Showing papers on "Grid-connected photovoltaic power system published in 2017"

Distribution Voltage Regulation Through Active Power Curtailment With PV Inverters and Solar Generation Forecasts

Abstract: Distribution voltage profiles are subjected to overvoltage limit violations from high penetration of grid-connected photovoltaic (PV) systems. Such voltage rises seen at the point of PV interconnection can be mitigated by adaptively changing the active and/or reactive power injection from the PV inverter. This work proposes a local voltage regulation technique that utilizes very short-term (15 s) PV power forecasts to circumvent imminent upper voltage limit violation or an overvoltage scenario. To provide these PV generation forecasts, a hybrid forecasting method is formulated based on Kalman filter theory, which applies physical PV generation modeling using high-resolution (15 s) data from on-site measurements. The proposed algorithm employs an active power curtailment based on these PV power forecasts, when the reactive power estimate given by a droop-based method cannot provide the desired voltage regulation within predefined power factor limits. The curtailment threshold values are calculated in such a way that this voltage regulation technique can reduce possible voltage limit violations. The effectiveness of the proposed method is demonstrated with case studies developed on a standard test feeder with realistic load and PV generation profiles.

On Distributed PV Hosting Capacity Estimation, Sensitivity Study, and Improvement

Abstract: This paper first studies the estimated distributed photovoltaic (PV) hosting capacities of 17 utility distribution feeders using the Monte Carlo simulation based stochastic analysis, and then analyzes the sensitivity of PV hosting capacity to both feeder and PV system characteristics. Furthermore, an active distribution network management approach is proposed to maximize PV hosting capacity by optimally switching capacitors, adjusting voltage regulator taps, managing controllable branch switches, and controlling smart PV inverters. The approach is formulated as a mixed-integer nonlinear optimization problem and a genetic algorithm is developed to obtain the solution. Multiple simulation cases are studied and the effectiveness of the proposed approach on increasing PV hosting capacity is demonstrated.

Review of cooling techniques using phase change materials for enhancing efficiency of photovoltaic power systems

Abstract: A significant fraction of the solar radiation falling on photovoltaic (PV) panels gets converted into heat thus reducing the efficiency of photovoltaic power plants. Generally the performance of PV panels falls by 0.5% for every degree rise in temperature, depending on the type of solar cells used. The temperature regulation of PV power systems therefore becomes important especially for areas experiencing consistently high temperatures to improve PV efficiency. The objective of the study is to review literature on photovoltaic cooling techniques using phase change materials (PCM) including PV-thermal systems and building integrated photovoltaic systems. The main aim is to identify important research areas to ensure reliable performance and commercially viability of the technology. Various parameters are required to be evaluated and optimized for the geographical location of interest to obtain the best output. Increase in electrical efficiency as high as 5% is observed with PV-PCM integrated systems. Study suggests that inorganic PCMs have a good potential for PV cooling. PCM based PV systems will be cost effective only for areas with high insolation year round with less inter-seasonal climatic variations. However, poor thermal conductivity and large undercooling are major problems associated with PCM. There are only few studies on performance testing, economic benefit identification, increase in PV panel lifetime and LCA analysis for testing the suitability of PCM as coolant for PV panels. In this study the research gaps are identified for follow up work. Market review suggests that PCM based PV cooling technology is not yet commercialized due to its inefficiency primarily because of technological challenges, high system costs and non-availability of reliable operating designs. The study suggests that PCM is still not an economic cooling technique for PV systems and further research is required.

