PROJECT MICYT 2008 at the UPC

Transcription

1 PROJECT MICYT 2008 at the UPC TITLE: Applicant: Improvement of the power system stability by using FACTS based on WTGs (WTGFACTS) Department of Electrical Engineering Technical University of Catalonia (UPC, Universidad Politécnica de Cataluña), Spain 1.- SUMMARY To maximize the wind energy connected to the grid, guaranteeing the correct operation and the stability in the steady- and transient states of the power system with high wind power penetration, this project proposes simulate and test the next topics: (1) improvements in the wind turbine grid-side converter controllers; (2) the applications of these converters will be extended, including solutions FACTS (Flexible AC Transmission Systems) and, therefore, the new solution will be called WTGFACTS; (3) novel algorithms for advanced grid services support (voltage and frequency) will be included in the wind turbine generator, in order to contribute to the power system dynamic stability. 2.- INTRODUCTION PROPOSED SOLUTION Proposed new features in the wind turbine generator (WTG) power converters. Analysis of the specific advantages of the implementation of FACTS functions: cost, interest of manufacturers and interest of the power system operators. Development of mathematical models, and implementation into a MATLAB/Simulink toolbox for simulation purposes. The various solutions in the field of WTGFACTS will be critically evaluated. Interaction between WTG and other electrical network components in generic situations will be refined. Accurate simulation models for the network and its components, for the electronic power converters and for the WTGs, will be created. Generator and power system stability protections will be analysed. WTGFACTS use evaluation in compliance with the grid codes and with the power system stability and reliability improvement. Based on specific studies of the WTG-network interaction, new recommendations for the grid connection will be proposed. Power quality improvement. Signal active conditioning features will be incorporated in the WTG electronic converter. Some of these features are the selective active filtering, the reactive power compensation and the flicker mitigation.

2 3.- OBJECTIVES OF THE PROJECT SPECIFIC OBJETIVES OF THE PROJECT 1) Search of the latest WTGFACTS research. Exploration of new features in the control of WTG power converters. Analysis of the specific advantages of the implementation of FACTS functions: cost, interest of manufacturers and interest of the power system operators. 2) Development of mathematical models, and implementation into a MATLAB/Simulink toolbox for simulation purposes. The various solutions in the field of WTGFACTS will be critically evaluated. Interaction between WTG and other electrical network components in generic situations will be refined. Accurate simulation models for the network and its components, for the electronic power converters and for the WTGs, will be created. In particular, network elements to be modelled are the power transformers and the synchronous and induction distributed generators which are directly connected to the network (without power converter). In the first simulation stage, these detailed models will be used to study their behaviour as isolated elements when disturbances occur in the grid, particularly when voltage sags are produced as a consequence of faults. The second simulation stage will deal their interaction with the WTGFACTS when the same disturbances are produced in the grid. The results of that interaction will allow the analysis of the generator and power system stability protections. 3) Evaluation of the WTG grid connection codes. The various national and international WTG grid connection codes will be assessed from a technical point of view. Generic situations that are not covered by existing codes will be studied. The WTGFACTS usefulness in the compliance of the grid codes and in the system stability and reliability improvement will be evaluated. Based on specific studies of the WTG-network interaction, new recommendations for the grid connection will be proposed. 4) Design of algorithms for advanced grid services support (voltage, frequency). Implementation of intelligent algorithms for helping to maintain the grid voltage and frequency, i.e. taking into account Thevenin impedance seen from the connection point and the actual active power flow. Design of algorithms for the network Thevenin impedance and the boundary conditions estimation. Design of algorithms for the optimal active and reactive injected power regulation. These algorithms must be optimal from the generation efficiency and from the grid services support points of view. 5) Power quality improvement. Signal active conditioning features will be incorporated in the WTG electronic converter. Some of these features are the selective active filtering, the reactive power compensation and the flicker mitigation. 6) Experimental validation of both the developed studies and the new controller simulation obtained results. Set up of an experimental scale workbench. 7) Publication of the results of this research in technical conferences and journals, as well as in working sessions and seminars with the WTG manufacturers. 4.- METHODOLOGY AND WORKING PLAN Task 1.- Modelled and classification of transient and quasi-stationary grid disturbances, with influence on the technical and economical assignation of the wind generation systems The initial task of the project is the realization of a detailed study about the influential grid faults and disturbances in wind generation systems. Their importance, influence and the type of suitable response will be established. Will be especially analyzed the problem of the voltage dips in the electrical grid.

