Optimal PWM Technology Research On The Attenuation Of Conducted EMI For Three-level Inverters

Conducted EMI is the inherent problem of power electronics converters.With the wide application of high-power and high-density power electronics equipment,the conducted EMI becomes more serious.The regular method to reduce conducted EMI is EMI filters that block the conducting path of EMI noise to restrain EMI,which can greatly decrease the conducted EMI but add the size and weight of the whole system.Nevertheless,the method based on optimal PWMs that construct the pulse series of output voltage can greatly reduce the level of conducted EMI without adding filter.Therefore,this paper focuses on researching the advanced PWM methods to reduce conducted EMI for diode neutral-point-clamped three-level inverter.Firstly,based on the operating principle and regular modulations of three-level inverters,deducing the voltage spectrum of regular PWM method by means of Fourier series to get the spectrum distribution,which is beneficial to designing optimal PWM methods.Then,in order to solve the problem that the energy of harmonics concentrate around carrier harmonics,the variable switching frequency PWM is proposed to spread the spectrum.This advanced PWM methods can decrease both conducted EMI and switching loss without altering the maximum current ripple.The conducted EMI can be reduced nearly by 20 dB during low frequency of EMI spectrum.In addition,because of the worse performance of zero common-mode PWM such as higher switching loss and serious conducted EMI,an optimal PWM method combines variable switching frequency and zero common-mode is proposed to restrain common-mode noise,switching loss,and conducted EMI at the same time.Finally,a 3kW prototype of three-level converter was built up to validate the performance of proposed PWM methods.Relevant experimental results can prove the advantage of optimal PWM methods.