Control Strategy for Three-Phase Grid-Connected PV Inverters Enabling Current Limitation Under Unbalanced Faults

Abstract: Power quality and voltage control are among the most important aspects of the grid-connected power converter operation under faults. Nonsinusoidal current may be injected during unbalanced voltage sag, and active or/and reactive power may include double frequency content. This paper introduces a novel control strategy to mitigate the double grid frequency oscillations in the active power and dc-link voltage of the two-stage three-phase grid-connected photovoltaic (PV) inverters during unbalanced faults. With the proposed control method, PV inverter injects sinusoidal currents under unbalanced grid faults. In addition, an efficient and easy-to-implement current limitation method is introduced, which can effectively limit the injected currents to the rated value during faults. In this case, the fault-ride-through operation is ensured, and it will not trigger the overcurrent protection. A non-maximum power point tracking (non-MPPT) operation mode is proposed for the dc–dc converter. The mode is enabled under severe faults when the converter cannot handle the maximum PV power. Finally, experimental validation is provided by implementing a method in an experimental setup, including a 2 kW PV inverter.

Monitoring system for photovoltaic plants: A review

Abstract: The Photovoltaic (PV) monitoring system collects and analyzes number of parameters being measured in a PV plant to monitor and/or evaluate its performance. In order to ensure the reliable and stable operation of any PV system, an effective monitoring system is essential. Moreover, the monitoring system keeps track on various electricity generation indices and fault occurrences. The cost and complexity of existing PV monitoring systems restricts their use to large scale PV plants. Over the past decade, different aspects of PV monitoring systems were reported in wide range of literature. In this paper, a comprehensive review of various PV monitoring systems is presented for the first time. This includes the detailed overview of all the major PV monitoring evaluation techniques in terms of their relative performances. Major aspects of PV monitoring systems which examines in this paper are: sensors and their working principles, controller used in data acquisition systems, data transmission methods, and data storage and analysis. The acquaintance of all these aspects are crucial for the development of effective, low cost, and viable PV monitoring systems for small and medium scale PV plants without compromising on the desired performance.

Very short-term photovoltaic power forecasting with cloud modeling: A review

Abstract: This paper endeavors to provide the reader with an overview of the various tools needed to forecast photovoltaic (PV) power within a very short-term horizon. The study focuses on the specific application of a large scale grid-connected PV farm. Solar resource is largely underexploited worldwide whereas it exceeds by far humans’ energy needs. In the current context of global warming, PV energy could potentially play a major role to substitute fossil fuels within the main grid in the future. Indeed, the number of utility-scale PV farms is currently fast increasing globally, with planned capacities in excess of several hundred megawatts. This makes the cost of PV-generated electricity quickly plummet and reach parity with non-renewable resources. However, like many other renewable energy sources, PV power depends highly on weather conditions. This particularity makes PV energy difficult to dispatch unless a properly sized and controlled energy storage system (ESU) is used. An accurate power forecasting method is then required to ensure power continuity but also to manage the ramp rates of the overall power system. In order to perform these actions, the forecasting timeframe also called horizon must be first defined according to the grid operation that is considered. This leads to define both spatial and temporal resolutions. As a second step, an adequate source of input data must be selected. As a third step, the input data must be processed with statistical methods. Finally, the processed data are fed to a precise PV model. It is found that forecasting the irradiance and the cell temperature are the best approaches to forecast precisely swift PV power fluctuations due to the cloud cover. A combination of several sources of input data like satellite and land-based sky imaging also lead to the best results for very-short term forecasting.

Rapid Active Power Control of Photovoltaic Systems for Grid Frequency Support

Abstract: As deployment of power electronic coupled generation such as photovoltaic (PV) systems increases, grid operators have shown increasing interest in calling on inverter-coupled generation to help mitigate frequency contingency events by rapidly surging active power into the grid. When responding to contingency events, the faster the active power is provided, the more effective it may be for arresting the frequency event. This paper proposes a predictive PV inverter control method for very fast and accurate control of active power. This rapid active power control (RAPC) method will increase the effectiveness of various higher-level controls designed to mitigate grid frequency contingency events, including fast power-frequency droop, inertia emulation, and fast frequency response, without the need for energy storage. The RAPC method, coupled with a maximum power point estimation method, is implemented in a prototype PV inverter connected to a PV array. The prototype inverter’s response to various frequency events is experimentally confirmed to be fast (beginning within 2 line cycles and completing within 4.5 line cycles of a severe test event) and accurate (below 2% steady-state error).

