E-mobility in Public Transport: Gaining a Head Start Through Optimization and Open Interfaces

The switch from diesel to electric vehicles in local public transport is gaining momentum. In the meantime, integrated software systems that combine depot management and the charging system have proven particularly effective. Two issues are especially significant here: Optimizing the interaction between driving operation and charging management on the one hand, and creating standard interfaces between various systems on the other hand.

The public transport sector has taken on a pioneering role in the conversion to alternative drives. The EU’s  Clean Vehicles Directive and its mandatory minimum quotas for the procurement of zero-emission vehicles are providing strong impulse in this process. Companies are therefore coming under increasing pressure to develop a practicable and future-proof electrification strategy.

The challenge: Only a few companies and suppliers have an overall understanding of the requirements of a public transport operation and the management of an electrical infrastructure. However, this is precisely what will be crucial in order to create the necessary structures quickly and use them efficiently in the long term while remaining independent of individual manufacturers’ technologies. For example, the interaction between driving operations and charging management will need to be optimized and standards for communication between the various systems created.

Fully Consideration of Operational and Electrical Influencing Parameters

So how can we ensure that buses are available on time and fully charged as needed – and do so as economically as possible?

The influencing factors and dependencies involved extend far beyond the limited battery range, for example. Each individual vehicle’s range is also influenced by the age of the battery, the outside temperature or a bus driver’s specific driving style. The charging infrastructure, the specific connected load and possible restrictions on the electrical supply due to grid fluctuations also exert a significant influence on vehicle charging. Last but not least, aspects such as

• grid-compatible charging,
• battery conservation or
• charging at favorable conditions

can become a relevant economic factor.

The fact is: Managing a driving operation powered by electricity requires a much more planned approach than other driving operations did in the past.

A large number of operational and electrical influencing parameters and their interdependencies need to be a taken into account and optimally balanced. This can now be done using software alone.

Automated Optimization of Complex Dependencies

In this regard, companies benefit from integrated depot and charging management systems designed specifically for zero-emission public transport. By combining the PSIeDMS depot management module with the PSIsmartcharging integrated charging management system, the PSIebus  system combines operational pre-planning and electrical systems data.

Vehicle and operational data is merged with weather forecast data as well as information on the feed-in points, transformers and charging columns.

This forms the basis for resource-conserving, demand-based charging processes. At the same time, in the event of imminent overload or restrictions in the energy supply, power is redistributed automatically, stabilizing the network status while still ensuring reliable operation.

To determine the charging strategy for each vehicle, the system uses PSI's integrated AI-based optimization software Qualicision. This enables all relevant criteria and their complex, sometimes even contradictory, dependencies to be balanced at high speed. In doing so, companies can individually prioritize, weight and flexibly adjust and display all parameters.

The following scenario is conceivable, for example: The minimum state of charge of a battery for the next scheduled route is incorporated into the overall planning as a requirement to be met, i.e. a restriction. In parallel, qualitative criteria such as a battery-friendly reduced maximum charging power or a decreased target state of charge of the battery are prioritized in relation to each other, weighted and also incorporated into the charging planning as criteria. The resulting slowdown in battery aging is definitely a relevant economic factor for large companies.

Standardised Communication Processes Between Depot and Charging Management

In the future, connected systems such as a Depot Management System (DMS) or an Intermodal Transport Control System (ITCS) will need to be closely interwoven with charging and load management systems, and these in turn with charging columns. As a result, interfaces need to be converted into standards. Only processes and responsibilities defined and standardized in this way will be able to ensure investment security and allow transport companies to freely select their suppliers.

The recently published VDV 463 interface originates from the Hamburg Hochbahn project. This standard describes the bilateral exchange of information between the depot and charging management system and defines its data format and transport protocol. This includes, for example, which operational parameters are transmitted from the DMS to the Charging Management System (CMS) via the charging request and how, where and at what priority level, and how the CMS sends back the charging planning in detail as charging information.

Specification of Interfaces Between Charging Management and Charging Stations

The open and certified OCPP 1.6 (Open Charge Point Protocol) interface already exists for the connection between the CMS and charging columns. It describes, on the one hand, how the messages between the two components are used for monitoring and charging control and, on the other hand, the expected behavior of the charging infrastructure and the buses, including the linked data.

The problem: The way in which messages are used in context remains open. For example, the protocol does not specify in sufficient detail which charging profiles must be used for central charging control or which data the charging stations need to provide to enable central monitoring and charging control. The same applies to the description of use of the charging profiles in the event of communication failures or faults to the power supply.

A clear definition of use of the smart charging profiles is exactly what is needed for the reliable charging and distribution of the electric buses in the depots.

Consequently, the different or incomplete implementation of the smart charging profiles causes high costs when connecting the charging columns to a load and charging management system. Therefore, PSI has specified the messages of OCPP 1.6 in the PSIready document. This includes, above all, the consideration of restrictions to the energy supply as well as the precise definition of an emergency operation, which is absent from most interface descriptions.

Long-Term Success With All-In-One System and Standards

The conversion to electric mobility has a considerable influence on the operational processes in transport companies. It is important to combine the processes of the depot with those of the charging management and to optimally balance the complex interdependencies. Standard efforts, such as in the environment of VDV standard 463, but also in the context of the interaction of charging management systems and charging stations, are also imperative in order to enable safe and efficient operation and manufacturer independence for the companies in the long term.