Electric energy monitoring for applying an energy storage systems in trolleybus DC traction

This article deals with practical implementation of modern energy monitoring system in Public Transport Company of Ústí nad Labem (PTCUL) city in the Czech Republic. The motivation for this project is based on the fact, that present configuration of traction lines, old-fashioned trolleybuses and traction substations do not allow for the effective use of recovered energy. The fundamental issue lies in the transfer of recovered energy back from the DC traction to the AC distribution network. In many cases, this is not a technical problem on the side of traction substation only, but the reverse flow of the electrical energy can cause problems even in the distribution network. The distributor of electrical energy lays down restrictive conditions for allowing the reverse transfer of energy. With the latest developments in the field of electrochemical energy storage systems and particularly by continuously declining their prices, a modern approach aims to use stationary or mobile energy storage systems for saving non-utilized energy from the DC railway and to re-use it for covering the consumption peaks. We have verified options for long range control of energy flows between substations and trolleybuses. Based on the long-term on-site measurement and performed data analysis in our dedicated software we have defined critical points for significant energy savings. Now we can precisely define energy flow at the AC input of substations, in the DC traction and in the trolleybuses, themselves. Those analyses have been used as a proposal for the fundamental design of trolleybus' onboard energy storage system.