Design Of EMI Filter Based On Impedance Mismatch

Power electronic switching devices which work on and off at high speed will generate a lot of electromagnetic interference(EMI), and will affect the normal operation of other equipment. The EMI filter which composed by passive LC is the primary means to suppress electromagnetic interference. Designers are generally assumed that the noise source impedance of 50? when they design the filters.This could cause actual performance of the filter and the design value not the same. At the same time, the inherent shortcomings of the passive filter would limit its application in some occasions.This article is analyzed from the impedance mismatch when the noise source impedance is not the same, the same filter insertion loss values will change. This will have an impact on the performance of the source impedance filter. This article analyzes the advantages and disadvantages of different noise source impedance measurement method in order to measure the source impedance and then measure the common mode noise source impedance AC output of the micro PV inverter using insertion loss and double current probe method in the experiment. Comparison of the measurement results show that the insertion loss method has the advantages of simple operation, but the result of two current probe method is more accurate. Active EMI filter has the advantages of small size and low insertion loss, and it could accord to the size of interference to change the insertion loss, so the active filter has been paid more and more attention on a number of occasions. Different from the analysis of active power filter from the point of compensation, this article carries on the analysis from the angle of equivalent impedance. The equivalent of active EMI filter to passive components can provide a clear reference for the filter design. According to the common mode noise source impedance is measured, current sampling voltage compensation type active EMI filter is selected to experiment equivalent impedance analysis. The experiment results show that the active filter and the equivalent capacitance have the same common-mode insertion loss.Experiments show that the noise source impedance is not a simple 50?, so it is necessary to measure the noise source impedance to provide reference for filter design. Research from the perspective of the equivalent impedance active EMI filter can automatically adapt to the interference of different sizes to provide a reference for the active filter.