Active power and frequency oscillation suppression strategy for parallel virtual synchronous generators system based on fractional-order virtual inertia

• Replacing the integer-order virtual inertia of the parallel VSG system with the fractional-order virtual inertia, compared with other control strategies that can suppress the active power and frequency of the parallel VSG system, it does not rely on communication and does not increase the control order of the system, which is convenient for design. • A small-signal state-space model of a fractional-order parallel VSG system is developed, and the stability of the parallel VSG system under the algorithm is demonstrated using root-trajectory analysis, and optimal order of the fractional-order is selected through the ℋ 2 and ℋ ∞ norm. • By adjusting the order of the fractional-order virtual inertia, the dynamic and steady-state response performance of active power and frequency in the parallel VSG system can be significantly improved. • Compared with the traditional PVSGS control strategy, the proposed strategy performs better in dynamic and stable states, with the adjustment time reduced by 68 %. The rate of change of frequency (RoCoF) performance has also been significantly improved by 57 %, enhancing the stability of the isolated microgrid. Although virtual synchronous generators (VSGs) operating in parallel can provide inertial and damping support for isolated microgrids, when load disturbances occur, it will lead to problems such as active power and frequency oscillations. Since the weak overcurrent capacity of VSG, active power and frequency oscillations can cause VSG to overload or even be damaged. Thus, it is essential to suppress the active power and frequency oscillations when parallel VSGs system (PVSGS) in isolated microgrids. Therefore, a PVSGS control strategy based on fractional-order virtual inertia is proposed in this paper. Replacing the integer-order virtual inertia of each VSG in the PVSGS with the fractional-order virtual inertia and appropriately adjusting the order of the fractional-order virtual inertia can effectively suppress the active power and frequency oscillations of the PVSGS without inducing steady-state error in the system. Compared with the traditional PVSGS control strategy, the proposed strategy performs better in dynamic and stable states, with the adjustment time reduced by 68 %. The rate of change of frequency (RoCoF) performance has also been significantly improved by 57 %, enhancing the stability of the isolated microgrid. Firstly, the oscillation mechanism and the influence of inherent parameters on stability of traditional VSG and PVSGS is analyzed. Moreover, a small-signal state space model of the fractional-order PVSGS is developed, and the stability of the PVSGS is proved by using the root locus analysis method. Then, the optimal fractional-order virtual inertia order of the PVSGS are selected by using the ℋ 2 and ℋ ∞ norm. Finally, an energy storage microgrid system with two 100kVA-VSGs validated the efficacy of the proposed control strategy.