Stability Margin Improvement Method For Power Systems With High Proportion Of Renewable Energy Based On Generalized Short Circuit Ratio

Due to the eco-friendly characteristic,exploitation and utilization of renewable energy has gradually become a new direction for the development of power energy in the world.Renewable energy generations are integrated into power grid through power electronic devices,which has the advantages of flexible control and rapid response,but also brings the problems of small inertia and weak anti-disturbance ability.Especially when large-scale renewable energy generations are integrated into power grid with multiple feeding points,strength of the AC grid becomes relatively weak and complex coupling relationship between devices and AC grid arises,leading to a series of oscillation problems.The challenges hinder the application and development of renewable energy technology,so it is urgent to find suitable indexes to describe the power grid strength when power electronic devices are integrated into the grid with multiple feeding points.Short circuit ratio is an important index to analyze the static stability of AC-DC system,and then extended to the small signal stability analyzation of the renewable energy generations.On the basis of taking the interconnection between systems into consideration,the mechanism of small signal stability in multi-infeed power electronic system is analyzed by generalized short circuit ratio,solving the inapplicability of short circuit ratio in multi-infeed power electronic system.Based on the accurate description of small signal stability from the perspective of power grid strength with generalized short circuit ratio,main influencing factors of this index are analyzed in this paper,and the sensitivities of generalized short circuit ratio with respect to main influencing factors are applied to improve the stability margin,guiding the planning and control of power systems with high proportion of renewable energy.The main works are summarized as follows:(1)With stability margin improved by grid-connected capacity status optimization,the limit of the overall grid-connected capacity with a certain small signal stability margin is explored.Based on the sensitivity of generalized short circuit ratio with respect to each renewable energy generation's capacity,the influence of grid-connected capacity on small signal stability is characterized,and the optimality condition of sensitivities is obtained when the whole grid-connected capacity reaches the limit.Furthermore,a grid-connected capacity limit calculation method for power systems with high proportion of renewable energy considering small signal stability is proposed.(2)With stability margin improved by grid line's admittance adjustment,the critical line of the system grid structure considering small signal stability is identified.Based on the sensitivity of generalized short circuit ratio with respect to each grid line's admittance,the influence of admittance on small signal stability is characterized,and a critical line identification method for power systems with high proportion of renewable energy considering small signal stability is proposed.(3)With stability margin improved by the involvement of renewable energy bases in frequency control and active power status optimization,the emergent frequency control method of power systems with high proportion of renewable energy after DC blocking fault is explored.In view of the over-frequency problem caused by the DC blocking fault,the frequency stability is improved by introducing renewable energy bases into frequency control.Moreover,based on the sensitivity of generalized operation short circuit ratio with respect to each renewable energy base's active power,the influence of active power on small signal stability is characterized.The emergent frequency control method is proposed to achieve both the frequency stability and the optimal small signal stability while adjusting the active power status.