• Journal of Power Electronics
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• v.11 no.6
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• pp.914-921
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• 2011

Commencing with incandescent light bulbs, every load today creates harmonics. Unfortunately, these loads vary with respect to their amount of harmonic content and their response to problems caused by harmonics. The prevalent difficulties with harmonics are voltage and current waveform distortions. In addition, Electronic equipment like computers, battery chargers, electronic ballasts, variable frequency drives, and switching mode power supplies generate perilous amounts of harmonics. Issues related to harmonics are of a greater concern to engineers and building designers because they do more than just distort voltage waveforms, they can overheat the building wiring, cause nuisance tripping, overheat transformer units, and cause random end-user equipment failures. Thus power quality is becoming more and more serious with each passing day. As a result, active power filters (APFs) have gained a lot of attention due to their excellent harmonic compensation. However, the performance of the active filters seems to have contradictions with different control techniques. The main objective of this paper is to analyze shunt active filters with fuzzy and pi controllers. To carry out this analysis, active and reactive current methods ($i_d-i_q$) are considered. Extensive simulations were carried out. The simulations were performed under balance, unbalanced and non sinusoidal conditions. The results validate the dynamic behavior of fuzzy logic controllers over PI controllers.

• Journal of Broadcast Engineering
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• v.15 no.6
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• pp.803-814
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• 2010

In this paper, we propose a frame structure for modified ATSC transmission systems which is used for a terrestrial 3D HDTV broadcasting. The modified ATSC transmission systems [2] see the potential of increasing a transmission capacity at reasonable TOV (Threshold of Visibility) by modifying channel codes of conventional ATSC systems and varying modulations. We use PN symbols (Pseudorandom Noise) in a guard interval which is used for avoiding the ISI (Inter Symbol Interference) to estimate and compensate the time-varying multi path channel effectively with a maximum transmission payload. With PN symbols in the guard interval, a CIR (Channel Impulse Response) in a time domain can be estimated and a compensation in a frequency domain can be achieved for the accurate channel estimation and compensation. The prosed frame structure is applied to the modified ATSC systems and computer simulations are performed for SER (Symbol Error Rate) performances in TU (Typical Urban)-6 Channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.5B
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• pp.974-984
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• 2000

A CMOS voltage driver circuit for voltage down converter is proposed. An adaptive biasing technique is used to enhance load regulation characteristics. The proposed driver circuit uses the NMOS transistor as a driving transistor, so it does not suffer from large Miller capacitances which is one of the problems with conventional PMOS driving transistor, and hence achieves good phase margin and stable frequency response. No additional complex circuit for frequency compensation such as compensation capacitor is required in this implementation. For the same current capability, the size of NMOS transistor in driver circuit is smaller than that of PMOS counterpart. So the smaller die area can be achieved. The circuits is implemented using a 0.8 ${\mu}{\textrm}{m}$ CMOS process and has a die area of 150 ${\mu}{\textrm}{m}$ x 360 ${\mu}{\textrm}{m}$. Proposed circuit has a quiescent power of 60 . In the current driving range from 100 $mutextrm{A}$ to 50 ㎃, load regulation of 5.6 ㎷ is measured.

• The Korean Journal of Physiology and Pharmacology
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• v.1 no.3
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• pp.263-273
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• 1997

The purpose of this study was to evaluate the effects of electrical stimulation on vestibular compensation following ULX in rats. Electrical stimulation (ES) with square pulse ($100{\sim}300uA$, 1.0 ms, 100 Hz) was applied to ampullary portion bilaterally for 6 and 24 hours in rats receiving ULX. After ES, animals that showed the recovery of vestibular symptoms by counting and comparing the number of spontaneous nystagmus were selected for recording resting activity of type I, II neurons in the medial vestibular nuclei (MVN) of the lesioned side. And then the dynamic neuronal activities were recorded during sinusoidal rotation at a frequency of 0.1 Hz and 0.2 Hz. The number of spontaneous nystagmus was significantly different 24 hours (p<0.01, n=10), but not 6 hours after ULX+ES. As reported by others, the great reduction of resting activity only in the type I neurons ipsilateral to lesioned side was observed 6, 24 hours after ULX compared to that of intact labyrinthine animal. However, the significant elevation (p<0.01) of type I and reduction (p<0.01) of type II neuronal activity were seen 24 hours after ULX+ES. Interestingly, gain, expressed as maximum neuronal activity(spikes/sec)/maximum rotational velocity(deg/sec), was increased in type I cells and decreased in type II cells 24 hours after ULX+ES in response to sinusoidal rotation at frequencies of both 0.1 Hz and 0.2 Hz. This result suggests that accompanying the behavioral recovery, the electrical stimulation after ULX has beneficial effects on vestibular compensation, especially static symptoms (spontaneous nystagmus), by enhancing resting activity of type I neurons and reducing that of type II neurons.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.111.5-111
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• 2001

