Research On Microgrid Energy Management And Hybrid Energy Storage Technology

With the rapid development of renewable energy power generation and smart grid,microgrid has attracted more and more attention from all over the world because of its advantages such as flexible networking,low loss,high reliability and controllable power quality.In this paper,the smooth switching of the AC microgrid between the grid connected and the isolated island mode,and the precise control of the parallel power distribution and the voltage sag compensation of the DC microgrid are the key technologies of the microgrid.In this paper,the above two key technologies are studied.Firstly,in order to realize the smooth switching of the two operating modes of AC microgrid,a unified control strategy for battery in hybrid energy storage is presented.Aiming at the deficiency of large disturbance and easy to fail of the traditional mode of operation of the switch,based on the analysis and research of constant power control in grid connected mode,as well as constant pressure constant frequency control in the isolated mode,a unified control strategy for the two operation modes switch of AC microgrid is proposed in this paper.The theoretical analysis and simulation results show that the proposed control scheme,which is equivalent to droop control in the isolated island mode,can maintain the stable voltage amplitude and frequency.Meanwhile,in the grid-connected mode,the system is equivalent to PQ control,photovoltaic and battery can track a given power value.Moreover,the inverter output voltage and frequency can be kept stable when the operation mode is switched,the range of power variation is very small,the system does not overshoot and has stable amplitude,which is much smoother than the traditional mode switching strategy.Secondly,in order to solve the problem that parallel power accurate allocation control and voltage sag compensation are hard to be achieved simultaneously in the DC microgrid,a hierarchical control strategy based on droop control is adopted in this paper,which achieves the reasonable distribution of current and power and compensates the bus voltage sag.Aiming at the deficiency of the shortcomings of the traditional droop control,based on the analysis of the structure and stability of two level controller,a hierarchical control system for DC microgrid based on droop control is designed.The simulation results show the effectiveness of the proposed method,and the droop theory and voltage sag compensation are verified on the dSACE experiment platform.Finally,the experiment platform of AC microgrid is established,and the hardware design and software design of inverter are completed.The experiment of microgrid operation mode switch from grid-connected to the isolated island is carried out,and the experimental results show that microgrid can realize smooth switching to ensure uninterrupted power supply of local load.Furthermore,the experiment of microgrid operation mode switch from the isolatedisland to grid-connected is carried out,the results show that the microgrid realizes the smooth and seamless switching,which verifies the feasibility of the proposed control strategy.