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Communication technology serves important functions in the power system energy management system (EMS). Recent studies found that cyber-attack and terrorist attack can cause failure of power system communication which affects EMS in various ways. This paper analyzes two impacts of communication failure on EMS, namely, system observability and system control. The first impact on system observability is studied using DC state estimation to identify unobservable states when loss of communication occurs at various locations. The second impact on system control is studied using DC OPF to find the loss of load caused by communication failure. Simulation studies on the two analyses are conducted on IEEE 14 bus and IEEE 30 bus systems. Results show that certain substations are more critical for system observability. Optimal upgrade strategy is provided in this paper to improve system observability. It is also shown that failure of communication will cause extra loss of load. By protecting certain substations, the system can expect less loss of load. It is concluded that communication system is crucial to the power system operation. This paper also gives suggestion to optimally improve communication systems.

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A time delay exists between driver input and vehicle braking state response during the working process of the anti-lock braking system (ABS), and the braking performance of vehicles will be further reduced due to the delay of controllers. This paper investigates a systematic method of stability analysis for time delay ABS, and the analysis focuses on the stability and critical delay algorithm of ABS with delay time. Firstly, the dynamic structure and modelling process of ABS are briefly introduced, and PD control algorithm is adopted to improve the control performance. Then, dynamic models of ABS with time delay are derived, and the full delay stability interval and critical time delay algorithm of ABS are deduced by using the generalized Sturm criterion method. Finally, the validity of the critical delay algorithm by the proposed method and the stability and accuracy of ABS with time delay, different road conditions, vehicle speeds and control parameters are illustrated by numerical simulations, and the results show that the critical time delay algorithm of ABS can be verified under different conditions.

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