Showing papers on "Grid-connected photovoltaic power system published in 2011"

Grid Converters for Photovoltaic and Wind Power Systems

Abstract: About the Authors. Preface. Acknowledgements. 1 Introduction. 1.1 Wind Power Development. 1.2 Photovoltaic Power Development. 1.3 The Grid Converter The Key Element in Grid Integration of WT and PV Systems. 2 Photovoltaic Inverter Structures. 2.1 Introduction. 2.2 Inverter Structures Derived from H-Bridge Topology. 2.3 Inverter Structures Derived from NPC Topology. 2.4 Typical PV Inverter Structures. 2.5 Three-Phase PV Inverters. 2.6 Control Structures. 2.7 Conclusions and Future Trends. 3 Grid Requirements for PV. 3.1 Introduction. 3.2 International Regulations. 3.3 Response to Abnormal Grid Conditions. 3.4 Power Quality. 3.5 Anti-islanding Requirements. 3.6 Summary. 4 Grid Synchronization in Single-Phase Power Converters. 4.1 Introduction. 4.2 Grid Synchronization Techniques for Single-Phase Systems. 4.3 Phase Detection Based on In-Quadrature Signals. 4.4 Some PLLs Based on In-Quadrature Signal Generation. 4.5 Some PLLs Based on Adaptive Filtering. 4.6 The SOGI Frequency-Locked Loop. 4.7 Summary. 5 Islanding Detection. 5.1 Introduction. 5.2 Nondetection Zone. 5.3 Overview of Islanding Detection Methods. 5.4 Passive Islanding Detection Methods. 5.5 Active Islanding Detection Methods. 5.6 Summary. 6 Grid Converter Structures forWind Turbine Systems. 6.1 Introduction. 6.2 WTS Power Configurations. 6.3 Grid Power Converter Topologies. 6.4 WTS Control. 6.5 Summary. 7 Grid Requirements for WT Systems. 7.1 Introduction. 7.2 Grid Code Evolution. 7.3 Frequency and Voltage Deviation under Normal Operation. 7.4 Active Power Control in Normal Operation. 7.5 Reactive Power Control in Normal Operation. 7.6 Behaviour under Grid Disturbances. 7.7 Discussion of Harmonization of Grid Codes. 7.8 Future Trends. 7.9 Summary. 8 Grid Synchronization in Three-Phase Power Converters. 8.1 Introduction. 8.2 The Three-Phase Voltage Vector under Grid Faults. 8.3 The Synchronous Reference Frame PLL under Unbalanced and Distorted Grid Conditions. 8.4 The Decoupled Double Synchronous Reference Frame PLL (DDSRF-PLL). 8.5 The Double Second-Order Generalized Integrator FLL (DSOGI-FLL). 8.6 Summary. 9 Grid Converter Control for WTS. 9.1 Introduction. 9.2 Model of the Converter. 9.3 AC Voltage and DC Voltage Control. 9.4 Voltage Oriented Control and Direct Power Control. 9.5 Stand-alone, Micro-grid, Droop Control and Grid Supporting. 9.6 Summary. 10 Control of Grid Converters under Grid Faults. 10.1 Introduction. 10.2 Overview of Control Techniques for Grid-Connected Converters under Unbalanced Grid Voltage Conditions. 10.3 Control Structures for Unbalanced Current Injection. 10.4 Power Control under Unbalanced Grid Conditions. 10.5 Flexible Power Control with Current Limitation. 10.6 Summary. 11 Grid Filter Design. 11.1 Introduction. 11.2 Filter Topologies. 11.3 Design Considerations. 11.4 Practical Examples of LCL Filters and Grid Interactions. 11.5 Resonance Problem and Damping Solutions. 11.6 Nonlinear Behaviour of the Filter. 11.7 Summary. 12 Grid Current Control. 12.1 Introduction. 12.2 Current Harmonic Requirements. 12.3 Linear Current Control with Separated Modulation. 12.4 Modulation Techniques. 12.5 Operating Limits of the Current-Controlled Converter. 12.6 Practical Example. 12.7 Summary. Appendix A Space Vector Transformations of Three-Phase Systems. A.1 Introduction. A.2 Symmetrical Components in the Frequency Domain. A.3 Symmetrical Components in the Time Domain. A.4 Components 0 on the Stationary Reference Frame. A.5 Components dq0 on the Synchronous Reference Frame. Appendix B Instantaneous Power Theories. B.1 Introduction. B.2 Origin of Power Definitions at the Time Domain for Single-Phase Systems. B.3 Origin of Active Currents in Multiphase Systems. B.4 Instantaneous Calculation of Power Currents in Multiphase Systems. B.5 The p-q Theory. B.6 Generalization of the p-q Theory to Arbitrary Multiphase Systems. B.7 The Modified p-q Theory. B.8 Generalized Instantaneous Reactive Power Theory for Three-Phase Power Systems. B.9 Summary. Appendix C Resonant Controller. C.1 Introduction. C.2 Internal Model Principle. C.3 Equivalence of the PI Controller in the dq Frame and the P+Resonant Controller in the Frame. Index.