Performance evaluation of stand alone, grid connected and hybrid renewable energy systems for rural application: A comparative review

Abstract: The energy demand across the globe has increased in many folds due to technological advancement, rapid growth in industries and increase in household energy demand. This led the engineers and planners to think and find the means to harvest the alternative energy sources other than the fossil fuel. Solar, wind, biomass, mini hydro are some of the resources used worldwide to generate energy as per the availability of resources. This paper presents a comparative performances of various stand alone solar photovoltaic(PV), grid connected PV and hybrid renewable energy system (HRES) studied across the globe. The standalone PV system is used to supply electricity to a small habitats/hamlets or to a single household. Hybrid energy system consists of two or more energy sources for generation of power for rural electrification in off grid locations and in grid connected PV systems, excess electricity produced is injected to the grid thereby generating additional income. The research works carried out by various researchers around the globe on renewable energy sources particularly for rural electrification is discussed in this paper. Besides this the utilisation of renewable electricity for Plug-in-Electric Vehicles (PEV) studied across the globe were also discussed.

A review of technical issues on the development of solar photovoltaic systems

Abstract: Today, photovoltaic (PV) plants are receiving a significant attention due to their intrinsic ability to directly transform solar energy in electrical energy. However, electricity generated from PV plants can rarely provide immediate response to load demand, as these sources do not deliver a regular supply immediately compatible with consumers’ needs. Recently, an important attention has been devoted to the use of energy storage in grid-connected PV plants, with the objective of adding flexibility in load management and overcoming some important power quality problems of real distribution grids. This makes PV plants more useful and attractive. Several battery management techniques have been underlying as a way to create more price-responsive demand and as a way to integrate PV plants more effectively into power grid. However, the development of energy policies constraint the wider deployment of PV systems. In this paper, various sizing, modelling, maximum power point tracking (MPPT) methods have been reviewed for the efficient operation of grid-connected PV systems. Dispatch strategies for stored energy that maximize the financial value of battery-PV systems along with several optimization techniques are discussed. Power quality and control technology issues of grid-connected PV systems are also covered. The economic and environmental benefits of grid-connected PV systems are underlined and operational and maintenance issues of PV-battery power systems have been included. The present paper aims at reviewing some technical challenges on the current state of PV systems based on energy policies, various cell technologies, MPPT and converter/inverter technology, energy management and scheduling techniques, reliability, power quality and control systems issues.

A comprehensive review on large-scale photovoltaic system with applications of electrical energy storage

Abstract: In order to mitigate energy crisis and to meet carbon-emission reduction targets, the use of electrical energy produced by solar photovoltaic (PV) is inevitable. To meet the global increasing energy demand, PV power capacity will be expanded ranging from large-scale (from ten to several hundred MWs) PV farms at high and medium voltage level to kilowatt residential PV systems at low voltage level. It is expected that the PV penetration will increase in power systems with the retirement of traditional carbon-emission emitting power plants. Solar energy is diurnal in nature and in practice, it is highly uncertain due to various perturbation effects. With the recent technological advancements and rapid cost reductions in electrical energy storage (EES), EES could be deployed to enhance the system's performance and stability. This paper presents a comprehensive review on the emerging high penetration of PV with an overview of EES for PV systems. The crucial element, the building block of solar panel and the solar cell are reviewed. The emerging cell technologies are presented. A study of solar power forecasting techniques, an important tool for the successful operation and planning of PV and EES is included. A selection of EES is presented and studied for PV system purposes. Future research and areas for improvements in recent works and related areas are identified.

