• 전기학회논문지P
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• 제58권4호
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• pp.588-591
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• 2009

We had experimental studies of microwave output generator. We experimented with a corrugate-shped K-band slow wave guide in the backward wave oscillator. It generated output 표 interaction between electron beam's generation and magnetic field. We estimated oscillation frequency at 24GHz by changing propagation velocity and group velocity. We identified movement by second harmonic of Cherencov interaction and slow cyclotron mode. In our study we achieved oscillation stabilization, generation of long pulse, improvement of oscillation efficiency and output.

• Journal of Power Electronics
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• 제18권1호
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• pp.212-224
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• 2018

For maintaining a reliable and secure power system, this paper describes the design and implement of a single-phase grid-connected inverter with an enhanced phase-locked loop (PLL) and excellent power control performance. For designing the enhanced PLL and power regulator, a full-bridge voltage-controlled inverter (VCI) is investigated. When the grid frequency deviates from its reference values, the output frequency of the VCI is unstable with an oscillation of 2 doubling harmonics. The reason for this oscillation is analyzed mathematically. This oscillation leads to an injection of harmonics into the grid and even causes an output active power oscillation of the VCI. For eliminating the oscillation caused by a PLL, an oscillation compensation method is proposed. With the proposed method, the VCI maintains the original PLL control characteristics and improves the PLL robustness under grid frequency deviations. On the basis of the above analysis, a power regulator with the primary frequency and voltage modulation characteristics is analyzed and designed. Meanwhile, a small-signal model of the power loops is established to determine the control parameters. The VCI can accurately output target power and has primary frequency and voltage modulation characteristics that can provide active and reactive power compensation to the grid. Finally, simulation and experimental results are given to verify the idea.

• 한국위성정보통신학회논문지
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• 제1권1호
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• pp.54-58
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• 2006

동작주파수를 쉽게 조절할 수 있는 신호생성용 안테나 (Antenna-Integrated Oscillator) 설계방법을 소개한다. 제안하는 회로는 광대역에서 부성저항을 갖는 능동회로 (Negative-Resistance Circuit)와 패치안테나로 구분되며, 오실레이터의 동작주파수는 안테나의 공진 주파수로 결정된다. 이러한 디자인 방법은 안테나와 오실레이터의 동작주파수 불일치로 인한 출력파워의 감소 가능성을 줄일 수 있다. 또, 제안하는 설계방법에서 안테나의 Feed 지점과 Feed 라인의 길이를 조절하여 최적의 출력파워를 낼 수 있음을 Load-Pull 시뮬레이션으로 확인하였다. C-band, X-band 회로를 각각 제작, 측정하였고 이를 통하여 설계방법의 타당성을 증명하였다.

• 한국전기전자재료학회논문지
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• 제16권3호
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• pp.253-262
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• 2003

In this paper, the interference cancellation system, which is used to cancel the feedback signal in the wireless communication system with the same frequency, is studied. The time varying feedback signal generated from transmitter antenna to receiver antenna reduces the performance of the receiver system. the interference cancellation system using adaptive feedback method(AF-ICS) is suggested to prevent the oscillation of the receiver system and maintain the maximum output power of the power amplifier by the reduction of time-varying feedback signal and also this paper conforms that the oscillation disappears from the output signal by cancellation of the feedback signal and the total output power is satisfied the system specification.

• Journal of Power Electronics
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• 제15권5호
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• pp.1207-1216
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• 2015

In order to suppress the low frequency oscillation of the neutral-point voltage for three-level inverters, this paper proposes a new discontinuous pulse width modulation (DPWM) control method. The conventional sinusoidal pulse width modulation (SPWM) control has no effect on balancing the neutral-point voltage. Based on the basic control principle of DPWM, the relationship between the reference space voltage vector and the neutral-point current is analyzed. The proposed method suppresses the low frequency oscillation of the neutral-point voltage by keeping the switches of a certain phase no switching in one carrier cycle. So the operating time of the positive and negative small vectors is equal. Comparing with the conventional SPWM control method, the proposed DPWM control method suppresses the low frequency oscillation of the neutral-point voltage, decreases the output waveform harmonics, and increases both the output waveform quality and the system efficiency. An experiment has been realized by a neutral-point clamped (NPC) three-level inverter prototype based on STM32F407-CPLD. The experimental results verify the correctness of the theoretical analysis and the effectiveness of the proposed DPWM method.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권2호
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• pp.55-60
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• 2006