Energy Management and Operational Planning of a Microgrid With a PV-Based Active Generator for Smart Grid Applications

Abstract: The development of energy management tools for next-generation PhotoVoltaic (PV) installations, including storage units, provides flexibility to distribution system operators. In this paper, the aggregation and implementation of these determinist energy management methods for business customers in a microgrid power system are presented. This paper proposes a determinist energy management system for a microgrid, including advanced PV generators with embedded storage units and a gas microturbine. The system is organized according to different functions and is implemented in two parts: a central energy management of the microgrid and a local power management at the customer side. The power planning is designed according to the prediction for PV power production and the load forecasting. The central and local management systems exchange data and order through a communication network. According to received grid power references, additional functions are also designed to manage locally the power flows between the various sources. Application to the case of a hybrid supercapacitor battery-based PV active generator is presented.

Optimal Power Flow Management for Grid Connected PV Systems With Batteries

Abstract: This paper presents an optimal power management mechanism for grid connected photovoltaic (PV) systems with storage. The objective is to help intensive penetration of PV production into the grid by proposing peak shaving service at the lowest cost. The structure of a power supervisor based on an optimal predictive power scheduling algorithm is proposed. Optimization is performed using Dynamic Programming and is compared with a simple ruled-based management. The particularity of this study remains first in the consideration of batteries ageing into the optimization process and second in the “day-ahead” approach of power management. Simulations and real conditions application are carried out over one exemplary day. In simulation, it points out that peak shaving is realized with the minimal cost, but especially that power fluctuations on the grid are reduced which matches with the initial objective of helping PV penetration into the grid. In real conditions, efficiency of the predictive schedule depends on accuracy of the forecasts, which leads to future works about optimal reactive power management.

Coordinated Active Power Curtailment of Grid Connected PV Inverters for Overvoltage Prevention

Abstract: Overvoltages in low voltage (LV) feeders with high penetration of photovoltaics (PV) are usually prevented by limiting the feeder's PV capacity to very conservative values, even if the critical periods rarely occur. This paper discusses the use of droop-based active power curtailment techniques for overvoltage prevention in radial LV feeders as a means for increasing the installed PV capacity and energy yield. Two schemes are proposed and tested in a typical 240-V/75-kVA Canadian suburban distribution feeder with 12 houses with roof-top PV systems. In the first scheme, all PV inverters have the same droop coefficients. In the second, the droop coefficients are different so as to share the total active power curtailed among all PV inverters/houses. Simulation results demonstrate the effectiveness of the proposed schemes and that the option of sharing the power curtailment among all customers comes at the cost of an overall higher amount of power curtailed.

