Research On Influence Mechanism Of Power Grid Parameters And Trajectory Characteristics On Transient Power Angle Stability

In recent years,power grid of China has gradually formed a pattern of West-to-East electricity transmission projects and North-South Mutual Supply.In the simulation study of the interconnected power grid,it is found that the dynamic response of the system after failure may present a more complicated situation.Therefore,studying the influence of different grid parameters on the transient power angle stability and mastering the distribution of the dominant mode in the parameter space can provide the basis for the formulation and optimization of the subsequent control strategy.The transient power angle stability is affected by model parameters such as power output and inertia of synchronous generators,load capacity,grid structure,etc.It is also affected by disturbance parameters such as fault location and type,fault clearing time,and generator-tripping time,etc.And a lot of research achievements have been achieved so far.Researchers have explored the corresponding trajectory characteristics based on the perturbation-based time response curves to reveal its relationship with the transient power angle stability.However,there are still problems in the study of the influence of parameters or trajectory characteristics on transient power angle stability.Identification of dominant modes and quantitative expression of transient power angle stability based on extended equal area criterion(EEAC),this paper studies the influence of synchronous generator inertia,fault clearing time,generator-tripping time and non-coherent of the synchronous generators within the cluster on transient power angle stability.The research results enrich the application of EEAC theory.The influence of other parameters on the transient power angle stability can be studied with reference to the ideas in this paper.The dissertation will focus on the following aspects to carry out research work.(1)Study the influence of synchronous generator inertia on transient power angle stability.Based on EEAC theory,from the perspective of the complementary-cluster,the mechanism of synchronous generator inertia affecting transient power angle stability is analyzed.It is pointed out that the change of inertia affects the transient power angle stability by generating the ? axis and P axis effects.For the first swing of power angle instability of the Hamilton system,if and only if the mutual admittance between the clusters is zero during the fault and the acceleration of the generators in critical cluster before the instability is greater than zero,the acceleration of the generators in remaining cluster before the instability is not less than zero,the law that the increase of inertia in critical cluster is beneficial to transient power angle stability,and the increase of inertia in remaining cluster is not conducive to transient power angle stability is strictly established.In addition,the influence of the change in the inertia on transient power angle stability margin will be uncertain.The correctness of the above analysis is confirmed by simulation results.(2)Study the influence of fault clearing time on transient power angle stability.The mechanism of fault clearing time affecting transient power angle stability is analyzed based on the EEAC theory.It is pointed out that the change of fault clearing time affects the transient power angle stability by generating the ? axis and P axis effects.For the first swing of power angle instability of the Hamilton system,the increase of fault clearing time will only produce the ? axis effect which is not conducive to stability.Under the premise that the dominant mode remains unchanged,transient power angle stability margin will decrease with the increase of fault clearing time.For the first swing of power angle instability of the non-Hamilton system,the increase of fault clearing time not only produces the ? axis effect which is not conducive to stability,but also produces P axis effect with uncertainties on the stability.When P axis effect is favorable for stability and its strength exceeds the adverse effect of ? axis effect,transient power angle stability margin will increase with the increase of fault clearing time.The correctness of the above analysis is confirmed by simulation results.(3)Study the influence of generator-tripping time on transient power angle stability.It is pointed out that the generator-tripping operation affects transient power angle stability by changing the equivalent electrical output power,the mapping power angle and the corresponding energy accumulation interval based on the EEAC theory.And based on this,the mechanism of generator-tripping time affecting transient power angle stability is analyzed.It is pointed out that the change of generator-tripping time affects the transient power angle stability by generating the ? axis and P axis effects.For the first swing of power angle instability of the Hamilton system,the increase of generator-tripping time will only produce the ? axis effect which is not conducive to stability.Under the premise that the dominant mode remains unchanged,transient power angle stability margin will decrease with the increase of generator-tripping time.For the first swing of power angle instability of the non-Hamilton system,the increase of generator-tripping time not only produces the ? axis effect which is not conducive to stability,but also produces P axis effect with uncertainties on the stability.When P axis effect is favorable for stability and its strength exceeds the adverse effect of ? axis effect,transient power angle stability margin will increase with the increase of generator-tripping time.The correctness of the above analysis is confirmed by simulation results.(4)Study the influence of non-coherent within the cluster on transient power angle stability margin.Based on the EEAC theory,it reveals the correlations between transient power angle stability margin and its components in the energy domain and the non-coherent within the cluster in the time domain from the perspective of energy.The simulation results indicate the complexities of the influence of power angle divergence or approaching non-coherent within the cluster on stability margin.This is because the change of degree of power angle divergence or approaching non-coherent within the cluster will simultaneously change the two parts of energy corresponding to the intra-cluster and inter-cluster power,which in turn affects transient power angle stability margin.And the effects of the two approaches may not be monotonous.Therefore,in the transient power angle stability analysis,the combined effects of P axis and ? axis effects generated by the parameter changes should be comprehensively taken into account to measure the change of transient power angle stability of the system.