Research On Fifteen-phase Permanent Magnet Synchronous Motor Drive Control System For All-electric Aircraft

All-electric aircraft can achieve zero emissions,no pollution,and effectively solve the problem of dependence on petroleum energy and traditional aircraft exhaust emissions.It has been selected as the "Top Ten Potential Technologies" by Scientific American in 2020.The electric drive system is used as a driving actuator to provide flight power,and the system puts forward higher requirements for its operating efficiency,dynamic performance and reliability.Compared with traditional three phase motors,multi-phase motors have more potential and advantages in terms of fault tolerance and high power.This paper takes the fifteen-phase permanent magnet synchronous motor(PMSM)drive control system for all-electric aircraft as the research object,focusing on the high efficiency,anti-disturbance,and fault tolerant control of the all-electric aircraft electric drive system.On the basis of analyzing the demand for electric drive system of all-electric aircraft,based on the idea of minimizing power consumption in all working conditions,a 3×5 phases PMSM motor structure which three sets of windings are efficiently matched and each set of windings is independently controllable is proposed.The base speed and rated torque of the three sets of five phase windings are matched according to the torque characteristics of the propeller and the operating conditions of the all-electric aircraft during design.When running,it is time-division multiplexed according to the torque demand of the working condition,so that each set of windings works in a high efficiency area as much as possible,thereby improving the operating efficiency of the electric drive system under all working conditions and achieving the purpose of extending the cruising range.In view of the proposed asymmetric winding fifteen-phase PMSM system subset control and harmonic suppression problems,the expression of harmonic characteristics of fifteen-phase PMSM is derived,the symmetrical and asymmetrical structure synthesized magnetomotive force harmonic order and the armature winding harmonic current are compared and analyzed.The results show that the order of the harmonic magnetomotive force of the asymmetric structure is different from the order of the symmetrical structure,and its amplitude and phase have also changed,but the highest harmonic amplitude of the asymmetric windings does not increase significantly.The mathematical model and vector control simulation model of asymmetric fifteen-phase PMSM based on three dq axis transformation are established,the harmonic suppression methods of four vector SVPWM and dual coordinate system vector control are studied.Simulation and experimental results show that the two methods can effectively suppress the harmonics generated by asymmetric windings,and the dual coordinate system control is better than the fourvector SVPWM control.In order to improve the anti-disturbance ability of the all-electric aircraft electric drive system,the influence of disturbance torque caused by changes in ambient air flow and motor parameter changes on the electric drive system is analyzed;A load torque feedforward control method based on linear active disturbance rejection control is proposed,the load torque observer and linear active disturbance rejection controller(LADRC)are designed,and stability analysis is performed.Simulation and experimental research on the anti-disturbance performance of the fifteen-phase PMSM speed closed loop system with load torque feedforward based on LADRC show that the proposed method can effectively suppress the influence of load disturbance and motor parameter changes on the motor speed.In order to increase the cruising range of the all-electric aircraft,the high efficient control strategy of fifteen-phase PMSM system driving propeller load under variable working conditions is studied.According to the torque demand of the propeller under flight conditions,an asymmetric fifteen-phase PMSM torque distribution strategy with the optimal efficiency is proposed.Simulation results show that the torque distribution strategy of efficiency optimal control can effectively broaden the high efficiency area of fifteen-phase PMSM,which illustrates the effectiveness of this asymmetric design.In order to effectively suppress the sudden change of the torque distribution of each set of windings during the efficiency optimal control,a torque distribution strategy based on the fuzzy control principle is further proposed,and the rule control based on the operating conditions are given for the flight conditions.Thus,a fifteen-phase PMSM electric drive system's windings subset control method is formed,that is,the torque distribution method is selected according to the flight condition stage,rule control is used in the climbing and descent phases,while suppressing the torque fluctuations during windings switching,and the fuzzy control torque distribution method is used in the cruise phase to achieve the goal of improving system operating efficiency and reducing torque fluctuations.In order to improve the reliability of the electric drive system,the thermal characteristics of different fault tolerance methods are analyzed.Taking the one phase open circuit fault as an example,the phase current amplitude and phase change of the armature windings under the fault tolerant control of five-phase six-arm SVPWM,the current hysteresis equal amplitude and the minimum copper loss are studied.The loss of various parts of the motor,the steady state temperature of the armature windings and the transient temperature under extreme conditions have also been studied.Simulation and experimental research results show that the temperature extreme point of the armature windings of the five phase six arm SVPWM fault tolerant control is much higher than the current hysteresis equal amplitude control and the copper loss minimum control under the rated load;And when the windings is asymmetric,the temperature distribution will be more uneven.Therefore,suggestions for design and use are put forward,for high power density multiphase motor,especially the asymmetric winding multiphase motor studied in this article,when windings fault tolerance,from the perspective of thermal stress reliability,it is not recommended to use five-phase six-arm control.And when fault tolerant operation is performed,it is necessary to limit the reduced power operation or short time equal power operation according to the designed insulation level and temperature.