Options for Control of Reactive Power by Distributed Photovoltaic Generators

Abstract: High-penetration levels of distributed photovoltaic (PV) generation on an electrical distribution circuit present several challenges and opportunities for distribution utilities. Rapidly varying irradiance conditions may cause voltage sags and swells that cannot be compensated by slowly responding utility equipment resulting in a degradation of power quality. Although not permitted under current standards for interconnection of distributed generation, fast-reacting, VAR-capable PV inverters may provide the necessary reactive power injection or consumption to maintain voltage regulation under difficult transient conditions. As side benefit, the control of reactive power injection at each PV inverter provides an opportunity and a new tool for distribution utilities to optimize the performance of distribution circuits, e.g., by minimizing thermal losses. We discuss and compare via simulation various design options for control systems to manage the reactive power generated by these inverters. An important design decision that weighs on the speed and quality of communication required is whether the control should be centralized or distributed (i.e., local). In general, we find that local control schemes are able to maintain voltage within acceptable bounds. We consider the benefits of choosing different local variables on which to control and how the control system can be continuously tuned between robust voltage control, suitable for daytime operation when circuit conditions can change rapidly, and loss minimization better suited for nighttime operation.

Control and Operation of a DC Microgrid With Variable Generation and Energy Storage

Abstract: Control and operation of a dc microgrid, which can be operated at grid connected or island modes, are investigated in this paper. The dc microgrid consists of a wind turbine, a battery energy storage system, dc loads, and a grid-connected converter system. When the system is grid connected, active power is balanced through the grid supply during normal operation to ensure a constant dc voltage. Automatic power balancing during a grid ac fault is achieved by coordinating the battery energy storage system and the grid converter. To ensure that the system can operate under island conditions, a coordinated strategy for the battery system, wind turbine, and load management, including load shedding, are proposed. PSCAD/EMTDC simulations are presented to demonstrate the robust operation performance and to validate the proposed control system during various operating conditions, such as variations of wind power generation and load, grid ac faults, and islanding.

Modeling and Control of $N$ -Paralleled Grid-Connected Inverters With LCL Filter Coupled Due to Grid Impedance in PV Plants

Abstract: Designing adequate control laws for grid-connected inverters with LCL filters is complicated. The power quality standards and the system resonances burden the task. In order to deal with resonances, system damping has to be implemented. Active damping is preferred to passive damping so as to improve the efficiency of the conversion. In addition, paralleled grid-connected inverters in photovoltaic (PV) plants are coupled due to grid impedance. Generally, this coupling is not taken into account when designing the control laws. In consequence, depending on the number of paralleled grid-connected inverters and the grid impedance, the inverters installed in PV plants do not behave as expected. In this paper, the inverters of a PV plant are modeled as a multivariable system. The analysis carried out enables to obtain an equivalent inverter that describes the totality of inverters of a PV plant. The study is validated through simulation and field experiments. The coupling effect is described and the control law design of paralleled grid-connected inverters with LCL filters in PV plants is clarified.

Local Reactive Power Control Methods for Overvoltage Prevention of Distributed Solar Inverters in Low-Voltage Grids

Abstract: The main objective of this study is to increase the penetration level of photovoltaic (PV) power production in low-voltage (LV) grids by means of solar inverters with reactive power control capability. This paper underlines weak points of standard reactive power strategies which are already imposed by certain grid codes, and then, the study introduces a new reactive power control method that is based on sensitivity analysis. The sensitivity analysis shows that the same amount of reactive power becomes more effective for grid voltage support if the solar inverter is located at the end of a feeder. Based on this fundamental knowledge, a location-dependent power factor set value can be assigned to each inverter, and the grid voltage support can be achieved with less total reactive power consumption. In order to prevent unnecessary reactive power absorption from the grid during admissible voltage range or to increase reactive power contribution from the inverters that are closest to the transformer during grid overvoltage condition, the proposed method combines two droop functions that are inherited from the standard cos φ(P) and Q(U) strategies. Its performance comparison in terms of grid losses and voltage variation with different reactive power strategies is provided by modeling and simulating a real suburban LV network.

