Planning And Optimization Method For Dynamic Var Compensation In Hybrid AC-DC Power Grid

The development and promotion of clean energy has received attention from various countries.In order to achieve long-distance and large-capacity cross-region transmission of clean energy,an AC-DC hybrid power grid with strong random,multiple DC,and variable operating modes has gradually formed in our country.With its advantages of fast adjustment speed and high reliability,dynamic var compensation has become an important tool for solving the voltage stability problem of hybrid ACDC power grids and ensuring the safety,stablity and economic operation.However,dynamic var compensation is not massively put into use currently due to its high cost.Reasonable planning for its installation location and capacity,and optimization of its reactive power output are the prerequisites to make it work best.This thesis focuses on the planning and optimization methods of dynamic var compensation in hybrid AC-DC power grids,mainly from three aspects: site selection planning,capacity planning,and output optimization.In terms of site selection planning,this paper firstly establishes a weak region division model for the purpose of narrowing the scope of research.Combined with the idea of hierarchical zoning to find several nodes with weak static voltage stability in large receiving-end AC-DC power grids.In order to select the best installation points of dynamic var compensation from these nodes,a pilot-node-determine model is established,and the nodes with the most improvement in the transient voltage stability of the power grid are chosen as the installation points by improved trajectory sensitivity index.In order to solve the shortcomings that BPA cannot process batch setting and calculation of multiple faults or different dynamic var compensation at present,this thesis also designs a batch interface program for BPA and MATLAB.In terms of capacity planning,in order to more accurately reflect the effect of dynamic var compensation on the strength improvement of the receiving end AC-DC system,an modified multi-feed effective short circuit ratio based on dynamic Thevenin equivalence is proposed.It overcomes the shortcoming of traditional multi-feed effective short-circuit ratio which is conservative due to the failure to account for the dynamic response process of compensator.Then based on the proposed modified multifeed effective short-circuit ratio,a comprehensive set of dynamic var compensation capacity planning method is established to achieve reasonable choice for capacity,improve the overall strength of the system and the balance of DC-HVDCs.In terms of var output optimization,based on the branch flow model,this thesis firstly builds a var compensation output optimization model aiming at minimizing the active power loss and voltage deviation of the AC-DC system which owns dynamic var compensators.Then convexificate of the model is conducted by secondary rotating cone relaxation and second-order cone relaxation.Lastly,based on alternative direction multiplier method(ADMM)algorithm,a var compensation output optimization model capable of partition calculation is established,which reduces the problem scale and solves the problem of information collection of mutiple regional power grids.