Analysis of the contribution of wind power plants to damp power system oscillations

Wind power has emerged as one of the most promising renewable energy sources. The very penetration levels of wind energy in power systems have altered several aspects of power system operation, such as system stability. Owing to the large penetration of wind power, transmission system operators (TSOs) have established special grid codes for wind farms connection. These grid codes require wind farms to provide ancillary services to the grid such as frequency and voltage regulation. In the near future, the capability of damping power system oscillations will be required. As a result of the development of such requirements, the concept of wind power plant (WPP) arises being de ned as a wind farm which is expected to behave similarly to a conventional power plant in terms of power generation, control and ancillary services. As future grid codes will require power oscillation damping contribution from wind power, the thesis is mainly focused on the analysis of the power system stabilizer (PSS) capability of wind power plants. The change produced by wind power plants based on di erent wind turbine technologies on power system small signal dynamics is analysed to determine their possible contribution to damp oscillations. The eff ect of the distance from the tie line to the wind power plant on the controller response and the influence of wind power plants proximity to synchronous generators are demonstrated to be critical factors. At this point several questions are raised as: What are the most critical factors? How can be ensure a proper contribution, at least the best possible response? Can it be ensured to be independent to the power system and the controller selected? To answer these questions, this thesis conducts research on proper selection of input-output signal pairs to damp out electromechanical oscillations using wind power plants without drawing attention to a particular control design. This is necessary conclusions about the power system independently of a particular controller. The capability to damp is an intrinsic characteristic of the system and should not be a ected by a particular controller (PSS). Firstly, di erent analysis techniques are compared, considering both controllability and observability measures and input-output interactions. This enables recommendations to be drawn so as to the selection of the the best signal pairs to damp power system oscillations considering di erent approaches, such as single-input single-output (SISO) and multivariable control (MIMO). Second, a new criterion to select the best input-output signals used by a PSS based on WPPs is presented, considering explicitly local and remote signals in the analysis. Taking into account fundamental design limitations and using controllability and observability concepts, the criterion is able to identify the most suitable pair of input-output local signals without consider any particular controller. Finally, due to the increase of wind power generation - including o shore locations - and the concept of an interconnected Pan-European network, a new o shore wind power plant AC network similar in design to the European SuperGrid \SuperNode", is analyzed. The cost e ect of choosing a nonstandard operating frequency on the o shore AC network is investigated. As the o shore AC network is isolated from onshore networks through the use of HVDC links, it may be operated in an asynchronous fashion and at a suitable frequency. The cost associated with operating the network at a fixed frequency in the range 20 to 120 Hz is investigated, focusing on the frequency-cost-scalings of electrical devices (such as cables, transformers and reactive compensation) and the related o shore infrastructures,L'energia e olica s'ha convertit en una de les fonts d'energia renovable m es prometedores. Actualment, l'elevat nivell de penetraci o de l'energia e olica a la xarxa el ectrica ha conduï t a la modi caci o del comportament de diversos aspectes d'aquesta, com per exemple, l'estabilitat. Degut a aquesta gran penetraci o, els operadors de xarxes de transmissi o (TSOs) han establert procediments d'operaci o especials per a la connexi o de grans parcs e olics. Aquests codis requereixen als parcs elics que realitzin serveis auxiliars al sistema el ectric com, per exemple, la regulaci o de freqü encia i la regulaci o de la pot encia reactiva. En un futur proper, la capacitat dels parcs e olics per esmorteir les oscil lacions del sistema de pot encia es requerir a (en l'actualitat ja existeixen esborranys de nous procediments d'operaci o que ho inclouen). A causa d'aquest requeriments, el concepte de central de generaci o d'energia e olica es de neix com un parc e olic que s'espera que es comporti de manera similar a una central de generaci o el ectrica convencional en termes de poder realitzar tasques tals com generaci o, control i serveis auxiliars. Ja que un futur requeriment dels operadors de xarxa ser a la contribuci o de l'energia e olica en l'esmorteiment de les oscil lacions de pot encia, en aquesta tesi s'estudia la capacitat de les centrals e oliques per actuar com estabilitzador dels sistemes el ectrics de pot encia. A m es a m es, s'analitza l'efecte de les centrals d'energia e olica al comportament din amic del sistema el ectric considerant l'estabilitat de petita senyal, per a determinar quina podr a ser la possible contribuci o proporcionada per aquestes tecnologies. S'ha estudiat que l'efecte de la dist ancia des d'el punt de connexi o amb la central d'energia e olica a la resposta del control estabilitzant i la influ encia de la proximitat de les centrals e oliques als generadors s ncrons s on factors cr tics. D'aquest fet surgeixen algunes preguntes com: Es aquest el factor m es cr tic? Com es pot assegurar una contribuci o adequada, si m es no la millor resposta possible, per ajudar a estabilitzar el sistema el ectric? Es poden asegurar quina ser a la contribuci o a l'estabilitat del sistema el ectric independentment de la xarxa i l'esquema de control escollit? Per respondre a aquestes preguntes, aquesta tesi ha realitzat investigacions sobre l'adequada selecci o de parells de senyals d'entrada-sortida per esmorteir les oscil lacions electromec aniques amb centrals e oliques evitant dissenyar el controlador i propossant met odes f acilment adaptables a qualsevol sistema el ectric. En primer lloc, s'han comparat diferents t ecniques d'an alisi tenint en compte tant les mesures de controlabilitat i observabilitat com les interaccions entre les senyals d'entrada i sortida. D'aquesta comparaci o, certes recomanacions es donen a l'hora de seleccionar els millors parells de senyals per esmorteir les oscil lacions del sistema el ectric de pot encia considerant diferents esquemes de control com ara entrada unica sortida unica (SISO) i control multivariable (MIMO). En segon lloc, s'ha proposat un nou criteri per seleccionar les senyals d'entrada i sortida utilitzades per un control estabilitzador per centrals d'energia e olica. On, a difer encia amb anteriors met odes de selecci o proposats, el criteri presentat considera expl citament tant senyals locals com senyals remotes dins el seu an alisi. Aquest criteri es capa c d'identi car la parella de senyals locals d'entrada i sortida m es adequada sense realitzar el disseny del controlador, considerant tant les limitacions fonamentals del disseny del controlador imposades per el sistema com els conceptes de controlabilitat i observabilitat. Finalment, a causa del augment de la generaci o d'energia e olica, principalment en localitzacions marines, i al concepte d'una xarxa el ectrica comuna Pan-Europea, s'ha realitzat l'an alisi d'un nou concepte de xarxa en corrent altern (AC) dins de les centrals d'energia e olica marina, amb un disseny similar al concepte investigat a la Super-Xarxa Europea \Supernode". En aquest treball s'ha investigat l'efecte que t e en els costos la tria una freqüencia nominal d'operaci o no est andard en dita xarxa en corrent altern. La xarxa en AC que es forma entre les turbines e oliques i el convertidor de transmissi o es aï llada tant de les xarxes terrestres per l' us d'enlla cos en corrent continu (HVDC) com de la pr opia de les turbines per el convertidor que porten incorporat. Aquest fet implica que aquesta xarxa pot ser operada sense sincronitzar a qualsevol freqüencia. En aquesta tesi, s'ha estudiat quin es el cost associat amb l'operaci o de la xarxa a una freqü encia fi xa dins del rang de 20-120 Hz, focalitzant principalment en l'escalat del costos dels diferents elements el ectrics (com ara cables, transformadors i compensaci o reatviva i infraestructures necessaris en instal lacions marines respecte la freqüencia