Investigation of Methods for Reduction of Power Fluctuations Generated From Large Grid-Connected Photovoltaic Systems

Abstract: Photovoltaic (PV) systems are presently allowed to inject into the grid all the power they can generate. However, in the near future, utilities are expected to impose additional regulations and restrictions on the power being injected by large centralized PV systems because of their possible adverse impacts. One of the main issues associated with large PV systems is the fluctuation of their output power. These fluctuations can negatively impact the performance of the electric networks to which these systems are connected, especially if the penetration levels of these systems are high. Moreover, the fluctuations in the power of PV systems make it difficult to predict their output, and thus, to consider them when scheduling the generating units in the network. The main objective of this paper is to investigate some methods that can be used to reduce the fluctuations in the power generated from a large customer-owned PV system, in the order of megawatts. This paper focuses on three methods: 1) the use of battery storage systems; 2) the use of dump loads; and 3) curtailment of the generated power by operating the power-conditioning unit of the PV system below the maximum power point. The emphasis in the analysis presented in this paper is on investigating the impacts of implementing these methods on the economical benefits that the PV system owner gains. To estimate the maximum revenues gained by the system owner, an linear programming optimization problem is formulated and solved. Moreover, the effect of varying different parameters of the problem is investigated through sensitivity analysis.

Energy Management and Power Control of a Hybrid Active Wind Generator for Distributed Power Generation and Grid Integration

Abstract: Classical wind energy conversion systems are usually passive generators. The generated power does not depend on the grid requirement but entirely on the fluctuant wind condition. A dc-coupled wind/hydrogen/supercapacitor hybrid power system is studied in this paper. The purpose of the control system is to coordinate these different sources, particularly their power exchange, in order to make controllable the generated power. As a result, an active wind generator can be built to provide some ancillary services to the grid. The control system should be adapted to integrate the power management strategies. Two power management strategies are presented and compared experimentally. We found that the “source-following” strategy has better performances on the grid power regulation than the “grid-following” strategy.

Forecasting power output of photovoltaic system based on weather classification and support vector machine

Abstract: Due to the growing demand on renewable energy, photovoltaic (PV) generation systems have increased considerably in recent years. However, the power output of PV systems is affected by different weather conditions. Accurate forecasting of PV power output is important for the system reliability and promoting large scale PV deployment. This paper proposes algorithms to forecast power output of PV systems based upon weather classification and support vector machine. In the process, the weather conditions are firstly divided into four types which are clear sky, cloudy day, foggy and rainy day. One-day-ahead PV power output forecasting model for single station is derived based on the weather forecasting data and historically actual power output data as well as the principle of Support Vector Machine (SVM). After applying it into a PV station in China (the capability is 20 kW), results show the proposed forecasting model for grid-connected photovoltaic systems is effective and promising.

Power Control Design of a Battery Charger in a Hybrid Active PV Generator for Load-Following Applications

Abstract: A hybrid generator with a photovoltaic energy conversion system is proposed with supercapacitors and lead-acid batteries in a dc-coupled structure. The objective of this system is to supply the prescribed reactive and active power to the grid. This paper focuses on the strategy, which makes it possible to ensure a high battery state of charge and overcharge security by designing a dedicated local control system. A continuous dynamic model and a control design of the power system studied are proposed in this paper. Simulation and experimental results illustrate the performances obtained.

Measured Performance of a 1.72 kW Rooftop Grid Connected Photovoltaic System in Ireland

