Research On Switched Capacitor Multilevel Inverter Technology

Multilevel inverter(MLI)is a type of power electronic equipment that can convert DC voltage into AC voltage.In the development trend of new energy,to research interfaces of new energy power generation systems is becoming more and more important.Compared with traditional MLIs,the switched-capacitor-based MLI is more flexible and its capacitor voltage can be balanced automatically.In this paper,based on the research of various switched-capacitor-based MLIs,a new multilevel power conversion circuit and system are proposed.By connecting an DC three-level unit with a H-bridge,a seven-level inverter is proposed.To combine the seven-level inverter with cascaded technology,a cascaded system is proposed.Compared with the existing cascaded MLIs,the proposed MLI has better output performance.Compared with the existing switched-capacitor-based MLIs,the proposed MLI has simpler structure and higher efficiency.The optimized modulation algorithm enables the circuit system to operate efficiently and provide high-quality AC output.The main research contents of the paper are given follows:(1)A switched-capacitor-based DC-DC 3-level cell is proposed.This unit is composed of a full bridge,two diodes and two capacitors.It uses different switch combinations to achieve series and parallel connection of capacitors with the dc source,and to achieve three different DC levels of output.(2)Based on the DC-DC 3-level unit,a seven-level switched-capacitor inverter is proposed.With SHE modulation,it outputs a staircase voltage waveform containing 7levels.Compared with the existing switched-capacitor-based MLIs,the number of components is reduced,and the circuit structure is simpler.On the premise of ensuring high inverter efficiency,the inverter avoids complex capacitor voltage balance control,and optimizes voltage ripple through the modulation strategy.(3)In order to improve the performance of the proposed MLI,a hybrid modulation algorithm is proposed.It makes the system output multilevel PWM voltage waveform and make power and voltage ripples of capacitors are balanced automatically.(4)To achieve the cascaded expansion of the proposed seven-level inverter circuit,both symmetric and asymmetric cascaded MLIs are proposed.The advantage of flexible structure is fully utilized to increase the number of system output levels.The systems can run efficiently and increase the output levels through appropriate modulation algorithm.In this paper,the topology structure,working principle,parameter design and modulation algorithm of this series of MLIs are analyzed in detail.On the basis of theoretical analysis,the feasibility of the proposed MLI and its modulation strategy are proved through simulation and experiment.