Photovoltaic Inverter System Research Articles

Grid-Connection Single-Stage Photovoltaic Inverter System with Double-Linear-Approximation MPPT

Grid-Connection Single-Stage Photovoltaic Inverter System with Double-Linear-Approximation MPPT

Passive islanding detection method using Wavelet Packet Transform in Grid Connected Photovoltaic Systems

In this paper, a new approach in the passive-islanding detection method has been studied for the grid-connected photovoltaic (PV) inverter system using the wavelet packet transform (WPT) and back propagation neural network (BPNN). This proposed method is based on the point of common coupling voltage measurement and processing of this signal with a WPT to find the normalized logarithmic energy entropy. The BPNN is used for decision-making mechanism to avoid threshold. With this technique, the islanding operation is able to detect within 40 ms. In addition, it is effective even when the power supplied by distributed generation and the power consumed by the load is matched. In order to verify the capability of the proposed method, the simulation and experimental results of a 1.2-kW PV inverter by IEC Std. 62116 are provided. The proposed technique can be applied to both single- and multi-PV systems.

The Effect of Digital Process of Single-Phase Photovoltaic Grid Connected Inverter

Digital control possesses evident advantages and has become a mainstream control of photovoltaic grid connected inverter.The mathematical model and parameter setting of the single phase photovoltaic grid connected inverter with L filter was introduced in the paper.It was analysed on the effect on system stability of digital process from the two aspects which were the zero-order-hold and one-step-delay control. The bode diagram was verified the theoretical analysis on system stability.The conclusions were made that the introduction of digital control reduces the critical stable gain of photovoltaic grid connected inverter system,system stability is varied with sample time, the parameters of L can affect the system stability range,zero-order-hold reduces the stability range and limits the performance improved of digital control system,one-step-delay control on photovoltaic grid connected inverter reduces again the stability range on the basis of the zero-order-hold control.

Design of a High-Efficient Grid-Connected Three-Phase Three-Level T-Type PV Power System

This paper intends to design a high-efficient grid connected three-phase three-level T-type photovoltaic inverter system which is operated with conjunction with grid. Different from the two-level topology mainly used previous, switch elements are increased by 6 pieces, it has the advantages such as the efficiency of the inverter, less stress in the switching elements, and less harmonic component in the output current. This paper will suggest the boost convert always supplying constant DC voltage for a three-phase three-level T-type photovoltaic inverter, and also presents the stability and excellence of the 3 level boost converter through experiments. Also, it offers the stable and high-efficient MPPT algorism and through solar irradiation change experiment and MPPT efficiency assessment, the excellence and efficacy of three-level T-type inverter was verified from experiments.

An improved islanding detection method based on correlation technique using reactive power variation

AbstractThis paper presents an improved islanding detection method based on a correlation technique using reactive power variation for a three‐phase grid‐connected photovoltaic (PV) inverter system. Using a conventional reactive power variation (RPV) method for anti‐islanding, the reactive power component of PV inverter output varies periodically within a range of fixed magnitude for the inverter output frequency to go beyond the threshold of the over‐frequency relay or under‐frequency relay. While the conventional RPV method depends on the frequency relays, the proposed method uses a correlation factor between the commanded reactive power and the corresponding inverter frequency as an islanding detection indicator without relying on the frequency relays. The correlation factor of the proposed method is based on the fact that the commanded reactive power of a PV has a strong correlation with the frequency of the inverter voltage when islanding occurs. The proposed method has fast islanding detection capability and high power quality. In order to verify the proposed islanding detection method, the anti‐islanding experimental results of a 250‐kW three‐phase PV inverter by IEEE Std. 1547.1‐2005 are provided. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Single-Phase High Step-up Converter With Improved Multiplier Cell Suitable for Half-Bridge-Based PV Inverter System

