Scientific Papers

2016-06-28 IMEKO - Analisys of failure rate of AC-DC micro-grids

Abstract - 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 interrup-tions. The performed analysis showed that dc microgrids 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 techni-cal 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.

2016-04-20 SPEEDAM 2016-  Multi-port Converters in Smart Grids Protection Selectivity

Abstract – Requests for high quality and continuity of supply have led to the study of DC micro-grids. The realization of these networks would allow exploitation of DC advantages, but it would also create fault clearance and selectivity problems because semi-conductors suffer over-currents and over-voltages.

The use of traditional DC circuit breakers is often not acceptable.

As an alternative, static switches can be installed to solve thesem problems, in spite of increases in power loss. In this work, a multi-port converter is proposed to solve the aforementioned problems. In addition, it is able to manage power flows and AC and DC I/O, improve stability, and decouple port voltages.

2015-11-05 AEIT-Zonal Electrical Distribution Systems in Large Ships_Topology and Control

Abstract: High quality and continuity of supply requirements make the introduction of zonal electrical distribution systems and storage devices on ships interesting. Zones can be operated in both AC and DC, but DC is preferable thanks to its advantages compared with AC benefits. The main DC drawback is the current fault interruption, due to current no zero-crossing. In this paper, a comparison between AC and DC zonal supplies is presented. Advantages and drawbacks of each structure are highlighted. In addition, a DC zone topology and a power flow control strategy are proposed.

2015-07-22 DC Networks Including Multi-port DC-DC Converters_Fault Analysis

Abstract: DC networks that include storage systems, renewable sources, DC loads and Front End Converters can provide some advantages compared with AC grids. However, the interruption of fault currents is difficult due to no-zero crossing of the current. Moreover, the fault clearing time of traditional DC circuit breakers can be too long for protecting power electronics switching components. Multi-port converters seem to be a good solution for solving the aforementioned problem. The introduction of a multi-port DC/DC converter, along with its configuration and a centralized control for power flow management, is proposed in the initial sections of this work. After this, the paper focuses on the study of system behavior during fault functioning conditions. Both pole-to-pole and pole-to-ground faults are investigated. The Authors propose some control strategies and hardware solutions to overcome DC protection issues during several fault types. Some numerical simulation results are provided.

2015-07-22 ICCEP-A Novel Approach in Multi-port DC-DC Converter Control.

Abstract: DC networks and storage systems are able to guarantee high reliability and continuity of supply to DC loads. They are also easily connectable to the majority of renewable sources, such as PV plants, due to the fact that they already work in DC. In this paper a multi-port DC/DC converter topology and a new control strategy are proposed. Following definition of each port's aim, the management algorithm (based on voltage droops) permits control of the power flow among ports, even if some of them are not working.