• Journal of Power Electronics
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• v.18 no.1
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• pp.251-265
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• 2018

To enable a master-slave control independent microgrid system (MSCIMGS) to supply electricity continuously, the microgrid inverter should perform mode transfer between grid-connected and islanding operations. Transient oscillations should be reduced during transfer to effectively conduct a seamless mode transfer. This study uses a typical MSCIMGS as an example and improves the mode transfer strategy in three aspects: (1) adopts a status-tracking algorithm to improve the switching strategy of the outer loop, (2) uses the voltage magnitude and phase pre-synchronization algorithm to reduce transient shock at the time of grid connection, and (3) applies the hybrid-sensitivity $H_{\infty}$ robust controller instead of the current inner loop to improve the robustness of the controller. Simulations and experiments show that the proposed strategy is more practical than the traditional proportional-derivative control mode transfer and effective in reducing voltage and current oscillations during the transfer period.

• Journal of Drive and Control
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• v.13 no.2
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• pp.1-9
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• 2016

In this paper, an elementary force fighting problem was investigated. The problem is encountered when a double-rod type EHA(electro-hydrostatic actuator) is combined with a single-rod type EHA to build a redundant actuator system with synchronized motion. When the rod-side chambers of the two different types of EHAs have the same effective piston areas and are simultaneously pressurized by an external load, the two EHAs behave identically, sharing the external load equally. However, when the piston head-side chamber of the single rod type EHA, having a larger effective area than the rod-side chamber, is pressurized by the external load, an abnormal force fighting between the two EHAs occurs, unless their pump speeds are properly decoupled. In this study, the output drive forces of each EHA were obtained from the cylinder pressure signals and applied to the position control for each EHA to maintain the balance between their pump speeds. Adding minor force difference feedback loops to the position control, the force fighting phenomena could be eliminated and steady state synchronization errors were reduced. The power consumption of the pumps also could be remarkably reduced, avoiding unnecessarily high load pressures to the pumps.

• Journal of the Korean Operations Research and Management Science Society
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• v.20 no.2
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• pp.159-178
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• 1995

Supervisory control is an approach based on formal language. it is used to model and control discrete event systems in which each discrete event process is represented as an automation. A supervisor is a generator that switches control patterns in such a way that a given discrete evenet process behaves in obedience to various constraints. A flexible manufacturing cell (FMC) is one of discrete evenet systems. Functions necessary for the operation of an FMC are characterized by operational components and informational compoments. The operational components can be modeled using the finite state machines and the informational components can be modeled using the abstract formalism which describes supporting operations of the cell controller. In this paper, we addressed function required for FMC control specification, software engineering aspects on FMC control based on supervisory control, a concept of event queue for resolving synchronization problem, and complexity reduction. Based on the mathematical model of an FMC. we synthesized the controller by integrating a supervisor for FMC with control specification that specifies event-driven operation of the cell controller. The proposed control scheme is stable mathematically so that the system always behaves on a controlled way even under the existence of uncontrollable events. Furthermore, using an event queue concept, we can solve a synchronization problem caused by the violation of instantaneity assumption of supervisory control theory in real life situation. And also, we can propotype a control software rapidly due to the modularity of the proposed control scheme.

• Journal of the Korea Society for Simulation
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• v.18 no.3
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• pp.73-82
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• 2009

Due to the many advantages including low price, low power consumption, and miniaturization, the CMOS camera has been utilized in many applications, including mobile phones, the automotive industry, medical sciences and sensoring, robotic controls, and research in the security field. In particular, the 360 degree omni-directional camera when utilized in multi-camera applications has displayed issues of software nature, interface communication management, delays, and a complicated image display control. Other issues include energy management problems, and miniaturization of a multi-camera in the hardware field. Traditional CMOS camera systems are comprised of an embedded system that consists of a high-performance MCU enabling a camera to send and receive images and a multi-layer system similar to an individual control system that consists of the camera's high performance Micro Controller Unit. We proposed the SL-AVS (Small Size/Low power Around-View System) to be able to control a camera while collecting image data using a high speed synchronization technique on the foundation of a single layer low performance MCU. It is an initial model of the omni-directional camera that takes images from a 360 view drawing from several CMOS camera utilizing a 110 degree view. We then connected a single MCU with four low-power CMOS cameras and implemented controls that include synchronization, controlling, and transmit/receive functions of individual camera compared with the traditional system. The synchronization of the respective cameras were controlled and then memorized by handling each interrupt through the MCU. We were able to improve the efficiency of data transmission that minimizes re-synchronization amongst a target, the CMOS camera, and the MCU. Further, depending on the choice of users, respective or groups of images divided into 4 domains were then provided with a target. We finally analyzed and compared the performance of the developed camera system including the synchronization and time of data transfer and image data loss, etc.

