Research On Fault-tolerant Control Of Five-phase Permanent Magnet Synchronous Motor Drive

Five-phase permanent magnet synchronous motor(5Ph PMSM)exhibits properties of high power density,reduced torque ripples and excellent fault-tolerant capacities,and this makes it a promising candidate in the application of warship electric propulsion system.The reliability is put as the first consideration to assess the performance of a warship where propulsion motor drives are expected to have backup mechanism to avoid motor drives stop working in emergency.The motor driver and mechanical position sensor are most fragile parts in a 5Ph motor drive,and their failures can lead to the breakdown of the whole warship if none fault-tolerant algorithms included in the control system.To improve reliabilities of five-phase motor in the application of warship propulsion system,this thesis focuses on fault-tolerant control of 5Ph PMSM drive targeting at above key issues.Firstly,winding function theory is conducted to analysis the stator Magnetic Motive Force(MMF)of motor drives.To guarantee a reliable operation of motor drive with open fault,MMF by remaining phases should be kept the same to that of healthy mode,and this is a basic rule for fault-tolerant control.Specially,by the preservation of Back Electromotive Forces trajectory of remaining phases circularly rotating,Clarke and Park Matrices for motor FOC under single-phase open fault is obtained.In a similar way,Clarke and Park Matrices fitted for two-phase open fault can also be acquired,by bounding rotor flux trajectory forming a circle at ?-? plane.With above transformations,5Ph PMSM fault-tolerant models at rotor-fixed coordinate frame are established where voltage and torque equations remains the same to fundamental parts of 5Ph motors in healthy mode.The decoupled modeling of 5Ph PMSM under fault conditions provide great convenience for implementation of motor Fileld Oriented Control(FOC)and position sensorless control.Based on fault-tolerant models developed,SVPWM,current and speed controls are studied subsequently.Unlike the healthy mode,the SVPWM under open fault relies on motor operational state.To tack this,estimation of Back EMFs of lost phases is performed,and a compensation technique of the reference voltage by these back-EMFs is proposed.This makes easier the composition of voltage reference by basic space voltage vectors.High-order flux linkage leads to harmonic currents,and a Proportion-Integration-Resonant control at synchronous rotating frame is suggested to suppress these harmonics,enhancing current tracking performance.The rotor speed also fluctuates due to nonlinearities of motor drive under fault conditions.A simple and effective sliding mode speed control is introduced tosmooth the speed,decreasing torque ripples.The rotor position is essential for FOC of 5Ph motor drive.High frequency(HF)injection based position sensorless control at low speeds including standstill is studied in this part.A promoted HF current injection is recommanded,and it has advantages of conventional HF current and voltage injections.For common issues shared by HF injections which include inverter dead-zone,sampling and zero-order discretization of digital control system and weak salient ratio of studied motor,a cross-correlation method is employed to reduce the adverse impact on the extraction of rotor position error signal in a noisy environment.There also presents nonlinearities in faulty motor drives,and Extend State Observer based rotor position calculation technique is proposed,resulting in an improved dynamic performance.Rotor initial position estimation based on correlation detection method is also studied,and it is insensitive to system noises and improves the accuracy for rotor initial position detection.In the next procedure,position sensorless control at medium-high speeds based on sliding mode observer(SMO)is performed.Stability study of SMO-based position sensorless control system is conducted,and by inserting a filter after observed back-EMFs in combination of a normalized quadrature phase-locked loop,a smooth estimated speed or rotor position can be obtained and then fed to motor vector control.A complex filter is proposed to smooth observed back-EMFs without phase distortion,resulting in reduced ripples in estimated position(or speed).For motor drive sensorless control under two-phase open fault,a multi-harmonics suppression technique is further applied to remove specific harmonics from observed back-EMFs.Decoupled models under various open fault conditions are confirmed by Finite Element Analysis(FEA)with Ansoft/Maxwell.A 5Ph PMSM drive set up is build in the laboratory,and FOC based speed tuning and position sensorless control are verified under motor drive healthy and fault conditions.