Transformerless Photovoltaic Inverter Research Articles

A Transformerless Photovoltaic Inverter With Dedicated MPPT For Grid Application

A Transformerless Photovoltaic Inverter With Dedicated MPPT For Grid Application

Integrated Common-Mode and Differential Mode Filter Circuit for Leakage Current Suppression in Transformerless Photovoltaic Inverter Systems

Integrated Common-Mode and Differential Mode Filter Circuit for Leakage Current Suppression in Transformerless Photovoltaic Inverter Systems

A Noninvasive Sliding Mode Observer Based Approach for Detecting Open-Circuit Faults in HERIC Inverters

This article presents a new technique for detecting and localizing the open-circuit (OC) faults in the semiconductor switches of the Highly Efficient and Reliable Inverter Concept (HERIC) converter. It is a transformerless Photovoltaic (PV) inverter based on the full-bridge topology, with two extra switches on the AC side called ac bypass switches. The proposed method uses a sliding mode observer (SMO) to detect faults in the AC bypass switch and main switches of the full bridge inverter. To diagnose OC faults in the AC bypass leg, two parallel SMOs are created based on the converter’s state space model. Similarly, two SMOs are designed for the main switches. A residual is generated by combining the observed and measured grid currents to accurately locate the OC fault within the inverter system. To localize the faulty main switch, once the fault is detected the inverter is reconfigured and based on the grid current the faulty switch is identified. A major benefit of this method is that it does not rely on additional sensors for fault diagnosis, making the system more robust. The effectiveness and reliability of this approach are demonstrated through simulation studies. In addition, a laboratory prototype is developed to validate the practical applicability of the method.

Review on Close Loop Control of Novel Transformer Less Inverter Topology for Single Phase Grid Converter

The continuous urge for improvement in our standard of living has increased the consumption of electrical energy by leaps and bounds. This hike in energy consumption, draining of fossil fuels and degrading global environment has led to invention of green power generation systems. Thus, the global demand for renewable resources has led to flourishing of photovoltaic (PV) market. The enabling technology in the PV systems is the inverter, which could be either: 1) with transformer isolated or 2) without transformer non-isolated (transformer-less inverter). Recently, single phase transformerless voltage source inverters (VSI) have been extensively used for distributed photovoltaic grid tied systems. The objective of this paper is to review a few notable topologies and propose a new topology for transformer-less photovoltaic inverter. The analysis and design of the proposed topology is verified by simulating it on PSIM. Furthermore, the simulation results are validated by testing a proof-of-concept laboratory hardware prototype rated at 250 W. Keywords— Photovoltaic (PV) systems, transformer-less, single phase inverter

A seven‐level switched‐capacitor based transformerless inverter with modified PWM strategy to enhance the performance of grid‐connected PV systems

AbstractAmong different types of transformerless photovoltaic inverters, multi‐level inverters based on switched‐capacitors (SC) are the burning topic of recent decades due to their potential advantages, such as, single source requirement, voltage boosting capability, and high power density. However, for a seven level output voltage, a conventional SC based inverter architecture uses more than two units of SC, a large amount of power switches, which then lead to capacitor voltage balancing problems. This paper presents a seven‐level switched‐capacitor transformerless inverter (SCTI), which is structured with only two SC units, ten power switches, and a single DC source. The proposed SCTI ensures voltage boosting capability, self‐voltage balancing, and low power semiconductor losses. Apart from these, a modified sinusoidal pulse width modulation (MSPWM) is also proposed in this work, which guarantees better thermal performance and low inverter output voltage THD for the proposed SCTI. The proposed SCTI along with the MSPWM is simulated in MATLAB/Simulink and PLECS computer simulation environments. A reduced scale laboratory prototype is also built and tested to ensure the feasibility of the proposed SCTI.

