Analysis On The Dynamic Interaction Of Wind Power And LCC-HVDC Power System

Large-scale and high-concentration wind power is transmitted over long distances through HVDC transmission in the northwest,north and northeast regions of China.The issue of system oscillation is prominent,which greatly affects the safety and stability of the power grid.The interaction between VSC and LCC-HVDC is studied in this thesis,specifically,the contents are as follows:(1)The basic structure of VSC is analyzed,and the mathematical equations of the components of VSC are established.The linearization equations are deduced in detail including inner current loop,outer voltage loop and phase-locked loop control.And a general VSC linearization model is established based on state space.The application scenarios of VSC single machine infinite system are built in PSCAD and Simulink respectively,and simulations are conducted.Simulation results both in PSCAD and simulink platform show that the time-domain waveforms coincide with each other in the case of small disturbance stability mode and unstable oscillation mode,which verifies the correctness of the linearized VSC model.(2)The basic structure of LCC-HVDC is analyzed,and the mathematical equations of components of LCC-HVDC system are established.The linearization equations of seven modules are derived in detail including rectifier,inverter and HVDC transmission line.A general method is presented based on matrix partitioning to integrate the lower-order state equations of each module into that of higher-order.The high-order linearization model of LCC-HVDC is established based on state space by applying this method.Finally,the application scenario of LCC-HVDC single machine infinite system is built and simulations are conducted.Simulation results both in PSCAD and simulink platform show that the time domain waveforms of the two modes coincide well,which verifies the correctness of the LCC-HVDC model.(3)The application scenario of infinite system with interaction between VSC and LCC-HVDC is designed.The linearization model of VSC and LCC-HVDC infinite system is established based on state space by applying the matrix partitioning method.Modal analysis of the sensitivity of parameter is conducted according to linearization model based on state space.The effect of parameters including short circuit ratio,VSC and LCC-HVDC control parameters on system stability is analyzed,and the critical value of system instability is obtained by applying eigenvalue locus method.Finally,the correctness of the linearization model and theoretical analysis results is verified by simulations in PSCAD.