• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.4
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• pp.297-304
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• 2013

This paper presents a improved control technique to overcome disadvantage when the inductor current of boost converter in PV system becomes DCM(Discontinuous Conduction Mode) due to the low insolation. MPPT(Maximum Power Point Tracking) output reference voltage could not be exactly followed by conventional dual-loop PI control method used typically because of the error between the actual current and measured current. Therefore, in this paper, Hybrid controller that changes the control method in DCM and CCM(Continuous Conduction Mode), and single state feedback controller are used to compensate that problem. The proposed control technique was verified by simulation using PSIM 9.0 and experiments.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.5
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• pp.358-368
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• 2020

Grid-connected inverters (GCIs) based on renewable energy sources play an important role in enhancing the sustainability of a society. Harmonic standards, such as IEEE 519 and P1547, which require the total harmonic distortion (THD) of the output current to be less than 5%, should be satisfied when GCIs are connected to a grid. However, achieving a current THD of less than 5% is difficult for GCIs with an output filter under a distorted grid condition. In this study, a novel harmonic compensation method that uses a digital lock-in amplifier (DLA) is proposed to eliminate harmonics effectively at the output of GCIs. Accurate information regarding harmonics can be obtained due to the outstanding performance of DLA, and such information is used to eliminate harmonics with a simple proportional-integral controller in a feedforward manner. The validity of the proposed method is verified through experiments with a 5 kW single-phase GCI connected to a real grid.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.520-523
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• 2016

This paper describes a DC-DC converter with MPPT control for thermoelectric energy harvesting. The designed circuit converts low voltage harvested from a thermoelectric generator into higher voltage for powering a load. A start-up circuit supplies VDD to a controller, and the controller turns on and off a NMOS switch of a main-boost converter. The converter supplies the boosted voltage to the load through the switch operation. Bulk-driven comparators can do the comparison under low voltage condition and are used for voltage regulation. Also, bulk-driven comparators raise system's efficiency. A peak conversion efficiency of 76% is achieved. The proposed circuit is designed in a 0.35um CMOS technology and its functionality has been verified through simulations. The designed chip occupies $933um{\times}769um$.

• IEIE Transactions on Smart Processing and Computing
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• v.4 no.3
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• pp.189-193
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• 2015

This paper provides the design techniques of a successive approximation register (SAR) type 12b analog-to-digital converter (ADC) for distributed maximum power point tracking (DMPPT) control in a photovoltaic system. Both a top-plate sampling technique and a $V_{CM}$-based switching technique are applied to the 12b capacitor digital-to-analog converter (CDAC). With these techniques, we can implement a 12b SAR ADC with a 10b capacitor array digital-to-analog converter (DAC). To enhance the accuracy of the ADC, a single-to-differential converted DAC is exploited with the dual sampling technique during top-plate sampling. Simulation results show that the proposed ADC can achieve a signal-to-noise plus distortion ratio (SNDR) of 70.8dB, a spurious free dynamic range (SFDR) of 83.3dB and an effective number of bits (ENOB) of 11.5b with bipolar CMOS LDMOD (BCDMOS) $0.35{\mu}m$ technology. Total power consumption is 115uW under a supply voltage of 3.3V at a sampling frequency of 1.25MHz. And the figure of merit (FoM) is 32.68fJ/conversion-step.

• Journal of the Korean Solar Energy Society
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• v.32 no.spc3
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• pp.245-254
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• 2012

In photovoltaic system, the characteristics of photovoltaic module such as open circuit voltage and short circuit current will be changed because of cell temperature and solar radiation. Therefore, the boost converter of a PV system connects between the output of photovoltaic system and DC link capacitor of grid connected inverter as controlling duty ratio for maximum power point tracking(MPPT). This paper shows the dynamic characteristics of the boost converter by comparing single-loop and two-loop control algorithm using both analog and digital control. Both proposed compensation methods have been verified with computer simulation to demonstrate the validity of the proposed control schemes.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.4
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• pp.335-342
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• 2016

This paper proposes an energy storage-assisted, series-connected module-integrated power conversion system that integrates a photovoltaic power conditioner and a charge balancing circuit. In conventional methods, a photovoltaic power conditioner and a cell-balancing circuit are needed for photovoltaic systems with energy storage devices, but they cause a complex configuration and high cost. Moreover, an imbalanced output voltage of the module-integrated converter for PV panels can be a result of partial shading. Partial shading can lead to the fault condition of the boost converter in shaded modules and high voltage stresses on the devices in other modules. To overcome these problems, a bidirectional buck-boost converter with an integrated magnetic device operating for a charge-balancing circuit is proposed. The proposed circuit has multiple secondary rectifiers with inductors sharing a single magnetic core, which works as an inductor for the main bidirectional charger/discharger of the energy storage. The secondary rectifiers operate as a cell-balancing circuit for both energy storage and the series-connected multiple outputs of the module-integrated converter. The operating principle of the cell-balancing power conversion circuit and the power stage design are presented and validated by PSIM simulation for analysis. A hardware prototype with equivalent photovoltaic modules is implemented for verification. The results verify that the modularized photovoltaic power conversion system in the output series with an energy storage successfully works with the proposed low-cost bidirectional buck-boost converter comprising a single magnetic device.

