Wide Area Inertia Estimation And Control Strategies Of Power System

With the growing global energy crisis,renewable energy generation technology has been rapidly developed and widely used,and the proportion of thermal generators has gradually decreased.The reduction of synchronous generators reduces the inertia of the system and affects the dynamic characteristics of the system significantly.Renewable energy such as wind power,due to its high output power fluctuation and randomness,is often decoupled from the power system through power electronic equipment,and its inertia is difficult to provide inertial support for the system.Synthetic inertial control designed for various inertial resources can respond to fluctuations of system in real-time and regulate stability of frequency.The wide-area coordinated control mechanism makes inertial control more comprehensive and efficient.Based on the wide area information,the inertia of the power system can be accurately evaluated,thus the placement of inertia resources of the system could be optimized to increase the inertia of the system effectively.The study of the inertia strength of the system and the placement and control mechanism of synthetic inertia resources has considerable value in theory and application for improving system stability.This paper focuses on the wide-area inertia estimation and control mechanism of the power system.The main work and research results are as follows:(?)Power system inertia estimation based on wide area information.In order to improve inertia assessment efficiency,slow coherency is used to group power system generators,and the participation factor is used to select the leading generator of the slow coherency generator groups.The relationship between the inertia time constant and the speed and capacity of the synchronous generator is established based on the rotor motion equation of the leading generator.The difference between the calculated and actual values of the system active power vacancy is compared,and the system inertia is accurately evaluated.Furthermore,the wide area information of the leading generator is extracted to improve the accuracy of the inertia estimation,and the influence of fault electrical distance and other factors on the estimation accuracy is analyzed.The paper designed a simulation experiment to verify the validity of the estimation method.(2)The inertia resources placement optimalization of power system.Based on the dynamic model of Kron's simplified system,the coherency performance index is used to characterize the energy loss caused by the suppression of system inertia in the power system transient.The paper establishes optimization model of inertia resource placement of the power system,taking the minimum system non coherency as the goal.The system configuration cost constraint and the node inertia level limit are considered.Besides,the effect of inertia control of renewable energy equipment synthesis on the inertia of the nodes is taken into consideration.And the model is simplified to improve the solution efficiency.The simulation experiments are conducted to verify the effectiveness of the proposed inertial optimization placement method.(3)Wide-area synthetic inertia control of power system.Synthetic inertia control methods for VSC-HVDC,DFIQ and Synchronous condenser are designed.The DFIG synchronous condenser rotor kinetic energy,and DC capacitor power is used to response system active fluctuations to provide inertia support for the system.The coupling mechanism of DFIG rotor speed and system frequency is proposed,and the coordinated control mechanism is designed so that the three kinds of inertial resources can simultaneously adjust their active output according to the system frequency fluctuation respectively.On this basis,the wide area information is used to eliminate the local control signal limitations,and the wide-area coordinated control is designed to enhance the inertial control effect,so that the synthetic inertial control can adjust the system dynamic response capability more accurately and efficiently,and meanwhile system stability can be improved.The paper designs simulation experiments to verify the effectiveness of the proposed inertia control method and wide-area coordinated control mechanism.