Showing papers on "Maximum power point tracking published in 2011"
Book•
21 Feb 2011TL;DR: In this article, the authors present an overview of the Grid Converter and its application in photovoltaic (PV) power converters, including the following: 1.1 Introduction. 2.3 Inverter Structures Derived from H-Bridge Topology. 3.4 Power Quality. 4.5 Adaptive Filtering.
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.
2,509 citations
25 Jul 2011
TL;DR: This chapter discusses Wind Energy Conversion System Configurations, which consists of Configuration of Fixed-Speed Wind Energy Systems, and Super- and Sub-synchronous Operation of DFIG, the largest and most complex of these 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.
1,007 citations
TL;DR: Simulation and hardware implementation of incremental conductance maximum power point tracking (MPPT) used in solar array power systems with direct control method and results indicate the feasibility and improved functionality of the system.
Abstract: This paper presents simulation and hardware implementation of incremental conductance (IncCond) maximum power point tracking (MPPT) used in solar array power systems with direct control method. The main difference of the proposed system to existing MPPT systems includes elimination of the proportional-integral control loop and investigation of the effect of simplifying the control circuit. Contributions are made in several aspects of the whole system, including converter design, system simulation, controller programming, and experimental setup. The resultant system is capable of tracking MPPs accurately and rapidly without steady-state oscillation, and also, its dynamic performance is satisfactory. The IncCond algorithm is used to track MPPs because it performs precise control under rapidly changing atmospheric conditions. MATLAB and Simulink were employed for simulation studies, and Code Composer Studio v3.1 was used to program a TMS320F2812 digital signal processor. The proposed system was developed and tested successfully on a photovoltaic solar panel in the laboratory. Experimental results indicate the feasibility and improved functionality of the system.
974 citations
TL;DR: A determinist energy management system for a microgrid, including advanced PV generators with embedded storage units and a gas microturbine is proposed, which is implemented in two parts: a central energy management of the microgrid and a local power management at the customer side.
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.
905 citations
TL;DR: In this article, an optimal power management mechanism for grid connected photovoltaic (PV) systems with storage is presented, where the structure of a power supervisor based on an optimal predictive power scheduling algorithm is proposed.
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.
902 citations
TL;DR: In this article, a design example is presented by experimental implementation of the proposed technique and practical results for the implemented setup at different irradiance levels are illustrated to validate the proposed scheme.
Abstract: Solar photovoltaic (PV) energy has witnessed double-digit growth in the past decade. The penetration of PV systems as distributed generators in low-voltage grids has also seen significant attention. In addition, the need for higher overall grid efficiency and reliability has boosted the interest in the microgrid concept. High-efficiency PV-based microgrids require maximum power point tracking (MPPT) controllers to maximize the harvested energy due to the nonlinearity in PV module characteristics. Perturb and observe (PO second, no steady-state oscillations around the MPP; and lastly, no need for predefined system-dependent constants, hence provides a generic design core. A design example is presented by experimental implementation of the proposed technique. Practical results for the implemented setup at different irradiance levels are illustrated to validate the proposed technique.
774 citations
TL;DR: In this paper, the authors discuss 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.
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.
731 citations
16 May 2011
TL;DR: In this article, the authors discuss and compare via simulation various design options for control systems to manage the reactive power generated by these inverters, and find that local control schemes are able to maintain voltage within acceptable bounds.
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.
707 citations
TL;DR: A novel variable step-size incremental-resistance MPPT algorithm is introduced, which not only has the merits of INC but also automatically adjusts the step size to track the PV array MPP.
Abstract: Maximum power point (MPP) tracking (MPPT) techniques are widely applied in photovoltaic (PV) systems to make PV array generate peak power which depends on solar irradiation. Among all the MPPT strategies, the incremental-conductance (INC) algorithm is widely employed due to easy implementation and high tracking accuracy. In this paper, a novel variable step-size incremental-resistance MPPT algorithm is introduced, which not only has the merits of INC but also automatically adjusts the step size to track the PV array MPP. Compared with the variable step-size INC method, the proposed scheme can greatly improve the MPPT response speed and accuracy at steady state simultaneously. Moreover, it is more suitable for practical operating conditions due to a wider operating range. This paper provides the theoretical analysis and the design principle of the proposed MPPT strategy. Simulation and experimental results verify its feasibility.