• Journal of Power Electronics
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• v.17 no.4
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• pp.1037-1047
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• 2017

The Differential Power Processing (DPP) converter is a promising multi-module photovoltaic inverter architecture recently proposed for photovoltaic systems. In this paper, a DPP converter architecture, in which each PV-panel has its own DPP converter in shunt, performs distributed maximum power point tracking (DMPPT) control. It maintains a high energy conversion efficiency, even under partial shading conditions. The system architecture only deals with the power differences among the PV panels, which reduces the power capacity of the converters. Therefore, the DPP systems can easily overcome the conventional disadvantages of PCS such as centralized, string, and module integrated converter (MIC) topologies. Among the various types of the DPP systems, the feed-forward method has been selected for both its voltage balancing and power transfer to a modified H-bridge inverter that needs charge balancing of the input capacitors. The modified H-bridge multi-level inverter had some advantages such as a low part count and cost competitiveness when compared to conventional multi-level inverters. Therefore, it is frequently used in photovoltaic (PV) power conditioning system (PCS). However, its simplified switching network draws input current asymmetrically. Therefore, input capacitors in series suffer from a problem due to a charge imbalance. This paper validates the operating principle and feasibility of the proposed topology through the simulation and experimental results. They show that the input-capacitor voltages maintain the voltage balance with the PV MPPT control operating with a 140-W hardware prototype.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.153-159
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• 2012

In photovoltaic system, the characteristic of photovoltaic module such as open circuit voltage and short circuit current will be changed because of cell temperature and solar radiation. Therefore, a boost converter of the PV system connects between the output of photovoltaic system and DC link capacitor of grid connected inverter as controlling duty ratio for maximum power point tracking(MPPT). This paper shows the dynamic characteristic of the boost converter by comparing single-loop control algorithm and two-loop control algorithm using both analog and digital control. The proposed both compensation method has been verified with computer simulation and simulation results obtained demonstrate the validity of the proposed control schemes.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.228-229
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• 2007

현재까지 계통연계형 태양광 시스템의 최대전력추종(MPPT)방법에 대한 많은 연구가 진행되고 있다. 그 중 대표적인 최대 전력 추종 방법에는 일정전압 제어방식, P&O(Perturbation and Observation)제어방식, IncCond(Incremental Condutance) 제어 방식이 있다. 이 중 일정전압 제어방식은 일사량, 온도 등을 고려해 특정한 값의 태양전지 출력전압을 고정시키도록 하여, 최대전력점 근처에서 동작하도록 제어하는 방식이다. 이 방식은 태양전지 입력 전류 센서가 필요없고, 저일사량 조건에서 다른 기법에 비해 우수한 효율 특성을 나타내고 있다. 하지만, 온도 및 일사 조건에 따라 변하는 최대전력전압지점을 추종하지 못해 다양한 조건에서 최대전력추종효율이 떨어지는 단점이 있다. 이에 본 논문에서는 다양한 일사 조건 및 온도 조건에 대응하는 최대 출력전압을 실시간으로 산출하여, 이를 통해 최대전력추종제어를 하는 방법을 제안하고자 한다. 제안된 기법은 다양한 일사조건 및 온도변화에 대해 능동적으로 대응하여 우수한 추종효율 특성을 나타내고, 또한 입력 DC 전류 센서를 제거하고, 내부 연산이 간단함으로써 경제적인 면에서 유리하다. 본 논문에서 제안된 최대전력 추종기법의 타당성을 검증하기 위해서 PSIM 시뮬레이션을 통해 그 타당성을 검증 하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.8
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• pp.686-696
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• 2017

The major objective of this study is to develop and verify the KAUSAT-5 based on the modular 3U CubeSat standard platform. In the mechanical system design of a 3U standard platform, subsystem and micro equipment functions/performance should be integrated and miniaturized on micro-sized PCBs and electrical capability was maximized to accommodate multiple payloads. KAUSAT-5 is 3U-sized Cubesat which will be operated in Low Earth Orbit(LEO), which implements mainly two scientific missions; one is to observe the Earth through infrared camera and the other is to measure space radiation with a Geiger Muller tube. An additional mission is to verify the equipment(device) such as VSCMG and fuzzy logic-based MPPT internally developed. The results of ETB, qualification and acceptance level environmental tests were shown to verify standard platform and KAUSAT-5 Cubesat.