The Analysis On Current Harmonic Of Permanent Magnet Synchronous Generator Under The Control Of PWM Rectifier

Permanent Magnet Synchronous Generator and PWM rectifier constitute the power generation system,which is referred to as the controllable permanent magnet power generation system(PMSG-PWM system).In this paper,the PMSG-PWM system is chosen to be the research object.According to the characteristics of the stator voltage and current controlled by the controlled rectifier in the grid connected system,the generation mechanism of harmonic current of permanent magnet generator under the control of PWM rectifier and the relationship between the system parameters and the current harmonics and the influence on the performance of the system are studied systematically.Firstly,the topology and operating principle of PMSG-PWM system are analyzed.Based on the topology of the PMSG-PWM system,the mathematical model of the permanent magnet synchronous generator and the full power PWM converter is established;And,the rotor flux oriented vector control is proposed and the operating characteristics of the PMSG under the control of the full power PWM converter are analyzed.Secondly,harmonic analysis about PMSG-PWM system is mainly analyzed;The mathematical expression of harmonics and the harm of harmonic wave are analyzed;Based on the mechanism of harmonic generation,this paper analyzes the time harmonic MMF in SVPWM modulation and the space harmonic MMF in the motor,and obtains the magnitude and direction of the harmonic magnetic field;Several methods to reduce the harmonics of motor are also described.Next,starting from the motor body,the influence of motor parameters on the inductance of the motor and the harmonic current of the system is analyzed;The finite element models of PMSG with two kinds of rotor structures,which are surface mounted and built in,are established with ANSYS software,and on the basis of the above analysis,the rotor structure,the influence of the gap length,the width of stator slot,and the thickness of permanent magnet on the inductance parameters are not only analyzed,but also using ANSYS software for simulation verification is analyzed;Furthermore,the influence of the motor parameters on the system harmonic is analyzed by simulation.Finally,the time harmonic magnetic field from PWM converter is analyzed;The principle of two modulation strategies of SPWM(sinusoidal pulse width modulation)and SVPWM(space vector pulse width modulation)are analyzed.On this basis,the stator voltage harmonic model of the PMSG under two modulation strategies of SPWM and SVPWM is established,and the harmonic current of generator stator current under different modulation ratio and carrier frequency is analyzed and calculated in detail;In the end,this paper gets the change regulation of the harmonic current with the variation of modulation ratio and carrier frequency,and the correctness of the conclusion is verified by simulation.