• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2001년도 춘계종합학술대회
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• pp.437-442
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• 2001

계통연계형 태양광 발전 시스템은 태양 에너지를 전기 에너지로 변환하는 태양 전지부와 발생 전력을 계통에 연계하는 진력변환장치로 크게 나눌 수 있다. 또한 전력변환부는 승압용 컨버터부와 DC전력을 AC로 변환하는 인버터부로 구성된다. 종래 인버터의 주회로 방식은 저주파 트랜스나 고주파 트랜스를 사용하는 방식이 채러되었으나, 최근 이러한 방식에 비해 소형 경량화가 기대되는 트랜스리스 방식이 많이 연구되고 있다. 본 논문의 승압부는 2상 부스트 컨버터를 이용하여 입력 전류와 출력 전압의 리플을 줄여, 각 전력 소자의 전압 스트레스를 줄이고, 입력 리액터를 소형화한다. 그리고, 인버터 부의 출력 고조파 성분을 저감하기 위해 정현파 PWM에서 얻어진 스위칭 시간을 기본값으로 하여 푸리에 급수로 유도한 PWM 스위칭 시간을 채택하였고, PSpice를 이용하여 변환기의 동작을 시뮬레이션하여 그 유효성을 검증하였다.

• 전력전자학회논문지
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• 제23권2호
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• pp.129-138
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• 2018

Previous single-phase transformerless inverters used active bypass switching circuits that need auxiliary power switches to minimize ground leakage current. However, switching and gate driving losses are increased due to the use of additional power switches. To cope with this drawback, this work proposes a transformerless inverter using a passive bypass filter without any auxiliary power switch. The operation and control of the proposed inverter are described. The ground leakage current characteristics are analyzed for the proposed inverter with the passive bypass filter. The experimental results of the proposed inverter for a 1.0kW prototype system are presented.

• Journal of Power Electronics
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• 제13권1호
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• pp.70-76
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• 2013

For high power high step-down dc-dc conversion applications, conventional three-level dc-dc converters are subject to extreme duty cycles or increased volume and cost due to the use of transformers. In this paper, a transformerless three-level dc-dc buck converter with a high step-down conversion ratio is proposed. The converter comprises two asymmetrical half bridges, which are of the neutral point clamped structures. Therefore, the output pulse voltage of the converter can be obtained in terms of the voltage difference between the two half bridges. In order to realize harmonious switching of the converter, a modulation strategy with capacitor voltages self balance is presented. According to the deduced output dc voltage function, transformerless operation without extreme duty cycles can be implemented. Experimental results from a 1kW prototype verify the validity of the proposed converter. It is suitable for ship electric power distribution systems.

• 한국태양에너지학회 논문집
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• 제33권6호
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• pp.92-97
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• 2013

This paper proposes DC offset current compensation method of transformerless fuel cell/PV PCS. DC offset current is generated by the unbalanced internal resistance of the switching devices in full bridge topology. The other cause is the sensitivity of the current sensor, which is lower than DSP in resolution. If power converter system has these causes, the AC output current in the inverter will generate the DC offset. In case of transformerless grid-connected inverter system, DC offset current is fatal to grid-side, which results in saturating grid side transformer. Several simulation results show the difficulties of detecting DC offset current. Detecting DC offset current method consists of the differential amplifiers and PWM is compensated by the output of the Op amp circuit with integrator controller. PSIM simulation verifies that the proposed method is simpler and more effective than using low resolution current sensor alone.

• Journal of Power Electronics
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• 제15권1호
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• pp.256-267
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• 2015

Grid-connected transformerless photovoltaic (PV) inverters (TPVIs) are increasingly dominating the market due to their higher efficiency, lower cost, lighter weight, and reduced size when compared to their transformer based counterparts. However, due to the lack of galvanic isolation in the low voltage grid interconnections of these inverters, the PV systems become vulnerable to leakage currents flowing through the grounded star point of the distribution transformer, the earth, and the distributed parasitic capacitance of the PV modules. These leakage currents are prohibitive, since they constitute an issue for safety, reliability, protection coordination, electromagnetic compatibility, and module lifetime. This paper investigates a wide range of multi-kW range power rating TPVI topologies and classifies them in terms of their leakage current attributes. This systematic classification places most topologies under a small number of classes with basic leakage current attributes. Thus, understanding and evaluating these topologies becomes an easy task. In addition, based on these observations, new topologies with reduced leakage current characteristics are proposed in this paper. Furthermore, the important efficiency and cost determining characteristics of converters are studied to allow design engineers to include cost and efficiency as deciding factors in selecting a converter topology for PV applications.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 전력전자학술대회 논문집
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• pp.105-106
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• 2016

