Three-loop Multi-variable Control of Triple Active Bridge Converter with Power Flow Optimization

With an objective to reduce the overall power loss in a Triple Active Bridge (TAB) DC/DC converter, a novel power flow optimization algorithm enabled by a three-loop control is proposed in this study. Detailed analysis to formulate closed form expressions of power transfer between the three bridges is presented using generalized harmonic approximation (GHA) based approach. Further, unlike the conventional two loop control scheme that only regulates the output voltages of the two output bridges of the TAB using only phase angles as the control parameters, the proposed control scheme aims at maximizing the overall conversion efficiency by engaging full-bridge duty ratios as control variables. To enable the third control loop, an optimization algorithm is presented that calculates the optimized power flow between the bridges to be used as reference signal. The algorithm also provides design insights related to the minimum leakage inductances required to ensure the required power flow between the bridges adhering to the modulated control variables. To elucidate the effectiveness of the proposed three-loop control, simulation and hardware analyses are also provided as a part of this study, which indicates an efficiency improvement of 4.5% as compared to the conventional two loop control scheme.