Design And Reactive Power Characteristics Of Dual Excited Synchronous Condenser

With the development of power system,large capacity units,UHV AC/DC transmission and large-scale interconnection across regions have become the main features,and the grid structure and operation characteristics of power system have changed dramatically.With the dramatic change of daily load curve and the use of high-voltage and long-distance transmission lines,the phenomenon of excess reactive power of transmission lines often occurs,which will cause over-voltage of the system and endanger the safe operation of the system.The traditional method to solve the over-voltage phenomenon is synchronous generator leading phase operation,but this method will not only reduce the stability of the generator,but also lower the capability of progressive operation.In addition,adding reactive power compensation equipment such as condenser and reactor is also a common measure,but these equipment not only increases the economic cost,but also has limited compensation capacity.The Dual-Excited Synchronous Condenser(DESC)has the advantages of high stability,strong phase advance ability and fast response speed.Using a specific excitation control method,it can achieve deep phase-advancing operation and obtain a short-term phase-advancing capability equivalent to the late phase overload capability,providing a new effective way to solve the system overvoltage problem.Compared with the traditional synchronous condenser,the DESC is slotted into the q-axis excitation winding on the big teeth of the rotor,while the different structure of the d-axis and q-axis excitation winding will affect the magnitude of the excitation magnetic field,the magnetic density distribution and the harmonic content,thus affecting the performance of the DESC.Therefore,it is necessary to optimize the slot distribution,slot pitch and slot size of the rotor field winding of the DESC,so as to obtain a rotor structure which can improve the fundamental flux density and reduce the harmonic content.In addition,the DESC has unique reactive power characteristics,which improves the stability of the system and can operate stably under a large amount of absorbed reactive power.These good performances are not only relate to the electrical structure,but also the excitation control.Therefore,an excitation control system different from the traditional one is proposed,which can greatly improve the overvoltage regulation function of the DESC.Based on the traditional Synchronous Condenser,this thesis proposes several rotor structures of different DESC.The effects of different slot distributions of q-axis field windings on air gap magnetic flux density,magnetic field distribution,and saturation are analyze.The unique excitation control strategy of the DESC is proposed,and the reactive power characteristics of DESC during steady state and transient operation of the system are studied.The main contents are as follows:(1)This thesis analyzes the working principle of the electrical structure of the dual-axis excitation modulated camera,deduces the mathematical model under synchronous coordinates,and establishes the time-step finite element model of the DESC.(2)In view of the large-tooth grooving of the motor,which affects the waveform of air gap magnetic density,several different rotor slot distribution scheme have been proposed for the DESC.After comparing and analyzing the air gap magnetic flux density with different slot numbers and slot pitch,a scheme with higher fundamental wave magnetic flux density and lower harmonic content is obtained.(3)On the basis of designing a DESC with suitable slot distribution,the groove structure of q-axis field winding is optimize.The slot parameters affecting the air gap flux density and total harmonic distortion of the motor are reveal.An analysis method combining the finite element method and the Taguchi method was used to establish the Taguchi orthogonal table,and a combination of design variables was obtained to optimize the air gap magnetic flux density quality characteristics of the DESC.(4)Aiming at the problem of improving the stability of the DESC during deep phase-in operation,a method of dual-channel excitation control was proposed,and the principle of dual-channel excitation control was revealed.This chapter simulates the reactive power characteristics of the DESC in steady state and transient operation,and studies the maximum phase advance operation ability of the dual-axis excitation camera under different d and q-axis excitation currents.The method of improving the transient stability of the DESC during deep phase advancement is presented.