Research On SSCI Caused By Grid-integration Of Doubly Fed Wind Power Generation

Doubly Fed Induction Generators(DFIG) are being more and more widely used in wind generation area with its flexibility on control. With the expansion of the scale of wind farms, the large-scale wind power is outgoing in series capacitor compensation circuit(short for series compensated lines). Because the series capacitor compensation technique improves line transmission capacity and enhances system stability, it is an economically realizing long distance transmission mature technology. According to the interaction of different objects, sub-synchronous oscillation wind turbines have three types. Sub-synchronous Resonance(SSR) is a phenomenon that can cause increased fatigue or critical failure of generator turbine shaft systems due to an nergy exchange between the generator and a series compensated transmission system, Sub-synchronous Torsional Interaction(SSTI) occurs when an interaction occurs between an HVDC link, FACTS device, or other power electronic controller and the mechanical mass system of a generator.Large-scale wind turbine generators with power electronic converters that operate near series compensated transmission lines are susceptible to un-damped sub-synchronous oscillations. This sub-synchronous oscillation is called Sub-synchronous Control Interaction(SSCI). With the rapid development of wind power technology, SSCI emerges as a new sub-synchronous oscillation phenomenon. The first SSCI event occurred for a wind farm in America in2009, which resulted in damage to the wind turbines. In this study, analysis the mechanism of double-fed wind turbine sends power through SSCI series compensated lines, and analyze the SSCI’s parameters characteristic, and finally gives the corresponding suppression measures.First,based on this,the small signal stability analysis is proposed,according to the single unite to infinite system where wind power flow through series compensated transmission lines, the multi-mass model,the induction generator model, the converter model and the gride model are established, these masked models are connected to form a system. Near steady operating point,the oscillation modes are analysed through the eigenvalues of the single unite to infinite system. In order to trace the influence of state variables to every oscillation mode in number, the participation factors are introduced,a conclusion is drawn out that,it is the interaction between the series compensated transmission line and the converter of the doubly fed induction generator that causes the Sub-synchronous Control interaction.Then the function of converter belonging to DFIG is simulated by using controlled voltage source at the AC side and controlled current source at the DC side, which averted the effects of higher harmonic caused by switching devices on the computation of electrical damping regarding to DFIG. Making use of the complex torque coefficient method and the equivalent simulation model, the generator’s electrical damping curve in sub-synchronous frequency domain was calculated, so that the influences of controller’s PI parameters, series compensation level and resistance of transmission lines on the generator’s electrical damping were investigated. Results indicated that augmentation of controller’s inner loop gain, decrease of integration time constant, increase of series compensation level and decrease of transmission line resistance all exacerbated the negative damping of DFIG.Using time domain simulation investigate the influences of controller’s PI parameters, series compensation level and resistance of transmission lines on the generator’s electrical damping by PSACD modol.Results is the same as complex torque coefficient method.Finaly,the supplementary hybrid sub-synchronous damping controller(H-SSDC) in the rotor side converter(RSC) was proposed to mitigate SSCI concerns. The validity of the H-SSDC was conformed in time domain simulation.