimizing the stress on the switching element and thus materializing a fast switching function. When a large input voltage is divided into small voltages in series through a DC link capacitor, power is supplied to each converter and the power of each LLC (Inductor-Inductor-Capacitor) converter can be divided and converted. However, such LLC converters, which are configured by the division of the input voltage, have power imbalance due to the parameter variation between active and passive elements of the power board, which results in an increase in the stress and heat of a particular element. As this problem of power balance necessitates a design for securing a power margin and as the heated element increases its volume, the efficiency and reliability of the LLC converter are degenerated. Accordingly, this study attempted to solve the problem of the power imbalance of LLC converters at each level using a coupled shunt inductor and multiple-input transformers sharing magnetic coupling.

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“…Conversely, their worst efficiency is reached when the unbalanced cell has a lower voltage than the rest of the series. Some CTP methods are the shunt inductor method [168], the boost shunting method, the multiple transformers method [168], the switched transformer method, the multisecondary windings transformer method [169], and the time-shared flyback converter method [170]. CTP methods suffer from high switching losses and slow balancing.…”

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“…However, the power range of DAB soft switching is usually narrow and the converter may have voltage and current sharing issues, making it unsuitable for high-power applications. Reference [7] proposes an ISOP system consisting of LLC converters as sub-models, which achieves a power balance of LLC at different levels using coupled parallel inductors and multiple input transformers with shared magnetic coupling. Reference [8] designed an ISOP-LLC system using a magnetic integration method based on the principle of magnetic flux cancellation, which reduces losses and improves the efficiency of the converter.…”