The Research Of Switched-Capacitor Multilevel Buck-Boost Inverter With Low Voltage Stress

The high frequency inverter in high-frequency AC power distribution system(HFAC PDS)is responsible for converting the DC voltage into AC voltage and conveying it to the high frequency AC bus.Now days the high frequency inverter requires new requirements of cost,output level number and switch voltage stress,especially for photovoltaic arrays with different output voltage levels working in time-sharing.The power density of the system can be improved by using the Buck-Boost structure inverter to replace the Buck inverter and Boost inverter.In order to solve the problem that most of switched-capacitor multilevel inverters cannot have the function of step-up and step-down at the same time,and the problem that the voltage stress of the switch of inverter is too high,a Buck-Boost switched-capacitor multilevel inverter topology with low voltage stress is proposed.The topology does not require magnetic elements and can be applicable to the high frequency field and can be extended to meet a wider input range and a constant output.The topology can work in boost mode or buck mode,and the voltage stress of all switches is less than the input.Firstly,this paper analyzes problem of the existing switched-capacitor inverter,and puts forward the inverter topology combining the Buck-Boost switched-capacitor with low stress structure.The principle of boost mode and buck mode are introduced under expansion unit or not,and the capacitor voltage balance is analyzed.Then the paper analyzes the voltage stress that the proposed topology has low stress characteristic.Compared with the existing inverter topology,the performance and cost advantages of the proposed topology are proved.The paper analyzes the advantages and disadvantages of the various modulation strategies and takes phase disposition pulse width modulation(PD-PWM)as the modulation strategy of the inverter.The capacitor and filter parameters are designed.Aiming at the balance of capacitor charging and discharging time,an inverter parameter optimization method is given.In order to keep the output voltage stable when the input voltage changes,the control strategy of the combination of input voltage feedforward and output voltage PI control is adopted,and the design method of controller parameters is given.Causes of the inverter conduction loss and switching loss are analyzed.Taking the proposed topology five level inverter as an example,the calculation formulas of all losses are given.The design flow of software and hardware circuit is given.Finally,the simulation and physical platform of five level inverter is built for verification.Experimental and simulation result show that the topology can efficiently realize the function of Buck-Boost inversion,and the switches meet the low stress requirement.The inverter has a good dynamic response when the input and the load change.