Multi-level Converter Technology Three-level Three-phase Cool Mosfet Neutral Point Clamping Inverter

The development of power converter technology has improved since the switching devices are commercialized.Multi-level Converters have attracted much interest especially after the emerging concept of smart grids and renewable energy systems.The penetrations of renewable energy application in power system involve different types of conversion to make multi-level converters more important.Multi-level converter plays a key role in power electronics application and is studied in detail in this thesis.This thesis describes multi-level converter topologies and its modulation technique as a literature review and proposes a new topology called CoolMosfet Neutral Point Clamping(CNPC)inverter.The carrier-based Sinusoidal Pulse Width Modulation(SPWM),as well as Space Vector Modulation(SVM)techniques,is used to investigate CNPC inverter topology.First,the proposed single-phase CNPC topology is designed and investigated with SPWM approach.The power loss evaluation of single-phase is also discussed.Then,three-phase CNPC inverter topology with SVM is performed to improve the utility ratio of DC voltage and the quality of output current.The conventional Three-Level Diode Neutral Point Clamped(3L-DNPC)inverter has high zero conduction loss and high reverse recovery loss because of its clamping diode.The conventional DNPC has IGBT structure which exhibits high on-state voltage,high non-zero conduction loss and so on.Therefore,a CoolMosfet Neutral Point Clamping(CNPC)inverter is proposed by using space vector modulation(SVM),where CoolMosfet is used as clamping diodes.In this way,the clamping diodes reverse recovery power losses are eliminated.More importantly,the new CNPC topology has a parallel structure of CoolMosfet so the current path soundly reduces the zero-vector on-state power loss.Finally,the Experimental results of single-phase prototype CNPC inverter are presented and a transformerless solar inverter is investigated by using the proposed CNPC topology including some key issues such as cost and leakage current.