599 citations
TL;DR: In this article, a distributed control strategy based on improved dc bus signaling is proposed for a modular photovoltaic (PV) generation system with battery energy storage elements, which is composed of three modular dc/dc converters for PV arrays, two grid-connected dc/ac converters, and one DC/dc converter for battery charging/discharging and local loads, which are available of either gridconnected operation or islanding operation.
Abstract: Modular generation system, which consists of modular power conditioning converters, is an effective solution to integrate renewable energy sources with conventional utility grid to improve reliability and efficiency, especially for photovoltaic generation. A distributed control strategy based on improved dc bus signaling is proposed for a modular photovoltaic (PV) generation system with battery energy storage elements. In this paper, the modular PV generation system is composed of three modular dc/dc converters for PV arrays, two grid-connected dc/ac converters, and one dc/dc converter for battery charging/discharging and local loads, which is available of either grid-connected operation or islanding operation. By using the proposed control strategy, the operations of a modular PV generation system are categorized into four modes: islanding with battery discharging, grid-connected rectification, grid-connected inversion, and islanding with constant voltage (CV) generation. The power balance of the system under extreme conditions such as the islanding operation with a full-charged battery is taken into account in this control strategy. The dc bus voltage level is employed as an information carrier to distinguish different modes and determine mode switching. Control methods of modular dc/dc converters, battery converter, and grid-connected converter are addressed. An autonomous control method for modular dc/dc converters is proposed to realize smooth switching between CV operation and maximum power point tracking operation, which enables the dc bus voltage regulation capability of modular dc/dc converters. Seamless switching of a battery converter between charging and discharging and that of a grid-connected converter between rectification and inversion are ensured by the proposed control methods. Experiments verify the practical feasibility and the effectiveness of the proposed control strategies.
585 citations
TL;DR: In this article, a fuzzy-logic controller for maximum power point tracking of photovoltaic (PV) systems is proposed, which improves the hill-climbing search method by fuzzifying the rules of such techniques and eliminates their drawbacks.
Abstract: A new fuzzy-logic controller for maximum power point tracking of photovoltaic (PV) systems is proposed. PV modeling is discussed. Conventional hill-climbing maximum power-point tracker structures and features are investigated. The new controller improves the hill-climbing search method by fuzzifying the rules of such techniques and eliminates their drawbacks. Fuzzy-logic-based hill climbing offers fast and accurate converging to the maximum operating point during steady-state and varying weather conditions compared to conventional hill climbing. Simulation and experimentation results are provided to demonstrate the validity of the proposed fuzzy-logic-based controller.
TL;DR: In this paper, the authors modeled the inverters of a photovoltaic (PV) plant as a multivariable system and analyzed the effect of the number of paralleled grid-connected inverters and the grid impedance.
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.
TL;DR: A novel MPPT algorithm is proposed by introducing a particle swarm optimization (PSO) technique that uses only one pair of sensors to control multiple PV arrays, thereby resulting in lower cost, higher overall efficiency, and simplicity with respect to its implementation.
Abstract: Multiple photovoltaic (PV) modules feeding a common load is the most common form of power distribution used in solar PV systems. In such systems, providing individual maximum power point tracking (MPPT) schemes for each of the PV modules increases the cost. Furthermore, its v-i characteristic exhibits multiple local maximum power points (MPPs) during partial shading, making it difficult to find the global MPP using conventional single-stage (CSS) tracking. To overcome this difficulty, the authors propose a novel MPPT algorithm by introducing a particle swarm optimization (PSO) technique. The proposed algorithm uses only one pair of sensors to control multiple PV arrays, thereby resulting in lower cost, higher overall efficiency, and simplicity with respect to its implementation. The validity of the proposed algorithm is demonstrated through experimental studies. In addition, a detailed performance comparison with conventional fixed voltage, hill climbing, and Fibonacci search MPPT schemes are presented. Algorithm robustness was verified for several complicated partial shading conditions, and in all cases this method took about 2 s to find the global MPP.
