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Model Predictive Control of CorPower Ocean Wave Energy Converter
KTH, School of Electrical Engineering (EES).
2016 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Wave power is currently a hot topic of research, and has shown great potential as a renewable energy source. There have been lot of progress made in developing cost effective Wave Energy Converters (WECs) that can compete with other sources of energy in regard to price and electrical power. Theoretical studies has shown that optimal control can increase the generated power for idealized WECs. This thesis is done in collaboration with CorPower Ocean, and investigates the use of economic Model Predictive Control (MPC) to control the generator torque in a light, point-absorbing, heaving WEC that is currently under development. The objective is to optimize the generator torque, such that the average generated power is maximized while maintaining a small ratio between maximum and average generated power. This results in a nonconvex cost function. Due to the highly nonlinear and nonsmooth dynamics of the WEC, two controllers are proposed. The first controller consists of a system of linear MPCs, and the second controller is a nonlinear MPC. Relevant forces acting on the WEC are identified and the system dynamics are modelled from a force perspective. The models are discretized and the controllers are implemented in Simulink. The WEC, together with the controllers, is simulated in an extensive Simulink model developed by CorPower Ocean. Several different types of ocean waves are considered, such as its energy content and its regularity. In the majority of cases, the controllers do not increase the performance of the WEC compared to a simple, well tuned controller previously developed by CorPower Ocean. Finally, possible improvements of how to reduce existing model errors are proposed.

Abstract [sv]

Vågkraft har de senaste åren visat stor potential som en ny, förnyelsebar energikälla. Det har skett många framsteg inom området med att ta fram ett robust vågkraftsverk som kan utmana andra energikällor i pris och elektrisk effekt. Teoretiska studier har visat att optimal styrning kan öka den elektriska effekten för idialiserade vågkraftsverk. Denna rapport är skriven i sammarbete med vågkraftföretaget CorPower Ocean, och undersöker hur ekonomisk Model Predictive Control (MPC) kan användas för att styra dämpningen i ett lätt vågkraftverk vars storlek är relativt liten våglängden. Målet är att optimera dämpningen, vridmomentet, i generatorerna så att medeleffekten maximeras samtidigt som toppeffekten minimeras, detta för att skapa ett stabilare system med mindre flutuationer mellan medel- och toppeffekt. För att nå detta mål krävs en icke konvex kostfunktion. På grund av stora olinjäriteter och diskontinuteter i systemets dynamik utvecklas två regulatorer; ett system av linjära MPC, samt en olijär MPC. Relevanta krafter som påverkar systemet identifieras och modelleras från ett kraftperspektiv. Modellerna diskretiseras, och regulatorerna implementeras och simuleras i en detaljerad Simulink modell av systemet, utvecklad av CorPower Ocean. Både regelbundna och oregelbunda vågset med varierande energiinnehåll har simuleras. Regulatorerna ökar inte vågkraftverkets prestanda jämfört med en enkel, väl inställd regulator utveklad av CorPower Ocean. Slutligen föreslås förbättringar för att minska modelfell i modellerna.

Place, publisher, year, edition, pages
2016. , 48 p.
Series
TRITA-EE, ISSN 1653-5146 ; TRITA-EE 2016:100
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-196859OAI: oai:DiVA.org:kth-196859DiVA: diva2:1049369
External cooperation
CorPower Ocean AB
Examiners
Available from: 2016-11-24 Created: 2016-11-24 Last updated: 2016-11-24Bibliographically approved

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