Topology Research On Switched-Capacitor Step-Up Multilevel Inverter

Multilevel inverters(MLIs)are widely used in the field of renewable energy utilization,such as distributed photovoltaic power generation.The reason behind is that they have the ability to produce more number of output voltage levels,which can reduce the total harmonic distortion(THD)of the output waveform.Therefore,the output power quality is improved,and the size of filters is reduced.Traditional MLIs have the disadvantages of complex topology,difficult control,and lack of boosting capability,which lead to their application scope being limited to a certain extent.In view of these problems,this paper presents a series of switched-capacitor(SC)MLIs with self-boosting and self-balancing capacity.They have the advantages of reduced power devices,high power density,multiple output levels and simple modulation strategy,etc.The proposed inverters are suitable for applications with low-voltage input sources such as distributed photovoltaic power generation.The main research motivations and innovations of the paper include:1.In view of the disadvantages of the traditional MLIs,such as its complex expansion structure and the need for additional isolated dc power supplies,a modular extended switched-capacitor multilevel inverter employing single DC source is proposed.The inverter can realize the self-balancing of the capacitor voltage without additional voltage balance control.Therefore,the modulation strategy is simplified.In addition,the inverter has the capability an independent inductive load.2.To further increase the output level of the inverter and reduce the number of components,a neutral-point-clamped switched-capacitor multilevel inverter is proposed.Through the modular expansion of the SC unit,each additional module of the inverter can increase 4 output voltage levels.Moreover,the complementary working mechanism between the switch pairs simplifies the modulation strategy.3.In order to enhance the boosting ability of inverters while outputting more voltage levels,a high-gain switched-capacitor multilevel inverter with a quadrupleboost ability is proposed.By controlling the unequal charging of the two capacitors,the nine-level voltage output of the inverter and the 4 times boost gain can be achieved at the same time.In addition,the inverter has the advantages of a single DC input and a few power devices.4.In view of the above mentioned problem that the inverters are limited to medium-and low-voltage applications due to their strong voltage boosting capacity,which leads to large voltage stress on the switches.A switched-capacitor multilevel step-up inverter with reduced voltage stress is proposed.The inverter eliminates the back-end H-bridge design for output voltage polarity conversion,which effectively reduces the voltage stress of the switches.Therefore,it is suitable for medium-and high-voltage applications.