Research On Harmonic Suppression Method Of Permanent Magnet Synchronous Motor And Back-to-back Test System

The thesis focuses on the characteristics of motor speed and current harmonic under Direct Torque Control with Permanent Magnet Synchronous Motor and thus proposes an optimized control strategy to suppress harmonic components and improve the NVH performance of electric vehicles.Firstly,the proposed harmonic suppression method are verified by the simulation of combining finite element model and Simulink model and the experiment of two motor back-to-back test system,respectively.Then,the interaction between the drive motor and the load motor in the back-to-back test system is studied.An improved approach using a Fluid Torque Converter is proposed for separating their mutual influences,which is verified by simulation analysis.The specific research contents and conclusions are listed as follows:(1)By studying on the harmonic suppression method of permanent magnet synchronous motor,a Direct Torque Control method of time-varying flux amplitude is proposed through setting axis current to zero in the control algorithm,based on the Direct Torque Control method of Space Vector Modulation.Under the improved control strategy,the suppression effect on speed harmonic components is obvious.Under the variable torque and variable speed conditions,the improved control strategy is further validated with the imporved dynamic response performance of the motor.(2)Simulation model of two motor back-to-back test system is built in Simulink,where the drive and load motor adopts speed and torque control,respectively.The vibration characteristics of the motor with the original and the improved DTC control strategy are analyzed and compared on the back-to-back test system.The speed harmonics are effectively suppressed and the harmonic amplitude at the 18 times fundamental frequency is reduced by 94.74%.Finally,the influence of the load motor on the speed harmonic characteristics of the driving motor on the back-to back system is studied.(3)The electric control-electromagnetic joint simulation model of the motor back-to-back test system is built by using Maxwell,Simplorer and Simulink.The main spectrum components of the electromagnetic force,including the harmonic components of the even-numbered current fundamental frequency and the 1,2,3,and 5 times current fundamental frequency near the switching frequency.(4)Two motor back-to-back test platform is established,which consists of hardware system,software system and data acquisition system.The control algorithms are developed and further applied for the test of the motor vibration characteristics.Compare with SVM-DTC,the improved DTC is able to effectively suppress the amplitudes of the rotational speed,current and vibration acceleration harmonic components of the drive motor.(5)An improved back-to-back system with the Fluid Torque Converter connection is proposed.The harmonic characteristics of the drive motor are closer to the motor itself.Then through the analysis of the control strategy,the improved back-to-back test system can provide experimental conditions for the verification of the motor drive algorithm.