• Journal of Communications and Networks
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• v.17 no.6
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• pp.602-608
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• 2015

In this paper, the limited error tracking problem is investigated for distributed leader-following wireless sensor networks (LFWSNs), where all sensors share data by the local communications, follower sensors are influenced by leader sensors directly or indirectly, but not vice versa, all sensor nodes track a reference state that is determined by the states of all leader sensors, and tracking errors are limited. In a LFWSN, the communicating graph is mainly expressed by some complete subgraphs; if we fix subgraphs that are composed of all leaders while all nodes in complete subgraphs of followers run on the sleeping-awaking method, then the fixed leaders and varying followers topology is obtained, and the switching topology is expressed by a Markov chain. It is supposed that the measurements of all sensors are corrupted by additive noises. Accordingly, the limited error tracking protocol is proposed. Based on the theory of asymptotic boundedness in mean square, it is shown that LFWSN keeps the limited error tracking under the designed protocol.

• JSTS:Journal of Semiconductor Technology and Science
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• v.10 no.1
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• pp.11-19
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• 2010

Register transfer level power macromodeling is well known as a promising technique for accurate and efficient power estimation. This paper proposes effective approaches based on the tablebased method for the RTL power macro-modeling. The new parameter SD, which characterizes the distribution of switching activities for each gate in the circuit, is one of the contributions. The new parameter SD has strong correlation with power consumption. We also propose an accurate table reference method considering the circuit characteristics. The table reference method is applicable for every table-based method and outputs more accurate power value. The experimental results show that the combination of the proposed methods reduces max error 30.36% in the best case, comparing conventional methods. The RMS error is also improved 1.70% in the best case.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.5
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• pp.422-428
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• 2013

Recently, we use a static synchronous compensator(STATCOM) with cascaded H-bride topologies, because it is easy to increase capacity and to reduce total harmonic distortion(THD). When we use equipment for reactive power compensation, dc-link voltage unbalances occur from several reasons although loads are balanced. In the past, switching pattern change of single phase inverter and reference voltage magnitude change of inverter equipped with power sensor have been used for dc-link voltage balance. But previous methods are more complicated and expensive because of additional component costs. Therefore, this paper explains reasons of dc-link voltage unbalance and proposes solution. This solution is complex method that is composed of reference voltage magnitude change of inverter without additional hardware and shifted phase angle of inverter reference voltages change. It proves possibility through 1000[KVA] system simulation.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.66 no.4
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• pp.213-218
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• 2017

The DC electrolytic capacitor for DC-link of power converter is widely used in various power electronic circuits and system application. Its functions include, DC Bus voltage stabilization, conduction of ripple current due to switching events, voltage smoothing, etc. Unfortunately, DC electrolytic capacitors are some of the weakest components in power electronics converters. Many papers have proposed different algorithms or diagnosis method to determinate the ESR and tan ${\delta}$ capacitance C for fault alarm system of the electrolytic capacitor. However, both ESR vary with frequency and temperature. Accurate knowledge of both parameters at the capacitors operating conditions is essential to achieve the best reference data of fault alarm. According to parameter analysis, the capacitance increases with temperature and the initial ESR decreases. Higher frequencies make the reference ESR with the initial ESRo value to decrease. Analysis results show that the proposed DC Bus electrolytic capacitor reference ESR model setting technique can be applied to advanced reference signal of capacitor diagnosis systems successfully.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.1
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• pp.115-126
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• 1996

In the time optimal control problem, bang-bang control has been used becaese it is the theoretical time minimum solution. However, to improve tracking speed performance in the time optimal control, it is important to select a switching point accurately which makes the velocity zero near the target track. But it is not easy to select the swiching point accurately because of the damping coefficient variation and uncertainties of modeling an actual system. The Adaptive model following control(AMFC) is implemented to relieve the difficulty and inconvenience of this task. The AMFC and make the controlled plant follow as closely as possible to a desired reference model whose switching point can be calculated easily and accurately, assuring the error between the states of the reference model and those of the controlled plant appoaches zero. The hybrid control method composed of AMFC and PID is applied to a tracking actuator of the magneto optical disk drive(MODD) in random access devices to improve its slow tracking performance. According to the simulaion and experimental results, the average tracking time as small as 20ms is obtained for a 3.5 magneto-optical disk drive. The AMFC also can be applied for other random access devices to improve the average tracking performance.

