• Journal of Power Electronics
• /
• 제16권6호
• /
• pp.2129-2138
• /
• 2016

The full-bridge inverter, widely used for single-phase photovoltaic grid-connected applications, presents a leakage current issue. Therefore, an AC bypass branch is introduced to overcome this challenge. Nevertheless, existing modulation strategies entail drawbacks that should be addressed. One is the zero-crossing distortion (ZCD) of the AC current caused by neglecting the AC filter inductor voltage. Another is that the system cannot deliver reactive power because the AC bypass branch switches at the power frequency. To address these problems, this work proposes an optimized hybrid modulation strategy. To reduce ZCD, the phase angle of the inverter output voltage reference is shifted, thereby compensating for the neglected leading angle. To generate the reactive power, the interval of the negative power output is calculated using the power factor. In addition, the freewheeling switch is kept on when power is flowing into the grid and commutates at a high frequency when power is fed back to the DC side. In this manner, the dead-time insertion in the high-frequency switching area is minimized. Finally, the performances of the proposed modulation strategy and traditional strategies are compared on a universal prototype inverter. Experimental results validate the theoretical analysis.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2002년도 추계학술대회논문집
• /
• pp.658-664
• /
• 2002

Unsteady flow characteristics and associated blade tonal noise of a cross-flow fan are predicted by a computational method. The incompressible Navier-Stokes equations are time-accurately solved for obtaining the pressure fluctuations between the rotating blades and the stabilizer, and sound pressure is predicted using Curie's equation. The computed fan performance is favorably compared with experimental data, and also indicates that the performance is not significantly altered by the random pitch effect at ${\phi}>0.4$. In the present study, the narrow-band noise characteristics of three impellers with a uniform and two random Pitch (type-A and-B) blades are compared by the SPL (Sound Pressure Level) spectra, and their frequency modulation characteristics of the BPF (Blade Passing Frequency) noise are also discussed.

• Journal of the Optical Society of Korea
• /
• 제20권6호
• /
• pp.762-769
• /
• 2016

The dynamic modulation transfer function (MTF) for image degradation caused by sinusoidal vibration is formulated based on a Bessel function of the first kind. The presented method makes it possible to obtain an analytical MTF expression derived for arbitrary frequency sinusoidal vibration. The error obtained by the use of finite order sum approximations instead of infinite sums is investigated in detail. Dynamic MTF exhibits a stronger random behavior for low frequency vibration than high frequency vibration. The calculated MTFs agree well with the measured MTFs with the slant edge method in imaging experiments. With the proposed formula, allowable amplitudes of any frequency vibration are easily calculated. This is practical for the analysis and design of the line-of-sight stabilization system in the remote sensing camera.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2004년도 하계학술대회 논문집 B
• /
• pp.1211-1213
• /
• 2004

CCFL(cold cathode fluorescent lamp) are used to backlight of LCD(liquid crystal display). CCFL dimming methods are used to pulse frequency modulation(PFM) or pulse width modulation(PWM). In this paper, design of CCFL driving and control circuit by half-bridge type series and parallel resonant inverter that variable frequency modulation method to control the output voltage current. Inverter switching frequency is higher than resonant frequency for stable operating, and it is possible dimming control. On the basis of equivalent circuit, the validity of this study is confirmed by the comparison of simulation and experimental result.

• Corrosion Science and Technology
• /
• 제20권5호
• /
• pp.231-241
• /
• 2021

The objective of this study was to evaluate total current under steady-state conditions for a material undergoing corrosion using the electrochemical frequency modulation (EFM) technique, taking into account the presence of solution resistance and double layer capacitance. The analysis involving linearization of the Tafel curve allowed for the estimation of corrosion parameters. Results showed that the output signal was dependent on fundamental frequencies and their multiples. In addition, the output signal almost manifested itself at frequencies that were sums of fundamental frequencies of the applied sinusoidal signal. The harmonics calculated showed a significant shift from the principal frequency of input signals. The investigation involved the influence of corrosion current and anode-to-cathode Tafel slope ratio on faradaic and non-faradaic currents (including the average and RMS). The model presented showed both qualitative and quantitative improvements over the previously developed EFM technique that ignored the influence of solution resistance and the double layer capacitance while assuming the applied DC potential corresponded to the corrosion potential of the corroding material.

• 음성과학
• /
• 제12권4호
• /
• pp.17-29
• /
• 2005

Time-frequency representation reveals some useful information about instantaneous frequency, instantaneous bandwidth and boundary of each AM-FM component of a speech signal. In many cases, the instantaneous frequency of each component is not constant. The variability of instantaneous frequency causes degradation of resolution in time-frequency representation. This paper presents a method of adaptively adjusting the transform kernel for preventing degradation of resolution due to time-varying instantaneous frequency. The transform kernel is the form of frequency modulated function. The modulation function in the transform kernel is determined by the estimate of instantaneous frequency which is approximated by first order polynomial at each time instance. Also, the window function is modulated by the estimated instantaneous. frequency for mitigation of fringing. effect. In the proposed method, not only the transform kernel but also the shape and the length of. the window function are adaptively adjusted by the instantaneous frequency of a speech signal.

