Harmonic quality of multilevel cascade inverters with random carrier phase pulse width modulation

The output harmonic quality of N series connected full-bridge dc-ac inverters is investigated. The inverters are pulse width modulated using a common reference signal but randomly phased carrier signals. Through analysis and simulation, probability distributions for inverter output harmonics and vector representations of N carrier phases are combined and assessed. It is concluded that a low total harmonic distortion is most likely to occur and will decrease further as N increases.

Applications and equivalent models for coupled inductor parallel interleaved converters

Parallel interleaved converters are finding more applications everyday, for example they are frequently used for VRMs on PC main boards mainly to obtain better transient response. Parallel interleaved converters can have their inductances uncoupled, directly coupled or inversely coupled, all of which have different applications with associated advantages and disadvantages. Coupled systems offer more control over converter features, such as ripple currents, inductance volume and transient response. To be able to gain an intuitive understanding of which type of parallel interleaved converter, what amount of coupling, what number of levels and how much inductance should be used for different applications a simple equivalent model is needed. As all phases of an interleaved converter are supposed to be identical, the equivalent model is nothing more than a separate inductance which is common to all phases. Without utilising this simplification the design of a coupled system is quite daunting. Being able to design a coupled system involves solving and understanding the RMS currents of the input, individual phase (or cell) and output. A procedure using this equivalent model and a small amount of modulo arithmetic is detailed.

PV string per-module maximum power point enabling converters

Many grid connected PV installations consist of a single series string of PV modules and a single DC-AC inverter. This efficiency of this topology can be enhanced with additional low power, low cost per panel converter modules. Most current flows directly in the series string which ensures high efficiency. However parallel Cúk or buck-boost DC-DC converters connected across each adjacent pair of modules now support any desired current difference between series connected PV modules. Each converter “shuffles” the desired difference in PV module currents between two modules and so on up the string. Spice simulations show that even with poor efficiency, these modules can make a significant improvement to the overall power which can be recovered from partially shaded PV strings.

The effects of coupled inductors in parallel interleaved buck converters

Interleaved switching and coupled inductors are proven methods for reducing DC-DC converter output ripple. This paper furthers discussions of these techniques to arrangements of many buck converters connected in parallel. The different possible arrangements of the DC-DC converters are discussed and criteria for fair comparisons between them are chosen. The effects of interleaved switching on ripple values are presented and subsequent effects of coupling the inductors is then investigated. A generalised solution for current ripple in n coupled inductor converters is presented. Simulations are used to verify the solution and characterise the converter and output ripple for all configurations.

Multi-converter topology evaluation for connection of low voltage DC sources

A design for a cascaded multilevel DC-DC converter is proposed. The applications of a multilevel converter and the design issues involved in changing from a single converter to multiple converters are discussed. Implementation of the multilevel system using multiple Cuk converters is suggested and explanations of design decisions are given. The merits of the proposed design are discussed.

High efficiency auxiliary power converters

The auxiliary load DC-DC converters of the Sunshark solar car have never been examined. An analysis of the current design reveals it is complicated, and inefficient. Some simple measures to greatly improve the efficiency are present which will achieve an overall worthwhile power saving. Two switch-mode power supply DC-DC converter designs are presented. One is a constant current supply for the LED brake and turn indicators, which allows them to be powered directly from the main DC bus, and switched only as necessary. The second is a low power flyback converter, which employs synchronous rectification among other techniques to achieve good efficiency and regulation over a large range of output powers. Practical results from both converters, and an indication of the overall improvement in system efficiency will be offered.

Geographic remoteness, area-level socioeconomic disadvantage and inequalities in colorectal cancer survival in Queensland : a multilevel analysis

Background To explore the impact of geographical remoteness and area-level socioeconomic disadvantage on colorectal cancer (CRC) survival. Methods Multilevel logistic regression and Markov chain Monte Carlo simulations were used to analyze geographical variations in five-year all-cause and CRC-specific survival across 478 regions in Queensland Australia for 22,727 CRC cases aged 20–84 years diagnosed from 1997–2007. Results Area-level disadvantage and geographic remoteness were independently associated with CRC survival. After full multivariate adjustment (both levels), patients from remote (odds Ratio [OR]: 1.24, 95%CrI: 1.07-1.42) and more disadvantaged quintiles (OR = 1.12, 1.15, 1.20, 1.23 for Quintiles 4, 3, 2 and 1 respectively) had lower CRC-specific survival than major cities and least disadvantaged areas. Similar associations were found for all-cause survival. Area disadvantage accounted for a substantial amount of the all-cause variation between areas. Conclusions We have demonstrated that the area-level inequalities in survival of colorectal cancer patients cannot be explained by the measured individual-level characteristics of the patients or their cancer and remain after adjusting for cancer stage. Further research is urgently needed to clarify the factors that underlie the survival differences, including the importance of geographical differences in clinical management of CRC.

A multilevel model of work-life : examining the impact of group structure and relational job design

One in five Australian workers believes that work doesn’t fit well with their family and social commitments. Concurrently, organisations are recognising that to stay competitive they need policies and practices that support the multiple aspects of employees’ lives. Many employees work in group environments yet there is currently little group level work-life balance research. This paper proposes a new theoretical framework developed to understand the design of work groups to better facilitate work-life balance. This new framework focuses on task and relational job designs, group structures and processes and workplace culture.

