• Safety and Health at Work
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• 제10권4호
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• pp.452-460
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• 2019

Background: Monitoring and control of PM_2.5 are being recognized as key to address health issues attributed to PM_2.5. Availability of low-cost PM_2.5 sensors made it possible to introduce a number of portable PM_2.5 monitors based on light scattering to the consumer market at an affordable price. Accuracy of light scatteringe-based PM_2.5 monitors significantly depends on the method of calibration. Static calibration curve is used as the most popular calibration method for low-cost PM_2.5 sensors particularly because of ease of application. Drawback in this approach is, however, the lack of accuracy. Methods: This study discussed the calibration of a low-cost PM_2.5-monitoring device (PMD) to improve the accuracy and reliability for practical use. The proposed method is based on construction of the PM_2.5 sensor network using Message Queuing Telemetry Transport (MQTT) protocol and web query of reference measurement data available at government-authorized PM monitoring station (GAMS) in the republic of Korea. Four machine learning (ML) algorithms such as support vector machine, k-nearest neighbors, random forest, and extreme gradient boosting were used as regression models to calibrate the PMD measurements of PM_2.5. Performance of each ML algorithm was evaluated using stratified K-fold cross-validation, and a linear regression model was used as a reference. Results: Based on the performance of ML algorithms used, regression of the output of the PMD to PM_2.5 concentrations data available from the GAMS through web query was effective. The extreme gradient boosting algorithm showed the best performance with a mean coefficient of determination (R²) of 0.78 and standard error of 5.0 ㎍/㎥, corresponding to 8% increase in R² and 12% decrease in root mean square error in comparison with the linear regression model. Minimum 100 hours of calibration period was found required to calibrate the PMD to its full capacity. Calibration method proposed poses a limitation on the location of the PMD being in the vicinity of the GAMS. As the number of the PMD participating in the sensor network increases, however, calibrated PMDs can be used as reference devices to nearby PMDs that require calibration, forming a calibration chain through MQTT protocol. Conclusions: Calibration of a low-cost PMD, which is based on construction of PM_2.5 sensor network using MQTT protocol and web query of reference measurement data available at a GAMS, significantly improves the accuracy and reliability of a PMD, thereby making practical use of the low-cost PMD possible.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 B
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• pp.586-589
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• 2001

In Case of High speed PM machines with surface-mounted magnet. A rare-earth PM with high remanence flux density is used on the rotor. Therefore, It is very difficult to adhesion and assemble PM on the surface of rotor, because of very repulsive force between magnets. So, for solving this problem, rotor with surface-mounted magnet is wholly magnetized after mounting magnetic-material on the surface. In this paper, In order to Magnetize rotor with surface-mounted PM, magnetizing machine is designed, analyzed and simulated for large PM machines using the 1dimensional analytical method and 2dimensional finite element method. (20-FEM).

• Journal of international Conference on Electrical Machines and Systems
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• 제3권1호
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• pp.40-47
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• 2014

Sinusoidal back-EMF waveform of vernier Permanent Magnet (PM) machines is analyzed in this paper. An analytical expression of Electromotive Force (EMF) of electric machines including vernier machines is developed to analyze EMF harmonics, and the effect of vernier PM machine pole ratio, the ratio of number of rotor poles to stator poles, on the EMF waveform. Moreover, this paper represents several Finite Element Analysis (FEA) models to verify the analysis based on the proposed expression, and the effect of tooth width ratio, which is the ratio of tooth width to tooth pitch, on back-EMF of vernier PM machines, and optimal tooth width ratio is obtained and verified by FEA. Finally, this paper makes comparisons between EMF waveform of vernier PM machines and that of traditional PM machines from the point of view of analytical EMF expression.

• 대한원격탐사학회지
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• 제37권2호
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• pp.321-335
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• 2021

미세먼지 (PM10) 및 초미세먼지 (PM2.5)는 인체에 흡수 가능하여 호흡기 질환 및 심장 질환과 같이 인체건강에 악영향을 미치며, 심각할 경우 조기 사망에 영향을 줄 수 있다. 전 세계적으로 현장관측기반의 모니터링을 수행하고 있지만 미 관측지역에 대한 대기질 분포의 공간적인 한계점이 존재하여 보다 광범위한 지역에 대한 지속적이고 정확한 모니터링이 필요한 상황이다. 위성기반 에어로졸 정보를 사용함으로써 이러한 현장 관측자료의 한계점을 극복할 수 있다. 따라서 본 연구에서는 다양한 위성 및 모델자료를 활용하여 2019년도에 대해 한 시간 단위의 지상 PM10 및 PM2.5 농도를 추정하였다. GOCI 위성의 관측영역을 포함하는 동아시아 지역에 대해 트리 기반 앙상블 방법을 사용하는 Boosting 기법인 GBRTs (Gradient Boosted Regression Trees)와 LightGBM (Light Gradient Boosting Machine)을 활용하여 모델을 구축하였다. 또한, 기상변수 및 토지피복변수의 사용유무에 따른 모델의 성능을 비교하기 위해 두 가지 festure set으로 나누어 테스트하였다. 두 기법 모두 주요 변수인 AOD (Aerosol Optical Depth), SSA (Single Scattering Albedo), DEM (Digital Eelevation Model), DOY (Day of Year), HOD (Hour of Day)와 기상변수 및 토지피복변수를 함께 사용한 Feature set 1을 사용하였을 때 높은 정확도를 보였다. Feature set 1에 대해 GBRT 모델이 LightGBM에 비해서약 10%의 정확도 향상을 보였다. 가장 정확도가 높았던 기상 및 지표면 변수를 포함한 Feature set1을 사용한 GBRT기반 모델을 최종모델로 선정하였으며 (PM10: R2 = 0.82 nRMSE = 34.9%, PM2.5: R2 = 0.75 nRMSE = 35.6%), 계절별 및 연평균 PM10 및 PM2.5 농도에 대한 공간적인 분포를 확인해본 결과, 현장관측자료와 비슷한 공간 분포를 보였으며, 국가별 농도 분포와 계절에 따른 시계열 농도 패턴을 잘 모의하였다.

