Energy and Power Demand of Public Transport Vehicles

Against the background of dwindling global energy resources and increasing climate change, the use of more energy-efficient and low-emission technologies is also a central task for local public transport.

Vehicles with electric drive systems have the option of using their traction motors as generators. This enables the recuperation of kinetic as well as potential energy during braking. This principle is already often used in road vehicles, trams and trolleybuses. However, a prerequisite for recuperation is that other consumers (auxiliaries or vehicles in the same feed section requiring energy) in the network can use the recuperated energy. Alternatively, a suitable energy storage system can be mounted. This way, it is possible to increase the utilizable part of the recuperated power.

Taking into account the significantly reduced energy demand through recuperation as well as reduced network transmission losses, energy savings of up to 30 percent can be reached, based on the total vehicle energy demand. At the same time, vehicle energy storage systems can contribute to a stabilization of the grid voltage and to reduced peak loads in the catenary grid. The determination of energy and power reserves is necessary for the dimensioning of an optimized energy storage solution. These parameters depend on a multitude of influence factors, including, for example, the local distribution of recuperation into the catenary, the route topography and the influence of ambient temperature on the auxiliary power demand.

Since vehicles as well as networks and environmental influences differ strongly according to the local characteristics, an individual analysis of these parameters, based on measuring campaigns, is necessary for the application of an optimized energy storage system solution.

Various measuring methods and test systems can be used to acquire the needed measuring data. The Fraunhofer IVI determined the energy and power demand of a modern tram (45 m, NGT D12DD) during a nine-month measuring campaign [1]. The data was recorded in relation to time and location during regular operation. Due to external requirements, the measurement setup was installed without interference with the vehicle controller.

The following subtasks were realized by Fraunhofer IVI:

• development of a measuring concept,
• realization of adequate measuring systems,
• integration of the measuring equipment into the vehicle as well as
• data acquisition and storage.

Extensive measuring campaigns result in large data sets which must be appropriately compressed, aggregated and presented in accordance with the demanded evaluation criteria. However, the volume of data is often several gigabytes large and exceeds the capabilities of conventional calculation tools, like Microsoft Excel or others.

Special software tools were developed for data evaluation and processing at the Fraunhofer IVI, which lead to very precise results through complex calculations.

Among the functionalities implemented are:

• Pre-processing of the measuring data including correction of missing values,
• Coordinate transformations,
• Determination of the local coordinates of the stops in the operator's network,
• Identification and assignment of stops in the measuring data,
• Integration of additional values measured (e. g. ambient temperature),
• Determination of the driven routes,
• Reproduction of the route network through continuous distance routes (splines),
• Evaluation of the data regarding different parameters as well as
• Graphical formatting and presentation of results.

[1] Klausner, S.; Lehnert, M.: Betriebsspezifische Auslegung von Energiespeichern für Straßenbahnen. eb - Elektrische Bahnen 106 (2008) 5, S. 237-246.

[2] Lehnert, M.; Klausner, S.; Bartholomäus, R.: Energieverbrauch bei Stadtbahnsystemen - Identifizierung von Einsparpotenzialen. Bahntechnik aktuell - Proceedings 14 (2008), S.15-26.