This longitudinal study investigates firm-survival in a peripheral region. The analysis relies on a unique longitudinal dataset, encompassing all firms in 17 Stockholm Archipelago islands during 2000-2019, collected through data triangulation methods. The study employs multivariate analysis accomplished by three-level logistic regression models of repeated observations (level-1) of the same distinct firms (level-2) situated in specific islands (level-3). The main novel results suggest that firms on islands with higher population density have an increased probability of exit – specifically, that there exists an overcrowding of local markets and a harsher selection process in these islands. While time-distance to the mainland have been discussed as problematic, the effect on firm-survival is insignificant. However, local access to essential services and infrastructures significantly lowers the likelihood of firm-exit. Islands with increasing institutional thickness have increased community dynamics with more knowledge spillovers, community-level learning, and entrepreneurial ecosystems, leading to a higher likelihood of firm-survival. A higher ratio of summer visitors increases the probability of exit, suggesting that firms on islands with seasonal dependability may have difficulties surviving the off-season. / Trots dess närhet till Sveriges största och snabbast växande marknad delar Stockholms skärgård många drag med andra regioner som befinner sig i periferin, det vill säga utkanten. Bland annat har skärgården svårigheter att dra nytta av den ekonomiska dynamik som är karakteristisk för centrala regioner. Trots den problematik som kan vara typisk för perifera områden (såsom brist på resurser och avfolkning), betonar forskare att beslutsfattare måste utgå ifrån den lokalspecifika och regionala kontexten. Små och medelstora företag i periferin förväntas inte enbart bidra med ökade intäkter till regionen, utan förväntas även tillmötesgå sysselsättningsefterfrågan. Frågan om vilka företag som överlever, och inte minst förklaringarna till företags överlevad, är därför särskilt viktig i dessa regioner. Trots att orsakerna till företags överlevnad länge diskuterats inom forskningen, råder det brist på studier som tar upp den kontext som avser periferi och faktorer som är betydelsefulla för en specifik kontext. Denna studie utgör ett bidrag till en sådan analys. Studiens resultat visar att överlevnadsmöjligheterna är sämre för företag som befinner sig på öar med högre andel fastboendebefolkning. Detta indikerar att på större öar, med en relativt sett högre befolkningsnivå, är konkurrensen mer påtaglig. Vidare, trots att transportmöjligheter till fastlandet ofta anges som problem i diskussioner, slår studien fast att tidsavståndet till huvudorter på fastlandet inte är viktigt för företags överlevnadsmöjligheter. Däremot har företag sämre utsikter för överlevnad på öar med högre andel sommargäster i relation till vinterbesökare. Tillgången till fiber/bredband, livsmedelsbutiker som är öppna året runt, och förskolor bidrar betydligt till överlevnadsmöjligheterna. Vidare konstaterar studien att ett mer aktivt föreningsliv på en ö ökar möjligheterna för överlevnad. För att komma fram till dessa samt andra resultat, har studien använt sig av en longitudinell ansats, som innebär att studieobjekten (företagen) följs över tid, liksom ett unikt empiriskt underlag. Detta material har samlats från flera olika typer källor, underlag och databaser som beskriver både öar och företag i Stockholms skärgård, där undersökningsperioden är mellan år 2000 och år 2019. Vidare tillämpar studien en i forskning om företags överlevnad tidigare mindre beprövad statistisk metod: i korthet undersöker studien företag och öarna där de finns, som om dessa vore enskilda ”individer”. Dessa ”individer” följs från sin födsel –från att de bildas – till dess att de dör, det vill säga läggs ned. Under tiden ”individerna” följs, så undersöks även vilken betydelse de yttre betingelserna på öarna liksom faktorer i företagens omgivning har för deras överlevnadsförmåga. Specifikt studeras 1 341 företag på 17 av Stockholms skärgårdens öar (kärnöar).

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19471号 / 理博第4131号 / 新制||理||1594(附属図書館) / 32507 / 京都大学大学院理学研究科数学・数理解析専攻 / (主査)准教授 竹井 義次, 教授 岡本 久, 教授 小野 薫 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Switched reluctance motor has features like robust structure, low cost, and wide speed extension range over conventional induction and synchronous motors. These features make it a promising choice for many applications from electric vehicle to aerospace industry. However, due to its silent structure, the characteristics of switched reluctance motor are highly nonlinear. The nonlinearity makes it difficult to control and results in degraded performance such as high torque ripple and acoustic noise compared with conventional induction machine or synchronous machine. New power converters and control methods have to be developed to improve its performance. In order to reduce the current ripple and torque ripple, a novel three-level converter for switched reluctance motor is proposed. The operation modes and modulation method are presented in detail. Simulation and experimental results show that compared to conventional two-level converter, the proposed three-level converter is able to reduce current ripple, torque ripple and acoustic noise significantly without increasing cost. A fast and accurate current controller is essential for the torque control of switched reluctance motor. An adaptive current controller for the three-level converter is developed to avoid the performance degradation caused by manufacture inconsistency. This controller has the ability to adjust its parameters according to the specific motor it drives. Fast dynamic and high accuracy could be achieved through parameter adaption. In order to reduce the cost, and compete with the well-developed sensorless brushless DC and induction motor drive system, a new position sensorless control method for switched reluctance motor is proposed. This method is effective under both low speed operation and high speed operation. It can start with heavy load. It does not have to align the machine before start up as what is needed for many sensorless brushless DC drive systems. The proposed converter and control methods are all verified by simulation and experimental results. / Thesis / Doctor of Philosophy (PhD)

No description available.

