Research On Multilevel Inverter And Its Extended Topology

Multilevel inverter has been concerned due to its low total harmonic distortion,low switching voltage stress,low switching loss,and the requirement of output filter is smaller.The classical multilevel inverter topologies include cascaded H-bridge inverters,neutral point clamped inverters and flying capacitor inverters.With the number of levels increasing,the harmonic distortion rate of the inverter is further reduced.However,the number of components required by the topology increases at the same time,which leads to the decrease of device efficiency,the increase of hardware cost and the decrease of power density.Therefore,using fewer components to achieve more levels has become an issue for scholars to study and explore.The problem of low power density in multilevel topology is discussed in this paper,and two single-supply multilevel inverter topologies with high power density and good scalability are proposed in this paper.The main research work of this paper is as followsFirstly,aiming at the problem that a large number of components are needed in the existing single-supply five-level inverters,which leads to the reduction of power density,an improved single-supply four-switch five-level inverter topology based on the voltage sharing technology of coupling inductance is introduced in this paper.Structurally,a coupled inductor and two diodes are added to the H4 two-level full bridge inverter.In terms of output characteristics,the LPS-PWM modulation strategy with frequency doubling capability is adopted,so that a pair of complementary power switches work at the fundamental frequency,and the other pair of high-frequency switches work at half of the output sine wave modulation frequency,thus effectively reducing the switching loss and electromagnetic interference caused by high switching frequency.The working principle and characteristics of the improved five-level inverter are analyzed detailed in this paper,the design method of key circuit parameters are discussed carefully,and the effectiveness of this topology is verified by detailed simulation and experiment.Then,in view of the contradiction between the boost capability of the existing nine-level inverter based on switched capacitor and the number of components required in its expansion performance,a basic unit of single-supply nine-level inverter with quadruple boost capability is proposed.The basic unit of the proposed nine-level inverter can be used as a separate inverter.Only nine switches,two diodes and two switched capacitors are needed in the basic unit to realize nine level output.In the working states,self-voltage balance is realized in each capacitor and no other control is needed.Based on the basic unit,four levels will be increased with every two switches,one independent diode and one capacitor added,so the topology has excellent scalability.A simple pulse width modulation scheme based on logic-gate is developed for the gating switch of the proposed topology.The working principle of the basic unit topology is introduced,the calculations of voltage/current stress on switches and the determination of the capacitance are given in this paper.The basic unit of the proposed topology is analyzed in detail through simulation and a prototype with output power of400 W,and it is compared with the recently reported nine-level inverter topologies to highlight the advantages of the proposed topology.