Position/speed sensor-less control of wind energy conversion systems based on Rotor-Tied Doubly-Fed induction generator systems

Mbukani, Mwana Wa Kalaga (2019-12)

Thesis (PhD)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The doubly-fed induction generator (DFIG) is amongst the most popular wind turbine generator in South Africa. This is partly due to the fact that its backtoback power converters are partially rated. More precisely, they are rated at 30% of the generator rated power. A new DFIG topology has been proposed recently. That is the rotor-tied doubly-fed induction generator (RDFIG). In this topology, the rotor side is connected to the grid while the stator side is connected to the power converter. It has been shown that this topology holds the advantage of higher effeciency compared to the standard DFIG topology. High accuracy in all the measurements is required for the optimum operations of wind energy conversion systems (WECSs). The measurement of the rotor position/speed is amongst the most important measurements when it comes to implement any control system for the WECS. The conventional method of measuring the rotor position/speed is to use an electronic/mechanical sensor (encoder or resolver). This measurement involves the use of long cables and in a harsh environment, this can lead to faulty operations of the WECS. In this thesis, several slip speed estimators for sensor-less control of RDFIGbased WECSs are developed and implemented. The proposed slip speed estimators are based on the association of different sliding mode observers and the PLL estimator. The association of the PLL estimator improves the estimation performance by reducing the noise created by the sliding control control functions. Also, the proposed PLL estimator helps in avoiding a phase shift of π in super-synchronous operating conditions. In addition, in this thesis, several sliding mode observers were developed in order to improve the estimation performance. The proposed sliding mode observers were satisfactory for all the operating conditions of the RDFIG-based WECSs. The robustness of the proposed slip speed estimators is validated experimentally under various operating conditions. A 5.5-kW custom-designed gridconnected RDFIG test-bench based on a National Instrument (NI) PXIe-8115 controller is used. The proposed slip speed estimators solve the problem linked to the failure of the electromechanical sensors. The overall sensor-less control strategy provides an alternative to the sensor-based control of the RDFIGs. Also, the proposed sensor-less vector control strategy can be used as a back-up in case the electromechanical sensor fails.

AFRIKAANSE OPSOMMING: Die dubbelgevoerde induksiegenerator (DFIG) is een van die gewildste windturbinegenerators in Suid-Afrika. Dit is deels as gevolg van die laer kapasiteit omsetters wat die DFIG benodig. 'n Nuwe DFIG-topologie is onlangs voorgestel: Die rotorgebonde DFIG (RDFIG). In dié topologie word die masjien se rotor aan die netwerk gekoppel en die stator aan laer kapasiteit omsetters. Dit is bewys dat hierdie topologie 'n hoër masjieneffektiwiteit het in vergelyking met die standaard-DFIG. Hoë akkuraatheid van metings word vereis vir die optimale beheer van windenergie-omsettingstelsels (WECS). Die meting van die rotorposisie en - spoed is van die belangrikste metings wanneer dit kom by die beheerstelsel van 'n WECS. Die konvensionele metode van rotorposisie- en rotorspoedmeting is deur middel van 'n kodeerder. Dié meting behels die gebruik van lang kabels in 'n fel omgewing, wat kan lei tot die foutiewe werking van die stelsel. In hierdie verhandeling word verskeie glipspoedafskatters vir die sensorlose beheer van 'n RDFIG-gebaseerde WECS ontwikkel en geïmplimenteer. Die voorgestelde glipspoedafskatter is gebaseer op die assosiasie van verskillende glymodus-observeerders en 'n PLL-afskatter. Die assosiasie van die PPLafskatter verbeter die afskattingprestasie deur die geruis van die glymodusbeheerstelsels te verminder. Die voorgestelde PPL-afskatter help ook om 'n faseskuif van π te vermy tydens super-sinchroonoperasie. In hierdie verhandeling word verskeie glymodusobserveerders ontwikkel om die afskattingsprestasie te verbeter. Die voorgestelde glymode-observeerders presteer bevredigend vir alle toestande van die RDFIC-gebaseerde WECS. Die kragtigheid van die voorgestelde glipspoedafskatters se geldigheid word onder verskeie toestande eksperimenteel getoets en bewys. 'n 5.5 kW netwerkgekoppelde RDFIG toetsbank gebaseer op 'n National Instrument PXIe-8115-beheerder word gebruik. Die probleem van gefaalde elektromeganiese sensors word deur die voorgestelde glipspoedafskatters opgelos. Die sensorlose beheerstrategie gee ook 'n alternatief vir tradisionele sensor-gebaseerde beheer van die RDFIG's.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107085
This item appears in the following collections: