(6)Fault-tolerant design approach for reliable offshore multi-megawatt variable frequency converters

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N. Vedachalam ^∗, A. Umapathy , G.A. Ramadass
National Institute of Ocean Technology, Ministry of Earth Sciences, Chennai , India

Received 16 March 2016; accepted 12 June 2016
Available online 23 June 2016

Abstract
Inverters play a key role in realizing reliable multi-megawatt power electronic converters used in offshore applications, as their failure leads to production losses and impairs safety. The performance of high power handing semiconductor devices with high speed control capabilities and redundant configurations helps in realizing a fault-tolerant design. This paper describes the reliability modeling done for an industry standard, 3-level neutral point clamped multi-megawatt inverter, the significance of semiconductor redundancy in reducing inverter failure rates, and proposes methods for achieving static and dynamic redundancy in series connected press pack type insulated gate bipolar transistors (IGBT). It is identified that, with the multi megawatt inverter having 3 + 2 IGBT in each half leg with dynamic redundancy incorporated, it is possible to reduce the failure rate of the inverter from 53.8% to 15% in 5 years of continuous operation. The simulation results indicate that with dynamic redundancy, it is possible to force an untriggered press pack IGBT to short circuit in < 1 s, when operated with a pulse width modulation frequency of 1 kHz.
© 2016 Shanghai Jiaotong University. Published by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).

Keywords: Fault tolerant; IGBT; Inverter; Redundancy.