Simultaneity factor, static and dynamic load management

  • Load management in general

    In electromobility, load management systems usually describe a way of controlling charging stations or wall boxes. This is used when you can't just use everything to its full capacity at the same time without overloading any fuse. Usually it is about the house connection or even the sub-distribution for the charging infrastructure, which could otherwise be loaded beyond its limits.

    In this context, one also likes to speak of the so-called simultaneity factor. This is about how to design the entire system. For example, if you have 22 kW available and connect a 22 kW charging station, you speak of a simultaneity factor of 1. But if you connect 2x 22 kW, you speak of a simultaneity factor of 0.5.

    [Total Available Power] : [Required Power] = [Simultaneity Factor]

    Of course, you can also have a simultaneity factor of > 1, in which case a load management is not necessary. To a certain extent one can also say that the case will never occur that everything is occupied at the same time. But it is definitely better to always have load management if the simultaneity factor is < 1. It's already enough that people meet at the charging stations for the summer festival and then they are all fully occupied at the same time once a year. This is where the question arises as to which parameters regulate this. Then comes the distinction between dynamic and static.

    The difference between static and dynamic load management

    Static and dynamic load managment

    With static load management, the wall boxes were linked to one another and they were told the maximum total power they can call up. They know what each charging point is allocated in terms of power anyway via the type 2 protocol. As an example, the power of 22 kW for 2x 22 kW charging point. If a car now draws 22 kW, the box allows this and does not regulate anything down. If there are two cars and each can only use 11 kW, the wall boxes already tell them that they are not allowed to use more than 11 kW. However, if one of the two wanted 22 kW, it would still only be allocated 11 kW.

    The transition from static to dynamic is also a bit fluid. When the wallbox not only knows what it allows the car to do, but also recognises what the car is actually pulling from the box. This happens, for example, when two 22 kW cars are each connected to one point, but the first is already fully charged and no longer draws anything. If the boxes are intelligent enough, they will recognize this and allow the car that is still charging to draw its full 22 kW. Here, some then wrongly speak of a dynamic load management. However, it is at best semi-dynamic, even if it already works a little dynamically.

    With dynamic load management, not only the boxes are linked, but a larger system. For example, the house connection is then monitored as a whole and it can be seen whether only the cars from the employee parking lot draw electricity or whether the office also needs a significant amount of electricity. Accordingly, it can then also regulate the total output of 22 kW for the wall boxes down to a total of 16 kW, because the office needs the remaining 6 kW.

    For this you need an additional electricity meter at the junction, which communicates with the charging stations. This then tells them what has already been used and how much is left for them.

    In the private sector, a simple static load management and appropriate safeguards are sufficient. However, if you are more limited and therefore want to use the available power more effectively, you use dynamic load management.

    You can see what this can look like in practice using my own "charging park": My own public charging station, in addition to 5 private charging points


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