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Seamless Mode Transfer of Utility Interactive Inverters Based on Indirect Current Control
Kyungbae Lim,Injong Song,Jaeho Choi,Hyeong-Jun Yoo,Hak-Man Kim 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.1
This paper proposes an indirect current control technique based on a proportional resonant (PR) approach for the seamless mode transfer of utility interactive inverters. Direct-current and voltage hybrid control methods have been used for inverter control under grid-connected and islanded modes. A large bandwidth can be selected due to the structure of single-loop control. However, this results in poor dynamic transients due to sudden changes of the controller during mode changes. Therefore, inverter control based on indirect current is proposed to improve the dynamic transients by consistently controlling the output voltage under all of the operation modes. A PR-based indirect current control topology is used in this study to maintain the load voltage quality under all of the modes. The design processes of the PR-based triple loop are analyzed in detail while considering the system stability and dynamic transients. The mode transfer techniques are described in detail for both sudden unintentional islanding and islanded mode voltage quality improvements. In addition, they are described using the proposed indirect control structure. The proposed method is verified by the PSiM simulations and laboratory-scale VDER-HILS experiments.
Exploration of Service Improvement Based on a Content Analysis of Consumer Reviews
KyungBae Park,Sung Ho Ha 한국인터넷전자상거래학회 2018 인터넷전자상거래연구 Vol.18 No.6
Deriving meaningful insights from massive amount of user-generated contents is not a trivial task. To tackle this issue, this study proposes an integrated text mining framework to uncover important latent dimensions buried in the textual information to efficiently track the changes in the dimensions over time by covariate of interests. In doing so, this study applies two stages of text analytics of sentiment analysis and topic model utilizing consumer reviews scraped from a popular online review site. The sentiment analysis is conducted as an objective measure to classify the polarity of reviews in order to leverage positive ones connotative of strengths and negative ones connotative of weaknesses. Subsequently, the structural topic model(STM) discovers dimensions(topics). In the STM, each customer review is represented as a probabilistic distribution over a set of underlying dimensions. This interdisciplinary approach highlights several implications theoretically and practically and the research framework leverages textual information to uncover, track, and compare the latent dimensions, and enables us to understand the relationships among the dimensions and covariates of interest.
Legal Problems and Assignments of Non-Standard Workers
( Kyungbae Cho ) 서울대학교 아시아태평양법연구소 2002 Journal of Korean Law Vol.2 No.2
Non-standard work constitutes one of the most controversial labor law issues. It is a form of employment developed by the personnel techniques founded on the employment flexibility. This form of employment create instability and inequality and dispense with the employer’s obligations in the labor law and the social security law. The non-standard worker’s legal status in Korea is very unstable, but the law rarely provides special protection for it. The Labor Standards Act and the Law for the Protection of Temporary Workers(1998) have provided some protection for non-standard workers under some of their articles. But the content and range of the protective articles are too simple and confined to solve in an efficient way the many legal problems arising from non-standard employment. The basic goal of the regulation of nonstandard employment is to achieve both flexible business operation and employment stability. The real employment need of the enterprise and the choice of the workers must reasonably be accommodated. For this reason, in the first place, amendment must be made to the Labor Standards Act articles dealing with the employment contract period and clarifications must be made regarding the legal effects of illegal use of non-standard employment. Second, the employment instability of non-standard employment must be removed and the regulation promoting improvements in the work conditions must be strengthened. Employment stability is an absolute pre-condition for a worker to exercise his/her rights under the Labor Standards Act and the Trade Union and Labor Relations Adjustment Act. And the lure of non-standard employment must be weakened by strictly enforcing the rule of “equal work, equal wage.” Third, the social balance of the burden of unemployment risk must be made more level between the worker and the employer. The current law only lessens the burden of the employer and demands the one-sided sacrifice of the worker. Furthermore, when coming up with a legislation to increase the stability of non-standard employment, the objective employment conditions, the tendency of the court’s interpretation of the law and the employer-worker relationship must all be taken into consideration. Last of all, the principle should be established that the use of non-standard worker can not be permitted for the execution of the normal and permanent activity of the enterprise.
Output Voltage Regulation for Harmonic Compensation under Islanded Mode of Microgrid
Kyungbae Lim,Jaeho Choi 전력전자학회 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.2
This study examines a P+multi resonant-based voltage control for voltage harmonics compensation under the islanded mode of a microgrid. In islanded mode, the inverter is defined as a voltage source to supply the full local load demand without the connection to the grid. On the other hand, the output voltage waveform is distorted by the negative and zero sequence components and current harmonics due to the unbalanced and nonlinear loads. In this paper, the P+multi resonant controller is used to compensate for the voltage harmonics. The gain tuning method is assessed by the tendency analysis of the controller as the variation of gain. In addition, this study analyzes the slight voltage magnitude drop due to the practical form of the P+multi resonant and proposes a counter method to solve this problem by adding the PI-based voltage restoration method. The proposed P+multi resonant controller to compensate for the voltage harmonics is verified through the PSIM simulation and experimental results.