Dynamic Feedforward Control for an Active Three Phase EMI Filter

Abstract

Power electronic systems usually produce high amounts of electromagnetic interferences (EMI) due to PWM operation. To comply with international standards on electromagnetic compatibility (EMC), e. g. EN 61800-3 in industrial applications [1], the EMI shall not exceed given limits. To reach these limits often filters need to be integrated into the system. The common solution is to add passive EMI filters consisting of capacitors and inductors [2]. Passive filters are often bulky and heavy, therefore active cancellation techniques for power electronic systems were introduced [3]. Active EMI filter (AEF) consists of an analog (and rarely also digital) circuit to actively suppress the disturbances by injecting an anti-noise signal. As discussed in [4], well-known closed loop feedforward or feedback structures for AEF have their limitation specially because of the limited amplifiers open-loop gain, delays due to the finite signal propagation speed in the circuit and the measurement accuracy. For this reason, active EMI cancellation by injecting synthesized signals was introduced. This paper introduces a method for generating a synthesized signal for a three-phase grid converter.