• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.7
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• pp.381-386
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• 2003

To provide a specified power quality under electric market system is becoming an important issue for customers and utility company. However, there is no realistic infra-structure to design a power system for the specified power quality. Present electric market is operating under the economic point of view. The low power price could be attractive, but the effect of low price could result the lower power quality for the long time and threat power system security. This paper presents a model which conceptualize the dynamic power quality control mechanism to minimize total cost of a society which is affected electric power quality. This model aims to produce a basic infra-structure to balance cost and quality under the electric market system.

• Journal of Periodontal and Implant Science
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• v.23 no.1
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• pp.16-26
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• 1993

In order to investigate the healing effect on inflammation and bone regeneration of low power density laser radiation in dogs, experimental periodontitis was made in dog mandibular 3rd, 4th premolars. All teeth were classified with four groups of two experimental group and control groups. The second group were irradiated on periodontitis site and the first group were control. The fourth group were irradiated on periodontitis site flap operation and the third group were flap control. Experimental groups were irradiated with GaAs low power density laser of pulse wave and continuous wave of 904nm every day by five days respectively and then control group and experimental groups were evaluated by histo-pathological study. The results were as follows : 1. Experimental periodontits site of dog were irradiated with GaAs low power laser results in reducing of pseudoepitheliomatous proliferation and inflammation at light microscope. 2. After irradiation with low power density laser, experimental groups were revealed that PDL forming activity were increased and newly formed collagen deposition were observed. 3. Low power density lsaer irradiation on experimental periodontits site after flap operation showed that decreasing of inflammation, reducing of osteoclast activity. Capillary proliferation, reduction of pseudoepitheliomatous proliferation. 4. After irradiation with low power density laser on flap experimental site, experimental groups were revealed that newly formed collagen in periodontal ligament and alveolar bone were detected on MT staining.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.2
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• pp.182-190
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• 2011

This paper proposes a LVRT (Low Voltage Ride Through) control strategy which should be satisfied by grid-connected wind power system when grid faults occur. The LVRT regulation indicates rules or actions which have to be executed according to the voltage dip ratio and the fault duration. Especially the wind power system has to support the grid with specified reactive current to secure the grid stability when voltage reduction ratio is over 10%. The LVRT regulation in this paper is based on the German Grid Code and full-scale variable speed wind power conversion system is considered for LVRT control strategy. The proposed LVRT control strategy satisfies not only LVRT regulation but also makes power balance between wind turbine and power system through additional DC link voltage regulation algorithms. Because it is impossible to control grid side power when the 3-phase to ground fault occurs, the DC link voltage is controlled by a generator side inverter using the DC link voltage control strategy. Through the simulation and experiment result, the proposed LVRT control strategy is evaluated and its effectiveness is verified.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.5
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• pp.470-474
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• 2014

This study proposes an improved synchronization control scheme for a low-cost 400Hz power supply for a no-break power transfer system. In the case of aircraft applications, the 400Hz power supply called ground power units is accepted and used as the external electrical power system during stopovers on ground. A momentary break in the supply occurs when shifting from one power source to another. To allow shifting without a break in the supply, the two power sources are momentarily connected in parallel. The proposed synchronization control is achieved by connecting an existing synchronization bus to the voltage zero-crossing signal of a generator power with discrete logic ICs and analog circuits. Therefore, unlike expensive controllers, such as DSP and CAN, the proposed control scheme is rather simple and may decrease operational cost. The practical feasibility of the proposed control scheme is proven by experimental results.

• Journal of Electrical Engineering and Technology
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• v.6 no.1
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• pp.67-75
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• 2011

The development of electric vehicle power electronics system control, composed of DC-AC inverters and DC-DC converters, attract much research interest in the modern industry. A DC-AC inverter supplies the high-power motor torques of the propulsion system and utility loads of electric vehicles, whereas a DC-DC converter supplies the conventional low-power and low-voltage loads. However, the need for high-power bidirectional DC-DC converters in future electric vehicles has led to the development of many new topologies of DC-DC converters. The nonlinear control of power converters is an active research area in the field of power electronics. This paper focuses on the use of the fuzzy sliding mode strategy as a control strategy for buck-boost DC-DC converter power supplies in electric vehicles. The proposed fuzzy controller specifies changes in control signals based on the surface and knowledge on surface changes to satisfy the sliding mode stability and attraction conditions. The performance of the proposed fuzzy sliding controller is compared to that of the classical sliding mode controller. The satisfactory simulation results show the efficiency of the proposed control law, which reduces the chattering phenomenon. Moreover, the obtained results prove the robustness of the proposed control law against variations in load resistance and input voltage in the studied converter.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.3
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• pp.223-230
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• 2017