• Journal of Power Electronics
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• v.15 no.1
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• pp.190-201
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• 2015

This paper uses the switching function approach to present a simple state model of the Vienna-type rectifier. The approach introduces the relationship between the DC-link neutral point voltage and the AC side phase currents. A novel direct power control (DPC) strategy, which is based on the sliding mode control (SMC) for Vienna I rectifiers, is developed using the proposed power model in the stationary ${\alpha}-{\beta}$ reference frames. The SMC-based DPC methodology directly regulates instantaneous active and reactive powers without transforming to a synchronous rotating coordinate reference frame or a tracking phase angle of grid voltage. Moreover, the required rectifier control voltages are directly calculated by utilizing the non-linear SMC scheme. Theoretically, active and reactive power flows are controlled without ripple or cross coupling. Furthermore, the fixed-switching frequency is obtained by employing the simplified space vector modulation (SVM). SVM solves the complicated designing problem of the AC harmonic filter. The simplified SVM is based on the simplification of the space vector diagram of a three-level converter into that of a two-level converter. The dwelling time calculation and switching sequence selection are easily implemented like those in the conventional two-level rectifier. Replacing the current control loops with power control loops simplifies the system design and enhances the transient performance. The simulation models in MATLAB/Simulink and the digital signal processor-controlled 1.5 kW Vienna-type rectifier are used to verify the fast responses and robustness of the proposed control scheme.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.5
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• pp.27-35
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• 2000

This paper deals with a control strategy for constant output power of SSRT(Soft Switching Resonant Type) FB(Full Bridge) DC-DC converter by an improved phase shift controller. When the FB DC-DC converter for the high density and the high effect control is operated in high speed switching, the switching loss and switching stress of the switching devices are increased. So, the soft switching method, which has the phase shift control with the digital I-PD controller, must be use in order to reduce its. And the output voltage that controlled by the digital I-PD controller tracks a reference without steady state error in variable input voltage. The validity of control strategy that proposed is verified from simulation results and experimental results by the DSP(TMS320C32).

• Journal of Electrical Engineering and Technology
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• v.12 no.1
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• pp.151-160
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• 2017

This paper presents a new technique of reference current generator based on Kalman filter (KF) estimator for three-phase shunt active power filter (APF). The stationary reference frame (d-q algorithm) is used to transform the load currents into DC component. The harmonics of load currents are extracted and the three-phase reference currents are generated using KF estimator. The work is simulated using Matlab/Simulink platform. To validate the simulation results, an experimental test-rig have been perform using real-time control dSPACE DS1104. In addition, hysteresis current control was used to generate the switching signal for the correction of the harmonics in the system. The non-linear load were constructed with three-phase rectifier which connected in series with inductor and parallel with resistor and capacitor. The results shows that the new technique of shunt APF embedded with KF is proven to eliminate the harmonics created by the non-linear load with some improvement on the total harmonics distortion (THD).

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.12
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• pp.2000-2007
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• 2016

Generally, in order to implement the CRM(Critical Conduction Mode), the analog controller is used rather than a digital controller because the control is simple and uses less power. However, according to the semiconductor technology development and various user needs, digital control system based on a DSP is on the rise. Therefore, in this paper, the CRM bridgeless PFC converter based on a digital control is proposed. It is necessary to detect the inductor current when it reaches zero and peak value, for calculating the on time and off time by using the current information. However, in this paper, the on-time and off-time are calculated by using the proposed algorithm without any current information. If the switching-times are calculated through the steady-state analysis of the converter, they do not reflect transient status such as starting-up. Therefore, the calculated frequency is out of range, and the transient current is generated. In order to solve these problems, limitation method of the on-time and off-time is used, and the limitation values are varied according to the voltage reference. In addition, in steady state, depending on the switching frequency, the inductance is varied because of the resonance between the inductor and the parasitic capacitance of the switching elements. In order to solve the problem, inductance are measured depending on the switching frequency. The measured inductance are used to calculate the switching time for preventing the transient current. Simulation and experimental results are presented to verify the proposed method.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.5
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• pp.609-615
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• 2020

In the modern society, the use of digital equipment is increasing along with the 4th industrial revolution, and the importance of image and signal processing is increasing. At the same time, research on noise reduction is being actively conducted. In this paper, we propose a switching filter algorithm for random-valued impulse noise cancellation. The proposed algorithm obtains the threshold value by determining the noise level present in the image, and threshold value is compared with the difference between the input pixel value and the reference value, and is used in the weight switching process of the filter. The final output of the filter is estimated by applying a pixel weight and a modified weight median filter according to the switching, and obtains a final output by comparing the estimated value with the input pixel value. To evaluate the performance of the proposed algorithm, we compared it with the existing methods using simulation and PSNR.