Introducing VSC’s Flexibility to Virtual Synchronous Generators by Difference Equations and Lyapunov’s Second Method

Abstract

Despite the advantage in frequency support, many virtual synchronous generators (VSGs) inherit drawbacks of real synchronous generators (SGs), e.g. problem of transient stability. This paper points out that it is not necessary for a voltage source converter (VSC) to operate exactly as an SG. Instead, the merits of VSCs should be better utilized to solve SGs’ drawbacks. Considering VSCs’ flexibility in active power control, this paper utilizes the energy function approach of Lyapunov’s second method in VSG design. In addition to the basic differential and algebraic equations of conventional VSGs, this paper introduces a difference equation to modify the virtual frequency of VSGs. The modified VSG successfully mitigates power angle oscillation and improves transient stability in a way that SGs and conventional VSGs can hardly do. Related RTDS simulations are also demonstrated in the paper.