• 대한기계학회논문집A
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• 제29권7호
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• pp.938-946
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• 2005

Friction is a dominant nonlinear factor in servomechanisms, which seriously deteriorates system accuracy. A friction compensator is indispensable to fabricate high-performance servomechanisms. In order to compensate for the friction in the servomechanism, identification of the friction elements is required. To estimate the friction of the servomechanism, an accurate linear element model of the system is required first. Tn this paper, a nonlinear friction model, in which static, coulomb and viscous frictions as well as Stribeck effect are included, is identified through the describing function approximation of the nonlinear element. A nonlinear element composed of two relays is intentionally devised to induce various limit cycle conditions in the velocity control loop of the servomechanism. The friction coefficients are estimated from the intersection points of the linear and nonlinear elements in the complex plane. A Butterworth filter is added to the velocity control loop not only to meet the assumption of the harmonic balance method but also to improve the accuracy of the friction identification process. Validity of the proposed method is confirmed through numerical simulations and experiments. In addition, a model-based friction compensator is applied as a feedforward controller to compensate fur the nonlinear characteristics of the servomechanism and to verify the effectiveness of the proposed identification method.

• 전력전자학회논문지
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• 제3권3호
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• pp.231-239
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• 1998

본 논문에서는 대용량에 적합한 영전압 스위칭 전브리지 PWM 직류/직류 변한기의 동특성 해석과 제어 루프의 설계에 대해 논하였다. 전압을 제어하기 위한 위상전이제어의 효과와 영전압 스위칭을 위한 변압기의 누설인덕턴스, FET의 적합 커패시턴스의 이용효과를 고려한 소신호 모델을 유도하였다. 이 소신호 모델은 PWM 벅 변환기의 등가모델에 시비율 변조에 대한 두 개의 종속 전원을 추가함으로써 모델링할 수 있다. 소신호 해석 결과를 근거로 하여 2-극점, 1-영점 보상회로를 사용한 전압제어기를 설계하였다. 설계된 제어기의 타당성을 검증하기 위해서 개루프 시스템과 폐루프 시스템의 소신호 해석결과를 비교하였으며, 2kW급 부하실험으로 설계한 전압제어기의 동특성이 우수함을 실험적으로 입증하였다.

• Journal of Power Electronics
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• 제16권1호
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• pp.38-47
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• 2016

This paper presents DG based droop controlled parallel inverter systems with virtual impedance considering the unequal resistive-inductive combined line impedance condition. This causes a reactive power sharing error and dynamic performance degradation. Each of these drawbacks can be solved by adding the feedforward term of each line impedance voltage drop or injecting the virtual inductor. However, if the line impedances are high enough because of the long distance between the DG and the PCC or if the capacity of the system is large so that the output current is very large, this leads to a high virtual inductor voltage drop which causes reductions of the output voltage and power. Therefore, the line impedance voltage drops and the virtual inductor and resistor voltage drop compensation methods have been considered to solve these problems. The proposed method has been verified in comparison with the conventional droop method through PSIM simulation and low-scale experimental results.

• 전력전자학회논문지
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• 제18권1호
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• pp.10-17
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• 2013

In this paper, a new active damping method of LCL filter without capacitor voltage sensors is proposed for 3 phase PWM Inverter. Normally, L filter or LCL filter is used as an output filter of grid connected PWM inverter. An LCL filter has more excellent performance than L filter to reduce harmonic current, so the small inductance value can be used. However, the resonance problem in LCL filter is happen due to the zero impedance by the addition of LC branch. To solve the resonance problem, the various active damping method has been proposed so far. Generally, the virtual resistor active damping methods is required to additional hardware sensors for measurement of capacitor voltage and current. In this paper, the new active damping method is proposed without any capacitor voltage or current sensors. In the proposed method, the resonance component of the capacitor voltage of LCL filter can be observed by a simple MRAS(Model Reference Adaptive System) observer without additional hardware sensors, and this component is suppressed by feedforward compensation. The validity of the proposed method is proven by simulation and experiment on the 3-phase PWM inverter system.