Abstract: The photovoltaic-energy storage unit, based on virtual synchronous generator （VSG） control, can be used to form island microgrid, and provide forceful support for the stable operation of microgrid. However, the imbalance between power consumption and generation in the cycle of running, will get the state of charge （SOC） of energy storage equipment beyond its safe operation region, due to the fluctuation and intermittent of distributed generator output. According to this issue, the method of adjusting droop coefficient according to SOC is introduced into the VSG control. Through analysis, it is found that it may be difficult to achieve the control target by changing the droop coefficient. During the regulating process, the system can even lose its stability. By introducing the concept of adaptive droop characteristic, further improvement of VSG control is made by translating the whole droop characteristic. The improved VSG control reduces the impact on system stability. The reasonable allocation of active power and the fast adjustment of SOC can be realized more effectively. Relevant theoretical analysis and proposed scheme are verified by the simulation system built with Matlab/Simulink simulation tool.

Key words: virtual synchronous generator, droop characteristic, photovoltaic microgrid, adaptive control, supercapacitor