• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.6
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• pp.695-701
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• 2018

For a power grid that has a high wind penetration level, when wind speeds are continuously fluctuating, the maximum power point tracking (MPPT) operation of a variable-speed wind turbine (VSWT) causes the significant output power fluctuation of a VSWT, thereby significantly fluctuating the system frequency. In this paper, an improved power-smoothing scheme of a VSWT is presented that significantly mitigates the frequency fluctuation caused by varying wind speeds. The proposed scheme employs an additional control loop based on the frequency deviation that operates in combination with the MPPT control loop. To improve the power-smoothing capability of a VSWT in the over-frequency section (OFS), the control gain of the additional loop, which is set to be inversely proportional to the rotor speed, is proposed. In contrast, the control gain in the under-frequency section is set to be proportional to the rotor speed to improve the power-smoothing capability while avoiding over-deceleration of the rotor speed of a VSWT. The proposed scheme significantly improves the performance of the power-smoothing capability in the OFS, thereby smoothing the frequency fluctuation. The results clearly demonstrate that the proposed scheme significantly mitigates the frequency fluctuation by employing the different control gain for the OFS under various wind penetration scenarios.

• The Transactions of the Korean Institute of Power Electronics
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• v.12 no.4
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• pp.300-309
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• 2007

In this paper, a grid-interactive photovoltaic (PV) system with the function of the power quality improvement is presented. The proposed system requires only one current-controlled voltage source inverter, which control the current flow at low total harmonic distortion and unity power factor, as well as simultaneously provide reactive power support. The proposed system operation has been divided into two modes (sunny and night). In night mode, the system operates to compensate the reactive power demanded by nonlinear or variation in loads. In sunny mode, the system performs power quality control (PQC) to reduce harmonic current and to improve power factor as well as maximum power point tracking (MPPT) to supply active power from the PV arrays, simultaneously. To verify the proposed system a comprehensive evaluation included simulation and experimental results are presented.

• Journal of Power Electronics
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• v.17 no.6
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• pp.1587-1599
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• 2017

This paper proposes a real-time implementation of an optimal operation of a double stage grid connected wind power system incorporating an active power filter (APF). The system is used to supply the nonlinear loads with harmonics and reactive power compensation. On the generator side, a new adaptive neuro fuzzy inference system (ANFIS) based maximum power point tracking (MPPT) control is proposed to track the maximum wind power point regardless of wind speed fluctuations. Whereas on the grid side, a modified predictive current control (PCC) algorithm is used to control the APF, and allow to ensure both compensating harmonic currents and injecting the generated power into the grid. Also a type 2 fuzzy logic controller is used to control the DC-link capacitor in order to improve the dynamic response of the APF, and to ensure a well-smoothed DC-Link capacitor voltage. The gained benefits from these proposed control algorithms are the main contribution in this work. The proposed control scheme is implemented on a small-scale wind energy conversion system (WECS) controlled by a dSPACE 1104 card. Experimental results show that the proposed T2FLC maintains the DC-Link capacitor voltage within the limit for injecting the power into the grid. In addition, the PCC of the APF guarantees a flexible settlement of real power exchanges from the WECS to the grid with a high power factor operation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.267-270
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• 2014

This paper presents a CMOS interface circuit for vibration energy harvesting. The proposed circuit consists of an AC-DC converter and a DC-DC boost converter. The AC-DC converter rectifies the AC signals from vibration devices(PZT), and the DC-DC boost converter generates a boosted and regulated output at a predefined level. A full-wave rectifier using active diodes is used as the AC-DC converter for high efficiency, and a schottky diode type DC-DC boost converter is used for a simple control circuitry. A MPPT(Maximum Power Point Tracking) control is also employed to harvest the maximum power from the PZT. The proposed circuit has been designed in a 0.35um CMOS process. The chip area is $530um{\times}325um$. Simulation results shows that the maximum efficiencies of the AC-DC converter and DC-DC boost converter are 97.7% and 89.2%, respectively. The maximum efficiency of the entire system is 87.2%.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.1313-1315
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• 2002

This paper proposes an inverter for the grid-connected photovoltaic system based on the transformer-less inverter. This system consists of a high frequency inverter bridge, high frequency transformer, diode bridge rectifiers, a DC filter, a low frequency inverter bridge, and an AD filter. The high frequency inverter bridge switching at 20kHz is used to generate bipolar PWM pulse, which is subsequently rectified by diode bridge rectifiers to result in a full-wave rectified sine wave. Finally, it is unfolded by a low frequency inverter bridge to result in a 60Hz sine wave power output. In this paper, the control algorithm for synchronous current feedback control method and a maximum power point tracking (MPPT) method using DSP are described. And, the simulation and experimental results are shown to verify the validity of the proposed system.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.1364-1366
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• 2002

