Research On Excitation Technologies Of Threephase Brushless Asynchronous Exciter For Aircraft Brushless Synchronous Starter/Generator

Aviation power to achieve start/generate integration technology is a key future development direction of aviation power.At present,China's aviation generator commonly used three-stage synchronous machine(TSMS)as a generator which equipped with a direct-current(DC)field exciter.Since the DC field exciter cannot provide field current for TSMS at rest and low speed,TSMS cannot provide the start torque for aviation engine starting.The aviation engine starting should be started by using a special starter which becomes useless "deadweight" after the engine starts.This engine-generator topology is not merely bulky,heavyweight,and the system is complex,low reliability.To reduce the engine-power system volume and weight,improve the system reliably,research on the excitation system of the TSMS and achieve the starting engine and generating power integration technology is essential.During the starting process of TSMS,the excitation system is faced with some key issues such as the complicated electromagnetic coupling,the unknown mathematical relationship between the system input(excitation voltage,excitation frequency and rotor speed)and output(the field current of TMSM),the hardly implementation of the closed-loop control of the field current of TMSM and the identification of rotating diode failures,the starter/generator system facing many challenges.To solve these problems,this paper focuses on the three-phase brushless asynchronous excitation system(TBAES),including excitation system output equations(ESOE),the analysis of open-loop operation of TBAES,the closed-loop control of TBAES and the online identification of rotating diode failures.Firstly,in order to obtain straightforward mathematical relationships between the field current TSMS,rotor speed,TBAES excitation voltage,and frequency,this paper presents the steady-state equivalent circuit of a TBAES.The ESOE of the excitation system are then derived based on this steady-state equivalent circuit.The steady-state performance of a TBAES could be efficiently evaluated without complex simulations by solving the ESOE.In addition,the ESOE could be used with particle swarm optimization(PSO)to identify the optimal operating points of the TBAES.A steady-state analysis can be used to derive some steady-state characteristics to provide a reference for the control scheme of the TBAES.The proposed mathematical model and theoretical findings are verified by experimental results.Secondly,this paper analyzed two excitation switch methods when the TBAES excited by the aerial three-phase source during the engine starting process.Based on the ESOE of TBAES,the operating principles and properties of TBAES both under three-phase excitation condition and single-phase excitation condition were analyzed.The switch between three-phase excitation and single-phase excitation during the high-speed region was analyzed.The theoretical analysis and experiments results show there is little restriction on the switching process when TBAES excitation source switches from three-phase excitation to single-phase excitation.Meanwhile,the switching process between the three-phase excitation and DC excitation method is analyzed.This paper proposed the equivalent circuit model and system equations of the TBAES which excited by the DC source.Based on the equivalent circuit model,the TBAES could be treated as an ordinary three-phase bridge diode rectifier.From the system equations,the needed TBAES field current could be calculated to obtain a desired TMSM field current.The optimal switching time was analyzed.The theoretical analysis and experiments results show that to reduce the TMSM field current oscillation during the switching process.The optimal switching time is the TBAES rotor flux vector angle before switching is equal to the rotor flux vector angle before switching.Thirdly,in order to control the field current of starter-generator during the starting process,this paper presents a closed-loop control method to control the TMSM field-current during the starting process of aviation engine.The presented method is based on the current source based TBAES equivalent circuit model which is uncoupled with the TBAES rotor slip.The theoretical analysis and experiments results show that the TBAES can be treated as a conventional threephase diode bridge rectifier to achieve closed-loop control of TMSM field-current.Finally,a novel identification method for the rotating diode failures is presented.The proposed method is based on the observation of the harmonic content of the TBAE rotor currents.To obtain rotating diode failures features,the expressions of TBAE rotor currents are derived first by analyzing the equivalent circuit of the TBAES under diode open-circuit and short-circuit conditions.Based on the Fourier analysis of the expressions of the TBAE rotor currents,the failure features of the rotating diode are obtained.Then,rotating diode failures are identified by the harmonic analysis of the estimated TBAE rotor currents.The experimental results have shown that the presented approach could be employed both under stationary and rotation conditions.