Showing papers on "Power optimizer published in 2011"

Power conversion and control of wind energy systems

Abstract: Preface. List of Symbols. Acronyms and Abbreviations. 1. Introduction. 1.1 Introduction. 1.2 Overview of Wind Energy Conversion Systems. 1.3 Wind Turbine Technology. 1.4 Wind Energy Conversion System Configurations. 1.5 Grid Code. 1.6 Summary. 2. Fundamentals of Wind Energy Conversion System Control. 2.1 Introduction. 2.2 Wind Turbine Components. 2.3 Wind Turbine Aerodynamics. 2.4 Maximum Power Point Tracking (MPPT) Control. 2.5 Summary. 3. Wind Generators and Modeling. 3.1 Introduction. 3.2 Reference Frame Transformation. 3.3 Induction Generator Models. 3.4 Synchronous Generators. 3.5 Summary. 4. Power Converters in Wind Energy Conversion Systems. 4.1 Introduction. 4.2 AC Voltage Controllers (Soft Starters). 4.3 Interleaved Boost Converters. 4.4 Two-Level Voltage Source Converters. 4.5 Three-Level Neutral Point Clamped Converters. 4.6 PWM Current Source Converters. 4.7 Control of Grid-Connected Inverter. 4.8 Summary. 5. Wind Energy System Configurations. 5.1 Introduction. 5.2 Fixed Speed WECS. 5.3 Variable Speed Induction Generator WECS. 5.4 Variable-speed Synchronous Generator WECS. 5.5 Summary. 6. Fixed-Speed Induction Generator WECS. 6.1 Introduction. 6.2 Configuration of Fixed-Speed Wind Energy Systems. 6.3 Operation Principle. 6.4 Grid Connection with Soft Starter. 6.5 Reactive Power Compensation. 6.6 Summary. 7. Variable-Speed Wind Energy Systems with Squirrel Cage Induction Generators. 7.1 Introduction. 7.2 Direct Field Oriented Control. 7.3 Indirect Field Oriented Control. 7.4 Direct Torque Control. 7.5 Control of Current Source Converter Interfaced WECS. 7.6 Summary. 8. Doubly-Fed Induction Generator Based WECS. 8.1 Introduction. 8.2 Super- and Sub-synchronous Operation of DFIG. 8.3 Unity Power Factor Operation of DFIG. 8.4 Leading and Lagging Power Factor Operation. 8.5 A Steady-State Performance of DFIG WECS. 8.6 DFIG WECS Start-up and Experiments. 8.7 Summary. 9. Variable-Speed Wind Energy Systems with Synchronous Generators. 9.1 Introduction. 9.2 System Configuration. 9.3 Control of Synchronous Generators. 9.4 SG Wind Energy System with Back-to-back VSC. 9.5 DC/DC Boost Converter Interfaced SG Wind Energy Systems. 9.6 Reactive Power Control of SG WECS. 9.7 Current Source Converter Based SG Wind Energy Systems. 9.8 Summary. Appendix A. Per Unit System. Appendix B. Generator Parameters. Appendix C. Problems and Answers Manual.

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.

Platform architecture for solar, thermal and vibration energy combining with MPPT and single inductor

Abstract: A 0.35µm CMOS energy processor with multiple inputs from solar, thermal and vibration energy sources is presented. Dual-path architecture for energy harvesting is proposed that has up to 13% higher conversion efficiency compared to the conventional two stage storage-regulation architecture. To minimize the cost and form factor, a single inductor has been time shared for all converters. A novel low power maximum power point tracking (MPPT) scheme with 95% tracking efficiency is also introduced.

Power electronics converters for wind turbine systems

Abstract: The steady growth of installed wind power which reached 200 GW capacity in 2010, together with the up-scaling of the single wind turbine power capability - 7 MW's has been announced by manufacturers - has pushed the research and development of power converters towards full scale power conversion, lowered cost pr kW, and increased power density and the need for higher reliability. Substantial efforts are made to comply with the more stringent grid codes, especially grid faults ride-through and reactive power injection, which challenges power converter topologies, because the need for crowbar protection and/or power converter over-rating has been seen in the case of a doubly-fed induction generator. In this paper, power converter technologies are reviewed with focus on single/multi-cell power converter topologies. Further, case studies on the Low Voltage Ride Through demand to power converter technology are presented including a discussion on reliability. It is concluded that as the power level increases in wind turbines, medium voltage power converters will be a dominant power converter configuration.

