• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 추계학술대회 논문집
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• pp.238-243
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• 2003

The solar cells should be operated at the maximum power point because its output characteristics are greatly fluctuated on the variation of insolation, temperature and load. The output power of solar cell is DC, therefore it is necessary to install an inverter among electric power converts. The inverter have to supply a sinusoidal current and voltage to the load and the interactive utility line. In the paper, the proposes a photovoltaic system designed with a step up chopper and single phase PWM voltage source inverter. Synchronous signal and control signal was processed by microprocessor for stable modulation. The step up chopper operates in continuous mode by adjusting the duty ratio so that the photovoltaic system tracks the maximum power point of solar cell without any influence on the variation of insolation and temperature because solar cell has typical dropping character. The single phase PWM voltage source inverter consists of complex type of electric power converter to compensate for the defect, that is, solar cell cannot be developed continuously by connecting with the source of electric power, from 10 to $20\%$. The single phase PWM voltage source inverter operates in situation that its output voltage is in same phase with the utility voltage. The inverter supplies an ac power with high factor and low level of harmonics to the load and the utility power system.

• Journal of Electrical Engineering and Technology
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• 제9권4호
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• pp.1296-1308
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• 2014

This paper presents a new zero voltage switching (ZVS) converter for medium power and high input voltage applications. Three three-level pulse-width modulation (PWM) circuits with the same power switches are adopted to clamp the voltage stress of MOSFETs at $V_{in}/2$ and to achieve load current sharing. Thus, the current stresses and power ratings of transformers and power semiconductors at the secondary side are reduced. The resonant inductance and resonant capacitance are resonant at the transition interval such that active switches are turned on at ZVS within a wide range of input voltage and load condition. The series-connected transformers are adopted in each three-level circuit. Each transformer can work as an inductor to smooth the output current or a transformer to achieve the electric isolation and power transfer. Thus, no output inductor is needed at the secondary side. Three center-tapped rectifiers connected in parallel are used at the secondary side to achieve load current sharing. Compared with the conventional parallel three-level converters, the proposed converter has less switch counts. Finally, experiments based on a 1.44kW prototype are provided to verify the operation principle of proposed converter.

• 전력전자학회논문지
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• 제4권6호
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• pp.491-499
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• 1999

본 논문은 새로운 제어기법의 고성능 전동차 추진용 IGBT VVVF 인버터에 관한 것이다. 현차 적용 전에 견인력 제어성의 우수함과 안정성을 검증하기 위해, 현차 조건에서 발생될 수 있는 경우에 대한 모의 주행시험을 실시하고 그 결과를 보인다. 모의 주행시험은 160톤의 차량을 등가화한 관성부하장치를 이용하여 정상상태는 물론 전압변동 등 각종 과도상태에 대해서도 실시하였다. 본 논문에서는 4병렬 접속된 견인전동기의 토오크 제어성 향상을 위한 벡터제어기법 적용과 공간벡터 변조기법에 동기방식을 적용하여 500Hz이하의 저주파 스위칭으로써 6스텝까지 연속 과변조 제어가 가능한 최적의 PWM방법을 제시한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 A
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• pp.443-445
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• 1995

Since the residential load is an AC load, while the output of solar cell is a DC power, the photovoltaic system needs the DC/AC converter to utilize solar cell and must provide the sinusoidal wave current and voltage with unity power factor in the case of driving to Interact with utility line. It is always necessary for the output of solar cell to operate in the vicinity of maximum power point, since it is greatly fluctuated by insolation. This paper treats that we will constitute a single phase PWM voltage source inverter and trace the modulation index which always maximize the output of solar cell in propotion to insolation variation and prove it by simulation that we can provide current wave, which is nearly sinusoidal wave with unity power factor, for load and utility line.

• Wind and Structures
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• 제37권1호
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• pp.1-13
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• 2023

Due to the irregular shape and the deviation of stiffness center and gravity center, buildings always suffer from complex surface load and vibration response under wind action. This study is dedicated to analyze the surface wind load and wind-induced response of an irregular building, and to discuss the possibility of top swimming pool as a TLD to diminish wind-induced vibration of the structure. Wind tunnel test was carried out on a hotel with irregular shape to analyze the wind load and structural response under 8 wind incident angles. Then a precise numerical model was established and calibrated through experimental results. The top swimming pool was designed according to the principle of frequency modulation, and equations of motion of the control system were derived theoretically. Finally, the wind induced response of the structure controlled by the pool was calculated numerically. The results show that both of wind loads and wind-induced responses of the structure are significantly different with wind incident angle varies, and the across-wind response is nonnegligible. The top swimming pool has acceptable damping effect, and can be designed as TLD to mitigate wind response.

