Online Efficiency Optimization of a Closed-Loop Controlled SiC-Based Bidirectional Boost Converter

This article presents an online efficiency optimization strategy for a digitally controlled, wide operating range silicon carbide based boost converter with bidirectional power flow. The proposed strategy minimizes switching losses at any given operating point by adjusting the converter switching frequency and dead times to optimally set the peak synchronous rectifier turn-
off
current. This results in the converter achieving zero-voltage switching quasi-square wave (ZVS-QSW) operation with minimum inductor current ripple. The optimal timing parameters are determined online by fit functions based on sensed input/output voltages and inductor current, and applied to the converter in a low-bandwidth feed-forward loop operating in conjunction with closed-loop regulation of the converter output voltage. The fit functions are developed from multivariate curve fitting of the analytical solutions of the minimum-conduction ZVS-QSW state plane over the complete range of operation. The proposed approach enables bidirectional operation with efficiencies greater than 97.5% for input voltages ranging from 200 to 400 V, step-up conversion ratios up to 2.5, and power levels between 2 and 8 kW. The converter also achieves efficiencies greater than 99% over wide power levels at boost conversion ratios lower than 2.