• Particle and aerosol research
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• v.18 no.4
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• pp.109-127
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• 2022

Recently, low-cost particulate matter (PM) sensors have been widely used in monitoring mass concentration. Maintaining the accuracy of the sensors is important and requires rigorous performance evaluation and calibration. In this study, two commercial low-cost PM sensors(LCS), Plantower PMS3003 and Plantower PMS7003, were evaluated in the laboratory and field with a reference-grade PM monitor (GRIMM 11-D). Laboratory evaluation was conducted with single/mixed particles of PSL (Poly Styrene Latex) in an acrylic chamber at 20℃ and relative humidity of 20%. Field evaluation was conducted inside a building of Yonsei University (Shinchon) from February 12 to March 31, 2022. In both evaluations, LCS measured values became different from reference measured values when the relative humidity was high or the outdoor air PM10/PM2.5 ratio was high. Based on the field evaluation, the LCS measured values were corrected through four different regression analysis models. As a result, the multivariate polynomial regression analysis model showed highest matching with the reference PM monitor (PM2.5 >0.9, PM10 >0.85). In this model, the PM10/PM2.5 ratio and relative humidity were chosen as independent variables.

• Journal of Power Electronics
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• v.15 no.3
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• pp.712-720
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• 2015

A model predictive current control (MPCC) method that does not employ a cost function is proposed. The MPCC method can decrease common-mode voltages in loads fed by three-phase voltage-source inverters. Only non-zero-voltage vectors are considered as finite control elements to regulate load currents and decrease common-mode voltages. Furthermore, the three-phase future reference voltage vector is calculated on the basis of an inverse dynamics model, and the location of the one-step future voltage vector is determined at every sampling period. Given this location, a non-zero optimal future voltage vector is directly determined without repeatedly calculating the cost values obtained by each voltage vector through a cost function. Without utilizing the zero-voltage vectors, the proposed MPCC method can restrict the common-mode voltage within ± V_dc/6, whereas the common-mode voltages of the conventional MPCC method vary within ± V_dc/2. The performance of the proposed method with the reduced common-mode voltage and no cost function is evaluated in terms of the total harmonic distortions and current errors of the load currents. Simulation and experimental results are presented to verify the effectiveness of the proposed method operated without a cost function, which can reduce the common-mode voltage.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.12
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• pp.547-552
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• 2002

In this paper, the path loss in domestic terrain environments for IMT-2000 are measured and considered. Domestic terrain environments are classified and received power is measured at 1.9201GHz. In addition, the Path loss is calculated with consideration of the radiation pattern of antennas based on the results of measurement. For the consideration of path loss in domestic terrain environments, each path loss are fitted with the same slope of a reference model as "COST-231 HATA Urban Model", and then both are compared. As a result, all of the path loss in domestic terrain environments are lower than the path loss of a reference model as "COST-231 HATA Urban Model". We found that a difference of path loss in domestic terrain environments and a reference model is 5dB in urban, 8dB in sparse urban, 12dll in dense suburban, 13dB in suburban, 19dB in sparse suburban, and 29dB in road.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.32B no.10
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• pp.1338-1346
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• 1995

In this paper, we suggest the implementation of a DGPS system using two low cost commercial C/A code GPS modules and modems and its efficient operational techniques to provide DGPS service which guarantees the position accuracy of better than 10 meters for more users. The proposed DGPS system can be implemented easil at low cost because it needs a GPS module and a modem for each reference station and user. The reference station makes plans of the receiving schedule from the satellite set at each period and then provides the correction data for various satellite sets in a period. The main contribution of this paper is that users can utilize the correction data continuously and efficiently through the recursive least squares lattice filtering method. Experimental results show the position accuracy of better than 10 meters using the suggested DGPS system in almost real time.

• Proceedings of the KIPE Conference
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• 1997.07a
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• pp.14-20
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• 1997

Due to several advantages of Pulse Width Modulated(PWM) Converter, such as unity power factor with low-harmonics and energy regeneration, PWM converter has been widely used in industrial application. In every application of energy conversion equipment, the design and implementation must be carried out considering performance and cost. High quality with low cost is the best choice for energy conversion equipment. High dc link voltage can reduce inverter and motor side losses and system dimension compare to low dc link voltage. Analog controller can make PWM converter cheaper without considerable degradation of the performance than digital controller. This paper shows the simplified analog controller-for 600V dc link voltage using stationary reference frame control and the simulation results.

