Adaptive synergistic control strategy for a hybrid AC/DC microgrid during normal operation and contingencies

This paper proposes an adaptive synergistic control strategy for a hybrid AC/DC microgrid to overcome its vulnerability to notable grid impedance variation provoked by load changes. Microgrid employs an internal DC link incorporating hybrid renewable resources represented by wind turbine generator, photovoltaic arrays and hybrid energy storage system. The latter comprises supercapacitor stacks for fast compensation and a hydrogen management scheme for long-term energy storage to counteract renewable resources indeterminacy. The internal DC link is attached to the AC side via a grid-side converter to constantly realize bus voltage and frequency constancy. The central premise of the proposed strategy during normal conditions is to meet load obligation via proper sharing of demanded power among hybrid resources and storage systems, optimize operation schedule of hydrogen management scheme to guarantee longer lifetime, enhance microgrid stability against abrupt loads disconnections when load shedding is activated during extremely low microgrid production. Accordingly, grid-side converter control structure is adaptively modulated based grid impedance estimation at the AC side in response to load manipulations to alleviate its impact on AC bus voltage stability. Furthermore, two series-connected resistive-type super fault current limiters are attached at the AC bus to mitigate large transient currents caused by different faults. The simulation results, so extensively obtained, reveal seamless exchange of desired load power during entire operational modes and decrease of bus voltage perturbations caused by extensive load variations thus enhancing microgrid robustness against parameters uncertainty. In addition, microgrid is maintained connected and protected during severe symmetrical and asymmetrical faults.