Accurate Small-Signal Phasor Transformation-Based Modeling of Secondary-Side Diode-Bridge Rectifiers for Battery Charging Applications

This paper analyzes a dc-dc resonant converter in the small-signal domain with a secondary-side diode-bridge rectifier for battery charging applications. The conventional approach that models the diode bridge circuit as an equivalent resistor results in excessive damping of high-frequency resonance in the case of a battery load, leading to inaccuracies in small-signal modeling. This paper proposes an improved method for small-signal modeling, representing the diode bridge with a battery load as a dependent voltage sink of constant magnitude and variable phase, to achieve accurate results. The effectiveness of this method is verified through phasor transformation-based small-signal modeling of a T-type bridge-based dc-dc converter with an LCC tank and a diode bridge connected to a battery. The proposed method is validated through hardware testing on a 4 kW, 85 kHz battery charger prototype, demonstrating the accuracy of the modeling technique for perturbation frequencies up to 55 kHz.