In this paper, a single-phase high step-up converter is proposed, designed not only to boost the relatively low photovoltaic (PV) voltage to a high bus voltage with high efficiency, but also to offer a neutral point terminal for the half-bridge-based inverters. First and foremost, two symmetrical high step-up converters are combined and integrated to derive an improved converter with neutral point terminal, which is strongly expected for the half-bridge-based inverters. Secondly, the voltage gain of the converter is extended and the narrow turn-off period is avoided by using the coupled inductor multiplier. Furthermore, the coupled inductor multiplier reduces the voltage stress of all the power devices. As a result, the low voltage-rated power devices can be employed to minimize the conduction losses. More importantly, all the active switches work in the zero-voltage-switching condition, which reduces the switching losses effectively. All these factors improve the circuit performance in the high step-up applications, especially for the half-bridge based PV inverter systems. Finally, the experimental results from a 500 W, 48 -760 V prototype at 100 kHz switching frequency are provided to verify the effectiveness of the proposed converter. The highest efficiency of the prototype is 96.5% and the efficiency is over 94% in a wide load range.

A Multilevel Medium-Voltage Inverter for Step-Up-Transformer-Less Grid Connection of Photovoltaic Power Plants

Recently, medium (0.1-5 MW) and large (>5 MW) scale photovoltaic (PV) power plants have attracted great attention, where medium-voltage grid connection (typically 6-36 kV) is essential for efficient power transmission and distribution. A power frequency transformer operated at 50 or 60 Hz is generally used to step up the traditional inverter's low output voltage (usually ≤400 V) to the medium-voltage level. Because of the heavy weight and large size of the power frequency transformer, the PV inverter system can be expensive and complex for installation and maintenance. As an alternative approach to achieve a compact and lightweight direct grid connection, this paper proposes a three-phase medium-voltage PV inverter system. The 11-kV and 33-kV PV inverter systems are designed. A scaled down three-phase 1.2-kV test rig has been constructed to validate the proposed PV inverter. The experimental results are analyzed and discussed, taking into account the switching schemes and filter circuits. The experimental results demonstrate the excellent feature of the proposed PV inverter system.

Fuzzy Logic Controlling of a Single Phase Seven-Level GridConnected Inverter for Photovoltaic system

This paper proposes fuzzy logic controller based a single-phase seven-level inverter for grid-connected photovoltaic systems, with a novel pulse width-modulation (PWM) control scheme. Three reference signals produces from fuzzy logic controller which are identical to each other are going to compare with the amplitude of the triangular carrier signal. The inverter is capable of producing seven levels( Vab = Vdc Vab = 2Vdc/3 Vab = Vdc/3 Vab = 0 Vab = −V dc/3 Vab= − 2Vdc/3 Vab = −V dc )of output-voltage levels from the dc supply voltage. The total harmonic distortion is reduces by this control strategy. The proposed system was verified through simulation.

Analysis and Suppression of High-Frequency Harmonics of High Power Photovoltaic Inverter System

According to the growing need for renewable energy. Grid-connected photovoltaic system is used in many territories. To suppress the high-frequency harmonics of high power photovoltaic inverter, a LC low pass filter (LPF) has been proposed in this paper. The following have been done in the study: analysis of the high power photovoltaic inverter system and its harmonics, method of high-frequency harmonics suppression, and simulation of high-frequency harmonics suppression. According to the normalization method, the parameters of LPF are calculated. Then the parameters are put into a simulation model. The simulation result show that THD is 7.26%. It is much less than the former 78.19%. So it can be widely used in power system to suppress the high-frequency and to ensure the quality of electric energy.

Z Source Inverter Using Renewable Energy System

This paper presents a high performance, low cost inverter for Photo voltaic systems based on Z-source concept. Traditional Voltage-source inverter and Current Source Inverter has improved to the new Z-Source Inverter. This impedance source inverter can provide a single stage power conversion concept where as the traditional inverter requires two stage power conversion. A new low cost solar cell powered Z-source inverter system is simulated and the results are compared with the traditional Voltage Source Inverter system. Performance analysis confirms that Z source inverter system is more appropriate for photo voltaic applications. The Z-source concept can be applied to all dc-to-ac, ac-to-dc, ac-to-ac, and dc-to-dc power conversion.

