Grid-tied Photovoltaic System Research Articles

Deadbeat Controller based Transformerless Inverter for Grid Tied PV System with Reactive Power Control

Deadbeat Controller based Transformerless Inverter for Grid Tied PV System with Reactive Power Control

Comparative Analysis of Single-Phase Grid-Tied PV Systems with Single and Double Power Conversion Stages

Comparative Analysis of Single-Phase Grid-Tied PV Systems with Single and Double Power Conversion Stages

Open‐source python‐OpenDSS interface for hybrid simulation of PV impact studies

This study introduces an open-source Python-OpenDSS simulation tool where the phasor simulation software OpenDSS is interfaced with an electromagnetic transient (EMT) program-type simulation tool implemented in Python environment. The tool is designed to perform impact study of photovoltaic (PV) integration in distribution systems. It is composed of an EMT model of a grid-tied PV system interfaced with a phasor model of the distribution network. The proposed tool provides an add-on that expands OpenDSS capabilities in order to perform various PV impact studies that cannot be performed inherently by OpenDSS since they require detailed modelling. This study describes the methodology and theory behind the interfacing of the EMT model with OpenDSS. The tool is tested with various case studies using the IEEE 37-bus system with multiple interconnected PV systems. The tool is validated by comparing its results with those of a full EMT model of the IEEE 37-bus system simulated using SimPowerSystems. The results indicate that the hybrid tool offers significant advantages over single-rate simulations that use either full phasor or full EMT simulation approach. It provides faster simulation time and less computational intensity, and the accuracy is remarkably close to the full blown, more complex and slower, EMT simulation.

Neutral Point Clamped MOSFET Inverter With Full-Bridge Configuration for Nonisolated Grid-Tied Photovoltaic System

Existing nonisolated full-bridge neutral point clamped (NPC) inverters for a single-phase grid-tied photovoltaic (PV) system have limitations such as shoot-through and low European Union (EU) efficiency. In order to address these limitations, an NPC superjunction MOSFET nonisolated inverter with full-bridge configuration (NIIFBC) is proposed in this paper. This inverter reduces the possibility of shoot-through, thereby improving the reliability of the grid-tied PV system. It controls the grid current by energizing two coupled inductors individually during positive and negative half-grid cycles. This obviates the possibility of reverse recovery loss in switches due to their body diodes. Furthermore, two external silicon carbide diodes of a clamping branch cause negligible reverse recovery loss in switches besides a constant common-mode voltage. Therefore, the main claims of NIIFBC are low leakage current, high EU efficiency, and reliability. A generalized leakage current model for the proposed inverter is developed. In order to validate the veracity of the model and the claims of NIIFBC, a 1-kW prototype is designed and developed. The experimental results of NIIFBC validate the claims made by the authors. Its performance comparison with the existing nonisolated full-bridge inverters is given. Furthermore, a variant circuit of NIIFBC operating at nonunity power factor is proposed.

Dynamic Performance Improvement of a Grid-Tied PV System Using a Feed-Forward Control Loop Acting on the NPC Inverter Currents

This paper presents a three-phase grid-connected photovoltaic (PV) system, which is implemented using the neutral-point-clamped (NPC) inverter. A current feed-forward control loop (FFCL) is proposed to improve the PV system dynamic behavior, due to the PV array being constantly subjected to sudden solar irradiance change, which causes voltage oscillations in the dc bus and, hence, interferes in proper PV system operation. As the current FFCL acts to speed up the calculation of the inverter current references, the dynamic response of the currents injected into the grid is improved. As a consequence, the dynamic behavior of the dc-bus voltage is also enhanced, reducing both settling time and overshoot. Besides the injection of active power into the grid, the PV system is also controlled to perform active power-line conditioning, so that load harmonic currents are suppressed, as well as load reactive power is compensated. However, the NPC inverter must be properly designed to guarantee that its power rating will not be exceeded, since both fundamental and nonfundamental current components flow through the grid-tied inverter. Extensive experimental results based on a digital signal processor are presented in order to evaluate the effectiveness, as well as the static and dynamic performance of the PV system.

