H5 Topology Research Articles

Design and Implementation of New Topology for Solar PV Based Transformerless Forward Microinverter

Recently, transformerless inverters play a vital role for single phase low voltage solar photovoltaic (PV) system due to low cost, lesser weight, small size and high efficiency. However, the leakage current produces electromagnetic interferences, current distortion on the grid with additional losses which affects the performance of the inverter. In this paper, a new inverter topology, to deal with the problem of leakage current is proposed. The various conventional H6 topologies are simulated, compared and evaluated based on the leakage current, performance and safety with the proposed inverter topology. This work focuses on transformerless inverter which is best suitable for module integrated converter (MIC) or microinverter. The proposed topology is employed with unipolar sinusoidal pulse width modulation, and it can reduce the common mode (CM) current. The performance analysis is carried out on different topologies using MATLAB/Simulink environment and the proposed inverter experimentally verified on a 150 W prototype. Based on the analysis, simulation and experimental results, the comparison also presented for future reference.

Comparative performance evaluation of full‐bridge, H5, and H6 topologies for transformer‐less solar converters

Nowadays, the use of transformer-less single-phase inverters is widespread for domestic photovoltaic applications due to the high efficiency that can be obtained. Here, three similar topologies of transformer-less inverters are compared to highlight their differences. They are the full-bridge, the H5, and H6 inverters. The analysis considers the efficiency, the leakage current, and the quality of the output current when different modulation techniques are adopted. The experimental tests are carried out in the same operating conditions and with the same experimental set-up, thus emphasising the advantages and drawbacks of each topology.

Research on transformerless dual‐buck full‐bridge grid‐connected inverter with H5‐type for PV systems

To eliminate the common-mode leakage current in the transformerless grid-connected photovoltaic (PV) system, inspired by the newly-developed embedded-switch H5 topology and dual-buck full-bridge grid-connected inverter (GCI), a novel transformerless dual-buck full-bridge GCI with H5-type (TDFGI-H5) topology for PV systems is firstly presented. Then, the operating modes and common-mode leakage current of TDFGI-H5 modulated by unipolar sinusoidal pulse-width modulation are analysed. The analysis result shows that TDFGI-H5 has the advantages of the three-level output, no shoot-through problem, high reliability, and can completely meet the condition of eliminating common-mode leakage current. Aim at the problem of the common-mode leakage affected by the switches' junction capacitances, the effect of switch's junction capacitance is explored in detail when TDFGI-H5 is in the transient process that converts from non-decoupling states to decoupling states. Finally, the results of experiment verify the correctness of the theoretical analysis.

Analysis on topology derivation of single-phase transformerless photovoltaic grid-connect inverters

Aiming at the leakage current problem of single-phase transformerless photovoltaic(PV) grid-connected inverters, the recent proposed topologies are classified and reviewed. These topologies are divided into half-bridge type and full-bridge type. The topology characteristics of transformerless PV inverter are analyzed. This paper presents some of transformerless PV inverter topologies and discusses the evolution laws among various topologies to clarify the interrelationship between them. Furthermore, according to the evolution laws, a new topology is proposed. Finally, Simulations and experiments compare leakage current suppression capability of the proposed topology, H5 topology and HERIC topology.

An H5 Transformerless Inverter for Grid Connected PV Systems with Improved Utilization Factor and a Simple Maximum Power Point Algorithm

Due to their small size, minimum cost, and great efficiency, photovoltaic (PV) grid-connected transformerless inverters have been developed and become famous around the world in distributed PV generators systems. One of the most efficient topologies of the transformerless inverter family is H5 topology. This inverter extracts a discontinuous current from the PV panel, which conflicts with the operation at maximum power point tracking (MPPT) conditions while the utilization factor of the PV degrades. This paper proposes improved H5 topology featuring a boost converter inserted in the middle between the PV panels and the H5 inverter. The design of the boost converter is planned to operate at continuous conduction mode to guarantee MPPT conditions of the PV. A new and simple off line MPPT algorithm is introduced and performance factors like efficiency and utilization factors of the proposed and convention H5 topology are compared. The simulation results indicate that the proposed system provides a preferable utilization factor and a simpler MPPT algorithm.

