| In recent years,with a large number of power electronic equipment connected and the increasing power load,the demand for reactive power in the power grid is increasing.Reactive power compensation equipment is connected to the system,for example,synchronous condenser based on rotation type or static synchronous compensator(STATCOM)based on power electronics type can effectively improve the reactive power regulation capability and voltage stability of the system.At present,the research on synchronous condenser mostly focuses on the motor body and variable frequency starting strategy,and there is less research on the impact of condenser integrating to AC power grid on itself and power grid stability.At present,the research on STATCOM mainly focuses on its topology and control strategy,there is little literature on the impact of STATCOM’s integrating to AC power grid on itself and power grid stability.When the synchronous condenser and STATCOM are connected to the power grid side at the same time,there are coupling effects and coordinated control problems in the access of two different types of reactive power compensation equipment,which have a great impact on the stability of reactive power compensation equipment.There is no literature report in this regard.The instability of reactive power compensation equipment is easy to lead to system instability and even disconnection.Therefore,it is necessary to study the stability of power grid with synchronous condenser and STATCOM access considering the detailed model of synchronous generator.This paper studies the influence of excitation control mode of synchronous condenser in grid-connection and speed-falling stage,and the influence of synchronous condenser and STATCOM on the stability of AC power grid when they are connected to multi machine system alone or simultaneously.The main research contents are as follows:Firstly,the influence of different excitation control modes of synchronous condenser on the dynamic characteristics of grid connection is studied.Three single excitation control modes of IEEE solid state static exciter / PI controller / PID controller are analyzed and compared;Combined with the characteristics of single excitation control mode,a three-stage sequential hybrid excitation control mode is proposed,which effectively improves the stator voltage establishment process of synchronous condenser;In order to further suppress the impact of synchronous condenser,a grid connection mode with pre-integrated energy-absorption impedance is proposed.The simulation results of PSCAD / EMTDC show the effectiveness and superiority of this scheme.Secondly,the small-signal modeling and stability analysis of synchronous condenser connected to two-generator system are studied.The state space model of double generators system with synchronous condenser and considering the detailed model of synchronous generator is established,which is linearized at the steady-state working point,and then the small-signal model is established;By comparing the response characteristics of small-signal dynamic model and PSCAD / EMTDC detailed electromagnetic transient model under the same disturbance,the accuracy of small-signal model is verified;Based on Lyapunov’s first method criterion,the root locus method is used to study the influence of the control parameters of the synchronous condenser excitation system on the small-signal stability of the system,and the variation range of the feasible region of the control parameters is obtained.The correctness of the feasible region of the parameters is verified by PSCAD / EMTDC,and the influence of the change of the control parameters in the feasible region on the system stability is compared,so as to provide a reference for the selection and optimization of the control parameters.Finally,the small-signal modeling and stability analysis of synchronous condenser and STATCOM connected to three-generator nine-bus system at the same time are studied.Considering the circuit mechanism and control system structure,establish the mathematical model of STATCOM,comprehensively consider the simultaneous access of rotating and power electronic reactive power compensation equipment,and establish the state space model of three-ganerator nine-bus system with separate access to synchronous condenser and simultaneous access to synchronous condenser and STATCOM through the connection network,The small-signal model of the system is established by linearization at the steady-state operating point;Based on the small-signal model,the eigenvalue analysis is carried out to study the impact of STATCOM access on the system stability margin,and compare the difference between the feasible region of control parameters with and without STATCOM connection;The effects of excitation system control parameters and STATCOM control parameters of synchronous condenser on small-signal stability of the system are studied;The coupling effect between different control systems is studied. |
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