Identification of low‐frequency oscillation mode and improved damping design for virtual synchronous machines in microgrid

Abstract

The low‐frequency dynamics of virtual synchronous machine (VSM) depends on multiple factors. In this study, the oscillation mode of a single VSM is first identified by exploring the evolution of oscillation from synchronous mode to sub‐synchronous mode with the variation of structure and parameters. The inter‐oscillation modes among multiple VSMs modelled in quasi‐state phasor domain are then studied by decomposing into mean motion and relative motion. Inspired by and weak‐coupling‐based coherency identification, the associated VSM group can be fast identified and used for effective stabilizer location. The approximate eigenvalues can be fast obtained by system decomposition in uniform‐damping scenarios or by extended‐equal‐area‐criterion approach in non‐uniform‐damping scenario. An improved design for lead–lag compensation is proposed to damp both synchronous and sub‐synchronous oscillation of VSMs. Effectiveness of the proposed control strategy in grid‐connected/islanded mode is verified with real‐time simulation.