Active cancellation of periodic EMI at all terminals of a DC-to-DC converter by injecting multiple artificially synthesized signals

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Active cancellation of disturbances of power electronic systems is an aspiring method in EMC to reduce passive filter sizes. Most publications on this topic deal with the cancellation of either common- or differential-mode disturbances at either the input or the output terminals. In most practical systems, all disturbance modes of all terminals must be suppressed simultaneously. This is no trivial task since the different injectors for the cancellation signals can affect each other. Therefore, a cancellation signal for the input terminals can worsen the disturbances at the output terminals, or vice versa. Additionally, due to mode conversion, common- and differential-mode EMI can also interfere. In this work, synthesized cancellation signals are utilized that have already shown a promising performance in the suppression of periodic disturbances since complex transfer functions and delay times can easily be compensated. Here, a multi-port canceller is applied that injects synthesized cancellation signals to reduce the disturbances at multiple terminals simultaneously. The fundamental problem of mutually coupled injectors is discussed and a mathematical description is formulated. From this description, the cancellation signals are calculated and requirements for the system are derived. This method is applied to a GaN-based 48 V/12 V DC-to-DC converter with a switching frequency of 1 MHz in a measurement setup for conducted emissions according to the automotive EMC standard CISPR 25. The coupling and decoupling are practically discussed. The effectivity of the method is shown by measurements at artificial networks. The total power of the generated cancellation signals is estimated.