A study of impact on power system stability originated from new islanding detection method in PV systems

AbstractIn Japan, a unique islanding detection method, named New Islanding Detection Method, is widely equipped with grid-tied photovoltaic generation systems (PVs) to accurately detect their islanding operation. However, some research results show that the extensive installation of new islanding detection method brings negative impacts on stability of main power grids. This is because the islanding detection method has a possibility to detect frequency fluctuation caused by main grid’s faults, and the resulting undesirable operation intensifies the frequency fluctuations more. The authors especially focus on a frequency feedback mechanism in the islanding detection method, and then clarify some impacts on the stability of main grids which are originated from the growth in penetration of the islanding detection method in PVs. Through numerical simulations and discussions on their results, the authors concluded as, (1) the transient stability can be improved when active power output of PVs are set to const...

Impact of Photovoltaic Tied to Electrical Grid System On Power Quality

The High Penetration of PV power into the existing electricity grid needs more study and analysis to enable safe operation. One of the major concerns is the impact of PV system on grid power quality .Poor power quality could cause disturbance and financial losses due to the use of power inverters. Harmonic distortion is a serious power quality problem that reduces power quality and consequently causes a number of problems to consumer and network. This Paper proposes a new strategy for power quality improvement in a three-phase grid connected PV Inverter with central and string configuration and controlling on them using Sinusoidal pulse width modulation and space vector modulation methods with LCL Filter .This paper investigates PV Inverter configuration and impact of them on PV Plant Performance and harmonics that produced by PV inverter. The design, modeling, and analysis of a grid-tied PV system were performed in the PSCAD software simulation environment. The simulations of Harmonic Distortion (Total Demand Distortion & Total Harmonic Distortion) were applied at Point of Coming Coupling and the results obtained were compared with the limits specified by IEEE STD 519-1992 standards.

Performance analysis of different grid-connected solar photovoltaic (PV) system technologies with combined capacity of 20 kW located in humid tropical climate

ObjectiveThis study presents the outdoor performance of five solar photovoltaic (PV) systems with five different solar cell technologies (poly-crystalline (pc-Si)), mono-crystalline (mc-Si), Copper Indium disulfide (CIS) thin-film, Amorphous Silicon (a-Si), and Heterojunction Incorporating thin (HIT) film. MethodsThe PV systems are installed on rooftop of buildings at the Kwame Nkrumah University Science and Technology, Ghana. The systems' energy output in 2014, module temperature as well as environmental data were collected and analysed. ResultsThe total annual energy delivered to the grid varies between 3133.2 kWh for CIS and 4572.1 kWh for pc-Si while the performance ratio varies from 48.84% (CIS) to 71.26% (for p-Si). The annual energy density ranges between 45.7 kWh/m2 for CIS and 195.8 kWh/m2 for HIT. The total actual energy delivered to the grid by all the systems in 2014 is 20.62 MWh. ConclusionsThe performance data shows, that, the CIS technology is least suitable while p-Si is the most suitable solar PV technology for the site considered, followed by a-Si, HIT and mc-Si respectively. If space is a constraint, then, the HIT based system is most suitable solar PV technology for this site and potentially, sites with similar climate. Practice implicationsThe findings from this study are useful in identifying solar cell technologies that are appropriate for this location and provide useful information to policy makers and individuals about the performance of grid-tied PV system in Ghana.

Sizing and Study of the Energy Production of a Grid-Tied Photovoltaic System Using PV syst Software

This paper describes analyses carried out on the sizing and simulation of a grid-tied photovoltaic system in Bucaramanga, Colombia with the virtual tool PVsyst. The simulation was primarily performed in order to understand the behavior of grid-tied photovoltaic installations at a specific location, while avoiding the oversizing or undersizing of the systems, thus projecting installations which better approximate real conditions. Theoretical calculations were performed conventionally in order to make comparisons of calculated data with simulation results. We highlight the good potential of the studied area, with 1882 kWh/m 2 at optimal orientation, which would generate 1375 kWh/year for a 1 kW PV system, with a yield factor of 72.7%. Losses are disaggregated in this paper, including a study of the behavior associated with the tilt and orientation of the system. Such information on potential and performance is a valuable reference for any possible sizing of photovoltaic projects at similar latitudes.

