Design of high reliability power converters for aerospace applications

In this doctoral thesis, methods to design high reliability power converters for mission critical aerospace applications are studied. Aircraft platforms are increasingly being electrified necessitating usage of power converters for interfacing on-board sources and loads. Reliability of power converter systems is a key design requirement for future electric aircrafts. This thesis concentrates on predicting wear-out and cosmic ray induced random failures of drive converters. Various system voltage levels as well as two converter topologies are studied. The predicted reliability curves under a short haul aircraft mission profile are presented. It is shown that cosmic ray induced random failures dominate at higher system voltages in silicon IGBT based power converters. It is noted that SiC devices are a natural choice due to their resilience against cosmic ray failures. In order to address availability requirement due to the dominance of random failures, fault tolerance of multi three phase machines is presented. ABC domain model of a dual three phase machine is presented which can be extended to N three phase machines. The developed model can also represent fault states in the machine. The fault mode operation of dual three phase machine demonstrated a limp-home functionality by extracting torque from the damaged winding set under open phase faults. Even under dual open phase fault, approximately 25% torque can be realized using the fault tolerant controller. Furthermore, the controller architecture using PR controllers are easily reconfigurable with minimal modification enabling faster and straight forward validation of firmware for certification purposes

Design of high reliability power converters for aerospace applications

In this doctoral thesis, methods to design high reliability power converters for mission critical aerospace applications are studied. Aircraft platforms are increasingly being electrified necessitating usage of power converters for interfacing on-board sources and loads. Reliability of power converter systems is a key design requirement for future electric aircrafts. This thesis concentrates on predicting wear-out and cosmic ray induced random failures of drive converters. Various system voltage levels as well as two converter topologies are studied. The predicted reliability curves under a short haul aircraft mission profile are presented. It is shown that cosmic ray induced random failures dominate at higher system voltages in silicon IGBT based power converters. It is noted that SiC devices are a natural choice due to their resilience against cosmic ray failures. In order to address availability requirement due to the dominance of random failures, fault tolerance of multi three phase machines is presented. ABC domain model of a dual three phase machine is presented which can be extended to N three phase machines. The developed model can also represent fault states in the machine. The fault mode operation of dual three phase machine demonstrated a limp-home functionality by extracting torque from the damaged winding set under open phase faults. Even under dual open phase fault, approximately 25% torque can be realized using the fault tolerant controller. Furthermore, the controller architecture using PR controllers are easily reconfigurable with minimal modification enabling faster and straight forward validation of firmware for certification purposes

System Level Reliability Assessment of Short Duty Electric Drives for Aerospace

The reliability performance of electrical machines and power electronics converters are generally verified separately, even if the two components are meant to be part of the same electric drive. Depending on the application, however, it might be necessary that the whole drive fulfils a certain reliability target, which is pre-defined by the application itself. An appropriate design approach should involve joint efforts between machine and converter designers, so that the final product is as optimized as possible, while still satisfying reliability constraints. In this work, a system level reliability study for short duty electric drives is proposed and implemented, using an aerospace electromechanical actuator as case-study. Concepts of statistical post-processing for the lifetime prediction of power modules are discussed throughout. Additionally, accelerated lifetime tests on electrical machine windings are performed for predicting the motor insulation’s time to failure. For the short duty aerospace drive under investigation, i.e. case-study, it is finally verified that the power electronics converter represents the reliability bottleneck

Femtocore: An Application Specific Processor for Vertically Integrated High Performance Real-Time Controls

In applications that require a high availability and high performance (for example aerospace),modular power electronics and multi-phase machines represent an advantageous choice. In this framework, a control system able to handle a high number of PWM signals and communication interfaces as well as featuring a high computational power is required. This paper proposes a novel HDL plus soft-core approach to be implemented on System-on-Chip hardware which allows for the efficient and modular implementation of the modern control techniques with strong guarantees in terms of determinism. The proposal lies in the adoption of a very simplified and optimized floating-point soft-core, the femtocore (fCore) and its tool-chain, which allows C-like implementation of complex algorithms in a HDL-design power electronics control framework. Several fCore units can be arranged for parallel processing to handle the time requirements of a complex modular system even with low sampling time (100 kHz or more). The proposed architecture is experimentally validated in a proof-of-concept, six-phase electric machine including a comparison against a traditional method