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.

Constant Power Control of DFIG Wind Turbines With Supercapacitor Energy Storage

Abstract: With the increasing penetration of wind power into electric power grids, energy storage devices will be required to dynamically match the intermittency of wind energy. This paper proposes a novel two-layer constant power control scheme for a wind farm equipped with doubly fed induction generator (DFIG) wind turbines. Each DFIG wind turbine is equipped with a supercapacitor energy storage system (ESS) and is controlled by the low-layer wind turbine generator (WTG) controllers and coordinated by a high-layer wind farm supervisory controller (WFSC). The WFSC generates the active power references for the low-layer WTG controllers according to the active power demand from or generation commitment to the grid operator; the low-layer WTG controllers then regulate each DFIG wind turbine to generate the desired amount of active power, where the deviations between the available wind energy input and desired active power output are compensated by the ESS. Simulation studies are carried out in PSCAD/EMTDC on a wind farm equipped with 15 DFIG wind turbines to verify the effectiveness of the proposed control scheme.

Neural-Network-Based MPPT Control of a Stand-Alone Hybrid Power Generation System

Abstract: A stand-alone hybrid power system is proposed in this paper. The system consists of solar power, wind power, diesel engine, and an intelligent power controller. MATLAB/Simulink was used to build the dynamic model and simulate the system. To achieve a fast and stable response for the real power control, the intelligent controller consists of a radial basis function network (RBFN) and an improved Elman neural network (ENN) for maximum power point tracking (MPPT). The pitch angle of wind turbine is controlled by the ENN, and the solar system uses RBFN, where the output signal is used to control the dc/dc boost converters to achieve the MPPT.

Method for distributed power harvesting using DC power sources

Abstract: A system and method for combining power from DC power sources. Each power source is coupled to a converter. Each converter converts input power to output power by monitoring and maintaining the input power at a maximum power point. Substantially all input power is converted to the output power, and the controlling is performed by allowing output voltage of the converter to vary. The converters are coupled in series. An inverter is connected in parallel with the series connection of the converters and inverts a DC input to the inverter from the converters into an AC output. The inverter maintains the voltage at the inverter input at a desirable voltage by varying the amount of the series current drawn from the converters. The series current and the output power of the converters, determine the output voltage at each converter.

A New Maximum Power Point Tracking Technique for Permanent Magnet Synchronous Generator Based Wind Energy Conversion System

Abstract: A new maximum power point tracking technique for permanent magnet synchronous generator based wind energy conversion systems is proposed. The technique searches for the system optimum relationship for maximum power point tracking and then controls the system based on this relationship. The validity of the technique is theoretically analyzed, and the design procedure is presented. The primary merit of the proposed technique is that it does not require an anemometer or preknowledge of a system, but has an accurate and fast response to wind speed fluctuations. Moreover, it has the ability of online updating of time-dependant turbine or generator parameter shift. The validity and performance of the proposed technique are confirmed by MATLAB/Simulink simulations and experimentations.

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.

Probabilistic Load Flow Including Wind Power Generation

Abstract: In this paper, a procedure is established for calculating the load flow probability density function in an electrical power network, taking into account the presence of wind power generation. The probability density function of the power injected in the network by a wind turbine is first obtained by utilizing a quadratic approximation of its power curve. With this model, the DC power flow of a network is calculated, considering the probabilistic nature of the power injected or consumed by the generators and the loads.

DC microgrids in buildings and data centers

Abstract: The debate on the use of Direct Current (DC) as a power distribution means has been raging for decades. Recently, one focus of the discussion has been the data center. For various reasons, AC remains the preferred method of power distribution in the data center, despite some disadvantages inherent to AC power. This is particularly interesting when one considers the fact that almost all of the critical payloads in the data center are DC loads.