3 Milestone: At the end of the task, will have a detailed study at disposal, characterizing and modelling the main grid disturbances and faults that affect to wind generation systems. Sub-tasks: Systemization of the nature of transient grid disturbances. Systemization of the nature of quasi-stationary grid disturbances. Modelled of the representative reference values of each grid disturbance typology. Task 2.- Analysis of the actual operation procedures and modification proposal It is about to study the operation procedures of power-frequency control (P.O. 7.1) and voltage control (P.O. 7.4), and to analyse the viability of the different types of wind generation systems (Also considering the possible inclusion of compensation systems) to participate in the ancillary services mentioned in these operation procedures. From this study, it will be proposed the necessary modifications that make possible to take advantage of the capacity of the wind generation systems to contribute to the operation system. Milestone: At the end of this task, will get the necessary modifications in the actual operation procedures that allow wind parks to participate in the ancillary services, according to the type of used technology. Subtasks: Study of the operation procedures P.O. 7.1 and P.O.7.4. Viability analysis of the participation of wind parks in the complementary services. A classification of the complied requirements according to the wind generator technology and the existence of compensation systems will be done. Proposal of modifications in P.O. 7.1 and P.O. 7.4 to include the different types of wind parks in the ancillary services. Task 3.- Search of literature on WTGFACTS Exploration of the existing WTGFACTS proposals, mainly with regard to the distribution network support by derivation connected WTGFACTS. In this stage, the implementation of STATCOM features, power quality active conditioning and power flow regulation will be especially interesting. Furthermore, the international standards about the WTG grid connection will be searched, where possible gaps in the legislation (with regard to the actual needs) will be identified. This task will require a serious effort of study and meditation on the different aspects to be developed in the research work. The critical reasoning and the preliminary working group conclusions will determine the initial expectations resulting from the future research work. Despite this task is defined to be limited in time, the involved activity will remain open throughout the project. Milestone: This task will conclude with a final report that include WTGFACTS technologies which are studied in this project, as well as in a comprehensive analysis to clearly define the working lines. Subtasks: Study of the existing WTGFACTS proposals. Search of the WTG grid connection international standards. Analysis of the main aspects to be developed in this research project.

4 Task 4.- WTGFACTS and other network elements modelling, and evaluation based on their simulation The best simulation platforms for each of the technologies will be considered. Initially, a MATLAB/Simulink toolbox will be designed, but the use of mixed platforms will be also evaluated, such as the implementation of PSCAD, PLECS or MISP power systems controlled from MATLAB/Simulink. The structure and general features of the toolbox resulting from the project will also be defined. In this stage, the models used in the rest of the investigations will be developed here, i.e. models for different network types, wind generator models, basic models for power converters, models for the primary controllers, fault and perturbation models, mechanical models, etc. The library models resulting from this task will be expanded throughout the project development. Despite this task is also defined to be limited in time, it will remain open throughout the project. Milestone: As a result of the extensive simulations developed in this task, strategies to optimize and refine the proposed control techniques will be considered. The conclusions from these simulations will determine the expected performance of the finally implemented WTGFACTS. Subtasks: Development of detailed models for the network elements. For example, linear and non-linear models for the power transformer (the transformer plays a significant role in the perturbations transmission), or the synchronous and induction distributed generators having the stator directly connected to the network (without power converter). These distributed generators are supposed to be located in the proximity of the WTGFACTS). Isolated behaviour exhaustive characterisation of the network elements when disturbances occur in the grid, especially when voltage sags originated by faults are produced. Study of the interaction between the network elements and the WTGFACTS, making model approximations where appropriate. Systematic evaluation of WTGFACTS solutions by considering the features inclusion in the WTG power converter as well as in specific power converters. Contingency analysis included in the standard grid connection codes for WTG, and others not included in such legislation. Suggestion of solutions to the legislation working groups. Task 5.- Design of advanced algorithms for grid support Control systems for the WTG support of the grid voltage and frequency will be designed in this task. Accurate and efficient algorithms for the network monitoring and synchronisation (even in fault conditions) will be used. One of the parameters to be estimated by the monitoring algorithms is the network impedance seen by the power converter. This information, as well as the supplied active power, will be used to determine the power converter injected current in order to efficiently support the voltage in the coupling point, even in fault conditions. Moreover, algorithms for the optimisation of the WTG available power will also be designed to enable its collaboration in the combined control of the grid frequency. Depending on the network conditions (steady-state or transient situations, identified by the monitoring algorithms, and wind conditions) different strategies for power control will be used. Milestone: Development of the control algorithm that allows the supporting by the WTG of the coupling point voltage and frequency, in disturbances presence. Subtasks: Design of control algorithms for the grid supporting, based on the previous requirements.