Realization of single-phase single-stage grid-connected PV system

This paper presents a single phase single stage grid-tied PV system. Grid angle detection is introduced to allow operation at any arbitrary power factor but unity power factor is chosen to utilize the full inverter capacity. The system ensures MPPT using the incremental conductance method and it can track the changes in insolation level without oscillations. A PI voltage controller and a dead-beat current controller are used to ensure high quality injected current to the grid. The paper investigates the system structure and performance through numerical simulation using Matlab/Simulink. An experimental setup controlled by the MicrolabBox DSP prototyping platform is utilized to realize the system and study its performance. The precautions for smooth and safe system operation including the startup sequence are fully considered in the implementation.

Efficient Single Phase Transformerless Inverter for Grid-Tied PVG System With Reactive Power Control

There has been an increasing interest in transformerless inverter for grid-tied photovoltaic (PV) system due to low cost, high efficiency, light weight, etc. Therefore, many transformerless topologies have been proposed and verified with real power injection only. Recently, almost every international regulation has imposed that a definite amount of reactive power should be handled by the grid-tied PV inverter. According to the standard VDE-AR-N 4105, grid-tied PV inverter of power rating below 3.68KVA, should attain power factor (PF) from 0.95 leading to 0.95 lagging. In this paper, a new high efficiency transformerless topology is proposed for grid-tied PV system with reactive power control. The new topology structure and detail operation principle with reactive power flow is described. The high frequency common-mode (CM) model and the control of the proposed topology are analyzed. The inherent circuit structure of the proposed topology does not lead itself to the reverse recovery issues even when inject reactive power which allow utilizing MOSFET switches to boost the overall efficiency. The CM voltage is kept constant at mid-point of dc input voltage, results low leakage current. Finally, to validate the proposed topology, a 1 kW laboratory prototype is built and tested. The experimental results show that the proposed topology can inject reactive power into the utility grid without any additional current distortion and leakage current. The maximum efficiency and European efficiency of the proposed topology are measured and found to be 98.54% and 98.29%, respectively.

Grid‐tied photovoltaic system based on PSO MPPT technique with active power line conditioning

This study presents a single-phase grid-tied photovoltaic (PV) system based on a global maximum power point tracking (MPPT) technique, which is performed by means of the particle swarm optimisation (PSO) method. The PSO-based MPPT technique is employed to solve problems related to mismatching phenomena, such as partial shading, in which the PV arrays are commonly submitted. Considering the search of the global maximum power point under partial shading, the effectiveness of the PSO-based MPPT technique is highlighted when compared with the well-known perturb and observe MPPT technique, since both the mentioned MPPT techniques are used to determine the dc-bus voltage reference to ensure a proper grid-tied inverter operation. A current generator algorithm based on a synchronous reference frame is proposed, which operates in conjunction with a dc-bus controller and MPPT algorithms, computing the reference current of the grid-tied inverter. In addition, the current generator controls the energy processed by the PV system to avoid over power rating of the grid-tied inverter, since the active power injection into the grid, reactive power compensation and harmonic currents suppression are carried out simultaneously. The performance and feasibility of the grid-tied PV system are evaluated by means of simulation and experimental results.

Sistema Fotovoltaico com Condicionamento Ativo de Energia Usando Mppt Baseado em Pso e Malha Feed-forward de Controle de Tensão do Barramento Cc

