Multi-scale Modeling And Analysis Of Transients For VSC-HVDC And AC System

In recent years,China has vigorously developed VSC-HVDC transmission projects.With the continuous interconnection of VSC-HVDC transmission systems,China's power grid has gradually changed from a single AC network in the early years to a hybrid AC-DC network.So it is very important to study the simulation and modeling of AC/DC hybrid network with VSC-HVDCtransmission system.According to the operation principle of VSC-HVDC transmission system,the mathematical model of VSC-HVDC two-terminal power supply system is established.According to the control mechanism of the control system of VSC-HVDC transmission system,the controller of the VSC-HVDC system based on PARK transformation and the controller of the VSC-HVDC system based on CLARK transformation are established respectively according to two modeling methods.The controller of VSC-HVDC system based on PARK transformation is designed from the point of accelerating the speed of the system,and the PI control parameters are set through typical control principles.The controller of VSC-HVDC system based on CLARK transformation is designed to enhance the stability of the system and tune PI(R)control parameters by using state space averaging method.The performances of the two controllers are compared in terms of system rapidity,stability and total harmonic distortion rate.By synthesizing the performance advantages of the two controllers,the double-loop control principle is adopted,the inner-loop current control is designed based on CLARK transformation,the outer-loop voltage control is designed based on PARK transformation,the rectifier side adopts constant power control mode,and the inverter side adopts constant DC voltage control mode.According to the idea of power system multi-time scale modeling,the multi-time scale mathematical models of power system components and power system equipment are established.Taking inductor as an example,a multi-time scale mathematical model of inductor is established based on Hilbert transform and adaptive frequency transient simulation.The power system equipment takes the power generation equipment as an example,and establishes the multi-time scale mathematical model of the power generation equipment by establishing the equations of the excitation system and the speed regulation system respectively.The control system model of VSC-HVDC transmission system is built on MATLAB/Simulink simulation platform to verify the accuracy of controller design.A hybrid AC/DC simulation model with VSC-HVDC system is built on MATLAB/Simulink simulation platform.Among them,the AC network adopts the electromechanical transient modeling method to establish the AC network model of 3 generators and 9 nodes,and the DC system adopts the VSC-HVDC system model with two power supply terminals.The transient characteristics of VSC-HVDC system with three-phase and single short-circuit faults on the AC buses on both sides of the system are investigated.In contrast,this paper establishes the equivalent electromechanical model of VSC-HVDC system on the electromechanical side and the equivalent electro-magnetic model of AC network on the electro-magnetic side.Similarly,three-phase and single short-circuit faults occur at the AC buses on both sides of the equivalent VSC-HVDC system,and the transient characteristics of the system are analyzed.