Research On The Energy Management Control Strategy Of Independent Photovoltaic Energy Storage System

Vigorously developing photovoltaic(PV)power generation can alleviate the problems of energy shortage,power supply shortage and environmental pollution in China.Independent photovoltaic energy storage system does not rely on power grid operation,and has been widely used in places without electricity or frequent blackouts.In the operation process of photovoltaic energy storage system,the instantaneous power balance,system stability and safe operation should be ensured.Therefore,how to effectively solve the problems of power distribution and energy management control of photovoltaic energy storage system is still imminent.In this study,super capacitor(SC)and vanadium redox batteries(VRB)were selected to form a hybrid energy storage system(HESS).In order to give full play to the performance advantages of HESS,this thesis studies the mathematical modeling,optimal distribution and energy management from the three levels of energy storage unit,energy storage module and energy storage system,so as to provide theoretical and methodological support for the application of independent photovoltaic energy storage system.Firstly,the structure of stand-alone photovoltaic energy storage system is introduced,and the mathematical model,working characteristics and converter control of PV,VRB and SC components in the system are analyzed.Maximum power point tracking-constant voltage control is adopted for photovoltaic cells;constant current-constant voltage control is adopted for all vanadium flow cells;power loop-current loop control is adopted for super capacitors.Secondly,the modular composite energy storage system architecture is built,and the two-layer power optimal distribution tactic is proposed,namely "upper optimal configuration-lower power distribution".In the " upper optimal configuration ",the maximum compensation power and the residual charging / discharging capacity of the energy storage module are considered for power distribution.Taking the HESS life cycle cost as the objective function,the optimal allocation model is constructed.The improved cuckoo algorithm is used to discuss the influence of different weight parameters on system constancy and configuration cost.In the " lower power distribution ",the variational mode decomposition method is used to distribute the power of the energy storage unit.The instantaneous frequency of the sub-modal signal is solved by Hilbert transform to determine the number of decomposition layers,which can effectively alleviate the phenomenon of mode overlap and signal over decomposition.Finally,an energy management tactic of stand-alone PV energy storage system considering the residual capacity of the energy storage module is proposed.Dividing the working pattern according to the different states of the system,and selecting the corresponding control circuit on the basis of the working pattern,which improves the flexibility of the system.The emulation results indicate that the system can toggle apace and smoothly in five working modes.Build the verification platform of key technologies of independent photovoltaic energy storage system,including hardware in the loop simulation platform based on Matlab GUI and demonstration platform of photovoltaic energy storage integrated system.The hardware in the loop simulation platform verifies the correctness of the optimal power allocation and energy management control strategy of the stand-alone photovoltaic energy storage system,the experimental platform verifies the effectiveness of the control function of the energy management system.