Research On Dual-Mode PV Inverter Control System And Multi-machine Parallel Technology

With the development of distributed photovoltaic power station and smart micro-grid,the trend of household photovoltaic inverter development will tend to dual mode photovoltaic inverter.This paper presents the background and significance of the project research by analyzing the development of distributed photovoltaic technology trends in the future.With dual mode photovoltaic inverter as the research project,this paper focus on the hardware solutions,hardware parameter optimization design,Stand-alone work control algorithm and Parallel control algorithm.The paper reviews the research status at home and abroad from dual mode PV inverter topologies,key technologies for stand-alone work control,and key technologies for multiple machines in parallel,and then completes hardware circuit design based on theoretical analysis and simulation modeling,and develops inverters.Control system,and finally build experimental platform to test the technology program feasibility.The main work of the thesis is as follows:(1)The dual mode photovoltaic inverter hardware solution was determined.According to the performance index,it is determined that the "interleaved boost circuit + full-bridge circuit" is used as the main power topology scheme,the TMS320F2809 is used as the control core,the main power topology scheme is simulated,and the hardware parameters are analyzed and designed in detail based on the overall scheme.(2)A control strategy for dual mode PV inverter operation mode was proposed.Setting 16 operating modes and adopting the two-level judgment basis of "external components +photovoltaic energy" as the operating mode switching logic,it was confirmed that this control strategy can achieve stable and reliable switching and effectively perform energy management.(3)Focused on the stand-alone control strategy and multi-machine parallel algorithm.A fuzzy controller was introduced into the disturbance observation method,and an adaptive variable-step MPPT control algorithm was designed to improve the tracking accuracy of the algorithm.The simulation and experimental verification were performed.The double closed-loop control algorithm of "voltage PI outer ring + current PR inner ring" was adopted,and analyzes the characteristics of high control accuracy of the algorithm from two aspects of theory and simulation;proposes an improved PQ drooping method,adds a differential link in the PQ drooping method,simulation and actual parallel experimental results prove that the algorithm effectively improves the current sharing control algorithm Dynamic response performance.(4)Build an experimental platform for experimentation.Developed a grid-connected photovoltaic inverter prototype,tested the steady-state accuracy of the constant power tracking and the tracking efficiency of the MPPT algorithm,tested various performance indicators of the off-grid and grid-connected operating modes,and tested the parallel operation control system of multiple machines,Stability and dynamic response of the current sharing algorithm.The experimental results show that the operation mode of the grid-connected PV inverter can be switched stably.The tracking efficiency of the MPPT algorithm is as high as 99.66%at 2500W power point,and the dynamic response performance is good.The efficiency can reach 92%when working off-grid.The efficiency is as high as 94%.The rest of the test items meet the requirements of the performance index.The stability of the two inverters is equalized,When the single inverter is switched on and off,the curreat sharing algorithm can achieve the current sharing control within 10ms.