Research On Cuk Multilevel Inverter

Photovoltaic power generation is one of the important ways to solve the problem of resource shortage and environmental pollution.In recent years,with the continuous improvement of voltage and power levels of power generation devices,higher requirements have been placed on the structure of power electronic converters.Multilevel inverter can achieve high power output with low voltage and power electronic devices,which is widely used in Photovoltaic power generation system.However,the traditional voltage-source multilevel inverters are derived from Buck DC converter,which can only operate in buck operation.When applied to a system where the input voltage varies widely,there will be certain limitations.Based on extensive reading of relevant literature about multilevel inverters,this paper concluded that multi-level inverters are generally extended from three-level inverters.Starting from the typical structure of three-level inverters,a novel Cuk three-level inverter is proposed.Based on Cuk converter,this inverter has single-stage non-isolated structure and the capability of buck-boost invertion.The discontinuous mode of the inductor current on the input side is selected,then introduced the working principle of the Cuk three-level inverter.Design the parameters of the inverter,derive the gain of the inverter,and then verified that the energy storage capacitor voltage in this mode is a constant value.On this basis,this paper built a mathematical model of Cuk three-level inverter,adopt PR control and one-cycle control for closed-loop control.Based on the theoretical analysis,the open-loop and closed-loop simulation verification of the Cuk three-level inverter was carried out.Based on the Cuk three-level inverter,two types of Cuk multi-level inverters have been obtained through expansion.According to the different location of the energy storage capacitors,they are divided into I-type Cuk multi-level inverter and II-type Cuk multilevel inverter.Taking the five-level inverter as the research object,introduce the working principle of I-type Cuk five-level inverter and II-type Cuk five-level inverter,andanalyze the principle of self-equalization of the energy storage capacitor.Finally,open-loop and closed-loop simulations are completed.In order to verify the correctness of the theoretical analysis and simulation results,this paper built two experimental prototypes of Cuk three-level inverter and Cuk five-level inverter,and completes experimental research on the proposed inverter.The experimental results verified the correctness of theoretical analysis and simulation results.