Browsing by Author "Watson, Alan J."

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    Asymmetrical Triangular Current Mode (ATCM) for Bidirectional High Step Ratio Modular Multilevel Dc–Dc Converter
    (IEEE, 2020) Pineda Fornerod, Cristian Andrés; Pereda Torres, Javier Eduardo; Rojas, Félix; Cerda, Carlos; Zhang, Xiaotian; Watson, Alan J.
    Direct current (Dc) networks have proven advantages in high voltage direct current (HVDC) transmission systems, and now they are expanding to medium- and low-voltage distribution networks. One of the major challenges is to develop reliable dc-dc voltage transformation achieving high efficiency and performance, especially at high voltage and high step ratio. New resonant modular multilevel topologies have arisen as an alternative, mainly because of advantages such as optional use of transformers, natural voltage balance, simple control, and soft-switching capability. However, this type of operation generates a high peak current, does not allow control of power flow in all power range, and has a limited range of voltage variation. This article proposes an asymmetrical triangular current mode applied to high step ratio modular multilevel dc-dc converters. The proposed modulation increases the efficiency and achieves bidirectional control of the power, soft-switching, and a natural balance of the voltage in the cell capacitors. The experimental results show the bidirectional operation and the capacitor voltage balance of the converter under different operating conditions with higher efficiency (97.72%) and lower peak current compared to previous reports of this topology using resonant operation.
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    Optimal ZCS Modulation for BidirectionalHigh-Step-Ratio Modular Multilevel dc-dc Converter
    (2021) Pineda Fornerod, Cristian Andres; Pereda Torres, Javier Eduardo; Rojas, Félix; Droguett Olea, Gabriel; Burgos Mellado, Claudio; Watson, Alan J.
    Recent developments in dc powered technologies have increased interest in highly efficient dc-dc converters, especially at high voltage and high-step voltage ratios. Modular multilevel converters (MMCs) are an attractive alternative approach to this demand because they can manage medium and high dc voltages while using standard semiconductor devices with high efficiency if they employ soft-switching techniques. However, the latest soft-switching techniques require resonant circuits, limiting their operation. This paper proposes an optimal modulation technique for a high-step-ratio dc-dc MMC, which achieves minimal rms current and zero-current switching. The proposed optimization generates trapezoidal or triangular current to operate the converter over a wide output voltage and power range, while using a simple control scheme to regulate the output voltage and the voltage balance among the floating cell capacitors. The theoretical analysis has been verified with a laboratory-scaled prototype, demonstrating the effectiveness of the approach and excellent dynamical response.