• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권6호
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• pp.2201-2216
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• 2015

Peak to average power ratio (PAPR) is one of the main imperfections in the broadband communication systems with multiple carriers. In this paper, a new crest factor reduction (CFR) scheme based on interleaved phase sequence called Dummy Sequence Insertion Enhanced Partial Transmit Sequence (DSI-EPTS) is proposed which effectively reduces the PAPR while at the same time keeps the total complexity low. Moreover, the prototype of the proposed scheme in field programmable gate array (FPGA) is demonstrated. In DSI-EPTS scheme, a new matrix of phase sequence is defined which leads to a significant reduction in hardware complexity due to its less searching operation to extract the optimum phase sequence. The obtained results show comparable performance with slight difference due to the FPGA constraints. The results show 5 dB reduction in PAPR by applying the DSI-EPTS scheme with low complexity and low power consumption.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
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• pp.1104-1107
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• 2005

This paper presents a comparison of core losses for the four cases of Switched Reluctance Motors (SRM) with different winding method and switching sequence. With concentrated winding SRM, two kinds of switching sequence are considered for one-phase exciting and two-phase simultaneously exciting driving. With both distributed winding and toroidal winding, two-phase exciting driving is considered. The ratio of calculated core losses to input power is able to be used a guide or reference for deciding the winding method and switching sequence of in the initial design stage of SRM.

• 대한전자공학회논문지SP
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• 제47권3호
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• pp.81-86
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• 2010

CORDIC (COordinate Rotation DIgital Computer) 은 간단한 하드웨어로 벡터의 위상으로의 변환이나 회전 등의 위상 연산을 할 수 있으므로 OFDM 수신 시스템에서의 주파수 동기부를 설계할 때 효과적으로 사용될 수 있다. 그러나 CORDIC 알고리듬에서 위상을 표현하는 방향 시퀀스 (direction sequence, DS) 가 선형적이지 않기 때문에 사용상의 많은 제약이 존재한다. 본 논문에서는 근사적 선형성을 지닌 LBDS (linearized binary direction sequence) 표현 방법을 제안하고, LBDS의 최대 위상오차에 대해 분석한다. 또한 DS로부터 LBDS로 변환하는 하드웨어와 그 역변환 하드웨어의 구조를 제안한다. LBDS를 채택하면 위상 추정, 주파수 오차 루프 필터링, 위상 보정 역회전 등 주파수 동기의 전 과정에 CORDIC과 일반적인 산술 연산기를 사용할 수 있다. T-DMB 복조기에 사용될 수 있는 22비트 LBDS에 대한 예도 기술된다.

• 한국ITS학회 논문지
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• 제5권2호
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• pp.61-71
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• 2006

본 연구는 신호교차로에서의 교통사고 감소방안에 대한 연구로써 이를 위하여 좌회전 현시 순서를 중심으로 연구를 진행하였다. 현재 우리나라는 1985년부터 기존에 사용하던 후행 이중 좌회전 방식을 직진 이동류의 통과효율 및 교차로의 용량을 높이고 소통을 증진시키기 위한 목적으로 선행 이중좌회전 방식으로 바꾸어 사용하고 있다. 이는 그 당시에 도로교차로가 비교적 협소하여 전용좌회전 차로가 거의 없었기 때문으로 선행 이중좌회전 방식을 적용해온 현시점에서 어느 방식이 교통안전과 소통에 더 적합한지를 분석할 필요가 있다고 생각된다. 본 연구에서는 먼저, 선행 좌회전과 후행 좌회전의 안전성을 분석하기 위하여 교차로를 '교차로 내', '횡단보도', '접근부와 유출부'로 나누었다. 이렇게 구분되어진 교차로를 '유효페이스 간격(EIP)'과 '상충기법'을 적용하여 안전성을 분석하였다. 연구 결과 후행 좌회전이 선행 좌회전 보다 전체적인 안전성이 좋은 것으로 나타났으며, 연간 418억원의 사고비용을 절감할 수 있는 것으로 분석되었다.

• ETRI Journal
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• 제30권4호
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• pp.495-505
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• 2008

This paper presents a parallel processing searcher structure for the initial synchronization of a direct sequence ultra-wideband (DS-UWB) system, which is suitable for the digital implementation of baseband functionalities with a 1.32 Gsample/s chip rate analog-to-digital converter. An initial timing acquisition algorithm and a data demodulation method are also studied. The proposed searcher effectively acquires initial symbol and frame timing during the preamble transmission period. A hardware efficient receiver structure using 24 parallel digital correlators for binary phase-shift keying DS-UWB transmission is presented. The proposed correlator structure operating at 55 MHz is shared for correlation operations in a searcher, a channel estimator, and the demodulator of a RAKE receiver. We also present a pseudo-random noise sequence generated with a primitive polynomial, $1+x^2+x^5$, for packet detection, automatic gain control, and initial timing acquisition. Simulation results show that the performance of the proposed parallel processing searcher employing the presented pseudo-random noise sequence outperforms that employing a preamble sequence in the IEEE 802.15.3a DS-UWB proposal.

