Photovoltaic Inverter Topology Research Articles

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.

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.

SOLAR PV SYSTEM WITH MULTI-LEVEL INVERTER USING PI AND FUZZY LOGIC CONTROLLER

This paper presents a single-phase multi-string Nine-level PV inverter topology for grid-connected photovoltaic (PV) systems with a novel PWM control and fuzzy logic scheme. The Multilevel inverters are extensively used due to their increased power rating reduced EMI, improving harmonic performance. Multilevel inverters are switched at low switching frequency when compared to two level inverters, a single-phase multi-string nine-level PV inverter topology for grid-connected photovoltaic (PV) systems using novel PWM control Technology. A photovoltaic (PV) system generates electricity by direct conversion. The PV strings are cascaded together in parallel configuration and connected to a Nine-level inverter to generate output voltage. Two reference sinusoidal signals are identical to each other with an offset equivalent to the amplitude of the triangular carrier signal were used to generate gate signals for the nine level inverter switches and it is to implement this PWM using PI current control algorithm. The proposed nine level inverter offers much less THD and can operate at near unity power factor. the frequency of it will be 50Hz and from the result we minimizes the number of components and devices as well as switching losses are reduced when compared to the conventional multilevel inverter topology and its interconnects for grid utilization. Fuzzy Logic Control (FLC), originating from control theory focused on mathematical representations of the open-loop mechanism to be controlled, is an integral aspect of fuzzy reasoning. Fuzzy Logic Control has been successfully extended to a wide range of practical issues, including warm water control, robot control, heat exchange, traffic junction control, cement kiln control, vehicle speed control, automotive engineering, and mcar parking and turning, power system and nuclear reactor, on-line shopping, washing machines, etc. The validity of the proposed inverter is verified through simulation andcompared with other technique. The output voltage will be in the form of stepped waveform. The proposed system produces less THD and reduction of steady state time KEYWORDS –Maximum Power Point Tracking(MPPT) algorithm, Boost Converter, FLC contreoller, PWM technique.

High Efficiency Transformerless Photovoltaic DC/AC Converter with Common Mode Leakage Current Elimination: Analysis and Implementation

Photovoltaic (PV) electricity is widely used because of its positive environmental impact. To properly feed this energy into the grid, an electronic power converter, known as a PV inverter, is needed, which may or may not use a transformer. This article details the analysis and design of a transformerless photovoltaic inverter topology for grid-connected applications. This converter offers high efficiency, a low number of elements, and negligible leakage current, which makes it a good alternative for this application. The converter has been validated through an experimental prototype and compared with other topologies with similar characteristics.

A new seven level boost-type ANPC inverter topology for photovoltaic applications

Developing of new photovoltaic inverter topologies is received more attention in the last few years. In particular, designing an active neutral-point-clamping inverter type structure is quite popular for PV applications. The output voltage is always half of the input voltage (vin), which further increases the voltage rating of dc-link capacitors in the conventional three-level ANPC. To rectify the above problem and increase the output voltage by reducing dc-link capacitors voltage rating, a new boost type seven-level ANPC inverter topology is proposed. The proposed topology consists of seven switches and one floating capacitor. The floating capacitor voltage is self-balanced, and the output voltage is 1.5 times higher than the input voltage. A detailed comparison for some power components, power loss and cost with other existing topologies are presented. Further, the proposed topology is validated in a prototype hardware setup for different load values.

Research on an Improved Single-Phase Unisolated Grid-Connected Photovoltaic Inverter

An improved single-phase unisolated grid-connected photovoltaic inverter topology is proposed to solve the common mode leakage current problem of unisolated grid-connected photovoltaic inverters. By analyzing the topology structure and voltage clamping principle of the improved inverter, the topology can maintain the same low input voltage as the full-bridge inverter, and ensure that the common-mode voltage in the continuation mode is clamped to the midpoint voltage of the bus, so as to effectively reduce the common-mode leakage current caused by the common-mode voltage suspension in the continuation mode. Moreover, the common-mode leakage current of the improved topology is smaller than that of the traditional H6-2D topology at similar conversion efficiency. The simulation results on MATLAB /Simulink platform show that the topology is feasible and effective.