• Journal of Magnetics
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• 제20권3호
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• pp.265-272
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• 2015

In recent years, flux switching machines (FSMs) have been an attractive research topic owing to their tremendous advantages of robust rotor structure, high torque, and high power capability suitable for intensive applications. However, most of the investigations are focusing on the inner-rotor structure, which is incongruous for direct drive applications. In this study, high torque and power densities of a new 12S-14P outer-rotor permanent magnet (PM) FSM with a DC excitation coil was investigated based on two-dimensional finite element analysis for in-wheel direct drive electric vehicle (EV). Based on some design restrictions and specifications, design refinements were conducted on the original design machine by using the deterministic optimization approach. With only 1.0 kg PM, the final design machine achieved the maximum torque and power densities of 12.4 Nm/kg and 5.93 kW/kg, respectively, slightly better than the inner-rotor HEFSM and interior PM synchronous machine design for EV.

• Journal of Electrical Engineering and Technology
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• 제12권1호
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• pp.262-271
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• 2017

This paper presents a novel concept of phase swapping to associate multiple flux weakening ranges to a non-salient PM machine without altering any hardware of the machine. The proposed concept enables a dual three-phase machine to be operated with different displacement angles between the two three-phase windings. Hence, different flux weakening ranges using winding switching can be accomplished by applying this concept. It was also demonstrated that the proposed concept can be utilized for the discrete step as well as continuous operation of the machines. Any application requiring a wide speed range operation of up to thirteen times the base speed can benefit from this proposed concept. Analytical, simulation, and experimental results are provided to validate the effectiveness of the proposed concept.

• 융합정보논문지
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• 제11권8호
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• pp.92-99
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• 2021

광산란법을 이용한 초미세먼지 측정기는 초 단위의 측정이 가능하고 휴대할 수 있는 크기로 설계될 수 있다. 또한 하나의 센서로 여러 크기별 (PM_1.0, PM_2.5, PM_4.0, 및 PM₁₀) 농도를 측정할 수 있다. 이 방식은 입자의 개수와 크기를 측정하고 이를 단위 부피당 무게인 농도로 변환하는 과정 때문에 큰 밀도를 가지는 황사에 대해서는 큰 오차를 나타낸다. 본 논문은 광산란 초미세먼지 측정기가 여러 크기별 PM 농도를 이용하여 황사 발생 시 초미세먼지(PM_2.5)의 농도의 오차를 정확히 보정할 수 있고, 황사가 발생하지 않을 때도 영향을 받지 않는, 다중 선형외기 기법의 기계학습에 의한 보정 기법을 제시한다. 두 가지 또는 세 가지의 PM 크기 입력만으로도 광산란 미세먼지 측정 장치의 황사 오류를 크게 보정할 수 있음을 보인다. 한 달 동안 중부권대기환경연구소의 베타레이 측정기와 광산란 측정기의 측정값을 비교·분석하였다. 황사가 없는 구간에서 이 두 장비의 상관계수(R²)는 0.927이었고, 황사를 포함한 전 구간에서 상관계수는 0.763이었지만, 기계학습을 통하여 상관계수가 0.944로 향상되었다.

• Journal of Electrical Engineering and Technology
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• 제13권6호
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• pp.2329-2334
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• 2018

This paper discusses the thermal effect of the number of permanent-magnet (PM) layers in an outer rotor machine. Depending on the number of axial-layer of PM, the operating temperature is compared analytically and experimentally. The electromagnetic analysis is performed using 3-dimensional time varying finite element method to get the heat sources depending on axial-layered PM models. Then thermal analysis is conducted using the lumped-parameter-thermal-network method for each case. Two outer rotor machines, which have the different number of axial-layer of PM, are manufactured and tested to validate the analysis results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.855-856
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• 2006

Inductance can be defined as several kinds of slops on the B-H curve, and at is classified into apparent, effective, incremental inductances, etc. In many research cases, its calculation and measurement are partially dealt. However it is hard to find the clear explanation of the inductance in the voltage equation of PM machines, and even its relationship with those classified inductances in the view point of design and characteristics analysis. Moreover some previous definition of inductance can not be used for the inductance of coils in PM machines. Therefore, in this paper the inductance is redefined for voltage equation of PM machines, and the methods of calculation by using finite element analysis method and measurement are explained.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2015년도 제46회 하계학술대회
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• pp.678-679
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• 2015

A prototype of a dual-stator axial-flux PM vernier machine with rated 5.5kW output power at 300rpm speed is constructed and tested to verify its competitive performance and the reliability of the proposed design approach and the FEM simulation results.