Study On Generator Control Unit Of Three-stage Variable Frequency AC Power Systems

As hydraulic systems and air systems are gradually displaced in more electric aircraft,the electric power needs to be enlarged drastically.The existing aeronautical generators do not have enough power.In order to supply more electric aircraft,more generators are needed to operate simultaneously.As a result,the complexity of the power system is increased correspondingly.Besides the main function of keeping the voltage stable at the voltage regulation point at variable speed and variable load,generator control unit(GCU)also need to operate in coordination with the bus power controller to locate and isolate aircraft grid faults.This paper is focused on three-stage variable-frequency generators with nominal frequency of 360 Hz to 800 Hz and nominal power of 250 k VA.Based on the need of voltage regulation and system control for the generator system,the design of the corollary general generator controller,the controlling strategy and the fault protection of the rotational rectifier is mainly studied.The operation principle of voltage regulation and startup excitation for the three-stage synchronous generator is introduced firstly.Based on the mathematical equations at dq coordinate system,the simulink models of the three-stage synchronous generator is derived.The voltage regulation strategy based on the fuzzy PI controller is furthermore proposed.Better voltage regulation performance can be achieved for the generator at full speed range and full load range with the proposed strategy,which is verified by simulation.Aiming at dual-channel more electric aircraft power system,this paper analyzes the general controlling strategy,protection function of GCU.The mechanism of differential protection misoperation is analyzed.The THD of excitation current for the main exciter at rotating-rectifier-fault state is analyzd in the view of commutation and verified through a 2D generator model in finite element analyzing software.The rotating rectifier fault system is established by co-simulation of finite-element model and Simplorer.The detection method of rotating rectifier short fault is presented based on DC-link voltage.Finally,the hardware is designed,the corresponding software is designed.The voltage regulation strategy is validated by experiments.It is proved that the dynamic performance of the generation system is improved by the presented strategy.