The Subsynchronous Damping Characteristic Analysis In UHVDC System And SSDC Design

Externally Along with the grid structure being more and more complex and the rapid development of the HVDC system, studying the subsynchronous oscillation (SSO)problem on HVDC system has more engineering practice significance. Hami-Zhengzhou ±800kV UHVDC (Ultra-High Voltage Direct Current) transmission system is the first UHVDC project for Xinjiang power outward transmission and also the first wind-thermal-bundled DC transmission project. The paper studies subsynchronous oscillations damping characteristics at the UHVDC converter station and the improvement strategy. The main research contents are as follows:(1) Analyze the application of complex torque coefficient method in subsynchronous oscillation study and research the complex torque coefficient method with the theoretical analysis in low amplitude continuous subsynchronous oscillation suppression effect. Propose the forced oscillation amplitude evaluation method and instantaneous disturbance attenuation time evaluation method.(2) Analyze subsynchronous oscillation generation mechanism in HVDC system, establish the PSCAD Ha-Zheng UHVDC system non-real time simulation model, and discuss the system time subsynchronous electrical component characteristics between the machine-net and AC-DC transfer through time domain simulation and MATLAB data FFT analysis. Conduct the related physical quantity time domain simulation under different conditions and the system electrical damping analysis. Compare the different effects of DC power, constant current PI controller parameters and the alpha angle on effect of damping.(3) Design narrow-band multi-channel structure subsynchronous damping controller for Ha-Zheng system, in which the modal filter using two order Butterworth filter. At last, the paper can verify that the SSDC designed can decrease Modal speed deviation and multiple mass torque to a low range and effectively improve the system electrical damping in Ha-Zheng.(4) Analyze concomitant voltage flicker in subsynchronous oscillation suppression with other device and study the reason for using additional blocking filter device to solve the problem.