Modeling and control of squirrel cage induction generator with full power converter applied to windmills

The project aims to develop a dynamic model, of a generation system of electrical energy with a variable speed wind turbine using a squirrel cage induction generator which is connected to the grid by a back to back frequency converter, for testing purposes. In the project has been done an analysis of the mathematical equations of the whole system, separating the mechanical system (turbine and gearbox) and the electrical (generator and converter). We study the control design of the machine which allow us to obtain the maximum wind power extraction, and we also study the control of the converter which couple the generator with the network. The proper functioning of the model is checked comparing the obtained results with some commonly known results.Outgoin

Sufficient conditions for controllability and observability of serial and parallel concatenated linear systems

This paper deals with the sufficient conditions for controllability and observability characters of finitedimensional linear continuous-time-invariant systems of serial and parallel concatenated systems. The obtained conditions depend on the controllability and observability of the systems and in some cases, the functional output-controllability of the first one.Peer ReviewedPostprint (published version

Control of multi-terminal HVDC networks towards wind power integration: A review

© 2015 Elsevier Ltd. More interconnections among countries and synchronous areas are foreseen in order to fulfil the EU 2050 target on the renewable generation share. One proposal to accomplish this challenging objective is the development of the so-called European SuperGrid. Multi-terminal HVDC networks are emerging as the most promising technologies to develop such a concept. Moreover, multi-terminal HVDC grids are based on highly controllable devices, which may allow not only transmitting power, but also supporting the AC grids to ensure a secure and stable operation. This paper aims to present an overview of different control schemes for multi-terminal HVDC grids, including the control of the power converters and the controls for power sharing and the provision of ancillary services. This paper also analyses the proposed modifications of the existing control schemes to manage high participation shares of wind power generation in multi-terminal grids.Postprint (author's final draft

Functional output-controllability analysis of fixed speed wind turbine

This paper deals with the concepts of functional output-controllability character of a finite-dimensional linear dynamical system. And a method for comput- ing the functional outputcontrollability consisting on the calculation of the rank of a certain constant ma- trix related to the system dynamics is introduced. The linear system under study is a fixed speed wind tur- bine (FSWT) formed by a squirrel cage generator con- nected directly to the grid. Due to the non-linear be- haviour of such system, the linear system model is calculated by means of a Taylor’s decomposition of the non-linear equations of the squirrel cage induction generator, being the system linearized around a steady state operating point. Finally, the study of the func- tional output-controllability of such system is done, and some boundaries are given to ensure functional output-controllability from some given operational val- uesPostprint (published version

Modeling and control of squirrel cage induction generator with full power converter applied to windmills