Analysing Photovoltaic Grid-Connected H5 Inverter with Artificial Intelligence for Induction Motor Load Testing and Evaluation

Recent advancements in transformerless photovoltaic (PV) grid-connected inverters have positioned them as a prominent technology for distributed PV power generation systems. This is attributed to their demonstrably superior efficiency, reduced cost, and compact size. Conversely, they are susceptible to common-mode currents, leading to significant electromagnetic interference and security risks, thereby compromising system reliability. We introduced an enhanced H5 variant topology, termed H5-D topology, which integrates a clamping diode to mitigate common-mode voltage fluctuations. The paper presents the simulation results comparing both topology’s configurations, with a focus on the H5-D topology’s efficiency in suppressing common-mode currents. Additionally, experimental prototypes were constructed and evaluated for both the original and the H5-D configurations topology. The results unequivocally demonstrate the superior performance of the H5-D topology. The experimental findings corroborate the effectiveness of the recommended/suggested topology in addressing current issues related to common-mode issues, thereby enhancing the reliability and performance of photovoltaic inverter systems.

Three‐phase common‐ground‐type photovoltaic inverter without shoot‐through problem

SummarySince there are common mode leakage current (CMLC) and shoot‐through problems in the conventional three‐phase transformerless photovoltaic (PV) inverters, the three‐phase common‐ground‐type transformerless dual‐buck inverters (DBIs) are derived. By shorting the neutral point of the three‐phase load and the negative terminal of the PV panel, the CMLC is eliminated. The DBIs has no shoot‐through problem and there is no current flowing through the body diode of the SiC metal oxide semiconductor field‐effect transistor (MOSFET). The three‐phase DBI combined with a buck‐boost converter is taken as an example to illustrate the operating principle of the derived inverters. The control strategy of the inverter is given. A prototype is built to validate the proposed inverter. Finally, comparison among the proposed inverter and other three‐phase inverters is given.

A Comprehensive Review on Space Vector Based-PWM Techniques for Common Mode Voltage Mitigation in Photovoltaic Multi-Level Inverters

Nowadays, transformer-less photovoltaic (PV) multi-level inverters (MLIs) are commonly employed in both industrial and residential settings. This structure has attracted increased attention due to its unique advantages, such as higher efficiency, lower cost and size, better waveform quality, and inherent fault tolerance. However, due to the removal of the transformer, the common mode voltage (CMV) becomes one of the crucial issues in transformer-less PV MLIs. The high-frequency variation in CMV results in a leakage current that deteriorates the line current quality, increases the PV power system losses, leads to severe electromagnetic emissions (EMI), reduces the PV array lifespan, and causes personal safety problems. In this regard, this paper presents a review of the existing and recent research on modulation techniques based on space vector pulse width modulation (SVPWMs) that overcome this issue in transformer-less three-level NPC-MLIs (3L-NPC-MLIs). The reduced CMV-SVPWM (RCMV-SVPWM) can be mainly categorized as an RCMV-SVPWM based on the vector type, based on virtual vectors, and based on the two-level SVPWM (2L-SVPWM). Their features and their limitations in terms of several main criteria are discussed. In the final section of this paper, some challenges and future trends for this research area are projected.

Transformerless Inverter with Charge Pump Circuit Concept for PV Application

This paper introduces a new single phase transformerless photovoltaic (PV) inverter for grid connected PV systems using the concept of a charge pump. It consists of four power switches, two diodes, two capacitors and an LC filter at the output stage. The neutral of the grid is directly connected to the negative terminal of PV panel. This common ground creates a constant Common Mode (CM) voltage and zero leakage current. Meanwhile, the charge pump circuit generates the negative bus voltage for the inverter during the negative power cycle. A unipolar Sinusoidal Pulse Width Modulation (SPWM) technique is applied to the proposed inverter with three level output voltage to reduce the output current ripple and the filter requirements. The main advantages of the proposed inverter are (1) the negative polarity of the PV is directly connected to the grid, so the leakage current eliminated, (2) it has a compact size, (3) peak of output voltage is equal to input dc voltage (unlike Neutral Point Clamped (NPC) inverter, Active NPC (ANPC) and some topologies, which requires two times of the peak ac-voltage magnitude), flexible grounding configuration and high efficiency. The operating principle and analysis of the proposed topology are presented in details. Experimental results of a 500 W prototype are demonstrated to validate the proposed topology and the overall concept. The obtained results clearly verify the performance of the proposed inverter and its practical application for grid connected PV systems.

