Virtual Synchronous Generator Design to Improve Frequency Support of Converter-Interfaced Systems

This article presents a control strategy based on the virtual synchronous generator (VSG) concept to improve the frequency support of converter-interfaced systems. The strategy has the flexibility to set virtual inertia, power-frequency droop, damping, and response speed. In previous VSG designs, the response speed depends on the virtual inertia; therefore, both specifications cannot be selected independently. In the present article, this limitation is overcome by using a VSG structure able to set the response speed independently of the other design specifications, giving an additional degree of freedom to provide frequency support. In addition, the ability to select the speed at which the VSG draws power from the dc side allows for better use of the available dc power supply. The proposed VSG does not require phase-locked loop to achieve the damping effect; it has a simple implementation and a systematic design procedure. The control strategy is validated in a multimachine case study based on the Argentinian power system, including several VSGs. Aspects such as oscillation damping and improvements in the rate of change of frequency (RoCoF) and frequency nadir are discussed and compared with previous VSGs.