Research And Application Of Switched-capacitor Based Multilevel Inverter Topologies

Compared to two-level full-bridge inverter,multilevel inverter(MLI)has the advantages of less total harmonic content,lower voltage stress,low electromagnetic interference,and high power upper limit.It is widely applied to medium-high power transmission,active power filter,uninterrupted power supply,electric vehicle,and renewable energy generation.Traditional MLIs,such as neutral-point-clamped(NPC)inverter and flying-capacitor inverter,suffer from the drawbacks of numerous switching devices and capacitors,voltage unbalance,and low voltage utilization ratio.Alternatively,switched-capacitor MLI has attained much attention and study due to its merits of fewer devices,voltage self-balance,and high voltage utilization ratio.The paper focuses on the application of switched capacitor in MLI.Several switchedcapacitor MLIs are proposed to improve the research of topologies.The details are as follows.1.Firstly,a switched-capacitor nine-level boost inverter is proposed for single-phase applications.The proposed topology can produce nine-level output and quadruple boost ability,using eight power switches,three diodes,and three switched capacitors only.Moreover,the capacitors in this topology can achieve self-voltage balance.2.The schematic of flying capacitor is introduced.Three hybrid MLIs with self-balance are presented.The first one is nine-level inverter using two switched capacitors and one flying capacitor.The switched capacitors can achieve voltage doubling and flying capacitor’s voltage gets balance on 1/2 input,resulting in more output levels.The second one is seven-level inverter with two capacitors,which utilize the principles of switched capacitor and flying capacitor.Thus,voltage-sharing and boost ability are accomplished.The third one is a hybrid seven-level inverter combining active NPC structure with switched capacitor.It can operate in three-phase mode with only one input.The capacitors of input side can realize voltage sharing automatically.3.One pair of switches in the MLIs introduced above must withstand high voltage stress,and their maximum output level is fixed.Therefore,two generalized switched-capacitor MLIs are proposed.The voltage stress of the devices in switched-capacitor units of the topologies will not increase with unit extending.Few devices are used for extending output level and enhance boost factor,which show their suitability for low-input and high-output-quality applicationsThe operation principles and parameters design for all topologies proposed are presented and analyzed in detail.The experimental verification is also conducted,which demonstrates the feasibility of proposed topologies and correctness of theoretical analysis.