A single‐phase seven‐level buck‐boost common ground transformerless inverter for grid‐connected photovoltaic system

AbstractTransformerless inverters have recently gained attention in view of their economic benefits and compactness for photovoltaic (PV) systems. However, the limited voltage regulation and common‐mode (CM) leakage current are major concerns in conventional transformerless PV inverters. This paper presents a single‐phase seven‐level buck‐boost common ground transformerless inverter (SLB2CGTLI) to achieve a wide range of output voltages and zero leakage current without any additional stages, respectively. The proposed converter utilizes switched capacitor (SC) cell to buck‐boost the input DC voltage and generates seven‐level voltage at the output terminals. A simple reconfiguration strategy is adopted in the switched capacitor cell to maintain the charge‐second balance across the capacitors. Moreover, the common ground between the AC grid neutral and the PV panel's negative terminal mitigates the leakage current completely. The theoretical steady state analysis for both buck and boost mode is presented and verified with simulation using MATLAB Simulink. The performance of the proposed inverter is analyzed and validated with experimental results by developing a laboratory prototype. Further, the dynamic response of the proposed converter is carried out using OP4510 real‐time simulator for the grid‐connected PV application.

Performance analysis of different transformer-less inverter topologies for grid-connected PV systems

Transformerless Photovoltaic (PV) inverters are gaining popularity compared to their transformer-based counterparts. They are more efficient, cost-effective, and smaller in volume. Despite this, parasitic capacitance causes the common mode current to flow between the PV array and the grid. In addition to losses, leakage current increases electromagnetic interference (EMI) and poses issues to the protection system. Transformerless inverters should therefore be so designed that the leakage current is minimized. Common mode voltage changes (VCM) causes the leakage current. There are a number of PV inverter topologies that have been designed to minimize these variations. This paper discusses H4, H5 and HERIC single-phase PV inverter topologies. Circuit simulations have been used for analysis. HERIC Topology is best one of these since it reduces the leakage current with lowest power loss due to ac bypass instead of usual dc side decoupling. It is a type of resonant converter that operates at high frequencies to achieve efficient power conversion. In this work comparison has been made between topologies for their effectiveness in reducing leakage current. Moreover, its variation with load has been studied, a perspective missed in other studies.

An Asymmetrical Dual Quasi-Z-Source Based 7-Level Inverter for PV Applications

This paper presents a new single-stage quasi-z-source (qZS) based power converter for Photovoltaic (PV) applications. This seamless topology is obtained by the fusion of two quasi-z-source networks with a 7-level cascaded multilevel inverter (MLI). The proposed converter requires fewer passive components and power switching devices compared to the seven-level topologies with impedance and quasi-impedance sources, reported in the literature. The proposed modulation technique achieves the required level of voltage boosting using the qZS networks while synthesizing seven levels in the output voltage waveform. While the proposed power converter can regulate the output voltage in the standalone mode, it can inject active power into the grid at Unity power factor (UPF) in the grid-connected mode of operation. This paper also aims to mitigate the leakage current, which is one of the major issues in transformerless PV inverters, by reducing the magnitude of voltage transitions in the parasitic capacitor and the suppression of higher-order harmonics in the ground leakage current. The steady-state and the dynamic performances of the proposed power converter during grid-connected mode of operation is assessed with simulation studies and are validated with experimental results.