Cosmic Radiation Reliability Analysis for Aircraft Power Electronics

Cosmic Ray induced failures are a major concern for the electronic system reliability of airborne and space systems. Power system voltages on aerospace platforms are on a steady upward trend. High voltage power converters suffer from Single Event Burnout failures caused by cosmic rays. The established standards propose a scaling factor based on measured background galactic cosmic rays intensity at operating altitude to apply de-rating factors. The radiation environment in the atmosphere can be increased due to the cascading of primary solar energetic particles during solar eruptions. In this work, the altitude profile of the radiation environment is simulated using a GEANT4 Monte-Carlo code. The failure rates due to both background Galactic Cosmic Rays and Solar Energetic Particles are quantitatively evaluated. Further to the known influence of geomagnetic shielding of cosmic rays, the geographical distribution of cosmic rays at flight altitudes of 10 km are also presented. The estimated cosmic ray intensity can then be combined with experimentally measured failure rate data to predict the impact on the reliability of power converters, giving a new level of accuracy in the modeling of such failure mode in more electric aircraft applications. It is shown for the first time in the scientific literature by using experimental data and state-of-the-art models, that the solar energetic particles storms fluxes vastly exceed the recommended standard and constitute a risk for the power electronics reliability

STRATEGIC BUSINESS PLAN FOR RAINMAKING DENMARK TO ENTER UK FERTILITY CLINICS INDUSTRY

EXECUTIVE SUMMARY Rainmaking Denmark, a vibrant venture capitalist firm, with the support of its business angels is looking forward to enter the UK Fertility Clinics Industry. This report presents a detailed business plan backed by extensive market research and analysis on more than 100 fertility clinics in the UK. The business plan is prepared by a group of four MBAs from the Nottingham University Business School. The goals are to clarify these questions: 1.Shall Rainmaking enter the UK market for fertility clinics? 2.How shall Rainmaking deliver superior value for customers and execute the strategy in an efficient and cost effective way? 3.What are the investment need and the ROI for such a project? The key deliverables of the project are: 1.Create a market survey and evaluate if the market is interesting according to Rainmaking’s 8 decision criteria 2.Create a Superior Value Curve based on the Blue Ocean concept and tools (i.e. how do we create value for the customers?) 3.Define a unique delivery model for executing the strategy (i.e. how do we execute the strategy in an efficient and cost effective way?) 4.Create a business case including an estimation of the investment need and expected Return on Investment Research and Analysis UK has a history of almost 2 decades in regulated infertility treatments since HFEA was formed in 1990. Currently there are over 100 fertility clinics in the UK approved by HFEA. Rainmaking will be entering the face of the competition with these clinics. Well-known tools like PEST Analysis, Porter’s Five Forces, Blue Ocean Strategy etc are used to identify the Macro/Micro forces which will affect the Fertility Clinics Business and also to identify the uncontested market space. Primary Strategies The four key strategies of the Rainmaking Fertility Specialists clinics are: 1. Web-based consultation and operations 2. Web-based Marketing 3. Streamlined clinic operations 4. Single Embryo Transfer to patients under the age of Rainmaking Investment Criteria Rainmaking is willing to invest a total sum of £2.6 Million to buy or to take a stake of not less than 40% in the fertility clinic business in UK. This total sum is divided into three parts : Hard capital investment of nearly 45%, by Rainmaking’s business angels and Soft capital investment of nearly 45% by Rainmaking’s four partner and the remaining 10% constitute for Rainmaking’ working hours contribution to run the business without charging anything. On the investment of £2.6 Million they are also looking forward for 20% - 25% return on investment (ROI). Thus, our task is to find a list of clinics that fits in the investment criteria. Together with the formulation of most appropriate equity structure that can provide the maximum return on investment. The Exit Rainmaking is willing to exit in year five and therefore look forward for the most viable and profitable option to exit

Failure modes and reliability oriented system design for aerospace power electronic converters

Aircraft electrification has been a major trend in aviation industry for past 20 years. Given the increasing electrical power requirement for future more electric aircraft and hybrid electric aircraft, research efforts has been ongoing in high power electrical conversion for air-borne systems. Safety critical nature of aviation systems places reliability of aerospace power converters as a critical design concern. In this paper, power electronic system reliability is studied with emphasis on lifetime limiting factors of critical sub components. Reliability of voltage source power converters at different system voltage levels are modelled for a starter generator drive converter. A key observation is that Si IGBT devices are sufficient with respect to reliability requirements in low and medium voltage systems (up to 540 V). At higher system voltages (above 540 V), multi level topologies are necessary for designing with Si IGBTs. In constant power profile drive, system reliability is minimally affected by wear-out failure of film capacitors in converter DC links. In multi level topologies without enhanced voltage derating, system reliability is dominated by cosmic ray induced random failures. Simulation results demonstrate that at high system voltages (810 V), 2 L topology with SiC mosfets outperform Si IGBT based 3 L topology with respect to reliability

Long-term effects of severe acute malnutrition on lung function in Malawian children: a cohort study.