Abstract: This paper presents results obtained from monitoring a 1.72 kWp photovoltaic system installed on a flat roof of a 12 m high building in Dublin, Ireland (latitude 53.4°N and longitude 6.3°E). The system was monitored between November 2008 and October 2009 and all the electricity generated was fed into the low voltage supply to the building. Monthly average daily and annual performance parameters of the PV system evaluated include: final yield, reference yield, array yield, system losses, array capture losses, cell temperature losses, PV module efficiency, system efficiency, inverter efficiency, performance ratio and capacity factor. The maximum solar radiation, ambient temperature and PV module temperature recorded were 1241 W/m2 in March, 29.5 °C and 46.9 °C in June respectively. The annual total energy generated was 885.1 kW h/kWp while the annual average daily final yield, reference yield and array yield were 2.41 kW h/kWp/day, 2.85 kW h/kWp/day and 2.62 kW h/kWp/day respectively. The annual average daily PV module efficiency, system efficiency and inverter efficiency were 14.9%, 12.6% and 89.2% respectively while the annual average daily performance ratio and capacity factor were 81.5% and 10.1% respectively. The annual average daily system losses, capture losses and cell temperature losses were 0.23 h/day, 0.22 h/day and 0.00 h/day respectively. Comparison of this system with other systems in different locations showed that the system had the highest annual average daily PV module efficiency, system efficiency and performance ratio of 14.9%, 12.6% and 81.5% respectively. The PV system’s annual average daily final yield of 2.4 kW h/kWp/day is higher than those reported in Germany, Poland and Northern Ireland. It is comparable to results from some parts of Spain but it is lower than the reported yields in most parts of Italy and Spain. Despite low insolation levels, high average wind speeds and low ambient temperature improve Ireland’s suitability.

A Frequency-Control Approach by Photovoltaic Generator in a PV–Diesel Hybrid Power System

Abstract: A photovoltaic (PV) system's output power fluctuates according to the weather conditions. Fluctuating PV power causes frequency deviations in the power utilities when the penetration is large. Usually, an energy storage system (ESS) is used to smooth the PV output power fluctuations and then the smoothed power is supplied to the utility. In this paper, a simple fuzzy-based frequency-control method is proposed for the PV generator in a PV-diesel hybrid system without the smoothing of PV output power fluctuations. By means of the proposed method, output power control of a PV generator considering the conditions of power utilities and the maximizing of energy capture are achieved. Here, fuzzy control is used to generate the PV output power command. This fuzzy control has average insolation, change of insolation, and frequency deviation as inputs. The proposed method is compared with a maximum power point tracking control-based method and with an ESS-based conventional control method. The numerical simulation results show that the proposed method is effective in providing frequency control and also delivers power near the maximum PV power level.

Photovoltaic DC-Building-Module-Based BIPV System—Concept and Design Considerations

Abstract: The photovoltaic (PV) modules used in the building-integrated PV (BIPV) system, generally, can be installed in different orientations and angles. Moreover, performance of the PV modules is easy to be affected by partial shadows and mismatch of their electrical parameters. Consequently, the conventional power configurations are difficult to obtain higher energy efficiency and reliability. Some improved power configurations of BIPV system have been presented to solve these problems. The objective of the paper is to give an overview of the existing solutions, and then, proposes an efficient and cost-effective power configuration of BIPV system from the energy conversion and control point of view. The proposed power configuration consists of plenty of PV dc-building module (PV-DCBM) and a centralized inverter. Each PV-DCBM includes a high step-up dc-dc converter integrated with a PV module into an individual electrical device. The PV-DCBMs are parallel connected, and then, connected to a common dc bus. The centralized inverter is connected to the grid. The design criterions, optimum design considerations, and design procedure of the proposed PV-DCBM-based BIPV system are proposed in this paper. The experimental results are presented to verify the validity and feasibility of the novel concept.

Online Optimal Reactive Power Control Strategy of PV Inverters

Abstract: This paper proposes a decentralized nonlinear autoadaptive controller for reducing system losses by the optimal management of the reactive power supplied by the inverters of photovoltaic (PV) units. This ancillary service can be furnished on the base of standard needs or on voluntary basis. The control design is based on an optimization procedure involving the sensitivity theory in conjunction with the Lyapunov function and provides control laws acting as references of the PV inverter local controller. PV inverters must operate in a decoupled manner in order to provide the reactive power imposed by the control law and to transfer the active power produced by PV modules. The experiences and results conducted in an indoor laboratory as well as on an actual distribution network managed by ENEL Distribuzione S.p.A. demonstrate its effectiveness in reducing system losses.

