• Journal of Power Electronics
• /
• 제16권6호
• /
• pp.2338-2349
• /
• 2016

This paper presents an impedance-matching-based control scheme for the harmonic resonance damping of multiple grid-connected-converters (GCCs) with LCL filters. As indicated in this paper, harmonic resonance occurs if a GCC possesses an output impedance that is not matched with the rest of the network in some specific frequency bands. It is also revealed that the resonance frequency is associated with the number of GCCs, the grid impedance and even the capacitive loads. By controlling the grid-side current instead of the converter-side current, the critical LCL filter is restricted as an internal component. Thus, the closed-loop output impedance of the GCC within the filter can be configured. The proposed scheme actively regulates the output impedance of the GCC to match the impedance of the external network, based on the detected resonance frequency. As a result, the resonance risk of multiple GCCs can be avoided, which is beneficial for the plug-and-play property of the GCCs in microgrids. Simulation and experimental results validate the effectiveness of the proposed method.

• Journal of Power Electronics
• /
• 제16권4호
• /
• pp.1565-1577
• /
• 2016

For grid-connected LCL-filtered inverters, dual-loop current control with an inner-loop active damping (AD) based on capacitor current feedback is generally used for the sake of current quality. However, existing studies on capacitor current feedback AD with a control delay do not reveal the mathematical relation among the dual-loop stability, capacitor current feedback factor, delay time and LCL parameters. The robustness was not investigated through mathematical derivations. Thus, this paper aims to provide a systematic study of dual-loop current control in a digitally-controlled inverter. At first, the stable region of the inner-loop AD is derived. Then, the dual-loop stability and robustness are analyzed by mathematical derivations when the inner-loop AD is stable and unstable. Robust design principles for the inner-loop AD feedback factor and the outer-loop current controller are derived. Most importantly, ensuring the stability of the inner-loop AD is critical for achieving high robustness against a large grid impedance. Then, several improved approaches are proposed and synthesized. The limitations and benefits of all of the approaches are identified to help engineers apply capacitor current feedback AD in practice.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2020년도 전력전자학술대회
• /
• pp.381-382
• /
• 2020

In the battery energy storage system, battery cells are connected in series to increase the operating voltage. Due to the difference in characteristics, the performance degradation of cells is dissimilar. This paper proposes an online DC internal impedance estimation for battery cells in the series string using a matrix-switched capacitor converter, which is already verified as useful for the series balancing of the cells. The simulation in the hardware in the loop test rig shows good accuracy and the feasibility of the proposed method.

• 한국정보통신학회:학술대회논문집
• /
• 한국정보통신학회 2016년도 춘계학술대회
• /
• pp.73-74
• /
• 2016

본 논문에서는 DTV용 광대역 사각형 루프 안테나에 대한 설계 방법에 대하여 연구하였다. 제안된 루프 안테나는 사각형 루프 안테나와 중앙 급전점과 연결하는 원형 섹터가 결합된 형태이다. DTV응용을 위해 75옴 입력 임피던스와 정합하도록 입력 반사계수와 이득 특성을 분석하였다. 최적화된 안테나를 FR4 기판에 설계하였고, 전압 정재파비(VSWR; voltage standing wave) < 2인 대역이 464-1,310 MHz으로 DTV 대역(470-806 MHz)에서 동작하는 것을 확인하였다.

• Journal of Power Electronics
• /
• 제13권5호
• /
• pp.896-908
• /
• 2013

Under high grid impedance conditions, it is difficult to guarantee the stability of grid-connected inverters with an LCL filter designed based on ideal grid conditions. In this paper, the theoretical basis for output impedance calculation is introduced. Based on the small-signal model, the d-d channel closed-loop output impedance models adopting the converter-side current control method and the grid-side current control method are derived, respectively. Specifically, this paper shows how to simplify the stability analysis which is usually complemented based on the generalized Nyquist stability criterion (GNC). The stability of each current-controlled grid-connected system is analyzed via the proposed simplified method. Moreover, the influence of the LCL parameters on the stability margin of grid-connected inverter controlled with converter-side current is studied. It is shown that the stability of grid-connected systems is fully determined by the d-d channel output admittance of the grid-connected inverter and the inductive component of the grid impedance. Experimental results validate the proposed theoretical stability analysis.

• 한국전자파학회논문지
• /
• 제23권5호
• /
• pp.551-558
• /
• 2012

본 논문에서는 집중 소자로 임피던스 대역폭과 공진 주파수 컨트롤이 가능한 이중 대역 루프형 그라운드 안테나를 제안한다. 제안된 안테나의 이중 대역 특성은 기존의 루프형 그라운드 안테나의 형태에 추가적인 공진루프 급전 구조를 삽입하여 구현하였다. 적절한 캐패시터와 인덕터를 사용하여 2.45 GHz와 5.5 GHz 대역에서 VSWR<3에서 각각 85 MHz와 725 MHz의 임피던스 대역폭을 만족시켰으며, 시뮬레이션과 측정 결과를 통하여 그 타당성을 입증하였다. 제안된 안테나의 면적은 $10{\times}5mm^2$로 작은 크기를 갖고 있을 뿐만 아니라, 구현하고자 한 이중 대역에서 좋은 방사 패턴과 안테나 효율을 나타내었다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2002년도 하계학술대회 논문집 B
• /
• pp.1134-1136
• /
• 2002

This paper proposes a FSK(Frequency Shift Keying) transmitter which has a inverter for power amplification instead of linear amplifier. As it can generate large signal using resonant circuit under the low voltage source even if the impedance of antenna is large as like a loop antenna of TWC(Train to Way-side Communication) system. In this paper, the proposed fully digital controlled transmitter including FSK modulation is presented and its control schemes are discussed.

• 전기학회논문지
• /
• 제66권1호
• /
• pp.144-152
• /
• 2017

A motor model and off-line diagnosis method of the induction motor having an interturn fault(ITF) is studied. The proposed method is based on the magnitude comparison of the six impedance in the d-q plane. To prove the impedance unbalance, the induction motor model is presented with an ITF circuit loop with a fault resistance. Then, six impedance components in the stationary d-q plane are defined depending on the connected phase windings. Finding the maximum and minimum magnitude of the six impedance, the ITF and the faulty phase can be founded. To verify the proposed method, the experimental results with an induction motor having an ITF are shown.

• Journal of Power Electronics
• /
• 제17권3호
• /
• pp.756-765
• /
• 2017

The control of the power conversion system (PCS) in a battery energy storage system has a challenge due to the existence of grid impedance. This paper studies an impedance model of an LCL-based PCS in the d-q domain. The feature of a PCS connected to a weak grid is unveiled by use of an impedance model and a generalized Nyquist criterion. It is shown that the interaction between grid impedance and the PCS destabilizes the cascaded system in certain cases. Therefore, this paper proposes a novel control method that adopts virtual resistors to overcome this issue. The improvement in the control loop leads the PCS to a more stable condition than the conventional method. Impedance measurement is implemented to verify the correctness of the theoretical analysis. Experimental results obtained from a down-scaled prototype indicate that the proposed control method can improve the performance of the PCS under a weak grid.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2004년도 ICCAS
• /
• pp.470-473
• /
• 2004

This paper presents conducted emission noise measurement from electronic equipment in frequency range of 1 MHz up to 30 MHz by small loop antenna. Small loop antenna measurement method can measure common-mode (CM) and differential-mode (DM) component of the noise on a pair of power line at the same time. The CM and DM can be measured separately. The theory of this measurement method is introduced and analyzed. The measured results were compared with the conventional measurement by Line Impedance Stabilization Network (LISN) and result a good trend between those methods.