Electromechanical Transient Modeling And Application Of Several New‐type Power Devices

At present,the power system is in a huge transformation process to a low-carbon system.The “three high characteristics” of the power system is more and more obvious,which are the high proportion of new energy generation,the high degree of power electronics,and the high proportion of power sending and receiving.The power system with those characteristics has significant differences in power structure,operating characteristics,and other aspects compared to the power system with traditional synchronous generators as the main power source,so it is generally called as the new-type power system.Various new types of power devices and their different operating characteristics pose new challenges to the design and operation of the power grid.At present,the stability analysis of large-scale power systems is mainly based on electromechanical transient simulation programs.In the process of power transformation and development,some large devices with new topologies and structures lack corresponding electromechanical transient models.And with the increasment of the system scale,the numerous number of electromechanical transient models for nonsynchronous-machine power sources brings difficulty to the process of selecting simulation models and corresponding parameters in electromechanical transient simulation.Deeply studying the electromechanical transient modeling and their application for specific new-type system and general nonsynchronous-machine power sources can enhance the research and analysis capabilities of new-type power systems and assist in the transformation and development of power systems.This dissertation conducts systematic research on the challenges faced by the electromechanical transient modeling of new power devices and the stability analysis of new-type power systems.The main research content and achievements are:(1)An electromechanical transient modeling method for an active modular multilevel converter(MMC)embedded in energy storage units was proposed,and an electromechanical transient simulation model for active MMC was established.The comparison between the electromechanical transient simulation results and electromagnetic transient simulation results under the same system conditions verified the correctness of the established electromechanical transient simulation model.The application of active MMC in power systems has been studied,and it has been proven that the active MMC can improve the power angle stability and frequency stability of power systems,achieve greater disturbance decoupling of AC and DC systems,and have more excellent operating characteristics compared to the traditional MMC.It is a future development direction of MMC-HVDC(High Voltage Direct Current).(2)A electromechanical transient modeling method for modular multilevel matrix converter(M3C)was proposed,and a electromechanical transient simulation model for M3 C was established.An iterative algorithm for power flow calculation is proposed for power systems containing the flexible low-frequency AC transmission system M3C-LFAC(Low Frequency AC Transmission System,LFAC);And based on the power flow calculation results,the initialization of electromechanical transient simulation was achieved for the power system containing M3C-LFAC.Based on the mathematical model of the M3 C and its controller,an electromechanical transient simulation model of the M3 C was constructed.The correctness of the model was verified by comparing the results of electromagnetic transient simulation and electromechanical transient simulation.The centralized and decentralized control methods of the M3C-LFAC system were studied,and an electromechanical transient stability analysis on an improved New England 39 node test system containing multi-terminal M3C-LFAC was conducted,demonstrating the dynamic characteristics of the M3C-LFAC system.(3)A unified electromechanical transient simulation model suitable for all nonsynchronous-machine power sources has been proposed,and corresponding parameter calculation methods have been provided.It can be applied to large-scale electromechanical transient simulation of power systems containing a large number of heterogeneous nonsynchronous-machine power sources.Based on this model structure,a small signal analysis model was derived.The influence of model parameters and control methods on system stability was studied for a four-machine testing system,and the mechanism by which various parts of the model affect the system stability was revealed.(4)A benchmark for evaluating the impact of nonsynchronous-machine power sources on power system angle stability has been proposed;and based on this benchmark,the small disturbance power angle stability and large disturbance power angle stability of a simple testing system were studied.A simple testing system was designed which maintain the power angle of the equivalent electromotive force of the synchronous generator relative to the receiving end system constant when the penetration of the nonsynchronous-machine power sources changes.Based on this premise,the change in power angle stability level of the synchronous generator was studied to determine the impact of the penetration of the nonsynchronous-machine power sources on the power angle stability.In addition,based on this simple testing system,the applicability of the electromechanical transient simulation method and the established unified nonsynchronous-machine power source electromechanical transient simulation model to the power angle stability analysis was verified.