Dynamic Modeling and Performance Analysis of a Grid-Connected Current-Source Inverter-Based Photovoltaic System

Abstract: Voltage-source inverter (VSI) topology is widely used for grid interfacing of distributed generation (DG) systems. However, when employed as the power conditioning unit in photovoltaic (PV) systems, VSI normally requires another power electronic converter stage to step up the voltage, thus adding to the cost and complexity of the system. To make the proliferation of grid-connected PV systems a successful business option, the cost, performance, and life expectancy of the power electronic interface need to be improved. The current-source inverter (CSI) offers advantages over VSI in terms of inherent boosting and short-circuit protection capabilities, direct output current controllability, and ac-side simpler filter structure. Research on CSI-based DG is still in its infancy. This paper focuses on modeling, control, and steady-state and transient performances of a PV system based on CSI. It also performs a comparative performance evaluation of VSI-based and CSI-based PV systems under transient and fault conditions. Analytical expectations are verified using simulations in the Power System Computer Aided Design/Electromagnetic Transient Including DC (PSCAD/EMTDC) environment, based on a detailed system model.

A review of the factors affecting operation and efficiency of photovoltaic based electricity generation systems

Abstract: One of the most popular techniques of renewable energy generation is the installation of photovoltaic (PV) systems using sunlight to generate electrical power. There are many factors that affecting the operation and efficiency of the PV based electricity generation systems, such as PV cell technology, ambient conditions and selection of required equipment. There is no much study that presents all factors affecting efficiency and operation of the entire PV system, in the literature. This paper provides a detailed review of these factors and also includes suggestions for the design of more efficient systems. The presented detailed overview will be useful to people working on theory, design and/or application of photovoltaic based electricity generation systems.

