Multi-variable Multi-constraint Optimization of Triple Active Bridge DC-DC Converter with Conduction Loss Minimization

This paper presents the design and development of an isolated three-port bidirectional DC-DC converter composed of three full-bridge modules and a high-frequency planar transformer. Besides the phase shift control, optimized power flow management along with the utilization of the duty cycle control for minimization of the system conduction losses are discussed and the control laws ensuring the minimum overall system losses are thoroughly studied. In order to calculate the accurate circuit RMS currents and to obtain the multi-variable optimized operating condition, a frequency domain analysis using generalized harmonic approximation (GHA) technique is employed for formulating the bridge voltage and current expressions that are key ingredients for the conduction loss minimization problem in the triple active bridge (TAB) converter. A 600 W TAB converter proof-of-concept has been built to verify all theoretical considerations and model-oriented analysis. While the converter has an input DC bus voltage of 160V, the two output ports of the converter can deliver 400W and 200W at voltage levels of 110-130V and 18-26V, respectively. The circuit topology is particularly relevant to multiple bus voltage electrical systems in space applications as well as in electric vehicles. With the implementation of proposed optimal phase-duty control, the experimental results show a full load efficiency increment of 0.8% compared to the conventional modulation technique with phase-control alone.