Research On Low Ripple Direct Torque Control Strategy Of Permanent Magnet Synchronous Motor

Permanent magnet synchronous motor occupy an important position in the field of industrial AC speed regulation due to their small size,high density and light weight brought about by their special structural characteristics.The DTC control strategy for permanent magnet synchronous motors are favored by many fields of work due to the simplicity of the algorithm structure and the high speed of dynamic response.However,due to some shortcomings of the DTC algorithm,the torque and flux ripples during steady-state operation of the motor will also be large,and the three-phase current harmonics will be large,and it will not be perfectly qualified for the demanding precise servo work.In this paper,aiming at the large shortcomings of the torque and flux ripples of the DTC control strategy of the permanent magnet synchronous motor,the research works on the suppression of the torque and flux ripples is carried out.Firstly,the mathematical model of permanent magnet synchronous motor is introduced in detail,and the mathematical models of permanent magnet synchronous motor in various space coordinate systems are derived based on the principle of space coordinate transformation.Theoretical analysis of the principle of flux linkage control and torque control of the direct torque strategy.The traditional direct torque control flux torque estimation method,hysteresis comparator,switch meter and other modules are derived.Combined with the traditional direct torque control block diagram,a traditional direct torque control system of permanent magnet synchronous motor is built,and its torque and flux linkage ripple are analyzed qualitatively and quantitatively.Secondly,in view of the discrete performance of the traditional permanent magnet synchronous motor hysteresis comparator and the lack of space voltage vector utilization,the reasons for the large torque flux pulsation of direct torque control are analyzed in detail.And start from these two points,first use a fuzzy controller to replace the hysteresis comparison function and voltage vector selection step,and directly perform fuzzy selection on the output voltage vector to avoid the ripples caused by the discrete hysteresis comparator.And on this basis,based on the duty cycle theory,a simplified duty cycle calculation method is added to further optimize the voltage vector selected by the fuzzy controller,and together with the fuzzy voltage vector selector to form an improved permanent magnet synchronization Motor direct torque control system.An improved direct torque control system for permanent magnet synchronous motors was built on the simulation platform,and the ripple suppression effect on the torque and flux linkage was analyzed qualitatively and quantitatively.Then,combining the predictive model of predictive torque control,rolling optimization and feedback optimization,the principles and steps of predictive control are explained,and based on this,the predictive torque control and torque prediction formulas are derived.The relationship between the function and the selection of the optimal voltage vector is analyzed.On the basis of the predicted torque,the second voltage vector is introduced to further optimize it,and the absolute value of the difference between the predicted value of the flux linkage and the torque and the corresponding reference value is used as input to design a fuzzy controller to calculate the action time of the second zero vector introduced.A predictive torque control system with the introduction of the second vector was built on the simulation platform,and the ripples suppression effect on the torque and flux linkage was analyzed qualitatively and quantitatively.Finally,an experimental platform was built,and through hardware and software design,the direct torque control strategy with fuzzy voltage vector selection combined with simplified duty cycle calculation and the predictive torque control strategy with the introduction of the second vector were experimentally verified.This article has 51 pictures,4 tables,and 106 references.