• Journal of Power Electronics
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• 제11권2호
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• pp.218-227
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• 2011

The subject of variable step size maximum power point tracking (MPPT) algorithms has been addressed in the literature. However, most of the addressed algorithms tune the variable step size according to two variables: the photovoltaic (PV) array voltage ($V_{PV}$) and the PV array current ($I_{PV}$). Therefore, both the PV array current and voltage have to be measured. Recently, maximum power point trackers that arc based on a single variable ($I_{PV}$ or $V_{PV}$) have received a great deal of attention due to their simplicity and ease of implementation, when compared to other tracking techniques. In this paper, two methods have been proposed to design a variable step size MPPT algorithm using only a single current sensor for stand-alone battery storage PV systems. These methods utilize only the relationship between the PV array measured current and the converter duty cycle (D) to automatically adapt the step change in the duty cycle to reach the maximum power point (MPP) of the PV array. Detailed analyses and flowcharts of the proposed methods are included. Moreover, a comparison has been made between the proposed methods to investigate their performance in the transient and steady states. Finally, experimental results with field programmable gate arrays (FPGAs) are presented to verify the performance of the proposed methods.

• Smart Structures and Systems
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• 제4권4호
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• pp.493-515
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• 2008

Semi-active control systems have attracted a great deal of attention in recent years because these systems can operate on battery power alone, proving advantageous during seismic events when the main power source of the structure may likely fail. The behavior of semi-active devices is often highly non-linear and requires suitable and efficient control algorithm. This paper presents the comparative study and performance of variable semi-active friction dampers by using recently proposed predictive control law with direct output feedback. In this control law, the variable slip force of semi-active variable friction damper is kept slightly lower than the critical friction force, which allows the damper to remain in the slip state during an earthquake, resulting in improved energy dissipation capability. This control algorithm is able to produce a continuous and smooth slip forces for a variable friction damper. The numerical examples include a structure controlled with multiple variable semi-active friction dampers and with multiple passive friction dampers. A parameter, gain multiplier defined as the ratio of damper force to critical damper control force, is investigated under four different real earthquake ground motions, which plays an important role in the present control algorithm of the damper. The numerically evaluated optimum parametric value is considered for the analysis of the structure with dampers. The numerical results of the variable friction dampers show better performance over the passive dampers in reducing the seismic response of structures.

• 한국중재학회지:중재연구
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• 제28권2호
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• pp.179-200
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• 2018

The purpose of this study is to investigate the effects of service training and arbitration support on superstore workers' work performance. The conclusion could be summarized as follows. First, as a result of Hypothesis 1 that service training and arbitration support for superstore workers would significantly affect the factor of workers' emotional labor, when surface acting of emotion and frequency of expressing emotions were the dependent variable, only arbitration support was positively correlated. When emotional diversity was the dependent variable, there was a significantly positive relationship with service training. Second, for Hypothesis 2 that service training and arbitration support for superstore workers would significantly influence the workers' job satisfaction, it was found that only organizational support was significantly positive when wage satisfaction was the dependent variable. When job satisfaction was the dependent variable, service training and arbitration support were significantly correlated positively. Third, for Hypothesis 3 that service training and arbitration support for superstore workers would significantly affect the service delivery level when service responsiveness was the dependent variable, service training and arbitration support were significantly positive. When service expertise was the dependent variable, there was also a significantly positive relationship with service training and arbitration. On the other hand, all the three independent variables-service training, organizational support, and arbitration support-showed a significantly positive relationship when the willingness and effort of service was the dependent variable.

