Analysis And Suppression Of Current Ripple In Three Phase Two Level PWM Inverter

Three phase two-level PWM inverter is widely used in AC motor drive,power conversion and other fields.Because the output current of PWM inverter contains ripple component,it will bring problems such as loss increase and performance degradation to the system.This paper analyzes the conventional PWM technology for Three phase two-level inverter,establishes the model of PWM and current ripple,and proposes an improved PWM algorithm to suppress the current ripple.Firstly,this paper introduces the carrier-based PWM and space vector PWM(SVPWM)for three phase two-level inverter,and deduces their unified implementation method in order to generate the same switching control pulse.The three degrees of freedom of pulse duty ratio,pulse position and pulse period in PWM technology are analyzed.Changing these three degrees of freedom will affect the current ripple and switching loss,but will not change the fundamental voltage output of the inverter.Then,on the premise that the pulse position is symmetrical in the center,the calculation method of current ripple slope and waveform is derived,and the current ripple in dq coordinate system is obtained by coordinate transformation.Analyzed the influence of three degrees of freedom in PWM technology on current ripple,and the causes of error in current ripple calculation model caused by resistance and dead time,and the correctness of the current ripple analysis is verified by simulation.Subsequently,based on the unified PWM implementation method and current ripple model derived in this paper,variable zero-vector distribution PWM(VZDPWM)is proposed.The realization process of VZDPWM is introduced.Different zero-vector distribution calculation methods are proposed to suppress the phase current ripple peak value,RMS value and q-axis current ripple peak value.The simulation of the double closed-loop system of the PMSM verifies the effectiveness of VZDPWM in suppressing current ripple.Finally,the experimental platform is built,and the experiments are carried out on the PMSM double closed-loop system and three phase resistive and inductive load.By changing the modulation ratio,switching frequency and zero-vector distribution,the experimental results of current ripple is close to the calculated peak value,which verifies the accuracy of the current ripple model.Compared with seven segment SVPWM,the experimental results show that VZDPWM2 can reduce the total harmonic distortion(THD),and VZDPWM3 can suppress the q-axis current ripple at high modulation ratio.