For many public transport companies, converting to alternative drive technologies is currently the greatest challenge. Electric vehicles in particular are increasingly finding their way onto the roads. But the acquisition of new fleets alone is not enough. The challenge lies much more in the necessary development of a new, comprehensive system, which also includes developing an appropriate infrastructure. Here, the charging management and range problems of e-vehicles come into play. They also require depot management systems geared specifically toward electric mobility. The intelligent expansion of tried and tested solutions can provide companies with enormous advantages when retrofitting their depots.
Regarding charging management, the alternatives over-night charging and op-portunity charging are still being discussed. However, more and more experts are coming to the consensus that charging at the depot, combined with smart DMS solutions, is preferable to opportunity charging. This means lower construction and logistical costs than those for equipping countless stops in the urban area with the required charging technology. In light of the expected rapid progress in battery technology and ever-greater ranges, this is also the more economical variant from a long-term perspective.
Solutions that can react quickly to disruptions or changes and thereby avoid earlier bottlenecks, such as long cycle times or downtime, are particularly important when expanding existing systems. After all, the overriding goal for the future is to always be able to reliably and automatically cover the next route with vehicles. PSI Transcom, for example, has expanded its depot management system PSItraffic with the smart E-DMS charging management module and the PSIsmartcharging module to supply power.
These are solution modules that can be used regardless of the charging infrastructure and which function with the most homogeneous interfaces possible, automatically controlling the changing processes.
The remaining range depends on the battery’s state of charge, or “SoC.” It specifies which route can still be taken and whether the current route can be completed according to schedule, or whether a vehicle must return to the depot for charging. Numerous factors over the course of the journey affect energy consumption during operation. As a result, the state of charge – and with this, the remaining vehicle ranges – change virtually every second. Once back at the depot, charging progress and the remaining charging time determine whether a bus retains the route assigned to it or whether it must be reallocated.
The PSItraffic add-on module smart E-DMS takes all of these interrelationships into account. The module periodically checks which vehicles at the depot best match which routes after how many minutes of charging time. As a result, it is not necessary to constantly charge every bus at the depot at the same time or to charge them to full capacity. These data are also the basis for optimally positioning the vehicles in the depot, which the DMS also takes care of.
This is the prerequisite for the best possible use of the limited space available at charging stations. As a result, not every bus at the depot requires its own dedicated charging station. This saves space as well as costs for charging infrastructure. For the DMS to receive information – ideally continually – and before entering the depot, vehicles must be equipped accordingly to enable them to continuously transfer reliable data to a stationary server. The smart E-DMS is supplied with live data over the implemented online interface, which enables a preview of the upcoming charging strategy.
The integrated PSIsmartcharging module provides the optimised charge management function. This forecasts the complete energy demand throughout the day, develops a sensible strategy for the existing charging infrastructure, and monitors adherence to the charging capacity. Because each vehicle and battery has different characteristics, energy consumption is never constant. For this reason, all unchanging master data (such as battery size) and variable vehicle and environmental data from daily operation (such as energy consumption) are stored in the DMS and form the basis for forecast calculations.
The outdoor temperature is also an important factor in this process. It significantly determines the energy requirements for heating and cooling, which in extreme situations can cost up to 40 percent of the battery power (provided that the heating/air conditioning systems of the vehicles are not operated with a separate energy source such as heating oil or diesel). For this reason, the DMS also considers how much energy is forecast to be required during the next day for the routes at the expected minimum or maximum daily temperatures.
Diesel and electric vehicles will have to work together in parallel in everyday operations for the next few years. As a result, each of these vehicle categories, with its own supply- related characteristics – which could hardly be more different – must be considered.