DC Voltage Utilization Improvement to Enlarge Power Balance Constraint Range for Photovoltaic Cascaded Inverter

In the three-phase photovoltaic (PV) cascaded inverter, the output power of PV arrays is not equal due to the difference of solar radiation, temperature and other factors, which leads to the over modulation of PV cascaded inverter. In order to solve the above problems, the carrier phase-shifted PWM (CPS-PWM) control strategy based on third harmonic injection is proposed in this paper, taking a single-stage high-frequency-link isolated cascaded PV inverter topology with clamping circuits as an example. It can not only improve the utilization of DC voltage, but also enlarge the power balance constraint range between the units in the phase of cascaded PV inverter, so as to ensure that all units can avoid over modulation under some serious power imbalance cases, and will not increase the third harmonic component injection of grid current. Firstly, the topology and working principle of the proposed inverter based on CPS-PWM control strategy are introduced. Then, the improved CPS-PWM control strategy which can improve the DC voltage utilization of the PV cascaded inverter is analyzed, and the control strategy of intra-phase power balance is emphatically analyzed in the overall control strategy of PV cascaded inverter system, and it is discussed that the proposed control strategy can also enlarge the power balance constraint range between the units of the cascaded inverter. Finally, the effectiveness of the proposed PV cascaded inverter based on the improved CPS-PWM control strategy is verified by the simulation and experimental results.

Optimal Photovoltaic Multi-String Inverter Topology Selection Based on Reliability and Cost Analysis

Inverters are the most vulnerable parts of the photovoltaic (PV) power plants. Therefore, choosing an appropriate inverter topology to maximize the reliability and availability of the PV power plants is very important, especially in the large scale power plants. This paper proposes a novel index named Total Financial Losses (TFL) to compare different inverter topologies from reliability and energy losses points of view. Initial cost, repair cost, financial losses due to the downtime and element losses, and environmental conditions are considered in evaluating the TFL index. Using this universal index, the optimal inverter topology and its switching frequency are determined when the TFL is minimized. Considering the fact that the reliability of power electronic devices is strongly dependent on their power losses and ambient conditions, the exact failure rates of vulnerable elements such as capacitors, switches, diodes, and cooling system are calculated. The system availability and frequencies of encountering the failure states are determined using the Markov method. Finally, the optimal photovoltaic inverter of the 150 kW power range is selected out of commonly used two-level and three-level topologies.

Research on the Three- phase Cascaded Dual-buck Grid-connected Inverter

The inhibition of common-mode leakage current is the key problem to be solved in cascaded photovoltaic grid-connected inverter. To eliminate the common-mode leakage current of cascaded dual-buck grid-connected inverter, a three-phase cascade double-buck photovoltaic grid-connected inverter (TPCDBGCI) topology is proposed in this paper. Meanwhile, a new phase-shifting carrier SPWM (PSCSWPM) control strategy that can make the single phase common-mode voltage and three phase differential-mode voltage constant in the half cycle is presented. Then, the simplified model and operating modes of TPCDBGCI are analyzed, which show that common-mode leakage current of TPCDBGCI is effectively suppressed. Finally, the experimental results verified the correctness of TPCDBGCI.

A novel photovoltaic inverter topology based on common mode current suppression

ABSTRACT Aiming at the problems of large leakage current and low efficiency of existing transformerless single-phase grid-connected photovoltaic inverters, a novel transformerless single-phase grid-connected photovoltaic inverter topology is proposed. In this topology, two freewheeling diodes are added to the single-phase full-bridge inverter, and the filter inductors are moved between the upper and lower bridge arms, so that the common mode voltage remains constant during the switching period and the common mode current is effectively suppressed. Finally, through simulation and the experimental platform of 3kW single-phase grid-connected photovoltaic inverter, it is verified that compared with the traditional full-bridge topology, the novel topology can effectively suppress the common mode current, while compared with the H5 and H6 topology, the novel topology reduces the system loss and improves the system efficiency.

Novel High-Frequency Isolated Cascade PV Inverter Topology Based on Multibus DC Collection

This article proposes a novel single-stage isolated cascade photovoltaic (PV) inverter topology based on a multibus dc collection. The PV power plant can be divided into many arrays, each of which supplies power to three cascaded isolated inverter units through a dc bus. This isolated inverter unit is composed of cascade isolated bridge cells (I-BCs) connected in input-parallel output-series (IPOS). Compared with a conventional two-stage isolated cascade PV converter, the proposed PV topology can totally eliminate the individual dc-link capacitors at the high-voltage (HV) side, which leads to extremely reduced system volume and eliminated the voltage-balancing control between the dc-link capacitors. This article, first, describes the basic principle and the carrier phase shift pulse-width modulation (CPS-PWM) applied to this topology and, then, analyzes the power balance constraints between the cascade three-phase units for the PV grid-connected system. Finally, the effectiveness of the novel topology is verified by the simulation and experimental results.

