Performance evaluation of PI controlled series stacked power delivery architectures for high-efficiency data centers

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Nazih, Yousef and Ismail, Abdelrahman and Faiad, Azza A. and Hamdan, Eman and Hamad, Mostafa S. and Abdel-Khalik, Ayman S. (2020) Performance evaluation of PI controlled series stacked power delivery architectures for high-efficiency data centers. Alexandria Engineering Journal, 59 (6). pp. 4821-4842. ISSN 1110-0168 (https://doi.org/10.1016/j.aej.2020.08.045)

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Abstract

Series-stacked architectures have been successfully deployed for data center applications at substantially higher efficiencies than conventional power delivery architectures. In the series-stacked architectures, servers are series-connected electrically to reduce the high step-down conversion stage of voltage utilized in the conventional architectures. Differential power processing converters are, therefore, used to regulate the servers’ voltages and compensate for the unpredicted mismatch between servers’ currents. The main contribution of this paper comprises novel control approaches based on PI controllers purposeful for the two architectures that have reported the highest reliability and efficiency in differential power processing namely: server-to-bus and server-to-virtual bus. Both systems employ a dual active bridge (DAB) converter to accommodate the fluctuating loads of each server. Unlike hysteresis current/voltage control commonly employed in the available literature, the proposed control approaches offer less complexity, lower harmonics, and higher immunity towards the noise, thus no need for high-quality sensors to successfully achieve voltage balance and/or optimal string current flow. Moreover, a comparative study has been structured between the investigated series-stacked architectures under the proposed PI control approaches showing the merits and the demerits of each architecture. The proposed controllers have been validated based on simulations and experimentally.

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