Research On Control Strategy And Energy Management Of Photovoltaic With Energy Storage System

With the depletion of fossil energy sources and the continuous deterioration of the environment,new energy generation represented by PV has received widespread attention.Due to the diversity of photovoltaic generation and the randomness affected by environmental changes,control and energy management of the energy of the whole system has become a current research focus.Based on the analysis of the status of photovoltaic power generation industry and related technologies,the control and energy management strategy of distributed photovoltaic with energy storage system composed of photovoltaic cells,batteries,local load and power grid is studied in detail.This paper selects common DC bus-type photovoltaic with energy storage system as a research object,because of this structure has good extensibility and stability that can make better use of solar energy.First of all,the mathematical model and output characteristics of photovoltaic units and energy storage units are analyzed,at the same time,the working principle of the power conversion unit: photovoltaic interface conversion circuit and bidirectional DC-DC conversion circuit are studied and corresponding parameters are designed.On this basis,the control strategies of each unit are designed,including the MPPT control and constant voltage control of the photovoltaic unit,and the charge and discharge control of the battery.An improved variable-step perturbation observation method was proposed to achieve the maximum power point tracking of photovoltaic units.The simulation results were compared with the traditional control methods to verify the superiority of the improved algorithm.Then,the mathematical model of the three-phase inverter is analyzed and transformed it into two-phase stationary coordinate system by dq coordinate transformation,which simplifies the design of the control strategy.The corresponding control strategy is adopted separately for the operating characteristics of the system that can both be connected to the network and run independently.Constant voltage control or PQ control is used during grid-connected operation to maintain the stability of DC-side bus voltage or to keep the output power constant;V/F control strategy is adopted when grid fault occurs to ensure that the AC-side output voltage amplitude and frequency meet the load demand.The simulation results verify that the control strategy adopted can make the system operate stably under different control objectives,independent of the fluctuation of PV and load power.Finally,the energy management of photovoltaic with energy storage system was studied and a coordinated management strategy based on DC bus voltage threshold is designed.According to different voltage thresholds,the system is divided into four working modes.The control methods of each unit under different modes and the energy flow of the system are analyzed in detail.At the same time,the switching strategies of each converter when the operating mode of the system changes are given.The simulation is carried out in Matlab/Simulink,the simulation results prove the feasibility of the energy management strategy.