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Journal ArticleDOI

Transformerless Inverter for Single-Phase Photovoltaic Systems

TL;DR: In this article, the authors proposed a new high-efficiency topology that generates no varying common-mode voltage and requires the same low-input voltage as the bipolar PWM full bridge.
Abstract: When no transformer is used in a grid-connected photovoltaic (PV) system, a galvanic connection between the grid and the PV array exists. In these conditions, dangerous leakage currents (common-mode currents) can appear through the stray capacitance between the PV array and the ground. In order to avoid these leakage currents, different inverter topologies that generate no varying common-mode voltages, such as the half-bridge and the bipolar pulsewidth modulation (PWM) full-bridge topologies, have been proposed. The need of a high-input voltage represents an important drawback of the half-bridge. The bipolar PWM full bridge requires a lower input voltage but exhibits a low efficiency. This letter proposes a new high-efficiency topology that generates no varying common-mode voltage and requires the same low-input voltage as the bipolar PWM full bridge. The proposed topology has been verified in a 5-kW prototype with satisfactory results
Citations
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Journal ArticleDOI
TL;DR: A general conceptual circuit for high-step-up, low-cost, and high-efficiency dc/dc conversion is proposed to derive the next-generation topologies for the PV grid-connected power system.
Abstract: The photovoltaic (PV) grid-connected power system in the residential applications is becoming a fast growing segment in the PV market due to the shortage of the fossil fuel energy and the great environmental pollution. A new research trend in the residential generation system is to employ the PV parallel-connected configuration rather than the series-connected configuration to satisfy the safety requirements and to make full use of the PV generated power. How to achieve high-step-up, low-cost, and high-efficiency dc/dc conversion is the major consideration due to the low PV output voltage with the parallel-connected structure. The limitations of the conventional boost converters in these applications are analyzed. Then, most of the topologies with high-step-up, low-cost, and high-efficiency performance are covered and classified into several categories. The advantages and disadvantages of these converters are discussed. Furthermore, a general conceptual circuit for high-step-up, low-cost, and high-efficiency dc/dc conversion is proposed to derive the next-generation topologies for the PV grid-connected power system. Finally, the major challenges of high-step-up, low-cost, and high-efficiency dc/dc converters are summarized. This paper would like to make a clear picture on the general law and framework for the next-generation nonisolated high-step-up dc/dc converters.

1,162 citations


Cites methods from "Transformerless Inverter for Single..."

  • ...Some circuit topologies or PWM control algorithms in the inverter side can be employed to minimize the leakage current effectively [12]–[14]....

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Journal ArticleDOI
TL;DR: This paper proposes a new topology, based on the H-bridge with a new ac bypass circuit consisting of a diode rectifier and a switch with clamping to the dc midpoint, which achieves high conversion efficiency and low leakage current.
Abstract: There is a strong trend in the photovoltaic inverter technology to use transformerless topologies in order to acquire higher efficiencies combining with very low ground leakage current. In this paper, a new topology, based on the H-bridge with a new ac bypass circuit consisting of a diode rectifier and a switch with clamping to the dc midpoint, is proposed. The topology is simulated and experimentally validated, and a comparison with other existing topologies is performed. High conversion efficiency and low leakage current are demonstrated.

743 citations


Cites background from "Transformerless Inverter for Single..."

  • ...This disconnection can be done either on the dc side of the inverter (like the topology from [4] and H5 topology from Solar Technologies AG [13]) or on the ac side (like the Highly Efficient and Reliable Inverter Concept (HERIC) topology from Sunways [12])....

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  • ...Transformerless PV inverters use different solutions to minimize the leakage ground current and improve the efficiency of the whole system, an issue that has previously been treated in many papers [4]–[11]....