TL;DR: An improved maximum power point tracking with better performance based on voltage-oriented control (VOC) is proposed to solve a fast-changing irradiation problem andSimulations and experimental results demonstrate that the proposed method provides effective, fast, and perfect tracking.
Abstract: In this paper, an improved maximum power point (MPP) tracking (MPPT) with better performance based on voltage-oriented control (VOC) is proposed to solve a fast-changing irradiation problem. In VOC, a cascaded control structure with an outer dc link voltage control loop and an inner current control loop is used. The currents are controlled in a synchronous orthogonal d,q frame using a decoupled feedback control. The reference current of proportional-integral (PI) d-axis controller is extracted from the dc-side voltage regulator by applying the energy-balancing control. Furthermore, in order to achieve a unity power factor, the q-axis reference is set to zero. The MPPT controller is applied to the reference of the outer loop control dc voltage photovoltaic (PV). Without PV array power measurement, the proposed MPPT identifies the correct direction of the MPP by processing the d-axis current reflecting the power grid side and the signal error of the PI outer loop designed to only represent the change in power due to the changing atmospheric conditions. The robust tracking capability under rapidly increasing and decreasing irradiance is verified experimentally with a PV array emulator. Simulations and experimental results demonstrate that the proposed method provides effective, fast, and perfect tracking.
TL;DR: In this paper, a novel MPPT method capable of RMPPT under partially shaded conditions (PSCs) is proposed, which is analyzed according to the RMPP position and verified by simulation and experimental results.
Abstract: Conventional popular maximum power point tracking (MPPT) methods are effective under uniform solar irradiance. However, under solar irradiance mismatching conditions [partially shaded conditions (PSCs)], these MPPTs can fail for real MPPT (RMPPT), because multiple local maxima can be exhibited on the power-voltage characteristic curve. Although some researchers have worked on RMPPT under partial shading conditions, the methods have some drawbacks in terms of complexity and requirements for additional circuits, etc. In this paper, a novel MPPT method capable of RMPPT under PSCs is proposed. The performance of the proposed MPPT method is analyzed according to the RMPP position and is verified by simulation and experimental results.
TL;DR: Underlines weak points of standard reactive power strategies which are already imposed by certain grid codes, and introduces a new reactive power control method that is based on sensitivity analysis that combines two droop functions that are inherited from the standard cos φ(P) and Q(U) strategies.
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.
Proceedings Article•
15 Jun 2011TL;DR: A 0.35µm CMOS energy processor with multiple inputs from solar, thermal and vibration energy sources is presented and a novel low power maximum power point tracking (MPPT) scheme with 95% tracking efficiency is introduced.
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.
TL;DR: In this article, the authors present a novel control strategy for achieving maximum benefits from these grid-interfacing inverters when installed in 3-phase 4-wire distribution systems, where the inverter is controlled to perform as a multi-function device by incorporating active power filter functionality.
Abstract: Renewable energy resources (RES) are being increasingly connected in distribution systems utilizing power electronic converters. This paper presents a novel control strategy for achieving maximum benefits from these grid-interfacing inverters when installed in 3-phase 4-wire distribution systems. The inverter is controlled to perform as a multi-function device by incorporating active power filter functionality. The inverter can thus be utilized as: 1) power converter to inject power generated from RES to the grid, and 2) shunt APF to compensate current unbalance, load current harmonics, load reactive power demand and load neutral current. All of these functions may be accomplished either individually or simultaneously. With such a control, the combination of grid-interfacing inverter and the 3-phase 4-wire linear/non-linear unbalanced load at point of common coupling appears as balanced linear load to the grid. This new control concept is demonstrated with extensive MATLAB/Simulink simulation studies and validated through digital signal processor-based laboratory experimental results.
