Modelling of asynchronous inertia of induction motor loads and studying the effect on the frequency response of renewable energy power systems with high wind power penetration

The inertia of renewable energy power systems is reduced, which causes the deterioration of system frequency response (SFR). The asynchronous inertia provided by the induction motor loads in the process of the SFR is worth studying. The asynchronous inertia model is established based on the small-signal analysis method and the relationship between the operating state of the induction motor and the asynchronous inertia is analyzed. The SFR model of renewable energy power systems including asynchronous inertia is established and the effects of asynchronous inertia on the dynamic of the SFR is analyzed. The asynchronous inertia has a time-varying characteristic and is influenced by the initial operating conditions and the torque-slip characteristic of the induction motor, the inertia time constant of the rotor, and the mechanical characteristics of the load. The asynchronous inertia reduces the maximum frequency deviation (FD), which enables the rate of change of frequency (RoCoF) to be reduced. The maximum RoCoF is not affected by the asynchronous inertia, but the steady-state FD is reduced. The asynchronous inertia has a more significant improvement on the dynamic of the SFR in the power systems with high renewable energy permeability. The conclusions are verified by the simulations and experiments.