Fundamental Research On Doubly Salient Machine Parallel High Voltage DC Electrical Power System For More Electric Aircraft

With the development of more electric aircraft(MEA)technology,the requirements for the capacity and performance of onboard electric power generation systems have gradually increased.The HVDC parallel electric power system(EPS)has outstanding advantages such as large capacity,high power quality,and high reliability,providing sufficient energy for the secondary energy system of MEA.However,the research on HVDC parallel EPS is getting started recently.In this paper,the fundamental science issues and key technologies on the HVDC parallel EPS based on the doubly salient electromagnetic generators(DSEGs)are studied.The output power and efficiency of the DSEG are improved and the dynamic performances are optimized.The current sharing control strategy,energy regeneration,and management are also studied.The work presents beneficial explorations for the realization of aircraft HVDC parallel EPS.The architecture of the HVDC parallel EPS based on DSEGs is presented and the HVDC parallel EPS is modeled and analyzed.The non-linear characteristics of the inductance and flux linkage in the DSEG are modeled with rapid and accurate methods based on machine learning.Based on the magneticcircuit co-simulation and the mathematic model of the DSEG inductance,the HVDC parallel EPS is modeled and analyzed in the Ansys Maxwell-Simplorer and Matlab/Simulink platform.The single-channel HVDC generator system is the fundamental of the HVDC parallel EPS.Starting from the single-channel HVDC generator system,the control method of the DSEG system is studied to improve the dynamic performance,output power and efficiency of the DSEG system.A control method based on capacitor energy is proposed for the diode rectification system,which improves the dynamic performance of the DSEG system.The control method of the active rectification in the DSEG system is deeply studied to improve the dynamic performance,output power and efficiency of the DSEG system.Using the active rectification to adjust the excitation current and phase current,a minimum copper loss control method is proposed.By using active rectification control parameters that minimize the change in excitation current when the load changes,the dynamic responses of the DSEG system are optimized.The advanced angle control is proposed to optimize the active rectification of the DSEG system.The output power is further improved and the loss is futher suppressed.The power density is improved,the loss is reduced,and the dynamic performance is optimized.The performance indexes of the DSEG system are significantly improved.The HVDC parallel EPS based on the parallel operation of two DSEGs is proposed.The current sharing control is studied in depth in the HVDC parallel EPS.A current sharing method based on capacitor energy control is proposed,which simplifies the structure of the current sharing system and achieves high precision current sharing control.The dynamic performance of the parallel system is also optimized.The performances of the conventional current sharing method and the current sharing method based on the capacitor energy control are compared.The current sharing accuracy,as well as the dynamic responses of paralleling in,splitting out,loading,unloading,and speed changes are studied.Compared to the conventional current sharing method,the current sharing based on capacitor energy control can significantly suppress the voltage variation and accelerate the dynamic response during the same dynamic processes.Aiming at the starter generator and the generator paralleling architecture,the special problems such as the backwards current of the parallel system based on the active rectifier system and the diode rectifier system are explored.The energy regeneration and management in the MEA are studied.The energy regeneration methods based on the diode rectifier and active rectifier are proposed,realizing the harvesting of the kinetic energy during braking.The problem of bus voltage caused by motor load energy regeneration is studied.By reducing the output power of the DSEG and the mode switching from generating to motoring of the doubly salient starter generator(DSESG),the regenerative energy is absorbed.The bus voltage is stable during energy regeneration,which significantly simplified the architecture of energy management.The 9k W DSEGs,corresponding generator control units(GCUs),and the bus power control unit(BPCU)are developed.The HVDC parallel EPS is implemented.A large number of experiments were carried out around the fundamental scientific issues and key technologies of the HVDC parallel EPS,which fully verified the performance advantages of the methods proposed in this paper.For the singlechannel DSEG system,70% of the copper loss is reduced under some operating conditions.The dynamic performance is significantly optimized: 85% voltage variation is suppressed and 78% dynamic time is reduced in some operating conditions.In the HVDC parallel EPS,the current accuracy is 2%.The voltage variation is suppressed and the dynamic process is accelerated.The influences of the speed change are also suppressed.By controlling the output power of the DSEG and four-quadrant operation of the DSESG,the management of feedback energy and the stable control of bus voltage are realized.The research work in this paper has laid the foundation for the application of HVDC parallel EPS for the MEA.