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Journal ArticleDOI
TL;DR: A new high-efficiency topology for transformerless systems is proposed, which does not generate common-mode currents and topologically guarantees that no dc is injected into the grid and has been verified in a 5-kW prototype with satisfactory results.
Abstract: The elimination of the output transformer from grid- connected photovoltaic (PV) systems not only reduces the cost, size, and weight of the conversion stage but also increases the system overall efficiency. However, if the transformer is removed, the galvanic isolation between the PV generator and the grid is lost. This may cause safety hazards in the event of ground faults. In addition, the circulation of leakage currents (common-mode currents) through the stray capacitance between the PV array and the ground would be enabled. Furthermore, when no transformer is used, the inverter could inject direct current (dc) to the grid, causing the saturation of the transformers along the distribution network. While safety requirements in transformerless systems can be met by means of external elements, leakage currents and the injection of dc into the grid must be guaranteed topologically or by the inverter's control system. This paper proposes a new high-efficiency topology for transformerless systems, which does not generate common-mode currents and topologically guarantees that no dc is injected into the grid. The proposed topology has been verified in a 5-kW prototype with satisfactory results.

561 citations


Cites background from "Transformerless Inverter for Single..."

  • ...One of these topologies is the full bridge with bipolar pulsewidth modulation [5], [11], [12]....

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  • ...References [5], [13], and [14] are proposals for two modifications of the full-bridge topology, which reduce the current ripple and improve the efficiency...

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Journal ArticleDOI
TL;DR: The generation mechanism of leakage current is investigated and the concepts of dc-based and ac-based decoupling networks are proposed to not only cover the published symmetrical inductor-based topologies but also offer an innovative strategy to derive advanced inverters.
Abstract: Single-phase voltage source transformerless inverters have been developed for many years and have been successful commercial applications in the distributed photovoltaic (PV) grid-connected systems. Moreover, many advanced industrial topologies and recent innovations have been published in the last few years. The objective of this paper is to classify and review these recent contributions to establish the present state of the art and trends of the transformerless inverters. This can provide a comprehensive and insightful overview of this technology. First, the generation mechanism of leakage current is investigated to divide the transformerless inverters into asymmetrical inductor-based and symmetrical inductor-based groups. Then, the concepts of dc-based and ac-based decoupling networks are proposed to not only cover the published symmetrical inductor-based topologies but also offer an innovative strategy to derive advanced inverters. Furthermore, the transformation principle between the dc-based and ac-based topologies is explored to make a clear picture on the general law and framework for the recent advances and future trend in this area. Finally, a family of clamped highly efficient and reliable inverter concept transformerless inverters is derived and tested to offer some excellent candidates for next-generation high-efficiency and cost-effective PV grid-tie inverters.

553 citations


Cites background from "Transformerless Inverter for Single..."

  • ...Furthermore, two passive diodes can be also inserted into the H6 transformerless inverter to achieve the passive clamping performance [83],...

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Journal ArticleDOI
Bo Yang1, Wuhua Li1, Yunjie Gu1, Wenfeng Cui1, Xiangning He1 
TL;DR: In this article, an improved single-phase inverter topology is presented to eliminate the common-mode leakage current in the transformerless photovoltaic grid-connected system, and the high efficiency and convenient thermal design are achieved thanks to the decoupling of two additional switches connected to the dc side.
Abstract: To eliminate the common-mode leakage current in the transformerless photovoltaic grid-connected system, an improved single-phase inverter topology is presented. The improved transformerless inverter can sustain the same low input voltage as the full-bridge inverter and guarantee to completely meet the condition of eliminating common-mode leakage current. Both the unipolar sinusoidal pulsewidth modulation (SPWM) as well as the double-frequency SPWM control strategy can be applied to implement the three-level output in the presented inverter. The high efficiency and convenient thermal design are achieved thanks to the decoupling of two additional switches connected to the dc side. Moreover, the higher frequency and lower current ripples are obtained by adopting the double-frequency SPWM, and thus the total harmonic distortion of the grid-connected current are reduced greatly. Furthermore, the influence of the phase shift between the output voltage and current, and the influence of the junction capacitances of the power switches are analyzed in detail. Finally, a 1-kW prototype has been simulated and tested to verify the theoretical analysis of this paper.

507 citations

References
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Journal ArticleDOI

40,330 citations


"Transformerless Inverter for Single..." refers background in this paper

  • ...Furthermore, it strongly reduces the leakage currents between the PV system and the ground, ensures that no continuous current is injected into the grid, and can be used to increase the inverter output voltage level [1], [2], [4]....

