Load management (charging station)

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The load management is a scheme for charging stations for electric cars for the cases where a local power grid insufficient charging performance can provide for the connected charging stations. In existing apartment buildings in particular , the house connection lines are often not designed for charging electric cars. The reinforcement of the house connections is associated with higher conductor cross-sections and thus thicker cables . Since power engineering systems are dimensioned for maximum performance, this increase in performance causes additional costs. Load management can avoid these load peaks to a certain extent, including the necessary expansion and the associated costs.

House connection

The house or building connection is the distribution network operator's transfer point . This is usually done in a house connection box . This is where the higher-level protection of the building takes place with the main fuses . These fuses define the maximum current that can be made available to the building.

Electricity consumption in residential buildings

The electrical load in apartment buildings fluctuates very strongly over the day and also has great differences between weekdays, Saturdays and Sundays. There are also differences between summer and winter. This consumption is abstracted and approximated by a standard load profile (H0) .

Design of house connections

Since 1955, DIN 18015-1 has regulated the assessment basis for the main electrical supply lines in buildings. In this standard, it is currently required that the charging points of electric cars be prepared for connection to the smart grid . According to Annex A of the standard, for example, a residential complex with 100 units results in a minimum connected load of 106 kW for the entire building.

Electricity consumption for electromobility

For the electric vehicles in a residential building, enough charging current should be made available that the user could easily drive the desired distance after the charging process. As a rule, the cars should be charged enough in the morning so that the commuters can cover their commuting route and the other people can cover their daily errands. For the commuters, the entire night is usually available for the charging process, everyone else can also carry out charging processes during the day. The load reserves in a building are usually so high at night that all necessary charging processes can be carried out.

Variants of load management

According to DIN VDE 0100-722, when designing the power grids in a building, it must be assumed that all charging stations for electric cars are used at the same time ( simultaneity factor = 1). According to the standard, this factor may be reduced if a load control is available.

The regulation can take place according to different specifications.

Static load management

The sum of the power consumption of all connected charging stations must not exceed a fixed, static value. This is usually specified by the network operator by means of appropriate protection after the meter for the charging infrastructure. If the network operator approves protection with z. B. three-phase 63  A , 43  k W of charging power are available for charging.

Dynamic load management

Here the upper limit for power consumption depends on the total power consumption of the building. If the rest of the building requires less electricity, the maximum charging power is dynamically adjusted. When the electricity consumption in the building rises again, the charging power is reduced again. The decisive variable for the regulation is the connection value of the entire building. At certain times, usually at night, more electricity is available for charging.

Sequential load management

sequential charging in electric cars

The charging current is limited by limiting the maximum permissible charging processes. When the upper limit is reached, no further charging processes can start. Only when one of the already active charging processes has ended can the next charging process start. However, all charging processes are always carried out with the specified maximum charging power.

Regulated charging power

regulated charging power for electric cars

The charging current is limited here by reducing the charging power at the individual charging stations. The more cars want to charge, the more the charging power is reduced for each connected car. All cars are charged, but the individual charging processes take longer.

Prioritized cargo

It enables individual users to bypass load management and, if necessary, to charge immediately and with maximum performance. This can be for professional parking spaces. B. apply to the boss or to the courier driver who depends on a quick load. This can be used in residential complexes if necessary, if there are special cases.

Implementation of load management

The load management variants described above can be implemented using different technical approaches.

Master-slave solutions

A higher-level charging station (master) controls other, lower-level charging stations (slaves). For this it is usually necessary that the charging stations come from one manufacturer, since the regulation is often based on proprietary systems. This requires communication between the charging stations (e.g. using two-wire or Ethernet cabling). The charging stations must therefore have a communication interface.

Backend systems

The charging stations are connected to a backend in the cloud . The backend regulates the individual charging stations. Communication here usually takes place via the OCPP protocol . The charging stations must therefore have a communication interface.

Charge controller

The individual charging stations are connected to a separate charging controller. There are different variants here. In addition to manufacturer-independent systems, there are also systems that can only communicate with selected OCPP-enabled charging stations or can only control the company's own charging stations. These systems work offline, but can also be monitored online via a cloud solution.

Special solutions

Special solutions are also being developed, such as the multiple use of a charging point by several vehicles.

Local networks

The low-voltage network is the electricity network that supplies a certain area with a mains voltage of 230 V / 400 V from a transformer station . These transformers usually have a rated power between 250 kVA and 1 MVA. From these transformers, several buildings and even entire streets are supplied with electrical energy. The distribution network operator must use electrical fuses in the transformer station to ensure that the maximum output of the transformer is not exceeded. Load management for electromobility must also take place within these networks so that overloading is prevented.

Since the current version of the "Technical Connection Rules for Low Voltage" (VDE-AR-N 4100), charging stations for electric cars with an output of 12 kW or more must be controllable by the network operator.

literature

Web links

Examples of load management systems:

Individual evidence

  1. ↑ DKE: The Technical Guide to Electric Mobility Charging Infrastructure. DKE, June 2016, accessed on April 17, 2019 .
  2. ↑ DIN: DIN 18015-1: 2013-09 . Ed .: Beuth Verlag.
  3. ↑ Thomas Klug: Whitepaper Electromobility in Residential Complexes - Manageable or Blackout? EAutoLader GmbH, July 9, 2018, accessed on April 15, 2019 .
  4. ↑ VDE: DIN VDE 0100-722: 2019-06 Installation of low-voltage systems . Ed .: VDE. April 2019.
  5. ↑ a b Load management for electric vehicles. The Mobility House, accessed April 17, 2019 .
  6. ↑ Installation instructions - wall charging station (Wall Connector, 32 A, three-phase). (PDF; 7.6 MB) Appendix B: Optional connection for load distribution. Tesla, Inc. , November 28, 2016, pp. 31-32 , accessed September 2, 2019 .
  7. ↑ Lars Baier: Load management for electromobility. building & automation, 2018, accessed April 17, 2019 .
  8. ↑ Bayerischer Rundfunk: Electricity networks under pressure. BR, April 12, 2019, accessed April 16, 2019 .
  9. ↑ BDEW: Position paper "Electromobility needs network infrastructure". BDEW, June 15, 2017, accessed on April 16, 2019 .
  10. ↑ VDE: Technical connection rules for low voltage. March 8, 2019, accessed April 17, 2019 .