Power-frequency oscillation modeling, analysis and suppression of multi-VSG grid-connected system

• Utilize the mechanical admittance model to elucidate the underlying physical mechanism of the system. • By applying circuit theory, analyze the dynamic response of multi-VSG grid-connected systems, providing a comprehensive expression of system dynamics without solving complex differential equations. • And propose an APFC-based strategy that effectively suppresses power-frequency oscillations and minimizes overshoot, while maintaining an intuitive, differentiation-free control method that is easy to implement. The virtual synchronous generator (VSG) enhances the inertia response of renewable energy system by mimicking traditional synchronous generators (TSG), but inherits the power-frequency oscillation issue of TSG. The grid impedance at the point of common coupling (PCC) leads to the interaction between VSG control loops, which complicates the dynamic performance of the multi-VSG grid-connected system. This paper investigates the modeling, analysis and suppression of the power-frequency oscillation for the multi-VSG grid-connected system. Initially, a mechanical admittance model of the multi-VSG grid-connected system is developed based on the electromechanical analogy principle, and the transfer functions under various disturbances are derived. Subsequently, the frequency-domain response of the transfer function is compared and analyzed with the simulation results to reveal the power-frequency oscillation behavior of the multi-VSG grid-connected system under varying system parameters. Finally, a power-frequency oscillation suppression strategy for the multi-VSG grid-connected system, based on active power feedforward compensation (APFC), is proposed in alignment with its oscillation characteristics, and the design parameters are provided. The efficacy of the proposed oscillation suppression strategy is validated through MATLAB/Simulink simulation and experimental testing.