Analysis of failure rates of AC and DC micro-grids

Nowadays dc distribution is gaining importance, as an increasing amount of loads is natively biased in dc. In addition, dc micro-grids are usually characterized by high efficiency and simple design. Moreover, they can better accommodate renewable generation and storage systems. These are the main benefits attributed to dc distribution grids. Reliability aspects, usually, are not sufficiently taken into account. This paper describes an initial methodological approach to compare (in both analytic and numerical way) ac and dc micro-grids. In particular, the analysis has been focused on the effects on loads of main supply interruptions. The performed analysis showed that dc micro-grids have a higher immunity to these events than that displayed by ac micro-grids. On the other hand, the front-end converter (FEC) interfacing ac main supply and dc micro-grid is a single point failure for the whole system. The paper describes (and analyses) some technical solutions to reduce the effect of FEC failure on loads. Moreover, the signals and alarms that should be used in order to maximize the obtained quality-of-service levels are reported, along with some diagnostic considerations.