With the growing penetration level of inverter-based power sources into the grid, the impact of low-inertia, damping and deployment of new controls has raised several questions concerning system stability. Virtual synchronous machine (VISMA) has been proposed to provide ancillary services necessary for grid stabilization. In a multi-VISMA microgrid, rotor angle stability of the power system is dependent on the active power balance after small perturbation. Using relevant analytical models are essential issues for microgrid stability analysis. This paper presents a comprehensive small-signal stability analysis to study inherent electromechanical oscillations in the virtual-rotors. The subsystems of the microgrid consisting of VISMA, network and load were all modelled in Synchronous Reference Frame. The small-signal model (SSM) was tested on IEEE-9 bus system with VISMA replacing electromechanical synchronous machines on the network. To validate the developed numerical analytics, dynamic responses of the SSM are compared with those of the non-linear system dynamics and the results reveal that the developed linearized SSM is sufficient to accurately characterize behaviour of the VISMA microgrid when operated in autonomous mode. Eigenvalues analysis and parameter sensitivities of the critical modes were investigated. Oscillatory participations of the VISMAs and steady stability limit of the microgrid was also carried out.