Improving work and life balance : building a multilevel model of work-life balance focusing on group structure and relational job design

One in five Australian workers believes that work doesn’t fit well with their family and social commitments. Concurrently, organisations are recognising that to stay competitive they need policies and practices that support the multiple aspects of employees’ lives. Many employees work in group environments yet there is currently little group level work-life balance research. This paper proposes a new theoretical framework developed to understand the design of work groups to better facilitate work-life balance. This new framework focuses on task and relational job designs, group structures and processes and workplace culture.

A multilevel investigation into the effects of the philosophical community of inquiry on 6th grade students' reading comprehension, interest in maths, self-esteem, pro-social behaviours and emotional well-being

This investigation measured the effects of a one year participation in an Australian Philosophical Community of Inquiry program on 280 sixth grade students' reading comprehension, interest in maths, self-esteem, social behaviours, and emotional well-being. A multilevel model for change was used to detect differences in the response variables, between a quasi-experimental group and comparison group. Results showed that, for participants, reading comprehension significantly increased while interest in maths decreased. No differences between the groups were found for pro-social behaviour and emotional well-being. Self esteem, however, declined for participants while nonparticipants' self esteem increased.

Primary control level of parallel distributed energy resources converters in system of multiple interconnected autonomous microgrids within self-healing networks

To minimise the number of load sheddings in a microgrid (MG) during autonomous operation, islanded neighbour MGs can be interconnected if they are on a self-healing network and an extra generation capacity is available in the distributed energy resources (DER) of one of the MGs. In this way, the total load in the system of interconnected MGs can be shared by all the DERs within those MGs. However, for this purpose, carefully designed self-healing and supply restoration control algorithm, protection systems and communication infrastructure are required at the network and MG levels. In this study, first, a hierarchical control structure is discussed for interconnecting the neighbour autonomous MGs where the introduced primary control level is the main focus of this study. Through the developed primary control level, this study demonstrates how the parallel DERs in the system of multiple interconnected autonomous MGs can properly share the load of the system. This controller is designed such that the converter-interfaced DERs operate in a voltage-controlled mode following a decentralised power sharing algorithm based on droop control. DER converters are controlled based on a per-phase technique instead of a conventional direct-quadratic transformation technique. In addition, linear quadratic regulator-based state feedback controllers, which are more stable than conventional proportional integrator controllers, are utilised to prevent instability and weak dynamic performances of the DERs when autonomous MGs are interconnected. The efficacy of the primary control level of the DERs in the system of multiple interconnected autonomous MGs is validated through the PSCAD/EMTDC simulations considering detailed dynamic models of DERs and converters.

Sustaining safety and mobility amongst older adults : the multilevel older driver self-regulation model

This multidisciplinary research advanced the current understanding of self-regulation – a critical component in safe and sustainable mobility for older adults. It investigates the sociodemographic and psychosocial factors that underlies older adults' self-regulation, and examines their travel behaviours using a combination of self-report, in-vehicle and wearable devices. This research developed a novel theoretical model that significantly predicts self-regulation and objectively driving behaviours among older drivers.

Socio-demographic characteristics, modifiable lifestyle factors, and health as predictors of mental health in midlife and older Australian women: a multilevel investigation

Background Poor mental health is a significant cause of morbidity and mortality, yet debate continues about factors most likely to predict poor mental health outcomes. Objective This cohort study examines the influence of modifiable lifestyle factors, menopausal symptoms, and physical health on the mental health of midlife and older Australian women. Methods: Random sampling was used to recruit women aged 40-55, from rural and urban areas of Queensland, Australia. Overall, 340 women completed mailed surveys on socio-demographic characteristics, midlife symptoms (Greene Climacteric Scale©), modifiable lifestyle factors, and mental health (SF-12©) in 2001, 2004 and 2011. Hierarchical repeated-measure models were used to explore the correlates of poor mental health over time. Results The mean age [SD] at baseline was 55 [2.7] years, most were married (73%, n=248) and 18% were pre-menopausal. The model suggested that variance in mental health widened and showed a non-linear increase with age. Decrements in mental health were associated with an increase in midlife symptoms (Greene psychological scale, P <0.01; Greene somatic scale, P <0.05), time (P <0.01), poor physical health (P <0.01) and individual variance (P <0.01). Socio-demographics and lifestyle factors had little influence on mental health over time. Conclusion Findings suggest that while women’s mental health may decline during midlife, the effect is temporary; in older women, physical health and individual factors seem to be increasingly significant. This research highlights the importance of active health promotion as a means of enhancing both physical and mental health in midlife women.

Change readiness : a multilevel review

The authors conducted a theoretical review of the change readiness literature and identified two major limitations with this work. First, while there is substantial agreement about the key cognitions that underlie change readiness, researchers have not examined the affective element of this attitude. Second, researchers have not adopted a multilevel perspective when considering change readiness. The authors address these limitations and argue that it is important to incorporate affect into definitions of the change readiness construct and also when measuring this construct. They then develop a multilevel framework that identifies the antecedents and consequences of individual, work group, and organizational change readiness. Next, the authors outline the theoretical processes that lead to the development of individual and collective change readiness. They then review theoretical and empirical evidence to identify the antecedents of change readiness at the three levels of analysis. Finally, the authors identify a number of suggestions to guide future research seeking to adopt a multilevel approach to change readiness.