Common-Mode Circuit Analysis of Current-Source Photovoltaic Inverter for Leakage Current and EMI

Leakage current and Electro-Magnetic Interference (EMI) are closely related to the common-mode (CM) circuit in transformer-less photovoltaic (PV) inverter systems. However, the correlation between them is elusive, as they are always studied independently because of the different frequency bands involved. This paper establishes the CM circuit models of the current source inverter (CSI), and the inherent relationship and the affecting factors between leakage current and CM EMI are revealed. Based on the established models, the leakage current and conducted EMI are accurately predicted with reduced computational burden. In addition, some suppression measures for leakage current and CM EMI are derived, including the effectiveness of connecting neutral wire. Finally, by simulations and experiments, the correctness of the theoretical analysis is verified.

Three-phase double-grounded buck-boost PV inverter without shoot-through problem

The conventional transformerless photovoltaic(PV) inverter has the common mode leakage current and shoot-through problems. In addition, the output voltage of the PV module is low under the shading condition, resulting in the inverter not working properly. A three-phase double-grounded buck-boost PV inverter without shoot-through problem is proposed. The front-end converter of this inverter is composed of two boost converters, which can realize boost conversion. The rear-end inverter consists of three dual-buck half-bridge inverters, which solves the shoot-through problem. In this topology, the load ground is connected to the negative ground of the PV module, eliminating the common mode leakage current. The operating principle and mode analysis are described in detail. Finally, a simulation circuit is built to verify the theoretical analysis.

The topology-based approach to leakage current suppression on transformerless photovoltaic inverters

With the increase in demand for renewable energy, photovoltaic power generation is gradually becoming the most promising new energy source. However, the electrical connection of PV cells to the grid, and parasitic capacitance between the PV cell and the ground can introduce severe leakage currents into the grid. The scientific community has developed various topology-based techniques to suppress leakage currents. This paper is dedicated to a review of these techniques. Firstly the H5, HERIC, FB-DCBP, oH5, H8, and H6 are analyzed. These techniques are then reviewed more fully in terms of quality, efficiency, size, and complexity. All six of these topologies can meet the requirements for leakage current suppression, and there is an increasing trend toward reducing the size and simplifying topologies. Finally, future trends in topology-based techniques for suppressing leakage currents are predicted. The significance of this paper is that it provides a comprehensive review and summary of the various topology-based techniques for suppressing leakage currents.

Review and comparison of methods for limiting leakage currents in single-phase transformerless PV inverter topologies

Transformerless inverters are widely used in different photovoltaic nonisolated ac module applications, mainly in grid-tied photovoltaic (PV) generation systems, due to the benefits of achieving high efficiency over a wide load range, and low cost. Various transformerless inverter topologies have been proposed to meet the safety requirement of low ground leakage currents, such as specified in the VDE-4105 standard and low-output ac-current distortion. Topology modifications of transformerless full bridge inverters are designed to balance and maintain a constant common mode output voltage, thereby eliminating or reducing leakage currents. This article reviews and compares the different methods for limiting leakage currents in known topologies of the full-bridge transformerless inverters, such as: H4, H5, H6, HERIC, and their improvements. The main topologies and strategies used to reduce the leakage current in transformerless schemes are summarized, highlighting advantages and disadvantages and establishing points of comparison with similar topologies. To compare the properties of different medium to high power inverters, PV inverter topologies were implemented using IGBTs and tested with the same components, same simulation parameters in PSPICE to evaluate their performance in terms of energy efficiency and leakage current characteristics. The detailed power stage operating principles, extended PWM modulator, and integrated universal gate driver with galvanic isolation in the transmission path of control signal for all IGBTs of the inverter, as well isolated and floating bias power supply for gate drivers are described.

