Research On Coordinated Control Strategy Of Multi Energy Storage Units In Photovoltaic System

With the rapid development of the economy,the problem of energy shortage and environmental pollution is becoming more and more serious.Solar energy has the advantages of wide distribution and green environmental protection.Therefore,the photovoltaic power supply system has been paid more attention.Because of the randomness of the output power of the photovoltaic cells,the energy storage system has become an important part of the stable operation of the photovoltaic power supply system.In order to realize the stable operation of the system and give full play to the advantages of each energy storage unit,the control strategy of the energy storage system has become a hot spot of research.Firstly,the overall structure of photovoltaic power supply system with multi energy storage units is introduced,and its working principle is analyzed.Then,a mathematical model of photovoltaic cells considering the effects of illumination and temperature is established,and a practical mathematical model of storage battery and supercapacitor is established.Secondly,the PV array maximum power point tracking using the incremental conductance method,and use PI to control the voltage tracking;current loop controller design of battery bidirectional DC/DC converter,realize the bidirectional power flow and charge discharge control,voltage and current double loop controller and the design of super capacitor bidirectional DC/DC converter,DC bus voltage stability super capacitor and bidirectional power flow and charge discharge control.Then,the control target of multi energy storage unit is expounded.Low pass filtering algorithm is adopted to make the super capacitor and battery assume the high-frequency part and smoothing part of the power fluctuation respectively.In view of the difference in charge state of battery pack,the improved SOC droop control strategy and hierarchical control strategy are adopted respectively to achieve energy balance between batteries and optimize their running state.Finally,the simulation model of independent photovoltaic power supply system with multiple energy storage unit in Matlab/Simulink,the storage unit coordinated control strategy is simulated.The results show that the proposed control strategy can realize the storage unit between the power allocation and enhance system stability.In addition,compared with the hierarchical control,the improved SOC droop control is more smooth and more conducive to the safe and stable operation of the energy storage system.