Este artigo apresenta a implementação de um sistema fotovoltaico (PV) monofásico conectado à rede elétrica com duplo estágio de conversão de energia, o qual não é afetado por problemas associados a sombreamentos parciais. Técnicas convencionais de rastreamento de máxima potência (MPPT), tais como perturba e observa (P&O), não rastreia o ponto de máxima potência global (GMPP) quando o arranjo PV opera sob condições de sombreamento parcial. Como resultado, o desempenho geral do sistema diminui. Este trabalho usa o método de otimização por enxame de partículas (PSO) para rastrear o GMPP, aumentando o desempenho do sistema PV. Simultaneamente, o sistema fotovoltaico é controlado para realizar o condicionamento ativo de potência, realizando supressão das correntes harmônicas e compensação da potência reativa da carga. Além disso, como principal contribuição deste trabalho, é proposta uma malha de controle feed-forward para reduzir variações bruscas de tensão do barramento CC, na ocorrência de transientes de radiação solar e/ou temperatura. Tais variações podem influenciar no desempenho do sistema PV bem como ocasionar danos às chaves de potência. Os desempenhos estático e dinâmico do sistema PV são avaliados por meio de resultados experimentais.

Hybrid Pulsewidth Modulated Single-Phase Quasi-Z-Source Grid-Tie Photovoltaic Power System

A hybrid pulsewidth modulated single-phase quasi-Z-source grid-tie photovoltaic (PV) power system is proposed. The hybrid pulse-width modulation (HPWM) combines the pulse-width modulation (PWM) and the pulse-amplitude modulation (PAM). The PWM works when the ac output voltage is lower than the dc source voltage; otherwise, the PAM operates the single-phase quasi-Z-source inverter (qZSI). The HPWM leads to the reduction of power loss, and the quasi-Z-source capacitance and inductance. An effective control strategy is proposed for the new PV power system to manage the maximum power point tracking (MPPT) of PV panel, grid-tie power injection, and dc-link voltage. A grid-tie current controller, combining a repetitive controller and a proportional-resonant regulator, achieves strong harmonic suppression, fast dynamic, and zero tracking error. A 500-W prototype is built to verify the new system. Power loss estimation and impedance design are detailed. Experimental tests validate the HPWM, new PV power system with higher efficiency, and the related control method.

Theoretical Comparison in Energy-Balancing Capability Between Star- and Delta-Configured Modular Multilevel Cascade Inverters for Utility-Scale Photovoltaic Systems

This paper provides a theoretical discussion and comparison in energy balancing between a modular multilevel cascade inverter based on single-star bridge cells (SSBC) and that on single-delta bridge cells (SDBC). Attention is paid to applications involving asymmetric active-power generation in utility-scale grid-tied photovoltaic systems. Both qualitative and quantitative evaluation metrics to assess the energy-balancing capability are introduced and applied to both SSBC and SDBC inverters. As for the SSBC inverter, six zero-sequence voltage waveforms with different harmonic content enabling enhanced energy-balancing capability are analyzed and compared regarding their effectiveness. This paper also emphasizes on the SDBC as an alternative to the SSBC and highlights its superior operating characteristics under asymmetric active-power generation.

High-Frequency-Link-Based Grid-Tied PV System With Small DC-Link Capacitor and Low-Frequency Ripple-Free Maximum Power Point Tracking

This paper proposes a grid-tied photovoltaic (PV) system consisting of modular current-fed dual-active-bridge (CF-DAB) dc–dc converter with cascaded multilevel inverter. The proposed converter allows a small dc-link capacitor in the three-phase wye-connected PV system; therefore, the system reliability can be improved by replacing electrolytic capacitors with film capacitors. The low-frequency ripple-free maximum power point tracking (MPPT) is also realized in the proposed converter. First of all, to minimize the influence resulting from reduced capacitance, a dc-link voltage synchronizing control is developed. Then, a detailed design of power mitigation control based on CF-DAB dynamic model is presented to prevent the large low-frequency voltage variation propagating from the dc-link to PV side. Finally, a novel variable step-size MPPT algorithm is proposed to ensure not only high MPPT efficiency, but also fast maximum power extraction under rapid irradiation change. A downscaled 5-kW PV converter module with a small dc-link capacitor was built in the laboratory with the proposed control and MPPT algorithm, and experimental results are given to validate the converter performance.

