The Edge load balancer can deal efficiently with unbalanced phase load and single phase EV charging. The information in this article is not required to work with Edge but gives a deeper understanding of the loadbalancer.
Summary: In order to perform efficient loadbalancing with phase imbalance the use of an energy meter is essential
Visualizing power
In EdgeManager the current usage of a chargepoint is shown in Ampere or Kilowatts, in the graphs the current usage of chargepoints are stacked. This view is convenient and effective to use for the basic insights in loadbalancing.
However, this hides the more complex reality of the electricity system, where electricity is delivered in 3 phases and each phase can have a different load. It is, however, impossible to make a clear graph that shows the 3-phase current use of all vehicles and energymeters over time. Because of this in Edge we give you the choice between 2 visualizations over time:
Amps(A): Are used to show the HIGHEST of the 3 phases. This is because a fuse will break when just 1 of the phases is overloaded. This is useful for getting insight into which vehicles use the highest load on the grid. Therefore, for just load balancing only the highest phase is the most relevant and it is shown in the overview. Note that this view can be misleading when a vehicle charges with 1 or 2 phases instead of 3 because the area of graphs is the same, while a vehicle might be charging with 1/3rd the speed
Kilowatts(KW): Are used to show the amount of power where all phases are taken into account. This is ideal for showing how fast the vehicles are charging. However, it does not show if the power is on a single phase or distributed over all phases.
Please note the slight difference in the 2 graphs above. They are both good enough for an indication of the power flow. However, for in depth analysis a 3-phase view is needed. The difference is best spotted at the 21:00:00 time mark.
3-phase visualization
Because it is impossible to visualize the 3 phase use of all chargepoints in a single graph we made a second visualization where the momentary phase usage is visualized. This view can be enabled by selecting the variable “Current(+3 phase)”. This enables a black vertical cursor where the phase imbalance can be visualized for that moment.
Phase imbalance and the loadbalancer
While most electric vehicles use 3-phase charging, there are vehicles that charge on 1 or 2 phases. When an EV charges at 16A on phase 1 (16, 0, 0) and another EV charges 16A on phase 2 (0, 16, 0). Effectively the load on the grid is still 16A (16, 16, 0). Adding these values up to 32A is what we do in the graphs in the Amps view. But for the loadbalancer the load is still 16A.
When charging stations are installed with phase rotation applied, it often happens that the charging station does not report the current on the correct phase (because the configuring the phase rotation in the charging station is often skipped or mistaken). When charging stations reports the current on the wrong phase, this could mislead the load balancer algorithm and results in blow fuses. Therefore, by default Edge will assume the worst for the reported power usage of the chargepoints and take the worst reported current of a phase and apply it over all phases. This guarantees safe operation.
The solution
Edge can only guarantee that the limits are not exceeded while loadbalancing with phase imbalance when it independently measures the power from the chargepoints with an energymeter.
However, when there is a subgrid with no energy meter, Edge will simply take the highest phase of each chargepoint and apply that value over all 3 phases for that subgrid/chargepoint. Thereby safe operation can be guaranteed.
For most locations where a single energymeter is installed at the main fuse this phase imbalance behavior does provide both convenience, safe operation and near optimal capacity use.
However, the use of an energymeter is not required when the phase rotation in the chargepoints themselves is configured correctly. If you wish Edge to perform the loadbalancing with phase imbalance in mind, please contact LMS support so we can check if together if the installation is done correctly and configure the Edge to trust the charging station measurements. Otherwise, Edge will assume the worst and operate with the highest phase for all channels.