Research On The Control Strategy Of Grid-Connected Photovoltaic Based On Improved Quasi-Z-Source Inverter

In recent years,the energy crisis and environmental issueshave promoted the rapid development of the new energy power genetation industry.Among them,distributed photovoltaic power generation system has the advantages of nearby utilization,cleanness and efficiency,thus it has a promising development prospect.The grid-connected inverter is the core component of distributed power generation system,and has important influence on the reliability and energy conversion efficiency of the system.In this paper,an improved quasi-z source inverter is used as a grid-connected inverter for distributed photovoltaic power generation system to improve the reliability and power quality of the whole system.Firstly,this paper introduces the development status ofdistributed photovoltaic power generation,whichexpatiated and summarized from three aspects of topology structure,modulation strategy and grid-connected control strategy.It also analyzes the working principle of the switched inductor quasi z-source inverter(SL-qZSI)in detail,and builds its mathematical model with the State-Space averaging method,and study the characteristics of the system.Secondly,it analyzes three kinds of common modulation strategy of switch inductor quasi Z source inverter.For the three kinds of traditional modulation strategy have the coupling problem of shoot-through duty ratio and modulation index,it uses a novel PWM modulation strategy,which adds a new control parameter Kto achieve the decoupling between shoot-through duty ratio and modulation index.And the performance of four modulation strategy gets the comparative analysis and simulation.Then,the control strategy of the whole photovoltaic grid connected system is designed,including three parts:maximum power point tracking,DC side voltage control and AC side current control.More specifically,An improved MPPT method is used to realize the tracking of photovoltaic array maximum power point;It improves DC link peak voltage direct control method,through measuring the sum of the two capacitor voltage in impedance source network to obtain the DC link peak voltage feedback value,and then realize the stable control of DC link voltage control of grid;It adopts the traditional current loop decoupling method to control the grid-connected current,thus the active power and reactive power can adjust independently.Finally,the main parameters of the whole PV system is designed,and it builds a complete system simulation model in Matlab/Simulink.The effectiveness of network control strategy is verified by simulation and analysis.The above three control parts ensure the high efficiency and high quality of grid-connected inverter.