| More electric aircraft is an electrification scheme of aircraft system with high technical feasibility and better economy.It can reduce the weight of aircraft structure,improve maintenance efficiency and reduce fire hazards.However,the electrification of aircraft system will drastically increase the proportion of electrical equipment,the total power demand and the difficulty of fault diagnosis.This paper mainly uses adaptive load management and the energy optimized design to solve the problems.The load management is fault-tolerant by further studing the fault diagnosis of typical electric equipment.The main research contents include:(1)The relationship between model complexity and simulation results is studied.In order to study the relationship between complexity of system model and simulation accuracy and time,the first-order dynamic model of main components in power system is combined to build an integrated simulation platform.Then,the steady-state and dynamic subsystem models of the core components of the system are established respectively,and the dynamic responses of the core components in the above models are compared.This method is used to analyze an industrial UAV.The results show that in order to improve the simulation accuracy,the dynamic model of double direction equipment with feedback power should be established.In order to reduce the simulation time,the steady-state model of other equipment should be used.This part of the research lays a foundation for the modeling of large aircraft systems.(2)The fault current model of permanent magnet synchronous motor with inter-turn or phase-to-phase short-circuit fault is derived.Aiming at increasing the reliability of electrical equipment,taking PMSM as an example,this paper mainly studies the inter-turn short-circuit fault which is the most difficult to detect and the phase-to-phase short-circuit fault which is the most destructive.The fault current model and winding function model of induction machine are extended to the modeling of inter-turn short-circuit fault of PMSM.The two models are validated and compared on the customized 2.59 k W test bench.The results show that both models can reflect the fault,but the fault current model has a better adaptability.Therefore,the deduction method is applied to the case of phase-to-phase short-circuit fault,and the fault current model of the phase-to-phase short-circuit fault of PMSM is obtained.There is no magnetic linkage component in the expression of short-circuit current,which achieves the decoupling of motor fault model.(3)Analytical expressions of faulty phase isolation paremeters are derived and fault diagnosis methods for inter-turn and phase-to-phase short-circuits of PMSMs are proposed.Aiming at solving the problem that negative-sequence components are susceptible to noise,the analytic expression phase angle sum of the extended symmetrical component of current is derived based on the fault current model of PMSM.The analytical expression can describe the relationship between the faulty phase isolation paremeters and the location and severity of the short-circuit fault,and apply it to inter-turn and phase-to-phase short-circuit situations of PMSMs.Compared with the traditional faulty phase isolation paremeters using fast Fourier transform,the proposed ones response faster and more independent from the integrity of historical measurement.A fault diagnosis method combining current-and voltage-signature residuals for isolating inter-turn and phase-to-phase short-circuit of PMSM is proposed and verified by experiments.This method can directly utilize the sensors installed in the motor and is easy to implement.This method has a low demand degree of sensor,and is easy to implement.(4)A fault-tolerant hierarchical load management method for aircraft electrical system is proposed.Firstly,an adaptive load priority regulation method is established by using fuzzy logic with load importance,power ratio and health level as input variables.The load priority regulation method can describe the working states of the load and improve the load shedding quality.Secondly,in order to solve the multi-time scale problem in top-level state monitoring and control,a hierarchical load management system including a task level,an optimization level,a detection level and the fault detection and isolation subsystems is proposed to improve computing efficiency by using different clocks at each level.Thirdly,the adaptive load priority regulation method is introduced into the optimization level to formulate load shedding strategy according to the load fault,so as to improve power quality and protect other healthy loads.This method is applied to the power system of a V-tail more electric aircraft.It is proved that the reduction strategy of the load management method can strike a balance between the high priority faulty load and the low priority healthy load,and the calculation efficiency is high.Compared with another dynamic priority load management method,the results show that the fault-tolerant hierarchical load management method proposed in this paper can effectively avoid further damage to power system caused by cascade effect of faults,so as to improve the reliability of more electric aircraft.(5)An energy analysis and optimization method for more electric aircraft based on exergy is proposed.Firstly,in order to describe the energy interaction between subsystems and solve the problem that traditional efficiency indicators can not reveal the upper limit of energy efficiency,the exergy analysis method for aircraft systems is proposed.The flight profile is taken into account.The optimization design of aircraft energy is simplified to the optimization problem of minimizing possible energy loss.The objective functions of minimizing the exergy dissipation for the secondary subsystems and the whole aircraft systems are formulated respectively to improve the design of the aforementioned V-tail more electric aircraft.The proposed energy optimization design method can provide a global optimization reference for the design of more electric aircraft. |
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