Research On Structure And Control Strategy Of Distributed MPPT Photovoltaic System

Photovoltaic technology is an important way to alleviate the global environmental crisis and energy crisis,which has drawn much attention from domestic and foreign researchers.Because of the distributed MPPT for every photovoltaic cell,the distributed MPPT photovoltaic system has high system efficiency and can greatly increase the power generation of the photovoltaic system,and has become the focus of current research.This paper took the distributed MPPT photovoltaic system as the research object,deeply studied MPPT algorithm and the influence of the partial shading of the PV modules on the every part of the system,and provided a theoretical basis for optimizing the structure and control strategy of photovoltaic power generation systems.Firstly,distributed MPPT photovoltaic system was taken as the research object,the system structure,working principle and the technical advantages were introduced in detail.And the existing problems of the distributed MPPT photovoltaic system were pointed out,such as the control means of the MPPT function,the partial shading of the photovoltaic module,DC bus voltage control and amplitude selection and overvoltage protection of DC bus voltage.Next,the MPPT control method of direct power control was given,and the theoretical basis of direct power control was derived in detail,the principle of continuous detection of working points and the closed-loop control design method of the system were described.Then,the model of tandem distributed MPPT system was established,and the coordination relationship between PV modules,power optimizer and inverter DC bus side was analyzed.Under the premise of the partial shading of PV,it was concluded that the maximum degree of shading the system can adapt to was proportional to power optimizer output voltage upper and lower voltage ratio,and summed up the methods of design about the output voltage range and rated output voltage of the power optimizer,the amplitude of the DC bus voltage of the inverter,and the the number of series components in the system.A DC bus voltage overvoltage protection method that not based on the communication principle was proposed to simplify the system structure.Finally,a power optimizer with MPPT function has been designed,including hardware design and software implementation.The hardware design included the design of the main circuit,the drive circuit,the detection circuit,the auxiliary power supply and minimum system of the digital control.The software implementation mainly gave the program flow charts of main program and interrupt service program.By building a simulation platform on MATLAB,the correctness of the theory in chapter 3 and in chapter 4 were verified.At the same time,a 300 W power optimizer prototype was set up to conduct an experimental study.Experimental results confirmed the correctness of theoretical analysis and design calculations in chapter 5.