In traditional distribution system, power flow was unidirectional; thus loads were usually aggregated into the substation as an equivalent constant bus in the original risk analysis of transmission system. Detail structures of the distribution system were absolutely ignored. However, distribution system is transformed from passive to active nowadays with more and more distributed generations (DGs) being integrated into it. So, distribution system not only can be considered as loads but also can be considered as virtual power plants to supply power to local loads and even to send power back to the transmission system sometimes. In this paper, a hierarchical method is presented to evaluate the impact of role changing of the distribution system in power system risk assessment. In the study, DGs can supply critical loads in distribution system through re-dispatching after some contingency happens. Discrete probability model is employed to simulate the intermittent output of DGs. Available supply capacity (ASC) is used as a general constraint to guarantee the security level of distribution system that needs high reliability. Also, an iterative calculation between transmission system and distribution network is adopted to derive the risk indices with considering detail structures of the active distribution network. Further, impact of some factors on system risk calculation, such as DGs' capacities, dispersions, locations, and component outage probabilities, are discussed. Finally, correctness and effectiveness of the proposed method are validated by a modified IEEE RTS and RBTS system.

Smart Grid is an inevitable trend of power grid, and smart grid comprehensive assessment system can conduct a comprehensive assessment of the overall characteristics of smart grid, which can reflect the current level of the development, find the weakness and the constraints in the network development, identify the distance to the target, ensure the smart grid development achieve a unification of the quality, speed and efficiency. At present, many countries are studying on the smart grid comprehensive assessment systems. This paper analyzes the IBM Smart Grid Maturity Model, the DOE Smart Grid Development Evaluation System, the EPRI Smart Grid Construction Assessment Indicators, and the EU Smart Grid Benefits Assessment System, and compares the development levels, evaluation objects, target ranges, applications differences between these systems and the “two type” grid index system, the smart grid development assessment index system, and the smart grid pilot project evaluation indicator system suggested by China. The thoughts and the principles of building smart grid comprehensive assessment system, and the issues which should be noted are proposed here, which can provide necessary references and supports to construct the smart grid comprehensive assessment system

The steady-state security region of the integrated energy system (IES) is a useful tool for rapid security assessment and security evaluation of the integrated energy system. A complete characterization of the IES steady-state security region is derived. The derivation is under the nonlinear and non-convex AC power flow model, the gas flow model, and the uncertainty of renewable energy without any linear simplification. Then a novel and robust computation scheme to compute the IES steady-state security region is proposed and shown to eliminate the estimation errors of the existing methods. It is shown that the IES steady-state security region is non-convex and composed of several disjoint components. Numerical studies are conducted to show that the IES steady-state security regions obtained from the existing methods can be inaccurate, while the proposed characterization gives an exact estimation of the IES steady-state security region that significantly improves the previously proposed methods.