Research On Power System Transient Stability Emergency Control Methodology

Interconnected operation of power grids is inevitable for optimum allocation of large-scale resources and economical operation of power systems.It brings huge economic benefits,while,however,impacting the safe and stable operation of power systems.On the one hand,the operation conditions and environments of power systems become more complex,the impact of random events expands,and the consequences of system dynamic behavior in operation are more difficult to estimated and controlled.On the other hand,the uneven distribution of power sources and loads,as well as the lag of power grid construction,make transmission capacity of power transmission corridors which connect sending and receiving ends easier to get close to or surpass the section power limits,and power systems run at a critical level for a long time.Although during the design phases of power systems,their adapting ability to various types of disturbances such as,fault,a sudden and large-rang load changing,generator tripping has been fully considered,sudden large disturbances may result in the power angle,frequency and voltage instability,which greatly increases the risk of large-area power system break down and collapse after big disturbances under extreme conditions.Therefore,safety protection system construction is the priority among priorities in power system construction.In order to ensure the safe and stable operation of power systems,the power system construction in our country is planned and configured as three lines of defense,which play a key role in preventing system collapses and big blackouts.Transient stability is one of the key factors in causing big blackouts,so its emergency control measures are important contents of power systems' three lines of defense,and of great significance to the construction of big blackout defense system.In this paper,power system transient stability identification,critical cut-set identification and transient stability emergency control that are all key issues of power systems' safe operation under the emergency condition are researched.The main research contents are as follows:1,Under the condition of limited PMU(Phase Measurement Unit)configuration number in WAMS(Wide Area Measurement System),a power system transient instability identification method is put forward based on the stable boundary information of critical generator pair's measured response trajectory.The comparisonamong the single machine potential energy ridge criterion,the unstable equilibrium point criterion and the criterion of concavity and convexity of the phase trajectory shows that using the criterion of concavity and convexity of the phase trajectory can discriminate the instability at the earliest.Based on the analysis of critical generator pair's phase trajectory geometrical characteristics,a hypothesis that the stability of critical generator pair is related to the concavity and convexity of their phase trajectory.It is proved that power system transient instability occurs when the critical generator pair's phase trajectory passes the point where the rotate speed is above zero and the seconder derivative is above or equal to zero.The misjudgment problem of the criterion of concavity and convexity of the phase trajectory caused by critical generator pair's phase trajectory distortion is solved.A sort overlap method that can be used to quickly choose critical generator pairs is proposed.The validity and rapidity of the proposed criterion of concavity and convexity of the phase trajectory of critical generator pair are verified by comparing it with an improved single machine potential energy ridge criterion through an example.2,This paper propose a method for accessing candidate cut-set of critical cut-set bases on structure and parameters of network,and an online critical cut-set fast detection method which detect critical cut-set from candidate cut-sets.By the stimulation of power system partition,the hypothesis which proposes that the distribution of critical cut-set has network structure and parameter related(NSPR)feature,by the simulation of WEPRI 9 bus system,the NSPR feature of the critical cut-set distribution is proved to be exist.The surface feature of the critical cut-set distribution's NSPR feature is recapitulated preliminary.This paper derives the inner product expression of the power deviation on the branch,and analyzes the influence of network parameters on the correlation degree between the vector modulus and the linear correlation.The index of correlation of critical cut-set in the evaluation branch is defined,the optimal search model of candidate cut set is put forward,and an efficient algorithm is given.A supplementary discriminant method is proposed with consider the time-delay problem of the critical cut-set key branch detection when ridge criterion is used only in the case of more serious faults.In view of the problem of misjudgment of critical cut-off set,the influence of the auxiliary discriminant method is proposed to eliminate the influence of the interference cut set.The validity of the proposed method is verified in WEPRI 9 bus system and WEPRI-36 bus system respectively.3,In order to improve the transient emergency control tripping machine plansetting efficiency,this paper proposes a transient stability emergency control tripping machine plan quickly setting method based on single generator equivalent analysize of critical group and time-domain simulation method.The relationship between the power regulation of single generator equivalent analysize of critical group and the emergency control of the single generator equivalent system is derived.The analytical calculation formula of the mechanical power adjustment of the equivalent single generator system is obtained by analyzing the geometric characteristics of the electromagnetic power of the equivalent single generator group.The kinetic energy of the cutting machine of the critical machine generator at the time of transient stability and stability is proposed.The simulation of IEEE 39 bus system and regional interconnected grid shows that the proposed emergency strategy can effectively avoid repeated a lot of time domain simulations.4.In order to realize the real-time decision and real-time control of the transient stability emergency,the strategy of taking the tripping measures when using the energy storage for the transient emergency control is put forward.The three order equivalent model of energy storage power supply is deduced,and the control low of intermediate control variables is calculated based on back-stepping.Furthermore,a nonlinear robust controller for transient stability of energy storage device is designed.A combined optimization algorithm of cutting machine is proposed to select the optimal unit merging,and the energy storage is put into operation at the same time.Based on the approximate equivalent model of two zone system including energy storage,the effective control period of energy storage is analyzed,and the calculation method of the time of withdrawal is given.Using the PSASP 7.0 user defined(UD)model to build the energy storage and controller model,through the WEPRI 36 node example verified the proposed method in reducing the amount of cutting machine can also make the transient stability emergency control effectively.