Mechanism Analysis And Simulation Research On Subsynchronous Oscillation Of Complicated AC/DC Power System

With the advent of hybrid AC/DC power grid era, the subsynchronous oscillation(SSO) of generators aroused by HVDC or series capacitor compensation is worthy ofattention. It may leads to serious damage on the shafting of large turbine generators andendangers the safe operation of power system.Hulun Buir League power system is currently the first large-scale themal powergeneration point to network hybrid AC/DC power grid. Its transmission of power is byHu-Liao DC system and Yi-Feng AC transmission line with series capacitor compensation.So its structure is complicated. Since Hu-Liaon DC project put into operation, thefrequently exceed standard in Hulun Buir generators has been existing for a long time. Thisproblem is mainly caused by the weak electrical damping of power grid and a sustaineddisturbance source. So we should analyse the problem in both two aspects, one is the SSOdamping characteristic of system, and the other one is the SSO disturbance source whichmaybe exist.This paper firstly analyses on typical signle machine AC/DC power system. It uses testsignal method to analyse the influencing factor on the SSO damping characteristic ofsystem. The results lay a foundation for the research on Hulun Buir League power system.Then the paper introduces how to design the parameters of Subsynchronous DampingController (SSDC) by the phase compensation method. And it uses the same method todesign the parameters of Hu-Liao DC system SSDC. After that, Based on PSCAD/EMTDC,a simulation model of Hulun Buir League AC/DC power grid is built to research on theSSO damping characteristic of Hulun Buir League power system under different operatingconditions and the damping action of SSDC. Finally, the paper researchs on the SSOdisturbance source and its characteristic. We can make a conclusion that: although HulunBuir League power system is stabilize, SSO won’t be instability, the damping of system islow which is due to Hu-Liao DC system and Yi-Feng AC transmission line with seriescapacitor compensation, so the amplitude of SSO will be big. And as the DC system isconnected with large electric arc furnace load on the inverter side, it may causes persistent disturbances to the system. So the SSO of Hulun Buir League power system is caused bythese two reasons.