An Improved Hybrid Modulation Method for the Single-Phase H6 Inverter With Reactive Power Compensation

Transformerless photovoltaic (PV) inverters are more widely adopted due to high efficiency, low cost, and light weight, etc. Many novel topologies and their corresponding modulation methods have been proposed, verified, and put into use, solely focusing on active power injection without leakage current issues. However, some new grid codes require PV inverters to have the ability of injecting reactive power into the utility for grid support. In order to map the challenge, an improved hybrid modulation method is proposed and evaluated for one nonisolated H6 topology as an example. With only simple modification for switching patterns and phase shift for current reference, the variable reactive power generation ability with zero crossing distortion is achieved, while the common mode voltage is also eliminated. The operation modes with the improved hybrid modulation approach are presented in detail and some design considerations are also provided. Extensive results from a 4-kVA prototype along with the SMPLIS simulation verify the proposed hybrid modulation method.

Comparative Analysis of Grid Connected Transformerless Photovoltaic Inverters for Leakage Current Minimization

Objectives: To make a comparative analysis of four transformerless topologies namely H5, H6, oH5 and H-Bridge Zero Voltage State Rectifier (HBZVR) in terms of leakage current and THD. Methods/Statistical Analysis: H5, H6, oH5 and HBZVR topologies have been simulated. Then these topologies are compared in terms of leakage current and THD. Based on the comparative analysis, the topology with less leakage current and THD has been chosen for photovoltaic interface. The interfacing circuit is simulated and realized as prototype to validate the results practically. Findings: It is found from the review that HBZVR topology has less leakage current and THD. This topology employs both galvanic isolation and Common Mode Voltage (CMV) clamping. It is found that the common mode voltage in HBZVR is almost eliminated. The conclusion derived from this paper may be helpful in selecting proper topology for PV interface. Application/ Improvements: Generally, in grid connected PV inverters, transformers provide galvanic isolation between the two electrical circuits, thus preventing the flow of leakage current between the stray capacitance of PV and ground. But, ransformers reduce the overall efficiency of the system, which lead to the development of transformerless PV system. Galvanic connection exists between the PV and grid in transformerless inverter, which leads to the presence of leakage current. So, to reduce leakage current, many topologies are introduced which employs either dc-decoupling or ac-decoupling to provide galvanic isolation. The HBZVR topology provides proper isolation for PV interface where the capacitance of the panel with respect to ground is large. Keywords: Comparison, Leakage Current, Isolation, Transformerless PV Inverters, THD

ESI: A Novel Three-Phase Inverter With Leakage Current Attenuation for Transformerless PV Systems

Adding the auxiliary switches to the conventional H-bridge inverter is an effective way to eliminate the leakage current for transformerless PV systems, such as H5, H6, etc. Inspired by the newly developed embedded-switch H6 topology, a novel embedded-switch inverter (ESI) is proposed in this paper for three-phase transformerless PV systems. First, the operation principle and characteristics of the proposed ESI are analyzed. Second, the common-mode model of the three-phase ESI is established, based on which the main factors that affect the leakage current are discussed. The finding reveals that the switching states with conventional modulation strategy result in high-frequency common-mode voltage, which is the source of leakage current. In order to solve the problem, a new modulation strategy is presented for ESI to eliminate the high-frequency leakage current. Finally, the time-domain simulation and the experimental tests are carried out. The results verify the effectiveness of the proposed solution.

Model of PV inverter in H4 and H5 topologies for power loss analysis

Model of PV inverter in H4 and H5 topologies for power loss analysis

No dead‐time modulation algorithm for an off‐grid inverter based on H6 topology

In this study, a no-dead-time modulation method based on the H6 topology is proposed. The main objective is to reduce the total harmonic distortion (THD) of the inverter output voltage and improve the output-voltage waveform quality. On the basis of the working state of the main circuit, the proposed method selects an appropriate switch modulation, thereby realising the objective of not inserting a dead time, most of the time. Simulations and experiments demonstrate that the modulation method suppresses the THD better than the conventional modulation algorithm, at all power factors and power levels. Furthermore, with the increase in power, the output current increases, but the current commutation interval decreases and the output-voltage suppression effect THD is better. It can also be concluded that simultaneously there is a higher DC-link voltage utilisation efficiency in the no-dead-time modulation method than in the conventional modulation method.