This paper places great importance on performance improvement of Galvanometer system used for laser display, laser processing, marking system. Fundamentally, we implement control system, on that assumption that laser source exists, and design basic PID controller. Hardware is composed of DSP(TMS320C32) chip, and the position compensation of Galvanometer is performed by using 16-bit A/D and D/A converter. Through frequency response analysis and simulation, the attribute of plant and controller is captured and then, total system is analyzed. We deliberate noise problem that can be caused from analog signal as driving signal for Galvanometer.

• 제어로봇시스템학회:학술대회논문집
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• 1995.10a
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• pp.416-419
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• 1995

A finite-dimensional approximation technique is developed for a class of spectral systems with input and output operators which are unbounded. A corresponding bounding technique on the frequency-response error is also established for control system design. Our goal is to construct an uncertainty model including a nominal plant and its error bounds so that the results from robust linear control theory can be applied to guarantee a closed loop control performance. We demonstrate by numerical example that these techniques are applicable, with a modest computational burden, to a wide class of distributed parameter system plants.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.662-667
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• 1996

For compensating the error motion of hydrostatic guideways, the structure and the theoretical design method of ACC(Active Controlled Capillary) are proposed. The maximum controllable range, micro step response and dynamic characteristics of ACC are analyzed experimentally for verifing the availability. The experimental results showed that by the use of ACC, the error motion within 2.7${\mu}{\textrm}{m}$ of a hydrostatic guideway can be compensated with the resolution of 27nm, 1/100 of uncontolled error, and the frequency band of 5.5Hz. From these results, it Is confirmed that the ACC is very effect to improve the moving accuracy of high or ultra precision hydrostatic guideways.

• Journal of Power Electronics
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• v.11 no.5
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• pp.713-718
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• 2011

This paper presents an online voltage disturbance estimator to achieve precise torque control of IPMSMs over a high speed operating region. The proposed design has a type of state-filter based on a Luenburger-style closed loop stator current vector observer. Utilizing the frequency response plot (FRF) approach, the estimation accuracy and the parameter sensitivities are analyzed. Accurate torque control and improved efficiency are provided with the decoupling of the effect of the parameter variations. The feasibility of the presented idea is verified by laboratory experiments.

• Journal of Power Electronics
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• v.8 no.1
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• pp.10-22
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• 2008

The wind-driven doubly fed induction generator (DFIG) is currently under pressure to be more grid-compatible. The main concern is the fault ride-through (FRT) requirement to keep the generator connected to the grid during faults. In response to this, the paper introduces a novel model and new control scheme for the DFIG. The model provides a means of direct stator power control and considers the stator transients. On the basis of the derived model, a robust linear quadratic (LQ) controller is synthesized. The control law has proportional and integral actions and takes account of one sample delay in the input owing to the microprocessor's execution time. Further, the influence of the grid voltage imperfection is mitigated using frequency shaped cost functional method. Compensation of the rotor current pulsations is proposed to improve the FRT capability as well as the generator performance under grid voltage unbalance. As a consequence, the control system can achieve i) fast direct power control without instability risk, ii) alleviation of the problems associated with the DFIG operation under unbalanced grid voltage, and iii) high probability of successful grid FRT. The effectiveness of the proposed solution is confirmed through simulation studies on 2MW DFIG.

• Journal of Institute of Control, Robotics and Systems
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• v.12 no.2
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• pp.101-105
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• 2006

Disk radial runout creates a periodic relative motion between the laser beam spot and tracks formed on an optical disk. While only focus control is activated, the periodic relative motion yields sinusoid-like waves in the tracking error signal, where one cycle of the sinusoid-like waves corresponds to one track. The frequency of the sinusoid-like waves varies depending on the disk rotational speed and the amount of the disk radial runout. If the frequency of the tracking error signal in the off-track state is too high due to large radial runout of the disk, it is not a simple matter to begin track-following control stably. It might take a long time to reach a steady state or tracking control might fail to reach a stable steady state in the worst case. This article proposes a simple method for reducing the relative motion caused by the disk radial runout in the off-track state. The relative motion in the off-track state is effectively reduced by a drive input obtained through measurements of the tracking error signal and simple calculations based on the measurements, which helps reduce the transient response time of the track-following control. The validity of the proposed method is verified through an experiment using an optical disk drive.