Siemens has an interesting article and some nice pictures about how they see fast charging evolving. I especially liked this bit about how a lot of fast chargers might destabilize the grid. This likely won't apply to a bus system, since there will be only 10-100 chargers in a city, not thousands.

"In addition to Siemens, the EDISON consortium includes the Technical University of Denmark (DTU) and its Risø-DTU research center, as well as Denmark’s Dong Energy and Østkraft power utilities, the Eurisco research and development center, and IBM. In the EDISON project, various working groups are responsible for developing all the technologies needed for electromobility. Here, Siemens is mainly responsible for fast-charge and battery replacement systems. "Siemens’ portfolio already contains many components that we are now adapting and reprogramming," says Sven Holthusen, who is responsible for the EDISON project at Siemens’ Energy Sector.

Contaminated Grid? One of Holthusen’s jobs is to study how the grid will be affected when millions of electric vehicles are plugged into it and disconnected every day. He is therefore carrying out his research at the Risø research campus, which has its own electricity grid. "This enables us to monitor the effects of such a situation on a small scale," he explains. In this context, things become particularly tricky if harmonics occur when batteries are hooked up to the 50-Hz grid, as these can resonate and unbalance the grid frequency. Such disturbances, which are referred to as "grid-quality contamination," can lead to failure of the entire network if large waves form."