Research perspectives and state-of-the-art methods in photovoltaic microgrids

Purpose Increased investment of a photovoltaic (PV) array makes it essential for the client to attain better results from the PV system. The nonlinearity of the PV array and the revolution and rotation of the earth require the appliance of maximum power point tracking (MPPT) to the system. Accordingly, grid connected PV systems have turn out to be renowned, because they do not require battery back-ups to accomplish MPPT. Stand-alone systems could also attain MPPT; however, they require appropriate battery back-ups for this function. Design/methodology/approach This survey intends to formulate a review on the PV-based microgrid (MG) systems. Here, the literature analyses on diverse techniques associated with PV-based MG systems. It reviews 65 research papers and states the significant analysis. Initially, the analysis depicts various controllers that are contributed in different papers. Subsequently, the analysis also focuses on various features such as PV capacity and inverter topology, and it also analyses the renewable grid source that are exploited in each paper. Furthermore, this paper provides the detailed study regarding the chronological review and performance achievements in each contribution. Finally, it extends the various research issues which can be useful for the researchers to accomplish further research on PV-based MG systems. Findings This paper has presented a detailed review on PV-based MG systems that were enumerated in the above sections. Here, various controllers along with their better achievements were analyzed and described. From the review, it was known that several PV-based MG systems were really at the point for enabling better power output and conversion efficiency. In conclusion, this paper reviewed about 65 research papers and declared the significant analysis. Initially, the analysis also focused on various controller classifications in PV-based MG systems that were reviewed in this paper. Subsequently, the analysis also focused on various features, such as PV capacity and inverter topology. The analysis also reviewed the performance achievements and renewable gird source that were exploited in PV-based MG systems. At last, this paper has presented various research issues which can be useful for the researchers to accomplish further research on the features of PV-based MG systems. Originality/value This paper presents a brief analysis of PV-based MG systems. This is the first work that uses PV-based MG systems for better regulation of MPPT.

Analysis of Terminal Voltage in Single-Phase Extended Three-Phase Transformerless PV Inverter Topologies

In this article, an insight view for the derivation of various existing three-phase transformerless PV inverter topologies which are extended from the single-phase configuration is presented. In this article, the topologies under the four categories like dc decoupled, ac decoupled, neutral point clamped (NPC) dc decoupled, and NPC ac decoupled of single-phase transformerless photovoltaic (PV) inverter configurations are considered and their extended three-phase configurations are given. Furthermore, the analysis of the terminal voltage for each three-phase PV inverter topology is also presented. The analysis given in this article is expressed using the switching function concept. The analytical waveforms obtained using the mathematical switching function equation is matching with the simulation results presented. In addition, the obtained analytical and simulation results are further supported with the experimental results from the developed lab prototype. Finally, a comparison is done for the considered three-phase transformerless inverter topologies in terms of the number of switches and diodes used, the number of switches and diodes conducting, etc.

Terminal voltage analysis for the transformerless PV inverter topologies in a single‐phase system

This study presents an analysis of the terminal voltage of the basic photovoltaic (PV) inverter topologies available in the literature. The presented analysis utilises the switching function concept. Use of switching function in the analysis enables the inclusion of the effect of the pulse-width modulation technique or the switching strategy on the terminal voltage of the reviewed configuration. It gives insight into the switching action effects on the terminal voltage and provides every detail of the high-frequency transitions in the terminal voltage for the given switching strategy. Using the terminal voltage expression derived in terms of switching function, the analytical waveforms are obtained for various configurations. These waveforms are compared with the simulation and experimental results waveforms to justify the analysis given. This study also presents a bar chart view of the switching and conduction losses of the switches in the reviewed PV inverter topologies. The magnitude of high-frequency components in the terminal voltage and the leakage current is also presented in this study. The PV inverter topologies are also compared in terms of other aspects such as a number of devices used, asymmetry in operation, filter requirement etc.

DC Decoupling-Based Three-Phase Three-Level Transformerless PV Inverter Topology for Minimization of Leakage Current

This letter presents a three-phase three-level cascaded photovoltaic (PV) inverter configuration based on the dc decoupling strategy. The given configuration requires two additional decoupling switches for the minimization of the leakage current. The leakage current is minimized by avoiding or restricting the change in terminal voltages, during the common zero state. Further, a common zero state in all the three phases is obtained using a phase opposition disposition pulsewidth modulation technique. Once the common zero state is realized, the dc decoupling switches are used to isolate the PV source and output load. Apart from the terminal voltage, the proposed configuration also reduces the transitions in the common-mode voltage. Further, this letter also presents an analysis of the terminal voltage using the switching function concept. From the given switching function analysis, an analytical expression of the terminal voltage is derived and is used to obtain the analytical waveform, which matches with the simulation results. In addition to the terminal voltage, the leakage current waveform is also given. Fast Fourier transform spectrums of both are shown. These results are further supported by the experimental waveforms which match both simulation and analytical waveforms. Further, the proposed cascaded multilevel inverter (CMLI) is also compared with the conventional CMLI.