Early nutritional insults may increase risk of adult lung disease. We aimed to quantify the impact of severe acute malnutrition (SAM) on spirometric outcomes 7 years post-treatment and explore predictors of impaired lung function.Spirometry and pulse oximetry were assessed in 237 Malawian children (median age: 9.3 years) who had been treated for SAM and compared with sibling and age/sex-matched community controls. Spirometry results were expressed as z-scores based on Global Lung Function Initiative reference data for the African-American population.Forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) were low in all groups (mean FEV1 z-score: -0.47 for cases, -0.48 for siblings, -0.34 for community controls; mean FVC z-score: -0.32, -0.38, and -0.15 respectively). There were no differences in spirometric or oximetry outcomes between SAM survivors and controls. Leg length was shorter in SAM survivors but inter-group sitting heights were similar. HIV positive status or female sex was associated with poorer FEV1, by 0.55 and 0.31 z-scores, respectively.SAM in early childhood was not associated with subsequent reduced lung function compared to local controls. Preservation of sitting height and compromised leg length suggest "thrifty" or "lung-sparing" growth. Female sex and HIV positive status were identified as potentially high-risk groups

Neurodevelopmental disorders in children aged 2-9 years: Population-based burden estimates across five regions in India.

BACKGROUND: Neurodevelopmental disorders (NDDs) compromise the development and attainment of full social and economic potential at individual, family, community, and country levels. Paucity of data on NDDs slows down policy and programmatic action in most developing countries despite perceived high burden. METHODS AND FINDINGS: We assessed 3,964 children (with almost equal number of boys and girls distributed in 2-<6 and 6-9 year age categories) identified from five geographically diverse populations in India using cluster sampling technique (probability proportionate to population size). These were from the North-Central, i.e., Palwal (N = 998; all rural, 16.4% non-Hindu, 25.3% from scheduled caste/tribe [SC-ST] [these are considered underserved communities who are eligible for affirmative action]); North, i.e., Kangra (N = 997; 91.6% rural, 3.7% non-Hindu, 25.3% SC-ST); East, i.e., Dhenkanal (N = 981; 89.8% rural, 1.2% non-Hindu, 38.0% SC-ST); South, i.e., Hyderabad (N = 495; all urban, 25.7% non-Hindu, 27.3% SC-ST) and West, i.e., North Goa (N = 493; 68.0% rural, 11.4% non-Hindu, 18.5% SC-ST). All children were assessed for vision impairment (VI), epilepsy (Epi), neuromotor impairments including cerebral palsy (NMI-CP), hearing impairment (HI), speech and language disorders, autism spectrum disorders (ASDs), and intellectual disability (ID). Furthermore, 6-9-year-old children were also assessed for attention deficit hyperactivity disorder (ADHD) and learning disorders (LDs). We standardized sample characteristics as per Census of India 2011 to arrive at district level and all-sites-pooled estimates. Site-specific prevalence of any of seven NDDs in 2-<6 year olds ranged from 2.9% (95% CI 1.6-5.5) to 18.7% (95% CI 14.7-23.6), and for any of nine NDDs in the 6-9-year-old children, from 6.5% (95% CI 4.6-9.1) to 18.5% (95% CI 15.3-22.3). Two or more NDDs were present in 0.4% (95% CI 0.1-1.7) to 4.3% (95% CI 2.2-8.2) in the younger age category and 0.7% (95% CI 0.2-2.0) to 5.3% (95% CI 3.3-8.2) in the older age category. All-site-pooled estimates for NDDs were 9.2% (95% CI 7.5-11.2) and 13.6% (95% CI 11.3-16.2) in children of 2-<6 and 6-9 year age categories, respectively, without significant difference according to gender, rural/urban residence, or religion; almost one-fifth of these children had more than one NDD. The pooled estimates for prevalence increased by up to three percentage points when these were adjusted for national rates of stunting or low birth weight (LBW). HI, ID, speech and language disorders, Epi, and LDs were the common NDDs across sites. Upon risk modelling, noninstitutional delivery, history of perinatal asphyxia, neonatal illness, postnatal neurological/brain infections, stunting, LBW/prematurity, and older age category (6-9 year) were significantly associated with NDDs. The study sample was underrepresentative of stunting and LBW and had a 15.6% refusal. These factors could be contributing to underestimation of the true NDD burden in our population. CONCLUSIONS: The study identifies NDDs in children aged 2-9 years as a significant public health burden for India. HI was higher than and ASD prevalence comparable to the published global literature. Most risk factors of NDDs were modifiable and amenable to public health interventions