DQ-Current Observer for Aiding the Control of Multiple Active Bridge Converters

Multiple port DC/DC converters have applications in many fields: hybrid energy storage systems where batteries are combined with supercapacitors, multi-level and multi-modular inverters that need multiple DC sources, and DC microgrids. Among these converters, the multiple active bridge (MAB) is particularly attractive due to its high-power transfer and galvanic isolation capabilities. This paper introduces a predictive observer for the converter inner AC currents in order to reduce the number of required current sensors and to use only output DC current sensors. Using this observer, the control of the converter exploits the real-imaginary techniques (dq-frame) without those AC current sensors, thus reducing the cost and complexity of the sensing system and the associated required hardware. This method is verified through simulations using MATLAB/Simulink and Plexim PLECS platforms, and implemented in a 1000 W triple-port prototype. The results show that the observer does not significantly alter the response of the converter in terms of power control, reaching the steady state in around 8 ms for a step in the power reference, even considering a 50% mismatch between the observer and the real transformer windings time constants.