Comparison between virtual synchronous generator and droop controlled inverter

With the growing interest in microgrids to support renewable-energy sources, such as wind power and photovoltaic systems, control of microgrid components, such as inverters, is of increasing importance. Droop controls are methods that without communication lines can stabilize power sharing and grid formation for power generators. A virtual synchronous generator (VSG) is a control method for inverters that mimics both steady-state droop characteristics and dynamic characteristics of synchronous generators (SGs) to enhance the inertia of microgrids. In this paper, some representative VSG control methods are presented and compared. Some characteristics that are not described clearly in the literature are analyzed, such as the different forms of damping effects in VSGs and the necessity of an inner voltage loop. A comparison of VSGs and droop controls leads to the conclusion that a VSG can be regarded as a special type of droop control that mimics the rotor inertia and damping effect of SGs. This is done by changing the compensator parameters of a droop control. Furthermore, in the droop control, if the compensator is designed properly, the dynamic performance of the system can be even better than SGs. Simulations and experimental results are provided to support the conclusions.