VSC MTDC systems with a distributed DC voltage control - A power flow approach

Abstract: In this paper, a power flow model is presented to include a DC voltage droop control or distributed DC slack bus in a Multi-terminal Voltage Source Converter High Voltage Direct Current (VSC MTDC) grid. The available VSC MTDC models are often based on the extension of existing point-to-point connections and use a single DC slack bus that adapts its active power injection to control the DC voltage. A distributed DC voltage control has significant advantages over its concentrated slack bus counterpart, since a numbers of converters can jointly control the DC system voltage. After a fault, a voltage droop controlled DC grid converges to a new working point, which impacts the power flows in both the DC grid and the underlying AC grids. Whereas current day research is focussing on the dynamic behaviour of such a system, this paper introduces a power flow model to study the steady-state change of the combined AC/DC system as a result of faults and transients in the DC grid. The model allows to incorporate DC grids in a N-1 contingency analysis, thereby including the effects of a distributed voltage control on the power flows in both the AC and DC systems.

Control method for a wind turbine

Abstract: The invention relates to a method of controlling a wind turbine having a rotor with pitchable wind turbine blades and a generator for producing power, where a pitch reference value for the wind turbine blades is determined, and an operational parameter representing a loading on the wind turbine rotor exerted by the wind is measured at time intervals. A variation parameter reflecting a variation of the operational parameter over time is determined and used in the determination of a minimum pitch limit value of the pitch reference value. The wind turbine is then controlled according to the pitch reference value only if the pitch reference value is above or equal to the minimum pitch limit value, and otherwise according to the minimum pitch limit value. The invention further relates to a method of controlling the change in the operational parameter as measured in two successive time steps is determined and the turbine then being controlled according to a safety control strategy if the difference between the operational parameter change and the variation parameter is above a certain alert threshold. The invention further relates to a control system configured to perform the above control method, and a wind turbine comprising such system.

A Multivariable Perturb-and-Observe Maximum Power Point Tracking Technique Applied to a Single-Stage Photovoltaic Inverter

Abstract: In this paper, a novel maximum power point tracking algorithm based on the perturb-and-observe (P&O) technique is introduced. The novelty of the approach is represented by the perturbation of more control variables, rather than just one. This allows the increase of the power extracted from the photovoltaic (PV) field as compared to the case of perturbation of a single control variable. The proposed technique overcomes the limitations of any existing tracking technique dedicated to PV arrays exhibiting a unique maximum power point, thus not only of the P&O approach, whenever dynamic constraints ensuring the correct system behavior must be fulfilled too. The proposed multivariable approach is described by means of its application to a single-stage one-cycle controlled PV inverter.

A study of maximum power point tracking algorithms for wind energy system

Abstract: This paper reviews and studies the state-of the-art of available maximum power point tracking (MPPT) algorithms. Due to the nature of the wind that is instantaneously changing, hence, there is only one optimal generator speed is desirable at one time that ensures the maximum energy is harvested from the available wind. Therefore, it is essential to include a controller that is able to track the maximum peak regardless of any wind speed. The available maximum power point tracking (MPPT) algorithms can be classified according to the control variable, namely with and without sensor, and also the technique used to locate the maximum peak. A comparison has been made on the performance of the selected MPPT algorithms on the basis of various speed responses and the ability to achieve the maximum energy yield. The tracking performance is performed by simulating wind energy system using MATLAB/Simulink simulation package. Besides that, a brief and critical discussion is made on the differences of available MPPT algorithms for wind energy system. Finally, a conclusion is drawn.

Performance and Economic Analysis of Distributed Power Electronics in Photovoltaic Systems

Abstract: Distributed electronics like micro-inverters and DC-DC converters can help recover mismatch and shading losses in photovoltaic (PV) systems. Under partially shaded conditions, the use of distributed electronics can recover between 15-40% of annual performance loss or more, depending on the system configuration and type of device used. Additional value-added features may also increase the benefit of using per-panel distributed electronics, including increased safety, reduced system design constraints and added monitoring and diagnostics. The economics of these devices will also become more favorable as production volume increases, and integration within the solar panel?s junction box reduces part count and installation time. Some potential liabilities of per-panel devices include increased PV system cost, additional points of failure, and an insertion loss that may or may not offset performance gains under particular mismatch conditions.

