Sensitivity Analysis and Frequency Dynamics of Grid-Connected Converters with Virtual Inertia

For the participation in the frequency control of the system, power converters can be controlled with different strategies and methods, sharing the common concept of virtual inertia capability. In this work, a sensitivity analysis of two main categories of converter controls with virtual inertia is presented. The considered schemes are a grid-following current vector control with additional virtual inertia block and a grid-forming control scheme based on virtual synchronous machine concept. A proper basis for the comparison is first assessed providing an analytical correlation between the control parameters of the two schemes. For the two control strategies, the sensitivity analysis of the most relevant factors is performed on the linearised model of the system. Time-domain simulations are also performed on the full non-linear model, investigating the frequency dynamics of the two control structures under different oscillating conditions. The analytical comparison and the results of the analyses indicate specific and distinct oscillatory characteristics of the examined control structures, pointing out for each of them opportunities and limitations for participation in the frequency dynamics of the system.