The project aims to develop a dynamic model, of a generation system of electrical energy with a variable speed wind turbine using a squirrel cage induction generator which is connected to the grid by a back to back frequency converter, for testing purposes. In the project has been done an analysis of the mathematical equations of the whole system, separating the mechanical system (turbine and gearbox) and the electrical (generator and converter). We study the control design of the machine which allow us to obtain the maximum wind power extraction, and we also study the control of the converter which couple the generator with the network. The proper functioning of the model is checked comparing the obtained results with some commonly known results.Outgoin

Digital tools for floating offshore wind turbines (FOWT): A state of the art

ABSTRACT: Operations and installation on offshore wind and especially floating are complex and difficult actions due to site accessibility and equipment availability. In this regard, digitalization is disrupting the wind section thanks to the development of advanced sensors, automated equipment, computational power, among other. All these allow to optimize and simplify different parts of the offshore wind power plant development (i.e. design, planning, installation, O&M, etc.). This fact is of special interest on maintenance, since the early detection of failures or malfunctions lead to reduced costly corrective maintenance. This paper presents a literature review of current state-of-the-art on the application of digitalization activities which can be applied for floating wind, including typical component failures, monitoring techniques and advanced digital tools as Digital Twin concept and Building Information Models (BIM). Finally, the review paper provides an analysis of existing gaps, needs and challenges of the sector to provide guides on research and innovation to foster offshore wind sector.The research leading to these results has received funding from the European Union’s H2020 Programme under Grant Agreement n◦ 815083 – Corewin

New rules for improving CAS capabilities when computing improper integrals. Applications in Math Education

In many Engineering applications the computation of improper integrals is a need. In [1] we pointed out the lack of some CAS when computing some types of improper integrals. Even more, the work developed showed that some improper integrals can not be computed with CAS using their build-in procedures. In this talk we will develop new rules to improve CAS capabilities in order to compute new improper integrals We will show some examples of improper integrals that CAS asMATHEMATICA, MAPLE, DERIVE or MAXIMA can not compute. Using advance techniques as Laplace and Fourier transforms or Residue Theorem in Complex Analysis, we will be able to develop new rules schemes for these improper integrals. We will also describe the conclusions obtained after using these new rules with our Engineering students when teaching Advanced Calculus. [1] José L.Galán-García, Gabriel Aguilera-Venegas, María Á. Galán-García, Pedro Rodríguez-Cielos, Iván Atencia-Mc.Killop. Improving CAS capabilities: New rules for computing improper integrals. Applied Mathematics and Computation. Volume 316, 1 January 2018, Pages 525-540.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Analysis of support structure of wind turbine tower

Wind turbines are being used to generate electricity as an alternative energy source to conventional fossil fu- els, and it is well known that wind towers must to sus- tain continuous vibration forces throughout their opera- tional life. In this paper, a stability analysis of bending deflection of a wind turbine steel tower is presented. The wind turbine is modelled as the structure of a sim- plified beam-column by a switched system. It is mod- elled by using a Hamiltonian system, which simplifies the system under study and allows to analyze the sta- bility dynamics of the system. An eigenvalue analysis have been done in order to analyze the stability of the system; finally, also, some transient simulations of the system are presented to verify the results obtainedPostprint (published version

Bit Error Probability and Capacity Bound of OFDM Systems in Deterministic Doubly-Selective Channels

© 2020 IEEE. This version of the article has been accepted for publication, after peer review. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. The Version of Record is available online at: https://doi.org/10.1109/TVT.2020.3011365[Abstract]: Doubly-selective channels, such as those that occur when the transmitter and the receiver move relative to each other at high speeds, are a key scenario for fifth generation (5G) cellular systems, which are mostly based in the use of the orthogonal frequency-division multiplexing (OFDM) modulation. In this paper, we consider an OFDM system using quadrature amplitude modulation (QAM) symbols and we show that, when transmitting over deterministic doubly-selective channels, the inter-carrier-interference (ICI) affecting a symbol can be well approximated by a complex-valued normal distribution. Based on this, we derive a lower bound for the link capacity using the Shannon-Hartley theorem. Finally, we provide an approximation of the bit error probability (BEP) using the well-known BEP expressions for Gray-coded QAM constellations over additive white Gaussian noise (AWGN) channels, and show numerical results that confirm that the proposed BEP expression approximates accurately the bit error ratio (BER) of the OFDM system for standardized channel models. The proposed closed-form analytical expressions for the capacity and the BEP do not only allow for discarding the need of computationally-costly Monte-Carlo system simulations, but also provide a theoretical framework to optimize the system parameters directly impacting on the achievable performance.Xunta de Galicia; ED431G2019/01This work has been funded by the Xunta de Galicia (ED431G2019/01), the Agencia Estatal de Investigación of Spain (TEC2016-75067-C4-1-R, PID2019-104958RB-C42), ERDF funds of the EU (AEI/FEDER, UE), and the National Natural Science Foundation of China (NSFC) under Grants no. 61850410529 and 61971313.China, National Natural Science Foundation of China (NSFC); 61850410529China, National Natural Science Foundation of China (NSFC); 6197131