Flexible Power Sharing Control of Isolated Input-Parallel-Output-Parallel AC-DC Converters Based on High Frequency Link Current Estimation

Abstract

This work proposes a voltage balance and flexible power sharing control strategy for modular input-parallel-output-parallel (IPOP) AC-DC converters with high frequency link (HF-link) isolation. The IPOP AC-DC converter consists of input parallel front end converter (IP-FEC) at the grid side and output parallel dual active bridge converter (OP-DAB) at the back end. The proposed scheme is built upon the estimation and control of HF-link current fundamental component. This approach integrates the parametric identification of each inductor in the HF-link based on the fundamental current perturbation algorithm, which enhances its resilience to gradual parametric variations associated with ageing. This strategy requires measurement of only two currents: grid current and load current using two low bandwidth current sensors, irrespective of the number of cells. The flexible power sharing control strategy enables controlled zero power operation of a cell (phase-shedding/plug-out) while still regulating its DC bus voltage. Additionally, for the subsequent phase-addition/plug-in process there is no need for any pre-charge circuits. The proposed scheme is validated through experiments performed on a 1.4 kW low-power laboratory prototype.