Research On Short Circuit Current Limiting Optimization In Ultra-High Voltage AC/DC Receiving-End Power Grid

In the early construction stage of China’s national UHV power grid, the situation of multi-infeed HVDC systems becomes more and more common. This thesis studies the characteristics of multi-infeed HVDC system and develops a series of comprehensive short circuit current limiting methods aimed at pure AC systems and AC/DC hybrid systems, respectively.Based on the research results of voltage stability in multi-infeed HVDC system, the shortcomings of MISCR (Multi-Infeed Short Circuit Ratio) proposed before is noted. A new definition of MISCR considering the impact of DC system control mode is defined. Different control mode of DC system results in different reactive power characteristics. With the modified items describing the impact of DC system control modes added into the power-flow model of AC/DC hybrid system, the new definition of MISCR is formulated. Case study of the planning power grid in Shandong province validates the effectiveness of this new definition of MISCR.In actual AC power system, the situation that single-phase short circuit current continues rising and exceeds the level of three-phase short circuit current appears more and more. The main reason of this situation and effective method to solve it is discussed. With investment cost and network tightness as objectives, the comprehensive limiting optimization mathematic model is founded, which combines the specific single-phase short circuit current limiting measures and traditional three-phase short circuit current limiting measures. This model can be solved by adaptive hybrid PSO algorithm. A modified IEEE 9 system and two regional power grid in Shandong province are used as examples to validate the effectiveness of the proposed comprehensive limiting method.In multi-infeed HVDC system, the short circuit current limiting optimization has to coordinate the relationship between limiting effect of limiting measures and their influence on MISCR. Two ways of limiting optimization from different perspectives are listed. From the perspective of power grid planning, a modified GN algorithm is proposed, which considers the impact of grid partition operation on MISCR. From the perspective of grid structure adjustment, a multi-objective optimization model with reasonable weighted MISCR value as extra objective is proposed. The multi-objective optimization model can be solved by NSGA-II algorithm. The planning power grid of Shandong province is used as example to validate the effectiveness of these two short circuit limiting optimization ways mentioned above.