• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.1988-1994
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• 2014

In a single-phase grid-connected power system consisting of a DC/DC converter and a DC/AC converter, the current drawn from renewable energy sources has a tendency to be pulsated and contains second-order frequency ripple components, which results in several drawback such as a power harvesting loss and a shortening of the energy source's life. This paper presents a new second-order harmonic current reduction scheme with a fast dc-link voltage loop for two-stage dc-dc-ac grid connected systems. In the frequency domain, an adequate control design is performed based on the small signal transfer function of a two-stage dc-dc-ac converter. To verify the effectiveness of proposed control algorithm, a 1 kW hardware prototype has been built and experimental results are presented.

• 전력전자학회논문지
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• 제12권3호
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• pp.258-266
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• 2007

자기부상열차는 초기부상에서 정상상태에 이르는 짧은 시간동안 전류변화가 매우 큰 단점이 있다. 본 연구에서는 이를 안정적으로 제어하기 위해서 다중루프제어를 적용하였다. 제어기가 포함된 전체시스템에 상태방정식의 특성방정식을 구하여 원하는 특성의 제어이득을 쉽게 구할 수 있도록, Bessel function 원형모델을 도입하여 극점을 설정하였다. 설정된 극점을 바탕으로 제어기를 구성하고, 시스템의 특성방정식을 구하여 계수비교 함으로써, 시스템의 안정된 제어 특성을 확인하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.712-717
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• 2001

This paper investigates the control problem of evaporator superheat, i.e., the difference between the temperature of the refrigerant at the entrance region of an evaporator and that at the exit region, for multi-type air-conditioning/refrigeration systems. Mathematical equations describing the characteristics of compressor, condenser, evaporator, and electronic expansion valve are first derived. Then, the transfer functions from the current input of the electronic expansion valve to wall temperatures of evaporator tube at two-phase region and superheated region, respectively, are derived. The stability and performance of the closed loop system with a PI controller are analyzed by Nyquist stability criterion. Simulation results are provided.

• 제어로봇시스템학회논문지
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• 제3권6호
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• pp.576-581
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• 1997

DC-DC converter with chopper is seen to have problems, such as, loop instability and degradation of transient response, due to the interaction between input filter and switching regulator. In this paper, the switching regulator consisting of input filter and double chopper is analyzed, and the state space model at continuous current mode and the transfer function between duty ratio of switching pulse and output voltage are derived. The controller in this paper is designed as feedforward(P) and feedback(PI) control scheme to minimize the variation of output voltage, and computer simulation results are presented to show the performance of the proposed controller.

• Journal of Electrical Engineering and Technology
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• 제13권5호
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• pp.1886-1900
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• 2018

This paper proposes a confronting feedback control structure and controllers for positive output elementary super lift Luo converters (POESLLCs) working in discontinuous conduction mode (DCM). The POESLLC offers the merits like high voltage transfer gain, good efficiency, and minimized coil current and capacitor voltage ripples. The POESLLC working in DCM holds the value of not having right half pole zero (RHPZ) in their control to output transfer function unlike continuous conduction mode (CCM). Also the DCM bestows superlative dynamic response, eliminates the reverse recovery troubles of diode and retains the stability. The proposed control structure involves two controllers respectively to control the voltage (outer) loop and the current (inner) loop to confront the time-varying ON/OFF characteristics of variable structured systems (VSSs) like POESLLC. This study involves two different combination of feedback controllers viz. the proportional integral controller (PIC) plus sliding mode controller (SMC) and the fuzzy logic controller (FLC) plus SMC. The state space averaging modeling of POESLLC in DCM is reviewed first, then design of PIC, FLC and SMC are detailed. The performance of developed controller combinations is studied at different working states of the POESLLC system by MATLAB-Simulink implementation. Further the experimental corroboration is done through implementation of the developed controllers in PIC 16F877A processor. The prototype uses IRF250 MOSFET, IR2110 driver and UF5408 diodes. The results reassured the proficiency of designed FLC plus SMC combination over its counterpart PIC plus SMC.

• 전기학회논문지P
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• 제51권4호
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• pp.175-185
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• 2002

In this paper, a new fully digital current control method of UPS inverter, which is based on an internal model control, is proposed. In the proposed control system, overshoots and oscillations due to the computation time-delay are compensated by explicit incorporation of the time-delay in the current control loop transfer function. The internal model controller is adopted to a second order deadbeat reference-to-output response which means that its response reaches the reference in two sampling time including computational time-delays. That is, the average current of filter capacitor is been exactly equal to the reference current with a time lag of two sampling intervals. Therefore, this method has an essentially overshoot free reference-to-output response with a minimum possible rise time. The effectiveness of the proposed control system has been verified by the simulation and experimental respectively. From the simulation and experimental results, the proposed system is achieved the robust characteristics to the calculation time delay and parameter variation as well as very fast dynamic performance, thus it can be effectively applied to the power supply for the critical load.

