Study On The Power Grid Out-of-Step And Splitting Analysis Based On PMU

Interconnection of power grids,making the stability of the power grid more and more serious.Although the stability control measures are in place,but there will always be unpredictable contingency in advance to make the stability of the power grid be destroyed,even serious out-of-step oscillation occurs,leading to the occurrence of large blackouts and bring disaster to the national economy and people’s lives.Out-of-step splitting is used as a back-up for stability control,which can minimize the effects of out-of-step.The current out-of-step criterion mainly includes the criterion of directly and indirectly reflecting the power angle.It is difficult to determine the out-of-step state of the power grid in different regions because of the complex grid structure and the different size of the grid area.Therefore,this thesis proposes a sub-regional grid out-of-step criterion based on the PMU,which has very important theoretical and practical value.Firstly,to solve the irrationality of using out-of-step criteria to determine the out-of-grid fault,a scheme of out-of-step solution is proposed.In the scheme,the PMU is used to acquire the synchronization vector information and the PMU is arranged by the PMU optimal solution which can solve the power flow equation;Based on the PMU to build a wide-area measurement system to achieve the out of step judgment and control.Secondly,this thesis proposes an improved clustering optimization method based on Manhattan distance definition,which is based on the shortcomings of the direct use of time-domain simulation to divide the cohomology cluster into practicability.This method of cohomology clustering overcomes the number of mutations in the sample data,which not only reduces the number of clusters,but also has more rationality.Thirdly,the greater the transient power angle instability,the more prone to out-of-step phenomenon,which proposed a power grid transient angle instability criterion.PMU and timing analysis method are used to predict the power angle,which can be used as a reference for subsequent out-of-step judgments.Finally,based on the problem of out-of-step judgment of power grid in different area,a method of judging out-of-step of power grid based on PMU is proposed,including out-of-step judgment method of small area grid based on equal area method and out-of-step judgment method for large regional power grid considering out-of-step of sub-network.The former combines the constant area rule and the electrical parameters of the generator rotor motion equation,which is simple and fast.The latter is mainly based on the difference of the voltage phase angle of the tie line,which takes into account the possibility of out-of-step power outages,can effectively determine the location of the out-of-step oscillation center,and then take the appropriate measures to splitting.The control measures after the out-of-step separation are mainly to take into account the power balance of the island after the splitting,to take the corresponding cutting machine,load shedding,resynchronization and other stability control measures to ensure that the isolated island can be stable operation.