Analysis of Maximum Power Point Tracking Efficiency of Inverters in Photovoltaic Systems

Os sistemas fotovoltaicos conectados à rede convertem diretamente a energia solar em energia elétrica entregando à rede elétrica de distribuição uma energia limpa e renovável. Esses sistemas são formados basicamente por um conjunto de módulos fotovoltaicos e inversores que são responsáveis por converterem energia elétrica em corrente contínua em energia elétrica em corrente alternada. Além de executar a conversão da energia elétrica em corrente contínua para corrente alternada, ele também é responsável pelo gerenciamento da energia entregue à rede e pelo seguimento do ponto de máxima potência. O seguimento do ponto de máxima potência é um processo de controle no qual o inversor procura manter o gerador fotovoltaico operando em uma região da sua curva característica na qual o produto corrente versus tensão tenha o seu valor máximo, de forma a otimizar a extração de potência do gerador fotovoltaico. Este trabalho apresenta um estudo de características elétricas de inversores utilizados em sistemas conectados à rede a partir de uma análise teórica e experimental. Os ensaios de inversores foram realizados no Laboratório de Energia Solar (LABSOL) da Universidade Federal do Rio Grande do Sul (UFRGS) onde foi utilizado um sistema fotovoltaico de 4,8 kW P e dez modelos de inversores de diferentes fabricantes. As características elétricas de inversores que foram medidas e analisadas são eficiência do ponto de máxima potência.

An Improved Grid Connected PV Generation Inverter Control System and Analysis of %THD for Inverter

In this paper we study the operational principle and the structure of the grid-connected photovoltaic system inverter control system and analysis of % THD for inverter with filter and without filter. Mainly the two inverter control methods. 1) voltage source inverter control method 2) power type PWM inverter control method. On the basis of above two kinds of inverter control methods, we will present an improved PWM inverter control system that can be applied in grid-connected PV generation and uses MATLAB/Simulink software to simulate and analyze. The result of the simulation shows that the improved inverter control system can effectively control the grid current waveform which tends to sine wave, means while it can achieve the maximum power point tracking, besides it is able to put the arbitrary power out to the load or to the grid, while the control system has a good stability. It also shows that as the increasing number of inductive load penetrate the grid, the load waveform distortion is produced, but it will not affect the reliability of power supply. In this paper, we study also the different types of inverter were designed by using MATLAB / SIMULINK and %THD (Total harmonics distortion) was compared.

Application and Simulation of SVPWM Control Techniques in Three-Phase PV Grid-Connected Inverter

The space vector pulse width modulation (SVPWM), as a new kind of vector control technique, has the advantages of high voltage utilization, less distorted output, simple control method, etc. In this paper, the control technique is applied to three-phase photovoltaic (PV) grid-connected inverter system. It uses double loop control method combined with PI control technique. The simulation model of PV grid-connected inverter system is established in Matlab/Simulink. The simulation results show that the application of SVPWM technique effectively improves the dynamic performance of PV grid inverter system and the THD of grid-connected current is low.

전압 이득이 향상된 단상 전류형 qZ-소스 인버터

This paper proposes a performance improvement of existing single-phase current-fed qZ-Source inverter. Voltage gain of the traditional voltage-fed full-bridge inverter and single-phase current-fed qZ-source inverter is only equal to or smaller than input voltage. The proposed inverter can obtain twice higher voltage gain than the single-phase current-fed qZ-Source inverter by adding an extra switch and a capacitor in the circuit. In addition, the proposed inverter shares the common ground between dc input and ac output voltage. Therefore, the proposed inverter can eliminate the possible ground leakage current problem when it is used for grid-tied photovoltaic inverter system. A 120 W prototype inverter is built and tested to verify performances of the proposed inverter.

Optimization of Photovoltaic Grid-Connected Inverter System

In order to increase the stability of grid connection of photovoltaic plant, effort has been made to study the grid connection principle of photovoltaic plant, mathematical model of grid-connected photovoltaic inverter and power grid distributed parameters, and improve traditional space vector control theory to keep d axis of d-q rotating coordinates consistent with the rotating space vector of network voltage and realize decoupling control over active power and reactive power of grid-connected photovoltaic system, through real-time detection of fluctuations in grid-connected current and network voltage, get voltage current dual-loop to place feedback control, which effectively compensates the modulating signal of inverter, reduces photovoltaic grid-connected output voltage and current harmonics so that the system has better robustness, and improves the reliability of grid connection.

