Three Phase PWM Inverter Conducted Common Mode Noise Modeling And Suppression

With the development of new energy technology,the application of three-phase Pulse Width Modulation(PWM)voltage source converter is more and more widely.In order to meet the requirements of the corresponding Electromagnetic Interference(EMI)standard,the EMI filter is usually added to the grid side,including differential mode filter and common mode filter.Because of the complexity of common mode noise source's internal impedance,the design of common mode filter is usually quite challenging,engineers need repeated trial and error.Therefore,it is significant to analyze the flow path of common mode noise and to establish the equivalent noise model to improve the accuracy and efficiency of the filter design.In addition,EMI filter usually has a relatively large volume and weight in the system,the cost is also higher,especially in large power system,the large current needs a thick wire and a large size magnetic core.At present,all countries attach great importance to the EMI problem of the power electronic system,and a lot of research has carried out on noise model and noise suppression technology.However,the existing literature,mainly concentrated on switching mode power supply and single phase converter.In the noise model of three-phase converter,some important factors have not been considered,such as the distributed capacitance between the mid-point of bridge arm and the ground.Some other models are too complex,and the practicality is not strong.In this paper,the common mode noise model of three-phase inverter is established,and the key parameters of the model are analyzed.A simple but practical equivalent circuit model is obtained.The accuracy of the proposed model is verified by experiments.Based on the model,the influence of the filter capacitor connected between the AC bus and the DC bus on the common mode noise is analyzed.In the common-mode noise suppression technology,some new technologies with low cost are being brought up,such as active filter,low common mode noise modulation strategy.But most of those are still at the stage of laboratory research,research level still lags behind the actual engineering requirement,and these methods still have some limitations to be solved.In general,passive filter is the earliest development,the highest reliability,the most widely used EMI noise suppression technology.Therefore,this study is mainly focus on the passive EMI filter technology and the original noise compensation.According to common-mode noise model and different applications,this paper presents three new common-mode noise compensation schemes.Two of them are realized by adding an auxiliary winding to the original energy storage inductor.They are suitable for three-phase four-wire system and three-phase three-wire system respectively.Since the auxiliary winding only passes the noise current and no power current,the winding can be very thin,almost no additional volume and cost,but can effectively reduce the requirements on EMI filter,reduce the filter size,cost savings.The third scheme is to construct a Wheatstone bridge to realize the noise balance by connecting an inductive impedance between the DC bus and AC bus.Compared to the conventional scheme of connecting capacitive impedance between the DC bus and the AC bus,the scheme proposed in this paper has a better effect on common mode noise suppression.Those new types of common mode noise suppression schemes proposed in this paper can reduce the requirement of CM filter in the whole system,which has important significance for the volume and cost control of the three-phase PWM inverter system.