Research On Suppression Of Beat Phenomenon For Electrolytic Capacitor-less Motor Drive System

In the motor drive system,as a support capacitor on DC-link,electrolytic capacitor has the disadvantage of low lifetime at high temperature,which reduces the stability and reliability of the drive system.Therefore,Electrolytic Capacitor-less Motor drive system with film capacitors instead of electrolytic capacitors and without the power factor correction has become a new direction to solve the problem.Electrolytic capacitor-less motor drive system can significantly improve the operating lifetime of the system and effectively reduce costs.However,due to the small capacitance of the film capacitor,when the rectifier circuit is a three-phase uncontrolled rectifier circuit,the DC-link voltage will fluctuate at 6 times the grid frequency,and this DC-link voltage fluctuation will cause the drive system while the motor run at a specific speed generates the beat phenomenon,which will adversely affect the operating performance of the motor.Therefore,this paper analyzes the electrolytic capacitor-less motor drive system of,studies the generation mechanism of beat phenomenon,proposes a DC-link voltage reconstruction strategy based on open-loop predictor to suppress beat phenomenon.The main contents of this paper are as follows:Firstly,the basic structure of permanent magnet synchronous motor is introduced,and then the mathematical model of permanent magnet synchronous motor under different coordinate systems is derived on the basis of introducing the principle of coordinate transformation.Then,based on the mathematical model of permanent magnet synchronous motor under rotational coordinate system,the dual closed-loop vector control technology of permanent magnet synchronous motor is expounded.Then,the space vector pulse width modulation technique(SVPWM)is introduced,which lays a foundation for the analysis of the subsequent beat phenomenon.Secondly,the structure of the three-phase AC input electrolytic capacitor-less drive system is analyzed,and the mathematical expression of the DC-link voltage is derived.On this basis,based on SVPWM technique,the relationship between the inverter output voltage and the motor reference voltage is analyzed,and the relationship between DClink voltage fluctuation and beat phenomenon is obtained.In order to suppress this beat phenomenon,a voltage reconstruction strategy based on open-loop repeat predictor is proposed,which uses the repeatability of DC-link voltage fluctuations to compensate and correct the DC-link voltage for pulse width modulation.Then,the Simulink model is built to verify the effectiveness of the suppression strategy through simulation.Finally,based on theoretical analysis and simulation verification,an experimental platform for electrolytic capacitor-less motor drive system is built,and the studied beat phenomenon suppression strategy is realized and verified.The experimental results confirm the effectiveness of the studied beat suppression strategy.