Research On Direct Torque Control Of Dual Three-phase Permanent Magnet Synchronous Moto

As the appearance of large amounts new permanent magnet materials,permanent magnet synchronous motors with many advantages have been extensive used in daily life and industrial manufacturing.In some special applications,there are continuous requirements for high power and high safety of motor AC speed control systems.Therefore,the multi-phase motor system that can achieve higher power and strong fault tolerance has become a research trend of many scholars.The widest range multiphase motor is the Dual three-phase Permanent Magnet Synchronous Machine(DTP-PMSM),which is an asymmetric six-phase PMSM.Dual three-phase PMSM has the preponderances of low voltage high power,strong fault tolerance,small torque pulsation,multi-dimensional control mode and other ordinary three-phase motor,DTPPMSM is mainly used in such as heavy ship power,national defense industry,metro light rail,electric vehicles and other precision transmission and important fields.In this paper,the Direct torque control(DTC)strategy of a Dual three-phase permanent magnet synchronous motor with isolated neutral points is studied in detail.Derive the mathematical modeling of Dual three-phase PMSM based on the space vector decoupling theory and the double d-q theory.Introduce the way to implement traditional vector control strategies based on two mathematical models,and build dual three-phase PMSM models and vector control models.Through the comparison of the two control methods,the space vector decoupling vector control with more flexible control dimensions was finally selected for subsequent experimental verification.Then it introduces the magnitude and position distribution of the voltage vector of the sixphase inverter,and introduces the traditional direct torque control strategy of the Dual three-phase PMSM from the aspects of flux torque estimation and control,and the selection of voltage switch tables.In view of the fact that the traditional direct torque control strategy does not take into account the current harmonics and does not accurately calculate the electromagnetic torque and stator flux linkage,resulting in large current harmonics,flux linkage,and torque fluctuations,it is proposed to apply direct torque control strategy based on the master-slave virtual vector duty cycle allocation in Dual three-phase PMSM drive system.The vector of the Dual three-phase PMSM is divided into the master virtual vector and the slave virtual vector to achieve precise control of the torque and flux linkage.And according to the evaluation function,the duty cycle of the master and slave virtual vectors is re-allocated,so that the two virtual vectors work together in a control cycle.Compared with the simulation results of the traditional strategy,the proposed strategy greatly reduces the flux fluctuation and torque fluctuation.Finally,a hardware experiment platform for Dual three-phase PMSM was built under the existing conditions in the laboratory.First,the traditional vector control experiment based on VSD and the traditional direct torque control experiment of the Dual three-phase PMSM were carried out to verify the benefits of the DTC strategy.Aiming at the current harmonics and torque flux pulsation of the traditional strategy,two sets of experiments based on direct torque control based on virtual vector synthesis and direct torque control based on master-slave virtual vector duty ratio are carried out.The experimental results show that the control strategy based on the master-slave virtual vector duty cycle reduces the 5th and 7th current harmonics,reduces the flux fluctuation and torque ripple,and proves the feasibility of the proposed strategy.