Research On Photovoltaic MPPT And Power Coordinated Control In DC Microgrid

With global energy crisis,environmental problems aggravating,and loads' demands for better power quality enhancing,the technology of distributed power generation based on renewable energy has been rapidly developing.However,distributed power generation is susceptible to environmental conditions and shows great randomness and volatility.If it's connected to the power grid directly,there will be negative impacts.The technology of microgrid has become the key to this problem.In this paper,the MPPT algorithm and the power coordination control strategy in DC microgrid,which consists of the distributed photovoltaic power generation module,the battery energy storage module,the inverter and DC loads,are studied.This paper introduces the component modules and their accesses to DC microgrid,Matlab/Simulink is used to study the modeling and control strategies of the photovoltaic power generation module,the battery energy storage module and the inverter link respectively.The general simulation model of PV array is built and the photovoltaic characteristics curves under different external conditions are simulated.PV's control modes of MPPT and CVC are designed and verified through simulation.Experiments are designed to analyze the charging and discharging characteristics of the battery module in Matlab/Simulink.These experiments verify the coincidence degree of characteristics between the battery's model and real one.Constant voltage control methods of battery are designed and verified through simulation.As for the inverter,the VOC method is adopted and verified through simulation.Based on the prerequisite of contant DC bus voltage in DC microgrid,this paper proposes a fuzzy control based,voltage sensor-less MPPT algorithm and designs the fuzzy MPPT controller detailedly.This algorithm eliminates voltage sensors and reduces the cost as well as the volume of the system.The fuzzy control is added to achieve the goal of variable step tracking.In this way,the MPPT speed is significantly improved.The superiority of the proposed algorithm is proved by comparing with the traditional perturb & observe algorithm under various conditions,and the proposed algorithm's influence on the system's performance under non-ideal condition is analyzed.Based on the obove simulation modules and control strategies,an overall simulation model of the DC microgrid is established and a power coordination control strategy is designed.According to the control target of the system,with the signal of DC-bus voltage taken as the basis,the conditions of battery overcharging,over discharging and overcurrent protection considered,the operational process of the DC microgrid is divided into four operating modes.The steady state and transient state of the four modes are simulated through examples.The results show that the strategy can effectively maintain the stability of the DC bus voltage and realize the smooth handoff between different operating modes.