• Journal of Power Electronics
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• 제11권4호
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• pp.583-590
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• 2011

Three-level NPC inverters have been put into practical use for years especially in high voltage high power grids. This paper researches three-level active power filters (APFs). In this paper a mathematical model in the d-q coordinates is presented for 3-phase 3-wire NPC APFs. The deadbeat control scheme is obtained by using state equations. Canceling the delay of one sampling period and providing the predictive value of the harmonic current is a key problem of the deadbeat control. Based on this deadbeat control, the predictive output current value is obtained by the state observer. The delay of one sampling period is remedied in this digital control system by the state observer. The predictive harmonic command current value is obtained by the repetitive predictor synchronously. The repetitive predictor can achieve a better prediction of the harmonic current with the same sampling frequency, thus improving the overall performance of the system. The experiment results indicate that the steady-state accuracy and the dynamic response are both satisfying when the proposed control scheme is implemented.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제50권4호
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• pp.170-178
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• 2001

Deadbeat technique has been proposed as a digital controller for an UPS inverter to achieve the fast, response to a load variation and to conserve a very low THD under a nonlinear load condition. This scheme contains a fatal drawback, sensitivity against parameter variation and calculation time delay. This paper proposes a second order deadbeat controller, which fundamentally solves the calculation time delay problem and certainly guarantees the robustness of the parameter's variation. RLP(Repetitive Load Predictor) which predicts the load current ahead of two sampling time and FVR(Fundamental Voltage Regulator) which eliminates the fundamental errors of the output voltage are also proposed for the second order deadbeat controller to apply to UPS inverter systems. These are shown theoretically and practically through simulation and experiment.

• Journal of Power Electronics
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• 제14권1호
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• pp.175-182
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• 2014

Tracking harmonic current quickly and precisely is one of the keys to designing active power filters (APF). In the past, the current state feedback decoupling PI control was an effective means for three-phase systems in the current control of constant voltage constant frequency inverters and high frequency PWM reversible rectifiers. This paper analyzes in detail the limitation of the conventional PI conditioner in the APF application field and presents a novel PI control method. Canceling the delay of one sampling period and the misadjustment for tracking the harmonic current is the key problem of this PI control. In this PI control, the predictive output current value is obtained by a state observer. The delay of one sampling period is remedied in this digital control system by the state observer. The predictive harmonic command current value is obtained by a repetitive predictor synchronously. The repetitive predictor can achieve better predictions of the harmonic current. By this means, the misadjustment of the conventional PI control for tracking the harmonic current is cancelled. The experiment results with a three-level NPC APF indicate that the steady-state accuracy and dynamic response of this method are satisfying when the proposed control scheme is implemented.

• 대한전자공학회논문지SD
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• 제45권6호
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• pp.37-42
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• 2008

H.264/AVC 복호기에서는 인트라 예측기 뿐만 아니라 움직임 보상기, 디블럭킹 필터 등 각 IP들이 복호화를 위한 참조 영상 값들을 필요로 한다. 이들 IP들은 참조 영상을 읽어들이기 위하여 외부 메모리에 빈번하게 접근하는데, 이때문에 시스템 동작 속도도 낮아지고 전력 소모도 증가한다. 본 논문에서는 공통적이고 반복적인 블록의 재사용을 통하여 연산량을 줄이고 전력 소모 및 메모리 대역폭을 최소화하도록 외부 메모리를 사용하지 않는 움직임 보상기와 연계한 인트라 예측기를 제안하였다. 제안된 인트라 예측기는 기존에 비해 $45%\;{\sim}\;75%$ 가량 사이클 수를 감소시켰다.

• 한국직업건강간호학회지
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• 제25권4호
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• pp.290-299
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• 2016

Purpose: The purpose of this study was to examine the relationship among physical and psychosocial risk factors, mental health, and presenteeism of South Korean hairdressers. Methods: This study is a secondary analysis of data extracted from the 2014 Korean Working Conditions Survey (KWCS), conducted by the Korea Occupational Safety and Health Agency. For the present analysis, 920 hairdressers were selected. Based on existing literature, a set of variables was chosen from the KWCS. A multiple logistic regression analysis was performed to examine the association among risk factors in working place, mental health, and presenteeism. Results: The prevalence of poor mental health and presenteeism was 45.1% and 36.0%, respectively. The results of multiple logistic regression analysis indicated that 'repetitive hand or arm movements,' were significant predictors of mental health (OR: 0.63, CI: 0.41~0.97), and 'role clarity' was a significant predictor of presenteeism (OR: 1.86, CI: 1.10~3.13). Conclusion: Based on these results, we suggest to improve the clarification of the role of hairdressers as a strategy to reduce their presenteeism.

• 대한임상검사과학회지
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• 제39권2호
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• pp.141-146
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• 2007

Obstructive Sleep Apnea-Hypopnea Syndrome (OSAHS) is a disorder characterized by the repetitive collapse of the pharyngeal airway during sleep, which leads to oxygen desaturation, sleep fragmentation, daytime sleepiness, and increased risk for hypertension and stroke. We investigated the clinical factors related to the severity of OSAHS. Polysomnography was performed in three hundred and ninety five consecutive adult patients with clinical symptoms of obstructive sleep apnea syndrome. All patients completed the sleep questionnaire and the Epworth Sleepiness Scale before polysomnography. Patients were classified into four groups based on the severity of their polysomnographic data: Non-OSA group, characterized by Apnea-Hypopnea Index (AHI) < 5; mild OSA group, by AHI 5-15; moderate OSA group, by AHI 16-30; and severe OSA group, by AHI > 30. Neck circumference was also measured at the cricothyroid level. A total of 395 patients (336 men and 59 women) were studied. In the non-OSA group, there were 55 patients; their mean neck circumference was $39.63{\pm}4.24cm$ and mean BMI was $24.48{\pm}3.53$. In the mild group, there were 101 patients; their mean neck circumference was $41.93{\pm}3.75cm$ and mean BMI was $25.33{\pm}2.94$. In the moderated group, there were 93 patients; their mean neck circumference was $43.27{\pm}3.50cm$ and BMI was $25.90{\pm}2.88$. In the severe group, there were 146 patients; their mean neck circumference was $44.94{\pm}3.93cm$ and mean BMI was $26.81{\pm}3.76$. Men had significantly larger neck circumference than women ($Mean{\pm}SD$, $43.72{\pm}3.83$ vs $39.17{\pm}4.30$, p < 0.001), and higher AHI than women ($29.12{\pm}22.65$ vs $14.63{\pm}14.11$, p < 0.001). Multiple regression analysis revealed that neck circumference was the most significant predictor of AHI. Neck circumference and BMI were positively correlated with the severity of OSAHS. The severity of OSAHS was greater in men than in women.