Browsing by Author "Mangwende, Edwin"
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- ItemModelling and grid impact of slip synchronous generator (SSG) on weak distribution grids(Stellenbosch : Stellenbosch University, 2019-12) Mangwende, Edwin; Vermeulen, H. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.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.