Common and Differential Mode EMI Noise for Multi-Converter System

The PWM motor drive system has well running characteristics and it has been widely used in the industrial and civilian equipment field， but the high speed switching action of the power device may cause serious problem of EMI by voltage and current transients. This paper based on the research of the differential mode interference and common mode interference of the system while multiple converters parallel has been accessed to the power grid. First we establish a system of the frequency domain model which shows the two converter parallel system of differential-mode voltage and common-mode voltage expression. Then we set up the experiment with the three power of size 1.5kw, 5.5kw and7.5kw converters parallel accessed grid. Finally we draw the conclusion from the data of the experiment：in the low frequency,the system of differential-mode current and common-mode current is relative to the phase difference between the multiple converters of differential-mode voltage source and common-mode voltage source; the probability of the offset phenomenon between the differential mode current common-mode current is increased by the number of the converters. In the high frequency, ,the system of EMI does not effect to the numble of converters.