Active Power Compensation in Microgrids and Nanogrids Under the Loss of Synchronization

As the power system becomes more inertia-less, several issues related to stability and control reliability have emerged, provoking desynchronization phenomena, firstly at the grid-tied inverters and propagating to the entire network. Thus, in order to enhance power system reliability and widen the inverter-based distributed generators withstanding capability under large transients, in this paper, an active power compensation scheme, which is partially untangled from the conventional phase locked loops (PLLs), is proposed. Considering PLLs’ vulnerability due to their high non-linearity, a more reliable physical magnitude is utilized such as the dc-side current, to improve PLLs’ in an indirect manner, by providing adequate response time to follow the abrupt frequency ramps. This is rendered feasible by introducing a series dc-dc converter at the dc-side, which provides the unique ability to mitigate dc current deviations, allowing the regulation of abrupt current trajectories during the loss PLL phase. Active power compensation and dc current retention are achieved simultaneously. The theoretical analysis is verified through extensive simulations, whereas experimental validation is carried out on a scaled-down test bench.