A three-phase to single-phase matrix converter for high-frequency induction heating

The paper describes a new three-phase to single-phase matrix converter featuring unity input power factor, very low input total harmonic distortion, and soft-switching over the full power range, for high frequency induction heating applications. A variable output pulse density modulation scheme has been proposed for stable operation of the converter, with the notable feature of requiring no on-line calculations for the synthesis of three-phase input current system. Practical issues in realising the converter, viz. line frequency synchronisation and output current circulation, are described. Good agreement between simulation and experimental results confirm the benefits of the proposed converter

Comparison of single-phase matrix converter and H-bridge converter for radio frequency induction heating

This paper compares the newly developed single-phase matrix converter and the more conventional H- bridge converter for radio frequency induction heating. Both the converters exhibit unity power factor, very low total harmonic distortion at the utility supply interface, good controllability under soft switching condition for a wide range of power, and high efficiencies, whilst still having simple structures. A novel switching control pattern has been proposed for the matrix converter in order to maintain the comparable performance to the H-bridge converter. Simulation and experimental results for both converters are presented. Comparisons between two converters have confirmed the excellent performance of the proposed matrix converter

Single phase matrix converter for radio frequency induction heating

Conventional converters for radio frequency induction heating usually follow an AC-DC-AC structure, which can exhibit non-unity power factor and introduce large harmonic currents into the utility supply. The need for a direct converter for radio frequency induction heating, featuring unity power factor, and sinusoidal input current, has motivated the development of a single phase matrix converter as an induction heater. A novel commutation strategy is therefore required to ensure smooth operation of the converter whilst creating a high frequency output under soft switching conditions. The operating principle and features of the proposed converter are described here, and experimentally verifie

TYPOLOGICAL TRANSFORMATION AMONG LATE PALEOLITHIC FLAKED CORE TOOLS IN VIETNAM: AN EXAMINATION OF THE PA MUOI ASSEMBLAGE

This paper explores typological transformations among late Paleolithic pebble tools excavated from Pa Muoi site in the Northwestern mountainous region of Vietnam. The site contains approximately 1665 pebble choppers over an excavation area of 449 m2. An attribute analysis is undertaken to examine the time-ordering of dimensional and morphological changes as reduction proceeds

Risk management of the Vietnamese banking system: A market research survey

The purpose of this paper is to examine risk management of the Vietnamese banking system. This is the first such study of the Vietnamese banking system. To be able to carry out a comparative analysis and provide policy recommendations for risk management, we carry out an original survey of Vietnamese commercial banks using a questionnaire. 42% of the interviewees are General/Deputy General Directors and 58% are Heads/Deputies of a risk management department. The Kruskal-Wallis, Pearson chi-square and other tests are employed to examine the relationship between risk management and bank efficiency. The survey results indicate that there is a difference between banks in terms of risk area identification, risk intensification methods prioritised, risk monitoring methods, efficiency improvement suggestions, awareness of other banks’ risk management systems and credit risk analysis

Performance of the banking sector of a developing country: a non-structural model using the disequilibrium approach

Based on the non-structural model – disequilibrium approach (Goddard and Wilson, 2009), this paper presents an empirical assessment of the degree of competition within the Vietnamese banking system from 1999 to 2009. We examine a greater number of environmental covariates and different dependent variables compared to previous applications of this model. Moreover, we use lagged input prices (to avoid endogeneity) and exclude assets (to avoid specification bias) in our models. The results indicate that the Vietnamese banking system operates in a monopolistic environment

Skeletal, Dentoalveolar, and Periodontal Changes of Skeletally Matured Patients with Maxillary Deficiency Treated with Microimplant‐assisted Rapid Palatal Expansion Appliances: A Pilot Study

Introduction: Microimplant‐assisted rapid palatal expansion (MARPE) has recently been offered to adult patients for correcting maxillary transverse deficiency. However, there is limited information in the literature on the success of this appliance and its skeletal and dental effects on skeletally matured patients. The purpose of this study was to investigate the immediate skeletal, dentoalveolar, and periodontal response to MARPE appliance using cone‐beam computed tomography in a skeletally matured patient as assessed by the cervical vertebral maturation method. Materials and Methods: Eight consecutively treated patients (2 females, 6 males; mean age of 21.9 ± 1.5 years) treated with a maxillary skeletal expander were included in the study. Measurements were taken before and after expansion to determine the amount of midpalatal suture opening, upper facial bony expansion, alveolar bone bending, dental tipping, and buccal bone thickness (BBT). Data were analyzed using a one‐way ANOVA and matched‐pair t‐test (α = 0.05). Results: Midpalatal suture separation was found in 100% of the patients with no dislodged microimplants. Total maxillary expansion was attributed to 41% skeletal, 12% alveolar bone bending, and 48% dental tipping. Pattern of midpalatal suture opening was found to be parallel in both the coronal and axial planes. On average, the absolute dental tipping ranged from 4.17° to 4.96° and the BBT was reduced by an average of 39% measured at the premolars and molars. Conclusions: The MARPE appliance can be a clinically acceptable, nonsurgical treatment option for correcting mild to moderate maxillary transverse discrepancies for skeletally matured adult patients with a healthy periodontium