The Photovoltaic(PV) generation system is a promising source of energy for the future. Since the need for renewable energy has been increased, the research of PV generation system has also been progressed. Recently, cost down of PV generation system has been accomplished and practical technologies of the solar energy developed, Moreover, grid connected PV generation system are becoming actual and general. Operational technology of the grid connected PV generation system is being a hot issue. Power output of PV system is directly affected by wether conditions. When AC power supply is needed, power conversion by an inverter and a MPPT control are necessary. In this paper, for stability improvement of PV generation system. Active filter(AF) function is added to PV generation system, and simulations of PV-AF system under various weather conditions are performed.

• Journal of Power Electronics
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• v.13 no.2
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• pp.313-321
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• 2013

This paper describes the operation analysis results of a communication-based DC micro-grid using a hardware simulator developed in the lab. The developed hardware simulator is composed of distributed generation devices such as wind power, photovoltaic power and fuel cells, and energy storage devices such as super-capacitors and batteries. Whole system monitoring and control was implemented using a personal computer. The power management scheme was implemented in a main controller based on a TMS320F28335 chip. The main controller is connected with the local controller in each of the distributed generator and energy storage devices through the communication link based on a CAN or an IEC61850. The operation analysis results using the developed hardware simulator confirm the ability of the DC micro-grid to supply the electric power to end users.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.182.1-182.1
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• 2010

본 논문에서는 3kW 영구 자석형 동기발전기(PMSG)를 이용한 풍력 터빈 시뮬레이터 개발에 대해 기술하였다. 풍력발전 시스템은 블레이드를 포함한 회전부, 동력 전달부, 발전기, 전력변환기로 크게 나눌 수 있으며, 시뮬레이터는 유도 모터와 PMSG, 인버터-컨버터와 제어 시스템으로 이루어진다. 시뮬레이터를 운전하기 위해서는 특정 속도의 바람 모델을 적용하여 풍력 발전기의 회전부에 걸리게 되는 토크와 회전 속도 값이 요구된다. 풍력 터빈 모델로부터 계산값을 시뮬레이터에 맞게 스케일링하여 유도 모터를 구동 한다. 발전기측 컨버터는 MPPT(Maximum Power Point Tracking) 알고리즘을 통해 제어하고 계통측 인버터는 유효 전력과 무효 전력을 제어하도록 한다. PSIM과 MATLAB/SIMULINK를 이용하여 컴퓨터 시뮬레이션으로 그 결과를 증명하였다.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.143-148
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• 2004

This paper presents the two modes for maximum power point tracking of the photovoltaic system. The method combines the merits of the two methods consisting of the open circuit method and the three point weight comparison method. The maximum point found by this method is exactly than by the open circuit method. By the simulation results, the actual maximum point can be found that is better than the Perturb and Observe (P&O) method or the three point weight method only one method, especially, in the case of non regular pattern of Power-Voltage (P-V) curve.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.293-294
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• 2016

태양광 발전 시스템은 그 필요성이 늘어남에 따라 다양한 연구가 진행되고 있다. 기존에 태양광 발전 제어 방식인 스트링 방식이나, 마이크로 컨버터 같은 방식 이외에도 그늘짐 등으로 인해 발생한 태양광 모듈의 전력 차이만을 부담하는 컨버터를 이용한 차동 전력 조절 방식도 연구가 되고 있다. 차동 전력조절기는 담당하는 전력이 적고, 스트링 컨버터를 통해 많은 전력이 전달이 되어 기존의 방식 보다 효율이 높다. 하지만, 태양광 모듈 MPPT 전압으로 부터 DC_link 전압만큼의 승압이 필요하다. 따라서, 고승압, 고효율 컨버터를 차동 전력 조절기로 사용을 하면 기존의 차동 전력 방식보다 더 나은 동작 특성을 가질 수 있다. 따라서 본 논문에서는 차동 전력 조절기로 고승압의 컨버터 토폴로지를 사용하여, 기존의 방식보다 고효율을 유지하면서 차동 전력 조절기의 기능을 수행하는 구조를 제안한다.