Research Of Complex Oscillation Characteristics Analysis And Damping Control Strategy Of Renewable Energy Integrated Power System

With the determination of the “double carbon” goal,it is an important way to develop renewable energy vigorously for promoting energy transformation and upgrading of China.Different from the traditional synchronous generator,renewable energy is generally connected to the grid via power electronic equipment,which possesses the characteristics of multi-timescale dynamic response and cannot provide sufficient inertia support.Actual power grid project operation shows that there exists complex oscillation problems in the renewable energy grid-connected power system.To ensure the safe and stable operation of renewable energy grid-connected power system,complex oscillation problem and damping control strategy of renewable energy grid-connected power system is urgent to be researched.In this paper,the renewable energy grid-connected power system is taken as the research object.Firstly,the characteristics of subsynchronous oscillation(SSO)and the simplified modeling method of grid-connected double-fed induction generator(DFIG)integrated into the weak grid are studied.Then,aim at the small disturbance stability issues of wind-thermal coupling system considering active frequency support control(AFSC),dominant factors of subsynchronous oscillation(SSO)modes determined by phase-locked loop(PLL)of the coupling system are detected.Furthermore,aim at the SSO issues of windthermal coupling system considering AFSC,the effective open-loop process(EOP)theory is introduced to analyze SSO and corresponding suppression strategies are proposed.Next,the impact of AFSC of photovoltaic on PLL-based photovoltaic of wind-photovoltaicthermal coupling system(WPTCS)is investigated.Finally,the optimal design method of probabilistic robust damping controllers(PRDCs)is proposed to suppress multiband oscillations in the power system integrated with wind farm.The main work of this paper and the results obtained are as follows:1.Aiming at the SSO issues observed in grid-connected DFIG-based wind farm in weak grid,eigenvalue distribution under different operation state and power grid strengths is analyzed considering both the model reduction and SSO characteristic.Two simplified models of DFIG in a weak grid are established to analyze SSO characteristic.The correctness of the proposed models is verified via eigenvalue distribution and time domain simulation.Based on the proposed simplified model,the impact of the parameters of the DFIG and its controllers on the small-signal stability of grid-connected DFIG in a weak grid is analyzed detailedly.2.Aiming at the oscillation issues of wind-thermal coupling system considering AFSC,the influence of AFSC on the electromechanical oscillation modes dominated by thermal generators and the subsynchronous oscillation modes dominated by PLL in DFIG is analyzed,and the main influence factors of SSO modes dominated by PLL in the coupling system are determined as the droop control under the high wind power permeability.The small disturbance equivalent model of PLL for the coupling system considering AFSC is derived.The specific influence of parameters of AFSC on the SSO dominated by PLL is investigated.Finally,the correctness of the above analysis is verified by time domain simulation.3.Aiming at SSO issues of wind-thermal coupling system considering AFSC,a multiple-input multiple-output(MIMO)model of wind-thermal coupling system with AFSC is established.Based on EOP theory,it is equivalent to a single-input single-output(SISO)system.Based on that,an improved stability criterion is constructed for SSO analysis.A phase reshaping controller is proposed to increase the stability margin of the coupling system within the subsynchronous frequency range.Finally,the validity of the proposed criterion and phase reshaping controller is verified by time-domain simulation.Simulation results is further verified by RT-LAB real time simulation.4.Aiming at SSO issues of WPTCS considering AFSC of photovoltaic,a simplified model of WPTCS with AFSC is established.Then,the corresponding eigenvalue distributions of PLL of photovoltaic dominant SSO between the simplified model and the detailed model are compared to verify the simplification correctness.Based on that,the transfer function of additional AFSC is derived.The impact of parameters of AFSC on the SSO dominated by PLL of photovoltaic is analyzed.Finally,the correctness of theoretical analysis results is verified via frequency-domain and time-domain simulation results.5.Aiming at the multiband oscillations issues observed in the power system integrated with DFIG,the probabilistic small-signal stability analysis(PSSSA)of power system integrated with DFIG is investigated via probabilistic collocation method(PCM).Furthermore,the optimal design method of PRDCs is proposed based on a novel algorithm of adaptive compass search(ACS).Meanwhile,the convention controllers designed by the residue method and particle swarm optimization(PSO)and probabilistic controllers designed by grey wolf optimizer(GWO),teaching learning-based optimization(TLBO),and particle swarm optimization(PSO)are proposed,respectively.Simulation results verify the superiority of PRDCs designed by ACS.