Transient Stability Analysis Of Shanghai Power Grid With Multiple HVDC Links

HVDC systems have evidence advantage in long distance bulk power transmission. So it has played an important role in the application of nation-wide power grid interconnection and China's power transmission from the West to the East. With the increment of power transmission, the security and stability problem has appeared in certain AC system with multi-infeed HVDC. This thesis focuses on the analysis of transient stability of Shanghai power grid with four HVDC links terminating in it, by using the power system simulation software PSS/E,The characteristics of HVDC transmission technology and the present situation of the power system development in China are discussed. For long distance bulk power transmission from West China to East China, there will be more and more HVDC links feeding power to different points in a same synchronized AC network, and such situation may affect the secure and stable operation of AC network The complicated AC/DC and DC/DC system interactions under large disturbances in multi-infeed HVDC systems are discussed. And the causes leading to commutation failures in a multi-infeed HVDC system are given. Due to the disadvantages of existed HVDC model, it is proposed that hybrid simulation methods can be used in analyzing the transient stability of multi-infeed HVDC systems.The mathematical models for electromechanical transient simulation of AC/DC power systems are studied. To build correct models of HVDC system, the differences between the QSS model and the classical model of DC converters are analyzed. According to whether considering the inductive transient processes in DC transmission line and the dynamic characteristics of the high frequency DC controller or not, the HVDC models can be classified into two kinds: HVDC response model and HVDC detail model. And the validity of these HVDC models is discussed. The HVDC models in PSS/E are classified and described in detail. Also, the models for excitation systems, the turbines and governing systems, load are studied. Based on those, the suitable models can be selected for the transient stability analysis of large-scale AD/DC power systems such as Shanghai power grid with four HVDC Links.PSS/E is the very powerful software which used for electromechanical transient simulation. As the simulation tool of this thesis, the main factions and characteristics of PSS/E are discussed. PSS/E has two primary simulators, one for steady-state analysis (power flow calculation) and one for dynamic simulation. The working file structure and the input format of power flow data and dynamic model data are presented. IPLAN is a programming language designed to be utilized as an enhancement to PSS/E. IPLAN offers modern control flow along with a rich set of expression operators.On PSS/E platform, taking the year of 2012 as the target year, the stability of Shanghai power grid with four HVDC links under differ faults occurred in AC and HVDC systems is analyzed. The interaction of AC/DC system during AC system fault and bipolar block of each HVDC link is analyzed. And the recovery characteristics of DC transmission lines within the multi-infeed HVDC systems are also researched. Through the comparison and analysis the consequences of the severe faults inside and nearby Shanghai power grid, the weak area is pointed out. The results show that the system is stable if any single circuit of Shanghai 500kV grid is three short circuited and then tripped in 0.1s. For bipolar pole fault in each HVDC links, the system is stable.