• 전기학회논문지
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• 제62권10호
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• pp.1487-1493
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• 2013

A new simple control method for active power filter, which can realize the complete compensation of harmonics is proposed. In the proposed scheme, a model-based digital current control strategy is presented. The proposed control system is designed and implemented in a form referred to as internal model control structure. This method provides a convenient way for parameterizing the controller in term of the nominal system model, including time-delays. As a result, the resulting controller parameters are directly set based on the power circuit parameters, which make tuning of the controllers straightforward task. In the proposed control algorithm, overshoots and oscillations due to the computation time delay is prevented by explicit incorporating of the delay in the controller transfer function. In addition, a new compensating current reference generator employing resonance model implemented by a DSP(Digital Signal Processor) is introduced. Resonance model has an infinite gain at resonant frequency, and it exhibits a band-pass filter. Consequently, the difference between the instantaneous load current and the output of this model is the current reference signal for the harmonic compensation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권2호
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• pp.683-701
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• 2012

IEEE 802.11 standard has achieved huge success in the past decade and is still under development to provide higher physical data rate and better quality of service (QoS). An important problem for the development and optimization of IEEE 802.11 networks is the modeling of the MAC layer channel access protocol. Although there are already many theoretic analysis for the 802.11 MAC protocol in the literature, most of the models focus on the saturated traffic and assume infinite buffer at the MAC layer. In this paper we develop a unified analytical model for IEEE 802.11 MAC protocol in ad hoc networks. The impacts of channel access parameters, traffic rate and buffer size at the MAC layer are modeled with the assistance of a generalized Markov chain and an M/G/1/K queue model. The performance of throughput, packet delivery delay and dropping probability can be achieved. Extensive simulations show the analytical model is highly accurate. From the analytical model it is shown that for practical buffer configuration (e.g. buffer size larger than one), we can maximize the total throughput and reduce the packet blocking probability (due to limited buffer size) and the average queuing delay to zero by effectively controlling the offered load. The average MAC layer service delay as well as its standard deviation, is also much lower than that in saturated conditions and has an upper bound. It is also observed that the optimal load is very close to the maximum achievable throughput regardless of the number of stations or buffer size. Moreover, the model is scalable for performance analysis of 802.11e in unsaturated conditions and 802.11 ad hoc networks with heterogenous traffic flows.

• 한국통신학회논문지
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• 제18권12호
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• pp.1855-1869
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• 1993

기존의 알로하 시스템은 불안정한 시스템으로 알려져있다. 또한 포획현상을 가지는 알로하 시스템도 불안정하다는 것이 증명되었다. 본 논문에서는 신호, 포획현상을 가지는 알로하 시스템에 전송 제어 알고리즘을 적용하고, 새로운 Lyapunov 함수를 도입하여 다차원 바르코프 연쇄 모델의 안정성을 증명하였다. 부가적으로 시스템의 전송효율을 구하고, 또한 시뮬레이션을 통하여 패킷 전송지연을 분석하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.1193-1196
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• 2005

In this paper, we presents a new multimedia service transmit method using IPv6. The IPv6 provides the address system of 128 bit and the address space which is infinite it provides. But it will not become the IPv4 and interchange not to be, it uses the DSTM Transition mechanism which will reach and the IPv4 center in the packet header the service type it will be able to support the service class of multi type (TOS) it secures the weak point of data transfer delay it puts a base in the IPv6. The efficiency of this proposed technique have been proven by MPEG-4 streaming video streaming of the IPv6 namely, 6Xtream embodied a order form/live streaming server and the client which it uses to be possible in base and real-time decoding method.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제22권1호
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• pp.63-74
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• 2018

In this paper, we study the initial value problem for neutral functional differential equations involving Caputo fractional derivative of order ${\alpha}{\in}(0,1)$ with infinite delay. Some sufficient conditions for the uniqueness and continuous dependence of solutions are established by virtue of fractional calculus and Banach fixed point theorem. Some results obtained showed that the solution was closely related to the conditions of delays and minor changes in the problem. An example is provided to illustrate the main results.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.184-188
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• 2001

In this paper, a new fully digital control method for single-phase UPS inverter, which is based on the double control loop such as the outer voltage control loop and inner current control loop, is proposed. The inner current control loop is designed and implemented in the form of internal model control and takes the presence of computational time-delay into account. Therefore, this method provides an overshoot-free reference-to-output response. In the proposed scheme, the outer voltage control loop employing P controller with resonance model implemented by a DSP is introduced. The proposed resonance model has an infinite gain at resonant frequency, and it exhibits a function similar to an integrator for AC component. Thus the outer voltage control loop causes no steady state error as regard to both magnitude and phase. The effectiveness of the proposed control system has been demonstrated by the simulation and experimental results respectively.

• 한국전자통신학회논문지
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• 제2권3호
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• pp.174-179
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• 2007

본 논문에서는 유전자 알고리듬을 이용하여 전력, 면적, 속도를 고려한 저전력 모듈 선택을 제안한다. 제안한 알고리듬은 최적의 모듈 선택을 통해서 전력 소모를 최소화 할 수 있다. 비교 실험에서는 최적 모듈 선택을 고려한 알고리듬은 최대 전력 감소량은 26.9 %를 얻을 수 있었고, 반면에 최소 전력 감소량은 9.0% 얻었다. 모든 벤치마크 평균 전력 감소량은 15.525%가 되었다.

• 한국통신학회논문지
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• 제29권11A
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• pp.1237-1243
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• 2004

This paper presents and analyses the closed-form expression of the average bit error rate (BER) for an asynchronous direct-sequence code division multiple access (DS-CDMA) system with coherent binary phase shift keying (BPSK) modulation scheme using a maximal ratio combining (MRC) diversity over a Rician fading channel. In addition to the average BER, outage probability, and user capacity of system are estimated as performance measures. The results are general enough so that it includes Rayleigh fading and nonfading channel with zero and infinite Rician factor, respectively, as special cases. The effects of various channel models, processing gains, and diversity orders on the system performances are also considered for the typical multipath delay profiles characterized by Rician fading channel.

• Journal of Communications and Networks
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• 제16권3호
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• pp.293-300
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• 2014

As energy harvesting communication systems emerge, there is a need for transmission schemes that dynamically adapt to the energy harvesting process. In this paper, after exhibiting a finite-horizon online throughput-maximizing scheduling problem formulation and the structure of its optimal solution within a dynamic programming formulation, a low complexity online scheduling policy is proposed. The policy exploits the existence of thresholds for choosing rate and power levels as a function of stored energy, harvest state and time until the end of the horizon. The policy, which is based on computing an expected threshold, performs close to optimal on a wide range of example energy harvest patterns. Moreover, it achieves higher throughput values for a given delay, than throughput-optimal online policies developed based on infinite-horizon formulations in recent literature. The solution is extended to include ergodic time-varying (fading) channels, and a corresponding low complexity policy is proposed and evaluated for this case as well.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 B
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• pp.652-654
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• 1996

A study of the coordinated control of a TCSC and an existing PSS is presented when both are used to damp the low frequency oscillations. TCSC is modeled by the first order delay model. Linear quadratic Gaussian controller is used for designing PSS and TCSC supplementary controller. The performance of the proposed controllers is simulated in a one machine infinite bus model. As a result, it is shown that to damp the low frequency oscillations efficiently, it is necessary to control TCSC and PSS simultaneously.