• Journal of Power Electronics
• /
• 제19권6호
• /
• pp.1575-1581
• /
• 2019

Due to the mismatched line impedance among distributed generation units (DGs) and uncontrolled harmonic current, the droop controller has a number of problems such as inaccurate reactive power sharing and voltage distortion at the point of common coupling (PCC). To solve these problems, this paper proposes a resistive-capacitive virtual impedance control method. The proposed control method modifies the DG output impedance at the fundamental and harmonic frequencies to compensate the mismatched line impedance among DGs and to regulate the harmonic current. Finally, reactive power sharing is accurately achieved, and the PCC voltage distortion is compensated. In addition, adaptively controlling the virtual impedance guarantees compensation performance in spite of load changes. The effectiveness of the proposed control method was verified by experimental results.

• 전기학회논문지
• /
• 제65권7호
• /
• pp.1193-1203
• /
• 2016

This paper proposes a droop control scheme to compensate the unbalanced line-to-line voltage of unbalanced 3-phase load which is coupled with two inverter-based distributed generations through unequal impedance lines. Unbalanced line-to-line load voltages occur due to using single-phase loads, which brings about bad effects on the coupled inverters and the distributed generations. In order to compensate the unbalanced line-to-line voltages, a positive sequence voltage control was used for sharing the active and reactive power and a negative sequence control was used for reducing the negative sequence voltage. The feasibility of the proposed scheme was first verified by computer simulations, and then experiments with a hardware set-up built in the lab. The experimental results were compared with the simulation results to confirm the feasibility of the proposed scheme.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1999년도 하계학술대회 논문집 F
• /
• pp.2546-2548
• /
• 1999

This paper describes characteristics of independent load sharing of parallel UPS systems and proposes a method of control which does not require control interconnections at each UPS system and compensates for line impedance. Simulation results of a two-module UPS system with different power latins and line impedance have demonstrated the feasibility of the proposed control scheme in load sharing.

• Journal of Power Electronics
• /
• 제16권2호
• /
• pp.695-703
• /
• 2016

A fuel cell power conditioning system for online diagnosis and load leveling under the condition of varying load is developed in this study. The proposed system comprises a unidirectional boost converter and a bidirectional buck-boost converter with a battery. The system operates in two different modes. In normal mode, the bidirectional converter is utilized for load leveling; in diagnostic mode, it is utilized to control load voltage while the boost converter generates perturbation current to implement the online diagnosis function through in-situ electrochemical impedance spectroscopy (EIS). The proposed method can perform EIS for a fuel cell under varying-load conditions with no influence on the load. The validity and feasibility of the proposed system are verified by experiments, and the design procedure of the proposed system is detailed.

• 한국전자파학회논문지
• /
• 제29권5호
• /
• pp.383-388
• /
• 2018

본 논문은 CMOS 공정을 이용하여 1.8 GHz 대역에서 임의의 부하 임피던스를 스위치 제어를 통해 가변 하는 6-포트 기반의 임피던스 변조기에 관한 연구이다. 1.8 GHz 대역 임피던스 변조기는 전력 분배기(Wilkinson power divider), $90^{\circ}$ 하이브리드 결합기(quadrature hybrid coupler), 그리고 각각의 서로 다른 부하 임피던스 선택을 위한 SP3T 스위치들로 구성하였다. 제안된 임피던스 변조기는 1.4~2.2 GHz에서 -13 dB 삽입손실과 10 dB 이상의 입/출력 반사손실 결과를 얻었다. 또한, 3.3 V의 안정적인 전원공급을 위한 LDO(Low Drop Output) 레귤레이터와 디지털 회로 제어가 간편하도록 SPI(Serial Peripheral Interface)를 집적화했으며, 칩 크기는 패드를 포함하여 $1.7{\times}1.8mm^2$이다.

