Study On Dynamic Stability Of Machine-Network In Power System

With the increasing capacity of generating units in modern power systems,the dynamic behaviors of generator sets have larger effects on power system stability than ever before.At present,the interaction and coordination between big generating sets and large-scale power grids have become important issues,which directly impact on power system security.According to theoretical analysis,simulation validation,field measurement and practical application,this thesis focuses on dynamic stability of machine-network in power systems.Some new ideas and main achievements are as follows:The thesis establishes machine-network coupling models and the related simulation platform.The steam turbine model considering steam pressure pulsation,water turbine model considering draft turbo water pressure pulsation and their control system model are established.Based on power system analysis software,machine-network coupling simulation platform is built up,which lays the foundation for studying machine-network coupling and its effect on power system dynamic stability.The thesis presents the resonance mechanism for power oscillation introduced by machine-network coupling.The characteristics of resonance mechanism power oscillation are analyzed in single machine system and multi-machine system under different modes.The resonance mechanism in power system is explained from the energy point of view.The characteristics of energy in power system and the relationship between inside and outside energy of power system are analyzed.The differences and relationship between resonance mechanism oscillation and negative damping mechanism low frequency oscillation,sub synchronous oscillation are studied.The thesis presents the sources of disturbance inducing power system low frequency oscillation of resonance mechanism.The effects of steam turbine thermal parameters,water turbine hydraulic parameters and rotor mechanical parameters on prime mover output power are studied.The disturbance sources,which may be introduce power system resonance mechanism power oscillation,are found.The difference of the tie line power oscillation,which introduced by the prime mover power disturbance and the load disturbance,are studied in theory.The conclusion can provide the reference to understand low frequency oscillation phenomenon occurred presently in power system. The machine-network dynamic parameters comprehensive measurement equipment based on the synchronous sampling is researched and applied in practice.Considering the dynamic coupling characteristics between steam turbine(and water turbine), generator and electric network,the steam turbine thermal parameters,water turbine hydraulic parameters,rotor mechanical parameters and electric parameters are measured, realizing machine-network dynamic parameter synchronized sampling.It provides the first-hand materials for researching machine-network dynamic security stability.The thesis presents and applies the machine-network dynamic security evaluation method based on field measurement.The field-measured data collected by the comprehensive measurement equipment are analyzed using Prony method according to the time-domain and frequency-domain characteristics.The dynamic coupling characteristics between turbine,generator and electric network are determined. Combined with power grid small disturbance stability analysis,the machine-network dynamic security evaluation based on the measured data is realized.Then the actual machine-network dynamic security evaluation system has developed based on field measurement to enhance the operator the monitor level of machine-network dynamic stability.