Research Of Subsynchronous Oscillation In Wind-thermal Bundled System

With the rapid development of wind power technology,the installed capacity of wind power is largely raised.Large capacity and long distance transmission has been the main solution for wind power consumption.Due to the great effectiveness in solving the problem of frequecy and voltage steability,wind-thermal bundling system sent out via HVDC transmission is becoming the main transmission for wind power.The interaction between thermal generator and HVDC system may cause sub-synchronous oscillation(sub-synchronous torision interaction).The sub-synchronous oscillation of this new system,wind-thermal bundling system sent out via HVDC transmission(WTBH system),is hardly studied by the existing researches.This paper does the research for this problem.Doubly-fed induction generator(DFIG)based wind farm sent out via HVDC transmission and WTBH system is the main research object in the paper.The sub-synchronous oscillation of each system is analyzed,especially the interaction between DFIG based wind farm and HVDC transmission and influence of DFIG-integration to SSTI.Detailed research contents is as follow.Thermal generator,DFIG generator,HVDC transmission system and AC network are constructed.The model of thermal generator contain six-mass model and PSS.Stator voltage-oriented control is applied in converter system of DFIG model.HVDC transmission system is expressed by the quasi-steady-state model.The DFIG sent out via HVDC system is analyzed by complex torque coefficient approach realized by domain simulation.The interaction between DFIG and HVDC system is also analyzed.The equivalent aggregation model of DFIG and controlled source model of converter are constructed to enhance computing efficiency and avoid the influence of high frequency switch device.The accuracy of equivalent models are verified.Based on the PSCAD/EMTDC simulation platform,the simulation model of DFIG sent out via HVDC system is constructed to analyze the influence from operating parameters of wind farm,weakness of AC system and parameters of HVDC control device to the system.The analysis shows that the interaction between DFIG and HVDC system is not obvious,but the change of AC system in rectifier has an impact on the damping characteristic of DFIG sent out via HVDC system.The block modeling of state-space of multi-sources system is studied.Base on the platform of simulink,the independent blocks consisting of each state-space model are connected,and the complex problem of generator-network interface is sloved by vector transfer.Small signal model of WTBH system is set by the block modeling,and the calculation of system parameters is given.The eigenvalue analysis of WTBH system is applied.The influence of the integration and operation of DFIG on SSTI of thermal generator is studied in detail.The key influence factors consist of wind speed,capacity of wind farm and distance between wind farm and rectifier.The results show that the integration of DFIG improves the modal damping of thermal shafting.The simulation model of WTBH system is constructed on the platform of PSCAD/EMTDC.The results of eigenvalue analysis are verified by time-domain simulation.