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Performance evaluation and comparison of low voltage grid-tied three-phase AC/DC converter configurations with SI and SIC semiconductor switches

Öztoprak, Oğuzhan
In this thesis, as compared to silicon IGBT (Si-IGBT) technology, the advantages of using higher efficiency and faster wide bandgap silicon carbide (SiC) semiconductor switches in low voltage three-phase grid-tied PWM DC/AC voltage source converters (VSCs) are investigated in terms of sizing, efficiency and economic considerations for MW-scale photovoltaic power plant applications. As the cost and energy efficiency of a VSC strongly affect the total system economics, this thesis proposes a design methodology optimizing the total cost of ownership (TCO) during the VSC design stage. Return on investment (ROI) and payback period (PP) are considered as the basic parameters for optimization. In the design, hybrid device (Si-IGBT with SiC diode, H-IGBT) and SiC-MOSFET semiconductor switches are weighed along with Si-IGBT technology based conventional design as reference. The power semiconductor module, passives (LCL filter), and heatsink are designed and compared with the reference design. A 30 kW VSC system is simulated, designed and tested in the laboratory to confirm the performance studies, then economic assessments are conveyed. Additionally, in this thesis, with wide bandgap devices switching at relatively high switching frequencies, the influences of feedback signal noise filter, PWM, and control delays on the VSC control performance are investigated. Grid current control and converter current control methods are compared via modelling and simulation, then recommendations made.