A low-cost BLDC motor with hall sensor is used to drive the position control of a facility security monitoring system in this paper. Low measurable frequency of the hall sensor signal in low-speed regions results in difficulty in obtaining accurate speed detection and position control. To improve system control performance, we propose a variable gain of position controller and stop mode control scheme according to the motor speed and error position with pre-set deceleration time. The proposed stop mode control scheme is activated around the stop position to forcibly move the BLDC motor to the stop position in low speed. In the proposed stop mode, the motor current is controlled by the actual speed with the reference rotating angle. The control performance of the proposed position control is verified through experiments at the actual rail guided facility security monitoring system.

• Physical Therapy Korea
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• v.6 no.2
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• pp.16-31
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• 1999

The purpose of this study was to assess the fatigue in lumbar and abdominal muscles in patients with chronic low back pain compared with normal subjects using spectral analysis with mean power frequency and median power frequency. The experimental group consisted of twenty subjects who had experienced chronic low back pain for over one year after the onset day. A control group consisted of twenty normal subjects with no history of low back pain. All subjects stood in an apparatus to perform sustained contraction in the lumbar and abdominal muscles for 30 seconds with 60% maximal voluntary isometric contraction (MVIC). The resulting electromyographic (EMG) recorded time serial data were transformed into frequency serial data by Fast Fourier Transformation (FFT). The results were as follows: 1) lumbar muscles measured, the frequency change ratio of both median power frequency and mean power frequency was significantly greater for experimental group compared with control group group (p<0.05). In measured two abdominal muscles (inferior rectus abdominis, obliquus externus abdominis) except superior rectus abdominis, the frequency change ratio of both median power frequency and mean power frequency was significantly greater for experimental group compared with control group (p<0.05). 2) In all three (longissimus thoracis, iliocostalis lumborum, multifidus) lumbar muscles measured, the initial frequency value of both median power frequency and mean power frequency was significantly lower for the experimental group compared with the control group (p<0.05). In the two (inferior rectus abdominis, obliquus externus abdominis) abdominal muscles measured (superior rectus abdominis not included), the initial frequency value of both median power frequency and mean power frequency was significantly lower for the experimental group compared with the control group (p<0.05). These results suggest that in patients with chronic low back pain there is a trend for more fatigue to occur in both lumbar and abdominal muscles than in the normal control group. This would seem to suggest that in treatment programs for patients with chronic low back pain, improvement of endurance in all trunk muscles should be considered.

• Smart Structures and Systems
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• v.14 no.4
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• pp.617-641
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• 2014

The energy constraint is still a common issue for the practical application of wireless sensors, since they are usually powered by batteries which limit their lifetime. In this paper, a practical compound energy efficiency strategy is proposed and realized in the implementation of a real time wireless sensor platform. The platform is intended for wireless structural monitoring applications and consists of three parts, wireless sensing unit, base station and data acquisition and configuration software running in a computer within the Matlab environment. The high energy efficiency of the wireless sensor platform is achieved by a proposed adaptive radio transmission power control algorithm, and some straightforward methods, including adopting low power ICs and high efficient power management circuits, low duty cycle radio polling and switching off radio between two adjacent data packets' transmission. The adaptive transmission power control algorithm is based on the statistical average of the path loss estimations using a moving average filter. The algorithm is implemented in the wireless node and relies on the received signal strength feedback piggybacked in the ACK packet from the base station node to estimate the path loss. Therefore, it does not need any control packet overheads. Several experiments are carried out to investigate the link quality of radio channels, validate and evaluate the proposed adaptive transmission power control algorithm, including static and dynamic experiments.

• Proceedings of the KIPE Conference
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• 2000.07a
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• pp.384-387
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• 2000

In this paper Power factor correction circuit of single-phase three-level boost converter is proposed. The advantage of the proposed control scheme for three-level boost converter are low blocking voltage of each power device low THD(Total Harmonic Distortion) and high power factor. The control scheme is based on the current comparator capacitor compensator and region detector, In simulations the proposed system is validated.

• Proceedings of the IEEK Conference
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• 2003.07d
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• pp.1295-1298
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• 2003

The steam generator level in a PWR is very difficult to control particularly at low power. And the constant control gain and time value are not adaptive in steam generator level controller. In normal operation constant control gain and time value have no problem. But there is problem at low power. So variable control gains based on the temperature are required. The best control gain is decided by the experienced knowledge. A fuzzy gain tuner is used for the gain tuning. In the design of fuzzy gain-tuner processing, the experienced knowledge is employed for making fuzzy rules.