TL;DR: A novel peak detection capability has been devised which, in contrast with conventional peak detection, can work robustly under changing wind conditions and performs self-tuning to cope with the nonconstant efficiencies of the generator-converter subsystems.
Abstract: This paper proposes a novel solution to the problems that exist in the conventional hill climb searching (HCS) maximum power point tracking (MPPT) algorithm for the wind energy conversion system. The presented solution not only solves the tracking speed versus control efficiency tradeoff problem of HCS but also makes sure that the changing wind conditions do not lead HCS in the wrong direction. It intelligently adapts the variable step size to keep up with the rapid changes in the wind and seizes the perturbation at the maxima to yield 100% control efficiency. For this purpose, a novel peak detection capability has been devised which, in contrast with conventional peak detection, can work robustly under changing wind conditions. The proposed MPPT performs self-tuning to cope with the nonconstant efficiencies of the generator-converter subsystems-a phenomenon quite rarely discussed in research papers so far. In addition, a smart speed-sensorless scheme has been developed to avoid the use of mechanical sensors. The experimental results confirm that the proposed algorithm is remarkably faster and more efficient than the conventional HCS.
TL;DR: A hybrid of indoor ambient light and thermal energy harvesting scheme that uses only one power management circuit to condition the combined output power harvested from both energy sources is proposed to extend the lifetime of the wireless sensor node.
Abstract: In this paper, a hybrid of indoor ambient light and thermal energy harvesting scheme that uses only one power management circuit to condition the combined output power harvested from both energy sources is proposed to extend the lifetime of the wireless sensor node. By avoiding the use of individual power management circuits for multiple energy sources, the number of components used in the hybrid energy harvesting (HEH) system is reduced and the system form factor, cost and power losses are thus reduced. An efficient microcontroller-based ultra low power management circuit with fixed voltage reference based maximum power point tracking is implemented with closed-loop voltage feedback control to ensure near maximum power transfer from the two energy sources to its connected electronic load over a wide range of operating conditions. From the experimental test results obtained, an average electrical power of 621 μW is harvested by the optimized HEH system at an average indoor solar irradiance of 1010 lux and a thermal gradient of 10 K, which is almost triple of that can be obtained with conventional single-source thermal energy harvesting method.
TL;DR: In this article, the authors investigated three methods that can be used to reduce the fluctuations in the power generated from a large customer-owned photovoltaic (PV) system, in the order of megawatts.
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.
TL;DR: In this paper, a high-efficiency inverter using MOSFETs for all active switches is presented for photovoltaic, non-isolated, ac-module applications.
Abstract: A novel, high-efficiency inverter using MOSFETs for all active switches is presented for photovoltaic, nonisolated, ac-module applications. The proposed H6-type configuration features high efficiency over a wide load range, low ground leakage current, no need for split capacitors, and low-output ac-current distortion. The detailed power stage operating principles, pulsewidth modulation scheme, associated multilevel bootstrap power supply, and integrated gate drivers for the proposed inverter are described. Experimental results of a 300 W hardware prototype show that not only are MOSFET body diode reverse-recovery and ground leakage current issues alleviated in the proposed inverter, but also that 98.3% maximum efficiency and 98.1% European Union efficiency of the dc-ac power train and the associated driver circuit are achieved.
01 Nov 2011
TL;DR: In this article, power converter technologies are reviewed with focus on single/multi-cell power converter topologies and case studies on the Low Voltage Ride Through demand to power converter technology are presented including a discussion on reliability.
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.
TL;DR: In this paper, an algorithm based on dc link voltage is proposed for effective energy management of a standalone permanent magnet synchronous generator (PMSG)-based variable speed wind energy conversion system consisting of battery, fuel cell, and dump load (i.e., electrolyzer).