• 한국병원경영학회지
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• 제13권4호
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• pp.1-26
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• 2008

This study examines the statistical relationship between medical specialists and managerial performance, using regression analysis with the number of medical specialists per 100 beds as the independent variable and the managerial performance index as the dependent variable. Managerial performance index incorporated the number of out-patients per specialist, the number of in-patients per specialist, the volume of revenue per specialist, the number of beds per specialist, and the average length of stay. To compare different groups of hospitals, dummy variable was applied to five groups of hospitals according to size: 100-299 beds, 300-599 beds, 600-899 beds, 900-1199 beds, and more than 1200 beds. The data consisted of 181 general hospitals with more than 100 beds, which included 28 public hospitals, 73 corporate hospitals, 64 university hospitals and 16 private hospitals. Of those, 87 hospitals were located in big cities and 94 hospitals in medium to small cities. This study used hospitals from the Korean Hospital Association, and data published in 2004. The collected data sample was analyzed using the SPSSWIN 12.0 version, and the study hypothesis was tested using regression analysis. The findings of this study are summarized as follows: Hypothesis 1 predicting a negative effect of the number of medical specialists on the number of out-patients per specialist was supported with statistical significance. The analysis of dummy variable showed causality in all the hospital groups larger than the group of 100-299 beds. Hypothesis 2 predicting a negative effect of the number of medical specialists on the number of in-patients per specialist was supported with statistical significance. The analysis of dummy variable showed causality in the hospital group of 300-599 beds when compared to the group of 100-299 beds. Hypothesis 3 predicting a negative effect of the number of medical specialists on the volume of revenue per specialist was not supported. However, the analysis of dummy variable showed that the volume of revenue per specialist increased in the hospital groups of 600-899 beds, 900-1199 beds, and over 1200 beds, when compared to the group of 100-299 beds. Hypothesis 4 predicting a negative effect of the number of medical specialists on the average length of stay was supported with statistical significance. The analysis of dummy variable showed causality in the hospital group of 300-599 beds, when compared to the group of 100-299 beds. Results of this study show that the number of the medical specialists per 100 beds is an important factor in hospital managerial performance. Most hospitals have tried to retain as many medical specialists as possible to keep the number of patients stable, to ensure adequate revenue, and to maintain efficient managerial performance. Especially, the big hospitals with greater number of beds and medical specialists have shown greater revenue per medical specialist despite the smaller number of patients per medical specialist. Findings of this study explains why hospitals in Korea are getting bigger.

• Wind and Structures
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• 제18권2호
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• pp.195-213
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• 2014

Recently, the horizontal axis rotor performance optimizer (HARP_Opt) tool was developed in the National Renewable Energy Laboratory, USA. This innovative tool is becoming more popular in the wind turbine industry and in the field of academic research. HARP_Optwas developed on the basis of two fundamental modules, namely, WT_Perf, a performance evaluator computer code using the blade element momentum theory; and a genetic algorithm module, which is used as an optimizer. A pattern search algorithm was more recently incorporated to enhance the optimization capability, especially the calculation time and consistency of the solutions. The blade optimization is an aspect that is highly dependent on experience and requires significant consideration on rotor control strategies, wind data, and generator type. In this study, the effects of rotor control strategies including fixed speed and fixed pitch, variable speed and fixed pitch, fixed speed and variable pitch, and variable speed and variable pitch algorithms on optimal blade shapes and rotor performance are investigated using optimized blade designs. The effects of environmental wind data and the objective functions used for optimization are also quantitatively evaluated using the HARP_Opt tool. Performance indices such as annual energy production, thrust, torque, and roof-flap moment forces are compared.

• 제어로봇시스템학회논문지
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• 제6권3호
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• pp.241-247
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• 2000

The reference model of an MRC (model reference control) provides the desired trajectory a plant should follow and thus the design of a reference model has a significant effect on control performance. In most control systems control input to a plant has some bounds and it is preferable to make use of as large control inputs as possible within the range of no saturation. In this paper a new approach of selecting the reference model is proposed for bounded control inputs. Design variables of the reference model are determined in such a way that maximizes the performance index within the range of no saturation. Moreover this variable reference model is regularly updated during control. This scheme is verified by application to the servo motor position control system in various simulations. The responses of the MRC with a variable reference model show better tracking performance than that with a fixed reference mode. Moreover by adjusting the update interval of the reference model the control performance can be further improved.

