In silico case studies of compliant robots: AMARSI deliverable 3.3

In the deliverable 3.2 we presented how the morphological computing ap- proach can significantly facilitate the control strategy in several scenarios, e.g. quadruped locomotion, bipedal locomotion and reaching. In particular, the Kitty experimental platform is an example of the use of morphological computation to allow quadruped locomotion. In this deliverable we continue with the simulation studies on the application of the different morphological computation strategies to control a robotic system

Multiterminal HVDC transmissions systems for offshore wind

Offshore wind is emerging as one of the future energy vectors. Offshore wind power plants locations provide more strong and constant wind speed that allows to extract more power compared to onshore locations. In addition, as wind turbine components transportation is less restricted to terrestrial infrastructure, bigger and more powerful wind turbines can be installed offshore. In Europe, 1,567 MW of offshore wind power was installed in 2013. It represents the 14\% of the total wind power installed in Europe. Offshore wind power plants near the shore can be connected to the main grid by means of conventional AC technology. However, if these wind farms are installed further than 80-100 km, the use of AC equipment is economically infeasible due to reactive power issues. In these applications, HVDC system based on static converters can be used. The projects build and commissioned nowadays are based on point-to-point connections, where, each wind farm or wind farm clusters are connected to the terrestrial grid individually. Consequently, these lines might be understood as an extension of the AC system. If different offshore wind farms are interconnected between them and connected at the same time to different AC systems, for example, different countries, the DC grid is created. This scenario creates one of the most important challenges in the electrical power system since its creation, more than 100 years ago. The most relevant challenges to be addressed are the stability and operation of the DC grid and the integration and interaction with the AC grid. This thesis addresses various aspects related to the future Multiterminal-HVDC systems for transmission of offshore wind power. First, the voltage control and the system operations are discussed and verified by means of emulations using an HVDC scaled experimental platform built for this purpose. Voltage stability might be endangered during contingencies due to the different inertia time constant of the AC and the DC system. DC systems only have the inertia of the capacitors compared to synchronous machines rotating masses of the AC systems. Therefore, in faulty conditions the power transmitted through the DC system must be reduced quickly and efficiently. For this reason, in this thesis a coordinated power reduction algorithm taking advantage of Dynamic Braking Resistors (DBR) connected to onshore converter stations and the ability of the power plants to reduce the generated power is presented. From the AC and DC grids integration point of view, the connection point between the offshore grid and the AC grid might be located remotely leading to a connection with a reduced Short Circuit Ratio (SCR). In the literature, several issues regarding the connection of transistor-based power converters to weak AC grid have been reported. In this thesis am advanced control for Voltage Source Converters connected to weak grids is presented and tested by means of simulations. From the AC and DC grids interactions, the voltage stability is not enough to operate a DC grid. Transport System Operators (TSO) operates the power flow through the cables and the power exchanged between by the power converters. In this thesis, a novel hierarchical power flow control method is presented. The aim of the proposed power flow control is to obtain the desired power flows changing the voltage control set-points while the system stability is ensured. Finally, a control procedure for offshore wind farms based on Squirrel Cage Induction Generators connected to a single power converter is introduced.L'energia eòlica marina emergeix com un dels vectors energètics del futur. Les localitzacions eòliques marines proporcionen vens més forts i constants que les terrestres, cosa que permet extreure més potència. A més a més, els aerogeneradors marins poden ser més grans i més potents ja que es redueixen les limitacions de gàlib existent en les infraestructures terrestres. A tall d'exemple, l'any 2013 a Europa es van instal.lar 1.567 MW de potència eòlica marina, cosa que representa un 14\% de la potència eòlica instal.lada a Europa. Els parcs eòlics marins poden ser connectats a la xarxa elèctrica terrestre utilitzant emparamenta convencional de corrent alterna, però quan la distancia amb la costa excedeix els 80-100 km l'ús d'aquesta tecnologia es torna econòmicament inviable degut a l'energia reactiva generada en els conductors. Per solucionar aquest problema, s'emparen els sistemes en corrent continua basats en convertidors estàtics. Els projectes construïts o projectats a dia d'avui es basen en esquemes de connexió punt-a-punt, on, cada parc eòlic o agrupació de parcs eòlics es troba connectat a la xara terrestre individualment. En conseqüència, l'operació d'aquestes línies es pot considerar com una extensió de la xarxa d'alterna. Però, si s'interconnecten diferents parc eòlics amb diferents xarxes terrestres d'alterna (per exemple, diferents països) en corrent continua, s'obtenen xarxes en corrent continua. Aquest nou escenari crea un dels majors reptes des de la creació dels sistema elèctric de potencia, ara fa més de 100 anys. Entre aquests reptes hi ha l'estabilitat i l'operació dels sistemes en corrent contínua i la seva integració i coexistència amb les xarxes en corrent alterna. En la present tesis s'han estudiat diferents aspectes dels futurs sistemes multi terminal en alta tensió en corrent contínua (HVDC, en anglès) per la transmissió de potencia generada mitjançant parcs eòlics marins. Primerament, es descriu el control de tensió i els modes d'operació dels sistemes multi terminal i es verifiquen en una plataforma experimental construïda per aquest propòsit. L'estabilitat de tensió dels sistemes en corrent continua, es pot veure afectada durant una falta a la xarxa d'alterna degut a la reduïda inèrcia dels sistemes multi terminal, només formada pels condensadors dels convertidors i els cables. Així la potència que no pot injectar a la xarxa ha de ser reduïda de forma ràpida i eficient. Per això, en aquesta tesis es presenta un sistema coordinat de reducció de potència que utilitza la resistència de frenat dels convertidors de connexió a la xarxa i els mètodes de reducció de potència dels parcs eòlics. Des del punt de vista de la integració de les xarxes en continua i en alterna, el punt d'interconnexió pot estar localitzat llunys dels grans centres de generació, la qual cosa implica tenir una potència de curtcircuit molt reduïda. En la bibliografia científica s'han descrit diverses problemàtiques a l'hora de connectar un convertidor de commutació forçada a les xarxes dèbils. Per tal de pal.liar aquests inconvenients, en aquesta tesis es presenta un algorisme avançat de connexió de convertidors a xarxes dèbils basat en control vectorial. Des del punt de vista de les interaccions i interoperabilitat dels sistemes en corrent alterna i continua, no n'hi ha suficient en garantir l'estabilitat, ja que el propòsit finals dels operadors de xarxa és fer fluir una potencia a traves de la xarxa per tal de satisfer la demanda. Per aquest propòsit en aquesta tesis es presenta un control jeràrquic de control del flux de potència que fixa el flux de potència a traves d'una xarxa multi terminal canviant les consignes del control primari, tot assegurant l'estabilitat del sistema. Per tancar la tesis, es presenta un nou controlador per parcs eòlics basats en aerogeneradors de gàbia d'esquirol controlats per un sol convertidor

