Research On A Four-phase Fault-tolerant Permanent-magnet Machine Used For Aerospace Servo System

In recent years,with the demand for reliability and fault-tolerant ability in aerospace servo applications,the multiphase fault-tolerant electric servo system is proposed.It has the advantages of simple structure,easy to maintenance,high power density and good fault-tolerant ability,which can meet the demand of aerospace sophisticated equipments.But the theoretical system of multiphase fault-tolerant electric servo system is still imperfect at present,and further researches are needed on the design,fault detection and diagnosis,and fault-tolerant control of multiphase servo motor.Focusing on these issues and with consideration of the background,the design,fault-tolerant control and temperature field distribution of four-phase fault-tolerant permanent magnet(PM)machine are investigated in this paper.And the major work can be summarized as follows:Firstly,selection of electromagnetic schemes,design and optimization of the four-phase fault-tolerant PM machine are studied.The 8-slot 6-pole single-layer fractional slot concentrated winding is adopted with consideration of the application background.And the blocked Halbach PM structure is employed to reduce torque ripple and PM loss.Further,proper thickness of the rotor core is selected to improve dynamic response performance.And influence of the slot width on short-circuit current is studied to give the principle for selecting slot width.Secondly,influences of open-circuit faults on machine performance and corresponding fault-tolerant control methods are investigated.The machine performance under different open-circuit faults are analyzed,and compensations are made by adopting fault-tolerant control methods.Further,finite element analysis(FEA)method is adopted to validate and compare the control methods.Research results show that the control methods based on the instantaneous power balance principle and constant magnetomotive force principle without limiting the zero-sequence current can ensure full output capacity and stability of operation under open-circuit faults.Thirdly,influences of phase short-circuit faults on machine performance and corresponding fault-tolerant control methods are investigated.Analytical calculation and FEA method are adopted to investigate the short-circuit current under winding terminal short-circuit fault and inverter switch short-circuit fault,and influence of the short-circuit current on machine performance is analyzed.Research results show that the inverter switch short-circuit fault has more serious impact on machine performance.Based on that,phase short-circuit fault-tolerant control methods are investigated,and better machine performance is achieved under control method based on the instantaneous power balance principle.Finally,thermal field distributions of the machine under normal and fault-tolerant operations are investigated.By adopting equivalence methods for key regions,the 2D thermal analysis model of the machine is established,and calculating methods of thermal conductivities and heat transfer coefficient of those key regions are given.Further,thermal field distributions of the machine under normal and fault-tolerant operations are evaluated by FEA method.Research results show that the machine can operate stablely under the given working condition.