Abstract: Aimed at the problem of bus voltage fluctuation caused by power fluctuation of load and distributed generation in DC microgrid, an expanded state observer (ESO) is introduced into the virtual DC motor (VDM) control and a hybrid energy storage frequency division control based on improved virtual DC motor (ESO-VDM) is proposed . Small signal modeling for VDM is conducted, the influence of inertia time constant H and damping coefficient D on the control system is analyzed, and the values of the two parameters are determined.In the case of power frequency division, the lithium battery is controlled by current closed-loop, and the ultracapacitor is controlled by ESO-VDM to improve its inertia and damping characteristics. The simulations with Matlab/Simulink are performed, and the results show that the proposed control algorithm makes full use of the advantages of hybrid energy storage device, smooths the output power of the battery, and improves the stability of the DC bus voltage.

Key words: DC microgrid;hybrid energy storage;virtual DC motor;extended state observer