Viability of active EMI filters for utility applications

The application of active circuitry to increase the performance per size and cost of utility-side EMI filters is considered. The major problems are power line frequency (60 Hz) rejection and the compensation of the feedback loop, which is influenced by the wide-ranging utility impedance. While analysis and simulations show that these problems prevent the practical application of active filtering to power supplies switching at around 75 kHz, results at 450 kHz demonstrate potential for substantial improvement of EMI filters for switching frequencies of a few hundred kHz, although with the cost of a complex compensation