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

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.

An approach to operational risk modeling and estimation of safety levels for deep water work class remotely operated vehicle-A case study with reference to ROSUB 6000

This paper presents a quantitative approach to operational risk modeling and estimation of safety integrity levels,required for the deep water electric work class remotely operated vehicle with reference to ROSUB6000 developed by the National Institute of Ocean Technology,India.ROSUB6000 is used for carrying out bathymetric surveys,gas hydrate surveys,poly-metallic nodule exploration,salvage operations,and meeting emergency response situations.The system is expected to be in operation for a period of 300 h per year,and has to be extremely safe and reliable.Methods and models for the quantitative assessment of operational safety and estimation of safety integrity levels for ROV are seldom available in the deep water intervention industry.The safety instrumented functions implemented in the ROV should be able to meet the SIL requirements of specific mission.This study indicates that the required safety factors are implemented into the design of the state-of-the-art ROV ROSUB 6000,considering IEC 61508/61511 recommendations on Health,Safety and Environment and it is found that the system is able to meet the required SIL for seven identified functions.This paper gives the design and safety engineers in the ROV industry,an overview of the numerical operational risk assessment methods and safety-centered ROV engineering.