Research On Reliability Evaluation Approach Of Power Grid And Reliability Basic Theory

Objective and quantitative reliability evaluation of power system can explore the weakness and point out a way for power system planning, operation and maintenance, in order to achieve the goal of keeping security, stability and reliability of power system operation, realizing the integration of reliability and economy. Recently, aiming at economical and social sustainable development, achieving greater scope of resource allocation optimization and promoting the development of China's energy intensive and efficient utilization, the receiving-end grid forms a large scale multi-infeed high voltage direct current system thanks to several high voltage / ultra high voltage direct current transmission projects commissioning successively. Meanwhile, to cope with energy crisis and global warming, the development and utilization of renewable energy and the research of smart grid have been the important component of energy strategy. However, distribution generation is stochastic and intermittent so that it throws more uncertainty into power system planning and operation. Based on advanced asset management, smart grid attaches special importance to reliability condition-based maintenance. Therefore, power system reliability research and application are facing huge amounts of main technical problems to overcome. For this reason, the dissertation discussed probabilistic risk evaluation of HVDC transmission system, adequacy and security evaluation of transmission system, and the basic theory of reliability. The main work is as follows:1. According to the operation characteristics and structure features of UHVDC/HVDC system, the reliability model and evaluation of DC systems was presented based on modeling of subsystems, considering the effects of protection and reactive compensation on system reliability. This paper built the commutation failure risk index system and further proposed the risk evaluation approach of multi-infeed HVDC system under AC system fault conditions considering multiple uncertain factors, which took the commutation voltage-time area as criterion. The DC systems of China south grid is used to validate the risk evaluation.2. An optimal load shedding model, which took polar power-direction coefficient as controlling variable, was proposed, for the complicated conditions and multi-constraints of AC/DC hybrid transmission system and HVDC operation characteristic. The model not only takes into account the outage of DC polar due to operation restricting, but also considers the case of HVDC power reverse. Meanwhile, to overcome the shortcomings of convergence difficulties of current primal-dual interior point methods with flat starting, the paper applied the pseudo transient continuation method to seek the optimal initial point, introducing the idea of converting the problem of finding an initial point into that of finding a stable equilibrium point of active-set based dynamic system. The numerical results demonstrate that the proposed approach provides a novel powerful tool for the adequacy evaluation of AC/DC hybrid transmission systems.3. The linear boundary of dynamic security region of the controlling unstable equilibrium point was determined on the basis of dynamical system theory. Then, Edgeworth series expansion based on semi-invariant was employed to calculate the weighted joint probability distribution. Consequently, power system transient stability probabilistic model, which avoided conservative and incomplete results using determinate analysis of transient stability, was established. The proposed transient stability probabilistic model can effectively take many uncertain factors into account, such as generator output and internal potential, load active power and reactive power, fault location, fault type, fault-clearing time, et al. Finally, the numerical results of IEEE 10-machine 39-bus system indicated that the proposed model and its solution are effective and feasible, and have broad prospects for engineering application.4. To overcome the distortion caused by the assumption that preventive maintenance intervals and repair time are exponential, this paper studied the system reliability model with multi-outage states and its analytical solution based on semi-Markov process derived from the fundamental theory on reliability mathematics, took protection system and its preventive maintenance for the instance. The paper also proposed optimum routine maintenance intervals for protection by minimizing the annual average economic losses, and then developed optimum routine maintenance decision system for protection. The numerical results of typical protection systems showed that the advantages of the proposed method are also reflected in high precision and fast speed.5. To break the limitation of assuming state transfer functions follow exponential distribution and to improve the fineness level of reliability study, reliability studies of electrical devices as an instance, a reliability model based on phase-type distributions was proposed, deriving from the stochastic process fundamental theory, which was solved by matrix-analytic method. On the basis, the optimum maintenance models aiming at reliability and economic were designed, respectively. To solve intermittent problem of distributed generation that classical distribution can not reflect, the paper also built stochastic models of wind turbine and solar photovoltaic system based on phase-type distribution, employed Edgeworth series to solve probabilistic power flow model on the basis of semi-invariant. At the end, the effects of distributed generator and reactive compensation on branch load security and voltage quality were analyzed.This dissertation is supported by the nation natural science foundation of China (No. 50337010, 50977032), the national basic research program of China (973 Program) (No. 2009CB219704), the ministry of science and technology of the people's republic of China (No. 2006BAA02A30), the crucial field and key breakthrough project in"Guangdong- Hongkong"(No. 2009A091300011), and high-tech industrialization key project in Guangdong (No. 2010A010200005).