Showing papers by "Marco Liserre 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.

Overview of Multi-MW Wind Turbines and Wind Parks

Abstract: Multimegawatt wind-turbine systems, often organized in a wind park, are the backbone of the power generation based on renewable-energy systems. This paper reviews the most-adopted wind-turbine systems, the adopted generators, the topologies of the converters, the generator control and grid connection issues, as well as their arrangement in wind parks.

Filter-Based Active Damping of Voltage Source Converters With $LCL$ Filter

Abstract: Pulsewidth modulation (PWM) voltage source converters are becoming a popular interface to the power grid for many applications. Hence, issues related to the reduction of PWM harmonics injection in the power grid are becoming more relevant. The use of high-order filters like LCL filters is a standard solution to provide the proper attenuation of PWM carrier and sideband voltage harmonics. However, those grid filters introduce potentially unstable dynamics that should be properly damped either passively or actively. The second solution suffers from control and system complexity (a high number of sensors and a high-order controller), even if it is more attractive due to the absence of losses in the damping resistors and due to its flexibility. An interesting and straightforward active damping solution consists in plugging in, in cascade to the main controller, a filter that should damp the unstable dynamics. No more sensors are needed, but there are open issues such as preserving the bandwidth, robustness, and limited complexity. This paper provides a systematic approach to the design of filter-based active damping methods. The tuning procedures, performance, robustness, and limitations of the different solutions are discussed with theoretical analysis, selected simulation, and experimental results.

Grid-Filter Design for a Multimegawatt Medium-Voltage Voltage-Source Inverter

Abstract: This paper describes the design procedure and performance of an LCL grid filter for a medium-voltage neutral-point clamped converter to be adopted for a multimegawatt (multi-MW) wind turbine. The unique filter design challenges in this application are driven by a combination of the medium-voltage converter, a limited allowable switching frequency, component physical size and weight concerns, and the stringent limits for allowable injected current harmonics. Traditional design procedures of grid filters for lower power and higher switching frequency converters are not valid for a multi-MW filter connecting a medium-voltage converter switching at low frequency to the electric grid. This paper demonstrates a frequency-domain-model-based approach to determine the optimum filter parameters that provide the necessary performance under all operating conditions given the necessary design constraints. To achieve this goal, new concepts, such as virtual-harmonic content and virtual filter losses are introduced. Moreover, a new passive-damping technique that provides the necessary damping with low losses and very little degradation of the high-frequency attenuation is proposed.

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.

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.

Performance Evaluation of Active Islanding-Detection Algorithms in Distributed-Generation Photovoltaic Systems: Two Inverters Case

Abstract: Grid-connected photovoltaic (PV) inverters employ an islanding-detection functionality in order to determine the status of the electrical grid. In fact, the inverter must be stopped once the islanding operating mode is detected according to standards and grid-code limits. Diverse islanding-detection algorithms have been proposed in literature to cope with this safety requirement. Among them, active methods based on the deliberate perturbation of the inverter behavior can minimize the so-called nondetection zone, which is a range of conditions in which the inverter does not recognize that it is operating in an undesired island. In most cases, the performances of these methods have been analyzed considering a highly dispersed generation scheme, where only one distributed-generation power system is connected to the local electrical power system (EPS). However, in some studies, it has been highlighted that if two or more PV inverters are connected to the same local EPS, their anti-islanding algorithms do not behave ideally and can fail in detecting the islanding condition. However, there is no systematic study that has investigated the overall capability of different anti-islanding methods employed on several inverters connected to the same EPS to detect islanding condition. This paper is a first attempt to carry out a systematic study of the performances of the most common active detection methods in a case of two inverters connected to the same EPS. In order to evaluate the global capability of the two systems to detect islanding condition, a new performance index is introduced and applied also to the case when the two inverters employ different anti-islanding algorithms.

Robustness analysis of active damping methods for an inverter connected to the grid with an LCL-filter

Abstract: Grid-connected converters usually employ an LCL-filter to reduce PWM harmonics. To avoid the well-known stability problems it is requested to use either passive or active damping methods. Active damping methods avoid losses and preserve the filter effectiveness but they are more sensitive to parameters variation. In this paper the robustness of active damping methods is investigated considering those using only the same state variable (grid-side or converter-side current) normally used for current control (filter-based) or those methods using more state-variables (multiloop). Simulation and experimental results validate the analysis.

Grid Synchronization in ThreePhase Power Converters

Abstract: This chapter contains sections titled: Introduction The Three-Phase Voltage Vector under Grid Faults The Synchronous Reference Frame PLL under Unbalanced and Distorted Grid Conditions The Decoupled Double Synchronous Reference Frame PLL (DDSRF-PLL) The Double Second-Order Generalized Integrator FLL (DSOGI-FLL) Summary References

Control of Grid Converters under Grid Faults

Abstract: This chapter contains sections titled: Introduction Overview of Control Techniques for Grid-Connected Converters under Unbalanced Grid Voltage Conditions Control Structures for Unbalanced Current Injection Power Control under Unbalanced Grid Conditions Flexible Power Control with Current Limitation Summary References

Thermal analysis of multilevel grid side converters for 10 MW wind turbines under Low Voltage Ride Through