Simulation and Performance Comparison of Si and SiC Based on a Proposed H6 Inverter for PV Grid-tied Applications

Multilevel transformerless inverters are widely employed in PV grid-tied applications because of their significant benefits in reducing switching losses and enhancing system efficiency. Wide bandgap (WBG) semiconductor devices such as SiC MOSFETs can increase the system performance and reduce the total losses due to their superior features over Si switching devices. This paper investigates a three level transformerless inverter based on H6 topology. The proposed topology is implemented with SiC MOSFETs and a modulation approach is adopted to reduce the number of conducting switches. Also, a detailed comparison of the use of SiC and Si switching devices in terms of switching and conduction losses, high switching frequency operation, filter size reduction, and thermal analysis and heat sink volume is presented. Simulation results show that total conduction and switching losses are reduced by about 50%, which allow a significant increase in either the switching frequency or the inverter power rating level for the same switching device losses. Additionally, operating at higher switching frequencies using SiC MOSFET leads to a significant reduction in volume and weight of the inductor filter. Furthermore, a thermal analysis is performed using COMSOL software to investigate the heat sink requirement.

Quasi‐resonant DC‐link H5 PV inverter

By removing transformer from PV inverters, they become more attractive for distributed power generation systems. Regardless of their some extra leakage currents, transformer-less inverters would be more advantageous regarding their higher efficiency. However, using traditionally hard-switching converters still causes to drastic switching losses, high di/dt and electromagnetic interference. Quasi-resonant DC-link techniques have promising features to provide zero-voltage switching (ZVS) condition for full bridge inverters, but they are not suitable for transformer-less PV inverters due to consequent high leakage current. In this study, a transformer-less PV inverter is proposed by adapting a proper quasi-resonant DC-link technique to the H5 topology. Using only two auxiliary switches, ZVS turn on and turn off for high-frequency bus switch and ZCS turn on and ZVS turn off for high-frequency switches of the bridge as well as ZVS turn on and turn off of the antiparallel diodes of main switches are realised. Zero current switching (ZCS) turn on and ZVS turn off for auxiliary switches and ZVS turn on and ZCS turn off for antiparallel diodes are also provided. To verify the proposed circuit operation, a 20 kHz 1 kW quasi-resonant DC-link H5 PV inverter prototype is implemented and operation characteristics, soft switching conditions and design rules are confirmed.

A Novel Photovoltaic Power Harvesting System Using a Transformerless H6 Single-Phase Inverter with Improved Grid Current Quality

The pumping of electric power from photovoltaic (PV) farms is normally carried out using transformers, which require heavy mounting structures and are thus costly, less efficient, and bulky. Therefore, transformerless schemes are developed for the injection of power into the grid. Compared with the H4 inverter topology, the H6 topology is a better choice for pumping PV power into the grid because of the reduced common mode current. This paper presents how the perturb and observe (P&O) algorithm for maximum power point tracking (MPPT) can be implemented in the H6 inverter topology along with the improved sinusoidal current injected to the grid at unity power factor with the average current mode control technique. On the basis of the P&O MPPT algorithm, a power reference for the present insolation level is first calculated. Maintaining this power reference and referring to the AC sine wave of bus bars, a sinusoidal current at unity power factor is injected to the grid. The proportional integral (PI) controller and fuzzy logic controller (FLC) are designed and implemented. The FLC outperforms the PI controller in terms of conversion efficiency and injected power quality. A simulation in the MATLAB/SIMULINK environment is carried out. An experimental prototype is built to validate the proposed idea. The dynamic and steady-state performances of the FLC controller are found to be better than those of the PI controller. The results are presented in this paper.

Modelling and Simulation of Hybrid Transformer Less Grid-tied Inverters for Dye Sensitized Photovoltaic System

Dye-sensitized solar cells affords a technically and economically trustworthy alternative for p –n junction photovoltaic devices which made by silicon. In divergence to the conventional photovoltaic device the task of light absorption and charge carrier transport separately functioned. Photons absorbed by a sensitizer, which is moored to the surface of a wide band semiconductor. Charge separation occurs at the interface via photo-induced electron injection from the dye into the conduction band of the solid. Charge collector collects the carriers are from the conduction band of the semiconductor. Because of broad absorption band of sensitizers it permits to yield a large fraction of sunlight. The conversion of incident photons into electric current is attained over a large spectral range from the UV region to the near IR region. Power electronics, the technology of efficiently processing electric power, plays an essential part in the integration of the dispersed generation units for good efficiency and high performance of the power system. Due to the characteristics of low cost and high efficiency, the transformer less photo voltaic grid- connected inverters have been popularized in the application of solar electric generation system in the residential market. Unfortunately, the leakage currents through the stray capacitors between the PV array and the ground are harmful. This paper presents modelling and simulation of dye sensitized solar system with hybrid transformer less inverter topologies and proved that H6 topology by using neutral point clamped (NPC)method for suppressing of leakage currents and to obtain excellent common mode voltages are the best compared to other topologies.

A reduced leakage current transformerless photovoltaic inverter

The transformerless inverters used in the grid connected photovoltaic (PV) system induce leakage current due to the absence of galvanic isolation and unstable common mode voltage. Even though, the leakage current is able to be reduced by using the H5 topology, it is still considered high due to the existence of junction capacitance in the switches during the freewheeling mode. In this paper, a six switches and two diodes single phase transformerless PV inverter with stable common mode voltage and reduced leakage current is proposed. The simulation of the proposed topology is carried out in MATLAB and validated experimentally. The results show that the proposed topology has lower leakage current as compared to the H5 topology.

A Quasi-Unipolar SPWM Full-Bridge Transformerless PV Grid-Connected Inverter with Constant Common-Mode Voltage

The unipolar sinusoidal pulsewidth modulation (SPWM) full-bridge transformerless photovoltaic inverter with ac bypass brings low conduction loss and low leakage current. In order to better eliminate the leakage current induced by the common-mode voltage, the clamping technology can be adopted to hold the common-mode voltage on a constant value in the freewheeling period. A full-bridge inverter topology with constant common-mode voltage (FB-CCV) has been derived and proposed in this paper, two unidirectional freewheeling branches are added into the ac side of the FB-CCV, and the split structure of the proposed freewheeling branches does not lead itself to the reverse-recovery issues for the freewheeling power switches and as such superjunction MOSFETs can be utilized without any efficiency penalty. The passive clamping branches consist of a capacitor divider and two diodes, is added into the dc side of the FB-CCV, therefore, the weakness of active damping branch has been overcome, and the better clamping performance has been achieved in the freewheeling period. In the dead time between the main switches and the freewheeling switches, the antiparallel diodes of diagonal main switches of the FB-CCV form the freewheeling path to clamp the common-mode voltage at a constant value, and a quasi-unipolar SPWM strategy is presented. The operation principle, differential-mode, and common-mode characteristics of the FB-CCV, Heric, H6, and HB-ZVR topologies are analyzed and compared in detail. Finally, the viability of the FB-CCV is verified by a universal prototype inverter rated at 5 kW.

Evaluation and analysis of transformerless photovoltaic inverter topology for efficiency improvement and reduction of leakage current

In transfomerless photovoltaic (PV) grid-connected inverter application, to reduce leakage current and to increase efficiency, many inverter topologies have been proposed. The method for increasing efficiency and reducing leakage current is evaluated and analysed in the present study. The operation of transfomerless PV inverter topologies with high-performance such as full-bridge, H5, H6, HERIC and paralleled-buck topology is analysed to calculate switching losses, conduction losses and free-wheeling losses. Device total losses for inverter topology are calculated according to the switching frequency and the output power. Also, a novel high-frequency model of inverter topology is proposed using the leg voltage and high-frequency equivalent circuit. The relation between the parasitic capacitor voltage and its leakage current is explained using the proposed high-frequency model. Also, the magnitude of the high-frequency voltage in the parasitic capacitor is derived mathematically. Efficiency of the several inverter topology according to the output power is compared and the leakage current is analysed using a novel high-frequency model. Finally, the efficiency and leakage current analysis are verified by simulation tool and 3 kW prototype.

