Study On The Optimization Of Photovoltaic-Storage Co-Generation System And Energy Storage Capacity

The new energy represented by photovoltaic has strong uncertainty and randomness,making a high proportion of new energy connected to the power grid will lead to a decrease in the regulation ability and anti-interference ability of the power system,thus bringing hidden dangers to the safe and stable operation of the power grid.Energy storage is an important means to ensure the safe and stable operation of new energy consumption and power system,but the high cost of energy storage is a serious obstacle to its large-scale application.Therefore,this thesis firstly studies the joint control of PV and energy storage systems,using a model-based predictive control method to smooth out PV output fluctuations and improve the voltage tolerance of the system when it is disturbed.Secondly,the optimal allocation of energy storage has also been studied in order to reduce the cost of storage.In this thesis,several important components of the photovoltaic storage system are first modelled and analysed.A photovoltaic storage system connected to the grid with a common DC bus is chosen as the object of study.The PV cell array,the Boost boost circuit and the PV grid-connected inverter are analysed and mathematically modelled respectively.The second-order RC equivalent circuit model of the energy storage battery is also established and the principle of the two operating states of the battery under the bidirectional DC/DC converter is analysed.Based on the theoretical analysis and the mathematical model,the PV MPPT control strategy and the energy storage charge/discharge control strategy are designed.Then,the traditional control strategy is improved by the idea of model predictive control for the problem of poor performance of the traditional double closed-loop control when subject to disturbance.Under normal grid conditions,based on the established value function,the optimal action command for the controller is derived by an optimisation method,and then the energy storage and PV power are controlled to interact in a coordinated manner in order to stabilise the DC bus voltage and promote a friendly grid connection.When a symmetrical voltage dip occurs in the grid,the current is used as a predictive model to control the switching tube action by solving for the switching state corresponding to the minimum value function,which enables the limitation of the inverter output current during low voltage ride-through and the use of energy storage to stabilise the DC bus voltage.It is verified through simulation that the MPC-based control strategy for grid-connected photovoltaic power generation system has good dynamic response performance and anti-disturbance performance.Finally,the optimal configuration of energy storage is studied.A multi-objective optimal configuration model for energy storage is established with the cost of energy storage,node voltage deviation and load power fluctuation as the objective functions.An improved whale optimisation algorithm is used to find the optimal solution.The proposed optimal allocation method is verified through case studies to reduce voltage and load power fluctuations while reducing costs.There are 69 figures,9 tables and 92 references in this thesis.