Research On High-Efficiency Suppression Strategy Of PWM Harmonics For Three-Level Inverter

The three-level inverter has the advantages of low output harmonic content,high efficiency,high power level and withstand voltage level,and little damage to the motor insulation.It is used in ship propulsion,heavy vehicles,steel rolling and power system have broad application prospects.In order to efficiently convert electrical energy,inverter drive systems usually use pulse width modulation(PWM)technology.This inevitably causes the motor to produce electromagnetic vibration,noise,torque fluctuations and electromagnetic interference(EMI),resulting in increased motor losses,reduced efficiency,and even interfere the normal operation of electrical and electronic equipment,affecting the reliability of the motor and drive system.Therefore,it is a key to reduce the harmonic content of PWM issue in the field of high-power frequency conversion.Based on the research of three-level space vector PWM(SVPWM)technology and spread spectrum modulation strategy,this paper proposes a high-efficiency PWM harmonic suppression method which suit three-level inverters and performs simulation verification.The phase voltage harmonic formula of the conventional three-level SVPWM is illustrated based on research of the working principle of the diode-clamped three-level inverter and technical principle of the three-level SVPWM is analyzed.The PWM harmonic distribution characteristics of the phase voltage and phase current by the Fourier analysis and spectrum analysis of the simulation model is intuitively showed.The results are compared with the two-level SVPWM technology.A novel three-level improved SVPWM technology(Vector Switching SVPWM,VSSVPWM)is proposed due to optimize the vector synthesis order of conventional bilateral regular sampling three-level SVPWM technology.The technical principle and implementation process of this proposed three-level VSSVPWM are discussed and analyzed in detail.Simulation verified its suppression effect on the PWM harmonics,and compared the harmonic characteristics of this strategy with different modulation ratios.PWM harmonic characteristics is pointed based on analysis of technical principle of random and periodic spread spectrum modulation.Random PWM(RPWM)and periodic carrier frequency modulation(PCFM)strategy applied to three-level SVPWM is proposed.The simulation model verifies its harmonic suppression and spread spectrum effects,and studies the influence of function types and parameters such as spread spectrum range and frequency modulation ratio on the harmonic suppression effect of spread spectrum technology.Combining the strategy of switching the three-level SVPWM vector synthesis sequence with random frequency modulation and periodic frequency modulation,respectively,the comprehensive random PWM(Comprehensive RPWM,CRPWM)technique and comprehensive periodic carrier frequency modulation(Comprehensive PCFM,CPCFM)technique based on the three-level VSSVPWM are proposed.The simulation results verify that the two comprehensive harmonic suppression technologies can further reduce the PWM harmonic content,and compare the harmonic characteristics in different modulation ratios.