Static synchronous generator model for grid-tied PWM inverters of renewable energy generation

Three-phase PWM inverters function as energy converters and grid-connected power generators in renewable energy generation systems, and its dynamic and stability characteristics affect the security and reliability of the entire generator sets and even the connected grid. The three-phase PWM inverters based on the VSG (Virtual Synchronous Generator) technology, which is referred to as the Static synchronous generator (SSG) in this article, possess the operation characteristics of Rotational Synchronous Generator (RSG), and thus enables a compatible connection of the new energy to the conventional power grid. This paper analyzes the inherent unity of SSG and RSG by the mathematical model and physical mechanisms, and applies the concept, tools and methods of the stability analysis in RSG to the SSG system. The equivalent inertia, damping and synchronizing coefficients are introduced for the dynamic analysis of SSG and the small-disturbance stability is analyzed accordingly.