In low-power grid-connected photovoltaic(PV) system, Single-phase transformerless full-bridge inverter is commonly used. However in transformerless photovoltaic application, the ground parasitic capacitance created by grounding between PV panels and ground. This ground parasitic capacitance inject additional current into the inverter, these currents cause electromagnetic interference problem, safety problem and harmonics problem in PV applications. In order to eliminate the ground current, This paper propose various inverter topologies in PV applications. These proposed inverter topologies are verified through simulation using PSIM.

• Journal of Power Electronics
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• 제18권4호
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• pp.997-1006
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• 2018

This paper proposes a transformerless photovoltaic (PV) power converter system based on the DC/AC boost inverter, which can solve the leakage current and second-order ripple power issues in single-phase grid-connected PV inverters. In the proposed topology, the leakage current can be decreased remarkably since most of the common-mode currents flow through the output capacitor, by-passing parasitic capacitors, and grounding resistors. In addition, the inherent ripple power component in the single-phase grid inverter can be suppressed without adding any extra components. Therefore, bulky electrolytic capacitors can be replaced by small film capacitors. The effectiveness of the proposed topology has been verified by simulation and experimental results for a 1-kW PV PCS.

• Journal of Power Electronics
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• 제15권4호
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• pp.920-928
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• 2015

Transformerless solar inverters have a higher efficiency than those with an isolation link. However, they suffer from a leakage current issue. This paper proposes a family of single phase six-switch transformerless inverter topologies with an ac bypass circuit to solve the leakage current problem. These circuits embed two unidirectional freewheeling current units into the midpoint of a full bridge inverter, to obtain a freewheeling current path, which separates the solar panel from the grid in the freewheeling state. The freewheeling current path contains significantly fewer devices and poor performance body diodes are not involved, leading to a higher efficiency. Meanwhile, it is not necessary to add a voltage balancing control method when compared with the half bridge inverter. Simulation and experiments are provided to validate the proposed topologies.

• Journal of Power Electronics
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• 제15권5호
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• pp.1329-1337
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• 2015

By placing distributed generation power sources beside a big nonlinear load, these sources can be used as a power quality enhancer, while injecting some active power to the network. In this paper, a new scheme to use the distributed generation power source in both operation modes is presented. In this scheme, a fuzzy controller is added to adjust the optimal set point of inverter between compensating mode and maximum active power injection mode, which works based on the harmonic content of the nonlinear load. As the high order current harmonics can be easily rejected using passive filters, the DG is used to compensate the low order harmonics of the load current. Multilevel transformerless cascade inverters are preferred in such utilization, as they have more flexibility in current/voltage waveform. The proposed scheme is simulated in MATLAB/SIMULINK to evaluate the circuit performance. Then, a 1kw single phase prototype of the circuit is used for experimental evaluation of the paper. Both simulative and experimental results prove that such a circuit can inject a well-controlled current with desired harmonics and THD, while having a smaller switching frequency and better efficiency, related to previous 3-phase inverter schemes in the literature.

• 전력전자학회논문지
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• 제12권5호
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• pp.355-363
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• 2007

본 논문에서는 무변압기형 3상 계통연계 PV PCS (photovoltaic power conditioning system)를 제안하였다. 태양전지의 국소 최대 전력점에서 발전하는 것을 방지하여 최대 전력점에서 발전을 하도록 개선한 P&O (perturb and observe) 방식의 MPPT (maximum power point tracking) 알고리즘을 제안하였다. 3상 전압형 인버터를 외부 직류 링크 전압제어기, 내부 전류제어기, 그리고 마이크로컨트롤러로 구현하기에 적합하도록 간단화한 공간벡터 변조법을 통해 제어하여 3상 계통연계 시 단위 역률을 실현하였다. 그리고 시스템의 안정성 향상과 역률 개선을 위해 직류 링크 전압을 더 빠르고 정확하게 제어하기 위한 알고리즘을 제안하였다. 모든 알고리즘과 제어기를 하나의 마이크로컨트롤러로 구현하고 제안된 알고리즘과 제어기의 우수성을 실험을 통해 검증하였다.