Research On Subsynchronous Oscillation Adaptive Mitigation Method Of Wind Power Integrated System

In the background of “carbon peak,carbon neutrality”,the development of new energy is imperative,and the installed capacity of wind power is increasing year by year.However,a large number of wind turbines connected to the power grid has increased the risk of sub-synchronous oscillation(SSO),which seriously threatens the safe and stable operation of the power grid.The SSO happened in wind power integrated systems has the characteristics of time-varying frequency.However,due to the modeling accuracy and the fixed-parameter structure of the controller itself,the traditional supplementary sub-synchronous damping controller(SSDC)may have the problem of weak adaptability.Therefore,it is necessary to design a subsynchronous oscillation mitigation method with wide adaptability.In this paper,the sub-synchronous oscillation adaptive mitigation method of wind power integrated system is studied as follows:(1)The doubly-fed induction generator(DFIG)-based wind power integrated system with static synchronous compensator(STATCOM)is taken as the test system in this paper,and the mathematical models and small-signal models of the DFIG-based wind farm and the compensated transmission line with STATCOM are established.The eigenvalue analysis method is used to identify oscillation mode and analyze participation factors of the test system.Finally,the results of the eigenvalue analysis are verified with accuracy by time-domain simulation and fast fourier transform(FFT)analysis.(2)The challenges faced by SSO mitigation in DFIG-based wind power integrated systems are analyzed deeply,and the rationales of weak adaptability of SSDC are revealed.Firstly,the influence of multiple variable operational parameters in both the generator side and the network side on SSO are analyzed,and the results show that wind speed,active/reactive power output of DFIG,number of DFIGs,series compensation level and short circuit ratio all have great influences on SSO.Considering the collective influences of these key parameters on SSO,the phase shift of the filter in SSDC and the compensation phase changes under different operating points are analyzed.By this way,the rationales of difficulties in adaptive mitigation of SSDC are revealed from the perspective of the phase compensation theory.(3)Since the model-free adaptive control method only uses online input-output data of the controlled system to design the controller,this method can be independent of the model,has strong adaptability and simple control algorithm,and thus has great application prospect.In this paper,the model-free adaptive control theory is introduced into the field of SSO,and an SSO supplementary control method based on modelfree adaptive control is proposed.Firstly,the structure of the model-free adaptive controller(MFAC)is designed and the suitable pseudo-partial derivative estimation method is selected.Secondly,according to the requirements and characteristics of SSO supplementary control,the core control algorithm of MFAC is designed and developed,the novel control criterion function is constructed,and the amplitude constraint of the controller output is added with the compensation signal being introduced.Thus,the novel MFAC algorithm is formed.Furtherly,under the proposed algorithm,it is theoretically proved that the tracking error of the closed-loop disturbed system is uniformly ultimately bounded(UUB)and bounded input-bounded output stable.Based on the stability analysis,methods of MFAC parameter design are accordingly proposed.Thus,the solid theoretical basis of MFAC is supplied.(4)The SSO supplementary control method based on MFAC is applied to DFIG and STATCOM.The selection method of installation site of supplementary controller is proposed based on the geometric measure,and the optimal installation sites of MFAC are determined.Furthermore,considering the influences of the six uncertain parameters,multiple simulation scenarios of sub-synchronous control interaction(SSCI)are constructed to verity the effectiveness and wide adaptability of MFAC.Additionally,the performances of MFAC to mitigate different SSO mechanisms are also tested.Results indicate that MFAC has remarkable mitigation effects on torsional interaction(TI)and SSO induced by phase-locked loop(PLL).The proposed sub-synchronous oscillation adaptive mitigation method in this paper does not depend on the detailed theoretical model of the system,but only gets the input-output data of the system in real time to update the control parameters,so as to avoid the modeling problem of the wind power integrated system.The results of cases show that the proposed method has good effectiveness,wide adaptability and applicability,which implies its broad application prospect and research value.