Distorted Stability Space and Instability Triggering Mechanism of EV Aggregation Delays in the Secondary Frequency Regulation of Electrical Grid-Electric Vehicle System

Aggregated electric vehicles (EVs) are emerging as promising resources for the frequency regulation of the electrical grid, but the aggregation dynamics caused by various aggregation delays make unknown threats against the frequency stability. To address this stability uncertainty, a general aggregation-delay model is established for the electrical grid-electric vehicle system, which integrates heterogeneous-delay effect and reveals the sequential impact process of aggregation delays during the frequency regulation. To precisely visualize the aggregation delay influence, the maximum aggregation delay interval is discretized by the Chebyshev nodes, which formulates a delay distorted matrix reducing the infinite operator dimension. With this matrix, the damping ratio and the sensitivity indexes are then extracted constructing a complete workflow to characterize the asymptotic stability for EV aggregation delays. By the proposed approach, the distorted stability space and uniform target eigenvalue are accurately revealed in a typical electrical grid-electric vehicle system. It is also demonstrated that the aggregation delays infect the frequency stability through three unstable modes in a low-frequency oscillation form.