• 전력전자학회논문지
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• 제26권2호
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• pp.75-81
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• 2021

This study analyzes the resonance characteristics caused by the mutual interference between LCL filters and the grid impedance under the parallel operation of the grid-connected inverter using the LCL filter. These characteristics are verified through simulation and experiment. Two inverters are used to connect to the grid in parallel, and the system parameters, including the LCL filter, are set to the same conditions. In the case of inverters running in parallel at the point of common coupling, the presence of grid impedance causes mutual interference between the LCL filters of each inverter, and the deviation of the filter resonance frequency is analyzed to understand the parallel inverter. The correlation between the number of devices and the size of grid impedance is simulated by PSIM and verified by MATLAB. By connecting the real-time digital simulator Typhoon HILS to the DSP 28377 control board, the mutual interference characteristics are tested under the condition of two inverters running in parallel. The experimental and analysis results are the same, indicating the validity of the analysis.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1990년도 하계학술대회 논문집
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• pp.372-375
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• 1990

A sinusoidal PWM type inverter using 1GBT and a new instantaneous current tracking control stategy is described. Its utilization as an interface for a grid-connected photovoltaic system with maxmum power tracking capability is explaned, and competer simulation along with waveforms are discussed. Finally, experimental results are analysed by state space avarge method to actual grid-connected systems.

• 한국전자통신학회논문지
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• 제19권4호
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• pp.661-668
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• 2024

전력전자 풀파워 컨버터 기반의 직접 구동 영구자석 동기 풍력발전 그리드 연계 시스템의 토폴로지를 기반으로 풍력터빈 모델과 그리드 측 인버터 모델을 연구하고, 기계측 정류기 제어 기반의 전류 및 속도 이중 폐쇄 루프 전략과 전류 및 전압 이중 폐쇄 루프를 기반으로 한 그리드 측 인버터 제어 전략을 설계하여 2레벨 연속 이중 폐쇄 루프 완전 제어 전략을 구현했다. MATLAB/Simulink를 이용하여 시스템 시뮬레이션 모델을 구축하였고, 풍속이 단계별로 변할 때의 장치의 동작을 시뮬레이션하였으며, 그리드 전압의 동일한 위상과 양호한 정현파 특성을 갖는 그리드 연결 전류를 출력하였다. 연결된 시스템이 안정적이고 효율적으로 실행되었다. 시뮬레이션 결과 모델의 타당성과 합리성, 제어 전략의 정확성과 타당성을 검증하였다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제16권4호
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• pp.451-462
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• 2016

Photovoltaic energy conversion becomes main focus of many researches due to its promising potential as source for future electricity and has many advantages than the other alternative energy sources like wind, solar, ocean, biomass, geothermal etc. In Photovoltaic power generation multilevel inverters play a vital role in power conversion. The three different topologies, diode-clamped (neutral-point clamped) inverter, capacitor-clamped (flying capacitor) inverter and cascaded h-bridge multilevel inverter are widely used in these multilevel inverters. Among the three topologies, cascaded h-bridge multilevel inverter is more suitable for photovoltaic applications since each pv array can act as a separate dc source for each h-bridge module. This paper presents a single phase Cascaded H-bridge five level inverter for grid-connected photovoltaic application using sinusoidal pulse width modulation technique. This inverter output voltage waveform reduces the harmonics in the generated current and the filtering effort at the input. The control strategy allows the independent control of each dc-link voltages and tracks the maximum power point of PV strings. This topology can inject to the grid sinusoidal input currents with unity power factor and achieves low harmonic distortion. A PID control algorithm is implemented in Arm Processor LPC2148. The validity of the proposed inverter is verified through simulation and is implemented in a single phase 100W prototype. The results of hardware are compared with simulation results. The proposed system offers improved performance over conventional three level inverter in terms of THD.