Abstract: In this paper, a novel algorithm, based on dc link voltage, is proposed for effective energy management of a standalone permanent magnet synchronous generator (PMSG)-based variable speed wind energy conversion system consisting of battery, fuel cell, and dump load (i.e., electrolyzer). Moreover, by maintaining the dc link voltage at its reference value, the output ac voltage of the inverter can be kept constant irrespective of variations in the wind speed and load. An effective control technique for the inverter, based on the pulsewidth modulation (PWM) scheme, has been developed to make the line voltages at the point of common coupling (PCC) balanced when the load is unbalanced. Similarly, a proper control of battery current through dc-dc converter has been carried out to reduce the electrical torque pulsation of the PMSG under an unbalanced load scenario. Based on extensive simulation results using MATLAB/SIMULINK, it has been established that the performance of the controllers both in transient as well as in steady state is quite satisfactory and it can also maintain maximum power point tracking.
TL;DR: This paper investigates the issues of ensuring global power optimization for cascaded dc-dc converter architectures of photovoltaic (PV) generators irrespective of the irradiance conditions and proposes a supervisory algorithm that attempts to establish the best suboptimal power regime.
Abstract: This paper investigates the issues of ensuring global power optimization for cascaded dc-dc converter architectures of photovoltaic (PV) generators irrespective of the irradiance conditions. The global optimum of such connections of PV modules is generally equivalent with performing the maximum power point tracking (MPPT) on all the modules. The most important disturbance occurs when the irradiance levels of modules happen to be sensibly different from a module to another - in this case, voltage-limitation requirements may be broken. The proposed supervisory algorithm then attempts to establish the best suboptimal power regime. Validation has been achieved by MATLAB/Simulink numerical simulation in the case of a single-phase grid-connected PV system, where individual MPPTs have been implemented by an extremum-seeking control, a robust and less-knowledge-demanding perturb-and-observe method.
TL;DR: A stand-alone hybrid power system consists of solar power, wind power, diesel engine, and an intelligent power controller that consists of a radial basis function network and an improved Elman neural network for maximum power point tracking.
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.
10 Nov 2011
TL;DR: A one-day-ahead PV power output forecasting model for a single station is derived based on the weather forecasting data, actual historical power output data, and the principle of SVM and results show the proposed forecast model for grid-connected PV systems is effective and promising.
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.
20 Mar 2011
TL;DR: In this paper, the inverter volt/var control for PV deployment on the distribution system is discussed and simulations are performed to illustrate the effectiveness of this type of control for photovoltaic deployment.
Abstract: Small- and large-scale wind and solar photovoltaic (PV) generation systems are interconnecting to the distribution system at a rapid pace. Penetration limits are often imposed due to the impact these additional distributed resource can have on voltage. In order to accommodate high penetration scenarios without impacting power quality or reliability, additional control functions must be utilized. A recent industry collaborative effort has identified key functions that allow these additional resources to coordinate with grid operations and provide a more grid-friendly response. This paper addresses one of these functions, inverter volt/var control. Simulations are performed to illustrate the effectiveness of this type of control for PV deployment on the distribution system.
TL;DR: A continuous dynamic model and a control design of the power system studied are proposed in this paper, which makes it possible to ensure a high battery state of charge and overcharge security by designing a dedicated local control system.
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.
TL;DR: In this paper, generalized power control strategies based on symmetric-sequence components are proposed to manipulate the delivered instantaneous power under unbalanced voltage dips, and two strategies for simultaneous active and reactive power control are proposed that preserve flexible controllability.
Abstract: During voltage dips continuous power delivery from distributed generation systems to the grid is desirable for the purpose of grid support. In order to facilitate the control of inverter-based distributed power generation adapted to the expected change of grid requirements, generalized power control strategies based on symmetric-sequence components are proposed in this paper, aiming to manipulate the delivered instantaneous power under unbalanced voltage dips. It is shown that active and reactive power can be independently controlled with two individually adaptable parameters. By changing these parameters, the relative amplitudes of oscillating power can be smoothly regulated, as well as the peak values of three-phase grid currents. As a result, the power control of grid-interactive inverters becomes quite flexible and adaptable to various grid requirements or design constraints. Furthermore, two strategies for simultaneous active and reactive power control are proposed that preserve flexible controllability; an application example is given to illustrate the simplicity and adaptability of the proposed strategies for online optimization control. Finally, experimental results are provided that verify the proposed power control.