Overview of maximum power point tracking technologies for photovoltaic power systems

Abstract: Photovoltaic modules have a single operating point where the output of the voltage and current results in the maximum power output. In most photovoltaic power systems, a particular control algorithm, namely, maximum power point tracking (MPPT) is utilized to take full advantage of the available solar energy. The operation of maximum power point tracking is to adjust the power interfaces so that the operating characteristics of the load and the photovoltaic array match at the maximum power points. This study reviews the latest techniques and provides background knowledge about the recent development in MPPT techniques. The paper can be used as a reference for future research related to optimizing the solar power generation.

Operation and Control-Oriented Modeling of a Power Converter for Current Balancing and Stability Improvement of DC Active Distribution Networks

Abstract: Future active distribution networks appear as a solution to the energy distribution challenges. In this context, dc systems show potential for reducing losses and electronic equipment costs. Power electronics is the main enabler to this initiative and strong research efforts are ongoing in order to find solutions and evaluate the benefits and requirements for the power converters to be applied in dc systems. There is evidence that bipolar dc networks are advantageous due to higher reliability and increased power transmission capability. In such a network, currents are typically unbalanced and, thus, increase feeder losses. Another challenge in dc active distribution networks is the overall voltage stability due to the presence of distributed energy resources and loads with their power electronics interfaces. This study proposes a power converter and its control principles, which is able to balance the currents in a bipolar dc network and improve its stability. Its operation principles, control-oriented modeling, and laboratory implementation are presented and verified through experiments.

MPPT Battery Charger for Stand-Alone Wind Power System

Abstract: In this paper, a buck-type power converter as the battery charger for the stand-alone wind power system is proposed. The proposed power converter can harvest the maximum power from the wind turbine while generating pulsating current for the battery bank to improve the charging efficiency. The maximum power point tracking function is realized by the constant on-time control, the circuit parameter design of the power converter, and the characteristics of wind turbine. The pulsating battery charging current is implemented by the discontinuous conduction mode operation of the proposed power converter. Also, the overspeed protection of the wind turbine can be naturally achieved when high power output occurs. Circuit simplicity and high reliability are the major advantages of the proposed power converter. Hardware experimental results from a 400-W prototype circuit are presented to verify the performance of the proposed power converter.

A variable speed wind generator maximum power tracking based on adaptative neuro-fuzzy inference system

Abstract: The power from wind varies depending on the environmental factors. Many methods have been proposed to locate and track the maximum power point (MPPT) of the wind, such as the fuzzy logic (FL), artificial neural network (ANN) and neuro-fuzzy. In this paper, a variable-speed wind-generator maximum-power-point-tracking (MPPT) based on adaptative neuro-fuzzy inference system (ANFIS) is presented. It is designed as a combination of the Sugeno fuzzy model and neural network. The ANFIS model is used to predict the optimal speed rotation using the variation of the wind speed as the input. The wind energy conversion system (WECS) employing a permanent magnet synchronous generator connected to a DC bus using a power converter is presented. A wind speed step model was used in the design phase. The performance of the WECS with the proposed ANFIS controller is tested for fast wind speed variation. Simulation results showed the possibility of achieving maximum power tracking for the wind and output voltage regulation for the DC bus simultaneously with the ANFIS controller. The results also proved the good response and robustness of the control system proposed.

Maximum Power Point Tracking using Fuzzy Logic Control for Photovoltaic Systems

Abstract: Renewable energy sources have a great concern nowa-days to overcome the conventional energy source problem. The solar energy is one of the renewable energy that is implemented in different scale. The Photovoltaic (PV) cell is used to convert solar energy into electrical energy. The PV has nonlinear characteristics between its current and voltage. In addition, the PV power is highly sensitive to the atmospheric conditions, in particular temperature and solar radiation. This makes the PV has different equilibrium points. Therefore, selecting equilibrium points that extract the maximum allowable power of the PV is mandatory in order to enhance the PV system efficiency and robustness [1]. The controller that can select the optimal operating point is defined as the Maximum Power Point Tracking (MPPT). MPPT is addressed by different techniques scattered in literatures. This paper proposes a modified Fuzzy algorithm for MPPT of the PV system in order to enhance its performance, in transient and steady state, and robustness and accelerate the recovery time due to a sudden change in the connected load. A comparison between the proposed technique and conventional techniques is illustrated.