| Large-scale power blackouts result in huge economic losses and negative social impacts.Using scientific and effective methods to restore power systems following a blackout helps shorten the outage time and reduce the outage losses.This dissertation investigates the parallel restoration methods for AC-DC hybrid power system to obtain fast and secure restoration strategies.In a subsystem,an optimal method is proposed to determine startup sequence of generating units considering the restoration time of transmission path.Using the high voltage direct current(HVDC)transmission systems,a novel parallel restoration method considering the collaboration among different subsystems is proposed.To improve the performance of the proposed parallel restoration methods,this dissertation develops a partitioning method.The main work of this dissertation is as follows:(1)The optimization model of the unit startup sequence considering the restoration time of transmission paths is established.Then,a path selection method,taking the restoration time,the capacitance to the ground,the number of branches and the capacity of the load into account,is proposed.A restoration method to determine startup sequence of generating units with the objective to maximize the restoration efficiency is proposed.This method considers the startup characteristics of generation units and the restoration time of transmission paths,which are selected due to the rapidity,safety and flexibility.It helps to improve the restoration efficiency within a subsystem.(2)The startup characteristic of HVDCs is analyzed.A restoration architecture of AC-DC hybrid power system is developed.On the basis of the generating unit startup sequence optimization model and the startup characteristics of HVDCs,an optimization model of AC-DC system restoration is constructed.This dissertation proposes a parallel restoration method for AC-DC power systems.By making use of the HVDCs in this method,the numbers of the power sources and the subsystems are increased.In addition,different subsystems can support each other during the subsystem restoration process.These are benefit for speeding up the restoration process of the outage system.(3)The influences of the network topology,the system condition before blackouts,HVDC systems and the restoration time of branches on partitioning problem are analyzed.Based on the improved label propagation algorithm and minimum spanning tree theory,a two-step partitioning method for AC-DC power systems is proposed.HVDCs are used preferentially as the tie lines to partition the outage system into several subsystems,which improves the performance of the AC-DC parallel restoration method.On the other hand,the difference of the restoration time among different subsystems is minimized.It helps to accelerate the interconnection of subsystems,which are divided by AC tie lines.(4)The basic characteristics of the proposed methods in this dissertation are demonstrated by employing standard test cases.A test case combining the present situation of a provincial power grid and the development trend of HVDC systems is built.The power system restoration process is simulated to verify the effectiveness of the proposed methods.An intelligent decision-making software for AC power system restoration is also developed for verifying some research results.In summary,this dissertation focuses on the parallel restoration methods considering the restoration time of transmission paths and the characteristics of HVDCs.A partitioning method based on the proposed parallel restoration method is further developed.These studies on the power system restoration are of great importance for both theoretical research and industrial application. |
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