In order to suppress lasing oscillation and obtain high light power, We have proposed a novel SLD which is formed with a straight and tilted waveguide. The window region is used to suppress lasing oscillation and reduce the facet reflectivity. High power and low reflectivity is obtained by the straight and tilted waveguide. Based on the theoretical analysis, we have fabricated the SLD with the waveguide of 500 $\mu$m length and window region of 50 $\mu$m by LPE equipment. Through the measurements of optical characteristics, the output light power of 3 mW was obtained at the 150 mA CW injection current and 25$^{circ}C$. We have confirmed that the proposed SLD has a 0.8 dB spectrum ripple lower than 1 dB which is sufficiently low reflectivity for preventing lasing.

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

• 전력전자학회논문지
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• 제15권1호
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• pp.17-26
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• 2010

본 논문은 군용 공중폭발탄에 사용하는 발진기의 에러를 최소화 하고, 그 효율을 극대화하기 위하여 시뮬레이션과 매우 유사한 형태의 통계적 모델링 방법을 제안한다. 제안된 방법은 일정하고 안정된 출력을 내는 실제 모델에서 실험 계획에 의하여 얻은 데이터로부터 통계적인 해석을 통하여 새로운 형태의 방정식을 구하였다. 그리고 그것을 바탕으로 각각의 전자 부품들을 출력과 일치되도록 모델링 한 후, 출력 예측이 가능한 시뮬레이션을 수행하고, 실제 모델의 출력 데이터와 비교하여 그 유용성, 정확도 및 정밀도를 입증하였다.

• Journal of Power Electronics
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• 제19권5호
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• pp.1270-1277
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• 2019

A problem with virtual synchronous generator (VSG) systems is that they are difficult to operate stably with photovoltaic (PV) power as the DC side. With this problem in mind, a PV-VSG control strategy considering the dynamic characteristics of the DC side is proposed after an in-depth analysis of the dynamic characteristics of photovoltaic power with a parallel energy-storage capacitor. The proposed PV-VSG automatically introduces DC side voltage control for the VSG when the PV enters into an unstable working interval, which avoids the phenomenon where an inverter fails to work due to a DC voltage sag. The stability of the original VSG and the proposed PV-VSG were compared by a root locus analysis. It is found that the stability of the PV-VSG is more sensitive to the inertia coefficient J than the VSG, and that a serious power oscillation may occur. According to this, a new rotor model is designed to make the inertial coefficient automatically change to adapt to the operating state. Experimental results show that the PV-VSG control strategy can achieve stable operation and maximum power output when the PV output power is insufficient.

• 전력전자학회논문지
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• 제14권3호
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• pp.220-227
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• 2009

본 논문은 고전압 DC 파워 서플라이 적용을 위한 높은 전환 비의 자려발진 DC/DC 전력 변환 회로에 관한 것으로써, 하나의 스위치, 하나의 인덕터, 그리고 다수개의 캐패시터와 다이오드로 구성된다. 기존의 극성 반전 형DC/DC 컨버터 회로와 비교하여, 고압 변환 트랜스포머 대신에 인덕터를 사용할 수 있어, 자기 소자의 부피 및 크기는 물론 원가저감이 가능하다. 또한 자려 발진(Self Oscillation) 방식을 사용하여 별도의 제어 IC가 필요 없으므로, 회로구성이 대단히 간단하고, 저가격의 전원 회로를 만들 수 있다. 또한 다이오드들의 전압 스트레스가 감소하여 저가격 고성능의 고압 변환장치 구현이 가능하다. 제안된 회로의 동작원리를 설명하고, 타당성을 Simulation 및 실험을 통하여 검증한다.