Research On Steady-state Security Region Analysis And Coordinated Control Of AC/DC Hybrid Power Grid

With the increase of the amount of direct current transmission in the power grid,the AC/DC hybrid power grid shows different operation characteristics compared with the AC power grid.How to effectively evaluate the security of AC/DC system,find out the weak links in the system,and take appropriate security control measures is particularly important for the safe and economic operation of the power grid.The steady-state security region is the set of the control quantities and the disturbance quantities which satisfy the power flow equations and all constraints of all electrical quantities in the system.The steady-state security region can get the feedback of the system's security information from a global perspective,and has advantages in the security monitoring and security control of the power grid.In this paper,the steady-state security region and coordinated control of AC/DC hybrid power grid will be studied,and the main work is as follows:1.The quasi steady-state models of AC system,LCC-HVDC(Line Commutated Converter-High Voltage Direct Current)transmission system and VSC-HVDC(Voltage Sourced Converter-High Voltage Direct Current)transmission system are built.And a analysis about each operation constraint in system is presented.Based on them,the definition,the geometric description and the qualitative description of equations of steady-state security region of AC/DC power system are completed respectively,so the research field of steady-state security region is extended from pure AC system to AC/DC hybrid system.2.Based on the models and the definition of steady-state security region of AC/DC system,some kind of solution and characterization methods of steady-state security region are studied,including effective boundaries screening,boundaries distances and operation margin calculation,fitting solution of boundaries expressions and fitting testing,corrected distances calculation and physical meaning analysis of calculation formulas based on the fitting results,probabilistic secutity analysis of the boundaries distances,accurate portrayal and verification of cross section by point-to-point method,etc.The conclusions of the advantages and disadvantages of these methods and their applications are refined.3.The analysis of introduction of LCC-HVDC,different control modes and operation modes of LCC-HVDC,power flow regulation participated by LCC-HVDC,introduction of VSC-HVDC,power flow regulation participated by VSC-HVDC influences on the steady-state security region are completed respectively.And influence laws of the DC transmission influences on boundaries evolution of steady-state security region of power system are summarized.4.Based on the theoretical researches of steady-state security region,the application research on coordinated control of AC/DC system is studied using the advantages of steady-state security region.The main contents include quantitative calculation of coordinated correction control and coordinated preventive control based on the transformed steady-state security region,qualitative judgment of coordinated control based on the cross sections of steady-state security region,economic operation control based on the steady-state security region considered operation targets,and coordinated control based on the steady-state security region with time axis considered time characteristics of control equipments.