Research Of Multi-Input Multilevel Inverter Based On Switched-Capacitor Structure

With the continuous deterioration of the global natural environment and the intensification of the energy crisis,photovoltaic power generation has attracted widespread attention due to its clean,safe,and reliable.Photovoltaic inverters,as an important part of photovoltaic power generation system,affect the stability and efficiency of the system.Multilevel inverters can output near-sinusoidal staircase voltage waveforms,which have the advantages of high output waveform quality,low voltage stress on switches,and low electromagnetic interference.Because of the advantages of the multilevel inverters,they have been widely used in the field of photovoltaic power generation.Based on the characteristics of multiple DC input power sources in photovoltaic power generation systems,this paper applies switched-capacitor technology to multilevel inverters,and proposes a series of multi-input switched-capacitor multilevel inverters as the junction of photovoltaic power generation and distribution system.The proposed inverters have the advantages of simple structure,a lower number of semiconductor devices,and self-balancing of capacitor voltage.They employ multiple DC sources which make them ideal to be employed in photovoltaic power generation based AC microgrids.The main research contents of the paper include:1.Aiming at the problems that the traditional multilevel inverter has a complicated structure and a large number of devices,a double-input switched-capacitor nine-level inverter is proposed.The proposed inverter has two input ports.In the structure of the inverter,two power sources and a capacitor are connected in series and parallel to output a nine-level voltage waveform.By improving the inverter topology,the proposed nine-level inverter reduces the number of switches and the cost of the inverter.2.The DC-side input port of the above double-input inverter is fixed and has no expansion capability.Based on this,a generalized multi-input switched-capacitor multilevel inverter is proposed.The proposed inverter has multiple input ports,which is more flexible in applications with multiple input power sources such as photovoltaic power generation,and the capacitor voltage is charged to a fixed value each cycle,which inherently solves the imbalance issue of capacitor voltage.3.In order to meet the boost demand of the photovoltaic power generation,a modular high-gain switched-capacitor multilevel inverter is proposed.The proposed inverter is composed of two switched-capacitor converters and a voltage polarity conversion circuit.The inverter uses a six-switch structure instead of the traditional H-bridge structure to realize the output voltage combination and level polarity conversion of the pre-stage converters,and can output required voltage levels by selecting two input sources as symmetric or asymmetric values.The proposed inverter has the advantages of a large number of output levels,high voltage gain,lower switches count and self-balance of capacitor voltage.This papaer analyzes the topology and working principle of a series of multi-input switched-capacitor multilevel inverters,and designs the modulation strategy of the proposed inverters.Meanwhile,the capacitor parameters and circuit losses are calculated.Finally,simulation and experimental results verify the correctness and feasibility of the proposed inverter structures.