Research On Relative Issues Of AC/DC Power System Stability Analysis And Control

Stability region estimation is very significant in many engineering fields especially in power systems. A lot of methods of stability region estimation have been proposed in the literature, some only estimate a subset of the stability region but with the problem of conservativeness, and others completely describe the composition of the stability boundary in mathematics but with the barrier of practical computation. The traditional study on stability region is only to the AC system, so far the study on the AC/DC power system stability region has been very lacked, and it needs further research by applying new theories and methods.Along with the DC transmission widely applied and the AC/DC hybrid power transmission system quickly increased, a series of new problems will appear. Although the characteristics of AC and DC transmission are totally different, the two have very close contact and very complicated interaction in the operation of actual power grids. AC/DC interaction is an important aspect in the study of power system stability, and is one of the most concerned problems in the field of power engineering, so wide and deep research on this subject should be continually developed.There has occurred several severe blackouts all over the world in recent ten years, which led to serious consequencies on the national economy and social life. Scholars domestic and abroad have applied advanced theories such as the complex system theory to the power system, detailed studies on the subject of cascading failure and blackout have been proceeded, and a lot of breakthroughs and achievements have been obtained. Now there still inevitably exists some problems in the issue of cascading failure and blackout, one is that the complete dynamics of the system is not considered, and the other is that there is little research on the AC/DC system.In this thesis, the relative problems of AC/DC power system stability analysis and control are studied in three aspects of AC/DC system stability region and stability boundary, AC/DC system interaction, and AC/DC system cascading failure and blackout, the main work is as follows:1. A full state DC model which includes complete DC operation modes is used, it nicely describes the inherent switching characteristics of AC/DC systems, the phase portraits of the single machine-infinite bus (SMIB) AC/DC full state system under different DC operation modes are calculated, the stability region characteristics and subsystem switching laws of the SMIB AC/DC full state system are analyzed, and the related characteristics of the SMIB AC system and the SMIB AC/DC simplified system are compared.2. An AC/DC interaction analysis algorithm based on the stability constrained optimal power flow is proposed, the algorithm is furtherly modified according to the operation experience of practical power grids, with which the computation burden can be reduced and the calculation efficiency can be increased, the AC/DC interaction of the2012North China-Central China-East China (3C) UHV interconnected power grid is calculated and analyzed applying the related algorithms of interface power flow transient stability limits calculation, generator trip and load shedding analysis, and DC emergency power lifting analysis.3. The mechanisms of the AC tie-line power swing phenomenon resulted from the interior and exterior DC line blocking contingency are respectively studied, the approximate calculation method of the power swing peak value is given, and the influential factors of the power swing peak value are analyzed, the calculation results and methods are compared and verified by simulation of the2012North China-Central China-East China (3C) UHV interconnected power grid.4. A dynamic cascading failure model considering the probability characteristics of the emergency control&protection device and DC system is proposed, with which dynamic simulation of the2010East China power grid is performed, under different DC operation modes, DC control parameters, AC/DC interconnection modes, and AC/DC capacity allocations, the outage power—outage probability power law curve is calculated, and the impact on the self-organized criticality of the system is analyzed.5. Preliminary analysis and mathematical modeling of the AC/DC capacity optimal allocation problem are proceeded, a cascading failure Monte Carlo simulation algorithm and an AC/DC capacity optimal allocation implicit enumeration algorithm are proposed, the modified IEEE39case system is calculated, the AC/DC capacity allocation optimal solution which can minimize the system cascading failure and blackout risk is obtained, the impact of various factors on the optimal AC/DC capacity allocation is analyzed.