Transient Mitigation in Mode Transitions for Composite DC-DC Converters

A decentralized hierarchical control architecture is proposed for composite systems. Automatic mode transitions are performed in a high-level main controller using a state machine that commands references for each partial-power converter module. Local converter module controllers perform gain-scheduled average current control. It is observed during mode transitions, that when the boost module and the dual active bridge (DAB) module change their output voltage simultaneously, there are unwanted transients in the system that induce instabilities. These transients occur because the boost converter is unable to handle the required voltage step up during the turn on of the DAB converter. To mitigate these transients, a boost voltage reference dynamic alteration and DAB reference ramp offset strategy has been proposed in the paper. Mathematical evaluation of the state machine, condition for transient occurrence and mitigation strategies have been presented. Validation of the theoretical hypothesis is provided by simulations and controller-hardwarein-loop (CHIL) test bed results.