Evolutionary learning and global search for multi-optimal PID tuning rules

With the advances in microprocessor technology, control systems are widely seen not only in industry but now also in household appliances and consumer electronics. Among all control schemes developed so far, Proportional plus Integral plus Derivative (PID) control is the most widely adopted in practice. Today, more than 90% of industrial controllers have a built-in PID function. Their wide applications have stimulated and sustained the research and development of PID tuning techniques, patents, software packages and hardware modules. Due to parameter interaction and format variation, tuning a PID controller is not as straightforward as one would have anticipated. Therefore, designing speedy tuning rules should greatly reduce the burden on new installation and ‘time-to-market’ and should also enhance the competitive advantages of the PID system under offer. A multi-objective evolutionary algorithm (MOEA) would be an ideal candidate to conduct the learning and search for multi-objective PID tuning rules. A simple to implement MOEA, termed s-MOEA, is devised and compared with MOEAs developed elsewhere. Extensive study and analysis are performed on metrics for evaluating MOEA performance, so as to help with this comparison and development. As a result, a novel visualisation technique, termed “Distance and Distribution” (DD)” chart, is developed to overcome some of the limitations of existing metrics and visualisation techniques. The DD chart allows a user to view the comparison of multiple sets of high order non-dominated solutions in a two-dimensional space. The capability of DD chart is shown in the comparison process and it is shown to be a useful tool for gathering more in-depth information of an MOEA which is not possible in existing empirical studies. Truly multi-objective global PID tuning rules are then evolved as a result of interfacing the s-MOEA with closed-loop simulations under practical constraints. It takes into account multiple, and often conflicting, objectives such as steady-state accuracy and transient responsiveness against stability and overshoots, as well as tracking performance against load disturbance rejection. These evolved rules are compared against other tuning rules both offline on a set of well-recognised PID benchmark test systems and online on three laboratory systems of different dynamics and transport delays. The results show that the rules significantly outperform all existing tuning rules, with multi-criterion optimality. This is made possible as the evolved rules can cover a delay to time constant ratio from zero to infinity based on first-order plus delay plant models. For second-order plus delay plant models, they can also cover all possible dynamics found in practice

Physics-based discrete modelling and digital control design for grid-side inverters for renewable energy

This work lays out the methodology of the analysis and consequent control design for the LC filter application on the example of a 5 MW wind turbine. The chapters progress sequentially through the different complexity steps from the continuous analysis to the discrete-space modeling to control algorithm design, integrated into a microcontroller-based hardware setup. The methods in each complexity step illustrate the process, starting with the identification of the control issue, through the control solutions, and ending with the evaluation using dynamic analysis.Diese Arbeit legt die Methodik der Analyse und des anschließenden Regelungsentwurfs für die LC-Filteranwendung am Beispiel einer 5-MW-Windturbine dar. Die Kapitel führen durch die verschiedenen Komplexitätsstufen von der kontinuierlichen Analyse über die Modellierung im diskreten Raum bis hin zum Entwurf des Regelalgorithmus, der in eine mikrocontrollerbasierte Hardware integriert ist. Die Methoden jedes Komplexitätsschritts veranschaulichen den Prozess, beginnend mit der Identifizierung des Regelungsproblems, über die Regelungslösungen und endend mit der Bewertung mittels dynamischer Analyse