• 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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• 제15권5호
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• pp.1338-1347
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• 2015

DC injection is a critical issue in transformerless grid-connected inverters. DC injection control based on virtual capacitor has the advantages of low cost, low loss, high accuracy and easy implementation. In this paper, the principle of DC injection control based on virtual capacitor was analyzed. In addition, the applicable conditions, working process, steady state error and advantages were also discussed in detail. The design of the control parameters based on virtual capacitor was proposed in a grid-connected inverter with LCL filter. The robustness of the control parameters was also discussed. Simulation and experimental results verify the validity of the analysis and demonstrate that this research has a certain value in engineering applications.

• Journal of Power Electronics
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• 제16권6호
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• pp.2129-2138
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• 2016

The full-bridge inverter, widely used for single-phase photovoltaic grid-connected applications, presents a leakage current issue. Therefore, an AC bypass branch is introduced to overcome this challenge. Nevertheless, existing modulation strategies entail drawbacks that should be addressed. One is the zero-crossing distortion (ZCD) of the AC current caused by neglecting the AC filter inductor voltage. Another is that the system cannot deliver reactive power because the AC bypass branch switches at the power frequency. To address these problems, this work proposes an optimized hybrid modulation strategy. To reduce ZCD, the phase angle of the inverter output voltage reference is shifted, thereby compensating for the neglected leading angle. To generate the reactive power, the interval of the negative power output is calculated using the power factor. In addition, the freewheeling switch is kept on when power is flowing into the grid and commutates at a high frequency when power is fed back to the DC side. In this manner, the dead-time insertion in the high-frequency switching area is minimized. Finally, the performances of the proposed modulation strategy and traditional strategies are compared on a universal prototype inverter. Experimental results validate the theoretical analysis.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 춘계학술대회 논문집
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• pp.1334-1339
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• 2004

This paper proposes transformerless power conversion system consisting of a single-phase diode rectifier and a shunt hybrid filter for the electric-railway system. The hybrid filter consists of a single tuned LC filter per a phase and a low-rated NPC type multi-level inverter. Compared with conventional active filters. Transformers are not used. Also, LC filter works as not only a harmonic filter tuned at the 5th harmonic frequency but also a switching-ripple filter. The rating of the active filter can be decreased by using a NPC type multi-level inverter. The simulation results confirm the validity of the system.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 춘계학술대회 논문집
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• pp.1427-1432
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• 2004

This paper proposes transformerless power conversion system consisting of a single-phase diode rectifier and a shunt hybrid filter for the electric-railway system. The hybrid filter consists of a single tuned LC filter per a phase and a low-rated NPC type multi-level inverter. Compared with conventional active filters. Transformers are not used. Also, LC filter works as not only a harmonic filter tuned at the 5th harmonic frequency but also a switching-ripple filter. The rating of the active filter can be decreased by using a NPC type multi-level inverter. The simulation results confirm the validity of the system

• 한국철도학회논문집
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• 제7권4호
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• pp.339-344
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• 2004

This paper proposes transformerless power conversion system consisting of a single-phase diode rectifier and a shunt hybrid filter for the electric-railway system. The hybrid filter consists of a single tuned LC filter per a phase and a low-rated NPC type multi-level inverter. Compared with conventional active filters. transformers are not used. Also, LC filter works as not only a harmonic filter tuned at the 3rd harmonic frequency but also a switching-ripple filter. The rating of the active filter can be decreased by using a NPC type multi-level inverter. The simulation results confirm the validity of the system.