A Two-Stage Robust Optimization for Centralized-Optimal Dispatch of Photovoltaic Inverters in Active Distribution Networks

Abstract: Optimally dispatching photovoltaic (PV) inverters is an efficient way to avoid overvoltage in active distribution networks, which may occur in the case of the PV generation surplus load demand. Typically, the dispatching optimization objective is to identify critical PV inverters that have the most significant impact on the network voltage level. Following, it ensures the optimal set-points of both active power and reactive power for the selected inverters, guaranteeing the entire system operating constraints (e.g., the network voltage magnitude) within reasonable ranges. However, the intermittent nature of solar PV energy may affect the selection of the critical PV inverters and also the final optimal objective value. In order to address this issue, a two-stage robust centralized-optimal dispatch model is proposed in this paper to achieve a robust PV inverter dispatch solution considering the PV output uncertainties. In addition, the conic relaxation-based branch flow formulation and the column-and-constraint generation algorithm are employed to deal with the proposed robust optimization model. Case studies on a 33-bus distribution network and comparisons with the deterministic optimization approach have demonstrated the effectiveness of the proposed method.

Solar Photovoltaic and Thermal Energy Systems: Current Technology and Future Trends

Abstract: Solar systems have become very competitive solutions for residential, commercial, and industrial applications for both standalone and grid connected operations. This paper presents an overview of the current status and future perspectives of solar energy (mainly photovoltaic) technology and the required conversion systems. The focus in the paper is put on the current technology, installations challenges, and future expectations. Various aspects related to the global solar market, the photovoltaic (PV) modules cost and technology, and the power electronics converter systems are addressed. Research trends and recommendations for each of the PV system sectors are also discussed.

Active power filter (APF) for mitigation of power quality issues in grid integration of wind and photovoltaic energy conversion system

Abstract: The deep integration of renewable energy resources, including solar photovoltaic (PV) and wind turbine (WT) energy, mainly depend on the inexpensive technological improvement of global emissions and the precise techniques for power quality. Grid-connected inverters act as key components in distributed generation systems for cutting-edge technology. The inverter connects the renewable energy sources and power distribution network systems for the conversion of power. In grid-connected systems, several current and voltage harmonics affect the system performances. Likewise, highly unstable devices coupled with the growing demand for nonlinear loads and renewable energy resources influence the power networks and systems performance in terms of power quality. The effective solutions to these problems are passive filters (PFs), static var generators, and active power filters (APFs). However, the use of PFs in a high-power system increases its cost, size, and weight. This study aims to assess the most advanced APFs by reducing the number of power switches and focus on the reduction of cost, size, and weight of grid-connected inverters. Several studies compared and evaluated reduced-switch-count APF inverter topologies, such as AC–AC, back-to-back, and common leg, under the single-phase and three-phase systems. Recently, cost-effective solutions to reduce the number of components, transformerless inverters, multilevel and multifunctional inverters based on the APF in PV, and wind energy conversion systems have been greatly explored. The current techniques and their limitations for developing advanced inverter-based devices for renewable energy systems are discussed with justifications. Therefore, this review would potentially help industrial researchers improve power quality in PV and WT energies and power distribution network systems.

A Supervisory Power Management System for a Hybrid Microgrid With HESS

Abstract: This paper proposes a supervisory power management system (PMS) for a grid interactive microgrid with a hybrid energy storage system. The key feature of the proposed PMS is reduced number of sensors required to implement the PMS. The PMS considers renewable power variation, grid availability, electricity pricing, and changes in local loads. It can detect the operating mode of system without measuring load currents and powers. A single-phase voltage source converter (VSC) transfers real power between dc grid and utility grid besides offering ancillary services such as harmonic mitigation, reactive power support, and unity power factor at the point of common coupling (PCC). In the proposed system, a better dc-link voltage regulation is achieved and the usage of supercapacitors reduces the current stress on the battery. The PMS also addresses extreme operating conditions such as load shedding, off-maximum power point tracking operation of photovoltaic, elimination of critical oscillation of hybrid energy storage systems power, islanded operation, and resynchronization with grid. The performance of the proposed PMS is verified by digital simulation and experimental studies.

