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Wide-Frequency EMI Suppression of Stationary Clocked Systems by Injecting Successively Adapted Cancellation Signals

Active cancellation can suppress electromagnetic interference (EMI) of clocked systems like power electronic converters. Considering clocked systems that operate stationary over a sufficient time, there are stable harmonics that can be individually suppressed by destructive sine waves. These sine waves can be superposed to create a synthesized wide bandwidth cancellation signal. Adaptive approaches have proven to be very effective to find the right parameters for each sine wave. Bothersome effects, like complex frequency characteristics or delays, can be compensated by appropriate amplitudes and phases. Therefore, this method does not suffer from the same limitations as active techniques with feedback- or feedforward-topologies. If the disturbances are constant over a sufficient time, the parameters for the cancelling sine waves can be found simultaneously or successively. Until now, only the first option has been shown with an adaptive cancelling FPGA system. Since the cancelling logic needed to be implemented for each cancelling sine wave and the resources of any FPGA are limited, the number of suppressible harmonics was limited as well. In this work, this limitation is resolved by a successive approach that enables the application of the method to a very large number of harmonics. The fundamental theory is discussed, and a robust algorithm is presented. A cancellation system is realized and applied to a 48V/12V DC/DC converter (e.g. for automotive applications) to suppress the frequency range of 150 kHz to 30 MHz in regard to the automotive EMC standard CISPR 25.