IMPLEMENTATION OF IMPEDANCE SOURCE INVERTER SYSTEM FOR PHOTOVOLTAIC APPLICATIONS

This paper presents a high performance, low cost inverter for photovoltaic systems based on Impedance-source concept. Traditional Voltage-source inverter and Current-source inverter has improved to the new Z-source inverter, with a unique X-shaped network in it. This Impedance-source inverter can provide a single stage power conversion concept where as the traditional inverter requires two stage power conversion for renewable energy applications. A new low cost solar cell powered Z-source inverter system is simulated and the results are compared with the traditional Voltage-source inverter system. Performance analysis, simulation and comparison have been confirmed that the Z-source inverter system is more appropriate for photovoltaic application than their counterparts. Hardware implementation is done to validate the proposed system.

Development of a Solar Photovoltaic Power System to Generate Electricity for Office Appliances

In this paper a solar photovoltaic power supply system was developed to power office appliances. The system forms an alternative power source to the government own utility power supply in Nigeria, which is unreliable and epileptic in nature. It consists of photovoltaic array, mounting frame, storage device, inverter, charge controller and wiring system. The solar power system was tested in Akure, Nigeria (Latitude 7.15 o N) and the results obtained showed a good performance of the system. The output of solar power system is a function of solar radiation. The power output was high between 10.00 and 16.00 hours, which corresponds to the period of high solar radiation and coincides with the office hours. An average solar power output of 334 watt was obtained during test, while the total load of office appliances carried by the system was 290 watt.

Z Source Inverter for Photovoltaic System with Fuzzy Logic Controller

In this paper, the photovoltaic system is used to extract the maximum power from sun to get the dc voltage. The output dc voltage is boost up into maximum voltage level by using the SEPIC converter. This converter voltage is fed to Z source inverter to get the AC voltage. The Z source inverter system can boost the given input voltage by controlling the boost factor, to obtain the maximum voltage. PWM technique which is used as to given the gating pulse to the inverter switches. Modified system is very promising for residential solar energy system. In stand-alone systems the solar energy yield is matched to the energy demand. Wherever it was not possible to install an electricity supply from the mains utility grid, or desirable, stand-alone photovoltaic systems could be installed. This proposed system is cost-effective for photovoltaic stand-alone applications. This paper describes the design of a rule based Fuzzy Logic Controller (FLC) for Z Source inverter. The obtained AC Voltage contains harmonics of both odd and even harmonics of lower and higher order. Higher order harmonics are eliminated with the help of Filters. Here the impedance network act as a filter to reduce the lower order harmonics obtained in the system. So with the help of FFT analysis this value is obtained to be 15.82%. DOI: http://dx.doi.org/10.11591/ijpeds.v2i4.335

단상 PV 인버터용 온라인 데드타임 보상기 연구

This paper presents a new software-based on-line dead-time compensation technique for single-phase grid-connected photovoltaic (PV) inverter system. To improve the mitigation of dead-time effect around the zero-crossing point of phase current, a selective harmonic elimination of instantaneous feedback current is used as an additional part of conventional current control scheme. Simulation and experimental results are shown to verify the effectiveness of proposed compensation method in the gridconnected power distributed generation systems.

Study of DQ Rotating Frame Control for Single-Phase Photovoltaic Grid-Connected System

Nowadays solar photovoltaic energy has become an important alternative energy sources. This paper focuses on single-phase PV grid-connected system, a reference frame which used for three-phase inverter has been used in this single-phase grid-connected inverter. The in-quadrature signal is generated used T/4 transport delay technique. This single-phase grid-connected inverter uses space vector pulse width modulation(SVPWM) method. Finally, the 3KW small power single-phase photovoltaic inverter system model is built to verify the presented control strategy by using the Matlab/Simulink.