Energy Control Strategies For Grid-connected PV System With Hybrid Storage

As the environment pollution and resource scanty become more and more serious,people seek solutions from renewable energy by increasing the efficiency of new energy and increasing their proportion in the whole energy structure.Among those various options of renewable energy,PV energy is one of the most popular choice with promising future.However,as more and more distributed photovoltaic power generation systems are integrated into the grid,the challenges faced by traditional power grids are also increasing.Due to the randomness of the PV plant output and the changes of load,it is necessary to improve the accuracy of predicting PV plant output to make sure the PV power system will participate in grid properly.Therefore,this paper presents an energy management strategy for grid-connected PV systems with hybrid energy storage devices.The power flow control of this system mainly includes the global maximum power point tracking control of the PV array,the grid-connected inverter control,and the charge and discharge control of the two energy storage devices.In order to the guarantee the use of solar resource captured by PV generation,a two-phase perturbation and observation method based on the particle swarm algorithm is proposed to ensure that the PV array is always operating at the global maximum power point.A battery with high energy density characteristics and a super capacitor with high power density characteristics are utilized as the hybrid energy storage device in this paper.The hybrid energy storage system is mainly used to balance the power at the DC bus,wherein the battery is used to balance the steady state power components,and the super capacitor is used to prolong the life of the battery by processing the transient power components.The battery and the supercapacitor are respectively connected to the DC bus using a bidirectional DC/DC converter,which can increase the flexibility of the system.In order to compensate for the power difference between the two ends of the DC bus,a charging and discharging power distribution rule between the battery and the supercapacitor is proposed in this paper.The key parameters in the rules are adjusted by fuzzy logic control.This control strategy can reduce the battery's peak current and dynamic stress while keeping the supercapacitor's charge constant would not exceed the upper and lower limits.At the same time,since the internal resistance of the supercapacitor is much smaller than that of the battery and the utilization rate of the proposed control method is also high,the overall loss of power is also reduced.Finally,the power quality and DC bus voltage in this system is guaranteed by the double-loop control of the grid-connected inverter.Finally,the reliability of the whole system is verified by MATLAB/Simulink simulation.The results of simulation experiments show that with the cooperation of each control strategy,the proposed system has a high utilization rate of photovoltaics,and can deliver high-quality electric energy to the connection points according to the dispatch requirements,and the energy storage equipment can be fully protected while exerting their own characteristics.