Analysis and control of nonlinear phenomena in electrical drives

PhD ThesisElectrical motors are key to the growth of any modern society. In order to ensure optimal utilisation of the motors, the shaft speed and armature current must be controlled. Currently, the most efficient way of achieving both speed and current control in electrical motors is through power electronic switching, thus making the system both nonlinear and time varying. The combination of electric motors and control electronics is referred to as electric drives. Due to the inherent nonlinear nature of electrical drives, the system is prone to complex dynamical phenomena including bifurcations, chaos, co-existing attractors and fractal basin boundaries. The types of nonlinear phenomena that occur in some of the more common electrical drive systems, namely permanent magnet dc (PMDC) drives, series connected dc (SCDC) drives and switched reluctance motor (SRM) drives, are considered for analysis in this project. The nominal steady state behaviour of these drives is a periodic orbit with a mean value close to the reference value. But as some system parameters are being varied, the nominal orbit of the system referred to as the period-1 orbit, may lose its stability leading to the birth of new attracting orbit that is periodic, quasi-periodic or chaotic in nature. The most common technique for performing stability analysis of a periodic orbit is the Poincaré map approach, which has been successfully applied in DC-DC converters. This method involves reducing the continuous time dynamical system into a discrete time nonlinear iterative map and the periodic orbit into a fixed point. The stability of the periodic orbit then depends on the eigenvalue of the Jacobian matrix of the map evaluated at the fixed point. However, for some power electronic based system the nonlinear map cannot be derived in closed form due to the transcendental nature of the equation involved. In this project, the recently introduced Monodromy matrix approach is employed for the stability analysis of the periodic orbit in electrical drives. This method is based on Filippov’s method of differential inclusion and has been successfully applied in the stability analysis of periodic orbits in both low order and higher order DC-DC converters. This represents the first application of the technique in electrical drives. The Monodromy matrix approach involves computing the State Transition Matrix (STM) of the system around the nominal orbit including the STM at the switching manifold (sometimes referred to as the Saltation matrix). Also, by manipulating some of the parameters in the Saltation matrix, it is possible to control the instabilities and thus extend the system parameter range for nominal period-1 operation. The experimental validation of the nonlinear phenomena in a proportional integral (PI) controlled PMDC drive, which is absent in literature, is presented in this thesis. The system was implemented using dsPIC30F3010 which is a low cost and high performance digital signal controller.Petroleum Technology Development Fund (PTDF) of Nigeri

The blue economy - cultural livelihood - ecosystem conservation triangle : the African experience

Publications costs were supported by the University of St Andrews to IO-Y and the New England Aquarium-Marine Conservation and Action Fund (MCAF) to NK.The concept of Blue Economy (BE) is recognised as central for sustainable development that incorporates socio-economic benefits and ecological conservation. However, in Africa, much of the emphasis on BE is placed on economic gains; as a result, traditional livelihoods and small-scale local operations are outcompeted by international corporations and government initiatives, with little or no regard for social inclusion and environmental sustainability. We argue that successful BE initiatives in Africa accentuate the involvement of local communities and promote sustenance of the natural ecosystem. We define success in terms of the sustainability balance among ecological, social and economic aspects. Drawing on extensive expert experiences, observational data and literature review of case studies across the African continent, we highlight two critical findings. First, large scale BE initiatives prioritise economic gains at the expense of environmental degradation and the exclusion of local communities. Second, using the full spectrum sustainability (FSS) evaluation, we show that successful BE interventions considered ecological, economic, socio-cultural and institutional objectives. Drawing on these case studies, we propose the adoption of a collaborative framework which amalgamates the top-down and bottom-up approaches to BE management. Achieving the goal of successful blue growth in Africa is now even more challenged by the implications of COVID-19 on the BE sectors. Reimagining and rebuilding a resilient BE in Africa post-coronavirus will require a strong political commitment to promoting a balance between economic, social and environmental benefits in line with the African Union's Agenda 2063 and the United Nations' Sustainable Development Goals.Publisher PDFPeer reviewe

Law enforcement assisted diversion : qualitative evaluation of barriers and facilitators of program implementation

BACKGROUND : Despite widespread interest in adoption, there has been limited systematic examination of Law Enforcement Assisted Diversion (LEAD) implementation, a model for police-led arrest diversion for those with substance use disorders (SUD). In the fall of 2017, the City of New Haven started a LEAD program. During the first 9 months of the pilot, only 2 clients were successfully diverted from arrest. Therefore, we examined the and barriers and facilitators of LEAD implementation. METHODS : We conducted semi-structured interviews and field observations of LEAD police officers and health care providers between August 2018 and June 2019. Interviews and field observations were analyzed using directed content analysis and guided by the Integrated Promoting Action on Research Implementation in Health Services framework. RESULTS : Lead professionals participated in 19 semi-structured interviews and three field observations. Barriers to arrest diversion implementation included procedural complexity of arrest diversion, concerns about reduced penalties for substance use among officers, stigma of SUDs, and a belief in a punitive role for policing. Facilitators included a positive longitudinal relationship with potential clients and an understanding of SUD as a chronic disease. CONCLUSION : We identified several barriers to LEAD implementation. Our results suggest promotion of SUD as a chronic disease, ongoing training of officers, and positive incentives for entering substance use treatment should be utilized to facilitate implementation.SUPPLEMENTARY MATERIAL : Appendix A: Interview guideThe National Institutes of Health (NIH) and the Department of Veterans Affairs.https://www.elsevier.com/locate/jsat2022-05-14hj2022Psycholog

Evaluating assumptions of scales for subjective assessment of thermal environments – Do laypersons perceive them the way, we researchers believe?

International audienc

The Nwagu Aneke Project

The Nwagu Aneke script is a syllabic system of writing, among the riverian Igbo people of Umuleri in the Omambala (Anambra) basin of present day Anambra State of Nigeria. A system which occupies a well-established niche in the history of writing, syllabic writing has traditionally been categorised as an intermediate stage between phoneticized pictographic and alphabetic systems. However, as this research project intends to demonstrate, the more we can understand the provenance, nature and other aspects of the script, the more we can understand certain aspects of the evolution of writing systems on which there is doubt, debate or paucity of reliable evidence. But beyond these, the Nwagu Aneke script promises to contribute excellent data for the study of the rudiments of visual communication and for the investigation of certain aspects of the interface between literacy and orality