High power multi-level converters are deemed as the mainstay power conversion technology for renewable energy systems including the battery storage system, PV farm and electrical vehicle charge station. This thesis is focused on the study of three-level DC/DC converter with multi-phase interleaved structure, with coupled and integrated magnetics to achieve high power density. The proposed interleaved phased legs offer the benefit of output current ripple reduction, while inversed coupled inductors can suppress the circulating current between phase legs. Compared with conventional non-interleaving three-level DC/DC converter with non-coupling inductors, both inductor current ripple and output current ripple are largely reduced by interleaving with inverse-coupled inductors. Because of the non-linearity of the inductor coupling, the equivalent circuit model is developed for the proposed interleaving structure. The model identifies the existence of multiple equivalent inductances during one switching cycle. A combination of them determines the inductor current ripple and dynamics of the system. By virtue of inverse coupling and means of controlling the coupling coefficients, one can minimize the current ripple and the unwanted circulating current. To further reduce the magnetic volume, the four inductors in two-phase three-level DC/DC converter are integrated into one common structure, incorporating the negative coupling effects. The integrated magnetic structure can effectively suppress the circulating current and reduce the inductor current ripple and it is easy to manufacture. This thesis provides an equivalent circuit model to facilitate the design optimization of the integrated system. A prototype of integrated coupled inductors is assembled with nano-crystalline C-C core and powder block core. It is tested with both impedance analyzer and single pulse tester, to guarantee proper mutual inductance for inductor current ripple and output current ripple target. With a two-phase three-level DC/DC converter hardware, the concept of integrated coupled inductors is verified, showing its good performance in high-voltage, high-power conversion applications. / Master of Science

This dissertation proposes a high-power, high-frequency and high-density three-level parallel resonant converter for capacitor charging. DC-DC pulsed power converters are widely used in military and medical systems, where the power density requirement is often stringent. The primary means for reducing the power converter size has been to reduce loss for reduced cooling systems and to increase the frequency for reduced passive components. Three-level resonant converters, which combine the merits of the three-level structure and resonant converters, are an attractive topology for these applications. The three-level configuration allows for the use of lower-voltage-rating and faster devices, while the resonant converter reduces switching loss and enhances switching capability. This dissertation begins with an analysis of the influence of variations in the structure of the resonant tank on the transformer volume, with the aim of achieving a high power density three-level DC-DC converter. As one of the most bulky and expensive components in the power converter, the different positions of the transformer within the resonant tank cause significant differences in the transformer's volume and the voltage and current stress on the resonant elements. While it does not change the resonant converter design or performance, the improper selection of the resonant tank structure in regard to the transformer will offset the benefits gained by increasing the switching frequency, sometimes even making the power density even worse than the power density when using a low switching frequency. A methodology based on different structural variations is proposed for a high-density design, as well as an optimized charging profile for transformer volume reduction. The optimal charging profile cannot be perfectly achieved by a traditional output-voltage based variable switching frequency control, which either needs excess margin to guarantee ZVS, or delivers maximum power with the danger of losing ZVS. Moreover, it cannot work for widely varied input voltages. The PLL is introduced to overcome these issues. With PLL charging control, the power can be improved by 10% with a narrow frequency range. The three-level structure in particular suffers unbalanced voltage stress in some abnormal conditions, and a fault could easily destroy the system due to minimized margin. Based on thoroughly analysis on the three-level behaviors for unbalanced voltage stress phenomena and fault conditions, a novel protection scheme based on monitoring the flying capacitor voltage is proposed for the three-level structure, as well as solutions to some abnormal conditions for unbalanced voltage stresses. A protection circuit is designed to achieve the protection scheme. A final prototype, built with a custom-packed MOSFET module, a SiC Schottky diode, a nanocrystalline core transformer with an integrated resonant inductor, and a custom-designed oil-cooled mica capacitor, achieves a breakthrough power density of 140W/in3 far beyond the highest-end power density reported (<100 W/in3) in power converter applications. / Ph. D.

