• 한국음향학회지
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• 제33권3호
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• pp.184-190
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• 2014

스피커 시스템은 가청 주파수 대역 20 ~ 20,000 Hz를 하나의 유닛으로 재생하는 것이 이상적이지만, 물리적으로 구현하기 어렵다. 따라서 두 개 또는 그 이상의 유닛을 사용하고, 멀티웨이 시스템으로 구성하여 오디오 대역을 커버한다. 멀티웨이 스피커 시스템에서는 고음과 저음의 유닛이 정상적으로 동작되도록 크로스오버 네트워크 필터를 필수적으로 사용해야 한다. 네트워크 필터의 크로스오버 주파수는 대부분 1 ~ 4 kHz 대역에 존재하며, 이 대역은 명료도의 기여율이 높고 음질에 미치는 영향이 아주 크다. 그러나 여러 가지 원인 때문에 크로스오버 주파수 대역에서 위상과 진폭 특성이 정확하게 결합되지 않은 경우가 많다. 즉, 유닛 간의 거리 차와 전기적인 특성 차이 때문에 크로스오버 주파수에서 유닛 간의 진폭과 위상 특성이 정확하게 결합되지 않아서 주파수 특성이 불규칙해지고, 그 결과 음질이 좋지 않고 명료성도 나빠진다. 크로스오버 주파수에서 유닛들을 정확하게 결합시키기 위해서는 각 유닛의 진폭 특성뿐만 아니라 위상 특성까지도 고려하여 결합시켜야 한다. 본 논문에서는 유닛 간의 지연 시간을 조정하여 크로스오버 주파수에서 평탄한 주파수 특성이 되도록 하는 방법과 유닛들의 주파수 롤 오프 특성도 고려한 필터 선택 방법을 제안하였다. 그 결과 크로스오버 주파수 대역에서 ${\pm}1$ dB의 평탄한 주파수 특성이 얻어지고 명료성도 향상되었다.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제2권2호
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• pp.115-121
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• 2002

This paper presents an evolutionary design of digital IIR filters using the genetic algorithm (GA) with modified genetic operators and real-valued encoding. Conventional digital IIR filter design methods involve algebraic transformations of the transfer function of an analog low-pass filter (LPF) that satisfies prescribed filter specifications. Other types of frequency-selective digital fillers as high-pass (HPF), band-pass (BPF), and band-stop (BSF) filters are obtained by appropriate transformations of a prototype low-pass filter. In the GA-based digital IIR filter design scheme, filter coefficients are represented as a set of real-valued genes in a chromosome. Each chromosome represents the structure and weights of an individual filter. GA directly finds the coefficients of the desired filter transfer function through genetic search fur given filter specifications of minimum filter order. Crossover and mutation operators are selected to ensure the stability of resulting IIR filters. Other types of filters can be found independently from the filter specifications, not from algebraic transformations.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.965-969
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• 2003

In this paper, the implementation technique of digital crossover network using perfect linear phase IIR filters is presented. This system has various advantages which cannot be obtained from analog crossover network such as linear phase response, flat group delay and sharp cut-off at low-order over audio frequency band. The simulation results show that the group delay response is maximally flat and twice more attenuation in stop-band than the prototype elliptic IIR filter at all desired frequency.

• 전력전자학회논문지
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• 제14권6호
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• pp.449-456
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• 2009

본 논문에서는 PFC단 링크 캐패시터의 실효 전류를 크게 저감 할 수 있는 링크 캐패시터 전류 스트레스 저감기법을 제안한다. 링크 캐패시터 선정 기준에는 여러 가지가 있으나 가장 큰 비중을 차지하는 것이 캐패시터 실효전류이다. 제안된 C-L 필터는 PFC단 출력 전류를 필터링하여 링크 캐패시터의 실효 전류를 크게 줄일 수 있고, 제안된 C-L-L-C 필터는 C-L 필터의 출력 전류 필터링 효과와 함께 L-C 필터가 DC/DC단 입력 전류를 필터링 함으로써 링크 캐패시터의 실효 전류를 더욱 크게 줄일 수 있다. 제안된 필터는 설계가 간단하고 PFC단의 Crossover frequency가 매우 낮아 C-L 필터 및 C-L-L-C 필터의 Cut-off frequency가 PFC단의 제어기 루프에 영향을 주지 않으므로 적은 소자를 가지고 손쉬운 방법으로 링크 캐패시터의 실효전류를 크게 줄일 수 있다. 제안된 필터의 이론적 해석과 설계 방법을 제시하며, 실험을 통하여 그 우수성을 검증한다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.973-978
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• 2005