• Journal of Embryo Transfer
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• v.27 no.4
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• pp.223-228
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• 2012

This study was designed to adopt two estrus synchronization protocols in zebu and crossbred heifers and their effects on pregnancy rate after timed artificial insemination (TAI). A number of 120 cyclic heifers were allotted for two different treatment groups and one control group. Heifers under protocol A were injected with GnRH at first day followed by a single dose of $PGF_{2{\alpha}}$ at Day 11 and injection of GnRH at the day of AI; and heifers belonged to protocol B were treated with GnRH, two $PGF_{2{\alpha}}$ injections at 11 days apart and injection of GnRH at AI. AI was done at fixed time (within 72~96 hours after $PGF_{2{\alpha}}$ injection) in both protocols and pregnancy was confirmed by rectal palpation on 80~120 days of post AI. In control group; local heifers were conceived higher (30%) proportion than that of crossbred heifers (25%; p<0.05). In protocol A, the local breed were conceived higher (38.9%) proportion compared with crossbred (25%; p<0.05). In protocol B, local breed heifers were conceived higher (38.9%) proportion compared with crossbred heifers (33.3%; p<0.05). The overall pregnancy rate in protocol A and protocol B was 33.3% and 36.6%, respectively. The proportion of pregnancy rate of local heifers (38.9%; Protocol A) was significant (p<0.05) in comparison with local heifers (30%) in control group (p<0.05). The overall pregnancy rate between pooled control group (28.3%) and treatment group (35%) was significantly (p<0.05) differ from each other's. Results of present study concluded that estrus synchronization followed by fixed time AI could be applied for higher pregnancy rate in zebu and crossbred heifers.

• Journal of Music and Human Behavior
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• v.16 no.1
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• pp.47-72
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• 2019

This study reviewed and analyzed English-written studies using a rhythmic tapping task for motor control of children with autism spectrum disorder (ASD). Inclusion criteria for the participants were children with ASD and typically developing (TD) children. The keywords used for the outcome variables included rhythmic tapping, timed movement, and synchronization. Ten studies were included in the final analysis. The included studies were analyzed in terms of target variables, auditory stimuli, and measurements. A meta-analysis was also conducted to examine how children with ASD performed rhythmic tapping tasks compared to children with TD. In the identified studies, five variables were used: timed movement control, timing reproduction, bimanual coordination, synchronization, and interpersonal synchronization. It was found that rhythmic tapping performance was analyzed in terms of accuracy and precision of the movement and reported as significantly correlated to social skills measures. The meta-analysis results showed that there were no significant differences between the ASD and TD groups in continuing rhythmic movements when the presented auditory stimuli ended, whereas there were significant group differences in their ability to maintain their motor performance consistently and to synchronize with auditory cue or with others. These results support the rhythmic tapping task as an effective measure for not only motor control but also social skills development in children with ASD.

• Proceedings of the KIEE Conference
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• 2006.10d
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• pp.143-145
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• 2006

This paper presents an overall control algorithm for a grid-connected wind-power generation system using a DFIG(doubly-fed induction generator) fed by back-to-back PWM converters. The control of DFIG is based on a stator-flux oriented vector control. The system enables not only fast and smooth synchronization but also high performance regulation of active and reactive power. Experimental results shows The feasibility of the control algorithm.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1480-1483
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• 1996

A set of approaches suggested to control the eccentricity is discussed in this paper. Among these, filter-integrator method is used to design the controller, which also includes the input signal synchronization, stabilizing filter and eccentricity source discrimination. Using the S/W that is coded for real time application of that controller, we simulated the operations of that one. The simulation results show the characteristics of eccentricity compensation and eccentricity discrimination. However, from these results, we can see that only proper stabilization strategy certificates the safe eccentricity control.

• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.57-61
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• 2006

As high speed internet users are tremendously increasing, three are keenly in need of development of high speed portable internet technology which can provide high quality wireless internet service cheaply even in the mobile. Unlike the FDD-CDMA, TDD-OFDMA has relatively poor wave environment with inducing interference, fading and delay because it agrees to multi-carrier modulation method and time-division radio telecommunication system. To solve this problem, it is necessary to develop repeater operating by digital signal processing method which have more strict wireless channel control and wave signal processing technology over TDD telecommunication equipments. This thesis is dealing with design and implementation of Digital RF Repeater which implemented 'Synchronization Acquisition Unit', 'TDD signal switching Unit', 'Feedback Signal Cancellation Unit'. Over this argument, we will develop digital RF repeater with more cheap, more adaptive in wave environment like oscillation control, adaptive wave monitoring and output increasing and having control function as a result it will be helpful for success in high speed portable internet service business.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2019.05a
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• pp.243-246
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• 2019

In cognitive radio networks, secondary transmitters should cease its transmission immediately under the detection of primary transmission in the spectrum they are using. Then they need to exploit another idle spectrums and resynchronize to the newly found idle spectrums. Most of related work presume the existence of separate control channel used by secondary users commonly for exchanging the information of idle spectrums. However, this presumption is not feasible in real world cognitive radio scenario. Therefore we address a proactive spectrum synchronization scheme with no need of separate control channel. Our scheme lets secondary users exchange the spectrum information periodically during normal communication process and determine the next spectrum band in advance of detecting primary transmission. We evaluate our scheme in a real world cognitive radio environments set up with USRPs.