Design of Smart Power Grid Renewable Energy Systems

Abstract: FOREWORD. PREFACE. ACKNOWLEDGMENTS. 1 ENERGY AND CIVILIZATION. 1.1 Introduction. 1.2 Fossil Fuel. 1.3 Depletion of Energy Resources. 1.4 An Alternative Energy Source: Nuclear Energy. 1.5 Global Warming. 1.6 The Age of the Electric Power System. 1.7 Green and Renewable Energy Sources. 1.8 Energy Units and Conversions. 1.9 Estimating the Cost of Energy. 1.10 Conclusion. 2 POWER GRIDS. 2.1 Introduction. 2.2 Electric Power Grids. 2.3 The Basic Concepts of Power Grids. 2.4 Load Models. 2.5 Transformers in Electric Power Grids. 2.6 Modeling a Microgrid System. 2.7 Modeling Three-Phase Transformers. 2.8 Tap Changing Transformers. 2.9 Modeling Transmission Lines. 3 MODELING CONVERTERS IN MICROGRID POWER SYSTEMS. 3.1 Introduction. 3.2 Single-Phase DC/AC Inverters with Two Switches. 3.3 Single-Phase DC/AC Inverters with a Four-Switch Bipolar Switching Method. 3.3.1 Pulse Width Modulation with Unipolar Voltage Switching for a Single-Phase Full-Bridge Inverter. 3.4 Three-Phase DC/AC Inverters. 3.5 Pulse Width Modulation Methods. 3.6 Analysis of DC/AC Three-Phase Inverters. 3.7 Microgrid of Renewable Energy Systems. 3.8 The DC/DC Converters in Green Energy Systems. 3.9 Rectifiers. 3.10 Pulse Width Modulation Rectifiers. 3.11 A Three-Phase Voltage Source Rectifier Utilizing Sinusoidal PWM Switching. 3.12 The Sizing of an Inverter for Microgrid Operation. 3.13 The Sizing of a Rectifi er for Microgrid Operation. 3.14 The Sizing of DC/DC Converters for Microgrid Operation. 4 SMART POWER GRID SYSTEMS. 4.1 Introduction. 4.2 Power Grid Operation. 4.3 The Vertically and Market-Structured Utility. 4.4 Power Grid Operations Control. 4.5 Load-Frequency Control. 4.6 Automatic Generation Control. 4.7 Operating Reserve Calculation. 4.8 The Basic Concepts of a Smart Power Grid. 4.9 The Load Factor. 4.10 A Cyber-Controlled Smart Grid. 4.11 Smart Grid Development. 4.12 Smart Microgrid Renewable Green Energy Systems. 4.13 A Power Grid Steam Generator. 4.14 Power Grid Modeling. 5 MICROGRID SOLAR ENERGY SYSTEMS. 5.1 Introduction. 5.2 The Solar Energy Conversion Process: Thermal Power Plants. 5.3 Photovoltaic Power Conversion. 5.4 Photovoltaic Materials. 5.5 Photovoltaic Characteristics. 5.6 Photovoltaic Effi ciency. 5.7 The Design of Photovoltaic Systems. 5.8 The Modeling of a Photovoltaic Module. 5.9 The Measurement of Photovoltaic Performance. 5.10 The Maximum Power Point of a Photovoltaic Array. 5.11 A Battery Storage System. 5.12 A Storage System Based on a Single-Cell Battery. 5.13 The Energy Yield of a Photovoltaic Module and the Angle of Incidence. 5.14 The State of Photovoltaic Generation Technology. 5.15 The Estimation of Photovoltaic Module Model Parameters. 6 MICROGRID WIND ENERGY SYSTEMS. 6.1 Introduction. 6.2 Wind Power. 6.3 Wind Turbine Generators. 6.4 The Modeling of Induction Machines. 6.5 Power Flow Analysis of an Induction Machine. 6.6 The Operation of an Induction Generator. 6.7 Dynamic Performance. 6.8 The Doubly-Fed Induction Generator. 6.9 Brushless Doubly-Fed Induction Generator Systems. 6.10 Variable-Speed Permanent Magnet Generators. 6.11 A Variable-Speed Synchronous Generator. 6.12 A Variable-Speed Generator with a Converter Isolated from the Grid. 7 LOAD FLOW ANALYSIS OF POWER GRIDS AND MICROGRIDS. 7.1 Introduction. 7.2 Voltage Calculation in Power Grid Analysis. 7.3 The Power Flow Problem. 7.4 Load Flow Study as a Power System Engineering Tool. 7.5 Bus Types. 7.6 General Formulation of the Power Flow Problem. 7.7 The Bus Admittance Model. 7.8 The Bus Impedance Matrix Model. 7.9 Formulation of the Load Flow Problem. 7.10 The Gauss Seidel YBus Algorithm. 7.11 The Gauss Seidel ZBus Algorithm. 7.12 Comparison of the YBus and ZBus Power Flow Solution Methods. 7.13 The Synchronous and Asynchronous Operation of Microgrids. 7.14 An Advanced Power Flow Solution Method: The Newton Raphson Algorithm. 7.15 The Fast Decoupled Load Flow Algorithm. 7.16 Analysis of a Power Flow Problem. 8 POWER GRID AND MICROGRID FAULT STUDIES. 8.1 Introduction. 8.2 Power Grid Fault Current Calculation. 8.3 Symmetrical Components. 8.4 Sequence Networks for Power Generators. 8.5 The Modeling of a Photovoltaic Generating Station. 8.6 Sequence Networks for Balanced Three-Phase Transmission Lines. 8.7 Ground Current Flow in Balanced Three-Phase Transformers. 8.8 Zero Sequence Network. 8.9 Fault Studies. APPENDIX A COMPLEX NUMBERS. APPENDIX B TRANSMISSION LINE AND DISTRIBUTION TYPICAL DATA. APPENDIX C ENERGY YIELD OF A PHOTOVOLTAIC MODULE AND ITS ANGLE OF INCIDENCE. APPENDIX D WIND POWER. INDEX.