5 Discretisation of the algorithms, and testing on the simulation platform by considering various network conditions and different locations of the WTG coupling point. Assessment of the algorithms on the experimental workbench by means of the dspace control platform. Incorporation of the algorithms in the DSP-based control system of the WTG power converter. Testing on the experimental workbench. Task 6.- Design of algorithms to improve the power quality of the network The WTG power converter is employed in this task to improve the power quality at the coupling point. Mainly, the harmonic current cancellation feature is required, but also other features are considered, such as flicker reduction, the subsynchronous resonances mitigation or the balanced of the load currents. First of all, the selective active filtering functionality will be designed. This functionality will mitigate the harmonic currents flowing through the network as a result of the existence of non-linear loads. Furthermore, the current harmonic effects on the fixed-speed WT equipped with an induction generator will be studied. Control algorithms will also be designed for the harmonic current cancellation of the doubly fed induction generator (DFIG) when the network can be considered rigid (network with a large short-circuit capacity), and when can be considered weak (network with a small short-circuit capacity). Other control algorithms to be implemented should enable the combined operation of several WTGs in such a way that the filtering capacity of each power converter will be dependent on its apparent power and on its connection point. Milestone: Improvement of the power quality at the coupling point. Subtasks: Design of the active selective filtering feature in the power converter by means of the simulation toolbox. Study of the harmonic current effects on the fixed-speed WT equipped with an induction generator and in the variable-speed WT equipped with a doubly-fed induction generator. Design of control algorithms for the cancellation of the harmonics generated by non-linear loads. Design of control algorithms for the combined operation of several WTGs. Task 7.- Development of the proposed control algorithms on a laboratory wind-generator prototype During the three years of the project, the group will develop prototypes in their researching laboratory to verify the different proposals. In a first stage, the group will use an available programmable voltage generator to supply individually the WTGFACT system and the rest of grid components (transformers, synchronous and induction generators with direct grid connection). In this way, will be validated their behaviour in presence of grid disturbances, mainly voltage dips (the programmable generator applies the voltage in terminals that all the components see when a grid fault happens). In the final stage of the project, the investigation group will develop a prototype as the indicated in Fig. 1. Initially, it is pretended to use a micro-grid constituted by a main generator of 40 kw and several distributed generators of 5 kw with different technologies: synchronous, asynchronous and double-fed. Nowadays, it is possible to control in closed loop the voltage and frequency of the main generator in the mentioned microgrid, being possible to modify the control parameters. In this grid, also there are simulators of the windgenerator mechanical power based on the use of DC motors working in closed loop. To develop this task, it will be necessary to design the suitable hardware to cause transient faults, by means of short-circuits in the

6 power system, or steady-state faults by means of the interchange of connections in the main generator. It will work in the homogenization of the power electronic processors, the mechanical power simulators and the controllers used in distributed generators. Likewise, it is expected to incorporate a power electronic processor that operates as STATCOM in this grid. The modifications in the existing grid will be made gradually and it will involve the final test of the developments carried out in the previous tasks. Considering any generator, firstly the correct operation of the power electronic processor will be tested and the correct operation of the micro-grid injected-current control system will be revised. Also, the correct operation of the protection system will be checked. Next, the correct operation of the mechanical power simulator will be revised and its integration in the above-mentioned structure will be homogenized. Distribution line Transformer Power Electronics AC AC Communication Electronics Transmission line Transformer Control Electronics FACTS Loads Grid supervisor system Fig. 1. Block diagram of the proposal system The grid-variables support and active conditioning algorithms previously designed will be meticulously evaluated on the experimental platform, valuing their properties faced with adverse grid and wind conditions. The observed phenomenon in this stage will infer reflections that enable to improve the development techniques and systems. The correct interpretation of the experimental results will permit to adjust the initially-proposed simulation models. Likewise, the observed behaviours and restrictions in this stage will open new investigation and study lines. In this stage, global conclusions about the performed work will be obtained, which should be strictly argued, coming to represent interesting contributions to the scientific community. Milestone: At the end of this task, will be available experimental results that validate the new proposed algorithms. Subtasks: Set up of the laboratory prototype and the necessary instrumentation. Adaptation and debugging of the algorithms in order to their operation in real-time. Tests and obtain of results.

