Research On Direct Torque Control System For Six-phase Symmetrical Windings Permanent Magnet Synchronous Motor With Multiple Opened Phases

When the windings of motors or the inverters break down,multi-phase motors can keep running under fault-tolerant condition owing to more control degrees,thus they are used widely in key fields such as aerospace drive system,locomotive traction system and marine electric propulsion system.Compared to multi-phase induction motors,multi-phase permanent magnet synchronous motors(PMSM)have the advantages of small volume,high efficiency and simple control system.Therefore,they become strong competitors for induction motors.Some research on fault-tolerant direct torque control for multi-phase permanent magnet synchronous motors have been done in this paper,concrete contents and conclusions are as follows.The research background and significance of this paper has been discussed in the first place.Research on classifications and mathematical models of multi-phase motor,control strategies for multi-phase motor and sensorless technique for PMSM has been introduced.Scholars have paid more and more attention to fault-tolerant control for multi-phase motors and direct torque control(DTC)for PMSM,however study on fault-tolerant DTC for multi-phase PMSM is rarely published.Sensorless technique applied to multi-phase PMSM under fault-tolerant condition is even rare,further exploration is necessary.Secondly,the mathematical model of six-phase symmetrical windings PMSM under fault-free condition is introduced.This can provide a theoretical basis for further study on the mathematical model of six-phase PMSM with multiple opened phases,and comparison between these two models can be done.Thirdly,the mathematical model of six-phase PMSM with two opened phases has been researched in this paper.Fictitious variables are proposed,and the relationship between fictitious stator flux linkage and electromagnetic torque can be deduced.The control of fictitious stator flux linkage,zero sequence current and electromagnetic torque can be realized by utilizing the remaining four-phase inverter bridge at the same time.The load capacity of motor with arbitrary two opened phases has been studied.The simulation and experimental results show that the system runs smoothly and has a fast dynamic response if proposed control strategy is adopted.Fourthly,the DTC system for six-phase PMSM with three opened phases has been studied.After three phases opening,the models of stator flux linkage and electromagnetic can be divided into the symmetrical type and the asymmetrical type.For the symmetrical type,the analysis method of direct torque control for three-phase PMSM are directly applicable.And for the asymmetrical type,fictitious variables are introduced,thus the electromagnetic torque can be instantaneously controlled under the condition that the trajectory of fictitious stator flux is forced to be circular.Finally,research on sensorless for six-phase PMSM with multiple opened phases has been done.Fictitious stator flux linkage,electromagnetic torque and speed,which are calculated by the current self-tuning stator flux linkage estimator and the speed observer,are applied to direct torque control.Sensorless for motor can be realized at high speed.The simulation and experimental results show that the sersorless DTC system for multiple-phase motor with opened phases can run smoothly when speed is over 100r/min.In order to verify the proposed control strategy,a set of DTC hardware system which uses TMS320F2812 DSP as core unit is introduced,and corresponding software systems are designed.The experimental results verify the feasibility and effectiveness of the system.