Closed-form Solution for Multi-Objective Optimal Analytical Balance Control for a Single-Stage Isolated MVAC-LVDC Converter in an Electric-Vehicle Ultra-Fast Charging-Station

The inevitable issue of parameter mismatch in single-stage cascaded isolated medium-voltage AC - low-voltage DC (MVAC-LVDC) converters, proposed for MV utility-grid interfacing in compact electric-vehicle ultra-fast charging-station (EV-UFCS) solutions, leads to unbalanced power transfer and losses in the constituting submodules. This paper analyses the drawbacks of the conventional power balance control (PBC) approach and proposes a multi-objective optimal analytical balance control (MOABC) as a remedy. The analysis of PBC strategy reveals its non-optimal pulse-width and phase-shift evaluation, leading to imbalance in losses (due to dissimilar ZVS modulations) and current stresses in the constituting submodules. The proposed MOABC follows an analytical solution approach to fulfill multiple objectives of LVDC bus voltage tracking, maximizing ZVS range of front-end (FE) and back-end (BE) MOSFETs, equalizing conduction losses among submodules and restricting grid-side current harmonics as per grid-code limits. An 11.7 kVA(pk) experimental setup is used where the proposed MOABC is implemented directly on Xilinx Z-7030 microprocessor, and the test results verify each objective’s accomplishment. Experimental comparison of MOABC with other control methods clearly present the proposed method’s advantages.