• 한국통신학회논문지
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• 제32권12C호
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• pp.1142-1148
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• 2007

본 논문에서는 OFDM (Orthogonal Frequency Division Multiplexing) 시스템에서 전송 신호의 PAPR(Peak-to-Average Power Ratio)을 효과적으로 감소시키기 위한 피크 신호 관찰 기반의 적응적 SLM (Adaptive Selective Mapping; ASLM) 기법을 제안한다. 제안 기법은 기존 SLM 방법에서의 복잡도 문제를 개선하기 위해, 매 OFDM 심벌마다 IFFT (Inverse Fast Fourier Transform) 결과에 대한 피크 신호 조정, 피크 조정된 신호의 FFT 결과와 원래 OFDM 심벌간의 부반송파별 전력차 비교를 통한 직교 부호 선택, 선택된 직교 부호만을 이용한 전형적인 SLM 과정의 3단계로 구성된다. 모의실험 결과, 제안된 ASLM 기법은 우수한 PAPR 감소 성능을 유지하면서도 기존 SLM 방법에 비해 훨씬 적은 IFFT 연산 및 PAPR 계산 횟수를 요구함을 확인하였다.

• Journal of Electrical Engineering and Technology
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• 제13권2호
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• pp.550-558
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• 2018

This paper presents the current limit strategy of voltage controller of delta-connected H-bridge static synchronous compensator (STATCOM) under an unbalanced voltage fault event. When phase to ground fault happens, the feasibility to heighten the magnitude of sagging phase voltage is considered by using symmetric transformation method in delta-structure STATCOM. And the efficiency to cover the maximum physical current limit of switching device is considered by using vector analysis method that calculate the zero sequence current for balancing the cluster energy in delta connected H-bridge STATCOM. The result is simple and obvious. Only positive sequence current has to be used to support the unbalanced voltage sag. Although the relationship between combination of the negative sequence voltage with current and zero sequence current is nonlinear, the more negative sequence current is supplying, the larger zero sequence current is required. From the full-model STATCOM system simulation, zero sequence current demand is identified according to a ratio of positive and negative sequence compensating current. When only positive sequence current support voltage sag, the least zero sequence current is needed.

• Journal of Power Electronics
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• 제15권1호
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• pp.268-277
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• 2015

In this paper, a dual-converter three-phase pulse width modulation (PWM) rectifier based on unbalanced one-cycle control (OCC) strategy is proposed. The proposed rectifier is used to eliminate the second harmonic waves of DC voltage and distortion of line currents under unbalanced input grid voltage conditions. The dual-converter PWM rectifier employs two converters, which are called positive-sequence converter and negative-sequence converter. The unbalanced OCC system compensates feedback currents of positive-sequence converter via grid negative-sequence voltages, as well as compensates feedback currents of negative-sequence converter via grid positive-sequence voltages. The AC currents of positive- and negative-sequence converter are controlled to be symmetrical. Thus, the workload of every switching device of converter is balanced. Only one conventional PI controller is adopted to achieve invariant power control. Then, the parameter tuning is simplified, and the extraction for positive- and negative-sequence currents is not needed anymore. The effectiveness and the viability of the control strategy are demonstrated through detailed experimental verification.

• Journal of Power Electronics
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• 제17권2호
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• pp.422-431
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• 2017

The equivalent circuit of a three-leg, four-wire voltage source converter (VSC) is derived using switching functions. Simulations and experiments are conducted (i) to investigate the effects of the zero sequence on VSCs when a three-phase imbalance exists and (ii) to use the consistency of simulations and laboratory experiments to validate the equivalent circuit. The impact of a three-phase imbalance on the VSC has yet to be fully investigated because of the lack of an equivalent circuit to show rigorously how the zero sequence currents flow through the VSC.

• ETRI Journal
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• 제39권6호
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• pp.782-793
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• 2017

This paper considers the use of the Partial Transmit Sequence (PTS) technique to reduce the Peak-to-Average Power Ratio (PAPR) of an Orthogonal Frequency Division Multiplexing signal in wireless communication systems. Search complexity is very high in the traditional PTS scheme because it involves an extensive random search over all combinations of allowed phase vectors, and it increases exponentially with the number of phase vectors. In this paper, a suboptimal metaheuristic algorithm for phase optimization based on an improved harmony search (IHS) is applied to explore the optimal combination of phase vectors that provides improved performance compared with existing evolutionary algorithms such as the harmony search algorithm and firefly algorithm. IHS enhances the accuracy and convergence rate of the conventional algorithms with very few parameters to adjust. Simulation results show that an improved harmony search-based PTS algorithm can achieve a significant reduction in PAPR using a simple network structure compared with conventional algorithms.