Yiwei Zhang

This paper focuses on the problem of load frequency control and sensor fault-tolerant control in the multiarea power grid. To solve these problems, a sliding mode control strategy based on an interval observer is designed. First, an interval observer is designed to obtain the boundary estimation information of the system state online, which is used to reconstruct the load disturbance online. Based on the reconstructed values, an integral sliding mode controller is designed to keep the system frequency stable when the load is disturbed. Then, sensor fault is diagnosed by interval residual. An augmented observer is designed to estimate sensor fault online by equivalent transformation, and the sensor fault is compensated by the fault estimation to reduce the influence of fault on system performance and ensure the reliable and stable operation of the power system. The simulation results show the superiority of the proposed control strategy.

One of the most frequently discussed notions in Wittgenstein’s Tractatus is the notion of simple object. However, among the literature on Tractarian objects, recent or classic, none has treated configurations of objects as a major and non-trivial issue. In this paper, I show that a detailed study of configurations of objects will yield a series of interesting and important results: it leads to a new understanding of the picture theory, helps us calculate the maximum numbers of internal and external properties of objects, and enables us to reinterpret and reach a solution to the notorious debate on whether properties and relations should be included as Tractarian objects.