An investigation into the grid compliance of the slip synchronous permanent magnet wind generator

Spies, Andries Theodorus (2013-03)

Thesis (MScEng)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: The slip synchronous permanent magnet generator (SSG) is a direct-driven direct-grid connected generator developed to alleviate the need for expensive gearboxes and solid-state power converters on wind turbine generators. This study identifies certain key areas where the current wind turbine generator (WTG) system does not comply with the grid code for wind energy facilities (WEF) as specified by the National Energy Regulator of South Africa. The current WTG system does not have a reactive power compensation device. The main focus in this study is the development of an on-load tap changer (OLTC) transformer to control the terminal voltage of the generator. By controlling the terminal voltage of the generator the excitation-mode of the SSG can be changed allowing for control over the reactive power output of the SSG. An OLTC transformer utilising a solid-state assisted mechanical diverter circuit is built and tested to determine the viability of using an OLTC as a reactive power control device. Practical test results show that the OLTC can successfully control the terminal voltage of the SSG without interrupting the load current. The required accuracy regarding power factor control capability was not met due to the large change in reactive power output per tap change operation. A method of using small shunt capacitor banks to provide additional reactive power in between consecutive tap changes is evaluated in simulation. Simulation results show that the addition of these small shunt capacitor banks dramatically improves the reactive power control accuracy. Additionally the grid code specifies that a WEF must have the ability to curtail the active power output during frequency disturbances. The effects of frequency disturbances on the SSG output is simulated and it was found that the SSG will comply with the minimum connection requirements as specified in the grid code. A method of using an IGBT switched DC load to limit the active power output of the WEF is developed and simulated. From the simulation results it was found that the proposed active power curtailment device will meet the minimum power curtailment response time requirements as specified in the grid code.

AFRIKAANSE OPSOMMING: Die glip sinchroon permanente magneet generator (SSG) is ʼn direkte dryf, direkte netwerk gekoppelde wind generator wat ontwikkel is om behoefte aan duur ratkaste en drywing elektroniese omsetters te verlig. Hierdie studie identifiseer sekere sleutel areas waar die huidige wind generator opstelling nie aan die netwerk kode spesifikasie soos uiteengesit deur die Nasionale Energie Reguleerder van Suid-Afrika voldoen nie. Die wind turbine generator stelsel beskik nie oor ʼn reaktiewe drywing beheer meganisme nie. Die belangrikste fokus in hierdie studie is die ontwikkeling van ʼn transformator tap wisselaar wat gebruik sal word om die generator se terminale spanning te beheer. Deur die terminaal spanning te beheer kan die opwekking modus van die generator verander word om dan die uittree reaktiewe drywing te beheer. ʼn Tap wisselaar wat gebruik maak van ʼn drywingelektronies gesteunde meganiese skakelaar is ontwikkel en getoets om die lewensvatbaarheid van die tegniek te ondersoek. Praktiese toets resultate toon dat die tap wisselaar suksesvol beheer oor die generator se terminaal spanning kon uitvoer, sonder om die las-stroom te onderbreuk. Ongelukkig is die vereiste akkuraatheid ten opsigte van die reaktiewe drywing beheer nie gehaal nie. Die rede hiervoor is dat die verandering in uittree reaktiewe drywing baie groot is vir opeenvolgende tap verstellings. ʼn Metode waar twee klein kapasitor banke geskakel word om reaktiewe drywing te lewer, tussen opeenvolgende tap veranderinge, is deur middel van simulasie ondersoek. Die simulasie resultate toon aan dat die toevoeging van die kapasitors ʼn drastiese verbetering in die beheerbaarheid van die uittree reaktiewe drywing het. Verder spesifiseer die netwerk kode ook dat ʼn wind plaas oor die vermoë moet beskik om die aktiewe drywing te verminder tydens ʼn netwerk frekwensie versteuring. Die effek wat ʼn frekwensie versteuring op die SSG het, is deur middel van simulasie ondersoek en daar is gevind dat die SSG aan die netwerk verbinding spesifikasie sal voldoen. ʼn Metode waarby ʼn IGBT geskakelde GS las gebruik word om die aktiewe drywing van die wind generator te beperk is ondersoek en gesimuleer. Vanaf die simulasie resultate is daar gevind dat die drywing beperkings toestel aan die minimum drywing en reaksie tyd spesifikasies soos vereis sal voldoen.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/80075
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