Hi again PF. I recently came across the term "virtual inertia" when reading about photovoltaics and power converters (DC/DC, DC/AC etc.). Article: http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=6953370, not sure if people are able to view the article, I have access via university library. I have problem understanding the term virtual inertia, PV modules themselves have no inertia, but when connected together with a energy storage device, a battery for example, can introduce virtual inertia to the grid, how? My background is from mechanical, just started learning electrical engineering. So from a mechanical background I have trouble understanding how the setup mentioned above can introduce inertia without any rotating parts, hence virtual inertia.