Selection of non-isolated DC-DC converters for solar photovoltaic system

Abstract: Concerns over environment and increased demand of energy have led the world to think about alternate energy sources such as wind, hydro, solar and fuel cells. Out of these, photovoltaic (PV) power generation systems have become increasingly important all over the world due its availability, cleanness, low maintenance cost and inexhaustible nature. But power produced by the photovoltaic system is stochastic in nature due to the variation of solar irradiation and cell temperature throughout the day. In order to track the varying power, a DC-DC converter with maximum power point tracker (MPPT) is used. Different MPPT algorithms have been proposed for tracking peak power from the PV panel. Selection of adequate DC-DC converter is also an important factor since it has an influence on overall performance of the PV system. This paper presents a comparative study on the characteristics of different non-isolated DC-DC converters and highlights the various research works that has been done on DC-DC converters based MPPT PV system. Study shows that selection of converter also has an impact on the overall performance of the PV system. Based on the survey and comparative study, selection criteria to choose DC-DC converter for PV system is described in this paper.

A Sensorless Power Reserve Control Strategy for Two-Stage Grid-Connected PV Systems

Abstract: Due to the still increasing penetration of grid-connected photovoltaic (PV) systems, advanced active power control functionalities have been introduced in grid regulations. A power reserve control, where namely the active power from the PV panels is reserved during operation, is required for grid support. In this paper, a cost-effective solution to realize the power reserve for two-stage grid-connected PV systems is proposed. The proposed solution routinely employs a maximum power point tracking control to estimate the available PV power and a constant power generation (CPG) control to achieve the power reserve. In this method, the solar irradiance and temperature measurements that have been used in conventional power reserve control schemes to estimate the available PV power are not required, and thereby, being a sensorless approach with reduced cost. Experimental tests have been performed on a 3-kW two-stage single-phase grid-connected PV system, where the power reserve control is achieved upon demands.

A Multilevel Transformerless Inverter Employing Ground Connection Between PV Negative Terminal and Grid Neutral Point

Abstract: For the safe operation of transformerless grid connected photovoltaic (PV) inverters, the issue of common mode (CM) leakage current needs to be addressed carefully. In this paper, a novel multilevel transformerless inverter topology is proposed, which completely eliminates CM leakage current by connecting grid neutral point directly to the PV negative terminal, thereby bypassing the PV stray capacitance. It provides a low-cost solution consisting of only four power switches, two capacitors, and a single filter inductor. As compared to half-bridge topologies, with this inverter a minimum of 27% and maximum of 100% more output voltage is obtained for the same dc-link voltage. The proposed inverter is analyzed in detail and its switching pattern to generate multilevel output while maintaining the capacitor voltage is discussed. Simulations and experiments results confirm the feasibility and good performance of the proposed inverter.

Power system stability analysis under increasing penetration of photovoltaic power plants with synchronous power controllers

Abstract: The utilisation of renewable sources brings many benefits to electric power systems, but also some challenges such as the impact that renewable power plants employing power electronics have on the grid, which is gaining importance as the penetration of this type of generating stations increases, driven by the construction of large wind or solar photovoltaic (PV) power plants. This study analyses the impact of large-scale PV power plants on a transmission grid for different penetration levels. The analysis considers power plants formed by a number of power converters employing synchronous power controllers (SPCs), that allow them to have a harmonious interaction with the grid, and compares their performance with that of conventional power converter controllers, assuming in both cases that the power plants participate in frequency and voltage regulation. The study addresses both the small-signal stability of the system and its response to large disturbances that alter the active power balance and frequency stability. The results of the analysis show that PV power plants using SPCs are able to limit frequency deviations, improve the oscillation damping, and reduce the stress of other generating units, thus having a beneficial impact on the power system.

