Coupled-Magnetic Filters with Adaptive Inductance Cancellation

Conventional filter circuits suffer from a number of limitations, including performance degradation due to capacitor parasitic inductance and the size and cost of magnetic elements. Coupled-magnetic filters have been developed that provide increased filter order with a single magnetic component, but also suffer from parasitic inductance in the filter shunt path due to imperfectly-controlled coupling of the magnetics. In this paper, we introduce a new approach to coupled-magnetic filters that overcomes these limitations. Filter sensitivity to variations in coupling is overcome by adaptively tuning the coupling of the magnetic circuit with feedback based on the sensed filter output ripple. This active coupling control enables much greater robustness to manufacturing and environmental variations than are possible in the conventional coupled-magnetic approach, while preserving its advantages. Moreover, the proposed technique also adaptively cancels the deleterious effects of capacitor parasitic inductance, thereby providing much higher filter performance than is achievable in conventional designs. The new technique is experimentally demonstrated in a dc/dc power converter application and is shown to provide high performance