Recently, subsynchronous interaction (SSI), a type of stability issue caused by interactions between power electronic converters and weak grids, has attracted great concerns. Many efforts have been made to use impedance/admittance-based methods for its modelling and analysis. However, most impedance/admittance models (IM/AMs) are aimed at higher-frequency dynamics and do not reflect the coupling effects between sub-and super-synchronous frequencies or the outer control loops, which, as indicated in this work, have significant impacts on the characteristics of SSI. To fill the gap, this study derives the explicit frequency-coupled AM for a typical grid-tied voltage-sourced converter by taking the coupling effects and outer-loop controls into full account and further investigates their impacts on the subsynchronous stability. The model itself and its effectiveness in predicting the stability of SSI have been validated with detailed electromagnetic transient simulations.
Vehicular edge computing (VEC) is a promising paradigm to offload resource-intensive tasks at the network edge. Owing to time-sensitive and computation-intensive vehicular applications and high mobility scenarios, cost-efficient task offloading in the vehicular environment is still a challenging problem. In this paper, we study the partial task offloading problem in vehicular edge computing in an urban scenario. Where the vehicle computes some part of a task locally, and offload the remaining task to a nearby vehicle and to VEC server subject to the maximum tolerable delay and vehicle’s stay time. To make it cost-efficient, including the cost of the required communication and computing resources, we consider to fully exploit the vehicular available resources. We estimate the transmission rates for the vehicle to vehicle and vehicle to infrastructure communication based on practical assumptions. Moreover, we present a mobility-aware partial task offloading algorithm, taking into account the task allocation ratio among the three parts given by the communication environment conditions. Simulation results validate the efficient performance of the proposed scheme that not only enhances the exploitation of vehicular computation resources but also minimizes the overall system cost in comparison to baseline schemes.
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