German conference focuses on electric buses – Dresden Conference
Key technology developments for electric buses
The second session brought three technical presentations on the development of electric bus technology. Dr Nagan Nieke of VEM Sachsenwerk GmbH opened with the optimisation of electric motors for buses and trams. The company makes electric motors for a wide variety of applications, including London’s Docklands Light Railway and, through Vossloh-Kiepe, hybrid buses in Leipzig and Dresden. Dr Nieke outlined the TEAM principle of influences on electric motor design, Thermal, Electrical, Ambient and Mechanical. In transport applications, the ambient conditions in which the motor operates is a key influence, road salt being quoted as a key issue for hybrid bus electric motors. Cooling, whether internal or external, natural or assisted, air or water, is also a key factor in selecting the appropriate electric motor and needs to be integrated into the overall vehicle cooling concept. VEM Sachsenwerk offers a modular motor system with a range of power outputs utilising standard end fittings for commonality of installation. Based on the expectations of the rail industry, motors are designed for a 30-35 year life which gives the possibility of reuse in a second generation of road vehicles.
For Schunk Bahn- und Industrietechnik GmbH, Key Account Manager, Wilfried Weigel, presented their development work on an overhead conductive charging system for fast charging electric buses at stops. Crossing over from rail technology, the system consists of a vehicle based pantograph with contact head and a charging point mounted 4.5m above the roadway. The specification allows for a maximum voltage of 750V DC with 500Amp continuous rating and a 30 second maximum 1000Amp rating for flash charging. To speed up connection at the charging point, the pantograph is spring loaded to the up position when released with an electric motor to return it to the rest position. The design allows for variation in vehicle positioning at the charging point including up to two percent away from parallel to the ‘Kassel Kerb’ required for positioning at the stop and four percent tilt to allow vehicle kneeling. The contact head has two positive, two negative, an earth and a control pilot contacts. The control pilot is the final one to engage and is key to TUV acceptance of at-stop top-up charging with passengers on board. The whole product is designed to require no input from the driver other than halting the vehicle within the appropriate parameters at the stop.
Dr Bernhard Riegel, Research and Development Manager for Hoppecke Advanced Battery Technology GmbH, gave a highly technical presentation on his company’s work on modular battery systems for electric buses, paying particular attention to maintaining optimum battery temperatures. Vossloh-Kiepe have installed Hoppecke battery systems in hybrid buses operating in Cologne and Amsterdam, and they will also feature in projects in Munster and Dresden.
The final presentation of the session, covering the Bombardier Primove inductive charging system, was presented from an operator’s perspective by Frank Brandt, Prokurist Controlling at Braunschweiger Verkehrs-AG. At the IAA in 2012, Solaris announced that Braunschweig had ordered the first electric Urbino 12 for a project featuring the Primove system. This vehicle has now been delivered and the associated infrastructure is progressing to completion for service in early 2014.
The TUV approved Primove system offers high energy transfer inductive charging from in ground installations with no moving parts. They are only powered when a vehicle is correctly positioned above them and require no input from the driver other than the correct positioning. Braunschweig has chosen route M19, a 12km circular starting from the main rail station as the pilot. This has the benefit of only one terminal point for longer duration charging and crosses all the city’s tram routes giving flexibility in the siting of top up charging points. To determine the optimum location of these, the route was analysed in terms of both the dwell time at stops and the probability of stopping. In the event, the operationally optimum second location proved impractical due to gas infrastructure in the area, so the next best had to be chosen. Glass fibre reinforced concrete is used to secure the below ground elements with the above ground control systems installed in a variety of structures to suit the local conditions. The first Primove installation was inaugurated at the main station in September 2013, housed in a traditional ‘Litfassaule’. It includes a display screen to describe the processes taking place. With a view to potential third party use, the system software is designed to recognise vehicles individually and bill for the energy taken.