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Book
26 Jul 1989
TL;DR: In this paper, the authors present a simulation of power switch-mode converters for zero-voltage and/or zero-current switchings in power electronic converters and systems.
Abstract: Partial table of contents: Overview of Power Semiconductor Switches Computer Simulation of Power Electronic Converters and Systems GENERIC POWER ELECTRONIC CIRCUITS dc--dc Switch-Mode Converters Resonant Converters: Zero-Voltage and/or Zero-Current Switchings POWER SUPPLY APPLICATIONS Power Conditioners and Uninterruptible Power Supplies MOTOR DRIVE APPLICATIONS dc Motor Drives Induction Motor Drives Synchronous Motor Drives OTHER APPLICATIONS Residential and Industrial Applications Optimizing the Utility Interface with Power Electronic Systems SEMICONDUCTOR DEVICES Basic Semiconductor Physics Power Diodes Power MOSFETs Thyristors Emerging Devices and Circuits PRACTICAL CONVERTER DESIGN CONSIDERATIONS Snubber Circuits Gate and Base Drive Circuits Design of Magnetic Components Index

5,911 citations


"Transformerless Inverter for Single..." refers background in this paper

  • ...Depending on the shape of the output voltage waveform, they can be classified in two groups, namely unipolar [ 5 ], [10], [11] and bipolar PWM [4], [5]....

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  • ...Depending on the shape of the output voltage waveform, they can be classified in two groups, namely unipolar [5], [10], [11] and bipolar PWM [4], [ 5 ]....

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  • ...In order to avoid a varying common-mode voltage, the full bridge has to be modulated with bipolar PWM, a modulation strategy that leads the converter to a low efficiency and a high current ripple [ 5 ]....

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  • ...It requires only four insulated gate bipolar transistors (IGBTs) and has a good trade-off between efficiency, complexity and price [ 5 ]....

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Journal ArticleDOI
TL;DR: In this article, the authors focus on inverter technologies for connecting photovoltaic (PV) modules to a single-phase grid and categorize the inverters into four classifications: 1) the number of power processing stages in cascade; 2) the type of power decoupling between the PV module(s) and the single phase grid; 3) whether they utilizes a transformer (either line or high frequency) or not; and 4) the kind of grid-connected power stage.
Abstract: This review focuses on inverter technologies for connecting photovoltaic (PV) modules to a single-phase grid. The inverters are categorized into four classifications: 1) the number of power processing stages in cascade; 2) the type of power decoupling between the PV module(s) and the single-phase grid; 3) whether they utilizes a transformer (either line or high frequency) or not; and 4) the type of grid-connected power stage. Various inverter topologies are presented, compared, and evaluated against demands, lifetime, component ratings, and cost. Finally, some of the topologies are pointed out as the best candidates for either single PV module or multiple PV module applications.

3,530 citations


"Transformerless Inverter for Single..." refers background in this paper

  • ...In PV inverters, it is important to achieve a high efficiency in a wide range of power and voltage of the PV array, since both variables exhibit great variations depending on the solar irradiation and ambient temperature [1], [4], [8]....

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  • ...These leakage currents can be avoided, or at least limited, by including damping passive components in the resonant circuit [1], [8]....

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  • ...Typical values of 2 mF for this capacitor limit the reduction in the MPPT efficiency to 1% in a 5-KW PV system [8]....

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  • ...A topology that generates no variable common-mode voltage is the half-bridge family of inverters, with two, three or more levels [1], [4], [8], [9]....

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Book
11 Oct 2007

708 citations

Proceedings ArticleDOI
07 Nov 2002
TL;DR: An overview on developments and a summary of the state-of-the-art of inverter technology in Europe for single-phase grid-connected photovoltaic (PV) systems for power levels up to 5 kW is provided.
Abstract: An overview on developments and a summary of the state-of-the-art of inverter technology in Europe for single-phase grid-connected photovoltaic (PV) systems for power levels up to 5 kW is provided in this paper. The information includes details not only on the topologies commercially available but also on the switching devices employed and the associated switching frequencies, efficiency, price trends and market share. Finally, the paper outlines issues associated with the development of relevant international industry standards affecting PV inverter technology.

564 citations