112
Autor: Klaudia Kostogłód
16 cze 2023
DLB, which stands for Dynamic Load Balancing, is a feature in Enelion chargers that allows for
controlling the power of car charging to not exceed the current limit of the main electrical
connection. Proper load management enables a fuller utilization of available power. Charging
points automatically utilize the maximum power possible and only limit it when necessary. This
increases the profits from charging services while reducing the average charging time for
vehicles.
In theory, power balancing for charging sounds simple. It would be enough to divide the
available power by the number of cars, resulting in the power with which each car should
charge. This approach is correct if all cars charge on the same phase. However, in real
installations, we deal with three-phase connections. This can be particularly misleading when
using power units without specifying the number of phases available in the connection. For
example, a 22 kW power in a three-phase installation and a 7.4 kW power in a single-phase
installation have the same current limitation of 32 amperes. This is especially important
because current is the limiting factor for the electrical connection.
In a typical installation, each charging point must have a reserved power in the electrical
connection. Reserved power is not utilized when a charger is not charging or has finished
charging. Because of this, only a small number of chargers can be connected to a single
connection, or the power capacity exceeds 50 kW, which requires an industrial connection and
incurs high fees for the available power.
By utilizing DLB, the number of charging points can be increased because after a charger
finishes charging, the power previously reserved for it becomes available for chargers that
need it. In the event that all devices are in use, the power and available current on each phase
will decrease accordingly to prevent overloading of the electrical connection. With this
feature, the number of charging points can be significantly increased within the available
power capacity of the connection.
Operation of DLB
The charging power of a vehicle depends on several factors, including the power and type of
the vehicle's onboard charger, battery state of charge, and charging cable size. The charging
power limited by DLB will be equal unless the vehicle's charging power is restricted for
another reason.
The minimum available current on a single phase for charging is 6A. If the current at each
station decreases to the minimum level (6A) and is not sufficient for all charging points, a
queueing mechanism is activated. Queueing, which involves cyclically switching charging
between vehicles, allows for servicing all vehicles simultaneously without overloading the
network. The queue is rotated every 5 minutes as follows: the charging station that has
delivered the most energy to a vehicle since exiting the charging queue is moved to the back
of the queue, and the station that has been waiting in the queue the longest begins charging.
For DLB to function properly, the stations in a given network must communicate with each
other. Chargers are connected through the Enelion chain (CAN bus), and in the case of
Lumina stations, through wifi-mesh. Chargers in the network must be powered from a shared
connection. To ensure proper network operation, connectors must be appropriately
addressed, meaning that each connector should have a unique number within the network.
fig. 1. An example schematic diagram of connecting Wallbox chargers
DLB in Charging Network
All chargers connected in a network will distribute the current in such a way that the total does
not exceed the electrical connection. DLB divides the current of the electrical connection
equally among the vehicles.
Example scenario of DLB operation in a charger with two connectors
In Vertica and Wallbox Duo Power chargers, DLB can be used to balance the power between
connectors. If one socket is not charging, the other socket will offer the full charging power. If
two vehicles are plugged in at the same time, the charger will always divide the current evenly
between the vehicles, although it doesn't mean that single-phase and three-phase vehicles
will receive the same power.
The electrical connection provides 32A per phase. If both connectors have the same limit set,
for example, 32A, the power distribution when two connectors are plugged in will be equal.
The first vehicle will receive the full current, and when the second vehicle arrives, the current
will be evenly divided between both vehicles.
In Enelion chargers, the criterion of equal current distribution has been adopted. This means
that all vehicles charging from the same phase will charge with the same current.
The following example illustrates on a graph how the power of a three-phase electrical
connection will be divided between two vehicles:
Nissan Leaf - with a single-phase onboard charger
Renault ZOE - with a three-phase onboard charger.
fig. 2. Division of the charging current by the DLB algorithm
The electrical connection has a power rating of 22 kW, which means a current limitation of 32
amps per phase. When charging two vehicles, we will divide the charging current into two,
resulting in 16 amps each. Due to the Nissan Leaf having a single-phase onboard charger, it will
charge at 3.7 kW, while the Renault ZOE with a three-phase onboard charger will charge at 11
kW.
DLB Configuration
DLB parameters for station configuration are set during installation. Each connector must
have the same DLB settings.
- Electrical connection current limitation
All chargers in the network are limited by the total power of the electrical connection,
which cannot be exceeded. Each station should be connected to the electrical
connection using a cable suitable for its charging power (for example, two Vertica
panels must be connected with a cable of appropriate cross-section or configured to
match the existing installation).
- Phase interlacing connected to the charger
To utilize the electrical connection power more efficiently, chargers can be connected
using phase interlacing, allowing for an even distribution of load among single-phase
vehicles.
fig. 3. Connection of chargers with phase rotation
DLB state machine
It has been assumed that the most effective and fair method of energy distribution is equal
distribution of electricity for each station. The dispersion of the DLB computing network
consists in the fact that each station counts the currents individually, and since they all have
the same data, because they communicate with each other, they obtain the same result - the
allocation of electricity to each station.
The DLB state machine consist of four states:
fig. 4 DLB state machine
IDLE
EV waiting state. The charger does not want to charge, i.e. it is not assigned the charging
current. The charger enters the IDLE state, e.g. after charging is complete.
WAITING
The state of waiting for the current to be released in the DLB network. The other chargers
count the new, equal current sharing. The charger with the lowest address in the WAITING
state always has priority in switching on for charging. From this state it is possible to go to the
BALANCING state or to the IDLE state when the transaction is completed.
BALANCING
The network balancing state is the only state where the charger is charging the car. Other
chargers balancing on the same phase treat this charger as 'balancing', i.e. respecting the
distribution of power equally between the other balancing chargers. The balancing phase in
the case of single-phase EV charging depends on the configured interlacing of the charger,
while in the case of three-phase charging it depends on the most heavily loaded phase.
SUSPENDED
Charging paused state. The charger does not participate in the energy distribution. The hold
can be due to charging completion, EV side hold, or too little current available. From this state,
the charger returns to the WAITING state, e.g. when it is the turn of the car to charge or the
available current in the network increases, e.g. by finishing charging another car.
Enelion Energy Guard
The DLB shares a constant current between the stations. In fact, it is not always possible to
get a dedicated connection just for chargers. In practice, the ordered power is provided for
the station and for other loads. Depending on the use of the building, the available power for
the chargers varies over time. If the building is heavily loaded and the charging station is
occupied, there is a risk of overloading the connection. The solution to this problem is the
Enelion Energy Guard. It is a device extending Dynamic Load Management (DLB) in Enelion
chargers, which monitors energy consumption in the entire building - from a single household
to the largest office parks. EEG constantly updates the maximum value of the available
current of each phase for DLB - ensures safety against overloading the power connection -
the total power of the building and chargers will not exceed the set limit. Energy transferred to
the building has priority over cars, which reduce the power used accordingly. When the energy
consumption of the building is low, the chargers will fully use the connection to charge the
connected cars as quickly as possible. In many cases, this solution allows you to install many
charging stations without the need to increase the power of the connection.
Below is a graph showing energy consumption in an installation with Energy Guard. Between
8am and 6pm, you can see that the power available to the charger has been reduced due to
the increased load on the grid.
fig. 5 Connection load diagram