Abstract: As the power level of a single wind turbine is continuously pushed up even to 7 MW, the wind power generation system are required to be more reliable, and able to withstand extreme grid disturbances. Moreover, it is becoming a need that the wind power generation system should be more active, and able to contribute to the grid recovery by injecting reactive current during grid faults. Consequently, the full-scale power converter solutions are becoming more and more popular to fulfill the growing challenges in the wind power application. Nevertheless, the loading of the power devices in full-scale power converters, especially during grid faults may compromise the reliability performance and further increase the cost of the system. In this paper, three promising grid side multilevel converter topologies for the next generation 10 MW wind turbines are proposed and basically designed as case study. The operation status, as well as loss and thermal distributions of power devices are investigated, simulated and compared aimed at various Low Voltage Ride Through (LVRT) conditions. It is found that the all of the proposed converter topologies will suffer from higher junction temperature in some heavy loaded power devices especially the diodes under LVRT, and both of the three-level and five-level H-bridge topologies show more potential to reduce the device stress than the well-known three-level Neutral Point Clamped topology.

Gain-scheduling-based droop control for universal operation of small wind turbine systems

Abstract: Universal operation of small-power wind turbine systems (grid-connected and island mode) may increase their penetration in the power systems. This paper proposes the use of gain scheduling to adapt the droop control gains to the different operation modes. It allows to achieve fast dynamic response in grid-connected mode and small voltage and frequency variations in island mode. An energy storage system contributes to ensure power balance between the wind turbine and the loads demand in island mode. The effectiveness of the proposed control method is verified by simulation and experimental results.

Photovoltaic Inverter Structures

Abstract: This chapter contains sections titled: Introduction Inverter Structures Derived from H-Bridge Topology Inverter Structures Derived from NPC Topology Typical PV Inverter Structures Three-Phase PV Inverters Control Structures Conclusions and Future Trends References

Grid Requirements for PV

Abstract: This chapter contains sections titled: Introduction International Regulations Response to Abnormal Grid Conditions Power Quality Anti-islanding Requirements Summary References

Stability analysis of grid inverter LCL-filter resonance in wind or photovoltaic parks

Abstract: Typically the resonance problems related to the use of LCL-filters in grid connected inverters are analyzed assuming the operation of a single inverter. Wind and photovoltaic parks may experience propagation of resonance from a poorly damped inverter to other systems connected in parallel. The paper focuses on the study of the resonance at a park system level with simulations and experimental results.

Grid Converter Control for WTS

Abstract: This chapter contains sections titled: Introduction Model of the Converter AC Voltage and DC Voltage Control Voltage Oriented Control and Direct Power Control Stand-alone, Micro-grid, Droop Control and Grid Supporting Summary References

Fractional-order based droop control of an universal wind-turbine system

Abstract: In this paper it is investigated the use of fractional-order controllers for an universal operation of small-power wind turbine system. Universal inverters should be able to work both connected to the grid both in island mode. Proper active/reactive control strategies are needed to get system work in universal operation. The aim of this paper is to investigate the use of fractional PI (PIα) for active and reactive power control of an universal wind turbine system in order to achieve a better trade-off between dynamical response and stability. The effectiveness of the proposed control method is verified by simulation and experimental results.

Grid Converter Structures for Wind Turbine Systems

Abstract: This chapter contains sections titled: Introduction WTS Power Configurations Grid Power Converter Topologies WTS Control Summary References

Generalized controller for small wind turbines working grid-connected and stand-alone

Abstract: Distributed power generation systems may be required to work in both grid-connected and stand-alone modes for ensuring the supply of critical local loads, maybe organized in micro-grids. Every time the micro-grid is disconnected and reconnected from the grid, a change in the control scheme is required leading to undesired transients and even lost of stability. In this paper, the use of the droop control is extended to both operation modes without commutating the control schemes. An islanding detection method is employed together with a synchronization algorithm achieving a successful micro-grid reconnection procedure. Simulation results prove the effectiveness of the proposed solution.

Grid Filter Design

Abstract: This chapter contains sections titled: Introduction Filter Topologies Design Considerations Practical Examples of LCL Filters and Grid Interactions Resonance Problem and Damping Solutions Nonlinear Behaviour of the Filter Summary References

Grid Current Control

Abstract: This chapter contains sections titled: Introduction Current Harmonic Requirements Linear Current Control with Separated Modulation Modulation Techniques Operating Limits of the Current-Controlled Converter Practical Example Summary References

Grid Requirements for WT Systems

Abstract: This chapter contains sections titled: Introduction Grid Code Evolution Frequency and Voltage Deviation under Normal Operation Active Power Control in Normal Operation Reactive Power Control in Normal Operation Behaviour under Grid Disturbances Discussion of Harmonization of Grid Codes Future Trends Summary References

Appendix B: Instantaneous Power Theories

Abstract: This appendix contains sections titled: 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 References

Harmonic control strategy for universal operation of wind turbine systems

Abstract: Universal wind power generation systems (WPGS) should be able to operate both grid-connected and in island mode without compromising the power quality. The control system of a universal WPGS has to manage the different connections and provide harmonic disturbances compensation. This paper proposes the use of resonant filters for harmonics rejection both in grid-connected and island operation mode but within a different control structure. The proposed control has been tested in simulation.

Appendix A: Space Vector Transformations of ThreePhase Systems

Abstract: This appendix contains sections titled: A1 Introduction A2 Symmetrical Components in the Frequency Domain A3 Symmetrical Components in the Time Domain A4 Components ?> ?>0 on the Stationary Reference Frame A5 Components dq 0 on the Synchronous Reference Frame References