Maximizing solar PV energy penetration using energy storage technology

Abstract: Many countries around the world are considering using solar energy technologies in their future energy planning. The intermittency and unpredictability nature of solar power generation, which can influence the power quality and reliability of the power grid especially at large-scale solar energy systems, constitute a drawback for use of solar technology. Precise research and investigations are needed to overcome this weakness helping solar power be used in power network in large scale. The variation in sun radiation may lead to over-production of electricity from solar PV generators at one time, and lack of production to satisfy the energy demand at another time. As a result, solar PV systems demonstrate a low-level of reliability in power systems. However, an energy storage technology would play a significant role in increasing the reliability of solar power generation systems. The objectives of this study are: firstly to review the issues in relation to grid-integration of solar PV systems, secondly, to review a range of storage devices that could technically and economically be used in association with solar PV energy in order to increase the solar energy penetration level with appropriate reliability in weak electric systems, and finally to present a model for solar PV system combined with battery and super-capacitor.

Grid regulation services for energy storage devices based on grid frequency

Abstract: Disclosed herein are representative embodiments of methods, apparatus, and systems for charging and discharging an energy storage device connected to an electrical power distribution system In one exemplary embodiment, a controller monitors electrical characteristics of an electrical power distribution system and provides an output to a bi-directional charger causing the charger to charge or discharge an energy storage device (eg, a battery in a plug-in hybrid electric vehicle (PHEV)) The controller can help stabilize the electrical power distribution system by increasing the charging rate when there is excess power in the electrical power distribution system (eg, when the frequency of an AC power grid exceeds an average value), or by discharging power from the energy storage device to stabilize the grid when there is a shortage of power in the electrical power distribution system (eg, when the frequency of an AC power grid is below an average value)

Grid integration aspects of large solar PV installations: LVRT capability and reactive power/voltage support requirements

Abstract: The current work focuses on two specific issues concerning grid-connected solar PV units, i.e. the fault ride-through capability, also called low voltage ride-through capability, and the voltage support function through reactive power injection during faults. With the first one the PV unit can actually provide some limited grid support, whereas with a defined reactive power characteristic it can give a complete dynamic grid support. These two requirements, already known for wind power generation but new for the PV, have been recently introduced in the German technical guidelines for connection to the MV grid. Scope of the paper is to implement these requirements in a large solar PV plant, modeled in DIgSILENT PowerFactory, in order to understand its operation, and to evaluate its behavior and impact on the grid, in terms of stability and voltage support during grid fault.

Towards next generation photovoltaic inverters

Abstract: Solar energy is under push to reach “grid parity” without additional subsidies and favorable policies. While cost and reliability are major concerns for both photovoltaic (PV) panels and PV inverters, comparable or exceeded grid functions and power quality can further help solar power become competitive to conventional generation technologies in the wholesale electricity market. This paper gives an overview of future development trends of PV inverters and proposes new requirements for next generation PV inverters under smart grid and/or microgrid environments. Approaches to address these requirements are also discussed from the research methodology perspectives. The goal of this paper is to draw the interests of the industry and academia in the new technical challenges of next generation smart PV inverters in addition to the “dollar per watt” overall PV system cost target.

Systems and methods for forecasting solar power

Abstract: A solar power forecasting system can provide forecasts of solar power output by photovoltaic plants over multiple time frames A first time frame may be several hours from the time of the forecast, which can allow utility personnel sufficient time to make decisions to counteract a forecasted shortfall in solar power output For example, the utility personnel can decide to increase power production and/or to purchase additional power to make up for any forecasted shortfall in solar power output A second time frame can be several minutes from the time of the forecast, which can allow for operations to mitigate effects of a forecasted shortfall in solar power output Such mitigation operations can include directing an energy management system to shed noncritical loads and/or ramping down the power produced by the photovoltaic plants at a rate that is acceptable to the utility to which the photovoltaic plants provide power