In this paper, we investigate an improved mobile robot localization method using Kalman filter. The highlight of the paper lies in the formulation of combined Kalman filter and its application to mobile robot experiment. The combined Kalman filter is a kind of extended Kalman filter which has an extra degree of freedom in Kalman filtering recursion. It consists of the standard Kalman filter, i.e., the predictor-corrector and the perturbation estimator which reconstructs unknown dynamics in the state transition equation of mobile robot. The combined Kalman filter (CKF) enables to achieve robust localization performance of mobile robot in spite of heavy perturbation such as wheel slip and doorsill crossover which results in large odometric errors. Intrinsically, it has the property of integrating the innovation in Kalman filtering, i.e., the difference between measurement and predicted measurement and thus it is so much advantageous in compensating uncertainties which has not been reflected in the state transition model of mobile robot. After formulation of the CKF recursion equation, we show how the design parameters can be determined and how much beneficial it is through simulation and experiment for a two-wheeled mobile robot under indoor GPS measurement system composed of four ultrasonic satellites. In addition, we discuss what should be considered and what prerequisites are needed to successfully apply the proposed CKF in mobile robot localization.

• Journal of Power Electronics
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• 제14권5호
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• pp.1047-1056
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• 2014

In most grid-connected inverters (GCI) with an LCL filter, since the design of both the LCL filter and the controller is done separately, considerable tuning efforts have to be exerted when compared to inverters using an L filter. Consequently, an integrated co-design of the filter and the controller for an LCL-type GCI is proposed in this paper. The control strategy includes only a PI current controller and a proportional grid voltage feed-forward controller. The capacitor is removed from the LCL filer and the design procedure starts from an L-type GCI with a PI current controller. After the PI controller has been settled, the capacitor is added back to the filter. Hence, it introduces a resonance frequency, which is identified based on the crossover frequencies to accommodate the preset PI controller. Using the proposed co-design method, harmonic standards are satisfied and other practical constraints are met. Furthermore, the grid voltage feed-forward control can bring an inherent damping characteristic. In such a way, the good control performance offered by the original L-type GCI and the sharp harmonic attenuation offered by the latter designed LCL filter can be well integrated. Moreover, only the grid current and grid voltage are sensed. Simulation and experimental results verify the feasibility of the proposed design methodology.

• Animal Bioscience
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• 제37권4호
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• pp.655-667
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• 2024

Objective: This study aimed to assess the impact of a hydroethanolic extract of walnut green husks (WGH) on rumen fermentation and the diversity of bacteria, methanogenic archaea, and fungi in sheep fed a high-concentrate diet. Methods: Five healthy small-tailed Han ewes with permanent rumen fistula were selected and housed in individual pens. This study adopted a self-controlled and crossover design with a control period and an experimental period. During the control period, the animals were fed a basal diet (with a ratio of concentrate to roughage of 65:35), while during the treatment period, the animals were fed the basal diet supplemented with 0.5% hydroethanolic extract of WGH. Fermentation parameters, digestive enzyme activities, and microbial diversity in rumen fluid were analyzed. Results: Supplementation of hydroethanolic extract of WGH had no significant effect on feed intake, concentrations of total volatile fatty acids, isovalerate, ammonia nitrogen, and microbial protein (p>0.05). However, the ruminal pH, concentrations of acetate, butyrate and isobutyrate, the ratio of acetate to propionate, protozoa count, and the activities of filter paper cellulase and cellobiase were significantly increased (p<0.05), while concentrations of propionate and valerate were significantly decreased (p<0.05). Moreover, 16S rRNA gene sequencing revealed that the relative abundance of rumen bacteria Christensenellaceae R7 group, Saccharofermentans, and Ruminococcaceae NK4A214 group were significantly increased, while Ruminococcus gauvreauii group, Prevotella 7 were significantly decreased (p<0.05). The relative abundance of the fungus Pseudomonas significantly increased, while Basidiomycota, Fusarium, and Alternaria significantly decreased (p<0.05). However, there was no significant change in the community structure of methanogenic archaea. Conclusion: Supplementation of hydroethanolic extract of WGH to a high-concentrate diet improved the ruminal fermentation, altered the structure of ruminal bacterial and fungal communities, and exhibited beneficial effects in alleviating subacute rumen acidosis of sheep.