| With the shortage of energy and the deterioration of the environment,it is urgent to find clean energy to replace traditional energy.Solar energy is a new type of pollution-free and renewable energy,combined with the high-efficiency and flexible characteristics of micro-grids,and has now been widely used.However,due to the low energy conversion rate of photovoltaic power generation and poor power adjustability in photovoltaic micro-grids,the energy cannot be used efficiently.Therefore,this article focuses on the maximum energy supply problem of photovoltaic micro-grids,which has theoretical significance and practical value.Taking photovoltaic micro-grid as the research object,focusing on maximum power point tracking(MPPT)control,energy storage module control,photovoltaic inverter control,and on-grid switching control,in-depth research on the grid-connected and off-grid systems Structure,and gives the control method of each link in different modes.First of all,as the basis for realizing the maximum energy supply,a fuzzy adaptive disturbance MPPT control combined with the power limit mode is improved to take the system overvoltage and overcurrent conditions into consideration,so that the inverter can operate in the MPPT mode under normal conditions.When the instantaneous power is too high,the power limit mode is combined with the excellent nonlinear system control characteristics of fuzzy MPPT,which can make the most reasonable use of photovoltaic energy.Secondly,in order to achieve the maximum active power output and the equal division of reactive power,based on the Newton iteration method,an improved droop control strategy based on the virtual impedance of the iteration method is proposed,the mathematical model is derived,and the overall controller is designed.The simulation obtained the waveform diagram of active power adjustment and reactive power sharing.After comparing with the traditional droop control,it shows the advantages of the control strategy given in this thesis.At the same time,the convergence analysis of the control method is carried out,and the root locus diagram is drawn to verify its feasibility.Considering that the virtual impedance itself has a weak damping phenomenon,the introduction of the system will bring about problems such as an increase in voltage drop and excessive output impedance of the system,which may easily cause the tie line to trip due to overcurrent and cause power supply interruption.Therefore,in order to make the photovoltaic microgrid system stable and smooth,the basic model is obtained by analyzing the state of charge and equivalent circuit of the lead-acid battery for the two major factors that affect the reliability of power supply,one of which is the energy storage link.After adding virtual impedance,the characteristics of distributed power and load are taken into consideration,and the overall system model is established,and its effectiveness is verified by simulation;the second is the switching between grid-connected mode and the off-grid mode,and the system is not affected by frequency and voltage deviation when grid-connected.It can operate stably when off-grid,and realize the power balance between distributed power sources and loads.The system models in the grid-connected mode and the off-grid mode are built on the Simulink simulation platform.The simulation verifies that the fuzzy control MPPT has smoother output waveform and larger output power than the disturbance observation method MPPT,and the limit is added when off-grid.The power link improves the reliability of power supply.The comparative analysis shows that compared with the traditional control method,the iterative virtual impedance control can achieve the maximum active power output and the equal distribution of reactive power,which improves the system’s utilization of distributed energy. |
PDF Full Text Request