• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.315-316
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• 2016

This paper proposes an enhanced distributed generation (DG) unit with an adaptive virtual impedance control approachin order to address the inaccurate reactive power sharing problems. The proposed method can adaptively regulate the DG unit thanks to the equivalent impedance, andthe effect of the mismatch in feeder impedance is compensatedto share the reactive power accurately.The proposed control strategy can be implemented directly without any requirement of pre-knowledge of the feeder impedances. Simulations are performed to validate the effectiveness of the proposed control approach.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.120-121
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• 2017

This paper proposes an enhanced distributed generation (DG) unit with an adaptive virtual impedance control approach in order to address the inaccurate reactive power sharing problem. The proposed method can adaptively regulate the DG virtual impedance, and the effect of the mismatch in feeder impedances is compensated to share the reactive power accurately. The proposed control strategy is fully distributed and the need for the microgrid central controller is eliminated. Furthermore, the proposed method can be directly implemented without requirement of pre-knowledge of the feeder impedances. Simulations are performed to validate the effectiveness of the proposed control approach.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.7
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• pp.631-636
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• 2007

An efficient obstacle avoidance algorithm is proposed in this paper to avoid dynamic obstacles using a collision vector while a tele-operated mobile robot is moving. For the verification of the algorithm, an operator watches through a monitor and controls the mobile robot with a force-reflection joystick. The force-reflection joystick transmits a virtual force to the operator through the Inter-net, which is generated by an adaptive impedance algorithm. To keep the mobile robot safe from collisions in an uncertain environment, the adaptive impedance algorithm generates the virtual force which changes the command of the operator by pushing the operator's hand to a direction to avoid the obstacle. In the conventional virtual force algorithm, the avoidance of moving obstacles was not solved since the operator cannot recognize the environment realistically by the limited communication bandwidth and the narrow view-angle of the camera. To achieve the dynamic obstacle avoidance, the adaptive virtual force algorithm is proposed based on the collision vector that is a normal vector from the obstacle to the mobile robot. To verify the effectiveness of the proposed algorithm, mobile robot navigation experiments with multiple moving obstacles have been performed, and the results are demonstrated.

• Journal of Power Electronics
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• v.17 no.1
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• pp.282-293
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• 2017

There exists a strong coupling between real and reactive power owing to the complex impedances in droop based islanded microgrids (MGs). The existing virtual impedance methods consider improvements of the impedance matching for sharing of the voltage controlled power (VCP) (reactive power for Q-V droop, and real power for P-V droop), which yields a 1-DOF (degree of freedom) tunable virtual impedance. However, a weak impedance matching for sharing of the frequency controlled power (FCP) (real power for $P-{\omega}$ droop, and reactive power for $Q-{\omega}$ droop) may result in FCP overshoots and even oscillations during load transients. This in turn results in VCP oscillations due to the strong coupling. In this paper, a 2-DOF tunable adaptive virtual impedance method considering impedance matching for both real and reactive power (IM-PQ) is proposed to improve the power sharing performance of MGs. The dynamic response is promoted by suppressing the coupled power oscillations and power overshoots while realizing accurate power sharing. In addition, the proposed power sharing controller has a better parametric adaptability. The stability and dynamic performances are analyzed with a small-signal state-space model. Simulation and experimental results are presented to investigate the validity of the proposed scheme.

• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.328-329
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• 2020

The AC/DC converter, which connects the AC grid to the DC grid in the microgrid, is a critical component in power sharing and stable operation. Sometimes the AC/DC converters are connected in parallel to increase the transmission and reception capacity. When connected in parallel, circulating current is generated due to line impedance difference or sensor error. As a result of circulating current, there is deterioration and loss in particular PCS(Power Conversion System). In this paper, we propose droop control with novel adaptive virtual impedance for reducing circulating current. Feasibility of proposed algorithm is verified by PowerSIM simulation.

• Journal of Power Electronics
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• v.15 no.3
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• pp.741-752
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• 2015

This study proposes a new solution for the parallel operation of microgrid inverters in terms of circuit topology and control structure. A combined three-phase four-wire inverter composed of three single-phase full-bridge circuits is adopted. Moreover, the control structure is based on adaptive three-order sliding-mode control and wireless load-sharing control. The significant contributions are as follows. 1) Adaptive sliding-mode control performance in inner voltage loop can effectively reject both voltage and load disturbances. 2) Virtual resistive-output-impedance loop is applied in intermediate loop to achieve excellent power-sharing accuracy, and load power can be shared proportionally to the power rating of the inverter when loads are unbalanced or nonlinear. 3) Transient droop terms are added to the conventional power outer loop to improve dynamic response and disturbance rejection performance. Finally, theoretical analysis and test results are presented to validate the effectiveness of the proposed control scheme.

• Proceedings of the IEEK Conference
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• 2002.06e
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• pp.33-36
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• 2002

본 논문은 고정 및 이동물체와의 효율적인 충돌회피 알고리즘으로 적응임피던스제어 알고리즘을 제안하였다. 일반적인 충돌회피 알고리즘은 이동로봇의 동적 특성을 고려하지 않고 최적의 경로생성에만 관심을 둠으로써 실제 이동로봇이 추종하기 어려운 경로를 생성하기 쉽다. 그러므로 이동로봇의 동적 특성을 고려한 충돌회피 알고리즘을 위해, 이동로봇과 장애물과의 상호작용관계를 가상의 힘으로 정의한 임피던스제어 알고리즘을 사용하였다. 하지만 이런 단순 임피던스제어 알고리즘만으로는 갑작스런 장애물의 출현 시 이동로봇의 속도가 증가하고 장애물이 사라지면 속도가 감소하는 비효율적인 속도제어라는 문제점을 가지고 있다. 그러므로 충돌 가능성에 따른 새로운 속도제어 방식을 고려한 적응임피던스제어 알고리즘을 제안하고 검증하고자 한다.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.1
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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.