Active Cancellation of Periodic Electromagnetic Disturbances for Passive Filter Reduction in Automotive dc-to-dc Converters

The electromagnetic compatibility (EMC) of power electronic systems is a severe issue since the switching of transistors can cause high levels of electromagnetic interferences (EMI). To reduce the EMI, passive filters are commonly applied that tend to be bulky, heavy and expensive. Active noise cancellation is a promising approach to get rid of these problems. Existing methods, namely active EMI filters, suffer from unavoidable delay times since they inject a cancellation signal that origins from a measured signal. These delay times limit the suppressible frequency range and the achievable EMI reduction. To resolve this issue, synthesized cancellation signals can be applied. Since the signal is artificially generated, there is no systematic delay and all bothersome effects, like phase-shifts or magnitude responses, can be compensated. It is only required that the cancellation signal can be synchronized with the power electronic system to maintain a destructive interference. However, this can be realized in most digital controlled systems. The method has already been successfully applied to automotive DC/DC converters. In this contribution, the state of the art and the innovation are described, a demonstrator and measurement results are presented, and the potential field of application is evaluated.