Analysis And Prevention Methods Of Power System Cascading Failures Based On Complex System Theory

In recent decades blackouts occurred frequently in large parts of the world, and cascading failures were the direct causes for most of them. The complexity of power system makes the electrical cascading failures have features of contingency, uncertainty, diversity and complexity. For a long time, China’s power grid is constituted by six relatively independent regional power grids, and implements a centralized management, which makes China’s power grid has not yet occurred nationwide large-scale power outages so far. The interconnection and intelligentization of power grids have improved the operational efficiency, but also have increased the operating uncertainty, which means an increased blackout risk. Therefore, it is very necessary to study the propagation mechanism of electrical cascading failures further, propose risk evaluation methods, and finally develop appropriate blackout prevention and control strategies against the characteristics of China’s power grid.Traditional reductionism method focuses on the dynamic behavior characteristics of individual components, for which it is difficult to reveal the dynamic behavior characteristics of the whole system both in the long-term process of power system evolution and in the short-term process of cascading failure propagation. The complex system theory prefers using the holism and reductionism combining method to reveal the global dynamic behaviors, which the traditional reductionism methods can hardly explain clearly. Hence, supported by the National Natural Science Foundation of China project (50977022), Study on the Assessment Methodology of Power System Cascading Failure Risk and the Identification of Self-Organized Criticality in Multi-time Scale, taking the power system cascading failures as the main study objective, using the complex system theory, from multiple perspectives and multiple levels the dissertation comprehensively analyzes the impact of various factors on the load loss distribution, including the power grid topology, operating conditions, operational and controlling strategies, and so on. The research results have a guiding significance to the establishment of blackout prevention and control strategies. The main work of this dissertation includes the following parts:1. Propose an assessment methodology of the cascading failure blackout risk based on Monte Carlo simulation method and cascading failure blackout model. This hybrid method, mixing Monte Carlo simulation and cascading failure blackout model, is used to attain accurate and sufficient statistical data for risk assessment of cascading failure blackouts in a short-term scale. The importance sampling method and the important path searching method can improve the convergence speed of Monte Carlo simulation method. Define the risk indices of system risk, branch risk, and N-1risk in order to evaluate the power system from multiple perspectives. The proposed risk assessment method can be used to research the impact of multiple factors on the load loss distribution, such as the operating conditions, operational and controlling ways, topology and so on, can be used to verify the validity of the other non-statistical risk indices, and is the basis of the power system cascading failure analysis and prevention.2. Study the impact of different types of topological evolution on the load loss distribution. Because the topology of power system has an important influence on the load loss distribution, in order to reflect the long-term evolution process of power system more truly, a temporal and spatial topological evolution model is added into the slow dynamics of ORNL-PSerc-Alaska (OPA) model, which considers the practical evolution factors related to building new power plants and substations, such as the construction time, siting and sizing, and so on. The topological evolution OPA model is used to study the load loss distribution under the typical topological evolution types (scale-free network, small-world network, random network and hybrid network), and the results show that reducing the characteristic path length of power system topology will decrease the cascading failure risk.3. Present a multi-stage transmission expansion planning (TEP) method considering blackout risk. Considering the coupling relationship between adjacent stages, a TEP-suited OPA model, suitable for long-term TEP problems, is presented to obtain blackout statistical data closer to the real data in a long-term scale; a power-law tail risk (PTR) index is proposed to assess blackout risk by measuring the tail characteristics of load loss distribution; improved adaptive multi-objective particle swarm optimization (MOPSO) algorithm effectively balances the solution diversity and the convergence speed; the bi-level optimization strategy reduces the calculating time of probabilistic risk indies. Considering the cascading failure blackout risk during the TEP process is a fundamental safeguard of preventing blackouts.4. Develop an optimal configuration model and algorithm of multiple flexible AC transmission system (FACTS) equipment considering blackout risk. The basic goal for traditional FACTS optimal configuration problem is to maximally improve the total transfer capacity with the lowest investment cost. The growingly large scale and the increasingly complicated operational and controlling ways of power systems increase the probability of blackouts, hence the developed model introduces the risk indices of PTR and expected load loss (ELL) as additional optimal objectives. The simulated results show that, without changing the topology of power systems, the developed model improves the total transfer capacity meanwhile enhances the power system reliability, which is a economical, flexible and effective method to prevent blackouts.