Current Ripple Mechanism with Quantization in Digital LLC Converters for Battery Charging Applicatio

Abstract

Mechanism of current ripple propagation in a digital controlled LLC converter is investigated from three aspects: battery load, quantization error and double line frequency perturbation at the input. With conventional Frequency Modulation (FM), every modulation step is accompanied by quantization error due to limited resolution of digital controllers. Large current ripple is propagated to the output due to poor frequency modulation and extremely low internal impedance of batteries, which hurts battery health seriously. The analytical model of output current oscillation is proposed considering the quantization effects and double line frequency input voltage perturbation. The synchronous Frequency Dither (FD) is proposed to improve quantization resolution and reduce current ripple further.

Existing System

Digitally Controlled DC-DC Converters.

Proposed System

In this paper, the current ripple propagation mechanism is investigated from three aspects: battery load, quantization error and double line frequency perturbation at input. Then the analytical model of output current oscillation is explored considering quantization effects and double line frequency perturbation at input. Synchronous Frequency Dither (FD) is proposed to improve effective quantization resolution and further reduce current ripple. A 2 kW on-board EV charger comprised of a boost PFC converter with a full bridge LLC converter was built to validate the analytical results of current oscillation and effectiveness of proposed synchronous FD.

Architecture

Battery charger comprised of a boost PFC stage and a full bridge LLC stage