• KIEE International Transactions on Power Engineering
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• 제3A권1호
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• pp.17-26
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• 2003

In this paper, the comparative steady-state operating performance analysis algorithms of the stand-alone single-phase self-excited induction generator (SEIG) is presented on the basis of the two nodal admittance approaches using the per-unit frequency in addition to a new state variable de-fined by the per-unit slip frequency. The main significant features of the proposed operating circuit analysis with the per-unit slip frequency as a state variable are that the fast effective solution could be achieved with the simple mathematical computation effort. The operating performance results in the simulation of the single-phase SEIG evaluated by using the per-unit slip frequency state variable are compared with those obtained by using the per-unit frequency state variable. The comparative operating performance results provide the close agreements between two steady-state analysis performance algorithms based on the electro-mechanical equivalent circuit of the single-phase SEIG. In addition to these, the single-phase static VAR compensator; SVC composed of the thyristor controlled reactor; TCR in parallel with the fixed excitation capacitor; FC and the thyristor switched capacitor; TSC is ap-plied to regulate the generated terminal voltage of the single-phase SEIG loaded by a variable inductive passive load. The fixed gain PI controller is employed to adjust the equivalent variable excitation capacitor capacitance of the single-phase SVC.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
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• pp.652-655
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• 1996

This paper develops an AC motor controller for applications. The AC motor controller is designed based on the variable structure control method and a variable structure disturbance observer is added to reduce the effects of exogenous disturbances. The designed controller is installed on the z-axis of a CNC machining center and milling experiments were performed. The results show improved performance on both position and speed tracking, when compared to the factory-designed servo controller.

• The Journal of Asian Finance, Economics and Business
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• 제7권11호
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• pp.575-583
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• 2020

Vietnam is the country with the largest animal feed production in Southeast Asia. Domestic animal feed manufacturing enterprises play an important role in animal husbandry in particular and in agriculture in general. However, domestic animal feed enterprises in Vietnam are encountering shortcomings. This paper is conducted to investigate the impact levels of external determinants on business performance of domestic animal feed manufacturing enterprises, including: (i) policy and economic mechanism, (ii) supply-demand of animal feed products, and (iii) nature and level of market competition. We presented a research method, explaining the dependent variable 'business performance' and the independent variables. Data were collected from 120 questionnaires from domestic animal feed manufacturing enterprises. Based on these data, we use Cronbach's Alpha, EFA and run regression model for assessing the impact levels of each independent variable on the dependent variable of business performance of domestic animal feed manufacturing enterprises. The results show that three external determinants including (i) policy and economic mechanism, (ii) supply-demand of animal feed products, and (iii) nature and level of market competition, have positive relationships with business performance. Based on the findings, some recommendations are given for improving business performance of domestic animal feed manufacturing enterprises to ensure sustainability.

• The Journal of Asian Finance, Economics and Business
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• 제8권2호
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• pp.625-633
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• 2021

This study analyzes the impact of the reward variable on employees' performance through work motivation and employee engagement. This study's specific purpose is to investigate employee engagement's mediating role in the relationship between reward and employee performance. The sample of research is the employee at Sukorejo, Pasuruan Indonesia. The sample is permanent employees at manufacture corporate. The sample size is 150 employees of the total 759 workers through the calculation of the Slovin formula. Respondents in this study were employees with the criteria for having worked for at least last five years. The data obtained is in the form of answers from employees to the statements submitted. The data analysis was used structural equation modeling partial least square. To test the relationship between variables, it was equipped with a Sobel mediation test of statistics. SmartPLS 3.0 is used to help analyze the relationship between variables. The result shows that the reward does not have a direct influence on the performance of employees. However, it has a significant positive effect on the performance of employees through employee engagement. While working motivation variable does not have the role as a mediation variable related to the effect of reward on employee performance.