7 Task 8.- Publication of results and conclusions It is about the redaction of papers and reports showing the techniques, contributions, results and conclusions of this work. This stage of the work should start in the moment that the work group will begin to prove certain grasp in the field of work and its objective will be to document and divulge the performed work. In this regard, the work will be initially expounded in international conferences, and later, attended to the suggestions that could appear in these scientific forums, will be prepared the corresponding papers in international journals of renowned prestige. JUSTIFICATION OF THE HIRED PERSONNEL S REQUEST A Laboratory Technician working full time during 18 months is required. His background must be in the power electronics design in order to collaborate on all laboratory tasks (assembly of the experimental scale workbench and measures), and with knowledge on simulation tools (mainly MATLAB/Simulink) to help in the control algorithms implementation. 5.- BENEFITS DERIVED FROM THE PROJECT, DIFUSION AND EXPLOTATION OF RESULTS This project searched for solutions to the problem of the stability in the electric system when wind generators are integrated in a massive way. The more significant working lines, where scientific contributions will be carried out, will be the following ones: Control algorithms will be developed for wind generators, so that their behaviour is optimized with: uncertainties in parameters of the grid-filter; unknown values in the grid impedance, saturations in the inductances of the grid-filter, etc. Algorithms will be developed to meet the last specifications about grid connection for wind generators, and especially regarding the behaviour under voltage dips in the power systems. It will be carried out a study about the power system stability when wind generators are massively integrated. The conclusions of this study will be very useful, not only for power system operators, but also for manufacturers of wind generators. Algorithms will be implemented so wind turbines take part in the power system ancillary services. Wind generators will be developed with FACTS functions. It will be analyzed the effect of this capacity on the stability of the grid. The success of the project would imply the development of power converters and of algorithms for wind generators that contribute to improve the power system stability and to verify the grid codes. Concerning social aspects, the project will contribute to the development of a technology capable of generating electric power in a more optimal way, by increasing the reliability of the electric system, but at the same time reducing the CO 2 emissions to atmosphere. In this way, it could also allow, not only Spain but also European Union, to reach the future objectives of installed and integrated wind power in the grid. 6.- BACKGROUND OF THE GROUP The working group of the Electrical Engineering Department of the Technical University of Catalonia (UPC) has conducted its activities in the two research priority lines of the department, Power Quality and Control of Electric Drives.

8 The research group has a solid experience that can be divided into three areas: (1) power quality, and more specifically, voltage sag effects on the network elements, (2) modelling of the network elements, (3) study and design of electronic power converters which are connected to the grid, particularly in applications involving renewable energy connection and power quality improvement. The result of all this experience is the publication of its research in international journals, the collaboration on public and private granted projects, the execution of doctoral thesis, and other thesis that are currently under development. The working group of the Department of Electrical Engineering of the UPC has developed next activities directly related to the areas covered in this project: The group has actively investigated in the study of the voltage sag effects on the network elements, and it has collaborated in next public and private granted projects: Analysis of the power quality regarding sags, interruptions and short-term interruptions in the HV and MV distribution network, and its interaction with industrial plants (PIE for the Utility ENHER), Voltage sag effects on the industrial equipment (CICYT DPI ) and Study of the symmetrical and unsymmetrical voltage sag effects on the electrical components (CICYT DPI ). The group has extensively worked in the design and control of active filters, hybrid filters, implementation of active conditioning functions in the power converters of WTGs and in photovoltaic (PV) generation, and has been involved in five public granted projects: Non-linear control applied to the design of the generator-inverter-load set (CICYT TAP C03-03), DC/AC conversion in multi-converter structures, sliding mode controlled (CICYT DPI C03-03), Harmonics in industrial and commercial installations (CICYT DPI ) and Power converters advanced topologies to improve the performance and the power quality in the integration of wind energy into the power system (CICYT ENE C03-00), Intelligent power processing in photovoltaic generation (CICYT ENE C02-00/ALT) and Advanced features for integration into the network of intelligent photovoltaic generators and monitoring of their operation conditions (CICYT ENE C02-01/ALT). The group is currently working in a public granted coordinated project for the inter-university cooperation with Brazil. Four universities of Spain and Brazil collaborate in this project, entitled Advanced concepts in grid connected power converters for increasing integration of distributed generators based on renewable energies (PHB ). Members of the group have worked during six months at the Institute of Energy Technology (Aalborg, DENMARK), and they have collaborated in the projects Power electronics applied to power quality improvement and renewable energy integration and Advanced control of power electronics for power quality improvement in grid connected wind turbines (PR ). The research group has published more than 25 articles in prestigious international journals (JCR indexed journals: IEEE, IET and EPSR) on topics which are directly related to this project. These papers deal with some of the most important elements of the power systems, i.e., induction machines, linear and non-linear three-phase transformers and single-phase and three-phase grod connected converters for variable speed drives. The content of these papers is extensive: the modelling and the parameters identification of the above mentioned power system elements, the full characterisation of their dynamic behaviour when voltage sags are produced in the grid, the study of their harmonic behaviour, the design of grid synchronization algortimhs for power converters during voltage sags, and the design of power control strategies for LVRT. Finally, the research group also has written about 150 articles in international congresses and 50 articles in national journals and in non-jcr international journals. Currently, there are five thesis in development stage, which are related to the topics of this project:

9 Analysis and forecast of the implementation and development of photovoltaic systems connected to the Catalonia network. PhD student / period: Jordi de la Hoz / Power hybrid filters. PhD student / period: Ignacio Candela / Control techniques for power quality improvement in FACTS based on grid connected DFIG. PhD student / period: Álvaro Luna / Advanced line-interactive control of PV power generators for grid integration improvement. PhD student / period: Gerardo Vázquez / Line-interactive control of WT for grid integration enhancement. PhD student / period: Daniel Aguilar / It is expected that three members of the group complete their PhD thesis during the three-year life of this project, so that it will support its research work. The project dedication of members Alvaro Luna (Research Assistant, 2 teaching hours a week) and Daniel Aguilar (granted by the CONACYT-UPC researchers training programme) will be very high because, practically, they have no obligations in our university related to the teaching or management, which is a guarantee of the work capacity of the research group.

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11 6.2 PUBLIC AND PRIVATE GRANTED PROJECTS AND CONTRACTS OF THE RESEARCH GROUP Indicate the project and contract grants during the last 5 years ( ) (national, regional or international). Include the grants for projects under evaluation. Title of the project or contract Relationship with the application presented (1) Principal Investigator Exponsored and Reference Project Term or date of the application (2) Non-linear control applied to the design of the generatorinverter-load set 1 Francesc Guinjoan Gispert and Culture TAP C /07/1997 to 31/12/2000 (C) DC/AC conversion in multi-converter structures, sliding mode controlled 1 Francesc Guinjoan Gispert and Culture DPI C /12/2000 to 01/12/2003 (C) Analysis of the power quality regarding sags, interruptions and short-term interruptions in the HV and MV distribution network, and its interaction with industrial plants 1 Joaquín Pedra Durán ENHER PIE Project 01/ to 01/12/1998 (C) Voltage sag effects on the industrial equipment 1 Joaquín Pedra Durán Harmonics in industrial and commercial installations 1 Joaquín Pedra Durán Study of the symmetrical and unsymmetrical voltage sag effects on the electrical components Advanced concepts in grid connected power converters for increasing integration of distributed generators based on renewable energies 1 Joaquín Pedra Durán 1 Pedro Rodríguez Cortés and Culture DPI Ministry of Science and Technology DPI and Science DPI and Science PHB /12/2000 to 28/12/2003 (C) 28/12/2001 to 27/12/2004 (C) 13/12/2004 to 12/12/2007 (C) 10/1/2007 to 09/1/2009 (C)

12 Intelligent power processing in photovoltaic generation 1 Pedro Rodríguez Cortés Advanced features for integration into the network of intelligent photovoltaic generators and monitoring of their operation conditions 1 Pedro Rodríguez Cortés (1) Write 0, 1, 2 or 3 according to: 0 = Similar project; 1 = Very related; 2 = Low related; 3 = Unrelated. (2) Write C or S if the project has been funded or it is under evaluation, respectively. and Science ENE C02-00/ALT and Science ENE C02-01/ALT 10/1/2008 to 09/1/2009 (C) 10/1/2008 to 09/1/2009 (C)

13 7.- TRAINING CAPACITY OF THE PROJECT AND THE GROUP The working group considers that the proposed research of this project could be used to develop a PhD thesis, as a minimum. Thus, it would be interesting for a granted FPI to benefit in his thesis from the large experience and learning ability that the group has acquired over the last years. In this sense, the development of high quality PhD thesis is guaranteed since the group has, currently, a good number of JCR journals published papers. The granted FPI student should take advantage of the contacts with national and international research institutes and with companies leaders in the wind energy field, as is the case of VESTAS.