Multivariate Statistics and Supervised Learning for Predictive Detection of Unintentional Islanding in Grid-Tied Solar PV Systems

Integration of solar photovoltaic (PV) generation with power distribution networks leads to many operational challenges and complexities. Unintentional islanding is one of them which is of rising concern given the steady increase in grid-connected PV power. This paper builds up on an exploratory study of unintentional islanding on a modeled radial feeder having large PV penetration. Dynamic simulations, also run in real time, resulted in exploration of unique potential causes of creation of accidental islands. The resulting voltage and current data underwent dimensionality reduction using principal component analysis (PCA) which formed the basis for the application ofQstatistic control charts for detecting the anomalous currents that could island the system. For reducing the false alarm rate of anomaly detection, Kullback-Leibler (K-L) divergence was applied on the principal component projections which concluded thatQstatistic based approach alone is not reliable for detection of the symptoms liable to cause unintentional islanding. The obtained data was labeled and aK-nearest neighbor (K-NN) binomial classifier was then trained for identification and classification of potential islanding precursors from other power system transients. The three-phase short-circuit fault case was successfully identified as statistically different from islanding symptoms.

An Efficient Modeling Technique to Simulate and Control Submodule-Integrated PV System for Single-Phase Grid Connection

The photovoltaic (PV) system that is based on submodule-integrated converters (subMICs) is capable of maximizing solar energy harvest by eradicating power losses due to intrapanel mismatch. Modeling and simulation of subMIC-based systems are important to study the effect of PV partial shading, prove new control strategies, analyze distributed system dynamics, optimize system configurations, and determine system parameters, etc. However, the simulation of such systems can be very challenging due to the large number of switching-mode power units, nonlinear nature of PV generators, and complication of the coordinating control. This paper provides an effective solution to simulate and control single-phase grid-tied PV systems that are based on a practical subMICs configuration. The approach includes the simplified PV cell model and averaged model for power converters, which consider all dynamic interactions among the maximum power point tracking (MPPT), PV submodule voltage regulation, dc-link voltage control, and double frequency ripple. The effectiveness of the proposed simulation and the subMIC system is validated by the comparison with a practical system based on centralized PV inverter under the real-world solar irradiance and various PV mismatch conditions, e.g., partial shading and uneven temperature distribution etc.

Electric Vehicle as an Energy Storage for Grid Connected Solar Power System

In the past few years the growing demand for electricity and serious concern for the environment have given rise to the growth of sustainable sources like wind, solar, tidal, biomass etc. The technological advancement in power electronics has led to the extensive usage of solar power. Solar power output varies with the weather conditions and under shading conditions. With the increasing concerns of the impacts of the high penetration of Photovoltaic (PV) systems, a technical study about their effects on the power quality of the utility grid is required. This paper investigates the functioning of a grid-tied PV system along with maximum power point tracking (MPPT) algorithm. The effects of varying atmospheric conditions like solar irradiance and temperature are also taken into account. It is proposed in this work that an Electric Vehicle (EV) can be used as an energy storage to stabilize the power supplied to the grid from the photovoltaic resources. A coordinated control is necessary for the EV to obtain desired outcome. The modeling of the PV and EV system is carried out in PSCAD and the proposed idea is verified through simulation results utilizing real field data for solar irradiance and temperature.

Modelling robustness for a flexible grid‐tied photovoltaic generation system

Robustness to modelling inaccuracy is a vital characteristic of a controller, because no matter how accurate a model is, modelling inaccuracies always exist. However, it is difficult to achieve satisfactory nominal and robust performance of a grid-tied photovoltaic (PV) generation system at the same time, using traditional controller design methods. To solve this problem, a μ-synthesis control method combined with the application of linear fraction transformation (LFT) is proposed in this study. The proposed method is designed with object transforming and implemented with DK iteration. The μ-analysis and simulation results prove that the objective can be achieved under various microgrid conditions, determined by factors such as grid connection point voltage, load conditions and component parameter perturbations. Compared with traditional controller design methods, the grid-tied PV generation system under μ-synthesis control exhibits comparatively large perturbation margin for nominal performance and robust stability, and simultaneously is capable of guaranteeing the preset perturbation range for robust performance.