Modelling and grid impact of slip synchronous generator (SSG) on weak distribution grids

Mangwende, Edwin (2019-12)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The integration of renewable energy resources is becoming more appealing, specifically Wind Turbine Systems (WTS) due to the innovative ways in which they are designed. These innovative designs make them economic viable to be used in power generation applications. Small wind turbine systems are ideal to reduce the power losses associated with feeding remote distribution grids, as these systems can be installed close to the loads. These systems are known as distributed generation as they are connected to the distribution network level, rather than to the transmission level as is the case for traditional generation systems. In this study the dynamic behaviour of a 15 kW, fixed speed fixed pitch downwind turbine that can form part of a distributed generation system, is investigated. The small wind turbine system uses a Slip Synchronous Permanent Magnet Generator (SS-PMG) also known as Slip Synchronous Generator (SSG). The generator is a direct driven and direct grid connected generator. This configuration is more efficient and reliable than traditional configurations, since the losses and cost associated with the gearbox and converter electronics, as well as the maintenance cost of these components, are eliminated. To study the dynamic behaviour of the WTS, both the mechanical and electrical components that form the system are modelled in the Simulink and DigSILENT platforms. The mechanical model comprises of the wind model, aerodynamic model and the mechanical drive train of the system whilst the electrical model consists of the SSG model and grid model. The new concept generator is an SSG whose build-in DigSILENT model does not exist. To study the dynamic behaviour of the WTS in DigSILENT a model is developed by transformation the SSG to a Permanent Magnet Synchronous Generator (PMSG). The PMSG is then implemented using the existing synchronous generator model of DigSILENT with a fixed field excitation. The rest of the mechanical system is modelled using the DigSILENT Simulation Language (DSL). Using the models developed from the dynamic equations, the transient stability of the system is analysed. A benchmark network for the weak power network with embedded WTS is represented as a Thevenin equivalent circuit. The network is analysed for single and three-phase faults. The systems interaction with the grid network is also analysed and whether the SS-PMSG is capable of Low Voltage Ride Through (LVRT) is investigated. Finally, the simulated results of both the Simulink and DigSILENT model are presented and compared.

AFRIKAANSE OPSOMMING: Die integrasie van hernubare energiehulpbronne word meer aanloklik, veral Wind Turbine Stelsels (WTS) as gevolg van die innoverende maniere waarop hulle ontwerp word. Hierdie innoverende ontwerpe maak hulle ekonomies lewensvatbaar om in kragopwekking toepassings gebruik te word. Klein wind turbine stelsels is ideaal om die drywingsverliese wat verband hou met die verspreiding van afgeleë verspreidingsnetwerke te verminder, aangesien hierdie stelsels naby die laste geïnstalleer kan word. Hierdie stelsels staan bekend as verspreide generasie aangesien hulle gekoppel word op verspreidingsnetwerkvlak, eerder as die transmissievlak soos in die geval van tradisionele generasiestelsels In hierdie studie word die dinamiese gedrag van 'n 15 kW, vaste-spoed vaste-invalshoek wind turbine, wat deel kan uitmaak van 'n verspreide generasie stelsel, ondersoek. Die klein wind turbine stelsel gebruik 'n Slip Sinchrone Permanent Magneet Generator (SS-PMG), ook bekend as Slip Sinchrone Generator (SSG). Die generator is 'n direkte-aangedrewe en direkte netwerk gekoppelde generator. Hierdie konfigurasie is meer doeltreffend en betroubaar as tradisionele konfigurasies, aangesien die verliese en koste verbonde aan die ratkas en omskakel elektronika, sowel as die onderhoudskoste van hierdie komponente, uitgeskakel word. Om die dinamiese gedrag van die WTS te bestudeer, word beide die meganiese en elektriese komponente waaruit die stelsel bestaan gemodelleer in die Simulink en DigSILENT platforms. Die meganiese model bestaan uit die wind model, aërodinamiese model en die meganiese aandryfstelsel van die stelsel terwyl die elektriese model uit die SSG model en netwerk model bestaan. Die nuwe konsep generator is 'n SSG waarvoor 'n ingeboude DigSILENT-model nie bestaan nie. Om die dinamiese gedrag van die WTS in DigSILENT te bestudeer, word 'n model ontwikkel deur die SSG te transformeer na 'n Permanente Magnetiese Sinkroniese Generator (PMSG). Die PMSG word dan geïmplementeer met behulp van die bestaande sinkroniese generator model van DigSILENT met 'n vaste veldopwinding. Die res van die meganiese stelsel word gemodelleer met behulp van die “DigSILENT Simulation Language (DSL)”. Deur gebruik te maak van die modelle wat ontwikkel is uit die dinamiese vergelykings, word die oorgangstabiliteit van die stelsel geanaliseer. 'n Maatstaf netwerk vir die swak kragnetwerk met geïntegreerde WTS word voorgestel as 'n Thevenin ekwivalente stroombaan. Die netwerk word geanaliseer vir enkel- en driefase foute. Die stelsel interaksie met die netwerk word ook geanaliseer en daar word ondersoek of die SS-PMSG Lae Spanning Deur Ry (LSDR) vermoë het. Ten slotte word die gesimuleerde resultate van beide die Simulink en DigSILENT-model aangebied en vergelyk.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107051
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