Modulation Techniques to Reduce Leakage Current in Three-Phase Transformerless H7 Photovoltaic Inverter

Recently, reduced common-mode voltage (CMV) pulsewidth modulation (RCMV-PWM) methods have been proposed to reduce the leakage current in three-phase transformerless photovoltaic (PV) systems. However, most of these studies only focus on leakage current elimination and neglect the overall performance of the PV systems on issues such as cost, voltage linearity, dc-link current ripples, and harmonic distortion. In this paper, a three-phase transformerless inverter, adapted from the single-phase H5 topology, is investigated. Since the H5 topology has been conventionally developed for a single-phase system, its adaptation to the three-phase system requires the development of corresponding three-phase modulation techniques. Hence, modulation techniques are proposed based on conventional PWM. The performances of the proposed PWM, in terms of CMV, leakage current, voltage linearity, output current ripples, dc-link current ripples, and harmonic distortion are studied and discussed via simulation and experiment. It is proven that the proposed topology is able reduce the leakage current without sacrificing the overall performance of the system.

Prediction of 2-level PWM inverter efficiency using MATLAB/Simulink

This article proposes a direct approach for the prediction of inverter efficiency using MATLAB/Simulink, instead of an indirect loss calculation approach based on analytical models. In analytical approach, efficiency is obtained by calculating individual losses separately, such as switching losses, conduction losses and harmonic losses using analytical models. However, this approach requires accurate analytical models and complicated calculations, due to the variation in the switching frequency, switching transient and modulation techniques. In the proposed approach, the actual waveform of the inverter system is directly generated using MATLAB/Simulink. The instantaneous voltage and current waveform including switching transients are generated. Thus, the proposed approach is very simple and convenient for efficiency prediction. The proposed approach also works for any system parameters or control methods, such as various pulse-width modulation (PWM) techniques, different switching frequencies, switching devices and load types. The proposed approach can be adopted for the efficiency prediction of any switching strategies and any types of inverters such as neutral-point-clamped (NPC) inverters, H bridge inverters and H5 topology, since the topologies are modelled as circuits in the MATLAB/Simulink program and no analytical model is required for the proposed approach. Furthermore, the proposed approach can provide operation techniques and conditions such as PWM techniques and switching frequency that offer high efficiency. In this article, inverter performance is evaluated for various PWM techniques and switching frequencies. The PWM technique and switching frequency that offer high efficiency is obtained. Finally, the proposed approach is verified by experimental results.

An improved transformerless grid connected photovoltaic inverter with reduced leakage current

Transformerless inverters are most preferred for grid connected photovoltaic (PV) generation system due to higher efficiency and lower cost. However, to meet the safety regulations, the leakage current which deteriorates the power quality and generates electro-magnetic interference in transformerless PV inverter, has to be addressed carefully. In order to eliminate the leakage current, an improved H5 topology is proposed in this paper. The operating principle, common mode (CM) characteristics, and the impact of junction capacitance of the switches on the CM voltage are investigated in details. The desired relationship among the junction capacitances is proposed to eliminate the CM leakage current. Three-level output voltage is achieved in the improved inverter employing unipolar sinusoidal pulse width modulation (SPWM). Furthermore, the European efficiency is improved by replacing the high frequency IGBT switches with MOSFETs. The proposed topology is compared with other transformerless topologies in terms of leakage current, different mode (DM) characteristics, and efficiency. The improved inverter topology is simulated in MATLAB/Simulink software to validate the accuracy of the theoretical explanations. Finally, a 1kW laboratory prototype has been built and tested. The experimental results show that the proposed inverter has a maximum efficiency of 98.0% and 97.45% European efficiency with 16kHz switching frequency.