Mission-Profile-Based Lifetime Prediction for a SiC mosfet Power Module Using a Multi-Step Condition-Mapping Simulation Strategy

The reliability analysis and lifetime prediction for SiC-based power modules is crucial in order to fulfill the design specifications for next-generation power converters. This paper presents a fast mission-profile-based simulation strategy for a commercial 1.2-kV all-SiC power module used in a photovoltaic inverter topology. The approach relies on a fast condition-mapping simulation structure and the detailed electro-thermal modeling of the module topology and devices. Both parasitic electrical elements and thermal impedance network are extracted from the finite-element analysis of the module geometry. The use of operating conditions mapping and look-up tables enables the simulation of very long timescales in only a few minutes, preserving at the same time the accuracy of circuit-based simulations. The accumulated damage related to thermo-mechanical stress on the module is determined analytically, and a simple consumed lifetime calculation is performed for two different mission profiles and compared in different operating conditions.

A Simple, Efficient, and Novel Standalone Photovoltaic Inverter Configuration With Reduced Harmonic Distortion

This paper is put forward a novel photovoltaic (PV) inverter topology for maximum solar power utilization, which incorporates a new maximum power point tracking (MPPT) scheme based on shading pattern identification using the artificial neural network, single-input and multi-output (SIMO) converter, and multilevel inverter (MLI). The performance of the proposed MPPT scheme is benchmarked under partially shaded conditions. In continuation, the PV voltage is fed to the SIMO converter, where the converter produces four independent (V1, V2, V3 and V4) voltages with different magnitudes. The MLI converts the dc output voltage of the SIMO converter into ac to feed the utility, with reduced harmonic distortion. This MLI consists of eight switching devices and produces thirty one level ac output voltage with very less harmonic distortion. The salient feature associated with the proposed topology is that the proposed MPPT scheme extracts utmost power in any weather conditions and MLI feeds the utility. An experimental prototype is designed and developed to verify the performance of the proposed PV inverter topology. FPGA Spartan trainer kit is used to program pulses required for the MLI and converter of the proposed topology.

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.

Efficient Transformerless MOSFET Inverter for a Grid-Tied Photovoltaic System

The unipolar sinusoidal pulse width modulation full-bridge transformerless photovoltaic (PV) inverter can achieve high efficiency by using latest superjunction metal–oxide–semiconductor field-effect transistor (MOSFET) together with silicon carbide (SiC) diodes. However, the MOSFETs are limited to use in transformerless PV inverter due to the low reverse-recovery characteristics of the body diode. In this paper, a family of new transformerless PV inverter topology for a single-phase grid-tied operation is proposed using superjunction MOSFETs and SiC diodes as no reverse-recovery issues are required for the main power switches for unity power operation. The added clamping branch clamps the freewheeling voltage at the half of dc input voltage during the freewheeling period. As a result, the common-mode voltage kept constant during the whole grid period that reduces the leakage current significantly. In addition, dead time is not necessary for main power switches at both the high-frequency commutation and the grid zero crossing instant, results low-current distortion at output. Finally, a 1-kW prototype is built and tested to verify the theoretical analysis. The experimental results show 98.5% maximum efficiency and 98.32% European efficiency. Furthermore, to show the effectiveness, the proposed topology is compared with the other transformerless topologies.

Three-phase Photovoltaic Systems: Structures, Topologies, and Control

Photovoltaic technology has experienced unprecedented growth in the last two decades, transforming from mainly off-grid niche generation to a major renewable energy technology, reaching approximately 180 GW of capacity worldwide at the end of 2014. Large photovoltaic power plants interfacing the grid through a three-phase power electronic converter are now well on the way to becoming a major player in the power system in many countries. Therefore, this article gives an overview of photovoltaic systems with a focus on three-phase applications, presenting these both from a hardware point of view, detailing the different photovoltaic inverter structures and topologies as well as discussing the different control layers within a grid-connected photovoltaic plant. Modulation schemes for various photovoltaic inverter topologies, grid synchronization, current control, active and reactive power control, maximum power point tracking, as well as grid integration requirements and support functions are reviewed.