Abstract
Aiming at the problems of transient over-current and over-voltage in the switching process of AC/DC hybrid microgrid in grid-connected mode and island mode, which leads to the sudden change of transmission power and seriously affects the power transmission quality. In this paper, an improved seamless switching control strategy of droop control with disturbance observer is designed. The main work is as follow: according to the diffident power transmission calculation methods of droop control in grid-connected mode and island mode, the adaptive switching is realized by detecting the current and frequency at Point of Common Coupling(PCC) of public power grid. Secondly, the switching from island mode to grid-connected mode will cause impact due to the difference of frequency, phase and amplitude between microgrid and public grid, and even cause system collapse. So the pre-synchronization control of frequency, phase and amplitude is designed. Based on the droop control, the disturbance observation(DOB) is added, which can quickly track the sudden change of system current, and suppress the sudden change by the difference between the tracking value and the actual value, so as to realize the smooth switching from island to grid. Finally, the effectiveness and feasibility of the control strategy are verify in Matlab/Simulink.
Highlights
In recent years, with the large increase of renewable resources such as solar energy and wind energy in distributed generation(DG) units, the concept of microgrid has been gradually taken into account
The AC/DC hybrid microgrid can be divided into grid-connected mode and island mode according to whether it is connected to the public grid through PCC or not
SIMULATION VERIFICATION OF CONTROL STRATEGY In the process of grid connected/island mode switching, due to the difference of frequency, phase and voltage amplitude between AC/DC hybrid microgrid system and public grid, impact occurs during mode switching, which affects the stability of the system
Summary
With the large increase of renewable resources such as solar energy and wind energy in distributed generation(DG) units, the concept of microgrid has been gradually taken into account. In reference [10], the idea of hierarchical control, combined with droop control It achieves seamless switching between island mode and grid-connected mode, and has plug and play of load unit and circuit recovery capability. The BIC transmission reference active power in the grid-connected modes is as follows: PrBeIfC = P∗dc. PRINCIPLE OF DISTURBANCE OBSERVER When switching between grid-connected mode and island mode, it will lead to power mutation, which will cause large deviation of AC/DC bus voltage and frequency, and seriously affect the stability of microgrid system. The system is globally asymptotically stable and the disturbance can be accurately tracked
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