Research On Modulation Strategy Of Electrolytic Capacitorless Pmsm Drives

Permanent magnet synchronous motor(PMSM)is widely applied in industrial driving field because of its strong structure,high torque current ratio and flexible control.The traditional motor drive system generally needs to use electrolytic capacitor with large capacity on the DC side.However,the electrolytic capacitor has disadvantages such as short life and large volume,which easily lead to the failure of the drive system.At present,the driving scheme using the small capacitance value thin film capacitors directly has attracted the attention of industry and academic circles.In order to improve the voltage utilization ratio at the DC side,the output voltage distortion caused by the fluctuation of the voltage bus should be considered when the motor runs to the overmodulation area with high modulation ratio.At the same time,overmodulation will bring about the increase of the input current harmonics.Therefore,a two-mode overmodulation strategy and a modulation strategy that can reduce the input current harmonics are studied in this paper.This paper analyses the modulation distortion caused by the traditional dualmode and its influence based on the analysis of the mathematical model of electrolytic capacitorless permanent magnet synchronous motor drive system and drive control structure.And the voltage distortion can be divided into type ? distortion and ?? distortion.The uncontrollable modulation region transition is revealed by the analysis of the output voltage vector trajectory in the overmodulation area based on the type ? distortion.The importance of accurate control moment into the six-step operation is revealed from the theoretical level demonstrates,which boosts the performance in overmodulation region in the electrolytic capacitorless drive system.In order to accurately control the time point of entering the six-step operation,it is very important to design an appropriate modulation region switching process.Firstly,the modulation region distribution suitable for the continuous expansion and contraction of hexagon boundary is studied.On the basis of new modulation region distribution.This paper proposes an optimal boundary voltage modulation strategy.The strategy by switching between the actual DC-link voltage and the fixed DC-link voltage used for SVPWM,can eliminate type ? distortion.At the same time,by analyzing and comparing the modulation effects of different fixed voltages,the optimal fixed voltages are obtained.The effectiveness of the proposed two-mode overmodulation strategy is verified by simulation and experiment.In order to reduce the harmonic of inverter input current,the extended dualcarrier PWM strategy is studied.By analyzing the structure of the motor drive system without electrolytic capacitor,different modulation areas are adopted in the high and low modulation ratio area,which effectively reduces the effective value of inverter input current.In order to meet the special switching state change of extended dualcarrier PWM strategy,the generation mechanism of pulse signals is constructed,and the pulse signals of upper and lower bridge arms are exchanged in specific current sectors.At the same time,considering the modulation region judgment of the extended dual-carrier PWM strategy,the voltage of the two-phase static system is corrected in the over-modulation region,and the given voltage vector is limited to the edge of the hexagon.Experiments were carried out on Matlab/Simulink simulation platform,and the simulation data verified the effectiveness of the method.Finally,through the theoretical analysis of the research strategy and on the basis of Matlab/Simulink simulation,the digital control algorithm is realized on the electrolytic capacitorless driver,and the modulation strategy is experimentally verified on the 2.2KW PMSM.The experimental results show that the permanent magnet synchronous motor can smooth and fast transition from linear area to the sixstep operation,and eliminates the type ? distortion,reduced voltage current THD.And the motor dynamic performance is significantly increased.