Fuzzy logic feed-forward impedance shaping of DAB converter in DC microgrid with CPL load

In a DC microgrid, the dual active bridge (DAB) converter is employed for voltage conversion and power transfer. DAB-based energy storage systems (ESSs) are known as constant power loads (CPLs). To improve the input current quality of DAB converter, an LC filter is cascaded to a DAB converter. Impedance interaction takes place between the impedance of the LC filter (Z(out)) and the impedance of the DAB converter (Z(in)). ESSs are affected by the impedance interactions of cascaded systems. This interaction leads to significant oscillation and instability, which in turn causes voltage fluctuation and power loss. To overcome instability, this paper proposes a modified fuzzy logic controller (FLC), an active voltage stabilizer (AVS), and feed-forward (FF) controller to reshape the impedance of the DAB converter. In the modified controller, the FLC handles precise voltage monitoring, the AVS handles the transient stability limit, and the FF controller removes the impedance interaction between Z(in) and Z(out). The feed-forward coefficient is calculated through the Routh-Hurwitz criterion. The suggested controller assures system stability during load variation, a quick dynamic response, and precise voltage monitoring. In addition, it achieves reductions in the settling time, rise time, and overshoot. This leads to reliable microgrid operation when compared to the traditional PI (PI + AVS), and (PI + AVS + FF) controllers. The modified controller is verified by results obtained with an OPL-RT-based hardware-in-the-loop (HIL).

Automated summary

In a DC microgrid, the use of a dual active bridge (DAB) converter for voltage conversion and power transfer is essential. However, the interaction between the impedance of the DAB converter and an LC filter cascaded to it can cause instability and voltage fluctuations. To overcome this, a modified fuzzy logic controller (FLC), active voltage stabilizer (AVS), and feed-forward (FF) controller are proposed to reshape the impedance of the DAB converter and ensure system stability. The modified controller achieves improved dynamic response, reduced settling time, rise time, and overshoot.