• 대한기계학회논문집A
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• 제34권5호
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• pp.619-628
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• 2010

차세대 의료기기 시장을 변화시킬 것으로 기대되는 형상기억합금(SMA) 기반의 최소침습용 의료기기는 시술자의 손동작과 같은 유연성과 섬세함을 구현할 수 있는 장점이 있다. 그러나 SMA의 비선형 열전기적 특성으로 인해 SMA 기반 차세대 의료기기 엑추에이터는 자유로운 방향조종 구현이 제한적이고 상용화에 있어서 큰 한계성으로 작용한다. 본 논문은 SMA의 효과적인 온도제어를 위해 전류-온도간의 개방루프 계단응답을 분석하고 1차 미분방정식 해와 비교하여 온도제어에 필요한 파라미터 $t_1$을 도출한 뒤 실험적으로 그 기능을 검증하였다. 또한 $t_1$은 전류를 입력으로 온도를 출력으로 하는 시불변 선형계의 특성함수의 폴(pole)이므로 주파수에 의한 온도제어에 관계된 파라미터인 것으로 나타났다. 본 논문의 결과는 SAM 기반의 차세대 의료기기 액추에이터의 효과적인 위치제어 설계에 응용될 수 있다.

• 전력전자학회논문지
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• 제4권4호
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• pp.349-356
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• 1999

본 논문에서는 철도차량용 보조전원장치에 순시전압제어기법을 적용할 때 발생하는 문제들의 해결방안을 제시한다. 비선형부하나 과도상태에서 빠른 응답특성을 얻기 위해 순시전압제어기법을 사용할 때 LC 필터의 공진문제와 존재하는 정상상태 오차가 더욱 심각해진다. 인버터 출력측 LC 필터에 기인하는 공진현상을 억제하기 위해 전압전달함수의 제동비를 증가시키기 위한 방안으로 필터 커패시터 궤환제어기가 고려되었다. 그리고 교류전압 순시제어시 존재하는 정상상태 오차를 제거하기 위하여 고이득 전달함수를 기존의 PI 제어기에 첨가하였다. 이론적인 분석이 시뮬레이션 결과와 함께 잘 설명되어져 있다. 제안된 기법의 타당성을 5kVA급 시제품에 대한 시뮬레이션과 실험을 통하여 입증하였다.

• Current Optics and Photonics
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• 제7권6호
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• pp.745-754
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• 2023

In order to test the recognition ability and accuracy of a target imaging simulator under the irradiation of solar stray light in a laboratory environment, it needs to be fixed on a five-axis turntable during a hardware-in-the-loop simulation test, so the optical system of the simulator should have a long exit pupil distance. This article adopts a secondary imaging method to design a projection optical system suitable for thin-film-transistor liquid crystal displays. The exit pupil distance of the entire optical system is 1,000 mm, and the final optimization results in the 400 nm-850 nm band show that the modulation transfer function (MTF) of the optical system is greater than 0.8 at the cutoff frequency of 72 lp/mm, and the distortion of each field of view of the system is less than 0.04%. Combined with the design results of the optical system, TracePro software was used to model the optical system, and the simulation of the target imaging simulator at the magnitude of -1 to +6 Mv was analyzed and verified. The magnitude error is less than 0.2 Mv, and the irradiance uniformity of the exit pupil surface is greater than 90%, which meets the requirements of the target imaging simulator.

• 전력전자학회논문지
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• 제19권3호
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• pp.276-282
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• 2014

In a single-phase grid-connected power system consisting of a dc-dc converter and a dc-ac converter, the current drawn from renewable energy sources has a tendency to be pulsated and contains double-fundamental frequency ripple components, which results in several drawback such as a power harvesting loss and a shortening of the energy source's life. This paper presents a new double-fundamental current reduction-scheme with a fast dc-link voltage loop for two-stage dc-dc-ac grid connected systems. In the frequency domain, an adequate control design is performed based on the small-signal transfer function of a two-stage dc-dc-ac converter. To verify the effectiveness of proposed control algorithm, a 1 kW hardware prototype has been built and experimental results are presented.