• Journal of Power Electronics
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• v.19 no.1
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• pp.168-178
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• 2019

Discrete space vector modulation (DSVM) is an effective method to improve the steady-state performance of the finite control set predictive control for permanent magnet synchronous motor drive systems. However, it requires complex computations due to the presence of numerous virtual voltage vectors. This paper proposes an improved finite control set model-free predictive control using DSVM to reduce the computational burden. First, model-free deadbeat current control is used to generate the reference voltage vector. Then, based on the principle that the voltage vector closest to the reference voltage vector minimizes the cost function, the optimal voltage vector is obtained in an effective way which avoids evaluation of the cost function. Additionally, in order to implement double-objective control, a two-level decisional cost function is designed to sequentially reduce the stator currents tracking error and the inverter switching frequency. The effectiveness of the proposed control is validated based on experimental tests.

• Journal of Institute of Control, Robotics and Systems
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• v.5 no.1
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• pp.79-87
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• 1999

For its simplicity and cost effectiveness in implementation, the Inverted DGPS is well suited for some specific applications like automatic vehicle location systems, where the monitoring station needs accurate position of the vehicles in the street. In the Inverted DGPS, the user sends its GPS position and associated satellite informations to the reference station, and the corrections are made at the reference station to get differentially corrected user position. A fundamental requirement in IDGPS is that the user and the reference station must use the same satellites when the corrections are made. But in practice, it is not often satisfied. Inverted DGPS is also suffered from performance degradation as the baseline become large like DGPS. IDGPS system using multi-reference station can resolve this problem. In this paper a simple multi-reference IDGPS algorithm is proposed and some experiments and analysis are peformed. Experiment results show that IDGPS can achieve the positioning performance as accurate as the DGPS can provide.

• The Journal of Information Systems
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• v.15 no.3
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• pp.107-129
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• 2006

The purpose of this study is to provide and validate an IT cost model hi which we link among cost center, cost object and flexible cost driver. in order to accomplish this purpose, this study utilizes ethnographic research methodology. At first we develop the cost model where the flexible cost driver is the distribution basis of overhead cost. For each cost driver, unit cost management model is also proposed. Then we employ the structured design methodology to validate the model. Based on the IT Cost requirements of a case company, the IT cost system was designed and developed for its test. The result shows the model we developed in this study is appropriate for managing IT resources and further, can be used as a reference model for calculating chargeback rates of other departments and IT budget of IT department.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.2
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• pp.151-159
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• 2021

Cost information in the Korean construction industry is mainly controlled by the government agencies. However, there have been wild-spread speculations among participants on the adequacy of these unit prices and difference with the actual market condition. Korean public-led unit prices are developed using mainly a top-down approach by a few designated public institutions. Due to the rapid fluctuations in market prices and high-volume of information, it is impossible for a few public institutions to properly consider market conditions. However, there are almost none private cost reference while many are available in other countries to supplement the public cost references. Needs for private cost references have recognized, and this study can be seen as a pilot study to support them. This study attempts to identify the problem areas of Korean cost references and to provide guidance by benchmarking other countries. This study has confirmed the need of developing market-driven cost references by employing a bottom-up approach in which a large number of various construction participants are fostered to provide their own cost information and share with others. It is envisioned that this study provides foundations for further study on the development on-line construction market platform based on abundant and appropriate cost information.

• Journal of Power Electronics
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• v.18 no.5
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• pp.1398-1408
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• 2018

In order to further improve the steady-state control performance of model predictive torque control (MPTC), a double-vector-based model predictive torque control without a weighting factor is proposed in this paper. The extended voltage vectors synthesized by two basic voltage vectors are used to increase the number of feasible voltage vectors. Therefore, the control precision of the torque and the stator flux along with the steady-state performance can be improved. To avoid testing all of the feasible voltage vectors, the solution of deadbeat torque control is calculated to predict the reference voltage vector. Thus, the candidate voltage vectors, which need to be evaluated by a cost function, can be reduced based on the sector position of the predicted reference voltage vector. Furthermore, a cost function, which only includes a reference voltage tracking error, is designed to eliminate the weighting factor. Moreover, two voltage vectors are applied during one control period, and their durations are calculated based on the principle of reference voltage tracking error minimization. Finally, the proposed method is tested by simulations and experiments.