Research On The Key Technique Of Variable Frequency AC Aircraft Power Supply Based On Dual-stator Winding Induction Generator

Recently,the development of the more/all electric aircraft presents the requirements on the extending the capacity and improving the quality and performance of the generating system.As more than 50% of the loads in the large aircrafts are insensitive to the frequency of the,variable frequency ac(VFAC)generating system has been the good candidate.As the core part of the generating system of the aircraft,the generator should be brushless and easily to be composed for the start-generating system.Dual-stator winding induction generator(DWIG)is a new type of the induction machine in recent years,which has the cage rotor with the natural brushless structure.There are two sets of windings on its stator: one is called as power winding,which is connected with the excitation capacitors and can directly output constant voltage VFAC power;the other one is named as control winding,which is connected with the static excitation converter through the filter inductances and used to regulate the generator excitation.The two sets of the windings have no electrical connection and the high-performance control can be easily achieved.The steady-state performances and the loading/unloading characteristics of the DWIG have been preliminarily validated in the previous work.However,many practical problems for the applications of DWIG have not been considered.To fully verify the proposed DWIG-based VFAC generating system,the following contents are deeply studied in this paper:(1)Aiming at the asymmetrical operation of DWIG,a method of asymmetrical operation analysis based on a three-port load network model is presented to achieve the quantitative analysis of the performance for the generating system with unbalanced loads.By using the proposed method of asymmetrical operation analysis,the influences of the parameters of the DWIG on the degree of the asymmetry are analyzed.According to the analysis,cage rotor has the ability to reduce negative-sequence rotating field,which makes DWIG have good capacity to operate with unbalanced loads.(2)In terms of the symmetrical short circuits in the two sets of the windings,the attenuation rules of the short-circuit current,the equations and time instant of the maximal short-circuit current are given by using the analytical method.The research shows that the form of the transient reactance of DWIG is similar to direct-axis sub-transient reactance of the synchronous machine with damper winding and it is inversely proportional to the peak of the short-circuit current.The research results in this paper is helpful to the better understanding of the transient characteristics of DWIG and the obtained analytical equations is useful to the estimates of the shout-circuit current of DWIG and the designs of the protection units and controllers for the generating system.(3)Due to the fact that the switching frequency of the high-power devices is limited and that the fundamental frequency of the VFAC system is relatively high,general modulation methods like space vector modulation induce the even-order-harmonic currents into the generator,of which the influence on the generating system should not be neglected.Aiming at this problem,the specific harmonic elimination is used in this paper to select different switching angles in the half cycle for the different fundamental frequency band,which minimizes the switching frequency while guaranteeing the quality of the voltage waveform.What's more,the flux tracking control is adopt to improve the SHEPWM modulation,which ensure the dynamic performance of the system and achieve the real-time control of SHEPWM modulation.This method can also applied to the medium-frequency converters,high-power converters and so on.(4)As to the problems of the harmonic elimination in VFAC power system of the aircraft,a compensation method of the paralleled APF is proposed.Firstly,a vector regulator at the stationary coordinate system is designed.This regulator has the advantages of simple implementation and the natural performance of selecting frequencies.Secondly,the a control strategy of the APF without the harmonic-current measurements are given as well.In addition,with respect to the feature that the fundamental frequency of the VFAC generating system is variable,a method of fundamental frequency observation based on the extended kalman filter is used to make the observation results have good static and dynamic performances in the relatively low observation cycle.(5)Aiming at the problems of the starting of DWIG,a speed sensorless control strategy based on the extended kalman filter is studied.Firstly,the system of vector control of DWIG based on the rotor flux oriented is deduced and the system diagram of the decoupled control is given.Secondly,based on the optimal estimation theory,the state equations of the DWIG is deduced,and state equations and the measurement equations of the DWIG are discretized according to the expressions of the state transition matrices of the linear constant discrete system.By using the Taylor expansion,the linear expressions of the state equations of the DWIG is given,and the implementation of the full-order kalman filter algorithm of the DWIG is obtained.Finally,the reduced-order kalman filter algorithm for the DWIG is given.This paper improves the theory on the DWIG and gives the concrete solutions to the key problems of the DWIG-based VFAC generating system in the aircraft,laying the foundations of the following studies on DWIG-based aircraft power system.