This thesis focuses on the study, implementation and improvement of a digital controller for a power factor correction (PFC) converter. The development of the telecommunications industry and the Internet demands reliable, cost-effective and intelligent power. Nowadays, the telecommunication power systems have output current of up to several kilo amperes, consisting of tens of modules. The high-end server system, which holds over 100 CPUs, consumes tens of kilowatts of power. For mission-critical applications, communication between modules and system controllers is critical for reliability. Information about temperature, current, and the total harmonic distortion (THD) of each module will enable the availability of functions such as dynamic temperature control, fault diagnosis and removal, and adaptive control, and will enhance functions such as current sharing and fault protection. The dominance of analog control at the modular level limits system-module communications. Digital control is well recognized for its communication ability. Digital control will provide the solution to system-module communication for the DC power supply. The PFC converter is an important stage for the distributed power system (DPS). Its controller is among the most complex with its three-loop structure and multiplier/divider. This thesis studies the design method, implementation and cost effectiveness of digital control for both a PFC converter and for an advanced PFC converter. Also discussed is the influence of digital delay on PFC performance. A cost-effective solution that achieves good performance is provided. The effectiveness of the solution is verified by simulation. The three level PFC with range switch is well recognized for its high efficiency. The range switch changes the circuit topology according to the input voltage level. Research literature has discussed the optimal control for both range-switch-off and range-switch-on topologies. Realizing optimal analog control requires a complex structure. Until now optimal control for the three-level PFC with analog control has not been achieved. Another disadvantage of the three-level PFC is the output capacitor voltage imbalance. This thesis proposes an active balancing solution to solve this problem. / Master of Science

abstract: Through a two study simulation design with different design conditions (sample size at level 1 (L1) was set to 3, level 2 (L2) sample size ranged from 10 to 75, level 3 (L3) sample size ranged from 30 to 150, intraclass correlation (ICC) ranging from 0.10 to 0.50, model complexity ranging from one predictor to three predictors), this study intends to provide general guidelines about adequate sample sizes at three levels under varying ICC conditions for a viable three level HLM analysis (e.g., reasonably unbiased and accurate parameter estimates). In this study, the data generating parameters for the were obtained using a large-scale longitudinal data set from North Carolina, provided by the National Center on Assessment and Accountability for Special Education (NCAASE). I discuss ranges of sample sizes that are inadequate or adequate for convergence, absolute bias, relative bias, root mean squared error (RMSE), and coverage of individual parameter estimates. The current study, with the help of a detailed two-part simulation design for various sample sizes, model complexity and ICCs, provides various options of adequate sample sizes under different conditions. This study emphasizes that adequate sample sizes at either L1, L2, and L3 can be adjusted according to different interests in parameter estimates, different ranges of acceptable absolute bias, relative bias, root mean squared error, and coverage. Under different model complexity and varying ICC conditions, this study aims to help researchers identify L1, L2, and L3 sample size or both as the source of variation in absolute bias, relative bias, RMSE, or coverage proportions for a certain parameter estimate. This assists researchers in making better decisions for selecting adequate sample sizes in a three-level HLM analysis. A limitation of the study was the use of only a single distribution for the dependent and explanatory variables, different types of distributions and their effects might result in different sample size recommendations. / Dissertation/Thesis / Doctoral Dissertation Educational Psychology 2016

In this thesis, field oriented control of permanent magnet synchronous motors using three-level neutral-point-clamped inverter is studied. Permanent magnet synchronous motors are used in high performance drive applications. In this study, the permanent magnet synchronous motor is fed by three-level neutral-point-clamped inverter. For three-level neutral-point-clamped inverter different space vector modulation algorithms, which are reported in literature, are analyzed and compared via computer simulations. The voltage balance on dc-link capacitors is also analyzed and a software control method is implemented in conjunction with the space vector PWM modulation, utilized. Nonlinear effects such as dead-time, semiconductor voltage drop and delays in gate drive circuitries also present in neutral-point-clamped inverter. The effects of these nonlinearities are studied and a compensation method for these nonlinear effects is proposed. The theoretical results are supported with computer simulations and verified with experimental results.

In this thesis, a new approach for single-stage power factor correction converters is proposed to increase their power ratings to be in the multiple kilowatts levels. The proposed techniques are based on the utilization of modified three-level resonant converter topologies. These topologies provide low component stresses, high frequency operation, zero voltage switching, applicability under a wide range of input and output conditions as well as added control flexibility. The proposed control algorithms are based on a combination of variable frequency and asymmetrical pulse width modulation control or variable frequency and phase shift modulation control. In either case, the variable frequency control is used to tightly regulate the output voltage, whereas, pulse width or phase shift modulation is used to regulate the dc-bus voltage as well as the input power factor. New converter topologies, their operation and steady state and dynamic analyses are presented in details. A modelling approach based on average multiple frequency methods is also proposed. This approach leads to the development of a full order state space model with the two control variables explicitly separated allowing a better controller design. The model can be used either at high level of detail expressing the non-linearities of the system or it can readily be simplified to a linear decoupled model for approximate solutions. Finally, a discrete time controller for the proposed converters, which is suitable for FPGA implementation, is presented. Analytical, simulation and experimental results are provided to verify the proposed concepts. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2008-01-30 14:28:15.725