• 전기전자학회논문지
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• 제22권3호
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• pp.539-547
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• 2018

계통 연계형 인버터는 단독운전 조건에서 반드시 전력 공급을 차단해야 한다. 이러한 이유로 분산 발전 시스템은 단독운전을 검출 기능을 반드시 가지고 있어야 한다. 분산 발전용 인버터에 적용되는 일반적인 방법 중에는 Slip-Mode frequency Shift (SMS) 단독운전 검출 기법이 있다. SMS 기법은 계통 전압의 주파수에 따라 무효 전력을 공급하여 단독운전 조건에서 계통 주파수를 허용 범위 밖으로 이동시키는 방법이다. SMS 기법은 안정적으로 단독운전을 검출할 수 있으며, 계통 전류에 고주파를 인가하지 않는다는 장점이 있으나, 무효 전류를 인가하기 때문에 계통 역률이 나빠져서 전력 품질의 저하를 가져온다. 본 논문에서는 계통 전원이 연결되어 있는 정상 조건에서 전력 품질 저하가 없는 수정된 SMS 기법을 제안한다. 600W 단상 인버터 실험을 통해 제안된 방법의 유효성을 검증한다.

• 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.

• Transactions on Electrical and Electronic Materials
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• 제18권5호
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• pp.265-272
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• 2017

This paper presents the dynamic modeling, analysis, and control of an AC/DC/AC-assisted, self-excited induction generator connected to the grid. The dynamic model includes wind turbine models with pitch control, gear boxes, self-excited induction generators, excitation capacitance, inductive load models, controlled six-pulse rectifiers, and novel state-space models of a grid-connected inverter. The system has been simulated to verify its capabilities of buildup voltage, stator flux response, stator phase current, electromagnetic torque, and magnetizing inductance variation during both the dynamic and steady states with a variable-speed prime mover. The complete setup of the above dynamic models was simulated using MATLAB/SIMULINK.

• Journal of Power Electronics
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• 제7권2호
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• pp.174-180
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• 2007

In this paper, a simple control method for two-stage utility grid-connected photovoltaic power conditioning systems (PCS) is proposed. This approach enables maximum power point (MPP) tracking control with post-stage inverter current information instead of calculating solar array power, which significantly simplifies the controller and the sensor. Furthermore, there is no feedback loop in the pre-stage converter to control the solar array voltage or current because the MPP tracker drives the converter switch duty cycle. This simple PCS control strategy can reduce the cost and size, and can be utilized with a low cost digital processor. For verification of the proposed control strategy, a 2.5kW two-stage photovoltaic grid-connected PCS hardware which consists of a boost converter cascaded with a single-phase inverter was built and tested.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2008년도 하계학술대회 논문집
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• pp.247-249
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• 2008

There are many types of grid-connected inverter controllers; Synchronous Reference Frame (SRF)-based controller is the most popular methods. SRF-based controller is capable for reducing both of zero-steady state error and phase delay. However, SRF-based controller has a complex algorithm to apply in real application such as digital processor. Resonant controller is also reduced zero-steady state error, but its transfer function has a high order. In this paper, a simple proportional control is applied for grid connected inverter with LCL filter. LCL filter is a third order system. Applying a simple proportional controller is not increased the order of closed loop transfer function. By this technique, the single phase model is easily obtained. To reduce steady state error, proportional gain is set as high as possible, but it may produce instability. To compromise between a minimum steady state error and stability, the single phase model is evaluate through Root Locus and Bode diagram. PSIM simulation is used to verify the analysis.

• 전력전자학회논문지
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• 제17권1호
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• pp.57-66
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• 2012

This paper proposes a performance improvement of grid-connected inverter system using sliding-mode based direct power control with a variable gain. The proposed control method determine variable gain of PI controller by using modeling at direct power control (DPC) applied to space vector modulation method. Also, this method use sliding-mode control to maintain excellent dynamic response of character of direct power control (DPC). The validity of the proposed algorithm are verified by simulations and experiments.