• 전력전자학회논문지
• /
• 제14권1호
• /
• pp.54-61
• /
• 2009

본 논문에서는 강압형 DC-DC 컨버터의 성능 개선을 위한 스위칭 기법인 2차 SDSDM (Space Dithered Sigma Delta Modulation)방식을 제안한다. PWM (Pulse Width Modulation) 방식은 일정 스위칭 주파수 대역에서의 고조파로 인해 소음, 전자파 장애, 스위칭 손실 등을 유발한다. 이러한 문제를 해결하기 위한 DSDM 방식의 일종인 1차 SDSDM은 랜덤 디더(Random Dither) 발생기가 1차 SDM의 양자화기(quatizer) 입력단에 위치하여 스위칭 주파수가 분산된다. 강압형 DC/DC 컨버터에 제안하는 2차 SDSDM의 방식을 적용한 실험 결과를 통해 타당성을 검증한다.

• 대한물리치료과학회지
• /
• 제7권2호
• /
• pp.567-577
• /
• 2000

In human body, catecholamines, such as epinephrine and norepinephrine, can be increased anxiety, blood pressure and pain etc. The inhibitory effects of TENS, electroacupuncture and massage on the release of epinephrine, norepinephrine from sympathetic nerve endings has already been known. However, the effects of silver spike point stimulation on the catecholamines was not well understood. Therefore, the purpose of this study was to characterize the SSP-induced inhibitory effects of catecholamines. The following results were obtained. (1) The studies on urinary catecholamines released that the levels of epinephrine and norepinephrine of continue type SSP stimulation group were significantly lower than those in the control group in human in vivo. (2) The dose-response curves of epinephrine and norepinephrine in rat aortic smooth muscle strips were increased dose dependent manner respectively. However, the contractile response of norepinephrine in rat aortic smooth muscle strips were slightly differentiated. It is concluded that the SSP stimulation reflects to the inhibitory effects of epinephrine and norepinephrine in men. Especially, we believe that the amplitude-frequency modulation, such as continue type a)1d frequency modulation type, of SSP stimulation plays a role in regulating catecholamines.

• 한국통신학회논문지
• /
• 제11권2호
• /
• pp.122-136
• /
• 1986

본 논문에서는 이동 무선 통신을 위한 새로운 변조 방식인 디지털 위상-주파수 혼합 변조 시스템(digital phase-frequency hybrid modulation system, PFSK)을 제안하고, 이 신호가 m~분포 페이딩 채널을 통과할 경우의 시스템의 오율 및 중단율에 관한 일반식을 구하였다. 특히 레일리 페이딩에 대해서는 다이버시트 수신 기법을 이용하였을 경우의 시스템의 오율 및 중단율에 관한 일반식을 유도하였다. 유오된 오율식에서 반송파 전력 대 잡음 전력비(CNR), 페이딩 지수, 다이버시티 branch의 수, branch사이의 상관 계수를 파라미터로 수치 계산을 하여, PFSK 시스탐과 같이 심볼 전송을 하는 QDPSK시스템의 성능을 오율 및 중단율의 측면에서 비교 평가하였다. 해석 결과, 강한 페이딩하에서는 PFSK시스템이 QDPSK 시스템에 비해 오율 특성이 우수함을 알 수 있었고, 다이버시티 기법을 사용하므로써 시스템의 성능을 크게 개선시킬 수 있음을 알 수 있었다.

• Journal of Power Electronics
• /
• 제14권3호
• /
• pp.531-540
• /
• 2014

A novel carrier-based PWM (CBPWM) strategy of a three-level NPC converter is proposed in this paper. The novel strategy can eliminate the low-frequency neutral point (NP) voltage oscillation under the entire modulation index and full power factor. The basic principle of the novel strategy is introduced. The internal modulation wave relationship between the novel CBPWM strategy and traditional SPWM strategy is also studied. All 64 modulation wave solutions of the CBPWM strategy are derived. Furthermore, the proposed CBPWM strategy is compared with traditional SPWM strategy regarding the output phase voltage THD characteristics, DC voltage utilization ratio, and device switching losses. Comparison results show that the proposed strategy does not cause NP voltage oscillation. As a result, no low-frequency harmonics occur on output line-to-line voltage and phase current. The novel strategy also has higher DC voltage utilization ratio (15.47% higher than that of SPWM strategy), whereas it causes larger device switching losses (4/3 times of SPWM strategy). The effectiveness of the proposed modulation strategy is verified by simulation and experiment results.