Comprehensive overview of grid interfaced solar photovoltaic systems

Abstract: Grid-connected solar photovoltaic (PV) systems are increasingly attracting the attention of industry and academia mainly motivated by potential to provide an alternative to the conventional fossil fuel generation. This helps to meet out the increasing energy demands and to limit the pollution of environment caused by fossil emissions. This paper presents a comprehensive overview of the grid-connected solar PV systems. The intention of this review is to provide a wide spectrum on architecture of grid-connected solar PV system and its constituent components such as solar cell, PV array, maximum power point tracking, filters, DC-DC converters, single-phase inverters, and three-phase inverters to the researchers, designers, and engineers working on solar energy and its integration into the utility grid. Brief overview of control techniques for the single and three-phase inverters has also been presented. More than 100 research publications on the topologies, configurations, and control techniques of grid-connected solar PV systems and their major constituent components have been thoroughly reviewed and classified for quick reference.

On Estimation and Sensitivity Analysis of Distribution Circuit's Photovoltaic Hosting Capacity

Abstract: A high penetration of residential photovoltaic (PV) panels can potentially cause a number of operational issues in the distribution circuit, necessitating the requirement to determine the largest PV generation, a distribution circuit can accommodate This paper presents a Monte Carlo-based hourly stochastic analysis framework to determine a circuit's PV accommodation limit or PV hosting capacity First, a mathematical formulation of the hosting capacity problem for bus overvoltage concerns is presented, followed by the proposed analysis approach In the proposed approach, the Monte Carlo method is used to simulate the scenarios of probable PV locations and sizes while the hourly analysis framework is used to include the daily variations in load and PV generation Next, a method to evaluate the percentage accuracy of the hosting capacity results is presented The sensitivity of PV hosting results to multiple parameters related to both feeder characteristics and simulation method are evaluated as well The utility of the proposed framework is presented using an actual 1247-kV distribution circuit In sum, by presenting a PV hosting analysis method, accuracy assessment framework, and sensitivity analysis approach, this paper provides a thorough understanding of the PV hosting capacity problem

Artificial Neural Network for Control and Grid Integration of Residential Solar Photovoltaic Systems

Abstract: Residential solar photovoltaic (PV) energy is becoming an increasingly important part of the world's renewable energy. A residential solar PV array is usually connected to the distribution grid through a single-phase inverter. Control of the single-phase PV system should maximize the power output from the PV array while ensuring overall system performance, safety, reliability, and controllability for interface with the electricity grid. This paper has two main objectives. The first objective is to develop an artificial neural network (ANN) vector control strategy for an LCL -filter based single-phase solar inverter. The ANN controller is trained to implement optimal control, based on approximate dynamic programming. The second objective is to evaluate the performance of the ANN-based solar PV system by simulating the PV system behavior for grid integration and maximum power extraction from solar PV array in a realistic residential PV application and building an experimental solar PV system for hardware validation. The results demonstrate that a residential PV system using the ANN control outperforms the PV system using the conventional standard vector control method and proportional resonant control method in both simulation and hardware implementation. This is also true in the presence of noise, disturbance, distortion, and nonideal conditions.

Delta Power Control Strategy for Multistring Grid-Connected PV Inverters

Abstract: With a still increasing penetration level of grid-connected photovoltaic (PV) systems, more advanced active power control functionalities have been introduced in certain grid regulations. A delta power constraint, where a portion of the active power from the PV panels is reserved during operation, is required for grid support (e.g., during frequency deviation). In this paper, a cost-effective solution to realize delta power control (DPC) for grid-connected PV systems is presented, where the multistring PV inverter configuration is adopted. This control strategy is a combination of maximum power point tracking (MPPT) and constant power generation (CPG) modes. In this control scheme, one PV string operating in the MPPT mode estimates the available power, whereas the other PV strings regulate the total PV power by the CPG control strategy in such a way that the delta power constraint for the entire PV system is achieved. Simulations and experiments have been performed on a 3-kW single-phase grid-connected PV system. The results have confirmed the effectiveness of the proposed DPC strategy, where the power reserve according to the delta power constraint is achieved under several operating conditions.