Modelling and control of doubly-fed induction generator systems in wind turbine applications

Mbukani, Mwana Wa Kalaga (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: The need to reduce the world's carbon foot print has led to a significant rise in wind energy generation. The doubly-fed induction generator (DFIG) is one of the most popular wind turbine generators partly due to its low rated backto- back converter. A constant DC-link voltage in the doubly-fed induction generator system's back to back converter allows for bidirectional power flow of the rotor power. Hence, effective control of the DC-link voltage is necessary. The presence of the switching elements in the back-to-back converter creates harmonics in the systems. LCL and L filters are mostly used to mitigate the harmonics. DFIGs are mainly connected to the grid, however, they can be used in stand-alone mode in isolated rural areas, where there are low loads with no grid connection. DFIGs in the stand-alone mode have to be controlled such that they provide voltage and frequency stability at varying load conditions and changing wind speeds. In this thesis, the power control of the grid-connected DFIG systems in wind turbine applications is presented. Power factor regulation is conducted since it helps in the reduction of the costs linked to the capacitor bank. Maximum power point tracking is also investigated. DC-link voltage control is analysed whereby the grid-side converter is controlled as a voltage-source converter. A comparative analysis of the LCL filter and L filter for switching frequencies below 5 kHz is done and described in this thesis. This is important for systems with low sampling frequencies. Furthermore, in this thesis, the control of a stand-alone DFIG together with simulation result, is presented. Experimental results are also given to demonstrate the effectiveness of the developed rotor-side control algorithm on a DFIG test bed.

AFRIKAANSE OPSOMMING: Die behoefte om die wêreld se koolstof spoor te verminder het gelei tot 'n groot toename in die windopwekking van energie. Die dubbel-gevoerde induksie generator is een van die mees gewilde wind-turbine opwekkers, gedeeltelik weens die lae kapasiteit rug-aan-rug omsetter. Die konstante GS-bus spanning in die induksie generator sisteem se rug-aan-rug omsetter maak twee-rigting vloei van die rotordrywing moontlik. Daarom is doeltreffende beheer van die GS-bus spanning nodig. Die teenwoordigheid van die skakelelemente in die rug-aan-rug omsetter skep harmoniek in die sisteme. LCL en L filters word meestal gebruik om die harmoniek te verminder. Dubbel-gevoerde induksie generators word meestal aan die network gekonnekteer, maar kan ook in alleen-staan modus gebruik word vir verafgeleë landelike gebiede met lae las en sonder network konneksies. Hierdie alleenstaande generators moet so beheer word dat hulle stabiele spanning en frekwersie onder verskillende lastoestande en windspoede kan verskaf. In hierdie tesis word die beheer van die drywing in die network-verbinde Dubbel-gevoerde induksie generator sisteme in die windturbine toepassings bespreek. Regulering van die arbeidsfaktor word toegepas aangesien dit bydra tot die verlaging van kostes wat gekoppel is aan die kapasitorbank. Die maksimum drywingspunt opsporing word ook ondersoek. Die GS-bus spanningsbeheer word geanaliseer waar tyders die netwerk-kant se omsetter as 'n spanningsbron beheer word. 'n Vergelykende ontleding van die LCL en die L filters vir skakel frekwensies onder 5 kHz is gedoen en in hierdie tesis beskryf. Dit is belangrik, veral in sisteme met lae monster frekwensies. Die beheer van 'n alleenstaande Dubbelgevoerde induksie generator en die simulasie resultate word beskryf. Die resultate van die eksperimente word gegee om die doeltreffendheid van die ontwerpte rotor kant beheer algoritme op n Dubbel-gevoerde induksie generator toetsbed demonstreer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101232
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