• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.261-270
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• 2015

In this paper, the Optimal Harmonic Stepped Waveform (OHSW) method is proposed in order to eliminate the selective harmonic orders available at the output of cascaded multilevel inverter (CMLI) fed by solar photovoltaic (SPV). This technique is used to solve the harmonic elimination equations based on stepped waveform analysis in order to obtain the optimal switching angles which in turn reduce the Total Harmonic Distortion (THD). The OHSW method considers the output voltage waveform as four equal symmetries in each half cycle. In the proposed method, a solar fed fifteen level cascaded multilevel is considered where the magnitude of six numbers of harmonic orders is reduced. A programmable pulse generator is developed to carry the switching angles directly to the semiconductor switches obtained as a result of OHSW analysis. Simulations are carried out in MATLAB/Simulink in which a separate model is developed for solar photovoltaic which serves as the input for cascaded multilevel inverter. A 3kWp solar plant with multilevel inverter system is implemented in hardware to show the effectiveness of the proposed system. Based on the observation the OHSW method provides the reduced THD thereby improving power quality in renewable energy applications.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2278-2288
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• 2017

Multilevel converter topologies are widely used in many applications. The cascaded H-bridge multilevel inverter (CHBMI), which is one of many multilevel converter topologies, has been introduced as a useful topology in high and medium power. However, it has a drawback to require a lot of switches. Therefore, the reliability of CHBMI is important factor for analyzing the performance. This paper presents a simple switch fault diagnosis method for single-phase CHBMI. There are two types of switch faults: open-fault and short-fault. In the open-fault, the body diode of faulty switch provides a freewheeling current path. However, when the short-fault occurs, the distortion of output current is different from that of the open-fault because it has an unavailable freewheeling current flow path due to a disconnection of fuse. The fault diagnosis method is based on the zero current time analysis according to zero-voltage switching states. Using the proposed method, it is possible to detect the location of faulty switch accurately. The PSIM simulation and experimental results show the effectiveness of proposed switch fault diagnosis method.

• Communications for Statistical Applications and Methods
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• v.13 no.3
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• pp.701-718
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• 2006

In cancer microarray experiments, the experimenter or patient which is nested in each experimenter often shows quite heterogeneous error variability, which should be estimated for identifying a source of variation. Our study describes a Bayesian method which utilizes clinical information for identifying a set of DE genes for the class of subtypes as well as assesses and examines the experimenter effect and patient effect which is nested in each experimenter as a source of variation. We propose a Bayesian multilevel mixed effect model based on analysis of covariance (ANACOVA). The Bayesian multilevel mixed effect model is a combination of the multilevel mixed effect model and the Bayesian hierarchical model, which provides a flexible way of defining a suitable correlation structure among genes.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.9
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• pp.892-902
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• 2009

An efficient sequential optimization approach for metamodel was presented by Choi et al. This paper describes a new approach of the multilevel optimization method studied in Refs. [2] and [20,21]. The basic idea is concerned with multilevel iterative methods which combine a descent scheme with a hierarchy of auxiliary problems in lower dimensional subspaces. After fitting a metamodel based on an initial space filling design, this model is sequentially refined by the expected improvement criterion. The advantages of the method are that it does not require optimum sensitivities, nonlinear equality constraints are not needed, and the method is relatively easy to understand and use. As a check on effectiveness, the proposed method is applied to an engineering example.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.2168-2180
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• 2014

In this paper, a generalized power loss algorithm for multilevel neutral-point clamped (NPC) PWM inverters is presented, which is applicable to any level number of multilevel inverters. In the case of three-level inverters, the conduction loss depends on the MI (modulation index) and the PF (power factor), and the switching loss depends on a switching frequency, turn-on and turn-off energy. However, in the higher level of inverters than the three-level, the loss of semiconductor devices cannot be analyzed by conventional methods. The modulation depth should be considered in addition, to find the different conducting devices depending on the MI. In a case study, the power loss analysis for the three- and five-level NPC inverters has been performed with the proposed algorithm. The validity of the proposed algorithm is verified by simulation for the three-and five-level NPC inverters and experiment for three-level NPC inverter.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.10a
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• pp.573-576
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• 2000

In this paper, analysis of operating characteristics of hybrid cascade multilevel PWM rectifier without bulky and heavy isolation transformers is presented. The multilevel PWM rectifier is analyzed by using the circuit DQ transformation whereby the static and dynamic characteristics and some useful design relationships are obtained. Then, the operating characteristics such as active/reactive power relationships with respect to control variables, DC voltages build up are presented. It will be shown that the DC voltages for the multilevel output generation may be directly built up from AC utility source. Finally, to confirm the validity of the analysis, MATLAB simulations are tarried out.

• Journal of Korean Public Health Nursing
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• v.30 no.2
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• pp.311-325
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• 2016

Purpose: This study was conducted to examine the individual and community level factors associated with physical activity and to identify its relative effects using a multilevel analysis among Korean adults in certain counties. Methods: A cross-sectional data of 39,547 adults (age range of 19~64 years) living in 82 counties from the 2013 Korean Community Health Survey (KCHS) was analyzed. Individual and social correlates from KCHS and physical environmental data from the Korean Statistical Information Service were collected. A multilevel logistic regression was performed using Stata 10.0 IC. Results: Multilevel analyses showed that the effect of social and physical environmental on engaging in moderate or vigorous physical activity (MVPA) was significant in comparison to the influence of individual correlates. The individual factors that were associated with participating in MVPA included gender, marital status, education, job, and household income. In the community level, social environmental factors associated with engagement in MVPA were higher satisfaction with healthcare service (OR=3.410, 95% CI=1.109~11.269), a high level of social support (OR=5.920, 95% CI=1.459~22.657) and social network (OR=1.025, 95% CI= 1.017~1.032). Conclusion: To promote moderate or vigorous physical activity in Korean adults in some counties, social environmental factors should be considered along with individual correlates.

• The Journal of Economics, Marketing and Management
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• v.10 no.5
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• pp.1-6
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• 2022

Purpose: To overcome the question that depends too much on expert's subjective judgment in traditional risk identification, this paper structure the multilevel generalized fuzzy comprehensive evaluation mathematics model of the risk identification of project, to research the risk identification of the project. Research design, data and methodology: This paper constructs the multilevel generalized fuzzy comprehensive evaluation mathematics model. Through iterative algorithm of AHP analysis, make sure the important degree of the sub project in risk analysis, then combine expert's subjective judgment with objective quantitative analysis, and distinguish the risk through identification models. Meanwhile, the concrete method of multilevel generalized fuzzy comprehensive evaluation is probed. Using the index weights to analyse project risks is discussed in detail. Results: The improved fuzzy comprehensive evaluation algorithm is proposed in the paper, at first the method of fuzzy sets core is used to optimize the fuzzy relation matrix. It improves the capability of the algorithm. Then, the method of entropy weight is used to establish weight vectors. This makes the computation process fair and open. And thereby, the uncertainty of the evaluation result brought by the subjectivity can be avoided effectively and the evaluation result becomes more objective and more reasonable. Conclusions: In this paper, we use an improved fuzzy comprehensive evaluation method to evaluate a railroad engineering project risk. It can give a more reliable result for a reference of decision making.

• Science of Emotion and Sensibility
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• v.19 no.4
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• pp.95-110
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• 2016

The purpose of this study was to propose a proper method for the multilevel mediation analysis, for which the hierarchical method should be utilized, then MLM (multilevel modeling) approach as a hierarchical method has been popularly utilized until MSEM (multilevel structural equation modeling) approach was not proposed. This purpose was covered by three research questions about statistical methods, analytic procedure, and real example. First, MSEM statistical method was preferred to MLM method for its estimation accuracy and analytic flexibility. Second, the four-step procedures of model building, assumption examination, model comparison, and coefficient testing were proposed for the multilevel mediation analysis. Third, the real data of 2695 students of elementary and secondary schools and 89 teachers were analyzed in the multilevel directions of $2{\rightarrow}2{\rightarrow}1$ and $1{\rightarrow}1{\rightarrow}2$. Out of these directions of $2{\rightarrow}2{\rightarrow}1$, and $1{\rightarrow}1{\rightarrow}2$ model, only the coefficient of $2{\rightarrow}2{\rightarrow}1$ model was significant at the 95% CI. Mplus programs used for the real example are attached on the Appendix. Based on the results, significance and limitations of this study, were discussed in detail.

• Journal of Power Electronics
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• v.14 no.1
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• pp.48-60
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• 2014

Multilevel inverters have been widely used for high-voltage and high-power applications. Their performance is greatly superior to that of conventional two-level inverters due to their reduced total harmonic distortion (THD), lower switch ratings, lower electromagnetic interference, and higher dc link voltages. However, they have some disadvantages such as an increased number of components, a complex pulse width modulation control method, and a voltage-balancing problem. In this paper, a novel nine-level reduced switch cascaded multilevel inverter based on a multilevel DC link (MLDCL) inverter topology with reduced switching components is proposed to improve the multilevel inverter performance by compensating the above mentioned disadvantages. This topology requires fewer components when compared to diode clamped, flying capacitor and cascaded inverters and it requires fewer carrier signals and gate drives. Therefore, the overall cost and circuit complexity are greatly reduced. This paper presents modulation methods by a novel reference and multicarrier based PWM schemes for reduced switch cascaded multilevel inverters (RSCMLI). It also compares the performance of the proposed scheme with that of conventional cascaded multilevel inverters (CCMLI). Simulation results from MATLAB/SIMULINK are presented to verify the performance of the nine-level RSCMLI. Finally, a prototype of the nine-level RSCMLI topology is built and tested to show the performance of the inverter through experimental results.