Novel Actively Tuned Resonant Filter Based Buck Converter Using Tunable Capacitor

In power electronic converters, resonant filters can be significantly smaller compared to the conventional low-pass filters. Such improvement is achieved due to the high attenuation offered by the resonant filter at the Pulse Width Modulation (PWM) frequency or switching frequency of the power converter. However in traditional resonant filters, due to the variation of filter component values under dynamic operating conditions, the high attenuation at the switching frequency cannot be maintained. In prior research, Tuned Resonant Filter (TRF) based on tunable capacitor has been introduced to address this problem. Tunable capacitor is intended to compensate the variations of the filter components. In this work, a novel control scheme for resonant filters with tunable capacitor is proposed that can automatically tune the capacitor value to achieve the desired filter performances under varying operating conditions. The proposed control scheme is realized through combination of tank voltage sensing, feedback, PI controller and driver circuits that can regulate capacitor bias voltage such that the effective impedance of the resonant filter is tuned to achieve the intended filtering operation. Analysis, design, and implementation of the proposed control scheme in a synchronous buck converter are presented to demonstrate an efficient circuit implementation. Experimental results are presented to validate the hypothesis that the proposed controller can successfully provide automatic tuning of the resonant filter under changing operating conditions and maintain the desired filter performance.