Active power-frequency oscillation suppression strategy for parallel VSG system based on fractional-order control scheme

Since most distributed power sources in microgrids lack the necessary inertia, the frequency stability of the system deteriorates. By emulating the dynamic characteristics of traditional synchronous generators, virtual synchronous generator (VSG) technology provides essential inertia support for power systems, emerging as an effective solution. However, while providing essential inertia and damping, VSGs inevitably induce active power oscillations, a problem that is critically exacerbated when multiple VSGs operate in parallel. To address this issue, this paper proposes an active power-frequency oscillation suppression strategy based on a fractional-order control scheme for the parallel VSG system. By incorporating two fractional-order feedback paths into the VSG active-power control loop, the proposed strategy provides additional degrees of freedom for shaping the active-power and frequency responses. Consequently, the proposed strategy effectively attenuates active-power and frequency oscillations in the parallel VSG system. Subsequently, the closed-loop stability of the parallel VSG system under the proposed fractional-order strategy is established using a Lyapunov energy function. Finally, hardware experiments on a two-unit parallel VSG platform show that, under a resistive-load disturbance, the proposed strategy reduces the maximum active-power overshoot from 9.4 % to 2.6 % and shortens the settling times of the active-power and frequency responses from approximately 0.50 s to 0.21 s, relative to traditional VSG control. This corresponds to an approximately 58 % reduction in settling time, while the desired 2:1 steady-state active-power-sharing ratio is maintained. The improvement in active-power–frequency dynamics is also retained under inductive-load and nonlinear-load disturbances.