Research On Frequency Stability Control Of Receiving End Power Grid With Large Penetration Of Renewable Energy

With the continuous adjustment of energy structure in China,renewable energy is gradually replacing the traditional synchronous generators.The large penetration of renewable energy integrated to the receiving end power grid has reduced the equivalent inertia and the frequency regulation ability of the power system.At the same time,large-scale AC/DC transmission has increased the risk of disturbance.It makes a significant change in power system frequency response characteristics,which brings challenge to the frequency stability of the power system.The frequency stability problem of the receiving end power grid with high proportion of renewable energy generation can be solved by exploring the frequency regulation ability of synchronous generators,make use of renewable energy control to participate in the system frequency regulation and other means.It is of great significance to solve the system frequency stability problem to master the system frequency response characteristics,fully excavate the frequency regulation ability of synchronous generators and study the optimal control method of renewable energy frequency control.The frequency response characteristics of the receiving end power grid is analyzed,and the optimal control methods to improve the frequency response capacity from the two perspectives of synchronous generators and renewable energy generators are discussed in this paper.The main work is as follows:(1)Based on the SFR model,the expressions of the system frequency response considering the dead zone of primary frequency regulation are derived,and the influence of key parameters of frequency regulation on the frequency response characteristics is comprehensively analyzed.The sensitivity index of key parameters is defined and the sensitivity of parameters to frequency response indexes are analyzed to quantify the influence degree of different parameters on these indexes.A index considering the frequency recovery speed is proposed to evaluate the frequency stability,which considering the static and dynamic characteristics of the frequency,and its weight coefficients is determined by entropy method.(2)In order to fully explore the primary frequency regulation ability of the synchronous generators,The "sensitivity of adjustment coefficient" is defined and its influencing factors are analyzed theoretically.The mathematical model of the optimization problem of the adjustment coefficient is established,and the nonlinear optimization problem is simplified to a linear optimization problem to avoid a lot of iterations.On this basis,an optimization method of adjustment coefficient for multi-machine power system is proposed.The improvement on primary frequency regulation of the power system is verified by the EPRI-36 system and an actual system as simulation examples.(3)In order to improve the inertial support function of wind generators and study the contribution of renewable energy frequency control to the actual system frequency,the frequency responses of internal,external and renewable energy generation systems are modeled respectively,and then the frequency response model of receiving end power grid considering renewable energy frequency control is proposed.The effect of virtual inertia coefficient on the index to evaluate frequency stability is studied,based on which a variable-coefficient virtual inertia control is proposed,and the frequency control parameters of wind turbine generators are optimized.Finally,the accuracy of the frequency response model and the effectiveness of the proposed optimization method are verified by Jiangsu power grid as an example.