• Journal of Power Electronics
• /
• 제16권3호
• /
• pp.1046-1055
• /
• 2016

A controller to mitigate the destabilizing effect of constant power load (CPL) is proposed for a DC/DC buck-boost converter. The load profile has been considered to be predominantly of CPL type. The negative incremental resistance of the CPL tends to destabilize the feeder system, which may be an input filter or another DC/DC converter. The proposed sliding mode controller aims to ensure system stability under the dominance of CPL. The effectiveness of the controller has been validated through real-time simulation studies and experiments under various operating conditions. The controller has been demonstrated to be robust with respect to variations in supply voltage and load and capable of mitigating instabilities induced by CPL. Furthermore, the controller has been validated using all possible load profiles, which may arise in modern-day DC-distributed power systems.

• Advances in Energy Research
• /
• 제3권2호
• /
• pp.81-95
• /
• 2015

Microgrid, which can be considered as an integration of various dispersed resources (DRs), is characterized by number of DRs interfaced through the power electronics converters. The microgrid comprising these DRs is often operated in an islanded mode. To minimize the cost, reduce complexity and increase reliability, it is preferred to avoid any communication channel between them. Consequently, the droop control method is traditionally adopted to distribute active and reactive power among the DRs operating in parallel. However, the accuracy of distribution of active and reactive power among the DRs controlled by the conventional droop control approach is highly dependent on the value of line impedance, R/X i.e., resistance to reactance ratio of the line, voltage setting of inverters etc. The limitations of the conventional droop control approach are demonstrated and a modified droop control approach to reduce the effect of impedance mis-match and improve the time response is proposed. The error in reactive power sharing is minimized by inserting virtual impedance in line with the inverters to remove the mis-match in impedance. The improved time response is achieved by modifying the real-power frequency droop using arctan function. Simulations results are presented to validate the effectiveness of the control approach.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2002년도 하계학술대회 논문집 C
• /
• pp.1850-1852
• /
• 2002

In this paper, we studies EMTP analysis and characteristics of critical voltage of pulse corona and load impedance on variable electrode length. To obtain a stable Pulse voltage, we designed a compact pulse generator switched MOSFET and tested their characteristics by adjusting electrode length and pulse repetition. As a result, critical voltage of pulse corona and load impedance on increasing electrode length were decreased. These results indicate we can control critical voltage of pulse corona and suppress arc discharging between two electrodes.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2002년도 춘계합동학술대회 논문집
• /
• pp.184-186
• /
• 2002

In this paper, we studies EMTP analysis and characteristics of critical voltage of pulse corona and load impedance on variable electrode length. To obtain a stable pulse voltage, we designed a compact pulse generator switched MOSFET and tested their characteristics by adjusting electrode length and pulse repetition. As a result, critical voltage of pulse corona and load impedance on increasing electrode length were decreased. These results indicate we can control critical voltage of pulse corona and suppress arc discharging between two electrodes.

• Journal of Power Electronics
• /
• 제19권1호
• /
• pp.234-243
• /
• 2019

Studying the control strategy of a microgrid under the load unbalanced state helps to improve the stability of the system. The magnitude of the power fluctuation, which occurs between the power supply and the load, is generated in a microgrid under the load unbalanced state is called negative sequence reactive power $Q^-$. Traditional power distribution methods such as P-f, Q-E droop control can only distribute power with positive sequence current information. However, they have no effect on $Q^-$ with negative sequence current information. In this paper, a stationary-frame control method for power sharing and voltage unbalance compensation in islanded microgrids is proposed. This method is based on the proper output impedance control of distributed generation unit (DG unit) interface converters. The control system of a DG unit mainly consists of an active-power-frequency and reactive-power-voltage droop controller, an output impedance controller, and voltage and current controllers. The proposed method allows for the sharing of imbalance current among the DG unit and it can compensate voltage unbalance at the same time. The design approach of the control system is discussed in detail. Simulation and experimental results are presented. These results demonstrate that the proposed method is effective in the compensation of voltage unbalance and the power distribution.