Research On The Variable-frequency AC Generation System With Hybrid Excitation Synchronous Generator

. Variable-Frequency (VF) AC power system has become the development direction of more/allelectric aircraft AC power system for its outstanding advantages of simpler structure, higher unitcapacity and higher efficiency. Large variable ranges of speed and load is the typical of VF powersystem. It has brought higher demands to the variable frequency AC synchronous generator and theGenerator Control Unit (GCU).Based on discussion of the VF power system characteristic and requirement, this paper exploresthe fundamental problem of variable frequency AC power generation system with hybrid excitationmachine (HEM) for aircraft power system applications. The effects of the different structures ofauxiliary air-gaps on magnetic field regulating and output characteristics of the new hybrid excitationsynchronous machine (HESM) with magnetic shunt rotor are investigated. The axial auxiliary air-gapstructure is helpful to increase the the room of the magnetic bridge for embedding excitation windingsand reduce the loss of excitation winding. According to the requirements of variable frequency ACpower system, the electromagnetic design of a30kVA hybrid excitation synchronous generator (HESG)is done. To broaden the magnetic field regulating range of HESG and adapt to the wide speed rangerequirements, the axial inhomogeneous air-gaps HESG structure is proposed,3D finite-elementanalysis (FEA) is performed to achieve the magnetic field distribution and transient field analysis, theload and no load operating characteristics are acquired. The results indicate that the proposed HESMhas good performance of flux regulation capability and achieved field discharge perfectly, it lays afoundation for the HESG applications to VF power system.The protection and control method of variable frequency ac power system based on HESG arediscussed systematically. According to the operation principle and characteristics of the HESM, thestructure of VF AC power system based on the HESM is presented, the operation principle andprotection scheme of the power sysem is investigated. AC sampling and control method of VF ACgenerator system digital automatic voltage regulator (DAVR) are studied. The method of PI parameterschange with the speed and three loops control method of output voltage loop and exciting current loopand load current loop are investigated. The simulation model of generation system is established inMATLAB，the simulation results show the validity of variable PI parameters control and tricyclicregulating algorithm.A digital voltage regulator for VF AC generator system based on HESG is designed, and tested on3kVA HESG experiment platform，the speed range from1250rpm to2500rpm. The experimental results show that the output voltage modulation at high speed is removed by varying the PI parameters,and tricyclic regulating reduced regulating time of sudden connection (disconnection) of load at speedof1250rpm.