Analysis and suppression of conductive EMI originated by an active power filter

In this paper, the generation and path of conductive EMI in an active power filter (APF) are analyzed and the method to suppress the noise is presented. APF is a kind of PWM converter, which aims at solving the harmonic problem originated by nonlinear-load in power system. As compensating the low frequency harmonic components, it also generates electromagnetic noise in high frequency band. Following the operation principle and implementation of an APF, the mechanism and flowing path of two kinds of conductive EMI noise generated by the APF are analyzed. Then, the EMI filter is designed to decrease the EMI noise. In order to further reduce the switching noise, the multi-modular approach has been applied. An additional advantage of this approach is the high equivalent switching frequency in large power rating converter. Field and experimental tests were conducted to verify the analysis and suppression measures.