Research On Chaotic Frequency Modulation To Reduce EMI Level Of High Frequency Isolated Quasi-Z Source Photovoltaic Grid-connected Micro-inverter

The problem of energy shortage and environmental pollution caused by the excessive development and utilization of traditional non-renewable fossil energy has become increasingly prominent.Photovoltaic power generation has attracted more and more attention and research due to its rich resources,green clean and other advantages.Inverter is one of the core components of photovoltaic power generation system.The integrated structure of micro-inverter can reduce the impact of photovoltaic panel damage and inverter fault on the system,and has incomparable advantages over traditional centralized inverters.As a new type of topology inverter,isolated quasi-Z-source micro-inverter is suitable for photovoltaic power system because of its high efficiency of power conversion,high boost ratio and electrical isolation.By increasing the working frequency of the inverter,the inductance and capacitance volume of the inverter can be reduced,so that the inverter has higher power density.However,high frequency switching action will produce lots of current and voltage mutations,resulting in electromagnetic interference,which affects the stable operation of other components or the whole system and power grid.Chaotic frequency modulation is a method to reduce the electromagnetic interference level of switching converter from the source.This method utilizes the broadband continuous spectrum characteristics of chaotic signals to broaden the electromagnetic interference noise energy peak to the surrounding continuous frequency band,so as to reduce the spectrum peak and make the circuit have better electromagnetic compatibility.In this article,the high frequency isolated quasi-Z source photovoltaic grid-connected micro-inverter is taken as the research object,and the chaotic frequency modulation technology is used to suppress the electromagnetic interference of the inverter.Firstly,the working principle of high frequency isolated quasi-Z source photovoltaic grid-connected micro-inverter was analyzed.The high frequency characteristics of each device in the inverter were analyzed based on device behavior,and the calculation method of each parasitic parameter was given.Based on the conduction EMI test principle and conduction EMI analysis of high-frequency isolated quasi-Z source photovoltaic grid-connected micro-inverter,the interference source of high-frequency noise and the conduction path of electromagnetic interference were clarified.Secondly,the chaotic signal generated by Chua’s circuit was analyzed,and a new multi-scroll chaotic system of symmetrical piecewise Chen system was designed,and the circuit implementation scheme was given.The chaotic signal and its spectrum waveform generated by the two chaotic systems were obtained by simulation.The two chaotic systems were compared from the perspective of numerical analysis and spectrum probability density,which provided chaotic frequency modulation spread spectrum signal for the subsequent suppression of electromagnetic interference of high frequency isolated quasi-Z source photovoltaic grid-connected micro-inverter.Then,the traditional PWM modulation and chaotic frequency modulation modes were analyzed in detail.From the perspective of spectrum quantification,the characteristics of chaotic frequency modulation inhibiting the EMI level of high-frequency isolated quasi-Z source photovoltaic grid-connected micro-inverter were analyzed.Through simulation,the PWM driving pulse spectrum of the inverter under constant frequency,sinusoidal spread spectrum and chaotic spread spectrum was obtained,and the effectiveness of chaotic frequency modulation in suppressing the EMI level of high-frequency isolated quasi-Z source photovoltaic grid-connected micro-inverter was verified.Finally,the main circuit,peripheral circuit and DSP software system of the isolated quasi-Z source inverter were designed,and a 300 W experimental prototype was built.Through Saber-Simulink co-simulation,it was verified that the EMI level of the inverter was significantly suppressed when the chaotic signal generated by the multi-scroll chaos of the even symmetric piecewise Chen system was used as the spread spectrum signal modulated by chaotic frequency.Meanwhile,the influence of different spread spectrum modulation coefficients on EMI level and grid current was verified by simulation.At last,the correctness of the theory and simulation was verified on the experimental prototype.