H9 and H10 Transformer-Less Solar Photovoltaic Inverters for Leakage Current Suppression and Harmonic Current Reduction

Now-a-days, transformer-less inverters integrating renewable energy resources as solar photovoltaic systems are commonly employed in many grid-connected distributed energy systems in both industrial and residential settings. Transformer-less photovoltaic (TLPV) inverters have attracted increased attention due to their unique advantages, such as increased efficiency, low cost, and ease of installation. Converting fluctuating solar dc power to consistent ac power has been a difficulty in the recent decade to avoid security risks like ground fault currents and leakage currents. Leakage current minimization is one of the most crucial factors in the TLPV inverters. Different TLPV inverter topologies have been presented in the past, with leakage current being reduced by galvanic isolation on the dc or ac side of the inverter, common mode voltage (CMV) clamping, and modulation techniques. This paper proposed two novel single-phase grid-tied TLPV inverter topologies with control blocks, which can handle a wide variety of grid voltages. The proposed TLPV inverters offer very small leakage current, reduced total harmonic distortion (THD), and improved power quality. Based on the number of semiconductor devices, the proposed inverters are termed as H9 and H10 inverters. The switches are controlled using the unipolar sinusoidal pulse width modulation, which results in constant common mode voltage and reduction in leakage currents to 11.09 and 11.73 mA for the proposed H9 and H10 inverters, respectively. The proposed H9 and H10 inverters minimize the THDs to 1.62 and 2.09%, respectively. Besides, the proposed H9 and H10 inverters exhibit 98.19 and 98.12% European efficiency. The simulations are carried out on MATLAB/Simulink and the results are experimentally validated using downscale laboratory test platforms

Analysis and Design of H5 Topology in Grid-Connected Single-Phase Transformerless Photovoltaic Inverter System

Objectives: The transformerless inverters are more efficient, less bulky and cost-effective. But the system faces the problem of leakage current on account of the elimination of isolation transformers. Thus, the problem needs to be mitigated through the inverter topology itself. The objective of this paper is to study and analyze a topology designed for reducing the leakage current. The H5 inverter significantly reduces the leakage current by checking the variation of common mode voltages. The topology uses only one extra switch apart from the conventional full bridge and is simple to design. Method: To reduce the leakage current H5 inverter topology has been designed which works on the basis of decoupling. This work is to be implemented in MATLAB/SIMULINK. The main parameters for analysis are efficiency, leakage current, common mode voltage and their variation with load. H4 and H5 topology will be simulated and results will be compared. Findings: The H5 topology has been found to be effective in suppressing the leakage current to a fairly acceptable magnitude. It has been observed that the H5 topology has a lower leakage current than the conventional H4 topology, i.e. 23mA as opposed to 402mA in H4 topology. But the leakage current increases to up to 5 times if the system is used at load less than the full load. Novelty: The study presents the H5 inverter topology and its SPWM modulation strategy. In order to verify the topology, simulation results are provided. The performance has been tested for different loads connected to grid. The leakage current has been found to be reduced to 23.37 mA but it rises to about 100mA if used at 10% of the full load. Keywords: PV Inverters; H5 Inverters; Leakage Current (Common Mode Current); Common-Mode Voltages; Transformerless Power Converters

A Transformerless Photovoltaic Inverter With Dedicated MPPT for Grid Application

A Transformerless Photovoltaic Inverter With Dedicated MPPT for Grid Application

Comparative Study of Leakage Current Suppression Schemes for Five-Level Photovoltaic Inverters

Solar photovoltaic power generation is crucial for combating climate change and promoting sustainable development. As the demand for renewable energy continues to rise, photovoltaic power generation offers a viable solution. This paper focuses on suppressing leakage currents in five-level photovoltaic inverters. By comparing and analyzing two types of inverters – the single-phase T-type five-level transformerless inverter and the single-phase asymmetric five-level transformerless inverter – using simulation and experimental data, the study reveals the effective suppression of leakage currents in both designs. The T-type inverter's unique configuration and advanced control algorithms significantly reduce leakage currents, while the asymmetric inverter's optimized design and operational parameters show notable proficiency in suppressing leakage currents. This research contributes to improving the performance and reliability of multi-level transformerless photovoltaic inverters, thereby supporting the widespread adoption of solar photovoltaic power generation as a sustainable energy solution.