Grid connected photovoltaic supply units for railway applications

Power supply systems in railway lines signalling systems require no-break service. In the last ten years, a large quantity of PV power systems have been tested in the Italian railways network in order to gain experience with the design of no-break power systems. The development of these systems has evolved from the traditional stand-alone configuration with high capacity storage batteries to grid-connected high reliability power systems with a reduced storage capacity. A new concept has been recently introduced using bi-directional power converters which send the excess energy from the PV array to the utility grid. A new grid-connected inverter with an intrinsic safety design has been introduced in order to avoid islanding. Protection is based on the use of particular circuit solutions which provide, in cases of electronic component breakdown, the islanding of the inverter.