A Novel Single-stage Single-phase Voltage-fed Quasi-Z-source Photovoltaic Grid-connected Inverter

Quasi-Z-source inverter can perform buck-boost conversion ability,bridge arm switches can be short and have no dead zones,and the AC output waveforms are of high quality.However,the boost factor of quasi-Z-source inverter is limited by modulation,it is not suitable for low input voltage and wide range of input voltage applications in new energy generation.Therefore,on the basis of the research of the traditional quasi-Z-source inverter,it is of great research value to improve its boost capacity.It is a frontier topic in the field of new energy generation.In order to improve the boost ability,power density and system performance of quasi-Z-source inverters.Based on the study of a large number of modified quasi-Z-source inverters with strong boost ability,an novel quasi-Z-source inverter with strong boost capacity is proposed.The working principle,modulation scheme,control strategy,magnetic integration design and key circuit parameters of the inverter are studied and designed.Finally,the important conclusions are obtained by simulation and experiment.A novel single-stage single-phase voltage-fed quasi-Z-source photovoltaic grid-connected inverter is composed of a magnetic integrated impedance network,a single phase inverter bridge and a LCL filter.According to the shoot-through state and nonshoot-through state of inverter,the expressions of capacitor voltage,inductance current and voltage gain are derived.Compared with other quasi-Z-source inverters,the proposed inverter has the advantages of strong boost ability,voltage stress of energy storage capacitor and power switch device are small.The advantages and disadvantages of various modulation strategies are analyzed,and the working modes of the high frequency switching process are analyzed.This paper analyzes the AC and DC magnetic flux of the magnetic integrated device and obtains the expressions of each magnetoresistance.On these basis,the magnetic integrated equivalent inductance and inductance current under different turns are studied deeply.Last the theoretical basis for the realization of energy storage inductor current zero-ripple wave is obtained.Based on the small signal model of a magnetic integrated strong boost ability impedance network,the influence of each parameter variation on the system performance is studied,and the correctness of the analysis is verified by simulation.The system transfer function is obtained and on this basis,the research analyzes the energy storage capacitor voltage outer loop,the output current inner ring control strategy and MPPT of photovoltaic cell voltage loop control strategy.To meet the performance indexes of the inverter,the design criterion of energy storage capacitance,magnetic integrated inductance,power switch device and LCL filter are derived.The 1kW 80-110VDC/220V50HzAC PSIM simulation and experiment of a novel single-stage single-phase voltage-fed quasi-Z-source photovoltaic grid-connected inverter have been completed.The results of PSIM simulation and the experimental results show that the proposed inverter has the advantages of strong boost ability,high reliability,high power density and good output waveform,and has verified the correctness and feasibility of the proposed circuit topology and control strategy.