Parking and charging management for electromobility

Sustainability implemented with consistency. This was the idea behind Germany’s largest electric filling station, which has been constructed at Bechtle’s headquarters in Neckarsulm. The challenge was to integrate 50 charging points into a parking garage with specific structural conditions and to supply it with power from the PV system on the roof.

More and more companies in Germany want to electrify their vehicle fleets. Bechtle, the country’s largest IT systems house, has incorporated the issue into its sustainability strategy. The company wants to increase to 10%, the number of electric and hybrid company cars in the medium term, according to Rainer Kury, the company’s corporate communications officer. Staff will be free to decide for themselves whether they want to change to a vehicle with an alternative drive concept, but the interest in such a change is growing all the time, he said.

Fig. 1: Cars on charge in Germany’s largest electric filling station.

The company issued a tender for a new staff parking garage which contained a provision that charging points must be provided for 50 electric vehicles. The planners chose to use “Zorro”, a charging system which is easy to maintain, from RTB a specialist in parking garage technology.

The parking garage challenge

It was important to the operator of what would become Germany’s largest electric filling station that the installation should be designed such that it would be capable of meeting future, as well as current, requirements: it should be easy to extend to accommodate more vehicles, the accounting system should comply with German law on weights and measurements, and there should be a power management system to facilitate optimum use of renewable energy.

Contemporary parking garages with steel structures do not include many load-bearing walls; their open design is characterised by vertical steel supports and cross bracing. This makes the question of how to integrate and install charging points a real challenge. If a floor-standing pillar were to be used, a collision guard would be needed too; this would take up valuable space and increase costs.

Furthermore, such structures offer no load-bearing wall onto which a classic wall box can be mounted. The only option is to install charging points on the narrow steel supports. The charging points themselves will have to be compact with no protruding edges. They must be safe, reliable, and fit into the overall look of their surroundings. The operator had one more requirement: electrical installations in the commercial sector must be regularly reviewed and their costs should not rise in direct proportion to the number of charging points.

The central power distribution solution

Goldbeck, a construction company from Bielefeld, which is mainly involved in commercial and municipal building construction, acted as the general contractor in building the parking garage. For this project, Goldbeck chose a charging system from a parking management specialist, RTB, which followed a simple philosophy: only the bare essentials should be located in the parking area itself; all other system components be fitted into the central control cabinet.

Fig. 2: Control components, protection and switching devices in a central cabinet.

True to this guideline, the charging point itself consists only of the type 2 charging socket inside a slim housing, an RFID reader to identify the user, and local status indicator LEDs. This means that a steel support is wide enough for two charging points to be mounted side by side. All the other components – protective and switching devices, charging controllers, and power meters – are housed in a central control cabinet. In this way, the modular system enables eight charging points to be supplied with power and controlled from each control cabinet. Several such control cabinets can be accommodated in a central, lockable plant room – ideally, future extensions will add eight charging points to the system each time.

Operator advantages

This approach has advantages for the operator too. Since no active power-carrying components are installed at the charging point itself, maintenance of the individual charging points is limited to a visual inspection and functional test. There is no need to open the individual charging point housings. If no vehicle is charging, the voltage present at the charging point itself does not exceed 12 V. The critical protective and switching devices are checked in the central plant room, where specific segments or control cabinets can be de-energised. Charging points supplied with power from a different module can still operate as normal during maintenance (Fig. 2).

Controlling the charging processes

RTB decided to use an EV charging controller from Phoenix Contact, in conjunction with DC residual current monitoring modules. This combination provides for high availability and prevents unnecessary servicing, thanks to an automatic reset function following any residual current caused by the vehicle.

These residual current monitoring modules monitor the charging current for DC residual currents above 6 mA and interrupt the charging process should such a current be detected. This means there is no need for costly type B residual-current operated circuit breakers as required by the IEC 61851-1 and IEC 60364-7-722 standards. The two-channel version of the module enables monitoring of two circuits with one device and two type B residual-current operated circuit breakers can be replaced by two low-cost type A circuit breakers.

Another benefit is that the monitoring modules are connected to the EV charging controllers. When the electric vehicle causing the error is disconnected from the charging station, the controller can reset the monitoring module automatically and the charging point is ready to perform its next charging process with no need for any further servicing.

Fig. 3: EV charging controllers and the power meters are controlled via a PC.

Once a user has been successfully identified, the relevant charging processes can be enabled via the standard RS485 interface and the overlying Modbus/RTU protocol. The charging capacity can also be varied in accordance with the IEC 61851-1 standard – in future, it will even be possible to control this depending on the PV power available from the roof of the parking garage.

Charging currents and capacities, as well as the amount of power which has already been charged, are recorded by a power meter. The power meters, which comply to MID, a directive issued by the European Parliament which defines fundamental requirements, are suitable for accounting for charging processes in compliance with the German law on weights and measurements.

Both the charging controllers and the power meters are read and controlled by an embedded system which runs the software for load management and, in future, also that for accounting for the charging processes in line with the relevant law. The combination of hardware and software has been submitted to the appropriate authorities for approval of this type of accounting.

The parking garage  also incorporates a control technology which is used to monitor parking spaces and provide users with dynamic guidance through the garage to the nearest available space, which will make parking so much more convenient for the company’s employees (Fig. 3).

The devil is in the detail

The approach of using remote charging points is not without its challenges. If the charging points are up to
50 m away from the charging controller, interference coupling and signal smoothing cannot be ruled out on the control pilot line, which is instrumental in the charging process, between the vehicle and the charging station. The EV charging controller from Phoenix Contact helps to resolve this issue in the new parking garage, as it controls and evaluates the signal line in accordance with IEC 61851-1. Previous experience in similar applications enabled the planners to optimise the evaluation algorithm with this in mind and design it to be so robust that charging could be performed in line with these specific demands, while also complying with the requirements from existing standards.

Fig. 4: Solar panels on the roof of the parking garage charge the vehicles.

Noise immunity on the signal lines leading to the charging point presents yet another challenge. The IEC 61851-21-2 standard currently being drafted includes specific requirements in terms of surge and burst tests for lines longer than 30 m. The EV charging controller meets these demands already – an important prerequisite for a robust solution in this environment.


By combining the core competencies of the firms involved in parking garage control technology, charging technology, and accounting processes, it has been possible to come up with a solution that fits the “fleet charging in a parking garage” application perfectly. All the necessary construction and maintenance factors have been taken into account, plus the system allows for the optimised use of renewable energy. The installation has run without a hitch from the very beginning (Fig. 4).

Contact Sheree Britz, Phoenix Contact South Africa, Tel 011 801-8200,

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Source: EE plublishers

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