• 대한기계학회논문집B
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• 제40권1호
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• pp.39-45
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• 2016

차량용 연료전지의 부하 변동시 열관리는 성능과 내구성에 직결되기 때문에 매우 중요하다. 본 연구에서는 작동 부하 조건 내에 온도를 유지할 수 있도록 하기 위한 열관리 시스템용 선형 상태 궤환 제어기를 설계하였다. 차량용 연료전지 열관리 모델은 레저버, 라디에이터, 바이패스 밸브, 팬 그리고 냉각수 펌프 등으로 구성하였으며, MATLAB/SIMULINK$^{(R)}$으로 개발하였다. 시스템 모델의 비선형성으로 인해, 부하 조건 $0.5A/cm^2{\sim}0.7A/cm^2$ 에서 온도 제어 지령을 정상적으로 달성하기 위해 PWM(Pulse Width Modulation)과 수정된 상태 궤환 제어기를 적용하였고 제어 알고리즘의 성능은 ITAE(Integral time weighted error)로 평가하였다. 수정된 상태 궤환 제어기가 저 부하 구간에서 다른 알고리즘에 비해 더 효율적으로 온도를 제어하는 것을 확인하였다.

• 전기학회논문지
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• 제62권4호
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• pp.502-509
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• 2013

It presents an efficient switching pattern, which expects a reduction of switching losses in a cascaded H-bridge PWM multilevel inverter. By the proposed switching scheme, the lower H-bridge module operates at low frequency of 60[Hz] because it assigns to transfer most load power. The upper H-bridge module operates at high frequency of PWM switching to improve THD of output voltage. The proposed switching pattern applies to cascaded H-bridge multilevel inverter with PD, APOD, bipolar, and unipolar switching methods. By computer-aided simulations, we verify the validity of the proposed switching scheme. Finally, we prove that the proposed PD and APOD switching patterns are better than those of the conventional one in efficiency.

• Journal of international Conference on Electrical Machines and Systems
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• 제1권4호
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• pp.405-411
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• 2012

This paper deals with direct torque control of an induction motor (IM) with constant switching frequency. The desired torque is obtained from the speed controller which is designed using the IP controller. Decoupling control of torque and flux is developed based on the energy model of IM using the IP controller strategies. The desired d-axis and q-axis stator voltage components are obtained from the designed controller, which decouples torque and flux. The constant switching frequency can be applied using space-vector pulse width modulation, since the desired stator voltage can be known from the decoupling torque and flux controllers. In order to achieve stable operation of the proposed IP controllers, the gains of the controllers are chosen by setting the poles in negative (left) half of s-plane and by choosing the rising time for the response of the step function. The proposed controller was verified in simulations using Matlab/Simulink and results have proven excellent performance. It was found that the proposed IP controllers can provide excellent performance to track the desired torque and speed and to reject the disturbance of load.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.401-401
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• 2009

Recently, demands for the development of compact, lightweight power supplies with higher power density and higher efficiency have been increased. Since Piezoelectric Transformer (PT) was emerged in device and material industry, it has been suggested as a viable alternative to the magnetic transformer in some applications. PT has some advantages such as low profile and mechanical energy transfer with little electromagnetic interface (EMI). Also, PT can provide high voltage stepping ratio with good isolation and requires no copper windings saving copper usage especially for large voltage conversion differences. Conventional control of PT converter has mainly two-way. One is the pulse frequency modulation (PFM) control method and the other is the pulse width modulation (PWM) control with frequency fixed method. It is known that the maximum PT efficiency can be obtained when it operates near the resonant frequency of the PT. And, also PT's resonant frequency moves according to the load condition. Therefore, selection of PT converter control method is very difficult. This paper analyzes general piezo-electric converter modeling and proposes a guide-line to selection of control method and stabilization control.

• Journal of Electrical Engineering and Technology
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• 제6권2호
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• pp.154-160
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• 2011

A new algorithm for estimating the fundamental frequency of power system signals is presented. The proposed algorithm consists of two stages: orthogonal decomposition and a complex Prony analysis. First, the input signal is decomposed into two orthogonal components using cosine and sine filters, and a variable window is adapted to enhance the performance of eliminating harmonics. Then a complex Prony analysis that is proposed in this paper is used to estimate the fundamental frequency by approximating the cosine-filtered and sine-filtered signals simultaneously. To evaluate the performance of the algorithm, amplitude modulation and harmonic tests were performed using simulated test signals. The performance of the algorithm was also assessed for dynamic conditions on a single-machine power system. The Electromagnetic Transients Program was used to generate voltage signals for a load increase and single phase-to-ground faults. The performance evaluation showed that the proposed algorithm accurately estimated the fundamental frequency of power system signals in the presence of amplitude modulation and harmonics.